Rubber bonds with metal

Rubber bonds well with metallic surfaces with suitable adhesives and this property is well utilized in many applications in the chemical industry, such as lining, metal rubber bonded anti corrosive molded components, diaphragms etc. 

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This is red lead monoxide, used as in inorganic accelerator for the curing of soft natural rubber lining in an autoclave. High temperature curing leads to blooming of lead film, which is the chemical resistance layer, but impairs bonding with metal. 

As with PSA, the phenolics are added primarily for increased cohesive strength and temperature resistance ([216], pp. 284-306). More phenolic is used in adhesives with higher strength requirements, e.g. for metal-metal bonding. Resins based on /j-/-butyl phenolics are most commonly selected ([216], pp. 284-306). They are usually present in the adhesive at 35-50 parts per 100 rubber (phr), with typical optima at 40-45 phr ([216], pp. 284-306). Significant deviation from this optimum may have drastic effects. 

This can be substantially improved by high black and high sulphur compounds. The only bottleneck is that not all metals are conducive to rubber bonding. Carbon steels are better than cast iron for bonding with rubber. Copper and zinc surfaces can be bonded with much ease. 

These same types of compounds are also more resistant to many acids at high temperatures than natural rubber can handle. Neoprene should not be used in parts which are bonded to metal for hydrochloric acid service because acid migration can cause failures. For hydrochloric acid service ebonite lined mild steel equipment is the correct selection. Ebonites form rubber hydrochloride film in contact with natural rubber and this film is the protective layer against corrosion. 

The test piece specified is a cylinder 29 0.5 mm diameter and 12.5 0.5 mm thick which can be used bonded or lubricated, in the former case the rubber can be directly bonded to metal plates or adhered later. Although cutting of the test piece, as opposed to moulding, is allowed, it is debatable as to whether cut test pieces can be readily produced with sufficient precision. In addition to the standard test piece, provision is made for using the product or a part of it but for some curious reason only under lubricated... 

In particular, they found enhanced bonding between metal surfaces and resins such as acrylics (solvent- and water-based), epoxy chlorinated rubbers, silicones, and polysulphides. It was noted that titanium complexes caused colouration with phenolics, whilst zirconium complexes did not. 

The high frictional coefficient (0.4 to 0.5 compared with < 0.1 for glass fibers) of asbestos fibers is crucial to its utilization in the frictional lining sector. In the manufacture of brake and clutch linings 20 to 60% asbestos is incorporated together with fillers, metal chips and preferably phenol resins and rubber into a composite material, which has to satisfy many requirements. Currently there are asbestos-free so-called semimetallic brake linings, which consist of mixtures of metal fibers, metal powders, cellulose fibers, aluminum silicate fibers and mineral wool bonded with synthetic resins. 

Another important use for polyisocyanates is in adhesives, usually as additives to rubber cements. For example, in rubber-to-metal adhesion, a chemical bond probably forms between the rubber and metal by reaction of the isocyanate groups with active hydrogens in the rubber and with the hydrated oxide layer on the metal surface. 

Beyond the particular process of cure in this case, the important problem which should not be neglected is the bonding of the rubber to the metal. This problem of adhesion of rubbers to metals is very weU covered in Reference [27] where a full description of the various tests is given. Another case of interest appears with the cure of a rubber when the cure is bound to various fabrics in order to get proofed materials such as hose. 

Efforts to bond rubber to metal without the use of metal plating led to what is believed to be the first research efforts in surface preparation prior to adhesive bonding. Strong and durable bonds of rubber to metal were necessary for rubber shock mounts for automobiles in the late 1920s, but they were limited to proprietary formulations used on specific metals. In 1927 solvent-based thermoplastic rubber cements for metal-to-rubber bonding were prepared from rubber cyclized by treatment with sulfuric or other strong acids. With these rubber cements strong bonds could be made to either vulcanized or unvulcanized rubber. 

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