One, Stress Relieving Annealing
Coiled springs produced using cold rolling technology commonly utilize lead-bath isothermal quenching cold drawn steel wires (carbon spring steel wire, wire for musical instruments) and oil-hardened tempering spring steel wire. These springs do not require quenching treatment and must undergo stress-relieving annealing. Typically referred to as tempering, it is also known as stress-relieving tempering or stress-relieving annealing.
Purpose:
Eliminate internal stress in cold drawing of metal wires and cold coiling of springs.
Maintaining consistent spring dimensions is crucial, as springs that have not been stress-relieved by heat treatment may experience increased outer diameter and size instability during subsequent processing and use.
Enhance the tensile strength and elastic limit of the metal wire.
④ Utilize stress-relieving annealing to control spring dimensions.
Note: Under the condition of the same material diameter, some materials have higher strength but slightly lower toughness, so the temperature can be higher. The second tempering of the tension spring and torsion spring should be about 20℃ lower than the first, and the holding time can also be shortened.
Two: Stress-relieving Annealing
The stress-relief annealing temperature and holding time for torsion springs greatly affect the initial tension of the spring. Lower temperatures and shorter times result in higher retained initial tension, whereas higher temperatures and longer times lead to lower retained initial tension. Figure 3-10 shows the experimental values of the relationship between the annealing temperature and initial tension. Generally, a temperature range of 200-300°C is suitable, with a holding time of 20-30 minutes. To retain a higher initial tension, the temperature can be lowered to as low as 180°C. It should be noted that the initial tension should be primarily based on the coiling force, with the stress-relief annealing temperature serving as a supplementary role.
Note: The stress-relieving annealing temperature for springs after shot blasting typically ranges from 180-220°C, with a holding time of 20-30 minutes. The tempering temperature must not exceed 250°C.
When adjusting dimensions through tempering, the temperature should be approximately 20℃ higher than the generally recommended temperature.
