Vacuum Heat Treatment of Thread Rolling Wheel

The thread rolling wheel is an external thread rolling tool. In the thread cutting tool and standard parts manufacturer, the thread rolling wheel is a key tool and an important tool in the production process. Its life and quality directly affect the accuracy of the processed taps, standard parts and other workpieces. The production schedule has an important impact. Therefore, the processing quality of the thread rolling wheel is particularly critical. Statistical analysis of the failure of the thread rolling wheel shows that heat treatment is undoubtedly the most important factor.

The GB/T971—2008 “Thread Rolling Wheel” standard stipulates that it is made of 9SiCr, Cr12MoV alloy tool steel, and the hardness is required to be 59~62HRC. But in actual production, in addition to the above two steels, there are CrWMn, 7Cr7Mo2V2Si (LD), 9Cr6W3Mo2V2 (GM), W6Mo5Cr4V2 (M2), 6Cr4W3Mo2VNb (65Nb) and so on. According to the different thread forming methods, the thread rolling wheel is divided into rolling and grinding, and there are bosses and no bosses according to the shape.

The technological process of rolling thread rolling wheel is: blanking – forging – annealing – machining (including thread rolling) – quenching and tempering – grinding both ends – grinding inner hole and keyway – finished product inspection.

Vacuum quenching According to Japan’s research on the life of Cr12MoV steel rolling wheel rolling stainless steel taps, the life of vacuum quenching is 3 to 4 times higher than that of salt bath quenching. The production practice of several major tool factories in China also draws the same conclusion, indicating that vacuum quenching is the preferred process for heat treatment of thread rolling wheels. The main process parameters are introduced as follows. 1 Preheating: 800~900℃x2min/mm, vacuum degree (66.7~1.3)x102Pa, and some units are preheated in two stages: 800℃ and 900℃. 2 Heating: 1020℃~1040℃ x 0.8~1.0min/mm, when the effective thickness is less than 40mm, it will be kept for 40min. Vacuum degree (6.7~5.3) x 104Pa, filled with high-purity nitrogen. 3 Cooling: high pressure gas quenching, vacuum degree (8.1~8.8) x 104Pa, the temperature of the workpiece should not be higher than 80 °C (the maximum temperature of the workpiece varies from factory to factory). 4 Tempering: The workpiece should be tempered in a basket when it is cooled to room temperature. After 190~210℃x3~4hx2 times of nitrate tempering, the hardness is all in the range of 60~52HRC, which meets the technical requirements. Some units have a tempering process of 200 ~220℃x3h+180~200℃x2h oil tempering; some units temper the air furnace at 220℃x5~6h for the first time and 220℃x2h for the second time.

Equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.