media blasting - special considerations?

[midgetracer]

Soda does a nice job of removing paint, but is quite expensive. It does very little for rust though. I glass bead wheels in a cabinet and have great results. It leaves a nice finish for powder coating. I have gotten many barrels of glass beads from a highway contractor who accidentally let them get wet in a rain storm. I've dried them on a tarp in the sun and have years of free media. Using a pressure blaster, I have a hard time removing rust and not warping the metal, especially on hoods and doors. For paint I use stripper for the large flat areas.

 

[Brentwood Bob]

thanks pooch. Bob

 

[pooch]

Just like to offer my thoughts on blasting after having done vintage blasting for a few decades.

When a panel is pressed from a flat sheet of metal into a shape, the outer half of the metal is stretched and the inner half is shrunk.

Blasting causes heat, heat causes metal to rise, (notwithstanding the fact that excessive pressure will blow a panel in), but with anything but the largest industrial gear, this is not an issue.

Most car panels that are have large surfaces are convex, ie, a door skin.

As you blast the outside of a door, the metal will rise out towards you, you are stretching an already stretched panel.

There is no problem with this , if you do not sit on one spot too long, and the panel relaxes to its natural stretched-pressed state after passing.

Where the problem lies, is doing INSIDE panels, where the pressing is concave and the metal is shrunk.

The slightest blasting will stretch this shrink and make the panel in fact flattish, makes the panel stretched on both sides.

Shrunk metal that has been stretched does NOT go back.

This makes too much metal in that spot, and it is now wavy.

For an example, if you blasted an A door on the inside skin and the blaster went through the access holes, it would look like the panel was blown in from the outside.

So, be very careful of blasting any shallow concaves and especially anywhere there are ribs or reinforcements crossing inside.

The metal WILL be sucked up and around the ribs, and it will NOT relax back into shape, just as if was blown in with excessive force from the outside.

I read 1/8 nozzles and 40 PSI.

Wow, who has 20 years to do a body?

The minimum for home blasting is 1/4 inch nozzle, 90 PSI and 20 CFM compressor, unless you want to die of old age before the silicosis gets you.

Here is a bit of info on "profile", it is the metal surface of craters and protrusions caused by the type of media used.

http://www.launcestonsandblasting.com.au/surface_profile/index.html

 

[thebanjoman]

The standard metal tube poked into the sand is useless.

I should make a better vid one day.

I was blasting behind my hand to stop the cam lens being peppered, so it obscured the vision.

And i should demonstrate a a bit better that the sand only pools out of bottle to a set "puddle".

When blasting, it only takes what it wants, when blast is stopped, sand stops flowing too.

I have more time than $$ so I've started tacking blasting the pieces by myself.

I made a 4x4x6 cabinet with 2x4s and an old torn tarp. staples, and a roll of Duct Tape. The cabinet is big enough to get my pieces in and the tarp enclosure does a decent job of keeping the media from going everywhere and a piece of the tarp helps funnel the media into a 5 gal bucket at the bottom to catch everything after it is used.

A piece of plexiglass for a view window and an old work shirt stapled and duct taped to the opening I made gives me good movement with gloves taped to the ends of the shirt sleeves. I used some expanded metal shelving inside for placing the work on. I use a good respirator even though the work is inside this cabinet. I'm not using sand but the Black Diamond from Tractor Supply and it looks like it is working out fairly well.

My 'contraption' Is very UGLY but large enough to house my parts and I've got about $50 in everything including the gun. I'll eventually have to blast the body but most of it is coming apart to repair so I can just and stick them in the cabinet. Doors, front cowl, wheels, trunk lid, etc.

My 80 gal compressor, a air pressure regulator and small oil/water separator right before the gun and a bigger separator at the compressor keeps the pressure right and the moisture out.

Using the bottle method described by Pooch here is working out well but I used a large funnel instead of a bottle with the same concept. I fill the funnel and it drops the media and is sucked up by the hose. No clogging and a steady stream of media. I am reusing the media after sifting it.

Thank you Pooch for posting the video and the ideas for this.

I won't be posting photos of my blast cabinet. I'd be too ashamed to show it.

 

[pooch]

The bottle or funnel is only for portable outside blasting. Total loss system.

In a cabinet, you can use a permanent piece of mesh, and shape the lower section into an inverted V.

Have a small hole at the bottom, and use a piece of 1 1/2 inch angle, and lay the suction in this trough.

Make sure the sides of the angle are above where the sand stops pooling when you stop blasting , or it will just continue to run out when stopped.

Constant recycling of sand.

Here is my portable home made one...

Here is my bought cabinet, which I chopped the bottom out and made it into a "funnel". The standard steel pickup tube was useless, it would suck up about a cupful of glass bead in spits and spurts and then stop.

And here is one I bought for $200, but have never got around to using it.
Doors both ends, elaborate sand traps at rear to minimise sand being sucked up and through fan, foot pedal, heavy duty work table.

Both cabinets work on the same principle, falling abrasive being sieved and recycled automatically.

 

[Craig Lewis]

I would remove as much paint and rust first with one of those course black stripping discs.
I buy the 10" discs from tool vendors and mount them in an air angle grinder. It's much faster and less unpleasant in my opinion.
After removing 95% with discs, you can probably finish up the edges and pits with the blaster in a couple hours.
Less damaging to the metal and less mess.

 

[Tom from Drippin']

I used the Sunchaser Tools, sander with "super discs". It's messy, but not nearly as bad as blasting. You can purchase the Makita sander cheaper direct from Makita. Check 'em out.

sunchasertools.com

 

[thebanjoman]

If I had a fence to go behind I'd do it. I have a hood and use a paint quality respirator. I know of the dangers of the dust and how much of a mess it makes.

I'll wait until air temps are in the 50s or below to tackle this. I have so much to do on this that I can keep going with the other aspects of the car till the temp makes it easier. I'll still see what prices I can get and will still do my rims and other small parts to see what works best.

I'm glad for the input I'm receiving here.

I've had the bodywork on hold for a while, too many things going on with family, health, and work.

I've found local powdercoating company that will blast the body for me at a reasonable rate. They do it by the hour, not the job ($75 /hr) . This sounds reasonable to me.

I have sent them a test, a mower deck I'm getting ready for spring and have been pleased with their work. I only had it blasted, not coated and it the work was good. I wanted to see what they can do before handing them the body. I know the metal for the deck was thicker, I wanted to see if I was happy with what they did before giving them the coupe body.

I've also spoken with others in the area who have had work done there (not recommendations from the company itself) and they were pleased with the work that was done for them.

Once I get the remaining screws out and the hardware off I should get them the body in March.

I'll give 'em a plug after its done and I see where i need to start patching.

 

[Smitty]

I am thinking of removing the paint with stripper before taking to the blaster..
What think?

Steve

 

[jimnungesser]

You might consider having the wheels powder coated, since it is more durable than paint and not much more than the cost of sand blasting.

 

[Kevin in NJ]

There is a misconception that sandblasting causes heat which then causes distortion.


We are all familiar with doing hammer on dolly work causing metal to stretch. This is from the metal being squished out.

When you use too much pressure or too much media in the stream you can beat the surface of the metal too much. This causes the surface of the metal to stretch out. Since the surface you are blasting is being lengthened, that surface will bulge out. Now I have to temper this bulge out with the fact that some surfaces may behave differently.

Now lets compare what happens with heat. The surface where the torch is applied get warmer faster then the far side. This means the torch surface will expand towards the torch while being heated. The difference is heated metal will be shrunk once it is heated beyond the plastic state. So the distortion will be different. On the middle of a convex door it will result in the overall curve being reduced.

So now what temp do you need to cause metal to shrink do to heat? Up into the 500* region gets you to the blue color which is where steel shrinks.

What happens when you have rapidly expanding air? It causes cooling. How do you think you put out a match? You are actually moving so much air that there is not enough heat to continue combustion. So exactly where do you get enough heat to significantly heat the surface of the metal?

The distortion is caused by the material beating and expanding the metal on the surface. This causes the metal to expand and make the metal curve towards the expanded metal.

To prevent distortion you need to limit the pressure and limit the amount of sand in the air stream. I have done 4 whole cars from thin French steel to my very rusty cabriolet and never had a distortion from the blasting.
Run 40 lbs or so and use the sand control to limit the amount of sand in the stream to the point at which you just see media in the air stream. I have tried to distort metal by pointing the stream at some test metal for an extended time and it would not move.

Sorry if I step on any toes with my writing.

If anyone can prove me different I am always open to facts. I have only been able to find that heat is not the cause of distortion.

 

[Doug in NJ]

I did a fair amount of outdoor blasting on my car (frame, top and bottom floorpans, etc.) with a typical generic Chinese pressure pot and a 17 CFM compressor, and I never saw any sign of distortion.

If you are concerned, try an experiment before working on your car: Get a nice flat thin piece of sheet metal, and blast away, with the highest pressure you can generate. See how what sort of damage you are capable of doing.

Doug

 

[wi0v]

The pressure blaster sold by Harbor Freight for $160.00 does an excellent job. I use a hooded sweatshirt and an old welding helmet with a plain glass. Have done a John Deere and a couple of other items. I used plain old silica sand (Not suppost to) but for the money can't be beat. Also have their cabnet blaster also less that $200.00.

 

[slobroy]

"I used plain old silica sand, but for the money can't be beat." I hope you have good insurance, cause your gonna need it. I'm a blaster by trade. If your using sand your asking for health issues. You may be fine for years but one day it will catch up to you. Most blasters now use fine crushed glass for metal if their any good. Keep the tip moving and back at least 8 inches from the surface. If you have any pits in your metal use a good fill and sand primer.

 

[thebanjoman]

"I used plain old silica sand, but for the money can't be beat." I hope you have good insurance, cause your gonna need it. I'm a blaster by trade. If your using sand your asking for health issues. You may be fine for years but one day it will catch up to you. Most blasters now use fine crushed glass for metal if their any good. Keep the tip moving and back at least 8 inches from the surface. If you have any pits in your metal use a good fill and sand primer.

I purposely used the term 'media' blasting in this thread because of the fact that the word 'sand' brings up lots of discussion. I've read enough on the Internet to know that even if 50% of what i've learned is true then I want no parts of sand in any way. Sand is for beaches and the lousy soil I found when I lived in Florida.

I have a cabinet, home made that I use for small stuff and even though it is contained I still wear a respirator when using it. I've only used the 'black beauty' media I bought from tractor supply and at about 40lbs pressure. It does a fair job but the body was just too big to work with. I can't do it outside because of my HOA and the bluebloods who would try and make my life miserable for wanting to and attempt it outside.

I have been searching for a reputable place that would do something this big and not destroy my parts. I found some places quite proud of their name, their work, and their prices and wanted to charge me way more than I could afford to do it so I continued to search for a place that would be more reasonable. I felt that there was such a place out there if I kept looking.

Once I found the place I gave them a test piece to do so I could judge their work, the time it would take to get it done and was pleased with what I got back. I never mentioned the body when I took them the mower deck to blast. After I got it back and looked it over I then asked about doing the Coupe. They looked at the pictures and said that they could do it by the hour and said they believed they could do it in about 4-8 hours. My front fenders are fiberglass so they will get the rear fenders, trunk, the body and minus the cowl and the hood. That is if I can finish getting the blasted screws out..

 

[banjobrad]

Go to Northern Tools and buy one of their small 50lb sand blasting outfits. These have
a small red hopper which you've probably seen around. Buy the 100lb bags of fine
silicon sand. Find an area where you can make a mess. Definitely slop on the strongest paint stripper you can find, and don't hesitate to waste a few bucks
going through a few gallons of the stuff. Take the panels down until they are just
gooey primer then hose all of this chemical crap off and let things dry. Start
your blasting, but don't get so close to the metal you warp it, just spray from a distance that gets the surface rust off the back sides of your panels. Don't
blast the good side, you can just sand these by hand or DA.
Hopefully you have or will invest in a good compressor. You need this more than
anything else when it comes to restoration.

B.G.

 

[Dennis Pereira]

I have personally used tons of sand for blasting Threw the years. But like every thing you need some common sense. proper protection. silicon is the second most abundant element after oxygen making up 27.7 percent of the earths crust by mass. information from wikipedia. One of my first jobs was for a commercial sandblasting and painting co.

 

[jrelliott]

Keep the blasting media dry! After purchasing your blasting media put into a 5 gallon paint container that has a lid with a good seal and a screw top lid. Keep it sealed up when you are not using it. Put the pick up tube of blaster gun in the screw top lid hole. Found that after doing this got better results. For Frame and a lot of other parts took to a professional who first steam cleaned the frame and parts then did the sand blasting, priming and painting. Was not cheap but got good results and have no rust anywhere.

 

[thebanjoman]

I've had the bodywork on hold for a while, too many things going on with family, health, and work.

I've found local powdercoating company that will blast the body for me at a reasonable rate. They do it by the hour, not the job ($75 /hr) . This sounds reasonable to me.

I have sent them a test, a mower deck I'm getting ready for spring and have been pleased with their work. I only had it blasted, not coated and it the work was good. I wanted to see what they can do before handing them the body. I know the metal for the deck was thicker, I wanted to see if I was happy with what they did before giving them the coupe body.

I've also spoken with others in the area who have had work done there (not recommendations from the company itself) and they were pleased with the work that was done for them.

Once I get the remaining screws out and the hardware off I should get them the body in March.

I'll give 'em a plug after its done and I see where i need to start patching.

I got the body back this morning from the blaster. They did a very good job and the cost was reasonable. I have a lot more patching than I thought. There was some previous patching done that was unknown and covered in filler.

The rear fenders are in really rough shape. I'll have to get photos posted of them. They are certainly above my skill level to repair.

Frederic County Customs in Winchester did the work. They are a powder coating shop so I had them do my wheels while they had the body.They powder coated my 16" wheels 'Fire Engine Red".

Father-in-law doesn't say much these days but its clear RED is his favourite color and the smile that came up when i showed them to him tells me he approves and we got the wheel color right.

 

[Terry NJ]

Doug, I hate to contradict you, But when I was working on the Essex, the boss sent the fenders out for S.B.ing and the came back twisted like kandy kanes or barber poles. These were 1920 Essex, not model A, definitley a rare bird. I can't say what the media or pressures were, but they were very distorted.
Terry

I did a fair amount of outdoor blasting on my car (frame, top and bottom floorpans, etc.) with a typical generic Chinese pressure pot and a 17 CFM compressor, and I never saw any sign of distortion.

If you are concerned, try an experiment before working on your car: Get a nice flat thin piece of sheet metal, and blast away, with the highest pressure you can generate. See how what sort of damage you are capable of doing.

Doug