Raw plywood Quality according to the appearance of the surface (acc. to the EN 635)

Raw plywood

Source from  : http://welde.bg/

The plywood panels are made by gluing together of 3 or more veneer sheets (plies). The grain of each ply is perpendicular to the plies above and below it. The phenol formaldehyde resin used as a gluing agent gives to the bonding a high resistance of weather conditions, microorganisms, cold and hot water. The cross-bounded construction of veneers guarantees exceptionally good mechanical qualities of the plywood panel such as: strength, stability, high resistance of strokes, vibrations and tension.
The plywood panels react far better to temperature influence than the metal and plastic materials. They are more stable under cold than under heat. The temperature range that can be used with no change in the appearance and mechanical characteristics is wider than 100°С.

The plywood panels are suitable for noise insulations. As the effectiveness of the insulation depends on the density of the insulation material, the plywood panels have a better ratio of density-noise insulation, compared to other materials (EN 13986).

For plywood production in Welde Bulgaria the most used species is Robusta poplar. But species like beech, birch and soft wood are also possible to be used. Various wood species can be combined in composing the plywood panels.
The formaldehyde emissions are low and correspond to the prescriptions of EN 717-2., i.e. the regulations of E1 class (the most safety one).

Sizes

The length is normally twice the width of a panel.
The standard sizes are:

  • Length, mm: 2500 ± 2.0;
  • Width, mm: 1250 ± 2.0;
  • Thickness, mm: 4; 6; 8; 10; 12; 14; 15; 16; 18; 21; 24; 25; 27; 28; 30.

The production equipment of Welde Bulgaria as per customer’s request enables additional treatment of the panels to be done: sanding, calibration, or cutting to size. The density of the poplar plywood is 450-500 кг/м3.

Thickness, mm Weight, kg Number of sheets
in a package
per sheet per package
4 6 1320 220
6 9 1480 168
8 12 1480 126
10 15 1480 101
12 18 1500 84
14 20 1480 72
16 23 1480 64
18 26 1450-1500 56
21 30 1450-1500 48
24 35 1480 42
28 41 1480 36
30 43 1480 34

Note: The values refer to plywood panels of 1250 х 2500 mm sizes.

Quality according to the appearance of the surface (acc. to the EN 635).

Grading of the plywood panels according to the surface appearance is performed based on two criteria – number of the defects as natural characteristics of wood, and defects caused over the production process.
The qualities acc. to the EN 635-3, in force since 2004, are as follows: E, I, II, III, IV. They correspond to the A, AB, B, BB, C qualities of the former standard BDS 384-76.

Categories of characteristics Appearance class
E I II III IV
Pin knots *)         Practically absent 3/m2 permitted Permitted
Sound intergrown knots Permitted up to an individual diameter of:
15 mm provided their cumulative diameter  does not exceed 30 mm/m2 50 mm 60 mm Permitted but see Note.
Such knots may have splits provided they are:
very slight slight
Unsound or non-adhering knots and knots holes Permitted up to an individual diameter of:
6 mm if filled and up to a number of 2/m2 5 mm if unrepaired
25 mm if filled and up to a number of 6/m2
  40 mm   Permitted but see Note.
Splits open Permitted if less than:
1/16 1/3 ½ Length unlimited
of panel length up to an individual width of:
3 mm 10 mm 15 mm 25 mm
and  up to a number of:
3/m 3/m 3/m unlimited
of panel width
if properly filled All splits greater than 2 mm in width to be filled
closed Permitted
Anomalies due to insects, marine borers, and parasite plants Not permitted Not permitted Marks of parasitic plants not permitted. Insects and marine borer holes permitted up to a: Permitted but see Note.
diameter of 3 mm vertically to the plane of the panel up to a number of 10/m2 width up to 15 mm and a length of 60 mm up to a number of 3/m2
Resin pockets and inbark Not permitted Permitted up to a width of Permitted but see Note.
6 mm if properly filled 40 mm
Resin streaks Not permitted Permitted if slight Permitted
Irregularities in the structure of the wood Practically absent Permitted Permitted
if very slight if slight
Discoloration which is not wood destroying Permitted if low contrast Permitted
Fungal decay, wood destroying Not permitted Not permitted
Other characteristics Practically absent To be considered under the category which they most closely resemble
*) Pin knots: sound intergrown knots of no more than 3 mm diameter
NOTE: Characteristics inherent to wood ate permitted provided that they do not impair the serviceability of the panel.

Classification according to characteristics inherent in wood.


E Quality

I Quality

II Quality

III Quality

IV Quality

 

Categories of defects Appearance class
E I II III IV
Open joints Not permitted Not permitted Permitted up to a width of:
3 mm 10 mm 25 mm
and up to a number of:
1/m 2/m unlimited
of panel width with joints
filled if more than 1 mm in width unfilled unfilled
Overlaps Not permitted Permitted up to a number of 1/m2 and up to 100 mm length Permitted up to a number of 2/m2 Permitted but see Note
Blisters Not permitted
Hollows, imprints and bumps Not permitted Permitted if slight Permitted
Roughness Not permitted Permitted if slight Permitted
Sanding through  Not permitted Permitted up to an extend of:
1 % 5 %
of panel surface
but  see Note
Glue penetration Not permitted Permitted Permitted but see Note
if slight and occasional up to an extent of 5 % of the panel surface
Foreign particles Not permitted Ferrous particles not permitted
Repairs
a) Patches
b) Shims
c) Synthetic fillers
Practically without defects Permitted if properly made and tightly filled up to a number of:
5/m2 unlimited
Not permitted Not permitted is permitted with limits of the category which it most closely resembles unlimited
Defects at the edges of the panel due to sanding or sawing Practically without defects Permitted up to Permitted but see Note
2 mm 5 mm 5 mm
from the edge
Other defects To be considered under the category which they most closely resemble
NOTE: Manufacturing defects are permitted provided that they do not impair the serviceability of the panel.

Classification according to manufacturing defects.

Physical and mechanical characteristics

  1. Moisture of the plywood (acc. to the EN 322): 10 ± 2 %.
  2. Squaredness variation after trimming: up to 1 mm/m.
  3. Variation out of the rated length and width (acc. to the EN 315): ± 3.5 mm.
  4. Variation out of the rated thickness (acc. to the EN 315):
    Rated thickness(t),
    mm
    Non-sanded panels SANDED PANELS
    Variation out of the thickness in a panel,
    mm
    Variation out of the rated thickness,
    Mm
    Variation out of the thickness in a panel,
    mm
    Variation out of the rated thickness,
    mm
     EN 315 Welde
    Bulgaria
    EN 315 Welde
    Bulgaria
    EN 315 Welde
    Bulgaria 
    EN 315 Welde
    Bulgaria
    ≥ 3
    ≤ 12
    1.0 0.8 + (0.8 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.5
    -0.4
    0.6 0.3 + (0.2 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.2
    – 0.4
    > 12
    ≤ 25
    1.5 1.0 + (0.8 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.8
    – 0.5
    0.6 0.3 + (0.2 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.4
    – 0.6
    > 25
    ≤ 30
    1.5 1.0 + (0.8 + 0.03 t)
    – (0.4 + 0.03 t)
    + 1.0
    – 0.8
    0.8 0.3 + (0.2 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.5
    – 0.8
    > 30 1.5 1.2 + (0.8 + 0.03 t)
    – (0.4 + 0.03 t)
    + 1.3
    -1.0
    0.8 0.3 + (0.2 + 0.03 t)
    – (0.4 + 0.03 t)
    + 0.5
    – 1.0
  5. Bonding strength:
    • Dry plywood: over 2.0 MN/m2;
    • After one hour stay in hot water: over 1.0 MN/m2.
  6. Formaldehyde emission class: Е1.
  7. Water resistance of the used resin: WBP mark

Application

  • In the building industry.
  • In the furniture industry.
  • Vessel production.
  • Wagon production.
  • Automobile production.
  • Packaging.
  • Sports equipment (ski, snowboards, etc.).

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