NATURAL STONES COATED WITH A PROTECTIVE LAYER, PROCESS FOR THEIR PRODUCTION
AND PLASMOCHEMICAL REACTOR
TECHNICAL FIELD
[0001] The present invention relates generally to couplings between equipment and, more
specifically, to a coupling or interface between a rotor and a balancing test machine.
BACKGROUND
[0002] Turbo machines (also sometimes called "turbo rotating machines") are a class of
machines which include compressors, turbine engines, and the like, and which include rotors
that, in operation, rotate at very high speeds, e.g., thousands or tens of thousands of
revolutions per minute (RPMs). The rotor typically includes a shaft that is supported axially
and radially for rotation in bearings. Given the size and weight of such rotors, even a small
unbalance in a rotor can greatly reduce the number of operational hours for a turbo machine.
For example, for a rotor having a weight of 500 pounds and an unbalance (e.g., center of
gravity offset) of a mere 0.001 inch, the force resulting from the unbalance would be about
2000 pounds when the rotor is rotated at 12,000 RPM, which force is observed as vibrations
that can rapidly ruin the bearings.
[0003] One way to address this problem is to balance test the rotors either as they are
being assembled in stages or after they are completely assembled, and then to make
adjustments to compensate for any detected unbalance. Such balance tests may be
performed by connecting the rotors or rotor stages to a balancing test equipment which
rotates the rotor under vacuum at high speed and has sensors, which detect imbalances, e.g.,
center of gravity offsets, during rotation.
[0004] A generalized high speed balancing test configuration is shown in Figure 1.
Inside a vacuum chamber 2, the pedestals 4 support a rotor 8 and a motor 6 of the balance
testing machine is connected to the rotor 8 to be tested via a coupling or interface 9. In
addition to a shaft, the rotor 8 may also have one or more elements coupled to the shaft, e.g.,
one or more impellers as described below. The coupling 9 transfers torque from the motor 6
to the rotor 8 and is provided as an element in the test system since there are typically many
different sizes and configurations of rotors 8 to be balance tested by the balance testing
machine and, therefore, the coupling 9 operates as an adapter between the various rotors 8 to
be tested and the balance testing machine. An exemplary coupling 9 is shown in Figure 2.
Therein, it can be seen that the coupling 9 has a generally conical shape which tapers toward
the end which fits onto the rotor 8, and has a relatively large diameter relative to the rotor 8.
In practice, the coupling 9 is heat shrunk onto the rotor 8 prior to balance testing, and then
removed for assembly into its respective turbo machine.
[0005] The use of such a coupling 9 as part of the balance testing process brings with it a
number of drawbacks. First, the coupling 9 is relatively heavy, e.g., on the order of 20-30 kg,
so that any eccentricity which it possesses makes the resulting unbalance that it adds to the
testing system large enough to adversely affect balance testing, thereby potentially resulting
in an unbalanced rotor 8. In fact, in some cases, the magnitude of the unbalance added by the
coupling 9 may reach 200% of the acceptable unbalance tolerance for the rotor 8. Second,
the method of attaching the coupling 9 to the rotor, i.e., heat shrinking, is time consuming,
complex and may damage the rotor surface itself.
[0006] Accordingly, it would be desirable to design and provide a coupling for a rotor to
a balance testing machine which overcomes the aforementioned drawbacks of existing
couplings.
SUMMARY
[0007] Systems, devices and methods according to these exemplary embodiments
provide couplings or interfaces usable, for example, in the balance testing of rotors. By
providing a friction fitting between the coupling and the rotor to be tested, heat shrinking of
the coupling onto the rotor can be avoided, thereby making the process faster and safer.
Additionally, the design can be lighter and introduce less unbalance into the test setup.
However, it will be appreciated by those skilled in the art that such advantages are not to be
construed as limitations of the present invention except to the extent that they are explicitly
recited in one or more of the appended claims.
[0008] According to an exemplary embodiment, a coupling includes a main body portion
having an extended thin portion therein, which is configured to fit a shaft of the balancing
machine and an extended insert portion, which is configured to fit an opening in the rotor. A
plurality of connection elements is disposed in holes in the main body portion of the coupling
and a ring is disposed over the extended insert and proximate exits of the holes in the main
body portion.
[0009] According to another exemplary embodiment, a method for connecting a rotor to
a balance testing includes the steeps of: inserting an extended insert portion of a coupling
device into an opening in the rotor, applying a torque to a plurality of connection elements,
which plurality of connection elements are disposed in a main body portion of the coupling
device, to force a ring disposed over the extended insert portion against a mating surface
around the opening of the rotor, and connecting a drive shaft of the balance testing machine
to an extended thin portion in the main body portion of the coupling device.
[0010] According to yet another exemplary embodiment, a balance testing system
includes a balance test machine including a drive shaft, a coupling, connected on one side to
the drive shaft, and a rotor, connected to receive torque from the drive shaft via the coupling,
the coupling including: a main body portion having an extended thin portion therein which is
configured to fit the drive shaft of the balance test machine and an extended insert portion
which is configured to fit an opening in the rotor, a plurality of connection elements disposed
in holes in the main body portion, and a ring disposed over the extended insert and proximate
exits of the holes in the main body portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings illustrate exemplary embodiments, wherein:
[0012] Figure 1 illustrates a generalized rotor balance testing setup;
[0013] Figure 2 depicts a conventional coupling for the balance testing setup of
Figure 1;
[0014] Figure 3 depicts a compressor having a rotor which is balance tested in
accordance with exemplary embodiments;
[0015] Figure 4 shows an end of a rotor to be balance tested in accordance with
exemplary embodiments;
[0016] Figure 5 shows a coupling device according to an exemplary embodiment;
[0017] Figure 6 shows a sectional view of the coupling of Figure 4(a) attached to
a rotor according to an exemplary embodiment;
[0018] Figure 7 is an exterior perspective view of a coupling connected to a rotor
according to an exemplary embodiment;
[0019] Figure 8 is a graph showing vibration associated with a rotor tested using a
coupling of the type illustrated in Figure 2 as compared to the same rotor tested using a
coupling according to exemplary embodiments; and
[0020] Figure 9 is a flowchart illustrating a method of connecting a rotor to a test
balance machine.
DETAILED DESCRIPTION
[0021] The following detailed description of the exemplary embodiments refers to the
accompanying drawings. The same reference numbers in different drawings identify the
same or similar elements. Also, the following detailed description does not limit the
invention. Instead, the scope of the invention is defined by the appended claims.
[0022] To provide some context for the subsequent discussion relating to couplings
according to exemplary embodiments discussed herein, Figure 3 schematically illustrates a
multistage, centrifugal compressor 10 which includes a rotor that is, preferably, balance
tested (and then balanced) prior to final manufacture and entry into service. Therein, the
compressor 10 includes a box or housing (stator) 12 within which is mounted a rotating
compressor shaft 14 that is provided with a plurality of centrifugal impellers 16. The rotor
assembly 18 includes the shaft 14 and impellers 16 and is supported radially and axially
through bearings 20 which are disposed on either side of the rotor assembly 18.
[0023] The multistage centrifugal compressor operates to take an input process gas from
duct inlet 22, to accelerate the particles of the process gas through operation of the rotor
assembly 18, and to subsequently deliver the process gas through outlet duct at an output
pressure which is higher than its input pressure. Between the impellers 16 and the bearings
20, sealing systems 26 are provided to prevent the process gas from flowing through to the
bearings 20. In the exemplary embodiment illustrated, the housing 12 is configured so as to
cover both the bearings 20 and the sealing systems 26 to prevent the escape of gas from the
centrifugal compressor 10. Also seen in Figure 3 is a balance drum 27 which compensates for
axial thrust generated by the impellers 16, the balance drum's labyrinth seal 28 and a balance
line 29 which maintains the pressure on the outboard side of the balance drum 27 at the same
level as the pressure at which the process gas enters via duct 22. It will be appreciated by
those skilled in the art that the centrifugal compressor illustrated in Figure 3 is provided here
merely as an example of one type of turbo machine which includes the type of rotor that is
typically balance tested prior to being completely assembled, and that the present invention is
not limited thereto.
[0024] An end 30 of the rotor assembly 18 shown in Figure 3(a) can, for example, be
configured as seen in Figure 4. Therein, it can be seen that the rotor end 30 is generally
circular in cross section with an opening 32 and a generally cylindrical outer surface 34.
According to one exemplary embodiment illustrated in Figure 5, a coupling 40 is designed
for interfacing the rotor end 30 with a balance test machine. Therein, the coupling 40
includes an extended insert 42, a ring 44 and a main body portion 46 having a plurality of
connection elements, e.g., torque screws, 48 disposed therein. The main body portion 46 has
an opening 50 formed therein which is configured to mate with a drive shaft (not shown in
this Figure, see Figure 6 described below) of the balance test machine. In this example, the
opening 50 is a hexagonally shaped opening although those skilled in the art will appreciate
that the opening 50 can take any desired shape depending upon the balance test machine
implementation. The main body portion 46 according to this exemplary embodiment has an
extended thin portion 5 1 therein which is configured to mate with a drive shaft 55 (seen in
Figure 6) of the balance test machine.
[0025] A side sectional view of the coupling 40 when connected to a rotor end 30 is
provided as Figure 6. Therein, one of the torque screws 48 is removed to better reveal its
corresponding threaded screw hole 52. In this example, the coupling 40 has six torque
screws 48 which are evenly (symmetrically) spaced around the circumference of the main
body portion 46 in corresponding screw holes 52, although those skilled in the art will
recognize that both the number and placement of the torque screws 48 may be varied. As
seen in Figure 4(b), the ends 54 of the torque screws 48 abut the ring 44 which rests on the
coupling 40. The ring 44 rests on the surface of the main body portion 46 without attachment
according to this exemplary embodiment and is pressured by the torque screws 48. The ring
44 provides uniform pressure so that friction is evenly transmitted on the rotor end and
avoids rotor end damage by the screws 48. According to one exemplary embodiment, the
torque screws 48 can be formed from a material having a tensile strength of 700 MPa,
although other values and materials may also be used.
[0026] To attach the coupling 40 to the rotor, the extended insert 42 is first inserted into
the opening 32 in the rotor end 30. For example, the extended insert 42 can be threaded and
screwed into corresponding threads provided in the opening 32 in the rotor end 30 using a
hexagonal torque key in the opening 50. Then, the torque screws 48 can be tightened, e.g.,
using a dynamometer key and applying 2-5 N-m of torque, so that the ring 44 is pressed up
against the outer surface 34 of the rotor end 30. Thus, according to this exemplary
embodiment, the coupling 40 is friction fit to the rotor and torque is transmitted from the
balance testing machine through the coupling 40 to the rotor via the friction connection. In
this exemplary embodiment, the shaft 55 of the balance testing machine is connected to the
coupling 40 via an opening 54 which mates with the extended thin (annular) portion 5 1 of the
coupling. This exemplary attachment feature has the further advantage of maintaining
concentricity of the coupling (to reduce/eliminate unbalance in the test setup). Figure 7
depicts the combined rotor and coupling 40 after they are attached to one another according
to this exemplary embodiment.
[0027] Thus, unlike the conical, heat-shrunk coupling 14 which was described above
with respect to Figure 2, the coupling 40 according to the exemplary embodiments of Figures
5-7 can be easily and mechanically attached to a rotor to be balance tested. This process is
both less time consuming and safer as it does not involve using a furnace to heat shrink the
coupling onto a rotor. Additionally, the exemplary coupling 40 is less likely to damage the
surface of the rotor than heat shrinking. Moreover, the coupling 40 can be manufactured to
weigh less than coupling 14 and introduce less unbalance into the system.
[0028] For example, a test was run by balancing a rotor first using the coupling 14 to
attach a rotor to the balance testing machine, and subsequently using the coupling 40 to
attach the same rotor to the balance testing machine, results of which are plotted in Figure 8 .
This test was performed using high speed balance equipment from Schenck GMBH which
was generally setup as shown in Figure 1 and which employed accelerometers as vibration
sensors. To generate the results shown in Figure 8, vibration of the rotor was measured at
both the drive end of the rotor, i.e., the end of the rotor connected to the coupling (results
enclosed in rectangle 60) and the opposite end of the rotor (results depicted below the
rectangle 60) in units of mm/s rms vibration as a function of RPMs. More specifically, the
dotted line 62 represents the measured vibration of the rotor connected to the balancing
machine via coupling 14, while the solid line 64 represents the measured vibration of the
rotor connected to the balance test machine via coupling 40. Comparing the two functions 62
and 64, it can be seen that vibration was markedly less, e.g., by about 25% at peak vibration
levels, when using the coupling 40 according to the afore-described exemplary embodiments,
than when using the coupling 14. Vibration differential on the other side of the drive was
less significant, as expected, since that end of the drive is further away from the interface
with the balance test system.
[0029] Thus according to one exemplary embodiment, a method for connecting a rotor to
a balance testing includes the steps illustrated in the flowchart of Figure 9. Therein, at step
70, an extended insert portion of a coupling device is inserted into an opening in the rotor.
Torque is applied to a plurality of connection elements at step 72 to force a ring disposed
over the extended insert portion against a mating surface disposed around the opening of the
rotor. A drive shaft of the balance testing machine is connected to an extended thin portion
in the main body portion of the coupling device at step 74.
[0030] The above-described exemplary embodiments are intended to be illustrative in all
respects, rather than restrictive, of the present invention. Thus the present invention is
capable of many variations in detailed implementation that can be derived from the
description contained herein by a person skilled in the art. All such variations and
modifications are considered to be within the scope and spirit of the present invention as
defined by the following claims. No element, act, or instruction used in the description of the
present application should be construed as critical or essential to the invention unless
explicitly described as such. Also, as used herein, the article "a" is intended to include one or
more items.

CLAIMS:
1. A coupling (40) for connecting a rotor to a balancing test machine, the coupling (40)
comprising:
a main body portion (46) having an extended thin portion (51) therein which is
configured to fit a shaft of said balancing machine and an extended insert portion (42) which
is configured to fit an opening in said rotor;
a plurality of connection elements (48) disposed in holes in said main body portion (46);
and
a ring (44) disposed over said extended insert (42) and proximate exits of said holes in
said main body portion (46).
2. The coupling of claim 1, wherein said connection elements are operable to push said ring
outwardly toward an end of said extended insert.
3. The coupling of claim 1 or claim 2, wherein each of said plurality of connection elements
is disposed in a recessed hole in said main body portion.
4 . The coupling of any preceding claim, wherein said connection elements are screws.
5 . The coupling of claim 4, wherein said holes for said screws are disposed symmetrically
about a circumference of said main body portion.
6. The coupling of any preceding claim, wherein said main body portion and said ring are
formed as cylinders having a substantially same diameter and said extended insert is a
cylinder having a smaller diameter than that of said main body portion and said ring.
7 . A method for connecting a rotor to a balance testing machine, the method comprising:
inserting an extended insert portion (42) of a coupling device (40) into an opening (32) in
said rotor (30);
applying a torque to a plurality of connection elements (48), which plurality of
connection elements (48) are disposed in a main body portion (46) of said coupling device
(40), to force a ring (44) disposed over said extended insert portion (42) against a mating
surface around said opening (32) of said rotor (30); and
connecting a drive shaft of said balance testing machine to an extended thin portion (51)
in said main body portion (46) of said coupling device (40).
8 . The method of claim 7, wherein each of said plurality of connection elements is disposed
in a recessed hole in said main body portion.
9. The method of claim 7 or claim 8, wherein said main body portion and said ring are
formed as cylinders having a substantially same diameter and said extended insert is a
cylinder having a smaller diameter than that of said main body portion and said ring.
10. A balance testing system comprising:
a balance test machine including a drive shaft (55);
a coupling (40), connected on one side to said drive shaft (55); and
a rotor (30), connected to receive torque from said drive shaft (55) via said coupling (40),
said coupling (40) including:
a main body portion (46) having an extended thin portion (51) therein which is
configured to fit said drive shaft (55) of said balance test machine and an extended insert
portion (42) which is configured to fit an opening (32) in said rotor (30);
a plurality of connection elements (48) disposed in holes in said mam body
portion (46); and
a ring (44) disposed over said extended insert (42) and proximate exits of said
holes in said main body portion (46).
11. The balance testing system of claim 10, wherein said connection elements are operable to
push said ring outwardly toward an end of said extended insert.
12. The balance testing system of claim 10 or claim 11, wherein each of said plurality of
connection elements is disposed in a recessed hole in said main body portion.
13. The balance testing system of any of claims 10 to 12, wherein said connection elements
are screws.
14. The balance testing system of claim 13, wherein said holes for said screws are disposed
symmetrically about a circumference of said main body portion.
15. The balance testing system of any of claims 10 to 14, wherein said main body portion and
said ring are formed as cylinders having a substantially same diameter and said extended
insert is a cylinder having a smaller diameter than that of said main body portion and said
ng.