The galvanizing process involves taking a fully fabricated piece of steel and placing it into a bath of hot zinc. The zinc adheres to the surface of the metal, creating a barrier that keeps the steel from corroding in wet or oily environments. When this process is completed, various tests and inspections are performed on the galvanized material to make sure that it complies with ASTM standards. The first of the two methods of measuring the thickness of a galvanized product involves magnetic thickness gauges. Different options of these gauges are available to perform this test. The second method involves using magnet or electromagnetic current to obtain a result.
The first method involves a tool that resembles a pencil. Inside is a spring loaded magnet that is placed on the surface of the material. The pencil style gauge is moved across the surface in a continuous motion. The magnet inside of the gauge is attracted to the steel and the thickness is read from a graduated scale right before the gauge is pulled from the surface. When using the pencil style gauge, the test must be performed on a flat surface. Gravity can affect the outcome of the reading if it is not done on a flat surface. The test should also be performed multiple times to get an accurate reading of the thickness.
A banana gauge is another gauge that can be used for measuring the thickness of galvanized products. The banana gauge can be used on any part of the material to determine coating thickness. The magnet on the banana gauge is surrounded by rubber and is placed on the surface of the material, running equal with the surface. The magnetic probe of the gauge is brought into contact with the surface and is continuously rotated clockwise until a click is heard and the coating thickness appears on the scale. The banana gauge can be used without fearing interference from gravity or recalibrating often.
The last gauge that can be used for this test is an electronic gauge. It is also known as a digital gauge. This gauge’s probe does not need to be calibrated but it does need to be calibrated with various shims of different thicknesses. The digital gauge measures the thickness of the galvanized coating by using a magnetic probe that is placed on the surface of the material. The thickness is than displayed digitally on a handheld monitor.
The thickness of the material can also be measured by a magnet or electromagnetic current. ASTM E 376 specifies the information needed to obtain the thickness of the material using this method. The conditions are intended to help provide the most accurate thickness possible. The measurements for this method need to be taken at least four inches from the edge of the surface to reduce edge effects from the material. The measurements should also be taken from widely scattered points on the material as well to obtain accurate measurements. Some good rules of thumb for obtaining an accurate measurement of thickness are holes, bends and edges should be avoided when performing this test. The tests should also be performed on regular areas of the coating, not on any extremely thick or thin points of the material. Five tests in different areas should also be completed when using this method to obtain a true value of the thickness of the coating across the entire sample.
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