A Collection of Reprints "Horizontal
versus Vertical Axis"
- The horizontal
machine is best applied to castings of greater length
than the diameter.
- Generally speaking,
when producing castings spun about a vertical axis, the
length of the cylinder should not greatly exceed the
centrifugal casting machines are generally used when the
diameter of the casting is large as compared with the
- Castings produced
in a horizontal centrifugal casting machine are usually
long as compared with the diameter.
- A bushing (casting)
whose length is less than twice its inside diameter would
generally be poured in a vertical centrifugal casting
machine and spun at 75G.
- True centrifugal
castings produced in a vertical axis machine generally
are held to a length not exceeding two times the inside
A Collection of Reprints "Directional
- In true centrifugal
casting, without a central core, the metal solidifies
from the outside toward the center (axis) of rotation in
most cases considering the length to diameter ratio.
- In semi-centrifugal
casting, cooling takes place from the periphery toward
the center and from the center toward the periphery due
to the center core.
- The true centrifugal
casting is spun about its own axis, has no central core,
and the cooling takes place from the periphery toward the
- The semi-centrifugal
casting is spun about its own axis, but does have a
centrally located core, and solidification proceeds from
the central axis toward the periphery as well as from the
periphery toward the central axis.
- The last part of the
metal in the mold cavity to solidify should naturally be
the gate. Thus is the use of the principle of directional
solidification which requires that the metal in the mold
cavity first solidify farthest from the gate
progressively toward the gate or source of fluid metal.
This fluid metal feeds the parts of the
casting progressively as the metal cools and solidifies,
producing a solid, dense casting.
- In true centrifugal
casting, the important consideration is that the cooling
takes place in only one direction, from the outside
toward the center of rotation.
- In semi-centrifugal
castings, with or without a gate, the direction of
cooling is not unidirectional, as the mold surface is in
contact with practically all surfaces of the castings. It
is necessary to insure that directional solidification
takes place from the maximum outside diameter of the
casting toward the center. In order to accomplish this it
is sometimes necessary to resort to the use of pads,
auxiliary gates or chills. Gear blanks, flywheels, and
brake drums are examples.
- A pure metal solidifies
at constant temperature and therefore is more difficult
to cast. The contraction of the cast metal after
solidification and during the period of cooling to room
temperature is important. The extent of this contraction
determines the shrink rule to be used in making the
pattern equipment and mold. The coefficient of expansion
(the shrink rule) is a measure of its tendency toward
cracking during the casting operation. The greater the
shrink rule is the more susceptible the cast metal is to
- A true centrifugal
casting is one essentially cylindrical in shape which is
produced without a center core and in which the direction
of solidification is from the outside of the casting
towards the axis of rotation.
- As soon as the entire
mold surface is covered with metal, it is desirable to
slow down the pouring rate to assist the casting in the
process of directional solidification. Metal molds due to
their higher rate of heat extraction over sand molds
require a rough practical pouring rate from 8 to 15 lbs.
per second. A satisfactory procedure is to pour the first
half of the metal at a high rate and then reduce the
pouring rate to about half that amount for the remainder
of the metal poured.
- Pits or shrink holes on
the inside of a casting are generally indicative of an
upset in the directional solidification. Metal molds,
especially when used with water cooling, can sometimes be
designed to promote directional solidification in
otherwise difficult to cast castings. The introduction of
an insulating material or pipe eliminator
into the bore of the casting immediately after pouring is
often of considerable benefit in promoting directional
solidification and reducing internal shrinkage porosity.
In extreme cases it is sometimes necessary to introduce
an exothermic type of pipe eliminator.
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Centrifugal Casting Machines
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Tulsa, Oklahoma USA 74170-2751