sibility as long as the heights are lower compared with a fil- ter installation in the main parting line. The examples above show only core prints with round shapes, but any other shape could be helpful in placing the filters.
In Fig. 10 and 11, an ingate system for a 25 ton main frame wind turbine casting is shown in which the filters are placed in the parting line between core print and mould. This core print is fairly large so installation is not a problem. The ar- rangement of the ingate tubes underneath the core print is designed to keep the system as symmetrical as possible. This system used eight Ø 200x35 mm filters. The recommenda- tion to place the filters in large castings in the parting line between core print and mould is not only valid for filters with an extraordinary strength, it also applies to any other filter types therefore this option could be a better solution.
Filters in Filter Chamber Cores
If there is no likely core print to install the filters, another op- tion could be a core, which could contain the filters. With such a core (Fig. 12 and 13), in principle we have a parting line where we could place whatever we need wherever we want. These cores can be easily connected with the ceramic ingate tubes during the moulding process, and one filter chamber core with an Ø 200x35 mm filter is suitable for a pouring weight of around 5–6 tons of ductile iron.
Fig. 14 shows a completed core. Before the foundry engi- neers install the filters in the core, the inner surface has to be coated and dried. After that, the filter chamber core can be connected with the ceramic ingate tubes or already be pre- pared with some tubes, as illustrated in Fig. 13. This system already has produced some very good results in planet carri-
ers with a pouring weight of around 5.5 tons where a single filter chamber core (with two filters) was installed.
Another advantage with this system is it is possible to get symmetrical ingate systems for pouring weights up to 20 ton ductile iron castings. Fifty ton castings have already been manufactured using such a system. Furthermore, it makes sense to check if such a system could be useful, even for filters made from a standard material. Maybe it could be an easy solution for a tricky casting.
Short or Long Pouring Times
Often foundry engineers ask for the optimal pouring time for large ductile iron castings, and in recent years some have preferred shorter pouring times and other favor longer pour- ing times. To give a general answer is difficult and often de- pends on the number of filters used. Nearly everybody who uses filters in large ductile iron castings is familiar with these two problems:
1. Freezing filters at the beginning of the pouring pro- cess.
2. Freezing/blocking filters at the end of the pouring process.
In nearly all cases of the first problem, the liquid iron is freezing in the filter due to a higher viscosity in combina- tion with a filter with too small holes (pressed filter) or pores (foam ceramic filter). A filter with bigger holes or pores helps in most of the cases (Fig. 15).
Figure 10. 25 ton wind turbine casting/polygonal core print.
Figure 12. Core with filter print for round filters.
Figure 11. 25 ton wind turbine casting/polygonal core print. 22
Figure 13. Core with filter print for square filters. International Journal of Metalcasting/Volume 8, Issue 2, 2014
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