Laminated Veneer Lumber (LVL) is one of the most widely used engineered wood products for construction applications. It is a type of plywood made from multiple thin veneer layers. This fact sheet summarizes basic manufacturing process of LVL compared to other structural engineered wood products.
Bed slats made from LVL
Raw material of LVL
LVL production started in 1941. It was made from 3.6mm thick Stitka spruce veneer and used for aircraft parts. As the demand for LVL became bigger, the USDA Forest Products Laboratory did a substantial amount of research related to improving its strength. Every region has its own common types of wood to use as raw material for LVL production. In USA, people usually use Douglas fir, Southern pine, Yellow poplar and other softwoods. In New Zealand and Southeast Asian countries, radiata pine, acacia and rubberwood are the most commonly used.
LVL manufacturing process
Veneer sheets are produced by rotary peeling. Typical veneer thickness for LVL production is 1.7 mm. Manufacturer will use a veneer lathe to peel the logs, in which way the wood is compressed with a nose bar while the veneer knife cuts the blocks into veneers. The lathe incorporates geometry and positioning of a knife as main manufacturing parameters important role to the quality of the veneer. The pressure bar applies a certain amount of pressure on the surface of veneer, so it will constantly be peeled from the log with a uniform thickness and without having any cracks.
Veneer storage at Weego factory
Next, the veneers are then dried to a certain moisture content of below 12%. There are 2 methods to dry veneers: natural sunlight or drier or kiln. In the case of sunlight, it may take 1 or 2 days until their moisture reaches the right level. In the case of drier, 1.7mm thick rubberwood veneer may take 8 – 10 minutes to reduce its moisture content to 8 to 10%.
In general, LVL production is similar to that of structural plywood. The main differences are the grain orientation of veneers and the times of pressing. With structural plywood, veneers are assembled across each other so the finished product will not only have better mechanical properties, but also will be dimensionally more stable. With LVL, veneers are all arranged along the longitudinal direction so it will have properties similar to solid lumber because each lamia is parallel to the board axis.
Different arrangement of plywood types
Defects on veneers are eliminated during the clipping process. Even if defects are left on each veneer sheet, random distribution of such defects during veneer assembly will make the finished LVL more uniform and strength properties comparable to that of high-grade lumber. After exterior adhesive, usually phenol formaldehyde (E0/E1/E2) is applied to the surface of each veneer sheet, they are assembled and pressed by cold press machine and hot press machine.
Hot press machine
Laminated Veneer Lumber (LVL) is a versatile wood-based product. Together with other types of plywood, LVL can be used for many structural applications. You can see LVL in truck bed decking, beams, sofa frames, signpost, skateboards and so on.