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Calenders and calendering equipment apply continuous heat and pressure to densify, smooth, or otherwise modify the properties of roll goods. Calender machinery is also used to enhance surface properties, reduce sheet thickness, and produce special effects such as a glaze, moiré, or polish. The equipment may require a large amount of floor space, or feature a multi-story design. Programmable logic controllers (PLCs), sensors, and computer software are used to control and monitor large calender machines in the textile and paper-making industries. Typically, calenders and calendering equipment are rated by the mass of material produced per unit of time. This production rate depends upon variables such as the process material, take-up capacity, and surface finish. Although calenders and calendering equipment are more expensive than extruders, the calendering process requires a minimum of cleaning. By contrast, extruders must be purged and cleaned after use.
How Calenders Work
Calenders and calendering equipment is used to process industrial plastics such as polyvinyl chloride (PVC), woven and specialty fabrics, and high-quality paper. With plastics, heated rollers squeeze films or sheets to produce materials that have a glossy finish. The calendering process begins by heating and mixing resins, pigments, stabilizers and plasticizers in an industrial mixer. This hot mix is then passed through a two-roll mill to form the sheet. The heavy sheet stock is passed through a series of heated, revolving calender rollers until the desired thickness is achieved. Because these rollers can be damaged by metal contaminants, some calenders and calendering equipment include integral metal detectors.
When the calendering process is complete, the hot sheet is cooled on a chill roller and removed as a finished sheet or film.
Calenders and calendering equipment is specified according to the
- Number of rolls- Machines are available in multi-roll configurations.
- Arrangement- Machines are available in an inverted L or Z arrangement, and made of either low-alloy cast iron or spheroidal graphite-iron. Drilled rolls are sometimes used for improved hear transfer.
- Specific gravity
- Product width and thickness
- Operating temperature
Calenders and calendering equipment with self-aligning roller bearings, cross-axis or roll-bending methods, direct drives, pre-loaders, and motorized nip adjustments is also available. Some equipment may also include special finishing rollers for gauging and embossing.