1. Spring material and technical requirements
The material of the spring is 50CrVA steel, the technical requirement hardness is HRC45-49; the length change of the compression spring within the specified load should meet the requirements. The processing process of the spiral compression spring is: coil spring → recrystallization annealing → cutting, correction → quenching → back Fire → polishing → grinding end face → correction → low temperature stress relief → finished product.
2. Heat treatment process of helical compression spring
(1) Recrystallization annealing
After the spring coil is formed, it must be subjected to recrystallization annealing treatment to stabilize the geometric dimensions of the spring and reduce the deformation during quenching. The recrystallization annealing temperature is 550-650℃, and the temperature is kept for 1-1.5h before air cooling. A small amount can be stored in a salt bath furnace In progress, a large batch of continuous resistance furnaces are used to control the atmosphere.
When quenching and heating in the salt bath furnace, the spring should be evenly tied with iron wire, or the spring should be heated on the mandrel. When heating, ensure that the surface of the spring is pentoxide and decarburized. The salt bath should be carefully deoxidized. It is heated in a box furnace with a controllable atmosphere, the heating temperature is 850℃±10℃, the heat preservation is 10-15min, and the quenching oil is cooled through the furnace.
After quenching, the tempering can be performed twice. First, corrective tempering, the corrective tempering temperature should generally be about 20 ℃ lower than the final tempering temperature, keep it for 10-15 minutes, and cool it out of the furnace. Then perform the final tempering, after the spring size is corrected , The spring is installed on the tempering setting fixture for final tempering. The tempering setting fixture should ensure that the pitch and free length of the spring meet the requirements. The tempering temperature is 420℃±10℃, the heat preservation is 30-35min, and the furnace is water cooled.
(4) Shot blasting
In order to improve the fatigue strength of the spring, it is necessary to perform shot blasting. The diameter of the projectile is 0.3-0.5mm. When compressed air is used for injection, the compressed air pressure is 0.4-0.5MPa; when the centrifuge is used for shot blasting, the linear velocity of the projectile is 70m/s. The service life of the shot blasting spring can be more than doubled