Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old July 11th 05, 09:57 PM
 
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Default Dust collector fires when shot peening

Anyone have experience with this? Where I work we have alot of dust
collector fires. Our collectors are connected to shot peening
equipment. Occassionally, I am guessing a spark is sucked into the
collector and lighting the filters on fire.

We have sprinklers in the machine but we would like to stop it from
happenign all togther. (Every time the sprinkler goes off the fire
department is notified). needless to say the fire department is not
happy with us.


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Old July 12th 05, 06:11 AM
Bruce L. Bergman
 
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Posted, and a courtesy copy e-mailed to the OP, just in case.

On 11 Jul 2005 13:57:29 -0700, wrote:

Anyone have experience with this? Where I work we have alot of dust
collector fires. Our collectors are connected to shot peening
equipment. Occassionally, I am guessing a spark is sucked into the
collector and lighting the filters on fire.

We have sprinklers in the machine but we would like to stop it from
happenign all togther. (Every time the sprinkler goes off the fire
department is notified). needless to say the fire department is not
happy with us.


Is this happening when they're cleaning certain metal items in the
peening bays? Many packed powdered metals are highly reactive,
especially when mixed - Thermite is ideally ~75% powdered iron and
~25% powdered aluminum, and it burns /really/ good and *very* hot, and
it provides it's own oxygen for the reaction...

http://en.wikipedia.org/wiki/Thermite

You need to neutralize the conditions that would set the mixture
off, like reaching a critical mass, heat and static charges. I do NOT
work in that industry, but that's never stopped me from passing on a
decent idea before... ;-P

Silly Wild-ass Guess Idea #1: Try putting a few water misting heads
(like they use on outdoor patios) spraying into the inlet airflow?
Add just enough moisture to cool off hot bits going in (without making
mud) and the moisture should cut the static electricity levels. Link
the mist water solenoid to the fan motor contactor, so they run with
the fan motor.

Silly Wild-ass Guess Idea #2: A dispenser for metering some
powdered limestone or something else that would keep the powder from
igniting as easily, into the incoming airflow to the cyclone and bag
tower.

A simple screw augur feeder from a bulk hopper, and a variable-speed
drive motor on the feed worm to meter it in during the day.

I picked powdered limestone out of my (tuchis) because they spray it
around in coal mines to reduce the fire hazards there. One of the
chemistry wonks here can probably come up with something much better
suited for the purpose of breaking up the thermite reaction that your
factory can buy cheap in bulk.

Like bulk sodium bicarbonate (baking soda - Class BC extinguisher
powder) or a mix of ammonium phosphate and ammonium sulphate (Class
ABC extinguisher powder). Class D extinguisher powder is finely
ground sodium chloride - table salt - but that might create rust
problems.

Adding a moderator powder to the waste stream would add to the bulk
and slightly increase the disposal cost of hauling off what you
collect in the bag farm. But if you can stop the fires before they
ever start that's a *very* small price to pay.

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.
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Old July 12th 05, 10:16 AM
Roger & Lorraine Martin
 
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wrote in message
oups.com...
Anyone have experience with this? Where I work we have alot of dust
collector fires. Our collectors are connected to shot peening
equipment. Occassionally, I am guessing a spark is sucked into the
collector and lighting the filters on fire.

We have sprinklers in the machine but we would like to stop it from
happenign all togther. (Every time the sprinkler goes off the fire
department is notified). needless to say the fire department is not
happy with us.

Could be static electricity igniting the dust initially, once alight
its gets the accumulated dust particles smoldering away until
you have a full blown fire in the collector system.

Static is often a problem in dusty workplaces - flour mills
used to be a classic for static flash fires until they worked
out that extracting dust was safer. Do a weblookup on
controlling static, easiest way is to earth out collectors, etc.
Its made worse if you multiple dust types and varying pipe
dimensions, varying pipe materials, also the more disturbance
in the air flow the greater the build up of static charges.

Quick and dirty check for static is to go touch part of the
system whlist holding an earthed out piece of metal. If
you get a zap theres static in the system.


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Old July 12th 05, 04:15 PM
carl mciver
 
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"Bruce L. Bergman" wrote in message
...

| Silly Wild-ass Guess Idea #1: Try putting a few water misting heads
| (like they use on outdoor patios) spraying into the inlet airflow?
| Add just enough moisture to cool off hot bits going in (without making
| mud) and the moisture should cut the static electricity levels. Link
| the mist water solenoid to the fan motor contactor, so they run with
| the fan motor.

That seemed like a good idea for a minute until I realized that moisture
and metal equals corrosion, and being that there's so much surface area
it'll corrode really fast. Piles of damp metal powder corroding quickly
gets really hot, and if not cooled down will go into meltdown, then possibly
fire, which would be a then be a real mother to put out.
Now if you had a non-reactive coolant, that might be another story.
Metal damp with anything might not get so much from the scrap yard as dry
stuff, though.



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Old July 12th 05, 04:43 PM
Lloyd E. Sponenburgh
 
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"carl mciver" wrote in message
nk.net...

"Bruce L. Bergman" wrote in message
...

| Silly Wild-ass Guess Idea #1: Try putting a few water misting heads
| (like they use on outdoor patios) spraying into the inlet airflow?
| Add just enough moisture to cool off hot bits going in (without making
| mud) and the moisture should cut the static electricity levels. Link
| the mist water solenoid to the fan motor contactor, so they run with
| the fan motor.

That seemed like a good idea for a minute until I realized that
moisture
and metal equals corrosion, and being that there's so much surface area
it'll corrode really fast. Piles of damp metal powder corroding quickly
gets really hot, and if not cooled down will go into meltdown, then
possibly
fire, which would be a then be a real mother to put out.
Now if you had a non-reactive coolant, that might be another story.
Metal damp with anything might not get so much from the scrap yard as dry
stuff, though.


We deal with a lot of fine, water-reactive metals in the pyrotechnics
business. The common wisdom is to _flood_ the reactants with water, rather
than simply misting them.

Creating very fine metal dusts abrasively always invites ignition. Many
metals, and some organic compounds and elements will become pyrophoric
(ignite upon contact with air) as soon as they are divided into sub-micron
sized particles. I've personally witnessed 2-micron magnesium ignite simply
by fluffing up the powder in air. Sub-micron titanium is horrific stuff.

Our dust collectors capture particles on filters being continually flooded
with a sheet of water. The material is plumbed away and allowed to react in
a large volume of water. Then the sludge is sedimented, dried, and
disposed of in a suitable manner, if it cannot be reprocessed.

LLoyd




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