The hardness of any material is termed as the resistance of any material to deform into a permanent shape. A pencil hardness test is a process in which the hardness of different materials; typically, the coating materials are determined. The pencil hardness test is used for many years, and it is popular in the film industry.

The film industry tester performs this test to determine the scratch hardness of a particular coated film. The test for determining the hardness of the pencil is very simple and easy, but you must have the proper tools and equipment to perform this test.

Hardness tests are simple but required the proper training, because if you made any minor mistake, your results would affect.

The results will be different if you choose the wrong test and the wrong equipment for the test. For measuring the hardness of the pencil, a simple graphite pencil is used. If you want to measure the hardness of the graphite pencil, the softest pencil is used to leave the scratch on the surface of the coating.

Types of pencils

There are many different types of graphite pencils available in the market. And when you try to measure the hardness of any specific category of the pencil of different brands, you will get different results.

Every brand has its own coating standard and percentage of coating on the surface of the pencil. There are tests used to measure the hardness of the pencil depends on the type of pencil.

You can use different types of test to evaluate the coatings on the pencil.

Every test is simple to perform, and you will get the uniform results. The types of pencils are categorized in different grades, which is determined by the amount of the graphite and clay used in them.

The mixture and the amount of graphite and clay will be responsible for the hardness and the softness of any pencil. There are different types of graphite pencils, and they are commonly categorized in H.B. levels.

The ‘H’ stands for the percentage of the hardness in the graphite, and ‘B’ stands for the blackness which soft in nature. The word H.B. stands for the hard and the black pencils used for writing and sketching.

The hardest pencil in this category is 9H, and from 2H, 3H, 4H, 5H, 6H, 7H, 8H are softer to harder. H.F. is the moderate level and comes in the middle of the hardness.

When it comes to the ‘B’ it is opposite 9B is termed to the softest from 8B, 7B, 6B, 5B, 4B, 3B, and 2B. Pencils are easily available with all these combinations of the ‘H’ and ‘B’.

Another common method for grading the graphite pencils are numbers such as #1=B, #2=HB, #2-1/2=F, #3=H and #4=2H. The most common types of pencil used for writing is the #2, the #2 shows the ‘H.B.’ grade of the pencil. It is soft and has more graphite which is smooth for writing.

Standard procedure for testing hardness

There are two different types of common tests for testing the hardness of the pencil. The tests are ASTM D3363, and JIS K-5600-5-4 used to measure the hardness of the pencil. Before starting any test, you just need the following things to perform the test.

  • If you want to achieve the accurate results, then you must need the pencil hardness tester. And if you are using the ASTM D3363 method, then you don’t need the pencil hardness tester, because in this test there is no need of any holder.
  • A sandpaper with400 grit.
  • A tool of 90 degrees.
  • Set of pencils especially used for testing the hardness.
  • Pencil sharpener according to the size of the pencil.
  • The plate of glass for the testing, due to its plain surface.

The procedure of the test

Before starting the test, you must have to place the film on the glass plate.

Then you have to sharpen the particular pencil for testing. After sharpening the pencil fix it in the 90-degree tool and place it on the sandpaper of 400 grit.

Then mount the pencil in the pencil hardness tester with the specific weight on it.

The amount of weight will help you determined the results. The angle of 45 degrees will allow the pencil to drop on the surface of the film. Push the tester in the forwarding position of ½. After placing the pencil, it is the time to rotate the pencil to the unused edge. Repeat the same process parallel to the first one.

You will notice that the two strokes of the coated film sample were scratched by the lead. If the one and both strokes can be made a scratch on the film, your test is failed. And if both strokes didn’t scratch the surface, your test will be passed.

You can repeat the process with the different types of pencils, to see the highest level of the pencil hardness.

Other types of testing’s

As we have discussed above, there is not only a single method of testing the hardness of the pencil.

There are many different types of tests used to measure the quality of the coating on the pencil. Some other tests are direct impact resistance, abrasion, yellowing, drying times, U.V. resistance, reverse impact resistance, oxidation, chemical resistance, humidity resistance, cross-hatch adhesion, salt spray resistance, acid resistance, gloss retention and many more tests.

Failure of the pencil hardness test

The main biggest failure of the pencil hardness test is the number of different procedures used in determining the hardness level in pencil.

Besides the two common tests, the companies will follow their own testing techniques in measuring the hardness of the pencil.

The common mistake is the low amount of the load weight used with the pencil hardness tester. If you use the less pressure on the pencil, the chances of the scratch will become low.

If you want to test the hardness of the different types of pencils, then it is necessary for you to use the different testing methods to get the best results.