Why the Elastic Retaining Rings For Reverse Shafts Break And Fail When Assemble?

- Mar 05, 2020-

According to the deformation and failure of the retaining ring for reverse holes, it can be generally divided into: the retaining ring has not been heat treated; the eccentric dimension c has reached the lower limit or is too small; there is no hardening or low hardness during the heat treatment. The following is a brief analysis of some causes of failure to facilitate their control and improvement.

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1.1 Retaining ring is not heat treated

The raw material for manufacturing the retaining ring for reverse holes according to the standard is generally 65Mn spring steel, and this material generally has a suitable hardness and elasticity index after being quenched and tempered. During the heat treatment process, if the processing site is poorly managed, sometimes the retaining ring is thrown off. If the operator mistakenly puts the retaining ring without heat treatment into the heat-treated box, the retaining ring with only the hardness of the raw materials will be mixed in, which will cause poor use.

Improving countermeasures: Strictly implement process regulations, strengthen on-site management, and prevent product landing.

1.2 The eccentric dimension c has reached the lower limit or is too small

When designing the retaining ring blanking die for the reverse hole, the eccentric dimension C has taken the lower limit or exceeded the lower limit, resulting in a small eccentric dimension of the retaining ring, which cannot generate sufficient elastic force and affect the elastic index of the retaining ring.

Improving measures: Adjust the mold design parameters appropriately so that the eccentric dimension c is within a reasonable range and ensure the elastic index of the retaining ring.

1.3 No hardening or low hardness during heat treatment.

Defects that cause deformation of the retaining ring for reverse holes during heat treatment usually include: the retaining ring is not hardened, the hardness is low or no hardness. They are often easier to feel during use, especially for low or no hardness retaining rings. Here we will focus on the situation where the retaining rings have no hardness.

Retainer ring heat treatment and quenching generally use a mesh belt type quenching furnace. Because the mesh belt is subjected to high temperature heating and running for a long time, it will cause local damage to the mesh belt, and individual retainer rings will be placed at the damaged place. At the discharge opening of the quenching furnace, the retaining ring will slowly fall into the quenching tank as the mesh belt runs to a certain angle, instead of falling into the quenching tank quickly according to the prescribed time. This causes the retaining ring sleeve to stay briefly at the blanking port and is not quenched in time. When it falls into the quenching pool, the temperature of the retaining ring has decreased and it has not reached the normal quenching temperature requirement, resulting in a very low hardness of the retaining ring or Without hardness, the elasticity of the retaining ring is poor, and the elastic fastening and fixing effect of the retaining ring is lost.

Improving countermeasures: 1) For the retaining ring without hardening, it can be judged by using the method of checking toughness. When testing the retaining ring quenched parts, if the retaining ring is not broken, you can use the method of testing hardness or metallographic analysis to further determine whether it is hardened and rework according to the test situation; 2) For the retaining ring with low hardness, check the hardness , Can be re-quenched and tempered heat treatment processing to achieve the required hardness requirements; 3) for the retaining ring without hardness, the retaining ring needs to be fully selected and treated, the selection can be through hardness testing or manual twisting and other methods To distinguish. After analyzing the defective parts to find out the cause, this batch of products can be re-hardened. Also, restore the device to normal.

2 Fracture failure analysis

According to the failure condition of the retaining ring, it generally means that during the assembly and use process, the retaining ring breaks, causing the assembly to fail.

1) Defective raw materials

The raw materials have defects such as segregation, delamination, foreign inclusions, and high hardness. Defects such as cracked edges and slight tearing of the stamped blanks cause heat treatment and cracks during heat treatment to cause cracks during use.

Improvement measures: Strictly control the purchase of raw materials. Select a reputable steel plant as a qualified supplier and require the steel plant to provide a quality certificate.

2) Poor heat treatment

It is well known that 65Mn steel has a tendency to overheat and temper brittleness during heat treatment. If during the heat treatment process, the temperature of the quenching furnace is caused by the failure of the temperature controller or other artificial factors, the overheating may be caused by the heating temperature being increased, and the metallographic structure of the retaining ring may be coarsened. The grain cannot be refined, which causes the retaining ring to break during use. In addition, when the retaining ring is tempered, a temperature range of 250 ° C to 400 ° C of the first type of tempering brittleness may be adopted, so that some parts have the first type of tempering brittleness, thereby reducing the toughness of the retaining ring and making the retaining ring Fracture occurs during use. Regarding the case of quenching without tempering, it is still a problem of on-site management. Due to some workstations not being cleaned up or individual products falling to the ground, the operator did not fully implement the relevant regulations, and the bad parts were mistakenly placed in the workstations that have been tempered by the retaining ring, which may cause quenching failure. Bad conditions of tempering.

Improvement measures: (1) Strictly implement the heat treatment process regulations. It is strictly forbidden to increase the quenching temperature arbitrarily during quenching to prevent the retaining ring from overheating to make the metallurgical grains coarse; (2) the retaining ring is in the tempering process, and it is to be avoided as much as possible. Tempering in the fire brittleness temperature area to prevent tempering brittleness. If conditions permit, you can consider using an isothermal quenching process instead of the traditional quenching and tempering process to improve the toughness of the retaining ring and prevent the retaining ring from breaking; (3) For hardening and tempering, you should work hard in strict operating procedures to prevent Product landing phenomenon. If you encounter individual pieces, they will be treated and isolated as scrap parts.

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3 conclusions

Although the deformation and fracture failure of the retaining ring for countersink shafts can be judged from the surface phenomenon, sometimes there are other reasons, so sometimes it is more difficult to solve. This requires us to continuously sum up experience in practice, to promote strengths and avoid weaknesses, and to use reasonable process methods to avoid these failures of the retaining ring, improve the assembly and use of the retaining ring, and meet user needs.