Shot Peening Success Stories for Modifying Surface Finish

Shot peening is primary thought of and used for metal fatigue, stress corrosion cracking and peen forming. The repeatable, surface finish of shot peening has benefits for reducing sliding friction in multiple industries. Following are some of these success stories for modifying surface finish:

• Food Industry Cheese Molds
• Pneumatic Conveyor Tubing

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Food Industry Cheese Molds

The cheese/dairy industry has found that uniform dimples provide a surface that can advantageously replace other surface treatments. The textured surface from shot peening often has a lower coefficient of sliding friction that is necessary for cheese release properties on some food contact surfaces. The dimples act as lubricant reservoirs for fat or other substances allowing the cheese product to slide easier through the mold on the peaks of the shot peening dimples. Testing has shown that shot peened finishes meet or exceed necessary requirements for cleaning in terms of microbial counts. This is due to the rounded dimples that do not allow bacteria to collect and reproduce. Sharp impressions left from grit blasting, sand blasting or broken media have proven to be less cleanable and have a much greater tendency for bacteria to collect and reproduce. Both glass beaded and stainless steel media have been used successfully in this application.

Pneumatic Conveyor Tubing

Pneumatic conveyor tubing can be up to 10 inches in diameter and is usually made of a stainless or aluminum alloy. It is used to transport plastic pellets at the facilities of molding companies or at various production, blending and distribution sites. Transported pellets degrade when contact is made with internal piping surfaces. The velocity of the pellets results in friction, heat and lost production. Using a variation of its Peentex process that produces directional dimpling, Metal Improvement Company can achieve a directionally textured surface that significantly reduces the formation of fines, fluff and streamers that can account for millions of pounds of lost and/or contaminated production each year. Directional shot peening has been found to be much superior to other internal treatments of the tubing, is often more economical and can be applied on-site. The directional surface finish has the added benefit of work hardening (when stainless or aluminum piping is used), thus extending the life of the surface treatment. The table shows test results from six different internal pipe treatments. A lower value of fines per 100,000 lbs conveyed is desirable. The directional shot peening resulted in one third of the fines of the next closest finish.

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