Evaluating Iron Filter Print Designs–30 Years Later

Minor filter print design changes can significantly affect molten metal



or over 30 years, the industry standard on the usage of filtration devices in the production of commercial

iron castings has evolved and grown, driven by continual increases in qual- ity requirements for all castings due to more severe end-use applications. Properly filtering iron castings involves utilizing the most optimally engi- neered filter print and gating system designs to ensure delivery of the clean- est and least turbulent metal to the mold cavity. Filter print and gating system designs also have evolved over the years in an attempt to produce the highest quality castings. Some filter print designs have

dramatically improved the cleanliness of molten metal and casting quality, but some concepts have not always proven to be optimal. In fact, some design changes have been put into practice, without being validated in molten metal due to the high cost of actual foundry trials. As a result, some less than optimal designs exist in the industry today, causing potential quality issues and unnecessary additional expense. Te initial work of this study focuses

on analysis and evaluation of several filter print design concepts using casting process simulation software employing sophisticated, first principle fluid flow analysis models. Te goal of this work is to investigate problems experienced in foundries and maximize the benefits of filtration to deliver the best possible quality molten metal to the casting cavity, thereby producing

36 | MODERN CASTING August 2017

• Maximize exposure of the filter inlet face to ensure maximum total flow.

• Maximize (four sided) support to ensure the inertial forces on the fil- ter from the iron flow do not surpass the strength of the filter.

Fig. 1. A centerline cross-section of standard vertical filter print flow velocity at 10% filled.

• Minimize the possibility of iron passing around (not through) the filter by designing the support ledge on the filter print outlet to match filter tolerance dimensions.

• Minimize turbulence by designing the filter print volumes so the flow smoothly transitions from inlet to outlet. Tese combined characteristics were used to define the basis for standard filter print design. Over the past 30 years, these designs

Fig. 2. Here is a vertical filter print with filter print inlet and outlet areas greatly reduced.

high quality castings. Te analysis uses industry standard filter print designs as the baseline for the fluid flow compari- sons and compares these results to filter print designs that have been altered for yield improvement. Industry standard filter prints are defined as those designed during the initial filter development for iron castings. Some of the key require- ments for optimal results were identi- fied during the development, including the following:

have been continually tested and have slightly evolved through applications and foundry evaluations. Te first simulations conducted in this study were used to evaluate these standard designs. Yield improvement is a high

priority for all foundries, and gating systems are analyzed as carefully as all other aspects of the casting process to reduce weight. Alterations are some- times made to standard filter prints to reduce weight without careful analysis of the effect on the fluid flow proper- ties on the gating system. Changes that adversely affect molten metal fluid flow can result in increased turbulence, non-uniform flow and a reduction in filtration efficiency. Several of these situations were also evaluated in this study.

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