Sensor Monitors Sand Compaction Mohamed Abdelrahman, Michael Baswell and S. Jagtap, Tennessee Technological University, Cookeville, Tennessee


T


he open loop of sand compaction in the lost foam casting method leaves it vulnerable to drift in compac- tion levels, which can be caused by sand temperature, humidity, sand amount and wear in the machinery used to vibrate the sand. Placing a sand compaction


sensor in the sand with the foam pattern results in closed loop control, which can eliminate the vulnerabilities of an open loop and reduce vibration time. The sensor measures changes in sand compaction, which


is affected by the mechanics of the vibration system, including motor and linkage wear, changes in the sand properties (fi ne content and loss on ignition percentage), and environmental changes (tem- perature and humidity). The differential sensor system


is comprised of multiple chambers where the sand is compacted, with each chamber having a different diffi culty in resisting and fi lling compaction (Fig. 2). The diffi culty of fi lling and compacting the sand can be controlled using chamber geometry and the direction of sand fi lling and compaction. Each of the chambers is equipped with a sensor to mea-


sure the degree of sand fi ll and compaction. Changes in the dielectric properties of the sensor when the sand is introduced into the chamber are refl ected in an increase in the capacitances (the ability to collect a charge of electricity) of the chambers. An electric voltage signal proportional to the capacitance of each sensor provides the sand fi ll in each compaction chamber. A microcontroller acquires the voltage signal and displays it for each chamber. It also implements an algorithm based on the differential measurements of the compaction in each chamber. In a repeatability test using intermediate density sand with three minutes of vibration, the in- strument produced results within one resolution value in nine out of 10 trials, proving it can moni- tor the repeatability of the fi lling process. Further tests confi rmed the sensor’s ability to measure the effectiveness of one compaction recipe against another, as well as compaction time.


For more information on the compaction sensor, download the full paper, “Online Differential Sand Compaction Sensor for


Fig. 2. Shown is a schematic of an online differential sand compaction sensor.


Optimizing the Lost Foam Process,” at www.moderncasting.com.


Stirring Process Could Lead to Higher Casting Strength Ginat Muginstein, Esther Kiperwasser, Ran Rosen and Dan Yadeni, Netanya Plasmatec, Netanya, Israel


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ost foam casting technology’s major limitation in producing automotive parts, particularly aluminum-silicon cylinder heads, is its relatively high porosity levels, which prohibit the casting of parts requiring high strength. Conventional lost foam casting has a


porosity size higher than 0.012 in. (0.3 mm), porosity ratio higher than 1% and dendrite arm spacing higher than 50µm. Diesel engine cylinder heads and gasoline turbo cylinder heads require high heat strength and at least 3% elongation. In order to achieve these properties, the porosity size and ratio should be less than 0.2 mm and 0.4%, and dendrite arm spacing must be less than 30 µm. One possible method for reducing porosity


uses a moving electric plasma arc on top of the molten metal, which creates a changing current fl ux that induces changing magnetic fi elds and creates intensive fl ows in the metal. The continuously running arc creates fl ow and turbulence that pushes the liquid metal between the solidifying grains and dendrites. This process, called plasma treatment


casting (PTC), was tested recently on a lost foam cluster with two cylinder heads. Optical


MODERN CASTING / December 2010


microscopy micrographs comparing conventional casting with the plasma-treated casting showed the treated samples exhibited fi ner microstructure. Both the dendrite arm spacing and silicon-aluminum eutectic phase microstructure were smaller and fi ner. The PTC stirring applies shear force on the growing dendrites, thus breaking the dendrite tips. The tips, in turn, become new nucleation sites for fi ner and smaller grains and dendrites. Compared to conventional casting, PTC


reduced porosity size by 70% to 0.1-0.03 mm and the porosity ratio by 80% to 0.2- 0.3% (Fig. 3). Further work is needed to examine the


infl uence of the reduction in porosity levels on a casting’s mechanical properties. MC


For more information, download the full paper, “Porosity Reduction in Lost Foam Casting of Cylinder Heads by an Advanced Metal Stirring Process,” at


www.moderncasting.com.


Fig. 3. Visual inspection after machining of the combustion chamber area of a conventional casting (top) and a plasma-treated casting (bottom) reveal the plasma-treated casting exhibited fi ner dendrite arm spacing.


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