APPARATUS FOR SINGLE CAVITY INJECTION MOLDING OF OIL SEALS

• US 3,754,846 A
• Filed: 01/21/1972
• Issued: 08/28/1973
• Est. Priority Date: 01/21/1972
• Status: Expired due to Term

• Current Assignee: James Robert Choate
• Original Assignee: James Robert Choate
• Inventors: Choate, James Robert
• Primary Examiner(s): Lazarus, Richard B.
• Application Number:
  US05/219,615
• Time in Patent Office: 585 Days
• Field of Search: 425/180,249,117,129,809,812,125,242,DIG.60,405 264/102
• US Class Current: 425/125
• CPC Class Codes: B29C 2045/0098 shearing of the moulding material, e.g. for obtaining molecular orientation or reducing the viscosity B29C45/0082 takes precedence
• CPC Class Codes: B29C 2045/14459 injecting seal elements
• CPC Class Codes: B29C 45/14 incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles B29C45/1671 takes precedence
• CPC Class Codes: B29C 45/14336 Coating a portion of the article, e.g. the edge of the article B29C45/14573 and B29C45/14598 take precedence
• CPC Class Codes: B29C 45/34 having venting means
• CPC Class Codes: Y10S 425/047 Seal ring
• CPC Class Codes: Y10S 425/06 Vacuum
• CPC Class Codes: Y10S 425/812 Venting

Abstract

In the repetitive single cavity injection molding of an oil seal reinforced with a casing, with vacuum being applied to the mold cavity, the molding composition is forced rapidly through fine orifices under high pressure and high internal shear into the mold cavity so that a predominant amount of the heat required for curing comes from the mechanical working. A three-part mold of special design is used wherein the orifices are annularly spaced about and formed between the mold top through which injection occurs and a center piece that defines the interior walls of the oil seal. The center piece is of a special three-part construction so that it functions as a vacuum valve and to assist in ejection of the completed seal. A casing of special design is used and mold pins are not required to support and align the casing.

Claims

1. A single cavity injection mold of at least three pieces defining a mold cavity of circular configuration having a common center line, said pieces comprising:

i. a mold top defining at least in part a fine orifice into said mold cavity and having an injection conduit connecting said fine orifice with a source of molding composition;

ii. a mating mold bottom adapted to accomodate and mate with a center piece; and

iii. a center piece extending through said mold bottom, mating therewith and defining at least in part an interior wall of the object to be molded, said center piece having a frusto-conical lower portion serving as a valve and mating with said mold bottom as a valve seat, a conduit connecting an evacuating means with said valve seat, said center piece being moveable a few thousandths of an inch upward into said mold cavity to open said valve and to free the molded article from said mold bottom, said valve including means for maintaining said valve in an open position as said mold cavity is being closed, evacuating means for placing a vacuum on said mold cavity through said valve means for closing said valve for of injection of a molding composition into said mold cavity.

2. a mold bottom mating therewith and adapted to accommodate and mate with a center piece;

and

3. The mold of claim 1 when adapted to mold a circular oil seal with a metal casing insert, and wherein said center piece is composed of three sections:

a stem, an intermediate section, and a top section, said top and intermediate section defining the interior surfaces of said oil seal and the critical oil seal lip, and said intermediate section having the diameter of the largest internal diameter of said oil seal.

4. The mold of claim 3 wherein An upper edge of said center piece and an inner wall of said mold top form said fine orifice, the same being annular, and wherein said mold top contains an annular accumulation and distribution cavity disposed between said fine orifice and said source of said molding composition, and wherein the mold parts mate to form a flashless joint about the outer circumference of said oil seal.

5. The mold of claim 4 wherein said top surface of said center piece forms with the under surface of said mold top a disk-shaped distribution conduit connecting said source of molding composition with said accumulation and distribution cavity.

6. The mold of claim 5 wherein said top section extends through said casing insert, wherein the diameter of said annular orifice lies within the largest diameter of said top section, and wherein the design of said oil seal is such that said oil seal is capable of being stripped off said center peice over said top section.

7. The mold of claim 3 wherein there are at least three of said fine orifices uniformly spaced about said injection conduit, the same being centrally located, said orifices being individually connected thereto by radial sprues, said critical oil seal lip being positioned in said mold cavity at a point remote from said injection orifices.

8. The mold of claim 7 wherein said top section of said center piece is recessed to form a flash lock connecting with the material in said sprues, wherein said center piece contains ejecting means for ejecting said flash lock, said flash lock along with the material in said sprues being first extracted from said mold top during mold opening and thereafter being ejected from said center piece with said ejecting means.

9. The mold of claim 7 wherein said top section of said center piece and the bottom surface of said mold top meet to form a flash-less joint at the inner periphery of said oil seal, and the mold parts are lightly gapped externally and circumferentially about said oil seal to form a flash joint.

10. The mold of claim 1 comprising in addition a removeable bridge section circular about said center line, inset in said mold top in the face thereof contiguous to said mold cavity, and defining with said mold top at least three radial distribution runners running between said bridge section and mold top from said injection conduit towards the periphery of said mold cavity which runners terminate in orifices downwardly directed into said mold cavity.

11. In a single cavity injection mold adapted to the repetitive molding of a circular shaft seal having an interior elastomeric sealing lip reinforced with a cylindrical case thereabout, said mold comprising at least three main circular sections having a common center line and defining a mold cavity, viz:

12. The mold of claim 11 wherein said upwardly-directed knife-edge sealing lip is located near the annular edge of said center piece and wherein after said mold is closed and the seals are established by said knife-edge sealing lips said ejector is adapted to be in the raised position to permit the application of vacuum through said seat and to be closed upon the commencement of injection.