U.S. patent application number 15/563816 was filed with the patent office on 2018-04-05 for snap-on liner retention device.
This patent application is currently assigned to Hunting Titan, Inc.. The applicant listed for this patent is Hunting Titan, Inc.. Invention is credited to William R Collins, Charles Levine, Debra Christine McDonald, Aaron Lee McGregor, Laura Montoya Ashton, Bradley Dean Schulte, Shane Matthew Wilson.
Application Number | 20180094910 15/563816 |
Document ID | / |
Family ID | 57006282 |
Filed Date | 2018-04-05 |
United States Patent
Application |
20180094910 |
Kind Code |
A1 |
Montoya Ashton; Laura ; et
al. |
April 5, 2018 |
Snap-on Liner Retention Device
Abstract
A shaped charge retainer ring for use in containing the liner of
a shaped charge and the explosive material.
Inventors: |
Montoya Ashton; Laura;
(Ithaca, NY) ; Collins; William R; (Burleson,
TX) ; Levine; Charles; (Waxahachie, TX) ;
McDonald; Debra Christine; (Whitney, TX) ; McGregor;
Aaron Lee; (Hillsboro, TX) ; Schulte; Bradley
Dean; (Cleburne, TX) ; Wilson; Shane Matthew;
(Waxahachie, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hunting Titan, Inc. |
Pampa |
TX |
US |
|
|
Assignee: |
Hunting Titan, Inc.
Pampa
TX
|
Family ID: |
57006282 |
Appl. No.: |
15/563816 |
Filed: |
April 1, 2016 |
PCT Filed: |
April 1, 2016 |
PCT NO: |
PCT/US16/25725 |
371 Date: |
October 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62142099 |
Apr 2, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42B 1/028 20130101;
F42D 3/04 20130101; F42B 3/08 20130101; E21B 43/119 20130101; F42B
1/02 20130101; F42B 1/036 20130101 |
International
Class: |
F42B 1/028 20060101
F42B001/028; F42B 3/08 20060101 F42B003/08; F42B 1/036 20060101
F42B001/036 |
Claims
1. A shaped charge apparatus comprising: a shaped charge case with
an axis, an inner surface, an outer surface, and a top surface; and
at least one circumferential retaining means for retaining a ring
on the outer surface.
2. The apparatus of claim 1, wherein the at least one retaining
means on the outside surface of the shaped charge case is a
circumferential groove.
3. The apparatus of claim 2, wherein the at least one retaining
means is a plurality of circumferential grooves.
4. The apparatus of claim 1, wherein the retaining means is a
thread.
5. The apparatus of claim 4, wherein the thread is a buttress
thread.
6. The apparatus of claim 1, wherein the retaining means is a
plurality of ridges.
7. The apparatus of claim 1, wherein retaining means is a plurality
of detents.
8. The apparatus of claim 1, wherein retaining means is a lip.
9. A shaped charge retaining system comprising: a shaped charge
case with an axis, an inner surface, an outer surface, and a top
surface; at least one circumferential groove on the outer surface;
a L-shaped inner retainer ring with an inner radial surface, an
outer radial surface, a lower axial surface, and an upper axial
surface, wherein the lower axial surface is adjacent to the top
surface of the shaped charge and the outer radial surface is
adjacent to the inner surface of the shaped charge; a L-shaped
outer retainer ring having an upper axial surface, a lower axial
surface, an inner radial surface, and an outer radial surface,
wherein the inner radial surface includes at least one
circumferential groove that interfaced with the shaped charge outer
surface circumferential groove; a liner with an inner surface and
an outer surface, wherein the liner is restrained axially by the
inner retainer ring and the outer retainer ring; and an explosive
material located between the outer surface of the liner and the
inner surface of the shaped charge case.
10. The apparatus of claim 9, wherein the at least one
circumferential groove on the outside surface of the shaped charge
case is a plurality of circumferential grooves.
11. The apparatus of claim 10, wherein the at least one
circumferential groove on the inner radial surface of the outer
retainer ring is a plurality of circumferential grooves.
12. The apparatus of claim 9, wherein the inner retainer ring is
composed of plastic.
13. The apparatus of claim 9, wherein the outer retainer ring is
composed of plastic.
14. The apparatus of claim 9, wherein the outer retainer ring and
the inner retainer ring are integrally formed into a single
retainer ring.
15. The apparatus of claim 12, wherein the inner retainer ring is
rated to function up to 400 degrees Fahrenheit.
16. The apparatus of claim 13, wherein the outer retainer ring is
rated to function up to 400 degrees Fahrenheit.
17. The apparatus of claim 9, wherein the inner retainer ring has a
low electrical conductivity.
18. The apparatus of claim 9, wherein the outer retainer ring has a
low electrical conductivity.
19. The apparatus of claim 9, wherein the inner retainer ring is
manufactured using an additive manufacturing process.
20. The apparatus of claim 9, wherein the outer retainer ring is
manufactured using an additive manufacturing process.
21. A method for making a shaped charge comprising: forming
explosive material inside of a shaped charge case; forming a liner
over the explosive material; and installing a first retainer ring
onto the shaped charge case, wherein the retainer ring prevents
axial movement of the liner and the explosive material within said
shaped charge case.
22. The method of claim 21, further comprising installing a second
retainer ring to the shaped charged case.
23. The method of claim 21, further comprising installing the
shaped charge in a charge tube.
24. The method of claim 22, wherein the second retainer ring
prevents axial movement of the first retainer ring.
25. The method of claim 21, wherein the forming a liner results in
a substantially frusto-conical shape.
26. The method of claim 21, wherein the forming explosive material
results in a substantially frusto-conical shape.
27. The method of claim 21 further comprising electrically
isolating the shaped charge.
28. The method of claim 21 further comprising manufacturing the
first retainer ring.
29. The method of claim 21 further comprising manufacturing the
second retainer ring.
30. The method of claim 28 wherein the manufacturing of the first
retainer ring includes additive manufacturing.
31. The method of claim 29 wherein the manufacturing of the second
retainer ring includes additive manufacturing.
32. A shaped charge comprising: A case having an apex end, an open
end having a rim, and a cavity extending into case from the open
end; a liner fitted into the open end of the case; an electrically
insulating ring adapted to fit over the rim of the open end of the
case.
33. The shaped charge of claim 32 wherein: the rim of the open end
of the case is substantially circular and comprises a substantially
cylindrical inner surface and a substantially cylindrical outer
surface; and the insulating ring is substantially circular and
comprises a substantially cylindrical inner surface and a
substantially cylindrical outer surface.
34. The shaped charge of claim 33 wherein: the inner surface of the
insulating ring has a smaller diameter than the inner surface of
the open end of the case.
35. The shaped charge of claim 33 wherein the outer surface of the
rim of the case comprises a retention feature.
36. The shaped charge of claim 35 wherein the retention feature
comprises a raised circumferential ridge.
37. The shaped charge of claim 35 wherein the retention feature
comprises a plurality of raised circumferential ridges.
38. The shaped charge of claim 35 wherein the retention feature
comprises a circumferential groove.
39. The shaped charge of claim 35 wherein the retention feature
comprises a plurality of circumferential grooves.
40. The shaped charge of claim 33 wherein the inner surface of the
rim of the case comprises a retention feature.
41. The shaped charge of claim 40 wherein the retention feature
comprises a raised circumferential ridge.
42. The shaped charge of claim 40 wherein the retention feature
comprises a plurality of raised circumferential ridges.
43. The shaped charge of claim 40 wherein the retention feature
comprises a circumferential groove.
44. The shaped charge of claim 40 wherein the retention feature
comprises a plurality of circumferential grooves.
45. The shaped charge of claim 33 wherein the wherein the inner
surface of the insulating ring comprises a retention feature.
46. The shaped charge of claim 45 wherein the retention feature
comprises a raised circumferential ridge.
47. The shaped charge of claim 45 wherein the retention feature
comprises a plurality of raised circumferential ridges.
48. The shaped charge of claim 45 wherein the retention feature
comprises a circumferential groove.
49. The shaped charge of claim 45 wherein the retention feature
comprises a plurality of circumferential grooves.
50. The shaped charge of claim 33 wherein the wherein the outer
surface of the insulating ring comprises a retention feature.
51. The shaped charge of claim 50 wherein the retention feature
comprises a raised circumferential ridge.
52. The shaped charge of claim 50 wherein the retention feature
comprises a plurality of raised circumferential ridges.
53. The shaped charge of claim 50 wherein the retention feature
comprises a circumferential groove.
54. The shaped charge of claim 50 wherein the retention feature
comprises a plurality of circumferential grooves.
55. The shaped charge of claim 32 wherein: the rim of the open end
of the case is substantially circular and comprises a substantially
cylindrical inner surface and a substantially cylindrical outer
surface; and the insulating ring comprises a substantially circular
end face, a substantially cylindrical inner wall extending axially
from the end face, and a substantially cylindrical outer wall
extending axially from the end face.
56. The shaped charge of claim 55 wherein the outer wall of the
insulating ring is adapted to fit outside the outer surface of the
rim of the case.
57. The shaped charge of claim 55 wherein the outer wall of the
insulating ring comprises a retention feature adapted to engage a
retention feature on the outer surface of the rim of the case.
58. The shaped charge of claim 55 wherein the inner wall of the
insulating ring is adapted to fit inside the inner surface of the
rim of the case.
59. The shaped charge of claim 55 wherein the inner wall of the
insulating ring comprises a retention feature adapted to engage a
retention feature on the inner surface of the rim of the case.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 62/142,099, filed Apr. 2, 2015.
BACKGROUND OF THE INVENTION
[0002] Generally, when completing a subterranean well for the
production of fluids, minerals, or gases from underground
reservoirs, several types of tubulars are placed downhole as part
of the drilling, exploration, and completions process. These
tubulars can include casing, tubing, pipes, liners, and devices
conveyed downhole by tubulars of various types. Each well is
unique, so combinations of different tubulars may be lowered into a
well for a multitude of purposes.
[0003] A subsurface or subterranean well transits one or more
formations. The formation is a body of rock or strata that contains
one or more compositions. The formation is treated as a continuous
body. Within the formation hydrocarbon deposits may exist.
Typically a wellbore will be drilled from a surface location,
placing a hole into a formation of interest. Completion equipment
will be put into place, including casing, tubing, and other
downhole equipment as needed. Perforating the casing and the
formation with a perforating gun is a well-known method in the art
for accessing hydrocarbon deposits within a formation from a
wellbore.
[0004] Explosively perforating the formation using a shaped charge
is a widely known method for completing an oil well. A shaped
charge is a term of art for a device that when detonated generates
a focused explosive output. This is achieved in part by the
geometry of the explosive in conjunction with a liner in the
explosive material. Generally, a shaped charge includes a metal
case that contains an explosive material with a concave shape,
which has a thin metal liner on the inner surface. Many materials
are used for the liner; some of the more common metals include
brass, copper, tungsten, and lead. When the explosive detonates the
liner metal is compressed into a super-heated, super pressurized
jet that can penetrate metal, concrete, and rock.
[0005] A perforating gun has a gun body. The gun body typically is
composed of metal and is cylindrical in shape. Within a typical gun
tube is a charge holder, which is a tube that is designed to hold
the actual shaped charges. The charge holder will contain cutouts
called charge holes where the shaped charges will be placed.
[0006] A shaped charge is a term of art for a device that when
detonated generates a focused explosive output. This is achieved in
part by the geometry of the explosive in conjunction with a liner
in the explosive material. Many materials are used for the liner;
some of the more common metals include brass, copper, tungsten, and
lead. When the explosive detonates the liner metal is compressed
into a super-heated, super pressurized jet that can penetrate
metal, concrete, and rock.
[0007] Within a typical gun tube is a charge holder, which is a
tube that is designed to hold the actual shape charges. The charge
holder will contain cutouts called charge holes where the shape
charges will be placed. A typical shaped charge is carried in a
cylindrical perforating gun.
[0008] Typically, the liner is held within the shaped charge case
using an adhesive material. Adhesives present issues during the
manufacturing process that incur additional costs and have
environmental issues. A need exists for a means of cheaply
retaining a liner and explosive material within the shaped charge
case without using adhesives. Additionally, it is desirable to
place an insulating and non-sparking material on the shaped charge
cases for a variety of reasons including safety.
SUMMARY OF EXAMPLES OF THE INVENTION
[0009] An example embodiment is a shaped charge apparatus having a
shaped charge case with an axis, an inner surface, an outer
surface, and a top surface, and at least one circumferential groove
on the outer surface. An L-shaped inner retainer ring with an inner
radial surface, an outer radial surface, a lower axial surface, and
an upper axial surface may be attached to the shaped charge case.
The lower axial surface of the inner retainer ring may be adjacent
to the top surface of the shaped charge and the outer radial
surface maybe adjacent to the inner surface of the shaped charge.
Another L-shaped outer retainer ring having an upper axial surface,
a lower axial surface, an inner radial surface, and an outer radial
surface, may be attached to the top of the L-shaped inner ring. The
inner radial surface of the outer retainer ring may include at
least one circumferential groove interfaced with the shaped charge
outer surface circumferential groove. The shaped charge may include
a liner with an inner surface and an outer surface. The liner may
be restrained axially by the inner retainer ring and the outer
retainer ring. An explosive material may be located between the
outer surface of the liner and the inner surface of the shaped
charge case.
[0010] A variation of the example embodiment may include the one
circumferential groove on the outside surface of the shaped charge
case being a plurality of circumferential grooves. At least one
circumferential groove on the inner radial surface of the outer
retainer ring may be a plurality of circumferential grooves. The
inner retainer ring may be composed of plastic. The outer retainer
ring may be composed of plastic. The outer retainer ring and the
inner retainer ring may be integrally formed into a single retainer
ring. The inner retainer ring may be rated to function up to 400
degrees Fahrenheit. The outer retainer ring may be rated to
function up to 400 degrees Fahrenheit. The inner retainer ring may
have a low electrical conductivity. The outer retainer ring may
have a low electrical conductivity. The inner retainer ring may be
manufactured using an additive manufacturing process. The outer
retainer ring may be manufactured using an additive manufacturing
process.
[0011] Another example embodiment may include a method for making a
shaped charge by forming explosive material inside of a shaped
charge case, forming a liner over the explosive material, and
installing a first retainer ring onto the shaped charge case. The
retainer ring may prevent axial movement of the liner and the
explosive material within said shaped charge case.
[0012] A variation of the example embodiment may further include
installing a second retainer ring to the shaped charged case. The
example may include installing the shaped charge in a charge tube.
The second retainer ring may prevent axial movement of the first
retainer ring. The forming of a liner may result in a substantially
frusto-conical shape. The forming of explosive material may result
in a substantially frusto-conical shape. The example embodiment may
include electrically isolating the shaped charge. It may include
manufacturing the first retainer ring. It may include manufacturing
the second retainer ring. The manufacturing of the first retainer
ring may include an additive manufacturing process. The
manufacturing of the second retainer ring may include an additive
manufacturing process.
[0013] Another example embodiment may include a shaped charge with
a case having an apex end, an open end having a rim, and a cavity
extending into case from the open end. It may have a liner fitted
into the open end of the case. It may have an electrically
insulating ring adapted to fit over the rim of the open end of the
case.
[0014] A variation of the example embodiment may include the rim of
the open end of the case being substantially circular. It may have
a substantially cylindrical inner surface and a substantially
cylindrical outer surface and the insulating ring being
substantially circular and a substantially cylindrical inner
surface and a substantially cylindrical outer surface. The inner
surface of the insulating ring may have a smaller diameter than the
inner surface of the open end of the case. The outer surface of the
rim of the case may have a retention feature. The retention feature
may include a raised circumferential ridge, a plurality of raised
circumferential ridges, a circumferential groove, or a plurality of
circumferential grooves. The inner surface of the rim of the case
may have a retention feature that may include a raised
circumferential ridge, a plurality of raised circumferential
ridges, a circumferential groove or a plurality of circumferential
grooves.
[0015] Further variations of the embodiment may include the inner
surface of the insulating ring with a retention feature. The
retention feature may include a raised circumferential ridge, a
plurality of raised circumferential ridges, a circumferential
groove, or a plurality of circumferential grooves.
[0016] Further variations of the embodiment may include the outer
surface of the insulating ring having a retention feature of a
raised circumferential ridge, a plurality of raised circumferential
ridges, a circumferential groove, or a plurality of circumferential
grooves.
[0017] Further variations of the embodiment disclosed may include
the rim of the open end of the case being substantially circular
and having a substantially cylindrical inner surface. It may also
have a substantially cylindrical outer surface. It may also have
the insulating ring having a substantially circular end face, a
substantially cylindrical inner wall extending axially from the end
face, and a substantially cylindrical outer wall extending axially
from the end face. The outer wall of the insulating ring may be
adapted to fit outside the outer surface of the rim of the case.
The outer wall of the insulating ring may include a retention
feature adapted to engage a retention feature on the outer surface
of the rim of the case. The inner wall of the insulating ring may
be adapted to fit inside the inner surface of the rim of the case.
The inner wall of the insulating ring may have a retention feature
adapted to engage a retention feature on the inner surface of the
rim of the case.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] For a thorough understating of the present invention,
reference is made to the following detailed description of the
preferred embodiments, taken in conjunction with the accompanying
drawings in which reference numbers designate like or similar
elements throughout the several figures. Briefly:
[0019] FIG. 1 is cross section of an example perforating gun.
[0020] FIG. 2 is a cross section view of a shaped charge with an
inner retainer ring and an outer retainer ring.
[0021] FIG. 3 is a cross section view of a shaped charge with a
single retainer ring.
DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION
[0022] In the following description, certain terms have been used
for brevity, clarity, and examples. No unnecessary limitations are
to be implied therefrom and such terms are used for descriptive
purposes only and are intended to be broadly construed. The
different apparatus, systems and method steps described herein may
be used alone or in combination with other apparatus, systems and
method steps. It is to be expected that various equivalents,
alternatives, and modifications are possible within the scope of
the appended claims.
[0023] Referring to FIG. 1, a typical perforating gun 10 includes a
gun body 11 that houses the shaped charges 12. The gun body 11
contains end fittings 16 and 20 which secures the charge tube 18
into place. The charge tube 18 has charge holes 23 that are
openings where shaped charges 12 may be placed. The gun body 11 has
threaded ends 14 that allow it to be connected to a series of
perforating guns 10 or to other downhole equipment depending on the
job requirement. Other design variations may use ends that are
bolted together. In FIG. 1, a 60 degree phase gun is shown where
each shaped charge 12 is rotated about the center axis by 60
degrees from one shaped charge to the next. Each shaped charge 12
has a corresponding scallop 21 milled into the gun body 11. Other
embodiments of this design are possible including zero degree phase
guns, where all the shaped charges are aligned. Other end fittings
or connections could be used in lieu of threaded fittings, such as
bolted fittings.
[0024] Referring to FIG. 2, an example embodiment is a shaped
charge 116 with a shaped charge case 111 having an axis 117, an
inner surface 108, an outer surface 118, and a top surface 107.
Shaped charge case 111 has circumferential groove 103 on the outer
surface 118. An L-shaped inner retainer ring 115 with an inner
radial surface 109, an outer radial surface 119, a lower axial
surface 120, and an upper axial surface 106 is attached to the top
surface 107 of the shaped charge case 111. The lower axial surface
120 is adjacent to the top surface 107 of the shaped charge case
111. The outer radial surface 119 is adjacent to the inner surface
108 of the shaped charge case 111. A L-shaped outer retainer ring
102 having an upper axial surface 122, a lower axial surface 121,
an inner radial surface 104, and an outer radial surface 105
engages with the shaped charge case 111. Its inner radial surface
104 includes at least one circumferential groove 123 that is
interfaced with the shaped charge outer surface circumferential
groove 103. The shaped charge 116 includes a liner 113 with an
inner surface 124 and an outer surface 125. The liner 113 is
restrained axially by the inner retainer ring 115 and the outer
retainer ring 102. An explosive material 112 is located between the
outer surface 125 of the liner 113 and the inner surface 108 of the
shaped charge case 111. The shaped charge case 111 has an apex end
126.
[0025] Another example embodiment may include the shaped charge
case 111 having an axis 117, an inner surface 108, an outer surface
118, and a top surface 107 and at least one circumferential
retaining feature 103 for retaining a ring on the outer surface.
The retaining feature 103 may be a circumferential groove, a
plurality of circumferential grooves, a thread, a buttress thread,
a plurality of ridges, a plurality of detents, a lip, or some other
retaining means that is well known in the art.
[0026] A variation of the example embodiment may include a
plurality of circumferential grooves 103 on the outside surface 118
of the shaped charge case 111. The inner retainer ring 115 may be
composed of plastic. The outer retainer ring 102 may be composed of
plastic. The inner retainer ring 115 may be rated to function up to
400 degrees Fahrenheit. The outer retainer ring 102 may be rated to
function up to 400 degrees Fahrenheit. The inner retainer ring 115
probably has a low electrical conductivity. The outer retainer ring
102 probably has a low electrical conductivity. The inner retainer
ring 115 may be manufactured using an additive manufacturing
process. The outer retainer ring 102 may be manufactured using an
additive manufacturing process.
[0027] Another example embodiment includes a method for making a
shaped charge by forming explosive material 112 inside of a shaped
charge case 111, forming a liner 113 over the explosive material
112, and installing a first retainer ring 115 onto the shaped
charge case 111. The retainer ring 115 prevents axial movement of
the liner 113 and the explosive material 112 within said shaped
charge case 111.
[0028] A variation of the example embodiment includes installing a
second retainer ring 102 to the shaped charged case 111. It could
also include installing the shaped charge 116 in a charge tube 18.
The second retainer ring 102 may prevent axial movement of the
first retainer ring 115. The forming of a liner 113 may result in a
substantially frusto-conical shape. The forming explosive material
112 may result in a substantially frusto-conical shape. The example
embodiment may further include electrically isolating the shaped
charge 116. It may include manufacturing the first retainer ring
115. It may further include manufacturing the second retainer ring
102. The manufacturing of the first retainer ring 115 may include
an additive manufacturing process. The manufacturing of the second
retainer ring 102 may include an additive manufacturing
process.
[0029] The outer retainer ring 102 and the inner retainer ring 115
may be integrally formed into a single retainer ring 215 as shown
in FIG. 3. Another example embodiment may include a shaped charge
216 with a case 211 having an apex end 226, an open end 208 having
a rim 230, and a cavity extending into case from the open end 208.
A liner 213 is fitted into the open end of the case. An
electrically insulating ring 215 is fitted over the rim 230 of the
open end 208 of the case 211. Explosive material 212 is located
between the liner 213 and the charge case 211
[0030] A variation of the example embodiment may include the rim
230 of the open end 208 of the case 211 being substantially
circular and having a substantially cylindrical inner surface 214.
It have include a substantially cylindrical outer surface 218. The
insulating ring 215 may be substantially circular. It may include a
substantially cylindrical inner surface 231 and a substantially
cylindrical outer surface 232. The inner surface 231 of the
insulating ring 215 may have a smaller diameter than the inner
surface 214 of the open end 208 of the case 211. The outer surface
218 of the rim 230 of the case 211 may include a retention feature
203 such as a raised circumferential ridge, a plurality of raised
circumferential ridges, a circumferential groove, or a plurality of
circumferential grooves.
[0031] In other examples the inner surface 214 of the rim of the
case may include a retention feature 203 such as a raised
circumferential ridge, a plurality of raised circumferential
ridges, a circumferential groove, or a plurality of circumferential
grooves. Further variations of the embodiment may include the inner
surface 231 of the insulating ring 215 having a retention feature.
The retention feature may include a retention feature 203 such as a
raised circumferential ridge, a plurality of raised circumferential
ridges, a circumferential groove, or a plurality of circumferential
grooves.
[0032] Further variations of the embodiment may include the outer
surface 232 of the insulating ring 215 has a retention feature 233.
The retention feature 233 may include a retention feature 203 such
as a raised circumferential ridge, a plurality of raised
circumferential ridges, a circumferential groove, or a plurality of
circumferential grooves.
[0033] Further variations of the embodiment disclosed may include
the rim 230 of the open end 208 of the case 211 being substantially
circular. It may have a substantially cylindrical inner surface 214
and a substantially cylindrical outer surface 218. The insulating
ring 215 may have a substantially circular end face 202, a
substantially cylindrical inner wall 235 extending axially from the
end face 202, and a substantially cylindrical outer wall 234
extending axially from the end face 202. The outer wall 234 of the
insulating ring 215 may be adapted to fit outside the outer surface
of the rim 230 of the case 211. The outer wall 234 of the
insulating ring 215 may include a retention feature 233 adapted to
engage a retention feature 203 on the outer surface 218 of the rim
230 of the case 211. The inner wall 235 of the insulating ring 215
may be adapted to fit inside the inner surface 214 of the rim 230
of the case 211. Alternatively, the inner wall 235 of the
insulating ring 215 may include a retention feature adapted to
engage a retention feature on the inner surface of the rim 230 of
the case 211.
[0034] Although the invention has been described in terms of
particular embodiments which are set forth in detail, it should be
understood that this is by illustration only and that the invention
is not necessarily limited thereto. Alternative embodiments and
operating techniques will become apparent to those of ordinary
skill in the art in view of the present disclosure. Accordingly,
modifications of the invention are contemplated which may be made
without departing from the spirit of the claimed invention.
* * * * *