While substitute materials have been tried in the past, they often met with limited success. For instance, in the 1970s and early 80s, the RAM Division of The Wallace Murray Corp. developed and sold an alumina-based, hard-fired, porous die known as the “Ceramic Die” for wet clay pressing. However, the high selling cost of the product eventually limited its universal expansion to users requiring extremely long, continuous runs, and the required intermittent cleaning of the die using hazardous liquids further limited its use.
More recently, the expansion and success of pressure casting using porous plastic materials has brought new life to research and development efforts involving RAM Pressing. Companies such as Porvair (see “Synthetic Molds go Mainstream,” Ceramic Industry, December 2000) and ResTech, another U.K.-based company working with synthetics, entered the fray and began developing their products. These synthetic materials are showing a great deal of promise for potteries looking to expand production while reducing their costs.
Porous resins have the added benefit of flexibility. Should the die halves contact each other either on or off the press, the die will give slightly rather than fracture as it would if made of plaster or another rigid material. While plasters used in RAM Press dies may deflect up to 0.003 in. before cracking, porous plastic will actually bend before breaking.
Additionally, the new materials allow potteries to use their dies for short production runs. The pottery can press parts, then clean the die and store it for use at a later date without noticeable die deterioration. The new materials can be drilled, taped, repaired and sanded. Damaged dies have often been restored and placed back into service, a trait not shared by other, less flexible materials.
Harder and stronger resins have been successfully integrated into the cutoff edge of “standard” porous plastic working dies. This marriage of materials provides the normal requirement for the airflow and porosity needed to press and release parts, yet wears more slowly on the cutoff edge. Other hard materials have also been integrated into the cutoff edge with similar success. These advances provide working dies to customers with a production life of over 20,000 cycles and more, easily twice the capability of standard synthetics.
Recently, strong interest in pressure casting led RAM Products to experiment with the concept and build a prototype machine using synthetic dies. The desired properties of the pressure cast mold and the RAM Press die are similar. Strength of material, porosity, cost per manufactured piece and ease of manufacturing with environmental considerations were listed as prime objectives. The requirements to easily operate presses and quickly release finished products are paramount.
Because the dies are more flexible than plaster and can be brought closer together without the risk of fracturing, they provide a closer bite-off. This results in less fettling or sponging and reduced labor cost for finishing. Since the die materials are more resistant to wear, they last longer even though they are run at closer tolerances than plaster. And because these dies last longer and are not changed as often, significant savings in machine setup and tear down time can be achieved, which translates into more machine use in longer production runs. Additionally, users of the new dies are experiencing an increase in yields. And the technology advances do not end there. Experimentation continues with other materials, such as porous steel, cast iron and new resins, polymers and plastics.
With the development of lower-cost pressure casting systems using these newer materials will come new levels of competition and better prices for an industry that has struggled to achieve the dream of profit and prosperity while creating beauty and art.