rheology_for_slip

8/7/2019 Rheology_for_Slip

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OLD HICKORYCLAY COMPANY

Why Slip Cast?

Produce difficult shapes,

especially hollow shapes withmany details

Productivity

Material utilization - scrapDrying efficiencies - defect

control

Firing efficiencies - fastercycles, placing density

Ease of producing varyingbatch sizes and formulas


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OLD HICKORY

CLAY COMPANY

Rheology,

But what is itreally?

Rheology is the basicunderstanding of how a

clay/water systems

properties interplaybetween the raw

materials, the chemicals,

and the mechanics of

mixing, storing, andforming processes


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OLD HICKORY

CLAY COMPANY

Rheology,

But what is itreally?

Another way I like todescribe rheology is;

the understanding of a

slips deflocculation andthe control of its long

term gel.


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RHEOLOGY


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OLD HICKORY

CLAY COMPANY

Keys to CreatingGood Rheology

1. Choosing good rawmaterials

2. Understanding your

chemicals

3. Learning to make

some physical property

measurements

4. Understanding thatproducing slip is a

dynamic process


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Raw MaterialsUnderstand what each raw

material is used for,

Plasticity, strengthVitrification

Thermal expansion

Sizing

Color

Dont be afraid to experiment

seek advise

look for the best availablematerial

dont get stuck on printed

formulas


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Chemicals,

Keep it Simple!

Deflocculants

Soda AshSodium Hydroxide (hard water

only)

Sodium Silicate

Darvan 811

Sulfate Control

Barium Carbonate

FlocculantEpson Salt

Vinegar

Plaster


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RHEOLOGY


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Chemicals,

Keep it Simple!

General Chemical Parameters(of dry batch weight)

Soda Ash 0.05-0.1%

Sodium Silicate 0.2- 0.4%Barium Carbonate 0.01-0.03%


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OLD HICKORY

CLAY COMPANY

Slip Production

is aDynamic Process

All knowledgeable andexperienced slip makers

understand that daily

physical measurementsdictate what change

options you have inorder control your

rheology.


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OLD HICKORY

CLAY COMPANY

Slip Production

is aDynamic Process

Your chemistry needs to

be changed according to

your raw material

variations. Your physical

measurements will leadto the answer.

What is the raw materialmost overlooked?


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OLD HICKORY

CLAY COMPANY

Slip Production

is aDynamic Process

What is the raw material

most overlooked?

WATER


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Physical Property

Measurements

Specific Gravity

ViscosityCast

Rate

FeelDrain quality

measure volume

Firming time

If you are just beginning - Chartyour data to narrow your

parameters


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OLD HICKORY

CLAY COMPANY

Physical PropertyMeasurements

B. Fill the emptycontainer with room

temperature water and

reweigh in grams.

C.Take the dried empty

container and fill with

slip poured through a

sieve(40mesh). Recordthe weight of the

container and slip.


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OLD HICKORY

CLAY COMPANY


D. Calculate the SpecificGravity as

Weight of container with Slip - weight of container

Weight of container with water - weight of container


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OLD HICKORY

CLAY COMPANY



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OLD HICKORY

CLAY COMPANY


Viscosity -A variety of measuring

methods have been

discussed in various articles

from a veterinarians syringe,to a flask with a rubber

stopper, to the drip method.

However, I prefer the PVC

pipe(8 to 10 inches), one endcapped with a 3/16 inch hole

drilled in the center.


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OLD HICKORY

CLAY COMPANY


Viscosity -Take the PVC tube and plug

the hole. Precisely measure

250 or 300 ml of water into

the flow tube. Mark theinterior of the tube so the

same amount of slip can be

measured on each test. The

head pressure height willeffect the final reading.


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OLD HICKORY

CLAY COMPANY


Viscosity -Fill the slip to the determined

mark in the flow tube, with

your finger over the hole.

Place the flow tube on astand above a 250 ml

graduated cylinder. Remove

your finger and record in

seconds (using a stopwatch)the time of flow between 50

and 250 ml.


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OLD HICKORY

CLAY COMPANY


Viscosity -The time measured will

eventually be an

excellent guideline in

determining the amount

of deflocculant needed to

obtain the viscosity for

the type of cast youdesire.


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OLD HICKORY

CLAY COMPANY


Cast -In the beginning, you will

need to establish a casting

rate relative to the Specific

Gravity and Viscosity. Thiswill help in establishing daily

parameters to produce the

slip and aid in resolving

casting problems when theyoccur.


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OLD HICKORY

CLAY COMPANY


Cast -Take a simple cup mold and

cast it for a fixed time. Then

drain and measure the weight of

the piece after a fixed time for

firming. Qualify the weight by

observing the drain cleanliness

and feel for moisture uniformity.

This information in conjunction

with Specific Gravity & Viscositywill yield you the total picture of

rheology.


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RHEOLOGY


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OLD HICKORY

CLAY COMPANY

RHEOLOGY

inSummary

In one word:

Balance

Balance between your

Raw Materials

&

Chemistry


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RHEOLOGY


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RHEOLOGY


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OLD HICKORY

CLAY COMPANY

VISCOSITY

The measurement ofthe consistency of a

slip which gives a

numerical value toits resistance to

flow.


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OLD HICKORY

CLAY COMPANY

THIXOTROPY

orGelation Characteristics

The tendency of a

slip to increase in

viscosity when left

undisturbed, due toa build-up of

structure within it,

and which can only

be destroyed by

agitation.


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