Plywood is the most popular and versatile wood-based panels nowadays. It’s a laminated product made up of numerous thin strips of wood laid in alternating directions and bonded with a different kind of glue. But due to its construction method, plywood is less susceptible to expansion or shrinkage. Why?
A board of made from solid wood is unstable and tend to expand or shrink across the grain based upon the moisture content in the wood. Because plywood is much stronger and less likely to expand or shrink along the grain, then it is much more likely to split with the grain than against.
By gluing numerous thin strips of veneers in alternating directions layer by layer, plywood is much less likely to expand or shrink in moisture environment, and this structure is much stronger than similarly sized lumber cut from a single tree.
Plywood is made from an odd number of layers, each layer called ply(typically 3, 5 or 7), with an equal number of plies on each side of the center ply. The plies face are parallel, and the grain of the surface plies follows the long side of the board(although not always). The sheet is the strongest parallel with (as opposed to against) the two surface plies.
How Plywood Is Made?
Plywood mills in China are usually small or medium sized. There are some steps that is important for plywood production.
Veneer Peeling & Drying
The plywood needs good quality and dry veneers. Veneers must be dry so that it can adhere to glue well. Otherwise, there will be bubbles created in production.
Paste Glue to Veneers
There is a special machine to paste the urea-formaldehyde glue on veneers. Not every veneer should be glued because adjacent veneers can glue together if only one is glued.
Cold Press and Hot Press
The veneers are pressed hard in order to make a board. Cold press is to save the cost.
The raw plywood must go through a calibration machine to make the board thickness even.
The last step of plywood production is to laminate veneers or papers on the surfaces. If a smooth face is required there will be a final sanding on the ply face.