15. What is the main function of gas welding powder?
The main function of welding powder is to form slag, which reacts with metal oxides or non-metallic impurities in the molten pool to generate molten slag. At the same time, the generated molten slag covers the surface of the molten pool and isolates the molten pool from the air, thus preventing the molten pool metal from being oxidized at high temperatures.
16. What are the process measures to prevent weld porosity in manual arc welding?
answer:
(1) The welding rod and flux should be kept dry and dried according to regulations before use;
(2) The surfaces of welding wires and weldments should be kept clean and free of water, oil, rust, etc.
(3) Correctly select welding specifications, such as the welding current should not be too large, the welding speed should be appropriate, etc.;
(4) Use correct welding methods, use alkaline electrodes for hand arc welding, short arc welding, reduce the swing amplitude of the electrode, slow down the rod transport speed, control short arc arc starting and closing, etc.;
(5) Control the assembly gap of weldments not to be too large;
(6) Do not use electrodes whose coatings are cracked, peeled off, deteriorated, eccentric or have corroded welding cores.
17. What are the main measures to prevent white spots when welding cast iron?
answer:
(1) Use graphitized welding rods, that is, use cast iron welding rods with a large amount of graphitizing elements (such as carbon, silicon, etc.) added to the paint or welding wire, or use nickel-based and copper-based cast iron welding rods;
(2) Preheat before welding, maintain heat during welding, and slow cooling after welding to reduce the cooling rate of the weld zone, extend the time the fusion zone is in the red-hot state, fully graphitize, and reduce thermal stress;
(3) Use brazing process.
18. Describe the role of flux in the welding process?
In welding, flux is the main factor to ensure welding quality. It has the following functions:
(1) After the flux melts, it floats on the surface of the molten metal to protect the molten pool and prevent erosion by harmful gases in the air.
(2) The flux has the functions of deoxidizing and alloying, and cooperates with the welding wire to obtain the required chemical composition and mechanical properties of the weld metal.
(3) Make the weld well formed.
(4) Slow down the cooling rate of molten metal and reduce defects such as pores and slag inclusions.
(5) Prevent splashing, reduce losses, and improve the welding coefficient.
19. What matters should be paid attention to when using and maintaining AC arc welding machines?
(1) It should be used according to the rated welding current and load duration of the welding machine, and do not overload.
(2) The welding machine is not allowed to be short-circuited for a long time.
(3) The regulating current should be operated at no load.
(4) Always check wire contacts, fuses, grounding, adjustment mechanisms, etc. and make sure they are in good condition.
(5) Keep the welding machine clean, dry and ventilated to prevent dust and rain from intruding.
(6) Place it stably and cut off the power supply after work is completed.
(7) The welding machine must be inspected regularly.
20. What are the dangers of brittle fracture?
Answer: Because brittle fracture occurs suddenly and cannot be discovered and prevented in time, once it occurs, the consequences will be very serious, not only causing major economic losses, but also endangering human life. Therefore, brittle fracture of welded structures is a problem that should be taken seriously.
21. Characteristics and applications of plasma spraying?
Answer: The characteristics of plasma spraying are that the plasma flame temperature is high and can melt almost all refractory materials, so it can be sprayed on a wide range of objects. The plasma flame velocity is high and the particle acceleration effect is good, so the coating bonding strength is high. It has a wide range of uses and is the best way to spray various ceramic materials.
22. What is the procedure for preparing the welding process card?
Answer: The program for preparing the welding process card should find out the corresponding welding process assessment based on the product assembly drawings, parts processing drawings and their technical requirements, and draw a simplified joint diagram; the welding process card number, drawing number, joint name, Joint number, welding procedure qualification number and welder certification items;
Prepare the welding sequence based on the welding process assessment and actual production conditions, technical elements and production experience; prepare specific welding process parameters based on the welding process assessment; determine the product inspection agency, inspection method, and inspection ratio based on the requirements of the product drawing and product standards. .
23. Why do we need to add a certain amount of silicon and manganese to the welding wire of carbon dioxide gas shielded welding?
Answer: Carbon dioxide is an oxidizing gas. During the welding process, the welding metal elements will be burned, thereby greatly reducing the mechanical properties of the weld. Among them, oxidation will cause pores and spatter. Add silicon and manganese to the welding wire. It has a deoxidizing effect and can solve the problems of welding oxidation and spatter.
24. What is the explosion limit of flammable mixtures, and what factors affect it?
Answer: The concentration range in which flammable gas, vapor or dust contained in a flammable mixture can occur is called the explosion limit.
The lower limit of the concentration is called the lower explosion limit, and the upper limit of the concentration is called the upper explosion limit. The explosion limit is affected by factors such as temperature, pressure, oxygen content, and container diameter. When the temperature increases, the explosion limit decreases; when the pressure increases, the explosion limit also decreases; when the concentration of oxygen in the mixed gas increases, the lower explosion limit decreases. For combustible dust, its explosion limit is affected by factors such as dispersion, humidity, and temperature.
25. What measures should be taken to prevent electric shock when welding in boiler drums, condensers, oil tanks, oil tanks and other metal containers?
Answer: (1) When welding, welders should avoid contact with iron parts, stand on rubber insulating mats or wear rubber insulating shoes, and wear dry work clothes.
(2) There should be a guardian outside the container who can see and hear the welder’s work, and a switch to cut off the power supply according to the welder’s signal.
(3) The voltage of street lights used in containers must not exceed 12 volts. The shell of the portable light transformer should be reliably grounded, and autotransformers are not allowed to be used.
(4) Transformers for portable lights and welding transformers are not allowed to be carried into boilers and metal containers.
26. How to distinguish between welding and brazing? What are the characteristics of each?
Answer: The characteristic of fusion welding is the bonding of atoms between the welding parts, while brazing uses an intermediate medium with a lower melting point than the welding parts – brazing material to connect the welding parts.
The advantage of fusion welding is that the mechanical properties of the welded joint are high, and the productivity when connecting thick and large parts is high. The disadvantage is that the stress and deformation generated are large, and the structural changes occur in the heat-affected zone;
Xinfa welding equipment has the characteristics of high quality and low price. For details, please visit: Welding & Cutting Manufacturers – China Welding & Cutting Factory & Suppliers (xinfatools.com)
The advantages of brazing are low heating temperature, flat, smooth joints, beautiful appearance, small stress and deformation. The disadvantages of brazing are low joint strength and high assembly gap requirements during assembly.
27. Carbon dioxide gas and argon gas are both protective gases. Please describe their properties and uses?
Answer: Carbon dioxide is an oxidizing gas. When used as a protective gas in the welding area, it will violently oxidize the droplets and metal in the molten pool, causing burning loss of alloy elements. The processability is poor, and pores and large splashes will be produced.
Therefore, it can only be used for welding low carbon steel and low alloy steel at present, and is not suitable for welding high alloy steel and non-ferrous metals, especially for stainless steel. Since it will cause carbonization of the weld and reduce the resistance to intercrystalline corrosion, it is used Get less.
Argon is an inert gas. Because it does not react chemically with the molten metal, the chemical composition of the weld is basically unchanged. The quality of the weld after welding is good. It can be used to weld various alloy steels, stainless steel and non-ferrous metals. Because The price of argon is gradually decreasing, so it is also used in large quantities for welding mild steel.
28. Describe the weldability and welding characteristics of 16Mn steel?
Answer: 16Mn steel is based on Q235A steel with about 1% Mn added, and the carbon equivalent is 0.345%~0.491%. Therefore, the welding performance is better.
However, the hardening tendency is slightly greater than that of Q235A steel. When welding with small parameters and small weld passes on a large thickness and large rigid structure, cracks may occur, especially when welding under low temperature conditions. In this case, appropriate measures can be taken before welding. ground preheating.
When hand arc welding, use E50 grade electrodes; when automatic submerged arc welding does not require beveling, you can use H08MnA welding wire with flux 431; when opening bevels, use H10Mn2 welding wire with flux 431; when using CO2 gas shielded welding, use welding wire H08Mn2SiA Or H10MnSi.
Post time: Nov-06-2023
