Shot Peening

[Phred]

Shot Peening - A Practical Guide For The Racer

The principal function of peening is to increase the fatigue life of cyclically stressed parts. Small steel balls (shot) hammer the part, compacting the surface, which relieves both surface and granular stresses. The process builds a tough outer layer which is very resistant to fatigue cracking. This protective skin actually strengthens the part. The usefull life of a properly peened part is usually two to five times that of an untreated part. Shot peening is of most benefit on con rods and crankshafts. It can also be applied to almost any part subject to fatigue cracking. The following preparation is necessary before a part is peened.

1. The part should be Magnafluxed or Zyglo inspected.

2. All sharp corners, nicks, maching flash, and similar stress risers should be removed, smothed, and properly radiused.

3. Precision finished surfaces, such as pin bores or journals, require masking prior to peening.

Intensity is the critical component in successful shot peening. High intensity peening will distort a thin section part. Peening intensity must be high enough to produce an effective skin, but not so great as to damage or distort the part. Controlling intensity in the peening process is accomplished by using shot of different density and diameter. It is also controlled by the distance from the gun nozzel, angle, air pressure, and exposure time. The intensity used for different parts also varies with the type of metal being peened. The ideal intensity for a specific part is determined by knowledge of metalergy, experimentation, and experience.

Double Shot Peening:

Most parts benefit from double shot peening, wherein the part is first peened using larger shot and high intensity. Then peened a second time using smaller shot, (usually fresh glass beads) and lower intensity. This produces a much improved surface appearance and considerably improves the fatigue life over single shot peening. Double shot peening is a patented process, U.S. Pat No. 3,073,022 issued to General Motors. The rights of which are not being enforced. I mention it only to underline the value of the process. The patent papers cover seven pages and include fatigue life charts showing life cycle comparisons between unpeened, single peened, and double peened parts. They leave no dought as to the advantages of double shot peening.

Phred

[Bambikiller240]

Great Post Phred! Thanks for adding to our knowledge base. Please feel free to post any technical info you would like to share to the forum.

Thanks again!

Carl

[Zvoiture]

Wow. And I was just going to ask.

steve

[symon]

That´s wonderful.

I always knew that about shot peening, but didn´t know about the technical facts. Many thanks for improving my knowledge.

[hmsports]

On of my friends who races a 280Z in ITS was breaking his half shafts on a regular basis until he had them shot peened. Hasn't broken one since.

Thanks for the technical explanation Phred!

[beandip]

Do you do this at your shop ? :classic:

[Tourniqet]

hey phred,

do you have any price estimates??

like for a block, crank or rods to be peened, or halfshafts?

thanks for the post!!!