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Metal Casting Technologies : June 2007
www.metals.rala.com.au 36 TECHNICAL FEATURE riser tube at the bottom. If the middle or bottom position of castings are solidified first then the filling channel will be blocked. When molten metal is pushed into the mold, solidification begins immediately half way through the filling process. The molten metal fluctuation in the mold is closely related to the pressure undulation. The filling channels from the bottom up should be kept unblocked until the molten metal moves to the top of the mold. In the mold filling and pressure holding stages the pressure undulation may take place which will introduce casting defects. In counter-gravity casting the whole forming process is divided into four stages, i.e. riser-tube filling, mold filling, pressure holding for the solid shell to form and increased pressure holding during the solidification of the whole casting. Filling rate is important to the quality of castings. Generally, filling rate is between 30--70mm/s. When average Fig. 7 Real pressure-tracing curves in casting production Fig. 8 Microstructure of the castings (a) by convenient gravity casting (b) under counter-gravity condition A B Belec Lab 3000s Spectrometer EXCELLENT PRECISION & ACCURACY! Beckwith Macbro Resin Coated Sands All grades of resin coated sand used for shell molding and shell cores for ferrous and non-ferrous applications PRODUCTS ■ Range of resin strengths from 1.0% to 5.0% ■ Silica, Zircon, Chromite coated sands or blended mixes ■ Coated Sands of different AFS typically from 50-90 AFS ■ Thermal Reclaimed Coated Sands SERVICES ■ Full technical and trouble shooting service. ■ On-site shell core and shell molding facility to evaluate the product applications. ■ Laboratory facility to ensure product quality. Contact : Rob Dalla Via (Resin Coated Sand Manager) 30 Devon Road Devon Meadows, Melbourne Telephone : +61 3 5995 4244 Mobile : 0417 332 723 Fax: +61 3 5995 5030 E-mail: email@example.com Website: www.beckwithmacbro.com.au