Filtration is widespread in foundries to capture impurities in the molten metal, consisting of slag formed during casting or spheroidisation treatment or inclusions of sand and/or undissolved inoculant. The purpose of the filters is also to avoid turbulence during casting.
Proservice can supply two main types of filters: ceramic foam filter and extruded filters for steel and cast iron, for all kinds of plants, automatic or no bake.
Ceramic foam filters are distinguished mainly by the type of coating and porosity.
Coatings can be Silicon Carbide (SiC) for use in grey or spheroidal cast iron. Zirconia (ZrO2), Graphite and Alumina(Al2O3) for filtering steel and large cast iron.
Porosity is measured in PPI, which indicates the number of pores per inch, which will be 10 in the case of 10 PPI filters, 20 in the case of 20 PPI filters, and so on. The fewer pores, the larger they are, and vice versa; the choice of porosity depends on the surface tension of the metal to be filtered.
Main benefits of using filters
- Reduction of rejects from inclusions
- Improved surface finish of castings
- Increased plate yield
- Increased machinability
- Reduction of over metals
- Reduction in machined rejects
ITACA Filter FOR CAST IRON
The trend in cast iron foundries is to use ceramic foam filters in almost all spheroidal cast iron production and some grey cast iron parts.
One can insert the filter vertically, horizontally, orobliquely, facilitating plate setting. The choice of porosity depends on the surface tension of the metal to be filtered, hence by the type of cast
iron. Spheroidal cast iron has a higher surface tension than grey cast iron and contains more oxides and sulfides due to the spheroidization treatment, which is why filters with 10 PPI are generally used for this type of cast iron. But this is not a fixed rule, some foundries with cleaner metals also use 20 PPI in spheroidal cast iron.
Particular attention must be paid to filter
blockage, which can occur with the massive
presence of oxides and sulfides, particularly with high Sulfur content in the base cast iron: Sulfur combines with Magnesium producing inclusions that clog the filter.
Filter capacity varies from cast iron to cast iron: data on the left are purely indicative, to discuss with Proservice technicians.
ITACA Filter ZR and ITACA Filter AG for Steel
There are two types of ceramic filters for steel, Zirconia-coated filters, and Alumina Graphite coated filters.
Generally, Alumina Graphite filters have better characteristics in terms of ease of ignition (the molten metal passes immediately and easily through the filter lattice), but their use for low carbon stainless steels limits the reuse of the casting stick as scrap since the filter contains carbon; whereas their use for carbon and low
alloy steels is optimal.
Zirconium filters are used in steel foundries and no-bake foundries for grey and ductile cast iron.
The purpose of using these filters is to block
inclusions in the steel or cast iron, reducing the additional costs of casting repairs.
The filters ensure the smooth entry of steel into the molds by avoiding turbulence that creates reoxidation in the metal.
Itaca Filter E
Extruded filters are used almost exclusively in the production of grey cast iron to regulate the flow and avoid defects due to earth
entrainment caused by excessive turbulence.
Extruded filters also have a minimal filter
capacity, which is why they are used in grey
cast iron production.
They can be used in any automatic or manual moulding plant. Adjusting the flow from turbulent to laminar and blocking inclusions reduces rejects and improves the surface appearance of castings.
These filters are also characterized by different porosities indicated by the CSI parameter,
Proservice technicians will be able to give you the right indications.