How is plywood produced

The debarking machine removes the bark by using either sharp-toothed grinding wheels or high-pressure water jets as the log is rotated. These logs then move onto another conveyor belt where a circular saw cuts them into sections suitable for making standard plywood sheets. The next step in this magical process requires the timber veneer to be made.

Before we get too carried away though, the peeler blocks must be heated and soaked to soften the wood, by steaming them or submerging them in hot water in a process that takes hours depending on the type of wood and a host of other characteristics.

Once heated the blocks are transported to the peeler lathe, where they are fed one at a time. The lathe rotates the block quickly and a knife blade peels a continuous sheet of veneer from the surface. Now that we have our sheet of veneer you can either choose to process it immediately, store it in a multiple-level tray or have it wound onto a roll. From here the next step requires cutting the veneer into usable widths. During this step, the optical scanners search for sections with unacceptable defects and those are clipped out.

Similar to The Terminator , but for plywood. Veneers will then be stacked according to grade, which can be done manually, or with our Terminator technology. Finally, the sorted sections are dried to remove moisture.

The process of laying up and gluing pieces together is now underway, which must be manually done, or semi-automatically through the assistance of machines. In the case of a three-ply sheet, the back veneer is laid flat and run through a spreader, applying glue to the upper surface.

That plywood is referred to as overlaid plywood and is most often used in the transportation, agricultural and construction industries. Plywood can also have a layer of liquid stain used to give it a more polished look, which is used for more decorative projects. Finally, plywood can be treated with a variety of different chemicals to promote different properties. For example, it can be treated to be more resistant to flames or decay. In general, there are two classifications of plywood, both of which have their own grading system.

They are rated depending on the grade of veneer that is used on their back and face as well as their exposure capability. That exposure capability can be either exterior or interior and usually depends on the type of adhesive used.

The D grade is the lowest with multiple defects while the N grade has very few defects. As a rule of thumb, plywood that is used for subflooring usually has a rating of C to D.

The face of this plywood is almost always free from defects, at least by the naked eye, given that it is used for its decorative purposes. Plywood can range quite substantially in size. As a result, clipping leaves some veneers end up with a smaller surface area. As you can expect, the green veneers produced by the peeling process are typically wet or full of moisture, and need to be dried.

Veneer drying is necessary for improved bonding, and is done by feeding the veneers into continuous or roller dryers at a controlled speed. These dryers produce heat from steam boilers that are fuelled by barks, discarded veneers, sawdust and other mill residues. Ideally, the moisture content of veneers should only be somewhere between six to 14 per cent by the time they make it through the other end of the dryer.

At this stage, they are also segregated as face, core or back veneers. The face is the surface that is to be used or seen. The back, as the term suggests, is the part that remains unused or hidden.

The core, meanwhile, refers to the centre layer. The process is meant to make composing the plywood layout easier. The plywood layout, for its part, will be controlled in terms of thickness, timber grain orientation, wood species, and the quality of the ply. Once the sheets are properly composed, they are then bonded with the use of adhesives.

The adhesives to be used at this point will depend on the type of plywood being produced. If the plywood is meant to be of the general or normal type, urea formaldehyde resins are typically used.

In most cases, they have been planted and grown in areas owned by the plywood company. These areas are carefully managed to maximize tree growth and minimize damage from insects or fire.

Here is a typical sequence of operations for processing trees into standard 4 ft by 8 ft 1. The logs are first debarked and then cut into peeler blocks. In order to cut the blocks into strips of veneer, they are first soaked and then peeled into strips. Just as with lumber, there is no such thing as a perfect piece of plywood. All pieces of plywood have a certain amount of defects.

The number and location of these defects determines the plywood grade. These standards not only establish the grading systems for plywood, but also specify construction, performance, and application criteria. Even though plywood makes fairly efficient use of trees—essentially taking them apart and putting them back together in a stronger, more usable configuration—there is still considerable waste inherent in the manufacturing process.

To improve this figure, several new products are under development. One new product is called oriented strand board, which is made by shredding the entire log into strands, rather than peeling a veneer from the log and discarding the core.

The strands are mixed with an adhesive and compressed into layers with the grain running in one direction. These compressed layers are then oriented at right angles to each other, like plywood, and are bonded together. Oriented strand board is as strong as plywood and costs slightly less. Bramwell, Martyn, editor. The International Book of Wood. Simon and Schuster, Duncan, S. The Complete Plywood Handbook. Tab Books, Forest Products Laboratory.

Wood Handbook: Wood as an Engineering Material. United States Department of Agriculture, Hornbostel, Caleb.