Hardness test for the wood finishing

The finishing industry needs some standard quality for their product. The big furniture company that sell big volume product usually set a quality standard for his product. There are some tests are held to ensure his products fulfill the standard quality that have been set up. When he goes to his vendor he always do some test to make sure his product fulfill 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 tests for to determine the hardness of the finish layer. There are several methods can be held for testing the hardness. Now in this article we want to discuss the pencil test to do hardness test. This method covers a procedure for rapid, inexpensive and easy to determine the film hardness of a given coating. The completely test method is according to the ASTM D3359 standard.

The tool required

• A set of drawing graphite leads pencils which 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 test is done. For NC, AC, precatalyzed  the finish layer should have 24 hours after its last coat. While the PU coating should has been stayed for at least 3 days from its last coat. 

• Apparatus for the test 

It is the tool to hold the pencil when it moved 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 test is held.

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

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

Place the finish panel in 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 direction of wood grain at an angle of 45 degrees. Started with the with pencil hardness HB-F, then repeat this process up the hardness scale until a pencil is found that cut through to the substrate for a distance of at least 3 mm. The hardness scale is base at the pencil where the finish is uncut. For example if the finish fails at HB-F, then the hardest of the finish is pencil the B graphite pencil. If the defects is already found with the HB-F then we step back with the softer pencil.

the pencil is moved on the finish

We must watch closely to examine the cutting or scratching the film. The checks could be made by close visual inspection with illuminated magnifying glass or monocular. 

 the defects when the hardness is failed