Technology, processing internal mixers

The oldest technology involved in the elastomer blending and vulcanization process is essentially a temperature controlled two roll mill as well as internal mixers followed by an optimum degree of crosslinking in autoclave molds (compression, injection, etc.) in a batch process or in a continuous process such as continuously heated tube or radiated tubes. A few examples of laboratory scale preparation of special purpose elastomeric blends is cited here. 

We are left with the question as to what, in relation to mixing in an internal mixer, is the optimum molecular structure of the pure rubber. As with most questions in rubber technology, there is no straightforward answer. The level of carbon black dispersion is important for the further processing of the mixtures (e.g., extrusion) and for the appearance and the mechanical properties of the vulcanized products. The level of carbon black dispersion in the plateaus observed is 95%, which is amply sufficient for many applications. 

This detailed article examines recent developments in rubber mixing technology. Section headings include early developments, the factors affecting the mixing of polymeric materials, the mixing process (incorporation, dispersion, roll mills, internal mixers, extmders), novel mixing concepts and systems, instruments for quality control and process optimisation, trends and opportunities, and conclusions. 24 refs. 

The effects of mixing temperature, mixer and processing technology on the dispersivity of zinc oxide nanoparticles in BR were investigated. It was foimd that dispersivity was improved at elevated temperature in an internal mixer and that blending the zinc oxide nanoparticles with stearic acid before mixing improved both aggregation and dispersivity. 3 refs. 

The development of the tilt mixer is ontlined and tilt mixer apphcations are listed. The diflerences between the tilt mixer and internal mixer are identified and dalafiom compounding trials carried out on rubber formulations processed using the latest and most advanced tilt mixer rotor design (G-III Technology) introduced by Moriyama. 

Powdered rubber based on E-SBR/carbon black compoimded in an internal mixer process is examined with respect to the advantages it affords in terms of enviromnental, handling and efficiency over conventional bale technology. This paper is the first part of a series of publications which discusses the individual rabber/filler systems in detail, and focuses on the system of carbon black-filled emulsion styrene butadiene rubber. It covers the selection of the raw materials, manufacture of products and their characterisation. 18 refs. 

A survey is made of trends in internal mixers for use in the rubber industry, and developments by Krupp Elastomertechnik and some other leading machinery manufacturers are examined. Aspects discussed include the operation of tangential and intermeshing rotors, wear resistant materials for mixer components, the replacement of pneumatic rams with hydraulic rams, optimisation of the mixing process through the use of variable speed drives, and developments in mixing technology for the preparation of silica filled tyre tread compotmds. 20 refs. 

ADVANCED TECHNOLOGY IN INTERNAL MIXERS AND RELATED PROCESSING EQUIPMENT... 

The paddle ridge width of a batch mixer was varied between 0.2-20 mm and the effects on the rubber mixing process were studied photographically. The distribution of carbon black in the mix was uniform with a width below 11 mm, while a width below 15 mm was required for efficient dispersion. 9 refs. Artieles from this journal can be requested for translation by subseribers to the Rapra produced International Polymer Science and Technology. 

The authors compare the performance of a variable intermeshing clearance mixer, which offers the possibility of varying the intermeshing clearance between the rotors in addition to the usual adjustable process parameters, with that of conventional mixers with intermeshing rotors. 3 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. Accession no. 773787... 

---