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Tennessee
Tech
University
- Appalachian Center for Crafts - Clay
Studio
Vince Pitelka, 2006
Soldner Mixer Instructions
The maximum capacity of the Soldner professional mixer is
260 lbs. of dry materials. If you
exceed this, your dry materials will end up all over the floor and/or the mixer
will bog down and the thermal overload switch on the motor will repeatedly kick
off. If you accidentally put in too
much water first, and need to add more than 260 lbs. of dry materials in order
to get the right clay consistency, you will have to remove some of the partially
mixed clay to avoid overloading the mixer.
Remember that the dry particles added to any claybody
continue to absorb water after mixing, causing a corresponding stiffening of the
claybody. To counteract this you
must mix your clay on the wet side. A
softer clay will become wetted more quickly and thoroughly, encouraging
bacterial growth, giving a much more plastic claybody.
It is worth it to risk clay a little on the soft side.
A claybody that is initially mixed stiff will take twice as long to age
to an ideal plasticity.
For porcelain, porcelaineous stoneware, and whiteware
bodies, always add Epsom salts as specified in the handout “Mixer Load Amounts
for Claybodies.” As indicated,
always dissolve the Epsom salts fully in hot water, and then include that in the
specified amount of water for the clay batch.
Mixing Clay from Dry Materials and Water
- What
to Do about Remaining Residue in the Mixer Tub - If there is
significant stiff or bone-dry clay residue left in the mixer from the last
batch, scrape down the walls and mixing bars with a wide spatula, and place
the scrap in the recycle barrels. Unless
you are mixing porcelain or whiteware, do not worry about the fine residue,
because it will immediately slake down in the water and blend with your
claybody with no impact. If
there are accumulations of damp-but-stiff
residue in the mixer, scrape from the walls and mixing bars and put
them in the recycle barrels. NOTE:
For mixing porcelain and whiteware, see the instructions below.
- Add
Water to the Mixer Drum First - The finished claybody will contain
approximately 20% water. In
other words, the amount of water is approximately equal to one fourth of the
total dry materials weight. A
5-gallon bucket of water weighs 40 lbs.
A batch containing 260 lbs. of dry materials will usually require 60
to 70 pounds of water to achieve a soft plastic clay.
Weigh your water carefully, and keep track if you need to add
additional water during mixing, so that you will know to add more initially
the next time. Remember that
there is no set amount of water that works for every claybody.
Each one different, and adding too much water to begin with causes a
lot more trouble than if you add too little and need to add more during
mixing.
- If
the Concrete Mixer Tub Is Dry - After pouring your water in the
mixer, use a sponge or cup to wet down the inside walls thoroughly.
This will discourage the clay from sticking to the walls.
- Adding
Dry Materials - Start the mixer and the exhaust fan.
Begin adding the dry materials, finest materials (clays) first,
coarsest materials last. For
whichever of the following materials your claybody contains, the correct
order is clays, non-plastics (feldspar, flint, pyrophylite, talc, etc.), and
finally the sand or grog. If the
recipe calls for Epsom salts, dissolve them in hot water, and use that as
part of the initial water in the mixer tub.
If the recipe calls for bentonite, macaloid, or veegum-T, use the
drill-mounted jiffy-mixer to blend them with some water and a little bit of
any of the other clays, and add that after you have added all the other
clays. Add the materials slowly,
and allow them to absorb into the developing slurry.
For full bags of raw materials,
with the mixer running lay each bag cross-ways on the mixer lid, slit the front
edge of the bag horizontally, and rake the materials into the grate opening in
the lid. You can rake a full
50-pound bag of materials into the mixer in a minute or so, and it should absorb
just fine.
As the water absorbs the dry
materials, initially the mass of very soft clay will rotate in the mixer like a
giant doughnut. Once all the dry materials are added and absorbed, the clay
should begin to tumble in large, rough chunks.
If this does not happen, it means you have added too much water, and your
only recourse is to add more dry materials.
If you started out with a full mixer load, then you will have to remove
some in order to make room for more dry materials.
- Adding
More Water or Slurry to the Mix - If you start with insufficient
water and add dry materials without carefully monitoring the consistency, at
some point the mix will become too stiff, and the mixer will begin to
strain. If there is any sign of
this, you need to add more water or slurry right away, but add it very
slowly. For adding water, use
the short green hose, and dribble water in extremely slowly over the
tumbling clay mass about six inches away from the center pivot.
Never add water at the center, or along the outer edge of the tub.
Add the equivalent of a few cups of water, let it absorb completely,
and then add more.
If you add too much water or
slurry all at once when the clay is too stiff, it will simply lubricate the
inside of the mixer tub, and the tub will spin freely while all the clay remains
in one big lump stuck to the mixer bars. If
this happens and there is only a little excess water or slurry, just let the
mixer run for a few minutes. The
moisture will soon be absorbed and the mixer will start working properly again.
If there is excessive water or slurry, you will have to add more dry
materials to absorb it. If the mixer
is already filled close to capacity, you will need to remove some clay before
adding more dry materials. The best
practice is to simply be very careful not to add excessive water or slurry to
the mixer tub after the clay has begun stiffening to plastic consistency.
Note: If the Mixer Shuts off
Automatically - Occasionally, if the mixer is overloaded it will shut
off automatically. If this happens
and the mixer is not over-full, it is because the clay is too stiff.
Dribble a little water over the clay, wait a few minutes, and re-start
the mixer. Keep dribbling water in
slowly with the mixer running, until the clay reaches the desired consistency.
If the mixer shuts off because it is over-filled, remove some clay, wait
a few minutes, and re-start the mixer. When
the remaining batch is adequately mixed, remove some of that and replace the
first portion you removed, and finish mixing it.
- Removing
Clay from the Mixer - When the clay is mixed to the desired
consistency, remove the loose chunks of clay from the tub.
Close the lid, turn on the mixer for a few seconds, shut it off,
raise the lid, and remove the loose chunks again.
Repeat this until the mixer is almost empty.
Use a scraper to remove the last of the clay from the walls and floor
of the tub and from the mixing bars.
- Mixer
Cleanup - It is not necessary to sponge out the mixer after each
use, but you must scrape off all thick deposits of clay from the walls and
floor of the tub and from the mixing bars, and remove the scraps from the
mixer. Do not leave any large
chunks or thick deposits of clay in the mixer, because these tend to dry
slowly, and may produce hard lumps of clay in a subsequent batch.
NOTE: The original
instructions that come with the mixer say it’s okay to not clean the mixer
after use, but in institutional situations that is not acceptable, except in the
following circumstance. If you know
for sure that someone else is mixing a similar claybody right after you, then
there is no need to clean the mixer. The
residual clay will still be soft, and will be easily absorbed into the next
batch. Otherwise, you must always
clean the mixer as described above.
Mixing Clay from Wet Scrap Recycle and Dry Clay Materials
When mixing clay from wet recycle, be sure to scrape off and remove any
thick accumulations of stiff or dry clay from the mixer, because these will not
slake down in wet recycle, and will produce hard lumps in your claybody.
Put no more than 175 lbs (about three and a half 5-gallon pails) of wet
recycle (less if it is quite fluid) in the mixer, start the mixer, and slowly
add your pre-mixed dry materials (see below) a little at a time until you get
the consistency you want. Watch the
consistency carefully, and be prepared to add more water with the hose as
described above if it proves necessary. To
prepare your dry materials, purchase a half-mixer-load of raw materials, put
them all in the big cardboard drum that is kept in the clay cage for this
purpose, clamp on the drum-lid, and roll the drum around on the floor for a bit
to intermix the dry components before slowly adding to the recycle.
Save any leftover dry mix for the next batch.
Preparing the Mixer for Mixing Whiteware or Porcelain
The following is not necessary for porcelaineous stoneware bodies, but
is important if you seek a very white porcelain or whiteware.
With a scraper, loosen and remove all residue of the previous clay batch.
Pour a few gallons of clean water in the mixer tub.
With a large sponge, wash down the mixer walls, mixing bars, and the
underside of the lid. Use the
scraper and/or a stiff brush to remove clay from behind the mixer bars.
Use a small bucket or scoop and a sponge to remove all water from the
mixer tub. For the whitest claybody,
repeat the water-wash at least one more time.
Maintenance
Consult the manufacturer’s information for more detailed maintenance
instructions. The older professional
mixers have a belt drive from the motor to the jackshaft (secondary shaft), that
must be carefully monitored and adjusted for belt tension.
The newer professional mixers have a gearmotor that drives the main chain
directly with no belt drive needing adjustment.
There are zerk (grease) fittings on the bearings at the top
of the main tub shaft, and at the bottom under the tub, and these should be
greased with a pump grease-gun once a month.
The main drive chain should be sprayed with aerosol
chain-lube once a month.
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