Controlling the heat treatment deformation of the drill tail starts from changing its quenching, heating, annealing and cooling

The drill tail is an important part of the rock drill, generally made of 35SiMnMoV steel or 30SiMnMoV steel. During the operation of the rock drill, the drill tail is subjected to high-frequency alternating impact and torsional stress of the piston. It is a typical rod that can withstand multi-impact compression, bending and torsion. At the same time, the contact surface of the rotating sleeve is also subjected to a large friction force, and the service conditions are harsh. , prone to early failure. Therefore, the drill tail requires high surface hardness, good wear resistance, and high bending and torsion fatigue resistance. The overall strength and toughness of the object are good. The heat treatment process of the drill tail is to carburize the surface of the outer circle and the inner hole to strengthen the surface. The depth of the carburizing layer is 0.8 - 1.2mm, the surface hardness is 58 -62HRC, the core hardness is 43HRC, and the radial runout is ≤0.10mm. During production, it was discovered that although a 0.4mm grinding amount was reserved before quenching the drill tail, due to workpiece structural factors and insufficient heat treatment process, the 40-inch workpiece was still deformed out of tolerance, seriously affecting the quality of the drill tail product, and causing some workpieces to fail and be scrapped.

After analyzing the causes and influencing factors of excessive bending deformation during heat treatment of drill rods, the following process improvement measures were proposed:

(1) Add a stress relief annealing process before quenching. The purpose is to remove machining stress, but it needs to be done multiple times, so this method is energy-consuming and time-consuming, the process cycle is long, and the effect is not ideal.

(2) Improve the quenching spreader and tool fixture to heat and cool the drill tail in a vertical state. This method has a better effect on reducing deformation of the workpiece.

(3) Perform pre-deformation processing. Give a certain amount of pre-deformation to the deformed part so that the bending deformation of the drill tail after quenching can be offset. Pre-deformation using multi-point light pressure is better.

After using the above technical improvements, the deformation of the drill tail has been reduced, but there is still a bending deformation of 0.3-0.88mm, and the out-of-tolerance rate is still 30%; on the other hand, the straightening drill tail is usually deformed to no more than 0.3mm, but the leakage After the carbon drill tail is straightened, the internal stress is relatively large, and the carburized layer is prone to defects, which reduces its fatigue performance. After analysis and production tests, it was found that the carburized layer of the workpiece has the characteristics of low yield strength and good plasticity, so that the drill rod will produce a certain plastic deformation under the action of tensile stress, so that the deformation of the workpiece can be corrected. The advantage of using this method is that the internal stress is reduced during correction, which significantly reduces the bending deformation deviation caused by the residual internal stress, and resolves the contradictions and problems caused by previous straightening measures. After adopting this improved process in production, the pass rate of straightening deformation reached 100010, achieving obvious technical and economic benefits. Zhengzhou Gao's is a heat treatment equipment manufacturer with unique research on workpiece heat treatment. Welcome your inquiry anytime.