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Metal Casting Technologies : June 2010
Supercharge Your Green Sand System Green sand systems wor harder and last longer with TRUBOND®. These sodium bentonite grades mull in quic ly and undergo a controlled hydration to develop a stronger, more elastic adhesive. TRUBOND delivers excellent green compressive and hot strength properties and maintains its wor ing bond in repetitive exposure to high heat loads and metal temperatures. SODIUM BENTONITE For more information and availability: ContactUs@metalcaster.com ® TRUBOND is a registered trademar . All rights reserved. ©2009 The baseline engine was the Jaguar 2.5L V6. Testing was done at the Roush NV Facility in Livonia, Michigan. NVH measurements included: overall engine sound power; component sound power; and cold start noise. Five microphones were positioned around the engine at a distance of one metre from the engine. The exhaust and intake, as well as the bell housing, transmission, and drive shaft were acoustically wrapped and the engine was installed on rubber mounts. Overall sound power With the magnesium block there was a significant increase in sound power, especially at high speed and load. The increase was 5-6 dBA in the 1250-1600 Hz range at 2500 rpm and 3-5 dBA in the 250-2500 Hz range at 4000 rpm. In the opinion of the NVH engineers, the major reason for the NVH increase was the engine design rather than the material change. The MPCC engine was a deep skirt design with unsupported crankcase walls. This weakened the bottom of the engine. As discussed in earlier progress reports, the change from a two-piece block (in aluminium) to a deep skirt was necessitated to address thermal expansion differences between magnesium and cast iron crank bore inserts. Component sound power The effect of replacing the aluminium oil pan and front engine cover with magnesium, either singly or jointly, was also measured. The results indicate that there was no significant noise increase when magnesium replaced aluminium. This is an important result; particularly with regard to the front engine cover which rather than being designed for greater stiffness, was actually designed for lower stiffness. As a fully compliant material, it did not contribute to noise radiation. Designing for greater compliance also enabled greater mass reduction through the use of thinner walls; 52 per cent mass reduction from aluminium to magnesium. Cold start noise Cold start testing was recommended to determine the effect of CTE mismatch between the magnesium block (26 x 105 per degree C) and the aluminium piston (22 x 105 per degree C). Both the magnesium block and the aluminium block used aluminium pistons. At equal temperatures, the bore/piston clearance would be greater for the magnesium block than for the aluminium block. The magnesium engine was subjectively louder at cold start and the sound quality was different. Rattles and sound pressure impulses were detected. Piston slap was also heard occasionally with the magnesium engine. In summary, the NVH performance of the magnesium engine was strikingly better than expected. With advanced design it is likely that the NVH difference could be made negligible.