I. Metal properties and welding parameters of titanium metal
Titanium metal has a small specific gravity (specific gravity of 4.5), high strength, good resistance to high and low temperature properties, in wet chlorine gas has excellent crack resistance and corrosion resistance.
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, the worse the welding performance.
Titanium has a strong activity above 300℃, easy to absorb hydrogen, oxygen and nitrogen atoms at high temperature, so that the material becomes brittle. Titanium begins to absorb hydrogen at 300℃, oxygen at 600℃, and nitrogen at 700℃.
Argon arc welding machine should have high frequency arc starting, current attenuation, gas delay protection, pulse device welding wire requires mechanical properties equivalent to the base metal.
Protective cover material should be made of purple steel or titanium, shape in order to protect the weld, so that the weld does not change color, the shield should be equipped with stainless steel mesh, play the role of gas buffer.
Two, titanium welding operation technology
Welded Titanium Tube cleaning before welding:
The material is bevelled with a rolling machine, and the oxidized skin, grease, burr, dust and so on within 25mm on both sides are polished with a wire brush, and then tested with acetone or ethanol.
Welding protection:
Argon protection should be learned before welding. When protecting, one person takes the shield to protect the top and the other person takes the shield to protect the bottom. The protector must be well matched with the welder, and the protective cover can be released after welding until the weld cools.
When welding, the weld should leave enough gap 3-5mm to facilitate the formation of arc pit;
Hold the welding gun in the right hand as low as possible tungsten electrode of the welding gun, hold the welding wire in the left hand, use thumb and middle finger to hold the wire forward;
Continuity and stability should be maintained when sending the welding wire, and good coordination should be made between the two hands to keep the weld smooth;
Eyes should always observe the depth of the molten pool and the flow of the welding liquid, the current should be adjusted according to the regulations, and the current is prohibited to be too large.
The argon gas of the nozzle is kept at 5ml, the protection gas at 25ml and the back at 20ml to ensure that the weld does not change color after the protection cover. When welding twice, leave a certain cooling time, so that the surface temperature is reduced to below 200℃, otherwise it is easy to produce crack embrittlement, welding position as far as possible to adopt flat welding and pipe mouth rotation welding.
When welding, the room should be dry and dust-free, the wind speed is less than 2 meters/second, and the wind is easy to cause arc instability. When sealing welding, try to use pulse device to make the weld forming beautiful.
Iii. Manufacturing process and maintenance technology of titanium equipment
Processing titanium pipe, titanium elbow, titanium tank material to meet the requirements, its toughness, strength, scalability to have a plate certificate, each titanium plate must be adjusted with a stick ruler, calculate the size of the material, to prevent excessive waste;
Plate cutting machine should be used, as far as possible to avoid the use of gas cutting, pipe use should be clear and accurate, strictly prohibit the repeated use of gas cutting, cut the plate after the chamfering machine to make a good groove, the break requirements are uniform;
After the initial molding of the plate rolling machine, the weld should be concave to facilitate 2 times of shaping after welding, because of the high price of titanium material (raw material 140 yuan /Kg or so, 400 yuan /Kg or so after processing) to eliminate waste.
Titanium plate maintenance and processing are very different, mainly environmental factors, material changes, welding can protect the protection, it is not double-sided protection with small current single-side protection, weld cracks can not be welded in the original weld, to use the way of welding plate;
Generally, when the wind is strong in the welding site, there should be a wind shelter device, and the rain cloth or iron plate should be used to shield the pipe. When the pipe is taken over, there should be a gap or dislocation welding because the inside can not be protected, and the weld should be properly widened and thickened.