The calendering is a molding method in which a thermoplastic plastically-heated thermoplastic material is extruded and expanded into a continuous sheet product having a predetermined size by using two or more relatively rotating roll gaps. It is the production of plastic film and sheet the main molding method.

·Calendering process
1, the process
Calender film and sheet molding generally go through the plastic feeding, rolling molding process.
a, Plasticized feed
This process is to plasticize the material, extrusion filter or through the open-smelting and further refining, and finally the plastic material into the calendar molding machine.
b, Calendering molding
This process is to feed the blank of the calender in the continuous extension through the calendar after further plasticizing and rolling into a certain thickness of the film or sheet.

2, process control factors
There are many factors that affect the quality of calendered products, mainly include: raw materials, process conditions (such as roller temperature, roll speed, roll distance, etc.). Mechanical equipment (such as roll deformation, etc.), as well as the production of auxiliary factors in the process. Now the main process control factors are described below.
a, Raw material properties
In general, the use of higher molecular weight and narrow molecular weight distribution of the resin, thermal stability is better, the physical and mechanical properties of products better, but will increase the rolling temperature and equipment load is not conducive to the production of thin products. In addition, the resin ash, water and volatile matter content can not be too large, too high ash will reduce the transparency of the product, and moisture and volatile matter content is too high will produce bubbles.
b, Roll temperature and roll speed
The material in the calendering required for the heat, a part of the supply by the heating roller, the other part from the material and the friction between the roller and the gap between the material flow velocity is inconsistent material shear caused by the role of their own. Friction heat generated in addition to the size of the speed and speed of the roller, but also with the viscosity of the material.
c, Roller speed ratio
The ratio of the linear velocities of the two rollers adjacent to the calender is called the roller speed ratio.
d, Roll distance and stock
The spacing between the rollers of the calender can be adjusted in order to accommodate varying thickness requirements of the various products and to vary the stock volume in the roll gap.

·Calendering molding equipment
Calender molding equipment mainly by the calendar and auxiliary components, the main component of the calendar is a group of parallel rollers, auxiliary parts, including the introduction, ginning, coiling, cutting and other devices.
1, rolling machine classification
Calenders are usually classified by the number and arrangement of rollers. Depending on the number of rolls, the calender has a twin roll, a triple roll, a four roll, a five roll or even a six roll calender. Production should be more of a three-roll and four-roller calendar.

2, the structural characteristics of the calendar
Rolling machine mainly by the base, frame, bearings, roller, roller distance adjustment device, roller deformation adjustment device and so on. Respectively, as follows:
a, Frame and rack
The base is fixed on a concrete foundation and is made of cast iron for fixing the frame.
b, Main bearing
Main bearing fixed to the rack for supporting the roller, the bearing clearance is generally 0.15% to 0.17% of the nip, usually using roller bearings, but also the use of bronze casting sleeve bearings.
c, Roller
Calender specifications are usually expressed in roll diameter and face length.
d, Roller distance adjusting device
Three roller and four roller calender along the chip running direction of the penultimate roller bearing position is fixed, and other rollers through the roll distance adjustment device for back and forth movement to meet the requirements of product thickness changes.
e, Roller deformation adjustment device
In the rolling process, the roller pressure on the material, and material on the roller will produce a reaction force, the roller deformation. Roller is the same as the simple support, the middle deformation of the largest, to both ends gradually reduced, resulting in products produced in the cross-section of the central thick, thin on both sides of the phenomenon.