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Preheating is an important step for welding tooth blade bucket cutting edge, as it reduces the risk of hydrogen cracking and improves the weld quality. Preheating involves heating the base metal, either in its entirety or just the region surrounding the joint, before welding. The required temperature and duration of preheating depend on factors such as the material type, thickness, design, and welding method.
According to some web sources, the recommended preheating temperature for welding tooth blade bucket cutting edge is between 300 to 400 degrees Celsius. The area to be welded should be preheated for at least six inches from the weld area. A Tempile stick 400 can be used to measure the preheat temperature. The entire cutting edge can be preheated in a furnace, which increases productivity and reduces stress in the cutting edge and rear cutting edge welds. However, it is important not to exceed temperatures of 200–250 ºC for Hardox cutting edges, as this may cause hardness loss.
The welding method and consumables should also be chosen carefully to avoid hydrogen cracking and ensure a strong and durable weld. Some recommended welding methods are MMA, MIG/MAG, FCAW. Soft welding consumables, with a yield strength of up to approximately 500 MPa should be used. Basic flux electrodes with a low hydrogen content should be used for MMA or FCAW3. Stainless austenitic consumables of type AWS 307 or AWS 309 can be used if preheating cannot be applied. Austenitic consumables should always be used for welding manganese steel adaptors to Hardox cutting edges.
The welding procedure should follow a fillet weld manner, with overlapping of weld passes in long, straight passes. No weld pass should be wider than 2.5 times the diameter of the welding rod12. Each pass should be cleaned of slag before proceeding with the next. The weld area should have normal air cooling after welding.
Induction preheat treatment for welding
Induction preheat treatment for welding is a method of heating the metal before welding to improve the weld quality and prevent cracking. Induction heating uses electromagnetic induction to heat the metal from within, without any direct contact with the heating tools. Induction heating is fast, efficient, uniform, and safe compared to other methods such as flame or resistance heating.
Induction preheat treatment for welding can be used for various applications, such as preheating and maintaining weld temperature, hydrogen bake-out, post-weld heat treatment (PWHT), shrink-fit processes, and others. Induction preheat treatment can be applied to different materials and geometries, such as pipe, plate, moving parts, and complex shapes.
The parameters of induction preheat treatment for welding depend on the material type, thickness, design, and welding method. The required temperature and duration of preheating are usually specified in the welding procedure specification (WPS). The heating tools should be placed on or around the part to create a magnetic field that induces eddy currents and generates heat. The temperature should be measured using a Tempile stick or a thermocouple. The heating tools should be removed after the welding is completed and the part should be allowed to cool naturally.
Some benefits of induction preheat treatment for welding are:
- It reduces the risk of hydrogen cracking and improves weld strength and ductility.
- It minimizes the temperature difference between the arc and the base metal, which reduces distortion and residual stress.
- It saves time and energy by reaching the target temperature faster and more uniformly than flame or resistance heating.
- It enhances safety by eliminating open flames, explosive gases, hot elements, toxic byproducts, and noise.