The flux-cored wire does not need additional protective gas, wind resistance and porosity resistance during welding, and the operation process performance is good!
It can also be used for welding various types of steel structures, including low carbon steel, low alloy high strength steel, low temperature steel, heat resistant steel, stainless steel and wear-resistant surfacing.
Therefore, the flux-cored wire is more widely used than the solid wire
The difference between flux-cored wire and solid wire
1. Production efficiency
In terms of production efficiency, the flux-cored wire adopts continuous welding mode, so the production efficiency is high. Compared with solid wire, the time of removing spatter and polishing weld surface is reduced because of less spatter and better weld forming.
2. Adaptability to steel
Compared with solid wire, because flux-cored wire generally transfers alloying elements through the flux-cored wire, the alloy composition can be easily adjusted from the formula to suit the requirements of the steel to be welded like a manual electrode. The solid welding wire each adjustment of the alloy composition, it must be re-smelted, the process is many, difficult to control, so it is difficult to meet the requirements of less and more varieties. And some alloy steel solid core wire drawing performance is poor, it is difficult to pull into the required wire. At this time, flux-cored welding wire shows its unique advantages.
3. Operating cost
Compared with manual electrode and solid wire, the price of flux-cored wire itself is very high. However, for large enterprises, after the use of flux-cored wire, the production cycle is shortened and the weld quality is easy to ensure, so the comprehensive benefits are very high.
4. Moisture resistance
Common cartridge wire has a continuous gap on the side of its steel skin due to the constraints of its manufacturing form. Therefore, the shelving time of the flux-cored wire after opening the package can not be too long to prevent excessive moisture absorption and affect the welding quality.
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Like many other solid-state processes, resistance spot welding (RSW) relies on the material's inherent volume resistivity as a means of generating heat when an electric current passes through it. This physical phenomenon is described by Joule-Lentz's law (Joule's first law), which states that the heat (Q) generated by an electrical conductor is equal to the current (I) multiplied by the voltage (V) and the time (t) that the current is allowed to flow, or Q = IVt. Ohm's law states that voltage (V) is equal to current (I) multiplied by resistance (R), or V=IR. This means that Joule's law can also be written (after substitution) as Q=I2Rt.
In other words, the heat entering the weld is equal to the current multiplied by the resistance and the square of the time the current flows through the weld. Incidentally, this equation assumes that resistance and current are constant, which is not always the case with resistance welding. To help us further understand resistance heating (and subsequent resistance welding), it may help us to understand the relationship between the bulk resistivity of some materials and others. For the purposes of this talk, we'll limit things to a few materials that are common in our lives. Finally, resistivity is indicated by the Greek letter rho (ρ) in ohm-meters (Ω•m).
The volume resistivity of the materials we use in everyday life varies greatly. Here are some simple conclusions:
Copper has a very low volume resistivity value. That means it's a good conductor. It is this low volume resistivity that allows us to weld aluminum and iron alloys with electrodes made of copper without having to weld copper electrodes to parts.
The difference in bulk resistivity between aluminum and iron is large (about three times). However, it's not so big that we can't relate one to the other.
So how does the above information help us connect various aluminum alloys or any other material using the RSW process? Part of the reason is that the material generates heat when an electric current passes through it, and this is where volume resistivity comes into play. As we mentioned earlier, the total heat entering the weld can be expressed as Q=I2Rt. With this in mind, it makes sense that when comparing aluminum to iron, we would need more current or welding time to make up for the difference in total heat reduction due to loss of resistance. Often, however, when determining the best method for resistance spot welding, we cannot focus on just one material property, in this case volume resistivity.
First, because aluminum has a lower melting point, it reaches the plastic range at much lower temperatures than iron. This also means that the same volume of aluminum requires less heat to produce a melting temperature than iron. However, for aluminum alloys, it is more difficult to maintain sufficient plasticity to constrain melting because the plasticity range is very narrow. (The actual process window for acceptable spot welding for aluminum welding will be smaller than for welding with iron because we have a narrower range of allowable variations in current and welding time).
We now know the challenges we face. In order to successfully connect aluminum using the RSW process, we must take into account its lower (relative to iron) body resistivity, melting point, and plastic range. To help put it all together, the following rules of thumb may be helpful.
Rule of thumb
For RSW processes, there are a number of standardized welding procedures available, and they come in many forms. With the above in mind, is it possible to relate the information contained in the steel welding procedure to the information contained in the aluminum welding procedure? More importantly, is it possible to see how the welding industry explains the difference between these two materials? The short answer is yes. Although not accurate, a review of the steel (uncoated high strength low alloy) and aluminum welding diagrams should yield the following rough approximations. I call it the 3-1-1/3 rule.
Rule 3: For a given specification and control metal thickness (GMT), the typical current value of aluminum is approximately three times that of steel. This higher current requirement is caused both by the lack of bulk resistivity in the aluminum required to generate the heat required for melting, and by the heat drawn from the weld by the surrounding material. One place this rule is broken is if the surface of the aluminum has been freshly cleaned (think aerospace applications). In these cases, it is not uncommon for the secondary current required to be four times or more than the current in steel.
Rule 1: For a given specification and GMT, the welding forces of steel and aluminum will be roughly the same. A certain amount of unaffected substrate must be present to enclose the newly formed solder core, although depending on many factors, aluminum and steel weld forces are roughly the same. Note that we are not talking about the forging power that many aluminium can benefit from when joined by the RSW process. That's another subject.
1/3 rule: For a given specification and GMT, the welding time for aluminum is about 1/3 of the welding time for steel.
This is where the narrow plastic range really comes into play. This narrowing means that the process window for aluminum is smaller. Therefore, low and very targeted welding time values must be used.
Now that we know how to do resistance spot welding in aluminum, the next step is to understand that not all aluminum is created equal. Regardless of the alloy, or the post-treatment solution, the complete labeling should specify the required information.
Once the type of aluminum alloy to be treated is determined, the next step is to use this information and consult the compatibility chart to understand the best treatment method. These diagrams are available from a variety of sources, including AWS C1.1 Recommended Procedure for Resistance Welding or RWMA Resistance Welding Manual. Finally we can create the following categories:
1) The degree of difficulty of combination in welding problems. This category is usually sorted by difficulty and can even include recommendations not to weld materials together.
2) Pre-cleaning requirements. This can range from never requiring (very rare) to surfaces that require chemical and/or mechanical cleaning before they can be welded. It is important to note that I have yet to see how the existing surface pretreatment on the market is included in these charts. If your material has such a coating, it may be beneficial to consult the manufacturer.
3) Corrosion resistance of the obtained weld metal. In particular, it is either as good as the base material or it is not.
4) Admit that the chart is incomplete. Just like surface pretreatment, the world of substrates is constantly evolving, so you may want to contact manufacturers to see how compatible they are with the material.
Once the compatibility problem has been solved, it is now only necessary to use the basic principles of RSW for welding. Anyone who has read the RWMA Q&A column for a long time will know this: Use the right sized device and have a power supply with the right electrode cap on the right designed part. If you do this, you will have a cost-effective and robust welding process. So, although there are other ways to connect metal materials, RSW is not going away anytime soon.
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Virtual welding is one of the most common defects.
Sometimes after welding it seems that the front and back of the steel belt welded together, but in fact did not achieve the degree of integration, the strength of the combination surface is very low, the weld in the production line to go through a variety of complex processes, especially through the high temperature furnace area and high tension tension area, so the weld in the production line is very easy to "cause broken belt accident," It has great influence on the normal operation of the production line.
The essence of virtual welding is that the temperature of the joint surface of the weld is too low during welding, the core size is too small or even has not reached the degree of melting, but has only reached a plastic state, and is barely combined after rolling, so it looks welded well, but in fact, it is not fully integrated.
Analysis of the causes and steps of virtual welding can be carried out in the following order:
(1) First check whether the weld joint surface has impurities such as rust and oil, or uneven and poor contact, which will increase the contact resistance, reduce the current, and the welding joint temperature is not enough.
(2) Check whether the amount of overlap of the weld is normal, and whether the amount of overlap on the drive side is reduced or cracked. The reduction of the amount of overlap will make the joint area of the front and rear steel strips too small, so that the total force surface will be reduced and can not bear the greater tension. In particular, the phenomenon of driving side cracking will cause stress concentration, and the cracking will become larger and larger, and finally pull off.
(3) Check whether the current setting conforms to the process regulations, and whether the current setting does not increase correspondingly when the thickness of the product changes, resulting in insufficient current in the welding and poor welding.
(4) Check whether the welding wheel pressure is reasonable, if the pressure is not enough, it will be due to the contact resistance is too large, the actual current is reduced, although the welding controller has a constant current control mode, but the resistance increases beyond a certain range (generally 15%), it will exceed the limit of current compensation, the current can not increase with the increase of resistance and the corresponding increase, can not reach the set value. In this case, the system will issue an alarm when it is working properly.
In actual operation, if the exact cause of the virtual welding can not be analyzed for a while, you can clean the head and tail of the steel strip, increase the amount of welding overlap, appropriately increase the welding current and welding wheel pressure again, and pay close attention to the formation of the weld during welding, in most cases, you can deal with the problem in an emergency.
Of course, if there are control system problems, or grid voltage fluctuations, so that the weld welding must be taken other measures to solve.
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What are the differences between 7075 and 6061 aluminum alloys
1. Different ingredients
The 7075 series mainly uses zinc as the main alloy, and the composition ratio reaches 6%. The 6061 series mainly uses magnesium and silicon as the main alloys, and the total composition ratio is low.
2. Different intensity
In terms of strength, 7075 is stronger, no less than steel, but only a little stronger than 6061.
3. The price is different
7075 is the lightest and strongest aluminum, and the price is super expensive, while 6061 is the most common aluminum, light, strong, and affordable.
4. Different practicability
7075 contains a high proportion of other metals, so welding, processing are more difficult, its proportion is higher, so it is generally not used as a frame material. 6061 Due to the low proportion of other metals, it can increase its strength and reduce its wind resistance through special shape and various treatments, and even reduce the weight by three times pumping the tube. On the whole, 6061 is a better material.
Second, the difference between zinc alloy and aluminum alloy
1. Different raw materials
Zinc alloy is an alloy with other elements added on the basis of zinc, and the commonly added alloy elements are low-temperature zinc alloys such as aluminum, copper, magnesium, cadmium, lead and titanium. Zinc alloys are manufactured by melting and become materials in die casting and stamping processes. Aluminum alloy is a general term for aluminum-based alloys, the main alloying elements are copper, silicon, magnesium, zinc, manganese, secondary alloying elements are nickel, iron, titanium, chromium, lithium and so on.
2, different scope of application
Zinc alloy can be divided into cast zinc alloy and deformed zinc alloy according to the manufacturing process, which can be used for die-casting meters, galvanized corrosion prevention on the surface of automobile parts shell poles, and galvanized treatment of boiler water wall pipes to improve high temperature corrosion resistance. Aluminum alloy is the most widely used non-ferrous structural material in industry, widely used in aviation, aerospace, automotive machinery manufacturing, shipbuilding, chemical industry and so on.
3, the soup temperature is different during processing
Zinc alloy at more than 400 degrees; Aluminum alloy more than 700 degrees.
4, processing equipment is different
Although both are called die casting machines, they can not be universal at all.
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About spot welder Contact welder electrode material composition
1, CuCr (chromium copper) and CuCrZr (chromium zirconium copper) What is the difference?
Common ground: all are copper alloy material, suitable for resistance welding electrode, with high hardness, strength; It has the characteristics of high temperature softening, can resist high temperature and maintain its chemical and physical properties at about 450℃ ~ 550℃; With certain wear resistance, long service life; It has good electrical conductivity.
Difference: In copper alloy smelting, CuCr only adds Cr element to copper; CuCrZr, in addition to adding a certain component of Cr element, also added Zr element, and Zr element has wear resistance, toughness and other characteristics, so CuCrZr compared with CuCr, the material has better wear resistance, has a longer service life, but also improve the high temperature softening temperature, so CuCrZr as an electrode material is more superior.
2. Why does the electrode stick when welding the galvanized sheet?
This is because the electrode material used is CuCr or CuCrZr, when the Cu in the material is welded to produce high temperature melting, the zinc (Zn) of the galvanized plate will react with Cu and Zn alloy, and CuZn is just the brass alloy composition, and a chemical reaction occurred, the loss of the electrode material, resulting in the phenomenon of sticking.
3, how to solve the bonding phenomenon when welding galvanized sheet?
a) The best solution is to use dispersion strengthened copper (CuAl2O3),CuAl2O3 is a superior resistance welding electrode material, its softening temperature is up to 900°, is a good electrical conductivity strength and wear resistance, long service life, does not produce electrode and workpiece sticking phenomenon.
b) If you want to use CuCr or CuCrZr, you can use two current welding method, spot welding machine must have two current output, the first current (small) will first break down the coating, the second current to weld the workpiece, so that the workpiece will be firmly welded, the electrode sticking phenomenon will also be improved.
4, what is KCF, why welding nuts, bolts to use it?
KCF is a special ferrochrome alloy, which is characterized by good hardness and strength toughness, and after special heat treatment process, it has the characteristics of low pressure insulation on the surface, and when welding nuts or bolts, the thread part is required to make insulation protection to prevent the burn of the screw due to shred; Because KCF is used as a bar forming material, the processing is more convenient and the cycle is shorter; Therefore, it is ideal to use KCF material as the positioning core.
Of course, ceramic materials can also be used as the positioning core, the hardness of ceramics is completely no problem, but because it is easy to break and break, it is not ideal, and the molding needs a mold, so the processing of special cores is more difficult, the production cycle is longer, and the cost of small batches is very high. If the batch is large and standardized, the cost will be lower.
5, electrode material introduction:
Chromium-zirconium copper (CuCrZr)
Chromium zirconium copper (CuCrZr) is the most commonly used resistance welding electrode material, which is determined by its excellent chemical and physical properties and good cost performance.
1) Chrome-zirconium copper electrode It achieves a good balance of the four performance indicators of the welding electrode:
Excellent electrical conductivity ---------- ensures the minimum impedance of the welding circuit and achieves excellent welding quality.
High temperature mechanical properties ---------- High softening temperature guarantees the performance and life of electrode materials under high temperature welding environment.
Wear resistant ---------- electrode is not easy to wear, prolong life, reduce costs?
High hardness and strength ---- ensure that the electrode head under a certain pressure is not easy to deformation and crush, to ensure the welding quality.
Instructions:
1) Chemical composition analysis of the alloy according to ZBH62-003.1-H62003.8;
2) The hardness of the alloy is measured according to GB230, and the average value is taken at three points for each sample;
3) Eddy current conductance meter for conductivity measurement (eddy current comparison method). Each sample is measured at three points, and its average value is taken. Samples with a diameter less than 15mm can be measured according to GB3048.2;
4) For softening temperature test, the sample is placed in the furnace with the temperature rising to 550℃ (after closing the furnace door, it is required to return to this temperature for 2h within 15Min and then quench water cooling, and the temperature value of the sample room is measured (taking the average value of three points).
5) Electrode is an industrial production of consumables, the amount is relatively large, so its price and cost is also an important factor to consider, chromium zirconium copper electrode relative to its excellent performance, the price is relatively cheap, can meet the needs of production.
6) Chromium-zirconium copper electrode is suitable for spot welding and convex welding of carbon steel plate, stainless steel plate, plated plate and other parts, chromium-zirconium copper material is suitable for manufacturing electrode caps, electrode connecting rod, electrode head, electrode grip, convex welding special electrode, welding wheel, conductive nozzle and other electrode parts.
Beryllium copper (BeCu)
Beryllium copper (BeCu) electrode material has higher hardness (up to HRB95~104), strength (up to 800Mpa/N/mm2) and softening temperature (up to 650℃) than chromium-zirconium copper, but its conductivity is much lower and poor. Beryllium copper (BeCu) electrode material is suitable for welding under high pressure sheet parts, as well as harder materials, such as welding wheels for welding seams; It is also used for some electrode accessories with high strength requirements, such as crank electrode connecting rod, converter for robots; At the same time, it has good elasticity and thermal conductivity, and is suitable for manufacturing stud welding collet. Beryllium copper (BeCu) electrodes are expensive, and we usually list them as special electrode materials.
Copper alumina (CuAl2O3)
Copper aluminum oxide (CuAl2O3) is also known as dispersion strengthened copper, it compared with chromium zirconium copper, has higher strength (up to 600Mpa/N/mm2), excellent high temperature mechanical properties (softening temperature of 900℃) and good electrical conductivity (conductivity 80~85 IACS%), with excellent wear resistance, long life. Copper aluminum oxide (CuAl2O3) is a kind of excellent performance electrode material, whether its strength, softening temperature or conductivity are very superior, especially for welding galvanized sheet, it does not produce the phenomenon of electrode and workpiece sticking as chromium zirconium copper electrode, without frequent grinding, effectively solve the problem of welding galvanized sheet, improve efficiency, reduce production costs. Aluminum oxide copper electrode has excellent welding performance, but its current cost is very expensive, so the current use can not be widely used, but the excellent welding performance of galvanized sheet and the widespread use of galvanized sheet, making its market prospects. Aluminum oxide copper electrode is suitable for welding of galvanized steel plate, aluminum products, carbon steel plate, stainless steel plate and other parts.
Tungsten (W), Molybdenum (Mo)
Tungsten electrode materials are pure Tungsten, tungsten-based high-gravity alloy, and tungsten-copper alloy. Tungsten-based high-gravity alloy is sintered by adding a small amount of nickel-iron or nickel-copper to tungsten, and tungsten-copper composite materials contain 10-40% Copper by weight.
Molybdenum tungsten electrode has high hardness, high melting point, high temperature performance and other characteristics, suitable for welding non-ferrous metal copper, aluminum, nickel, such as the switch of copper braided strip and metal sheet welding.
Appendix: Chemical and physical properties of electrode materials
1) Chromium-zirconium copper (CuCrZr) molding process:
Vacuum melting → hot forging (extrusion)→ solid melting → cold forging (drawing)→ aging treatment
The above process, coupled with strict quality control, ensures excellent electrical conductivity, high strength and good wear resistance of the material.
The standard electrode head, electrode cap and shaped electrode are produced by cold extrusion process and precision machining to further improve the density of the product, and the product performance is more excellent and durable to ensure stable welding quality.
Round rod specifications φ3.0 ~45mm, the box or disk is generally forged according to the requirements of customers.
Chemical composition and physical properties of Al 2 O 3 Cu and BeCu
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Clear View tanks are unparalleled in the safe handling of propane, are extremely weather and corrosion resistant, lightweight and offer the ability to view the level of fuel through the tank.
Corrosion / Weather Resistant
Due to the composite fiberglass construction, Clear View propane tanks can be used in manyenvironments. By design and materials, the fiberglass tank may be used on a vessel, a forklift or an outdoor BBQ alike with little worry of the effects of sun, salt or weather. For aesthetic purposes, cylinders can be easily be cleaned by power-washing with a soap and water solution. Sand-blasting or painting of the cylinders is not necessary. UV additives and stabalizers have been applied to the casing material. Finally, as part of the approval, Clear View fiberglass tanks are tested and approved down to -40F / -40C.
Lightweight, with a Clear View
Fiberglass propane tanks weigh 50% less than steel counterparts and 20% less than aluminum. This lighter weight makes the tanks easier to handle. The ability to view the propane through the fiberglass tank removes all guessing as to the level. Additionally, the translucent quality of the tank allows you to view fuel level as the tank is being filled.
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It is difficult to operate stably because people are in an unnatural position during the welding. At the same time, the operation also has to lift the heavy welding torch and cable, which increases the difficulty of the operation. In addition, the molten iron in the molten pool is easy to sag and form a convex weld pass, which causes the molten iron to flow in serious cases. Therefore, the welding parameters should be strictly controlled in order to obtain a good weld formation.
First of all, ensure that the butt gap between the two plates is guaranteed to be 3mm, not too large or too small, too large will cause breakdown, welding tumor, the phenomenon of concave welding pass, too small will cause the back is not welded through, not fused.
Backing weld
Welding process: The welding parameters are set to 18.5V and 130A.
Angle before welding: Keep 90° on both sides of welding gun and groove, and 80-90° on the back side. When transporting the bar, the zigzag shape or positive crescent type is used, and the middle is stopped on both sides to prevent the edge from biting on both sides, and the middle is too high or through the silk.
Filler welding
Clean up the spatter and welding slag produced by the base welding before welding.
Welding process: Welding parameters are set to voltage 19V, current 140A.
Angle before welding: Keep 90° on both sides of welding gun and groove, and 75-85° on the back side. When the bar is used, the zigzag shape or positive crescent type of rod is used. The middle belt is stopped on both sides, which can prevent the appearance of too high in the middle of the biting edge on both sides. The short arc welding is used when welding. Cover welding begins when the weld pass is about 1mm lower than the base material.
Capping weld
Clean up the spatter and welding slag produced by the base welding before welding.
During the welding process, the welding parameters are set to the voltage 18V and the current 110-120A.
Angle before welding: Keep 90° on both sides of welding gun and groove, and 75-85° on the back side. When transporting the bar, the zigzag shape or positive crescent type transporting bar is used, the middle belt is paused on both sides, and the left and right sides are fully integrated with the base material to swing, which can prevent the appearance of the middle of the biting edge on both sides from being too high.
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1) Personal protective equipment Metal welding and cutting workers should wear appropriate labor protection products before work, such as dust masks, welding gloves, welding work clothes; Wear safety goggles or face mask when operating; Wear rubber shoes when working in wet places or on rainy days. For special operations, you can also wear a long tube breathing apparatus to prevent smoke hazards. To prevent arc damage, choose different types of filters according to the strength of the current. Wear light colored canvas work clothes, tie the cuffs, buckle the neckline, can reduce its damage to the skin.
2) Pre-work inspection and cleaning Before the operation of various containers, pipelines, workpieces stained with flammable gas and solution, should be inspected first, wash away toxic and harmful, flammable and explosive substances, relieve the pressure of containers and pipelines, and eliminate the closed state of containers. Before the fire, the material in the container should be sampled and analyzed, and the work should be carried out after it is qualified; When welding and cutting closed hollow workpieces, air holes must be left. Work in the container, there should be human supervision, and have good ventilation facilities and lighting facilities.
3) Pay attention to site safety details In order to prevent fire and explosion accidents, the workplace should be carefully checked before operation, and flammable and explosive items should not be stored around the workplace. When performing gas welding or gas cutting operations, it is necessary to carefully check the bottle valve, pressure reducing valve and hose, and there can be no air leakage phenomenon; Screw and remove the valve should be done according to the operating procedures.
In the welding operation, it should be noted that the current is too large, the wire sheath damage will produce high temperature; Poor contact at the joint can cause a fire. Therefore, the operation should be carefully checked before the replacement of defective equipment. In addition, it should also be noted that when welding, cutting pipes, equipment, heat conduction may cause flammable and explosive items at the other end to catch fire or even explode. Check carefully before operation and remove dangerous items at the other end.
When cutting old equipment and scrap steel, pay attention to removing flammable and explosive items included in them. At the job site, a sufficient number of fire extinguishing equipment should be equipped, and the effective period of the fire extinguishing equipment should be checked to ensure its effective use. After the welding and cutting operations, the site should be carefully inspected to eliminate the remaining kindling and avoid future problems.
4) For the prevention of electric shock accidents, the welding machine shell and non-charged metal components must protect the ground (or zero), and the insulation resistance should be large enough. The terminal should be covered with a cover; Welding handle, welding pliers and welding cable insulation; At the same time, distance should be kept between charged bodies and between charged bodies and other objects. The welding machine and the power cord should be placed in a place that is not accessible to the human body.
When climbing and welding, it should be noted that the distance from the high-voltage grid is not too close, the cable used for operation can not be wrapped around the body or on the shoulder, the cable should be tied to the scaffolding and other facilities, so as not to step on the foot, resulting in damage to the insulation layer. When moving, repairing and repairing the welding machine, replacing the fuse, changing the polarity and other operations, the power switch must be cut off.
Wear insulated gloves when pushing and pulling the power knife, and the person should stand on the side to prevent the arc spark from burning the face. In the event of electric shock, the power supply should be cut off immediately and on-site first aid should be carried out.
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Copper contact tip, the color is purple, but not entirely pure copper, sometimes it also adds a small amount of deoxidation elements or other elements to improve the material and performance, so it is also a copper alloy. At present, domestic copper processing materials can be divided into four types according to the composition: oxygen-free copper, deoxidized copper, ordinary copper and special copper with a small amount of alloying elements. Copper is widely used in the production of conductive and thermal equipment. It is also used in some non-oxidizing acids, bases, salt solutions and a variety of organic acids, which have good corrosion resistance and are used in the chemical industry. Although the electrical and thermal conductivity of copper is second only to silver, it has good weldability, and can be made into various semi-finished products and finished products by cold and thermoplastic processing.
Chromium zirconium copper contact tip, with high strength, hardness, conductivity and thermal conductivity, and wear resistance, crack resistance and softening properties, after a long time after treatment hardness, strength, conductivity and thermal conductivity are significantly improved, easy to weld. Widely used in motor commutator, welding machine, seam welding machine and so on.
Chromium zirconium copper contact tip, has good electrical conductivity, thermal conductivity, high hardness, wear resistance and explosion resistance, crack resistance and high softening temperature, welding electrode loss is less, welding speed is fast, the total cost of welding is low, suitable for welding welding machine electrode related accessories, in Europe and the United States welding gun, mainly with copper conductive contact tip, mainly used in Europe and the United States protective gas to argon gas mixture. The arc is long, the gas cooling performance is poor, the main way of the failure of the conductive contact tip is caused by the micro arc between the hole wall of the conductive contact tip and the welding wire, so the conductive copper with better conductive conductivity is used as the conductive contact tip, and the CO2 gas is used as the protective gas in Asia, the arc is short, the gas cooling ability is strong, and the conductive contact tip is mainly chromium zirconium copper on the welding gun in Japan and South Korea. Japan believes that the failure of the conductive contact tip is mainly caused by the friction loss between the inner hole wall of the conductive contact tip and the welding wire, so the harder chromium zirconium copper material is mainly used. Since China mainly uses CO2 gas as a protective gas, chrome zirconium copper conductive contact tip should be selected. The national standard for the conductive contact tip is 9mm, but most of the existing conductive contact tip on the domestic market is far lower than this standard, the process standard is uneven, resulting in the conductive contact tip inner hole wall burr, the wire is not smooth, good conductive contact tip in the unit price is relatively high but the reaction in the service life, is often several times the general conductive contact tip. It also reduces the disadvantages of frequent replacement of the conductive contact tip (time saving). The most important thing is that the good welding effect greatly improves the production efficiency, and brings greater development and benefits to the production enterprises!
Comparison of life of conductive contact tip
1. Material is the main reason affecting the life of the conductive contact tip. The conductivity test confirmed that the conductivity of the common copper contact tip on the market is only about 80%IACS, which is far lower than the national standard, so the service life is low.
Good conductive contact tip copper material/chromium zirconium copper material strictly implement national standards, conductivity above 100%IACS, so it has a long service life.
2. The manufacturing process is the second reason that affects the life of the conductive contact tip. The forming of holes is the bottleneck of making conductive contact tip. Due to the difficulty in forming the inner hole of the conductive contact tip, the "extrusion forging" forming method of the copper pipe with larger aperture is generally adopted in our country. The so-called "extrusion forging" is to insert a steel wire with a suitable diameter into the copper pipe with a large hole, rotate the copper pipe at one end, reduce the inner hole of the copper pipe by reducing the outer diameter of the copper pipe, and finally extract the steel wire to make the hole shape.
This production method only partially solves the forming problem of the inner hole of the conductive contact tip, and has disadvantages. See Figure 1 - Common market conductive contact tip. The conductive contact tip is suitable for welding wire diameter of 0.8mm. The aperture on the right side of the contact tip after extrusion forging is 1.01mm, which is the working part of the contact tip. The left aperture without extrusion forging is 1.39mm, the hole depth is 18mm, and this part is basically not working. It is calculated that the length of the non-working part of the hole accounts for 40% of the total length, which greatly reduces the life of the conductive contact tip.
The good conductive contact tip is produced by copper tube produced by patented technology. The diameter of the inner hole of the copper tube is as small as 0.9mm, and the aperture is consistent and smooth on the full length of the conductive contact tip, which greatly improves the service life of the conductive contact tip.
Combined with the above two life factors, the service life of the good conductive contact tip is more than double that of the common conductive contact tip on the market.
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1. Welding splash
The splash produced by laser welding seriously affects the surface quality of the weld and can contaminate and damage the lens. Generally, after laser welding is completed, many metal particles appear on the surface of the material or workpiece, attached to the surface of the material or workpiece.
Spatter cause: The surface of the processed material or workpiece is not cleaned, there are oil stains or pollutants, and it may also be caused by volatilization of the galvanized layer.
The solution:
A. Pay attention to cleaning materials or workpieces before laser welding.
B. Splash is directly related to power density. Appropriate reduction of welding energy can reduce spatter.
2. Cracks
2. The cracks produced by continuous laser welding are mainly hot cracks, such as crystal cracks, liquefaction cracks, etc.
The cause of the crack is mainly caused by excessive shrinkage force before the weld is not completely solidified.
Solution: Filling wire, preheating and other measures can reduce or eliminate cracks.
3. Stomata
The surface porosity of weld is a defect that is easy to appear in laser welding.
Causes of stomata:
A. The laser welding pool is deep and narrow, and the cooling speed is fast. The gas produced in the liquid molten pool is too late to overflow, which easily leads to the formation of pores.
B, the weld surface is not cleaned, or galvanized zinc vapor volatilization.
Solution: Clean the surface and weld surface before welding to improve the volatilization of zinc when heated. In addition, the blowing direction also affects the formation of stomata.
4. Bite the edge
The biting edge refers to: the weld is not well combined with the base material, there is a groove, the depth is greater than 0.5mm, the total length is greater than 10% of the weld length, or greater than the length required by the acceptance standard.
Reasons for edge biting:
A. The welding speed is too fast, and the liquid metal in the weld will not be redistributed on the back of the small hole, forming A biting edge on both sides of the weld.
B, the joint assembly gap is too large, the molten metal in the joint filling is reduced, and it is also easy to bite.
C, at the end of laser welding, if the energy decline time is too fast, the small hole is easy to collapse, and it will also cause local edge biting.
The solution:
A. Control the processing power and speed matching of laser welding machine to avoid edge biting.
B. The edge of the weld found in the inspection can be polished, cleaned and repaired to make it meet the requirements of the acceptance standard.
5. Weld accumulation
The weld is obviously overfilled, and the weld is too high when it is filled.
The cause of weld accumulation: the wire feed speed is too fast or the welding speed is too slow.
Solution: Improve the welding speed or reduce the wire feed speed, or reduce the laser power.
6. Welding deviation
The weld metal does not solidify in the center of the joint structure.
The reason for this situation: inaccurate positioning during welding, or inaccurate filling welding time and welding wire alignment.
Solution: Adjust the welding position, or adjust the repair welding time and the position of the welding wire, as well as the position of the lamp, the welding wire and the weld.
7. The weld is dented
Weld concave refers to the phenomenon of concave weld metal surface.
The reason for the weld depression: when brazing, the solder joint center is poor. The center of the spot is close to the lower plate and deviates from the center of the weld, resulting in partial melting of the base material.
Solution: Adjust the light matching.
8. Bad weld forming
Poor weld forming includes: poor weld ripple, uneven and irregular weld, uneven transition between weld and base material, poor weld and uneven weld.
The reason for this situation: when the weld is brazed, the wire feed is unstable, or the light is discontinuous.
Solution: Adjust the stability of the equipment.
9. Uneven weld bead
Uneven weld path refers to: when the weld trajectory changes greatly, the corner is prone to uneven weld path or molding.
Cause: the trajectory of the weld changes greatly, and the teaching is uneven.
Solution: Welding under the best parameters, adjust the Angle of view, so that the Angle is consistent.
10. Surface slag inclusion
Surface slag inclusion refers to: in the welding process, the skin slag inclusion that can be seen from the outside mainly appears between layers.
Cause analysis of surface slag inclusion:
A, multi-layer and multi-pass welding, the interlayer coating is not clean; Or the surface of the previous layer of weld is not smooth or the surface of the weldment does not meet the requirements.
B, welding input energy is low, welding speed is too fast and other improper welding operation technology.
The solution:
A. Select reasonable welding current and welding speed. The interlayer coating must be cleaned during multilayer and multipass welding.
B. Polish the weld to remove the slag on the surface, and repair the weld if necessary
What are the laser welding processes? Laser welding is a new type of welding, laser welding is mainly for thin-wall materials, precision parts welding, spot welding, butt welding, overlap welding, sealing welding, etc., its characteristics are: with a high depth to width ratio, small weld width, small heat affected zone, small deformation, fast welding speed. The weld is smooth and beautiful, and there is no need to handle or only a simple processing procedure after welding. The weld has high quality, no porosity, can reduce and optimize the impurities of the base material, the tissue can be refined after welding, and the strength and toughness of the weld are at least equal to or even more than the base metal. Precise control, small focus point, high precision positioning, easy to achieve automation. It can realize the welding between some dissimilar materials.
1, laser self-fusion welding
Laser welding is the use of laser beam excellent directivity and high power density and other characteristics of the work, through the optical system to focus the laser beam in a very small area, in a very short time to be welded to form a highly concentrated energy heat source area, so that the solder to be melted and formed a solid solder joints and welds. Laser welding: the depth to width ratio is large; High speed and high precision; Small heat input, small deformation; Non-contact welding; Not affected by magnetic field, no need to vacuum.
2, laser wire welding
Laser wire filling welding refers to the method of pre-filling a specific welding material in the weld and melting it with laser irradiation or filling the welding material at the same time of laser irradiation to form a welding joint. Compared with non-wire welding, laser wire filling welding solves the problem of strict requirements for workpiece processing and assembly. Smaller power welding thicker parts; By adjusting the composition of the filler wire, the microstructure properties of the weld area can be controlled.
3, laser flight welding
Remote laser welding is a kind of laser welding method which uses high-speed scanning lens to process long working distance. High positioning accuracy, short time, fast welding speed, high efficiency; Will not interfere with the welding fixture, optical lens pollution less; Arbitrary shape welds can be customized to optimize structural strength, etc. Generally, the weld has no gas protection, and the splash is larger. It is widely used in thin high-strength steel plate and galvanized steel plate such as body covering parts.
4, laser brazing
The laser beam emitted by the laser generator is focused on the surface of the welding wire and heated, so that the welding wire is heated and melted (the base material is not melted) to wet the base material, fill the joint gap, and combine with the base material to form a weld to achieve a good connection
5, laser swing welding
By swinging the reflection lens inside the welding head, the laser swinging is controlled to stir the welding solution pool to promote the gas overflow from the solution pool and refine the grain. At the same time, the sensitivity of laser welding to incoming material gap can be reduced. Especially suitable for aluminum alloy, copper and dissimilar materials welding.
6, laser arc composite welding
Laser-arc composite welding combines two kinds of laser and arc heat sources with different physical properties and energy transmission mechanisms to form a new and efficient heat source. Composite welding features: 1, compared with laser welding, bridge ability is enhanced, improve the organization. 2, compared with arc welding, small deformation, high welding speed, deep penetration. 3, and the length of each heat source and make up their own shortcomings, 1+1>2.
Welding is a processing process and connection method that combines atoms between two workpieces by heating, pressurizing, or both. Welding is widely used for both metals and non-metals.
Development history of welding technology
Forge welding technology appeared in Egypt in 3000 BC.
In 2000 BC, the Yin Dynasty of China used casting and welding to make weapons.
1801 - H.Davy of England discovers electric arc.
1836 - Edmund Davy discovers acetylene gas.
1856 - James Joule, an English physicist, discovers the principle of resistance welding.
1959 - Deville and Debray invent hydrogen - oxygen welding.
1881: Frenchman De Meritens invents the earliest carbon arc welding machine.
1881: Dr. R. H. Thurston of the United States spent six years to complete all the experiments on the strength and extensibility of a full range of copper-zinc alloy brazing materials.
1882 - The austenitic manganese steel invented by Robert A. Hadfield of England and named after him is patented.
In 1885, Elihu Thompson, an American, patented a resistance welding machine.
1885 - Russian Benardos Olszewski develops carbon arc welding technology.
1888: Russian H. l. C. L.
1889-1890: C. L. Coffin, an American, performed the first arc welding using a light wire as an electrode.
In 1890; The American C. L. Coffin proposed the concept of welding in an oxidizing medium.
1890 - British man Brown makes the first attempt to rob a bank using oxygen and gas cutting.
1895 - Bavarian Konrad Roentgen observes X-rays produced by a stream of electrons passing through a vacuum tube.
1895 - Frenchman Le Chatelier receives a certificate for inventing the oxyacetylene flame.
1898: German Goldschmidt invented thermite welding.
1898: The German Klein. Schmidt invented arc welding of copper electrodes.
1900: Strohmyer invented the thin-coated electrode.
In 1900, the French Fouch and Picard made the first oxy-acetylene cutting torch.
1901 - German Menne invents oxygen spear cutting.
1904: The Swede Oscar. Kjellberg established the world's first electrode factory - ESAB's OK Electrode factory.
In 1904, Avery invented the portable steel cylinder.
1907: When demolishing the old Central railway station in New York, more than 20% of the engineering cost was saved due to the use of oxy-acetylene cutting.
1911 - Philadelphia & Suburban Gas Company builds the first 11-mile line to be welded using oxygen solvent gas welding.
1912: The first oxy-acetylene gas welded steel pipe was put on the market.
1912 - The Edward G. Budd Company in Philadelphia produces the first all-steel automobile body welded with resistance spot welding.
Circa 1912: In order to produce the famous Model T car, the Ford Motor Company in the United States completed the modern welding process in the laboratory of its factory.
1913 - Avery and Fisher perfect acetylene cylinders in Indianapolis, USA.
1916: Ansel. The first is the invention of X-ray nondestructive testing in the welding zone.
1917: During World War I, 109 ship engines captured from Germany were repaired using arc welding, and half a million American soldiers were transported to France using these repaired ships.
1917: Webster & Southbridge Electric Company in Massachusetts used arc welding equipment to weld 11 miles of pipeline with a diameter of 3 inches.
1919: Comfort A. dams forms the American Welding Society (AWS).
1919 - C.J.Halslag invents AC welding.
1920 - Gerdien discovers the heat flux effect.
1920 - Fulagar, the first steamship with an all-welded hull, is launched in England.
Circa 1920: Began using arc welding to repair some valuable equipment.
Circa 1920: The Johnson Process for welding steel pipes using resistance welding is patented.
Circa 1920: The Poughkeepsie Socony, the first oil tanker built using the welding method, is launched in the United States.
Circa 1920: flux-cored wire is used for wear-resistant surfacing.
1922 - Prairie Pipeline Company successfully completes the laying of an 8-inch diameter, 140-mile crude oil pipeline from Mexico to Texas using oxy-acetylene welding technology.
1923: Stody invents surfacing welding.
1923: The world's first floating roof storage tank (used to store gasoline or other chemicals) is built; Its advantage is that the tank can be raised or lowered like a telescope by a welded floating roof and tank wall, so that the volume of the tank can be easily changed.
1924: Magnolia Gas Company builds 14 miles of all-welded natural gas line using oxy-acetylene welding technology.
1924: H.H. ester was the first in the United States to use X-ray photography to test the quality of castings to be installed at a steam pressure of 8.3Mpa for the Boston Edison power plant.
1926: American Langmuir invented atomic hydrogen welding.
1926: Alexandre invented the principle of CO2 gas shielded welding.
1926: A.O.Smih company in the United States took the lead in introducing the production method of applying a protective solid coating (that is, manual arc welding electrode) on the metal electrode for arc welding.
1926: Chromium-tungsten-cobalt alloy receives the first patent for flux-cored wire.
1926: Americans M. Hoart and P.K. evers obtain a patent for the use of helium as an arc protection gas.
1927: Lindberg successfully flew the Ryan monoplane over the Atlantic Ocean, with a fuselage made of welded steel tubes.
1928: The first structural steel welding code, Code for Fusion Welding and Gas Cutting in Building Structures, is published by the American Welding Society, which is the predecessor of today's D1.1 Structural Steel Welding Code.
1930: The Georgia Railroad Center uses a continuous welding method to lay the railroad in two tunnels. The welded track was put into use two years later when the line was through.
1930: The former Soviet Union Robinov invented submerged arc welding.
1931 - The Empire State Building is built with a welded all-steel structure.
1933: The first joint welded using the arc welding process was laid with a long transmission line with no liner construction.
1933 - San Francisco's Golden Gate Bridge, then the highest suspension bridge in the world, opens to traffic, made of 87,750 tons of welded steel.
1934 - Barton Welding Institute is established.
Barton Institute founder Yevkin Oskalovich Barton
The largest welded iron bridge over the River Deniebe in Europe - Barton Bridge
1934: The Unheated pressure Vessel Code is published by the API - ASME collaboration.
1935: Linde Air Products of the United States perfected the submerged arc welding technology.
1936: Wasserman invented low temperature brazing.
1939: American Reinecke invented the ion flow spray gun.
1940 - Exchequer, the first all-welded ship, is launched at Ingalls Shipyard in the United States.
1941: American Meredith invented tungsten inert gas shielded arc welding (helium arc welding).
1941: During World War II, ships, aircraft, tanks and various heavy weapons were manufactured using a large number of welding techniques.
1943: Behl invented ultrasonic welding.
1943: Aircraft builders first welded the hollow blades of aircraft steel propellers using atomic hydrogen welding, submerged arc welding, and MIG welding.
1944: British Carl invented explosive welding.
1947: The invention of electroslag welding in the former Soviet Union by Bopo Noebech (Voroshevich).
1949 - The first FORD car with an all-welded structure made using arc and resistance welding processes rolls off the assembly line.
In 1950, Americans Muller, Gibson and Anderson obtained the first patent for the excessive welding of MIG.
1950 - German F. B. uhorn discovers plasma arcs.
Circa 1950: Electroslag welding is first used in production in the former Soviet Union.
1953: Hunt invented cold pressure welding.
1953: The former Soviet Union Lyupovsky, Japan Sekiguchi and others invented CO2 gas shielded arc welding.
1954: Self-protecting flux-cored wire was put into production at Lincoln Electric Company in the United States.
1954 - The Nautilus, the first welded nuclear submarine, enters service with the U.S. Navy.
1954: Benard invents the tubular electrode.
1955: Thom, USA. Claverd invents high-frequency induction welding.
1956: Harbin Welding Research Institute was established in China.
1956: The former Soviet Union Chudikov invented friction welding technology.
1957: The invention of electron beam welding by Schgill in France.
1957: The former Soviet Union Kazakov invented diffusion welding.
1957: "Welding" is published, which is the first professional welding magazine in China.
Circa 1957: The United States, the United Kingdom, and the former Soviet Union all used CO2 as a protective gas in the process of short circuit welding.
1960: Airco of the United States introduced the metal pulse gas welding process.
1962: The patent for gas welding was granted to the Belgian Arcos.
1962 - Electron beam welding is first used on supersonic aircraft and B-70 bombers.
1964: The patent for the hot wire welding method and the coordinated control of the MIG welding method is granted to the American Manz.
1965 - The welded Appllo 10 spacecraft successfully landed on the moon.
1967: Arada invented continuous laser welding.
In 1967, the world's first submarine pipeline was successfully laid in the Gulf of Mexico, which was manufactured by the Krank Pilia company of the United States using the thermal thread process and welding process.
1968: Welded 22 floors above the John Hancock Center in Chicago to create the world's tallest sharp-angled steel structure at 1,107 feet.
1969: Linde Company of the United States proposed the hot wire plasma arc spraying process.
1970: Thyristor inverter welding machine came out.
1976: Arada invented series electron beam welding.
Around 1980: Semiconductor circuits and computer circuits are widely used to control welding and cutting processes.
Circa 1980: Use steam brazing to weld printed circuit boards.
1983: The circular top of the 160-foot diameter flap structure on the space shuttle was welded using the submerged arc and shielded welding method and inspected using a radiographic flaw detector.
1988: Welding robots began to be widely used in automobile production lines.
Around 1990: Inverter technology has been greatly developed, and the result is a reduction in the weight and size of welding equipment.
1991: The British Welding Institute invented friction stir welding and successfully welded aluminum alloy plates.
1993: The United States Army Abrams main battle Tank was successfully welded using a robot-controlled CO2 laser.
1996: A research group of more than 30 people headed by B.K.Lebegev, academician of the Barton Welding Institute in Ukraine, researched and developed the welding technology of human tissue.
2001: Human tissue welding was successfully applied in clinic.
2002: Welding of the Three Gorges Turbine is completed, the largest turbine in the world that has been built and is currently under construction.
1985:Huarui was established
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How to judge the size of the current listen to a welder who has been engaged in welding for more than 10 years, beginners can correctly weld the current when welding will be very important to the quality of welding, because the welding current has a great impact on the molding of the weld.
The welding current is too small, which will cause the phenomenon of non-penetration, non-fusion and sticking electrode. The current is too large, will cause welding penetration, edge bite, and welding nodules and other quality defects.
How should the welder choose the right welding current when welding?
The master said that the correct choice of welding current needs to be selected according to a variety of parameters. Like the thickness of the weldment, the diameter of the electrode and the welding position.
For manual arc welding, the size of the welding current depends on the diameter and size of the electrode, which is usually the diameter of the electrode multiplied by the empirical coefficient.
The experience coefficient of the common 2-4 mm electrode is 30-40, and if the diameter of the electrode is 4-6, the experience coefficient is 40-60. It can be adjusted appropriately according to the specific situation of the site.
In the field, the welder can intuitively judge according to the actual situation, the arc is difficult, the welding rod is easy to stick, the forming is not smooth, and the welding rod is difficult to melt. On the contrary, if the welding spatter is too large, the weld pool is excessive, and the welding rod is red, the current is too large.
The size of the welding current selection also depends on the technical level and operating habits of a welder. Some novices need to adjust the current size according to the ammeter on the welding machine at the beginning, and experienced welders can judge by experience and the sound emitted when the welding rod burns.
According to the master, the sound emitted by the appropriate current is very uniform and smooth, and the shape and sound of the molten pool can be adjusted in a timely manner.
The old master said that each welder has its own skills and experience, and the current selection varies from person to person.
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In the industrial manufacturing of nuclear power, construction, oil and gas pipelines, when the position of structural parts is difficult to adjust, welding in non-planar positions is inevitable. Overhead welding is the most difficult of the four basic welding positions. Therefore, it is of great significance to improve the weld forming quality and process adaptability of overhead welding. In the process of overhead welding, when the heat input is too small, it is difficult to penetrate the base metal, and when the heat input is too large, it will lead to an increase in the volume of the weld pool. In this case, the tail of the molten pool, which has lost the support of the arc force, will flow downward under the action of gravity and complete the solidification. In addition, even if the base metal can be completely penetrated, it is difficult to form a high enough additive solid on the back weld, and even a concave defect will be formed, significantly reducing the shape and mechanical properties of the welded joint.
This paper presents a new overhead welding technique, which uses a laser-arc hybrid heat source and adds a copper liner (COL) on the back of the weld. The weld morphology, mechanical properties and microstructure of the joint under three forming methods of copper gasket, ceramic gasket (CEL) and no gasket (NOL) were compared in order to improve the welding quality and mechanical properties of the joint. In addition, the process window and process adaptability of the process were also studied.
Figure 1- Test methods: (a) schematic diagram of overhead welding, (b) backbend test method, (c) process adaptability test (dislocation) assembly method, (d) process adaptability test (butt gap) assembly method
Figure 2- The macro morphology of the weld and the mechanical properties of the welded joint under different welding parameters and forming methods
Figure 3- Forming mechanism of the back side when COL is used in overhead welding
Figure 4- Microstructure of the top center of the back weld under different forming processes and parameters: (a) NOL-140A, (b) CEL-140A, (c) COL-140A, (d) COL-150A, (e) COL-160A, (f) COL-170A
Figure 5- Hardness distribution of weld section: (a)NOL-140A, (b) CEL-140A, (c) COL-140A, (d) COL-150A, (e) COL-160A, (f) COL170A
Figure 6- Detection results of copper content in the weld: (a) NOL-140A, (b) CEL-140A, (c) COL-140A, (d) COL-150A, (e) COL-160A, (f) COL-170A
Figure 7- Macroscopic morphology of weld back and cross section under different butt gap and dislocation: (a) cross-sectional topography of 0-1.00mm dislocation, (b), (c), (d), (e) cross-sectional topography of 0.25, 0.50, 0.75 and 1.00mm dislocation, (f) cross-sectional topography of 0.50-2.00mm butt gap, (g), (h), (i), (j) 0.50, 1.00, 1.50 and 2.00 mm butt clearance
The main conclusions are as follows:
In this paper, the macroscopic morphology and mechanical properties of the downward welding joint with three forming methods are analyzed. By adding COL to the back weld, the weld appearance quality and process adaptability of LASer-arc hybrid overhead welding were improved.
(1) In the process of overhead welding, the use of COL can eliminate the concave defects of the back weld, and significantly improve the appearance and quality of the weld. COL can be used to form a stable backing and solid under different misalignment and butt clearance. The backing plus solid and its width are not less than 0.71 and 3.66 mm respectively.
(2) The use of COL can expand the process window of laser-arc hybrid overhead welding and improve the process adaptability. When the welding current is 140-170A, the butt gap is 0.5-2.0mm, or the dislocation is 0-1.0mm, a good weld can be obtained.
(3) When COL is used, the cooling rate at the back weld strengthening is accelerated, the grain is refined, and the hardness is increased. The concave defect of the back weld does not significantly reduce the tensile strength of the welded joint, but the specimen with backing plus solid can withstand greater loads in the back bending test.
(4) The test results of copper content in welds show that the use of COL does not significantly affect the content and distribution of copper in welds.
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Methods to prevent welding cracks
1. Select materials correctly
Choose alkaline low-hydrogen electrode and flux to reduce the content of diffused hydrogen in weld metal; Do a good job in the selection of base material and welding material matching; If the technical conditions permit, materials with good toughness (such as welding materials with a lower strength level) can be selected, or "soft" covers can be implemented to reduce the residual stress on the surface; If necessary, chemical analysis, mechanical properties, weldability and crack sensitivity tests are carried out on the base material and welding material before manufacturing.
2. Welding operation is carried out in strict accordance with the correct process specifications obtained by the test
Mainly includes: strictly according to the specification of welding rod drying; Select appropriate welding specifications and wire energy, reasonable current, voltage, welding speed, interlayer temperature and correct welding sequence; Check and treat spot welding; Clean the root of double-sided welding; Carefully clean the groove and welding wire to remove oil, rust and moisture.
3. Select a reasonable welding structure to avoid excessive restraint stress; Correct groove form and welding sequence; Reduce the peak of welding residual stress.
4. Preheating before welding, slow cooling after welding, controlling interlayer temperature and post-welding heat treatment are effective methods to prevent cold cracks for high-strength steel with poor weldability and unavoidable high-restraint structural forms. Preheating and slow cooling can slow down the cooling rate (prolong the residence time of △t 800~500℃), improve the microstructure of the joint, reduce the hardening tendency, and reduce the microstructure stress; Post-welding heat treatment can eliminate welding residual stress and reduce the content of diffused hydrogen in the weld. In most cases, stress relief heat treatment should be carried out immediately after welding.
5. Hammering immediately after welding to disperse the residual stress and avoid causing high stress areas is one of the effective ways to prevent cold cracks during local repair welding.
6. In the weld root and the weld surface where the stress is relatively concentrated (the restraint stress of the heat affected zone is low), the welding rod with lower strength level is often used to achieve good results under high restraint.
7. The use of inert gas shielded welding can maximize the control of the hydrogen content of the weld and reduce the sensitivity of cold cracks, so TIG and MIG welding should be vigorously promoted.
Method of preventing welding hot crack
1. Limit the content of elements and harmful impurities that are prone to segregation in steel and welding materials, especially the content of S, P, and C, because they not only form low melting point eutectic, but also promote segregation. C≤0.10% thermal crack sensitivity can be greatly reduced. If necessary, chemical analysis of the material, low power inspection (such as sulfur printing, etc.).
2. Adjust the chemical composition of weld metal, improve the organization, refine the grain, improve plasticity, change the shape and distribution of harmful impurities, reduce segregation, such as the use of austenite plus less than 6% of the ferrite biphase structure.
3. Improve the basicity of the electrode and flux to reduce the content of impurities in the weld and improve the degree of segregation.
4. Select a reasonable groove form, weld forming coefficient ψ=b/h > 1, avoid narrow and deep "pear-shaped" weld, (welding current is too large will form a "pear-shaped" weld), prevent the cylindrical crystal in the center of the weld, resulting in center segregation to form a brittle section; Multi-layer and multi-pass welding is adopted to disrupt segregation aggregation.
5. The use of small (appropriate) welding line energy, for austenitic (nickel-based) stainless steel should try to use a small welding line energy (no preheating, no swing or less swing, fast welding, small current), strict control of the interlayer temperature, in order to shorten the residence time of weld metal in the high temperature zone;
6. Pay attention to the protection of arc retraction, arc retraction should be slow and fill the arc pit to prevent the thermal crack caused by arc pit segregation;
7. Try to avoid multiple repairs to prevent lattice defects from gathering and producing polygonal hot cracks;
8. Take measures to minimize the joint stress, avoid stress concentration, and reduce the stiffness near the weld, properly arrange the welding order, and try to make most of the weld welding under a small stiffness, so that it has room for shrinkage.
Methods to prevent reheat cracking
1. When selecting materials, attention should be paid to the carbide forming elements that can cause precipitation, especially the content of V. When high V steel must be used, special attention should be paid to welding and heat treatment.
2. Avoid the reheat sensitive area during heat treatment, which can reduce the possibility of reheat crack, and do heat treatment process test before heat treatment if necessary.
3. Minimize residual stress and stress concentration, reduce residual height, eliminate edge bite, incomplete penetration and other defects, and polish residual height and weld toe smoothly if necessary; Increase preheating temperature, slow cooling after welding, reduce residual stress.
4. Appropriate line energy to prevent heat affected zone from overheating and coarse grains.
5. Under the premise of meeting the design requirements, choose a lower strength grade of the electrode to release a part of the stress eliminated by the heat treatment process (let the stress relax in the weld), which is good for reducing reheat cracks.
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First stop:EXPOMAFE 2023 BRAZIL@9-13th,May 2023
When we first arrived at the airport, the weather was not very good.But we are so happy to be in this beautiful country again.
The show was held at the Sao Paulo Expo-Exhibition & Convention Center. We packed our bags and checked into the hotel to wait for the show to start the next day.
Looking forward to meeting our customers
Our booth No.I132,We displayed and tested our products on site.
We were very happy to meet many old and new partners, and hope that we can cooperate happily in the future
Second stop:FABTECH 2023 MEXICO @16-18th,May 2023
Mexico is a very beautiful country, we were very happy to be here for the exhibition.
In Mexico, our company also has many customers who have cooperated with us for a long time to come to our exhibition hall, and we are also very happy to meet new friends
Our booth is NO.3039
We brought a lot of the company's best-selling products and new products to show
Last stop:BEIJING ESSEN FAIR @27-30th,June 2023@Shenzhen,Booth No.15006
We are waiting for your...
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Welding quality testing refers to the testing of welding results, with the purpose of ensuring the integrity, reliability, safety and serviceability of welding structure. In addition to the requirements of welding technology and process, welding quality inspection is also an important part of welding structure quality management.
This time we will talk about the welding quality test method: tightness test.
So how to test the tightness of welded joints?
In general, the following methods can be used for detection:
1. Sinking test
Used for small vessels or pipes subjected to low internal pressure. Before inspection, the container or pipe should be filled with compressed air at a certain pressure (0.4-0.5MPa), and then submerged to check the tightness, such as right leakage; Bubbles must occur in the water. This is also a common part of the bicycle tube to check for air leaks2. Water holding test
The static pressure generated by water dead weight is used to check whether the structure has leakage phenomenon. Based on visual inspection, it is suitable for general welding structure which is not compressed but requires sealing.
3. Ammonia leakage test
It is used in the same way as coal drainage leakage test, and its sensitivity is higher than kerosene leakage test. Before the test, paste a white strip or bandage soaked with 5% HgNO3, aqueous solution or phenolphthalein reagent on the easy observation side of the weld, and then fill the container with ammonia or add compressed air with 1% nitrogen.
If there is leakage, it will stain the white paper strip or bandage. The solution of 5%HgNO3 was black spot, and the solution of phenolphthalein was erythema.
4. Kerosene leakage test
It is used for welding structure with small internal pressure and certain sealing requirement. Kerosene has strong permeability and is very suitable for sealing inspection of welds. Before inspection, brush lime water on the side of the weld for observation, and brush kerosene on the other side of the weld after drying. If there are penetration defects, the lime layer will spill coal oil spots or kerosene belts. The observation time was 15-30min.
5. Helium mass spectrometry test
Helium mass spectrometry test is the most effective means of sealing test at present. Helium mass spectrometer is very sensitive and can detect helium with volume fraction of 10-6. The container was filled with helium before the test, and the leak was detected outside the weld of the container. The disadvantage is the high price of helium and the long inspection period.
Although helium gas is highly permeable, it takes a long time to penetrate very small gaps that cannot be detected by other means, often tens of hours in some thick-walled vessels. Proper heating can speed up leak detection.
6, air tightness test
Air tightness test is a conventional test means for boiler, pressure vessel and other important welded structures requiring air tightness. The medium is clean air, and the test pressure is generally equal to the design pressure. The pressure should be increased step by step during the test.
After reaching the design pressure, apply soapy water on the outside of the weld or sealing surface and check whether the soapy water is bubbling. Because of the risk of explosion in the air tightness test, it should be carried out after the water pressure test is qualified.
Air tightness test is different from pressure test:
1, its purpose is different, air tightness test is to test the tightness of the pressure vessel, pressure test is to test the pressure strength of the pressure vessel. Secondly, the test pressure is different. The air tightness test pressure is the design pressure of the container, and the air pressure test pressure is 1.15 times of the design pressure.
Air pressure test is mainly to test the strength and tightness of the equipment, air tightness test is mainly to test the tightness of the equipment, especially the small penetration defects; The air tightness test focuses more on whether the equipment has small leakage, and the air pressure test focuses on the overall strength of the equipment.
2, the use of media
Air is generally used in the actual operation of the air pressure test. In addition to the air tightness test, ammonia, halogen or helium is used if the medium is highly toxic and leakage or easy penetration is not allowed
3. Safety accessories
Air pressure test, do not need to install safety accessories on the equipment; Air tightness test is generally carried out after the installation of safety accessories (tolerance gauge).
4. Order
The air tightness test should be carried out after the pressure or hydraulic test is completed.
5. Test the pressure
The pressure test pressure is 1.15 times the design pressure, and the internal pressure equipment needs to be multiplied by the temperature dressing coefficient; Air tightness test medium for air test pressure for design pressure, such as the use of other media, should also be adjusted according to the medium situation.
6. Use occasion
Pressure test: hydraulic test is preferred. If the hydraulic test cannot be used due to the equipment structure or support, or the equipment volume is larger, the pressure test is generally used. Air tightness test: medium for high or extremely harmful medium, or do not allow leakage.
Air pressure test belongs to pressure test, in order to check the pressure strength of equipment. Air tightness test belongs to the compact test, in order to test the sealing performance of the equipment.
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Dehydrogenation treatment, also called dehydrogenation heat treatment, or called post-welding heat treatment.
The purpose of post-heat treatment of the weld area immediately after welding is to reduce the hardness of the weld area or eliminate hydrogen and other harmful substances in the welding area. In this point, the role of post-heat treatment and post-welding is partly the same.
After welding, the cooling rate of weld and welding joint is reduced by heat, which promotes hydrogen escape and avoids hardness appreciation.
(1) The post heating for the purpose of improving the performance of the welded joint and reducing its hardness can be effective only when the welding zone is still at a high temperature after welding.
(2) The post heating in order to prevent low temperature cracks is mainly to promote hydrogen energy to be fully excluded in the welding zone.
The removal of hydrogen depends on the temperature of the afterheat and the holding time. The temperature for the main purpose of dehydrogenation is generally 200 ~ 300 degrees, and the afterheat time is 0.5 ~ 1 hour.
For welds under the following conditions, post-heat dehydrogenation treatment should be carried out immediately after welding (4 points) :
(1) The thickness is greater than 32mm and the standard tensile strength σb is greater than 540MPa;
(2) low alloy steel material with thickness greater than 38mm;
(3) Butt weld between the embedded nozzle and the pressure vessel;
(4) Welding process evaluation to determine the need for hydrogen elimination treatment.
The value of afterheat temperature is usually expressed by the following formula:
Tp = 455.5[Ceq] p-111.4
mode, Tp -- afterheat temperature ℃;
[Ceq]p -- carbon equivalent formula.
[Ceq]p=C+0.2033Mn+0.0473Cr+0.1228Mo+0.0292Ni+0.0359Cu+0.0792Si-1.595P+1.692S+0.844V
To reduce the hydrogen content in the welding zone is one of the important effects of post heat treatment. It has been reported that hydrogen diffuses outward from the mild steel weld in 1.5 to 2 months at 298K.
Increasing the temperature to 320K shortens the process to two to three days and nights, while heating to 470K takes 10 to 15h.
The main function of post-heat and dehydrogenation treatment is to prevent the formation of cold cracks in weld metal or heat-affected zone.
When the preheating is not enough to prevent the formation of cold cracks, such as in the welding of high-restraint joints and hard-to-weld steel, the post-heating process must be used to reliably prevent the formation of cold cracks.
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The operating procedures are as follows:
1, argon arc welding must be operated by special personnel switch.
2. Check whether the equipment and tools are good before work.
3. Check the welding power supply, whether the control system has ground wire, and add lubricating oil to the transmission part. For normal rotation, argon and water must be unblocked. In case of water leakage, call for immediate repair.
4. Check whether the welding gun is normal and the ground wire is reliable.
5. Check whether the high-frequency arc starting system and welding system are normal, whether the wire and cable joints are reliable, and whether the adjusting mechanism and wire feeding mechanism are in good condition for automatic electrode argon arc welding.
6, according to the material of the workpiece to choose polarity, good welding circuit, general material with DC positive connection, aluminum and aluminum alloy with reverse connection or AC power supply.
7, check whether the welding groove is qualified, the surface of the groove shall not have oil, rust, etc., on both sides of the weld within 200mm to remove oil and rust.
8, for the use of fetal gear to check its reliability, the welding parts need to preheat also check the preheating equipment, temperature measuring instrument.
9. The control button of argon arc welding shall not be far away from the arc, so that it can be closed at any time in case of failure.
10, the use of high frequency arc must often check whether there is leakage.
11, equipment failure should be power off maintenance, operators shall not repair themselves.
12, in the vicinity of the arc is not allowed to naked and naked storm other parts, not allowed to smoke and eat near the arc, so as to avoid ozone, smoke inhalation in the body.
13. Wear mask and gloves when grinding thorium tungsten electrode, and abide by the operating rules of grinder. The best choice is cerium tungsten pole (less radioactive). The grinder must be equipped with a suction device.
14. Operators should wear electrostatic dust masks at all times. Minimize the high frequency electrical action time during operation. Continuous work shall not exceed 6 hours.
15, argon arc welding work site must be air circulation. Ventilation and detoxification equipment should be activated during work. When the ventilation device fails, it should stop working.
16. Argon gas bottle is not allowed to be smashed, and must be placed with a support, and away from the open flame more than 3 meters.
17. When argon arc welding is carried out inside the container, a special mask should be worn to reduce the inhalation of harmful smoke. The vessel should be monitored and coordinated by a person outside.
18. Thorium tungsten rods should be stored in lead boxes to avoid injury due to the concentration of a large number of thorium tungsten rods, the radioactive dose beyond the safety regulations.
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