PPP - The RAM Process and Porous Plastic

March 1, 2001
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A prototype of the pressure casting machine that uses synthetic dies.
For more than 50 years, the RAM Process™ has been synonymous with plaster. Companies such as U.S. Gypsum have worked with RAM Products, Inc., to fine-tune and develop plasters such as Ceramical™* specifically for RAM pressing. Potteries and potters using the RAM press made this plaster the product of choice for making press dies to be used with bodies containing approximately 16 to 26% moisture content by weight. For many potteries, plaster is still the product of choice for RAM-pressed dies—but other potteries have begun looking for alternatives.

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.

Synthetic Dies for RAM Pressing

Early in 2000, RAM Products joined ResTech to form ResTechUS. The company immediately set about to improve on the number of pressings that could be successfully produced from the synthetic formulation originally developed by ResTech. The result is a RAM Press die that yields, on average, over 15 times the number of pressings of plaster, yet costs only eight to 10 times more. This means that the initial costs can be quickly recouped through the additional production capabilities of the synthetic dies.

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.

Increasing U.S. Acceptance

Not until successful implementation of pressure casting in the U.S. using these new materials did porous plastic get favorable attention in North America. Even though a limited number of potteries, mostly in the U.K., were using the new materials for wet clay pressing as early as four years ago, many of the major U.S. potteries reviewed and discarded the concepts for a variety of reasons, including cracked and warped dies and insufficient cost benefit ratios. In retrospect, however, the problems had as much to do with the learning curve as it did with a lack of understanding of the materials and their manufacturing techniques.

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.

Improving Pressure Casting Technology

ResTechUS began selling RAM Press dies early in 2000. Some of the most notable potteries in the country are now testing and/or using these dies.

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.

For More Information

For more information about using synthetic molds in RAM pressing, contact RAM Products, Inc., 1091 Stimmel Rd., Columbus, OH 43223; (614) 443-4634; fax (614) 443-4813; e-mail info@ramprocess.com; or visit http://www.ramprocess.com.

*Ceramical is a trademark of USG.

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