Abrasive Blasting as a finish

[Swede]

Glass bead or abrasive blasting is something that doesn't come up too often here. As a means of obtaining a uniform, pleasing finish, it's hard to beat.

A few years back, I invested in a benchtop blasting setup, and filled it with glass beads. At 80 PSI, a few passes with a cheap gun does nice work. Although it looks anodized, the body parts of this gadget were glass bead blasted:

Now comes the question... glass beads are outstanding for aluminum and copper alloys. Something like aluminum oxide, though, is generally needed for ferrous objects. I do a ton of aluminum work, and prefer to leave my bench rig set up with the beads.

Alox media is expensive. Does anyone know a way of either recycling the media, or capturing it somehow, without having to invest in another cabinet? I tried it a bit outdoors using a plastic was tub, and the media simply went everywhere. I'd guess less than 20% was captured by the wash tub.

One thought I had was using a cheap media like sand, but typical play sands are too coarse. BTW, media with silica (like sand) is very dangerous to breath and requires the use of a respirator or other clean method to avoid inhilation.

 

[b.lindsey]

Swede, why not keep a small pail for each media and change them out as needed, storing the one not being used. I would think a blask of clean air around the interior of the cabinet would minimize cross contamination. Just a thought.

Bill

 

[Path]

Swede,

That is an outstanding piece of work .. the finish is absolutely perfect.

Can you tell us more about your bench set up I would like to make one also.
Also what was your process to get that finish?


Pat H.

 

[lazylathe]

We have blast cabinets at work and the way they work is that the vacuum
is attached to the back middle of the cabinet.
A l-shaped form is welded to the back inside of the cabinet.
When you sandblast the lighter dirt is lifted up towards the back of the unit and
whisked away by the vacuum.
The heavier media drops back tot he bottom and is recycled.

They run off compressed air of course.
I think i can find some pics of the recycling system.
Will post them soon!

Andrew

Can't seem to find the correct picture... Only the automatic recycling one...
But here is a link to a home made one:
http://www.blasterforum.com/do-yourself-20/diy-homemade-sandblast-cabinet-19854/

 

[petertha]

Yes, Id like to know more about your setup too. One theme that seemed to come out in my recent googling of home shop equipment is demands on compressors. I got the impression relatively high CFM's & pressure required equated to a pretty good sized compressor HP to keep up. But I dont have a good feel for how long people were blasting parts, most were auto resoration type projects.

Does plastic media require less energy because its perhaps lighter? How long did it take to do those (beeautiful) parts for example?

 

[Blogwitch]

I use glass bead for all materials, even steel.

It gives that very nice frosted finish that looks so good.

Unfortunately, once you blast steel, it will start to show signs of corrosion in a matter of minutes, especially if your have handled it with bare hands. The way I get around that problem is to put the blasted parts into a sealed plastic bag containing a propriety rust inhibitor. This keeps it rust free until the metal is ready for it's priming coat.


John

 

[Mawitö]

Hi, i used a sandblaster for several years for marvel not metal, we had some kind of attachment like a big round brush, but in the center you can screw the sandblaster's gun, the brush fibers prevent the aluminum oxide from spreading as long as your workpiece was close to the brush.

We never used it because the cabinet method is much better, but maybe convining this method with your actual cabinet could be useful.

Mawito

 

[Omnimill]

I use Alox for both Aluminium and Steel. You don't need a large compressor, mines only 2HP with 25L tank. It's a good idea to hook a shop Vac up to the cabinet as well if you have one.

Most of this was blasted with my old setup - Aluminium, Stainless Steel and Titanium.

Vic.

 

[petertha]

... I invested in a benchtop blasting setup...
... thought I had was using a cheap media like sand, but typical play sands are too coarse...

When you say 'benchtop' model, does yours look like this one by chance? They use that same term. Its from a (Canadian) store called Princess Auto. We have other names for PA, but not appropriate on a family forum ;D I suspect similar to USA Harbour Freight ...well maybe not even

Someone made a good comment about debris crud getting circulated out one opening & spent abrasive settling to the bottom? I was wondering about that. I'll have to take a look & see if it's that sophisticated, might just be a box?

In terms of sand, on a completely unrelated project, I discovered that ceramic supply places have a very wide range of sand products, sieve sizes, different minerals etc. I saw products ranging from play sand grit to almost talc size, so maybe you can find something useable.

 

[Mawitö]

Someone made a good comment about debris crud getting circulated out one opening & spent abrasive settling to the bottom? I was wondering about that. I'll have to take a look & see if it's that sophisticated, might just be a box?

Yes, at least the one i used it was just a box and works exactly as Andrews described.
Mine looks like this:

In the superior part we had a big vacuum, this is to extract the dust not the sand, in the inferior part we had another vacuum to extract the sand and filter it, but it broke and we did that by hand, we just put a bucket and something to crib the aluminum oxide and gravity does the rest as you can imagine from the picture above.

In this way , even by hand, and cleaning the sand that got stuck in the corners and some that went flying in the room we recover more or less 95% of sand.

Mawito

 

[Omnimill]

My current setup is half way down this page:

http://www.homemodelenginemachinist.com/index.php?topic=14801.msg152693#msg152693

You can see the extraction hose on the right hand side. I think the idea of connecting a shop vac is to ensure the box doesn't leak too much grit due to over pressure. You can get the manual for the cabinet here:

http://www.machinemart.co.uk/pages/download?d=E5D9F008-EC8C-4DD1-BAD4-99740CFCF586&a=stream

Vic.

 

[lazylathe]

The ones we have at work are like Mawitö's!
Except bigger!

Empire sandblasters are great tools and are trouble free.
Requires a lot of space and lots of CFM's to run effectively.

The small bench top ones also work quite well.
If you look at dental sandblasters you get a wide range of sizes and some that have up to 4 different media cartridges.

A bit of what i do!
Go to page 6 for the sandblaster.
http://www.renfert.com/bausteine.net/file/showfile.aspx?downdaid=6634&sp=..

Andrew

 

[Swede]

For those who asked, the parts in question only take a few minutes to convert a reasonably milled surface to that even, frosty look. It's quite easy to do, actually hard to screw up, and all done in a cheap $99 cabinet. I guess I'm worried about contaminating the glass beads with a more aggressive media like Alox.

I want to blast steel parts for phosphating/parkerizing. In an experiment, I did samples of steel using alox and glass beads, put them under a microscope, and noticed barely any difference. The glass beads peen a bit more, while the alox cuts, but to the naked eye, the finish is identical. On aluminum, alox can be too aggressive and you end up with a fuzzy, over-blasted finish.

I'm thinking I'll just use glass beads for everything.

I've used my benchtop cabinet for a while now with no vacuum attached... it leaks a tiny bit from overpressure, but nothing horrible.

If you have a compressor, you are 2/3 of the way there. A benchtop rig and a tub of glass beads is a nice addition to a shop. Just got to keep abrasives away from machine tools!

 

[TorontoBuilder]

I use glass bead for all materials, even steel.

It gives that very nice frosted finish that looks so good.

Unfortunately, once you blast steel, it will start to show signs of corrosion in a matter of minutes, especially if your have handled it with bare hands. The way I get around that problem is to put the blasted parts into a sealed plastic bag containing a propriety rust inhibitor. This keeps it rust free until the metal is ready for it's priming coat.


John

I couldn't help resurrecting this thread since I haven't seen this issue mentioned recently and I know John still uses the forum and I really would like an answer from someone with bead blasting experience.

Does bead blasting cast iron prior to machining yield a smoother overall finish on the areas that remain unmachined? I read RCDONS Red Wing engine build on his own site, and while I love the result, the one thing I didn't like was the really rough looking paint despite multiple coats.

 

[Charles Lamont]

To prepare an iron casting for a smooth paint finish you ideally need to file, rub down and apply a polyester filler before the primer. Bead blasting will provide a good key for the filler or primer but will not remove surface defects.
I am using bead blasting to put the final finish on the aluminium castings of my current project, but these need to be fettled to the point that file marks are pretty much invisible to the naked eye before blasting. See the last three photos here: http://www.charleslamont.me.uk/Seagull/sump.html

 

[Blogwitch]

T,
As I said, I only use fine glass bead. The more it is used the finer it gets as the beads shatter and give extra cutting edges, but ends up like talcum powder, which is when I change it. I use about the finest ones you can get as some are like tiny ball bearings, and can in fact give a 'dimpled' finish on say aluminium.
It hardly removes any of the original material, and does definitely give a much better finish on non ferrous materials.
If you are wanting to smooth down casting marks, then you will need a rather high pressure in your blasting cabinet and use a very coarse aluminium oxide medium. Hold the nozzle on one part of the component and you will soon dig out a trough.
In your situation, if you want a nice smooth finish, is to take off the high spots with files and abrasive paper, then use a very thin skim of car bodyfiller, and then rub down smooth. I tend to use Milliput epoxy putty instead of body filler, and once applied to the surface, contour it down with wet hands, removing any excess as I am doing it. I can obtain very smooth finishes like that, and once achieved, let the remaining putty cure for 24 hours.
Jason B is really the one to ask, as he does a lot of fabrication and I think he uses the same material as me, Milliput.

http://www.proopsbrothers.com/5-x-s...tty-modelling-car-body-boat-x1015d-3323-p.asp

John

 

[ShopShoe]

In the USA, TP Tools have cabinets, parts, and supplies. They have kits and plans to build your own cabinets:

http://www.tptools.com/Build-Your-Own-Cabinet-and-Trim-Kits.html

I want to build a cabinet, but I don't have the space for one in my shop right now. I have bought other things from them. Usual disclaimer: I am not connected to them other than being an occasional customer.

--ShopShoe

 

[TorontoBuilder]

Thanks Charles, John and Shoe...

So glass bead blasting isnt appropriate for what I want but rather rely on elbow grease, files, sanding and filler for cast iron parts.

Bronze and Aluminum though can be finished from smooth to have frosted appearance.

Its good for me and my arthritis then that I have a heavy duty flex shaft dremel tool.

 

[Charles Lamont]

Just being pedantic about terminology, I would call that a matt finish. "Frosted" is the result of using an engineer's scraper on a machined surface, as seen on the best machine tool slides.

 

[Blogwitch]

SS,
Why would you want to build a cabinet when they are very cheap already done with light, gloves, gun + everthing else other than compressor and medium. Converted from UK prices, about 100 to 120 bucks.

John