In chemical production, titanium equipment and pipelines are widely used, and they have good high and low temperature resistance and corrosion resistance. Other phenomena such as cracks and embrittlement often occur in titanium materials during welding. The main contents are as follows: 1) Metal properties and welding parameters of titanium. 2) Practical operation skills of titanium welding. 3) Manufacturing technology and maintenance of titanium equipment.
I. Metal properties and welding parameters of titanium metal
Titanium metal has low specific gravity (specific gravity is 4.5), high strength, good high and low temperature resistance, and excellent crack resistance and corrosion resistance in wet chlorine gas. The mechanical properties and welding of titanium are related to the purity of titanium material. The higher the purity, the better the performance, the lower the purity, the sharp decline in plasticity and toughness, and the worse the welding performance. Titanium is very active above 300℃, and it is easy to absorb hydrogen, oxygen and nitrogen atoms at high temperature, making the material brittle. Titanium began to absorb hydrogen at 300℃, oxygen at 600℃ and nitrogen at 700℃.
Welding process parameters
Argon arc welding machine should have high frequency arc ignition, current attenuation and gas delay protection, and the mechanical properties of welding wire for pulse device should be equivalent to that of base metal.
The protective cover should be made of purple steel or titanium, and the shape is convenient to protect the weld, so that the weld does not change color. Stainless steel wire mesh should be installed in the protective cover to play the role of gas buffer.
Second, the operation technology of titanium welding
Cleaning before welding: Bevel the material with a hobbing machine, polish off the scale, grease, burr and dust within 25mm on both sides with a wire brush, and then wipe with acetone or ethanol.
Welding protection: learn argon protection before welding. When protecting, one person holds a shield to protect the top and one person holds a shield to protect the bottom. The protector must cooperate with the welder. After welding, the protective cover can not be released until the weld is cooled. One-sided welding and double-sided molding should pay special attention to the protection of the back. If the protection is not good, the welding liquid will not flow and there will be no molding. ?
When welding, the weld should have enough 3-5mm gap to facilitate the formation of arc pits. Hold the welding torch as low as possible with the right hand and the welding wire with the left hand. When feeding welding wire, maintain continuity and stability, cooperate well with both hands, and keep the weld flat. Eyes should always observe the depth of molten pool and the flow of welding liquid. The current should be adjusted according to regulations, and it is forbidden to be too large. Keep 5ml of argon gas at the nozzle, 25ml of shielding gas and 20ml at the back to ensure that the weld seam behind the protective cover does not change color. When welding twice, it is necessary to leave a certain cooling time to reduce the surface temperature to below 200℃, otherwise cracks and embrittlement will easily occur, and the welding position should be as flat as possible and the nozzle should be rotated. When welding, the room should be dry and dust-free, and the wind speed should be less than 2m/s, which is easy to cause arc instability. When welding the cover surface, try to use the pulse device to make the weld shape beautiful.
Three, titanium equipment manufacturing technology and maintenance technology
Materials for processing titanium pipes, titanium elbows and titanium cans should meet the requirements, and their toughness, strength and flexibility should be certified by plates. Each titanium plate must be adjusted with a rotary ruler, and the size should be calculated when cutting to prevent the chips from being too large. When cutting plates, shears should be used and gas cutting should be avoided as much as possible. When using pipes, the pipeline should be clearly and accurately marked, and it is forbidden to reuse gas cutting. After the plate is cut, the groove should be processed by chamfering machine, and the breach should be uniform. The weld should be concave inward to facilitate secondary molding after welding. Due to the high price of titanium (raw material is about 140 yuan /Kg, and processing 400 yuan /Kg), waste should be eliminated.
The maintenance and processing of titanium plate are quite different, mainly due to environmental factors, material changes and so on. Weld can be protected, but small current can not be protected on both sides. After the weld is cracked, it can't be welded on the original weld, but it should be repaired. When there is wind at the welding site, there should be shielding devices, such as tarpaulin or iron plate. There should be gaps or dislocation welding when taking over, because it can't be protected inside, and the weld should be widened and thickened appropriately.
The rest is learning by doing.