B4


The Manila Times


FRIDAY


July 23, 2010


BUREAU OF PRODUCT STANDARDS


Republic of the Philippines Department of Trade and Industry


PHILIPPINE NATIONAL STANDARD Plywood – Specification Foreword


The Philippine National Standard Specification for Plywood, PNS 196:1992 has been reissued by the Bureau of Product Standards.


PHILIPPINE NATIONAL STANDARD Addendum


This addendum to the Philippine National Standard 196:2000 Plywood specifications was prepared by the Bureau of Product Standards upon the recommendation of the Technical Committee on Wood-Based Panels - Plywood (BPS/TC 35).


The following provisions shall be added in Table 3 Thickness, number of plies and tolerances: Thickness, mm Number of Plies Explanation


Add 4.5mm and 6mm plywood thickness Add the word “minimum” to the number of plies


The 4.5mm and 6mm plywood thickness were added as these are the nearest metric conversions of the 3/16” and 1/4” sizes.


The word “minimum” was added to the number of plies as some applications like marine plywood demand more plies as specified in BS 1088.


1 Scope


This standard specifies the requirements for general purpose plywood. 2 Definitions


For the purpose of this standard, the following definitions apply: 2.1 adhesive


any cement, glue or resin used in bonding together two or more pieces of wood by surface attachment 2.2 bark pocket


a comparatively small area of bark around which normal wood has grown 2.3 blister


a bulge on the surface due to a separation of the constituent plies or veneers, usually at the glue line. If the separation is visible at edges of the board, the defect is termed delamination


2.4 bonding


the act of uniting the layers of a plywood assembly preferably applied by the use of resin adhesives 2.5 burl


woody growth on the log which is sound, harder than the surrounding wood, round or horizontally ridged, formed by protruding limbs, twigs or stubs, appearing as though exuded from the trunk


2.6 closed split a split in the veneer, which during the process of manufacture into plywood, has completely closed, and is visible only as a fine line on the face or back of the panel


2.7 core gap (core void)


an open joint extending through or partially through a panel, which results when side by side core or center veneers are not tightly butted together


2.8 cross break


separation (break) of the wood cells across the grain. Such breaks may be due to strains resulting from unequal longitudinal shrinkage, or to external forces


2.9 cross bonding


veneer used in the construction of plywood with five or more plies. In five-ply construction, it is placed at right angles between the cores and faces


2.10 cross-grained


the term applied to a sheet of plywood when the width of the sheet is greater than its length 2.11 dead knot


knot usually produced by dead branches embedded in the wood 2.12 dent


slight hollow or small depression on the surface of the panel generally attributed to dirt or foreign materials introduced between the press platen surface and the surface of the panel being pressed


2.13 delamination


a visible separation between plies that would normally be firmly glued together in the pressing operation 2.14 exterior plywood


refers to the type of plywood intended for outdoor or marine uses, also known as type I 2.15 face


the surface of the plywood showing veneer of higher grade than that of the outer side or back. However, the terms face and back do not apply when the same grade of veneer is used on both sides of the plywood


2.16 face-plywood


a plywood faced with a material other than wood, such as metal or plastic 2.17 fillers


an additive often combined with adhesive resins to modify bonding characteristics of the resin mix 2.18 gap


a void in the core ply due to a split or other open defect. It also results from improper jointing face veneers, called gapped joint


2.19 glue line


the resultant layer of adhesive effecting union between any two adjacent plies in the assembly 2.20 hardwood


a general term used to designate lumber produced from broadleaf or deciduous trees in contrast to softwood produced from evergreen or coniferous trees


2.21 heartwood


the wood extending from the pith to the sapwood, the cells of which no longer participate in the life process of the tree. Heartwood may be infiltrated with gums, resins, and other material that usually make it darker and more decay resistant than sapwood


2.22 interior plywood


a type of plywood intended for inside uses, having a limited moisture resistance 2.23 interlocked grain (cross grain)


a grain of certain species wherein the axis of the fibers of the wood reverses direction after each of the several growth cycles, thus interlocked


2.24 lap


a condition where the veneers used are so misplaced that one piece over laps the other and does not make a smooth joint


2.25 lumber-core a wide board made up of well machined lumber strips properly dried and glued together


2.26 lumber-core plywood a plywood made up of face/back veneer, crossband core veneer and well composed kiln dried lumber core. It is commonly called plyboard


2.27 open defect


any check, split, open joint, crack, loose knot, worm hole, or other defects interrupting the smooth continuity of the plywood surface


2.28 panel


a sheet of plywood 2.29 patches


insertions of filler or sound wood placed and glued into panels from which defective portions have been removed 2.30 pin knot


a sound knot less than 6.40 mm in diameter 2.31 ply


the stratum or layer used in referring to the successive layers of veneer in plywood panel 2.32 plies


the individual layers of veneer forming the plywood 2.33 plywood


an assembled product made of layers of veneers and/or lumber-core held together by an adhesive, the chief characteristics of which is the alternate cross layers, distributing the longitudinal wood strength. In its simple form, it consists of three layers of thin wood, firmly glued together, with the grain direction of the middle layer at right angles to that of the two parallel outer layers. The use of the term is broadened to include products referred to as blockboards, stripboards and plyboards which use lumber core


2.34 shake


a separation along the grain, the greater part of which occurs between the rings of annual growth 2.35 shear


a measure of the resistance of parallel planes in a body to slide over each other 2.36 shim


an insert in the form of a narrow strip of veneer 2.37 slip-joint


the method of laying up veneers in flexible bag mouldings in which the edges are bevelled and allowed to override at the scarfed area


2.38 smear


spots or marks of usually sticky substances on the surface of the panel due to the excess of wood putty used to fill up open defects


2.39 sound knot


a solid knot as hard as the surrounding wood with no sign of decay or deterioration 2.40 splice


the cutting/elimination of defective portion of a ply during the veneering process and subsequently joined by means of automatic splicer machine


2.41 split


lengthwise separation of the wood fibers due to the tearing apart of the wood cell, caused chiefly by shrinkage in drying and careless handling


2.42 stain


a discoloration on the wood, or any color other than the natural color of the wood 2.43 warp


the distortion due to stresses causing departure from a plane or true form


PNS 196:2000 Addendum 01:2010


PNS 196:2000 ICS 79.060.10


2.44 wood-filler


an aggregate of resin and strands or shreds of wood which are used to fill openings and to provide a smooth durable surface


3 Classification and designation Plywood shall be classified according to the following: 3.1 Based on bonding quality 3.1.1 Type I - Exterior 3.1.2 Type II - Interior


3.2 Based on appearance according to its surface grades which are determined by defects inherent in wood, and by manufacturing defects visible on finished panels. 3.2.1 Grade A 3.2.2 Grade B 3.2.3 Grade C 3.2.4 Grade D 3.2.5 Grade E 4 Construction of panels


4.1 In general, the grain of adjacent plies shall be at right angles. Plies symmetrical to one another relative to the center ply or the core shall normally have the same thickness and shall consist of the same species of wood or of species having similar physical characteristics. They shall be produced in the same manner, i.e., either by rotary cutting or by slicing and shall be placed with their grain oriented in the same direction.


4.2 The substitution, of one ply by a pair of plies with the grain parallel to each other is permissible, provided they are balanced by a similar pair of plies of equal total thickness and on a corresponding position to the center ply on the core.


4.3 The outer plies shall be laid with the tight side of veneer outermost.


4.4 Non-perforated paper strips for jointing on interior veneer shall not be used. If they are used for edge joints or to repair splits in the outer plies, they shall normally be removed afterwards.


4.5 In the normal dry condition, no outer ply shall have a thickness less than 0.8 mm and no inner ply shall have a thickness greater than 5 mm. 5 Bonding of Plywood


5.1 Type I (Exterior) - The bond for type I plywood shall withstand all weather and water exposures and shall not be affected by microorganisms and shall pass the cyclic boil test described in annex C.


5.2 Type II (Interior) - The bond for type II shall retain its strength when occasionally subjected to thorough wetting and drying conditions and shall pass the test prescribed in annex C. 6 Grading of plywood and its allowable defects


6.1 Appearance of surfaces - The appearance of surfaces for each grade of plywood shall be as indicated in table 1.


6.2 Allowable defects - The allowable defects for each grade of plywood for general purposes with outer veneers shall be as indicated in table 1. Defects, which are limited in number, size or extent, are enumerated or evaluated per square metre, calculated as an average of their incidence over the total surface of the panel, with the exception of checks, splits and open joints, which are related to one metre of panel width.


6.3 Determination and application of grades of panels - The grade of plywood by appearance is determined by the grade of the two surfaces of the panel.


6.3.1 The better quality is called face; the opposite side is called back. 6.3.2 The grade of the plywood describes first the grade of the face followed by the grade of the back. 7 Inner plies and cores


7.1 The inner plies and cores may contain defects or characteristics of the material, or manufacturing defects, but only in so far as their effect on the plywood panel falls within the requirements of all relevant parts of this standard.


8 Joints


8.1 For grade A, veneers forming the outer ply shall be well matched in color and of similar grain. Up to a panel width of 1500 mm, the outer ply shall be of one or two veneers, the joint being well made and approximately at the centre of the panel. For panels wider than 1500 mm the outer plies may consist of well jointed veneers, of not less than 600 mm width.


8.2 For grade B, its surface shall be reasonably matched in color and of similar grain. The number of veneers which form the outer plies of a panel is not restricted, provided, the joints are well made.


Table 1 – Permissible defects for the classification by appearance of surfaces of general purpose plywood with outer veneers


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