1、Designation: D 4145 83 (Reapproved 2002)Standard Test Method forCoating Flexibility of Prepainted Sheet1This standard is issued under the fixed designation D 4145; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes a procedure for determiningthe flexibility and adhesion of organic coatings (paints) onmetallic s
3、ubstrates that are deformed by bending when thesheet is fabricated into building panels or other products.1.2 The metal substrate must be capable of passing this testwithout fracturing and with no excessive grain development.1.3 The values stated in inch-pound units are to be regardedas the standard
4、. The values given in parentheses are forinformation only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bil
5、ity of regulatory limitations prior to use.2. Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 T-benda description of the severity of a bend interms of the thickness (T) of the sheet to which the coating hasbeen applied; as used in this test method, the T-bend rating isthe minimum
6、 number of thicknesses of metal around which thecoated sheet is bent (Fig. 1), or if bent around a die, the numberof thicknesses of metal equivalent to the diameter of the die toachieve no fracture or removal of the coating.3. Summary of Test Method3.1 Prepainted panels are bent 180 around progressi
7、velymore thicknesses of metal or larger diameter dies, the end pointbeing when failures no longer occur. The panels are examinedat low magnification (5 to 103) after each bend for fracture ofthe coating (cracking) and, for loss of adhesion pickoff, bymeans of a tape pull-off test.4. Significance and
8、 Use4.1 Organic coatings on precoated sheet are subjected tostresses when fabricated into products by roll forming, brakebending, or other deformation processes. These stresses canexceed the flexibility or adhesive strength of the coating,resulting in fracture of the coating, exposing the substrate,
9、 orloss of adhesion to the substrate. This test is a means ofevaluating the ability of a coating system to withstand thestresses of fabrication.4.2 The bend direction, whether the axis of bend is across oralong the rolling diameter of the metal, and the temperature ofthe specimen when it is bent aff
10、ect the results of this test andshould be agreed upon between the supplier and the user.25. Apparatus5.1 A means of holding one end of the specimen rigidlywhile making the bend is needed. A bench vise with smoothjaws or with smooth inserts, preferably of a soft metal to avoiddamage to the coating, h
11、as been found to be satisfactory.5.2 If the metal is not bent around itself as in Fig. 1, a seriesof bending dies with smoothly rounded ends may be used asguides around which the specimen is bent (Fig. 2).5.3 Magnifier, capable of 5 to 103 magnification forexamining the specimen for coating fracture
12、 and pickoff after1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.53 on Coil Coated Metal.Current edition approved March 25, 1983. Published July 1983.2Scotch Brand #610 ta
13、pe manufactured by 3M Co., St. Paul, MN or equivalent,or as agreed upon between the supplier and the user.NOTE 1The above bends are expanded for clarity. They are actuallyflat against themselves in the test.FIG. 1 T-Bend Test in Which the Coated Specimen is BentAround Itself1Copyright ASTM Internati
14、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.testing. A stereomicroscope has been found useful for thispurpose.6. Procedure6.1 Bending the Coated Specimen Around Itself:6.1.1 The coated specimen shall be at least 2 in. (50 mm)across the bend direction, by
15、 a length sufficient to make therequired number of bends. A 2 by 6-in. (50 by 150-mm) size isconvenient. The specimen shall be at 62F of the temperatureagreed on.NOTE 1A triangle-shaped specimen (Fig. 3) has been found conve-nient for making T-bend tests. This shape leaves a portion of each bendexpo
16、sed for later examination and for a permanent record.6.1.2 Secure about 0.5 to 0.75 in. (13 to 20 mm) of one endof the specimen in a vise or holding jig as shown in Fig. 1.Bend the free end of the specimen 90 in a smooth and uniformmanner so that the coating is on the outside of the specimenafter it
17、 is bent.6.1.3 Continue to bend the specimen until the bent end canbe inserted in the jaws of the vise. Tighten the vise to completethe 180 bend, which is called an OT bend. Take care to tightenthe vise sufficiently so that the apex of the bend is as flat as canbe reasonably achieved.6.1.4 Examine t
18、he bend using a hand lens or low-powermicroscope for cracks in the coating.6.1.5 Apply pressure-sensitive tape2along the bend. Rubthe tape flat; then, holding the specimen firmly, remove the tapewith a rapid movement at an angle of 180 to the bend surface.Examine the tape for coating removed from th
19、e surface of thespecimen (that is, pickoff). In the case of a coated steelspecimen (for example, galvanized steel), examine the tape todetermine whether pickoff is between the organic coating andthe metallic surface or between the metallic coating and thebase steel.6.1.6 Secure the bent end of the s
20、pecimen in the vise andbend the free end 90. Continue to bend the free end around thefirst (OT) bend to complete a 180 bend, and tighten in the viseas before. This makes a 1T bend (Fig. 1). Examine undermagnification and by taping for cracking and pickoff, as withthe OT bend.6.1.7 Repeat this proced
21、ure, making a 2T, 3T, etc., bendsuntil no cracking or pickoff occurs.6.2 Bending the Coated Specimen Around a Die:6.2.1 The coated specimen shall be at least 2 in. (50 mm)across the bend direction.6.2.2 Secure the specimen and bending die in a vise orholding jig (Fig. 2). Bend the specimen 180 aroun
22、d the die ina smooth and uniform manner.6.2.3 Examine the bend for cracking as in 6.1.4 and for lossof adhesion as in 6.1.5.6.2.4 Express the T-bend to no cracking or no pickoff as thenumber of thickness around which the metal is being bentequal to the thickness of the die.7. Report7.1 Report the fo
23、llowing information:7.1.1 Identification of the material, such as coil number andlocation within the coil if the sample was coated on a coil line,7.1.2 The coating system, coating thickness, and applicationand cure conditions,7.1.3 The temperature at which the specimen is bent,7.1.4 The bend directi
24、onwhether across or along therolling direction of the sheet,7.1.5 The minimum T-bend to no paint fracture, and7.1.6 The minimum T-bend to no pickoff.8. Precision38.1 On the basis of an interlaboratory study of this testmethod, in which two operators in each of five laboratoriestested panels coated w
25、ith paints of different flexibility andadhesion, the standard deviation was found to be:3Supporting data are available from ASTM International Headquarters. RequestRR: D01-1034.FIG. 2 T-Bend Test Using a Die Around Which the Specimen isBentNOTE 1The above bends are expanded for clarity. They are act
26、uallyflat against themselves in the test.FIG. 3 Triangular Specimen for T-Bend TestD 41452Standard DeviationAluminumGalvanizedSteelT-bend to no fracture 0.55 1.33T-bend to no pickoff 0.76 2.098.2 Based on these standard deviations, the following crite-ria should be used to judge the acceptability of
27、 results at the95% confidence level:8.2.1 RepeatabilityMeasurements obtained by two opera-tors in a single laboratory should be considered suspect if theydiffer by more than:AluminumGalvanizedSteelT-bend to no fracture 0.4 1.8T-bend to no pickoff 0.9 3.38.2.2 ReproducibilityTwo measurements obtained
28、 in dif-ferent laboratories, each the mean of measurements made bytwo operators within a laboratory, should be considered suspectif they differ by more than:AluminumGalvanizedSteelT-bend to no fracture 2.5 10.1T-bend to no pickoff 1.8 10.69. Keywords9.1 coating flexibility; prepainted sheet; T-bend
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32、STM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 41453
