Mr. - J. Tyler Teague re - Is there a good “Do it Yourself
Ventilation Book” type book for our industry?
Please put the book and sources on the orchid site for all of us. I
am moving and will be adding a small shop ventilation system to my
intended shop .
A source of fans, blowers, and general mechanical surplus items is
SURPLUS CENTER - Lincoln Ne. - 1-800-488-3407 I have not purchased
from them, but some of my associates have and rate this place as Very
Good Value.
ROBB
Dear all, I am once again trying to stay out of the fray as much as
possible. Like I have said before, this website can be addictive. I
am responding because I was asked specifically so don’t complain
because I talk too much. There are some particular things that you
need to know about hoods for the investment casting and jewelry
industry that I have not seen in this thread. They may have been
there but I don’t read this every day. Please forgive me.
The hoods for particulate in the investing areas are of a slightly
different design than hoods for fumes. The use of hoods that are
really designed to remove heat (kitchen ventilation hoods) are not
really suitable for our industry. There are certainly ways to
increase the effectivness of these types of hood designs but in
general, any hood that has an up-draw system is not for us. These
types of up-draw hoods pull fumes and or particulates, up and through
our breathing zones. Generally we are standing in front of these
things as we work with some fan or air conditioning vent blowing
around the air in the room. Most of the hoods that I have seen used
like this are simply hung above a work station, most times attached
to a wall. Two sides and the front of the area under the hood are
open to the room with no limitations. This means that as the hood
draws, it is drawing from all sides but the wall that it is attached
to. If you calculate the area that is available to draw from and the
cfm (cubic feet per minute) of air that your hood can draw, you will
see that the velocity of the air that you can move is dang near
nothing. What I am saying is that the force of someone simply
walking by the “vented” area has more force than the hood above your
area. Air velocity is a much more important thing to consider than
just cfm alone. Now if you restrict the area from which the air can
be drawn, then you can increase the velocity of the draw and increase
the effectivness of the hood.
In order to modify these types of hoods so that you can use them in
the safest manner, you would need to make sure that the system is
closed on 3 sides of the hood all the way down to your table. Then
you would need to limit the size of the opening in the front from the
top down using some clear plexiglass or lexan. Clear so you could
still see what your doing. Basically this would start to change your
hood from an up-draw to a back draw system. You could make one more
modification by putting a full width baffle from the inside front of
your kitchen hood that extends back and down about 3/4 of the
distance between your hood and the table top. You would leave
adequate space in the back of this arrangment to create a back draw
hood. This baffle would have a few 1/2 inch holes drilled at the
top, near the origin at the hood, so that any fumes that did rise due
to heat that were missed by the back draw velocity could also be
captured there. I hope your following this descriptioin. I just
know someone is going to ask for drawings but please remember that
this is what I do for a living. If I keep giving everything away, I
will continue to get poorer and poorer. I just don’t want any of you
to get hurt.
Most of the kitchen hood designs depend on heat rising and you being
a reasonably good cook. I would dare say that even with the best
kitchen hood, you can smell what your cooking all over your house. I
just hope that your cooking smells better than mine. If you can
smell food cooking all over the house, imagine having various
chemicals wafting about your shop or factory. Even worse is the
silica in the investment powder. It doesn’t smell but it sure can
cause some damage to your lungs. Here I go again with the lung
thing. What I have just described is okay for plating purposes and
some light chemical work but is still no good for investing or
devesting.
Particulate hoods for investing and devesting need to be very strong
and very targeted because particulates are solids and can collect
while fumes tend to dissapate. This means that when you are pouring
your investment powder into your mixing bowl or machine, you need a
back draw vent practically sitting on the lip of the bowl so that any
powder (silica), cloud is immediately drawn back into the vent and
away from your breathing zone. This couldn’t be any more important
when you are “quenching”. The steam from quenching carries a much
smaller silica particulate into the air that can be breathed deeper
into the lungs. Again, the use of a hood system that is closed on
all sides except for a limited area in the front and draws to the
back over your quench tank is imperative. Some of you will say that
you wear a mask but I can assure you that unless you are mask savey,
clean shaven, and vigilantly clean they don’t help that much. Beside
that, like I said, the particulates collect and can float around
through the general ventilation system to affect everybody. Better
to get it out of the building.
Now I am not exactly handing you fish, but I am at least telling you
things to consider as you go out fishing.
One book that is about $69.00 is called, Laboratory Fume Hoods: A
User’s Manual by G. Thomas Saunders
http://www.amazon.com/exec/obidos/ASIN/0471569356/ganoksincom-20
Also check out this website. It’s free
http://www.pp.okstate.edu/ehs/LINKS/Fumehood.htm
Now let me go back to my cave…
Best Regards,
J. Tyler Teague
JETT Research
[Edited Ton: Add Amazon link]
Oops! Upon reading what I wrote I neglected to say that for simply
removing the heat and fume of a small burnout oven, these types of
kitchen hoods are ok. You can enhance the performance of these hood
for the purpose of controlling the heat and fume of a burnout oven by
again, limiting the area from which they draw air. It is ideal to
get them down as close to the top of the oven that seems appropriate.
That they extend a little out beyond the door opening helps to
exhaust heat when you are opening and closing the door. Closing up
the back and the 2 sides while leaving the front open for access will
really help you a lot by increasing the velocity of the draw from
the front the same as for a fume hood. Sorry for leaving that out.
Best Regards,
J. Tyler Teague
JETT Research