Elastomer Processing
Generally elastomer processing involves two major steps. First one is the designing of a mixing formulation for a specific end-use and the second one is the production process by which rubber compound is transformed into final product. When designing a mi
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Abstract Generally elastomer processing involves two major steps. First one is the designing of a mixing formulation for a specific end-use and the second one is the production process by which rubber compound is transformed into final product. When designing a mixing formulation the compounder must take account not only of those vulcanisate properties essential to satisfy service requirements but also cost of the raw materials and the production process. There should always be a compromise between cost of production and quality of the product. This chapter is an attempt to deal with different processing techniques normally used in the rubber industry.
1 Introduction The processing of a rubber formulation is a very important aspect of rubber compounding [1]. The raw polymer can be softened either by mechanical work termed mastication or by chemicals known as peptisers. Under processing conditions various rubber chemicals, fillers and other additives can be added and mixed into the rubber to form an uncured rubber compound. These compounding ingredients are generally added to the rubber through one of the two basic type of mixers; two roll mill or internal mixers.
2 Two Roll Mill The first use of the two roll mill was in the 1830s in USA. Hancock’s Pickle was patented in 1837, although models had actually been in use from the early 1820s. M. A. Fancy R. Joseph S. Varghese (&) Technical Consultancy Division, Rubber Research Institute of India, Kottayam 686 009 Kerala, India e-mail: [email protected]
P. M. Visakh et al. (eds.), Advances in Elastomers I, Advanced Structured Materials 11, DOI: 10.1007/978-3-642-20925-3_5, Springer-Verlag Berlin Heidelberg 2013
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Fig. 1 Two-roll rubber mixing mill (Website for this image: http:// gdrubbermachine.com)
The first machine that appears suitable for rubber was a twin rotor design patented by Paul Pfleiderer in 1878/1879 [2]. Two roll mill consists of two horizontal, parallel heavy metal rolls which can be jacketed with steam and water to control the temperature [1–17]. These rolls are connected to the motor through gears to adjust the speed. Rolls turn towards each other with a pre set adjustable gap or nip to allow the rubber to pass through to achieve high shear mixing (Fig. 1).
2.1 Friction Ratio The speed of the two rolls is often different [41–46]. The back roll usually turns at a faster speed than the front roll, this difference increases the shear force. The difference in roll speeds is called friction ratio, which is dependent upon the mill’s use. For natural rubber mixing a ratio of 1:1.25 for the front to back roll is common [3].
2.2 Cooling Cooling is employed either through cored rolls or through peripherally drilled rolls. The principal one employs cored rolls i.e., water is sprayed onto the outside of an axially drilled central core.
2.3 Other Attachments Mills are fitted with a metal tray under the rolls to collect droppings from the mill. Guides are plates which are fitted to the ends of the rolls to prevent th
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