ASTM B555-86 pdf free.Standard Guide for Measurement of Electrodeposited Metallic Coating Thicknesses by the Dropping Test.
The thickness of a metal coating is often critical to itsperformance.This procedure is useful for an approximate determina-tion when the best possible accuracy is not required. For morereliable determinations, the following methods are available:Test Methods B 487,B 499,B 504, and B 568.
This test assumes that the rate of dissolution of thecoating by the corrosive reagent under the specified conditionsis always the same.
The following factors will affect the accuracy of acoating thickness measurement made by this method:Any foreign material on thesurface to be tested,including lacquer，grease，corrosionproducts, and conversion coatings, will interfere with the testand must be removed. Tarnish and conversion coatings canoften be removed by mild burnishing with a soft,clean pencileraser.Variation from thestated concentrations will introduce an error unless the thick-ness factor is adjusted accordingly.Test solutions cannot bereused.The thickness factor for a given solu-tion，being a function of the temperature,must be known forthe temperature at which the test is made. Specimens to betested should be allowed to reach room temperature beforetesting.
The thickness factor is also a func-tion of the dropping rate. The thickness factors given in Section10 are for a dropping rate of 100 drops/min and will remainvalid for the range of 95 to 105 drops/min.The thickness factors given inSection 10 are valid only if the test solution is rapidly drainedoff, as from a flat surface inclined 45o from the horizontal. Thetest cannot be made on a horizontal surface or at a location thatdoes not permit rapid drainage.
Drop Size -Variation in drop size may alter thepenetration rate. The tip of the dropping apparatus shouldconform to the dimensions given in Fig. 1 and should be keptclean.The presence of an alloy layer at the coating-substrate interface may obscure the end point andintroduce an uncertainty as to the amount of alloy included inthe thickness measurement.The end point (the time atwhich the coating has been penetrated and the substrateexposed) is characterized by a change in the appearance of thesurface on which drops are falling. This is a matter of personaljudgment and may not always be clearly defined， dependingupon the coating-substrate combination and the extent ofalloying, if any. Such errors may be minimized by standardiz-ing the test method with identical specimens with a knowncoating thickness determined by other means.The dropping tests de-scribed in this document are intended for use on nominallypure”coatings. The thickness factors listed in Section 10 areexpected to vary with gross variations in the composition of thecoating,as might result from codeposition of an alloyingcomponent.The specific effects，on the thickness factors，ofimpurities or of inclusions from brighteners or other additionagents can be appreciable.Uncertainty from these sources maybe minimized by standardizing the test method against stan-dards，prepared from the same type of plating solution，thethicknesses of which have been determined by other methods.ASTM B555 pdf download.