ASTM_D_4145_-_10.pdf

Designation:D414510Standard Test Method forCoating Flexibility of Prepainted Sheet1This standard is issued under the fixed designation D4145;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()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 substrates 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 standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.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-bility of regulatory limitations prior to use.2.Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 T-bend,na description of the severity of a bend interms of the gauge or thickness(t)of the sheet to which thecoating has been applied;as used in this test method,theT-bend rating is the minimum number of thicknesses of metalaround which the coated sheet is bent(Fig.1),or if bent arounda die,the number of thicknesses of metal equivalent to thediameter of the die to achieve no fracture or removal of thecoating.3.Summary of Test Method3.1 Prepainted panels are bent 180 around progressivelymore thicknesses of metal or larger diameter dies,the end pointbeing when failures no longer occur.The panels may beexamined with or without low magnification(5 to 10)aftereach bend in order to determine if the coating fractured(cracked).If loss of adhesion or pickoff is to be determined,this examination shall occur after performing a tape pull-offtest.4.Significance and 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 which exposes the substrate,or in the loss of adhesion of the coating to the substrate.Thistest is a means of evaluating the ability of a coating system towithstand the stresses of fabrication.4.2 The bend direction,whether the axis of bend is trans-verse to or along the rolling direction of the metal,and thetemperature of the specimen when it is bent can affect theresults of this test and should be agreed upon between thesupplier and the user.5.Apparatus5.1 A means of holding one end of the specimen rigidlywhile making the bend is needed.Damage to the coating whilemaking the bend must be avoided.Various bending tools suchas a vise with smooth jaws or with smooth inserts,a bendforming tool(Fig.2),a brake press(Fig.3)or a combination oftools have 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.4).5.3 Bend Forming Tool.5.3.1 A manual or automated operation forming tool ca-pable of facilitating the T-bending of a sample may be used.Anarbor press with an appropriate fixed V-shaped die and move-able wedge has been found to be satisfactory for this purpose.5.4 Magnifier.5.4.1 A magnifier capable of 5 to 10 magnification forexamining the specimen for coating fracture and pickoff aftertesting.A stereomicroscope has been found useful for thispurpose.5.5 Clear Adhesive Tape.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 a length sufficient to make therequired number of bends.A 2 by 6-in.(50 by 150-mm)size is1This 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 June 1,2010.Published August 2010.Originallyapproved in 1983.Last previous edition approved in 2002 as D4145 83(2002).DOI:10.1520/D4145-10.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 convenient.The specimen shall be held at 75 6 10F(24 65.5C)temperature,or as agreed upon between purchaser andseller.The bend direction will be longitudinal or in the samedirection with respect to the rolling or flow direction of thesheet,or as agreed upon between purchaser and seller.NOTE1A triangle-shaped specimen(Fig.5)has been found conve-nient for making T-bend t