The Banbury can be said too mix in four ways::

1. Milling ::







is the action of the rotors wiping material through the periphery of


the bore of the sides. This milling is more effective than the 2-roll milling


as the angle of incidence of rotor-to-side is much sharper than the case


of 2-roll mills.The mass of rubber in front of a rotor wing is subject to


rolling action which causes heavy molecular shear in the layers of rubber.


Material which has already passed between the side and rotor is also


subject to some rolling motion






2.. Kneading ::


is caused by the rotor tips when material which has been deformed


by milling is carried to the center of the chamber and relaxed. In Banbury


as the connecting gears are of uneven ratio, there are at least ten variable


tip phases which constantly change the quantity of the mass and its


conformation. At one moment both rotor tips may be directly opposed, at


the next revolution the tips are no longer directly opposed but are


pushing and working the material in a slightly different combination. This


kneading results in shear, folding over and periodic relaxing of the stock.










3.. Longitudinal Cut--back ::






is most apparent in the 2-mill mixing as the operator


strips off stock from the mill roll and feeds back elsewhere along the roll.This


action is accomplished in a Banbury by the longitudinal spiral or helix to the


wing tip, which is designed to continually force the material to the center of


the chamber. A small portion of the material is sheared off the center bank at


the top by the rotor and, after a trip around the rotor, re-enters the bank at a


different point. Since the banbury rotor is actually designed with two


opposing spiral wings or tips which have unequal lengths, a longitudinal


smearing and rolling action also takes place at the juncture zone of the


opposing wings on a given rotor.






4.. Lateral Overlap ::






is the action by which a portion of the material in


front is pushed over into the opposite chamber or side, and is then worked in


with material in front of that rotor until such time as some of it is again


pushed back to the other rotor. This closely approximates a condition where


material is being mixed on two adjacent mills, and strips are continually


being swapped between mills






There are basically three ways of mixing rubber in an internal mixer






1 Conventional Method :Developed originally for Natural rubbers,


consists of adding the elastomer first followed by the dry


ingredients and finally the liquid ingredients, once the dry materials


are well dispersed.






Adv : This method achieves dispersion and distribution of all


ingredients, including fillers of very small particle size.






Disadv : Usually longer mixing cycle because of the difficulty in


incorporating liquid ingredients once the dry materials have been


dispersed in the rubber matrix.