Volumes of production

Because of the setup costs and running times involved, tooling is expensive, making calendering exclusively a very high-volume production process. The minimum length for production varies between 6,500 and 16,400 feet, depending on the gauge of the sheet.

Unit price vs. capital investment

Calendered sheets are often further converted in order to be turned into products, but the price of the sheet before it is converted is highly cost-effective if large enough orders are fulfilled. Capital investment is extremely high.

Speed

Once the process is running at optimum speed—which can take several hours to achieve—it is superfast.

Surface

The rollers can be ultrasmooth to give a shiny surface, or embossed with patterns that are transferred onto the final sheet.

Types/complexity of shape

Flat, thin sheet.

Scale

The thickness of a PVC sheet is generally between 1/425 and 1/20 inch. The width of the rolls is up to 60 inches.

Tolerances

Not applicable.

Relevant materials

Calendering can be used for a range of materials, including textiles, composites, plastics (mainly PVC), or paper, where it is used to smooth the surface.

Typical products

Paper, used for newsprint, and large-scale plastic sheet or film. It can also be used as a finishing process for other papers and textiles.

Similar methods

In terms of plastic production, extrusion (p.96) is the closest comparable method for producing continuous sheet material. There is also blown film (p.92).

Sustainability issues

Calendering is a largely automated process that requires continuous heat and rotation and so relies on large amounts of power. However, the machines operate at incredibly high speeds to reduce cycle times which maximizes this energy use. Excess material is minimal.

Further information

www.vinyl.org

www.ecvm.org

www.ipaper.com

www.coruba.co.uk

Blown Film

The best way to summarize the blown-film process is to think of blowing bubblegum, but on a giant industrial scale. Producing plastic that is on the physical scale of a building involves a massive tubular bubble of inflated plastic being blown upward into a vertical scaffolding structure.

The technique takes its name from the action of the plastic granules, which are heated (1) and fed vertically by a stream of air through a horizontally placed cylindrical die (2), to form a thin-walled tube that is blown to form a huge plastic bubble (3). This bubble is fed vertically by a stream of air in the top of the die to form a tower of plastic (4). Varying the volume of air in the bubble controls the thickness and width of the film, which gradually cools as it rises, tapers, and, several feet up, eventually subsides completely into a flattened tube (5). This flat tube passes through a series of rollers on its way back down to ground level (6), where it is wound onto a giant roll, ready for despatch (7). The edges of this sheet material can be trimmed off to produce sheets, or it can be left as a tube to be used for plastic shopping bags and garbage bags.

–  Allows for the production of a material with uniform properties across the whole length and width.

–  Blown film is not always ideal —for example, the process of casting film can be a better option for applications that require high optical clarity.