Vacuum Quenching of Corrugated Ring Spring

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The corrugated ring spring of the inlet and outlet valves of small compressors is one of the important parts that directly affects the displacement.

The corrugated annular spring sheet (as shown in Figure 1) is stamped and formed from 50CrVA cold-rolled strip steel, and then quenched, with a hardness requirement of HRC≥58. Its working conditions are very harsh, with a working temperature of 180ºC and a spring sheet with a thickness of 0.15~0.6mm. The pressure is 7~200kgt/cm2, the compression beats 1450 times per minute, and bears considerable impact. Since the spring sheet works under the action of vibration and periodic alternating stress, the spring sheet must have high fatigue resistance and hardness, and its surface is not allowed to have defects.

Figure 1

In the past, the heat treatment process used salt bath quenching, and later changed to protective atmosphere vibrating bottom furnace quenching, but the rejection rate was as high as 30-40%. Moreover, the hardness of the spring sheet after quenching is neither high nor uniform, and its service life fluctuates between 1000 and 6000 hours, and the average life is less than 3000 hours, and the quality is extremely unstable.

From the analysis of the fragments of the bomb tube in the past, it is mainly due to insufficient fatigue and impact strength, most of which are caused by improper heat treatment.

In response to the above-mentioned problems, we carried out a vacuum quenching test on the bullets and achieved good results. After the wavy ring spring is vacuum quenched, the service life is more than twice that of salt bath quenching, and the quality is stable. The vacuum quenching process and other aspects are now introduced:

Vacuum Quenching Process of Spring Sheet

(1) Heat Treatment Process Specification

The corrugated ring spring is heated in a 30-kilowatt vacuum furnace, the quenching temperature is 860 ± 5ºC, the holding time of each furnace is 50 minutes, and the vacuum degree during heating is 10-3 Torr. The heat treatment process specification is shown in Figure 2. The quenching oil is ZZ-1 vacuum quenching oil, and the oil temperature is controlled above 40ºC. The oil fluidity is better. After oil quenching, the surface of the spring sheet is smooth, without oxidation and decarburization, and the hardness is HRC≥58.

Figure 2

(2) Loading Method

The spring sheet was originally clamped and quenched with a clamp, but the phenomenon of quenching is still not hardened. After that, the spring plates are stringed with lead wire and arranged one by one in the material frame. There is a certain gap between the two spring plates, so that the quenching oil can quickly flow to the surface of the shrapnel, so that each piece is hardened. The size of the material frame is 300X220X150mm (length X width X height), and the furnace capacity per frame is 5~10kg.

(3) Tempering Plastic Surgery

Due to the high requirements for the wave shape of the wave-shaped ring spring, calibration must be performed after the vacuum is scorched. Before tempering and shaping, the spring sheets are stacked in a clamp to ensure the height of the waveform, and then placed in a 450ºC box furnace for tempering for 2~2.5h to transform martensite into troostite.
In order to prevent the martensite spring sheet from chipping when clamped by the clamp, the spring sheet should be tempered in oil at about 200ºC to obtain the tempered martensite structure, increase physical properties and reduce brittleness. After the spring is tempered, it is placed in clean water and cooled to obtain a deep blue oxide film (that is, bluish).

(4) Boiling Water Drying

After the spring sheet is tempered and water-cooled, such as drying or baking, the surface is prone to yellow rust, which will affect the oiling and maintenance. After tempering and water cooling, immediately put it into clean boiling water (100ºC) to heat, and then air-cooled, so that the water evaporates, and it is cooled to room temperature and oiled. The shelf life can be up to two years.

Learn more:

Vacuum Heat Treatment Furnace

Vacuum Carburizing Furnace

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