Crushed Glass as a Blasting Medium

[shipard]

Hi Everyone,

I am in the process of stripping down my 1972 911, it is almost at the the stripped shell stage. So i am now doing some research around the sand blasting vs soda vs dry ice and i came across crushed glass etc.....so a quick question has anyone ever used crushed glass as a blasting medium ? guess you could use the same blasting equipment as sand. I have read a few threads on blasting mediums from this forum, Does anyone have any thoughts or happy to add some input to my question or thoughts on this ? I value others opinions or experience who have been down this path before and there reasons for their choice of medium.

Below is a link i found that refers to crushed glass, I have no connection with this business, just doing some research to see whats out there.

http://www.bicarb.com.au/ have a quick read under the blasting tab second page, pasted their words below.

Crushed glass - Our media of choice. Available in a range of grit sizes, crushed glass is ideal for automotive blasting. The particles are relatively light weight compared to all other abrasive blast medias. It is also only slightly harder than panel steel on the MOHs scale of hardness (6.5 vs 6). Combind these 2 key properties and you have a blast media that does not harden panel steel like garnet, the fine particle size leaves a very mild profile and ultimately dramatically reduces the risk of panel distortion when compared to all other abrasive medias. The glass has quite sharp edges and can quickly remove rubbery coatings and underbody sealers.
The glass leaves no residue on the panels.

cheers

clayton

[Haasman]

Clayton- No direct experience with glass but I recently had sought out a soda blaster for an old 51 Chevy truck project. I ran into two businesses, one a media blaster and the other a body and paint, and they both recommended not to soda blast. I was told that paint manufacturers will not guarantee their products (primers AND paints) if the metal has been soda blasted.

So instead the blaster uses high-temp ovens to burn off paint and then they use aluminum oxide for clean up. So far the parts they have done for me were also them powder coated. I am very pleased with the results, especially since they are powder coated twice for complete coverage. It seems that one coating leaves the edges of metal thin. I experienced this as rust along the edges within months after a previous vendor had done a one stage coating.

An additional benefit from this method is the lack of hot-spots and metal deformation from the heat generated during sand blasting on metals.

[chris_seven]

Media blasting will always be an issue and the statements that the sellers of media make can be ambitious.

The effect of media on a panel is concerned with the kinetic energy of the particle that hits the panel.

Brittle particles that explode when they hit the steel are not particularly effective and will take a considerable time to blast and shell and a high cost for the media.

Tougher particles with high kinetic energy will produce high levels of residual stress which can lead to cracking and distortion once a car is driven and some of the stresses are relieved by reversed loading.

I have never been enthusiastic about media blasting shells. Soda isn't too bad but won't generally remove corrosion and is very expensive for complete shells.


High temperature ovens that burn the paint are not great as burning paint reaches surface temperatures of around 1200degC which causes significant distortion.

We use a local company with a Controlled Pyroysis Oven which is regulated at 390degC with an inert environment which turns all the paints and sealants to ash but never burns.

We then high pressure jet wash to remove all the ash and clean the shell to remove the resulting flash rusting by dipping in an inhibited Phosphoric/Citric Acid solution.

This produces a clean and relatively shiny finish that is moderately passive without any media to have to clean out.

If you use a Pyrolysis method on a 911 shell you will need to remove the Outer and Middle Sills to take out the heater silencers or on the later cars they will turn to ash and fall to the bottom of the cavity and create a serious corrosion risk.

[robmog]

glass is cheap, usually recycled, its great on rust pitting and less hazardous than sand (silicosis).
if you are on a budget and have a good compressor, its the way to go.
it is messy DIY.
but… be careful not to work an area too long, the heat can cause warping.
i have never experienced this problem but you hear about it all the time.

[shipard]

Thanks for your helpful advice.....also whats the best way to clean up......just an industrial or commercial vaccum cleaner ?

i do have a budget but i also like to enjoy the process and using my hands and learning new skills, while working through the restoring process.

cheers
clayton

[robmog]

vac up most then use compressor air nozzle in nooks and crannies.
make sure you plug the rear torsion bar tube, grit in there is a no no
what they say about finding sand everywhere is true.

[blue72s]

I am in the process of stripping down my 1972 911, it is almost at the the stripped shell stage. So i am now doing some research around the sand blasting vs soda vs dry ice and i came across crushed glass etc.....so a quick question has anyone ever used crushed glass as a blasting medium ? guess you could use the same blasting equipment as sand.

What's wrong with dry ice blasting?

[shipard]

nothing wrong with dry ice blasting.......i am researching different blasting mediums, i think i have basically excluded soda. I am still very much considering dry ice as it seems to have lots of advantages and no messy used medium to clean up for years afterwards ie sand etc. I came across glass medium and was wondering who had used it or had experience with it, hence my question.

[blue72s]

Media blasting will always be an issue and the statements that the sellers of media make can be ambitious.

The effect of media on a panel is concerned with the kinetic energy of the particle that hits the panel.

Brittle particles that explode when they hit the steel are not particularly effective and will take a considerable time to blast and shell and a high cost for the media.

Tougher particles with high kinetic energy will produce high levels of residual stress which can lead to cracking and distortion once a car is driven and some of the stresses are relieved by reversed loading.

I have never been enthusiastic about media blasting shells. Soda isn't too bad but won't generally remove corrosion and is very expensive for complete shells.


High temperature ovens that burn the paint are not great as burning paint reaches surface temperatures of around 1200degC which causes significant distortion.

We use a local company with a Controlled Pyroysis Oven which is regulated at 390degC with an inert environment which turns all the paints and sealants to ash but never burns.

We then high pressure jet wash to remove all the ash and clean the shell to remove the resulting flash rusting by dipping in an inhibited Phosphoric/Citric Acid solution.

Do you know if dry ice particles are brittle or tough?

Is phosphoric acid dipping what SPL (UK) does and if so, it is not recommended because chemicals can get trapped in the seams and box sections, which can cause issues later in life.