1、Designation: C839 82 (Reapproved 2010)Standard Test Method forCompressive Stress of Porcelain Enamels by Loaded-BeamMethod1This standard is issued under the fixed designation C839; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e 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.INTRODUCTIONMany methods and tests have been used in the industry to determine the relative compressive stressof porcela
3、in enamel ground coats and cover coats. Three methods have been most commonly used.They are loaded-beam, warp, and split-ring methods. In the loaded-beam method the measure of stressis the load required to bring a specimen back to a plane after it has been bowed by controlledapplication of the ename
4、l under test to one side of the specimen. The degree of the deflection of aspecimen from a plane caused by controlled application of enamel to one side is the indicatingmeasure of stress in the warp test. The indicating measurement in the split-ring test is the forcerequired to just open a split rin
5、g after controlled application of test enamel to the outside surface ofa ring.1. Scope1.1 This test method covers the measurement of the com-pressive stresses (Note 1) developed by fired porcelain enamelsusing the loaded-beam method.NOTE 1Although some may interpret the calculations that are used in
6、this test method as indicating compressive load, it is commonly referred toas compressive stress within the porcelain enamel industry.1.2 This test method is limited to the use of the loaded-beammethod. However, this method includes charts (Fig. 1 and Fig.2) that provide for conversion of loaded-bea
7、m test results towarp and ring stress values.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 ad
8、dress 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 ASTM Standards:2A424 Specifi
9、cation for Steel, Sheet, for Porcelain Enamel-ing3. Terminology3.1 Description of Term Specific to This Standard3.2 compressive stress or stressa term used to designatethe degree of compression that exists in a porcelain enamel onsteel after processing.4. Significance and Use4.1 All porcelain enamel
10、 coatings or glass coatings are bynecessity under some degree of compression at room tempera-ture. The desired degree of compression or stress depends uponthe type of ware and the end use of the item. Some method ofdetermining relative compressive stress of enamels is neces-sary to establish the sui
11、tability of an enamel for a proposedapplication.5. Apparatus5.1 Furnace, suitable for simultaneous firing of at least six1 by 12-in. (25 by 305-mm) specimens in vertical hangingposition.5.2 Firing Rack, suitable for furnace.1This test method is under the jurisdiction ofASTM Committee B08 on Metallic
12、and Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.This test method was developed at the National Bureau of Standards under thesponsorship of the Porcelain Enamel Institute, Inc., and was published as PEITechnical
13、 Publication No. T-30 (1973).Current edition approved April 1, 2010. Published June 2010. Originallyapproved in 1976. Last previous edition approved in 2005 as C839 82 (2005).DOI: 10.1520/C0839-82R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
14、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3 Loaded-Beam Test Apparatus (see Fig. 3 and
15、 Fig. 4). 5.4 Metric Weights, slotted, 1 to 500 g.Metric Equivalentsin. mm in. mm0.02 0.51 0.10 2.540.04 1.02 0.12 3.050.06 1.52 0.14 3.560.08 2.03FIG. 1 Conversion Chart for Loaded-Beam Stress to Warp StressFIG. 2 Conversion Chart for Loaded-Beam Stress to Ring StressC839 82 (2010)25.5 Laboratory B
16、alance, accurate to 10 mg with necessaryweights (1 to 100 g).5.6 Brushing Template,2116 by 101516 in. (52 by 278 mm)(see Fig. 5 for one example of achieving the desired end result).5.7 Stencil Brush.5.8 Fluorescent Light Fixture with diffusion panel andadjustable support.6. Test Specimens6.1 Six spe
17、cimens are required for each enamel tested.6.2 Specimens 1 by 12 in. (25 by 305 mm) shall be cut byshearing from flat sheets of 20-gage Commercial Quality TypeII enameling iron (see Specification A424) with thickness0.036 6 0.002 in. (0.91 6 0.05 mm). The 12-in. dimensionMetric Equivalentsin. mm in.
18、 mm14 6.35 134 44.4538 9.53 2116 52.39716 11.11 31116 93.6812 12.7 4 101.658 15.88 4516 109.540.866 22.0 858 219.081 25.4 101516 277.81114 31.75 12 304.8112 38.1 16 406.411116 42.86FIG. 3 Loaded-Beam Test ApparatusC839 82 (2010)3should be cut perpendicular to the direction of rolling of sheet.Care s
19、hould be exercised to prevent formation of burrs duringshearing. Burrs that are formed may be removed by carefullyfiling edges or by lightly touching edges to a sanding belt.Since opposing sides of the sheet may produce slightlydifferent results, one side of the sheet should be scribed in sucha mann
20、er that the scribe mark will appear about 1 in. from oneend of the resulting strips after shearing. A14 -in. (6.35-mm)diameter hole should be punched in one end of the specimenfor hanging purposes during drying and firing. The center ofthe hole should be on the center line716 in. (11 mm) from theend
21、 of the specimen. Specimens should be numbered foridentification during the testing procedure. They may bepermanently identified by metal stamping on the scribed sidewhile being supported on an anvil (see Fig. 6).7. Procedure7.1 Application of Ground Coat to Test Strips:7.1.1 Subject the specimens t
22、o a pickle procedure normalfor ground coat application. Pickle in a suspended verticalposition to prevent distortion.7.1.2 Measure and record metal thickness of the test speci-mens.7.1.3 Apply a medium high-temperature ground coat (1520to 1540 F (825 to 840 C) by spraying. With scribed sides up,firs
23、t spray the back sides of strips to give 1.5 g dry weight perstrip. Dry and cool. Reverse the strips and spray a like amounton the face side. Dry and cool. Use a relatively dry spray toavoid formation of beads on the edges of the strips (Note 2).7.1.4 Fire the strips in a vertical hanging position a
24、t theoptimum time and temperature for the ground coat. Thepreferred procedure is to fire multiples of six simultaneously.Cool in a suspended position, avoiding drafts or forced cooling.7.1.5 Weigh and record the weight of each strip to thenearest 0.01 g.FIG. 4 Loaded-Beam Test ApparatusNOTE 1See Fig
25、. 3 for metric equivalents.FIG. 5 Brushing TemplateC839 82 (2010)47.1.6 Place each strip on the test apparatus with the scribedside down.7.1.7 Measure and record the ground coat residual load,which is the weight in grams required to cause the strip to justrest on the three knife edges of the fixture
26、. Discard any stripshaving zero or negative stress (reverse bow) or having positiveload of more than 50 g.NOTE 2More consistently uniform and usable specimens will result ifa spraying technique is developed whereby a few hundredths of a gramless enamel is applied to the back than to the face. This p
27、ractice reducesthe possibility of developing a concavity in the strip as viewed from theface side.7.2 Application of Test Enamel:7.2.1 Apply test enamel to the face side of six ground-coated specimens by spraying. Apply the enamel to yield a dryweight of 30 g/ft2(323 g/m2,or212 g per strip). Use are
28、latively dry spray to avoid formation of beads along edges.After drying and cooling, use a template to brush back 11116 in.(43 mm) from each end of strip, leaving 858 in. (179 mm) ofcover coat on the strip. Wipe the edges and back of strips witha felt pad and dust with a soft-bristled brush or wool
29、duster.7.2.2 Fire panels, again in a vertical hanging position, atoptimum temperature and time for the test enamel as covercoat. Cool in a vertical position, avoiding forced cooling.Rapid cooling produces greater residual compressive stresses.7.2.3 Weigh each strip to the nearest 0.01 g and record.7
30、.3 Measurement of Load:7.3.1 Center each coated strip individually over the threeknife edges of the fixture with face side upward and punchedhole to left. Stops or blocks may be of aid in centering thestrips on knife edges.7.3.2 Centrally load the strip with slotted weights over thecenter knife edge
31、 until the strip just touches the central knifeedge. A strong diffuse light source behind the test fixturefacilitates observation of the end point.7.3.3 Measure and record the uncorrected compressive loadof each of the cover-coated test strips. The load, in grams,required to cause the strip to just
32、touch the central knife edgeis the uncorrected compressive load.7.3.4 Corrected load is uncorrected compressive load minusresidual ground coat load (see 7.1.7).8. Calculation8.1 Calculate the corrected load, L, by subtracting theresidual ground coat load from the uncorrected compressiveload.8.2 Calc
33、ulate the compressive stress, Sc, for each testspecimen as follows:Sc5 L 31.80W30.036Ti(1)orSc5 L 31.80W30.914Tm(2)where:Sc= compressive stress of the specimen, gf/in. (or gf/mm),L = corrected load for cover-coated strip, gf,1.80 = calculated fired weight of enamel on 858 -in. (219-mm) length of str
34、ip equivalent to 30 g/ft2(323 g/m2)(dry),W = actual fired weight of test enamel on strip to thenearest 0.01 g,Ti= actual metal thickness, in., andTm= actual metal thickness, mm.8.3 Determine the average of the six compressive stressvalues and report as the compressive stress of the testedenamel.8.4
35、If the end use of the test data requires a statisticalcomparison of samples, the standard deviation and statisticalerror of the six specimens comprising one lot may be calcu-lated by the root-mean-square method. The compressive stressof the enamel may then be reported as the numerical average ofthe
36、test values together with their statistical error (see Appen-dix X1 for an example of data treatment).9. Conversion of Test Results9.1 Conversion charts may be used to make approximateconversions of results of the loaded-beam test method in termsof other test methods (or vice versa if necessary). Fi
37、g. 1provides for conversion of loaded-beam test results to warpvalues. Fig. 2 may be used to convert loaded-beam results toring-stress values.NOTE 1Wipe all bisque cover coat enamel from sides, ends, and back of ground coated test sample before firing cover coat.NOTE 2See Fig. 3 for metric equivalen
38、ts.FIG. 6 Detail of Test SpecimenC839 82 (2010)510. Precision and Accuracy10.1 The precision and accuracy of this test method arebeing developed.APPENDIX(Nonmandatory Information)X1. EXAMPLE OF DATA TREATMENTX1.1 Table X1.1 provides sample values for six specimensto illustrate the application of for
39、mulas necessary for themeasurement of compressive stress.X1.2 The following compressive stress values for indi-vidual specimens are calculated by applying the formula:Sc= L 3 (1.80/W) 3 (0.036/Ti) (see Section 8):Specimen No. Compressive Stress (Sc)1 5252 5243 4964 5105 4886 481_Mean 504X1.3 Calcula
40、te the statistical error of the determination asfollows:e 5 1.05 s (X1.1)where:e = statistical error of the mean value for the samples at the95 % confidence level, ands = standard deviation of the six individual values from theaverage of all six.NOTE X1.1The factor 1.05 applies only when the number
41、of speci-mens is six and the confidence level is 95 %. For larger or smallernumbers of specimens, use the “a” values for that number shown in Table2, Part 2, of STP 15 D.3X1.4 Calculate the standard deviation, s, as follows:s 5(Sc2(Sc!2nn 2 1(X1.2)where:n = number of specimens,(Sc2= sum of the squar
42、es of the stress values of the sixindividual specimens, and(Sc)2= square of the sum of the six stress values.X1.5 The following calculations are involved in applyingEq X1.2:Specimen ScSc21 525 275 6252 524 274 5763 496 246 0164 510 260 1005 488 238 1446 481 231 361_ _(Sc= 3 024 1 525 822 = (Sc2Mean
43、Sc= 504s 51 525 822 29 144 57665(X1.3)51 525 822 2 1 524 096551 72655 =345.2s 5 18.6X1.6 Applying Eq X1.1, e = 1.05 3 18.6 = 19.5.X1.7 Compressive stress value for example Enamel A thusbecomes 504 6 19.5.3Special Technical Publication 15 D, available from American Society forTesting and Materials, 1
44、916 Race St., Philadelphia, PA 19103.TABLE X1.1 Sample ValuesEnamel Specimen No.Application (g),WResidualLoadFinal Load Corrected Load, L Metal Thickness, TiA 1 1.76 1 486 485 0.0342 1.71 12 482 4703 1.80 7 475 4684 1.82 30 517 4875 1.77 5 458 4536 1.75 5 447 442C839 82 (2010)6ASTM International tak
45、es no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. 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 re
46、sponsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed 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 addres
47、sed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible 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 th
48、e 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).C839 82 (2010)7
