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ABOUT PLYWOOD

WHAT IS PLYWOOD?

 

1Introduction

Another name: Multilayer board

 

One of the commonly used materials for furniture is a wood-based panel. A group of veneers are usually glued together according to the direction of the wood grain of adjacent layers perpendicular to each other. Usually, the surface board and the inner layer board are symmetrically arranged on both sides of the center layer or the board core. The slab made of the veneer after gluing is criss-crossed according to the direction of wood grain, and pressed under heating or non-heating conditions. The number of layers is generally an odd number, and a few have even numbers. The difference in physical and mechanical properties in the vertical and horizontal directions is small. Commonly used are three-ply board, five-ply board and so on. Plywood can improve wood utilization and is a major way to save wood. It can also be used as a material for aircraft, ships, trains, automobiles, buildings and packing boxes.

The usual length and width specifications are: 1220×2440mm, 1250×2500mm, 915×1830mm, etc., while the thickness specifications generally include: 3, 5, 9, 12, 15, 18mm, etc. The main tree species are: willow, pine, poplar, eucalyptus and so on. The main origins of high-quality plywood with all mixed wood: Indonesia and Malaysia. Main origin of plywood with poplar core: China.

 

2:The basic principle

In order to improve the anisotropic properties of natural wood as much as possible, so that the properties of plywood are uniform and the shape is stable, the structure of general plywood must abide by two basic principles: one is symmetry; the other is that the fibers of adjacent layers of veneer are perpendicular to each other. The principle of symmetry is to require that the veneers on both sides of the symmetrical central plane of the plywood should be symmetrical to each other regardless of the nature of the wood, the thickness of the veneer, the number of layers, the direction of the fibers, and the moisture content. In the same plywood, veneers of a single species and thickness can be used, or veneers of different species and thickness can be used; however, any two layers of veneers that are symmetrical to each other on both sides of the symmetrical central plane must have the same species and thickness. The face and back panels are not allowed to be of the same tree species.

To make the structure of plywood meet the above two basic principles at the same time, its number of layers should be odd. Therefore, plywood is usually made into odd-numbered layers such as three layers, five layers, seven layers, nine layers, and eleven layers. The names of each layer of plywood are: the surface veneer is called the surface board, the inner veneer is called the core board; the front board is called the panel, and the back board is called the back board; in the core board, the fiber direction is parallel to the board It is called long core board or medium board.

 

3:Type

 

In order to make full and reasonable use of forest resources to develop plywood production and make the best use of materials, according to the current use of plywood, plywood is divided into finishing plywood (used for furniture, sewing machine tabletops and various electrical appliances shell that need to be coated with transparent paint on the surface), decoration plywood (used as construction, furniture, vehicle and ship decoration materials), General plywood (suitable for packaging, padding and other purposes) and veneer decorative plywood (used as high-grade decorative materials for construction, furniture, vehicles, ships, etc.), According to the glue strength plywood types are divided into:

(1) Class I (NQF) – weather-resistant, boiling water-resistant plywood. This type of plywood has properties such as durability, resistance to boiling or steam treatment, and can be used outdoors.

(2) Class II (Ns) – Water-resistant plywood. It can withstand immersion in cold or short-term hot water, but not boiling.

(3) Class III (Nc) – plywood not resistant to moisture.

 

4:Related introduction

 

Plywood is a three-layer or multi-layer board-like material that is made of wood sections that are peeled into veneers or sliced into thin wood, and then glued with adhesives. Usually, odd-numbered veneers are used, and adjacent layers of veneers are used. The fiber directions are glued perpendicular to each other. The plywood produced with wood as the main raw material, due to the rationality of its structure and the fine processing in the production process, can generally overcome the defects of wood and greatly improve the physical and mechanical properties of wood. Plywood production is to make full use of wood, An important method to improve the properties of wood.

Decorative veneer

1) Decorative veneer veneer plywood is a wood-based panel made of natural wood decorative veneer pasted on plywood. Decorative veneer is a thin wood chip made of high-quality wood by planing or rotary cutting.

2) Features of decorative veneer veneer plywood: Decorative veneer veneer plywood is one of the most commonly used materials for interior decoration. Because the decorative veneer on the surface of the product is made of high-quality wood through planing or rotary cutting, it has better decorative performance than plywood. This product is natural, simple, natural and noble, and can create a living environment with the best affinity and elegance.

3) Types of decorative veneer veneer plywood: decorative veneer veneer plywood can be divided into single-sided decorative veneer veneer plywood and double-sided decorative veneer veneer plywood according to the decorative surface; Veneer veneer plywood, Class II decorative veneer veneer plywood and Class III decorative veneer veneer plywood; according to the texture of decorative veneer, it can be divided into straight grain decorative veneer veneer plywood and pattern decorative veneer veneer plywood. The most common is one-sided decorative veneer veneer plywood. Commonly used materials for decorative veneers include birch, ash, oak, oak, elm, maple, beech, and walnut.

4) Classification of decorative veneer veneer plywood: my country’s decorative veneer veneer plywood standard stipulates that decorative veneer veneer plywood is divided into three grades: superior product, first-class product and qualified product. Manufacturers and consumers are reminded that other grading forms do not meet my country’s decorative veneer veneer plywood standards. For example, some manufacturers mark the grade as “AAA”, which is an enterprise behavior.

5) Performance requirements of national standards for decorative veneer veneered plywood: The current recommended standard in my country is GB/T 15104-94 “Decorative veneer veneered wood-based panels”. At present, most enterprises implement this standard in production. This standard specifies indicators for decorative veneer veneer plywood in three aspects: appearance quality, processing accuracy, and physical and mechanical properties. Its physical and mechanical performance indicators include: moisture content, surface bonding strength, dipping and peeling. GB 18580-2001 “Indoor Decoration Materials – Formaldehyde Release Limits in Wood-Based Panels and Their Products” also stipulates the formaldehyde release limit indicators for this product.

The national standard stipulates that the moisture content index of decorative veneer veneer plywood is 6% to 14%.

The surface bonding strength reflects the bonding strength between the decorative veneer layer and the plywood substrate. The national standard stipulates that this index should be 50MPa, and the number of test pieces that meet the standard should be 80%. If the index is unqualified, it means that the bonding quality of the decorative veneer and the base plywood is poor, which may cause the decorative veneer layer to open and bulge during use.

Dipping peeling reflects the bonding performance of each glued layer of decorative veneer veneer plywood. The failure of this index indicates that the glue quality of the board is poor, which may cause glue opening during use.

Formaldehyde release limit. This indicator is a mandatory national standard implemented by our country on January 1, 2002. This is the “birth certificate” of related products. Products that fail to meet this standard are not allowed to be produced from January 1, 2002; It is also the “Market Access Certificate” for related products. Products that do not meet this standard are not allowed to enter the market circulation field from July 1, 2002. Exceeding the limit of formaldehyde will affect the health of consumers. The standard stipulates that the formaldehyde emission of decorative veneer veneer plywood should reach: E1 grade 1.5mg/L, E2 grade 5.0mg/L.

Decorative veneer selection

In recent years, in the production of plywood, many varieties of designs and colors have been derived, the most important of which is to paste a thin layer of decorative veneer veneer on the surface of the original plywood, called decorative veneer veneer plywood, the market It is referred to as a decorative panel or a veneer panel.

It is worth noting that common veneers are divided into natural wood veneer veneers and artificial veneer veneers. Natural wood veneer is a veneer veneer made of precious natural wood through planing or rotary cutting. Artificial veneer is made of veneer by rotary cutting of relatively cheap logs, pressed into wooden squares by a certain process of glue, and then sliced to make decorative veneer (technical wood) with beautiful patterns.

Usually the veneer attached to the natural wood veneer veneer is often a tree species with good pattern and high value, such as cypress, oak, rosewood, ash, etc. But it should be stated in the trade name, such as “cypress veneered plywood”, or “ash sliced plywood”, or “cherry wood veneer”. The “veneer”, “slicing” and “plywood” in several ways reflect the basic characteristics of “plywood”. However, it cannot be abbreviated as cypress three-plywood, ash three-plywood, etc., because these abbreviations refer to the panels and bottom plates of plywood being made of cypress or ash. Another problem is that more and more furniture is produced from veneer, although these furniture have the appearance of wood grain such as “cypress wood”.

Design selection points

1) Select plywood of different types, grades, materials, decorations and formats according to the nature of the project, the location of use, environmental conditions and other factors.

2) Plywood veneered with precious wood sliced veneer should be used for decoration.

3) The plywood used for building interior decoration shall comply with the provisions of GB50222 “Code for Fire Protection Design of Building Interior Decoration”.

4) Type I or Type II plywood should be considered for concealed parts that may be damp and places with high waterproof requirements, and Type I plywood should be used for plywood used outdoors.

5) Transparent varnish (also known as varnish) should be used for panel decoration to retain the natural color and texture of the wood surface. The choice of panel material, pattern and color should be emphasized; if the pattern and color of the panel do not need to be considered, it should also be reasonable according to the environment and cost Select plywood grade and category.

5: National standard

Ingredients and preparation

3.1 Veneer veneer wood veneer produced by rotary cutting, semicircular rotary cutting, planing or sawing.

3.2 Surface outer ply refers to the surface veneer of plywood.

3.3 Panel face glue The surface panel with better appearance quality.

3.4 The back is the panel on the other side of the panel.

3.5 Central layer central ply The central layer of plywood, other layers are symmetrically arranged on both sides of it.

3.6 Core board cross band, lateral ply inner layer unit whose texture direction is perpendicular to the surface board texture.

3.7 Long middle plate centres, longitudinal ply The inner veneer whose grain direction is parallel to the surface grain.

3.8 Core sandwich plywood or the center layer of composite plywood.

3.9 Splicing joint The connection of adjacent veneer strips in the same layer.

3.10 Longitudinal edge joint Two pieces of edge-aligned veneers are spliced along the longitudinal edge, and the seam is in the same direction as the grain of the veneer.

3.11 end joint Two pieces of veneer with the same edge are spliced along the extreme edge, and the seam is perpendicular to the grain direction of the veneer.

3.12 miter scarf joint Two pieces of veneer are spliced along the end of the inclined panel or the edge of the inclined panel.

3.13 Finger joint The ends of two veneers are processed into finger-shaped tenons and staggered on the plane.

3.14 Adhesive glue, adhesive is used to glue two surfaces to each other.

3.15 Glue the bond with adhesive.

3.16 adhesive layer glue linc A thin layer of adhesive that glues two adjacent surfaces together.

Grain

4.1 grain: The texture formed by the arrangement direction of wood fibers in China.

4.1.1 straight grain: wood grain is straight and parallel or nearly parallel to one of the two main directions (longitudinal or widthwise) of the veneer

4.1.2 angle grain: The wood grain is not perpendicular to the edge of the veneer.

4.1.3 irregular grain: The wood grain is straight down due to the abnormal structure of the wood.

Type

5.1plywood: A group of veneers are usually glued together according to the wood grain direction of adjacent layers perpendicular to each other. Usually, the surface board and inner layer board are symmetrically arranged on both sides of the center layer or core.

5.1.1 long grained plywood: the plywood whose surface grain is parallel or nearly parallel to the long side of the board.

5. 1.2 Cross grained plywood: The plywood with the grain of the surface board almost parallel to or close to the short side of the board.

5.1.3 plywood for general use: plywood suitable for a wide range of uses.

5.1.4 special plywood can meet the plywood of special purpose.

5.1.5 Eltetior plywood: a plastic platen with weather resistance, water resistance and high humidity resistance.

5.1.5.1 Type 1 plywood: weather-resistant plywood, this type of plywood is durable, resistant to boiling or steam treatment, and can be used outdoors.

5.1.6 Interior plywood: Plywood that does not have the adhesive properties of long-term water immersion or high temperature.

5.1.6.1 Type 2 plywood: Water-resistant plywood, this type of plywood can be dipped in cold water, or withstand short-term hot water dipping, but not resistant to boiling.

5.1.6.2 Type 3 plywood: Moisture-resistant plywood, this type of plywood can withstand short-term cold water immersion and is suitable for indoor use.

5.1.6.3 Type 4 plywood: non-moisture-resistant plywood, this type of plywood is used indoors under normal conditions, and has certain bonding strength.

5.1.7 Structural plywood: plywood with limited mechanical property requirements.

5.1.8 Star plywood: The plywood made of veneer texture arranged in a star shape.

5.2 Core plywood: plywood with a core.

5.2.1 Block board: The board core is composed of wooden strips, which can be glued or not glued between the wooden strips.

5.2.2 Callular board: The board core is composed of a honeycomb structure. Usually, there should be at least two layers of veneers with vertically arranged wood grains on both sides of the board core.

5.3 Composite plywood: The board core (or some layers) is composed of materials other than solid wood or veneer. Usually, there should be at least two layers of veneer with wood grains arranged vertically on both sides of the board core.

5.4 Decorative plywood: Two surface veneers or one of them is a decorative veneer.

5.5 Molded plywood: Non-planar plywood formed by pressure in a die.

5.6 Scarfed plywood: Two or more plywood panels are glued together with inclined planes to increase their format size.

5.7 Finger jointed plywood: Two or more sheets of plywood are glued together by means of interlaced joints on the edge of the board to increase the size of the plywood.

5.3 Length of panel: The dimension along the wood grain direction of the panel.

5.9 Width of panel: the dimension perpendicular to the extreme length.

5.10 Thickness of panel: The size that is vertically suitable for the panel surface.

Formation

6.1 Lay-up: the configuration of each layer of veneer in the slab according to the grain direction and thickness.

6.1.1 Cross-banded plies: vertical arrangement of wood grains of two adjacent veneers.

6.1.2 Star formation: Two adjacent layers of single-phase wood-grained star-shaped arrangement configuration.

6.1.3 Parallel grain plies: the wood grains of two adjacent layers of veneer are arranged in the same direction.

6:Various defects

Material defects

 

7.1.1 Knots: Branches wrapped in wood.

7.1.1.1 Pin knots: healthy joints with a diameter not exceeding 3mm.

7.1.1.2 Inter grown knots: Formed by living knots of trees. The knots are closely connected with the surrounding wood or the part of the joint with the surrounding wood is greater than 3/4 of the length of the perimeter of the cross section, the texture is hard, and the structure is normal.

7.1.1.3 Dead knots: formed by the dead branches of trees, the knots are connected with the surrounding wood, or the connected part is only 1/4 or less than 1/4 of the length of the perimeter of the cross section, The texture is hard or soft, and sometimes falls off to form a cavity.

7.1.1.4 Partially intergrown knOts: the part of the joints around the knot and the surrounding wood is more than 1/4 to 3/4 of the length of the cross-sectional perimeter, and the texture is hard.

7.1.1.5 Sound knots: no rotten knots.

7.1.1.6 Unsound knots: the knots with no more than 1/3 of the decayed part on the knot section.

7.1.1.7 rotten knots: knots with more than 1/3 of rotten knots on the cross section.

7.1.1.8 knot holes: Holes caused by knot falling off.

7.1.2 Abnormal structure: Defects formed by abnormal wood structure, such as wrinkles. corrugated pattern. Staggered grain, spiral grain, etc.

7.1.3 Resin pocket: Lentil-shaped cavity in wood, which contains or has contained resinous substances.

7.1.4  Inbark bark pocket: The bark that is completely or partially wrapped in wood due to the growth of the tree.

7.1, 1.5 Sound knots: There are no rotten knots.

7.1.1.6 Unsound knots: the knots with no more than 1/3 of the decayed part on the knot section. 

7.1.1.7 Rotten knots: Knots with more than 1/3 of rotten knots on the cross section.

7.1.3  Discoloration: Any change in the normal color of wood is called discoloration, which can be divided into chemical discoloration and fungal discoloration.

7.1.8.1 False heartwood: The color of the center part of sound wood is different from that of normal wood, usually dark brown or reddish brown, and usually its density and hardness are relatively high.

7.1.8.2  Chemical stain: wood discoloration caused by chemical reaction between wood components and some foreign substances.

7.1.8.3  Mold: hyphae and spores of mold on the wood surface.

7.1.8.4 Blue stain: also known as blue stain, the color of sapwood becomes gray, slightly light blue or light green.

7.1.8.5 Pith flecks: the wounded tissue formed by the cambium being attacked by insects before the wood is felled.

7.1.8.6 Flecks streaks: It is formed at the initial stage of wood rot fungus intrusion into wood, and brown color is often seen. Tan or purplish red spots.

7.1.9 Decay rot: due to the invasion of wood-rot fungi, the cell wall material is decomposed, resulting in soft wood, decreased strength and density, and often changes in wood texture and color.

7.1.9.1 Incipient decay: The erosion of wood by fungal growth causes slight changes in its chemical composition (generally before drying), showing slight changes in hardness and discoloration, resulting in changes in wood properties.

7.1.10 Row nail holes: Holes caused by hooks and pickers’ tools during log shipment.

7.1.11 Split, end split: Separation of fibers along the direction of the wood grain, usually starting at one end and extending through the thickness of the veneer.

7.1.12 Check: Separation of short fibers of the surface plate, usually not starting from the edge of the plate, not always extending through the thickness of the veneer.

Processing defects

7.2.1 Open Joint: The splicing between two adjacent veneers in the same layer is not tight.

7.2.1.1 Core gap: The plywood core board or the separation gap in the board core.

7.2.1.2 Centers gap: the gap between the long and medium boards of plywood.

7.2.2 Overlap: In the same layer of veneer, two adjacent veneers (or two parts of a cracked veneer) overlap each other.

7.2.3 Blister: Local separation due to glue failure between adjacent layers of veneers.

7.2.4 Delamination: The separation of two adjacent veneers due to lack of glue or poor gluing.

7.2.5 Hollow: local depression on the surface plate.

7.2.6 Imprint: local indentation on the panel.

7.2.7 Bump hump: local overthickness appearing on the surface plate.

7.2.8 Lathe check cutting check: The tiny crack that can appear when the loose side of the panel is arranged outwards.

7.2.9 Torn grain: The surface of plywood is rough and uneven due to fiber tearing.

7.2.10 Roughness: roughness of plywood surface.

7.2.11 Sandlng through: Due to the excessive sanding of the surface plate, the adhesive layer or the next layer of veneer is exposed at the partially ground through.

7.2.12 Glue penetration: Adhesive seeps out of the surface of the surface to contaminate the surface of the surface.

7.2.13 Inclusion of gummed tape: The inside of plywood contains gummed tape.

7.2.14 Metallic inclusions: Plywood contains metal objects such as staples.

7.2.15 Defects at the edges of the panel: Defects at the edges of the panel due to sanding, sawing or collision.

7.2.16 Warping: generally regular deformation, part or all of the surface of corrugated board is curved.  

Repair

8.1 Repaired plywood: The plywood whose defect has been repaired with filler or veneer patch.

8.2 Filling: filling holes and other defects with fillers.

8.3 Insert: Use good veneers of various shapes to embed the parts where the defects have been dug out in advance.

8.4 Patck plug: a geometric veneer for digging and filling.

8.5 Shim: Narrow and long veneer sheet for repair.

Surface condition

9.1 Sanded plywood: The plywood whose surface has been sanded by a sander.

9.2 Scraped plywood: The plywood whose surface is scraped off by a scraper.

 

Further processing

 

10.1.1 Prefinished plywood: The plywood that has been specially treated by the manufacturer and does not need to be modified when used.

10.1.2 Overlaid plywood, faced plywood: plywood with decorative veneer, wood grain paper, impregnated paper, plastic, resin film or metal sheet on the surface.

10.2 Treated plywood: Plywood treated with chemicals during or after manufacture, used to control the physical properties of the material.

10. 2.1 Preservative treated plywood: plywood treated with fungicides or insecticides in order to improve extreme durability.

10.2.2 Flame-retardant plywood: In order to retard the spread of flame, the plastic platen treated with flame retardant.

10.2.3 Resin treated plywood: Plywood treated with resin by impregnation or other methods.

10.3 Direct print plywood: Print directly on the surface of plywood with simulated wood grain or other patterns.

10.4 Embossed plywood: embossed color patterns on the surface of plywood.

10.5 Machining

10.5.1 Transformed plywood: Plywood processed by mechanical finishing or bonding, such as cutting, profiling sawing, scarfing, drilling, milling, etc.

10.5.2 Curved plywood: plywood processed by one or several times of bending.

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