ASTM C660-81(2020)

Standard Practices for Production and Preparation of Gray Iron Castings for Porcelain Enameling

ABSTRACT
These practices are intended for production and preparation of gray iron castings for porcelain enamelling. Design of the casting should be such as to minimize variations in temperature during firing and cooling. The governing factors in pattern layout and shop control are elimination of discontinuities, chill, and inclusions at or near the surfaces to be coated. Visual inspection methods for enamelling surfaces should place emphasis on the detection and remedy of porosity, sand inclusions, and gas holes. Porosity consisting of essentially subsurface pinholes, shallow covered blows, body scars, or shrinkage near the surface may or may not be acceptable for correction, depending upon severity.
SCOPE
1.1 These practices are intended to indicate certain casting characteristics and pre-enameling practices which will facilitate finishing by the wet- or dry-process methods of porcelain enameling. All of the listed recommendations are based on experiences with gray iron casting and enameling.  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 77.140.80 - Iron and steel castings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.12 - Materials for Porcelain Enamel and Ceramic-Metal Systems

Relations

• Refers: ASTM A126-04(2023) - Standard Specification for Gray Iron Castings for Valves, Flanges, and Pipe Fittings
• Effective Date: 01-Nov-2023
• Refers: ASTM A278/A278M-01(2020) - Standard Specification for Gray Iron Castings for Pressure-Containing Parts for Temperatures Up to 650 °F (350 °C)
• Effective Date: 01-May-2020
• Refers: ASTM A126-04(2019) - Standard Specification for Gray Iron Castings for Valves, Flanges, and Pipe Fittings
• Effective Date: 01-Nov-2019
• Refers: ASTM A74-17 - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 01-Oct-2017
• Refers: ASTM A74-16 - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 01-Feb-2016
• Refers: ASTM A74-15 - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 15-Sep-2015
• Refers: ASTM A126-04(2014) - Standard Specification for Gray Iron Castings for Valves, Flanges, and Pipe Fittings
• Effective Date: 01-Apr-2014
• Refers: ASTM A74-13a - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 01-Jun-2013
• Refers: ASTM A74-13 - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 01-Apr-2013
• Refers: ASTM A48/A48M-03(2012) - Standard Specification for Gray Iron Castings
• Effective Date: 01-Oct-2012
• Refers: ASTM A278/A278M-01(2011) - Standard Specification for Gray Iron Castings for Pressure-Containing Parts for Temperatures Up to 650&#176F (350&#176C)
• Effective Date: 01-Mar-2011
• Refers: ASTM A126-04(2009) - Standard Specification for Gray Iron Castings for Valves, Flanges, and Pipe Fittings
• Effective Date: 01-Oct-2009
• Refers: ASTM C286-99(2009) - Standard Terminology Relating to Porcelain Enamel and Ceramic-Metal Systems
• Effective Date: 01-Sep-2009
• Refers: ASTM A74-09 - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 01-Jan-2009
• Refers: ASTM A74-08a - Standard Specification for Cast Iron Soil Pipe and Fittings
• Effective Date: 15-Dec-2008

Overview

ASTM C660-81(2020) - Standard Practices for Production and Preparation of Gray Iron Castings for Porcelain Enameling provides comprehensive guidelines for the manufacturing and pre-treatment of gray iron castings intended for porcelain enamel coatings. Porcelain-enameled gray iron combines a durable, glass-like inorganic surface with the strength of iron, making it ideal for many industrial and architectural applications. This standard addresses critical aspects ranging from casting design to surface preparation and cleaning, aiming to optimize coating performance and minimize defects during porcelain enameling processes.

Key Topics

• Casting Design Considerations

  • Minimize temperature variations during firing and cooling to prevent warping, spalling, and enamel defects.
  • Maintain uniform section thickness to ensure consistent enamel application and structural integrity.
  • Incorporate smooth transitions between different section thicknesses and avoid abrupt changes.

• Material Selection

  • Select gray iron types best suited for enameling, typically those with ferritic microstructures, as specified in relevant ASTM standards.
  • Control elemental content (carbon, silicon, phosphorus, manganese, sulfur) to support optimal enamel adhesion and avoid surface defects.

• Foundry Practices

  • Eliminate surface discontinuities, internal chills, or inclusions, particularly on surfaces to be enameled.
  • Use molding techniques and shop controls to minimize contaminants harmful to the coating process.

• Surface Preparation

  • Emphasize thorough visual inspection for porosity, sand inclusions, gas holes, and other defects.
  • Apply mechanical (sand or grit blasting) and/or chemical cleaning methods to achieve a roughened, contaminant-free surface.
  • Avoid peening the surface with shot and ensure cleaning media do not introduce contamination.

• Pre-Enameling Treatments

  • Use heat treatment processes (normalizing, subcritical annealing) to prepare casting surfaces and relieve stresses.
  • Store castings in a dry environment and avoid prolonged aging before enameling.

Applications

The ASTM C660-81(2020) standard is widely used by foundries, fabricators, and manufacturers producing gray iron components requiring porcelain enamel coatings. Key applications include:

• Architectural Elements

  • Bathtubs, sinks, panels, and fixtures requiring a durable, decorative, and corrosion-resistant surface.

• Cookware and Appliances

  • Cookware, oven parts, and appliances that benefit from the chemical resistance and cleanability of porcelain enamel.

• Industrial Equipment

  • Components in heating systems, chemical processing, or piping where enamel provides wear and corrosion resistance.

Following this standard ensures:

• Enhanced enamel adhesion and longevity
• Reduced occurrence of coating defects (e.g., blistering, spalling, porosity)
• Consistent product quality compatible with both wet-process and dry-process porcelain enameling methods

Related Standards

The practices outlined in ASTM C660-81(2020) are closely linked to other standards in the field of gray iron casting and ceramic-metal systems, including:

• ASTM A48/A48M – Specification for Gray Iron Castings
• ASTM A74 – Specification for Cast Iron Soil Pipe and Fittings
• ASTM A126 – Specification for Gray Iron Castings for Valves, Flanges, and Pipe Fittings
• ASTM A278/A278M – Specification for Gray Iron Castings for Pressure-Containing Parts
• ASTM C286 – Terminology Relating to Porcelain Enamel and Ceramic-Metal Systems

Adhering to these standards alongside ASTM C660-81(2020) supports best practices in material specification, production consistency, and surface finishing for porcelain-enameled gray iron products.

Keywords: ASTM C660, gray iron casting, porcelain enamel, surface preparation, casting design, enamel coating, wet-process enameling, dry-process enameling, foundry practices, industrial standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C660 − 81 (Reapproved 2020)
Standard Practices for
Production and Preparation of Gray Iron Castings for
Porcelain Enameling
This standard is issued under the fixed designation C660; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Porcelain-enameled gray iron is a composite of a vitreous or glassy inorganic coating, bonded to a
casting by fusion at temperatures above 800 °F (425 °C). Porcelain enamels are a family of coatings
available in a wide variety of compositions and properties, but all are characterized by their glass-like
nature. Selection of an appropriate porcelain enamel must be made on the basis of the end-use
requirements. Certain casting design features and processing considerations can facilitate the
application and efficient use of the selected enamel.
Two general types of enamels are available for use on cast iron. These are commonly referred to
as wet-process and dry-process enamels (see Terminology C286). In wet-process enameling, a slurry
of wet-ground materials is dipped or sprayed on the casting, the water removed by drying, and the
coatingmaturedbyheatinginafurnaceforsufficienttimetobringaboutfusionoftheglassyparticles.
In dry-process enameling, dry-powdered glassy material is applied by dusting onto a redhot casting
that has been ground-coated by the wet process prior to firing. The partially matured dusted coating
is returned to the furnace to complete the fusion process. In general, wet-process enamels are thinner
over-all than dry-process enamels.
1. Scope Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 These practices are intended to indicate certain casting
Barriers to Trade (TBT) Committee.
characteristics and pre-enameling practices which will facili-
tate finishing by the wet- or dry-process methods of porcelain
2. Referenced Documents
enameling. All of the listed recommendations are based on
2.1 ASTM Standards:
experiences with gray iron casting and enameling.
A48/A48MSpecification for Gray Iron Castings
1.2 The values stated in inch-pound units are to be regarded
A74Specification for Cast Iron Soil Pipe and Fittings
as standard. The values given in parentheses are mathematical
A126 Specification for Gray Iron Castings for Valves,
conversions to SI units that are provided for information only
Flanges, and Pipe Fittings
and are not considered standard.
A278/A278M Specification for Gray Iron Castings for
1.3 This standard does not purport to address all of the
Pressure-Containing Parts for Temperatures Up to 650°F
safety concerns, if any, associated with its use. It is the
(350°C)
responsibility of the user of this standard to establish appro-
C286 Terminology Relating to Porcelain Enamel and
priate safety, health, and environmental practices and deter-
Ceramic-Metal Systems
mine the applicability of regulatory limitations prior to use.
3. Recommended Casting Characteristics
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
3.1 Design of the casting should be such as to minimize
ization established in the Decision on Principles for the
variations in temperature during firing and cooling. Section
thickness should be uniform to eliminate possible warping and
fire cracking of castings; to facilitate an even rate of heating
ThesepracticesareunderthejurisdictionofASTMCommitteeB08onMetallic
andInorganicCoatingsandarethedirectresponsibilityofSubcommitteeB08.12on
Materials for Porcelain Enamel and Ceramic-Metal Systems. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2020. Published December 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approvedin1970.Lastpreviouseditionapprovedin2015asC660–81(2015).DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0660-81R20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C660 − 81 (2020)
and cooling and to prevent possible spalling, hairlining, and 4.2.3 Manganese content of the iron must be sufficient to
blistering of the porcelain enamel. balance the sulfur content. A slight excess of manganese is
preferred in order to assure sulfur tie-up; that is, Mn, per-
3.2 When a variation in section thickness is unavoidable,
cent=(1.7×S, percent)+0.3.
the transition of the two sections should be gradual and
4.2.4 High phosphorus content of 0.70 % may be desirable
smooth. Abrupt changes in sections give rise to significant
for improved strength at enameling temperatures. Phosphorus
differences in heating and cooling rates, resulting in nonuni-
in the iron has no reported association with boiling defects in
form coating conditions.
the coating.
3.3 Special styling techniques should be used for designing
4.3 When pouring thin-walled or complex shapes to be
appendages, internal passages, and lug-fastening faces so as
enameled, one must consider the effect of metal composition
not to emplace a mass of metal near an otherwise uniform
onmicrostructure.Whiteormottledstructureswillnotroughen
enameling surface.These design considerations should include
adequately during cleaning, and also may introduce other
a thorough review of the available mold-making techniques in
problemsinthecoatingprocess.Siliconcontentover2.4%and
conjunction with the pattern designer.
the use of heater strips may be effective, but a suitable anneal
3.4 Where functional or mating surfaces of an enameled
is the desirable corrective measure.
casting are a design consideration, allowances must be in-
4.4 Metal having a microstructure containing massive car-
cluded for the thickness of the coating and the method of
bides and high pearlite content will introduce enameling
application. The optimum thickness of wet-process enamels is
problems. Heat treatments employed to obtain desired me-
about 10 mils (0.25 mm) in dry process enamels it is about 40
chanical properties in the casting should minimize these
mils (1.0 mm).
problems.
3.5 Sharp edges on castings should be avoided, because
4.5 Where annealing is a regular part of the foundry
neither the wetnor dry-process coatings will adequately cover
operations,anoxidizingfurnaceatmosphereishighlydesirable
sharp edges. Inside and outside corners should be rounded to
in order to produce easily removed scale and obtain decarbur-
uniform thickness and generous radii provided for fillets and
ized enameling surfaces. Decarburized surfaces are advanta-
outside corners.
geous to enameling.
3.6 Material identifications for the castings should be se-
4.6 Heating and cooling cycles employed in the enameling
lected from appropriateASTM specifications which are found
process cause transformations that affect microstructure. Ap-
under the various headings for gray iron.
propriate metallurgical constituents used to stabilize or retard
3.6.1 An example of the more desirable types of iron for
these conditions should not be incorporated until a thorou
...