Article PEEL Ply
July 11, 2018
Adhesives: A Key Element in Ensuring the Quality of Plywood
The production of plywood involves the glueing together of several layers of thin sheets of wood known as wood veneers. Wood veneers are placed one on top the other and affixed to each other using glue such that each subsequent layer has a grain pattern that is at right angles compared to the one above it. Before understanding the role of adhesives in plywood quality, the basic production process has to be understood.
Plywood: The Manufacturing Process
Wood Veneer Production
To manufacture plywood, first the individual wood veneers or thin sheets of wood have to be obtained. This is achieved through a process known as the rotary-cutting of logs. Here, a log is loaded on to the appropriate machinery and then rotated about its longitudinal axis as a cutter peels the log at a predetermined thickness. The thickness of each wood veneer or layer is usually under 2.5mm.
A glue spreader machine now spreads adhesives on these veneers. The machine achieves a uniform spread of glue thickness across the wood veneer. Now, the layers of veneer with alternating grains are stacked one on top of the other and compressed or pressed together using what is called a hot press machine.
The machine creates an environment of high temperature as well as pressure, ensuring that the glue cures fully, thus bonding the layers firmly to each other. The count of layers of wood veneer used is usually an odd number. This is done to add to the strength of the plywood. The exact number of wood veneers used per sheet of ply can vary, usually from 3 to 13, depending on the requirement.
Once the production process has been completed, the adhered plywood sheets are put through the acid test, i.e., quality checks. Some of the key tests include glue shear strength, dry strength, and resistance to microbes, water and moisture.
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