During the production of large electrical porcelain specimens the shaping, drying, and green handling stages are extremely sensitive. Severe faults and defects can occur in these stages if the body is not sufficiently strong, plastic, or has a poor drying characteristic.
For example, cracks may appear that either require repair/reprocessing work, or may not be recoverable at all.
- Shaping Faults
- Key to have good shaping characteristics is to use clay with a high level of work ability – what some call plasticity. For this reason, Face impex test that assesses the work ability of clay and/or bodies. The test characterizes the amount of work energy that can be applied to a clay (or full body formulation) without cracks occurring. This can indicate either how hard a clay (or body) can be worked, or how likely the clay (or body) is to crack under given conditions.
- A high work ability can also help resist the formation of cracks during drying – see section Drying Faults
For more details about this test, please see the article on work ability in our Technical Documentation section.
- Drying Faults
- Using clay with a good mineralogy, in terms of drying shrinkage, can help reduce the build up of drying stresses during the drying process – allowing faster drying and/or reduced drying cracks.
- The balance of work ability – see the Shaping Faults section – to drying performance is key in the use of clay for electrical porcelain production. A clay with high work ability may still lead to drying cracks if the work ability comes from minerals with poor drying characteristics.
- Face impex pvt ltd offers a range of products with minerals that provide a good balance of work ability and drying performance – allowing faster production or higher yields.
- Firing Faults
- Often electrical porcelain specimens are very large. This makes their firing difficult and sensitive to several potential faults.
Large electrical porcelain specimens must be fired very carefully in order to allow all gases generated during firing to be released, in order to prevent large firing defects such as blue/black coring. For this reason, it is important to use clays with low amounts of gas forming material – for example, low carbon. This allows specimens to be fired faster and/or with less blue/black core defects.