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Start Gaining I


n the U.S., metalcasting is an approximately $30 billion industry. Assuming metal- casting facilities lose about 5% of their revenue to scrap


or rework, the industry is losing $1.5 billion a year. We are using tech- nologies that have been around for 50 to 100 years, so why are we still losing money? Te industry currently has a lack of


process knowledge. To be profitable, metalcasters need adequate knowledge of their various processes to make the specific parts needed by their customers.


Part Specific Range


Process Knowledge


Failed castings, whether occurring as internal or external scrap or rework, become a significant operating cost that could be reduced by controlling the variables critical to specific parts. DR. HATHIBELAGAL ROSHAN, MAYNARD STEEL CASTING CO., MILWAUKEE, WISCONSIN


It is not enough to collect data on


the subprocesses inside the facility, such as molding, coremaking or finish- ing, to control process parameters in a general way. Process knowledge is the list of process variables, their collection and visualization systems, and analysis used to determine the ranges of rel- evant variables related to the product characteristics for specific castings. The key to process knowledge is that it looks at how factors affect products on a specific level. Even in the same foundry, the process parameters used may produce an


Table 1. Factor and Response Table for Green Sand Molding Factor (X)


Method of Measurement


New sand GFN(X2-1)


New Sand, 140 screen (X2-2) Condition of screens (X2-3) Inadequate new sand (X2-4) Ramming density, X2-5


Sand compaction/squeeze pressure (X2-6)


Mold hardness (X2-7)


Backing sand extending to mold surface (X2-8)


Inadequate support after stripping (X2-9)


Unclean molds (X2-10) Rusty chills (X2-11)


Mold assembly-excessive jolting (X2-12)


Mold assembly-Incomplete closure of mold (X2-13)


Molds not clamped propertly (X2-14)


24 | MODERN CASTING May 2013 Units


Sieve analysis report Yes/No Sieve analysis report Yes/No Visual observation Yes/No Visual observation Yes/No Scale


Pressure gauge


g/cc psi


Continuous/ Discrete C/D


Discrete Discrete Discrete Discrete


Continuous Continuous


Hardness tester Number Continuous Visual observation Yes/No


Discrete Visual observation Yes/No


Visual observation Yes/No Visual observation Yes/No Visual observation Yes/No


Visual observation Yes/No Visual observation Yes/No


Note: The Part Specific Range column is left intentially blank here. Each metalcasting facility should determine this range for its own operations.


Discrete


Discrete Discrete Discrete


Discrete Discrete


acceptable casting for one part but not another. For example, in the melting of steel, an aluminum con- tent of 0.06% maximum may be sat- isfactory for one part, while another part requires 0.03% maximum alu- minum content to avoid conchoidal fracture of the test specimens. By understanding the factors in


various operational processes that lead to specific results (such as casting defect type), metalcasters can establish a range in which the process can fluc- tuate for each part while still produc- ing a saleable casting.


Response (Y)


Y2-6 (Casting defect:burn on/burn-in, penetration) Y2-6


Y2-13 (Broken molds) Y2-13


Y2-7 (Hot tear) Y2-6


Y2-2 (Inclusions); Y2-6 Y2-2; Y2-5 (Erosion)


Y2-13 Y2-2


Y2-11 (Blowholes, pinholes) Y2-2; Y2-13


Y2-14 (Flash) Y1-1 (Casting dimensions); Y2-14


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