Fabrication of Elastomers

Techniques used in the actual fabrication of rubber parts are essentially the same as those discussed for plastics as described previously—compression molding, extrusion, and so on. Furthermore, most rubber materials are vulcanized (Section 15.9), and some are reinforced with carbon black (Section 16.2). 

Concept Chedi 15.14 For a rubber component that is to be vulcanized in its final form, should vulcanization be carried out before or after the forming operation Why Hint You may want to consult Section 15.9. 

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During fabrication of elastomer products like car tires different elastomer formulations often need to be covulcanizes. At the interface between an SBR and an NR layer, an interfacial layer with a modulus higher than either SBR and NR had been detected (145,171). In images detected using Hahn-echo method... 

Latex They constitute an intermediate stage of the bulk of synthetic elastomers, both from a volume and a value standpoint, which are produced today. While varying obviously in composition, the various systems are analogous to natural rubber lattices in that they are an aqueous dispersion of small particles of the particular elastomer. One of the principal advantages of latex technology resides in the fact that it is the oldest method for the fabrication of elastomer or elastomeric coated goods. Thus much of the considerable technology developed for natural rubber lattices was adaptable to synthetic elastomers as they appeared. 

Belt Conveyors. A belt conveyor is made up of an endless fabric or elastomer covered belt that traverses between two or more pulleys, and is supported at intermediate points by idler roUs. These conveyors can handle a wide range of materials, from fine powders to large, lumpy stone and coal. Material can be transported at rates of over 5000 t/h and the conveyors operated at belt speeds ranging from 20 to 300 m /min over very long distances. VersatiHty, reHabiHty, and range of capacities have made belt conveyors the most commonly used bulk handling conveyors in industry. 

Pinch The industrial equivalent of controlling flow bv pinching a soda straw is the pinch valve, Mves of this tvpe use fabric-reinforced elastomer sleeves that completely isolate the process fluid from the metal parts in the valve. The valve is actuated bv applying air pressure directly to the outside of the sleeve, causing it to contract or pinch. Another method is to pinch the sleeve with a linear actuator with a specially attached foot. Pinch valves are used extensively for corrosive material service and erosive sliirrv senice. This type of valve is used in applications with pressure drops up to 10 bar (145 psi),... 

To assess the effect of elastomer degradation on composite performance, additional composites were fabricated with the same 121°C cure epoxy without any addition of the elastomer (211. The expansion behavior of the modified epoxy composite was similar to the toughened material. For electron doses less than 10 rads the CTE of the toughened and untoughened composites were essentially the same which suggests that the epoxy matrix and not the elastomeric component controls the thermal expansion behavior. 

In particular in the case of elastomer fibers, such compounds (in many cases silicone compounds) add up to 2.5-8% of the weight of the fibers. Besides problems in removing these oily components during pretreatment, for example, washing of the textiles, the compounds are then detected in the wastewater in considerable amounts. As the addition of such auxiliaries is required for technical purposes, an optimization of the situation has to be achieved by direct cooperation between the fiber/yarn/fabric producer and the textile dyehouses. 

Polyurethanes are used for the fabrication of fibers, while crosslinked polyurethanes are employed as lacquers and adhesives, as coatings for textiles and paper, and as elastomers and foams. 

By varying the nature of the side chain, R, various elastomers, plastics, films, and fibers have been obtained. These materials tend to be flexible at low temperatures, and water and fire resistant. Some fluoroalkoxy-substituted polymers (R = CHXFJ are so water repellent that they do not interact with living tissues and promise to be useful in fabrication of artificial blood vessels and prosthetic devices. 

Construction fabrics -of EPDM [ELASTOMERS, SYNTHETIC - ETHYLENE-PROPYLENE-DIENE RUBBER] (Vol 8) - [GEOTEXTILES] (Vol 12)... 

The surface of PDMS is hydrophobic which results in poor wettability with aqueous solvents and promotes non-specific protein adsorption. It is also relatively inert to chemical modification [25]. The liquid silicon rubber chosen for fabrication of the reaction plate contained pyrogenic silicic acid as a filler. Aside from its effect on elastomer properties the silicic acid can be expected to provide additional silanol... 

Similar to these hard plastic applications, the use of elastomers has a number of advantages over silicon as biosensor housing material. Besides fabrication cost and brittleness as described above (PDMS is about 50 times less expensive than siUcon on a per volume basis), moving parts are extremely difficult to make in the stiff silicon material without increasing the overall size significantly. Also, valves, which will be discussed in more detail below, need a soft material as valve seat to close completely (thus, elastomers have to be... 

Bayer has developed a process for the ROMP of cyclopentene, giving an allpurpose elastomer, on pilot-plant scale. Raw materials were cheap and the product had properties akin to those of natural rubber. Therefore, it was evaluated for the fabrication of tires. However, because of technical difficulties (the properties of the tires were less satisfactory under driving conditions) this process has never been put into operation. 

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