Softwood plywood

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Lecture 14 Plywood
Bowyer, Ch. 14
Uses

• Softwood plywood
• Structural
• Similar to OSB
• Sheathing, subflooring, concrete forms, etc.
• Hardwood plywood
• Typically decorative
• Furniture, flooring, cabinetry, etc.

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Species Use For Structural Plywood

• Douglas-fir and SYP dominate U.S market
• Plywood is classified by use and/or veneer grade
• sheathing
• siding
• concrete form
• marine use
• Grades are based on quality of face and back
  veneers
• Species is sometimes used in grade designation
• Veneers are classified by strength properties of
  species
• Low density hardwoods (aspen, cottonwood, gums,
  and poplar) may be used as core material

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Commercial Species Groups
Grouped according to density/strength
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Manufacturing Steps

• Cut blocks to length and debarking
• hydration and heating - particularly important in
  the winter
• softens the wood
• Typically soaking, may also be done by steaming
  or spraying with hot water
• peeling - rotary cut or sliced
• Clipping of veneer
• rotary cut is to 54
• sliced veneer - edges are squared
• veneer drying - impingement (jet) dryers
• Adhesive coating and lay up
• pressing - heat cures the glue (low pressure
  process)
• Trimming, cooling, sanding, packaging and shipping

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Veneer Cutting
Slicing (decorative applications) Peeling
(structural and decorative)
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Veneer Handling and Drying
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Adhesive Coating and Lay-Up

• Adhesive is either automatically or manually
  applied
• Veneer layers are oriented at 90 angles
  (balanced layering is important)
• lower quality veneers in core
• faces may be different species for decorative and
  hardwood plywood

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Pressing

• High temperature, multi-opening press
• Loose assembly becomes a panel

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Veneer yield affected by1. Diameter of block
2. Peeler core diameter3. How close block is to
a perfect cylinder
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Veneer Grades
N Natural Finish are virtually blemish-free A
B Grades allow small tight knots
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32/16 32 inch span for roof sheathing / 16 inch
for subflooring Exposure 1 Manufactured with
waterproof adhesive Exposure 2 - (Interior)
adhesive is only water resistant Exposure 3
(Interior) non-water resistant adhesive