Uses of Ebonites

It has been estimated that the consumption of rubber in ebonite products increased on an average of about 6% a year until 1951 when different plastics appeared in the market as competitive materials [6]. But because of the superiority of ebonites in acid and chlorine duties, it still maintains its place in the process industries as a material of construction as evidenced by its increased use in anticorrosive lining of chemical process vessels and tanks for the process industries and rolls for steel and textile and paper and pulp industries. 

The choice between materials for a particular application may be determined by a combination of technical economic and aesthetic considerations. Ebonites have a great dimensional stability in moist conditions with freedom from deterioration caused by oxidation and excellent resistance to various chemicals. The temperature of use is limited where the material is under mechanical load, owing to its comparatively low softening point. This can be overcome by suitable compounding to some extent. A further weakness in appearance is the tendency of ebonite to develop an acid surface and to 

Natural rubber ebonites cannot be produced in brilliant colours which can be obtained with a number of synthetic rubbers like nitrile and resins such as high styrene. Ebonite products can be classified according to their primary uses as mentioned below. 

Water meter components, pipe connectors, piston rings for hot water pumps, textile machinery accessories, and surgical apparatus. 

Chemical resistant pipes and tank lining, moulded anode rings for mercury cells, roller coverings and other chemical equipment linings. 

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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. 

The increased use of rubber in automotive, aerospace, and industrial applications has driven the requirement for strong and robust bonds between rubber and metal. Much literature has been published on the history and technology of bonding rubber to metal [1,2,3,4,5,6,7, 8]. The earliest historical methods of attaching rubber to metal involved attaching the rubber by mechanical means or by the use of ebonite. Mechanical... 

The ebonite compound before cure is a rather soft plastic mass which may be extruded, calendered and moulded on the simple equipment of the type that has been in use in the rubber industry for the last century. In the case of extruded and calendered products vulcanisation is carried out in an air or steam pan. There has been a progressive reduction in the cure times for ebonite mixes over the years from 4-5 hours down to 7-8 minutes. This has been brought about by considerable dilution of the reactive rubber and sulphur by inert fillers, by use of accelerators and an increase in cure temperatures up to 170-180°C. The valuable effect of ebonite dust in reducing the exotherm is shown graphically in Figure 30.3. 

Hard products may also be made by vulcanising rubber (natural or synthetic) using only about two parts of sulphur per 100 parts of rubber. In these cases either the so-called high-styrene resins or phenolie rubber compounding resins are ineorporated into the formulation. These compounds are processed using the methods of rubber technology but, like those of ebonite, the produets are more akin to plastics than to rubbers. Examples of the usage of these materials are to be found in battery boxes, shoe heels and ear washer brushes. 

Initially, vulcanization was accomplished by heating elemental sulfur at a concentration of 8 parts per 100 parts of rubber (phr) for 5 h at 140°C. The addition of zinc oxide reduced the time to 3 h. Accelerator in concentrations as low as 0.5 phr have since reduced time to 1-3 min. As a result, elastomer vulcanization by sulfur without accelerator is no longer of commercial significance. An exception is the use of about 30 or more phr of sulfur, with httle or no accelerator, to produce molded products of hard mbber called ebonite. 

The use of a special ebonite as the thermoplastic material in the printing process of electro typing, a method of producing metal replicas of printing surfaces. 

Ebonite dusts are used in the production of ebonite compounds to minimise and control the exothermic reaction of the crosslinking of large volumes of sulphur with diene rubbers. 

Basic operations such as mastication, mixing, calendering and extrusion are similar for ebonite and soft rubber. The problems, especially in the compounding and vulcanization process which arise in the manufacture of ebonites, are quite different from those with soft rubbers and different tests are used for control of manufacture and for the assessment of the quality of the product. The outstanding differences between ebonites and soft rubbers are detailed below. 

Ebonite is chemically stable and so its resistance to ageing is remarkable and can be achieved without the use of antioxidants unlike soft rubbers. 

Before an item of equipment lined with ebonite or any soft rubber leaves the workshop it is tested for non-porosity. According to regular practice, the only reliable method of determining this is that which makes use of a spark tester or inductor and a test voltage of 20,000 to 25,000 volts. For this purpose the spark tester or the inductor has been proved successful. 

Reductant. Generally, coke or coal is used, but charcoal can be substituted. Ebonite from hard rubber batteries was previously used, mainly as a disposal route, but is now phased out following the decline in the use of the material as a battery case. Some processes smelt whole batteries and employ the polypropylene cases and separators as the reducing agent. 

Rubber linings consist of ebonite or soft rubber based on natural or synthetic polymers. They account for the largest group of materials used for surface protection in chemical plants. Synthetic elastomers are becoming more and more important since they have greater chemical and mechanical stability than natural materials and less susceptibility to mechanical damage. 

Separation and clean-up of ebonite for use as a fuel in conjunction with gas fired burners... 

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