Evacuated,displacement compression molding

Abstract

Abstract A process of molding long thin-wall tubular bodies from thermosetting plastic molding compounds wherein the tubular body lengths may be several times the diameters. The process is accomplished by loading a predetermined quantity of molding compound into a female mold cavity closed at one end by a force mandrel. After closing the other end of the female mold with a balance mandrel, the loaded cavity is evacuated by applying a vacuum of from one-to-five mm. pressure for a period of fifteen-to-thirty minutes. The mold temperature is raised to the minimum temperature at which the resin constituent of the compound will soften or plasticize and a pressure of 2500 p.s.i. is applied by the balance mandrel on the load within the cavity for a period of from five-to-fifteen minutes. while maintaining this vacuum, temperature, and balance mandrel pressure, a pressure of approximately 3500 p.s.i. is applies by the force mandrel onto the compound load to thereby displace the balance mandrel. This normally requires three-to-five minutes for the force mandrel to complete its stroke. The mold temperature is then increased to and maintained at 300-350 degree F. for a period of thirty- to-sixty minutes while maintaining the vacuum and pressure of both mandrels. The force mandrel is force-cooled to effect its thermal shrinkage for easy removal from the tubular article which is left in the female mold. The balance mandrel is then used to push the molded tubular article from the female mold. A mold insert may be attached to the female mold to permit molding of exterior spiral threads on one end of the molded article.

Inventors

• 👤 W Heier

Bibliographic Details