Describe Plywood

PLYWOOD :      

The plywood is a board prepared from thin layers of timber called veneers or plies. Thus, the meaning of term ‘ply’ or ‘veneer’ is a thin layer of timber. Three or more veneers, in odd numbers, are placed one above the other and these are held in position by application of suitable adhesive. While pasting these, it is ensured that the direction of grains/fibres of successive layers is at right angles to each other. The placing of veneers across each other this way increases the longitudinal and transverse strengths of plywood.

More precisely, the plywood manufacture has following stages

- The surface of the tree trunk is sliced to remove the bark.

- Then the trunk is held horizontally at two ends, on a ‘lathe-like-machine’. The machine has a longitudinal knife cutter. The trunk is given rotary motion while the knife-cutter is gradually moved towards the centre of the trunk. This results in peeling of the trunk producing veneers/plies. Veneer/ply thickness various from 0.5 mm to 2 mm.

- The plies are then dried in the kiln to remove the moisture.

- The plies are then, cut to desired lengths and widths.

- Then three or more plies [in odd Nos.]  are glued and pressed to each other. Generally the No. of layers varies from 3 to 13. It is ensured while pressing that the fibre directions of adjoining plies, is cross to each other.  The pressing may be at ambient temperature or at a higher temperature up to 150º C. Pressing at higher temperature is called ‘Hot Pressing’. And pressing at ambient temperature, it is called ‘Cold Pressing’.

- The next operation is trimming the edges to the exact desired size.

- The last operation is to buff the surfaces & edges by fine and soft grinders.

          Technically, a product as explained above is called ‘plywood’.
  
    The plywood constructed this way, are available with the following thicknesses.      

   Available thicknesses in mm – 3, 4, 6, 8, 9, 10, 12, 15, 18 & 25

         And for all the above thicknesses, following sizes available.

           

Sr. No.	Length in Meters	Width in meters
1	2.44	1.22
2	2.44	0.92
3	2.14	1.22
4	2.14	0.92
5	1.84	1.22
6	1.84	0.92

                             

           These plywood are classified in two types.

     1.  Commercial plywood      &        2. Marine plywood 

  Commercial plywood is that plywood which does not have the ability to resist humid & wet conditions. Hence it should be used in dry areas like living rooms, bed rooms, offices, shops etc. The timber used for constructing commercial plywood does not have adequate durability in humid and wet conditions or, say, it is not water resistant. Also, the adhesive used for pasting veneers may not be water resistant and may get diluted with water, leading to plywood splitting.

 Marine plywood or Water-proof plywood has the ability to resist humid and wet conditions. Hence it is to be used in wet areas like shutters/trolleys below Kitchen platform, Bathroom cabinets, Sign boards etc. The timber used for constructing marine plywood has adequate durability in humid and wet conditions or, say, it is water resistant. Also, the adhesive used for pasting veneers is water resistant and is not affected by water.