1、 SURFACE VEHICLE RECOMMENDED PRACTICE J2634 MAR2015 Issued 2003-01 Reaffirmed 2015-03 Superseding J2634 JAN2003 Scribing of Coatings in Preparation for Testing of Wheels and Wheel Trim RATIONALE J2634 has been reaffirmed to comply with the SAE five-year review policy. _ SAE Technical Standards Board
2、 Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibilit
3、y of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2015 SAE International All rights reserved. No part of this publication may be reproduced, s
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5、90 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J2634_201503 ForewordThis scribing test procedure has been agreed to as the preferred method of preparing a part
6、 to evaluatethe coating systems used for automotive wheels and wheel trim due to observed variability associated withscribing methods.The intent is to recognize, by the industry, a single common method for sample preparation. This commonprocedure will benefit all by reducing the testing complexity,
7、eliminate the need for specialized test equipment andfacilities, utilize improved methods, increase test efficiency, and reduce the overall number of special testsrequired to approve a paint or paint system.Scribing is utilized to simulate a break in the coating which may occur in the field and whic
8、h results in corrosionsites. The ability of the part to resist corrosion with such damage provides an indication of the expected fieldperformance under these conditions.Comparative testing of alternative coatings and pretreatment systems using scribing allows discrimination of theperformance levels.
9、This scribing method is important to ensure consistency in the exposure of the metal substrate, which providesactive corrosion sites.This scribing method was developed based on testing on automotive wheels and wheel trim but may be used onother components as well.1. ScopeThis SAE practice is intende
10、d for the sample preparation of test pieces for automotive wheels andwheel trim. The practice provides a consistent scribing method for use on test panels and or component partswith substrate chemical pretreatment and coating systems. Test specimens can then be subjected to variouscorrosion tests in
11、 order to evaluate performance without significant variations of the degree of exposure of thesubstrate. The scribing is used to create a break in the coating/finishing as can occur in the field throughgravel and other damaging conditions.NOTE Significant variability is attributed to surface contour
12、, coating hardness/softness, operatorreproducibility, and the scribing tool and its condition.2. ReferencesThere are no referenced publications specified herein.3. Definitions3.1 ScribeA scribe is a line, which cuts through all surface coatings and pretreatments and exposes the metalsubstrate to the
13、 environment.4. Equipment and Test Materials4.1 Scribe Tool A straight shank, tungsten carbide tip lathe tool, Tool Style E-4 with a 0.4 mm (1/64-inch) noseradius.4.2 Laboratory Scribing FixtureSee attached drawing of fixture with the test specimen (Figure 1) orequivalent.FIGURE 1LABORATORY SCRIBE F
14、IXTURE4.3 Conductivity Metersuch as; Fluke 73 Series Multimeter, or equivalent.4.4 Magnifying Glass10X4.5 Holding Assists/FixturingHolding devices such as wood blocks/shims are typically used to hold thespecimen in place in a suitable configuration for scribing. Movement of the specimen during scrib
15、ing maycause an irregular scribe._ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 1 of 65. Specimen PreparationShould the component be too large to fit in a test chamber or if it would significantlyreduce the test capacity then a test section should be cut from the component. Care should be used to prev
16、entdamage to test surfaces. When cutting the test section from a component/panel, it is recommended that the specimen be sized to fitwithin the fixture specimen mounting area.NOTE 1When preparing a wheel sample it is recommended to remove the back half rim section to reducethe required test space an
17、d to improve the ability to fixture the part for scribing.NOTE 2When scribing a wrought component it is important to consistently scribe with the same orientationand direction relative to the grain of the material to reduce part to part test variability.6. Scribing Tool Preparation6.1 Fasten a sharp
18、, straight shank tungsten carbide tip lathe-cutting tool at approximately a 45 degree angle to thespecimen surface in the Laboratory Scribing Fixture, (Figures 1 and 2).FIGURE 2LABORATORY SCRIBE FIXTURE WITH TEST SPECIMEN6.2 Inspect and verify the scribing tool sharpness. Visual review of the tool a
19、t a set frequency is necessary; use ofan optical comparator is recommended. A correctly scribed specimen would appear uniform in contour, (SeeFigure 3). Note that a defective tool will not create a uniform “V” cut. (See Figures 4, 5, 6, 7)_ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 2 of 6FIGURE 3CO
20、RRECT SCRIBING, UNIFORM AND SYMMETRICAL SCRIBEFIGURE 4A BROKEN SCRIBE TOOL RESULTS IN NO V-NOTCH ANDTHE PAINT FILM IS REMOVED ON THE SURFACE_ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 3 of 6FIGURE 5SCRIBED WITH INSUFFICIENT PRESSURE TO CUT THROUGH TO SUBSTRATEFIGURE 6SLANTED SCRIBE, INCORRECT ANGLE
21、, NON-UNIFORM_ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 4 of 6FIGURE 7SCRIBED WITH EXCESSIVE FORCE, SUBSTRATE ISPLOWED UP ON SIDES OF SCRIBE7. Test Procedure7.1 Level the test sample on the scribing fixture using a holding device/fixturing for support (Figure 2). Position thearea to be scribed ver
22、tically along the cutting guide path.NOTE 1Make sure that the holding device will accommodate the sample to be scribed, in a horizontalposition, without movement.NOTE 2Certain specimens may be constructed of metal substrates with a contour. These parts may deformduring the scribing process unless th
23、ey have a conforming backing material to support them.Without support the sample will deform resulting in the sample being unacceptable for testing.7.2 The operator should use one hand to secure the test specimen while scribing with the scribing fixture. Placethe scribing tool on the test specimen a
24、nd exert sufficient pressure to permit a uniform “V” cut in the coating(s),as well as the base metal, exposing the metal substrate as a uniform line. Any scribe line must be checked toensure penetration to the metal substrate as described in 7.3 for its full length, (See Figure 3)CAUTIONDo not apply
25、 excessive pressure on scribing, just enough to penetrate the coating to the substrate.Excessive pressure on scribing will damage the coating and result in rupture, (Reference Figure7)._ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 5 of 67.3 Conductivity Testing7.3.1 First position the conductivity me
26、ter probes on the un-scribed surface and to the substrate metal to verify thecoating is not conductive. If the coating is conductive the conductivity meter will not be an effectiveevaluation tool.7.3.2 If the sample does not demonstrate conductivity then proceed. Clean the scribe line by air blow-of
27、f orbrushing; then use a conductivity meter and magnifying glass to check the scribe line for penetration throughthe coating(s) to the substrate metal surface. Check the conductivity meter function by crossing the probeleads. Then place one probe on an un-coated area. Trace the other probe down the
28、length of the scribeline. A continuous electrical reading should be detected. 7.3.3 If a dis-continuous reading is found re-scribing the same scribe is not acceptable, select another sample oranother site on the same sample. Another scribe may be accommodated on the same test piece.Consideration mus
29、t be given in locating an additional scribe to ensure the expected corrosion will not crossover to the prior scribe or extend into an edge, 20 mm separation distance is typical. The prior defectivescribe must be permanently identified as invalid to preclude it being used inadvertently for data colle
30、ction.7.3.4 If checking platings, the multimeter, conductivity method is not applicable and the 10X magnifying glass isrecommended as for conductive coatings.7.4 The scribed sample should be tested without delay. All samples must begin testing within 24 hours of scribingor be discarded. Sample stagi
31、ng during the 24 hour period must be free from contamination or exposure tohigh humidity or corrosion products.7.5 With consistent scribing, corrosion should appear on both sides of the scribe line. If not, review the testprocedure and equipment for any procedure inconsistency or equipment malfuncti
32、on. Figures 3, 4, 5, 6, 7.7.6 Always review special customer requirements or procedures. These may specify other pre-test conditioningand/or the location and orientation of the sample within a test chamber.8. Test Duration8.1 Scribing is intended as a step in sample preparation for subsequent testin
33、g. The duration of such testing isaddressed within those test procedures. Scribed samples however must be processed into the subsequenttesting as per 7.5.PREPARED BY THE SAE WHEEL FINISHING LAB TESTING SUBCOMMITTEEOF THE SAE WHEELS STANDARDS COMMITTEE_ SAE INTERNATIONAL J2634 Reaffirmed MAR2015 6 of 6
