Rubber compounding equipment

Tread-type rubber compound extruded in a variety of thicknesses and widths for use in tyre retreading. The standard section is in the shape of a regular trapezium, but variations are made to suit particular types of tyre and different makes of moulding equipment. 

Control of the temperature of rubber compound whilst being processed in extruders and injection moulding machines is vital if the product from these processes is to be uniform in quality. Failure to control temperatures in processing equipment can lead to scorching of the compound as it emerges from the extruder die or injection machine nozzle. Most modem items of processing equipment are fitted to a temperature control unit using either oil or water as the circulatory medium. 

Carbon black Finely divided carbon made by incomplete combustion or decomposition of natural gas or petroleum-based oils in different types of equipment. According to the process and raw material used, it can be furnace (e.g., HAF), thermal (e.g., MT), or channel carbon black (e.g., EPC), each having different characteristics, such as particle size, structure, and morphology. The addition of different types of carbon blacks to rubber compounds results in different processing behavior and vulcanizate properties. 

Rubber manufacturers develop their own rubber compounds suitable for constructing chemical plants and equipment possessing the chemical and physical properties to match the functional... 

Calender - A machine equipped with two or more heavy, internally heated or cooled rolls, used for the continuous sheeting or plying up of rubber compounds. 

ASTM D3182, 1989(2001 )e 1. Standard practice for rubber - Materials, equipment and procedures for mixing standard compounds and preparing standard vulcanized sheets. 

Another option for the production of gas-phase-BR with a well-controlled molar mass comprises a two-step process. In the first step the production of (ungelled) BR with a high molar mass (ML 1 + 4/100 °C) ranging from 70-180 MU is performed. This rubber is well suited for the gas-phase process as it is less sticky than BR with low molar mass. In a subsequent process step the high molar mass BR is masticated in order to make the rubber processable in standard compounding equipment. In the second process step Mooney viscosities (ML 1 + 4/100 °C) are adjusted to the range 10-70 MU [564-567]. 

Electric resistivity. The electric resistance measurement is the same as discussed below under volume resistivity, to which this measurement is temporary adapted. For flexible materials, special electrode systems are developed to clamp sample and electric wires. The measuring equipment is based on a Wheatstone bridge circuit. The conductivity of metal powder-containing epoxy was measured in special dies equipped with built-in brass electrodes inserted to the die. The material was cured in the die to assure good contact with electrodes. Special sample holders and clamping devices are used for precise determination of rubber compounds containing carbon black. ... 

Poly([ethyl acrylate]-g-plvalolactone) was found to be easily processable on conventional rubber working equipment. It was easily processable on a two-roll mill, had excellent calendering properties, could be compression molded at 225-230°C, and could be Injection molded at 225°C. Extrusion was more difficult requiring high temperatures (250°C) and slow extrusion rates. Physical properties of the graft copolymers were similar to those of the parent elastomeric polyacrylates that had been compounded with carbon block and chemically crossllnked. 

In addition to the liquid polysulfides, polysulfide millable gum elastomers have been used for many years with conventional rubber processing equipment. Compounds based on solid elastomers are being used in the manufacture of paint spray hose, rollers, and printing blankets for the graphic arts industry. New applications for these versatile materials are still being developed. 

Stickiness is the ability of a rubber compound to stick to a nonrubber surface such as a metal or textile fabric surface. Excessive stickiness to metal can result in poor release from mills and problems in process equipment. On the other hand, the destruction of compound stickiness can cause slippage of the compound against metal surfaces in extruders or the rotors of an internal mixer. Various compounding additives, such as mill release agent.s or external lubricants, are used to control the level of stickiness. Note, compound stickiness and tackiness are not the same property. 

Some capillary rheometers (such as the Monsanto Processability Tester") are equipped to directly measure the die swell of the rubber compound after it exits the die. This is done with special optical die swell detectors. Running die swell is measured at... 

The EVA copolymers are slightly less flexible than normal rubber compounds but have the advantage of simpler processing since no vulcanization is necessary. The materials have thus been largely used in injection molding in place of plasticized PVC or vulcanized rubber. Typical applications include turntable mats, based pads for small items of office equipment, buttons, car door protection strips, and for other parts where a soft product of good appearance is required. 

Calendering is the forming operation in which the rubber compound is sheeted or spread evenly onto fabric. The calender is a heavy-duty machine equipped with three or more chrome-plated steel rolls that revolve in opposite directions (Figure 14.23). The rolls are heated with steam or circulated water the gearing allows the rollers to operate at variable speeds like the mill rolls. Fabric or wire is passed through the calender rolls, and compound is applied above and below to fully cover the material. 

Until recently, it was generally understood that only a few percent of ground rubber can be used in new tires. Scrap Tire Management Council reports that 5% of recycled tire rubber is used in an original equipment tire for the Ford Windstar. Although no other information on the amount of devulcanized rubber used in new tires is available in open literature, a possibility exists for the use up to 10 wt.% of recycled tire rubber in new tire compounds (Myhre and MacKillop, 2002). It was reported that actual road tests of buck tire containing 10 wt.% of the devulcanized rubber in the tread exhibited tread wear behavior almost equal to that for standard type with the new rubber compound (Fukumori et al., 2002). The increase in the amount of recycled mbber in tires is growing but it is likely that results will not be available for a number of years. 

There are three basic procedures for mixing rubber compounds in an internal mixer namely, the conventional method, the rapid oil addition method, and the upside-down mix method. Many variations of these three methods are also used to suit the special characteristics of individual formulations and equipment. It is, in general, necessary to add particulate fillers early in the mixing cycle, so that good dispersion is achieved as a result of the high shear stress and high viscosity at the lower temperatures then prevailing. Similarly, the oils and plasticizers which reduce viscosity should be added later. Upside-down procedures and variants of it are attempts to implement these ideas in practice. 

The items are those recommended by (a) manufacturers, either in technical bulletins or in Material Safety Data Sheets, (b) the Manufacturing Chemists Association, or (c) the National Safety Coxmcil, for use by personnel while responding to fire or accidental discharge of the chemical. They are intended to protect the lungs, eyes, and skin. There are many plastics and rubber compounding ingredients, as well as the monomers themselves, which are toxic and pose fire and explosion hazards. The user must consult a Material Safety Data Sheet (MSDS) for the specific properties and safety hazards associated with the chemicals handled. An MSDS will provide specific recommendations on the required personal protective equipment that should be used when handling a certain chemical. 

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