Plywood

PLYWOOD

Plywood is an engineered wood sheet material made up of fine layers or flimsy strands of wood veneers attached together by placing wood grains 90 degrees to one another. It is one type of manufactured board which can be described as a mixture of medium density fibre board (MDF) and Chip Board (Particle Board).

It is a complex material and attaches resin and fibre sheets of wood. The outer most veneer sheets in a plywood panel are called/faces. The interior ply/plies which have their grain directions parallel to that of the faces are termed as core/centre. Other sheets which have grain directions perpendicular to that in the face are termed as cross bands. 29ilieup Inige om

Plywood has become much popular nowadays because of its relatively low moisture content which makes various tasks easy to perform. Mostly for outdoor uses plywood has become very important to use.

1. CLASSIFICATIONS OF PLYWOOD

Based on various aspects, plywood can be classified as follows:

Based on direction of Grains: Plywood may be classified based on the direction of grains in the plies. Normally the alternate plies are oriented at 30° or 60° in star plywood. The faces are arranged with the grain at 45° to that of the centres in diagonal plywood. When the plies are bonded together with water-soluble glues such as casein glue, interior grade plywood is obtained and when bonded with phenol formaldehyde adhesive it is identified as exterior grade plywood which is completely water proof.oile

Based on Grade: Plywood may be classified based on the grades for general purposes. It depends upon the bond strength developed by the adhesive used for bonding the veneers:

* Boiling water resistant or BWR Grade, and

* Moisture resistant or MR Grade.

 Based on type of wood: Plywood may be classified based on the type of wood and properties.

❖ Softwood Plywood which is also known as spruce-pine-fir or SPF because it's made from spruce, pines, and fir. If made from spruce the prominent grains are coated by a system so that this kind of plywood becomes more effective as hard as concrete and used for shuttering strands and construction.

❖ Hardwood Plywood is made from angiosperms. This type of plywood is identified by its firmness, hardness on surface, inflexibility, resistance quality. This can be used to bear heavy weight.

❖ Tropical Plywood: Different types of timbers of tropical area are mixed to make this type of plywood. Though previously it was only collected from the Asian region, now also from Africa and America it is collected. Tropical plywood popular for some special qualities like Strength, wolly Density, Evenness, Inflexibility, Resistance quality and Thickness.

❖ Aircraft Plywood: Woods from Mahogany, Spruce, Birch are used to make Aircraft Plywood. The African mahogany gives usable structural aircraft plywood. Among birch trees European birch is good. This type is famous for strength. This type is also made from Mahogany, Spruce, Birch but the special quality is that this is resistant to heat.

❖ Decorative plywood is also called overlaid plywood. Usually made from woods of ash, oak, Red oak, birch, Maple, mahogany, Philippine mahogany also called seraya, rosewood.

❖ Flexible Plywood: As the name suggests, flexible plywood is used for making flexible furniture or structures. The furniture of eighteenth century was mostly of curved structures. These are made from Baltic Birch.

❖ Marine Plywood: The type of plywood which can be used in moisture, humid, wet environment is called marine plywood. Even it can be used in moisture for long period. The layers of marine plywood bear too small core gap to feel that doesn't permit the wood to fix water inside the gaps. It is also fungal resistant.

Based on Appearance: Plywood for general purposes should be classified into three types, namely, AA, AB and BB based on the quality of the two surfaces, namely, A and B in terms of general permissible defects. The type of plywood should, therefore, be designated by the kind of surfaces of the panels. The better quality surface should be called 'face', and the opposite side should be called 'back'. If the face and the back are of the same quality, they are not distinguished. The type of plywood would denote first the quality of face followed by the quality of back. For example, Type AA should have both surfaces of quality A, Type AB should have face of quality A and the back of quality B and Type BB should have both the surfaces of quality B. Structural plywood panels are available in following sizes. 2400 x 1200 mm, 2100 × 1200 mm, 1800 x 1200 mm, 2400 x 900 mm, 2100 × 900 mm, 1800 × 900 mm.

2. USES OF PLYWOOD

❖ It has good strength both along as well as across the grains and are extensively used for partitions, ceilings, doors, concrete form work, plywood boards, lamin boards etc.

❖ It has better splitting resistance due to the grains in adjacent veneers in cross direction as such nailing can be done very safely even near the edges.

❖ Plywood has cross-grained construction, the tendency to shrink or swell is reduced and hence it can be curved into desired shapes.