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Forming Skinned Foam Plastic using Porous Metal Molds

IP.com Disclosure Number: IPCOM000078548D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Raczek, TA: AUTHOR

Abstract

Porous metals or porous mold materials exhibit the property of skinning on expansion cast ABS resins. However the foamed plastic becomes physically embedded in the porous metal during molding and, therefore, is difficult to remove from the mold without fracturing the molded material. A porous metal mold material without a permeable coating can be used only when the mold surface is smooth, the pore size is very small, and the molded part tends to shrink away from the mold surfaces sufficiently, to break away or disengage the embedded plastic. An example of such a part is a molded rod. A molded cylinder shrinks over the inside diameter mold core and is impossible to remove without fracturing the plastic material.

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Forming Skinned Foam Plastic using Porous Metal Molds

Porous metals or porous mold materials exhibit the property of skinning on expansion cast ABS resins. However the foamed plastic becomes physically embedded in the porous metal during molding and, therefore, is difficult to remove from the mold without fracturing the molded material. A porous metal mold material without a permeable coating can be used only when the mold surface is smooth, the pore size is very small, and the molded part tends to shrink away from the mold surfaces sufficiently, to break away or disengage the embedded plastic. An example of such a part is a molded rod. A molded cylinder shrinks over the inside diameter mold core and is impossible to remove without fracturing the plastic material.

In this process, the release of the foam molded plastic can be greatly improved by coating the mold cavity surface of the porous metal, such as sintered bronze, with a RTV Silicone Rubber* coating. The excess is wiped off flush with the cavity surface, while filling the pores of the sintered metal with a gas permeable material which also functions as a mold cavity surface and a release material. For example, a sintered bronze mold material was used as a cavity insert to mold the ratchet wheel portion of a part. Conventional expansion cast ABS would result with a porous tooth surface, or at best, a nominal solid film on the tooth surfaces. By using a porous metal insert to mold the ratchet portion, a def...