CREEP RESISTANT METAL TO PLASTIC INTERCONNECTION

Abstract: A creep resistant metal to plastic interconnection is provided wherein the plastic member (14) is restrained from creeping or pulling apart from a metal member (12) by use of a metal sleeve (16).

Description: TITLE CREEP RESISTANT METAL TO PLASTIC INTERCONNECTION. FIELD OF THE INVENTION This invention relates to a metal to plastic interconnection 5 device. More particularly, the invention relates to a device for interconnecting plastic and metal parts to restrain both axial and circumferential movement of the parts. BACKGROUND OF THE INVENTION Press fitted parts are typically made of metal due to plastic 10 creep problems. Interconnected plastic parts tend to change dimensions and creep or pull apart as they are subjected to stresses and changes in temperature. These changes prevent the parts from maintaining an adequate seal and resist pull out forces. Accordingly, there is a need for a device which fixes the movement between plastic and metal parts for interconnections. 15 SUMMARY OF THE INVENTION The present invention involves an insert molding or post mold press fit of a metal sleeve to the inner diameter of a plastic molded part which is then press fitted to another part. The plastic molded part with the insert is then press fitted to a rigid metal housing. Surprisingly, it has been 20 found that the resistance to creep or pull apart increases during the period after the parts have been press fitted together. This is believed to be due to cold flow of the plastic material into surface imperfections in the rigid metal housing. In another embodiment of the invention a metal sleeve is press 25 fitted over a plastic part, after which a metal or plastic body is inserted into the plastic part. The cold flow characteristic mentioned above also occurs in this embodiment. The invention will be more fully described by reference to the acompanying drawings wherein like numerals refer to like parts. 30 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the interconnection of this "f. invention. FIG. 2 is a longitudinal, sectional view, illustrating the structure and association of the sleeve within plastic and metal parts. 35 FIG. 3 is a cross-sectional view taken along line 3-3. FIG. 4 is an elevational view of another embodiment of the invention in which a base member is plastic and a metal sleeve is fitted onto the outside of the base member. FIG. 5 is a top view of the embodiment shown in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 1-3 of the drawings, rigid base member 12 has an annular opening 10 which extends into base member 12 for receiving plastic body member 14. Plastic body member 14 is cylindrical in shape and is adapted to receive sleeve member 16. The interfitting parts are dimensioned to be press fitted together. With sleeve member 16 in place, plastic body member is press fitted into base member 12 to form an interconnection. In an alternative embodiment shown in FIGS. 4 and 5, sleeve member 16 is positioned over the outer circular surface of plastic base member 22 and cylindrical plastic or metallic member 24 is press fitted into the base member. Member may be hollow or solid. The interconnection of this invention has broad applications wherever plastic and metal parts are joined together. Plastic parts can be made economically by molding processes. These parts are less expensive and lighter in weight than parts which are machined or molded from metal. In addition, the use of thermoplastic parts is particularly desirable from a recycling standpoint. Preferred plastic materials which can be recycled include thermoplastic polyesters such as those disclosed in U.S. Patent 4,352,904. Such materials may contain fillers or reinforcing agents such as glass fibers. Other materials having similar properties such as modified epoxies, polyurethanes, various polyhydrocarbons, acrylics, polyvinyl chloride, polyamides, polyacetals and acrylonitrile may be used. The metal parts for the interconnection may be steel, aluminum, brass or various well known alloys. Typical applications for the interconnection of this invention include engine block and transmission case core plugs, steering wheel gear plugs and numerous other applications where one part is press fitted on the inside or outside of another part. EXAMPLE In one application of the present invention end cap dust covers for an automotive streering rack were fabricated from a reinforced polyester compositon, Rynite ® 545 sold by E. I. du Pont de Nemours & Co. The dust covers were assembled to form an interconnection as shown in FIGS. 1-3. Base member 12 was cast aluminum and metal sleeve 16 was made from mild steel. Pull tests were conducted over a three day period under the environmental conditions shown in the following table: TABLE Press in force for both samples were in excess of 1000 Lbf. Pull out force measured over 850 Lbf at breakage of the end of the cap without any sign of pull out in the press fit area.

Claims: CLAIMS 1. A metal to plastic interconnection comprising a rigid metal base having an annular opening therein for receiving a cylindrical plastic body member, said plastic body member having a longitudinal passage for receiving a metal sleeve, said sleeve extending axially into said plastic body member for a portion of the length of said body member, said body member and said sleeve member being dimensioned to be press fitted into said annular opening in said metal base to form said interconnection. 2. The interconnection of Claim 1 wherein said plastic body member is a thermoplastic member. 3. A metal to plastic interconnection comprising a plastic base member having a circular outer surface and an annular opening for receiving a cylindrical body member, a metal sleeve dimensioned to be press fitted onto the outer surface of said plastic base member, said cylindrical body member being dimensioned to be press fitted into said annular opening of said plastic base member to form said interconnection. 4. The interconnection of Claim 3 wherein said plastic base member is a thermoplastic member.

Inventors: FITHIAN PAUL CHARLES, NELSON KENNETH W JR, FITHIAN, PAUL, CHARLES, NELSON, KENNETH, W., JR.
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: F16B4
IPC codes: F16B4, F16B17, F16L47