High precision disc rolling scissors vacuum heat treatment

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High-precision disc rolling scissors (hereinafter referred to as rolling scissors), the material is Cr12MoV, and the parallelism and thickness tolerance of the finished product are within 0.005mm. In recent years, with the rapid development of the market economy, the supply period is further shortened, and the original production process can no longer meet the requirements of the fast pace. Therefore, it is necessary to adopt some new processes to meet the requirements of rapid production.

The heat treatment of rolling scissors originally used salt bath quenching, cold treatment, and pit furnace tempering. In the process of heat treatment, there are two problems that are difficult to overcome, one is the large deformation of the knife body, and the other is that the scissors blade (the outer circle part) is easy to bump and fall off. In order to ensure the yield, the method used is to increase the amount of wear on both ends, outer circle and inner hole after heat treatment.

Taking φ254mm scissors as an example, the grinding amount of both ends, outer circle and inner hole is 0.8~1mm, 0.8~1mm, 0.6~0.8mm respectively. As a result, the production efficiency is very low, resulting in a waste of manpower and material resources. For the φ280mm×φ150mm×5mm rolling scissors required by the unit, the parallelism of the scissors is 0.004mm, and the thickness tolerance is ±0.002mm, which is very difficult to manufacture. Therefore, it was decided to use vacuum heat treatment to reduce the deformation after heat treatment and prevent bumping, so as to achieve the purpose of reducing the wear amount of each size of the scissors after heat treatment, so as to improve the production efficiency. Through the test, the flatness of the two end faces after heat treatment is controlled within 0.12mm. Considering the grinding deformation, the amount of residual grinding is determined to be 0.3~0.4 mm, the deformation of the outer circle and inner hole is controlled within 0.15 mm, and the amount of residual grinding is determined as 0.4~0.5mm, which achieves the expected effect and meets the user’s supply requirements.

Process flow:
φ280mm × φ150mm × 5mm, the material of the rolling scissors is Cr12MoV, and the heat treatment quenching hardness is 58～62HRC, as shown in the figure. The shape and size before heat treatment are the outer circle 280.4±0.05mm, the inner hole φ149.5±0.05mm, and the thickness 5.4±0.5mm.

1. Furnace loading method:
The vacuum furnace charging basket is shown in the figure. The diameter of the original load-bearing beam is only 20mm. In order to avoid the deformation of the load-bearing beam during the heat treatment of the φ280mm rolling scissors, which will affect the heating effect, it was changed to a stainless steel tube with a wall of φ80mm and a maximum wall of 5mm, which can be installed in one furnace. 20 pieces.

2. Vacuum heat treatment process
Quenching: For Cr12MoV disc rolling scissors, several temperatures such as 1000°C, 1020°C, and 1040°C are used for quenching, and the preheating temperature is 550°C and 840°C. In order to ensure that the rolling scissors have the hardness that meets the technical requirements and the minimum deformation, the final quenching temperature is selected as 1020℃. The quenching heating and holding time is determined according to the literature and the factors such as the furnace load and the basic temperature uniformity time. The final quenching heating temperature is selected as 1020℃, and the holding time is 45-50min.

Cold treatment and tempering: immediately after quenching, put it into a cold treatment incubator for cold treatment, so that the retained austenite after quenching continues to be transformed into martensite. The cold treatment temperature is -70 ~ -80 ℃, and the holding time is 1h. To prevent austenite stabilization, cold treatment must be carried out within 1h after quenching.

Equipment selection: The VOGQ series vacuum air quenching furnace produced by SIMUWU is a high-quality product for this type of brazing process. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum quenching process. With more than ten years of sales and manufacturing experience, it is exported to developed regions in Europe, America and Asia. It is a widely acclaimed vacuum furnace product.