After the stainless steel tube cold billet is heated, there is generally a temperature difference between the radial direction and the axial direction. When the end compensation of the induction coil is properly adjusted and the furnace is well sealed , the axial temperature difference can be controlled at 30-50 °C , while the center temperature is low in the radial direction. After the perforation , the temperature of the inner hole of the blank is increased due to the deformation work and the frictional heat , and the outer surface is lowered in temperature due to the diffusion of heat and the heat absorption of the tool. According to the test data , the temperature of the inner hole of the blank is generally higher than the outer surface temperature by 80-150 ° C , and the induction reheating of the stainless steel hollow billet is carried out under such conditions. Whereas at high temperatures the induction heating , since the stainless steel tube current penetration depth larger blank , longer heating times , or using high-power heating , the blank will further increase the temperature of the inner bore. This is not desirable. Want is , stainless steel tube hollow billet by extrusion before the reheating , a temperature slightly lower than the inner surface of the outer surface , so as to minimize the temperature difference between the inner and outer surfaces of the steel pipe after extrusion.
For this reason , it has been proposed , stainless steel pipe perforated front blank induction heating material used frequency furnace. The induction reheating of the hollow billet before extrusion after perforation is more advantageous by using a high frequency heating furnace .
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