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This company was plagued with drying cracks in their solid porcelain pieces. After some time they discovered that the deaired plastic material received from their suppliers had laminations (revealed in a cross section cut of the slug). Since they were not wedging, but simply inserting the clay into their hand extruders and presses, these laminations produced built-in weaknesses - the stresses of drying later exploited these. The obvious fix seemed to be to buy a mixer/pugmill to remix the clay. But that did not work. Why? Commercial pugmills commonly have multiple shafts, hundreds of blades, large powerful motors, separate mixing and vacuum chambers, shredders, high-compression heads, etc. Many small studio pugmills have none of these features. They are still great for recycling and mixing clay that will later be wedged. But for the machine-forming purposes of this company, this pugmill actually made the laminations worse! Would a deairing pugmill have solved the problem? There is still room for caution will studio equipment in production settings.
Glossary |
Laminations
Laminations because of improper pugging of a clay body will cause separations and drying cracks in the ware. |
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Glossary |
Pugmill
The practice of removing air from clay as it is pugged. Deaired clay has better forming properties and produces a smoother fired surface. |
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