Types of methods for evaluating the hardness of organic coating film

The test method for determining the hardness of organic colors using a pendulum hardness tester

 

Test method for determining the hardness of paint film using standard graphite pencils

Test method for determining the hardness of organic dyes using a damping pendulum device

 

This test is divided into two methods based on the difference in the type of pendulum:

 

Test method A using a conical pendulum

 

KONIG Pendulum) – the time of movement (oscillation) of the KONIG pendulum from 3 to 6 degrees in seconds

 

Test method B using a burning pendulum

 

(PERSOZ Pendulum – time of movement (oscillation) of Persoz pendulum from 4 to 12 degrees in seconds)

Summary of the test method

 

The damped pendulum test is known as a sensitive method to determine the difference in coating hardness. Hardness means resistance to deformation. In fact, the hardness is determined by the resistance to deformation of the paint film. The pendulum is placed on the surface of the cover and the decrease in oscillation is checked. This reduction is determined by the device, the lower the number of oscillations, the lower the hardness. Oscillation time is affected by a combination of physical and mechanical properties of the paint film, including hardness, elasticity, friction coefficient of the sample under test. By reducing the hardness and increasing the tensile or friction coefficient, the time and number of oscillations are reduced.

These two methods (conic and burning) are originally designed based on the oscillation amplitude of the pendulum due to changes in the film surface which prevents the pendulum from oscillating and reduces the number of oscillations. The faster the reduction, the smoother the surface. The two methods (Conic and Persoz) are different in terms of round-trip time and amplitude of oscillations. In general, the round trip time (to reach equilibrium) of the conic pendulum is half of the round trip time of the Persous pendulum. Persous pendulum has more sensitivity than conical pendulum for measuring the hardness of soft coatings, but it may not be suitable for hard and slippery coating because this pendulum makes less contact with the surface and has a lower friction coefficient.

Test method A- conical pendulum

 

Equipment

 

The device includes a support base to hold the pendulum, a test sample and a pendulum swing counter. The base has a holder that releases the pendulum from a certain place without applying additional force and moves it on the surface of the test sample. The conical pendulum has an open structure, a horizontal bar is placed on top of it, and two balls with a diameter of ± 0.005 mm are located below it. The lower part of the device ends with an indicator. A vertical rod with a movable weight on it is connected to the horizontal rod of the pendulum, which is responsible for the balance of the pendulum. The total weight of the pendulum should be 200±0.2 grams. The stopwatch is measured with a timer in order to measure the damping time of the pendulum oscillations.

Conditions and preparation of the test sample

 

A uniform coating is applied on a hard surface such as glass or metal at the temperature and humidity agreed between the customer and the seller and with the thickness of the dried film surface agreed upon. (The thickness of the coating must be controlled because the thickness affects the result of the time and the number of oscillations of the pendulum. The thickness must be at least 25 µm or more to reduce the effects of the following.)

 

Test method

 

After the test sample (prepared test plate) is kept for at least 16 hours at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5% RH, the hardness should be measured.

The sample should be placed on the support base and the pendulum should be slowly moved to the primary support point.

The pendulum should be deflected by 6 degrees and then released and the cornometer should be turned on immediately.

Record the time of round-trip oscillations to reduce the angle from 6 to 3 degrees for the conical pendulum.

Repeat the test steps for at least 2 points of the test sample surface.

 

Test method B- Persous Pendulum  Equipment The device includes a support base to hold the pendulum, a test sample and a pendulum swing counter. The base has a holder that releases the pendulum from a certain place without applying additional force and moves it on the surface of the test sample. The pendulum of the high-pressure type has a horizontal rod on top of it, and under the rod there are two balls with a diameter of 8 ± 0.005 mm, and the pendulum is hanging on it. The lower part of the device ends with an indicator. A vertical rod with a movable weight on it is connected to the horizontal rod of the pendulum, which is responsible for the balance of the pendulum. The total weight of the pendulum should be 500±0.1 grams. The center of gravity should be 60±0.1 mm below the support and the pointer should be placed at a distance of 400±0.2 mm below the screen.And take the test After the test sample (prepared test plate) is kept for at least 16 hours at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5% RH, the hardness should be measured.The sample should be placed on the support base and the pendulum should be slowly moved to the primary support point.The pendulum should be deflected by 12 degrees and then released and the cornometer should be turned on immediately.Record the time of round-trip oscillations to reduce the angle from 12 to 4 degrees for the high-pressure pendulum.Repeat the test steps for at least 2 points of the test sample surfaceCheck for slipping or sliding of the pendulum. If the pendulum slips during the test, the result is unacceptable and the test must be repeated.

the report

 

Report the following information:

 

The average and range of the obtained values ​​for the hardness tester to be reported in seconds obtained for the test sample.

Manufacturer factory and hardness tester model should be reported.

The average and the obtained range of the thickness of the panels and the method used to determine the thickness during the test should be reported.

Temperature and relative humidity should be reported during the test.

The requirements and conditions of the color application technique on the surface of the test plate used should also be reported.

 

Test method for determining the hardness of paint film using standard graphite pencils Summary of the test method A coated panel is placed on a fixed horizontal surface. The pencil used as a hardness tester is firmly placed on the film at a 45° angle by the operator and moved against the direction of the operator with a uniform force, the drawn line should be at least 6.5 mm. The process of measuring the hardness of the coating is started with the hardest pencil and continues with less hard pencils.
Transfer and use Hardness measurement by means of a pencil hardness tester is used to check the hardness of industrial coatings and to check the resistance to the hardness of coating or transparent films. This test method is also used to evaluate and improve the quality of coatings, especially when the applied coating is dried under heat. This test method can be useful for evaluating production control in a laboratory. It should be considered that the results obtained in different laboratories can be different when the pencil hardness tester of the same brand is not used. Equipment A complete set of standard pencils with different hardnesses from 6B to 6H is required. Pencils used for drawing or drawing are used with the following hardness:The difference between the scale of two graphite pencils

the keeper

Mechanical pencil sharpener – pencil sharpener for preparing pencil tips

No. 400 sandpaper

Sample preparation and conditions

 

The surface should be covered using the appropriate tools so that a smooth surface with a firm and solid substrate and the appropriate quality is implemented to represent the appropriate surface. The conditions of complete drying before the start of the test are determined according to the agreement between the buyer and the seller.

 

The thickness of the coating surface is determined according to the agreement between the buyer and the seller. The minimum thickness of the dry film of jet paint is recommended to reduce the impact of the following on the test result, mµ25. The test should be performed at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5%.

Test method

Apply the coating to the surface with the agreed thickness. Before performing the test, shave the tips of the pencils with a mechanical sharpener so that 5-6 mm of the pencil tip is visible.

Then drag the pencil vertically at a 90-degree angle on the sandpaper to remove the sharpness of the pencil tip and obtain a section with a regular and smooth arc without any corners or edges. In the figure below, wooden pencil and mechanical pencil are shown as hardness testers.

To perform the test, place the coated piece horizontally on a flat surface, starting with the hardest pencil. The pencil is placed on the surface with the help of a wheel at an angle of 45 degrees, and the surface of the film is scratched by a uniform pressure of 6.5 mm.

Repeat this with less hard pencils until the first pencil that does not scratch the film within about 3mm of the 6.5mm line is determined (perform the test twice for each sample). The hardness of this pencil is reported as film hardness. Continue this process until the surface of the film is completely scratched. In order to measure the hardness of the film, the scratches created on the surface of the film should be considered faded. Write down the number of the hardest pencil that does not create a complete scratch on the surface.