Calender

A calender typically consists of three or more rollers arranged in a specific configuration (e.g. vertical or Z-shaped). The rollers can be heated or cooled to control the material properties during the process. The material is fed between the rollers, with the gap and the pressure determining the thickness and surface texture of the end product. In some calenders, the material is also vulcanised during the process to bring it directly into its final, stable form.

Steps in the calendering process

• Material feed: the raw material, for example a rubber compound, is fed into the calender.

• Roller contact: the material is passed through the rollers and brought into the desired shape.

• Cooling or heating: temperature-controlled rollers stabilise the material structure and vulcanise it if required.

• Take-up: the finished material is rolled up or stacked as film, web or sheet.

Depending on the material and application, there are different calender configurations:

• Vertical calender: rollers are arranged vertically one above the other, ideal for large-area materials.

• Horizontal calender: rollers are arranged horizontally and are suitable for thicker materials.

• Z-shaped calender: the rollers are arranged in a Z shape to ensure high precision and material control.

Calenders are used in numerous industries, especially where precise, high-quality sheet materials are required:

Rubber and plastics industry

• Production of rubber sheets: manufacture of sheet materials for seals, conveyor belts and other applications.

• Plastic films: production of smooth and precise plastic films for packaging or technical applications.

Textile industry

• Coating: application of rubber or plastic layers to textiles for waterproof or protective applications.

• Smoothing: improving the surface texture of fabrics.

Paper and packaging industry

• Paper smoothing: calenders are used to smooth and finish paper surfaces.

• Flexible packaging: production of multi-layer films for food packaging.

Construction industry

• Roofing membranes: manufacture of waterproof and durable roofing materials.

• Insulating materials: production of coated films for thermal or acoustic insulation.

The calendering process offers numerous advantages:

• Precision: uniform thickness and surface quality of the material.

• Versatility: adaptable to different materials and applications.

• Efficiency: high production speeds with consistent quality.

• Cost savings: reduction of material waste through precise processing.

Despite the advantages, there are some challenges when using a calender:

• Maintenance: regular calibration and maintenance are required to ensure roller precision.

• Material requirements: different materials require specific settings, such as temperature or pressure.

• Costs: purchasing and operating a calender can be expensive.

Although calenders and extruders are both used to process materials, the processes differ significantly:

Criterion	Calender	Extrusion
Material output	Flat webs or films	Profiles, hoses, round cords
Precision	Very high for thickness and surface	High precision for complex shapes
Material type	Elastomers (rubber), plastics, paper	Mainly elastomers (rubber) and plastics
Typical applications	Rubber sheets, films, coatings	Hoses, hose rings, profiles, round cords

• Which materials can be processed in a calender? Calenders are suitable for elastomers (rubber), various plastics, paper and composites.

• How is material thickness controlled in the calender? Material thickness is determined by the roller gap and the pressure applied.

• What maintenance does a calender require? Regular calibration, cleaning of the rollers and checking the heating or cooling are necessary.

The calender is an indispensable tool in materials processing, particularly in the manufacture of rubber sheets for punched parts or seals. Thanks to its high precision, versatility and efficiency, it enables the production of high-quality materials of consistent quality. The possibility of vulcanisation during the process also achieves a stable final form, making the calender an important part of modern production processes.