GB/T17657-2013 Test Method for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels: Determination of Bond Strength
17 Determination of bonding strength
17.1 Principle
To determine the bonding quality of single-panel artificial boards by causing shear failure of the adhesive layer of the specimen under tensile load
17.2 Instruments and equipment
17.2.1 Universal mechanical test, select an appropriate load range according to product requirements, with a measurement accuracy of 1% of the load value
Artificial board universal testing machine. png
17.2.2 Sink.
Boiling water tank. png
17.2.3 Heating device.
17.2.4 Blast drying oven, capable of maintaining a temperature of (63 ± 3) ° C.
Drying oven 1. png
- 2. 5 vernier calipers. Graduation value 0.1 mm. Range 0 mm~150mm
17.3 Specimen dimensions
The length is l=(100 ± 1) mm, and the width is b=(25 ± 1l) mm.
The specimens are divided into Type A and Type B. The shear section length of Type A specimens is 25 mm; The shear section length of the B-type specimen is 13 mm.
17.4 Preparation of test specimens
17.4.1 The test piece should be prepared according to Figure 21 or Figure 22. When preparing the test piece, the direction of the wood grain of the core board between the tested adhesive layers should be perpendicular to the length of the test piece. The width and depth of the groove of the test piece should be according to the small dimensions and requirements shown in Figure 21 or Figure 22. The depth of the groove door should be sawn to 2/3 of the thickness of the core plate. For blockboard and laminated board, the two panels of specimen 1 and specimen 2 serve as one layer of core board.
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explain:
Blob.png follows the texture direction.
Note:
Shear length l1=(25 ± 0.5) mm;
Shear width (specimen width) b1=(25 ± 0.5) mm;
Saw path width b2=2.5mm~4mm;
Thickness=plate thickness;
The minimum distance between fixtures is l2=50mm.
Figure 21 Example of 7-layer plywood specimens
17.4.2 Due to the need to test the bonding strength of each adhesive layer, test specimens must be made for each adhesive layer. An equal number of specimens should be sawn in the direction of the plywood surface and back board. For plates with 3-9 layers, the entire thickness of the plate can be used as the test piece. For boards with more than 9 layers, excess layers should be removed by planing, sawing, or sanding methods.
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Note:
Shear length l1=(25 ± 0.5) mm;
Shear width b1=(25 ± 0.5) mm;
Saw path width b2=2.5 mm~4 mm;
The minimum distance between fixtures is l2=50 mm.
Figure 22 3-layer blockboard and laminated board specimens
17.5 Method
17.5.1 Measure the length and width of the shear surface of the specimen (see 4.1).
17.5.2 Sample pretreatment
The test pieces shall be pre treated according to the following conditions according to their respective plywood category. The specimen should be placed in a wire frame during pre-treatment. There should be a certain distance between the specimens and they can move freely. During immersion, each specimen should be completely submerged in water.
17.5.2.1 24 hour cold water immersion: Immerse for 24 hours at a water temperature of not less than 17 ° C. The recommended temperature for the experiment is (20 ± 3) ℃.
17.5.2.2 Hot water immersion: Immerse in hot water at (63 ± 3) ° C for 3 hours, and then cool at room temperature for 10 minutes.
17.5.2.3 Boiling Drying Boiling: Soak in boiling water for 1 hour. Then dry in an air blown drying oven at (60 ± 3) ° C for 16-20 hours. Soak in boiling water for 1 hour. Then place in cold water at a temperature below 30 ° C for at least 1 hour.
17.5.2.4 72 h boiling water boiling: Soak in boiling water for (72+1) h. Then place in cold water at a temperature below 30 ° C for at least 1 h
- 5. Clamp both ends of the test piece in a pair of movable fixtures of the testing machine to form a straight line. The center of the test piece should pass through the axis of the movable fixture of the testing machine. The distance between the clamping part and the groove of the test piece should be within 5 mm.
During the test, the load should be uniformly applied. The specimen should be destroyed within (30 ± 10) seconds from the start of loading. Record the maximum load value, accurate to 10N
17.6 Expression of Results
17.6.1 Based on the failure of the adhesive layer on the shear section, estimate the wood failure rate of the specimen by visual inspection, expressed as a percentage, with an accuracy of 10%. See Appendix B. If the specimen exhibits abnormal failure, record its failure characteristics (notch fracture, surface plate cutting, core plate cutting, surface plate peeling). See Appendix C. When the surface plate peeling area exceeds half of the cutting area, estimate the wood failure rate to the nearest 10%,
17.6.2 The wood failure rate of one or ten plates is equal to the arithmetic mean value of the wood failure rate of all relevant test pieces, accurate to 1%.
17.6.3 The bonding strength of the test piece shall be calculated according to equation (13) or equation (14), accurate to 0.01 MPa:
A-type specimen:
blob.png (13 )
blob.png (14)
In the equation:
XA and XB – the bonding strength of the specimen, in megapascals (MPa);
Pmax – maximum failure load, in Newton (N);
B – The width of the specimen after cutting, in millimeters (mm);
L – The length of the specimen after cutting, in millimeters (mm),
17.6.4 The bonding strength of thick core structural plywood specimens shall be calculated by multiplying the value calculated in 17.6.3 by the coefficient specified in Table 1 as the bonding strength value of the specimens
Table 1 Adhesion strength coefficient values for different thickness ratios
The thickness ratio of the core plate to the surface plate, t
coefficient
1.50≤t＜2.00
2.00≤t＜2.50
t≥2.50
one point two
one point four
one point six
17.6.5 During the determination of the bonding strength of the test piece, any abnormal damage such as notch breaking, core plate cutting, core plate shearing, and surface plate peeling shall be observed. When calculating the bonding strength value, the following regulations shall be followed:
a) If the bond tensile shear strength value of various abnormal failure specimens meets the minimum value of the index specified in the standard, it shall be included in the statistical record; If it does not meet the specified minimum indicator value, it will be removed and ignored.
b) When the number of abnormal failure specimens excluded exceeds half of the total number of specimens, additional sampling inspection should be conducted.
17.6.6 During the process of making specimens or after wet treatment, if it is found that any adhesive layer of the specimens has been opened, the bonding strength value and wood failure rate of the specimens shall be calculated as zero and included in the statistical records.
