Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
1997-11-24
2001-09-25
Rosenbaum, I Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Assembling or joining
C029S897200, C029S527200, C156S307300, C156S308600
Reexamination Certificate
active
06292995
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of producing a vibration isolation mount assembly comprising at least one metal bracket member bonded to a volume of a resilient elastomeric material. The bonding of the elastomeric material to the metal bracket is improved by electrostatically spraying the metal brackets with an epoxy coating prior to adhering the rubber to the metal bracket members, but after vulcanization of the rubber material. The resulting adhesive bond between the rubber and the epoxy-coated metal bracket is stronger, more corrosion-resistant and capable of surviving a high temperature environment.
BACKGROUND OF THE INVENTION
Vibration isolation mount assemblies, also referred to as engine or powertrain mounts, are used in vehicles to isolate the vibrations produced by the engine and/or powertrain assemblies of a motor vehicle. These assemblies usually are made of two structural members or metal bracket members bonded to a volume of a resilient material, such as rubber, by an adhesive means. These assemblies must be strong enough to withstand the large number of cyclic vibrations associated with engines or powertrains. In addition, the assemblies must be able to withstand the various atmospheric events which cause corrosion of metal components. While satisfying these engineering conditions, the assemblies also must be cost-effective, which means they must be economical to produce from readily available engineering materials associated with automobile manufacture.
Various constructions and methods have been utilized in the past to manufacture engine and powertrain mounts which meet these conditions. One such construction is described in U.S. Pat. No. 4,987,679 to Rau dated Jan. 29, 1991, entitled “Vehicular Powertrain Mount Assembly”. The engine mount of this patent is manufactured from a pair of metal brackets which are bonded to a volume of vulcanized rubber sandwiched between the brackets, at least one of which is a stamped cold-rolled steel. The bonding material between the rubber and the metal brackets is a two part epoxy adhesive. While Rau clearly discloses bonding between metal and rubber, Rau does not disclose the use of any precoating on the metal brackets. However, in order to obtain the required corrosion resistance to withstand the hostile environment of an automotive mount while still avoiding premature failure resulting from stress-corrosion mechanisms, it is necessary to utilize some sort of metal preparation, particularly for ferrous alloys such as steel. Typical metal preparations include zinc coating, phosphate coating or other coating procedure, such as E-coat. Typically, E-coats can survive corrosive conditions, but fail in elevated temperature applications and contain undesirable heavy metal additives such as lead. However, it is well known that structures such as taught by Rau fail generally at the interface between the corrosion-resistant metal coating and the metal, resulting in a debonding between the rubber and the metal. The failure typically is not due to the strength of the adhesive, typically an epoxy, but due to the quality of the adhesion at the adhesive-metal coating interface. Coatings such as phosphate offer good adhesion under dry, ambient conditions, but have inferior performance in extreme conditions since phosphate does not provide sufficient protection from corrosive elements. Since Rau teaches a metal to rubber bond interface, a corrosion-resistant coating must be applied to steel, and all known metal coatings utilized to provide the necessary corrosion resistance also pose some environmental concern for the manufacturer.
U.S. Pat. No. 5,030,515 to Ozawa dated Jul. 9, 1991 provides a different solution for bonding rubber to metal. Ozawa teaches bonding metal to vulcanized rubber by spraying coating or dipping a primer consisting of an epoxidized diene to first coat the metal surface. The primer coat is obtained by mixing diene polymer with epoxidizing agent and filler materials in a solvent. After this epoxidized rubber primer coat is allowed to dry (i.e. the solvent is allowed to evaporate), a covercoat adhesive consisting of a halogenated polymer or rubber adhesive composition is applied over the primer coat, which in turn is allowed to dry. The surface containing the covercoat and the rubber surface are brought together and cured by heating at an elevated temperature, 250°-400° F. (121-205° C.). Clearly the reaction involves joining the covercoat to the unvulcanized thermoset polymer by promoting chemical bonding between the covercoat and the thermoset polymer as the polymer and the covercoat are cured together. Curing the covercoat to a vulcanized thermoset polymer would result in weak bonding and poor adhesion between the polymer and the covercoat. Furthermore, it is well known that such high curing temperatures would degrade vulcanized rubbers. All of the examples of Ozawa support bonding the uncured covercoat to an unvulcanized thermoset material as the materials are simultaneously cured.
U.S. Pat. No. 4,079,168 to Schwemmer dated Mar. 14, 1978 discloses coating a substrate with a fusible powdered epoxy resin coating composition and then heat bonding unvulcanized elastomeric compositions to the coated substrate using two stage adhesive primer systems. However, as Schwemmer notes, whole epoxy resins are generally excellent adhesives, they do not readily bond to cured rubber surfaces. When epoxy paint coating is used to join the materials after vulcanization of the rubber elements, the epoxy coating tends to crack after a period of time resulting in corrosion of the exposed underlying surface. Thus, Schwemmer's solution is to vulcanization-bond the elastomeric rubber to the epoxy-coated substrate through the adhesive system. Thus, chemical bonds are formed between the adhesive and the rubber.
However, no reliable system exists for bonding a metal substrate to vulcanized rubber, while providing both a strong bond and corrosion resistance of the interface between the substrate and the vulcanized rubber.
SUMMARY OF THE INVENTION
The present invention provides a method for bonding a vulcanized rubber surface to a metal substrate. The surface of the metal substrate first is degreased. Then epoxy powder is electrostatically sprayed on the surface of the clean metal substrate so as to cover all exposed areas of the substrate. the powder-coated substrate is then cured at a preselected elevated temperature. A volume of vulcanized rubber is provided. The surface of the rubber which is to be joined to the epoxy coated metal substrate is cleaned with a solvent which does not detrimentally affect the strength of the vulcanized rubber, yet which removes oil, grease, extraneous particles and any fillers or anti-oxidants that may bloom to the surface during or after vulcanization of the rubber. A first chemical pretreatment is applied to the rubber, which increases the surface energy of the rubber and improves its wetting performance. After the rubber surface is pretreated, a bonding agent is applied to the interface between the vulcanized rubber surface and the epoxy-coated metal substrate, and the rubber surface and the metal substrate are placed in contact with each other. Pressure is applied to the parts across the interface while the bonding agent cures so that a strong bond forms across the interface between the vulcanized rubber substrate and the epoxy-coated metal substrate.
An advantage of the present invention is that a vulcanized volume of rubber can be adhered to a metal substrate using an epoxy type adhesive in which the bond interfaces between the vulcanized rubber and the metal substrate can withstand high temperatures for extended periods without separation.
Another advantage of the present invention is that the bond and the metal bracketry are protected from corrosion by the electrostatically-applied epoxy powder coat which is more environmentally friendly than deposition by dipping, spraying etc. Furthermore, the electrostatically-applied epoxy coat is less hazardous to personnel and to
Corbin Douglas C.
Siciliano David G.
Bridgestone Corporation
Cuda Rosenbaum I
Hornickel John H.
Nguyen T.
Palmer Meredith E.
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