Benefits of filtering the molten metal
1) Filtering improves quality of castings.
2) No expensive rework or total rejection.
3) Inclusion free castings
4) A small gating systems
5) Improved castings yields.
6) Filtering is cost effective as cost of scrap and rework is cut.
7) Reduction in the number of defects per castings.
8) Reduction in number of welds to repairs the castings.
9) Extending the usable life of crucibles by increasing the numbers of molds poured per crucibles.
Types of filters
a) Ceramic foam
b) Reticulated ceramics
c) Cellular filter
Properties of filters:
1) Must effectively remove the inclusion particles, but not offer excessive resistance to metal flow.
2) Must withstand thermal and mechanical stresses that occur during mold pouring.
3) Do not corrode due to metal- slag-filter interaction nor erode due to forces acting on the filter during metal flow.
Commercially produced filters are:
1) Straight pores with constant cross section(honeycomb type) , as obtain by extrusion
2) Interconnected pores, with numerous changes in direction and cross-section, as obtained with foams.
3) Funnel shapes with narrow slots in the funnel body.
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