|Monthly Tech-Tip |
At first it appeared to be the lack of a tapered die. Two were designed. The first did not solve the problem (right). Although it was tapered, it was only 5/8" thick (left overlay on the bottom right). Before going to a longer tapered die (bottom right overlay) we did a rethink. The clay being fed into this pugmill has already been processed in an industrial pugmill having 40 blades in the main chamber, a compression auger to a very efficient shredder, a vacuum chamber with about 20 more blades and another auger feeding a very long nose with dual compression dies. And a very powerful motor to drive the clay out the nose. The small pugmill here only has one shaft with few auger-like blades in the two chambers. A "screen" shreds the clay on the way into the vacuum. Each time the clay goes through the screen could its cohesiveness actually be compromised more by not being knitted back together properly in the nose? That could have been solved by the longer gently tapered die. But, it would not likely have worked, the clay would simply back-feed into the vacuum chamber because the design and power would not be sufficient to push it out the die. In the end the problem was fixed, but no how you might think: They turned off the vacuum!
The practice of removing air from clay as it is pugged. Deaired clay has better forming properties and produces a smoother fired surface.