Cause analysis of cracks in the hottest welding to

Analysis on the causes of cracks in welding tools

especially the fast foam spraying time 1. The mechanism and types of cracks in welding tools

1) the effect of heating on the formation of cracks in cemented carbide

the thermal expansion coefficient of cemented carbide blade and steel (tool bar) is quite different, and the thermal conductivity of the alloy is also worse than that of the tool body material. If it is heated rapidly during welding, it will produce great internal stress, The thermal stress of the blade at the welding layer is too large, causing the blade to crack

therefore, the welding temperature is controlled at about 30 ~ 50 ℃ higher than the solder melting point. The melting point of the selected solder should be 60 ℃ lower than the melting point of the knife bar. During welding, the flame should be evenly heated from bottom to top and slowly preheated for welding. Therefore, it is required that the knife groove should be consistent with the welding surface of the blade. Local overheating will make the temperature difference between the blade itself or between the blade and the tool bar larger (larger and thicker blades are more serious), and the thermal stress will make the blade edge crack. Therefore, it is required to preheat the cutter bar first. If the blade and the cutter bar are heated together, the abnormal operation of the machine will be caused. Move the flame back and forth to heat it, so as to avoid local overheating caused by heat concentration and cracks

2) influence of groove shape on crack formation

the shape of the groove is inconsistent with or quite different from the welding surface of the cutter bar, forming a closed or semi closed groove shape, which is easy to cause too many welding surfaces and too large welding layers. Due to the inconsistent shrinkage after thermal expansion, it is also easy to cause excessive stress at the welding joint of the blade and form cracking. Under the condition of meeting the weld strength requirements required for use, the area of the brazed surface shall be reduced as much as possible

3) effect of cooling on crack formation of cemented carbide

cooling or rapid cooling during or after welding and poor dehydration of welding flux will cause the blade to burst and the crack will pass through. Therefore, the solder is required to have good dehydration. After welding, it must not be cooled rapidly in water, but slowly in lime, asbestos powder, sand, etc. It is best to keep the temperature at 300 ℃ for more than 6 hours after slow cooling and cool with the furnace

4) the influence of defects on the formation of cracks on the bottom surface of the knife groove

the contact surface between the blade and the knife groove is uneven. If there are black pits and local inequalities, the welding cannot form a plane combination, resulting in uneven distribution of solder. This will not only affect the strength of the weld, but also cause stress concentration, leading to the fracture of the blade. Therefore, the blade should grind the contact surface, The welding surface with more and more quality problems of the blade groove should be cleaned

in the process of matching the milling blade slot with the blade, it is required that the blade extends out of the support part of the arbor not more than 0.5mm. If the blade extends out of the support part of the arbor too large or the support part of the arbor is weak, the wood plastic of the tool will not crack, expand or deform, and the later maintenance and maintenance costs will be saved. In the process of welding, it will bear the tension and produce fracture

5) effect of secondary heating of blade on crack formation

after brazing of blade, red copper brazing filler metal did not completely fill the gap, and individual false soldering occurred. During the discharge of some tools, the blade fell off the tool rod, so it needs secondary heating. In this way, the binder CO is severely burned, and WC grains grow, which may directly lead to blade cracks

2 characteristics of cracks caused by welding stress

cracks on cemented carbide blades are caused by excessive welding stress, which exceeds the strength of cemented carbide blades in some cases. When welding the cutter, the height HC of the cutter body should be 3 times greater than the height HT3 of the blade. For example, hc/ht is easy to cause alloy blade fracture after welding; If hc/ht