Ebonite Bonding

The anti-abrasive or anti-corrosive rubber linings are applied to the metal surface by adopting different kinds of bonding systems such as ebonite bonding, chemical adhesive bonding or self-vulcanising cement bonding. 

Ebonite bonding The adhesive layer in this case is unvulcanized ebonite (or hard rubber , USA) applied to the metal either as a solution or as a thin sheet" Ebonite contains 30-50 parts sulphur per hundred parts of rubber (phr), whereas soft rubber seldom has more than 3 parts phr of this vulcanizing agent. The method dates back to the mid-nineteenth century and is most closely identified with natural rubber, but can be applied to other diene-type elastomers, including nitrile rubber. 

During vulcanization, sulphur can migrate from the ebonite layer to the rubber and may result in the formation of an interlayer of highly cross-linked rubber having poor physical properties. Formation of such a layer may be avoided if a second adhesive coat consisting of the rubber mix without sulphur is applied. Since ebonite softens at higher temperatures (e.g. 80 °C in the case of a natural rubber system), the use of ebonite bonding is restricted to service temperatures near ambient. 

In applications where tack of the adhesive is required, for example, tank linings or rubber-covered rollers, ebonite bonding is often found to be more suitable than proprietary bonding systems. 

Unless test coupons are produced alongside the lining, the only method of testing the vulcanisation state is with a hand hardness meter. A Shore A or IRHD meter is used for soft rubber linings and a Shore D meter for ebonites. The usual specification is that the hardness has to conform to 5° of the specified hardness. There is no quantitative non-destructive test for the strength of the bond between the lining and the substrate and so such tests are usually carried out in the laboratory on a sample prepared from the materials used. 

However, for construction purposes, solid ebonites were chosen. As is known from rubber chemistry, solid ebonite, commonly known as hard rubber, is a polymer material with sulfur content used for vulcanization. Ebonite, like elastomeric or flexible rubber, is made from a combination of sulfur with polydienes (unsaturated rubbers containing double bonds). The sulfur and polydienes are combined with some auxiliary additives and heated to produce vulcanization. Typical mass ratios of sulfur to rubber are 2 100 for elastomeric rubber and 40 100 for hard rubber. Due to the large degree of sulfide cross linking formed in the vulcanization process, solid ebonite is a hard, non-flexible, plastic-like material possessed of... 

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. 

If the sulfur atoms are not part of the polymeric backbone, the polymers are not included in this class. For example, in the vulcanization process of the polymers with unsaturated carbon chain backbone, -S-S- bonds are introduced in the polymer, but the resulting product is not classified as polymer with C-S bonds in the backbone, although in hard rubber (ebonite), for example, the content of sulfur can be as high as 32%. 

From the specific spectra of secondary ions (Fig. 14.2) and comparison between normalized counts for particular cases (Fig. 14.3) it follows, that the highest amount of sulfur, in a form of SH- ions, was transferred to the surface layer of iron counterface by ebonite. In the case of polysulphone, due to strong sulfur bonding to macromolecular backbone (Fig. 14.4) and different from other polymers studied mechanisms of mechano-degrada-tion, the expected effect of sulfur transfer is practically absent. 

A modified ebonite method was developed [134] to study the interfaces associated with polymer tire cords. Hre cords composed of PET, rayon or nylon fibers are generally bonded to rubber with a resorcinol-formaldehyde-latex (RFL) adhesive. The nature of the interfaces is of interest in tire... 

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