Our company has recently received a batch of orders for PI Shape Beam body welding and heat treatment used in the coal mine roadway. The product is 3.2m long, 150mm wide, and 150mm high. The length exceeds the maximum size of the heat treatment furnace in our factory. If a new heat treatment equipment is added, the minimum investment is 180,000 yuan. Based on the principle of reducing the input cost, our company decided to develop a new heat treatment process. After thorough consideration of various factors in the field, we decided to use the method of high-frequency induction heat treatment.
1. Induction heat treatment application
Using the company’s existing pool for water cooling, designed a lifting beam mechanism (see Figure 1), we started with a 20mm copper tube around four times to make a sensor, the current 900A, after heat treatment product hardness is not enough. Later it changed to a 20mm copper tube to make an inductor by winding 3 times. The frequency was changed from 50Hz to 2000Hz by using the frequency converter to get the current of 1457A. The equipment cost only more than 20,000 yuan. After many tests, it was found that the higher the frequency used was, the more the thermal treatment effect was towards the surface and the lower the frequency used was, the more the thermal treatment effect was towards the heart. Finally, the induction hardening process was determined: the beam was adjusted to 1451A and preheated to 0.59cm/s after the 60s, and the temperature was about 900℃. Tempering process: After the current was adjusted to 1451A and preheated for 8s, the beam was reduced at a speed of 4.58cm/s at a temperature of about 400℃.
FIG. 1 Induction heat treatment process for shaped beams
2. Mechanical property testing after heat treatment
Pressure test: As shown in FIG. 1, when 294kN was applied to two fulcrum points with a distance of 1.5m, PI Shape Beam was deformed. When the applied pressure reached 343kN, PI Shape Beam was deformed. After the release of the pressure, the deformed beam could bounce back, leaving only 2mm deformation and no weld cracking. The welding process shall be evaluated in accordance with NB/T47014 — 2011 Welding Procedure Qualification for Pressure Equipment, and the weld shall be tested in accordance with GB/T2654 — 2008/ISO 9015-1:2001 Welding Joint Hardness Test Method. After testing the bending, tensile strength, elongation after fracture, impact toughness, surface hardness, and other technical indicators, all qualified.
3. The conclusion
Our company completed the processing of this product according to the welding and heat treatment process. This equipment is simple equipment developed by our company through initiating the technical backhands of our company, which achieves the effect of small input and large output and is a result of small changes in scientific and technological innovation.