Shot Peening Media Review

Shot peening media used in industry typically consists of small spheres of cast steel, conditioned cut wire (both carbon and stainless steel), ceramic or glass materials. Very often cast or wrought carbon steel is employed.

Stainless steel media is used in applications where iron contamination is a concern. Carbon steel cut wire, conditioned into near round shapes, is being specified more frequently due to its uniform, wrought consistency and great durability. It is available in various grades of hardness and in much tighter size ranges than cast steel shot. Glass beads are also used where iron contamination is of concern. They are generally smaller and lighter than other media and can be used to peen into sharp radii of threads and delicate parts where very low intensities are required.

Shot peening media

Cast steel shot is created by atomizing molten steel, then heat treating and sieving the resulting material.

Advantages:

  • More durable (longer life) than glass and ceramic shot
  • Available in carbon steel and stainless steel
  • Ability to achieve the highest intensity
  • Easiest to maintain spherical particles

Disadvantages:

  • More difficult than cut wire shot to maintain spherical particles
  • Less durable than cut wire shot
  • High material cost

Cut wire shot is created by cutting drawn steel wire to lengths approximately the same size as the width of the wire. The resulting wire is then rounded to remove the sharp edges.

Advantages:

  • Produces uniform results due to its consistency in size, shape, and hardness
  • Tends to wear down into smaller diameter rather than fracture into particles with sharp edges
  • More durable (longer life) than cast steel, glass, and ceramic shot
  • Available in carbon steel and stainless steel
  • Ability to achieve the highest intensity
  • Easiest to maintain spherical particles

Disadvantages:

  • High material cost
  • Limited sizes

Glass shot is created by atomizing molten soda lime, then sieving the resulting material.

Advantages:

  • Available in wide range of sizes
  • Low cost material
  • Inert material, will not cause ferrous contamination or leave residue on work piece
  • Environmentally friendly

Disadvantages:

  • More difficult than steel media to maintain spherical particles
  • Less durable than steel and ceramic media
Effects of Shot Hardness:
 
It has been found that the hardness of the shot will influence the magnitude of compressive stress. The peening media should be at least as hard or harder than the parts being peened unless surface finish is a critical factor. For a large number of both ferrous and nonferrous parts, this criterion is met with regular hardness steel shot (45-52 HRC).
 
The increased use of high strength, high hardness steels (50 HRC and above) is reflected in the use of special hardness shot (55-62 HRC).
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