Redesigning Metal Spray Room (help needed)

[Lampard8]

Hi all,

I'm working on a project to redo a metal spraying room, in terms of its ventilation and removal of metal dust in the air. The room is used to spray heated metal dust onto shafts that have been worn. Previously another engineer set up 2 exhaust fans on the wall of the room connected to ducts going to the atmosphere. The engineer also installed a motor and exhaust unit in the roof of the room attached to a ducting material that sucked air immediately behind the lathe onto which the shaft would be placed.

At the moment nothing seems to be working how it should in the room because the room gets very hot quickly and the metal dust quickly builds up in the air in the room and doesn't seem to be getting extracted quickly enough.

So far the research I did led me to believe that I needed to find the required CFM of the room and what the exhaust fans were actually pulling. Unfortunately, I cannot find any CFM values anywhere for the fans, the only data I have for them are the voltage, current, rpm and actual diameter. I have calculated, however, the required CFM of the room based on its size and # of air changes (based on safety standards).

Can anyone help me on this? I have been going in circles with this one and I need to solve this problem soon at work...

Thanks in advance!

 

[berkshire]

The best way if you can do it, is to find the fan manufacturers name plate, not the data plate on the motor.
If you have a make and model number with the diameter you can look up the manufacturers information, If not your best bet is to do a flow test of the fans you have. You may also find that metal dust has built up on the blades and made them inefficient.
You should note, if you redo this room, you may have to add dust collection equipment you do not currently have, depending on where you are in the world.
B.E.


The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Lampard8]

You are right I do have to add dust collection equipment, possibly an air filter or water bath. With respect to the nameplates, i searched all the info and found nothing online on the manufacturer websites. I did consider a flow test but I'm wondering if the cost of purchasing flow testing equipment will be more than just replacing with standard fans that I know the cfm of. Is there any way to calculate the cfm of these fans? They are both 4" and 6" diameters respectively. ALso, do you think these fans can be affecting the efficiency of the extractor at the center of the room alongside the lathe?

 

[berkshire]

Without knowing what kind of fans you have there, I doubt that you are pulling more than 350 to 400 cfm from the axial flow fans in the wall.
The fan on the duct in the roof? is that a centrifugal or is that also an axial flow fan?
Regarding purchasing flow measuring equipment. It may be cheaper to hire a test and balance firm to come in and measure the actual flow for you.
Whilst not advising you what to do because I do not have enough information to make that call, I would suggest that for point of operation fume and heat removal you look at welding fume removal fans from companies like Plymovent.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[chicopee]

Here are some thoughts.Before embarking haphazadly of buying test equipment, contact your insurance company providing your worker's compensation coverage for them to assist you in evaluating the air handling equipment. Normally, insurance companies with national and international reputations will have industrial hygienists or field representatives to assist their clients so as to mitigate future claims. Their requirements for maintaining a healthy environment within the spray room will be based on the ACGIH threshold limit values of the contaminants within the spray room.

You can also fax the fan manufacturers for their data sheets on the two fans and these sheets should have fan performance curve or tabulated data. Don't be surprised if you'll need a better exhaust system in order to cope with the pressure drop thru thedust collection system.

The extractor efficiency could be compromised if the make up air openings are insufficient in size.

 

[Metallisation]

There are guidelines relating to the design of spray rooms and extraction systems. Check out the international thermal spray association website.
I would warn against welding fume extractors for metal spray as the dust loading on the filter system is too great for most welding extractors.
There are a couple of reputable companies who are very familiar with metal spray applications. Suggest you contact Camfil-Farr and/or Donaldson-Torit - both very familiar in this field. Not cheap, but effective and safe.