Centrifuge Casting.pdf

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Centrifuge Casting

Centrifuge casting is the third main branch of centrifugal casting processes used forindustrial manufacture of cast parts. For more detailed information on the other twomanufacturing processes that fit into the category of centrifugal casting see, truecentrifugal casting and semicentrifugal casting. Developing an understanding of thesetechniques will greatly assist in learning about centrifuge casting, since the mainprinciples that govern centrifuge casting are the same for all centrifugal castingprocesses. Centrifuge casting is different in that castings manufactured by thecentrifuge casting process need not have rotational symmetry. With centrifuge casting,metal castings of desired shapes can be manufactured with all the distinct benefits ofcastings produced by a centrifugal casting process.

The ProcessIn centrifuge casting manufacture, molds employed to produce the desired castings arearranged around a central sprue. These molds contain all the necessary geometry for thecast part, as well as the gating system. Runners travel from the central sprue to the moldentrances.

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Centrifuge Casting http://thelibraryofmanufacturing.com/centrifuge_casting.html

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During the pouring phase of centrifuge casting manufacture, molten material is introducedinto the central sprue. The entire system is rotated about an axis with the central sprue atthe center of rotation. When an object is rotated, forces are produced that act directlyaway from the center of the axis of rotation. It would be known from the previousdiscussions concerning the other two branches of centrifugal casting, that the utilization ofthe forces of centripetal acceleration which act to push material away from the center ofrotation is the trademark characteristic of all the manufacturing processes of centrifugalcasting. Centripetal force is not only utilized to distribute molten material through a mold,but to help control the material properties of a cast part.

In centrifuge casting manufacture, the molten material to produce the casting is poured intothe central sprue. Centripetal forces from the rotating apparatus push this material outwardfrom the center, through the runners and into the molds.

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When the correct amount of molten metal to manufacture the casting is poured anddistributed completely into the molds, the apparatus will continue to rotate as solidificationis occurring.

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After the castings have completely solidified, the apparatus will stop rotating and the partscan be removed.


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Centrifuge Casting ManufactureThere are many specific advantages in the quality of parts manufactured by centrifugecasting. Since the metal is forced into the mold, the mold cavity usually fills completely andcast parts with thin walled sections are possible. Also, great surfaces can be produced bycentrifugal casting, which is another characteristic of castings manufactured by a processthat uses large amounts of force to fill a mold.

One of the most notable features, specific to the centrifugal casting processes anddiscussed in the preceding sections, is the effect of centripetal forces acting continuouslyon the material as the casting solidifies. Molten material that solidified under greater forcewill be denser than the same material that solidified under less force. This can be observedin a round cylinder manufactured using the true centrifugal casting process.

Figure:108

During the solidification of this part the mold was rotating. The forces acting on thematerial farther from the center were greater than the forces that were acting on thematerial closer to the center. Consequently, it can be seen in the manufactured part that thedensity is greatest in the outer regions and decreases towards the center.

Another specific effect that the centripetal forces used in centrifugal casting methods haveon the material of a cast part is that impurities, such as inclusions and trapped air, tend tocollect and solidify in the less dense material closer to the center of the axis of rotation.

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This happens because the material itself is denser than these impurities, when subject tocentripetal forces the denser metal pushes to the outer regions, forcing the lighterimpurities to the less dense inner regions. These effects of centripetal forces on a castingcan be observed not only in cast cylindrical tubes but also in all the wide variety of partsthat can be manufactured using the centrifuge casting process as well.

Figure:110

It can be seen that the density of the material varies throughout the cast part. The leastdense section of the part will be the section that was closest to the center of rotation. Thedensity of the material of the casting will increase with increasing radial distance from thecenter. Also, impurities that were present in the metal will have collected in the areas of thecasting closest to the center of rotation.

Figure:111


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In a carefully planned centrifuge casting operation, the cast part can be designed to bemanufactured in such a way that the less dense region containing the inclusions is removedafter the production of the casting. This will create a finished part of pure, dense material.

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