Adhesion characterizes force of coupling between film and substrate. Adhesion in a greater degree depends on cleanliness of a substrate, a correct choice and carrying out of preliminary processing of a surface, and also from conditions of formation of a covering. The size of adhesion influences such properties of covering, as crashworthiness, flexibility, stability to external influences and to corrosion. Adhesion can be estimated by several various methods. The most widespread are exfoliation and cross-section cuts method . In the latter case trellised cuts on all surface of a covering are made. Then the sticky tape is put on cut covering and quickly leaves. Adhesion estimate on ability of film squares to remain on substrate or to exfoliate together with the tape. This method is very fast, but it allows to judge adhesion only relatively. Results express in points.
Definition of adhesion by means of film erasure is connected with use of a special tester. At such test the firm metal scraper moves on a surface of a covering with constantly increasing force of pressing until the covering will not be removed. The force necessary for removal of covering represents value of adhesion.
Hardness can be characterized as ability to resist to formation of scratches, abrasion, etc. the Most widespread method is measurement of hardness by means of a pencil, in spite of the fact that this way insufficiently exact and subjective. Pencil slate pencils of increasing hardness are pressed into a covering under a corner 45о until the film will not be scratched or while on it the trace is not formed. Hardness express number of the firmest slate pencil which does not scratch the covering, or does not form on it a trace.
Can be used other methods of coverings hardness estimation. Among them there is the method of hardness definition in the pendular way and on cave-in of a prism.
Abrasion stability is one more test which helps to determine ability of the covering to resist to mechanical damage. Usually abrasion stability is measured at use of abrasive action installation. The given device causes coverings abrasion when the plate with the covering contacts to moving abrasive circles or a tape of the certain hardness. Results of test express in the form of weight loss of the covering for the certain number of courses of using up element.
Other method is based on abrasive action of falling sand. The device consists of the bunker with a vertical tube from which sand or a powder of silicon carbide falls on the plate with the covering, located under a corner 45о. Results are estimated by quantity of the abrasive material necessary for removal of the covering of certain thickness.
Coverablility of sharp edges - parameter, which is of great importance, if the covering is depositrd on the product with sharp edges to prevent corrosion or to provide demanded electric isolation. There is no tool method for direct definition of this parameter. Usually for coverablility measurement of sharp edges use well processed square steel cores with the pointed ends. On cores the covering is deposited, then thickness of the covering on the ends of product compare to thickness of covering on its sides. A parameter of coverablility represent in the form of percentage of covering thickness on the sharp and flat side of product.
Chipping stability characterizes ability of covering to resist to destruction at impact by any subject. In spite of the fact that stability to chipping can be correlated with stability to impact, good crashworthiness does not mean, that stability to chipping it will be obligatory high. Test for impact means not only shock influence, but also deformation of a covering with a substrate. At test for stability to chipping the substrate is not deformed, and the covering receives impact in full. Most often in test methods of stability to chipping apply gravel of the various sizes, lead fraction or other firm materials. The test method at which the gravel set in motion by a high pressure, strikes on a cold covering is typical. Chipping stability judge on weight of the film material broken away from the substrate.
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