C2 - Blasting Media for non-cast steel pcs.?

[Tom D.]

Partners: Really good stuff in the archives about cleaning and bead blasting. Thanks for those postings.

Most of the prior discussions focus on aluminum and major engine castings like the heads and the block. What about the valve covers, oil pan, timing cover and etc.? Reasons to not sand-blast these items?

Thanks again!

Tom Dingman
4889
MI Chapter

[Joe C.]

Re: C2 - Blasting Media for non-cast steel pcs.?

Tom,

I see no reason not to blast sheetmetal parts to obtain a clean surface for paint. ust be sure to apply primer/surfacer first, then wet sand, then apply paint. You can skip the primer if you apply heavier coats of paint to level the stippled surface left by the media blast.
When you mention valve covers, I assume that you mean the sheetmetal type. Absolutely DO NOT blast aluminum covers. Those are best done by "tumbling" in media such as walnut shells.

Joe

[Jack H.]

One caveat...

On items like intake manifold and oil pan where there are typically 'internal structures' welded in, you can catch grains of blast media in corners/junctions... These can free up an migrate with oil flow/air flow after the engine is assembled and do internal damage. So, it's important to WATCH what you're doing and make sure the finished part is REALLY clean!

[Michael H.]

Good Story About Sand Blasting

Here's a series of posts from a few years ago on this very subject. Hope the link works.

https://www.ncrs.org/forum/archive18.cgi?review=142898

[Chuck S.]

Re: C2 - Blasting Media for non-cast steel pcs.?

Media blasting includes industrial sand blasting, and cabinet bead blasting.

The media for industrial sand blasting is much coarser, and the pressure and volume is much greater than cabinet blasting. In fact, for many industrial sand blasters, "sand" is not a euphemism...they literally use a product called "river sand". They may even use slag or metallic media for very heavy duty jobs. When something has been industrially sand blasted, do not expect to cover the blasting texture with a single coat of paint; as Joe says, you will probably have to apply surfacer and sand to get it smooth.

Cabinet bead blasting is another world away in media, pressure level, and voluem. Sometimes called "glass beads", this media is essentially finely ground glass. Glass beads come in different grades (sizes) and when you buy from someone that knows what their selling, it is graded into Mil Spec classifications. Glass beads will leave a matte finish on a part; the "tooth" left by cabinet blasting is perfect for painting, and I would expect a single primer dip to cover the texture.

The matte finish left by glass beads, however, IS NOT perfect for plating unless you want a dull siver cad finish...plating will not cover the texture because you only have a few tenths of a thousandth of an inch of finish thickness. If you have covers, actuators, or otherparts that will be zinc plated and then dichromated, I recommend mechanical cleaning and then steel wool burnishing. You can bead blast those parts, but you will have to burnish the surface back to shiny if you want an authentic looking zinc finish.

There are other media for cabinet blasting that are both more aggressive (faster) such as aluminum oxide, and gentler (but slower) like walnut shells. I have tried walnut shells on aluminum...while it did no damage, I couldn't see any cleaning happening either. Unless it something highly visible like valve covers or an intake manifold, I would try cleaning the aluminum with dilute phosphoric acid solution. Large, highly visible aluminum parts I would have professionally restored (Some used to call it re-skinning...I don't know if that was correct terminology or not.)

[Chuck S.]

Everything You Ever Wanted To Know...

About media blasting, including a wide range of media types and aggressiveness: www.tptools.com

[Joseph K.]

Re: Everything You Ever Wanted To Know...

There is a local man that blasts with soda bicarbinate and the results are beyond anything I have yet to see for preparing an item for painting or plating. Smooth as a baby's Butt.......................My two cents.......Joe