Summary of general scratch resistance tests for automotive materials

Product Introduction

For friends who make car interior and exterior materials, scratch testing is essential, which is a routine item for quality control of car interior and exterior surfaces. Due to the different environments, parts and types of plastic parts for automobile interior and exterior decoration, different scratch test methods have been formed. Let's learn together today. Five common test methods and principles for scratch resistance.

1. Five-finger scratch test:

That is, five metal finger-shaped scraper heads under different loads. Scratches are scratched across the surface of the material and the visibility of the scratches is compared visually.

Test equipment:

It mainly consists of five parts: test bench, scraper rod, scraper head, weight anddrive.

Test Steps:

Before the experiment, fix the sample on the test bench and attach a highly polished tungsten carbide scraper to the top of the scraper rod. 1mm or 7mm. The other end of the scraper bar is attached with a weight. Determine the installation position, quantity and load of the scraper rod according to the sample size and test requirements. The scraping distance is generally set to 100mm ~ 200mm, and the scraping speed is 100mm/s.

Test Evaluation:

After the test is completed, it is required to perform a visual inspection in a well-lit environment, typically bright northern sunlight or D65 standard light source. For scratches, the scratch line can be presented at the most clearly visible angle by changing the angle between the sample and the observer. During the evaluation, close 10% of the range at both ends of the start point and the end point of de scratch out, that is, take only the 80% range in the center as the effective evaluation.on area.

Precautions:

1) The surface of the sample is flat to ensure uniform force throughout;

2) Before the test begins Carefully put down the suspended scraper head, otherwise the scraper head may form a dent at the starting point under the influence of weight;

3) If the sample size is smaller than the test stroke, the scraper head must be the edge of the sample should be lifted into a suspended state in time to prevent damage to the scraper head from contact with the metal table.

2. Hardness test pen scratch test method

Test instrument:

Hardness test pen It mainly includes: pen holder, spring, scraper head, pressure adjustment slider, etc. During the test, springs with different specifications can be replaced to to reach the required pressure range. The scraper headis generally a semicircular tip with a diameter of 1mm, 0.75mm, 0.5mm and so on.

testTest steps:

Install the scraper head and spring that meet the requirements before the test, put the pressure adjustment block on the required pressure scale, such as 10N or other specified values, and then hold the test pen perpendicular to the surface of the test sample, press the scraper head to the level with the front port of the pen holder or to a certain depth, and draw a certain distance on the surface of the sample, such as 100mm .

Note: The pencil hardness method is a traditional method used to evaluate the scratch resistance of high gloss non-skinned surfaces, such as: PC/ABS, PMMA/ABS, PET, etc.; the pencil hardness without scratches Values ​​are used to evaluate the level of scratch resistance, and hardness is not the only criterion for determining the scratch resistance of a surface.

Testevaluation:

Generally, the visual method is used to evaluate the scratches on the surface of the sample, and the scratches can be judged according to the corresponding standards. The basic principle of the hardness test pen scratch test is similar to that of the five-finger scratch test. The scraping method is more suitable for quality control at the production site, but this method also has inevitable defects, that is, there are human factors in the manual operation process, and the scraping speed is uncontrollable. The evaluation method of the hardness test pen scratch test is the same as that of the five-finger scratch test.

3. Grid-scratch test method

Grid-scratch test:

Yes Draw a grid on the surface of the material with a fixed load and spacing, measure the color change at the scratch and use the degree of whitening to characterize the scratch resistance of the material.

Note: At present, various material manufacturers and car manufacturers are widely using Yilixin cross-shaped notch testing machine to complete the scratch resistance test of materials. The crab head is a bolal tip with a diameter of 1mm. The specified load is applied to the crab head via a lever, such as 5N, 10N, 15N, 20N, etc. As an example, take the scratch resistance test standard GMW14688 for interior plastic parts from a North American car company.

Scratch test method:

The instrument automatically guides the movement of the scraper head, the speed is 1000mm/min, the scratch distance is 2mm, the length is 40mm, and one direction Scratch at least 20 scratches, then rotate the sample 90 degrees, repeat the above process in the vertical direction, and finally form a criss-cross grid scratch.

Test Evaluation:

Test the L value before and after scratching (L represents color depth) with a colorimeter and calculate AL*, the how cavethe AL* value, the clearer the whitening of the color after scratching and the worse the scratch resistance of the material. It is more objective to use the instrument measurement method to evaluate the test results. At present, the grid scrape test method is widely used.

The condition and load of the scratch head are the main factors influencing the scratch test:

Use a new scratch head and a used 20,000 times On the same automotive polypropylene plastic Grid scraping experiment, illustrating the effect of scraper head condition on grid scraping test results.

Various scraping head grid test results

scratch head

Scrape for L

L after scrape

△L

0 times

28.15

28.11

-0.04

20000 times

28.15

28.64

0.49

As shown in the table above: grid scraping test under 10N load according to standard GMW14688 This showed that AL* did not change significantly when using a new scraper head, i.e. the material did not turn white , but the result obtained by using the scraper head 20,000 times was that the AL* value was significantly larger, and the reason for the analysis was that after using the scraper head for a certain number of times, the spherical tip wears out severely and the size and shape canand have changed, which can not meet the test requirements. Therefore, during the test, it is necessary to record the number of times the scraper head is used, and to check the size and shape of the scraper head, replace it in time when the requirements cannot be met.

Note: The grid scrape test uses a handle to load the load and the balance of the lever must be adjusted regularly. Adjust the balance of the handle to ensure that the force value loaded on the surface of the material meets the requirements.During the test, it is necessary to select the appropriate load according to the materiallproperties, because the load determines the severity level of the scratch test, too large or too small can not effectively display the scratch resistance of the material The advantages and disadvantages of wiping performance.

Different scraping head grid test results

Payload

Scrape before L

L afterscraping

△L

10N

28.15

28.11

-0.04

15N

28.28

29.48

1.21

20N

28.47

32.39

3.92

As shown in the table above: The data is the test results of the same grade of automotive polypropylene material under three loads of 10N, 15N and 20N. The above table that the L of the material ounder the load of 10N in principle does not change and that the material does not turn white. material appears white. It is clear that it is very important to choose the right load when performing the scratch test of the grille.

4. Rubbing color fastness scratch test method

Rubbing color fastness scratch test:

It is the most basic color fastness evaluation index of textiles.d is to test the dry wiping cloth and wet wiping cloth against the colored cloth, then consult the gray scale for stains. The degree of staining of the cleaning cloth is rated with five being the best and one being the worst .

Note: The test method for color fastness to rubbing is simple, but the field of application is expanding. Many car manufacturers apply this method to the scratch resistance test of plastic products and have established the corresponding test standard. Based on test standard D451010from a French car manufacturer explains the scratch resistance test method of plastic parts for interior and exterior decoration of cars. The specific parameters are shown in table 3.

The standard clearly specifies the main parameters of the friction head, load, speed, etc. In addition to dry friction, it also specifies wet friction in the presence of liquids such as water , alcohol, soapy water and petrol. Rubbing color fastness test method, that is, first dip different kinds of liquids on the standard rubbing cloth, and then test the color fastness to rubbing.

Wet Friction:

It can better simulate the friction and wear of plastic parts when affected by fluids, such as distilled water that can simulate wet friction rain Scratch resistance of plastic exterior trim parts in snowy weather, soapy water friction simulates the friction and wear conditions to which you candust parts are exposed during vehicle washing. The wet rub color fastness test method compensates for the shortcomings of other kinds of scratch resistance test methods and reinforces the influence of liquid on the scratch resistance of materials.

Test evaluation:

The evaluation of plastic products after the test includes two parts, namely the staining degree of the friction cloth and the evaluation of the surface condition of the material, and then The color difference meter and the gloss meter are used to measure the color change and gloss change of the material before and after the test. At the same time, the gray scale of color change can be used to judge the samples after the test. Fifth grade is the best and first grade is the worst.

When performing the wet rubbing scratch test, color fastness, the specified volume of liquid should be removed in strict accordance with the requiredand to act on the standard rubbing cloth. For volatile liquids such as alcohol and petrol, it is recommended to attach the standard rubbing cloth to the Immerse after rubbing on the head to prevent excessive volatilization of the liquid from affecting the test results.

5. Other test methods

Paperclip scraping method:

The scraping head is Paperclip, the sample size is generally 152mm x 152mm, and the load is 0.75kg. During the test, the sample is placed on the bottom plate of the test device, and the fonze edges are respectively parallel to the bottom plate. Release the loaded paperclip and slowly pull the sample at a steady speed. Scratches, the scratches are parallel to the edge of the sample, the shear distance is at least 100mm, the sample can be guided with a ruler to ensure that the scratches are parallel to the edge of the sample, and the scratch distance can be recordedearth at the same time. After scraping, rotate the sample 90 degrees in one direction and pull the sample along the other edge until all four directions are scratched. The degree of scratching of the samples was visually evaluated.

TABER friction tester scraping method:

It is a linear reciprocating scraping test method and a circular friction test method. Different scraper heads can be configured as needed and the load and speed can be adjusted. Once adjusted, the equipment runs automatically throughout the test process and the repeatability and reproducibility of the test is ideal.

Summary

There are many test methods for the scratch resistance of automotive plastic parts, scratch head, load, sample relative motion condition of the scratch head is the most important technical element to determine the test method. The methods for evaluating the scratch resistance of plastics zare divided into visual method and instrument measurement method.

The five-finger scratch test method and the hardness test pen scratch method have similar testing principles and evaluation methods. The five-finger scratch test method is more instrumental, the test speed is controllable, and the test repeatability and reproducibility are stronger. The scratch test of the hardness test pen is more convenient and suitable for quick testing at the production site.

The grid scraping test method uses an electrical scratch tester. The instrument operates automatically throughout the testing process to form grid-like scratches. The colorimeter is used to measure the whitening of the material after scratching, and the test results more objectively; the rub resistance-scratch method successfully applies the textile color fastness test to the rub resistance test of plastic parts.

With wet friction, the frictional resistance of plastic parts can be quickly measured in the onpresence of different liquids, which compensates for the shortcomings of other scratch resistance test methods and can better simulate practical applications.

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