Method for Making a Shaft Seal

1. Field of the Invention

This invention relates to shaft seals, also known as oil seals, designed for sealing against fluid leakage along shafts such as engine crankshafts and motor vehicle drive transmission shafts, and in a preferred embodiment to shaft seals of the type including a polytetrafluoroethylene sealing element.

2. Description of the Prior Art

Prior art techniques required a forming operation, after molding the seal, to form the polytetrafluoroethylene sealing lip into the desired shape. This later forming operation required additional time, handling, and expense, and if not done perfectly, could result in a seal I.D. that was not concentric with the seal O.D.

It is therefore an object of the present invention to provide an improved method for manufacturing a seal having a polytetrafluoroethylene sealing lip, which method eliminates any post-molding operations and provides a more economical method for producing an improved seal.

A method for manufacturing a shaft seal of the type having a polytetrafluoroethylene sealing lip comprising placing a metal shell (if desired), a synthetic rubber blank prep form and a sintered polytetrafluoroethylene washer in a mold and then closing the mold to simultaneously form (or die-form) the polytetrafluoroethylene sealing lip, mold this elastomer into the desired shape and bond the anchor portion of the polytetrafluoroethylene sealing element to the elastomeric body.

The present invention will be more fully understood be reference to the following detailed description thereof, when read in conjunction with the attached drawings, wherein like reference numerals refer to like elements and wherein:

FIGS. 1-4 are each partial cross-sectional views through different molds for manufacturing, according to the present invention, a shaft seal having a formed polytetrafluoroethylene sealing lip.

With reference now to the drawings, FIG. 1 shows a transfer mold 10 for use in making a shaft seal 12 of the type having a metal shell 14, an annular ring 16 of elastomeric material, such as synthetic rubber, and a flexible, non-elastomeric sealing lip 18 preferably made of polytetrafluoroethylene. In the prior art, a post-molding operation was required in order to form the polytetrafluoroethylene sealing lip 18 into the desired shape. However, according to the present invention, the sealing lip portion of the sealing element 18 is formed into the desired shape at the same time that ring 16 is molded and bonded to the anchor portion of the sealing element 18 and to the metal shell 14. The transfer mold 10 comprises a lower mold cavity section 20, an upper mold cavity section 22, a ram 24, and a center ring 26, all of which mold parts are well-known in the art, including the operation thereof. In making the seal 12, the metal shell 14 is placed in a mold cavity 32 of the mold 10, and then a sintered polytetrafluoroethylene member, preferably in the shape of a flat, annular washer, is placed in the mold, for example, in the position shown by the dotted lines 28. A synthetic rubber blank prep form is then placed in an annular cavity 30 and when the mold is closed to the position shown in FIG. 1, the polytetrafluoroethylene member (28) is formed into a sealing element 18 having the desired shape, as shown, the synthetic rubber is transferred by flowing from the cavity 30 into the mold cavity 32 to produce the annular ring 16, and the annular ring 16 is bonded to the metal shell 14 and to the sealing element 18 all at the same time. This method of manufacture eliminates any post-molding, forming operations and provides a more economical method for producing an improved seal 12. During molding, any excess polytetrafluoroethylene is pinched off, as it also is in the embodiments of FIGS. 2-4. The mold is usually closed for about 3-4 minutes and a temperature of about 360.degree.-400.degree. F. and a pressure of about 16,000-20,000 psi is used in the embodiment shown in FIG. 1, as well as the embodiments shown in FIGS. 2-4.

FIG. 2 shows another transfer mold 40 for making a seal 42 of the type having an annular metal shell 44, an annular ring 46 of elastomeric material forming an auxiliary lip 48, and a polytetrafluoroethylene sealing element 50. The mold 40 includes a lower section 52, a core 54, an upper section 56, a ram 58, a pair of stripper rings 60 and 62, and a plurality of support pins 64 for holding a portion of the metal shell 44 in place as the mold is closed, all of which, and the operation of which, are well-known in the art. The seal 42 is made according to the present invention similarly as was described above with respect to FIG. 1, by placing the metal shell 44 in the mold, placing in the mold a flat, annular polytetrafluoroethylene washer (as shown in FIG. 1 at 28) to form the sealing element 50, and placing a synthetic rubber blank prep form in a cavity 66, and then closing the mold 40 to bond the annular rubber ring 46, the metal shell 44 and the sealing element 50 together while simultaneously molding the ring 46 and forming the sealing lip portion of the sealing element 50 in their desired shapes, with any excess polytetrafluoroethylene pinched off as shown at 68.

FIG. 3, shows a compression mold 70 for use in producing a seal 72 of the type having a metal shell 74, an annular ring 76 of elastomeric material and an annular polytetrafluoroethylene sealing element 78 having a sealing lip 80. The mold 70 includes a lower mold cavity section 82, an upper mold cavity section 84 and a center ring 86. According to the process of the present invention, the shell 74, a flat, annular polytetrafluoroethylene washer and an annular synthetic rubber blank prep form are placed in the mold and then the mold is closed, simultaneously bonding the parts of the seal together while molding the ring 76 and forming the polytetrafluoroethylene sealing element 78 in its desired shape as shown in FIG. 3.

FIG. 4 shows another embodiment of the present invention of a compression mold 90 for making a seal 92 of the type including an annular, elongated elastomeric sleeve 94 having a polytetrafluoroethylene sealing lip 96 bonded to one end thereof. The mold 90 includes a lower mold cavity section 98, an upper mold cavity section 100 and a center ring 102. An annular synthetic rubber blank prep form is placed in the mold along with a polytetrafluoroethylene member in the shape of a flat washer. Upon closing the mold, the elastomeric sleeve 94 is molded and bonded to the polytetrafluoroethylene sealing element 96 and the sealing element 96 is simultaneously formed into the desired shape, with any excess polytetrafluoroethylene being pinched off.

In each of the embodiments described above it is noted that the flexible, non-elastomeric sealing element has a holding or anchoring portion (the flat portion bonded between the shell and the elastomeric body) and a formed sealing lip portion.

This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims. For example, the exact nature such as the shape and material of the metal shells (when used), the shape and nature of the annular elastomeric rings and the shape of the polytetrafluoroethylene sealing elements and their sealing lips need not be identically as shown in the various embodiments of FIGS. 1-4. Further, while the polytetrafluoroethylene is preferably placed in the molds in each of the above embodiments as a flat washer, as shown in FIG. 1, this is not essential and other shapes, such as a disc or a conical form, can be used. To improve bonding between the synthetic rubber portion of each seal and the polytetrafluoroethylene sealing element, the polytetrafluoroethylene element can be etched as is well-known in the art to provide a large number of small pits for the rubber to flow into to provide mechanical bonding. Also, the metal case can be phosphated and cemented prior to insertion in the mold to enhance the production of the chemical bond as is also well-known in the art. The molds can be hydraulically or mechanically closed, for example.