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Hi Brent,
In almost all cases, when alternative blast medias are
used it is as a result of regulation of silica dust, which can and will kill you
if you do not use proper remediation methods.
This does not usually mean that the new and/or alternative
method is better, only that it meats someones criteria for an
alternative.
The main reason that silica was the only main media in use
for many years are as follows:
1. Quartz is cheap
2. It provides a nice crisp angular profile if the media
is properly graded.
3. If purchased from a good supplier, it will have less
than 3/10 of one percent of contaminants.
4. It will generally contain less than 1/10 of 1 percent
of moisture.
I have never had failures with copper slag media, since I
have never used it. All impurities in blast media will to some extent become
imbeded in the base metal.
You might be fine using copper slag, but from my
experiance as a contractor, any risk is too much when it comes to possible
warranty costs.
An immersion service will disbond many coatings that will
last almost forever above water and pressure.
I hope this helps you in some way. There are many way to
solve the problem and we all are budget constrained at some point so there may
be more than one correct answer.
Best Regards,
Jim K
----- Original Message -----
Sent: Tuesday, August 12, 2008 1:37
PM
Subject: RE: [PSUBS-MAILIST] Copper Slag
Blasting Media
Hello
Jim,
Thank you for your input.
It got me to go ask some more questions and search for more
reading materials. What type of coatings have you had trouble applying
over a copper slag blasted metal surface, and how did you prep the bare
surface after blasting. Where copper slag is derived is also
important.
I have found that
copper slag blasting media removes, old paint, rust, and other materials about
three times faster then silica quartz sand media. Also the metal surface
is much rougher, which allows my coatings to adhere better, mechanically
speaking.
I talked with three
different metal fab guys that use copper slag commercially in my area, and
they don't recall having any trouble with coatings not adhering properly to a
copper slag blasted metal surface. I do however plan to use a metal prep
cleaner, etcher regardless.
One
of the guys I spoke to used to work in a Washington state metal fab company,
and he said that Washington state OSHA rules wouldn't allow them to use silica
sand as a blasting media at all. Idaho rules appear to allow commercial
businesses to use silica sand blasting media. But they still have
safety regulations regarding it's
use.
http://www.osha.gov/SLTC/etools/silica/protect_against/protect_against.html
http://www.osha-safety.org/osha_crystalline_silica.asp
If one
uses Copper slag blasting media they still of course should use good
safety equipment.
Abstract
"This research investigates occupational
exposure to metal and total particulate aerosols during abrasive
blasting operations using one substitute abrasive, copper slag. Airborne
exposures to metal (As, Be, Pb, Cr, Cd, V, and Ti) and total particulate
aerosols from two copper slag sources are evaluated by the collection
and analysis of personal breathing zone samples during abrasive blasting
operations in both indoor and outdoor settings. Results from this
research indicate that abrasive blasting operations using copper slag
abrasive can generate, in a relatively short time, total particulate,
lead, arsenic, and chromium exposures that exceed permissible exposure
limits (PELs) set by the Occupational Safety and Health Administration
(OSHA). Results also show statistically significant differences in
exposure concentrations between slag sources. A correlation between
total particulate concentrations and metal concentrations is indicated
in both slag sources and in both indoor and outdoor settings. Results of
this research allow occupational health and safety professionals to make
a more informed determination of the degree of health risk posed to
workers during abrasive blasting operations using commercially obtained
copper slag abrasive. " |
Regards,
Brent
Hartwig
From: kocpnt@tds.net
To: personal_submersibles@psubs.org
Subject: Re:
[PSUBS-MAILIST] The Ugly Duckling Submarine
Date: Sun, 3 Aug 2008 15:15:32
-0500
Hi Brent,
It's up to you, but blasting with copper slag will
contaminate the surface of the sub if you are doing serious blasting. The
copper does inhibite many types of coatings from bonding as well as they are
capable of. I do this stuff for a living, and while it is messy, it's really
hard to beat a good clean quartz sand blast. Be sure to use respirators and
other controls to minimize exposure to silica dust.
Best Regards,
Jim K
----- Original Message -----
Sent: Tuesday, July 29, 2008 9:27
PM
Subject: [PSUBS-MAILIST] The Ugly
Duckling Submarine
Hello SMMOM's, (Submadman
Organization Members)
Well my
sub has come off it's high horse, It doesn't look so high and might now that
it's off it's pedestal and trailer. It looks and feels a lot
different now.
Just so you
all know I haven't been completely goofing off of late, here are some new
photos of my K-250 taken apart in preparation for copper slag blasting. I
started a new blog page that I can add photos to. So let me know if it works
ok.
http://k-250-submarine-refit.spaces.live.com/photos/cns!5085D10EB6AFE47C!124/
No
worries, I took plenty of pictures and notes as I took it apart. I'll share
that data at a pace.
So now
as George would say, it's Full Bore Boggy submarine
building.
Regards,
Brent
Hartwig
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