The pouring height of the casting was around 5 m and the height of the casting above the ingate level was around 3.5 m. Both systems achieved good results, but the second system in- volves more effort and cost because each filter requires its own tube connection to the system. In that system, a bigger cross section at the bottleneck and at the downsprue tubes is used, so two tubes with a diameter of 150 mm each are required to get a pouring time of around 80s. In the system with the high resis- tance filter and 150s pouring time, two downsprue tubes with a diameter of 100 mm are necessary to get the pouring time of 150s. Just this difference reduces the iron weight of the return of the downsprue tubes of approximately half a ton. In Figure 20, the difference of both ingate systems is clearly shown.
The system with 16 filters also could be designed in the same way as the system with the standard filters (Fig. 21).
But if the foundry engineer were to use the system with 40 filters with a longer pouring time (the number of filters
cannot be further reduced due to the lower total flow of the standard filters), the velocity in each of the 40 ingate tubes comes to less than approximately 25 cm/s. This simple fact is described in the so-called equation of continuity (Bernoul- li’s flow through equation).
Volume flow = A x c Eqn. 4
This equation says that for a constant volume flow, the larger the cross section (A) flowed through, the lower the velocity (c). In the example, it will have 40 times the 80 mm cross section of the ingate tubes, with a very large total cross sec- tion (approximately 2010 cm²) and because of that a very low velocity. On the other hand, the system with the high resistance filters (16 filters and 16 ingate tubes Ø 80 mm) has a total cross section at the ingates of approximately 804 cm².
Usually engineers would be happy to reduce the velocity “as much as we can” at the ingates to reduce the risk for turbu- lence. But then they also could get an extremely high risk of freezing filters if the average velocity comes below 25 or 30 cm/s in the ingate tubes or in the filter chambers, espe- cially at the end of the pouring process. This critical velocity also depends on the resistance to the flow of the filters in combination with the viscosity of the liquid iron. With an ingate tube diameter of 80 mm, which we need for filters with a diameter of 200 mm, we need to reduce the pouring time down to approximately 80s if a high number of filters are used in a 45 ton casting.
Figure 19. Ingate system, 45 tons of ductile iron, 40 filters. Summary
New high resistance filter materials give us a very effective opportunity to simplify the ingate systems for large ductile iron castings and reduce costs and the risk of filter break- ages. They do not relieve the foundry engineer from his ob- ligation to calculate and design the ingate systems by taking account of the important main parameters:
• Velocity. • Symmetry.
Both parameters are easier to check because of an effective reduction of the number of filters that have to be installed.
Figure 20. Comparison of Ingate systems for 45 tons of ductile iron.
REFERENCES
1. “New Theory on How Casting Filters Work,” Thorsten Reuther, Foundry Magazine “Casting,” (May 2009).
2. “The Influence of the Ceramic Filter on the Flow in Gate Systems,” Lubomir Bechny, Petr Hajnik, Josef Burian, Hartmut Hofmann, Foundry Magazine “Erfahrungs-austausch,” (November 2000).
3. “Molten Metal Filtration,” Justyna Baginska, Logan Yeager, Bhawadwaj Mathukumilli, Ahmad Alraddadi, Homoud Albalawi, Students Project, Penn State University, Final Report (December 2012).
Figure 21. Ingate systems, 45 tons of ductile iron, 16 filters. 24 International Journal of Metalcasting/Volume 8, Issue 2, 2014
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