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What does gage R & R mean to the foundry?

What Does Gage R & R Mean to the Foundry?

The panel: "Application of Gage R&R--What Does it Mean to the Foundry?" introduced Gage Repeatability and Reliability (Gage R&R) to the Molding Methods and Materials Division this year. V. LaFay, Hill & Griffith Co, said, "Foundries must judge the reliability of numbers used in any decision-making. Failure to recognize variations in generated numbers may result in inaccurate decisions, misdirected capital expenditures and costly retraining."

According to M. Mizzi-Krysiak, George Fischer Foundry Systems, Inc, Gage R&R studies examine the measurements of multiple operators to determine the variation of both testing equipment and the appraiser's performance. For these measurements to be accurate, she said, test samples must be unvarying. "Practical Aspects of Applying Gage R&R in the Foundry" were described in a case study by J. Parr, Dofasco, Inc.

Foundry Sand Control

The most commonly encountered sand system design problems were also discussed by Mizzi-Krysiak in "Sand Testing and Sand System Design." Though foundrymen have control over some variables in a sand system, such as water, bond, carbonaceous material and new sand additions, the variables that the foundryman has less control over can be major factors affecting the uniformity, composition and properties of the sand.

These factors include rate and amount of core sand influx, sand temperature, sand cooling systems, mixing, composition and processing of return sand and amount of fines removed. "Adequate control of these factors, she said, "requires control of the entire system, including sand mixing, molding, pouring, shakeout, cooling, sand handling equipment, dust collection equipment, screens, magnetic separators and general molding-floor practices."

She also described several recent trends in sand testing. "Strength tests such as green tensile and splitting tensile have been looked upon in the past as redundant or superfluous." Today, tensile testing of molding sand may provide a better approach for the control of high compaction molding sands than compressive strength testing. Many mold failures, such as failures due to pattern stripping, are failures in tensile rather than compressive strength, she explained.

R. Heine, Univ of Wisconsin-Madison and R. Green, AIMCOR, presented "Compactibility, Green Strength and Moisture as Related to Green Sand Processing Efficiency." Sand system processing efficiency is a parameter that measures the transient compactibility, green strength and moisture content properties of foundry sands and relates them to some stable endpoint. This condition is no longer influenced by either further processing or change in processing variables.

Establishing these stable, or equilibrium properties has been the subject of six years of research and several previous papers by these two authors. System efficiency parameters, which permit measuring the extent to which the properties of the processed sand approach the equilibrium properties of a fully processed sand, have been an outgrowth of this research. Property relationships of moisture, compactibility and green strength in relationship to sodium bentonite clay percentage were presented graphically for both new, dry clay and methylene blue clay.

The new edition of the AFS Mold & Core Handbook was introduced in a panel discussion. "The previous edition was twenty years old in 1985, the time its rewrite began. New quality demands by management, criticism of the book's organization and contents prompted the revision," said R. Peddicord, Unimin Corp.

The new edition will be available later this year and was completely revised, with much new material added, by AFS Division 4 committees. J. Young, Morie Co. Inc, described the first section, Unbonded and Reclaimed Sands. He said much new information on chemical analysis, minerology, sampling and analysis of incoming sand is included.

The other sections in the reorganized handbook are: Clay Bonded Sands, which now includes 49 separate sand tests; Chemically Bonded Sands, which includes much new nobake data; an entirely new Mold and Core Coatings section with newly developed coating tests; and a final section of detailed test procedures. These sections were introduced by D. Dalton, Thiem Corp; R. Burritt, Southern Foundry Resins; and R. Praski, Carpenter Brothers, Inc.

Defect Diagnosis

"Experiences in Defect Diagnosis--Penetration" were discussed by G. DiSylvestro, American Colloid Co. He noted that high density molding equipment has created severe penetration problems in the past and that vertical molding and gating practice have added to conditions promoting burn on, burn in and penetration. "Hard molds and solid cores contribute to low permeabilities in the sand and develop high dynamic pressures during pouring. These conditions create surface abnormalities and cause cleaning difficulties with sand removal," he explained.

R. Smith and W. Traeger, Ashland Chemical Co, covered "Veining: Literature Review and Laboratory Investigation." There are two requirements that must be met for veining to occur. The first is that the mold or core must develop a fissure crack from expansion-contraction forces or from handling. Second, the metal must be fluid enough to enter the crack or fissure.

Test castings were made with various sand grades and types, different resin binder levels, additions of cushioning agents such as clay/dextrine blends and other additives such as ferrous oxide, hematite and magnetite. Among the conclusions: finer grades of sand were found to be more prone to veining than somewhat coarser grades. Cushioning agents, hematite and magnetite also were effective in eliminating or reducing veining.

EPC Modeling

"The major concern for producing an iron or steel casting using the evaporative pattern casting process (EPC) is the casting carburization which is caused by the diffusion of carbon contained in the polystyrene mixture into the casting," said H. L. Tsai, Univ of Missouri-Rolla.

Tsai presented a three-part mathematical model encompassing the three coupling processes occurring in the EPC mold which influence casting carburization: heat/mass transfer in the sand mold; casting solidification; and diffusion of carbon in the casting.

Tsai concluded that casting carburization occurs within minutes after pouring a typical thin-section casting, due to the fact that the casting has not completely solidified when polystyrene diffusion takes place. He suggested that, "The only practical method to reduce a casting carbon defect appears to the application of a vacuum, so that the polystyrene mixture can be sucked out from the sand mold rapidly."

Environmental Concerns

Concerns over levels of formaldehyde and other chemicals in foundry air are behind R&D in various areas. J. Cavanaugh, Acme Resin Corp, discussed "Hotbox Odor Control: New Resins and Tighter Process Controls." Cavanaugh related the development of a new foundry resin which reduces formaldehyde emissions during mold curing.

He also discussed process factors which can control formaldehyde. For example, the amount of catalyst used might be increased. More of the resin would be reacted, reducing the amount of formaldehyde evolved.

Thermal sand reclamation may burn off organic binder from sand grains. However, complete combustion of the material is necessary to avoid violating pollution regulations, according to D. S. Leidel, Tanoak Enterprises, Inc. "But the complete breakdown of the complex hydrocarbons, which foundry resins mostly are, is not easily accomplished," Leidel noted.

In "Plasma Processing: A Realistic Alternative In Thermal Sand Reclamation?" Leidel concluded that the plasma arc processing of foundry sands may well provide a means of solving air pollution problems in the near future.

PHOTO : M. Mizzi-Krysiak, George Fischer Foundry Systems, Inc, discussed the importance of sand

PHOTO : system analysis tests made throughout foundry sand systems in identifying sources of

PHOTO : variation.

PHOTO : Previewing the new edition of the AFS Mold & Core Handbook were (l-r): W. Rossbacher, Acme

PHOTO : Resin Corp; D. Jablonski, Thiem Corp; R. Burritt, Southern Foundry Resins, R.Praski,

PHOTO : Carpenter Bros, Inc; J. Young, Morie Co, Inc; R. Peddicord, Unimin Corp; J. Serra,

PHOTO : Carpenter Bros, Inc.
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Publication:Modern Casting
Date:Jul 1, 1989
Previous Article:Combine training and SPC for quality improvement.
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