1 Main content and scope of application
This standard specifies the measurement method for the bonding strength of ordinary plywood defined by GB9846.2.
2 Reference standard GB9846.2 plywood terms and definitions
GB9846.8 plywood measurement of gluing strength extraction method GB9846.9 plywood specimen sawing GB9846.10 size of plywood in mm measurement
3 Measuring tools and instruments
3.1 vernier calipers, the reading accuracy of the graduation is 0.01g.
3.2 Constant temperature water bath, 30-100°C.
3.3 Tensile testing machine, load reading accuracy is 5N.
3.4 Air convection drying box, the temperature of each point in the box can be maintained at 63±3°C.
4 Sampling and test pieces
4.1 Sample are drawn according to the provisions of GB9846.8.
4.2 Sawing the test piece according to the provisions of GB9846.9.
4.3 The shear section of the test piece should not contain material defects and processing defects that affect the bonding strength.
5 Procedures
5.1 According to GB9846.10 measure size of a plywood board test piece as specified
5.2 The test piece shall be processed under the following conditions according to the plywood types and sizes to which it belongs:
a. Type I plywood: Put the test piece in boiling water for 4h, then dry it in 63±3C air convection drying oven for 20h, then boil it in boiling water for 4h, take it out and cool it at room temperature for 10min. When cooking the test piece, immerse all the test piece in boiling water and cook with a cover. Note: The rapid inspection method of 3h boiling is allowed in the factory production. The measured result is multiplied by the coefficient 0.9 as the glue strength value of the product inspection. However, when there is a dispute between the supply and demand parties, the Type I plywood is still boiled at 28h. The drying cycle method is used as a method to promote cutting.
b. Type Ⅱ plywood: The test piece is immersed in hot water of 63 ± 3°C for 3 hours, and then cooled at room temperature after taking it out 10mim. When immersing the test piece, all the test pieces shall be immersed in hot water and covered.
Note: The rapid inspection method of 63 ± 3°C and immersion for 1 hour is allowed in the plywood factory production. The measured result is multiplied by the coefficient 0.82 as the glue strength value of the product inspection, but in case of disputes between the supplier and the buyer, the Type Ⅱ plywood needs to be re-inspected At the time, the 3h hot water immersion method is still used as the arbitration method
c. Type Ⅲ plywood: immerse the specimens in water at 63±3°C for 2h, then place each specimen flat in a 63±3°C air convection drying oven for 1h, take it out and place it at room temperature for 10min.
d. Type IV plywood: dry test specimens with moisture content that meet the requirements. Note: The moisture content of the test piece should be controlled at 8%~12%.
5.3 Clamp both ends of the test piece in a pair of movable fixtures of the testing machine to make 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 notch of the test piece shall be within 5mm.
5.4 Load the test piece at a constant speed until it fails, and the loading speed is 10 MPa/min. The reading of the maximum damage load should be accurate to 5N.
6 Calculation and expression of test results:
6.1 According to the damage of the adhesive layer of the shear section, use visual inspection to estimate the wood damage rate of the test piece, expressed as a percentage, and the estimation is accurate to 10%. Refer to Appendix B (reference piece. If the test piece is abnormally damaged, write down its damage Features (notch broken, surface board split, core board cut, or surface board peeled off, refer to Appendix C (reference parts. Note: When the peeling area of the surface board exceeds half of the cut area, the wood damage rate is estimated to be accurate to 10 %.
6.2 The wood damage rate of one or several boards is equal to the arithmetic mean of the wood damage rate of all relevant specimens, and this value should be accurate to 1%.
6.3 The bonding strength of the test piece is calculated by the following formula: Type A test piece X A=P/(AXB
.................................... (1B type specimen BB=P/(AX BX0.9
............................. (2 in the formula: XA, BB-the bonding strength of the test piece MPa; P- Maximum failure load N; A is the width of the shear section of the test piece in m; B is the length of the shear section of the test piece in mm.
6.4 For the gluing strength of the thick core structure plywood test piece, the value calculated according to 6.3 should be multiplied by the coefficient specified in Table 1 as the gluing strength value of the test piece. Table 1 Bonding strength values of different thickness ratios The ratio coefficient of the thickness of the core board and the surface board is 1.50 ~ less than 2.002. 00 ~ less than 2.502. 50 more than 1.2 1.4 1.6
6.5 In the bonding strength test of the test piece, any abnormal damage such as notch breakage, surface plate cut, middle plate shear, or surface plate peeling, etc.