ASTM B ASTM F ASTM B ASTM D A number in parentheses indicates the year of last reapproval. A superscript epsilon?
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ASTM B ASTM F ASTM B ASTM D A number in parentheses indicates the year of last reapproval. A superscript epsilon? This standard has been approved for use by agencies of the Department of Defense.
Chemical conversion coatings are too thin to be measured by this test method. The values given in parentheses are for information only. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Referenced Documents 2. Terminology 3. Current edition approved April 15, Published May Originally approved in Last previous edition approved in as B — 97 An adjustment will affect the outcome of subsequent readings.
Summary of Test Method 4. A probe is placed directly on the coated surface in a perpendicular position and electronic circuitry is used to convert a reference signal into a coating thickness measurement.
The eddy currents in turn create a secondary magnetic? The characteristics of this secondary? This eddy-current method is nondestructive and is suitable for measuring the thickness of anodic coatings on aluminum, as well as the thickness of most nonconductive coatings on nonmagnetic basis metals. Apparatus 6. They may be coated aluminum plates, or may be foils or shims of? Calibration and Standardization 7.
A Certi? There is no standard time interval for re-calibration, nor is one absolutely required, but a calibration interval can be established based on experience and the work environment. A one-year calibration interval is a typical frequency suggested by many instrument manufacturers.
Attention shall be given to the factors listed in Section 8 and to the procedures described in Section 9. They are advantageous for adjustments on curved surfaces, and are more readily available than coated standards. Resilient foils should be avoided if possible.
Foils are subject to indentation and should, therefore, be replaced frequently. Standards suitable for many applications of the test method are commercially available and may be used provided the certi? When possible, back up the basis metal of the standard or of the test specimen with a sufficient thickness of similar material to make the readings independent of the basis metal thickness. A way to determine if the basis metal thickness exceeds the critical thickness is to make measurements before and after backing up the basis metal with similar metal at least 3 mm mils thick.
If there is no difference between the readings, the critical thickness is exceeded. Because of this, and despite the use of special probes or?
Factors Affecting the Measuring Accuracy 8. Its value should be determined experimentally, if not supplied by the manufacturer of the measuring instrument, since it depends on both the measuring frequency of the probe system and the electrical conductivity of the basis metal.
For a given basis metal, the higher the measuring frequency, the smaller the critical thickness of the basis metal. Therefore, measurements made too near an edge or inside corner will not be valid unless the instrument is speci? The in? If the basis metal is rough it may also be necessary to check, and adjust if necessary, the zero of the instrument at several positions on a sample of the uncoated rough substrate.
If the roughness of the substrate surface is small, relative to the coating thickness, its effect will probably be negligible. Both the test surface and instrument probe should be kept free of foreign material.
Procedure 9. Give appropriate attention to the factors listed in Section 8. The effects of properties of the substrate composition, shape, roughness, edge effects, electrical properties and coating composition, mass, surface roughness , as well as ambient and surface temperatures, may require adjustments to be made to the instrument.
If not, either use the back-up method in 7. Local variations in coating thickness may also require that a number of measurements be made in any given area; this applies particularly to a rough surface see 8. Accuracy Report NOTE 1—Although, theoretically, this test method can be used for measuring nonconductive coatings on a magnetic basis metal, its use for coatings below 25? Precision and Bias Keywords ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard.
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ASTM B 244
Standard Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings on Nonmagnetic Basis Metals with Eddy-Current Instruments1 This standard is issued under the fixed designation B ; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. Scope coil to basis metal spacing, can be calibrated to indicate the 1. Factors Affecting the Measuring Accuracy a nonconductive coating on a nonmagnetic basis metal.