ASTM B940-2005(2014) Standard Practice for Testing Non-Chromate Coatings on Zinc and Cadmium Surfaces《在锌和镉表面非铬酸涂层试验的标准实施规程》.pdf

1、Designation: B940 05 (Reapproved 2014)Standard Practice forTesting Non-Chromate Coatings on Zinc and CadmiumSurfaces1This standard is issued under the fixed designation B940; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year

2、 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 practice covers a procedure for evaluating theprotective value of chemical and electrochemical conversioncoat

3、ings produced by non-chromate (chromate being defined asa compound that has chromium in the plus six oxidation state,and as such, chromium compounds in other oxidation states,such as plus three, shall not be excluded) treatments of zinc andcadmium surfaces.1.2 The protective value of a non-chromate

4、coating isusually determined by salt-spray test and by determiningwhether or not the coating possesses adequate abrasion resis-tance when applied for that purpose.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This stan

5、dard 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. Referenced Documents2.1 A

6、STM Standards:2B117 Practice for Operating Salt Spray (Fog) Apparatus3. Terminology3.1 Descriptions of Terms:3.1.1 time to failuretime to failure will depend on the typeof coating tested. The minimum expected protective valueobtainable in a given salt spray test is given in Appendix X2.3.1.1.1 Discu

7、ssionIn most instances, failure is defined asthe first appearance on significant surfaces of white corrosionproducts visible to the unaided eye at normal reading distance,except that the presence of white corrosion products at sharpedges (for example, on threaded fasteners) and at junctionsbetween d

8、issimilar metals should not be considered failure. Insome instances, it may be desirable to regard the first appear-ance of red rust as failure.3.1.2 significant surfacesin general, significant surfacesare those surfaces that are visible and subject to corrosion orwear, or both, except that surfaces

9、 that are normally difficult tocoat by electroplating or mechanical deposition may be ex-empt. The designation of significant surfaces may be indicatedon the drawing.4. Significance and Use4.1 This practice is applicable to non-chromate coatings thatare colorless, colored, electrochemically applied

10、or non-electrochemically applied. The zinc or cadmium, or both, maybe electrodeposited, mechanically deposited, hot-dipped,rolled, or in the form of castings.4.2 Because of variables inherent in the salt-spray testwhich may differ from one test cabinet to another, interpreta-tion of test results for

11、 compliance with expected performanceshould be specified by the purchaser.4.3 Properties such as thickness, color, luster, and ability toprovide good paint adhesion are not covered in this practice,nor are the chemical composition and the method of applica-tion of these finishes.5. Conditioning5.1 A

12、gingBefore subjecting a non-chromate coating totest, check with the chemical producer to determine if aging isan issue that needs to be considered.5.2 Preparation of SpecimenThe test surface must be freeof fingerprints and other extraneous stains and must not becleaned except by gentle wiping with a

13、 clean, dry, soft cloth toremove loose particles. Oily or greasy surfaces should not beused for testing, and degreasing with organic solvents is notrecommended.6. Procedure6.1 Salt Spray TestExpose the clean specimen to a 5 %solution salt spray and conduct the test in accordance with the1This practi

14、ce is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatingsand is the direct responsibility of Subcommittee B08.07 onConversion CoatingsCurrent edition approved Nov. 1, 2014. Published November 2014. Originallyapproved in 2000. Last previous edition approved in 2009 as B940

15、05(2009)1.DOI: 10.1520/B0940-05R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM Internation

16、al, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1latest revision of Practice B117. Unless otherwise specified,only those surfaces that are positioned in the test chamber inaccordance with Practice B117 are considered pertinent forevaluating failure. The exposed

17、 surfaces of the test specimensshall be free of all visible defects, such as scratches or pits, orboth, and shall be flat. The surfaces shall not be cleaned withabrasive materials or abrasive chemical agents that may etchthe exposed surfaces. Corrosion found on surfaces within14 ofan inch of the edg

18、es of the exposed specimens shall not beconsidered significant to the test.6.2 Abrasion Resistance TestFor those non-chromatedcoatings designed and specified by the chemical producer asabrasion-resistant, rub the non-chromated surface with agritless, soft gum eraser (art-gum) for 2 to3sbyhand (about

19、ten strokes) using normal pressure (about 70 kPa (10 psi) anda stroke approximately 50 mm long. The non-chromate coatingshould not be removed or worn through to the underlying metalas a result of this treatment.7. Keywords7.1 non-chromate coatingsAPPENDIXES(Nonmandatory Information)X1. NATURE OF COA

20、TINGSX1.1 The primary purpose of non-chromate finishes used asa replacement for chromate finishes is to retard the formationof white corrosion products upon exposure to stagnant water,moist atmosphere, or stagnant environments containing or-ganic vapors, such as may emanate from certain plastics,pai

21、nts, and other organic materials. These finishes will notprevent the growth of metallic filaments, commonly known as“whiskers.”X1.2 Coatings covered by this practice generally containoxides of the basis metal in varying proportions. They may beproduced by either chemical or electrochemical processes

22、 fromsolutions free of hexavalent chromium compounds.X1.3 The quality of the non chromate film depends to alarge extent on the chemical purity and the physical conditionof the basis surface to which it is applied. In order to producean acceptable coating, it is essential that the surface be properly

23、cleaned and free of heavy metallic impurities such as lead, orcopper, which may interfere with the proper formation of thecoating.X1.4 The color and luster produced by a given treatmentwill depend to some extent on the surface condition of themetal to which it is applied and may vary from part to pa

24、rt, oreven on one single part.X2. PROTECTION BY NON-CHROMATE COATINGSX2.1 The minimum degree of protection that can be ex-pected from non-chromate coatings on electrodeposited zincwhen subjected to a 5 % salt spray test is 12 h.X2.2 This value is given for guidance purposes only and isnot to be cons

25、trued as endpoint requirements. All types of zincand cadmium coatings can be non-chromated, and there may ormay not be differences in the protection afforded by thenon-chromate, depending on the type of coating and themethod of processing, so the actual protection required shouldbe established to th

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