downs on thu 30 jan 97
I have a problem I hope someone can help with. My father had a
welder build me a homemade pugmill. The design has a hopper to load
the clay, an auger to push it thru a joint of pipe connecting to
smaller auger which them pushes it out a 3 inch exit pipe. It has no
vacume pump as we were not technically sure how to do that, but it
would be much better than nothing, which is what I have now! The
first motor we tried (I think it was 1/2 horsepower with a gear
reduction) worked great, the speed was good. However, after only
15 minutes of pugging it locked up. In his effort to force it to
turn by means of a 24" pipe wrench, my father(although good
intentions) cracked the housing. We got another motor without the
gear reduction which turns so fast it threw clay out the hopper for
the distance of about a mile. My question is, what size of motor
should I look for, will it be nessesary to have a gear reduction, and
where on earth would I find one. The local electric moter shop here
has not been able to help me.
I'm new to clayart and am really enjoying getting mail each morning,
and have learned alot. Hope someone can give me advice, as it really
stinks to have that setting in the barn and have to wedge clay by
hand.
Thanks,
Denise Downs
Rt. 1 Box 19
Pampa, Tx 79065
downs@pan-tex.net
Danny Brumfield 6282 on fri 31 jan 97
Use belt drive. Put a tiny wheel on the motor shaft, and a great big
wheel on the pug mill. This will give lower speed and more power,
like on a drill press. Also, check the specs on factory-made pug
mills to find out what rpm/horse power is required for such a machine.
--
"Do you recognize my voice, Mandrake?"
Paul Monaghan on fri 31 jan 97
downs wrote:
>
> ----------------------------Original message----------------------------
> I have a problem I hope someone can help with. My father had a
> welder build me a homemade pugmill. The design has a hopper to load
> the clay, an auger to push it thru a joint of pipe connecting to
> smaller auger which them pushes it out a 3 inch exit pipe. It has no
> vacume pump as we were not technically sure how to do that, but it
> would be much better than nothing, which is what I have now! The
> first motor we tried (I think it was 1/2 horsepower with a gear
> reduction) worked great, the speed was good. However, after only
> 15 minutes of pugging it locked up. In his effort to force it to
> turn by means of a 24" pipe wrench, my father(although good
> intentions) cracked the housing. We got another motor without the
> gear reduction which turns so fast it threw clay out the hopper for
> the distance of about a mile. My question is, what size of motor
> should I look for, will it be nessesary to have a gear reduction, and
> where on earth would I find one. The local electric moter shop here
> has not been able to help me.
> I'm new to clayart and am really enjoying getting mail each morning,
> and have learned alot. Hope someone can give me advice, as it really
> stinks to have that setting in the barn and have to wedge clay by
> hand.
> Thanks,
> Denise Downs
> Rt. 1 Box 19
> Pampa, Tx 79065
> downs@pan-tex.net
Hi Denise,
What you really need is some up front engineering at least "back of the
envelop" engineering. I would expect to use a 3/4 or 1hp motor and
absolutely with a gear box. The reason is that you are trying to
compress an almost incompressible material and force it through a die.
The size of the die will make a tremendous difference in how fast the
clay will flow. The compression will result in thousands of pounds of
force being exerted on the auger flutes. So what you really need is slow
sustained constant force. The larger the die, the less the compression,
the faster the flow and hence the less pressure on the auger.
The way to approach the problem is to work back from the rate of
extruded clay (in pounds/hour or pounds/min.) all the way to the power
required from the motor. Instead of getting into all the hairy
engineering calculations here's a simple way to do it (and I'll make you
an honorary "Engineer"). Take a point on the auger shaft and measure
the DISTANCE the auger travels in one revolution. This will give you a
good approximation of how many inches of clay will be pushed out of the
pipe in one revolution. Let's say for example that 1/2 inch will be
extruded with each revolution and you want 1 inch/minute to be
extruded. Then the auger speed must be 2 revolutions/min.(rpm). If the
motor speed is 1750 rpm then you need a 1750/2 or 875:1 speed reducer.
This is awfully slow so a 10:1 would be reasonable. The numbers are not
as important as the methodology. The more gear reduction the greater
the power at the auger. Now this all assumes that your auger is strong
enough to take the load if you restrict the output. But for
unrestricted output this should be a good approximation with minimal
stress on the auger. The other assumptions is that the clearance
between the auger flutes and the chamber walls is small enough to
eliminate or rstrict "blowby" where the clay pushes back past the flutes
and not out the end.
Now admittedly Denise this leaves out a lot of the engineering design
considerations but will give you an acceptable working solution. I hope
thi helps and let me know if you have any other questions.
gear reducers and gear reduced motors can be foud at Grainger and many
other mechanical equipment houses.
Cheers,
Paul :-)
--
Paul J. Monaghan email: paul@web2u.com
WEB2U Productions --- http://www.web2u.com
The "COOLEST" Site on the WEB
"The Computer Secrets are hidden at www.web2u.com/secret"
Craig Martell on fri 31 jan 97
Hi Denise: I used to be an agent for Venco pugmills so maybe I can help you
out a little. I am not a mechanical engineer though, so don't expect too much.
First of all, I think you already know the answer to the gear reduction
question after the hasty exit the clay made from your mill without one.
Without knowing what your barrell size at the largest diameter is, I will
venture an opinion of about 1.0 to 1.5 hp to run this mill. 1/2 hp is
totally inadequate to pug clay, which is why your motor quit so soon. I
would go with 1.5 hp if the mill is in constant use every day and is used in
cold conditions. Cold clay is tough to move and takes a lot of hp.
The RPM at the shaft(auger), should be about 25rpm. That will work the clay
slow enough to gain some good mixing and it's also slow enough that you
won't get pasted to the wall by flying clay. This is what the gear reducer
does. It reduces the motor speed to the shaft and delivers more torque and
power to the load (clay). 4" Venco mills use a 2hp motor that turns at 1430
RPM and a 60.57 to 1 gear ratio, provided by the gear reducer. This gives a
shaft speed of 24 RPM and a lot of muscle to push the clay through the mill.
Venco uses SEW Eurodrive gearboxes and there are some SEW guys in Texas, if
you can't find anyone else to help you out. In fact, there is an assembly
plant in Dallas, I think. Their agents work out of their homes and will
sometimes make house calls but you have to be totally "up front" about what
you're doing. If it isn't worth their time, they might give you some good
advice on where to go and what to get. There are agents in: Richardson,
Crosby, Round Rock, Plano, Dallas, and Houston. If you want to contact any
of them, let me know and I'll give you their phone number.
If you can afford it, a parallel helical gearmotor will give you the best
performance, but it's always a question of money. SEW might have some used
or reconditioned stuff you could get. Here's a number for you: Southwest
Region Operations SEW Eurodrive, George E Booth, 3950 Platinum Way, Dallas
Tx 75237 (214)330-4824.
I hope this doesn't turn out to be a "wild goose chase", and give you a big
headache. Regards, Craig Martell-Oregon
Vince Pitelka on fri 31 jan 97
>My question is, what size of motor
>should I look for, will it be nessesary to have a gear reduction, and
>where on earth would I find one.
Denise -
I have a fairly large homemade de-airing pugmill (4"-extrusion) I built
sixteen years ago. It has a five hp. motor and a large Falk shaft-mounted
gear reduction box. It is way overbuilt, but it has never failed me and it
will do at least 1500 lbs per hour. When building a homemade pugmill one
must always overbuild. I modified the design from a set of plans from Harry
Davis, and way last summer I promised plan sets to several people on
Clayart, but I had just moved, and the plans must have slipped through a
temporal rift in the space-time continuum. I will eventually find them. In
the mean time, let me give you a few suggestions. You ALWAYS need a good
stout gear-reduction for a pugmill. In addition, the motor should have a
small belt-small pulley on it and the gear-reduction box a large one. I
have never measured the exact speed of the auger in my mill, but I would
guess it to be about 1 1/2 RPM.
I got my gear-reduction box in a junkyard for $40 bucks in perfect shape,
but at that time it retailed in the mill-supply stores for $1100. They are
obscenely expensive when purchased new. Of course, you do not need one as
large as the one I used. If they have lots of factories in your area,
expecially if they have lots of factories going out of business, then
someone has a bunch of gear-reduction boxes on hand which they might be
willing to sell for cheap. I have seen lots of them in scrap-yards. The
advantage of a shaft-mounted gear reduction is that the main auger can be
mounted on several very stout pillow-block or flange-mount bearings, with
the gear box mounted on the shaft between them, and the auger and barrel
extending to one side beyond the bearing. Walker-type mills have bearings
on both ends of the shaft, and discharge to the side, but all other
single-shaft mills I know of have both bearings at one end, with the
tail-end of the shaft unsupported within the barrel. The action of the
pugging keeps it centered, unless the shaft is too small, in which case it
could twist and bind just as happened with your pugmill. I believe the main
shaft on my mill is 1 15/16" dia.
In Harry Davis's original plan he specified a homemade gear reduction in a
steel-box housing, with heavy 1/4" steel plate on either end of the housing,
at 90 degrees to the auger shaft. Flange-mount bearings mounted on these
plates support two or three jackshafts (I can't remember which - you would
have to figure the reduction) and the main auger. Harry Davis recommended a
two-horsepower motor. The initial drive from the motor to the first
jackshaft was from a small twin-belt pulley on the motor to a large one on
the jackshaft. A small chain sproket on the first jackshaft drove a large
one on the second jackshaft, and a small sproket on the second shaft drove a
large sprocket on third one or on the auger. You must make sure that the
bearings supporting the auger are very heavy-duty, and can stand the
thrust-load of the pugging-action.
The barrel on mine is 8" inside-diameter, and as I said, Harry Davis
recommended a 2 hp. motor. If your barrel is smaller, and if you get or
build an adequate gear-reduction box, then you can use a smaller motor, but
no smaller than one hp. under any circumstance. As I said, overbuild.
A pugmill requires that the blades be mounted at an appropriate angle to
move the clay at the correct speed at the correct RPM, and it absolutely
requires approximately a 1/4" space between the end of the blades and the
inside of the barrel. This shoves the clay against the inside of the
barrel, and in order for the pugmill to operate correctly the clay must
stick to the inside of the barrel while the blades are turning. It is this
friction that makes the thing work - the inside of the barrel trying to hold
the clay static, and the auger trying to turn it.
I should mention also that a mild-steel (not aluminum or stainless steel)
pugmill is only good for pugging stoneware and colored earthenware.
Porcelain and white earthenware will react with the mild-steel, resulting in
discoloration of the clay, and a rock-hard deposit forming on the inside of
the barrel and the backsides of the blades.
I have gone on long enough about this, but as you can see, I love this
stuff. If you tell me more about your design and about what happened to it
when it froze up, I can probably help you fix it.
- Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Vince Pitelka on sat 1 feb 97
In reading some of this other fascinating information on pugmills, I
realized that yesterday I stated the auger speed on my homemade mill as 1
1/2 rpm. It would be pretty hard to pug 1500 lbs. per hour at that speed.
In actuality it turns 1 1/2 revolutions per second, or 90 rpm. There,
doesn't that sound better?
- Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
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