Ventilation in a metal machine shop?
Hi all,
We have a small CNC machine shop, working mostly with aluminum, stainless steel and some plastics, and I've been thinking lately about what sort of ventilation we should have in the shop.
We've got three machines:
1. A small turning centre, that has a port to attach ducting for air removal, but we haven't hooked anything up to it yet. It is pretty unpleasant though, when you open the door on it after it has been doing a lot of work; the air is hot and smelly (maybe coolant smell more that metal?).
2. An enclosed horizontal mill. We're just getting this machine up and running, so we haven't done much work on it yet. I wonder if its going to smell too after running?
3. A vertical mill where the entire top is open and exposed. Never noticed too much smell coming from it, but that just means the air is getting mixed well with the rest of the shop...
I wonder if we should be doing more about the air quality in the shop and if I should be more concerned about the long term effects. So I put the question out to all of you:
What sort of ventilation, or air removal systems do you have in place in your shops and what are your thoughts on the hazards of the air quality associated with metal machining?
Very curious to hear peoples responses.
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We open all the doors and windows!
Most of the time cutting almost any kind of metal will not smell at all. If you are getting foul odors or smoke look at your cutting fluids first. If they are dirty or rancid that is your problem. Clean coolents don't smell bad. Also if you have a job that is making alot of smoke you can get a "Smog Hog" or something like it to filter out the smoke. Goodluck!
Be carefull what you wish for, you might get it.
Thanks for the tips, JROM.
Its not that we get smoke or anything, but in the turning centre (because its enclosed), when you open it up, the air is pretty warm and I'm betting its just coolant thats been mistified that smells. I'm betting we'll start seeing that in the (enclosed) horizontal mill when it get up and running.
In the summer, we open up all the doors and windows too, but in the winter, temperatures hit freezing so thats not an option.
So I'm wondering if we should put in some ducting and fans...
Try using Dayton 8" inline duct fan with 8" dia. ducting.cut hole in back sheet mtl. cover use flange with flex duct run up to ceiling and over to window. you can use a piece of plywood in window take it out when lokin up for night.i've done this for years works great.
inexpensive also ,all can be bought at Grainger.
air filter
What you want is a FILTERMIST air filter, it removes oil mist from the air, returns the oil back to machine and the warm air that you have paid good money to heat is returned back into workshop, one FILTERMIST could filter your turning centre and machining centre, they are a very simple design so reliable and cheap to run.
When I first started with CNC machines, couple of lathes couple of mills, I found that everything in the shop was getting a thin film of something oily on it. We use a water mix coolant and I figured this was from the coolant mist that escaped from the machines. With the lathe sometimes you could see mist coming out of the gaps around the door and on the mills we had the same warm mist inside when they were opened.
I installed a central mist collector system with ducts to all the machines. It sucks all the mist through big filter bags that collect the coolant residue and returns the air to the shop. We have now expanded to sixteen machines all on the system and don't have any oily residue on anything. It was not cheap; the fan and filter unit was about $3500 and getting all the duct installed eventually brought the total close to $15,000 but it was worth it.
One thing I did notice on a personal level immediately after getting the system up and running on the first machines was that everybody stopped coughing as much. We had not noticed we were doing it more beause the first four machines were installed over a sixteen month period so there was not a sudden build up of mist. Now if the guys forget to turn the system on in the morning you notice it within half an hour.
An open mind is a virtue...so long as all the common sense has not leaked out.
If you're working with a lot of stainless, you might want to make sure you're collecting mist and smoke pretty effectively.
I know nobody likes the "O" word (OSHA)... but with the implementation of their standard on hexavalent chromium in 2006, they're on the lookout for compliance. Whether or not the standard has any teeth or not remains to be seen.
To your original question, there are several ways to solve your problem. If you're getting a smell, are you using a coolant besides straight oil? Most semisynthetics and water based coolants will start to get an odor when the ph is out of whack in the mixture. Test your coolant and make sure you have the correct amount of biocides and whatnot in them. Bacteria and mold can cause those odors.
For your enclosed machines, a couple of machine mountable mist collectors may be the way to go, or one that can handle the output from both your machines. For the open machine, an ambient unit with a hood would do the trick. Plus, they re-circulate the air in your shop saving money on climate control (sometimes upwards of about 40% or so) when opening windows and doors isn't an option.
Electrostatic collectors are great, and pretty efficient, although they cost more up front. On the flip side, they save money on the back side because you don't have to replace filters.
Media units with disposable filters cost less up front, but you pay for filter changes. They're about as efficient as esp collectors, but tend to use more electricity due to the amount static pressure they create pulling air through the filters.
I'd stay away from centrifugal collectors unless you like to change bearings and impellers yearly. The can also get out of ballance when the impellers load up unevenly and transfer vibration to the spindle.
Not trying to pitch you... just offering an opinion... I hope it's not taken the wrong way.
*EDIT*
Ok... just noticed you're from Canada, so no OSHA worries for you, but you might want to think aboput how much vapor and whatnot you're breathing in when working with stainless... chrome hex is some pretty noxious crap.
Dave
www.industrial-clean-air.com
With a little checking on google, I don't think hexavalent chromium is a constituent of stainless steel bars. I doubt that simple mechanical cutting is going to produce it, but laser and plasma cutting could perhaps produce a reactive zone where other compounds are formed.
If hexavalent chromium were a common contaminant of stainless, then we'd not see it used in food preparation equipment, IMO.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Stolen from: http://www.osha.gov/SLTC/hexavalentchromium/index.htmlOriginally Posted by HuFlungDung
Industrial uses of hexavalent chromium compounds include chromate pigments in dyes, paints, inks, and plastics; chromates added as anticorrosive agents to paints, primers, and other surface coatings; and chromic acid electroplated onto metal parts to provide a decorative or protective coating. Hexavalent chromium can also be formed when performing "hot work" such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state.
Chromium, the element is a constituent of stainless steel and chromium the element is not very reactive; at least at the temperatures you get in food handling equipment.
I think the potential hazard from welding or cutting stainless steel is probably greatly over-estimated because the percentage of chromium is normally below 20% and the material is only hot enough to react to the hexavalent chromium form for a very short time. Still you never know with these pointy headed safety types; after all gypsum wallboard is a hazardous waste material!!!!!!
An open mind is a virtue...so long as all the common sense has not leaked out.
It's my understanding that if it's inert, there's no danger. It's when chromium is in a gaseous state that it becomes a hazard.
Hex Chrome is an IARC-1 carcenogen, and 8 out of 100 people exposed to it develop lung cancer.
http://www.epa.gov/iris/subst/0144.htm
http://www.osha.gov/SLTC/hexavalentc...tory_text.html
While chances of exposure when machining are less than welding and cutting, there's still that chance.
Speaking of gypsum, that's part of the reason I do what I do for a living now. I was a plasterer for 20+ years and was exposed to all kinds of airborne crap on a daily basis, including gypsum dust and free silica, as well as asbestos on certain occations.
I'd rather be safe than sorry is all I'm saying... the only real way to find out if exposure is occuring is to test for chrome hex levels in the area where potential exposure from materials is happening. If concentrations are less than 2.5 micrograms per cubic meter, you're golden. If more than 2.5, regular testing is suggested, and more than .5 micrograms per cubic meter, toxic exposure is happening and corrective actions need to be taken.
Dave
www.industrial-clean-air.com
Interesting, if not a little alarming.
What would the equation be for release of Cr+6 ions into the air from cutting metal, either with heat or with tools? Just because 'chromium' is present doesn't mean there is any provable risk if the sequence that produces it is highly improbable under ordinary conditions.
Indeed, is chrome as an alloy in a hexavalent state within the mix?
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
In an alloy chromium is present as chromium the metal, or element if you want to talk chemically. I highlighted your comment which is pertinent; the situation is that if you expose molten chromium to atmospheric oxygen it may oxidize and one of the oxidation states is Cr+6. However, naturally occurring chromium exists almost exclusively in its ionic form as the Cr3+ ion, which is known as ‘trivalent chromium’. Now the whole point is that it cannot exist as an independent ion with 3 or 6 positive charges; it has to latch onto one or more negative ions that balance the charges to be electrically neutral. I have no idea what these negative ions could be but possibly they could arise from any flux being used or simple contaminants on the metal surface. I think it is improbable that much, if any, chromium six is produced in welding, laser or plasma cutting; normally in any chemical reaction the most stable product is formed and that is the trivalent form. But nobody can prove that which is why I made the comment about pointy headed types.
The real hazard with chromium six is when compounds based on Cr+6 are used; notice these are pigments. Many stable pigments are what chemists call coordination complexes; a positively charged metal ion surrounded by negative ions which are very often derived from coal tar or by synthesis from petroleum products; sometimes they are derived from plant materials, in these cases they are organic anionic compounds where organic simply means they contain carbon atoms. These combinations of organic anions and metal cations can stabilize an oxidation state for the metal that does not occur naturally, and are often highly coloured. If you know anyone who dyes fabric and uses a two part dye with the coloring operation being done with a pigment which is then fixed using a mordant solution, they are creating coordination complexes embedded in the dyed fabric from the reaction between the pigment and metal salts in the mordant. Sometimes there is a dramatic color change during the fixing, or mordanting. Many times pigments based on organic compounds are not stable and they will bleach particularly when exposed to high temperatures or UV radiation, i.e. bright sunlight. The anionic compounds do not have to be derived from compounds that contain carbon, they can be inorganic which just means they don't contain carbon atoms. (Chemists are not very original when it comes to naming things.) Many times these inorganic coordination complexes are very stable even at high temperatures.
The reason these compounds can be hazardous to humans either as cancer causing agent (carcinogenic), genetic material damaging agents (mutagenic) or by causing birth defects (teratogenic) is because our metabolic chemistry uses all sorts of biochemical compounds that are chemically similar or even identical to coordination complexes. Actually the oxygen transport protein, hemoglobin, contains what is essentially a coordination complex the 'heme' which actually holds the oxygen; and is a brilliant color. Many enzymes in the body, especially the ones involved in oxidation reactions which utilize antioxidants from the diet, and correct DNA damage, among other things, also contain 'coordination complexes' and chromium in its trivalent form is essential at a very low level in the human diet.
I have no idea what the precise chemical or biochemical mechanism would be that allows chromium six to cause problems; I doubt that anyone knows. But it is certain that exposure to it can cause an increased incidence of certain cancers; so it is a good idea to avoid it if possible. The point is do not be paranoid; when welding or cutting any metals a proper respirator should be worn because there are a lot of potentially nasty things produced. And in the case of cutting it is the metal particles; but these, and any chromium compounds, will be filtered out by a correctly fitting mask.
And I hope I haven't bored anyone.
An open mind is a virtue...so long as all the common sense has not leaked out.
Re: Ventilation in a metal machine shop?
Just for anyone's info, electrostatic SUCKS! Don't buy into that crap. They are a maintenance nightmare.
www.turtleracingproducts.com
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