Internal mixer fill factor

The compounds were mixed in three steps The first two steps were done in an internal mixer with a mixing chamber volume of 390 mL. The mixing procedures employed in the first two steps are indicated in Table 29.2. The starting temperamre was 50°C and the cooling water was kept at a constant temperature of 50°C. The rotor speed was 100 rpm and the fill factor 66%. After every mixing step the compound was sheeted out on a 100-mL two-roll mill. The third mixing step was done on the same two-roll mill. The accelerators and sulfur were added during this step. 

Figure 11. Experimental circulation time in an internal mixer as a function of fill factor.

Mixing experiments were performed by a Plasticorder PL 2000 internal mixer (Brabender). A rotor speed of 50 rpm and starting temperature of 50 °C were used for all tests. A fill factor of 0.7 was chosen for low-filled blends, while it was reduced to 0.6 for highly filled blends in order to keep the mass temperature below 100 °C. Two series of silica-filled blends, with and without additives, were prepared according to Tables 6.2 and 6.3 by variation of mixing time and silica loading. 

The rubbers used were S-SBR (Sprintan SLR-4601, Styron Deutschland GmbH), NR (SMR 5, Nordmann Rassmann) and epoxidized natural rubber (ENR 25 and ENR 50, Weber Schaer GmbH Co. KG, Germany) with 25 mol% and 50 mol% epoxy groups, respectively. Carbon black (Corax N220, Evonik Industries) was used as filler. To prepare filled rubber blends, rubbers were mixed with 50 phr filler in an internal mixer. The initial chamber wall temperature T was kept constant at 50 °C. The rotor speed was 50 rpm and the fill factor was 0.6. 

In the preceding section, the effect of the shape of the rotors on the mixing behavior of BR rubber in a two-dimensional internal mixer was shown, and it is obvious that the void in the mixer affects the mixing behavior. However, there have been a few studies of the void in the mixer. Kim and White (1989) and Kim (1990) investigated the distribution of the rubber in an internal mixer using different types of rotors and various fill factors and explained the effect of void on the flow in terms of the starvation effect. 

Two-dimensional internal mixers made of brass having three different radii of each chamber were used. The (e), (g), and (h) type rotors made of stainless steel similar to those in Fig. 3 were used. The land width of these rotors was 4 mm. Fill factors of 0.6, 0.7, and 0.8 were used. The fill factor of 0.9 was not used because of the high torque to rotate the rotor. In these experiments, the clearance between the rotor tips and the mixing chamber wall was 1 mm. The speed ratio of the two rotors was 1 1 and the rotor speed was 5rpm. The phase angle between the two rotors were 90°. Whenever fine powders such as carbon black, pigment, and so on, were mixed into rubber in the two-dimensional internal mixer equipped with transparent window, we could not observe the mixing behavior except for the start and the end of the... 

As a tangential rotor type mixer, a Werner and Pfleiderer GK-2 internal mixer was used with a chamber volume of 3150 cm. The mixer was operated at a fill factor of 76%, the optimum with regard to mixing efficiency for such a type mixer. Rotor speeds of 46 and 50 rpm were used, running at a friction factor of 1.1. A ram pressure of 5 bars (maximum oil pressure on the plunger of the ram) and a wall temperature of 40°C held constant throughout the mixing cycle. 

Fill factor - The amount of the total free volume available in an internal mixer oeeupied by the mixed compound at the end of the mixing cycle. 

The most important feature of instantaneous power control in an internal mixer is the control of the viscosity of the mixing material. It was shown that the Mooney viscosity fluctuation of the mix could be decreased by using instantaneous power control. During the autocontrol mixing, the parameters of the mixing process, such as the rotor speed, filling factor, ram pressure and mix temperature, affected the mix quality. The effect of some of these parameters could be decreased by using instantaneous power control. Instantaneous power control... 

A Banbury-type internal mixer with a 250 ml capacity was used for mixing the compounds. The fill factor was 0.7 and the rotor speed was 100 rpm. After mastication of the rubber for 1 minute, carbon black was added over a period of 1 minute. After an additional 2 minutes, the compound was dumped. All dumped compounds were crumbly and a small amount of the free filler remained. After dumping, the compounds were immediately milled with a 6-inch two-roll mill in order to develop further mixing and to observe mill processability. Photographs (see Figures 6.48-6.57) of the rubber on the mill were taken after milling for 2 minutes. The speed of the fast roll was 28 rpm and the friction ratio was 1 1.26. 

A Banbury-type internal mixer with a 250 ml capacity was used. The fill factor was 0.7 and the rotor speed was 100 rpm. First the mixer was cleaned with gum rubber. 

The mixer was Moriyama internal mixer, model D3-75, with a 3 litre capacity. The fill factor was 0.7, and the rotor speeds were 72.2 rpm for the front rotor and 52.1 rpm for the back rotor. Also, a laboratory size Banbury mixer was used to assure the similarity of mixing performance. 

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