Determination of the strength of paperboard

This standard is equivalent to the international standard ISO 2759 "Cardboard - Determination of Bursting Degree"

1 Topic content and scope of application

This standard stipulates the method of determining the burst strength of paperboard using the principle of incremental hydraulic pressure.

This standard is applicable to the determination of various types of cardboard (including solid cardboard and corrugated cardboard) with a burst strength of 350-5500 kPa (3.6-56.1 kgf/cm).

This standard does not apply to high elongation and multi-layer composite corrugated cardboard.

2 Reference standards

Take GB/T 450 paper and paperboard samples

GB/T 451.2 Determination of paper and board quantification

GB/T 4678 The first part of the terminology for paper, board, and pulp

GB/T 10739 Standard atmosphere for sample processing and testing of pulp, paper and paperboard

3 Terms

The bursting resistance and bursting resistance index are shown in GB/T 4687--7.36 and 7.37 in 1984.

4 Principle

In accordance with the provisions of the instrument with a certain pressure to clamp the sample between the upper and lower chucks, with a reciprocating constant speed hydraulic pressure tube, the film and the sample raised until the sample ruptured, the maximum hydraulic pressure, That is, the burst strength of the sample.

5 Instruments

5.1 Clamping system

To hold the specimen securely and evenly, the upper and lower chucks are two parallel annular planes, flat and grooved (see Appendix A), and the dimensions of the chuck system are given in Appendix A.

5.1.1 The upper chuck and the pressure shaft are connected by steel balls or similar joint devices to ensure that the pressure distribution of the chuck is even.

5.1.2 The upper and lower chucks shall be concentric. The maximum error of the concentricity shall not exceed 0.25mm. The surfaces of the two chucks shall be flat and parallel to each other. See Appendix B for the inspection method of the chuck.

5.1.3 In order to prevent the sample from slipping, there should be enough clamping force between the two chucks. The magnitude of the force is not limited to the damage of the specimen. The general clamping force is not less than 690kPa (7kgf/cm) (see Appendix C). ). In the determination of corrugated board, the pressure is 690kPa (7kgf/cm). Although most cardboard corrugated sheets are collapsed due to slippage, due to the different compressive strength of corrugated board, the test pressure should be specified in the test report and whether the corrugation is It was collapsed.

5.2 Film

5.2.1 The film is circular and made of rubber elastic material. See Appendix F for its dimensions.

5.2.2 When fixing the film, the upper surface of the film is about 4.7mm lower than the upper surface of the lower chuck.

5.2.3 elastic resistance of the film, when the film protrudes 10mm below the surface of the chuck, the resistance range is 170-220kPa (1.7-202kgf/cm2). When the protrusion is 18mm, the resistance range is 250-350kPa (2.5 -3.6kgf/cm2).
The film should be inspected frequently. If it is found that the film does not meet the requirements, it should be replaced in time. When installing the film, all air trapped under the film must be driven off.
5.3 Hydraulic System Use a piston to push a suitable liquid (eg, chemically pure glycerol, glycol containing corrosion inhibitors, or low-viscosity silicone oil) and apply uniform pressure under the film until it breaks. The hydraulic system and the used liquid should be free of air bubbles. The liquid delivery volume of the piston is 170±15 mL/min (see Annex E). The piston must be driven by the motor.
5.4 Pressure gauge
5.4.1 Bourdon tube pressure gauges are used within 25% to 75% of the gauge range. It must not be used below 15% and above 85%. The minimum diameter of the dial scale is 95mm, and the arc of the scale is not less than 270°. The accuracy at any point within the working range should be 0.5% of the maximum range of the dial. The pressure gauge should have a vent hole and the dial should be divided into at least 70 compartments.

5.4.2 The expansion of the pressure gauge should be stable within 20% within the range of positive working range. Even if it reaches the maximum range, the liquid to be lost does not exceed 0.4 mL (see Appendix E).

5.4.3 The friction torque between the pressure gauge and the pointer is about 0.3mN.m. The pointer inertia is within 1-10g.cm2 (see Appendix D).

5.4.4 The operating inertia of the pressure sensor is negligible, and the error of the barrier and pressure recorder is within 0.2%. In digital display devices, after the sample ruptures, the reading does not change by more than 1 unit.

5.5 Calibration Pressure gauge calibration see Appendix D;
Check the hydraulic body see Appendix E;
Test sample chuck in Appendix C;
Film size specifications in Appendix F.

6 sample taking, preparation and treatment
6.1 The sample is taken according to the provisions of GB/T 450, each sample cut into 100mm × 100mm.
6.2 Samples should be treated according to GB/T 10739 temperature and humidity.

7 Test procedure Samples taken and processed according to the standard must be tested under the specified standard temperature and humidity conditions.
First select the appropriate measurement range. It must be done with a long range of pressure gauges.
Put the sample between the upper and lower chucks. The specimen must exceed the entire area of ​​the upper chuck. Drop the upper chuck and adjust to the desired pressure. Turn on the instrument and increase the pressure at an appropriate rate until the sample breaks. Return the piston until the film is below the surface of the lower chuck, read the gauge (or digital display) pressure, and then lift the upper chuck. The reading is zeroed back for the next test.
If the specimen is found to be slipping or broken due to crushing, the degree should be discarded.
Samples evenly cut along the transverse web were measured on the front and back surfaces with 10 specimens each facing the film. However, in one test, the specimens that had been pressed by the chuck were not allowed to be tested.

8 Calculation of test results The burst resistance X (kPa.m2/g) is calculated from the following equation:

Where: P - average burst strength, kPa;
W - quantification of the sample, g/m2.
The bursting resistance and bursting resistance index take three significant figures.

9 Precision of test results The degree of precision of the results depends on the uniformity of the sample and other factors such as the error of the pressure gauge, the condition of the clamping force, the pressurization rate, the presence or absence of air in the system, and the condition of the film.

Numerical Item Repeatability Reproducibility Range 3.8-8.5 5.8-9.6
General <5 10

10 Test report The test report shall include the following contents: the national standard number; the instrument used and the number; the standard temperature and humidity conditions during the test;
Average burst resistance (report positive and negative results as necessary);
If required, report breaking index;
The coefficient of variation or 95% confidence interval of the reported results;
The clamping pressure used in the measurement;
When measuring corrugated cardboard, specify whether the corrugation is collapsed;
What is the deviation from this method?

Source: Ke Yin Network