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Shot Peening

Overview

Shot peening is a cold-working process in which a metal part is bombarded by tiny balls of steel, Stainless Steel, cut-wire, glass or ceramic shot. Although shot peening is often confused with abrasive blasting, the two processes have very different effects. Abrasive blasting is used primarily to rid metals of corrosion and rust, while shot peening is used to work-harden metal and to increase its fatigue strength.

Although simple in concept, shot peening has become quite technical in recent years. Different shot types (grade, type, hardness, and shape), varying impact angles, intensities, velocities, nozzle-diameters, peening-times, the type of material and the surface coverage can all affect the end-physical properties of the peened metal.

Superior Shot Peening has over 50 years of experience, and have peened almost every commercial metal known to man including exotic metals such as hastaloy, titanium and zirconium. Our plant is equipped with automatically controlled shot peening machines that are capable of processing parts of different shapes and sizes with consistent and accurate results. Our mobile crews are equipped with similar, portable machines and can do work almost anywhere in the world.

Whether done in-house or in the field, Superior Shot Peening adheres many stringent customer-specified standards, all of which are easily accommodated. We are capable of handling custom shot peening jobs of all types from the very large to the very small and are experienced working under a variety of difficult conditions.

We pride ourselves on our superior quality control methods and are able to offer a choice of several quality control tests to our customers. Florescent dye penetrant, visible dye check, almen strips and 10X magnification inspections can be used individually or in combination per customer specification. Our test equipment is constantly checked for calibration and is traceable to the National Institute of Standards and Technology. A certificate of compliance is issued with each order.

Technical Information

Benefits of Shot Peening
Shot peening is used in a wide variety of industries on an even wider variety of parts. Parts typically shot peened include: threads of all kinds, ID bores and OD flex points, crankshafts, gears, torsion bars, springs, valves, exhaust manifolds, blades, discs, turbines, compressors, marine rudders, axles, hammers and anvils, bicycle frames, landing gear, boat hulls, drill bits, and pipeline. Depending on the specific part, shot peening can accomplish all of the following:

  • Increases fatigue strength
  • Prevents cracking due to wear, hydrogen embrittlement, corrosion and stress
    Enhances lubricity by creating small pores in which lubricants can accumulate
  • Prevents fretting
  • Prevents galling
  • Creates a uniformly textured, finished surface ready for immediate use or for paint and coatings
  • Can be used to curve metal or straighten shafts without creating tensile stress. This process is known as Peen forming.
  • Can permit the use of very hard steels by reducing brittleness
  • Will close up surface porosity in coatings
  • Allows for the substitution of lighter materials without sacrificing strength and durability
  • Can increases spring life 400% to 1200%
  • Can increase gear life more than 500%
  • Can increases drive pinion life up to 400%
  • Can increases crankshaft life 100% to 1000%
  • Can increase the fatigue strength of damaged parts extending the wear and delaying replacement costs

If you have questions about the benefits shot peening can bring to your particular project, please contact us. Our qualified staff will be happy to assist you in every phase of the project.

Other Shot Peening Uses
Shot peening has become useful for a variety of highly specialized applications. Our shot peening technicians are skilled in all of the following alternate specialized applications.

Flow Treatment of Pipe: Used primarily in the transport of polymer pellets used in the oil and gas industries. Polymer pellets will slide against the inside of a smooth pipeline, melt and form streamers or angel hair. These long polymer fibers will contaminate the pellet flow and clog up the transfer system. When the inside of pipeline is roughened by shot peening, the polymer pellets bounce or roll instead of sliding along the inside of the pipe. The pellets’ contact with the side of the pipe is shortened, and formation of angel hair is prevented.

Peen Forming: Sheets of various metals can be shot peened into concave, convex or flat shapes. This shot peening application is especially prominent in the aerospace and automobile industries. Shot peening of automobile and aircraft has allowed the industries, over the years, to reduce the weight of automobiles and airplanes by 30-50% saving (several hundred pounds). This, combined with the fatigue- and corrosion-resistance benefits of shot peening, makes peen forming a highly useful technique.

Straightening: Shot peening can return bent shafts back into tolerance, which will reduce waste or replacement costs

Search Peening: Corrosion is not always visible. Sub-surface corrosion is particularly common in areas directly surrounding metal fasteners, screws, nail, etc. Search peening is a technique in which small, problem areas are peened, and the hidden corrosion is exposed and eliminated. Search peening is preferable to many other corrosion removal methods because it actually strengthens the metal while removing the corrosion.

History of Shot Peening
Shot peening is not a new process. People have long known that pre-stressing or work-hardening metal could create harder and more durable metals. The process of peening was used in forging processes as early as the Bronze Age to strengthen armor, swords and tools. Gun barrels in the civil war were subject to peening to increase the hardness of Damascus steels, and the fillets of crankshafts in early European racecars were hand-peened with specially-made hammers by 1922.

Of course, peening has evolved substantially in the late 20th and early 21st centuries, but the general idea remains the same. Shot peening the material with thousands of tiny balls of high-velocity shot works in much the same way as peening with a hammer did in medieval times.

So why does pre-stressing of metal work? The atoms in the surface of a piece of manufactured metal will be under (mostly) tensile stresses left over from grinding, welds, heat treatments and other stressful production processes. Cracks promulgate easily in areas of tensile stress because the tensile stresses are already working to pull the atoms of the metal apart. By shot peening the material you introduce a layer of compressive stress by compacting the material.

As the shot peening is performed, the atoms on the surface of the metal become crowded and try to restore the metal’s original shape by pushing outward. The atoms deeper into the metal are pulled toward the surface by their bonds with the atoms in the compressive layer. These deeper atoms resist the outward pull creating internal tensile stress that keeps the part in equilibrium with the compressive stress on the surface. Tensile stresses deeper in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start on the interior.

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