1、Designation: C660 81 (Reapproved 2010)Standard Practices forProduction and Preparation of Gray Iron Castings forPorcelain Enameling1This standard is issued under the fixed designation C660; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the 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.INTRODUCTIONPorcelain-enameled gray iron is a composite of a vitreous or glassy inorganic coating, bonded to ac
3、asting by fusion at temperatures above 800 F (425 C). Porcelain enamels are a family of coatingsavailable in a wide variety of compositions and properties, but all are characterized by their glass-likenature. Selection of an appropriate porcelain enamel must be made on the basis of the end-userequir
4、ements. Certain casting design features and processing considerations can facilitate theapplication and efficient use of the selected enamel.Two general types of enamels are available for use on cast iron. These are commonly referred to aswet-process and dry-process enamels (see Terminology C286). I
5、n wet-process enameling, a slurry ofwet-ground materials is dipped or sprayed on the casting, the water removed by drying, and thecoating matured by heating in a furnace for sufficient time to bring about fusion of the glassy particles.In dry-process enameling, dry-powdered glassy material is applie
6、d by dusting onto a redhot castingthat has been ground-coated by the wet process prior to firing. The partially matured dusted coatingis returned to the furnace to complete the fusion process. In general, wet-process enamels are thinnerover-all than dry-process enamels.1. Scope1.1 These practices ar
7、e intended to indicate certain castingcharacteristics and pre-enameling practices which will facili-tate finishing by the wet- or dry-process methods of porcelainenameling. All of the listed recommendations are based onexperiences with gray iron casting and enameling.1.2 The values stated in inch-po
8、und 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.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is there
9、sponsibility 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:2A48/A48M Specification for Gray Iron CastingsA74 Specification for Cast Iron Soil Pipe an
10、d FittingsA126 Specification for Gray Iron Castings for Valves,Flanges, and Pipe FittingsA278/A278M Specification for Gray Iron Castings forPressure-Containing Parts for Temperatures Up to 650F(350C)C286 Terminology Relating to Porcelain Enamel andCeramic-Metal Systems3. Recommended Casting Characte
11、ristics3.1 Design of the casting should be such as to minimizevariations in temperature during firing and cooling. Sectionthickness should be uniform to eliminate possible warping andfire cracking of castings; to facilitate an even rate of heatingand cooling and to prevent possible spalling, hairlin
12、ing, andblistering of the porcelain enamel.3.2 When a variation in section thickness is unavoidable,the transition of the two sections should be gradual and1These practices are under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and are the direct responsibility of Subcommi
13、ttee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved April 1, 2010. Published June 2010. Originallyapproved in 1970. Last previous edition approved in 2005 as C660 81 (2005).DOI: 10.1520/C0660-81R10.2For referenced ASTM standards, visit the ASTM website, ww
14、w.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.smoo
15、th. Abrupt changes in sections give rise to significantdifferences in heating and cooling rates, resulting in nonuni-form coating conditions.3.3 Special styling techniques should be used for designingappendages, internal passages, and lug-fastening faces so asnot to emplace a mass of metal near an o
16、therwise uniformenameling surface. These design considerations should includea thorough review of the available mold-making techniques inconjunction with the pattern designer.3.4 Where functional or mating surfaces of an enameledcasting are a design consideration, allowances must be in-cluded for th
17、e thickness of the coating and the method ofapplication. The optimum thickness of wet-process enamels isabout 10 mils (0.25 mm) in dry process enamels it is about 40mils (1.0 mm).3.5 Sharp edges on castings should be avoided, becauseneither the wetnor dry-process coatings will adequately coversharp
18、edges. Inside and outside corners should be rounded touniform thickness and generous radii provided for fillets andoutside corners.3.6 Material identifications for the castings should be se-lected from appropriate ASTM specifications which are foundunder the various headings for gray iron.23.6.1 An
19、example of the more desirable types of iron forenameling purposes are the normally ferritic Class 20 irons(see Specification A48/A48M for Gray Iron Castings). Theycast more readily into complex shapes, and are better suited tothe coating process.3.6.2 Some applications, such as valve bodies, may req
20、uireother types of gray iron for which Class B, Specification A126,would be selected. Other appropriate Specifications would beA74 and A278/A278M, in which the lowest strength class ispreferable for coating purposes.3.7 Parting lines coincident with an enameling surfaceshould be accessible for grind
21、 finishing.4. Recommended Foundry Practices4.1 The governing factors in pattern layout and shop controlare elimination of discontinuities, chill, and inclusions at ornear the surfaces to be coated.4.2 Metal compositions and unnecessary increases of car-bon equivalents in hypereutectic irons that giv
22、e rise to coarsegraphite or kish in heavy sections should be avoided. Heavycombined carbon will result in the formation of kish during theenameling fire and may cause poor adherence, spalling, orblistering, or combination thereof.4.2.1 For lighter section castings14 in. (6.35 mm) thick andunder, the
23、 desirable range for carbon equivalent is 4.3 to 4.5 %.Carbon equivalent is generally calculated as: C.E. = percenttotal carbon +13 (percent silicon + percent phosphorus).4.2.2 Sulfur in excess of 0.14 % and out-of-balance sulfurwill cause enamel defects.4.2.3 Manganese content of the iron must be s
24、ufficient tobalance the sulfur content. A slight excess of manganese ispreferred in order to assure sulfur tie-up; that is, Mn,percent = (1.7 3 S, percent) + 0.3.4.2.4 High phosphorus content of 0.70 % may be desirablefor improved strength at enameling temperatures. Phosphorusin the iron has no repo
25、rted association with boiling defects inthe coating.4.3 When pouring thin-walled or complex shapes to beenameled, one must consider the effect of metal compositionon microstructure. White or mottled structures will not roughenadequately during cleaning, and also may introduce otherproblems in the co
26、ating process. Silicon content over 2.4 % andthe use of heater strips may be effective, but a suitable annealis the desirable corrective measure.4.4 Metal having a microstructure containing massive car-bides and high pearlite content will introduce enamelingproblems. Heat treatments employed to obta
27、in desired me-chanical properties in the casting should minimize theseproblems.4.5 Where annealing is a regular part of the foundryoperations, an oxidizing furnace atmosphere is highly desirablein order to produce easily removed scale and obtain decarbur-ized enameling surfaces. Decarburized surface
28、s are advanta-geous to enameling.4.6 Heating and cooling cycles employed in the enamelingprocess cause transformations that affect microstructure. Ap-propriate metallurgical constituents used to stabilize or retardthese conditions should not be incorporated until a thoroughstudy is made of their eff
29、ect on the coating results. Examples ofpearlite stabilizers are tin or manganese.4.7 Shakeout techniques must be geared to both castingwarpage and potential effect on enameling results. Castingsshould be fully separated from the sand once shakeout isstarted to prevent high internal stress that would
30、 later causecasting warpage or cracking or enameling defects.4.8 Contaminants, harmful to the coating process, should beavoided in the molding sands and cores for castings to beenameled. Carbonaceous coatings for cores and molds arereported to be particularly harmful.5. Recommended Pre-Enameling Pra
31、ctices5.1 Visual inspection methods for enameling surfacesshould place emphasis on the detection and remedy of porosity,sand inclusions, and gas holes. Porosity consisting of essen-tially subsurface pinholes, shallow covered blows, body scars,or shrinkage near the surface may or may not be acceptabl
32、e forcorrection, depending upon severity.5.1.1 Non-continuous metal consisting mainly of misrun (inwhich metal fails to fill out the mold cavity) or cold shut(imperfect fusion of metal against metal) should not be coatedwhere appearance requirements of the finish are involved.Mold shifts, core shift
33、s, or improperly aligned patterns result-ing in an improperly positioned casting surface are not detri-mental to the coating processes unless they give rise to unequalheating rates.5.1.2 Machined or ground surfaces and metallic-cosmeticrepairs should be cleaned by appropriate methods prior toinspect
34、ion.5.1.2.1 Cosmetic repair of various-surface blemishes, usingmetallic or ceramic fillers, should be made subject to agree-ment by coater and founder, and influenced by economic andfeasibility aspects.C660 81 (2010)25.1.2.2 Metal-filler repairs of blemishes after elimination bymechanical methods su
35、ch as grinding should be based on theextent and condition of the repair area. Under certain circum-stances repair methods such as welding, brazing, or mechanicalpeening may not be wholly desirable.5.1.2.3 Ceramic-filler repair on small-subsurface holes thatdo not contain inclusions can usually be ma
36、de with a water-based, quartz-clay-soda ash putty.5.1.3 White fractures due to chilled iron at edges and sharpcorners, and structures containing massive carbides are notreadily decomposed during enameling. Such castings should beheat treated to a softened condition prior to mechanicalcleaning.5.1.3.
37、1 Oils and greases, whether used for temporary sur-face preparation or resulting from machining operations,should be removed by methods that will produce an enamel-compatible surface.5.1.3.2 Thermal cleaning or heating the casting sufficientlyto burn out organic soil is the most desirable pretreatme
38、ntmethod prior to mechanical cleaning.5.1.3.3 Oxide films, scale, and similar surface matter shouldbe removed by mechanical cleaning.5.1.3.4 Cleaning prior to the enameling process shouldremove foreign material and produce a sharply roughenedsurface without peening or contaminating it.5.1.3.5 Two me
39、chanical cleaning methods usually em-ployed are sand blasting and airless grit blasting. Shot is notrecommended, as it tends to peen rather than cut the surface. Athird category of tumbling is rarely used. In all mechanicalcleaning methods, the longer the cleaning time, the lesstendency there is for
40、 boil-type defects. Grit or sand used toclean castings should be free of extraneous matter such asnonferrous metal, cutting oils, paint, dust, or other soils thattend to contaminate enameling surfaces.5.1.4 Chemical cleaning processes used to remove organicsoils should be followed by a roughening ac
41、tion such asblasting. Pickling is not resorted to since it gives rise to defectsin enameling.5.1.5 Heat treating employed prior to enameling if per-formed in an oxidizing atmosphere will minimize boilingdefects and partially relieve stresses. Two general types areconsidered for different heat treati
42、ng results:5.1.5.1 Normalizing the casting for partial graphitization ofmassive combined carbon and decomposition of pearlite is onetype of heat treating. Normalizing should be done in the 1625to 1650 F (885 to 900 C) temperature range and for 1 h/in. ofsection with a minimum of 20 min at temperatur
43、e per casting.5.1.5.2 The other type of heat treating is subcritical annealto partially graphitize pearlite. Subcritical annealing should bedone in the 1360 to 1420 F (735 to 770 C) temperature rangeand for 1 h/in. of section with a minimum of 20 min percasting.5.1.6 Enameling operations should begi
44、n on castings assoon as possible, within a week after foundry finishing.5.1.7 Castings should be stored in a dry place. They shouldnot be “aged.” If aged castings are to be enameled, anannealing treatment prior to enameling operations is beneficial.ASTM International takes no position respecting the
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46、 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 addressed to ASTM International Hea
47、dquarters. 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 the address shown below.This st
48、andard 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/).C660 81 (2010)3
