1、-ASTM D224b 87 W O759510 00247b1 3 M kt-04-40 Designation:D 2246-87 AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race SI.,Philadelphla,Pa.19103 fleprinted from the Annual Book o f ASTM Standards,Copyright ASTM if not listed in the current combined index,will appear in the next edition.Standard Te
2、st Method for Finishes on Primed Metallic Substrates for Humidity-Thermal Cycle Cracking This standard i s i s s u e d under the k e d designation D 2246;the number immediately following the designation indicates the year of originai adoption or,i n the case of revision,the year of last revision.A n
3、umber i n parentheseis indicates the year of last reapproval.A superscript epsiion(e)indicates an editorial change since the last revision or reapprovai.1.Scope 1.1 This test method describes conditions for testing an organic coating on a primed metailic substrate for cracking from humidity-thermal
4、cycling or from loss of plasticizer,or both.1.2 This standard may involve hazardous materials,oper-ations,and eqitipinent.This standard does not purport to address all o f the safety problems associated with its irse.It is the responsibilty o f the user o f this standard to establish appropriate sde
5、ty and health practices and determine the applicability o f regitlatory limitations prior to irse.2.Referenced Document 2.1 ASTM Standard:D609 Test Methods for Preparation of Steel Panels for Testing Paint,Varnish,Lacquer,and Related Products3 3.Summary of Test Method 3.1 The tendency of an organic
6、coating to develop cracking from humidity-thermal cycling or from loss of plasticizer,or both,is measured by alternate exposure in the humidity cabinet and in the cold box.At the end of the exposure period,the panels are rated for their degree of cracking.4.Significance and Use 4.1 This test method
7、provides an accelerated means of determining the tendency of an organic coating to fail by cracking when exposed to humidity-thermal cycling.5.Apparahis 5.1 Hitmdity Cabinet,of such design and construction as to maintain a relative humidity of 100%with condensation on the test specimens at all times
8、 and a temperature of 100 f 1F(38 f 0.5C).5.2 Cold Box,of such design and construction that a temperature of-10 f 3F(-23 f 1.5C)can be maintained.NOTE-Most commercial household freezers are capable of main-taining this temperature.5.3 Rack,as shown in Fig.1,for supporting test speci-mens at an angle
9、 of O to 30 from the vertical position in This test method is under the jurisdiction of ASThl Committee D 1 on Paint and Related Coatings and Materiais and is the direct responsibility of Subcom-mittee W1.27 on Accelerated Testing.Current edition approved May 29,1987.Published July 1987.Onpinally pu
10、blished CIS D 2246-64 T.Last PCZUOUS edition D 2246-65(1981).Anniid Book cfA&?hStondards,Vol 06.01.such a manner as t prevent contact between them during the test procedure.5.4 Grid,of thin wires 3 by 8V2 in.(75 by 215 mm)constituting one hundred and two Y2-h.(1 3-mm)squares,held in a frame Y 2 in.w
11、ide,with outside dimensions 4 by 9%in.(100 by 240 mm).6.Test Specimens 6.1 The test specimens shall be either samples of metallic products,prepared and coated in accordance with the specified production schedule,or coated metallic panels.The recommended panel size i s 4 by 12 i n.(100 by 305 mm).7.P
12、reparation of Test Specimens 7.1 The test specimens shall consist of steel meeting the requirements of Test Methods D 609,cleaned and prepared for coating in accordance with Procedure A of D-609.If desired,the metal panels selected for coating with organic coatings may be of any selected composition
13、 and may be cleaned and prepared according to cornmercial practice or by any procedure that is mutually agreed upon.7.2 After coating,the specimens shall not be cleaned,and they shall be handled oniy by the edges.8.Procedure 8.1 Support panels or specimens so that they will be held in a position O t
14、o 30 from the vertical in such a manner as to prevent contact between the panels during the test.8.2 Place the panels in a humidty cabinet at 100F(38C)and 100%relative humidity for a period of 24 f Y2 h.Then transfer them to the cold box at-10 f 3F(-23 f 1.5C)aiiowing a maximum of 30 s for the trans
15、fer.Leave the panels in the cold box for a period of 20 f 1 1 2 h.Remove the panels and allow to remain at room temperature for a period of 4 f Y2 h,during which time rate them.This constitutes one cycle.Run the test for 15 cycles or as mutually agreed upon,During any interruption of the normal cycl
16、ing,as on weekends,always leave the panels in the cold box.9.Evaluation of Test Specimens 9.1 Lay the specimen upon a horizontal surface,finish side up,with the framed grid(5.4)placed upon it so that the bottom 8Y2 in.(225 mm)is covered by mesh.(The frame itself excludes the first Y2 in.(13 mm)from edges of the specimen which may have been handled,or which may otherwise not be representative of the general area.)Make an evaluation by counting the number of grid squares within which one or more c