10 replies to this topic

[Bluemini]

What do they fire out of the blaster when they shot peen? It must be something fairly forgiving, but fairly abrasive too right but not sand or bead?

[Purple Tom]

They do use very small pieces of steel or lead shot I believe, my Dad used to work for a company who shot peened the blades from Rolls jet engines, and he 'liberated' a container of shot, its very heavy, and makes excellent ballast for off road vehicles

[bigfinger]

Shot Peening involves bombarding a material with small spherical media called shot. Each piece of shot is the modern day version of the hammer/ stone used in the past.

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. This pulls, towards the surface, the atoms in the deeper layers, which resist the outward pull, thereby creating internal tensile stress that keeps the part in equilibrium with the compressive stress on the surface.

The tensile stresses, resulting from Shot Peening, deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start on the interior.

Hence the reason rolls did it to the blades i think.

[Jammy]

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. This pulls, towards the surface, the atoms in the deeper layers, which resist the outward pull, thereby creating internal tensile stress that keeps the part in equilibrium with the compressive stress on the surface.

The tensile stresses, resulting from Shot Peening, deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start on the interior.

TMF Translation: It makes stuff harder!

[Purple Tom]

lmao Jammy!

Good description bigfinger, i'd have said that, if I knew the science behind it :fear: Dad did explain once, but I've slept since then.

It doesn't just make it harder though, it also makes it tougher.

[Bungle]

It doesn't just make it harder though, it also makes it tougher.

dont let the northerners see this they will spray each other :grin:

[dklawson]

The toughness is already there in the core. The detailed description above is accurately describing work hardening the surface.

I used to work in steel fabrication and one of the commercial finishing machines available was called a "WheelAbrator" This machine was sort of a conveyer fed shot-peening machine. We'd take wheels and other parts (non-work-related) and put them on pallet to run them through. The parts came out looking gorgeous... free of paint, scale, rust. The pallets on the other hand looked awful.

[bigfinger]

youre all too kind all i did was google 'shot peen' :cheese:

when i used to machine castings they were sent away and shot peened... makes the surface alot arder and better looking reduces the chance of cracks etc etc we used to do it to cumming gearbox housings.

i did sound dead clever there for a bit though didnt i


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[Bluemini]

So in normal terms, is it the same as shot blasting? I have a blaster at work that we use to clean cast iron and run it with 'sharp sand'. Can it be used for doing con rods and cranks???

[Sprocket]

So in normal terms, is it the same as shot blasting? I have a blaster at work that we use to clean cast iron and run it with 'sharp sand'. Can it be used for doing con rods and cranks???

No, shot peening does not abrade the surface, sand blasting does. Shot peening rounds off imperfections where cracks may start, but also increases the strength as it creates millions of tiny, smooth dimples, a bit like a golf ball, which increases surface area. Its this increased surface area as well as the localised work hadening that gives extra strength . Thats part of the theory behind the back drilled crankshafts that MED produce. Read something about it in CCC magazine many years ago.

[bluebottle]

we do a lot of shotpeening in work to de-stress machined alloy, and make it far more crack resistant. it gets rid of the marks left after machining, which can lead to stress risers in the grain of the metal.
we also do the bore of larger bolt hole going through alloy fitting with tool thats called a rotapeener, this, as its name would suggest is a rotary sort of flapper wheel that has the same effect as shot peening.
all of our stuff is very tightly controlled, being aircraft stuff, and you have to use the right spec of shot for the right material.