Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Ventilation and control of dusts when grinding
2001
RFQ: LOOKING TO BUY A USED DUST COLLECTOR 15,000 ACFM - 17,000 ACFM.
MARTIN G [last name deleted for privacy by Editor]- Mexicali Baja California, Mexico
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
Dust collection for titanium grinding
Q. Dear sirs and mams,
I would like some advice on controlling titanium and grinding/buffing wheel particulate from titanium grinding processes. A fire code prevents the use of only a dust collector. It states that the process must involve a wet collector or fume scrubber. I assume it is to cool the titanium dust or to prevent an explosion, i.e., hydrogen. But, a fume scrubber wouldn't be able to handle the buffing wheel fallout, since it is meant for gas/liquid transfer. Would a wet dust collector be applicable?
Thank you in advance.
Kyle H [last name deleted for privacy by Editor]equipment mfg. - Forest City, North Carolina
2003
2003
A. May I suggest that you don't buy a wet collector per se but use the following route.
l. For the dry dust, try to collect as much as possible in a rudimentary collector ... you'd need a transport velocity of probably around 4,000 FPM.
2. Then I'd reduce the duct velocity to max. 3,000 FPM and into the WET unit !
3. The wet unit to consist of a horizontal mist eliminator using vertical sine curved blades. Design velocity 1,200 FPM max. Blade design is critical! Use PVC construction but could be PP which costs more!
On an Australian metal finishing site there was even a very recent write-up on these units, albeit on the more expensive and, in your case, unnecessary higher efficiency units.
4. Make the eliminator having two separate banks of blades, both equipped with wash-down (nozzles) ... what I'd term a C-Clone-2.
5. Your knockout efficiency, if the unit is made to Hoyle, so to speak, will be 12 micron capture. But if it is necessary to improve on the capture of the dry Ti dust, then spray with a wetting agent like TSP [trisodium phosphate ⇦ this on eBay or Amazon [affil links] ]. Obviously you'd need a mini tank + pump + water make-up valve. PE tank, MS pump, toilet type water make-up valve
Cincinnati Millicron used to have a dry dust problem where TSP made a helluva difference to the capture efficiency.
I hope that this makes sense to you ...but if you have any further questions, doubtless we'll hear from you.
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
Q. I am currently working on a titanium welding process and one of the byproducts is fine Titanium dust. We collect this in a canister and filter.
I am having trouble determining how to dispose of the dust safely as from researching the internet I have found that the fine Ti dust is combustible in the air and is even more combustible in water!
Any suggestions?
titanium welding - Sydney, Australia
February 25, 2008
(1994)
by Miles L. Croom
on AbeBooks
or eBay
or Amazon
(affil links)
Q. I am looking to add a dust collection system in my polish room. I understand there are considerations for types and incompatibility of dust from grinding and buffing operations. Can you recommend a type and CFM of system suitable for my specific application? Also any warnings on dust incompatibility for safe operation. The room is approx. 10,000 cubic feet, I am belting and grease wheel (as coarse as 60#) on cast aluminum, bronze, and some stainless steel, rarely on mild steel. Then buffing using standard buffs and compounds, etc. We are a 2-man shop, making most dust from a wheel polisher, I would like to pull most of the air at the wheel polisher, also pulling all the fines out of the entire room, while letting the heavies go ahead and hit the floor. Most everything is custom work, so I do not want to put catches on all the buff heads.
I hope this is enough info for you to help.
Thanks for your time and consideration.
Dave Barrpolishing - Centralia, Washington
A. Dave,
My background has been in plastics and misc. acid scrubber designs but never, ever for grinding operations. But I am trying (?) to be helpful as no one else has so far responded.
10,000 cubic feet. Ah. Consider how many air changes you would want to make each hour. In an office building I think it is around 10 per hour. That comes to l,667 CFM. And I consider that to be too much.
Why ineffectively vent the whole area when effectively you could exhaust close to the 'emissions' of dust using far, FAR less CFM? Control, control, control is always the key word in good ventilation design. This means a damn good hood design. Mild steel, of course.
Scrubbers? Heck, you misuse the word slightly. I think that you'd need a cyclone ... 60 micron & larger capture efficiency, I believe. Simple. Crude. Easy to collect the dust. Low on maintenance. Low on cost.
Fan? Definitely an el-cheapo centrifugal. Mild steel. But, without seeing your buffing design set-up, I'd hazard a guess of 200 CFM max. max. for each unit and that may be far too much.
Ducting size? Ah, design for around 3,500 FPM so that the solids can be easily 'transported'. Don't go much slower! (by the way I'd never use that speed for acid fumes!)
Food for thought ... and if it makes sense to you, please come back to finishing.com and say so.
Cheers!
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
P.S. Regarding the above, I'd think that instead of a cyclone (which would cost some $$$ but far less than a 'scrubber'), how about a knock-out box.?
For example, let's assume/guess that the final airflow was 300 CFM. To ensure that the dust (solid) particles don't clog up the ducting we need a good speed, as mentioned, of min. 3,500 FPM. This is equivalent to 4" dia. (in some bad news cases they go up to 5,000 FPM)
Let's make a box which has a full width divider in the center ... and, obviously, a clean out near/at the bottom. The horizontal running ducting should transition to 6" dia. and be 8" long (= 15 degr. of tan) on both sides. The box, for 300 CFM, could be 10" wide and min. 8" long. The bottom of the box should be 8" below the transition and the divider stops 6" above the bottom. Lastly, let's extend the box's height above the transition by 1" or 2" and ensure that you have a minimum straight run of ducting of at least 4 x dia. = 2 feet before the unit.
The idea here is to slow the air down and have the dust impinge on the divider and fall down in the box and not be influenced by the (now far slower) air stream near the bottom.
I suggest you go to a competent sheet metal fabricator who may well want to improve on this design.
This is rude, crude, simple, inexpensive and fairly effective and would not generate hardly any pressure drop, too.
Q. Your theory sounds good, I'm more looking for a plug and play system as I don't have time to build. I'm more interested in learning the application as to which is better, a bag house or cyclone or?, for tallow impregnated cloth and aluminum dust. Also there may be concerns about types of dust and compatibility inside an enclosed area, also even the fan blade causing a spark? I think there are some safety factors I need to be aware of before purchasing.
Thanks for your input.
Dave Barr- Centralia, Washington
A. Hi Dave,
You raise an interesting question about 'compatibility' but if you could knock-out the aluminum dust successfully, I wouldn't think that that is a problem ... you'd need to have micron sized dust in the 50 µm or so range to be explosive, I think.
Then you mention a tallow impregnated cloth. Isn't that very sticky? If so, a bag house would surely plug up prematurely.
Re the fan, heck, go, if you are concerned, to an aluminum fan! But all fans should be protected.
If you wanted a virtually fail-safe system, I'd go to a steel 'eliminator box' with wide angle solid cone sprays and a bank of sophisticated eliminator blades (horizontal airflow!) so that you could constantly wash down the dust yet use a low GPM water. For 300 CFM you'd need one jet which @ 20 psi water pressure would generate about 0.9 GPM.
I should warn you that my background was heavily into blade type mist eliminators ... over 2 million CFM, all annotated.
To save on water you could operate via a good timer for a l minute burst of water every 5 minutes. The blades could be stainless, mild steel, PVC (my favorite) or PP. ... The PVC blades would be the least expensive. And if you wanted to improve the wettability of the particles, then you'd need a tank, a pump, a strainer and good old trisodium phosphate ⇦ this on eBay or Amazon [affil links] . Works like a ruddy charm.
More food for thought. ... and THANKS for the thanks! Most people don't acknowledge!
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
Combined dust collector for aluminum and steel dust?
Q. We are looking to contain our dust from grinding & buffing. We work with both aluminum and steel parts. I have been getting conflicting information from suppliers of dust collectors. We are considering using a wet scrubber with a booth. Some people tell us we can use the same system for both metals and others tell us that we must have separate booths for each? Any help would be appreciated.
Thanks,
MIKE MOOREPROJECT MANAGER - HASTINGS, Nebraska, US
2004
A. Maybe the advocates of separate systems are worried about a thermite reaction between aluminum and iron oxide powder?
Steve Bizub- St Louis, Missouri
2004
A. Typically don't mix ferrous grinding with any flammable dust like aluminum. The sparks from ferrous grinding will set the aluminum fines in the duct on fire.
Burl M FinkelsteinKason Industries, Inc. - Newnan, Georgia - Newnan Georgia USA
August 16, 2017
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