SEAL CONSTRUCTION FOR A MOLD STRUCTURE FOR ENCAPSULATING GLASS WITH A GASKET

Abstract: A unique dynamic seal assembly is used in a mold structure for encapsulat­ ing a glass window assembly with a gas­ ket. The seal assembly resiliently sup­ ports the window assembly (30) and cooperates with the mold structure (31) for defining a gasket forming cavity (45, 46). The mould structure typically in­ cludes two cooperating mold sections (32, 33) each of which can be provided with a groove (37, 43) for receiving a sep­ arate dynamic seal assembly. Each seal assembly includes a first sealing body (42, 70, 90, 120) having a sealing surface which faces and is adapted to sealingly contact the window assembly. The first seal (47, 48, 73, 92, 122) element is formed of a non-deformable, non-com­ pressible material and is connected to a second seal element (49, 75, 93, 123) formed of a deformable, non-compressi­ ble material which is responsive to pres­ sure applied to the first seal element for adjusting the position of the first seal ele­ ment in the mold to accommodate thickness variations in a window assembly contacting the first surface. The first seal ele­ ment is typically formed of a Teflon material and is movable in a vertical direction to accommodate thickness variations in a window assembly contacting the first sealing surface. The second seal element is formed of a silicone rubber material or is a tube (123) filled with a non-compressible fluid.

Description: Technical Field The present invention relates to a seal assembly for use in an injection molding process and, more particularly, to a seal assembly for use in a mold for making encapsulated window structures. Background Art Initially, fixed window assemblies for vehicles were comprised of a plurality of elements including adhesive sealants applied around the marginal edges of a glass sheet, suitable mechanical fasteners such as metal clips, and exterior decorative trim strips disposed to cover the junction between the marginal edges of the glass sheet and the adjacent portions of the vehicle frame. Such window structures were costly, especially from a labor standpoint, since it was necessary to assemble the individual elements along the vehicle assembly line. Subsequently, in an endeavor to improve the above window structure, unitary window assemblies of the type illustrated in U.S. Patent No. 4,072,340 were developed. These window assemblies included a sheet of glass, an adjacent frame, and a casing or gasket of molded material, such as polyvinylchloride, extending between the frame and the peripheral edge of the window to hold the sheet of glass and the frame together. Fasteners were provided at spaced locations along the frame such that the entire assembly could be guided into a location over the opening in a vehicle body as a unit. Other types of unitary window assemblies are disclosed in U. S. Patents Nos. 3,759,004 and 4,364,595. While such unitary window structures greatly reduce the time required to mount the window assembly in an associated vehicle, such structures are relatively costly, since the individual components required to produce each window assembly generally must be manually assembled. Recently, window assemblies have been formed by encapsulating at least a portion of the periphery of a sheet of glass with a gasket material. Typically, the gasket is formed by curing a polymeric gasket-forming material in situ on the glass sheet to encapsulate a predetermined portion of the marginal edge of the sheet. The gasket can be polyurethane and formed, for example, by a reaction injection molding process. A mold structure which can be utilized to encapsulate a glass sheet with an integrally molded gasket is disclosed in U.S. Patent No. 4,561,625 issued to W. R. Weaver and assigned to the assignee of the present invention. In this patent, the mold structure includes at least two mold sections having facing surfaces cooperating to define a chamber for receiving a glass sheet. A resilient seal means is positioned in at least one of the mold sections about at least a portion of the periphery of the chamber and functions to resiliently support the glass sheet within the chamber. Each mold section includes a metallic main body portion, and the seal means maintains at least the portion of the glass sheet located inwardly of the seal means in spaced-apart relationship with the metallic main body portions of the mold sections. Also, in the Weaver patent, the seal means cooperates with predetermined portions of the glass sheet and the mold sections for defining a gasket forming cavity having a configuration corresponding to the gasket to be formed on the glass sheet. At least a portion of the facing surfaces of the mold sections disposed outwardly of the gasket forming cavity are in metal-to-metal contact with one another. This enables the amount the seal means is compressed and the dimensions of the gasket to be controlled. The prior art seals are typically deformable, static silicone rubber or Teflon® coated elastomeric seals. In order to accommodate differences in contour or edge profile which occur between individual glass sheets, these seals must be deformed sufficiently to fill "low spots" and prevent gaps between the glass and the seal which would cause excessive flash formation on the gasket being molded. This deformation causes very high pressure on the high spots, resulting in seal fatigue and leading to premature seal failure. In some instances, the excessive pressure may cause breakage of the glass sheet. In all cases excess pressure distorts the seal contour resulting in distorted molded gasket shapes. Disclosure of the Invention The present invention relates to a unique seal assembly for a mold structure for molding a gasket in situ around the periphery of a glass window assembly. The seal assembly is adapted to resiliently support the window assembly within the mold structure and cooperates with the mold structure for defining a gasket forming cavity. One seal structure of the present invention is dynamic and includes a deformable seal element which automatically compensates for pressure differentials caused by low and high spots in the sheet of glass. With the present invention, excessive pressure generated at a high spot on the glass is transferred to an adjacent low spot to equalize the pressure along the whole length of the seal. More specifically, the mold structure typically includes two cooperating mold sections, each of which can be provided with a groove for receiving a separate dynamic seal assembly. Each seal assembly can be of the dynamic type or one of the seal assemblies can be a static type. The dynamic type seal includes a first seal element formed of a non-deformable, non-compressible material having a first surface adapted to sealingly contact a window assembly. The seal assembly also includes a second seal element formed of deformable, non-compressible material and connected to the first seal element and responsive to pressure applied to the first seal element for adjusting the position of the first seal element in a mold to accommodate thickness variations in a window assembly contacting the first surface. In one embodiment, the second seal element is formed of a rubber material having a durometer hardness of approximately seventy. In another embodiment, the second seal element is a fluid filled bladder positioned between the first seal element and the cooperating mold section. In either case, when increased pressure is applied to a local area of the seal as a result of a contour difference between the seal and the window assembly, the second seal element deforms to automatically transfer at least a portion of the applied pressure to adjacent areas of the seal. Such a seal construction produces a more effective seal and reduces seal fatigue, thereby increasing the life of the seal, and assures molding an undistorted, true to design, molded gasket. The first seal element can be formed of a non-deformable, non-compressible material such as a Teflon material having a durometer hardness of approximately ninety. It is accordingly an object of the invention to produce an encapsulation seal useful in the production of flash-free plastic material encapsulated products. The resultant seal structure may be satisfactorily utilized in the production of encapsulated glass sheet products to provide the desired flash-free product without subjecting the glass assembly to excessive stresses which might otherwise cause breakage of the glass. Brief Description of the Drawings In the accompanying drawings: Figure 1 is a fragmentary sectional view of a prior art window assembly and mold structure; Figure 2 is a fragmentary elevational view of the prior art window assembly and seal of Figure 1; Figure 3 is a fragmentary sectional view of a window assembly and mold structure incorporating a seal assembly in accordance with the present invention; and Figure 4 is a fragmentary sectional view of an alternate embodiment of the seal assembly shown in Figure 3. Statement of the Invention In accordance with the present invention, there is provided a seal assembly for a mold for encapsulating a window assembly, comprising a first seal element formed of a substantially non-deformable, non-compressible material and having a first surface adapted to sealingly contact a window assembly, and a second seal element formed of a deformable, non-compressible material and connected to said first seal element and responsive to pressure applied to said first seal element for adjusting the position of said first seal element in a mold to accommodate thickness variations in a window assembly contacting said first surface. Description of the Preffered Embodiment There is shown in Fig. 1 a window assembly 10 positioned within a mold structure 11 utilizing a seal according to a prior art mold structure of the type disclosed in above-mentioned U.S. Patent No. 4,561,625, which is herein incorporated by reference. The mold structure 11 includes a lower section 12 and an upper section 13 which are coupled to suitable means (not shown) for opening and closing the mold sections 12 and 13. The mold structures 12 and 13 are typically formed of a rigid material such as, for example, steel or aluminum. Also, each of the mold sections 12 and 13 can be provided with passageways (not shown) for circulating a suitable coolant or heating fluid through the respective mold sections. The mold sections 12 and 13 are provided with recessed portions 14 and 15 respectively in facing relationship to one another such that, when the mold sections are closed, the recessed portions 14 and 15 cooperate to define a sheet receiving or glass clearance chamber for receiving the window assembly 10 on which a gasket is to be formed. When the mold sections are open, the window assembly 10 is positioned on the lower section 12 so that the outer peripheral portion of the lower surface of the glass rests on a resilient lower seal 16 positioned within a groove 17 formed in the upper surface of the lower section 12. After the window assembly 10 is suitably positioned on the seal 16 of the lower mold section 12, the upper mold section 13 is lowered into position to enable the outer peripheral portions of the facing surfaces 18 and 19 of the cooperating mold sections 12 and 13 respectively to be clamped in metal-to-metal contact, as shown in Fig. 1. The upper mold section 13 carries a resilient upper seal 20 positioned in a groove 21 formed opposite the groove 17. The upper seal 20 cooperates with the lower seal 16 to press yieldingly against the glass sheet window assembly 10 and resiliently support the window assembly within the glass clearance chamber. The chamber or space between the surfaces of the recessed portions 14 and 15 is slightly larger than the thickness of the window assembly 10. However, it will be appreciated that the glass clearance chamber can be formed of any shape as long as the chamber is sufficiently large to avoid any glass-to-metal contact between the glass sheets of the window assembly 10 and the metallic mold sections 12 and 13. For example, the portions of the mold sections 12 and 13 which are below and above respectively the central portion of the glass sheet window assembly 10 can be removed such that each mold section will be generally ring-shaped. The seals 16 and 20 are preferably formed of a silicone rubber material and secured within the respective grooves 17 and 21 by means of a suitable adhesive. In addition to resiliently supporting the window assembly 10 within the glass clearance chamber, the seals 16 and 20 cooperate with selected portions of the window assembly 10 and the mold sections 12 and 13 for defining a gasket forming cavity utilized to form a gasket 22 about the peripheral edge of the window assembly 10. More specifically, in Fig. 1, the gasket forming cavity is defined by the cooperation of a lower gasket shaping surface 23 of the lower mold section 12, an upper gasket shaping surface 24 of the upper mold section 13, portions 16a and 20a of the seals 16 and 20 respectively, and the peripheral edge portion of the window assembly 10. The gasket forming cavity can be constructed to form the gasket 22 on either the entire periphery of the window assembly 10, or on a selected peripheral portion. Once the mold sections are closed, a flowable polymeric gasket forming material can be injected into the cavity through suitable inlet means (not shown). Referring to Fig. 2, there is show an elevational view of a portion of the window assembly 10 and the lower seal 16. While the seal 16 ideally constructed with a contour which conforms to the contour of the edge of the window assembly 10, due to the normal glass forming and bending operations, the window assembly often has a contour which is slightly different from the contour of the seal 16. In Fig. 2, there is shown at 25 a difference in contour between a peripheral edge portion of the window assembly 10 and an upwardly facing portion of the seal 16. The lower surface of the window assembly 10 in the area 25 is spaced upwardly from the seal 16 when the window assembly is placed in the upper surface of the seal 16. The contour difference 25 forms a space or gap 26 which, prior to the injection of the gasket forming material, must be sealed in order to prevent leakage of the gasket forming material past the seal 16, thereby producing undesirable flash on the finished gasket. When the upper mold section is placed on the top of the window assembly 10, pressure is applied in the direction of the arrow 27. The gasket 16 will tend to deform by compressing in the regions on either side of the gap 26 and, if enough pressure is applied, the region of the gasket 16 adjacent the contour difference area 25 will contact the facing surface of the window assembly 10 to eliminate the gap 26. However, when such contact occurs, relatively little pressure is applied to the seal 16 by the area 25 of the window assembly 10, thereby increasing the possibility of a blowout which will allow leakage of the gasket forming material and prevent fill-out resulting in an incomplete gasket. In addition, the regions of the seal 16 on either side of the gap 26 are subjected to increased pressure which causes increased seal fatigue and results in premature seal failure. Further, if the increased pressure is excessive, breakage of the window assembly can occur. There is shown in Figure 3 a seal assembly according to the present invention. A window assembly 30, similar to the window assembly 10, is positioned in a mold 31 having a lower section 32 and an upper section 33. The mold sections 32 and 33 are typically formed of a metallic material and have recessed portions 34 and 35 respectively to form a chamber for receiving the window assembly 30 and preventing glass-to-metal contact between the window assembly and the mold sections. A stationary lower seal body 36, constructed of a substantially non-deformable, non-compressible material such as Teflon (registered Trade Mark) material having a nenty durometer hardness, is positioned in a groove 37 and has a sealing surface 36a which engages a lower surface of the window assembly 30 to support the window assembly above the lower section 32. The groove 37 has an upwardly facing bottom wall 39 upon which the seal 36 rests and a side wall 40 against which the seal 36 is retained by a clamp 41. The clamp 41 can be retained in the groove 37 by any suitable fastener means. An upper seal body 42 is constructed of three sections and is located in a groove 43 formed in the upper section 33 and has a sealing surface which engages the window assembly 30. The upper seal 42 is retained in the groove 43 by a clamp 44 which in turn can be retained in the groove 43 by any suitable fastener means. The lower section 32 and the upper section 33 have a lower cavity 45 and an upper cavity 46 respectively formed therein for forming a gasket which is similar to the gasket 24 in Figure 1. The upper seal body 42 includes an outer section 47, a center section 48, and an inner section 49. The outer section 47 and the center section 48 can be formed of a non-deformable, non-compressible material such as Teflon (registered Trade Mark) material having a ninety durometer hardness. The inner section 49 can be formed of a deformable, non-compressible material such as silicone rubber having a seventy durometer hardness. The outer section 47 is similar in shape to the lower seal body 36 and abuts a side wall 50 of the groove 43 formed in the upper mold section 33. The outer section 47 also rests against a bottom wall 51 of the groove 43 and is of such a length that it does not extend out of the groove 43 and into the upper cavity 46. The center section 48 includes a sealing surface 52 which engages an upper surface of the window assembly 30. A V-shaped groove 53 is formed in a side wall of the center section 48 abutting the inner section 49 and adjacent the end of the center section 48 opposite the sealing surface 52. The center section 48 is spaced from the bottom wall 51 of the groove 43 and the sealing surface 52 extends beyond the adjacent end of the outer section 47. One end of the inner section 49 is formed with a generally planar surface 54 which abuts the bottom wall 51 of the groove 43. A side wall of the inner section 49 abutting the center section 48 extends into the groove 53 and partially covers the end of the center section 48 adjacent the groove 53 leaving a gap 55 between the outer section 47 and the inner section 49. The opposite side wall of the inner section 49 includes a first planar surface 56 abutting a surface of the clamp 44. A second planar surface 57 of the side wall extends from the planar surface 54 to an intersection with an edge of the planar surface 56. The surfaces 56 and 57 are formed at an angle with respect to the vertical such that the side wall defined by these surfaces extends outwardly. The inner section 49 also has an outwardly extending sealing surface end defined by a pair of planar surfaces 58 and 59. The planar surface 58 intersects the planar surface 56 along one edge and intersects the planar surface 59 along an opposite edge. The planar surface 59 intersects the side wall of the inner section 49 which abuts the center section 48. When the lower mold section 32 and the upper mold section 33 are closed together such that a facing surface 60 of the lower section 32 contacts a facing surface 61 of the upper section 33, the sealing surface 38 of the lower seal body 36 will contact the lower surface of the window assembly 30. The lower seal body 36 will prevent gasket forming material in the lower cavity 45 from entering the groove 37 and the recessed portion 34 of the lower mold section 32 thereby preventing the formation of flash. At the same time, the sealing surface 52 of the center section 48 will contact the upper surface of the window assembly 30 to prevent gasket forming material in the upper cavity 46 from entering the groove 43 and the recessed portion 35 of the upper mold section 33. However, since the thickness of the window assembly 30 will vary from unit to unit, the center section 48 will accommodate such variations in a generally vertical direction by sliding against the outer section 47 while deforming the inner section 49 as required. The section 47 also provides a glass contacting surface to accommodate misaligned or oversized sheets. The length of sheets can vary due to variations in curvature from one sheet to another. Thus, the lower seal body 36 functions as a static seal while the upper seal body 42 functions as a dynamic seal. In some applications, it may be desirable to eliminate the outer section 47 such as where the upper seal body 42 will abut an insert to be molded into the gasket. Also, the outer section 47 could be utilized between the lower seal body 36 and the side wall 40 in the lower mold section 32 as a spacer. Typically, the upper and lower seals extend around those portions of the window periphery to which the gasket is to be molded. If the gasket is to be formed around the entire periphery of the window assembly, the upper and lower seals in the mold will be formed as rings.

Claims: A seal assembly, for a mold for encapsulating a window assembly (30) comprising a first seal element (48) formed of a first material which is non-compressible, including a first surface adapted to sealingly contact a window assembly, a second surface, and a third surface, a second seal element 49 formed of a material which is deformable relative to the material used for the seal (48) and which is also non-compressible, including a first surface abutting said second surface of said first seal element, the second seal element responsive to pressure applied to the first seal element for adjusting the position of the first seal element in the mold, thereby accommodating thickness variations in the window assembly contacting the first surface of the first seal characterised in that a third seal element (47) is provided, formed of a non-compressible material which is non-deformable relative to the material used for the second seal, including a first surface abutting the third surface of the first seal element. The seal assembly, according to Claim 1, wherein the first seal element (48) has a durometer hardness of about 90. The seal assembly, according to Claim 1, wherein the second seal element (49) has a durometer hardness of about 70. The seal assembly, according to Claim 1, wherein the first seal element (48) is formed of a polytetrafluoroethylene material. The seal assembly, according to Claim 1, wherein the second seal (49) element is formed of a silicone rubber material. The seal assembly, according to Claim 1, further comprising clamp means (44) for retaining the first, second, and third seal elements in the mold. The seal assembly, according to Claim 1, wherein the first seal element (48) includes a generally V-shaped notch (53) formed in the second surface thereof, the second seal element (49) extending into the generally V-shaped notch.

Inventors: BARTECK, WERNER, W.
Applicants: LIBBEY-OWENS-FORD CO.
Application year: 1988
Main classification: B29C39
IPC codes: B29C39, F16J15, B29L31, B29C33, B60J1