Determination of paint film hardness by pencil method under GB/T 6739 standard

Introduction

In the Coatings industry, the hardness of the paint film is a key performance parameter, which is directly related to the mass, durability and applicability of the coating. The GB/T 6739 standard provides a method for determining the hardness of the paint film, the pencil method. This article will discuss in depth the principle, operation, result representation and application of this method, as well as precautions and importance.

1. The principle of measuring the hardness of paint film by pencil method

The pencil method is a simple and effective method for measuring the hardness of paint films. The principle of this method is to use a pencil with a known hardness label to scratch the paint film, and the hardness of the paint film is indicated by the pencil hardness label. In the test, the load applied by the tip of the pencil on the surface of the paint film should be (750 + 10) g.

2. Materials and equipment

In order to determine the hardness of the paint film by the pencil method, the following materials and equipment are required:

Pencil Hardness Tester: Used to apply a pencil tip load.

Wooden drawing pencils: including pencils of different hardness grades, from softer to harder grades are 9B-8B-7B-6B-5B-4B-3B-2B-B-HB-F-H-2H-3H-4H-5H-6H-7H-8H-9H. Pencils of different hardness are used for coatings of different hardness.

Sandpaper: The particle size of the sand is 400, which is used to smooth the tip of the pencil.

Substrate: Select the same type of material as the actual use as the test substrate.

3. Operation points

When measuring the hardness of the paint film by the pencil method, the following operation points should be paid attention to:

First, cut off about 5-6mm of wood from one end of the pencil, leaving a complete cylindrical pencil lead. Then, make the lead lead circle vertically on the sandpaper until the lead tip is ground flat and has a sharp edge. Repeability this step before each use of the pencil to ensure that the lead tip is in good condition.

Fix the paint template, insert the pencil into the instrument, and place the tip of the pencil on the paint film surface. Then, push the pencil at least 7mm away from the operator at a speed of 0.5~ 1mm/s.

Observe whether the paint film is scratched. If there is no scratch, use a pencil with higher hardness to test until a scratch of at least 3mm long occurs. If a scratch of more than 3mm has occurred, the hardness of the pencil needs to be reduced and the repeability tested until the scratch length no longer exceeds 3mm.

During the observation process, the coating surface can be wiped with a soft cloth, absorbentcottonph and an inert solvent, or wiped with an eraser to remove debris from the pencil lead, making it easier to assess the damage of the paint film.

4. Results presentation and application

The results of the pencil method for determining the hardness of paint films are divided into two types: plastic deformation and cohesive failure. Plastic deformation indicates permanent indentation on the surface of the paint film, but no cohesive failure. Cohesive failure indicates visible scratches or scratches on the surface of the paint film. Pencil hardness of paint films is usually expressed by the hardest pencil hardness and requires two parallel measurements to ensure accuracy.

The pencil method for determining paint film hardness is widely used in the Coating industry. It can be used to evaluate the hardness of different Coating materials, thereby providing Coating manufacturers with quality control data to help them improve their products. In addition, the pencil method can also be used to study the performance of coatings of different hardness under different environment conditions to meet specific application needs.

5. Precautions and Importance

When measuring the hardness of the paint film by the pencil method, special attention should be paid to the following matters:

When sharpening the pencil, make sure that the lead lead is cylindrical, without any damage, and exposed 5~ 6mm.

After each stroke, the end face of the lead core should be re-smoothed with the specified water sandpaper to ensure the accuracy of the test.

Conclusion

The pencil method for determining paint film hardness under the GB/T 6739-2006 standard is a simple and reliable method for evaluating the hardness and performance of coatings. Measuring by the pencil method can provide Coating manufacturers with quality control data and help them improve their products. This method has a wide range of applications in the Coating industry and is essential for Coating mass assurance and product improvement. Therefore, understanding and mastering the pencil method for determining paint film hardness is an important task for practitioners in the Coating industry, which helps to improve the mass and Reliability of Coating products.