Plywood is a composite materials of thin wood layers(which usually called plies) and resins, the inner structures is the plies rotated up to 90 degrees to ensure the strength, then both sides are coated with thin veneers. Plywood can be used to furniture(doors, cabinets),decoration(floor, ceilings, etc),packing and construction, etc.
Here is a typical sequence of operations for processing trees into standard plywood sheets:
1）Log selection: It’s the initial step of the plywood manufacturing process. At this stage, the logs are carefully identified and segregated in terms of species and quality to find logs that would produce veneers with acceptable physical and aesthetic characteristics.
Once suitable logs are selected, they are then made to go through a conditioning process to assure that good quality veneer is produced during the peeling process. This process usually involves spraying the logs with water. Some other mills, especially in cold places use heat as a way to improve the quality of peeling
2）Debarking the logs: once the logs have been cut to length, they are loaded into debarking machines, the bark will be removed using a debarking machine to improve cross-section roundness.
3)Peeling logs: Using a rotary lathe machine, the logs will be turned against a sharp knife and peeled into thin veneers, the veneers produced in the the form of continues sheets or immediately clipped into a predetermined width and length. The cutting process is like sharpening a pencil except that the blade is parallel with the log. The veneers are then clipped to a usable width to allow for shrinkage and trim.
4)Drying the veneer: veneer drying is one of the most crucial phases of veneer production. The natural veneers are wet, they must be dried to improve bonding and avoid going mold, what’s more, if the veneers are full of moisture, bubbles will emerge in the process of hot press.
Veneers drying is done by feeding the veneer sheets into belt dryers or roller dryers for peeled veneers as well as press dryers for smooth and flat decorative veneers. The moisture content of veneers should be 6-14% after they arrive to the other end of dryer.
5)Glue spreading: A glue spreader will spread the veneers with glue on both sides to ensure the adhesive evenly spread on alternate layers of veneers. On this stage, only half veneers should be glued. And glue types depends on the plywood quality requirements, the urea formaldehyde resin will be used for normal plywood, while melamine or phenolic glue should be used in marine plywood. The content of formaldehyde should be controlled also for interior plywood
6)Assembling plywood sheets: after properly drying and gluing the veneers, they are then composed into plywood sheets in customized size, this may be done manually or semi-automatically with machines. The veneers placed on top of an unglued veneers so that the stack alternate, each adjoining layers is rotated up to 90 degree in a process we call cross-gaining, it is able to resist splitting when nailed at the edges, minimize expansion and shrinkage and improve its stability.
7)Pre-pressing: the plywood sheets are pre-pressed in the cold pressed machines at a controlled hydraulic pressure. It need at least 20 minutes, not only ensure the plywood sheets are flatten, but also solidify and effectively bond the veneer plies in each panel. It also can shorten the processing time of hot press.
8)Hot-press: the plywood sheets are loaded into hot press machines, when the plywood panels begin to take shape. the hot press plywood are multi-opening machine. With each sheet loaded in the separated slot, then the iron board closed up and heated the panels. the time and temperature vary depending on the different wood species, plywood thickness and the design of plywood. The pressure ensures good contact between layers of veneers and the heat causes the glue to cure properly for maximum strength. After some time, the hot press machine open again and sheets are unloaded.
9)Trimming: after hot press, the plywood sheets are then pass through the double sizer to be trimmed to their final size with squire and clean edges.
10)Sanding: the plywood sheets pass through the industrial sander to get smooth surface and uniform thickness. Depending on different customers’ requirements, the plywood can either be sanded on the face or both face and back.
11)Packing: the finished plywood will be packed, stacked and stamped accordingly according to different customers’ requests.. The stamps will usually indicate a grade-trademark that is meant to inform buyers about the plywood’s exposure rating, grade, mill number, and other factors. the plywood will be strapped together in pallets and moved to warehouse to await shipment