(First published in Wire Technology International, May 2000)
In modern surface treatment technology, shot peening with blast wheels has generally replaced other time-consuming and expensive processes for 
increasing the fatigue strength of springs. This economical and environmentally friendly process also permits the design of light-weight and lower-cost components.
While it has little effect on parts exposed to straight torsional or compressional stresses, shot peening for surface compaction is particularly good for parts subject to alternating bending or torsional stresses such as coil, suspension, valve, leaf, cup and clutch springs.
How Spring Fatigue is improved
In the shot peening process, an abrasive is thrown at the surface of springs 
before they are subjected to any tension or stress in order to obtain a local distribution of compressive and tensile stress. The abrasive hitting the surface at velocities of up to 100 mps (328 fps) causes permanent spherical indentation. The metal layers below the peened surface undergo a deformation. The equilibrium of the two forces produces a compressive stress within the metal.
The indents made in the upper surface layers are tangential and perpendicular to the surface, while in the lower layers, the tension causes a permanent deformation. As a result, shot peened springs undergo a preliminary stress before being put into actual use. Stress that springs are subjected to during their service life corresponds to the preliminary stress inflicted on them by shot peening. Especially in the case of tension, the previous surface compression reduces the tension peaks. In this way, shot peening improves spring fatigue strength.
Primary Machine Features
To achieve the intensity needed as well as a uniform surface treatment, appropriate shot peening machine components are required. The principle of blast wheel shot peening is based on the use of the high kinetic energy of the abrasive resulting from its mass and impact velocity. So shot peening machine performance depends to a great extent on the efficiency of the blast wheels.
Blast Wheel Units
Patented blast wheel units are the core of shot peening machines from DISA. One or several wheels can be used on these machines which offer the advantages of short treatment times, high abrasive throughput, high-energy impact, uniform blasting of optimum intensity and control of blast stream direction and area.
Shot Separator
Well-cleaned abrasive is essential for good shot peening. Crushed shot must be removed immediately to maintain process integrity. Cleaning is done via the shot separator, through which the abrasive passes during each cycle. The separator uses wind sifting at a constant efficiency. Also, an electronic feeder adds new abrasive to replace spent and eliminated grains.
Dust collector
Shot blasting generates dust that must be removed from the shot blast cabinet to ensure proper functioning of the shot separator. Each of our machines incorporates a dust collector and we offer a full range of dry filters designed to specific peening machines.
Shot Peening Spring Applications
DISA shot peening machines can be configured for processing coil, leaf or cup-type springs.
Shot peening configuration for suspension coil springs and for valve springs
In a continuous longitudinal double-strand operation outputs of up to 1200 suspension springs per hour are possible. A single strand system can output up to 6000 valves springs per hour.
Batch-type shot peening drum
Valve springs can also be processed in a batch-drum configuration.
Shot peening system for non-tensioned or pre-tensioned leaf springs
In this continuous longitudinal single-strand operation, output depends on the part application.
Shot peening machine configuration for cup and clutch springs
In this cycled rotary operation, a robotic device is used to automatically turn over the workpieces after half of the passage through the blast cabinet. Cycle time is six to 15 seconds per spring.