shot blasting

jerry · Post by **jerry** » Tue May 13, 08 9:02 pm

Will it damage the threaded part on suspension if i have parts blasted ie spring hangers,threads round pumpkin etc.

Ivor · Post by **Ivor** » Tue May 13, 08 9:13 pm

Yep. You've got to mask them off with plenty of insulating tape, or plug threaded holes.

Post by **TyreFryer** » Tue May 13, 08 9:32 pm

And it wrecks leaf springs if you don't dismantle them first, the grit gets in between the leafs and wears them.

MrNorm · Post by **MrNorm** » Tue May 13, 08 9:36 pm

???? nothing wrong with blasting threads, I've done it many times and it cleans em up a treat.

Maybe its the terminology - you mention shot blasting which is a REAL heavy duty process using steel shot, and unecessary for both spring hangers and I would say any axle worth saving.
I guess its possible the threads could be damaged by that??

But sand or media blasting is what you'd use for this, and it is fine

Ivor · Post by **Ivor** » Tue May 13, 08 9:53 pm

I don't want to contradict yo gavin, but I shot blasted some studs on an old axle case (using silica sand) and the thread clearance between the nut and the stud was knackered, to the point that the nuts wobbled on the threads.

However, with some of the "soft" media like corn cob and walnut shells, no problem.

So Gav, do you think I was a little too rough?

Jon Benn · Post by **Jon Benn** » Tue May 13, 08 10:18 pm

Use glass bead, turns to dust on impact, removes the rusty stuff but not the good metal underneath. Sorted

MrNorm · Post by **MrNorm** » Tue May 13, 08 10:54 pm

Ivor wrote:So Gav, do you think I was a little too rough?

Mystifies me! What pressure were you using?!!! I use pretty aggressive alumina and never had any problems - any more than wire brushing a thread would.
Agree that glass beads are even less aggressive - I use them too, but I have to say I have never heard of threads being damaged and never experienced it myself.
I had my entire bodyshell blasted with sand and that didn't get eaten away! And that is 'soft' steel, not hardened alloy that bolts/studs are made of.

Wait a minute....this wasn't on one of your Subeams or something? They were made from an alloy of steel and chocolate

Blue · Post by **Blue** » Wed May 14, 08 9:14 am

Steel shot will leave the surface looking like sandpaper, great for paint adhesion but not what you want on a thread or a section where a bearing sits or bush fits. I always mask those areas off with a good winding of gaffer tape. I think these commercial firms use far higher pressure equipment than the stuff we use at home, and it is much more aggressive.

jerry · Post by **jerry** » Wed May 14, 08 12:40 pm

Thanks for the info guys.Spoke to the blasting company really helpfull and as blue said needed to tape up the threads with gaffer tape and made blanks for the pumpkin and axle flanges.Dropped of parts, bloke seemed impressed with my handywork apparently its quite common for people to turn up with paper over the blanked of areas

One more question, if the leaf springs are disassembled can they be blasted or will it affect the way they are tempered.

Blue · Post by **Blue** » Wed May 14, 08 6:28 pm

Yep be sure to make those covers tight on the axle case, I used silicon sealer as well, you do not want shot getting inside the case, you wouldn't get it all out if you did...

Bryan · Post by **Bryan** » Wed May 14, 08 9:38 pm

did you use a company in woking jerry?

jerry · Post by **jerry** » Wed May 14, 08 10:01 pm

Elgamec located in Ash Bryan.About 15 mins from me.

MrNorm · Post by **MrNorm** » Wed May 14, 08 10:31 pm

I think everyone is agreed that SHOT blasting (which uses steel SHOT - hence the name, right?) could risk damaging threads (depending I assume on the pressures and also the grade of shot). It's actually not an abrasive process but peens the metal and is usually used for castings, removing flashing or scale etc. The peening can be used to induce compressive stresses to increase strength

My point was that SAND or MEDIA (which includes glass bead, walnut, corn plastic) blasting is something I've used a lot and never had a problem with threads, even with a course alumina, and also that SHOT blasting was probably unneccessary for the purposes of removing rust on any of our car stuff, including leaf springs and axle housings. If the rust is so bad you need shot blasting, the parts may be pretty far gone anyway.
A decent sandblaster will get rid of everything bar huge flakey chunks of rust.
Just clarifying what I said as I'm not sure it was interpreted correctly - I would not use shotblasting and I don't think it's not necessary.

As to my belief that sand/media blasting is safe, Ivor was certainly clear that he used sand (not shot) and had damage, which certainly surprises me, but evidently there must be circumstances where that can happen - so I learned something there! On my home setup I frequently blast threads with no issues, maybe a wimpy home setup is the reason?

Bottom line, if someone else is doing it ask them, and if there is any risk it is easy enough to tape up the threads and nothing to lose......though of course the reason I blast them is when they are all cruddy and rusted!

jerry · Post by **jerry** » Wed May 14, 08 10:49 pm

Gav you mentioned media blasting springs so i take it it does not affect the way they are tempered.

MrNorm · Post by **MrNorm** » Wed May 14, 08 10:58 pm

jerry wrote:Gav you mentioned media blasting springs so i take it it does not affect the way they are tempered.

No it doesn't, I'm quite sure of that!

Tempering changes the internal grain structure of a metal and a surface treatment won't affect that.