1、Designation: C 282 99 (Reapproved 2005)Standard Test Method forAcid Resistance of Porcelain Enamels(Citric Acid Spot Test)1This standard is issued under the fixed designation C 282; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers a
3、 procedure for evaluatingporcelain enamels in their resistance to citric acid exposure atroom temperature. No attempt is made to categorize porcelainenamels as to their acid-resistance or non acid-resistanceproperties, since the requirements in the several branches of theindustry differ.1.2 The test
4、 method is applicable for ware of various shapesproviding they contain a substantially flat area approximately50 mm in diameter.1.3 The test method is not applicable to finishes on chemicaland hospital ware, which may come in contact with strongmineral acids, nor to cooking utensils, which may come
5、inprolonged contact with hot acid solutions.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 regulat
6、ory limitations prior to use.2. Summary of Test Method2.1 The test method consists of a 15 min exposure of the testsurface to a small pool of 10 % citric acid, and an evaluation ofthe effect in terms of the change in appearance and the “relativecleanability” of the surface resulting from the treatme
7、nt.3. Significance and Use3.1 This test method is intended specifically for testing theporcelain enamel finish on stoves, refrigerators, table tops,sinks and other sanitary ware, laundry appliances, architecturalunits, etc., where the surface may come in contact with foodacids at room temperature.3.
8、2 Citric acid has been chosen as the test medium becauseit is one of the most common of the food acids and willgenerally provide a measurable result in its action on porcelainenamel.4. Apparatus4.1 Dropper Bottle, or medicine dropper,4.2 Watch Glass, 25 mm in diameter with fire polished edge,4.3 Tow
9、el, soft cotton, and4.4 Drafting Pencil, conventional graphite, degree 3B.5. Reagents and Materials5.1 Citric Acid SolutionDissolve 10 g of anhydrous citricacid crystals (H3C6H5O7) in 100 mL of water. Solution shall beprepared not more than 48 h prior to use.5.2 Cleaner SolutionDissolve 10 g of tris
10、odium phos-phate (Na3PO4) in 1 L of tap water.6. Sampling6.1 The test specimens may be articles of commerce, piecescut from articles of commerce, or laboratory specimens pre-pared especially for this test.NOTE 1Processing variables in the application and drying and firingoperations materially affect
11、 the degree of attack by the acid on the surfaceof porcelain enamels. Sample specimens used for classification of acidresistance must be processed under identical conditions to the commercialware they represent.7. Procedure7.1 Thoroughly wash area to be tested using a soft cottontowel moistened with
12、 a warm, 1 % solution of trisodiumphosphate. Rinse in warm, running tap water, and dry with asoft towel by blotting. Store the specimen at a temperature of26 6 1C (79 6 2F) for a time sufficient to bring it within thisrange prior to and during the test.NOTE 2If, when rinsing, the water gathers in dr
13、ops on the surface,repeat washing treatment until water spreads evenly.7.2 On articles of commerce, select areas that are horizontalor nearly horizontal in service. Place the specimen in a positionsuch that a flat area at least 38.1 mm in diameter is horizontal.1This test method is under the jurisdi
14、ction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved Sept. 15, 2005. Published September 2005. Originallyapproved in 1951. Last previous edition approve
15、d in 1999 as C 282 99.This test method is based on the Test for Acid Resistance of Porcelain Enamels(Citric Acid Spot Test) Bulletin T-21, of the Porcelain Enamel Institute.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.With the spe
16、cimen and the citric acid solution at 26 6 1C (796 2F), place several drops of the solution on the test area toform a pool, and immediately cover with a clean watch glass inthe inverted position. Use a quantity of solution that is justsufficient to fill the inverted watch glass except for a small ai
17、rbubble (three to six drops are usually required, depending uponthe dropper and the curvature of the watch glass). After 15 minof treatment, remove the watch glass and immediately rinse thespot of solution from the surface. Dry the specimen with a dry,clean, soft cotton towel by blotting (not rubbin
18、g).NOTE 3The test surface must be thoroughly dry before grading. Thepresence of a slight film of water on the surface may change the rating ofspecimens near the borderline between classes.8. Grading8.1 Grade the test specimen within 2 h after exposure to thetest solution using the procedure outlined
19、 in the diagram, Fig.1. Rate each specimen with the appropriate classification grade,AA, A, B, C or D, as explained in Table 1. The criteria referredto in Fig. 1 and Table 1 are described as follows:8.1.1 Visual ExaminationView the specimen at variousangles with respect to the light source and eye,
20、in order todetect whether the “treated area” differs in any respect from the“protected area.” Use partially diffused daylight, supplementedif necessary by artificial light, the total intensity being approxi-mately that available within a few feet of an outside window,but do not examine in direct sun
21、light. During observation, holdthe specimen no nearer the light source (such as a window)than the minimum diameter of the source.NOTE 4The term “treated area” refers to that portion of the specimenwhich has been subjected to acid solution confined by the watch glassduring treatment. The term “protec
22、ted (untreated) area” refers to the areaadjacent to the treated area.NOTE 5Some colored porcelain enamels exhibit a change in color asa result of the acid treatment. Since the test is designed primarily toevaluate durability, color changes as revealed by this test should beignored except where other
23、wise specified.8.1.2 Dry-Rubbing TestUsing the flat point of a degree3B, conventional graphite drafting pencil held in a normalwriting position and applied with firm pressure, draw two ormore approximately parallel lines extending across the treatedarea. Starting with gentle pressure and then applyi
24、ng graduallyincreasing pressure, rub repeatedly across the lines with a dry,clean, soft cotton towel as illustrated in Fig. 2. If marks arecompletely removed from the treated area, the specimen shallbe rated as Class AA. Otherwise, continue as directed.NOTE 6The pencil point should be prepared by ho
25、lding a sharpenedpencil in a normal writing position and rubbing on abrasive paper (1/0Emery polishing or 400-grit silicon carbide or aluminum oxide abrasivepaper) until the minimum diameter of the flat, circular cross section is halfthat of the full graphite core.8.1.3 Blurring-Highlight TestIn a w
26、ell-lighted location,hold the specimen so that the image of a small light source,such as a frosted lamp bulb, is observed as a highlight in theprotected area, the line of vision being within 45 perpendicu-lar to the surface (a desk lamp with an incandescent bulb isrecommended for this purpose). Focu
27、s the eyes on the image ofthe light source, then slowly shift the specimen just sufficientlyto bring this image into the treated area observing it as it passesacross the boundary line between the two areas. Ignore anycolor difference in the enamel due to staining. If a definiteblurring of the image
28、is observed as it passes from theprotected to the treated area, the specimen shall be rated asClass C or Class D. Proceed to 8.1.5 to determine finalclassification. If a blurring image is not observed, the specimenshall be rated as Class A or Class B. Proceed to 8.1.4 todetermine final classificatio
29、n.8.1.4 Wet-Rubbing TestUsing the procedure specified in8.1.2 mark the treated area and rub the marks with a clean, softcotton towel which has been dipped in water and twisted toremove any excess. For this test, make new marks in a locationFIG. 1 Flow Sheet of Test Procedure for Classification of Tr
30、eated SpecimensTABLE 1 Requirements for Respective Classes of AcidResistanceClassification RequirementsClass AA No visible stain, andPass dry-rubbing testClass A Pass blurring-highlight test, andPass wet-rubbing testClass B Pass blurring-highlight test, andFail wet-rubbing testClass C Fail blurring-
31、highlight test, andPass disappearing-highlight testClass D Fail disappearing-highlight testC 282 99 (2005)2other than that used for the dry-rubbing test. Do not use soap,abrasive, or similar cleaning material. If the marks are com-pletely removed from treated area, the specimen shall be ratedas Clas
32、s A. Otherwise it shall be rated as Class B.8.1.5 Disappearing-Highlight TestThis test is similar inall respects to the blurring-highlight test specified in 8.1.3,except that the criterion in this case is the complete disappear-ance of the highlight in the treated area. If the highlight isvisible in
33、 the treated area, the specimen shall be rated as ClassC. If the highlight disappears in the treated area, the specimenshall be rated as Class D.9. Report9.1 Report the assigned grade for each specimen. If thecitric acid treatment is performed at temperatures outside thestated tolerances, this varia
34、tion should be reported.10. Reproducibility10.1 Since variations may occur during enameling whichaffect the acid resistance, several specimens should be treatedto determine the class of commercial ware.10.2 Ratings of individual specimens shall be considered asdue to actual differences in the acid r
35、esistance of the speci-mens, not to differences in the test procedure.11. Precision and Bias11.1 The precision and bias of this test method is beingestablished.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this stan
36、dard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be revie
37、wed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsibl
38、e technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
39、shohocken, 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).FIG. 2 Method of Applying and Rubbing Pencil Marks on theTreated AreaC 282 99 (2005)3
