Sand blasting a bare shell at home, the problems I faces and the solutions I found. To start with I was constraining the tap that mixes the media in, because I got ripped off bad when buying garnet and only had three bags and wanted to get the most out of them.
The general rule is that you can run garnet through four times, but I found you can keep running it through and it still works it just gets dusty and a finer grain. After I got a really good deal on garnet in
Melbourne I'll tell you where later, the limiting factor was time, tips, and my air supply. So with just enough air to make this worth doing about 18 cfm I wanted to minimize any restrictions between the pump and the tip, so all taps were wide open and I set the regulator entering the blaster tank to 90PSI.
I started with a fabric hood and plastic safety glasses and the media kept blasting them mat and I was blind. I got some practice polishing acrylic with a gas torch, and I didn't want to spend hundreds of dollars on a blasting helmet so I taped window glass over a face visor. I could wear ear protection under it and a dust mask. Lots of media is coming back at you when blasting in the trunk and cabin, so I had to change the glass three times.
I found it helpful to have the work light as close to your work as possible but I was always tripping over the stand and the power leads, so I took the light off the stand and clamped it directly to the car and found this much better.
I tried to get away with not sifting my media on account that the undercarriage was already very clean but this was a big mistake, the smallest flake of paint seems to instantly block the blaster tip which was a
3.5 mm. If you have a nice funnel that fits into the blaster and a sifter that sits on of the funnel then sifting is no trouble at all and good insurance that when your blasting you won't have to stop for a blocked tip.
I have heard that water can block up your blaster but
I never had a problem, despite the water separator on my blaster dribbling into the media on the floor and I was compelled to avoid shoveling the wet mess back into the blaster. Thankfully any wet media got caught in the sifter anyway.
You need to tune your blasting system to suit the air you have available to make it as effective as possible. I'd recommend as a minimum for blasting parts 12
CFM for a shell 18 CFM.How it works is the faster the media comes out of the nozzle the more effective it will be as in work done per bag of media and time. More pressure means more speed, whilst all traditional air compressors create high pressure, your loosing it through the blasting tip so you need to constrain the air with your blasting tip size to maintain pressure. After I blasted my shell I found a great recourse for you that graphs out the tips to suit your air.
http://www.dawson-macdonald.com/media/parts-and-accessories/BorideNozzleCatalog
.pdf
For me to blast at 100psi which would require a 3 mm tip with about 18 CFM, it's like you have a magic wand that makes clean steel and it's really satisfying. You could blast at lower pressure which is what happens when your ceramic tips wear out passing more volume at lower pressure, but you'll struggle if you have a hard pitted rust like I have had on the inner floor pan of both my restorations.
If your shopping for an air compressor then you need to consider that they generally quote the flow rate CFM without the load of pressure, meaning it will pump this much if you leave the tap open making no pressure, meaning under pressure your actual CFM will be less. You also want to consider the duty cycle of your air compressor, I think they might be roughly one to one and you will probably abuse that. I let my air compressors cool down when I was sifting media and I took my time. I also put them under a bench and walled it up with sheets to keep out the dust, this trapped in the heat but I'm sure that blasting dust will kill any machinery.
A rough formula guide
To blast a large shell inside and out the way I did, you can expect to need.
200kg of garnet
5 ceramic tips
2-4 days labor
3 sets of glass lenses for your visor
These are the guy's who took very good care of me in
Keilor Melbourne
http://www.abss.net.au/contacts
.php
- published: 02 Nov 2013
- views: 19693