تخته لایه PLYWOOD

Plywood is made from an odd number of constructional veneers bonded face to face with the grain running in alternate directions تعریف تخته لایه

مزایای تخته لایه It shrinks, warps, twists and swells less than ordinary wood and has great resistance to splitting at the ends Plywood's main advantage is that by gluing together an odd number of layers of veneer, a material that is lightweight and workable, yet rigid and strong can be obtained plywood can be manufactured in sheets far wider than the trees from which it was made. High uniform strength - wood is times stronger along the grain than across the grain. Crossing the adjacent sheets tends to equalise the strength in all directions. Ease of fabrication of curved surfaces One of the important aspects in the manufacture of plywood is that it results in the conservation of timber by the elimination of the waste.

The manufacture of plywood can be divided into two main stages The production of veneers The assembly and pressing of veneers into plywoodplywood فرایند تولید تخته لایه تهیه روکش چسب زنی روکشمونتاژ پیش پرس پرس مشروط سازی (خنک کردن)

فرایند تولید تخته لایه آماده سازی روکش ها برای چسب زنی In general however most veneers wether rotary cut or sliced, are cut to size and squared by a dry clipper, edge jointed, taped or spliced and graded into cores, cross bands, or face veneers prior to being assembled for gluing and pressing.

فرایند تولید تخته لایه چسب زنی روکش Roller coaters Curtain coaters These apply adhesive in a thin film or curtain of adhesive to one side of the veneer as it passes through the coater. spray coaters

فرایند تولید تخته لایه چسب های مورد استفاده Urea formaldehyde glues are extensively used for interior and intermediate grade bonding Phenol-formaldehyde glues are standard for exterior bonds Fillers may be used to assist in reducing penetration of the glues into the wood, increase its viscosity at the critical time before setting, and tend to fill small cavities between veneers, thus preventing starved joints. Fillers are usually finely ground inert minerals such as clay or wood/grain flour finer than 180 mesh. پرکننده (فیلر)

فرایند تولید تخته لایه The pre-press (see Pic 1) which is unheated operates at pressure slightly below that of the hot-press. Pre-pressing can takes up to 50 sheet at a time, with a pressing time of 3 to 4 minutes پیش پرس

Hot pressing is carried out in a hydraulic press incorporating multiple heated Platens between which each individual panel assembly is subjected to heat and pressure. Hot press pressure for softwood pine plywood usually range between 1242 to 1380k Pa. Platen temperatures of around 120 degree Celsius are used and pressing times for panels 3.5 and 22 mm are 2.75 and 9.5 minutes respectively پرس گرم فرایند تولید تخته لایه

In hot pressing a considerable amount but not all of the water in the glue line escapes in the form of steam. Moreover, hot pressed panels are often dipped or sprayed with water immediately after removal from the press in order to restore the moisture in the face plies. Consequentially, a conditioning or redrying period is necessary and hot pressed plywood is usually hot stacked in solid piles for periods ranging from one or two hours to overnight. In this way the glue joints attain full cure and the moisture content of the panels is reduced and equalised through out the panels before further processing is carried out مشروط سازی (خنک کردن) فرایند تولید تخته لایه