Glass beading

[tfburke3]

This message is to implore parts vendors,sellers of old parts to not galss bead parts prior to sale to make them look better.Looking for some alum. cases etc,mostly on ebay,its terrible to see the parts I need,but they have been blasted to improve.Let the builder decide as there is no returning once this is done.One vendor looks like his cases where blasted by a local bridge restoration crew.I have done this myself,but with fine beads and I made the decision.
So,If your sitting on a pile to put on ebay,dont think your impoving the part with your glass beader.Just my opinion.
Tom

[sirhrmechanic]

Great thought Tom.

I would also add... don't bead blast parts that are going to come into contact with OIL. Getting it all out is difficult and still risks introducing glass into oil.

Somewhere on here I posted a thread on case restoration showing what can be accomplished without beading.

Don't get me wrong... abrasive blasting has its place and it is invaluable in scouring out rust and getting parts totally clean. But it is NOT a 'one size fits all' solution. Used wrong, you will do a lot more harm than good with glass/starblast/walnut or (my latest hate) soda blasting. Know what/when and why you are using it. If in doubt about whether to blast something... post it and let some folks who have BTDT weigh in.

Thanks, Tom! It's a great reminder. I'll see if I can link my earlier thread.

EDIT: Here is the thread talking about case cleaning without bead blasting....
http://www.antiquemotorcycle.org/bbo...an-Chief-Motor

Cheers,

Sirhr

[Robert Luland]

All the insides of my cases are painted with Glyptal for that reason thou I agree with the soda blasting thing. Bob L

[sirhrmechanic]

Hi Bob:

Glyptal is great, but be careful with 'used' cases. It is utterly critical to get all the oil out of the cases and to heat/bake it on per instructions. Otherwise, it can come off and make a real mess of an engine! We've had a couple come into the shop where every orifice was plugged with improperly-applied Glyptal or similar inside-crankcase coatings.

We have stopped using Glyptal in favor of vacuum impregnation on crankcases that have porosity and or issues that make oil-tightness questionable. We use Impco in Rhode Island and the prices are really reasonable. They will take cases and vapor degrease (it really gets the oil out of the castings) and then put the parts in a vacuum chamber. When a very high bar vacuum is reached, they flood the chamber with liquid acrylic and then reverse the vacuum, causing all the pores in the aluminum or cast iron to fill with acrylic. The parts are then cured and are utterly impermeable to oil, water, etc. It is an aircraft process we have used for years. The only downside is that it will 'lock' the finish into your crankcase. So if you bead blast then VI, it will always have an un-natural grey finish. However, a nicely burnished case will stay lovely forever and oil will just wipe off.

Where it is really valuable is with cases that have been repaired/stitched and where there is some question that there is porosity. Old aluminum castings will often 'weep' oil right through the metal, even when structurally sound. VI will utterly eliminate that.

Anyway, just another of those techniques that is well proven and is very valuable for old cases. And IMHO, a lot safer and better than Glyptal -- which I also use all the time, but for sealing electrical components such as windings. Again, I don't condemn Glyptal by any means. It is a superb finish, especially on new castings. And if applied right, it works as advertised. Just be sure not to cut corners.

BTW, VI also works for cast iron and if you have water-cooled engines with thinning cast-iron walls, the VI can help arrest the corrosion and, again, seal porosity. The only caveat is that VI will NOT help or repair structural issues. If your metal is truly punky or is actually broken/cracked, you must repair that first and use the VI as a backup. It will not add structural integrity to metal that is fundamentally... rotted away.

Anyway, just some thoughts and another reason why I thank Tom for starting this thread.

Cheers,

Sirhr

[T. Cotten]

Glyptal is good, Folks, but....

Those of you with OHVs with leaky petcocks risk P4gas fouling the oil, and Glyptal has little resistance.

Back to beads, anything blasted must be scrupulously cleaned of course. Common sense should rule with any application.
I prefer brushing with impregnated wheelbrushes such as "Nylox" and "Adalox" prior to a very hot soapy water wash. There is no substitute for carefull attention to detail.

Another concern with blasting is low pressure. Pressure must be high enough to make the abrasives "bounce", rather than embed. (This may seem counter-intuitive, but it was the standard of professionals in the field.)

....Cotten

[BoschZEV]

Another concern with blasting is low pressure. Pressure must be high enough to make the abrasives "bounce", rather than embed. (This may seem counter-intuitive, but it was the standard of professionals in the field.)

This definitely is counter-intuitive, and sounds a bit like an old wive's tale. At very low velocity (i.e. low pressure) the hard, brittle glass beads will hit the relatively soft and ductile Al case with enough energy to do some cleaning but not enough to overcome the yield strength of the Al and embed themselves. The mechanism at work is the momentum of the glass particle (mass x velocity) coupled with its cross-sectional area gives rise to a very high localized pressure (pressure = force / area). If this pressure is higher than the yield strength of the Al they will embed, otherwise they will transfer some of their energy to the surface of the Al and bounce back off carrying the rest of their initial energy with them.

At higher velocity they definitely will have enough energy to embed if they remain in one piece, but at some point they also will have enough energy to shatter into smaller pieces of glass. If they break in half, each piece will retain half the initial energy until it is deposited in the Al (or carried off if the piece bounces). Anyway, what is counter-intuitive is that there really doesn't seem to be any physical mechanism that would embed glass beads at low pressure (velocity) but cause them to bounce at higher velocity.

[T. Cotten]

BoschZEV!

The theory is that the media must have enough force to work-harden the molecular "skin" of the surface. Glass beads are balls, and you want them to hammer a bright surface, not cut.

There are many alternatives to beads, of course.
(I served seven years at the lab in the attachment.)

....Cotten

[sirhrmechanic]

I can't say I know the physics of it all, though am familiar with processes like shot peening which can be used in high-performance engine parts... though perhaps this is an obsolete technique in these days of CNC and fancy new shapes out of fancier alloys.

I can say from a practical sense that while I don't generally reduce the pressure in the cabinet (I run glass at relatively high pressure... lower for walnut or plastic and I never use steel or starblast)... I do vary the distance of the work to the nozzle, depending on what I am trying to accomplish. You can do a lot with oblique angles and 'dusting' a part from a couple of feet away.

After blasting, I also hot-water wash everything (with soap) and then wire brush or scotchbrite to burnish away the sharp edges left by blasting. That said, there are a million different ways to do 'neat' things with a bead cabinet. It's a wonderful tool. To the OP's point, however, it can also be a very destructive device when used as a one-size-fits-all solution to cleaning things for eBay or similar.

I always remind folks that a hammer is a precision tool... in the right hands it puts a precise amount of energy in a given location in an instant. Nothing else gives that level of precision... but in the wrong hands a hammer merely breaks things and causes problems. Use it like a scalpel and you'll be rewarded with amazing results. Use it like, well, a hammer... and you'll just break things.

Cheers,

Sirhr

[BoschZEV]

The theory is that the media must have enough force to work-harden the molecular "skin" of the surface. Glass beads are balls, and you want them to hammer a bright surface, not cut.

Your response doesn't quite address the statement you originally made, about embedding with low pressure and bouncing with high. It does raise another point, though, and that is about the shape of the glass beads. Because glass is brittle it shatters into beads with sharp edges, not into balls. Those sharp edges are what make it such a good abrasive.

Back to the embedding vs. bouncing issue. If there is enough pressure/velocity for the glass beads to abrade away material (i.e. physically knock atoms off the material), there is enough for them to embed themselves in the Al. Doing so displaces the Al, causing local strain, and work hardening the surface to some extent. However, for your low vs. high pressure statement to work it would require that somehow the low pressure glass beads could embed themselves without displacing Al atoms. That is physically impossible, since the process of embedding only can happen by moving Al out of the way to make room for the glass beads. Also, it would require that as you increased the pressure the glass beads would somehow -- though some mechanism you haven't as yet explained -- cease to be embedded in the Al even though they have enough energy to physically displace the Al in order to introduce dislocations (i.e. to work harden the surface).

I think what you will find with bead blasting at different pressures is the following:

"Really low" pressure: the glass bounces off the surface because the velocity is too low for it to do anything
"Low" pressure: abrasion begins, albeit at a very slow rate
"somewhat low" pressure: once individual glass beads have enough energy to displace more than a few atomic layers at a time, embedding begins
"medium" pressure: faster abrasion and deeper embedding
"high" pressure: even faster abrasion, and even deeper embedding

[rwm]

i throw some gristle in your beef stew. what if the bouncing off glass beads or shards are met by in coming beads. they will get bounced back onto your aluminium case. they'll hit your case the second time with lower velocity, more broken edges and causing them to embed.
i boiled a set of cases in grand ma's old pressure canner. they cam clean and never got much hotter then a running temp.

[BoschZEV]

i boiled a set of cases in grand ma's old pressure canner. they cam clean and never got much hotter then a running temp.

I bought a very large galvanized washing tub at a swap meet that nicely holds one side of a set of cases and fits on the barbeque. The nice thing about using boiling water (plus soap and a stiff nylon brush) is the temperature is self-regulating, ensuring the parts never get above 212-degrees (although for some reason Europeans only manage to get their water to 100-degrees...).

I've never bothered to test one soap vs. another but I use Dawn based on the fact it's what's used to remove oil & tar from birds caught in oil spills. Of course, that just could be marketing hype based on Dawn donating their soap rather than it actually working better. But, it doesn't etch Al like TSP and other industrial strength degreasers do, doesn't cost much more than generic brands (at least in the quantities I use it for degreasing motorcycle parts), and seems to work as well as I can imagine any soap working, so I'll continue to use it unless there's a convincing reason to change.

[exeric]

I used to use powdered Tide, and thought it had no equal; however, I haven't seen it, or looked for it in years. It seems like there are no powdered detergents on the shelves anymore.

[rwm]

I used to use powdered Tide, and thought it had no equal; however, I haven't seen it, or looked for it in years. It seems like there are no powdered detergents on the shelves anymore.

that's because we live in a world of super size everything. it's cheaper for tide to add water to a large tub and sell you more. you can find product called washing soda in a powder.

[sirhrmechanic]

And, for the record, Tide in the Dishwasher does a great job on cylinder heads. However, having to sleep on the sofa for two weeks afterwards is not worth it. However I still get to use the oven to install valve guides. When the "Little Ms." is not home.

Cheers,

Sirhr

[harleytoprock]

On the glassbead embedding, you guys are stating facts without any scientific testing. So I got a bushel of tomatos and threw them at my garage door. Soft underhand throw resulted in a bounce back. Over head high speed pitch resulted in a smashed tomatoe. So there you have scientific research. Next I'll throw golf balls at my neighbor and see which throw nets the loudest scream. Well I gotta go clean the tomato mess.