Hardness Test for the Wood Finishing

The finishing industry needs some standard quality for their product. The big furniture company that sells big-volume products usually sets a quality standard for his product. There are some tests held to ensure his products fulfill the standard quality that has been set up. When he goes to his vendor, he always does some testing to make sure his product fulfills the quality. When he sells his product, then he can show the test result to convince and attract his buyer. 

One of the common tests for the wood finishing layer is the hardness test. The hardness test is a test to determine the hardness of the finish layer. There are several methods that can be held for testing the hardness. Now in this article we want to share about the pencil test to do the hardness test. This method covers a procedure for rapid, inexpensive, and easy to determine the film hardness of a given coating. The complete test method is according to the ASTM D3359 standard.

The tool required

• A set of drawing graphite leads pencils that meet the following scale of hardness.

These pencils come in various degrees of hardness, following the 6B-5B-4B-3B-2B-B-(HB-F)-H-2H-3H-4H-5H-6H, and are generally supplied by any leading pencil manufacturer. The grade of a pencil is determined by the amount of baked graphite and clay in its composition.

• Sandpaper

The #400 grade sandpaper is used to sand the pencil tip to make a flat cut of the edges. 

• A piece of wood finish panel as a subject for testing. 

The finish panel has to be completely dry before the test is done. For NC, AC, precatalyzed, the finish layer should have 24 hours after its last coat. While the PU coating should have stayed for at least 3 days from its last coat. 

• Apparatus for the test 

It is the tool to hold the pencil when it moves to let the pencil scratch the finish layer. A certain pressure is needed to make sure the standard test is done. 

the apparatus to do the hardness test

How the test is held.

Sand the tip or the lead with #400 grade sandpaper to make his tip absolutely flat with a sharp circumcenter edge.

 the pencil tip is sanded to get flat with a sharp circumcenter edge.

Place the finish panel on a level, firm, horizontal surface. The pencil is held firm in the testing tool. Then move the test tool 3 inches forward on the film surface in the direction of wood grain at an angle of 45 degrees. Started with the pencil hardness HB-F, then repeat this process up the hardness scale until a pencil is found that cuts through to the substrate for a distance of at least 3 mm. The hardness scale is based on the pencil where the finish is uncut. For example, if the finish fails at HB-F, then the hardest of the finish is "the B graphite pencil.". If the defect is already found with the HB-F, then the result is the softer pencil.

the pencil is moved on the finish

You need to watch closely to examine the cutting or scratching of the film to find the result. The checks could be made by close visual inspection with illuminated magnifying glass or a monocular. 

 the defects when the hardness is failed