What is calendering Calendering is a method of continuous forming of thermoplastic plastics into thin films or sheets through a series of heated rollers. In the process of rubber processing, the rubber can be calendered into film with a certain thickness and width, or the pattern can be pressed on the film for the next step of product forming. Calendering is also used to make fabric and steel cord glue, so that film and film, film and glue fabric, etc. Therefore, it is one of the main processes of rubber processing. In plastic processing, calendering method is mainly used for processing PVC film, sheet material, artificial leather, floor leather, waterproof roll material and so on.
Calendering process ①Film and sheet: The blanks sent to calender are detected by metal detector to prevent inclusions from damaging the surface of rollers.The product is then rolled to a certain thickness by the calender roll, then left the calender by the pull-off roll support, and then cooled and coiled. When necessary, embossing treatment is carried out between the lead-off roll and the cooling roll. The factors affecting the quality of calendered products are roll temperature, roll speed, roll speed ratio, roll gap stock and roll distance.
②Compound with fabrics: there are two methods of gluing and rubbing. The roll pressure of calender is used to make the film stick on the fabric, which is called glue sticking. For example, the speed of two rolls (v2 and v3) is equal when the four roll calender is used to double-sided glue sticking at one time, and the glue is pressed on the fabric by the roll pressure. If there is more glue accumulated between the two rollers in the above method and the glue is pressed into the gap of the fabric structure by the pressure of the glue, it is called pressure glue, which is an improvement of the above method. In actual production, textile fabrics are usually glued on one side and pressure glued on the other. Rubbing takes advantage of the different rotational speeds of calender rollers to rub the rubber into the seams and twists of fabrics. Rubbing in three-roll calender, the speed of middle roll is greater than that of upper and lower roll
Sticking method has less damage to fabrics and faster production speed, but the adhesive layer and fabric adhesion is slightly lower. It is mostly used in thin fabrics and cord fabrics with thinner warp and weft density. Rubbing is suitable for tight canvas fabrics. Polyvinyl chloride artificial leather can also be produced by similar methods.
Operation essentials of calendering process The adjustment of roller spacing is mainly realized by the movement of roller bearings along the sliding groove of the frame. The design of the roller spacing adjusting device meets the requirements of easy operation and high precision. It also needs a safety mechanism, that is, the adjusting device is equipped with switches to prevent excessive adjustment. When adjusting the roller spacing, the operation is required to be fast and accurate, and rough adjustment and slight adjustment should be made in operation. Combining the two ways of adjusting, i.e. the speed of adjusting distance in two stages, fast and slow, which are provided by the adjusting device, should be cooperated effectively in operation. When the calender works, besides transferring part of the heat from the roller to the bearing and rotating at high speed for a long time under the driving of the roller, the bearing itself produces a large amount of friction heat, partly due to the flow of air, through heat exchange. The form spreads around, and the other part is taken away by circulating flow.
