A calender process flow diagram is illustrated in Fig. 3. In this process, rubber is dissolved by an organic solvent and then mixed with other constituents. The NASC sheet is molded in a roller-type calender.
Preparation of rubber paste is fulfilled in three steps including plasticizing, mixing and dissolving. The mixing and plasticizing steps are the same as those in the molding process. The gross rubber should be separated into small pieces, and then dissolved into the rubber paste by organic solvents, such as gasoline, benzene, methylbenzene and ethyl acetate.
In the mixing step, rubber paste, filling material and reinforcing fibers are mixed, and good quality gross rubber particles with suitable diameter, humidity and hardness are prepared.
Rubber—►Plastication —►Dissolving rubber—»
Reinforcing fibers—►Surface treatment—► Drying —i
Compatibilization fibers –
Fig. 3. A calender process of NASC
The calender process is carried out with two rollers rotating in the opposite directions. Gross rubber particles are fed into the clearance between rollers, and manufactured into NASC sheets. The operating principle of a roller-type calender is shown in Fig. 4.
Fig. 4. The operating principle of a roller-type calender
The operating parameters of the calender process mainly include speed ratio of rollers, calender speed (roller surface speed), roller temperature, feed speed, roller clearance and extrusion pressure.
The two rollers are usually thermally stabilized by steam and cool water, respectively. Accordingly, they are called hot roller and cold roller. The appropriate speed ratio of two rollers is in the range of 1.04-1.06.