Rubber calendering process

- Oct 06, 2019-

See how the film is calendered


    Film calendering is the use of a calender to form a sleek film with a specified section thickness and width, such as hoses, tape inner and outer layers and interlayer film, tire cushion film, barrier film and oil film. When the thickness of the calendered film is large, and it is difficult to ensure the quality of the first calendering, two or more thinner films can be separately calendered, and then laminated to a film of a predetermined thickness or a film of two different sizes. The film can be made into a conforming film, and the rubber material can be made into a certain section thickness and width, and the surface has a certain pattern, that is, a film having a certain geometry in the cross section. Therefore, the calendering of the film includes tableting, film bonding and molding.


    (1) Tableting


    Films with a section thickness of 3 mm or less can be calendered at one time using a calender, which is a tablet.


    The quality requirement for calendered film is that the surface of the film is smooth and not drawn; the interior is dense, without holes, bubbles or sponges;


    The thickness of the surface is uniform and precise, and the shrinkage deformation rate of each part is uniform.


    The tableting process is divided into two main methods: three-roll calender pressing and four-roll calender pressing depending on the equipment. It can also be tableted with a two-roll calender and an open mill, but the film thickness is too low.


    The tableting process is shown in Figure 13-9. In the figure, (a) and (b) are three-roller press sheets, and (c) is a four-roll mill press. The three-roll calender press is divided into two methods, wherein a is no glue-calendering method between the middle and lower rolls, and b is a glue-filling method between the middle and lower rolls. Appropriate amount of accumulated glue can make the film surface smooth, reduce internal bubbles, improve the density inside the film, but increase the calendering effect. This method is applicable to benzene rubber. If too much glue is accumulated, it will bring in bubbles. The glueless rule is the opposite, applicable to natural rubber.


    When the four-roll calender is used for tableting, the shrinkage rate of the film is smaller than that of the three-roll calender, and the section thickness precision is high, but the calendering effect is large, which should be paid attention to in the process. When the thickness of the film section is very precise, it is best to use a four-roller tablet, and the film thickness ranges from 0. 04 to 1.00 mm. If the film thickness is 2-3 mm, it is also preferable to use a three-roll calender.


    The main factors affecting the tableting process and quality are the roll temperature, the roll speed, the type of raw rubber, the plasticity of the rubber and the rubber content.


    The roller temperature is high, the viscosity of the rubber is low, the flowability is good, the shrinkage of the semi-finished product is low, and the surface is smooth; but if it is too high, bubbles and scorch are easily generated; if the temperature of the roller is too low, the fluidity of the rubber is lowered, and the surface of the semi-finished product is made. Rough, shrinkage increases. Therefore, the roller temperature should be determined according to the type of raw rubber, the plasticity and the gelatinization rate of the formula. Usually, the formula has a high gel content, the plasticity of the rubber is lower or the elasticity is larger, and the calender roll temperature should be suitably higher; otherwise, the opposite is true. In addition, in order to smoothly transfer the film between the rolls in a predetermined direction, it is necessary to maintain an appropriate temperature difference between the rolls. For example, natural rubber tends to stick to the heat roller. When the film is transferred from one roller to the next roller, the roller temperature of the latter should be appropriately increased, and the synthetic rubber is just the opposite. The temperature difference between the rolls is generally in the range of 5 to 10 °C.