Fig. 2. In the centrifugal casting process, the force created by the spinning mold creates an even layer of liquid metal.
vertical, though some can spin at other angles. Horizontal machines are used primarily for true centrifu- gal castings, while vertical machines are used for all three methods. As shown in Figure 2, the centrifugal
casting process involves three basic steps: 1. Liquid metal is poured into a rotating hollow cylinder (i.e.,
the die or mold).
2. Centrifugal forces compress the liquid to the cylinder’s outer wall.
3. Metal solidification begins along the wall and moves inward to produce a symmetri- cal component.
Centrifugal casting produces enhanced grain structures that result
in consistent mechanical and physi- cal properties. During the casting process, the denser alloy is forced to the outside of the mold while less dense material, such as impurities, slag and dross, remain nearer to the inside diameter. The solidification front of the casting from the outer edge inward forms a casting with a dense grain structure. In effect, the casting is produced through layer- by-layer solidification toward a hol- low center, as shown in Fig. 3. Properly executed vertical centrifu-
gal castings also are free from shrink- age. Te metal freezes as it contacts the mold, driving solidification to the inner diameter. As a result, the inner and outer surfaces aren’t competing with each other during solidification, eliminating the possibility of internal shrinkage voids. Centrifugal castings do not
require extensive gating and riser systems. This reduces cleaning and finishing costs compared to traditional castings. Waste also is minimized, because the process limits scrap castings resulting from shrinkage and gas. In addition, sand cores can be used
in place of metal dies, which allows for more than one material to be processed and increases design possibilities. All metals that can be cast via
traditional metalcasting can be cast centrifugally. Centrifugal casting also allows the metalcaster to en- hance a casting’s properties through additions to the melt. During cast- ing, the centrifugal force pushes denser additions, such as tungsten carbide, to the outer diameter where it will increase the wear resistance of the part’s outer surface while maintaining ductility in the interior of the casting.
In spite of these advantages, the
vertical centrifugal casting process includes relatively strict design criteria. The most demanding constraint is that the component must be symmetrical in regard to its weight around the central axis. If it isn’t, it cannot be cast centrifugally. Te casting’s length can be no
more than three times its diameter. If 26 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2013
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60