Production Process of plywood – Short description
The logs are conditioned in water basins. Conditioning involves softening the wood by exposure of the peeler blocks to both heat and moisture by way of soaking in hot water vats. Than the logs undergo the debarking process after which they are divided according to its quality and length.
Manufacturing of wet veneers
The logs are peeled in a rotary peeling machine by a knife mounted parallel to the log’s axis. In this way we get a continuous wet veneer sheet, which is cut to sizes defined by production process. Standard thickness of veneers is 1.5 mm, but depending on client’s specification it is possible to peel veneers of different thickness too.
Manufacturing of dry veneers
Wet veneers undergo the drying process in a roller system through the length of the dryer. The output of this process are dry veneers. The veneers are sorted (quality control), repaired (the defected places are repaired by removing the defect and inserting a patch or wedge) and jointed along or across the fibers so as to make sheets of the required size.
In this production phase veneers are laid-up in assemblies (an assembly – plies of veneers with glue coating every second veneer). Number of plies is determined by the final thickness of plywood. As result of exposure to high temperature and pressure the glue between the plies hardens and the plywood is ready.
Trimming the plates to smaller formats according to clients’ orders. Trimming is proceeded on modern packet saws, which guarantee precise cutting.
Plywood undergoes the thickness calibration in order to get the plates of similar thickness and sand them. For surface polishing a four-shaft mechanical polishing machine is used. First two shafts are equipped with sand paper of granulation 60 when the other two – with granulation 100.
Depending on the processing type, the surface of plywood might be coated with:
» film, as result of pressing phenolic or melamine film to plywood surface. A modern panel coating line is used for this process.
» varnish, plywood surface is coated on varnishing line with the UV-hardened varnish,
» oil, plywood is coated with mineral oil, while the edges might be painted with acrylic paint or oil, depending on clients needs,
» polypropylene, as result of pressing 1.6 mm thickness polypropylene on the plywood surface.
Quality control of finished product is based on European Standards or standards delivered by the customer. Both surfaces of plywood are visually inspected by employees of quality control department. At this stage also final mesurements are made. Defective items are reclassified. They are not used for realisation of customer’s order.