Four roll calender

Figure 35.43 shows a general layout of a dual-purpose calender line for coating steel cord and textile cord. The heart of the production line is the four-roll calender in an S-configuration. Two mbber sheets are formed in the upper and lower nip. The thin sheets are guided to the middle nip and the cords are coated in the middle nip between the two rubber sheets. Generally outer roll bending is applied on rolls 2 and 3 to compensate the roll deflection caused by the nip force in nip 2. Rolls 1 and 4 can be set crossed respectively to rolls 2 and 3. 

Figure 13.3 Topping on both sides on a four-roll calender.

In the case of a three-roll calender, an alteration to the fabric nip does not affect the rubber layer thickness, since it is a movement of the bottom roll in relation to the fixed bearing middle roll. With a four-roll calender the stack or the breast roll type where the two top rolls are adjustable, the opening or closing of the fabric nip does, in practice, frequently result in a disturbance of the top roller nip. 

The 121 sample films were formulated into a replicate series. Those utilizing emulsion polymerized PVC were cast from plastisol onto glass plates and fused in a circulating hot air oven. Those incorporating suspension polymerized PVC were fluxed via a Banbury and two-roll compounding mill and finished on an inverted L 8-inch X 16-inch four-roll calender. Plastisol films were of nominal 8-mil thickness calendered film was 4 mils. 

PP/EPDM blends Santoprene ), with their high melt viscosity and melt strength, are easily calendered. The material is normally premixed in a Banbury or other intensive mixer. The melt temperature should be about 190°C. Roll temperature should be about 70-120°C. Conventional four-roll calenders can produce quality sheet with thickness 0.4 to 1 mm. 

Essential steps in making conveyor belts are (1) drying the fabric (2) frictioning of the hot fabric with a rubber compound and topping to give additional rubber between plies and the outer ply and cover, using a three- or four-roll calender (3) belt building and (4) vulcanization. 

The formulation is useful for production of sheets by calendering (on a four roll calender equipped with an embossing machine). The sheet manufactured has excellent scratch, wear, and slip resistance, and it is suitable for use as flooring material. 

In addition to the conventional three- or four-roll calendering procedures used for the production of sheet material, two important variations are practised with TPU, namely hot-melt calendering and film lamination. 

Figure C.l Diagram of a four roll calender. (Ref Billmeyer, F.W., Textbook of Polymer Science, Interscience, New York, 1965, p. 493)...

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