CPT International 04/2015

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K COREMAKING / BINDERS Figure 3: Precision control of reclaimed & new silica sands to prevent mold erosion and dimensional inaccuracy Figure 4: Melt treated with specially designed Foseco fluxes to ensure high cleanliness metal quality, mold design and its preparation these defects can be reduced significantly and eliminated. Melt cleanliness The quality of the metal being poured into the mold is critical to the final casting integrity, therefore the quality control of incoming raw materials is essential as is the subsequent processing of these materials. The melting of copper-based alloys presents special problems in that hydrogen and oxygen are readily dissolved in the melt and can subsequently combine to form water vapour which creates porosity in the casting. Without the presence of oxygen, hydrogen alone may also cause pin-hole defects. The levels of residual hydrogen is reduced to below 1ppm through the use of degassing units (FDU) with high efficiency rotor designs. The FDU is an automated, environmentally-friendly melt treatment system for aluminium and copper-based alloys and uses patented rotors (XSR) to create an innovative pumping action that is key to its performance and delivers high levels of degassing and cleaning within a short timeframe, improving productivity and reducing heat loss and energy consumption. Different sized units make it applicable for all bath, furnace and ladle sizes. The pumping action brings the melt into the rotor to ensure excellent contact with the inert gas. The huge number of very small inert gas bubbles created will float to the surface, taking the hydrogen with it resulting in a significant reduction in overall hydrogen content as well as removing oxides, which are also carried to the surface. Optimized metal cleanliness is obtained using additions of specially designed fluxes for bronze alloys (Albral, Elektro, Deox Tubes and Slax (Figure 4). Mold filling and metal flow control The running system design is critical to ensuring a non-turbulent flow of Figure 5: Stelex PrO and Sedex filters reduce inclusions and eliminate metal turbulence metal into the mold cavity to avoid oxidation reactions and erosion. To ensure the incoming metal is both inclusion free and to eliminate turbulence; ceramic foam filters (Sedex or Stelex PrO) are installed in the running system. The correct application and filter support methods are advised by Foseco to eliminate any potential risk of breakage and ensure maximum benefits are achieved (Figure 5). The foundry has also replaced sand sprues, runners and ingates that can easily be the source of sand inclusions through erosion with specially manufactured systems (Kalmin 70 A) that are highly resistant to erosion and offer the benefit over traditional ceramic materials of being highly insulating and hence avoiding the temperature loss observed with other products (Figure 6). Similar materials are used for the feeding sleeves (Kalmin 700), with the high insulation value allowing the feed metal to stay liquid longer, reducing the size of feeders required with the associated reduction in the requirements for liquid metal and post-casting operations to remove and re-work the feeding area. The performance of these sleeves is complemented by the use of highly exothermic (Termorit PW) or insulating topping compounds. Metal/Mold Interactions Refractory mold coatings are used to improve surface finish through applying a very fine refractory material to the mold surface, additionally this inert layer prevents adverse interaction between the molten metal and the mold’s sand and binder components. The coating also provides a barrier to prevent gases evolved from the thermal decomposition of the mold entering the liquid metal and potentially creating pin holes on solidification. The coating applied at Fundilusa (Teno Coating ZBBP) contains a zircon refractory for ultimate protection and has a very low gas evolution to ensure it does not contribute to gas defects. Conclusion It is only through consideration of the whole process that effective solu- 20 Casting Plant & Technology 4/<strong>2015</strong>
tions can be provided that combine together to provide optimized and cost effective casting production. In the case described the focus is on the elimination of surface defects that require an increased machining tolerance, resulting in increased costs both in terms of casting yield and machine tooling and process time. However the problems cannot be addressed in isolation as singularly they do not solve the problem, for example good coating practice does not eliminate inclusions from slag related defects. Addressing the true need of the customer requires an approach that focuses on the whole foundry process rather than on the performance of individual products. www.foseco.com Figure 6: Insulated sprues, runners and ingates create a highly erosion resistant running system CAN-ENG FURNACES INTERNATIONAL LIMITED GLOBAL EXPERT THERMAL PROCESSING SOLUTIONS FOR HIGH PRESSURE DIE CASTINGS (HPDC) AND ALUMINUM STRUCTURAL COMPONENTS CAN-ENG TECHNOLOGY Maintains Dimensional Stability • Improves Mechanical Properties CAN-ENG FURNACES INTERNATIONAL LIMITED is the industry leader in the development of automated heat treating systems for the processing of HPDC and light-weight aluminum structural components. For an innovative response to your design challenges, email Tim Donofrio at: tdonofrio@can-eng.com to learn about CAN-ENG’s latest advances in energy saving technology, material handling and automations. VISIT US AT EUROGUSS 2016, 12-14 JANUARY 2016 TO LEARN MORE. STAND 7-761 PO Box 235, Niagara Falls, NY 14302-0235 | www.can-eng.com | T. +1 905.356.1327 | F : +1 905.356.1817 Casting Plant & Technology 4/<strong>2015</strong> 21
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Page 45 and 46: Figure 1: voestalpine Nortrak casts
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