Home shot peening

[abn]

I haven't even done a web search yet...but I thought I'd start here. I'm wondering if anyone has experience with shot peening and whether it is appropriate for a home shop environment or are the variables and subsequent surface inspections complicated enough to be better left to the pros. Can you explain the variables involved? A text recommendation would be welcome as well. Thanks.

[1erful]

abn: I am hoping that there are a lot of replies as I have the same questions. WALT

[WJHartson]

I have been involved with shot peening in an industrial environment. We used Wheelabrator equipment. It was a high maintenance area. Dust collection system was always a problem as well as repairs to the cabinets. We shot peened large steel stud for stress relieving and cleaning purposes. There was always steel shot on the floor causing lots of cleanup. The steel shot was feed into a wheel with buckets that then slungs the shot at the studs while they turned on a conveyor.

I would not recommend it for the home shop. Unless you are going to a lot of work that need shot peening for surface prep or stress relieving. I would bring the item to a shop and pay them to do it. The equipment is also expensive.

[gizmo2]

This may or may not be on the right path; but here goes. Many in the shooting fraternity pressure plate their bullets with molybdenum disulfide, using a tumbler of some sort and steel bearings. Problem is the weight of the 'shot' quickly exceeds the oomph of the setup. My set up is small sipper cups and plain BB's, limiting the weight to less than 6 pounds. Would something like this get the results you are looking for?

[WJHartson]

Maybe the question of what are you trying to do with the shot peening process is in order to give you assistance further.

[CompositeEngr]

The BB idea doesn't have enough force to do any shot peening (unless they are falling from a considerable distance). The pellets need to hit the surface hard enough to deform it a bit.
Shot peening works by inducing a compressive stress in the surface of the part to counteract any residual tension left from machining.

[crypto]

This may be of interest to someone. I once made myself a set of parallels of oil hardening gage stock. When they returned from heat treat they were all slightly warped. Sizes were 6"x2", 6"x 1-1/2" etc., etc. I sandblasted them to remove the scale from heat treat and found that the sandblasting had acted as a peening operation on the concave side and had removed much of the warpage.

I should add that the sandblast medium was a very coarse grit. Probably the same grit used to sandblast ship's hulls.

[Axel]

shot peening can be done in the home workshop. I bought a beadblasting cabinet a few years ago on it was some info on how to convert it to a shotpeening cabinet...but I never tried...

[docsteve66]

You ask about the parameters of shot peening. I have zero hands on shot peen work experience, we had shot peen jobs in aircraft over haul. The varibles were of course things like shot type (composition, weight, etc), pressures used, time blasted, angles of blast.

We had a "materials lab" that tested the finished product. Getting the specs right was tricky. also the specs that worked once might not work next time. Most of the shot peen was to increase service life. In effect if you had a serive life of 1000 hours, shot peen might reduce mean time between failure or increase actualy life of the part. But the shot peen peole did not know if they had done any thing, positive or negative, for a long time and even then only on a statistical basis. So in a home shop, it is hard to gather the numbers needed to decide if you are doing some thing worht while.

As said above, you are trying to put a compressed shell around a part by shot peening (at least thats the common intent if memory serves) so that when the part is "stretched" the compressed area is still compressed and cracks do not develope. Old automobile springs were bad about breaking, due to stress induced cracks. Shot peening greatly extended the springs life, but still some broke, some un peened stuff held up for years. I think on things like connecting rods, cranks etc, you think a long long time, and say do it!!!!. You will never be sure what you did was really helpful except by seeing if you failure changes. but the experiementer seldom makes (or can afford to make) a single change, such as shot peening, nor for sure does the operation stay the same- if you make it stronger, you push it harder (either work it harder or work it longer).

Nuff preaching- unless you wish to become a REAL expert in shot peen, take your item to some one who has equipemnt and experience with the problems you wish to solve. In other words as example: some earth moving equipment is peened, springs cranks etc for high proformance engines are peened. If you want a super duper shovel for wife's rose garden, go to the earth mover not the engine man, it not a job for the average homeshop unless you aretype that goes for "junk science" where you do it and hunt for evidnece that your solution was a smart solution. Too much of that out there .

Steve

[WJHartson]

Steve,

Think you said it all. The biggest problem with this subject is the lack of understanding of what is to be accomplished with the process.

Joe