1、FORD LABORATORY TEST METHOD BI 169-01 PROCEDURE TO SCRIBE COATINGS AND MEASURE CREEPBACK AND CORROSION PROPAGATION Application This method covers the scribing of coatings on rigid surfaces to expose the base metal using a handheld tool. After corrosion testing, the method for measuring the amount of
2、 corrosion propagation and coating delamination from the scribed line is described. Apparatus Required Scribing Tool A replaceable carbide cutting tip is mounted to a custom made handle, Figure 1. This scribe tip is a V shaped carbide turning insert manufactured by Valenite having part number VBGT 3
3、31 PF3 VP9610. The diamond shaped tip has a 35 angle with a 0.016 inch radius. Note 1: Limited trials on e-coated steel panels found the tip to expose a 0.2 0.25 mm width of substrate with medium pressure. Note 2: There are several types of cutting tips available in the industry as specified by diff
4、erent specifications. No attempt has been made to compare results to this cutting tip. Maintenance: Tool shall be inspected for wear and breakage before each test. Wear can also be evaluated by scribing a painted panel and evaluating the width of the scribe line compared to a new tip. Damaged or wor
5、n scribes shall be replaced. Ruler / Scale, 1 mm divisions. Two needed. Straight Edge Date Action Revisions Rev. 02 2017 05 03 Revised Added reporting requirement/table K. Redlin, NA 2015 10 09 Revised Added photos A. Wedepohl, NA 2011 07 14 Activated J. LaDuke, NA Controlled document at www.MATS Co
6、pyright 2017, Ford Global Technologies, LLC Page 1 of 6 35 included angle 0.016 inch (0.406 mm) radius Figure 1. Handheld manual scribe FORD LABORATORY TEST METHOD Page 2 of 6 Copyright 2017, Ford Global Technologies, LLC Scribing Procedure BI 169-01 1. The scribing tool shall be applied so the cutt
7、ing edge is at an 80 angle in the scribe line direction and 90 with the plane of the panel. See Figure 3 and Figure 4 respectively. Figure 3 Figure 4 2. For part testing, a horizontal scribed line is required. 3. For test panel testing, a diagonal line may be included with a horizontal line when req
8、uested. These lines should be made as outlined on Figure 5. 4. Using a straightedge, scribe a line between 70 mm and 80 to 100 mm in length. If scribing on a curved surface, use a flexible straightedge and maintain the scribe angles to the best of ones ability. The scribe must extend down to the sub
9、strate. Multiple passes over the same line may be required, especially for thick coatings. In some cases it helps to apply minimal pressure on the first scribe to avoid fracture and chatter of the paint system surrounding the line. Metal shavings are a good visible indicator that the substrate has b
10、een reached. For zinc coatings on steels (with or without paint) a minimum of three passes is recommended to reach the substrate. If in doubt, use magnification to visually inspect the scribe to determine if the substrate has been reached. 5. Wipe away the loose coating debris with a cloth and verif
11、y that the scribe is free of metal burrs. 6. Measure the width of the scribe in the substrate under low magnification and record the values. 7. Unless otherwise indicated, by the corrosion test procedure, the flat panel is intended to be oriented 15 +/- 5 from the vertical with the scribe lines faci
12、ng upward. 90 Direction of Scribe 80 FORD LABORATORY TEST METHOD Page 3 of 6 Copyright 2017, Ford Global Technologies, LLC BI 169-01 Figure 5 Flat Panel Evaluation Procedure 1. After the completion of the corrosion test wash the panels to remove salt deposits and inspect the scribed line for flaking
13、 of the coating, bubbling of the coating, and corrosion spread from the scribed line. All of these changes are included in the creepback measurement. If run down of corrosion products obscures the measurement, then a weak phosphoric or citric acid solution may be used to clean the surface. 2. Disreg
14、ard the first and last 10 mm of the scribed line. 3. Divide the line into five equal segments with each segment being at least 10 mm in length. See Figure 6. 4. Measure the maximum propagation of corrosion to the nearest 0.5 mm for each segment. Oblique lighting can be used to highlight lifting and
15、bubbling of the coating. Recommend using one ruler to define the segments and the second ruler to measure the creepback. 5. Use the formula in the calculation section to determine the mean value. 6. Figures 7, 8, and 9 show examples of measurement on scribed panels. Scribe on this side 30 +/- 15 0 +
16、/- 5 angle 20 mm min 10 mm min FORD LABORATORY TEST METHOD Page 4 of 6 Copyright 2017, Ford Global Technologies, LLC BI 169-01 X1 X2 X5 X3 X4 h Figure 6 Scribed Line after Corrosion 10 mm 10 mm Calculation: Average creepback from the scribe line = Where: h = Width of scribed line (Xn-h) 1 5 X = Tota
17、l maximum spread of creepback above and below the line A lab report generated from this method should include all relevant sample identification and all measurement data acquired, as shown in Table 1. The “Average Creep” is the average creep distance for all five segments, as calculated above. The “
18、(Xn-h) Sample Max” is the highest individual measurement obtained for a sample, adjusted for the width of the scribed line. SCRIBE CREEP MEASUREMENTS per FLTM BI 169-01 Sample X1 X2 X3 X4 X5 Average Creep (Xn-h) Sample Max Sample 1 0 0 0 0 0 0.0 0.0 Sample 2 0 4 0 1 6 1.7 5.5 Sample 3 3 1 1 0 2 0.9
19、2.5 Sample 4 1 5 0 0 0 0.7 4.5 Sample 5 0 1 1 2 0 0.3 1.5 Sample 6 0 0 0 3 0 0.1 2.5 Sample 7 0 0 0 3 1 0.3 2.5 Table 1 5 L Figure 6. FORD LABORATORY TEST METHOD Page 5 of 6 Copyright 2017, Ford Global Technologies, LLC References: ASTM D1654, Volvo VCS 1021,29 BI 169-01 Figure 7. Bubbles in the coa
20、ting on an aluminum substrate. Figure 8. Corrosion and bubbling of the coating on a steel substrate. Figure 9. Bubbling of the coating on a steel substrate. FORD LABORATORY TEST METHOD Page 6 of 6 Copyright 2017, Ford Global Technologies, LLC BI 169-01 Figure 10. If there are doubts regarding the extent of the creepback, measure the creepback and then remove the paint with paint remover and measure a second time. Use the higher average.
