Air Nozzle Peening
From Shot Peening
Air nozzle peening involves using compressed air to propel any shot media with the help of a nozzle in the direction of the metal part to be peened. Shot media could include spherical cast steel, conditioned cut wire, glass beads, or ceramic beads. Air nozzle peening is generally selected over wheel type peening (which uses a rotating, centrifugal wheel to propel shot) when the direction of the media must be more accurately focused. Frequently, multi-nozzle setups are utilized to shot peen complex parts that have more surface area than one nozzle can cover. The velocity of the shot determines the energy of the shot stream and is adjusted by modifying air pressure and nozzle settings. The Almen strip system is an important part of the controls which establish the repeatability of the shot peening process which is expected in today’s equipment.
Why is shot peening so important?
Shot peening has become a critical process in many industries due to its ability to improve metal fatigue properties and extend the life of critical components that could potentially fail. Metal fatigue occurs when cyclic loading and the associated tensile stress cause a crack to start in a highly stressed area. Shot peening is able to mitigate this by imparting a high magnitude, residual compressive stress at the surface in the potential failure area.
The shot peening compressive stress is opposite the applied tensile stress that causes a crack to start. Parts that have been shot peened are able to survive 3-10 times longer due to the surface being placed in a residual compressive state.