DEVELOPMENT OF BANBURY MIXER

The Banbury internal mixer was introduced to the rubber industry in 1917; the first mixers were supplied to Goodyear for mixing tyre compounds. For many years these mixers bore numerical designations for different sizes. These numbers approximated the quantity of 22" X 60" in mills that a specific Banbury mixer could replace. Soon after the first internal mixers were introduced, increases in speed, power and ram pressure made this relationship no longer meaningful. The earliest mixers had the same basic fundamentals of operation as those which are in service today. A ram is necessary to push raw materials into the mixing chamber, two counter rotating rotors perform the mixing action, and a door at the bottom discharges the completed batch to a secondary piece of machinery. Improvements continued to increase the value of the design for mixing applications, despite changes in materials and in expectations. The F-series Banbury mixers were introduced during the early 1970s. Unlike the earlier mixers, these F-series machines carried designations for each model which defined chamber volume. The F-series Banbury mixers not only introduced many new mechanical improvements, but were designed with the user in mind. Loading and discharge features and maintenance features were designed to emphasise the mixing capabilities of the machine rather than loading, unloading and maintaining. When the F-series mixer hoppers were enlarged to accept bales and slabs of rubber more readily, the hopper door angle was steepened to assist in more rapid introduction of material to the mixing chamber. The junction between the hopper and the mixing chamber was provided with replaceable throat wear plates. These permit maintenance in an area subject to significant wear because of the action of the ram, well ahead of wear to the chamber. In the latest models, replaceable wear plates have been extended further into the hopper to increase the stiffness of the assembly. The end-frames have been significantly strengthened and the access to the dust seals has been enlarged to assist maintenance or replacement. Within the mixing chamber the rotor end-plates have been converted to a one-piece design, eliminating occasional contamination associated with older, two-piece designs. This design also prevents the end-plate being dislodged from its fitting, reducing the incidence of mechanical failure. Rotor journals are now tapered, eliminating the need for bearing sleeves. Overall manufacturing tolerances have been reduced, lowering vibration and yielding longer useful service life. The wall thickness of the sides has been increased by nearly a factor of 2 over older models, in response to the higher loads experienced with modern mixing procedures. The dual-circuit cooling design and the size and location of the bored cooling channels provide highly improved heat transfer.