Pencil Hardness Test
Definition - What does Pencil Hardness Test mean?
A pencil hardness test is a type of evaluation method that is performed to determine the hardness of a material, typically coating materials. To perform a pencil hardness test, graphite pencils of varying hardness are moved across a coating's surface. Its hardness relative to the graphite pencils is determined by the softest pencil that will leave a scratch on the surface of the coating.
Corrosionpedia explains Pencil Hardness Test
The test is popular, partly because it is a portable process. The pencils are small, and if a mechanical holder is used to carry the pencils, then it too is often compact and readily portable. Another reason is because it is simple. All that is required is a set of pencils and a person to drag the pencil across the coating material. These reasons make a pencil hardness test ideal for testing coatings because it can be done quickly in the field.
Due to its simplicity, pencil hardness tests are subject to some variation from test to test and from tester to tester. It is absolutely critical that a pencil hardness test be performed in the same fashion each time. Therefore, it is generally recommended to have some mechanical means of performing a test. A pencil holder is a mechanical device that holds the pencil at a set angle and prevents it from slipping. A pencil holder will typically have wheels on it so that a smooth motion can be exerted while attempting to scratch the coating.
There is a spectrum of pencils available, which are labeled according to their graphite hardness. It is common for 6B to be the softest pencil in a hardness tester pack of pencils. The pencils then increase in hardness as they go from 6B to 5B to 4B and so on, until they reach a single B. Then hardness continues as the pencils go from HB to F to H to 2H to 3H and all the way up to 9H. The 9H pencil is normally the hardest in the set.