Review of As-Cast Surface Finish Standards for Sand and Die Castings

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Meredith Spencer
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1 Latest Revision: 11/20/2006 Review of As-Cast Surface Finish Standards for Sand and Die Castings By Scott Lammers and Walt Stein Abstract A review of as-cast surface-finish standards, how to specify them, and how to use them to indicate the deficient casting process that caused them. While standards for die castings will not be treated in this article, die casters with surface-appearance issues may want to use surface-appearance standards for sand castings as a guideline. Definition of Terms SCRATA Steel Castings Research and Trade Association Referenced Standards Price AA CS-E18 Cast Surface Comparator N/A ASTM A Standard Practice for Steel Castings, Surface Acceptance Standards, Visual Examination $29 3 BS Specification for examination of the surface texture of precision steel castings $98 4 C-9 Gar Electrofinishing Cast Microfinish Comparator $63 1 MSS SP Quality Standard For Steel Castings for Valves, Flanges, Fittings and Other Piping Components - Visual Method for Evaluation of Surface Irregularities $154 2 MSS SP Quality Standard for Evaluation of Cast Surface Finishes - Visual and Tactile Method $160 2 ISO Visual examination of surface quality of steel castings $33 4 SFSA SCRATA Comparators for the Definition of Surface Quality, set of 31 visual standards N/A 5 Standards for Aluminum Sand and Permanent Mold Castings, 2000 $50 1 Available through 1) AFS* 2) MSS* 3) ASTM* 4) Techstreet 5) CDC, UK Cost about $900 around No longer available *Plus shipping and handling

2 2 of 5 Review of As-Cast Surface Finish Standards of Sand Castings 2 of 5 As-Cast Surface Finish Standards for Sand and Die Castings (date of origin in parentheses) C-9 Cast Microfinish Comparator (early 60s) Sand Castings Die Castings Ferrous Non-ferrous Ferrous MSS SP-112 AA CS-E18 BS (1993) (1966 or before) MSS SP-55 ASTM 802 ISO (1961) History Since casting was started by the people of the Black Sea area around 4000 B.C., the quality of as-cast surface finishes had to have followed shortly thereafter. SCRATA merged with BCIRA and became CTI in 1996? The dates under each standard in the above tree indicate original-revision and withdrawal dates. Definitions The International Committee of Foundry Technical Associations 1 has divided surface defects into the following categories: Metallic Projections Cavities Discontinuities Surface Defects Incomplete Casting Incorrect Dimensions Inclusions or Structural Anomalies

3 3 of 5 3 of 5 Characterization of Each Standard C-9 is a tactile standard, one whose coupons range for applications from die casting to ferrous greensand casting. Its coupons are correlated with the following descriptions: Description RMS Die Investment Shell Mold Centrifugal to Permanent Mold Permanent Mold Normal non-ferrous Sand Normal Ferrous Green Sand MSS SP-112 is a tactile standard for sand castings. MSS SP-55 is a standard for steel sand castings, with photos. It makes a verbal comparison with SCRATA: Type I II III IV V VI VI VIII IX X XI XII Description Hot Tears and Cracks Shrinkage Sand Inclusions Gas Porosity Veining Rattails Wrinkles, Laps, Folds and Coldshuts Cutting Marks Scabs Chaplets Weld Repair Areas Surface Roughness

4 4 of 5 Review of As-Cast Surface Finish Standards of Sand Castings 4 of 5 Use and Interpretation of As-cast Surface Finish Standards OEM Responsibility To merely cite a standard on the drawing or P.O. or, worse, on both is an incompetent move seen throughout the industry. A relationship must be established between the requirements of the P.O. and receiving-inspection criteria. The drawing or family of drawings must state the same specific criteria. These as-cast surface-finish criteria must be able to be cast by the foundry. If not, the relationship between the OEM and the foundry will continue on its assumptive and non-productive ways. These costly ways can adversely affect shop relationships. It is best to specify a range of tactile standards especially if the casting is to be coated afterward. Requiring too fine a finish will not allow the initial coating to strongly adhere. Surface defects should be specified tailored to the OEM product. If a parting-line crease from a core could initiate a corrosion site or crack in a pump casting, then a photo or tactile sample should be provided. If excessive pitting occurs in the casting, the surface-finish standard can determine at what point rework charges should be initiated if the casting is shipped with these defects. Foundry Responsibility The foundry salesman must respond to the surface-finish standards detailed in the RFQ from the OEM stating that to meet a standard is either unobtainable or is obtainable at a higher price. The typical cleaning-room procedure is to table-blast the casting, and chip and grind. As-cast acceptance standards should be provided on the workbench. It is not normal for castings to be reblasted for it increases added-value cost. It is not necessary to use only the standard designed for that metal or process. For example, while MSS SP-55 is for steel, it may be used as a guideline for cast iron. The OEM and foundry can agree to any standard for mutual benefit. It would be best, however, to specify MSS SP-112 for all ferrous castings. Conclusions Specifying as-cast surface-finish standards will not alleviate all problems. Doing such will, however, will remove the guessing game between the OEM and the foundry, and will keep finger-pointing to a minimum and responsibility for problems to the deserving party.

5 5 of 5 5 of 5 Bibliography 1) ASM Cast Irons, 1996, p287 2) Surface Engineering Measurement Standards for Inorganic Materials, Stanley Dapkunas, April Other Contributors Lynne Karabin of the Aluminum Association Guy of Gar Electroforming

MANUFACTURING PROCESSES

1 MANUFACTURING PROCESSES - AMEM 201 Lecture 10: Casting Technology DR. SOTIRIS L. OMIROU CASTING - Basics - A material in a liquid or semisolid form is poured or forced to flow into a die cavity and allowed