Metal skins paint preparation

[linen beige 15]

I don't recall having ever used any coal slag so I can't give a definitive answer. I would compare it's hardness and sharpness to the oxides and go from there.

[Sarge 3,465]

If you're referring to Black Diamond, ect blasting media that stuff is way too aggressive for any sheetmetal under 1/8". It will deeply etch nearly any metal in a big hurry and is mainly used for heavily painted/rusted thick items. Aluminum oxide or glass bead in the lighter grades works about the best for most media cabinets. The amount of dust, air pressure and evacuation system all are factors in determining what media to use in your cabinet. The cabinet should come with a list of what media is recommended for it in the manual.

I prefer the lighter grades of glass bead myself, takes a bit longer but a lot less surface filling/prep on the thinner metals and won't destroy cast aluminum.

Sarge

[MikesRJ 558]

I didn't say "media" Mike. I said "Bead". As in glass...............

Senior Moment, I said "media" not you, my bad!

[MikesRJ 558]

Jim, Mike,

just curious on your opinion of using coal "slag" ( and I don't know / care if its media or whatever) to blast the skins for paint prep...........

Couldn't say, I've never used it. I only resort to any kind of blasting when there isn't another less aggressive way.

[Save Old Iron 1,571]

So officially,

no one can say "media" "glass", " bead" or "beads" in this thread.

only "primer", "glaze" or "metal prep" are acceptable

Thank you

Come Again

Don't make me go CAPS LOCK on you guys

:)

[Save Old Iron 1,571]

Sarge,

since I've outlawed the word "m$d$A" from this thread,

the "black stuff" I bought appears to be coal slag marked "Fine 3060".

does that make any sense ?

to me, coal slag could easily be renamed black diamond.

having lived in Scranton Penna for most of my childhood, I remember my grandfather coming home with similar material in his pants cuffs when he worked in the coal mines.

i loaded some up in a spot blaster and it did do very quick work of making a muffler rust and scale free.

can't say it did much damage at 75 psi.

thanks

[Sarge 3,465]

At 75 psi I'm surprised the nozzle even works. Unless it's a pressure pot system you either have to use above 100psi or a very high cfm flow rate to move your media. And btw-media is the correct word for any material used in blasting.

Coal Slag, Black Beauty, Black Diamond are all basically the same thing, just depends upon region. Since we're not in the Belt, they charge around $7/50lb bag for the stuff around here. Useful for pot systems (with the correct nozzle/gun system) but only when doing heavy work, like a large semi-trailer. At work we used that material for blasting the coating off the local 36" gas pipeline. With the high-volume rotary air systems and large nozzles the blasters could clean a 24" wide pattern all the way around the weld joints in less than 2min. It also left some serious scars on the high alloy pipe for the joint coating to bite. Rough enough that one wouldn't want to run your knuckles across..

Just fyi- "3060" is one of the many combination grits available. Using two different grits like this (30/60) allows the material to blast off heavy rust scale and very thick paint and yet still retain a smoother finish overall. In my media cabinet most times it is filled with 170/400 glass beads. This is for two reasons - mostly allowing me to work with light cast aluminum alloys and leaving a smoother finish on steel for painting. If you run into the common "kid with a paint brush" on a tractor the glass is not up to the task without a lot of time.

Good general purpose medium grade aluminum oxide will last longer and produce more cutting efficiency for most of the work folks use a blasting cabinet to do.

Sarge

[Save Old Iron 1,571]

Sarge,

I have a run of the mill 5hp 50 gal compressor and have not setup the blasting cabinet yet.

Your feedback makes me think this media is useful for such items as hubs, mule drive, and the outside of wheel rims (probably not the bead area)

crap, I said bead and media on my own post !!.

So thanks, I'll check out the alternate medias and learn a few new things this weekend.

:notworthy:

[Sarge 3,465]

Honestly, read the manual that came with the equipment. Many make the mistake of running the wrong media and destroy new tools . Air pressure, gun orifice size/nozzle all must be considered when picking media grades/types . For example, my current gun on the pressure pot I use outdoors will not work with Black Diamond, no matter what grit/size , it just eats the tip . The gun head is designed for use with Slicon Carbide or Aluminum Oxide only. I have run some washed types of silica through it and that works just fine .

BTW-I am fully liscened and trained for Hazmat work, and own a full array of protective equipment . I do not recommend anyone using silica-based media of any sort .

Back to your original question-

For deeply pitted metal , I thoroughly blast the parts clean, degrease and even sometimes use the DA sander to finish the surface off . The parts are either coated with epoxy primer, red oxide primer or polyester filler to take care of the pitting . The Polyester I use directly reads to apply it to bare metal, never on top of any primer . There are many types of fillers out there, each one has it's unique recommendations from the manufacturer. At any rate, whether to bare metal or over primer the whole thing must be properly sealed before final top coating. If not, the rust will come right back through.

Sarge

[Save Old Iron 1,571]

Thanks Sarge,

I finally hooked up the blast cabinet yesterday and the results were excellent on the thicker metal parts such as hubs, seat springs and the mule drive parts.

The coal slag definitely "frosts" the metal but nothing that 2 coats of primer and a sanding can't cover up.

My next question would be how to determine if the coal slag will damage the body skins. I heard conversation about "warping" and "distortion" happening from using media which is too aggressive.

Is this warping pronounced enough to see or do I need a straight edge to tell ?

Thanks for all the advise so far.

.

[Sarge 3,465]

Most warping issues on sheetmetal are from heat and very coarse media will do just that, makes the surface very hot. I know from experience you have to really focus on one area to create a problem, but it can happen. More likely is damage from the stress of heavy blasting which can lead to brittleness and cracking. I'd much rather put a few extra hours on the compressor than spend half a day repairing a hood that was overblasted. As a plus, the coal slag will be much quicker removing paint runs and thick spots that most grades of ground glass or glass beads will hardly touch.

Just a note-some folks' definition of distortion is in fact "frosting", nothing more than the surface of the metal being somewhat pitted from blasting . It all depends on velocity of the media, crank things way up and you can literally blow holes even in heavier metals.

Sarge

[Save Old Iron 1,571]

It all depends on velocity of the media, crank things way up and you can literally blow holes even in heavier metals.

Sarge

A few more comments and questions on this topic.

First is the life of the coal slag media.

I have blasted 4 hubs, 4 rims, 2 seat housings, 4 seat springs, 3 hitches, 2 belt guards and 4 tachmatic brackets and 4 floor boards. All this on 10lbs of slag and its still going strong. Is slag this long lived ?? Does it regenerate its sharp edges as it blasts apart ? I'm truly amazed on how little media I have had to use to accomplish all this work.

The setup I'm using is a HF cabinet - 5 mm nozzle with 50 gal / 10cfm compressor at 90 psi at the compressor. Media is 30/60 coal slag. After all this work, the nozzle is still intact and never a gun clog !

From a standpoint of warping the sheet metal, I purposefully tried to overheat the sheet metal by keeping the gun in one spot. Maybe my setup is not that powerful, but I did not see any evidence of heating the metal. I have not yet tried a larger or smaller nozzle. What difference in performance would I expect to see on a larger or smaller nozzle?

Thanks

[bitten 134]

Wow... I got lucky on my "media blaster". My father-in-law had an old gravity fed one that I was able to replace the hose on and use. Went to the local farm store got some aluminum oxide and used it ran out and next trip got the glass bead, been using it ever since. I have had no problems with it. I think if I had read this before hand I would have been worried about PSI, proper tips, and so on.

Sometimes ignorance is bliss.

I have looked in to buying a cabinet but they seem to small or to much $$. Before my E-Tank was made I was using a plastic 55 gal container and capturing my media. Now all I have to do is the hood and fenders witch wont fit in the 55 gal container so my driveway will be getting a new coat of glass bead.

I have no experience doing body work and really no one to show me. I have read a lot and have had to redo some things but so far I'm real glad with the outcome. I do want the best looking finish I can give but as off now it wont be going into a museum. I do seem to be taking along time to complete this project and am not sure if my process is right or wrong. I'm sure I'm taking extra steps that are not necessary but in till I know the difference this is how I will do it. It seems like there are as many ways to do the clean, prep, paint and finish as there are people doing it.

Live and learn. When I quit learning hopefully it will be my last day on earth.

[Sarge 3,465]

The slag should last a long time, and yes it does regenerate it's cutting edges a bit as it degrades. At 90psi and only 10cfm, better leave it alone if it's working well for you. Bigger nozzles equal much more cfm required- my compressor here is 80 gal/27cfm. Using a 4mm air jet with a 5-7mm tip taxes the pump pretty hard but I'm also running 150psi . In comparison, if I used coal slag in this cabinet the glass lense and possibly the cabinet wouldn't last long at that pressure. If yours hasn't started cutting the nozzle a bit it may be a carbide or hardened steel head. Ceramics are ok but don't last very long unless you use a less aggressive media.

It sounds like your current setup is working ok, better off leaving it as-is if the tip isn't wearing out quickly. If nothing else, post up a sunlight pic of some fresh blasted sheetmetal- it will show if it's getting deeply pitted. A smaller nozzle will probably just clog , larger one would kill the compressor trying to keep up or run low on pressure . I just prefer a smoother finish and work with a lot of delicate cast materials-mostly carbs. The smaller media is also easier to rinse out of passages where larger types can literally jam themselves in tight.

To heat the metal, it takes a pretty aggressive media, a very high volume of air and a lot of pressure. Mine will heat thinner metals above 20ga if I concentrate on a spot for very long-hot enough to be easily felt through the cabinet gloves.

Sarge

[Save Old Iron 1,571]

Sarge,

thanks for the explanation of tip sizes and materials.

I'll try to post a sunlight picture of a sheet-metal piece, maybe half blasted to show a bare metal pre and post blasting divide line for comparison.

Ditto on the Plexiglas viewing port and the replaceable vinyl protectors. The replaceable vinyl covers work well ,but if you don't get all the adhesive areas perfectly flat , media can start collecting between the lense and the protector and cause more visibility issues.

Replacement of the plexi with tempered glass will be the first modification I will try to make on the cabinet.

Just don't hold your breath for any quick updates !

Again, thanks for benefit of your experiences. All starting to make sense now. :notworthy: