Subject: Re: Need Sand blasting Help

From: [email-masked] (Grant Erwin)
Date: Fri, 8 Sep 1995 20:53:46 GMT

Roger Hoover wrote:

I'm trying to sandblast cast iron radiators and it is very slow going
(multiple hours per radiator and I can't get them totally clean).

I'm using an ALC F-90 siphon blaster with a 1/4" nozzle that requires
15 CFM @ 80PSI (I've tried ceramic and steel as well as 13/64" and
5/16" nozzles as well).

The compressor is a 2-stage 5hp 60gal rated at 17.9 cfm @ 125 psi,
17.8 cfm @ 175 psi and is fed unregulated to the blaster through 20ft
of 1/2" iron pipe and 50 ft of 3/8" hose.  The compressor runs
continuously while blasting.

(snip)

Roger, I have a couple of pieces of advice for you. First, your
blasting problems result from your using a siphon arrangement. Any
"real" sandblasting requires a pressure pot. Second, you can probably
cut a *lot* of effort by first removing the paint chemically, and 
then blasting only the scale.

How to remove paint chemically? 

1. go to the supermarket, and near where they sell floor cleaners, buy
a can or two of Red Devil lye. It's cheap.

2. find a container big enough to submerge your object in. Kids 
standalone wading pools come in handy here - it's the end of the
summer.

3. fill the thing with water, add lye, add object, wait 12 hours

4. remove object, rinse very well, let dry (all paint will be GONE)

5. You can do a first order neutralization if you like, using something
acidic. I just put the lye solution down my drain, figuring it will
help clean out my pipes.

A word of caution: Lye (sodium hydroxide) is a powerful chemical. It
is dangerous. Do not leave this thing unattended in your driveway, as
any passerby who happened to dip their whatsis in could sue you. Also,
the solution of powdered lye in water is a very exothermic reaction,
so you can get some local boiling, so eye protection is a very good
idea.

Finally, if you do this on something like a lathe bed, be aware that
most of those zippy little nameplates are made from zinc or something
that lye just eats as in gone. Also, you should degrease whatever you
want to unpaint first, as fats + lye = soap and you don't want some
weird white junk all over your parts.

As for what grade of sand to use, it shouldn't matter hardly at all
compared to you using a pressure blaster instead of a siphon tank.

--
Grant Erwin                     | Senior Member, Technical Staff
Cascade Design Automation Corp. | Internet:  [email-masked]
3650 131st Ave SE, Suite 650    | TEL:       (206)-649-7613
Bellevue, WA  98006             | FAX:       (206)-649-7600

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From: Mike Rehmus <[email-masked]>
Date: 9 Sep 1995 23:37:17 GMT

Might just find that dumping lye down the sewer is illegal.  If you 
do much of it, best check it out or they may come visit you with
very expensive charges.

Best,

Mike Rehmus

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From: [email-masked] (J. Kimberlin)
Date: 9 Sep 1995 17:28:08 -0700

>do much of it, best check it out or they may come visit you with

Mike, I might disagree a little.  A lot of the drain cleaners are simply 
lye and toilet cleaners are lye too.  Thousands of people do this every 
weekend when cleaning their tubes.  Municipal sewage treatment plants 
monitor their pH quite closely.  Basic, up to about pH 8 or 9 won't kill 
the bacteria they depend upon for gas production and aerobic digestion.  

On the other hand don't even think about dumping your sulfuric acid 
copper pickle bath down the sewer.  If you are near the sewage treatment 
plant as I am, you could easily cause an upset.  The rule in 
environmental testing is to adjust the pH of samples to less than 2 to 
inhibit bacterial growth.  Basic doesn't really seem to hurt and is quite 
diluted from general flushing, dishwashing, etc., so that a real slug of 
concentrated sodium hydroxide, or other caustic substance ends up rather 
harmless.

I have to admit however, that removal of paint, grease and other cleaning 
operations using caustic, produce an effluent that should not go down the 
drain.  The effluent is sometime high in lead, chrome, copper, zinc, tin, 
and other metals that kill the beasties we all expect to see when we 
vacation at the seashore or on the river banks.

JerryK

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From: [email-masked] (Russ Kepler)
Date: Sun, 10 Sep 1995 16:47:35 GMT

>do much of it, best check it out or they may come visit you with

Uhh, Mike, a little clue: lye is used most commonly as drain cleaner. 
Unlikely that it's going to be illegal to dump in that manner.  Now
lye plus paint - that might be a problem in some locales.  Careful
about neutralizing the lye with an acid, that might be construed as
waste treatment somewhere as well.

I once asked about this of the local sewer folks (in conjunction with
dumping blueing solution, something that's about 75% lye) and the
local plant manager said that he'd thank me to do it - seems that
acidification is a real problem and that they neutralize with lye
themselves.  I guess your locale could be different, though.

-- 
Russ Kepler posting from home  [email-masked]

                      Please don't feed the Engineers