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Process for selectively compressing granular material in a molding box

  • US 4,828,007 A
  • Filed: 12/05/1988
  • Issued: 05/09/1989
  • Est. Priority Date: 12/17/1986
  • Status: Expired due to Term
First Claim
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1. A process for compressing granular material in a molding box having a pattern plate, a casting pattern on said pattern plate and a mold frame mounted on said pattern plate so as to define therewith a mold cavity around said casting pattern comprising the steps of:

  • (a) feeding said granular material to said mold cavity such that said granular material surrounds and covers said casting pattern thereby forming a surface layer of said granular material;

    (b) applying a first pressure surge D1 of compressed medium to said surface layer of said granular material at a first rate of pressure change over time so as to produce a first pressure p1 over said material wherein said granular material fills any irregularities in the casting pattern;

    (c) reducing the pressure over said material to a level p3;

    (d) thereafter applying a second pressure surge D2 of compressed medium to said surface layer of said granular material at a second rate of pressure change over time so as to produce a second pressure p2 over said material wherein said granular material is compressed wherein said second rate of pressure change over time is greater than said first rate of pressure change over time; and

    (e) reducing the pressure over said material to atmospheric pressure.

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