Apparatus for injection molding articles from aminoplastic material

Claim 1

Apparatus for injection molding articles from aminoplastic material, comprising: a. a hopper arranged for receiving and holding aminoplastic material in an unplasticized state; b. a mold including at least two portions which may be joined together to define a mold cavity between the two portions, one portion including an injection opening for allowing the entrance of aminoplastic material into the mold cavity with the opening forming a portion of the molding surface of the mold cavity and with the opening forming from four to 100 percent of the projected cavity area of the mold cavity, the mold further including input means for receiving a first liquiD at a first fixed temperature of a value to allow the setting of the aminoplastic material within the mold cavity, means for circulating the first liquid substantially throughout the mold, and output means for conducting the circulated first liquid out of the mold; c. a metering housing, the housing including an entry from the hopper and an exit for metered aminoplastic material, the housing further including input means for receiving a second liquid at a second fixed temperature of a value to change the aminoplastic material received from the hopper to a fusible state, means for circulating the second liquid substantially throughout the housing, and output means for conducting the circulated liquid out of the housing; d. means, positioned within the metering housing, for metering the aminoplastic material from the hopper to the exit of the metering housing in a controlled fashion; e. a sprue block having an accumulation chamber formed therein arranged to receive the aminoplastic material from the exit of the metering housing, the sprue block further including an input means for receiving the second liquid for maintaining the aminoplastic material in the fusible state, means for circulating the second liquid substantially throughout the sprue block, and output means for conducting the circulated liquid out of the sprue block; f. insulating means positioned between the sprue block and the mold for aiding in maintaining the temperature difference between the sprue block and the mold; g. transfer means arranged at least partially within the sprue block to receive the aminoplastic material from the accumulation chamber and inject the aminoplastic material into the injection opening of the mold, the transfer means including a ram for pushing the aminoplastic material from a position in the transfer means adjacent the accumulation chamber to and into the mold cavity and a transfer cylinder for supporting and guiding the transfer ram, the transfer cylinder extending at least from the accumulation chamber within the sprue block to the mold cavity within the mold to maintain substantially the same area from the accumulation chamber to the mold, the ram including an input means for receiving the first liquid, means for circulating the first liquid in at least the tip of the ram pushing the aminoplastic material, and output means for conducting the circulated liquid out of the ram, the transfer means including means for positioning the tip of the ram pushing the aminoplastic material such that at the end of the stroke of the ram, the ram end forms a portion of the boundary of the mold cavity and substantially fills the injection opening including ram position sensing means for providing a first output to the ram position control means during the portion of the stroke of the ram before the ram tip reaches the mold cavity and for providing a second output to the ram position control means indicating the ram tip is positioned at the boundary of the mold cavity, the first output causing the ram tip positioning means to urge the ram towards the mold and the second output causing the ram tip positioning means to at least momentarily stop the movement of the ram; h. means for supplying the first fixed temperature liquid to the mold and the ram; i. means for supplying the second fixed temperature liquid to the metering housing and the sprue block; j. means for separating the mold portions; and k. mold portion position sensing means for providing a first output to the ram tip positioning means indicating the mold portions are joined and for providing a second output to the ram tip positioning means indicating the mold portions are separated, the second output causing the ram tip positioning means to urge the ram into the mold cavity to thereby separate a molded article from the mold portion adjacent the transfer means, the ram tip positioning means thereafter retracting the ram.