08-07

Discussion on pipeline welding degaussing process

2022-08-07

In the welding operation of power engineering construction, the phenomenon of magnetic bias blowing affecting the welding process sometimes occurs. The formation of magnetic bias blow is the result of the presence of remanence in the pipe metal. In general, remanence is divided into two types: induction magnetism and process magnetism. Induction magnetism often occurs in the process of pipe making in factories, such as metal smelting, loading and unloading by electromagnetic crane, stopping steel pipe in strong magnetic field, completing non-destructive inspection by magnetization method, placing steel pipe close to strong power supply line, etc. Process magnetism often occurs during assembly and welding operations and the use of magnetic grippers, clamps and direct current welding pipelines, such as long-term contact with electric wires connected to direct current power supply, exposed sections of wires or short circuits between electric welding clamps and pipes. When welding steel pipes with magnetic properties, problems such as difficulty in arc ignition, destruction of arc combustion stability, arc deviation in a magnetic field, and splashing of liquid metal and slag from the welding pool are often caused. In order to stabilize the welding process and improve the quality of the welded joint, the magnetized steel pipe must be demagnetized before welding. In general, it is difficult to achieve complete demagnetization of welded steel pipes. Therefore, when the residual magnetism is insufficient to affect the welding quality, the welding is allowed. The degaussing process for the joint between a single steel pipe and a steel pipe is as follows: ① Determine the size and direction of the remanence field of the steel pipe; ② Select the degaussing method and technical means; ⑧ Use the selected degaussing method to degausse the steel pipe or welded joint; ④ Check the amount of remanence after degaussing to see if it meets the requirements. Commonly used degaussing methods are divided into: direct current or alternating current, with the aid of electromagnets or permanent magnets established magnetic field methods. Here we mainly analyze the DC degaussing process. As shown in the figure: The principle of degaussing is to form a magnetic field opposite to the direction of the remanence field of the steel pipe around the degaussing pipeline, and control the strength of the formed magnetic field by controlling the current size, so as to achieve the purpose of degaussing. A coil composed of flexible welding wires with a cross section of 35~50mm is arranged on the steel pipe to form a closed loop. One end of the two welding wires is respectively connected to the positive and negative poles of the DC welding power supply, and the other end is respectively connected to the metal plate fixed on the demagnetized pipeline, so that the magnetic field formed by the two welding wires acts in the opposite direction to the remanence field of the steel pipe. As the current was gradually increased, the result of the action of the degaussing magnetic field was periodically checked on the steel pipe (measurement was made when the power was turned on). When necessary, control the current (usually there should be a current adjustment device) or change its direction (the method of changing the welding wire on the DC welding power source). After the demagnetization, in order to smoothly reduce the magnetic flux, the current should be gradually reduced within 1 min until the zero value, and then cut off the power supply. When a single steel pipe is degaussed, a coil of 8 to 12 turns can be wound along the outer circle at one end of the steel pipe to degaussing at the maximum magnetic field value, and then the other end of the steel pipe is degaussed in the same way. When a single steel pipe is demagnetized to the butt joint of the steel pipes, the distance between the two steel pipes shall not be less than 300mm, and a coil of 18-20 turns shall be wound at a distance of 80-100mm from the end face of each pipe, and then demagnetized according to the above method. On individual occasions, it is recommend to use the scheme of degaussing the electrode holder and the metal plate into the electrical system. Short-circuit the electrode inserted in the electrode holder to the metal plate for approx. 10 s at 300 A current. Then disconnect. After each short circuit and disconnection cycle, check the magnetic strength of the pipeline, and repeat the above demagnetization process if necessary. When the assembled butt joint is demagnetized, a welding wire with a cross section of 35~50mm is wound on the end of the butt joint to form a common coil of two steel pipes, as shown in the above figure. The coils can be wound overlapping (clockwise or counterclockwise) for a total of 16 to 22 turns. At this time, the number of turns should be on the steel pipe with larger remanence. This degaussing process is often optimal. The magnetic field method established by alternating current, by means of electromagnets or permanent magnets, is basically the same as the principle of direct current demagnetization.

08-06

New and old welding technologies have been used, seen and heard.

2022-08-06

The installation of chemical equipment is a key step before the production of chemical equipment. Welding technology directly affects the performance of the equipment. Most of the operating environment of chemical equipment is relatively harsh. Therefore, welding is of great significance to the manufacture and use of chemical equipment. The following is a summary of various welding technologies. New welding process and new technology 1 Welding robot The outstanding performance of welding technology progress is the development of welding process from mechanization to automation, intelligence and information. The application of intelligent welding robot is an important symbol of high automation of welding process. Welding robot breaks through the traditional way of welding automation and makes it possible to produce small batch automation. Most of the welding robots are arm-type machines with fixed positions, which are taught and intelligent. Teaching robot: through teaching, memory welding trajectory and welding parameters, and in strict accordance with the teaching program to complete the welding of products. With only one teaching, the robot can accurately reproduce each step of the teaching. This kind of welding robot is widely used, suitable for mass production, used in the fixed station of the assembly line, its function is mainly to teach reproduction, the strain capacity of environmental changes is poor. There is no use for small batch production of large structures on the construction site. Intelligent robot: It can automatically determine the starting point, space trajectory and related parameters of the weld according to simple control instructions, and can automatically track the weld trajectory, adjust the welding torch posture, adjust the welding parameters and control the welding quality according to the actual situation. This is the most advanced welding robot, with smart, lightweight, easy to move and other characteristics, can adapt to different structures, different locations of the welding task, the current practical application is very few, is still in the research and development stage. In welding robots, spot welding robots account for 50% ~ 60%, which consists of three parts: robot body, spot welding system and control system. The degree of freedom of the robot body is 1~5, and the control system is divided into body control and welding part control. The welding system mainly includes: welding controller, welding tongs and auxiliary parts such as water and electricity (underwater welding). 2 Application of computer software The application of computer software system in the field of welding mainly has the following aspects: 1. Computer simulation technology includes simulation of welding thermal process, welding metallurgical process, welding stress and deformation. Welding is a complex process involving arc physics, heat transfer, metallurgy and mechanics. Once the various processes in welding have been computer simulated, the computer system can be used to determine the best design, process and welding parameters for welding various structures and materials. Traditionally, the welding process is always determined through a series of experiments or based on experience, in order to obtain a reliable and economical welding structure, computer simulation as long as a small number of verification tests to prove the applicability of numerical methods in dealing with a problem, a large number of screening work can be completed by the computer, save a lot of test work, thus greatly saving manpower, material resources and time, it is of great significance in the welding of new engineering structures and new materials. The level of computer simulation technology also determines the scope of automated welding. In addition, computer simulation is also widely used to analyze the strength and performance of welded structures and joints. 2. Database technology and expert system are used for welding process design and selection of process parameters, welding defect diagnosis, welding cost budget, real-time monitoring, welding CAD, welder examination, etc. Database technology has penetrated into all aspects of the welding field, from raw materials, welding test, welding process to welding production. Typical database systems include welding procedure qualification, welding procedure specification, welder file management, Welding materials, material composition and performance, weldability, welding CCT diagram management and welding standard consulting system. These database systems provide favorable conditions for various data and information management in the welding field. Welding expert system mainly focuses on process formulation, defect prediction and diagnosis, computer-aided design and so on. In the existing welding expert system, process selection and process formulation are the most important application fields, and the real-time control of welding process is an important development direction. 3. Computer-aided quality control (CAQ) technology is used for product data analysis, real-time monitoring of welding quality, etc. In addition, computer-aided design/manufacturing (CAD/CAM) is increasingly used in Welding processing, mainly for CNC cutting, welding structure design and welding robots.

08-05

Welding defects and causes, very important experience!

2022-08-05

Welding is a key work in the construction of large-scale installation projects, and its quality and efficiency directly affect the safe operation of the project and the manufacturing period. Due to the different level of skilled workers, the welding process is uneven, and there are many defects. The types and causes of defects are sorted out to reduce or prevent the generation of welding defects and improve the quality of the project. 1. weld size is not required The welding wave is thick, the shape is uneven, the weld reinforcement height is too low or too high, and the welding wave width is different. Fillet weld unilateral or excessive sag is the weld size does not meet the requirements, the reason is: 1. The weld groove angle is improper or the assembly clearance is uneven. 2. The welding current is too large or too small, and the welding specification is improperly selected. 3. The speed of the strip is uneven, and the angle of the welding rod (or welding rod) is improper. 2. crack The shape of the crack end is sharp, the stress concentration is serious, and it has a great influence on the alternating and impact load and static tension, which is the most dangerous defect in the weld. According to the causes can be divided into cold cracks, hot cracks and reheat cracks. (Cold crack) refers to the crack produced below 200 ℃, which is closely related to hydrogen, and its main causes are: 1. It is inappropriate to select preheating temperature and slow cooling measures after welding for large and thick workpieces. 2. The selection of welding materials is not appropriate. 3. The welding joint is rigid and the process is unreasonable. 4. The weld and its vicinity produce brittle and hard tissue. 5. improper selection of welding specifications. (Hot crack) refers to the crack (mainly solidification crack) generated above 300 ℃, which is mainly caused: 1. Influence of ingredients. It is easy to appear when welding pure austenitic steel, some high nickel alloy steel and non-ferrous metals. 2. The weld contains more harmful impurity elements such as sulfur. 3. Improper selection of welding conditions and joint forms. (reheat crack) stress relief annealing crack. Refers to the high-strength welding zone, due to post-weld heat treatment or high temperature use, in the heat affected zone produced intergranular cracks, the main reason is: 1. Improper heat treatment conditions for stress relief annealing. 2. The influence of alloy composition. Elements such as chromium molybdenum vanadium boron have a tendency to increase reheat cracking. 3. Improper selection of welding materials and welding specifications. 4. Unreasonable structural design causes large stress concentration. 3. stomata During the welding process, the cavity formed in the weld metal or on the surface due to the gas not being able to escape in time is caused: 1. Welding rod, flux drying is not enough. 2. The welding process is not stable enough, the arc voltage is too high, the arc is too long, the welding speed is too fast and the current is too small. 3. The oil and rust on the surface of filler metal and base metal are not removed. 4. The arc striking point is not melted by the backward method. 5. The preheating temperature is too low. 6. The positions of arc striking and arc extinguishing are not staggered. 7. The welding zone is poorly protected and the molten pool area is too large. 8. The AC power source is prone to stomata, and the stomata tendency of DC reverse connection is the smallest. 4. weld bead During the welding process, the molten metal flows to the weld outside the unmelted base metal to form a metal tumor, which changes the cross-sectional area of the weld and is detrimental to the dynamic load. Its causes are: 1. The arc is too long and the bottom welding current is too large. 2. The current is too large during vertical welding, and the strip is not properly swung. 3. The weld assembly gap is too large. 5. crater There is obvious lack of meat and depression in the end of the weld. Its causes are: 1. The welding arc closing operation is improper, and the arc extinguishing time is too short. 2. During automatic welding, the wire feeding and the power supply are cut off at the same time, without stopping the wire first and then cutting off the power. 6. undercut After the arc melts the base metal at the edge of the weld, there is no replenishment of the weld metal and the gap is left. The undercut weakens the stress section of the joint, reduces the strength of the joint, causes stress concentration, and may cause damage at the undercut. Its causes are: 1. The current is too large, the arc is too long, the speed of the strip is improper, and the arc heat is too high. 2. Submerged arc welding voltage is too low, welding speed is too high. 3. The inclination angle of welding rod and welding wire is incorrect. 7. slag inclusion Non-metallic inclusions are present within the weld metal or at the fusion line. Slag inclusions have an effect on mechanical properties, and the degree of influence is related to the number and shape of inclusions. Its causes are: 1. Each layer of welding slag is not cleaned during multi-layer welding. 2. There is thick rust on the weldment. 3. improper physical properties of electrode skin. 4. The shape of the welding layer is poor, and the groove angle design is improper. 5. The ratio of weld width to weld depth is too small, and the undercut is too deep. 6. The current is too small, the welding speed is too fast, and the slag is too late to surface. 8. incomplete penetration There is local incomplete fusion between the base metal or between the base metal and the deposited metal. It generally exists in the weld root of single-sided welding, which is very sensitive to stress concentration and has a great influence on the performance of strength fatigue. Its causes are: 1. Poor groove design, small angle, large blunt edge and small gap. 2. The angle of welding rod and welding wire is incorrect. 3. The current is too small, the voltage is too low, the welding speed is too fast, the arc is too long, and there is magnetic bias blowing. 4. There is thick rust on the weldment and it is not cleaned up. 5. Welding deviation during submerged arc welding.

08-05

How to write the year-end summary of the welder? Celebrities give you inspiration!

2022-08-05

One year has passed, and all welders must be "thinking about it" and worrying about the year-end summary. Xiao Bian has specially found some famous people's "year-end summary of welders". I believe you will be able to think well after reading it! Zhu Ziqing Edition These days, my heart is quite restless. Seeing that the examination day is getting closer and closer, many of the welding equipment sold have not been paid back. There are so many reasons for the customers, but there is no way to talk about them. So my thoughts are tangled up...... Thinking like this, I looked up fiercely. I didn't realize that there were only a few thin calendars left on the wall. I gently tore off another one. I think the target will not reach the standard tomorrow...... Cangyang Gyatso Edition Welding production is so complicated that if you catch up or not, the progress will be there, no more, no less. If you change or not, the opinions of the leaders will be there, and they will not increase or decrease. Come to the company's office, or copy the electronic file home, indifferent, liver trembling, bow their heads, and write a report. Zhen Huan Edition Today, when it was mentioned that the production line project was approaching, the small owner felt very weak. I was afraid that the overtime work was cut off last night, which disturbed my mind. It was all because of the recent noise of urging progress. In addition, after getting up early, I heard that the plan would be changed. I thought that the trial operation of the production line was imminent. Last night, I was even more upset. If the assembly process can be carried out step by step and advance without fighting, it will be excellent! Lu Xun Edition Leaving the workshop where the machines roared and disturbing God, and entering the office, the table was piled with two opinions on the rectification plan: one was the opinion of leader A and the other was the opinion of leader B. Winter has been quite cold, but the back is a layer of cold sweat. The plan is destined to be adjusted and many places have to be revised. It seems that the responsibility does not lie with me. For example, if I am used to knives, can I play with sticks this time? Zhao Zhongxiang Version This is a cold and windy season. The welding baby Xiao Huang is like a defeated Siberian stray dog, and her heart is white, like Alaska shrouded in ice and snow. Today, he was scolded by the leaders again. The failure was handled for three days and did not recover. In desperation, he had to pack his bags and disappear on the company's horizon like a penguin who could not find a home...... tongue tip version At 11 o'clock in the night, after writing the last technical report, Xiao Chen got up and closed the computer and made himself a bucket of * * pickled beef noodles with boiling water. This is the best gift for welding engineers to continue to fight for themselves. Chinese welding people prefer to sit in front of the window and enjoy the unique fragrance of instant noodles quietly at night. The hot steam fumigates his cheeks, moistens the dry and astringent eyes, and soothes the wounded soul. Then, looking at the still bustling traffic outside and any lighted window that does not belong to me, I was thinking about how to become a famous welding master... Divine Comedy Edition High task is my love, heavy indicators to catch up indefinitely. What kind of work is the most ah the most helpless, what kind of data results is the most happy ...... leisurely said the reasons left, let the wages swept away all the haze.

08-02

Welding of copper and copper alloys

2022-08-02

Weldability of copper and copper alloys 1. The high thermal conductivity of copper. At room temperature, the thermal conductivity of copper is about 8 times larger than that of carbon steel. It is difficult to heat the copper weldment locally to the melting temperature, so the energy concentrated heat source should be used during welding. 2. Copper and copper alloy welding often cracks. The location of cracks in the weld, fusion line and heat affected zone. The fracture is intergranular failure, and obvious oxidation color can be seen from the cross section. In the process of welding crystallization, a small amount of oxygen and copper form Cu2O, and form a low melting point eutectic (α Cu2O) with α copper, and its melting point is 1064 ℃. Lead is insoluble in solid copper, and lead and copper form a low melting point eutectic with a melting point of about 326 ℃. Under the action of welding internal stress, cracks are formed in the fragile parts of the welded joints of copper and copper alloy joints at high temperatures. In addition, hydrogen in the weld can also cause cracks. 3. Pores often occur in welds of copper and copper alloys. Porosity in pure copper weld metal is mainly caused by hydrogen. When CO gas is dissolved in pure copper, pores may also be caused by water vapor and CO2 gas generated by the reaction of carbon monoxide and oxygen. The tendency of pore formation during welding of copper alloys is much greater than that of pure copper. Generally, the pores are distributed in the center of the weld and near the fusion line. 4. When welding pure copper and copper alloy, there is a tendency to reduce the mechanical properties of the joint. In the welding process of copper alloy, the oxidation of copper and the evaporation and burning of alloying elements will occur. Low melting point eutectic and various welding defects lead to the decrease of strength, plasticity, corrosion resistance and electrical conductivity of welded joints. Welding method of copper and copper alloy There are many welding methods for copper and copper alloys, such as gas welding, carbon arc welding, welding rod manual welding, tungsten argon arc welding, submerged arc welding, plasma welding, etc. They have different applications, and must be selected according to the type of copper and copper alloy, the thickness of the weldment, the shape of the product structure, the production conditions, the welding productivity, the quality requirements of the joint, etc.

08-01

Red copper and brass welding method

2022-08-01

Introduction: The methods of welding copper include gas welding, carbon arc welding, manual arc welding and manual argon arc welding. Automatic welding can also be used for large structures. 01 Gas welding of copper Butt joints are most commonly used for welding copper, and lap joints and T-joints are used as little as possible. Two kinds of welding wires can be used for gas welding, one is the welding wire containing deoxidizing elements, such as wire 201 and 202, and the other is the general copper wire and the cutting strip of the base metal, using the gas agent 301 as the flux. Neutral flame shall be used for gas welding of copper. 02 Manual arc welding of copper In manual arc welding, red copper electrode copper 107 is used, and the welding core is red copper (T2, T3). The edge of the welding place shall be cleaned before welding. When the thickness of the weldment is greater than 4mm, it must be preheated before welding, and the preheating temperature is generally about 400~500 ℃. With copper 107 electrode welding, the power supply should be DC reverse connection. When welding, short arc should be used, and the welding rod should not be swung laterally. The reciprocating linear motion of the welding rod can improve the forming of the weld. Long welds shall be welded by step-back method. The welding speed should be as fast as possible. During multi-layer welding, the slag between the layers must be completely removed. Welding should be carried out in a well-ventilated place to prevent copper poisoning. After welding, flat head hammer should be used to knock the weld to eliminate stress and improve the quality of the weld. 03 Manual argon arc welding of copper When red copper manual argon arc welding, the welding wire used is wire 201 (special red copper welding wire) and wire 202, and red copper wire, such as T2. Before welding, the oxide film, oil and other dirt on the welding edge of the workpiece and the surface of the welding wire must be cleaned to avoid defects such as pores and slag inclusion. Cleaning methods are mechanical cleaning and chemical cleaning method. When the plate thickness of butt joint is less than 3mm, no groove shall be opened; when the plate thickness is 3~10mm, V-shaped groove shall be opened, and the groove angle shall be 60~70mm; when the plate thickness is greater than 10mm, X-shaped groove shall be opened, and the groove angle shall be 60~70mm; In order to avoid incomplete welding, generally no blunt edge is left. According to the plate thickness and groove size, the assembly clearance of the butt joint is selected in the range of 0.5~1.5mm. Manual argon arc welding of red copper usually adopts DC positive connection, I .e. tungsten electrode is connected to negative electrode. In order to eliminate pores and ensure reliable fusion and penetration at the root of the weld, it is necessary to increase the welding speed, reduce argon consumption, and preheat the weldment. When the plate thickness is less than 3mm, the preheating temperature is 150~300 ℃; when the plate thickness is greater than 3mm, the preheating temperature is 350~500 ℃. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. 04 Carbon arc welding of copper Carbon electrodes and graphite electrodes are used in carbon arc welding. The welding wire used for carbon arc welding of red copper is the same as that used for gas welding. It can also be cut from the base metal and flux used for gas welding of red copper, such as gas 301, etc. (copper aluminum online)

07-31

How much do you know about stainless steel?

2022-07-31

Stainless steel is a high-alloy steel that resists corrosion. Has a beautiful surface, do not have to go through the plating color or paint and other surface treatment, so many machinery factory to show their own is stainless steel, often do not do any paint treatment, and the black material (the so-called black material is the general steel name) must be rust-proof treatment. Simple classification of stainless steel Stainless steel can be roughly divided into three categories: 200 series, 300 series and 400 series, of which 300 series is the most commonly used. 200 series and 400 series are substitutes for 300 series in a certain way. Strictly speaking, 400 series is not called stainless steel, but stainless iron. Because it does not contain nickel, it can be attracted by magnets. However, the 200 series and the 300 series are made of nickel, so they are not magnetic and cannot absorb iron. 304 is the most common variety in the 300 series, so the price trend of the whole stainless steel can be judged from the price change of the 304. The 200 series contains less nickel, the 400 series does not contain nickel, and the 300 series contains the most nickel, so the 300 series is most affected by the nickel price. 300 series can be simply divided into 304, 304L, 316, 316L, 321, 309S, 310S, etc. The distinction is based on the different contents of various metal elements and the different characteristics of stainless steel with different contents. The difference between 304 and 304L lies in the different carbon (C) content. The one with L means low carbon, also called low carbon, and the difference between 316 and 316L is the same. Morphological classification of stainless steel Stainless steel can be divided into coil, plate, profile, steel pipe and parts five categories, the most important is the coil and plate. Profile is a variety of different types of materials made of plate, angle steel, flat steel, I-beam, channel steel. Steel pipe mainly refers to seamless steel pipe, and seamless steel pipe is the opposite of welded pipe, the difference is whether a forming. Parts mainly refers to elbows and flanges and other small things. Coils and plates are actually the same, but the factory forms are different. Coils are rolled one by one, and plates are rolled one by one. If they are manufactured as plates, they are also called original plates, which are usually thick plates, because if they are very thick, they cannot be rolled, and generally they cannot be rolled over 16mm. If there are rolls and plates, the prices of rolls and plates are often different. If the rolls are purchased, they are calculated according to the actual weighing. Therefore, if the prices are high and the plates are calculated according to the theory, the prices are low. The reason is that there is a difference. For example, the actual price of 10mm thick may be 9.6mm, and there will be a price difference in the middle. Stainless steel plates are divided into hot rolling and cold rolling according to the different rolling processes of the rolling mill (the rolling mill is the machine name of the rolling plate). Hot rolling is usually marked as NO. 1 Cold rolling is marked as 2B or BA(BA has a better surface than 2B, is brighter, and is close to the mirror. The best one is the mirror surface. The mirror surface has no in stock and needs to be processed). For example, 304 often purchases plates, which means that the rolls must be leveled into plates by a machine. This machine is a leveler. Kaiping can be opened into different lengths by Kaiping machine. If it is not regular length, it is called fixed opening, which means fixed opening size, because customers often put forward different length requirements according to actual needs. At this time, the roll is important, and the regular board cannot meet the requirements. Domestic cold rolling is generally below 3mm, hot rolling is generally above 3mm, and the thickness of 3mm is both hot rolling and cold rolling, but the thickness of imported cold rolled plate can reach below 4mm or even below 6mm. Hot-rolled plates of 3mm to 12mm are called medium plates, and plates above 12mm are called thick plates, which can be as thick as 120mm or more. They are also called hot-rolled medium plates, while cold-rolled plates are cold-rolled thin plates. Characteristics and uses of the main types of stainless steel 304: As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, stamping, bending and other hot workability, no heat treatment hardening phenomenon, non-magnetic, the use of temperature minus 193 degrees to 800 degrees. Uses: tableware, kitchenware, water heaters, boilers, auto parts, medical equipment, food machinery, storage wine, pressure vessels (chemical machinery, chemical equipment). 304L as a low-carbon 304 steel, in the general state, the corrosion resistance and 304 almost, but after welding and after the elimination of stress, it anti-intergranular corrosion is good, in the absence of heat treatment, can also maintain good corrosion resistance, generally used at 400 degrees, Uses: petrochemical industry, building materials. 321 adding Ti element in 304 steel to prevent intergranular corrosion, suitable for positive 430 to below 900 degrees, non-magnetic; Uses: Products that are not heat-treated after welding, such as automobile exhaust, heat exchangers, containers, etc., are not suitable for food processing equipment due to the addition of Ti. 316 low carbon, add MO elements, so his corrosion resistance and atmospheric corrosion resistance and high temperature strength performance is particularly good, can be used under harsh conditions, suitable for use below 900 degrees, non-magnetic. Uses: equipment used in sea water, chemical, dye, paper, acetic acid, fertilizer and other production equipment, food industry and coastal facilities, products with special requirements against intercrystalline corrosion. 309S/310S these two materials, the content of nickel and chromium is relatively high, while increasing the content of Si, so that it has high temperature resistance and corrosion resistance, of which 309S can withstand repeated heating below 980, 310S use temperature reaches 1200 degrees, continuous use temperature can be 1150 degrees, non-magnetic. Uses: suitable for high temperature electric furnace equipment, drying equipment and other key parts, furnace materials, aviation, petrochemical, electric power, etc. 200 series is similar to the 304 cheap economy. Uses: food processing utensils, kitchen equipment, food processing equipment, filters, milk cans, durable consumer goods, washing machine accessories, water heaters, steel furniture, building decoration, decoration. In terms of fatigue resistance, 201 the hardness is larger, the toughness is not as good as the 304, or the fatigue resistance of the 304 is better.

07-30

Four welding methods of copper

2022-07-30

The color of copper is purple-red, so it is called copper. In the humid air copper surface will produce a layer of basic copper carbonate, commonly known as patina (patina). Copper often contains a small amount of bismuth, lead, sulfur, oxygen, phosphorus, antimony, arsenic and other impurity elements, all impurities will reduce the conductivity of copper, especially phosphorus is the most obvious, but phosphorus is a good deoxidizer of copper, so phosphorus is still a beneficial element in copper. Copper has high plasticity in both cold and hot states, but its strength and hardness are low. The strength of copper can be improved by cold working. But at this time, the plasticity is significantly reduced (about 6%), and the conductivity is also reduced by 1-3%. After cold working of copper by 550-600 ℃ annealing, the plasticity can be completely restored. Copper still has high plasticity at low temperatures, but at high temperatures of 400-700 ℃, the strength and plasticity are greatly reduced. The thermal conductivity of copper is much better than that of steel, and the thermal conductivity of copper is 7 times that of steel. As the temperature rises, the gap is even larger. A large amount of heat is conducted out, and the base material is difficult to melt locally. A heat source with high power and concentrated heat must be used, and sometimes preheated, and the heat affected zone is very wide. Welding copper (commonly known as industrial pure copper) methods include gas welding, manual carbon arc welding, manual arc welding and manual argon arc welding, and automatic welding can also be used for large structures. 1. Gas welding of copper Butt joints are most commonly used for welding copper, and lap joints and T-joints are used as little as possible. Two kinds of welding wires can be used for gas welding, one is the welding wire containing deoxidizing elements, such as wire 201 and 202, and the other is the general copper wire and the cutting strip of the base metal, using the gas agent 301 as the flux. Neutral flame shall be used for gas welding of copper. 2, Manual arc welding of copper In manual arc welding, red copper electrode copper 107 is used, and the welding core is red copper (T2, T3). The edge of the welding place shall be cleaned before welding. When the thickness of the weldment is greater than 4mm, it must be preheated before welding, and the preheating temperature is generally about 400~500 ℃. With copper 107 electrode welding, the power supply should be DC reverse connection. When welding, short arc should be used, and the welding rod should not be swung laterally. The reciprocating linear motion of the welding rod can improve the forming of the weld. Long welds shall be welded by step-back method. The welding speed should be as fast as possible. During multi-layer welding, the slag between the layers must be completely removed. Welding should be carried out in a well-ventilated place to prevent copper poisoning. After welding, flat head hammer should be used to knock the weld to eliminate stress and improve the quality of the weld. 3. Manual argon arc welding of copper When red copper manual argon arc welding, the welding wire used is wire 201 (special red copper welding wire) and wire 202, and red copper wire, such as T2. Before welding, the oxide film, oil and other dirt on the welding edge of the workpiece and the surface of the welding wire must be cleaned to avoid defects such as pores and slag inclusion. Cleaning methods are mechanical cleaning and chemical cleaning method. When the thickness of the butt joint plate is less than 3mm, no groove is opened; When the plate thickness is 3~10mm, open a V-shaped groove with a groove angle of 60 ~ 70o; When the plate thickness is more than 10mm, open an X-shaped groove with a groove angle of 60 ~ 70o; In order to avoid incomplete welding, generally no blunt edge is left. According to the plate thickness and groove size, the assembly clearance of the butt joint is selected in the range of 0.5~1.5mm. 4, red copper manual argon arc welding DC is usually connected, that is, the tungsten electrode is connected to the negative electrode. In order to eliminate pores and ensure reliable fusion and penetration at the root of the weld, it is necessary to increase the welding speed, reduce argon consumption, and preheat the weldment. When the plate thickness is less than 3mm, the preheating temperature is 150~300 ℃; when the plate thickness is greater than 3mm, the preheating temperature is 350~500 ℃. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. There is also carbon arc welding of copper. The electrodes used in carbon arc welding are carbon electrodes and graphite electrodes. The welding wire used for carbon arc welding of red copper is the same as that used for gas welding. It can also be cut from the base metal and flux used for gas welding of red copper, such as gas 301, etc.

07-29

Advantages and precautions of induction heating equipment when welding aluminum

2022-07-29

The advantages and precautions of induction heating equipment in aluminum welding, the advantages of induction heating equipment for brazing are many, the biggest advantage of induction brazing is to use the principle of electromagnetic induction heating to weld a variety of metals together. In addition, the brazing reaction only acts on the base metal in the range of several microns or tens of microns, and has almost every influence on the deep structure of the base metal. When using electromagnetic induction heating equipment for aluminum welding, the following points need to be paid attention. 1. The melting point of aluminum Since aluminum and aluminum alloy are relatively low, special attention should be paid to the selection of aluminum brazing filler metal, because this will lead to a small difference between the melting points of the base metal and the brazing filler metal. Therefore, special attention should be paid to the temperature control during the welding process. 2. Selection of solder When using solder for brazing, special attention should be paid to the temperature difference between the base metal and the solder. Therefore, when selecting aluminum or aluminum alloy for soldering, the solder should be carefully selected according to the characteristics of tin. 3. Oxidation treatment Because there is a layer of oxide film on the surface of aluminum, we need to destroy the oxide film during aluminum welding, otherwise brazing cannot be carried out, but this will lead to oxidation of the surface of the weldment, so when brazing, it is recommended that you choose electromagnetic induction heating equipment with nitrogen protection.

07-29

Aluminum has become the preferred material in the era of automotive lightweight

2022-07-29

With the increasing calls for environmental protection, consumption reduction and emission reduction in China, automobile lightweight has become the general trend, and with the increasing technical difficulty of engine research and development, whether it is fuel vehicles or new energy vehicles, lightweight is imperative. Big data shows that using aluminum instead of steel can reduce the weight of the whole vehicle by 30%-40%, the engine can reduce the weight by 30%, the radiator can reduce the weight by 20%-40% compared with copper, and the body can reduce the weight by more than 40%. From this point of view, aluminum instead of steel, weight reduction effect is remarkable. In contrast, the aluminum body structure is lighter and stronger. Audi, Weilai, etc. have used all-aluminum body structures, and aluminum alloys are also widely used in aerospace, automobiles, machinery, ships, and chemicals due to a variety of excellent properties. And other fields. Today, I will mainly talk about the welding of automobile air conditioning condensers, evaporators, water tank radiators, oil coolers and other components. Current aluminum alloy brazing methods include flame brazing, furnace brazing, inert gas brazing, vacuum brazing, and induction brazing. In the increasingly severe situation of industrial upgrading and environmental protection, it is difficult to introduce high-skilled flame brazing talents, so induction brazing has become a very suitable welding method, and induction brazing has no open flame, less investment in process funds, and high welding efficiency., Low labor dependence and high degree of equipment automation are widely used in the welding of automotive aluminum materials. The advantages of improving product welding quality, saving costs and efficiency have become the only choice for major companies. Induction Brazing Equipment