Feeding of Hollow Cylindrical Castings

Topics: Length, Liquidus, Temperature Pages: 14 (4151 words) Published: April 8, 2013
Feeding of Hollow Cylindrical Castings
Chief Executive, Sandell Associates, Kolkata, India and Vienna, Virginia, U.S.A OP-37
internal centerline shrinkage, which was unacceptable. A
major factor is the blockage of feed metal flow which result in micro-porosity or voids in the solid casting. These voids add up to produce a centerline shrinkage.
Feeding covers methods adopted to produce castings without
shrinkage defects. In the case of solid solution alloys like steel, this is achieved by ensuring that the feeders solidify later than the castings. Simply stated, a feeder must contain enough liquid metal to compensate for the volume contraction occurring while the casting cools from the liquidus to the

solidus temperatures.
Computerised methods for deriving riser sizes based on
relative solidification times are readily available .One of the earliest attempt at mathematical riser sizing was derived from Chvorinov’s equation, which established a relationship
between the solidification time of a casting to its volume-tosurface area ratio .This ratio was called the modulus of
solidification. Wlodawer 2 developed extensive data based
on this modulus concept, for determination of riser sizes,
with a twenty percent safety factor. Empirically, Caine 3,
using his FreezingRatioand Bishop et al 4, using the
ShapeFactorratiodeveloped formulae and curves prescribing
riser diameters for various casting volumes, shapes and sizes. The Steel Founders’ Society of America (SFSA) has
The paper deals with the methodology and the manufacturing
process used to successfully develop a long cylindrical casting, called the Hollow Shaft. Both experience as well as a rough
estimate of the Niyama Criterion indicated strong possibilities of a centerline shrinkage The methodology was based on (1 )
The Shape Factor and Feeding Distance formulae specified in
the SFSA Feeding and Risering Guidelines for Steel Castings1, (2) Use of a padding and (3) Heuver’s circle method. A formula for assessing the length of the critical mushy zone derived
from the Niyama Criterion has been developed. The hollow
cylinder was cast without any internal or external defects.
Keywords :Feeding Distance, Hollow Shaft, microporosity,
mushy, Niyama,
During the year 2000 the author operated a modern no-bake
foundry located near Kolkata (India) producing sophisticated carbon and alloy steel castings, based on the use of phenolic urethene binder. A development order was executed for a low
alloy steel Hollow Shaft casting for a German manufacturer
of high–speed locomotives. These castings were subjected
to severe stresses in high speed service, and therefore had
to meet strict norms for internal soundness and metallurgical properties The Hollow Shaft (Fig. 1) was basically a thinwalled cylinder of internal diameter 224 mm, with a uniform
thickness, except at the base at one end (Fig. 2)The overall length was 1435 mm. Such cylinders were normally prone to
Fig. 1 : Hollow Shaft Casting Fig. 2 : Critical Dimensions of the Hollow Shaft Casting 68th WFC - World Foundry Congress
7th - 10th February, 2008, pp. 201-206
Proceedings of 68th World Foundry Congress 202 7th-10th February 2008, Chennai, India recommended the method based on Bishop’s Freezing Ratio
for determining riser diameters in their monogram titled "The Feeding and Risering Guidelines for Steel Castings 2001" 1.
Obtaining a sound casting will require that the riser not only contains adequate volume of liquid metal, but is also
positioned in such a way that the liquid is able to flow
throughout the volume of the casting, till solidification is complete. Determination of the feeding distance is therefore an important consideration in obtaining sound hollow
cylindrical castings.
The feeding distance is defined as the length from the edge
of the riser to that point on a casting which can be fed
without micro porosity or...
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