FIELD OF THE INVENTION
The present invention generally relates to brush seals that are deployed in turbo
machinery delivering high mass and flow outputs for example, steam turbines,
gas turbines, compressors, pumps in power and process industry to reduce
process leakage through the brush seals. In particular, the invention relates to
non contact seals for example labyrinth seals deployed in turbo machinery. More
particularly, the invention relates to a method for manufacturing brush seals for
turbo machinery operable at lower radial rotor-stator clearances with improved
leakage performance.
BACKGROUND OF THE INVENTION
US Patent No US2007/0214628 A1 discloses a method of forming brush seal
segments comprising the steps of mounting a pair of full form plates having
opposite arcuate edges in back-to-back relation and wrapping wire about the
form plates in multiple passes to form wire runs at angles, e.g., 35-45° relative
to radii of the arcuate edges. Half form plates are assembled to opposite sides of
the full form plates adjacent one edge of the subassembly. The wire wrap
adjacent the one edge of the full form plates is removed. Welds are applied
between each adjacent half and full form plates. The inner edges of the wrapped
wire and inner frame members of the full form plates are removed. The
assembly is then separated to form a pair of arcuate brush seal segments.
US 2007/0079493 A1, reported a method of making brush seal wherein the
winding of the wires is done in radial manner with the help of a number of plates
placed at required angles , the intersecting portion of the wires are cut and fused
together to achieve rectangular bristle packs having the wires at an angle. These
strips are rolled to achieve the required circularity.
Patent No US 2005/0116423 describes a method of holding wires using a shrink
fit kind of circular ring.
Patent No US 2006/0130323 A1 teaches means for replacing damaged portion of
a working seal to regain full working function with low leakage.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for manufacturing
brush seals operable at lower radial rotor-stator clearances with improved
leakage performance, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a method for manufacturing brush
seals operable at lower radial rotor-stator clearances with improved leakage
performance, which provides higher bristle compactness with desired
manufacturing tolerances.
A still another object of the invention is to propose a method for manufacturing
brush seals operable at lower radial rotor-stator clearances with improved
leakage performance, which selects a circular configuration of the form plates to
produce circular seal segments.
Yet another object of the invention is to propose a method for manufacturing
brush seals operable at lower radial rotor-stator clearances with improved
leakage performance, which allows direct angular winding to desired dimensions
in an angular winding machine.
A further object of the invention is to propose a method for manufacturing brush
seals operable at lower radial rotor-stator clearances with improved leakage
performance, which allows production of substantially higher number of seal
segments from a single form plate.
A still further object of the invention is to propose a method for manufacturing
brush seals operable at lower radial rotor-stator clearances with improved
leakage performance, which provides accurate geometric tolerances through use
of circular form plates and assembly fixtures.
SUMMARY OF THE INVENTION
Accordingly, there is provided to a method for manufacturing brush seals
operable at lower radial rotor-stator clearances with improved leakage
performance. According to the invention, an angular winding operation is carried-
out to achieve a predetermined cant angle of the bristle, which essentially
resides on selection of winding/form plate. The winding plate is provided with
two circular grooves to house circular strips/half form plates on either side of the
plate. The winding plate with the circular strips is mounted through an assembly
fixtures on an angular winding machine for carrying out the winding process in
the desired angle. Three such wound plates are again assembled on the fixtures
with two additional circular strips disposed on the top and bottom to secure the
winding. The Outside diameter of the projected portion of the wire is machined
to a required size to relive the wires. The relieved wire ends are secured or fused
together by a TIG welding. After the TIG welding process, the OD of the wire is
machined to a required dimension and the wires are thereafter relieved at ID and
at sides through a known wire cut EDM process. This relieves the wires totally
from the fixture. The bristle packs are assembled in a housing and ensured that
it is rigidly fixed. The seal assembly is taken for final internal diameter machining
again though a wire cut process to achieve the required ID with required
concentricity tolerances.
According to the inventive method of manufacture of brush seals:
- a basic change is made in the process for winding the wire, wherein a
form plate on which the winding is done on a rotating form plate while
winding spools are stationary in lieu of the method adopted in the prior
art wherein the form/winding plate is a stationary element, and a winding
machine moves around the form plate. To simplify the winding process
angular winding machine is used and it also enhances the productivity of
the winding process;
- form plates and half form plates as winding fixtures is used in the present
invention;
- the form plates after winding are not stacked for relieving the wires from
the form plates as done in prior art but are assembled in circular fixtures
to relieve the winding.
- the prior art process for initial use of radial winding process, has been
dispensed with in the present invention.
- the prior art concept of balanced pressure plate, to secure the closeness
of the wires to achieve better compactness has been dispensed with in
the present invention.
The prior art process of making basic form plate grooves has been achieved and
using a rectilinear groove plate has been dispensed with in the present invention.
According to the invention, a plurality of forming plates and an angular winding
machine is employed to achieve circular bristle strips directly.
The present invention uses a method of TIG welding for holding the wires
together in a predetermined lay angle.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l is an elevational view of the brush seal winding plate (full form plate) for
angular winding of the wire according to the invention.
Fig.2 is a sectional view of the brush seal winding plate as shown in Fig.l, the
circular grooves for fixing the circular plate with relief grooves are also shown in
this figure.
Fig.3 shows an elevational view of the winding plate with bristle wound on it for
the designed lay angle.
Fig.4 is a 3d View of the angular winding machine used for carrying out winding
with a certain lay angle.
Fig.5 show a cross sectional view of the wound plate, indicating the location of
circular strips in dotted sections between the winding plate and the bristles.
Fig.6 shows a cross sectional view of the winding plate with outer circular strips
in position after assembling in the fixture.
Fig.7 is a cross sectional view of the assembled wound plates with outer circular
strips showing the details of wire cut EDM on the OD and ID.
Fig.8 is an assembled view of the wound bristle plates on the fixture before
relieving the wires from the plates on OD and ID.
Fig.9 is an assembled view of the wound bristle plates on the fixture after
relieving the wires from the plates after the OD and ID wire cut operation.
Fig. 10. is an assembled view of the wound bristle plates on the fixture,
illustrating the details for TIG welding operations for the fusion of free end of the
bristles.
Fig.11. shows the fixture assembly of the invention depicting the complete
relieving operations of the bristles from the form plate after sector wire cutting
operation.
Fig.s 12 A and 12 B shows the cross sectional views of the wound wires in the
assembled fixture with details of relief grooves.
Fig.13 A shows a cross sectional view of the wound wires in the assembled
fixture after finish machining of OD.
Fig. 13 B shows a sectional view of the bristle pack after complete relieving.
Fig 14 shows the finished product of the bristle pack which is a sector of the
concentric circle.
Fig 15 shows an assembled bristle packs on the seal holder which is in two
halves.
Fig 16 shows a sectional view of the brush seal.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in an exemplary embodiment as depicted in
the accompanying drawing. There can however be other embodiments of the
same invention, all of which are deemed covered by this description.
It is known that brush seal is a concentric split assembly consisting of bristle
packs. The invention described herein for the manufacture methodology of the
bristle packs. Bristle packs are embodiments consisting of free bristle of alloy
wire which are packed together so that they become an impervious screen to
arrest the leakage through the wires. At the Inner Diameter (ID), the bristles are
free while at the other end, the free wires are fused so as form a pack to hold
the wire lay in its position. The wire lay angle is an important design and
functional feature of the bristle pack. The usual wire lay is 35°to 45° from the
radial direction at a point on the seal circle. This kind of lay allows the rotor seal
interaction without causing high obstructing forces leading to high vibrations of
the rotor. This feature of bristle compliance to deflection allows the seal designer
to achieve low radial clearances between the bristles which are mounted on a
stationary casing and the rotor. To arrange the bristles compactly in a particular
lay angle is the challenge. The present invention succeeded to lay the bristles at
a particular angle in a controlled manner, and assemble in a casing or housing
for completing the brush seal to achieve quality of bristle pack with required
geometric tolerances.
The bristles which are thin alloy wires of dia varying from 0 0.1mm to 0 0.15mm,
are arranged in a particular lay as described above. To achieve this, a winding
plate as shown in Fig. 1 is designed in an innovative manner. This plate has
grooves machined on the O.D. at a particular angle having particular depth. The
groves help in retaining the wire at the angle desired and also acts as a primary
separator between the adjacent grooves. The depth and thickness of the
separator fins, (shown by thin lines), corresponding to radius of the fin top to
ensure non breakage of the wire during winding, are selected after several
iterations, and the angle and required compactness to avoid wire slippage at the
macro level is achieved. A plurality of micro indentations in the groove is
provided to avoid wire to wire strand slippage. The circular configuration of the
form plate with angular winding, results in circular bristle packs which can be
directly assembled to obtain a concentric seal of required size. This results in
better geometric tolerances than a rolled circular seal strip from a rectangular
size.
The sectional view as shown in Fig.2 has two circular grooves with relief groove
within them. The circular groove according to the invention, is for
accommodation the circular strips within necessary geometric tolerance. The wire
is wound with these circular strips in place as these circular plates are meant to
be the base support to the bristles at the end where the will be fused together
by TIG welding. These are also called as half form plates. According to the
invention, the two strips on either side achieve two bristle packs on a single plate
which is unique to this invention. The provision of relive groove, which is again
an another feature to ensure that during the TIG welding process, the circular
strips along with the bristles are adequately separated from the parent
fixture/form plate. Without the relief groove, there is a possibility of TIG welding
spreading to the parent winding plate which makes the process of relieving the
pack from the plate, ineffective.
The wires are wound in several layers to achieve the desired thickness. The
winding plate is fixed on the angular winding machine in which it is located and
oriented with the help several fixtures of the winding machine in such a manner
that each groove is wound in a radial manner. After winding one such groove,
the fixture is rotated by the pitch angle of the groove so that the next groove
becomes aligned for radial winding. The winding machine is designed in such a
manner that the angular winding in achieved sectorally through radial winding by
suitable alignment of the plate with respect to the rotational axes. The picture of
the winding machine is given in Fig. 4.
Three such wound plates are assembled in a circular assembly fixture after
putting the circular brazing strips in position on either side of the wound plates.
Here it is necessary to put full circular rings/ strips wherein before the winding
process the circular strips were cut to size of the winding plate groove
circumference. The mention of full circular strips allows proper alignment of the
outer strips to a required O.D. The sectional view of the wound plates with outer
circular strips in the fixture is shown in Fig. 6.
The assembled wound plates in the fixture are subjected to wire cut EDM to
relieve the wires from the OD side and also the ID side. The necessary wire cut
dimension is shown in Fig.7. While Fig.8 shows the assembly.
After the wire cut machining of the OD and the I.D with allowance for final
machining, the assembly drawing as given in Figure 9 represents clearly the
relieved O.D and I.D of the wires from the wind plates.
In this condition, the bristles on the free wires on the O.D need to be fused
together through TIG welding. Fig. 10 depicts the details that are to be achieved
for the TIG welding process. The sectional view of the assembly after the O.D
and I.D wire cut is shown in Fig. 12 A before TIG welding and in Fig. 12 B after
TIG welding of O.D.
After the TIG welding, the bristles on all the three plates within the assembled
fixture is again sent to EDM wire cut machining for machining of the sectors at
prescribed angles. The angle of the sector is dependent upon number of bristle
packs that are planned to be used for building the seals. If it is proposed to use
6 packs for one seal, the sector angle is 60°while angle of the sector is 90°if it is
proposed use 2 sectors for one concentric seal. The method of using sectoral
bristle packs will also help in partial repair of the damaged seal so as to reduce
the cost and also the down time. The half cut shown at the beginning and end of
the sector as given in Fig. 11 is also an innovative step as the partial groove
helps to reuse the circular fixture again for the next set of same size seals.
After the above operation, the bristle pack which is circular in shape and also
with wires wound at a particular angle is freed from the winding plate and is
ready to be assembled in the seal housing. The individual bristle pack is shown in
Fig. 14.
The six bristle pack sectors are assembled in a circular split seal holder and thus
the assembly of the bristle pack into the seal holder is completed. The view of
the brush seal is shown in Fig. 15. While Fig.16 depicts the sectional and detail
views of the brush seal housing. The design of the seal housing is user specific
and will be designed accordingly.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be
understood that the invention is not to be limited to the disclosed embodiment,
but on the contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended claims.
WE CLAIM
1. A method of manufacturing brush seal for turbo machinery, comprising
the steps of:
- winding a wire on a circular winding plate having a plurality of grooves
configured at an angle corresponding to the wire lay inclination; a
plurality of separators(fins) with depth and thickness so as to achieve
circular seal segments; a multiple groove separators having depth to
maintain desired wire position including wire continuity during the
process of winding; and micro indentation within the groove to restrict
slippage during winding within the each groove, wherein radius on the
top of the fins (separators) is selected to eliminate breakage of the
winding at sharp corners of the winding plate;
- at least two circular grooves of said plurality of grooves disposed on
the winding plate for accommodating the circular strips (thickness <
1mm) formed on either side of the winding plate to produce two bristle
packs and support for TIG welding for the bristles from a single form
plate; and
- providing circular fixtures for stress relieving of the wires from the
plate, and machining all the bristle packs in a single reference direction
for all machining operations including machining of final internal
diameter of the seal to achieve higher productivity, quality of
dimensions, and uniformity of finish.
2. The method as claimed in claim 1, wherein a plurality of relief grooves for
easy separation of the bristle pack from the circular strips after TIG
welding, are provided.
3. The method as claimed in claim 1, wherein direct angular winding in an
angular winding machine is carried-out, wherein the form plate is rotated
about a predetermined axis, and wherein the winding machine having
multi strands with a plurality of spools including tensioners.

ABSTRACT

A method of manufacturing brush seal for turbo machine, comprising the steps of,
winding a wire on a circular winding plate having a plurality of grooves configured at an
angle corresponding to the wire lay inclination; a plurality of separators(fins) with depth
and thickness so as to achieve circular seal segments; a multiple groove separators
having depth to maintain desired wire position including wire continuity during the
process of winding; and micro indentation within the groove to restrict slippage during
winding within the each groove, wherein radius on the top of the fins (separators) is
selected to eliminate breakage of the winding at sharp corners of the winding plate; at
least two circular grooves of said plurality of grooves disposed on the winding plate for
accommodating the circular strips ( thickness < 1mm) formed on either side of the
winding plate to produce two bristle packs and support for TIG welding for the bristles
from a single form plate; and providing circular fixtures for stress relieving of the wires
from the plate, and machining all the bristle packs in a single reference direction for all
machining operations including machining of the final internal diameter of the seal to
achieve higher productivity, quality of dimensions, and uniformity of finish.