[Mgs] question about paint prep

[Barney Gaylord]

The most important feature of a sand blaster is that it requires a 
LOT of air flow.  So if you have a small air compressor you will have 
short trigger time before you lose air pressure, and a long wait for 
the compressor to recover and build up pressure again.

A suction blaster uses a venturi in the spray nozzel to "suck" air up 
through the media pickup hose.  In reality the blasting media is 
pushed up the hose by the pressure differential between atmosphereic 
air pressure and absolute pressure at the venturi.  In simpler terms, 
the pressure available to move air flow and plasting media up the 
pickup hose is less then one atmosphere (less than 14.7 psi).  As 
such, the suction blaster is limited in the amount of blasting media 
that can be picked up and delivered to the gun.  It is useful for 
small jobs like a valve cover for instance, but cleaning a set of 
wheels to bare metal would take all day.  It is commonly used with 
limited air supply, like a 1 or 2 HP compressor.  The suction blaster 
can also be very cheap, so it may be a good deal for occasional use 
on small jobs.

A pressure blaster applies compressor pressure to the media supply 
tank.  It can apply up to 10x as much pressure on the media pickup 
hose, therefore supplying an almost unlimited amount of blasting 
media to the gun, very useful for big jobs.  A pressure blaster will 
typically require a large amount of air flow.  My fairly efficient 
2HP belt drive twin cylinder single stage compressor can produce 7.5 
cfm at 90 psi.  This is enough to operate a small (Harbor Freight 
low-end unit) pressure blaster with about 50% duty cycle (one minute 
trigger time followed buy one minute recovery time for the 
compressor).  It works for moderate size jobs like body sills, frame 
and suspension parts, as long as you have enough time to work with 
only 50% duty cycle.

Read this for a primer on using a pressure blaster: 
http://mgaguru.com/mgtech/tools/ts118.htm

If you are contemplating blasting an entire car body, frame and 
suspension parts, then you really should have a larger 
compressor.  Minimum size compressor for continuous blasting would be 
5HP belt drive 2-stage compressor (usually on a 60 gallon air 
tank).  Even at that you might think it's a bit slow when processing 
half a squae foot per minute for paint removal or 1/4 square foot per 
minute for rust removal.

For fast production blasting the sky is the limit for compressor 
size.  A local franchise of Media Tech has a 75HP electric compressor 
on a 150 gallon air tank.  Electricity to run it is something like $7 
per hour, but the guy can clean a whole unibody car body to bare 
metal inside and out in about 5 hours.  He would like a larger 
compressor to be more productive.


At 09:49 PM 10/4/2011 -0700, Clayton Kirkwood wrote:
>....
>.... I'd like it if somebody knew the qualitative difference between 
>a suction blaster and a pressurized blaster; I'd love to force 
>myself into buying a pressurized blaster unit and a bigger air compressor.
>....