Since Selee introduced the first silicon carbide based ceramic foam filter in the late 1980s, the product line has grown substantially and the company has delivered hundreds of millions of these filters into a variety of casting applications.
This filter has gone through some improvements over the years, and Selee’s latest silicon carbide offering has been the “Selee IB” formulation introduced in 2002, which is considered by many foundries to have the highest hot strength of any silicon carbide based filter on the market.
Now Selee are introducing an aluminosilicate-based foundry filter. One of the biggest reasons for this change stems from the fact that the production of silicon carbide powder is a costly, environmentally unfriendly process with a significant portion of the world’s supply coming from China. In mid-2008, Chinese governmental export policies and local supply/demand dynamics resulted in dramatic price increases and declining availability. Since that time, conditions have eased somewhat, but remain volatile and unpredictable. These events mobilised Selee to embark on a new product development program in order to protect its customers from price increases and filter shortages.
A significant amount of time and resources were devoted to the program, and in January 2010 Selee developed “Selee IC™”, an aluminosilicate-based filter that was completely free of silicon carbide, yet capable of meeting the thermal shock and refractoriness challenges of iron and aluminium foundry filtration applications.
Aluminosilicate does not have a thermal conductivity equivalent to silicon carbide, but its thermal expansion is equivalent, and its refractoriness is quite good. These attributes, combined with a newly engineered ceramic formulation, enabled the creation of a product that is equal in performance with a far more stable supply chain. All aluminosilicate powder for this product is sourced in the United States, which eliminates the impact of ocean freight costs, exchange rate fluctuations and political risks to the company’s USA-based plant.
Through extensive characterisation and testing of this filter, there is evidence suggesting that liquid slags tend to wet and adhere better to the surface of Selee IC relative to silicon carbide.
Figure 1 displays micrographs of spent IB and IC filters run under similar conditions in molten iron. In the micrograph on the left, the slag poorly wets the silicon carbide structure and does not penetrate into the ceramic, whereas in the micrograph on the right, the slag wets the surface of the Selee IC filter quite well and actually penetrates slightly into the intergranular porosity. Figure 2 additionally demonstrates the effectiveness of the Selee IC filter in capturing liquid slag. In this particular case, the slag wets the ceramic so well that it even spans across ceramic struts.
Figure 1 displays micrographs of spent IB and IC filters run under similar conditions in molten iron. In the micrograph on the left, the slag poorly wets the silicon carbide structure and does not penetrate into the ceramic, whereas in the micrograph on the right, the slag wets the surface of the Selee IC filter quite well and actually penetrates slightly into the intergranular porosity
Figure 2 additionally demonstrates the effectiveness of the Selee IC filter in capturing liquid slag. In this particular case, the slag wets the ceramic so well that it even spans across ceramic struts
Selee and Ceramic and Alloy Specialists (CAS), the South African distributors of Selee’s products, have been partners in the iron and aluminium filtration market in South Africa for nearly two decades.
For further details contact Ceramic and Alloy Specialists on TEL: 011 894 3039 or visit www.ceramicalloy.co.za or www.selee.com.