The flow velocity of the conveyor belt rubber compound as it passes through the roll gap of the calender is very high, resulting in significant elastic deformation. Once the rubber compound exits the roll gap, it immediately undergoes elastic recovery, causing the sheet to contract longitudinally and increasing its cross-sectional thickness. This not only affects the precision of the cross-sectional thickness but also impacts the smoothness of the sheet’s surface.

Qingdao Tailiu Rubber Co., Ltd. Contact: Manager Ma Mobile: 13780657773 Phone: 0532-85100571

The flow velocity of the conveyor belt rubber compound as it passes through the roll gap of the calender is very high, resulting in a significant degree of elastic deformation. Once the rubber compound exits the roll gap, elastic recovery immediately occurs, causing the sheet to contract longitudinally and increasing its cross-sectional thickness. This not only affects the precision of the cross-sectional thickness but also impacts the smoothness of the sheet’s surface. The degree of shrinkage in the calendered rubber compound depends on the properties of the compound, the calendering process, and the process conditions. The phenomenon of performance anisotropy observed in calendered sheets is referred to as the calendering effect. The tensile strength and thermal conductivity of the film are greater along the calendering direction than across it, while its elongation behaves exactly the opposite. The calendering effect arises because, as the compound passes through the roll gap, linear macromolecular chains are stretched, deformed, and oriented, and geometrically asymmetric filler particles align along the calendering direction.

The calendering effect in conveyor belts can affect the quality of isotropic products and should be minimized as much as possible. Common and effective methods include appropriately increasing the calendering temperature and the storage temperature of semi-finished products, slowing down the calendering speed, appropriately increasing the plasticity of the compound, adjusting the feed rate to the calender, and mold curing. Additionally, when designing formulations, the use of fillers containing anisotropic particles—such as kaolin, magnesium carbonate, and certain types of calcium carbonate—should be avoided as much as possible. Of course, for products requiring anisotropic properties, the calendering effect is not only harmless but can actually be utilized. Since the moisture content of textile fabrics is generally relatively high—for example, cotton fabrics can reach about 7% and rayon about 12%— and although the moisture content of polyester fabrics used in nylon conveyor belts is lower, it is still above 3%, the moisture content of textiles intended for calendering must generally be controlled below 1%. Otherwise, it will reduce the bond strength between the rubber compound and the textile, leading to quality issues such as rubber peeling from the calendered semi-finished product, air bubbles within the rubber compound, and sponginess or delamination in the vulcanized rubber. Therefore, the textiles must be dried before calendering.

Fiber fabrics are typically dried using vertical or horizontal dryers equipped with multiple hollow rollers. As the fabric passes sequentially over the roller surfaces, it is heated to remove moisture. The specific drying temperature and feed speed depend on the type of fabric and drying requirements. Excessive or insufficient drying adversely affects the performance of the textile. Dried textiles should not be left to sit for too long; otherwise, they must be tightly wrapped in plastic sheeting to prevent moisture reabsorption. In production, the drying process can be integrated with the calendering process to form a continuous production line, allowing the textiles to enter the calender for coating immediately after leaving the dryer. At this point, the textiles are still relatively warm, which facilitates the penetration and bonding of the rubber compound.