The process involves wet blending of the ceramic mixture and wax, granulating and then drying. The dried mixture is molded and further shaped before going into a high temperature oven for sintering. The dryness of the mixture is crucial at this stage because any residual water will form steam that will cause cracks and fissures in the final product, reducing its strength and insulating properties.
A major supplier of automotive electrical parts has installed three of the new dryers for its ceramic-wax mixtures. Its most recent installation, the model LE-18, is 6 feet in diameter and approximately 10 feet in height. The complete package included an external electrical heater, fresh air supply fan with inlet filter and the interconnecting ductwork.
Through this gentle action of piling and leveling, the ceramic mixture is dried without caking or agglomeration. Because it is a plug flow operation, the retention time can be determined accurately and adjusted by a variable speed drive on the trays. At the center of each tray a circular section is cut out, making room for the fans that are mounted vertically on an axial shaft.
The drying medium enters through a side mounted vertical manifold and leaves the unit through a roof exhaust. The fans mix the incoming hot air with the air inside the dryer and circulate the drying medium over each material bed. This method of heating allows the precise temperature control necessary to avoid melting of the binders. Furthermore, the multiple hot air inlets allow different temperature zones in the top and bottom of the dryer.
The new dryer takes a wet feed with 10% free moisture and discharges a uniform granular mixture with less than 0.3% moisture. Drying temperatures are carefully controlled to prevent melting the binder while drying in the shortest possible time. A belt conveyor carries the ceramic mixture to the top of the dryer, where it is fed continuously through a rotary airlock. The dried material is discharged through another airlock underneath the dryer directly into a vibratory separator, and then into totes for removal to other parts of the plant.
An interesting design modification for the new dryer is the “D-breeching” fitted to the roof. This attachment extends the roof in the area of the exhaust flange, thus minimizing turbulence and reducing dust carryover.
The dryer can easily handle unplanned changes in feed rate because the essential drying parameters of temperature, layer depth and transfer frequency remain unchanged.
Prior to implementing the new dryer, drying at the automotive parts facility was accomplished by manually spreading a bed of material on the drying trays and loading them into a static oven. The product suffered from non-uniformity due to overdrying at the top of the bed and underdrying at the bottom of the bed.
Abrasion is often a concern when using a continuous dryer for ceramic materials. The new dryer overcomes this problem with its gentle material handling.
Production staff at the automotive parts facility were initially skeptical of the new dryer until they saw one operating in a different part of the plant. They had an opportunity to run the ceramic-wax mixture through the dryer and were immediately impressed, not only with the product quality, but also the dryer’s ease of start-up and operation. They installed one dryer, and on the basis of its excellent operation have ordered two additional dryers for these ceramic mixtures.
The dryer can also be used for other ceramic materials, especially where good temperature control and gentle handling are important. It offers many benefits for ceramic drying, especially when it can replace labor intensive and inefficient drying methods.
**In a stagewise operation, the material spends a fixed time on each shelf before being transferred to the next. Each shelf represents a "stage."