How to measure film Hardness with Pendulum?

1 Overview

The hardness of the paint film refers to the resistance of the surface of the painted object when it is penetrated by another object. The dried coating should have a certain degree of hardness in order to withstand physical external damage and protect the surface of the object. Therefore, the hardness of the paint film is an important index reflecting the mechanical properties of the coating, and the determination of the paint film hardness is an important part of the paint quality inspection.

QHB pendulum damping Tester is manufactured with reference to 5101522-1973 (E), and the period conforms to the standard period range of 1.4±0.02s stipulated in the national standard. The device uses a photoelectric control system for automatic counting, which avoids errors caused by visual observation, and has the advantages of stable performance, high accuracy, good reproducibility, and simple operation. Its performance is better than the QBYI type and L type pendulum Hardness Tester stipulated by the Ministry of Standards. It is not only suitable for testing hardness, but also can be used as an arbitration method for hardness testing. It is a relatively professional testing instrument at present. The application of the QHB pendulum damping Tester fills the gap that our factory cannot detect the hardness of the paint film.

2 Determination of paint film hardness

2.1 Working principle

When the pendulum rod touching the surface of the paint film swings at a certain period, if the surface is softer, the swing amplitude decays faster, and vice versa. The expression of the hardness of the paint film is expressed by the ratio of the number of vibration amplitudes of a gravity pendulum with a certain weight placed on a standard glass plate within a specified angle range:

H~n/n ₀

n-the vibration amplitude of the gravity pendulum swinging on the paint film

n ₀ —the vibration amplitude of the gravity pendulum swinging on the standard glass.

2.2 Instrument materials

(1) Use the QHB type Kqing pendulum, the gravity pendulum swings , and the number of amplitudes is automatically counted by the photoelectric control device. The total mass of the pendulum is 200±0.2g, and the inherent swing period of the pendulum can be adjusted by moving the sliding weight on the connecting rod perpendicular to the crossbar. On the standard glass plate, the amplitude frequency of the pendulum from 6° to 3° is 718 ± 8 times, the damping time is 250 ± 10 s, and the swing period is 1.4 ± 0.02 s.

(2) Standard glass plate: made of standard polished glass of 010mm or 10mm and 5mm.

(3) A small screwdriver, ether, light silk cloth.

(4) Lever micrometer: Accuracy 2μm.

2.3 Preparations

(1) Prepare a paint film on a glass plate, and its thickness should meet the standard.

(2) Put the dry test panel in an environment with a temperature of 32±2°C and a relative humidity of 50±5% for 16 hours, which is the so-called state conditioning for 16 hours.

(3) Check whether the instrument is level, if not, adjust the foot screws. After the instrument is level, place the standard glass plate on the bench.

(4) Wipe the supporting steel ball with a light silk cloth (or tissue paper) moistened with ether. Place the pendulum under the same environmental conditions as the test for 10 minutes

(5) Check whether n ₀ is 718 times ± 8 times, if not within this range, adjust the sliding weight on the pendulum, and record the value of n ₀ after adjustment .

2.4 Accuracy test

Calculate the cycle value and error by measuring the amplitude times and damping time (see Table 1).

2.6 Operation steps

(1) Place the tested panel on the workbench with the paint film facing up, turn the handle of the workbench to raise the tray until the bead presses the glass plate.

(2) Adjust the pendulum to check whether the zero point of the scale and the pendulum tip at the rest position are in the same vertical position.

(3) Use the start handle to push the pendulum bar to 6°, and block the pendulum bar with the pendulum bar stop device. At this time, the counter indicator should be 0, otherwise press the reset button.

(4) Loosen the swing bar stop device, and the counter will count automatically. When the swing reaches 3°, the counter stops counting automatically.

(5) Measure at three different positions on the same test plate, and record the results of each measurement and the average of the three measurements.