ASTM C743-1987(2014)e1 Standard Test Method for Continuity of Porcelain Enamel Coatings《搪瓷涂层连续性的标准试验方法》.pdf

《ASTM C743-1987(2014)e1 Standard Test Method for Continuity of Porcelain Enamel Coatings《搪瓷涂层连续性的标准试验方法》.pdf》由会员分享，可在线阅读，更多相关《ASTM C743-1987(2014)e1 Standard Test Method for Continuity of Porcelain Enamel Coatings《搪瓷涂层连续性的标准试验方法》.pdf（4页珍藏版）》请在麦多课文档分享上搜索。

1、Designation: C743 87 (Reapproved 2014)1Standard Test Method forContinuity of Porcelain Enamel Coatings1This standard is issued under the fixed designation C743; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis

2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEIntroduction was added and minor units abbreviations corrected editorially in June 2014.INTRODUCTIONThis test provides a means to evalu

3、ate a porcelain enamel coating for pinholes, discontinuities, andinsufficient application to better assess the ability of the coating to protect the substrate.1. Scope1.1 Porcelain enamel coatings are applied to metals toprovide protection from corrosion as well as to enhance theirappearance. This t

4、est method permits the easy detection ofdiscontinuities and areas of light coverage, not readily seen byvisual inspection, which limit the protection to the substrate.Somewhat similar tests applicable to the thicker glass coatingsused for chemical reaction vessels are found in Test MethodsC536 and C

5、537.1.2 Values stated in SI units are to be regarded as thestandard. Inch-pound units are provided for information only.1.3 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-pr

6、iate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C536 Test Method for Continuity of Coatings in GlassedSteel Equipment by Electrical TestingC537 Test Method for Reliability of Glass Coatings onGlassed

7、Steel Reaction Equipment by High Voltage3. Terminology3.1 air-gap voltagevoltage needed to arc through a defectthat is open to both the surface of the porcelain enamel and themetal substrate. The length of the air gap is estimated bymeasuring the enamel thickness.3.2 overvoltagedifference between an

8、 applied test voltageand the air-gap voltage for the porcelain enamel being tested.3.3 RMS voltageroot mean square voltage, or “average”voltage, shown on ac test meters.3.4 peak voltagefor ac meters, the voltage that willdischarge across the air gap or across a defect. The peakvoltage is the RMS vol

9、tage multiplied by 1.414.4. Apparatus4.1 A nondestructive coating thickness gage with a range ofat least 0 to 0.5 mm in 0.03 mm increments (0 to 20 mils in 1.0mil increments).4.2 Either an ac or a dc high-voltage discharge test instru-ment with a continuously variable output voltage over therange of

10、 at least 0 to 4 kV as indicated on a built-in voltmeter.The instrument shall be capable of being set to 0.1 kV and shallhave an insulated cable and probe and a means for indicating(light, meter, or bell) a voltage discharge. Before use in thistest, the high-voltage discharge test instrument shall b

11、e cali-brated in accordance with the procedure set forth in Annex A1.4.3 A test probe constructed of 100 mesh wire gauze asillustrated in Fig. 1.5. Test Specimens5.1 Porcelain enameled specimens of any size may be usedin this test. The enamel shall be removed from an edge or theback of the specimen

12、to provide an electrical ground for the testinstrument. If the probe is wider than the specimen, the edgesof the specimen shall be masked with electrical insulating tapeto prevent discharges from occurring at the edges whereporcelain coverage may be light.6. Conditioning6.1 Before testing, wash the

13、specimens with a 1 weight %,solution of trisodium phosphate on a soft cellulose sponge,1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatingsand is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.

14、Current edition approved May 1, 2014. Published June 2014. Originallyapproved in 1973. Last previous edition approved in 2009 as C743 87 (2009).DOI: 10.1520/C0743-87R14E1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Ann

15、ual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1rinse with tap water, and then rinse with distilled water. Thendry the speci

16、mens thoroughly in air.7. Procedure7.1 Measuring the Enamel ThicknessMeasure the enamelthickness at a minimum of three locations on the specimen.Make these measurements to the nearest 0.03 mm (1.0 mil) inaccordance with the operating instructions for the thicknessgage. Use the maximum value obtained

17、 as the enamel thick-ness.7.2 Selecting the Test VoltageThe test voltage to be useddepends upon the purpose for conducting the test.The test canbe used to determine (1) the presence of defects open to boththe enamel surface and the base metal, (2) the location of areasof light coverage in addition t

18、o defects open to both the enamelsurface and the base metal, or (3) compliance with a specifi-cation. According to the users purpose for conducting the test,the following three instructions correspond respectively to (1),(2), or (3) above:7.2.1 Test Method AFor Open Defects:7.2.1.1 Determine the air

19、-gap voltage that corresponds tothe enamel thickness from the calibration curve described inthe annex. This value is the test voltage.7.2.1.2 Probe the specimen in accordance with 7.3.7.2.2 Test Method BFor Light Coverage and Open De-fects:7.2.2.1 Determine the air-gap voltage that corresponds tothe

20、 enamel thickness from the calibration curve described inthe annex.7.2.2.2 Arbitrarily select the overvoltage to be used. (In-creasingly smaller defects are located with this test as theovervoltage is increased. Therefore, confidence that warepassing this test will have a long, corrosion-free servic

21、e life isincreased as the overvoltage is increased.)7.2.2.3 Add the selected overvoltage to the air-gap voltage.This value is the test voltage.7.2.2.4 Probe the specimen in accordance with 7.3.7.2.3 Test Method CFor Compliance with a SpecificationSpecifications for continuity of coating will be in t

22、erms of dcovervoltage or peak ac overvoltage (these are identical).Determination of the test voltage depends on whether a dc oran ac test instrument is used.7.2.3.1 DC Test InstrumentsDetermine the test voltage inaccordance with 7.2.2, substituting the specified overvoltagefor the selected overvolta

23、ge as in 7.2.2.2 and 7.2.2.3.7.2.3.2 AC Test InstrumentsDivide the specified overvolt-age by 1.414, then determine the test voltage as in 7.2.2,substituting the specified overvoltage divided by 1.414 for theselected overvoltage as in 7.2.2.2 and 7.2.2.3.7.2.3.3 Probe the specimen as shown in 7.3.7.3

24、 Probing the Specimens:7.3.1 Connect the ground wire of test instrument to the basemetal of the specimen.7.3.2 Turn on the test instrument.7.3.3 Set the output voltage (as indicated on the built-involtmeter) to the value selected in 7.2.7.3.4 Let the voltage stabilize for 15 s.7.3.5 Hold the probe w

25、ith a light pressure at approximately30 to the surface of the specimen.7.3.6 Probe the specimen at a rate of 3 to 4 in./s (75 to 100mm/s).FIG. 1 Test ProbeC743 87 (2014)127.4 Locating Discontinuities:7.4.1 When the probe passes over a discontinuity, a sparkwill arc across the discontinuity to the gr

26、ound provided by thebase metal. This spark can be seen and heard. In addition, mostinstruments are equipped with an auxiliary light that flasheswhen a discontinuity is located. Some instruments also have anaudible signal or digital counter to aid in the detection ofdiscontinuities.7.4.2 When a disco

27、ntinuity is located, a failure in thecoating is present.8. Report8.1 The report shall include the following:8.1.1 Title of test, ASTM designation, and issue.8.1.2 Enamel thickness,8.1.3 Air-gap voltage,8.1.4 Method of selecting test voltage (Test MethodA, B, orC),8.1.5 Overvoltage used,8.1.6 Name an

28、d model of test equipment,8.1.7 Whether or not discontinuities were present,8.1.8 Type of specimen tested,8.1.9 Number of specimens tested, and8.1.10 Type of enamel tested.9. Precision and Bias9.1 No statement is made about either the precision or biasof this test method since the result merely stat

29、es whether thereis conformance to the criteria for success specified in theprocedure.10. Keywords10.1 continuity; glass coating; high voltage test; light cov-erage; porcelain enamel; porcelain enamel thicknessANNEX(Mandatory Information)A1. CALIBRATING THE TEST INSTRUMENTSA1.1 Even though each test

30、instrument is equipped with abuilt-in voltmeter, the discharge voltage across a given air gapwill vary from instrument to instrument. Therefore, eachinstrument must be calibrated by determining its air-gapvoltage curve.A1.2 Specimens RequiredThree specimens of each of 15enamels are required to deter

31、mine the air-gap voltage for thetest instrument. These 15 enamels shall spread over the rangeof thicknesses from 0.1 to 0.5 mm (4 through 18 mils) asuniformly as possible. These specimens shall be prepared asoutlined in 4.1 and 5.1.A1.3 Procedure:A1.3.1 Puncturing the Enamel Coating :A1.3.1.1 Connec

32、t the ground wire of the test instrument tothe base metal of the specimen.A1.3.1.2 Turn on the test instrument.A1.3.1.3 Raise the output voltage of the test instrument toits maximum and allow it to stabilize for 15 s.A1.3.1.4 Hold the probe with a light pressure at approxi-mately 30 to the surface o

33、f the specimen.A1.3.1.5 Probe the specimen at a rate of 75 to 100 cm/s (3to 4 in./s).A1.3.1.6 Discard all specimens that are not punctured bythis treatment.A1.3.2 Reprobing the Specimens:A1.3.2.1 Reprobe the specimens that were punctured by thehigh-voltage probe in a manner similar to that outlined

34、inA1.3.1.1 through A1.3.1.4, except that the test voltage shall be100 V initially and shall be increased in increments of 100 Vuntil a discharge occurs. A 15 s stabilization period shall beobserved for each increase in voltage before reprobing the testspecimens. This procedure may be expedited by st

35、arting thereprobing of duplicate specimens at 300 V lower than thebreakdown voltage noted for the first reprobed specimen, thenincreasing the voltage by increments of 100 V. The dischargevoltage determined in this manner is defined as the air-gapvoltage.A1.4 Measuring the Enamel ThicknessMeasure the

36、enamel thickness at three locations on the surface of thespecimen. Make these measurements close to the area wherethe discharge occurred. Make these measurements to thenearest 0.025 mm (1.0 mil) in accordance with the operatinginstructions for the thickness gage. Average the three measure-ments to g

37、ive the average enamel thickness which is assumedequivalent to the length of the air gap.A1.5 Calculations Calculate the average enamel thick-ness and air-gap voltage for each specimen. Plot these averagesand fit the least squares line (of the form y=a+bx) throughthese averages as follows:a 5 (x2(y

38、2(x(xy!/N(x22 (x!2# (A1.1)b 5 N(xy 2(x(y!/N(x22 (x!2#where:a = intercept,b = slope,C743 87 (2014)13N = number of specimens,x = average thickness of an enamel, mils, and average airgap voltage of an enamel, kV.The resulting curve is the calibration curve.NOTE A1.1The equations given here are for hand

39、 computation or deskcalculator use only. If the least squares line is fitted by digital computer,any accurate library program may be used.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this st

40、andard 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 reviewed every five years a

41、ndif 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 theresponsible technical committee,

42、 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 Conshohocken, PA 19428-29

43、59,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/).C743 87 (2014)14