U.S. patent application number 09/843711 was filed with the patent office on 2002-10-31 for method and apparatus for refurbishing valves.
This patent application is currently assigned to Kinectrics Inc.. Invention is credited to McGoey, Lennard J..
Application Number | 20020158049 09/843711 |
Document ID | / |
Family ID | 25290804 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020158049 |
Kind Code |
A1 |
McGoey, Lennard J. |
October 31, 2002 |
METHOD AND APPARATUS FOR REFURBISHING VALVES
Abstract
A method and apparatus for in situ refurbishment of valve seats
are disclosed in which a worn valve seat is initially ground to a
flat surface, a buildup of weld metal is deposited on the flat
surface, and the weld buildup is machined to the final dimensions
of the valve seat. The apparatus comprises a machining apparatus
for machining and machining of the valve seat, a gas metal arc
welding apparatus for deposition of weld metal, and support
structures to support the weld buildup as it is being formed.
Preferably, the support structures are in the form of metal chill
blocks which act both to support the buildup of weld metal and to
act as heat sinks and remove excess heat from the buildup,
resulting in a higher quality buildup of metal.
Inventors: |
McGoey, Lennard J.;
(Mississauga, CA) |
Correspondence
Address: |
Mr. Roland H. Joachim
Ridout & Maybee
Suite 2400
One Queen Street East
Toronto
ON
M5C 3B1
CA
|
Assignee: |
Kinectrics Inc.
|
Family ID: |
25290804 |
Appl. No.: |
09/843711 |
Filed: |
April 30, 2001 |
Current U.S.
Class: |
219/76.14 |
Current CPC
Class: |
B23K 9/046 20130101;
Y10T 29/49407 20150115; Y10T 29/49728 20150115 |
Class at
Publication: |
219/76.14 |
International
Class: |
B23K 009/04 |
Claims
What is claimed is:
1. An apparatus for refurbishing a worn valve seat of a high
temperature, high pressure safety valve in situ, said valve seat
being generally circular and being provided at one end of a hollow,
cylindrical valve nozzle which is attached to a valve body of said
valve, said valve seat being accessible through an access opening
in said valve body located above said valve seat, said apparatus
comprising: (a) valve machining means mountable to said valve, said
valve machining means having first cutter means extendable into the
valve body through the access opening for initially machining the
worn valve seat to a flat annular surface having an inner perimeter
and an outer perimeter; (b) a gas metal arc welding apparatus
mountable to the valve having a welding head with a consumable
electrode, the welding head being extendable through the access
opening and being rotatable in a circle located substantially
parallel to and above the flat surface of the valve seat to deposit
a buildup of weld metal from said consumable electrode onto said
flat surface; and (c) a pair of metal support structures for
supporting the buildup of weld metal as it is being deposited by
the gas metal arc welding apparatus, said pair of support
structures comprising: (i) an inner support structure which is
positioned inwardly of the inner perimeter of the flat surface
during deposition of the weld metal buildup and which has an outer,
substantially vertical cylindrical surface which forms an inner
support wall for the weld metal buildup, said inner support wall
having a height sufficient to support the weld metal buildup; and
(ii) an outer support structure which surrounds the outer perimeter
of the flat surface during deposition of the weld metal buildup and
which has an inner, substantially vertical cylindrical surface
which forms an outer support wall for the weld metal buildup, said
outer support wall being located proximate the outer perimeter of
the flat surface and having a height sufficient to support the weld
metal buildup. said valve machining means also having second cutter
means extendable into the valve body through the access opening for
machining the weld metal buildup to a desired final height and
profile.
2. The apparatus of claim 1, wherein said inner support structure
comprises a cylindrical metal sleeve, a cylindrical outer surface
of which corresponds to the substantially vertical cylindrical
surface of the inner support structure.
3. The apparatus of claim 1, wherein said height sufficient to
support the weld metal buildup is about the same as a final height
of the weld metal buildup.
4. The apparatus of claim 3, wherein the inner support structure is
received inside the end of the valve nozzle in which the valve seat
is provided.
5. The apparatus of claim 1, wherein the outer support structure
comprises an annular block of metal, a cylindrical inner surface of
which corresponds to the inner, substantially vertical cylindrical
surface of the outer support structure.
6. The apparatus of claim 5, wherein the annular block of metal
comprising the outer support structure is made up of two C-shaped
segments which are releasably connectable to one another.
7. The apparatus of claim 6, wherein the end of the valve nozzle on
which the valve seat is provided protrudes above a surface of the
valve body immediately adjacent to said valve seat, and wherein the
two C-shaped segments of the outer support structure clamp an outer
cylindrical surface of the end of the valve nozzle.
8. The apparatus of claim 1, wherein said valve machining means
includes a central alignment shaft having a distal end provided
with outwardly expanding clamping means which secure the distal end
of the alignment shaft inside the valve nozzle with the alignment
shaft protruding substantially vertically therefrom, said
interchangeable cutter means being rotatable about said shaft and
being movable axially along said shaft.
9. The apparatus of claim 1, wherein said access opening of said
valve body has a flat outer surface situated above and
substantially parallel to the flat surface of the valve seat, said
apparatus further comprising a mounting plate to which a base of
the gas metal arc welding apparatus is secured, said mounting plate
being attachable to the flat outer surface of the access opening
and having a side extending horizontally outwardly from said access
opening, the outwardly extending side of the mounting plate having
mounting means for attachment to the base of the gas metal arc
welding apparatus.
10. The apparatus of claim 9, wherein the base of the gas metal arc
welding apparatus is provided with mounting apertures which receive
a plurality of studs extending upwardly from the outwardly
extending side of the mounting plate.
11. The apparatus of claim 10, wherein the mounting apertures in
the base of the gas metal arc welding apparatus are in the form of
parallel slots which permit adjustment of the base of the gas metal
arc welding apparatus relative to the access opening.
12. A method for refurbishing a worn valve seat of a high
temperature, high pressure safety valve in situ, said valve seat
being generally circular and being provided at one end of hollow,
cylindrical valve nozzle which is attached to a valve body of said
valve, said valve seat being accessible through an access opening
in said valve body located above said valve seat, the method
comprising: (a) initially machining the worn valve seat to a flat
annular surface having an inner perimeter and an outer perimeter
using a valve machining means mounted to the valve body and having
cutter means extending into the valve body; (b) installing an inner
support structure inwardly of the inner perimeter of the flat
surface of the valve seat, said inner support structure having an
outer, substantially vertical cylindrical surface which is located
proximate the inner perimeter of the flat surface and extends above
the flat surface to at least a predetermined height; (c) installing
an outer support structure outwardly of the outer perimeter of the
flat surface of the valve seat, said outer support structure having
an inner, substantially vertical cylindrical surface which is
located proximate the outer perimeter of the flat surface and
extends above the flat surface to at least said predetermined
height; (d) depositing a buildup of weld metal on said flat surface
between said support structures, using a gas metal arc welding
apparatus mounted to the valve and having a welding head with a
consumable electrode extending through the access opening into the
valve body, the buildup of weld metal being deposited while
rotating the welding head in a circle substantially parallel to and
above the flat surface of the valve seat so as to deposit a buildup
of uniform thickness to approximately the predetermined height; and
(e) machining the buildup of weld metal to the final desired
height, thickness and profile of the refurbished valve seat.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an apparatus and a method for
refurbishing valve seats, and is more particularly concerned with
refurbishing valve seats of high temperature, high pressure safety
valves in situ.
BACKGROUND OF THE INVENTION
[0002] High temperature, high pressure safety valves are commonly
used throughout the steam systems of power generation plants. To
maintain proper sealing, the valve seats of these valves must be
regularly lapped to remove steam cutting and chattering damage.
Once more than 1/4 inch of material has been removed from the valve
seat, the entire valve must be removed and replaced. Replacement of
the valve involves cutting the worn valve from the pipes to which
it is connected and installing a new or reconditioned valve in its
place. This is a time-consuming, expensive procedure.
[0003] Several methods for in situ valve repair are known in the
prior art. For example, U.S. Pat. No. 4,593,445 (Snyder et al.),
issued on Jun. 10, 1986, describes an apparatus and method for
remotely refurbishing valve seats in the steam chest of a turbine
generator. The method described by Snyder comprises grinding away a
sealing layer of the worn valve seat, building up the valve seat by
deposition of weld metal using a gas tungsten arc welder including
a solid wire feeder for feeding chromium-steel wire to the
electrode. The next step of the process comprises machining of the
buildup of weld metal to achieve the desired profile.
[0004] One disadvantage of the Snyder process is that, although,
Gas tungsten arc welding is believed to provide a higher quality
weld than other welding processes, Gas tungsten arc welding can
also be significantly slower, particularly when producing a weld
buildup of a metal such as stainless steel.
SUMMARY OF THE INVENTION
[0005] The present invention provides a method and apparatus for in
situ refurbishment of valve seats in which the valve seat is taken
down to a flat surface, a buildup of weld metal is deposited on the
flat surface by gas metal arc welding, utilizing a consumable
electrode, up to a height and width which is greater than the final
dimensions of the valve seat, and the built up valve seat is then
machined to its final dimensions.
[0006] The use of gas metal arc welding in the process of the
present invention, rather than Gas tungsten arc welding as in the
Snyder et al. patent, permits more rapid buildup of weld metal on
the ground down surface of the valve seat, resulting in improved
efficiency. In general, the use of gas metal arc welding permits a
wider bead of weld metal to be laid down on the valve seat. In
order to assist in maintaining the quality of the buildup, support
structures are provided at the inner perimeter and outer perimeter
of the valve seat to support the buildup as the weld metal is being
laid down and to prevent roll over of the metal beads.
[0007] Furthermore, since the buildup of weld metal is laid down
more rapidly in the method of the invention, the support structures
preferably comprise solid chill blocks made of a metal such as
copper or stainless steel which act as heat sinks to dissipate heat
away from the buildup as it is being laid down. Preferably, a pair
of chill blocks are provided, comprising an inner block in the form
of a solid cylinder or a cylindrical sleeve or ring which is
mounted in the hollow interior of the valve inward of the valve
seat, and an outer chill block comprising two C-shaped rings which
clamp around the upper end of the valve nozzle.
[0008] The use of support structures such as chill blocks permits a
high quality buildup to be maintained through the use of gas metal
arc welding.
[0009] Accordingly, in one aspect the present invention provides an
apparatus for refurbishing a worn valve seat of a high temperature,
high pressure safety valve in situ, the valve seat being generally
circular and being provided at one end of a hollow, cylindrical
valve nozzle which is attached to a valve body of said valve, said
valve seat being accessible through an access opening in said valve
body located above said valve seat, said apparatus comprising: (a)
valve machining means mountable to said valve, said valve machining
means having first cutter means extendable into the valve body
through the access opening for initially machining the worn valve
seat to a flat annular surface having an inner perimeter and an
outer perimeter; (b) a gas metal arc welding apparatus mountable to
the valve having a welding head with a consumable electrode, the
welding head being extendable through the access opening and being
rotatable in a circle located substantially parallel to and above
the flat surface of the valve seat to deposit a buildup of weld
metal from said consumable electrode onto said flat surface; and
(c) a pair of metal support structures for supporting the buildup
of weld metal as it is being deposited by the gas metal arc welding
apparatus, said pair of support structures comprising: (i) an inner
support structure which is positioned inwardly of the inner
perimeter of the flat surface during deposition of the weld metal
buildup and which has an outer, substantially vertical cylindrical
surface which forms an inner support wall for the weld metal
buildup, said inner support wall having a height sufficient to
support the weld metal buildup; and (ii) an outer support structure
which surrounds the outer perimeter of the flat surface during
deposition of the weld metal buildup and which has an inner,
substantially vertical cylindrical surface which forms an outer
support wall for the weld metal buildup, said outer support wall
being located proximate the outer perimeter of the flat surface and
having a height sufficient to support the weld metal buildup; said
valve machining means also having second cutter means extendable
into the valve body through the access opening for machining the
weld metal buildup to a desired final height and profile.
[0010] In another aspect, the present invention provides a method
for refurbishing a worn valve seat of a high temperature, high
pressure safety valve in situ, said valve seat being generally
circular and being provided at one end of hollow, cylindrical valve
nozzle which is attached to a valve body of said valve, said valve
seat being accessible through an access opening in said valve body
located above said valve seat, the method comprising: (a) initially
machining the worn valve seat to a flat annular surface having an
inner perimeter and an outer perimeter using a valve machining
means mounted to the valve body and having cutter means extending
into the valve body; (b) installing an inner support structure
inwardly of the inner perimeter of the flat surface of the valve
seat, said inner support structure having an outer, substantially
vertical cylindrical surface which is located proximate the inner
perimeter of the flat surface and extends above the flat surface to
at least a predetermined height; (c) installing an outer support
structure outwardly of the outer perimeter of the flat surface of
the valve seat, said outer support structure having an inner,
substantially vertical cylindrical surface which is located
proximate the outer perimeter of the flat surface and extends above
the flat surface to at least said predetermined height; (d)
depositing a buildup of weld metal on said flat surface between
said support structures, using a gas metal arc welding apparatus
mounted to the valve and having a welding head with a consumable
electrode extending through the access opening into the valve body,
the buildup of weld metal being deposited while rotating the
welding head in a circle substantially parallel to and above the
flat surface of the valve seat so as to deposit a buildup of
uniform thickness to approximately the predetermined height; and
(e) machining the buildup of weld metal to the final desired
height, thickness and profile of the refurbished valve seat.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will now be described, by way of example only,
with reference to the accompanying drawings in which:
[0012] FIG. 1 is a perspective view of the valve body of a
conventional high temperature, high pressure safety valve;
[0013] FIG. 2 is a perspective view of the valve body of FIG. 1
illustrating the mounting of a mounting plate of the preferred
apparatus to a flat upper surface thereof;
[0014] FIG. 3 is a perspective view of a valve machining apparatus
for use in the preferred method and apparatus of the present
invention;
[0015] FIG. 4 is a preferred gas metal arc welding apparatus for
use in the preferred method and apparatus of the present
invention;
[0016] FIG. 5 is a cross-sectional side elevational view of the
valve body of FIG. 1 with the mounting plate attached thereto, and
with the welding head of the welding apparatus depositing a buildup
of weld metal on the valve seat;
[0017] FIGS. 6 and 7 illustrate machining heads for machining the
buildup of weld metal to the final dimensions of the valve
seat;
[0018] FIG. 8 is a cross-sectional side view of a valve seat prior
to refurbishing;
[0019] FIG. 9 illustrates a valve seat after the initial machining
operation, with the desired profile of the valve seat being shown
in dashed lines;
[0020] FIG. 10 illustrates the buildup of weld metal between the
chill blocks, with the final profile of the valve seat being
indicated by dashed lines;
[0021] FIG. 11 is a cross-sectional side view of the valve seat
after the final machining operation; and
[0022] FIG. 12 is a perspective view of the chill blocks of FIGS. 5
and 10 shown in isolation.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0023] FIG. 1 illustrates a valve body 10 of a typical high
pressure, high temperature safety valve of the type used in steam
systems of power plants. Valve body 10 has an inlet 12, an interior
cavity 14 and an outlet 16 which is arranged at about 90.degree. to
the inlet 12. Steam travels through the valve from inlet 12 to
outlet 16 in the direction indicted by arrows A and B. When
installed in a power plant, the valve preferably has the
orientation shown in FIG. 1.
[0024] Permanently secured inside the inlet 12 of valve body 10 is
a generally cylindrical valve nozzle 18 having a lower end 20
seated in the valve inlet and an upper end 22 which projects above
a bottom wall 24 of the interior cavity 14 of valve body 10. This
is most clearly shown in FIG. 5.
[0025] As also shown in FIG. 5, the cylindrical wall 26 of valve
nozzle 18 has a generally constant thickness in the upper end 22 of
nozzle 18, with the inner surface 28 of wall 26 tapering outwardly
toward the bottom of the valve nozzle 18 in order to gradually
constrict the inlet opening toward the upper end of the valve
nozzle 18.
[0026] As best shown in FIG. 8, the upper end 22 of valve nozzle 18
is provided with a valve seat 30 which is acted upon by a valve
disc (not shown) in order to open and close the valve. FIG. 8 shows
a typical valve seat configuration, the valve seat 30 having a
centrally located annular upstanding lip 32 of substantially
rectangular cross section having a substantially vertical inner
wall 34, a substantially horizontal upper wall 36 and a
substantially vertical outer wall 38. Located inwardly of annular
lip 32 is an inwardly and downwardly sloped portion 40 extending
from the vertical inner wall 34 of lip 32 to the substantially
vertical inner surface 28 of wall 26 at the upper end 22 of valve
nozzle 18. To the outside of annular lip 32 is a horizontal portion
42 extending between the vertical outer wall 38 of lip 32 and the
outer surface of valve nozzle 18. To enhance clarity of the
drawings, it is to be noted that the size of the lip 32 in relation
to the remainder of nozzle 18 is exaggerated in the drawings.
[0027] As shown in FIG. 1, the valve body 10 has a flat,
substantially horizontal upper surface 46 provided with a plurality
of threaded mounting studs 48 to which the bonnet (not shown) of
the valve is bolted. The upper surface 46 of valve body 10 is
provided with an opening 50 through which access can be gained to
valve seat 30 once the valve is disassembled in situ. Once the
height of the valve seat 30 has been reduced by 1/4 inch from its
original height by wear and refinishing, the method and apparatus
of the present apparatus are preferably applied in situ in order to
restore the valve seat 30 to its original dimensions. Having now
described the valve body 10 and valve seat 30, a preferred
apparatus according to the present invention will now be described
below.
[0028] The preferred apparatus of the invention comprises means for
shaping the valve seat and means for depositing new metal to build
up the valve seat.
[0029] The shaping means preferably comprises a portable machining
apparatus 52, as shown in FIG. 3, having a handle 54, a motor
housing 56, a rotating cutter 58, an alignment shaft 60 with an
outwardly expanding clamping mechanism 62 located at its distal end
64, and a hand wheel 66 to raise and lower cutter 58. The machining
apparatus 52 is attached to valve body 10 by inserting the distal
end 64 of alignment shaft 60 into the valve nozzle 18, turning a
tightening nut or the like (not shown) to cause the clamping
mechanism 62 to exert outward pressure on the inner surface 28 of
valve nozzle 18, thereby causing the alignment shaft 60 and the
valve nozzle 18 to be aligned in the same direction.
[0030] Once the machining apparatus 52 is clamped in the valve
nozzle 18, the rotating cutter is rotated in a plane perpendicular
to the alignment shaft 60 and is lowered by rotating hand wheel 66
to contact the valve seat 30.
[0031] The means for adding metal buildup to the valve seat
preferably comprises a welding apparatus 68 as illustrated in FIG.
4. Welding apparatus 68 comprises a base plate 70 having a pair of
elongate openings 72 for securing the welding apparatus 68 to the
valve body 10. Extending vertically upwardly from the base plate 70
is a height adjustable mounting shaft 74 to which a welding device
76 is secured. Welding device 76 includes a generally downwardly
extending hollow tube 78, the distal end 80 of which contains a
welding nozzle 82, a contact tip 115 and a consumable electrode
116. The tube 78 has upper and lower vertically extending portions
84 and 86 which are connected by a central portion 85 which extends
downwardly and radially outwardly, so that the lower vertical
portion 86 is spaced radially outwardly from the axis about which
tube 78 is rotated. Therefore, rotation of the tube 78 of the
welding device 76 causes the welding head 82 to rotate in a circle
having substantially the same diameter as valve nozzle 18.
[0032] The welding apparatus 68 is preferably supported on a base
plate 106 which is mounted to the flat upper surface 46 of valve
body 10 as shown in FIG. 2. Base plate 106 has an aperture 108
which registers with the opening 50 in valve body 10 and mounting
apertures 110 which allow securement of base plate 106 to threaded
studs 48 using nuts 107. In addition, base plate 106 has one side
112 extending outwardly of the aperture 108, the outwardly
extending side 112 having a pair of threaded mounting studs 114 to
which the base plate 70 of the welding apparatus 68 is secured.
[0033] Preferably, the welding device is a gas metal arc welding
device. Gas metal arc welding is an example of open arc welding
using a fusible electrode, which is to be distinguished from gas
tungsten arc welding which uses a non-fusible tungsten electrode.
As used throughout this application, the term "gas metal arc
welding" includes "flux cored arc welding". Although gas metal arc
welding can be significantly faster than gas tungsten arc welding,
it is generally believed that gas tungsten arc welding will provide
a higher quality buildup with fewer inconsistencies than gas metal
arc welding. However, the apparatus of the invention is capable of
providing a high quality weld buildup with gas tungsten arc welding
due to the use of support structures to support the metal buildup
during the welding operation. Preferred examples of support
structures are now described below.
[0034] Preferred support structures are shown in isolation in FIG.
12, comprising an inner chill block 88 and an outer chill block 90
comprising a pair of C-shaped segments 92 and 94. As shown in FIG.
10, inner chill block 88 comprises a hollow metal sleeve having a
cylindrical outer surface which provides an inner support for the
metal buildup during the welding operation. As shown in FIG. 10,
the inner chill block 88 is mounted inside the upper end 22 of the
valve nozzle 18, such that its outer surface 96 provides an inner
support for the weld buildup.
[0035] Segments 92 and 94 are assembled to form annular outer chill
block 90, the substantially vertically extending inner surfaces 98
and 100 of segments 92 and 94 providing an outer support for the
weld buildup. Although the support structures shown in the
preferred embodiment of the invention comprise chill blocks 88 and
90, alternate support structures could also be used. For example,
the inner chill block may be replaced by a solid cylinder of metal
or by a support ring having thinner walls than those of chill block
88. However, it is particularly preferred that the support
structures have relatively thick walls as shown in the drawings, in
order to act as heat sinks and remove heat from the metal deposited
by the welding device. The inventors have found that this improves
the quality of the weld buildup. Preferably, the chill blocks 88
and 90 are comprised of copper, but may instead be formed of
another metal such as stainless steel.
[0036] The operation of the preferred apparatus will now be
described below.
[0037] FIG. 8 illustrates valve nozzle 18 with valve seat 30 seated
in valve body 10 prior to refurbishment by the method of the
invention. Firstly, the valve is disassembled to expose the valve
seat 30 through opening 50 as shown in FIG. 1. Next, the machining
apparatus 52 is attached to the valve body 10 by inserting the
alignment shaft 60 downwardly through the opening 50 and into the
valve nozzle 18. The clamping device 62 is then expanded outwardly
to exert outward pressure on the inner surface 28 of valve nozzle
18, thereby securing the machining apparatus 52 with alignment
shaft 60 parallel to the valve nozzle 18.
[0038] Next, the rotating cutter 58 is activated and is lowered to
the valve seat 30 by turning hand wheel 66. In this initial
machining operation, the cutter 58 is fitted with a flat cutting
head 102 as shown in FIG. 3 in order to machine the valve seat 30
to below the lower end of the inwardly sloped portion 40 as
illustrated in FIG. 9. After the initial machining operation, the
valve seat 30 has a flat upper surface 104 upon which new metal can
be built up.
[0039] Following the initial machining operation, the inner chill
block 88 is inserted into the upper end of valve nozzle 18 such
that its outer surface 96 provides an inner support wall for the
weld metal buildup. Similarly, the outer chill block 90 is
assembled from C-shaped segments 92 and 94 to clamp the outer
surface 44 of valve nozzle 18, thereby providing an outer support
wall for the weld metal buildup. Both the inner and outer chill
blocks 88 and 90 extend above the flat surface 104 of valve seat 30
to a height which is about the same as the final height of the weld
metal buildup. Preferably, the chill blocks have a total height of
at least about 1 inch and extend above the flat surface 104 of
valve seat 30 by about 1/2 to 1 inch. The inner chill block 88
preferably has a diameter to be closely received inside the valve
nozzle, preferably 2.5 to 3 inches. The outer chill block 90
preferably has a thickness of about 1/2 to 3/4 inches.
[0040] Next, the base plate 106 is secured to the flat upper
surface 46 of valve body 10 as described above. The welding
apparatus 68 is then attached to the base plate 106 with the tube
78 containing the welding head 82 extending downwardly through the
opening 50 in the valve body 10. In order to ensure proper
positioning of the welding head 82 relative to valve seat 30 as in
FIG. 5, the elongate openings 72 in base plate 70 of the welding
apparatus 68 allow front to rear alignment of the welding apparatus
68 relative to the valve seat 30.
[0041] After mounting and positioning the welding apparatus 68, the
welding operation is commenced by rotating tube 78 about a vertical
axis and depositing weld metal from consumable electrode 116 on the
flat upper surface 104 of valve seat 30. Rotation of the welding
head 82 and deposition of weld metal is continued until the weld
buildup reaches a height dimension which is at least as great as
the final height dimension of the valve seat, as illustrated in
FIG. 10, showing the height of the final weld buildup being
slightly higher than the tops of the chill blocks 88 and 90, and
being greater than the final dimensions of the valve seat 30 shown
in dashed lines.
[0042] After the completion of the weld metal buildup as shown in
FIG. 10, the welding apparatus 68 is removed from the valve body 10
and the machining apparatus 52 is re-installed as described above.
The desired profile of the valve seat is restored to that shown in
FIG. 11 by using a plurality of cutter heads, two of which are
illustrated in FIGS. 6 and 7. The cutter head 118 shown in FIG. 6
has a first cutter 120 which restores the vertical inner wall 34 of
annular lip 32 and the inwardly sloped portion 40, a second cutter
122 which restores the vertical outer wall 38 and the outer
horizontal portion 42 of the valve seat 30, and a third cutter 123
which restores the vertical portion of inner surface 28. Cutter
head 124 illustrated in FIG. 7 includes a first cutter 126 to
restore the horizontal upper wall 36 of the annular lip 32, and a
second cutter 128 which restores the outer surface 44 of the valve
seat 30. Once the profile of the valve seat 30 is restored by rough
and fine machining, it is manually lapped in order to provide a
smooth finish to the restored seat. Preferably, the final
dimensions of the restored valve seat 30 are substantially
identical to the dimensions of a new valve seat.
[0043] Although the invention has been described in connection with
certain preferred embodiments, it is not intended to be limited
thereto. Rather, the invention includes all embodiments which may
fall within the scope of the following claims.
* * * * *