STELEX PrO filters have also been successfully employed in the production of very large sg iron castings. Previously, it has not been possible to filter these castings due to problems with chill, filter capacity and filter strength. Practical experience has shown the benefits of filter-clean castings and, more specifically, improvements in surface finish leading to significant savings in fettling and cleaning operations.

The effectiveness of STELEX PrO foundry filters is due to their foam structure. Some 90% of the volume consists of open, reticulated, interconnected pores. This produces many changes in direction and velocity, leading to intensive contact with the filter surface which allows small non-metallic particles to be retained within the foam structure.

Due to the open pore structure and large surface area, STELEX PrO filters are highly effective in the removal of slag, sand, refractories and deoxidation products suspended in the metal stream.

STELEX PrO foam filters enable smooth, non-turbulent mould filling, thereby reducing the risk of reoxidisation defects and moulding sand erosion problems.

Filtration effectiveness is largely dependent on the correct application and positioning of the filter. Foseco Service Engineers are able to provide technical application support for the calculation and design of gating systems. For correct filter positioning, Foseco’s standard filter print designs are recommended.

STELEX PrO filters are available in a variety of sizes in 10 ppi porosity (ppi = average number of pores per linear inch.).

The Al2O3+C based refractory system in STELEX PrO filters give a number of significant advantages over traditional zircon oxide ceramic products:

• consistent priming even at low pouring temperatures;
• increased filtration capacity;
• better flow-rate characteristics;
• flexible location in the pouring system;
• filter floats more easily in KALPUR direct pour units reducing risk of chill;
• no disadvantages when re-melting.

STELEX PrO filters are routinely tested to ensure compliance with specifications. Important product attributes which are regularly checked include filter dimensions and weight, ultrasound velocity, cold compression strength and porosity.

The benefits of foam filtration are seen throughout the foundry. Depending on the alloy and the application, many of the following benefits are achievable:

Scrap Control

• lower levels of scrap produced;
• improved ability to diagnose scrap problems due to a clearer separation of metal and mould factors;
• reduction in expensive machine scrap;
• running systems and downsprues fill smoothly and remain full, reducing the risk of gas bubbles entering the mould cavity.

Productivity Improvements

• higher tonnes shipped to tonnes melted ratio (yield) due to the elimination of long running systems;
• simplified gating systems since the filter itself will reduce velocity and smooth the flow of liquid metal
• simplified patter designs can allow a foundry to reduce mould sizes or increase castings per mould;
• higher yields mean more moulds per melted tonne;
• frequently possible to reduce pouring temperatures;
• lower levels of cash tied up in work-in-progress.

Casting Quality Improvements

• greater consistency in casting cleanliness;
• reduction in the variability of metal flow of hand-poured castings leading to increased casting consistency;
• improved mechanical properties due to greater metallurgical consistency;
• increased fluidity of the metal improves casting finish, appearance and surface details.

After Cast Operations

• reduced welding, repair and heat treatment costs;
• improved machinability and reduced tool wear;
• machining allowances can be reduced with confidence due to a lower level of inclusions;
• reduction in inspection and expensive time-consuming non-destructive testing operations;
• faster cycle times, especially where there are major savings in after-cast operations, increasing work schedule flexibility and foundry competitiveness.