Volumes of production
As many as 600 wooden trays can be produced in a day. Minimum orders from Neville and Sons are 50 units.
Unit price vs. capital investment
An affordable ratio for small-scale production makes this method of forming highly suitable for small- and large-scale runs. Molds for trays are produced in aluminum covered in a stainless steel sheet, which makes them cost-effective even for batch production. Unit prices are very low.
Speed
One tray can be produced every five minutes.
Surface
The surface color, and to a degree the finish and pattern, are controlled by the melamine sheet that is used in the pressing process. Decorative patterns, colors, and nonslip surfaces are available.
Types/complexity of shape
Embossed sheets with a fairly low-draw impression, up to a maximum of approximately 1 inch.
Scale
Neville and Sons can produce products measuring up to 23½ by 17½ inches.
Tolerances
Not applicable.
Relevant materials
Most veneers are suitable. However, the material used for trays is generally birch, beech, or mahogany.
Typical products
Given the shallowness of the depth achievable, this process is limited to products such as trays and automotive trim with the kind of walnut effect you would expect to find in high-end brands.
Similar methods
A process that allows for much more depth and possibilities with curving plywood is deep 3-D-forming (p.83). Also relevant, but using a completely different technology, is the inflated wood by Curvy Composites (p.184).
Sustainability issues
The crossdirectional grain structure of plywood minimizes material consumption while maintaining excellent strength. Pressing the plywood in the form of the tray featured here requires a number of processes, including a fair amount of heat to melt and bond the glues and veneers.
Further information
www.nevilleuk.com
3: Continuous
Calendering
Blown Film
Exjection®
Extrusion
Pultrusion
PulshapingTM
Roll Forming
Rotary Swaging
Pre-Crimp Weaving
Veneer Cutting
Components that are made from continuous lengths of a material
This chapter looks at components that are made according to the same principles that are used to make sausages, or, in other words, components that are the result of material being fed through a shape to produce long lengths of the same profile. It also looks at continuous strips of wood and plastic, woven lengths of metal, and continuous lengths of bent steel. It celebrates a rich assortment of processes that use a range of dies to form materials that can be produced in infinitely long length but which, with one exception, have the same cross-sectional shape along the whole length. Many of these processes are extremely cost-effective because they can produce identical multiples, cut from the same strip or section.
Calendering
The essence of calendering is captured in this image, which shows a ribbon of plastic being passed over polished steel rollers to form a continuous length of plastic sheet.
Calendering has traditionally been used as a finishing process applied to textiles and paper, using heat and pressure to give a smooth, shiny surface. In the nineteenth century, however, it was developed so that multiple rollers could produce rubber sheet. It is a large-scale process, both in terms of the volumes it can produce and the sheer size of the machine that is used to form the sheet material itself (or to add texture to existing sheet materials).
Imagine a machine that has at its heart a series of steel rollers resembling a clothes mangle, that press materials into continuous lengths of thin sheet. Although still used for finishing paper, some forms of textiles, and various types of elastics, calendering is the preferred method for forming high volumes of PVC sheet at a fast rate. In the realm of plastic production it competes with extrusion (see p.96) in the production of both rigid and flexible plastic sheet.
When it is used in this sort of plastic production, the setup usually includes at least four heated rollers, rotating at different speeds. Before this, however, hot granules of the plastic are fed into a kneader where they reach a gelling stage. They are then fed, via a conveyor belt, through the first of the heated rollers. The rollers are carefully controlled to produce the correct thickness and finish. Embossing rollers can be used to add texture and the sheet material then passes through cooling rollers prior to being wound onto a giant roll.
– Produces long, continuous rolls without joins.
– Excellent method for producing large quantities of flat sheets.
– Suited to very large-scale production only.