Testing Times
Xylan® coatings are manufactured by Whitford Ltd and have a range of coatings to suit most applications, whether used for automotive, industrial bake-ware or for aerospace projects. However, no matter what the application is, the coating system must be applied correctly and there are ways and means of testing the functionality and performance of the coating. In terms of standard tests used within the coating industry, these fall into two categories, destructive and non-destructive. However, whatever method is adopted must reflect the actual coating process.
Destructive testing, can be a draw back if the opportunity is not available to process test plates during all the process stages.
The first test, identified a “cross-hatch” test, determining the adhesion of the coating. This requires a sharp blade to make a series of cuts through the coating. A series of horizontal lines are etched across a similar pattern of vertical lines. Special tape with aggressive adhesive is then applied to the pattern. As the tape is pulled off, a check is made to see if paint is removed by the tape. This will determine the strength of the bond.
The second test, identified as “pencil hardness” test, determines whether the coating system has been cured correctly and indicates the hardness of the coating. The drying and curing temperature are vital to achieving the required performance from the PTFE coating. This method requires a pencil being ground flat and making a line about 10/15mm long, if the pencil you start with scratches the surface of the coating, go down the pencil grades until you come to the first pencil that doesn't scratch the coating. Repeat the test, and if you get the same results, you have determined the 'Pencil Hardness' of the coating you are testing, it's that simple, There are some coatings so hard that the 9H pencil won't scratch them-all of these coatings get a 9H rating to designate their hardness.
Non-destructive tests have the advantage of not being lost during production, unlike the tests above.
The first test is for coating thickness, also known as dry film thickness (DFT), this method requires obtaining dedicated equipment from a company that specialises in such test methods. Eddy current techniques are used to non-destructively measure the thickness of nonconductive coatings on nonferrous metal substrates. A high-frequency alternating current (above 1 MHz) is used to set up an alternating magnetic field at the surface of the instrument's probe. When the probe is brought near a conductive surface, the alternating magnetic field will set up eddy currents on the surface, the equipment will then translate this to a coat thickness.
The above tests are applied regularly during the coating production process, however, there other other methods and these include; abrasion, reverse impact resistance, direct impact resistance, cross-hatch adhesion, oxidation, gloss retention, UV resistance, yellowing, blistering, drying times, chemical/solvent resistance (using both the rubbing and spot/time tests), salt spray resistance, humidity resistance, acid and caustic resistance, the VOC and HAP contents.