Titanium has a small specific gravity (specific gravity is 4.5), high strength, good resistance to high and low temperatures, and excellent crack resistance and corrosion resistance in wet chlorine. The mechanical properties and welding of titanium are related to the purity of titanium materials. The higher the purity, the better the performance. The lower the purity, the sharp drop in plasticity and toughness, and the worse the welding performance.
1. Metallic properties and welding parameters of titanium
Titanium is very active above 300°C and easily absorbs hydrogen, oxygen, and nitrogen atoms at high temperatures, making the material brittle. Titanium begins to absorb hydrogen at high temperatures of 300°C, oxygen at 600°C, and nitrogen at 700°C.
The argon arc welding machine should have high-frequency arc initiation, current attenuation, and gas delay protection, and the pulse device welding wire requires mechanical properties equivalent to the parent material.
The material of the protective cover should be purple steel or titanium, and the shape should be convenient for protecting the weld to achieve the weld without discoloration. A stainless steel wire mesh should be installed in the protective cover to play a gas buffering role.
2. Titanium welding operation technology
Cleaning before welding:
Use a beveling machine to make a groove for the material, use a wire brush to polish the oxide scale, grease, burrs, dust, etc. within 25mm on both sides and then wipe with acetone or ethanol.
Welding protection:
Before welding, you must first learn argon protection. During protection, one person holds the shield to protect the upper part, and the other person holds the shield to protect the lower part. The protector must cooperate well with the welder. After welding, you must wait until the weld cools down before you can loosen the shield. For single-sided welding and double-sided forming, pay special attention to the protection of the back. If it is not well protected, the welding liquid cannot flow and there will be no forming.
When welding, the weld should have enough gap of 3-5mm to form an arc pit. Hold the welding gun in your right hand and try to lower the tungsten electrode of the welding gun. Hold the welding wire in your left hand and use your thumb and middle finger to clamp the welding wire and feed it forward. When feeding the welding wire, you should maintain continuity and stability. The two hands should cooperate well to keep the weld flat. The eyes should always observe the depth of the molten pool and the flow of the welding liquid. The current should be adjusted according to regulations and excessive current is prohibited.
The nozzle argon gas is kept at 5ml, the shielding gas is kept at 25ml, and the back is kept at 20ml to ensure that the weld does not change color after the protective cover. When welding twice, a certain cooling time should be left to reduce the surface temperature to below 200℃, otherwise, cracks and brittleness will easily occur. Flat welding and nozzle rotation welding should be used as much as possible.
When welding, the room should be dry and dust-free, the wind speed should be less than 2 meters/second, and strong winds can easily cause unstable arcs. When capping welding, try to use a pulse device to make the weld beautiful.
3. Manufacturing process and maintenance technology of titanium equipment
The materials used for processing titanium tubes, titanium elbows, and titanium tanks must meet the requirements. Their toughness, strength, and elasticity must have a plate certificate. Each titanium plate must be adjusted with a ruler. The size must be calculated when cutting materials to prevent excessive scraps. Shearing machines must be used when cutting plates, and gas cutting should be avoided as much as possible. The lines must be clearly and accurately marked when using pipelines. Repeated use of gas cutting is strictly prohibited. After cutting the plate, a chamfering machine is used to make a groove. The groove must be uniform. After the plate is rolled by the plate rolling machine for the first time, the weld should be slightly concave to facilitate the second shaping after welding.
There is a big difference between the maintenance and processing of titanium plates. The main factors include environmental factors, material changes, etc. The weld should be protected if it can be protected. If it is impossible to protect both sides, use small current single-sided protection. After the weld cracks, do not weld on the original weld. Welding should be done by patching the plate. When the welding site is windy, there should be a wind shelter, and a tarpaulin or iron plate should be used for shielding. When taking over the pipe, there should be a gap or staggered welding because the inside cannot be protected. The weld should be appropriately widened and thickened.
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