Centrifugal casting machine must have the
provision for the given dimensions of the turbine
bearing.
(1) length of bearing= 700mm
(2) diameter of bearing=1200mm
(3) Weight of the bearing = 3tonne
(4) Required output speed during pouring of
molten metal = 10 rpm
(5) Required output speed after pouring =300 rpm
(6) Thickness of the job = 100mm
III. HOW THIS PROJECT BENEFICIAL TO
INDUSTRY?
Manufacturing point of view, the equipment
cost is economical and its design is similar as center
lathe machine. By this point, this project will
beneficial to industry.
IV. SCOPE OF THE WORK
The scope of work concerns to the development of
a centrifugal casting equipment to produce steam
turbine bearing with gradient of properties. Steam
turbine bearing which is a thrust bearing require
different properties in different areas of their body,
such as high thermal fatigue resistance in the top,
high wear resistance in the vane and low weight in
the body. Reliable processing techniques for that
purpose have not been established yet, and results
obtained so far reveal sharp and undesirable
interfaces. A possible solution might be a well
controlled sequential pouring technique of different
materials that lead to a smooth gradient of
composition/properties between different turbine
bearing's functional areas, using centrifugal casting.
For this special purpose, a design of a horizontal axis
centrifugal casting machine will be developed. A
sketch of the equipment is developed and established
the main components. Finally, the design and
selection of the system‘s components will be done
accordingly to the main goals of this work.
IV. MACHINE COMPONENTS
The general idea of designing this special
purpose machine came from the headstock and
tailstock assembly of the centre lathe machine. The
job is supported between the faceplate of the
machine during pouring and rotating of the mould.
The job is not long in length so roller support is not
required as required to conventional horizontal
centrifugal casting for long cylindrical job. The
machine is same as lathe with separate tailstock and
headstock assembly. The list of various component
that will be used in this special purpose machine as
follows:
(1) Headstock assembly
1) A 3-phase induction motor
(30 hp with input speed=1440 rpm)
2) Helical gearbox
3) Hollow Shaft
4) Taper Roller Bearing
5) Faceplate
(2) Tailstock assembly
1) Faceplate
2) Taper Roller Bearing
3) Hollow Shaft
4) Molding Flask and its attachment
(3) Rotating Mould
(4) Guideways
(5) Leadscrew
(4) Variable Freqency Drive
V. PROCESS CYCLE FOR MANUFACTRING
OF TURBINE BEARING
The casting process is usually performed on a
horizontal centrifugal casting machine (vertical
machines are also available) and includes the
following cycle as shown in figure 2
A. Mold preparation
The walls of a cylindrical mold are first coated
with a refractory ceramic coating, which involves a
few steps (rotation, drying, and baking).[4] Once
prepared and secured, the mold is rotated about its
axis at high speeds (300RPM).
B. Pouring
Molten metal is poured directly into the rotating
mold, without the use of runners or a gating system.
The centrifugal force drives the material towards the
mold walls as the mold fills.[3][ During this process ,
the rotating speed of mould should be low(10 RPM)
PAPER IDENTIFICATION NUMBER(318)
so that molten metal cannot come outside to the
mould.
C. Cooling
With all of the molten metal in the mold, the mold
remains spinning as the metal cools. Cooling begins
quickly at the mold walls and proceeds inwards. [4]
D. Casting removal
After the casting has cooled and solidified, the
rotation is stopped and the casting can be removed.
E. Finishing
While the centrifugal force drives the dense metal
to the mold walls, any less dense impurities or
bubbles flow to the inner surface of the casting. As a
result, secondary processes such as machining,
grinding, or sand-blasting, are required to clean and
smooth the inner diameter of the part.
VI. FUNCTION OF THE COMPONENTS
A. 3-PHASE INDUCTION MOTOR
An induction or a synchronous motor is a type
of AC motor where power is supplied to the rotor by
means of electromagnetic induction. These motors
are widely used in industrial drives,
particularly polyphase induction motors, because
they are rugged and have no brushes. Single-phase
versions are used in small appliances. Their speed is
determined by the frequency of the supply current, so
they are most widely used in constant-speed
applications, although variable speed versions,
using variable frequency drives are becoming more
common. The speed of induction motor is determined
by the following application:
ns=
where ns = synchronous speed of the motor in rpm
f = frequency of the main supply
P= number of magnetic poles per phase.
B. HELICALGEAR(DOUBLE-STAGE-REDUCTION)
Helical gears are similar to spur gears except
th