Processed Wood

7/30/2019 Processed Wood

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PLYWOOD

DefinitionA board formed of three or more layers of veneer

cemented or glued together, usually with the grain

of adjacent veneers running at right angles toeach

other.

Plywood was developed to provide panels with

a dimensional stability lacking in sawn timber,

extra width without jointing and good strength

properties along and across the sheet.


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GRADES

There are two grades of plywooddepending upon the bond strength

developed by the adhesive used for

bonding the veneers.

1. Boiling water resistance or

BWRGrade2. Moisture resistance orMR

Grade


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AUSTRALIAN AND NEW ZEALAND

GRADING SYSTEM OnlyA grade surface veneers are suitable for aircraft

construction 'A' a high quality appearance gradeveneer suitable for clear finishing. Marine plywood to

AS/NZS 2272 has two A grade faces and an A or Bgrade core.

'S' an appearance grade veneer which permitsnatural characteristics such as knots as a decorativefeature subject to agreement.

'B' an appearance grade suitable for high quality paintfinishing.

'C' a non-appearance grade with a solid surface. Allopen defects such as knot holes or splits are filled.

'D' a non-appearance grade with permitted openimperfections. Limited numbers of knots and knot holes

up to 75 mm wide are permitted.


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CLASSIFICATION BY APPREARANCE

Plywood for general purposes shall 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 permissibledefects.

The type of plywood shall, therefore, be

designated by the kind of surfaces of thepanels. The better quality surface shall be

called face, and the opposite side shall be

called back.


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Permissible Categories of Defects

Type of

surface

Max. No. of categories

of permissible defectsper Sq. m

A 3B 5


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MATERIALS

TimberAny species of timber may be used for plywoodmanufacture.

1.

Indian Oak2. Cinnamon

3. Maple

4.

Mango5. Neem

6. Teak

7.

Rosewood etc.


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ADHESIVES

1. The adhesive used for bonding theveneers in different grades of plywood

shall be the corresponding type of

adhesive as specified in IS 848: 1974.2. Extenders (A substance added to the

adhesive either to reduce the cost of

gluing or to reduce penetration throughthe veneers or both) conforming to IS

1508 : 1972 may be used with the

synthetic resin adhesive(amino resins ).


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MANUFACTURING PROCESS OF PLYWOOD

SELECTING THE LOG STRIPPING THE BARK PEELING THE LOG

MAKING A CONTINUOUS RIBBON OF WOOD CUTTING AND STACKING GLUING THE WOOD

PRESSING THE WOOD TRIMMING, SANDING, AND FINISHING FINAL PRODUCT
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AS PER IS 303 POINTS TO BE REMEMBER DURING

MANUFACTURING

The veneers for all the grades shallbe either rotary cut or sliced. The

veneers shall be sufficiently smooth

to permit an even spread ofadhesive.


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TREATMENT

Treatment given to the plywood either at the

veneer stage or after converting the veneers into

boards.

Veneers from non-durable species and sapwood of

all species when used for plywood manufactureshall be soaked in 1.25 percent solution of boric

acid or 1.9 percent solution of borax at a

temperature of 85-90C for a period of 1O-40minutes depending upon the thickness of the

veneers or the veneers may be dipped in 2 percent

solution of boric acid or 3 percent borax solution

for 2 minutes and block stacked at least for two


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ASSEMBLY

1. Thickness

The thickness of all veneers shall be uniform

within a tolerance of 5 percent.

Face and back of veneer shall be of same

species having similar mechanical and

physical properties.


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Dimension Tolerance

a) Length +6mm -0mm

b) Width +3mm -0mm

c) Thickness

1) less than 6mm 10%

2) 6 mm and above 5%

d) Squareness 0.2 %

e) Edge straightness 0.2%


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THICKNESS

Board Thickness mm3 ply 3, 4, 5, 6

5 ply 5, 6, 8, 97 ply 9, 12, 15, 16

9 ply 12, 15, 16, 1911 ply 19, 22, 25

Above 11 ply As ordered


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METHODS OF TEST FOR PLYWOOD

IS 1734 (Part 1): Determination of densityand moisture content.

IS 1734 (Part 2): Determination of resistance

to dry heat. IS 1734 (Part 3): Determination of fire

resistance.

IS 1734 (Part 4): Determination of glue shearstrength.

IS 1734 (Part 6): Determination of waterresistance.


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IS 1734 (Part 8): Determination of pH value.

IS 1734 (Part 9): Determination of tensile

strength.

IS 1734 (Part 10): Determination ofcompressive strength.

IS 1734 (Part 18): Impact resistance test on

the surface of plywood.

IS 1734 (Part 20):Acidity and alkalinity

resistance test.


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Class Type Designation

Flat pressed, single layer - FPS

Flat pressed-three layer 1 FPT 1

Flat pressed multilayer and

graded

2 FPT2

Extrusion pressed, solid - XPS

Extrusion pressed, tubular - XPT


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Any species of wood or any other ligno-cellulosic material may be used in the

manufacture of particle board.

Adhesive -Any suitable type of synthetic resinconforming IS : 848 -1974 may be used for thepurpose of bonding. However, for flat-pressed

three layer, multilayer and graded boards of

Type I, BWR or BWP type adhesive should beused.


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1.

Wood particles for the manufacture of particleboards shall be produced by cutting wood

and/or any other suitable ligno-cellulosic

materials into shavings, flakes, splinters or

slivers on a suitable chipping machine.

2. The wood particles shall be dried in a

mechanical drier.

3. The dried particles shall be graded to required

sizes and thoroughly blended with the requisite

quantity of adhesives in mechanical mixers or

applicators.


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PRESERVATIVE TREATMENT

A suitable preservative may be added to the

particle mix at the stage of rinsing of

adhesive.

a) Sodium pentachlorophenate to the extent of

0.2 percent, and

b) Pentachlorophenol to the extent of 0.2

percent.


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THICKNESS

The thickness of particleboards are 6, 9, 12, 15,

18, 19, 22, 25, 27, 30, 35and 40 mm.


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Dimension Tolerance

Length - for all lengths 8 mm

Width - for all widths 8 mm

Thickness - Above 25 mm 2.5 %

Thickness up to and including

25 mm

5 %


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Density - The mean density of the boards, shallbe between 500 to 900 kg/m3. The densityshall not vary from one sample to another by

more than ten percent of the mean density.Moisture Content -- The mean moisture

content of the boards, shall not be less than 5

percent and not more than 15 percent. Themoisture content of individual test specimenshall not vary from the mean percentage by

more than 3 percent.

W t Ab ti Th t


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Water Absorption - The mean waterabsorption of the boards, shall not exceed the

prescribed limits given in table for various types

of boards after both 2-hours and 24 hoursimmersion.Water

Absorption, percent

FPS FPT1 FPT2 XPS XPT

2 Hours 25 10 40 40 40

24

hours

50 20 80 80 80

Workability - The particle boards shall not crackor split when drilled, sawed and nailed

perpendicular to the surface.

S lli g i W t Th lli i


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Swelling in Water - The mean swelling inthickness, length and width, shall not exceedthe limits given in table for various types of

boards.Thickness Swelling, percent2 h soaking


Thickness 10 8 12 5 5Length 0.5 0.5 0.5 2 2

Width 9 6 9 4 4

Swelling Due to Surface Absorption The


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Swelling Due to Surface Absorption - Themean swelling in thickness due to surface

absorption, shall not exceed the limits given in

table for various types of boards.

Swelling due tosurface absorption,

percent


2 Hours 9 6 9 4 4


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METHODS OF TEST FOR PARTICLE BOARD

IS 2380:1977 (Part 1 to Part 23)


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LOW DENSITY PARTICLE BOARD

Timber and other Iigno-cellulosicmaterial like bagasse, solapith, jute

sticks, rice husk, pea-nut shells, etc,

may be used for the manufacture ofthese boards. These shall be light

weight materials of bulk density

preferably not exceeding 400 kg/m3

and shall be free from extraneous

matter and dust.


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HIGH DENSITY PARTICLE BOARD

Type o fresin

Grade

Type 1 BWR Grade AGrade B

Type 2 WWR or

CWR

Grade A

Grade B


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FIBER HARDBOARD

Sheet material generally exceeding1.5 mm in thickness, manufactured

from lignocellulosic fibres with the

primary bond deriving from the feltingof the fibres and their inherent

adhesive properties. Bonding

materials and/or additives may be

added.


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Medium Hardboard -A homogeneous fibrebuilding board havinga density exceeding 0.35

g/cm3 but not exceeding 0.8 g/cm3.

Standard Hardboard -A homogeneous fibre

building board havinga density exceeding 0.80

g/cm3.

Tempered Hardboard -Hardboard which has

been further treatedin the course of

manufacture in order to modify one or more of

their properties ( this may have the effect of

altering the density ).


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BLOCK BOARD

A board having a core made up ofstrips of wood, each not exceeding 25

mm in width, laid separately or glued

or otherwise joined to form a slabwhich is glued between two or more

outer veneers with the direction of the

grain of the core blocks running at

right angles to that of the adjacent

outer veneers.


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GRADES

Grade 1:- Exterior grade of blockboard which ismeant for bus bodies, railway coaches,

prefabricated houses, etc, where it is likely to

be exposed to high humidity.

Grade 2:-Interior grade of blockboard which ismeant for furniture, partition, panelling, ceiling,

etc.

Each of the grades specified have of the


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Each of the grades specified have of the

following two types:

Type 1 Blockboards, Decorative Type:-These are blockboards with decorative face

veneers on one or both sides for use in high

class furniture, panelling, interior decoration,

partitions, etc. Type 2 Blockboards, Commercial Type :-

These are blockboards with veneers of

commercial timber on both sides and are usedfor ordinary furniture, table tops, partitions and

panelling to be painted over, flooring and seats

of bus bodies, railway carriage, etc.

THE GRADES AND TYPES OF BLOCKBOARDS BY


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THE GRADES AND TYPES OF BLOCKBOARDS BY

SYMBOLS

Grade and Type SymbolExterior grade, decorative

type

XDEC

Exterior grade, commercial

type

XCOM

Interior grade, commercialtype

ICOM

Interior grade, decorative IDEC


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SOME ADDITIONAL INFORMATION

Structural plywood:- A plywood of thehighest grade of structural exterior capability

used between joists and such to create

rigidity and provide a base for other surfacefinishes.


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PLYWOOD FOR CONCRETE SHUTTERING WORKS

TYPES (IS 4990: 1993)

Types

Description Designation

1 Plywood for concrete shuttering

work ( plain )

CS


work with plastic coating ( coated )

CSC


work with suitable overlay ( film

faced )

CSFF


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The size of plywood is not restricted by the size of

the tree it came from, but the size of the presstable used to make it.

Solid wood is 20 times stronger along the grainthan across. Plywood over 10mm thick is almostequal in strength in both directions.

Timber shrinks mostly across the grain. Shrinkageis almost eliminated in plywood due to the layers

being in alternate directions. Plywood can be formed or bent to make a curve.

Plywood does not split at the edges when nailed orscrewed.


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BLOCK BOARD HARD BOARD


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Processed Wood