Plywood
- 2. Plywood is a a manufactured wood panel made from thin sheets of wood veneer Plywood layers (called veneers or plys) are glued together.
- 3. HISTORY Plywood was invented, in the 19th century, by Immanuel Nobel, father of Alfred Nobel. Nobel realized that several thinner layers of wood bonded together would be stronger than one single thick layer of wood, and invented the rotary lathe used in plywood manufacturing.
- 4. Structural Characteristics A typical plywood panel has face veneers of higher grade than the core veneers.The principal function of the core layers is to increase the separation between the outer layers where the bending stresses are highest, thus increasing the panel's resistance to bending.In bending, the maximum stress occurs in the outermost layers, one in tension, the other in compression. Shear stress, by contrast, is higher in the center of the panel, and zero at the outer fibers.
- 5. The most common dimension is 1.2m×2.4m or the slightly larger imperial dimension of 4 feet × 8 feet. Plies vary in thickness from 1.4 mm to 4.3 mm. The amount of plies depends on the thickness and grade of the sheet .
- 6. Types of plywood:- 1.Soft plywood 2.Hard plywood. 3.Tropical plywood. 4. Decorative plywood. 5.Marine plywood. And Other types.
- 7. 1.SoftPlywood :-Softplywood is usually made either of cedar, Douglasfir or spruce, pine, and fir (collectively known as spruce-pine-firor SPF) or redwood and is typically used for construction and industrial purposes.
- 8. 2.Hard Plywood:-Hardplywood usually made up of Birch plants. Birch plywood is characterized by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Birch plywood has excellent surface hardness, and damage- and wear-resistance.
- 9. 3.Tropical Plywood:- Tropical plywood is made of mixed species of tropical wood. Tropical plywood is superior to softwood plywood due to its density, strength, evenness of layers, and high quality. Tropical plywood is widely used in the UK, Japan, United States, Taiwan, Korea, Dubai, and other countries worldwide. It is the preferred choice for construction purposes in many regions due to its low cost. However,in many countries’ forests have been over- harvested, including the Philippines, Malaysia and Indonesia, largely due to the demand for plywood production and export..
- 10. 4.Decorative plywood:-Usually faced with hard woodincluding ash, oak, redoak, birch, maple, mahog any , rose wood, teak and a large number of other hardwoods. Formica, metal and resin-impregnated paper or fabric bonded are also added on top of plywood at both side as a kind of ready for use in the decoration field. This plywood is a lot easier to dye and draw on than any other plywoods.
- 11. 5.MarinePlywood:-Marine plywood is manufactured from durable face and core veneers,so it performs longer in humid and wet conditions and resists to fungal attack. Each wood veneer will be from tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. Marine plywood is frequently used in the construction of docks and boats. It is much more expensive than standard plywood.
- 12. Other types of plywoods include fire retardant, moisture-resistant, sign-grade and pressure-treated. However, the plywood may be treated with various chemicals to improve the plywood's fireproofing. Each of these products is designed to fill a need in industry.
- 13. Production:-Plywood production requires a good log, called a peeler, which is generally straighter and larger in diameter. The log is laid horizontally and rotated about its long axis while a long blade is pressed into it, causing a thin layer of wood to peel off (much as a continuous sheet of paper from a roll).
- 14. The sheets are then patched, graded, glued together and then baked in a press at a temperature of at least 140°C (284 °F), and at a pressure of up to 1.9 MPa to form the plywood panel. The panel can then be patched, have minor surface defects such as splits or small knot holes filled, re-sized, sanded .
- 15. Plywood for indoor use generally uses the less expensive urea-formaldehyde glue, which has limitedwater resistance, while outdoor and marine- grade plywood are designed to withstand rot, and use a water resistant phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity.
- 18. Grades:- Grading rules differ according to the country of origin. Most popular standard is the British Standard (BS) and American Standard (ASTM). List some general indication of grading rules: A-Face and back veneers practically free from all defects. A/B-Face veneers practically free from all defects. Reverse veneers with only a few small knots or discolorations. A/BB-Face as A but reverse side permitting jointed veneers, large knots, plugs, etc. B-Both side veneers with only a few small knots or discolorations.
- 19. B/BB-Face veneers with only a few small knots or discolorations. Reverse side permitting jointed veneers, large knots, plugs, etc. BB-Both sides permitting jointed veneers, large knots, plugs, etc. WG-Guaranteed well glued only. All broken knots plugged. X-Knots, knotholes, cracks, and all other defects permitted.
- 20. Applications:- Plywood is often used to create curved surfaces because it can easily bends. It has been used for marine applications since WWII. Softwood plywood few applications:- Floors, walls and roofs in house constructions. Wind bracing panels. Vehicle internal body work. Packages and boxes. Fencing.
- 21. Hardwood plywood few applications:- High-end loud speakers. Insulation boxes for Liquefied Natural Gas (LNG) carriers. Floors, walls and roofs in transport vehicles. Playground equipment. Furniture. Wind turbine blades. Musical instruments. Sports equipment.