1、Designation: C 660 81 (Reapproved 2005)Standard Practices forProduction and Preparation of Gray Iron Castings forPorcelain Enameling1This standard is issued under the fixed designation C 660; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the 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.INTRODUCTIONPorcelain-enameled gray iron is a composite of a vitreous or glassy inorganic coating, bonded to
3、 acasting by fusion at temperatures above 800F (425C). 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-userequi
4、rements. 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 C 286).
5、 In 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 appl
6、ied 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
7、are 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 This standard does not pur
8、port 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 ASTM Standards:2A
9、48/A 48M Specification for Gray Iron CastingsA74 Specification for Cast Iron Soil Pipe and FittingsA 126 Specification for Gray Iron Castings for Valves,Flanges, and Pipe FittingsA 278/A 278M Specification for Gray Iron Castings forPressure-Containing Parts for Temperature up to 650F(350C)C 286 Term
10、inology Relating to Porcelain Enamel andCeramic-Metal Systems3. Recommended Casting Characteristics3.1 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
11、; to facilitate an even rate of heatingand cooling and to prevent possible spalling, hairlining, andblistering of the porcelain enamel.3.2 When a variation in section thickness is unavoidable,the transition of the two sections should be gradual andsmooth. Abrupt changes in sections give rise to sign
12、ificantdifferences 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 otherwise uniform1These practices are under the j
13、urisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and are 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 1970. Last previous edition
14、approved in 1999 as C 660 81 (1999).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.1Copyright ASTM Internati
15、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.enameling 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 ename
16、ledcasting are a design consideration, allowances must be in-cluded for the 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,
17、becauseneither the wetnor dry-process coatings will adequately coversharp 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 specifi
18、cations which are foundunder the various headings for gray iron.23.6.1 An example of the more desirable types of iron forenameling purposes are the normally ferritic Class 20 irons(see Specification A 48/A 48M for Gray Iron Castings). Theycast more readily into complex shapes, and are better suited
19、tothe coating process.3.6.2 Some applications, such as valve bodies, may requireother types of gray iron for which Class B, SpecificationA 126,would be selected. Other appropriate Specifications would beA74and A 278/A 278M, in which the lowest strength class ispreferable for coating purposes.3.7 Par
20、ting lines coincident with an enameling surfaceshould be accessible for grind 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
21、 unnecessary increases of car-bon equivalents in hypereutectic irons that give 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 t
22、hereof.4.2.1 For lighter section castings14 in. (6.35 mm) thick andunder, the 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
23、sulfurwill cause enamel defects.4.2.3 Manganese content of the iron must be sufficient 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 i
24、mproved strength at enameling temperatures. Phosphorusin the iron has no reported 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 roug
25、henadequately during cleaning, and also may introduce otherproblems in the coating 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 pearli
26、te content will introduce enamelingproblems. Heat treatments employed to obtain 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 re
27、moved scale and obtain decarbur-ized enameling surfaces. Decarburized surfaces 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 con
28、ditions should not be incorporated until a thoroughstudy is made of their effect 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 fro
29、m the sand once shakeout isstarted to prevent high internal stress that would 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
30、molds arereported to be particularly harmful.5. Recommended Pre-Enameling Practices5.1 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 covere
31、d blows, body scars,or shrinkage near the surface may or may not be acceptable 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 coatedwhe
32、re appearance requirements of the finish are involved.Mold shifts, core shifts, 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 meta
33、llic-cosmeticrepairs should be cleaned by appropriate methods prior toinspection.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.5.1.2.2 Metal-filler
34、repairs of blemishes after elimination bymechanical methods such 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-su
35、bsurface holes thatdo not contain inclusions can usually be made with a water-based, quartz-clay-soda ash putty.C 660 81 (2005)25.1.3 White fractures due to chilled iron at edges and sharpcorners, and structures containing massive carbides are notreadily decomposed during enameling. Such castings sh
36、ould beheat treated to a softened condition prior to mechanicalcleaning.5.1.3.1 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
37、 casting sufficientlyto burn out organic soil is the most desirable pretreatmentmethod 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
38、 a sharply roughenedsurface without peening or contaminating it.5.1.3.5 Two mechanical 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 mechanica
39、lcleaning methods, the longer the cleaning time, the lesstendency there is for 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 cleani
40、ng processes used to remove organicsoils should be followed by a roughening action 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 partial
41、ly relieve stresses. Two general types areconsidered for different heat treating 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 1650F (885 to 900C) temper
42、ature range and for 1 h/in. ofsection with a minimum of 20 min at temperature 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 1420F (735 to 770C) temperature rangeand for 1 h/in. of section
43、with a minimum of 20 min percasting.5.1.6 Enameling operations should begin 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 op
44、erations is beneficial.ASTM International takes 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 infringem
45、ent 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 andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or
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47、own 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 19428-2959,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).C 660 81 (2005)3
