Michael Wendt on thu 29 nov 01
Jim,
We mix 300 lb batches at a time and never preblend. The trick is to mix the
clay portions into the water/darvan first since they are the hardest to
disperse and will tend to lump and gum while the spars and the silica and
the other nonplastic components mix in quite well.
The same is true for the nondeflocculated bodies we mix, ... the clay is
always added to the water and mixed first, screened very fine and then the
other ingredients are added. This works especially well if you want to make
insulating fire brick using clay, grog and sawdust.
Regards,
Michael Wendt wendtpot@lewiston.com
Jim asked:
Is premixing dry materials together required or overkill for mixing casting
slip in larger volumes ?
Ceramic Design Group on thu 29 nov 01
on 11/29/01 6:02 PM, Jim Murphy at nomocor@HOME.COM wrote:
> Hello all!
>
> I've been using a Lehman 1-gallon jar mixer to blend small experimental
> batches of Cone 10 porcelain casting slip. It seems to work well for
> 1-gallon of casting slip.
>
> I don't buy premixed powdered clay - I weigh the separate ingredients and
> add them to the water in the following order: (1) Ball Clay blend; (2) Three
> different Kaolins; (3) Two Feldspars; (4) Pyrax HS Pyrophyllite; and (5)
> Flint. I use Darvan 811 to defloc.
I hope you have selected the correct ball clays for casting as well as the
correct kaolins for casting. You selection(above) presents good
diversification of materials within each grouping. You are on the right
track.
>
> Soon, I want to mix a larger volume of casting slip using a Lehman 55-gallon
> mixer/reclaimer (1/2 hp motor, two 4" impellers).
These are the lower end of Chuck Lehmans equipment line. Buy the heavy duty
fiber glass tanks with the integral lid/motor impeller arrangement. They use
220V 2 HP motors on the 100 gallon tanks and 1HP 220V motors on the smaller
50 gallon tanks. They will last you a life time and can take some major
abuse. The 55 gallon tanks use smaller motors with 2 props and have a ring
that holds the angled motor/shaft arrangement on the rim of the tank. Could
be better designed.
> I'm wondering now - for larger volumes (50-gallons) - whether I need to
> premix all of the dry materials together first and then add them to
> water/Darvan to get a homogeneous mix.
No. Chuck Lehman's machines are extremely well designed and made to blunge
completely the dry mix with the water and the deffloculant.
>
> If I were using a 50/50 Ball Clay & Talc recipe I don't think I'd be too
> concerned ... but with 8 different dry ingredients ... ????
Doesn't matter. We blunge 100 gallon tanks all the time with many
ingredients. We also have very cool 50 gallon tanks that Chuck made up for
us with variable speed 1 HP 220v motors that are really nice pieces of
equipment.
>
> If I need to premix the dry ingredients, I'll need to purchase a drum
> rotator. See hyperlink below for example:
You don't need to spend the money.
>
>
>
> I know I could pay my ceramic supplier to premix & bag the dry ingredients
> for me but I'd prefer to have more control and keep the secret recipe secret
> for now. (LOL)
Yeah sure.
>
> Sooooo, I'm asking for advice from you experienced casting slip experts out
> there.
>
> Is premixing dry materials together required or overkill for mixing casting
> slip in larger volumes ?
Yes
Here's our secret that I'll share with you without LOL.
Figure out the amount of water you will need for the larger quantity of
slip. Subtract 5 gallons from that and put that five gallons aside. Figure
out the amount of Darvan 811 you will need for that volume and deduct about
50 ml from that total and also put that aside. Add the water (less the 5
gallons) to the blunger, then add the deffloculant (less the 50 ml) and
blunge that up for about 15 minutes. Get good measuring containers like
graduated cylinders. Get a good viscosimeter(a Zahn Cup from Gardiner CO))
and a good device for measuring SG (Pykenometer from EJ Payne)
Start adding the dry ingredients. We add the the plastics first and then the
non-plastics. Blunge completely, say for a few hours until you have a smooth
mixture. Take you SG readings and your viscosity readings, using the devices
that are appropriate. Make a small adjustments at a time by adding the
reserve water and the reserve Darvan 811. Blunge overnight and then take new
readings in the morning. SG and viscosity will change on a daily basis and
you will need to monitor your slip and make the necessary adjustments.
Casting slips need to age just like plastic mixtures.
Call me if you have any questions. I'd be glad to help.
Jonathan
--
Jonathan Kaplan
CERAMIC DESIGN GROUP
PO Box 775112
Steamboat Springs, CO 80577
(970) 879-9139
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
Jim Murphy on thu 29 nov 01
Hello all!
I've been using a Lehman 1-gallon jar mixer to blend small experimental
batches of Cone 10 porcelain casting slip. It seems to work well for
1-gallon of casting slip.
I don't buy premixed powdered clay - I weigh the separate ingredients and
add them to the water in the following order: (1) Ball Clay blend; (2) Three
different Kaolins; (3) Two Feldspars; (4) Pyrax HS Pyrophyllite; and (5)
Flint. I use Darvan 811 to defloc.
Soon, I want to mix a larger volume of casting slip using a Lehman 55-gallon
mixer/reclaimer (1/2 hp motor, two 4" impellers).
I'm wondering now - for larger volumes (50-gallons) - whether I need to
premix all of the dry materials together first and then add them to
water/Darvan to get a homogeneous mix.
If I were using a 50/50 Ball Clay & Talc recipe I don't think I'd be too
concerned ... but with 8 different dry ingredients ... ????
If I need to premix the dry ingredients, I'll need to purchase a drum
rotator. See hyperlink below for example:
I know I could pay my ceramic supplier to premix & bag the dry ingredients
for me but I'd prefer to have more control and keep the secret recipe secret
for now. (LOL)
Sooooo, I'm asking for advice from you experienced casting slip experts out
there.
Is premixing dry materials together required or overkill for mixing casting
slip in larger volumes ?
Also, if a drum rotator is required, how long would you say it takes to
rotate/blend 250 Lbs of dry materials together ? (I would need to blend two
separate batches (two drums) due to the dry weight drum rotator capacity
limitations - need about 500 Lbs. total dry mix for 50-gallons of slip.)
Thanks in advance,
Jim Murphy
Jim Murphy on fri 30 nov 01
Thanks to all for the mixing instructions and convincing me I do not need to
premix the dry ingredients. This means I can stop thinking about whether I
need to sell my motorcycle to make room in the garage for another piece of
machinery (drum rotator) - YES !!!
Thanks again,
Jim Murphy
P.S. to Jonathan Kaplan:
1. "I hope you have selected the correct ball clays for casting as well as
the
correct kaolins for casting."
I took the advice from June/July and ordered FC-340 Ball Clay from Old
Hickory. Also, I've included Velvacast (large-particle size) Kaolin in the
recipe.
2. "The (Lehman) 55 gallon tanks use smaller motors with 2 props and have a
ring
that holds the angled motor/shaft arrangement on the rim of the tank. Could
be better designed."
I think Lehman has improved their design slightly. The 55-gallon mixer I
recently purchased has the
integral lid/motor impeller arrangement - motor bolted through fiberglass
lid which is bolted to
the tank. A removable plexiglas oval-shaped "window" in the lid allows entry
into the tank.
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