Shotpeening Springs | Increase Compression Spring Fatigue Life

			Spring Shotpeening
Shotpeening increases the fatigue life of compression springs at least 30 percent and has often increased the life from 2 to 10 times. Shotpeening may be applied to highly-stressed compression springs made from material, typically over .062" in diameter, with smaller shot being applied to smaller sized springs. Extension and closely wound torsion springs are difficult to shotpeen because the tiny steel shot (about 1/64" average diameter) is often to large to fit in between adjacent coils. Shotpeening can be applied to extension and torsion springs, however expensive processes are required to spread coils in order to achieve full shot coverage. Closely wound springs also do not get shotpeened on the interior area of the coils where the stress is highest and where shotpeening does the most good. The longer fatigue life due to shotpeening is accomplished by the following combination of effects: 1. Surface irregularities are hammered smooth. 2. The wire surface is cleaned and sharp burrs are dulled 3. The wire surface is slightly work hardened, which raises the tensile strength and elastic limit. 4. Most important, beneficial compressive stresses are trapped near the surface which must be overcome by the destructive tensile stresses that cause fatigue failure before breakage occurs. If shotpeened springs are electroplated, they should be heated immediately thereafter to relieve hydrogen embattlement. Shotpeening springs made from oil-tempered wire is an efficient method to remove the scale and clean the wire to prepare it for electroplating. Shotpeening stainless steel springs must be done with care to prevent the steel shot from adhering to the surface, as shot will rust and pit the wire. Wire brushing, tumbling or passivating will overcome this objection.

Spring Shotpeening