(12) United States Patent
`Tassaroli
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,943,943 B2
`Feb. 3, 2015
`
`USOO8943943B2
`
`(54) EXPLOSIVE CARRIEREND PLATES FOR
`CHARGE-CARRIERS USED IN
`PERFORATING GUNS
`
`(71)
`(72)
`(73)
`(*)
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`(21)
`(22)
`(65)
`
`(51)
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`(52)
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`(58)
`
`Applicant: Tassaroli S.A., Mendoza (AR)
`
`Inventor: Carlos Jose Tassaroli, Mendoza (AR)
`Assignee: Tassaroli S.A., Mendoza (AR)
`Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 90 days.
`Appl. No.: 13/672,801
`
`Filed:
`
`Nov. 9, 2012
`
`Prior Publication Data
`US 2013/O1 18342 A1
`May 16, 2013
`
`(2006.01)
`(2006.01)
`(2006.01)
`
`Int. C.
`F4F5/00
`E2IB 43/II6
`E2IB 43/19
`U.S. C.
`CPC ............. E2IB 43/116 (2013.01); E2IB 43/I 19
`(2013.01)
`USPC ......... 89/1.15; 175/4.55; 175/4.56; 175/4.57;
`175/4.58; 175/4.59
`
`Field of Classification Search
`CPC. E21B 43/117; E21B 43/119: E21B 43/1185:
`E21B 43/116; E21B 43/1195: E21B 43/11852;
`E21B 43/11855; E21B 29/02: E21B 43/11;
`E21B 43/14: E21B 17/07: E21B 34/063:
`E21B 43/11857: E21B 47/12: E21B33/13;
`E21B33/138
`
`
`
`USPC .................................. 89/1.15; 175/4.55 4.59
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5/1958 Udry .............................. 175/46
`2,833,213 A *
`4,850,438 A * 7/1989 Regalbuto .
`175/4.56
`2013/01 18342 A1* 5, 2013 Tassaroli ....
`... 89.1.15
`2014/0096670 A1* 4/2014 Bell et al. ....................... 89.1.15
`* cited by examiner
`Primary Examiner — Samir Abdosh
`(74) Attorney, Agent, or Firm — Frommer Lawrence &
`Haug LLP. William S. Frommer
`(57)
`ABSTRACT
`Explosive carrier end plates for charge-carriers utilized in
`guns for the perforation of petroleum producing wells. Each
`gun is mounted coupled vertically with similar guns inside the
`casing of the well, and each gun is a hollow cylinder in the
`interior of which there is a corresponding tubular carrier that
`has multiple peripheral mountings for a radial placement of
`the shaped-charges. The carrier is mounted in the gun by
`means of a top insulating end plate that has a retractable
`electrical spring contact capable of pushing upwards, and a
`bottom insulating end plate. The end plates have a centering
`clip for anchoring in a respective window of the cylindrical
`wall of the carrier. Both end plates have a single removable
`insert axially fitted between two tubular inserts, which
`present reciprocal guiding and positioning means for a pin
`keyway slot to enable mounting with the end plate. A pin and
`groove are provided between the peripheral cylindrical walls
`of end plates and the guns wall, for anchoring in and posi
`tioning the end plate to guide the exit of eachjet of the shaped
`charges.
`
`9 Claims, 6 Drawing Sheets
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`GHD
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`US 8,943,943 B2
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`1.
`EXPLOSIVE CARRIEREND PLATES FOR
`CHARGE-CARRIERS USED IN
`PERFORATING GUNS
`
`FIELD OF THE INVENTION
`
`The present invention relates to assemblies of guns used in
`the petroleum industry for the perforation of wells and, more
`particularly, it is directed to convenient improvements on
`explosive carrier end plates for charge-carriers used in guns
`for the perforation of petroleum producing wells.
`The process of well perforation consists of the perforation
`of the metallic casing of the well, of the isolating cement
`Surrounding the casing, and of the layers of rock in the pro
`ducing formation by means of explosives housed within per
`forating-guns; achieving, through bore holes produced by
`shaped charges, a connection between the depths of the pro
`ducing Zone and the interior of the well.
`
`10
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`15
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`BACKGROUND OF THE INVENTION
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`2
`detonator from short-circuit and ground, connecting the deto
`nator of the gun immediately above the fired gun to the circuit.
`This allows said detonator to later receive the electronic ten
`Sion, albeit with opposing polarity to the previous gun. This
`switch, while it is in its initial position, in repose, before
`moving, allows the electrical charge, positive or negative, to
`reach the bottom gun and maintains the remaining and unfired
`portion of the gun assembly short-circuited and grounded.
`It is also disclosed in the referred application P110102655
`that, in each gun, each charge carrier is limited by two insu
`lating and centralizing end plates: the bottom with a central
`orifice through which the firing line and the unit ground to a
`tab located on the outer edge of the end plate pass, placing the
`unit ground in contact with the outer shell of the gun, which
`acts as the ground for the entire gun assembly (bottom end
`plate without retractable contact pin), both cables are tied to a
`connector, and the top end plate that has a spring-loaded
`electrical contact pin which functionis, on one hand, to assure
`constant electrical contact with the preceding Switch, in spite
`of variances in lengths that can be produced, and on the other,
`to prevent failure of the cables that connect the guns due to
`twisting, as frequently occurs with current practices. The
`bottom plate without said pin, serves to connect the ground to
`the gun assembly, and to space and centralize the charge
`carrier within the gun. Both end plates serve to protect the
`elements that form the series of guns (top Sub, tandem Sub,
`and bottom Sub) from fragments produced by the explosion,
`in Such a way that these parts may be used again.
`In the referred Argentine patent application P110102655,
`the top and bottom end plates of each carrier comprise cylin
`drical pieces with diameters greater than their height, the
`exterior of which is a cylindrical surface of a diameter that is
`intermediate between the inner diameter of the hollow cylin
`der of each gun and the external diameter of the respective
`carrier tube. Each piece has a means to center the carrier and
`an annular recess that is aligned with the corresponding end of
`the carrier.
`The existing end plates used in TCP systems (tubing-con
`veyed perforation) have a fixed insert (the end plates and
`inserts are currently made of aluminum and steel, and formed
`by various pieces). In order to be able to use them in the
`so-called Wireline Systems, the inserts must be removed and
`the retractable contact pin with the wiring contact screw must
`be placed in the top of the assembly.
`
`25
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`30
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`The perforation of petroleum producing wells is realized
`by lowering into the well various metallic perforating-guns of
`different lengths, the respective charge carriers of which are
`charged with shaped charges, connected by joints and fired in
`a vertical fashion, one after another, resulting in a single unit
`of joined perforating-guns for the perforation of various
`Zones, in a single lowering.
`Each perforating-gun contains a carrier tube or charge
`carrier in which shaped charges, for use in the petroleum
`industry, of varying geometries are set, Each of the shaped
`charges detonate conjointly as the charges are in contact with
`a detonating cord, formed by a sheath containing in its interior
`a granular explosive with controlled properties, through
`which the deflagration advances initiated by an electronic
`detonator, The explosion of the detonating cord detonates the
`shaped charges sympathetically.
`Perforating guns are detonated one at a time beginning
`from the bottom and continuing in an upward fashion. After
`each detonation, the gun assembly is repositioned vertically
`in Such away that the lowest gun that remains active is located
`at the desired depth of perforation.
`The detonator of each gun is activated by an electronic
`signal sent from the surface to the mouth of the well, by way
`of an electronic cable, the conductor of which is protected by
`a steel wire-mesh. Despite having but a single conductive
`wire to carry any electrical tension to the gun assembly, the
`charge is passed through diodes and polarized after the deto
`nation of the bottom gun, so as to ensure that the electric
`current only arrives at the desired gun.
`The arming of the guns, i.e., the mechanical assemblage
`and the electrical connections of the assembly to establish the
`required firing sequence, is carried out at the wellhead, usu
`ally under unfavorable general conditions, making it neces
`sary to provide means to simplify both the arming and the
`electromechanical connections in order to avoid human error.
`Argentine patent application P110102655 discloses a pres
`Sure activated electromechanical changeover Switch provid
`ing the electrical connection. The Switch has a conductive
`dart, which is activated at a predetermined pressure set by a
`mechanical fuse in the shape of an expendable ring that
`breaks under stress from the explosion. On receiving the
`impact produced by the explosion of the shaped charges
`located in the charge carriers of the lowest active gun in the
`gun assembly, the dart breaks the mechanical fuse and trips
`the Switch. The dart acts as a switch between contacts that are
`exposed in the housing of the apparatus and releases the
`
`SUMMARY OF THE INVENTION
`
`50
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`55
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`60
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`65
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`This Summary is provided to introduce a selection of con
`cepts in a simplified Rim that are further described below in
`the Detailed Description. This Summary is not intended to
`identify key features or essential features of the claimed sub
`ject matter, nor is it intended to be used as an aid in determin
`ing the scope of the claimed Subject matter.
`The improvements proposed, according to the present
`invention, are characterized by a new constructive solution
`for the end plates, incorporating three clips, which, when
`placed in an adequate fashion on the periphery of said end
`plates, having been designed with certain elastic properties,
`automatically center each charge carrier in the respective gun.
`Furthermore, according to the present invention, the cen
`tering clips are designed to anchor the end plates to the carrier
`at the moment of their insertion into the gun assembly; simi
`larly, the arrangement of the centering clips is such that they
`establish a connection of the electrical ground between the
`charge carrier and the interior of the gun. To carry the elec
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`US 8,943,943 B2
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`3
`trical ground to the carrier connector, it is enough to simply
`attach a cable whose end is trapped between the carrier and
`the surface of the end plate.
`Always in accordance with this invention, included in each
`end plate is an axial cavity with an interlocking pin-and
`keyhole anchoring system—consisting of a linear rib on the
`inside of the orifice and a receiving ridge on the insert for
`a quick and unequivocal mounting of the corresponding
`insert. One of the inserts contains an electrical retractable
`contact pin, typically located on the top end plate of each
`carrier, while the other insert simply contains a tubular orifice
`to permit the passage of wires, to be used in the bottom end
`plate. With these improvements, the end plate orifices have
`differentiated dimensions for their respective interlocking
`pin-and-keyhole apparatus wherein either the contact pm or
`the insert slide.
`The dimensions of the corresponding ribs are different to
`ensure that the retractable contact pin can only be placed in
`the top end plate; therefore, this system avoids the risk that the
`retractable assembly could be mounted in the bottom end
`plate by mistake as the rib will not fit into the keyhole of the
`insert. However, as these end plates and their inserts may be
`utilized interchangeably in Wireline Perforating and in Tub
`ing-Conveyed Perforating (TCP), it is possible to locate the
`bottom insert into both ends of the carrier system to fit the
`needs of the chosen perforation method.
`Also in accordance with the current invention, the exterior
`cylindrical wall of the end plate has a groove, or keyhole.
`Upon placing the charge carrier in its entirety inside the gun,
`the groove is aligned with an anchoring pin at the bottom of
`the gun, which assures accurate orientation of the jet charges
`with notches on the exterior of the gun (these notches are also
`known as scallops in industry jargon). Because of the loca
`tion of the anchoring pin at the bottom of the gun, the charge
`carrier can only be loaded into the gun through one side.
`Other characteristics and advantages of the invention shall
`be explained in the following paragraphs.
`
`5
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`4
`(101) Central opening passage of (100)
`(102) Wall limiting one end of (101)
`(102) Axial orifice of (102)
`(103) Concentric annular rabbet to fit the corresponding end
`of charge carrier (2)
`(104) Straight rabbets in the exterior wall of (100), parallel to
`the axis of the piece and offset by 120°
`(105) Minor segments of recesses prolongations of (104)—
`arranged radially in a way that closes one end of (100)
`(106) Junctions that connect each section of the recess (105)
`with the concentric annular rabbet (103)
`(107) Pinto guide and position the insert (300)
`(108) Retention screw for insert (300) in opening (101)
`(109) Central contact screw (CR)
`(110) Tip of screw (109)
`(111) Connection terminal
`(112) “Keyhole”/groove in the outer wall of (100), to fit (10)
`(113) Beveled portion of the interior wall of the concentric
`annular rabbet (103)
`(200) Bottom end plate
`(201) Central opening passage of (200)
`(202) Wall limiting one end of (201)
`(202) Axial orifice of (202)
`(203) Concentric annular rabbet to fit the corresponding end
`of charge carrier (2)
`(204) Straight rabbets in exterior wall of (200), parallel to the
`axis of the piece and offset by 120°
`(205) Minor segments of recesses prolongations of (204)
`-arranged radially in the wall that closes one end of (100)
`(206) Junctions that connect each section of the recess (205)
`with the concentric annular rabbet (203)
`(207) Pinto guide and position the insert (400)
`(208) “Keyhole'/groove in rectangular cross-section of the
`outer cylindrical wall of (200)
`(209) Reinforcement of the wall (208)
`(210) “Keyhole'/groove cooperating with the guide (11) of
`gun (1)
`(211) Beveled portion in the interior wall of the concentric
`annular rabbet (203)
`(CR) Retractable contact pin
`(300) Insert for the top end plate (100)
`(301) Keyway slot for cooperation with pin (107)
`(302) Spring for retractable contact (CR)
`(400) insert for bottom end plate (200)
`(401) Keyway slot for cooperation with pin (207)
`(402) Holes for extraction of the insert
`(403) Hole for the passage of wire
`(500) J-shaped metal centering clip
`(501) Straight larger section of each metal centering clip
`(502) Elbow end of section (501) for anchorage in window
`(2) corresponding to charge carrier (2)
`(503) Short straight section perpendicular to section (501) of
`each metal centering clip
`(504) Curved section of each metal centering clip
`(505) Terminal tab of section (504), to couple each metal
`centering clip to the edge of the outer wall of the end plate
`(100) and (200)
`
`DESCRIPTION OF THE DRAWINGS
`
`40
`
`In the attached figures:
`FIG. 1 is a schematic cross-section of a perforating gun and
`its interior charge carrier with a pair of end plates (top and
`bottom), according to this invention, including enhanced
`details of the end plates.
`FIG. 2 is a perspective view of the top end plate.
`FIG. 3 is another perspective view of the top end plate of
`FIG. 2 from an opposing side.
`FIG. 4 is a cross-section perspective view of the top end
`plate with the respective retractable contact insert.
`FIG.5 is a perspective view of the bottom end plate with the
`respective central insert, shown in projection.
`FIG. 6 is another perspective view of the bottom end plate
`of FIG. 5 from an opposing side.
`In all figures, like reference numbers represent correspond
`ing or Substitute elements.
`
`45
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`50
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`LIST OF MAIN REFERENCES
`
`(1) Perforating gun
`(2) Charge carrier
`(2) Anchoring slots for the end plates (100) and (200)
`(3) Openings for the shaped charges
`(10) Pin attached to gun wall for fitting and positioning the
`end plate (100)
`(11) Guide for the locking pin in the wall of gun 1
`(100) Top end plate
`
`60
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`65
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`DETAILED DESCRIPTION OF THE INVENTION
`
`The following is a detailed description of exemplary
`embodiments to illustrate the principles of the invention. The
`embodiments are provided to illustrate aspects of the inven
`tion, but the invention is not limited to any embodiment. As
`those skilled in the art will appreciate, the scope of the inven
`tion encompasses numerous alternatives, modifications and
`equivalent; it is limited only by the appended claims.
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`US 8,943,943 B2
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`In relation to FIG. 1, the gun (1) is a steel tube, of treated
`material, with a charge carrier (2) inside. The carrier is a tube
`slightly smaller in diameter than the inner diameter of the gun
`(1) which has openings (3) for multiple shaped-charges (not
`shown), and mounted, at both ends, in centering end plates
`whose bodies are made of an insulating material; the top end
`plate (100) has a retractable contact (RC) and the insulating
`bottom end plate (200).
`The end plates (100) and (200) are molded in plastic mate
`rial, with a general cylindrical shape with a diameter greater
`than its height, the exterior of which has a cylindrical surface
`of an intermediate diameter between the inner diameter of the
`hollow cylinder (1), which constitutes the gun, and the outer
`diameter of the carrier's tube (2). Pieces (100) and (200) have
`peripheral means of centering the carrier (2), a corresponding
`passing central opening (101) and (201), and a corresponding
`concentric annular rabbet (103) and (203) of reciprocal fit
`with the corresponding end of the carrier (2).
`In end plates (100) and (200), the passing central openings
`(101) and (201) are limited at one end by respective walls
`(102) and (202), which have axial holes (102) and (204") for
`the passage of wires (not shown). Said walls (102) and (202)
`constitute an insertion limit for corresponding inserts (300)
`and (400).
`The cylindrical pieces that constitute the end plates (100)
`and (200) have, respectively, at least three straight peripheral
`recesses (104) and (204), parallel to the axis of the piece and
`arranged offset at 120°, prolonged within respective minor
`sections (105) and (205) radially extended in the wall that
`forms one of the ends of the piece and furnished with respec
`tive passages (106) and (206), which extend into the concen
`tric annular rabbet (103) and (203), which fits in the corre
`sponding end of the carrier (2).
`A metal centering clip (500) is adapted to each of the
`above-mentioned recesses. All three metal centering clips
`(500) of each end plate constitute the self-centering means of
`the carrier (2) within the gun (1).
`Each metal centering clip (500) has a general “J”-shape,
`comprised of a Substantially straight long arm (501), and set
`parallel to the axis of the piece in the annular rabbet (103) and
`(203) against the inner wall of said rabbet, and at its end has
`an elbow abutment (502) to anchor the apparatus to its respec
`tive window (2) of the cylindrical wall of the carrier (2). The
`long arm (501) connects, through a short perpendicular sec
`tion (503), with a minor curved arm (504) that terminates in a
`45
`tab (505) to connect to the edge portion, or the outer wail, of
`the piece (100) or (200). In all cases, the long arm (501) goes
`through passage (106) or (206) of the end plate, and the short
`section (504) of the metal strip is adapted in the recess section
`(105) or (205) of said end plate. The curved arm (505) is
`adapted to the straight peripheral recess (104) or (204) of the
`end plate with an outward curvature to make tangential con
`tact with the inner face of the guns wall (1). In this way, the
`elastic properties of all three curved arms (505) constitute a
`means of auto-centering for the corresponding end plate.
`In both end plates (100) and (200), the inner wail of the
`concentric annular rabbet (103) and (203), for fitting the
`corresponding end of the carrier (2), have a beveled section at
`one end (113) and (211) that enables, the placement of each
`metal clip within the end plate, by allowing elastic angular
`movement of the end of the corresponding arms (501), to
`favor the insertion of the elbow abutments (502) in the slots
`(2) of the carrier (2).
`For Wireline perforating (with wires), the upper end plate
`(100) is fitted with a retractable insert (300) for the contact pin
`(RC), triggered by a spring (302). The central cavity (101) of
`the end plate (100) has a pin used as a linear guide for the
`
`55
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`6
`insert (300), the cylindrical wall of which has a corresponding
`“keyhole” (301). The body of the insert (300) is held within
`the cavity (101) by a stop screw (108) (FIG.2). Located on the
`interior end of the retractable contact pin is a screw (109)
`whose tip (110) contacts the switch (not shown); the wire—
`crimped to a terminal (111)—carries the live charge to the
`contact of the connector (not shown) of the carrier (2).
`The physical pressure of the metal centering dips (500) on
`the inside wall of the gun (1) electrically connects the carrier
`(2) to ground. With one wire connected to one of the metal
`centering clips (500) of the inner end plate (200) the ground is
`conducted to the connector (not shown) of the carrier (2).
`The upper end plate has a "keyhole” (112) in its face with
`the largest diameter. When the charge carrier (2) is introduced
`to the gun (1), the "keyhole' (112) surrounds a pin (10)
`welded to the inside of one end of the gun (1); this fixes the
`carrier (2) to the gun (1) and guides the exit of each jet of the
`shaped charges (not shown) with the outer rabbet manufac
`tured in each gun, called a “scallop’.
`In the lower end plate (200), the central cavity (201) has a
`guiding pin (207) to place the tubular insert (400), whose
`cylindrical wall has a keyway slot (401) with holes for extrac
`tion (402) with an appropriate tool, and a hole (403) for the
`wiring. In TCP operations, two of the orifice-type inserts
`(400) are used in each of the respective ends of the carrier
`assembly. In Wireline operations, the insert with retractable
`connecting pin (300) is used in conjunction with the orifice
`type insert (400), each set within their respective ends, upper
`and lower, of the carrier tube.
`Said lower end plate (200) has a rectangular keyhole (208),
`with a reinforcement (209) that prevents the end plate from
`being placed on the carrier in an incorrect fashion, in which
`the pin (210) is introduced. The pin anchors the charge carrier
`(2) inside a keyway guide (11) placed in the other end of the
`gun (1).
`What is claimed is:
`1. In explosive carrier end plates for charge-carriers uti
`lized in guns for the perforation of petroleum producing
`wells, wherein each gun is vertically coupled with similar
`guns inside the casing of the well, and each gun is a hollow
`cylinderin which is located a corresponding carrier that holds
`explosive shaped-charges; and wherein the carrier is a tube
`having an outer diameter Smaller than the inner diameter of
`the hollow cylinder, and having multiple peripheral mount
`ings for radial placement of the shaped-charges which are in
`contact with a detonation cord that contacts an electrically
`operated detonator, and wherein each carrier has mounted on
`the upper end thereofan upper end plate and on the lower end
`thereof, an insulating end plate with a retractable electrical
`spring contact capable of pushing upwards; the improvement
`comprising:
`wherein each end plate comprises a cylindrical piece, each
`cylindrical piece having a cavity and a dominant diam
`eter with a cylindrical surface whose diameter is inter
`mediate to the inner diameter of the hollow cylinder and
`the outer diameter of the carrier tube, each cylindrical
`piece having a peripheral means for centering the carrier,
`a central opening passage, and a concentric annular rab
`bet that reciprocally fits with a corresponding end of the
`carrier; wherein
`the cylindrical piece of each end plate having at least three
`straight peripheral recesses parallel to the axis of the
`cylindrical piece and separated from each other in an
`equiangular fashion and extending radially in the wall
`formed by an end of the cylindrical piece and provided
`for the passage of a respective concentric annular rabbet
`that fits in the corresponding end of the carrier;
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`US 8,943,943 B2
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`5
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`10
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`7
`a “J”-shaped metal centering clip provided at each recess,
`having a Substantially straight long arm with an elbow
`abutment for anchoring in a respective window of the
`cylindrical wall of the carrier and a minor curved arm
`with a terminal tab to hook on the edge portion of the
`outer wall of the cylindrical piece that matches the
`straight section of the recess;
`said curved arm being of an elastic metal for self-centering
`the end plate and being tangentially in contact with an
`inner face of the wall of the gun, and providing electric
`contact between said carrier and the gun;
`the cylindrical piece of each end plate having a central
`opening axially fitted with a single removable insert and
`presenting reciprocal guiding and positioning means
`that is congruent between the walls of said cavity and the
`corresponding insert; and the peripheral cylindrical wall
`of the cylindrical piece having means for positioning the
`cylindrical piece with the wall of the gun.
`2. The improvement according to claim 1, wherein the
`respective central opening passage of each cylindrical piece
`of each end plate is limited at one end by a wall with an axial
`hole; said wall constituting an insertion limit for the corre
`sponding insert.
`3. The improvement according to claim 1, wherein each
`cylindrical piece has a cylindrical peripheral wall with a
`straight rabbet extending from one end of said wall with a
`length less than said wall, constituting a keyway slot that
`cooperates with a shaft secured to the wall of the gun, at one
`end of the inner face of said gun wall, thereby guiding the exit
`of each jet of the charge.
`4. The improvement according to claim 1, wherein the
`inner wall of the concentric annular rabbet for receiving the
`corresponding end of the carrier-tube has a beveled end por
`tion for placement of the centering clip.
`5. The improvement according to claim 1, wherein one of
`35
`the removable inserts is a cylindrical tubular piece in which is
`mounted a retractable contact pin, wherein the guiding and
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`positioning means within the central opening of the end plate
`comprise a straight rib and a cooperating keyhole formed
`within the cylindrical wall of said removable insert.
`6. The improvement according to claim 1, wherein one of
`the removable inserts is a tubular piece which has plural holes
`parallel to the axis of the tubular piece for receiving a tool to
`extract the tubular piece or to run wires, and wherein the
`means for guiding and positioning within the central opening
`of the end plate comprises a straight rib and a cooperating
`keyhole formed within the cylindrical wall of said removable
`insert.
`7. The improvement according to claim 1, wherein the
`central opening passage of each cylindrical piece is axially
`fitted with the single removable insert, wherein the guiding
`and positioning means comprises a pin formed by a straight
`rib with a section cooperative with a peripheral slot of a
`keyway formed in the cylindrical wall of the corresponding
`insert, and wherein the pins and keyways of the pieces that
`form the inserts of the end plates are differentiated by size.
`8. The improvement according to claim 5, wherein the
`central opening passage of each cylindrical piece is axially
`fitted with the single removable insert, wherein the guiding
`and positioning means comprises a pin formed by the straight
`rib with a section cooperative with a peripheral slot of a
`keyway formed in the cylindrical wall of the corresponding
`insert, and wherein the pins and keyways of the pieces that
`form the inserts of the end plates are differentiated by size.
`9. The improvement according to claim 6, wherein the
`central opening passage of each cylindrical piece is axially
`fitted with the single removable insert wherein the guiding
`and positioning means comprises a pin formed by the straight
`rib with a section cooperative with a peripheral slot of a
`keyway formed in the cylindrical wall of the corresponding
`insert, and wherein the pins and keyways of the pieces that
`form the inserts of the end plates are differentiated by size.
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`k
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`k
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`k
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`k
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