ASTM_C_660_-_81_2015.pdf

Designation:C66081(Reapproved 2015)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 revision,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 acasting 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-userequirements.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 toas wet-process and dry-process enamels(see Terminology C286).In wet-process enameling,a slurryof wet-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 applied 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 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 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.1.3 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 regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2A48/A48M Specification for Gray Iron CastingsA74 Specification for Cast Iron Soil Pipe and 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 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;to facilitate an even rate of heating1These practices are under the jurisdiction 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 May 1,2015.Published June 2015.Originallyapproved in 1970.Last previous edition approved in 2010 as C660 81(2010).DOI:10.1520/C0660-81R15.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 and 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 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 otherwise 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 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,becauseneither the wetnor dry-process coati