( 1) Test principle
Gurley stiffness refers to the maximum bending force that the paper sample bears in two different directions under a small load pendulum deflection angle, namely:
Gurley stiffness =88.9R G (W1+2W2+4W3)/3
In the formula, W1—— the weight , mg;
W2——the weight of the added weight on the 2in position of the pendulum, mg ;
W3——the weight of the added weight on the 4in position of the pendulum, mg;
R G - the indicated value of the dial;
88.9 —— The number of milligrams on the 1-grid scale when the 5g weight is placed in the upper notch (that is, the 1in position);
5 - the distance from the rotary axis to the pressurized part of the pendulum.
If a sample with a length of 88.9mm (3.5in) and a width of 25.4mm (lin) is taken, and a weight of 5g is added to the notch , then:
Gurley stiffness=88.9R G
( 2 ) Gurley Stiffness Tester
Figure 2-45 Gurley Stiffness Tester
1—fixture; 2—sample; 3—bearing; 4—weight; 5—dial; 6—pendulum; 7—power switch
The Gurley Stiffness Tester is mainly used for the determination of the stiffness of paper, and it can also be used for the determination of the stiffness of thin cardboard. It consists of a transmission part and a test part, as shown in Figure 2-45, the transmission part includes a motor, a rotating disk, a rod connected with a sample fixture and a scale, and an indicator light, and the test part includes a pendulum, a dial and weights . The Gurley stiffness Tester indicates the stiffness by the maximum bending force required to bend the sample to a certain degree, that is, a sample of a certain size moves a pendulum of a certain weight. When the bending force of the sample is lower than the weight of the pendulum itself, the pendulum automatically swing back. When the force reaches balance, read the indicated value of the pointer, and then calculate the Gurley stiffness.
(3) Test method
①Sample collection and processing: Sampling according to GB 450, cutting a 50mm×25.4mm sample along the paper web, and performing temperature and humidity pretreatment on the sample according to the requirements of GB10739.
②Adjust the level of the instrument, select an appropriate weight and place it on the weight bayonet of the pendulum. Adjust the pendulum so that the pointer is at the zero position of the dial.
③ Clamp the sample in the middle of the fixture, the upper end of the sample is vertical and in contact with the bottom plate of the fixture, about 1/4in deep, so that the lower end of the sample moves the horizontal plate of the pendulum.
④Press the switch on the lower right, and the sample lever moves the pointer to the left. When the sample leaves the pendulum for a moment, read the indicated value of the pointer. Then press the switch on the lower left side, and the sample lever will move the pointer to the right to read the indicated value of the pointer.
⑤ Take the average value of the indicated values in the left and right directions, and then calculate the stiffness of the sample.
The test results are expressed as the arithmetic mean of all test results.
