1、 FORD LABORATORY TEST METHOD BI 117-01 Date Action Revisions 2001 03 19 Revised Editorial no technical change A. Cockman 1989 04 24 Printed copies are uncontrolled Page 1 of 3 Copyright 2001, Ford Global Technologies, Inc. THICKNESS MEASUREMENT OF PAINT FILMS Application This procedure details recom
2、mended practices and equipment for measurement of thickness of paint films on metallic substrates. Apparatus Required Permascope or Leptoscope, or equivalent Note: If other measuring principles are applied these must be indicated in the test report and if required coordinated with Product Engineerin
3、g. Measurement Principle Two (2) types of instruments can be used depending on whether the substrate is magnetic iron or steel, or non-magnetic metals. The instrument consists of a gauge head connected to an indicating unit. A magnetic flux is produced when the probe tips are placed in contact with
4、a paint film over a ferritic substrate. The paint film acts as an air gap in the magnetic circuit. The magnetic impedance of the gauge head varies as a function of the air gap length, i.e. the thickness of the paint film, and thickness is read directly on the scale of the recording instrument. When
5、the substrate is a non-magnetic metallic, an Eddy current system is utilized. A high frequency magnetic field is created in the probes measuring system and Eddy currents are generated when the probe is placed onto the non-magnetic substrate. Magnitude of the Eddy current depends on distance between
6、metal and probe, shape and electrical conductivity of specimen. The gauge must be standardized against base materials of the same composition, geometry, heat treatment and surface treatment (such as phosphating or galvanizing) for maximum accuracy. Note: The following factors may have an influence o
7、n the results: 1. Surface roughness and waviness of the surface. FORD LABORATORY TEST METHOD BI 117-01 Page 2 of 3 Copyright 2001, Ford Global Technologies, Inc. 2. Magnetic conditions of the substrate material. 3. Thickness of the substrate material. 4. Hardness of the coating and pressure applied
8、to gauge head during test. (A constant pressure probe should be used where feasible.) 5. Curvature of the surface (measurement should be taken parallel to the curvature axis). 6. Distance from the measuring point to an edge of the material under test. Edge effects should be avoided. 7. Deviation of
9、the magnetic probe axis from a perpendicular to the area to be measured. (The probe should be normal to the measured surface.) 8. Area of test piece, minimum 30 mm x 30 mm. 9. Some standards from instrument manufacturers are only of nominal film thickness. (see Note on Page 3) Calibration Thickness
10、standards are furnished with the instrument and are used to calibrate the gauge as follows: 1. Warm up the instrument for 20 minutes before use. 2. Select the proper scale range for the estimated coating thickness. 3. Calibrate the instrument as prescribed in the manufacturers manual. 4. For test pa
11、nels and bodies the calibration must be performed on steel body skin panels ground to a surface finish of 0.9 - 1.8 micrometers, unless otherwise specified. Calibrations in cases when either an uncoated specimen is not available or the magnetic properties of the coated and uncoated specimens are dif
12、ferent: 1. Select proper scale range (first reading). 2. Place gauge head on coating (second readings). 3. Insert suitable thickness standard between coating and gauge head. 4. If the second reading on the instrument is not equal to the original reading plus the thickness of the standard, the calibr
13、ating control should be adjusted until the instrument indicates the expected value of coating thickness plus standard. FORD LABORATORY TEST METHOD BI 117-01 Page 3 of 3 Copyright 2001, Ford Global Technologies, Inc. 5. Repeat this procedure two (2) or three (3) times to adjust the gauge correctly fo
14、r the particular base metal. Procedure Paint over Magnetic or Non-Magnetic Metal Substrates 1. Warm up the instrument for 20 minutes before use. 2. Select scale range for estimated thickness. 3. Adjust or zero gauge on an uncoated area of the base metal of the test specimen. This should be done on a
15、n area having the same contour as the test specimen and may require removal of some paint with a suitable solvent or paint remover. 4. Select a standard according to the requirements of the Instrument manufacturer and insert between the uncoated specimen and gauge head or probe and adjust indicator
16、to read the thickness of the standard. 5. Place probe on painted area of the specimen and read thickness of coating. Possible errors with Paint on Finished Bodies Measurements on areas, where due to different type of body construction, increased metal thickness exists, also edges, sharp radii, and c
17、loseness to trim moulding may not be accurate because of interaction with the flux lines of the instrument. Note: Standards and instrument correlation checks against certified coating thickness Calibration Standards for non-magnetic coatings on steel should be carried out at a minimum of six (6) mon
18、thly intervals (Source of certified standards, US Department of Commerce, Washington, D.C.). Evaluation Report type of equipment, scale range, location of measuring points, average, minimum-maximum range, and if appropriate Standard Deviation. Chemicals, materials, parts, and equipment referenced in this document must be used and handled properly. Each party is responsible for determining proper use and handling in its facilities.
