Lumber and Wood Industries
Lumber and Wood Industries
Canada's lumber and wood industries include manufacturers that convert logs (by mechanical processes of sawing, peeling, slicing or chipping) into lumber, veneer, plywood, particle board and oriented strand board (formerly called flake-, chip- or wafer-board ), and that produce, as residual by-products, wood chips, sawdust and shavings. Lumber is the most significant product in volumes manufactured.
Over 60 000 people are employed directly in manufacturing lumber, plywood, veneer and wood-based panels. The market value of primary wood products in 1995 exceeded $12 billion, of which 80% was attributed to lumber sales. Over 80% of softwood lumber production is exported, therefore this industry makes a significant contribution to Canada's BALANCE OF PAYMENTS.
The primary wood-products industry consumes about half the roundwood cut in Canada; the PULP AND PAPER INDUSTRY uses the remainder. Over 95% of logs used to manufacture lumber, plywood and other wood-based panels are softwoods (primarily CONIFERS); the rest are hardwoods (deciduous TREES). In Canada the principal softwood lumber species are DOUGLAS FIR, SPRUCE, PINE, HEMLOCK and western red CEDAR; BIRCH and MAPLE are the predominant hardwood species. Over 95% of the nearly 60 million m3 of lumber manufactured annually in Canada is softwood (of which BC produces 60%). Softwood plywood is manufactured predominantly in BC (responsible for 80%). Hardwood lumber and plywood are produced mainly in Ontario and Québec.
About 20% of Canadian lumber production is consumed in the domestic market; 80-85% of exported lumber is purchased by the US. During the 1980s, Canadian lumber producers were subjected to a number of impositions by the US on their penetration of that market, resulting in constraints imposed on softwood lumber exported to the US (see SOFTWOOD LUMBER DISPUTE). The European Community and Japan are also important markets, with lesser volumes going to Australia and Latin America.
More than 85% of the softwood plywood produced is used domestically; the majority of exported plywood goes to Britain and other EC countries. The US imports a small amount of Canadian export plywood, having itself a strong domestic industry. About half of Canadian particle board and oriented strand board are consumed in Canada; the majority of exports goes to the US.
During the period from 1970 to 1995, the number of sawmills decreased from an estimated 1800 to below 1000 because of the trend towards larger, more technically efficient manufacturing complexes. A significant innovation in this period was the development of high-volume, small-log processing systems.
Lumber and Plywood Manufacturing
Merchantable timber is felled and cut into logs for transport to sawmills. Mechanical or hydraulic debarking is the first step in converting a sawlog into lumber. In conventional sawmills, large logs are placed on a moving log carriage and passed repeatedly through a band or circular saw, each pass producing boards that normally require further processing on edgers, resaws and trimsaws.
In sawmills processing small logs, the primary unit may be a chipper-canter with integrated sawing units, or a system of multiple-band or circular saws, designed to operate at speeds up to 100 m per minute. About three-quarters of the lumber produced in Canada is further processed in planer mills that smooth the rough surfaces and dimension the pieces. Over half the lumber is dried to remove excess moisture, either in dry kilns for several days at temperatures sometimes exceeding 80°C, or by air for several months.
Plywood is wood reduced to thin sheets of veneer, glued together with the grain direction of adjacent sheets at right angles. This cross-lamination makes the panel stable and redistributes the inherent directional-strength properties. Plywood is an engineered product.
Veneers are produced by holding a log firmly at each end in a lathe and rotating it against a knife that moves towards the axis of rotation. The veneer exits from the lathe knife in a continuous ribbon of wood that is clipped to desired widths or to eliminate defects. After drying the veneers are sorted into sets, each of which will form a plywood panel of the desired thickness and size. Alternate sheets are coated with glue, which forms a waterproof bond when subjected to high temperature and pressure in a hot press. The rough plywood panels are then trimmed and may be sanded.
To ensure uniform quality, lumber and plywood are graded into categories by standardized procedures. Most of the lumber produced in Canada is used in CONSTRUCTION, mainly for house building; it is classed as dimension lumber and is graded into width and use categories. Other classes of lumber include clears, factory lumber and shop lumber, used to manufacture high-quality moldings, panelling and flooring, or to obtain clear cuttings for components in such items as doors and windows.
Softwood plywood is produced in 3 grades: sanded (for high-quality finishing), unsanded (for construction use) and overlaid (for special uses). For general construction and other structural purposes, the most common type of panel is sheathing, the unsanded grade. About half the plywood used in Canada is for house building and agricultural construction; industrial uses take up another third; the balance is consumed in a multitude of miscellaneous uses.
Particle Board and Oriented Strand Board
Wood particle board is a panel product manufactured by bonding particles of wood together with an adhesive in a press. Since the product is manufactured from small pieces of wood, properties of the finished board, such as density, hardness and elasticity, can be engineered into the panel. The furnish for particle board is sawdust or planer shavings or solid wood flaked or chipped specifically for that purpose.
The various wood elements are screened and separated by size and shape so that their integration in the finished product can be controlled. The particles are then dried by heat and circulation and mixed with thermosetting bonding agents. The mixture is then meshed together in a layup for final pressing under heat.
The most common type of particle board manufactured in Canada is the 3-layered, graduated mat-formed variety. By preparing the core and surface material separately, segregating the coarser materials into the centre and the finest particles on the surface, the manufacturer can create a board that can be sanded to an even, smooth surface, and that has the desired mechanical properties in each layer.
The fibre lengths of the particles are distributed in a random pattern, so that internal stresses average to zero, resulting in an extremely stable finished product. Major uses of particle board are furniture and cabinet panels and cores, and floor underlay; minor uses include interior wall sheathing and mobile-home decking.
Oriented strand board is an engineered, structural panel-board made from large, thin strands cut from roundwood. Like particle-board, the panel is manufactured from pieces of wood which can be designed in size, thickness and profile, allowing the properties of the board to be engineered into the panel. These strands are mixed with waterproof phenolic resin and interleaved together in thick mats, which are then bonded together under heat and pressure. The result is a solid, uniform building panel with high strength and water resistance, properties that make strand board suitable for most construction applications. Some examples of uses are wall and roof sheathing, subflooring and underlay, cladding and soffits. The panels are also widely used for farm structures, industrial packaging, crating and warehouse pallets.