Effect of shot blasting on, stress relaxation in springs

Conclusions

• 1. Relaxation (weakening) of stress is particularly intense during the first 50–100 h of stress and depends on the type of hardening treatment. Thus, in the case of an initial stress of τ₀=60 kg/mm², the stress relaxation after 500 h reaches 6.5 kg/mm² for unhardened springs, 5.2 kg/mm² for hardened springs not under stress, and 0.5 kg/mm² for hardened springs under stress.

• 2. The intensity of relaxation increases and the positive effect of shotblating is weakest under a stress exceeding the yield strength (88 kg/mm²) for V1 wire 4 mm in diameter.

• 3. Cold hardening of springs under static stress by shotblasting increases the wearability of the springs [1] and considerably increases the stability of their elastic characteristics, and thus eliminates the lengthy operation of scragging. The cold hardening of springs by shotblasting requires 4–8 min; the scragging operation takes 24–48 h.