U.S. patent application number 12/316717 was filed with the patent office on 2010-06-17 for rotary sliding vane compressor and blade therefor.
This patent application is currently assigned to FLSmidth A/S. Invention is credited to Louis S. Schwartz, David Waage.
Application Number | 20100150766 12/316717 |
Document ID | / |
Family ID | 42240772 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100150766 |
Kind Code |
A1 |
Schwartz; Louis S. ; et
al. |
June 17, 2010 |
Rotary sliding vane compressor and blade therefor
Abstract
Disclosed is a blade for a rotary blade compressor. The blade
has at least two section pieces, with any two adjacent section
pieces being radially aligned with each other at a junction,
wherein further there is a force applying means at said junction
forcing the adjacent blade section pieces apart from each other in
an axial direction. The edges of said blade will thereby be
positioned to form a seal against the head plates of the
compressor.
Inventors: |
Schwartz; Louis S.;
(Northampton, PA) ; Waage; David; (Cobleskill,
NY) |
Correspondence
Address: |
Daniel DeJoseph;FLSmidth Inc.
2040 Avenue "C"
Bethlehem
PA
18017
US
|
Assignee: |
FLSmidth A/S
|
Family ID: |
42240772 |
Appl. No.: |
12/316717 |
Filed: |
December 16, 2008 |
Current U.S.
Class: |
418/266 |
Current CPC
Class: |
F01C 21/0881 20130101;
F04C 18/3442 20130101; F05C 2201/021 20130101; F05C 2201/028
20130101; F05C 2203/0808 20130101; F05C 2253/04 20130101 |
Class at
Publication: |
418/266 |
International
Class: |
F01C 1/00 20060101
F01C001/00 |
Claims
1. A compressor blade for a rotary vane compressor having a rotor
with blade receiving slots and a cylindrical housing having
opposite head plates, said blade being substantially rectangular
and having two opposed substantially radial sides and a first and a
second opposed substantially axial sides, with said first side
adaptable to being received in a slot of said rotor, said blade
having at least two section pieces, with any two adjacent section
pieces being radially aligned with each other at a junction,
wherein the blade further comprises a force applying means at said
junction forcing the adjacent blade section pieces apart from each
other in an axial direction.
2. The blade of claim 1 wherein the force applying means exerts a
force sufficient to keep each radial side in a sealing relationship
with an adjacent head plate of the cylindrical housing.
3. The blade of claim 1 wherein the force applying means is located
interior to the blade.
4. The blade of claim 3 wherein the force applying means is at
least one compression spring.
5. The blade of claim 1 wherein the radially aligned section pieces
are attached to each other by a combination joint comprising a lap
joint that transitions into a butt joint, said butt joint being in
the vicinity of the first axial side and said lap joint being in
the vicinity of the second axial side.
6. The blade of claim 5 wherein the combination joint provides an
air seal in all potential planes of air leakage flow.
7. The blade of claim 1 wherein said blade is self lubricating.
8. A compressor blade for a rotary vane compressor having a rotor
with blade receiving slots and a cylindrical housing having
opposite head pieces, said blade being substantially rectangular
and having two opposed substantially radial sides and two opposed
substantially axial sides, with a first of said substantially axial
sides being adaptable to being received in a slot of said rotor,
said blade having at least two section pieces that are radially
aligned with each other at a junction, wherein further the blade is
self lubricating.
9. The blade of claim 8 which is manufactured from graphite or a
composite graphite.
10. The blade of claim 8 further comprising means to automatically
compensate for blade wear in an axial direction during operation
within a rotary compressor.
11. The blade of claim 8 further comprising means to mechanically
push the blade into the rotor slot during operation within a rotary
compressor.
12. A compressor blade for a rotary vane compressor having a rotor
with blade receiving slots and a cylindrical housing having
opposite head plates, said blade being substantially rectangular
and having two opposed substantially radial sides and two opposed
substantially substantially axial sides, with one substantially
axial side adaptable to being received in a slot of said rotor,
said blade having at least two section pieces and further being
self-spreading so that said section pieces will spread apart from
each other in an axial direction during operation without the need
for a separate spreading device such as a spring.
13. A rotary sliding blade compressor comprising: a housing
defining a closed cavity having an inner cylindrical wall and a
pair of spaced parallel end walls; a slotted rotor eccentrically
positioned within said cavity to define with said cylindrical wall
and said end walls a compression chamber; a plurality of blades
slidably mounted in the slots of said rotor; means to rotate the
rotor about an axis to move said blades generally radially of the
rotor toward and in sealed engagement with said cylindrical wall
during such rotation; inlet ports for a gas to be compressed and
outlet ports for compressed gas communicating with said compression
chamber; said blades being substantially rectangular and having two
opposed substantially radial sides and a first and a second opposed
substantially axial sides, with said first side adaptable to being
received in a slot and said second side being adaptable to being in
a sealing relationship with said inner cylindrical wall, said
blades forming pockets between the wall and rotor which vary in
volume as the rotor rotates, with at least one blade having at
least two section pieces, wherein any two adjacent section pieces
are radially aligned with each other at a junction, wherein further
there is a force applying means at said junction forcing the
adjacent blade section pieces apart from each other in an axial
direction so that the each radial side of the blade is constantly
in a sealing relationship with an adjacent end wall.
14. The compressor of claim 13 wherein the force applying means is
located interior to the blade.
15. The compressor of claim 14 wherein the force applying means is
at least one compression spring.
16. The compressor of claim 13 wherein the radially aligned section
pieces are attached to each other by a lap joint that transitions
into a butt joint, said butt joint being in the vicinity of the
first axial side and said lap joint being in the vicinity of the
second axial side.
17. The compressor of claim 13 wherein said at least one blade is
self lubricating.
18. The compressor of claim 17 wherein at a predefined point of
wear of said at least one blade there is a controlled leakage of
air across the blade from one pocket to an adjacent pocket.
19. The compressor of claim 18 further comprising means to detect
said controlled leakage of air.
Description
BACKGROUND OF THE INVENTION
[0001] A "sliding" rotary vane compressor is a positive
displacement machine that uses a rotor, which may be, but is not
necessarily, eccentric, placed within a cylindrical chamber that is
located within a rotor housing and is used to compress compressible
fluids such as gases. The rotor has slots along its length, and
each slot contains a blade, i.e. a vane. The vanes are thrown
outwards (radially) by centrifugal force when the compressor is
running and the vanes move in and out of the slot. The outer
(radial) edge of the blades will follow the contour of the inner
chamber wall, and the two side (axial) edges of the blades will
each be adjacent to a side head plate of the compressor. The vanes
thereby create individual cells or pockets of gas which, because of
the vanes' movement, are compressed as the rotor turns. The vanes
sweep the cylinder, sucking air in on one side and ejecting it on
the other. As each cell approaches the discharge port, its volume
is reduced and the compressed fluid is discharged. The compressor
can be utilized to compress any gas, including air. (The use of the
terms "radial" and "axial" and derivatives thereof as locations on
a compressor blade of the invention are in reference to the blade's
placement within a compressor.)
[0002] A major concern with sliding vane compressors is discharge
temperature, which must be controlled within reasonable limits to
avoid serious mechanical damage to the compressor. Uncontrolled
discharge temperature can lead to thermal growth of internal
components causing jamming, internal components degrading or
melting and lubrication failure.
[0003] One cause of increased discharge temperature is the leakage
of air from pocket to pocket within the compressor. As gas is
compressed, its temperature will increase, so that gas within a
compressor will be at its greatest temperature at the point of
discharge from the compressor. If air from a compressor pocket
leaks "backwards" to preceding pockets opposite the direction of
movement of the rotor, the air temperature in a preceding pocket
will increase, with the subsequent increase in the air discharge
temperature as the pocket moves to the discharge point. With this
cycle being continuously repeated, this will result in a steady
increase in discharge temperature, causing the problems discussed
above.
[0004] Poorly sealing blades are the main causes for leakage from a
pocket that is at a higher pressure to an adjacent pocket that is
at a lower pressure. Leakage across each blade becomes
significantly greater when the compressor is designed to operate at
higher discharge pressures, in which case the differential pressure
across each blade increases. Numerous conditions may cause
excessive leakage across a blade. The major sources for leakage are
intermittent sealing contact of the blade tip at the cylinder wall,
little or no axial sealing contact at the head plates located at
both ends of the cylinder housing, and poor sealing contact in the
rotor slot.
[0005] Leakage paths across the blade tip at the cylinder wall and
within the rotor slot can be corrected by precision machining of
the blade, cylinder, and rotor. This invention addresses the major
leakage paths that are created by poor sealing at the head
plates.
[0006] A significant leakage path is for air to travel from one
pocket to an adjacent pocket in the area between an axial edge of a
vane and an adjacent side head plate of the compressor. This
leakage condition can exist at each head plate at both ends of the
cylindrical cylinder. It is therefore an object of this invention
to have a rotary vane compressor that provides a tight seal between
the vanes and both compressor head plates.
[0007] In order to create a tight axial seal at head plates a
multi-sectioned blade has been developed, in which the axial edges
of the end sections are forced against the compressor's end plate.
However, using a multi-sectioned blade may create its own
disadvantage in that another significant leakage path is for air to
travel from one pocket to an adjacent pocket at the joints between
the multiple piece blade sections. It is therefore a further
objective of this invention to have a joint at adjoining blade
sections that provides a tight seal while automatically
compensating for wear.
[0008] An oil flooded rotary vane compressor utilizes oil as both a
lubricant and a sealant. An oil free compressor will typically
utilize a self-lubricating blade. Such blades, however, are much
more subject to wear then conventional compressor blades. If a worn
blade breaks it can cause great harm to the compressor, and
therefore it a further object of this invention to have a means of
detecting advanced blade wear in a self-lubricating blade before a
blade wears to the extent that it breaks and causes damage to the
compressor.
DESCRIPTION OF THE DRAWINGS
[0009] The above and other objects, features, and advantages will
become more readily apparent from the following description,
reference being made to the accompanying drawings. The drawings are
not necessarily drawn to scale.
[0010] FIG. 1 is a sectional view, cut radially, of the interior of
a sliding vane compressor having straight blades.
[0011] FIG. 2 is a sectional view, cut radially, of the interior of
another embodiment of a sliding vane compressor having angled
blades.
[0012] FIG. 3 is a longitudinal sectional view, showing a portion
of one end of a sliding vane compressor cut in the axial
direction.
[0013] FIG. 4 is a side elevational view of one embodiment of an
assembled two piece compressor blade of the present invention as it
would be installed in the compressor, with a portion of the tip
depicted, and also depicting in relief an internally situated
compression spring that is used to apply force axially to each
blade piece.
[0014] FIG. 4A is a view from the direction of arrows C of a side
edge of the blade of FIG. 4.
[0015] FIG. 5 is an isometric elevational view of a disassembled
two piece blade of the present invention, depicting the primary
sealing surfaces of the overlapping lap joint.
[0016] FIG. 6 is an isometric elevational view identical to FIG. 5,
but depicting the secondary sealing surface of the overlapping
joint.
[0017] FIG. 7 is a side elevational view, of a disassembled two
piece blade with two compression springs.
[0018] FIG. 8 is a side elevational view of an assembled three
piece blade with one compression spring at each overlapping
joint.
[0019] FIG. 9 is a side elevational view of a disassembled four
piece blade with one compression spring at each overlapping
joint.
DESCRIPTION OF THE INVENTION
[0020] The above and other objects are realized by the present
invention which provides for a multiple piece blade for use in a
rotary sliding vane compressor. Each blade section is designed to
provide ongoing sealing as the blade wears. The blade may be used
in both oil lubricated and oil free compressors.
[0021] The blade utilized in the present application is made from
multiple radially cut sections. It is a feature of the present
invention that an axially directed force originating in the area in
which the sections are joined is incorporated within the blade and
is utilized, as the blade wears, to force adjacent blade sections
apart from each other to thereby create a tight seal of the axial
outer edges of the multi-sectioned blade against the head plates of
the radial compressor. The force is applied automatically to adjust
axially and compensate for thermal growth and blade wear while
providing a seal of the blade against the head plate.
[0022] The blade is made from two or more radially cut sections
that can accommodate a spring loaded feature. In one example,
compression springs may be used to spread the blade sections
axially to create a tight seal where the ends of the blade rub on
the head plates. This spring loaded action automatically adjusts
axially and compensates for thermal growth and blade wear.
Manufacturing the blade out of two or more pieces is also a feature
of the invention, as it is difficult to economically manufacture
blades for large compressors in one single piece. Furthermore, long
single piece blades are prone to warping, which will cause the
blade to jam in the rotor slot. The blade will break if it can not
move freely up and down within the rotor slot. Thus, it is
preferable to manufacture a long blade from two or more shorter
blade sections cut width-wise (radially) and not length-wise
(axially).
[0023] Referring to the drawings by characters of reference, in
FIG. 1 sliding vane compressor 100 is depicted, consisting of a
housing in which there is enclosed an essentially cylindrical
chamber 102 having an elongated cavity having a circular cross
section, with a cylindrical rotor 101 having a circular cross
section eccentrically and rotatably placed within chamber 102.
Formed in rotor 101 is a plurality of radially extending grooves or
slots 103 which extend from the surface 110 of the rotor to a point
111 in the interior of the rotor. Each of the slots accommodates a
freely sliding blade or vane 104. The sliding vane compressor can
utilize straight (as shown in FIG. 1) or angled (as shown in FIG.
2) rotor slots.
[0024] During rotation in the direction shown by arrow R of the
rotor each vane 104 is thrown outwards by centrifugal force so that
its outer edge sweeps the internal cylindrical surface 112 of
chamber 102. The free space between adjacent vanes is thus divided
into closed cells (such as 105, 106, 107). Inlet 108 and outlet 109
extend through housing 102. Air or other fluid at atmospheric
pressure is taken in at stationary fluid inlet 108 in the direction
of arrow A and is thus compressed as the free space in each cell
diminishes as the rotor turns and the compressed air exits at
stationary fluid outlet 109 in the direction of arrow B.
Accordingly in the operation of a rotary vane compressor the closed
cells to either side of any particular vane are at different
pressures as the vane passes from the inlet port to the outlet
port.
[0025] The present invention can be advantageously utilized on
essentially any prior rotary vane compressor. Therefore, it can be
used on rotary vane compressors having a rotor mounted in an
elongated cavity which may be cylindrical with, for example, an
essentially circular, elliptic, or epitrochoidal cross section
formed therein. In certain prior art compressors the bore of the
cavity can have an undercut in which the rotor sits lower in the
housing in which case the cross section of the cavity would not be,
for example, a perfect circle.
[0026] FIG. 2 illustrates a compressor similar to the compressor
depicted in FIG. 1 with the exception that the rotor slots 203 are
angled away from the center of the rotor. Angled slots allow deeper
slots to be cut into the rotor profile while still providing a
significant rotor core (the undisturbed center area of the rotor).
Deeper slots are necessary to provide for wear allowance,
especially in the case where lubrication is provided from blade
wear. A significant rotor core provides the majority of strength
and stiffness in a rotor. Excessive slot depth with slight or no
slot angling will reduce the rotor core significantly, thus
lowering the strength and stiffness of the rotor. The rotor may
bend under load, thus creating a problem with operating at minimal
clearance.
[0027] Another feature of angled slots is a portion of the
centrifugal force acting on the blade is absorbed into the rotor
slot. The blade tip does not rub on the same plane as the resulting
centrifugal force acting on the center of gravity of the blade as
it rotates about the axis of the rotor. This reduces rubbing
pressure of the blade tip on the cylinder wall and the result is
less wear at the blade tip, less frictional losses from the blade
rubbing on the cylinder wall, reduced discharge temperature due to
lower frictional heat, and less shaft power to operate the
compressor.
[0028] If the blades of the present invention are utilized in an
oil free compressor it is preferred that they be self lubricating.
A self lubricating blade must wear to provide lubrication, and
therefore will require a greater slot depth than a conventional
compressor blade, since it is important to maintain sufficient
engagement of the blade in the rotor slot or the blade might be
thrown out of the slot, which can jam the compressor and cause
breakage. Although the question of increasing slot depth without
weakening the core of a rotor may be addressed by increasing the
size of the rotor, this goes against the ideal of using the
smallest compressor block to produce the greatest amount of
compressed air. In view of the above, an angled slot may be
preferred in an oil free compressor to provide significantly
greater slot depth while providing an ample core area.
[0029] Typically, the angled slot will be at an angle of from about
1.degree. to about 30.degree. from a line that extends from a point
on the center of the blade tip as the blade tip contacts the
cylinder wall, the point of the maximum blade extension out of the
rotor slot, with respect to the center of the rotor. Although
increasing the slot angle provides the benefits of increasing the
allowable slot depth, increasing the size of the undisturbed center
core, and reducing frictional rubbing at the tip, it also increases
the maximum distance the blade must extend out of the rotor slot.
This requires the blade to be much stronger and larger, which
greatly increases the mass of the blade and resulting centrifugal
forces acting on the blade. As a result of diminishing returns, the
preferred angle is from about 20.degree. to about 25.degree. and
preferably about 22.degree..
[0030] With the rotation of the rotor, the blades are thrown
outward toward the inner wall or surface (112, 212, with reference
to FIGS. 1 and 2) of the cylindrical chamber. In both FIG. 1 and
FIG. 2 the rotor is eccentrically placed within the cylindrical
chamber of the compressor, and accordingly the outer surface (110,
210) of the rotor is variably placed from the inner surface of the
cylindrical chamber. Accordingly, centrifugal force will throw the
blade (104, 204) out of the slot (103, 203) the furthest in those
regions of the compressor where the outer surface of the rotor is
furthest from the inner surface of the cylindrical chamber. In
those regions where the outer surface of the rotor is closest to
the inner surface of the cylindrical chamber the blades may not
significantly extend out from the slots.
[0031] Referring to FIG. 3, a compressor comprises a housing 300
having a cylindrically bored chamber 301 therein. End plates or
walls 302 close the ends of the bore. Rotor shaft 303 is
eccentrically rotatable in the bore 301 and is rotatably driven by
a prime mover such as a motor (not shown). A circular cylindrical
rotor 304 is fitted on the shaft 303 and is formed with radially
extending slots. A blade or vane 305 is radially slidable through
the slots so that rotation of the shaft 303 causes the rotor 304
and blade 305 to rotate therewith in a unitary manner. In the
present invention the blade 305 extends past the edge 304a of the
rotor to form a tight seal on the head plate 302.
[0032] FIG. 4 illustrates a two-piece blade 400 of the present
invention, having sections 403 and 404 that are radially aligned
with each other at junction 411. Blade 400 is substantially
rectangular in shape and has upper axial side 401 which, when the
blade is operational in a compressor, is proximate to and in sealed
engagement with internal cylindrical surface (112, 212) of
compressor chamber (102, 202). Lower axial side 402 is under normal
operational conditions always inserted within slot (103, 203).
Radial sides or edges 408 of the blade will be abutting end wall or
head plate 302 (FIG. 3) to form a seal to prevent air from leaking
around the axial edge of a compressor blade into an adjacent
pocket.
[0033] It is a feature of the present invention that there is a
force applying means at the junction 411 of any adjacent blade
sections that constantly acts upon the adjacent blade section
pieces to force them apart from each other in an axial direction.
For example, interior to the blade there can be at least one
compression spring 407 which is biased to constantly force the two
blade pieces 403 and 404 axially apart to thereby accordingly force
each blade edge 408 into a sealing engagement with its adjacent
head plate. As the edges wear the compression spring will continue
to force the blade pieces further apart to thereby compensate for
the wear and to keep the edges in a constant sealing relationship
with the head plate.
[0034] In a preferred embodiment the upper portion 405 of the joint
of the two blade pieces 403 and 404 comprises an overlapping lap
joint in combination with a butt joint. Such a combination joint
provides a seal in all potential planes of air leakage flow. For
example--the vertical upper portion 405 of the lap joint provides a
seal across the thickness (FIG. 4A, direction .rarw.E.fwdarw.A) and
along the length (axially, direction .rarw.D.fwdarw.A), but does
not provide a seal across the width (radially, direction
.rarw.F.fwdarw.A) of the blade. The horizontal lower portion 603a
and 603b (see FIG. 6), at the base of the main overlapping joint
405 and transitioning to a butt joint, provides the seal across the
radial width (direction .rarw.F.fwdarw.). In the lower jointure
portion 406 the two pieces 403 and 404 are preferably in a butt
joint, end to end relation with each other, so that the composite
lap joint and butt joint forms a S shaped joint. Preferably, when
the blade is in operation within a compressor at least all of lower
area 406 is located within the rotor slot. The advantage of this
"S" type overlapping joint is that it provides a seal in all
normally anticipated planes of leakage flow. For example, the joint
provides a seal across the thickness, along the length, and across
the width of the blade.
[0035] Alternatively, portions of the two (or more) blade pieces
can be joined together by other type of edge joints such as tongue
and groove joints, sliding slot joints, V-joints, dovetail joints,
lap joints or a combination thereof.
[0036] FIG. 4a shows one side edge of blade 400 as seen from the
perspective of arrows C. Depicted is trailing surface 408a and
leading surface 408b. With reference to blade tip 401a, when a
self-lubricating blade is utilized, the geometry of the machine
(cylinder size, shape, rotor diameter, slot angle, etc) will cause
the blade tip to eventually wear to the optimum profile. However,
this will not happen in the short term with non-lubricating blades,
as they will have better wear properties. In either scenario, if
new blades are installed and the tip profile is not optimum there
may be undesirable leakage over the blade tip (that is, the tip
makes a poor seal). Thus, it is desirable to machine the optimum
tip profile (as close as possible) into a new set of blades to
minimize the break in period.
[0037] The material of construction of the blade will be dependent
upon whether it is desired that the blade be self-lubricating. If
the blade is not self-lubricating it can be constructed of, for
example, a carbon-fiber resin composite, magnesium, aluminum or
various reinforced resin bonded materials. If the blade is
self-lubricating, materials of choice include solid graphite,
composite graphite, or any other binder material with additives
that provide lubrication. Lubrication additives include any dry
lubricant that lowers friction such as PTFE, graphite, hexagonal
boron nitride, molybdenum disulfide, and various plastic
resins.
[0038] During operation the sections of the compressor blade remain
forced apart, such as in the depicted example by the compressive
spring force, in an axial direction as shown by arrows
.rarw.D.fwdarw. on FIG. 4. As the blade wears pocket air will flow
into the area between the separating portions. Preferably, the
blade is machined with a joint that provides optimum sealing in the
absence of oil. In this regard, when a combined lap joint/butt
joint junction is utilizing as illustrated, air will flow down the
area between the separating lap joint but will be stopped in the
area formed by seal surfaces 603a and 603b (FIG. 6) where the lap
joint transitions to a butt joint, which horizontal transitioning
area acts as an air seal. The spring force may be either increased
or decreased to thereby adjust the rubbing pressure of the blade
against the head plates. If the rubbing pressure on the head plates
is too light, there may not be a sufficient seal on the head
plates, whereas if it is too heavy the blade will wear excessively
along its length and in addition there will excessive frictional
heat. In addition, the spring force will serve to provide a blade
that automatically compensates for differences in thermal growth in
the axial direction, that is, it will provide an adequate seal at
the head plates independent of the operating temperatures.
[0039] Numerous means can be used to spread the blade sections.
These include one or more compression springs, leaf springs, wave
springs, air springs, or any other means that uses a mechanical
means or differential pressure to create a spreading force. The
spreading force can vary (such as with a compression spring) or be
constant (as with an air spring) with respect to the amount of
joint displacement.
[0040] The blade can also be constructed to be self spreading at
the joint without the need for a spring or any other separate
spreading device. The joint can be offset from the center of the
blade (in the thickness direction) to provide unequal lateral areas
within the joint. The larger area faces the higher pressure
(leading side) of the blade and the smaller area faces the lower
pressure (trailing side) of the blade. The pressure in the leading
pocket is significantly higher than in the trailing pocket when
sealing is required. The higher pressure in the leading pocket acts
on the larger lateral area in the joint. The lower pressure on the
trailing side of the blade acts on the smaller lateral area in the
joint. This creates a spreading force at the joint that overcomes
the opposing force at the blade ends that rub at the head plates.
The result is a natural spreading force that automatically
increases with differential pressure across the blade, providing
optimum sealing at the head plates when needed most.
[0041] The combination of a lap joint and a butt joint has a
further advantage. As the blade's upper surface becomes worn by
contact with the internal cylindrical surface of the compressor
chamber, the blade will gradually start to withdraw from the rotor
slot. Eventually lower area 406 will extend out from the slot.
Contemporaneously with the wearing of the blades upper surface 401,
side edges 408 of the blade will also begin to be worn through
contact with end plates 302. Adjoining surfaces 506a and 506b (FIG.
5) of the butt joint will separate as the axial forces drive
sections 403 and 404 apart, and there will be leakage across the
blade from the higher pressure pocket to the lower pressure pocket.
This leakage is not necessarily completely detrimental, as
excessively worn blades are likely to break independently of
whether there is leakage across a blade. A broken blade can cause
possible and perhaps significant mechanical damage within the
compressor.
[0042] It is a feature of the preferred embodiment of the invention
that when the self-lubricating blades of the present invention wear
they are designed to cause leakage at a point before the wear
becomes so excessive as to cause possible breakage; in effect at a
predefined point of wear of said at least one blade there is a
controlled leakage of air across the blade from one pocket to an
adjacent pocket. This feature, coupled with the fact that high
leakage across a blade will cause the discharge temperature of the
compressor to rise significantly, results in a system of monitoring
blade wear. Therefore, a preferred embodiment of the invention
employs a compressor that utilizes multi-piece blades having a S
shaped, combination lap and butt, joint coupled with a temperature
sensor at the discharge of the compressor and a processor means
that serves to automatically shut down the compressor when a
specified temperature is reached. This feature can prevent
significant mechanical damage to the compressor. Alternatively or
in addition, the blade can be designed with one or more holes
through its thickness that, when the blade is not worn or lighten
worn, will always be within the rotor slot. As the blade is worn to
a predetermined point these holes will become exposed to the air
pockets and consequently air will leak therethrough from a high
pressure pocket to a low pressure pocket. Thus, the blade of the
present invention will not only automatically compensate for wear
in the radial direction (by continuing to move further out of the
slot with wear) but also in the axial direction. In addition to
compensating for wear in the axial direction, the blade of the
present invention automatically compensates for differences in
thermal growth in the axial direction so that it will provide a
seal at the head plates independent of the operating temperatures
of the compressor. Further, the force of the axial blade side
rubbing (due to the spreading force from the axially directed
force) on the head plates mechanically pushes the blade into the
rotor slot, opposing to a certain extent the centrifugal force
throwing the blade out of the slot and lessening the rubbing
pressure of the blade tip on the cylinder wall.
[0043] FIGS. 5 and 6 illustrate a disassembled two piece blade of
the present invention having matching lap joint surfaces 501a and
501b, and pre-formed holes 502a and 502b for receiving a
compression spring. As the blade pieces are forced apart axially,
some of the pocket air may flow radially in the widening gap
between the separating pieces in the direction of arrow F. The path
of the air will be hindered by matching sealing surfaces 603a and
603b, which begins that portion of the blade in which there is a
transition between a lap joint and a butt joint. The separation of
matching surfaces 604a and 604b to the butt joint will not have a
bearing on air flowing between adjacent pockets in a compressor,
since those surfaces are typically located within the rotor slot
under normal operation of the compressor of the invention.
[0044] FIG. 7 illustrates a disassembled two piece blade of the
present invention having pre-formed holes 702a, 702b, 703a and 703b
for receiving two compression springs 704. In certain instances
more than two springs may be desirable between adjacent blade
pieces or other type of springs may be used.
[0045] FIG. 8 illustrates an assembled three piece blade of the
present invention having end segments 801 and 803 and middle
segment 802. A compression spring 804 is located at each
interlapping joint between adjacent blade sections.
[0046] FIG. 9 illustrates a disassembled four piece blade of the
present invention having end segments 901 and 904 and middle
segments 902 and 903. A compression spring 905 is located at each
interlapping joint between adjacent blade sections.
[0047] Preferably, multi piece blade segments may be made
interchangeable for all size compressors, assuming the blades have
the same blade width and thickness. In such a case the end segments
of the blades of FIGS. 8 and 9 are interchangeable with those of
FIG. 4, and the middle segment of the blade of FIG. 8 are
interchangeable with the middle segments of the blades of FIG.
9.
[0048] It is to be understood that the form of this invention as
shown is merely a preferred embodiment. Various changes may be made
in the function and arrangement of parts; equivalent means may be
substituted for those illustrated and described; and certain
features may be used independently from others without departing
from the spirit and scope of the invention as defined in the
following claims.
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