US2595615A - Initiating device for suspended explosive charges - Google Patents

Description

May 6, 1952'v w.-s. SWEETMAN INITIATING DEVICE FOR SUSPENDED EXPLOSIVE CHARGES Filed March 2, 1948 W. G. SWEETMAN Patented May 6, 1952 INITIATING DEVICE FOR SPENDED EXPLOSIVE CHARGES William G. Sweetman, Houston, Tex.

Application March 2, 1948, Serial No. 12,544

6 Claims.

This invention relates to a device for detonating explosives and particularly to a device for use as an initiator for setting off explosive charges in a well.

In my co-pending application, Serial No. 721,433, filed January 10, 1947, now Patent No. 2,566,682, there is disclosed a novel form ofinitiating device for setting off explosives in a well. That device comprised a weighted member which was adapted to slide down a cable from which an explosive was suspended in a well and to close an electrical initiating circuit to the explosive by impact of a firing pin retractably mounted in the sliding member upon an electrical contact mounted on the suspending cable and connected to the fuse of the explosive. The sliding member was provided with a source of electrical current, either self-contained or externally supplied, which fiowed through the firing pin when the latter made contact with the aforesaid stationary electrical contact. While this initiating device has proven quite successful in actual use, instances have occurred where a foreign object such as a rock or rag or other electrically nonconductive object will accidentally become interposed between the stationary electrical contact and the firing pin on the sliding contact and will prevent the setting-off of the explosive charge. If, however, an attempt is then made to withdraw the cable carrying the explosive charge and the initiating mechanism in order to make a fresh start, the interposed object may become dislodged at some point along the path of withdrawal and permit closure of the contact, with the result that the explosive charge may be set off in the well at some point other than originally selected and consequently cause undesired damage to the well or its casing. Also if this accidental firing should occur at or near the mouth of the well, there would be great hazard to the equipment at the top of the well and to the men engaged in the operations.

In other instances, the shock of the impact of the sliding member on the stationary contact member may cause the firing pin to rebound so sharply as to break the circuit too quickly to permit transmission of the requisite firing current. Moreover, in the embodiment employing dry cell batteries mounted in the sliding contact to supply the current, the force of the recoil of the firing pin may be great enough to collapse the batteries or so damage them as to make their removal for replacement purposes costly and time-consuming.

Accordingly, a principal object of the present invention is to provide an improved form of initiating device for explosives in a well which in-- cludes features which overcome the above described defects.

An important object is the provision of means for forcibly separating the contact members in the event of a mis-fire in order to assure a positive break in the electrical circuit to the explosive charge.

Another object is to provide more effective and positive contact of the firing pin during closing of the firing circuit.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate one embodiment in accordance with this invention.

In the drawings:

Fig. l is a longitudinal sectional view through an initiating device in accordance with an embodiment of this invention, showing the parts of the device in the normal circuit-closing position;

Fig. 2 is an elevational view, partly in section, of a portion of the device illustrating another position of some of theelements of the device;

Fig. 3 is a cross-sectional view along line 3-3 of Fig. 1; and

Fig. 4 is a longitudinal sectional view of a well showing the relative positions therein of an explosive charge and the initiating device at the stage of operation corresponding to that illustrated in Fig. 1.

Referring to the drawings and first to Fig. 4, there is shown a well bore lined with a casing ID. A wire line or cable ll extends into the well and has suspended from the lower end thereof a container l2 adapted to enclose an explosive charge and provided with an electrical detonator fuse, indicated by the numeral 13, which is of any suitable or conventional form for detonating the explosive charge in container [2. A stationary electrical contact, designated generally by the numeral 14, is mounted on cable H a substantial distance above container l2 and is tightly clamped to the cable by means of clamping screws l5. An electrical conductor lead It extends from stationary contact M to fuse l3. Slidably mounted on cable I I is a sliding contact member, designated generally by the numeral I1, carrying a firing pin l8 extending from its lower end and adapted to close the electrical circuit to fuse [3 when firing pin l8 comes in contact with stationary contact I4.

Stationary contact member l l comprises a metallic block 20 having a longitudinal bore 2| through which cable Il may be inserted and tightly clamped therein by means of clamping screws 15. Seated in the upper end of block 20 is an insulating block 22 in the upper face of which is embedded an annular contact ring 23, concentrically surrounding cable ll. Contact ring 23 is constructed of copper or any other suitable electrically conductive metal. Conductor lead [6 is threaded through a suitable bore 24 in blocks 20 and 22 and is connected to contact ring 23.

Sliding contact I! comprises a generally cylindrical body 25 which is preferablyv constructed of steel or other heavy electrically conducting metal, and is provided with a removable head 26 of similar heavy metal, in order that body 25 will have substantial weight sufficient to overcome the buoyancy afiect of any of the fluids normally present in wells in which the device is conventionally run. Body 25 and head 26 are provided with a longitudinal slot 2'! which extends radially from the axis of the body to the exterior thereof in which cable H may be laterally inserted when the sliding contact is to be mounted on the cable. Longitudinally spaced keeper pins 23 extend laterally through body 25 across slot 21 to hold body 25 on the cable while permitting the body to slide freely thereon.

Body 25 is bored longitudinally at one side to form a battery chamber'zii in which a battery 39, such as a conventional dry cell battery, may be inserted with its positive terminal 31 downwardly directed. The metal case of the battery, which is its negative terminal, is arranged to be in contact with the wall of chamber 29 and with head 28 when the latter is connected to the upper end of body 25, as illustrated. A passageway 32 of somewhat smaller diameter than chamber 29- forms an extension of the latter to a point adlament the lower end of body 25 where an opening 33 of still smaller diameter is provided for the reception of firing pin 13. Passageway 32 is provided with an insulating liner 34. Slidably mounted in liner 3% is a piston 35, constructed of insulating material, through which the upper end of firing pin 18 extends. The portion of firing pin 58 which extends through opening 33 is enclosed in an insulating sleeve 36. The inner end of firing pin is is electrically connected by means of a flexible electrical conductor 31 to a metal washer 38 mounted transversely in insulating sleeve 34 and pressed against the positive battery terminal 3 i by a coil compression spring 39. Electrical connection between firing pin l8 and positive terminal 3| is thus established, while, by means of insulating elements 34, 35 and 35, the firing pin is insulated from the negative side of the battery and its extensions, as represented by body 25. Head 26 is provided with a metal detent 49 which presses against cable I I and is slidable thereon to assure good electrical contact between the sliding contact and the cable, the latter forming the ground connection for the electrical circuit. Spaced from chamber 29, body 25 is bored longitudinally throughout its length to provide a passageway 4i, and head 26 is likewise provided with a registering passageway 42 of slightly smaller diameter than passageway 4i. Slidably inserted in passageways M and 42 is an elongated rod d3 of greater length than the combined length of passageways 4i and 42 to thereby extend for an appreciable distance above the upper end of head 26, when rod 43 has been fully inserted within passageways 4| and 42. The upper end of rod 43 is provided with a knob 44 adapted to form a striking surface for the upper end of the rod. The lower end of rod 43 is provided with a head 45 which, at the point of connection with rod 43 is enlarged to approximately the diameter of passageway 4| to form a shoulder ii; about the lower end of rod 43. A coil spring :3! is mounted in passageway 4| encircling rod 43 and is held in compression between head 26 and shoulder 41. Head 45 may be pointed at its lower end, as at 8, and is provided at an intermediate point thereof with a transverse of opening 49 which is adapted to receive a shear pin B which is adapted to be inserted laterally through a suitable opening in body 25 into opening 49. Shear pin 50 is provided with a threaded head 5| for engaging suitable threads in the body opening through which the shear pin is inserted. Opening 59 is so placed with reference to the lower end of head 45 that the latter will be held fully retracted inside body 25 when shear pin 50 is in place in opening 49.

Theabove described device is employed in the following manner for detonating explosives: Stationary contact It will be threaded over the end of cable l I and firmly clamped in place at a desired distance above the lower end of the cable. Container l2 and its enclosed explosive charge will be tied to the end of the cable and conductor it connected to fuse l2. The cable carrying these elements will then be lowered into casing Ii] until it attains the desired depth therein. Sliding contact I! will then be mounted on the cableat the top of the well and released to slide down the cable. When firing pin I8 strikes contact ring 23, the electrical circuit between battery 3G and the fuse will be closed and current will flow to detonate thefuse and set off the main explosive charge. When firing pin 58 strikes contact ring 2.3, the pin will recoil in passageway 32. However, coil spring 3? will absorb the shock of this recoil and prevent its transmission to the end of the battery thereby protecting the latter against batteringby the inner end of the firing pin. At the same time ,coil spring 3'? will tend to slow up the recoil of the firing pin and so act to maintain contact of the pin with contact ring 23 for a time suflicienttopermit adequate flow of firing current through the circuit. This will constitute the normal operation of the device and when the explosive has been set-oii, cable II will be withdrawn from the well bringing with it sliding contact ii and stationary contact i4, since the latter will normally be positioned on cable ll far enough above container [2 as to remain undamaged by the explosion. Thus the initiating device can be re-used as often as required for setting oif additional charges of explosives. Only occasional replacement of battery 36 will be required to restore the device to full operative condition.

In those cases where a mis-fire may occur, as by a rag or other electrically non-conductive object becoming interposed between contact ring 23 and firing pin 18, it will be necessary to withdraw the entire firing string including the explosive charge from the well. In order that this may be accomplished with complete safety, the following procedure may be employed: A weighted object 52, indicated in broken outlines in Fig. 4, such as an iron block, will be slidably mounted on cable H and will be released to slide down the cable and forcibly strike knob M. This will drive rod 43 downwardly with sufiicient force to break shear pin 58 and drive the rod through body 25 and. cause the lower end of head 45 to strike contact ring 23. Body 25 will rebound upwardly away from contact ring and will be urged in this reverse movement by coil spring 41, which is normally chosen of such strength as to fully support a weight in excess of that of sliding contact l'l, as a whole. This will cause head 35 to protrude from body 25 for a distance greater than the length of firing 'pin l8, so that with the retraction of sliding contact I! on rod 43, the firing pin will be pulled completely away from its contact with contact ring 23 and as contact I! will be held in this retracted position by the strength of coil spring 41, the electrical circuit to the exhmllllllltllllll plosive charge will be completely broken and maintained in this broken condition so that the firing string may now be withdrawn from the well with complete safety. If for any reason firing pin [8 should not be pulled completely away from contact ring 23, despite the contact of head 45 with the contact ring, the latter contact will in any event create a short circuit in the firing circuit which will prevent transmission of battery current to the fuse and so render the device safe for removal.

It will be understood that various changes and alternations may be made in the details of the above-described illustrative embodiment of this invention without departing from the scope of the appended claims but within the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. An electrical initiator for setting olT an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a well, a carrier slidable on said cable, an electrical detonator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a source of electric current mounted on said carrier, a second contact connected to said current source and mounted on said carrier to engage the detonator contact upon impact therewith of said carrier to thereby place said detonator in circuit with said current source, and a plunger member yieldably retained within said carrier and projectible therefrom by percussive force into engagement with said detonator contact.

2. An electrical initiator for setting off an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a well, a carrier having a guide for movement along said cable, an electrical detonator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a source of electric current mounted on said carrier, a contact connected to said current source and mounted on said carrier to engage the detonator contact upon impact therewith of said carrier to thereby place said detonator in circuit with said current source, and a plunger member yieldably retained Within said carrier and projectible therefrom by percussive force into engagement with said detonator contact.

3. An electrical initiator for setting off an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a well, a carrier having a guide for movement along said cable, an electrical detonator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a source of electric current mounted on said carrier, a movable firing pin electrically connected to said source normally extending from said carrier to engage the detonator contact upon impact therewith to thereby place said detonator in circuit with said current source, recoil-absorbing means in said carrier connected to said firing pin, and a plunger member yieldably retained within said carrier and projectible therefrom by percussive force into engagement with said detonator contact.

l. An electrical initiator for setting off an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a well, a carrier slidable on said cable.

an electrical detonator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a self-contained source of electric current enclosed within said carrier, a firing contact connected to said current source and mounted on said carrier to engage the detonator contact upon impact therewith of said carrier to thereby place said detonator in circuit with said current source, and a plunger member yieldably retained within said carrier and projectible therefrom by percussive force into engagement with said detonator contact.

5. An electrical initiator for setting off an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a well, a carrier slidable on said cable, an electrical detonator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a self-contained source of electric current enclosed within said carrier, a firing contact connected to said current source and yieldably extending from said carrier to engage the detonator contact upon impact therewith of said carrier to thereby place said detonator in circuit with said current source, plunger means longitudinally slidable in said carrier, resilient means normally urging said plunger means downwardly out of said carrier, retaining means normally holding said plunger means within said body and releasable by percussive impact on the upper end of said plunger means to release said plunger means for forcible impact upon said detonator contact to thereby cause retraction of said carrier from engagement with said detonator contact.

6. An electrical initiator for setting off an explosive charge in a well, comprising in combination with a cable for suspending an explosive charge in a Well, a cylindrical carrier having a guide for downward movement on said cable, an electrical initiator adapted to be connected to said charge and having a contact mounted on said cable in the path of said carrier, a movable firing pin protruding from the lower end thereof for engagement with said contact to place said detonator in circuit with said current source, a selfcontained source of electric current enclosed within said carrier connected to said firing pin, a recoil-absorbing spring mounted in said carrier in engagement with said firing pin, an elongated plunger slidably mounted longitudinally of said carrier and extending from the upper end thereof, spring means engaged between said carrier and said plunger normally urging the plunger downwardly out of said carrier, a shear pin arranged in said carrier to hold said plunger retracted within said carrier,-said shear pin being breakable by percussive impact on the upper end of said plunger to release same for forcible impact upon said contact.

WILLIAM G. SWEETMAN.

REFERENCES CKTED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 341,536 Zalinski May 11, 1886 1,273,825 Coby et a1 July 30, 1918 1,458,925 Barab June 19, 1923 2,059,488 Prikel Nov. 3, 1936 2,390,676 Alexander Dec. 11, 194.5

Images