Rubber industry requirements

Special fine-particle kaolin clays are commonly used in rubber compounding as economic diluents, mainly to reduce the cost and improve processability. Clays that are used by the rubber industry require further processing to remove larger particles and impurities, which prevents the decrease of the rubber product s cured physical properties. 

The liquid nitrile rubbers are generally used as nonvolatile and nonextractable plasticizers. They also function as binders and modifiers for epoxy resins. Their moderate heat resistance limits their ability to meet industrial requirements. Hence, attempts have been made to improve their thermal and oxidative resistance by saturating the polymer backbone. 

The use of a PTC, tetramethylammonium hydroxide, to carry out the coupling under aeration of nitrobenzene and aniline to give nitroso diphenylamine (which on catalytic reduction with H2 gives 4-aminodiphenylamine, required in the rubber industry) may be cited as a green chemistry route compared to the established process based on p-nitrochlorobenzene and aniline where Cl is wasted (Bashkin et al. 1999). 

An instrument for measuring temperatures, in the rubber industry the term is usually applied to an instrument for determining the surface temperature of mill and calender rolls, moulds, etc. The instrument is usually based on thermocouples or, where higher accuracy is required, platinum resistance thermometers. Infrared (IR) techniques are now used which have the advantage of non contact but require careful calibration for the emissivity of the surface. 

Petroleum oils are offered to the rubber industry to meet two basic processing and compound requirements to act as a processing additive, or to act as a rubber extender and softener. The classification depends upon the oil volume added to the rubber compound. As processing additives, the oil addition level is usually no more than 5-10 phr for additions in excess of this the oils are regarded as extenders. 

The oil companies supplying the rubber industry claim that there is no effect on ageing properties when sulphur is present in an oil (up to 6% is possible). They claim that the refining removes the active mercaptans and sulphides and the remainder of the sulphur is complexed into polycyclic compounds and there is no evidence that this type of sulphur has any effect on cure. This claim may be true in some circumstances. However, it is known from practical experience that with certain polymers and compounds the claim is incorrect, especially when the high sulphur oils are used as test media. Oils supplied to the same oil specification from oil fields in different parts of the world, and meeting all the requirements of the specification may, because of widely different sulphur levels, have serious effects on high temperature ageing. 

Sulphur in its amorphous form is known in the rubber industry as insoluble sulphur . Insoluble sulphur is used by the rubber industry as, if not converted to the rhombic form by excessive processing heat, it will remain undissolved in the rubber and thus cannot bloom to the surface of the unvulcanised rubber compound. This is a factor which is very important for products which require a number of processing assembly steps in their manufacture. 

A number of the materials used in the rubber industry to prevent sticking of hot rubber compounds to themselves or machinery have a certain degree of environmental hazard associated with them and thus require controlled application. Machinery for this purpose is designed to minimise any atmospheric pollution. 

A large variety of hose constructions are produced by the rubber industry for a wide range of applications. To contain transported liquids, usually under pressure, it is necessary to reinforce the hose construction with fabric, yam or short fibres to constrain expansion of the rubber. Although hand-built construction using fabric still represents a proportion of the production, it is also very common to use yams either braided or knitted directly onto the hose liner. For heavy duty purposes it is also necessary to use wire, in a braided form, to either reinforce or protect the hose from external damage. Use of short fibres as reinforcement represents a small proportion of hose production and requires specialised dies for extrusion to orientate the fibres circumferentially. 

The major manufacturers of factory size processing equipment for the rubber industry also offer a range of equipment of a suitable size for laboratory use. Specific requirements can usually be accommodated in addition to a range of standard equipment. Many of the items will be built to specific demand from the customer. 

In the early days of the rubber industry all mixing was carried out on two-roll mills. Now this situation only occurs occasionally, or when small or expensive batches of material are required, e.g., silicones or fluorocarbons. Mill mixing is an efficient method for breaking down agglomerates and, over a period of time, with good operatives, good homogeneity can be achieved. One batch, however, can take some 30-40 minutes to mix. 

The spreader most commonly found in the rubber industry has a working width across the application roller/blade of 1.5 metres. Wider spreaders (up to 4 metres) exist for very wide cloth coating but they require special control of the bending of the doctor blade and have compensatory mechanisms to overcome this problem. 

Tyre building requires a number of specialised items of equipment, which are specific to this part of the rubber industry. 

Details are given of aBrite-Euram project which is aimed at meeting health, safety and environmental requirements in the European rubber industry through the development of improved formulations. Participants in the four year project, which began in September 1997, include 14... 

A number of techniques have been developed to measure melt viscosity. Some of these are listed in Table 3.8. Rotational viscometers are of varied structures. The Couette cup-and-bob viscometer consists of a stationary inner cylinder, bob, and an outer cylinder, cup, which is rotated. Shear stress is measured in terms of the required torque needed to achieve a fixed rotation rate for a specific radius differential between the radius of the bob and the cup. The Brookfield viscometer is a bob-and-cup viscometer. The Mooney viscometer, often used in the rubber industry, measures the torque needed to revolve a rotor at a specified rate. In the cone-and-plate assemblies the melt is sheared between a flat plate and a broad cone whose apex contacts the plate containing the melt. 

Sometimes particles are encouraged to agglomerate to yield granules, for example, for pharmaceutical applications which may require the addition of liquids or other binders. In the ceramics, paint, plastics and rubber industries, however, reducing or eliminating agglomerate formation is of overriding importance. 

Much carbon disulphide is used in the rubber industry, particularly as a solvent for sulphur chloride in vulcanisation by the cold process or vapour process. It is also employed in the manufacture of numerous organic compounds used for the acceleration of vulcanisation, for example thiocarbanilide, alkyl xanthates (particularly zinc alkyl xanthates) and substituted dithiocarbamates (see p. 262). Many other compounds, such as ammonium thiocyanate and certain organic dyes containing sulphur, also require the use of carbon disulphide in their preparation. 

In the past decades the rapidly expanding automobile industry required increasing numbers of tires with various characteristics. This led not only to the development of new rubber grades, but also to the development of new carbon blacks required by the increasingly refined application processes and to the development of a new and better manufacturing process, the furnace black process. Unlike the old channel black process, this process allows the production of nearly all types of carbon black required by the rubber industry. It also meets the high economic and ecological requirements of our times. 

It can be seen that every type of vulcanization system differs from every other type in the kind and extent of the various changes that together produce the vulcanized state. In the vulcanization processes, consideration must be made for the difference in the thickness of the products involved, the vulcanization temperature and thermal stability of the rubber compound. The word cure to denote vulcanization is believed to have been coined by Charles Goodyear and the same has been a recognized term in rubber industry circles [2]. The conditions of cure will vary over a wide range according to the type of vulcanizate required and the facilities available in a rubber factory. Many factors must be predetermined, including the desired hardness of the product, its overall dimensions, the production turnover required and the pretreatment of the rubber stock prior to vulcanization. Hardness will normally be determined by the composition of the stock but it can also be influenced by the state of cure. 

The rubber industry has traditionally paid more attention to measuring the recovery after removal of an applied stress or strain, i.e. set, than to creep or stress relaxation. This is partly because relatively simple apparatus is required and it is a convenient way to get an indication of the state of cure, but also because it appears at first sight that set is the important parameter when judging sealing efficiency. Set correlates with relaxation only generally and it is actually the force exerted by a seal that usually matters, rather than the amount it would recover if released. 

Current environmental regulations necessitate that new concepts be used in the design of industrial cooling water systems. Equipment selection and component layout related to these regulations are discussed. Special emphasis is given to the power requirements needed for the system. The subject matter for this paper was developed from observations of rubber industry manufacturing operations. 

Covering metallic shafts, rolls and rollers with rubber is required for many applications such designs are used in the textile, printing, and many other industries. For producing coatings, molds with a vertical axis are often filled through inlet holes located along the diameters of the mold... 

Elastomers require, in most applications, to be reinforced by fillers in order to improve their mechanical properties. Carbon black and silica have been used for a long time in the rubber industry to prepare composites with greatly improved properties such as strength, stiffness and wear resistance. These conventional fillers must be used at high loading levels to impart to the material the desired properties (1). The state of filler dispersion and orientation... 

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