Method and apparatus for molding a plate

Abstract

A method and apparatus for molding a plate having highly detailed surface features from a thermosetting resin with a high concentration of a filler such as graphite. The method an apparatus provides for the formation of a preform of casting material and the placement of the material in a cavity mold which is precisely temperature controlled, has vacuum assist operating throughout the molding operation. The molding pressure is rapidly increased to flow the material through the molding cavity prior to the onset of curing and uniquely positioned ejector pins are provided for removal of the molded plate without damage to the detailed surface features.

1 . A process for compression molding of a fine grained mixture of a resin and at least 50% filler material into a highly detailed molded part, comprising the steps of: 
 forming, at a first pressure, a preform of resin and filler mixture in a predetermined weight sufficient for molding the molded part, the cross sectional area of the preform being substantially less than the area of the part to be molded;    positioning the preform in a mold cavity at about the geometrical center of the product outline; and    molding the preform into the molded part by compressing the preform between mold segments defining the mold cavity in a molding machine which closes and applies pressure to the halves of the mold cavity to apply a second pressure to the molded part within a time interval sufficient to fluidize and flow the material to all parts of the mold cavity prior to the onset of curing of the resin in the mold.    
     
     
         2 . The process of  claim 1  wherein the first pressure is at least 400 psi.  
     
     
         3 . The process of  claim 1  wherein the second pressure is at least 300 tons.  
     
     
         4 . The process of  claim 1  wherein the time interval is within about 0.5 to 3 seconds.  
     
     
         5 . The process of  claim 1  wherein the filler material is graphite.  
     
     
         6 . The process of  claim 5  wherein the graphite comprises at least about 50% of the mixture by weight.  
     
     
         7 . The process of  claim 1  wherein the forming of the preform is performed on a separate press  
     
     
         8 . The process of  claim 1  wherein the preform is maintained in a climate controlled environment between the forming and the molding steps.  
     
     
         9 . The process of  claim 1  wherein the molding process also includes applying a vacuum to the mold cavity as it is closed and maintaining the vacuum in the mold cavity throughout the molding process.