|Monthly Tech-Tip |
A shrinkage only version of the SHAB test.
A cone decimal representation of the cone value.DRLN - Dry Length (V)
A measurement in decimal inchesFRLN - Fired Length (V)
A measurement in decimal inches
To evaluate shrinkage, absorption and color to assure it is consistent with the specification.
200. Definitions and Standards
In general, low temperature clays are tested at cone 04 only, mid fire at cone 6 and high fire at cone 8, 10 and 10 reduction. A complete list of Axner bodies and their ID numbers can be found in the JIT inventory system.
Cone Decimal: A representation in decimal of the position of a witness (firing) cone that recognizes the geometric rather than arithmetic nature of its fall and accounts for information gleaned from guide and guard cones. For a right bending cone x, 1 oclock is considered the starting position. 2 oclock is considered cone x-1.7 (75% of the temperature rise is needed to begin cone bending to this point), 3 oclock is cone x-1.8, 4-5 oclock is considered cone x.0. Touching is only considered cone x.0 if the guard cone has not moved. Values are rationalized by averaging in the case of excessive movement in the guard cone (for example, if the guard cone is at 2 oclock and the firing cone 3 oclock as can happen in slow firings)
Absorption: A value determining by:
(Wet weight - Dry weight) / Dry weight * 100
Fired Shrinkage: A value determined by:
(Fired length - Dry length) / Fired length * 100
310. Production Duties
Take a quality control test sample from each batch and mark the bag with the batch number and name of the clay.
320. Lab: Prepare test bars
Roll the sample into a one-inch thick slab.
Place a 1.9mil plastic sheet over the slab and remove the plastic.
Smooth the bar top if needed so a crisp set of length markings can be made.
Stamp the bar as follows:
-batch number of the upper right
-ID number upper left (last three digits of Axner catalog number)
-Date on which test bar made on bottom center
-Cone upper right corner with OX prefix if needed (e.g. OX6 for cone 6 oxidation, 10 for cone 10 reduction)
-Create shrinkage marks lengthwise along the center at exactly 5 inches (dip marker in non-stick powder like corn starch or talc to get a crisp set of marks
Place bars on cookie sheets to dry (take care not to bend them during transfer to avoid warp during firing)
Record observations about plasticity, stiffness, hard chunks, grit, etc.
Allow bars to completely dry
Measure and record the distance between the outer edges of the length marks
Stage the bar(s) for firing
330. Lab: Fire test bars
Kiln loading check list:
-Create a sturdy load by aligning posts
-Place a witness cone on each shelf.
-Make sure the thermocouple projects into the kiln at least one inch and that no metal on it comes into contact with the skin of the kiln
-Program the kiln to hold the temperature at 200 degrees maximum for four hours and use the auto fire standard rate with a 10 minute hold at temperature
340. Lab: Measure fired test bars
Place test bars in air-tight containers (keeping bars from the same shelf together with the witness cone) until measurements can be done. Do measurements as soon as possible.
Measure and record in the computer the distance between the outer edges of the marks and the cone decimal value.
Weigh the bar and record the weight.
Record a value for soluble salts on the fired surface and a rating of the color compared to standard. Record any observations worth noting about fired character (e.g. speckle development, variegation).
Stage the bar for boiling.
350. Lab: Weight boiled bars
Boil each batch of bars for 5 hours and soak for 19.
Blot and weigh each bar (do not allow to stand after blotting) and record the weight.
360. Lab: Bar storage
Keep one sample of each firing temperature and file it for future reference.
400. Test Evaluation
Contact Ron Roy with test results of runs that appear off standards.
500. Future additions
Bar picture uploads
Bullers rings in each firing
Bar preparation on boards that do not require movement of bar
Smaller bars, firing on bar edge for more even heat penetration
Less elaborate markings on the bar, only cross reference to computer
Measurement in metric with 10cm wet length
Standard firing curves and holds
Measurement of water content, drying performance and particle size
SHAB Shrinkage and absorption test procedure for plastic clay bodies and materials
Tests conducted on bodies made from materials, as opposed to the materials themselves.
ASTM-C373 Water Absorption
|By Tony Hansen|
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