Sheet Materials
Plywood is strong and lightweight and is, therefore, an ideal material to use for manufacturing cases. It is composed of between 3 and 7 plies, or veneers, that are bonded together with a synthetic resin adhesive. Generally, the greater the number of plies, the greater the strength of the plywood. Each one is assembled for gluing with the grain being at a 90o angle to the adjacent one. The whole panel is then subjected to pressure and heating and once cooled, it is trimmed into sheets. The cross-laminated construction means that when the plywood is subjected to moisture, it prevents individual veneers from swelling or shrinking and distorting the panel.The two main types of adhesives used are:
- urea formaldehyde (UF)
- phenol formaldehyde (PF).
UF is used in the production of moisture resistant interior plywood that can survive exposure to all-weather conditions for a limited period. PF bonded plywood has a higher moisture resistance and this means that it can survive longer and it is for this reason that it is frequently used in the packaging industry.
The characteristics of each veneer are designated by face marking or veneer grades. For commercial plywood, the type of adhesive used and the veneer characteristics are two of the most important factors when selecting a plywood that is best suited to an application.
There has been an increasing demand in recent years for OSB cases. OSB is manufactured using the same process as wood chipboard but small roundwood logs are used for the particles rather than timber waste. The logs have the bark removed, are cut to length and are then waferised by a process that reduces them to strands. The strands are dried to a moisture content of between 3% and 8% and they are blended with phenol formaldehyde adhesive and either paraffin slack wax or a wax emulsion.
3 layers or ‘mats’ are then formed to produce the OSB and each layer alternates between strands orientated in one direction and strands that are at a right angle to the adjacent layer. This provides OSB with similar properties to plywood and it is, therefore, an ideal alternative case material that is both light and easy to nail.
