" " wisno wood furniture finishing: Adhesion test in the furniture finishing

Friday, July 16, 2010

Adhesion test in the furniture finishing

Adhesion in the finishing layer.

Adhesion power is the bonding between the different materials. The adhesion in the finishing layer is the strength of the bond between the finishing with the surface beneath.
Finishing with good adhesion will ensure that the finishing layer adhere properly with the substrate they applied. A finishing layer will pull off from his substrate is he has poor adhesion. A good adhesion is very important for the finishing layer. No matter how nice a finishing look like, it will be useless if it does not have good adhesion. 

Adhesion test  
Adhesion strength in the finishing illustrates the power of the finishing layer to not peeling off since the taxable traction. But of course there is a limit of the adhesion power in the finishing.  A finishing layer will always exfoliate off if it scraped with a knife hardly. Since that  a standard test is developed to determine the strength of adhesion power of the finishing. There are some tests to exam the finishing layer, but the most common is a cross-cut test. Cross-cut test is a simple and easily conducted test to determine the strength of the adhesion in a finishing layer.
 

A cross-cut test on a finishing layer is done as follow:
  •  A finishing layer is sliced with a knife to create parallel lines that intersect to form small squares. Actually there is a special tool that could be used to make the incision lines on this finishing layer. But a small knife with a sharp tip can be used. There are should be 100 boxes made from the intersection line, so we make 10 lines which intersect each other. The distance between the lines is approximately 2.5 millimeters. So there will be formed a 100 boxes with about 2.5 mm X 2.5 mm size. Use a ruler and a sharp knife to form straight and same size lines.

 Cut the finish with the sharp knife
  • Then put on and attach a clear tape to the boxes. Make sure that the clear tape is firmly attached to the surface, and then suddenly pull off the tape from the finishing surface. The tape has to be pull of quickly and suddenly.
 The tape is attached on the finish
  • Then see the results, how many boxes of the finishing layer are pull off. The less boxes are pull off is the better adhesion power. A finishing layer with a good adhesion is shown with no box springs up. More boxes apart from the surface indicate the less of the adhesion quality. Usually a layer of finish is said to fail in this adhesion test if more than 10% of the box is pull off from his underneath layer.. 
    The good adhesion test result


    The bad adhesion test result


    This adhesion test is one of the standard test is needed at a finishing industry. In an industry that does the finishing job continuously should do this adhesion test periodically to ensure that every product he produce are already meet the finishing standards. Of course this test can not be done on all products as they will damage the product. Some panels with the same finishing system with the production line can be run for the purpose of the test.
    We also need to make sure that the finish is already dry when we do the test. A layer of nitrocellulose finish needs minimum one day from the final top coat application to be well prepared in the test. Another type of finish such as PU or varnish of course requires longer drying time.
    Failure in the adhesion test means there is a failure of the finishing process. A finishing layer which failed in an adhesion test it must be regarded as a failed product. And what we need to do is to strip the finishing and re finish with new finishing systems and materials.


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