US3401631A

US3401631A - Explosive cutting device

Info

Publication number: US3401631A
Application number: US580071A
Authority: US
Inventors: Harold W Hannagan; Robert L Dobrei
Original assignee: Explosive Technology Inc
Current assignee: Explosive Technology Inc
Priority date: 1966-09-16
Filing date: 1966-09-16
Publication date: 1968-09-17
Anticipated expiration: 1985-09-17

Description

p 1968 H.W. HANNAGAN ETAL 3,401,631

EXPLOSIVE CUTTING DEVICE 3 Sheets-Sheet 1 Filed Sept. 16, 1966 Attorneys n m. G n m H W M m H Robert L. Dobrei LIIIIIIIZia l 1968 H. w. HANNAGAN ETAL 3,401,631

EXPLOSIVE CUTTING DEVICE 3 Sheets-Sheet 2 Filed Sept. 16, 1966 Q5 mm 4 T m W M. r J O v w M WL 5% 0 f .D a HmM w p 1968 H. w. HANNAGAN ETAL 3,401,631

EXPLOSIVE CUTTING DEVICE Filed Sept. 16, 1966 s Sheets-Sheet 3 INVENTORS Harold W Hannagan Robert L. Dobrei Attorneys United States Patent 3,401,631 EXPLOSIVE CUTTING DEVICE Harold W. Hannagan, Napa, and Robert L. Dobrei, Fairfield, Calif., assignors to Explosive Technology, Inc., Fairfield, Calif., a corporation of California Filed Sept. 16, 1966, Ser. No. 580,071 13 Claims. (Cl. 102-24) ABSTRACT OF THE DISCLOSURE Explosive cutting device formed of at least two sections and having non-yieldable latching means for securing the free ends of the sections and also having safety features to prevent inadvertent firing.

This invention relates to and explosive cutting device and more particularly to an explosive cutting device in which explosives are utilized for cutting relatively large objects.

In patent application Ser. No. 481,009, filed Aug. 19, 1965, there is disclosed an explosive Cutting device. However, it has been found in the commercialization of an explosive cutting device that it is desirable to simplify the same and also it is desirable to incorporate additional safety features. There is, therefore, a need for a new and improved explosive cutting device.

In general, it is an object of the present invention to provide an explosive cutting device which has additional safety features.

Another object of the invention is to provide an explosive cutting device of the above character which is constructed so that it will not release fragments durmg firin Aiother object of the invention is to provide an explosive cutting device of the above character in which safety devices have been incorporated to prevent 1nadvertent firing of the explosive cutting device.

Another object of the invention is to provide an explosive cutting device of the above character which cannot be fired when it is not in place upon the object which is to be cut.

Another object of the invention is to provide an explosive cutting device of the above character in which a completely shielded release cable is utilized for firing the same.

Another object of the invention is to provide an explosive cutting device of the above character which has been greatly simplified in its construction and which can be economically manufactured.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment is set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1 is a side elevational view of an explosive cutting device incorporating the present invention mounted upon a pipe which is to be cut.

FIGURE 2 is a cross-sectional view taken along the line 2-2 of FIGURE 1.

FIGURE 3 is a cross-sectional view taken along the line 3--3 of FIGURE 2.

FIGURE 4 is a cross-sectional view taken along the line 44 of FIGURE 2.

FIGURE 5 is a cross-sectional view taken along the line 55 of FIGURE 2.

FIGURE 6 is a cross-sectional view taken along the line 66 of FIGURE 2.

FIGURE 7 is a cross-sectional view similar to FIG- URE 6 but showing the firing mechanism in a fire condition.

3,401,631 Patented Sept. 17, 1968 FIGURE 8 is a cross-sectional view taken along the line 8-8 of FIGURE 2.

In general, the explosive cutting device consists of a linear shaped explosive charge which is wrapped around the tubular object to be cut. A shield formed of at least two sections is mounted on the tubular object and encloses the linear shaped explosive charge. The shield is formed so that it can be split apart so that it can be slipped over an elongate object. Means is provided for rigidly securing the sections together so that fragments cannot escape during the explosion. A firing mechanism is provided on the shield for detonating the linear shaped explosive charge. A number of other novel features are included in the firing mechanism to prevent accidental firing.

More particularly as shown in the drawings, the explosive cutting device consists of a shield 11 which is formed of two

half sections

12 and 13. The

half sections

12 and 13 are substantially U-shaped in cross-section and have top wall portions 12a and 13a, respectively, and spaced parallel

side wall portions

12b and 13b, respectively, to thereby provide a shield which is open on the inner side. Hinge means 16 is provided for connecting the two ends of the

half sections

12 and 13 and consists of hinge portions and which are formed integral with the

sections

12 and 13. The

portions

12c and 13c are interconnected by a hinge pin 17 to thereby permit the

sections

12 and 13 to swing about the hinge pin 17 and to permit the same to fit over an object such as pipe 21 which is to be cut. The

sections

12 and 13 can be formed of a suitable material, as for example, they can be formed by sand casting utilizing a material called Vulcanite which is a spheralytic heat-treatable iron. This material is particularly adavntageous because it is stronger than normal cold rolled steel and, in addi tion, the casting process makes it possible to cast in r inforcing webs 12d and 13d, respectively, in

sections

12 and 13. As can be seen, the reinforcing webs extend radially and are perpendicular to the

side Wall portions

12b and 13b. Overlapping end portions He and 13e are also provided.

When the shield 11 is in position on the pipe 21, the shield in combination with the pipe 21 forms an annular chamber 22 which encircles the pipe 21. A flexible linearshaped explosive charge 23 is disposed within the chamber 22 and encircles the object to be cut. The linear-shaped explosive charge can be of any suitable type. For example, it can be of the type marketed under the trademark Jetcord by Explosive Technology, Inc. of Fairfield, Calif. As is well known to those skilled in the art, such a linear-shaped explosive charge consists of a shaped metal member 27 of a suitable material such as lead which is substantially V-shaped or chevron-shaped in cross-section to concentrate the explosive effects. The open side of the V or chevron is positioned so that it faces in the direction in which the cut is to be made in the object. An explosive charge 24 is embedded within the metal member 27 and extends longitudinally of the metal member. The explosive charge can be of any suitable material such as RDX, PETN, TNT or any high explosive.

A holder or band 29 is provided for positioning the linear-shaped explosive charge 23 with respect to the shield 11 and to the pipe 21 and is formed of a suitable flexible material such as an extruded plastic. Each side of the band is provided with spaced parallel raised portions or beads adjacent the outer side margins of the band 29 which are adapted to receive the lower extremities of the

shield sections

12 and 13. As can be seen from FIGURE 2, the

beads

31 and 32 snugly receive the lower extremity of the

side wall portions

12b and 13b of

sections

12 and 13. The explosive charge 23 is disposed within an enclosed elongate chamber 33 formed in the band 29 so that it encircles the pipe 21. Suitable means is provided for securing the band 29 to the pipe 21 and can be of the type disclosed in copending application Ser. No. 481,009, filed Aug. 19, 1965, or alternatively, it can consist of pieces of Velcro tape which are secured to the ends of the band and then are overlapped and fastened together in a manner well known to those skilled in the art to cause the band 29 to form a snug -fit with the pipe 21. The band 29 is, of course, positioned so that the linear shaped explosive charge 23 is properly positioned with respect to the pipe.

A breech 36 is :formed as an integral part of the section 13 and carries a breech block assembly 37. Toggle means is provided for releasably latching the

sections

12 and 13 about the pipe 21 and into a rigid unitary assembly and consists of a lock handle 38 which is pivotally mounted by a pin 39 in an ear 41 formed integral with section 12. A U-bolt 42 has its ends extending through a rod 43 pivotally mounted in the handle 38 and retained therein by nuts 44. The U-bolt 42 is adapted to engage a quick disconnect fitting 46 formed as an integral part of the section 13 as shown in FIGURE 1. Thus, it can be seen that when the handle 38 is raised, the toggle is broken and the U-bolt can be readily lifted off of the fitting 46 and, conversely, when it is desired to rigidly clamp the

sections

12 and 13 together, it is merely necessary to place the U-bolt 42 over the fitting 46 and then to press downwardly n the handle 38 until the longitudinal axis of the U-bolt 42 extends below the center of the pin 49 to close the toggle assembly and to rigidly interconnect the

sections

12 and 13.

The breech block assembly 37 consists of a breech block 48 which is substantially cylindrical and which is provided with arcuate cut-

outs

49 and 51 provided in an annular inwardly extending flange 52 provided on the bottom of the breech block. The cut-

outs

49 and 51 are adapted to receive the sidewise extending

arcuate lugs

53 and 54 provided on the top of the breech 36. The breech 36 is provided with a centrally disposed bore 56 which extends therethrough (see FIGURE 2). A 'detonator cartridge assembly 57 is adapted to be positioned in the bore 56. This detonator cartridge assembly is substantially identical to the detonator assembly disclosed in copending application Ser. No. 481,009, filed Aug. 19, 1965, and as therein disclosed consists of a cartridge 58 which has a primer 59 mounted in the upper end thereof. A sleeve 62 formed of a suitable resilient material such as rubber is mounted on the carriage. A blasting cap 63 is mounted at the lower end of the sleeve so that it is immediately adjacent the linear-shaped explosive charge 23 carried by the holder 29.

A sensing pin 66 is slidably mounted in the breech 36 in a bore 67 which extends in a direction parallel to the bore 56 in the breech. Means is provided for spring loading the sensing pin 66 so that it is normally yieldably urged in an inwardly direction with respect to the shield 11 and consists of a spring 68 disposed in a well 69 provided in the breech 36. The lower end of the spring engages a cross pin 71 mounted in the pin 66 and the other end of the spring 68 is engaged by a retaining ring 72 mounted on the upper portion of the well 69. It can be seen that the sensing pin 66 is of such a length so that when the shield 11 is engaged with the object 21 to be cut, the upper portion of the sensing pin protrudes above the breech 36.

The breech block assembly 37 also consists of a base plate 76 which is secured to the breech block 48 by cap screws 77 (see FIGURE The base plate 76 is provided with an arcuate slot 78 which is adapted to receive the sensing pin 66. The base plate 76 is also formed with a small centrally disposed bore 79 for a purpose hereinafter described. The bore 79 is provided with a chamfer 81 (see FIGURE 2) which opens into a larger bore 82 and which is also provided with a chamfer 83. A rotor plate 86 is pivotally mounted upon the base plate 76 by a pin 87. The rotor plate 86 is generally rectangular in configuration and is provided with an open-ended slot 88 at the end remote from the pivot pin 87 which receives the sensing pin 66. The rotor plate 86 is also provided with an elongate slot 89 in which a firing pin 92 is disposed. The firing pin 92 is provided with a shoulder 93 which is adapted to engage the upper surface of the rotor 86. One portion 89a, of the slot 89, is of a size which will permit the shoulder 93 to pass therethrough, whereas the remaining portion is relatively narrow and will not permit the shoulder 93 to pass therethrough. As can be seen from FIGURES 6 and 7, the rotor plate is also provided with a ramp which inclines downwardly and inwardly from the top side of the rotor plate and which is adapted to be engaged by the shoulder 93 so that as the rotor plate is rotated about the pivot pin 87 to move the rotor plate from a position in which the firing pin 92 extends through the hole 89 to a position in which the firing pin 92 is in the outer extremity of the portion 89b of the slot 89, the firing pin is released.

Means is provided for yieldably retaining the rotor plate 86 in a position in which the firing pin is raised or, in other words, is in a safe position and consists of a spring 94 which is mounted upon a ball plunger 96 and has one end engaging the breech block 48 and has the other end engaging the rotor plate 86. The spring 94 serves to keep the rotor plate 86 in the proper alignment when the breech block assembly 37 is positioned over the breech 36 such that the sensing pin 66 will engage the open end slot 88, and also to prevent the rotor plate 86 from flopping around loosely when the breech block assembly 37 is out of engagement with the breech 36. The ball plunger 96 serves a dual purpose. First, it serves as a post for the spring 94. Secondly it carries a spring-loaded ball 9611 which protrudes through the base plate 76 and is adapted to engage a hole 97 in the top surface of the breech to indicate to the operator when the breech block assembly has been properly positioned on the breech.

The breech block 48 is provided with a bore 98 which extends vertically through the breech block 48. The firing pin 92 is provided with an enlarged cylindrical portion 92a which is slidably mounted in the bore 98. A spring 99 is mounted on the upper portion of the firing pin 92 and has one end engaging the upper extremity of the bore 98 has the other end engaging the enlarged portion 92a of the firing pin 92 to yieldably urge the firing pin 92 in a downward or inward direction.

Means is provided for triggering the firing mechanism or for controlling the movement of the firing pin within the breech block 48 and consists of a slider 101 which is slidably mounted in a large bore 102 provided in the breech block 48. The bore 102 extends in a direction at right angles to the bore 98. The upper side of the slider 101 is provided with a rectangular recess 103 which is large enough to receive the lower extremity of the enlarged portion 92a of the firing pin. The lower side of the recess 103 is formed by a fiat planar surface 104 on which the lower extremity of the cylindrical portion 92a travels. The slider 101 is also provided with a slot 106 (see FIGURE 8) and in which the firing pin 92 is disposed. The slot 106 has one portion 106a which is of such a width that it will permit the enlarged portion 92a of the firing pin 92 to pass therethrough, whereas the remaining portion 106b of the bore 106 is sufiiciently narrow to prevent the passage of the enlarged portion 92a therethrough. Means is provided for yieldably urging the slider towards the safe position and consists of a spring 108, One end of which engages the inner end of the slider 101 and the other end of which engages the inner extremity of the bore 102.

Means is provided to permit manual retraction of the firing pin 92 against the force of the spring 99 and consists of a pull ring 109 connected to a short length of flexible cable 111 mounted in the outer end of the firing pin 92. Means is also provided for operating the slider 101 to cause firing of the firing mechanism and consists of a cable release assembly 112. The cable release assembly consists of a male quick-release assembly 113a which mates with a female quick-release assembly 113b which is threaded" into the bore 102. A cable assembly 114 is connected to the assembly 113a and to an operating handle 116. The cable assembly consists of a metal pushpull control cable 117 which has one end connected to a riged sliding member 118 mounted within the fitting assembly113zz and has the other end secured to an activating'plunger or button 119 in the handle 116. The cable assembly also includes a flexible armored sheath 121 which is protected by a covering 122 of suitable material such as plastic. The handle 116 consists of a cylindrical member 123 with a'large bore 124 formed therein. The cable assembly 114 is secured to the member 123 by set screws 126. A spring 127 is mounted in the bore 124 and has one end engaging the lower extremity of the bore and has theother-end engaging the activating button 119 to yieldably urge the activating button and the cable attached thereto into a retracted position. A safety button 128 is mounted in the button 119 and is normally yieldably urged outwardly by a Spring 129 disposed in a bore 131- provided in the button 119. As can be seen, the safety button 128 prevents the activating button 119 from being depressed into the handle member 123 until the safety button has been pressed inwardly to clear the member 123. Y

1 Operation and use of the explosive cutting device may now be briefly described as follows. Let it be assumed that it is desired to cut a pipe such as pipe 21 shown in FIG- URE 1. An explosive charge holder 29 with the linearshaped explosive charge 23 therein is wrapped around the pipe so that the area immediately beneath the explosive charge 23 defines an annulus on which the cut is to be made in the pipe. The holder 29 is secured to the pipe by utilizing the Velcro tape hereinbefore described. The shield 11 is then taken and the two halves are opened up and are placed around the pipe 21 in a position overlying the holder 29 with the sides being in alignment with the spaces provided between the

beads

31 and 32 on the holder29. The-U-bolt 42 is then placed over the end fitting 46 with the handle 38 in a raised position. The handle thereafter is brought downwardly until the U-bolt 42 passes over the center of the pivot pin 39 to securely lock the shield 11 to the pipe 21 as shown in FIGURE 1. At the time that the shield is being latched into place onthe pipe 21, the spring-loaded sensing pin 66 engages the'holder 29 and'is pushed upwardly against the force of the spring 68 so that the upper extremity of the pin 66 protrudes from the breech 36.

' After the shield 11 has been latched in place, the breech block assembly 37 is taken and placed over the breech 36 in such a manner that the sensing pin 66 is disposed in the arcuate slot 78 provided in the base plate 76. At the same time, the cut-

outs

49 and 51 receive the

lugs

53 and 54. The'breech block assembly 37 is then rotated in a clockwise direction as viewed in FIGURE 5 so that the

lugs

53 and 54 are engaged by the flange 52 provided on the breech block 4 8. The breech block assembly 37 must be rotatedsufliciently sothat the firing pin 92 is cleared for operation as will be apparent hereinafter. This ensures that the maximum interlocking lug and flange area will be engaged between the breech block assembly and the breech to thereby prevent the breech block assembly from being accidentally blown'off.

As can be seen from 'FIGURES -6 and 7, the breech block 48 is rotated in a clockwise direction, the sensing pin 66 which is stationary causes the rotor plate 86 to be rotated about its pivot pin 87 in a counter-clockwise direction against the force of the spring 94 so that the portion 891': of slot 89 is moved into registration with the firing pin 92 as shown in FIGURE 7. Thus, it can be seen that if the breech block 48 is not rotated sufliciently far enough, the firing 'pin will not clear the rotor plate 86 and the breech block assembly 37 cannot be operated to fire the detonator cartridge assembly 57. In the embodiment shown in the drawings, the rotation of the breech block 48 must be through substantially 90 before the firing pin 92 is cleared.

In the event it is desired to remove the breech block assembly 37 after it has been placed in position, this can be accomplished by merely rotating the breech block 48 in an opposite or counter-clockwise direction. The in clined ramp 90 which is provided in the rotor 86 engages the collar 93 of the firing pin 92 and as the rotor 86 is moved in a clockwise direction, the firing pin 92 is urged upwardly against the force of the spring 98 and into the portion 89b of slot 89 so that the firing pin cannot be fired. Thereafter, the breech block assembly 37 can be removed. When the breech block assembly 37 has been rotated to the proper place, the pin 96 drops into the recess 97 to hold the breech block assembly 37 in the proper angular position and to prevent it from sliding around on the breech.

As soon as the breech block assembly 37 is in place, the male assembly or connector 113a on the end of the cable release assembly 112 is connected into the female assembly 113b on the breech block assembly. As soon as this has been done, the ring 109 is pulled upwardly to cock the firing pin 92. This is accomplished by raising the firing pin 92 against the force of the spring 98 so that it is lifted out of the hole 106a provided in the slider 101 and to permit the slider to be pushed to the right by the spring 108 as viewed in FIGURE 2 and so that the firing pin is disposed in portion 106!) of slot 106 and the collar 92a engages the upper surface 104 on the slider. The operator can readily tell Whether cocking has taken place because there is an audible click when the spring 108 pushes the slider 101 beneath the firing pin 92.

The cutting device is now ready to be fired. The opera tor then steps away to a remote location taking the handle 116 of the cable release assembly 112 with him to a suitable safe distance. The operator then fires the explosive cutting device by depressing the safety button 128 with one hand and then at the same time pressing inwardly with the other hand on the large actuate button 119 to advance the cable 117 and the sliding member 118 carried thereby into the breech block assembly. The sliding member 118 engages the slider 101 and shifts it to the left as viewed in FIGURE 2 against the force of the spring 108. When approximately of an inch of movement has taken place, the portion 106a of the slot 106 in the slider 101 is moved into registration with the firing pin 92 and permits the firing pin 92 to be rapidly urged therethrough under the force of the spring 98 to pass through the small hole 79 provided in the base plate 76 and to impinge upon the primer 59 to detonate the same. Detonation of the primer fires a non-electric blasting cap 63 which initiates the explosive charge 23. The initiation of the charge 23 causes cutting of the pipe as described in copending application Ser. No. 481,009, filed Aug. 19, 1965. In brief, as the linear shaped explosive charge 23 explodes, the metal jacket or sheath 27 is propelled outwardly in the area that is away from the pipe and being cut or, in other words, in the chamber 22. Explosion in the area which is facing the pipe is propelled inwardly in a concentrated jet to partially penetrate the pipe. It is believed that the linear shaped explosive charge actually causes a scoring of the pipe which causes a stress concentration in the area. The shock Waves generated by the linear shaped explosive charge and the over-pressure from the expanding gases within the shield 11 then serve to break the pipe at the point at which it has been scored.

After the explosive charge has been detonated and the pipe has been cut, the entire explosive cutting device can be removed. All the parts can be re-used for the next cut with the exception that a new detonator cartridge assembly 57 will have to be provided as Will an additional length of the holder 28 with the linear shaped explosive charge carried thereby. The shield 11 with its breech and the breech block assembly can be used repeatedly in making cuts in pipe or other objects.

In the design of the above identified explosive cutting device, a great many safety criteria have been met to make use of the explosive cutting device substantially fool-proof. For example, the explosive cutting device cannot be actuated unless it is mounted on the pipe to be cut. This is accomplished in two ways. First, the U-bolt 42 which locks the two

half sections

12 and 13 together cannot be taken off of the end fitting 46 unless the breech block assembly 37 has been removed. This is true because there is mechanical interference between the parts. Thus, to remove the shield, it is first necessary to remove the breech block assembly 37. Second, when the shield 11 is off of the pipe, it is impossible to fire the same because the sensing pin 66 does not project above the breech. Since this is the case, placement of the breech block assembly 37 on the breech and rotation of the same will not cause pivotal movement of the rotor plate 86 and, therefore, the firing pin 92 will not be freed. As also pointed out previously, it is the engagement of the sensing pin 66 with the rotor 86 that causes freeing of the firing pin.

The explosive cutting device cannot be fired unless the toggle mechanism formed by the U-bolt assembly 42 and handle 38 and associated parts is completely latched. This is true because until the handle 38 is moved to the completely closed position, there is a substantial space between the two halves and the detonator cartridge assembly 57. For this reason, if the detonator assembly 57 should be accidentally fired, the linear shaped explosive charge would not be initiated. Thus, it is only when the detonator cartridge assembly 57 is immediately adjacent the linear shaped explosive charge 23 that the charge 23 will be initiated.

An automatic mechanic interlock is provided so that the firing pin cannot be fired unless the breech block is properly engaged. As pointed out previously, this is true because unless the breech block 48 is rotated through a sufiicient angle so that the rotor plate 86 is shifted to place the portion 89a of slot 89 in alignment with the firing pin 92, the firing pin will not be free.

All fragmentation upon explosion is contained within the shield. This escape of fragments is prevented in two ways. First, the charge holder 28 is provided with a pair of beads on each side of the same which engage the outer sides of the

sections

12 and 13. When the linear shaped explosive charge is initiated, the internal bead is forced out against the inner surface of the shield 11 to form a relatively tight seal with respect to the shield to thereby eliminate the escape of any substantial fragments between the holder 28 and the shield 11. Second, the two sections are rigidly interconnected to prevent them from being blown apart even momentarily during the explosion to prevent escape of fragments of any substantial size. In addition, the point at where the two halves mate with each other there is provided an overlapping of the metal that also prevents escape of fragments of any substantial size.

As explained previously, the explosive cutting device is designed so that it can be used repeatedly and has a substantially unlimited life.

This means for releasing the firing pin has been completely shielded in the form of the cable assembly 112 to prevent inadvertent firing. The explosive cutting device cannot be actuated without the use of the cable assembly 112. This is because the slider 101 is dee ly recessed within the breech block assembly 37 so that it is difficult to obtain acces to the slider 101. In addition, the slider 101 must be pushed a substantial distance before the portion 106:: of slot 106 comes into registration with the firing pin 92. In addition, the spring 108 which engages the slider 101 is relatively strong. Thus, it is very difiicult to physically depress the slider 101 without the use of the cable assembly 112. The force of the spring 108 and the amount of movement required for the slider 101 are suflicient to prevent inadvertent firing in the event the explosive cutting device is accidentally dropped or struck.

The cable release assembly 112 is constructed in such a manner that it can be operated only by the use of two hands. Thus, one hand must be utilized to depress the safety button 128, while the other hand is utilized to depress the actuator button 119 against he force of the relatively strong spring 127. The cable release assembly is automatically reset because as soon as the button 119. is released, it is pushed outwardly and at the same time, the safety button 128 pops outwardly as soon as it clears the cylindrical member 123.

In addition to the foregoing safety features, all the parts which form the firing mechanism and the interlocks are fail-safe. That is, if they fail, the operator still will not be subjected to an unsafe condition.

It is apparent from the foregoing that there has been provided an explosive cutting device which has many inherent safety factors which are very desirable for such a unit. The firing mechanism which is the breech block assembly is relatively simple in construction and has relatively few moving parts which makes it less expensive to manufacture and assemble.

We claim:

1. In an explosive cutting device for cutting a tubular object, a holder encircling the tubular object at the point at which the cut is to be made in the tubular object, said holder having a lienar shaped explosive charge mounted therein and substantially encircling the tubular object along the line at which the cut is to be made in the tubular object, a shield encircling said tubular object and overlying said linear shaped explosive charge carried by the holder, said shield being separable and including means rigidly latching said shield to said tubular object, and means carried by the shield for detonating the linear shaped explosive charge within the shield, said means for detonating the linear shaped explosive charge comprising a breech carried by the shield, at detonating assembly mounted in the breech and disposed adjacent the linear shaped explosive charge, a breech block assembly removably mounted on said breech, said breech block assembly including a firing pin, and safety means carried by said breech and said breech block to prevent the firing pin from actuating the detonating assembly unless the shield is in engagement with the article to be cut, said safety means including a sensing pin mounted in the breech, means carried by the breech for yieldably urging the sensing pin in an inward direction towards the object to be cut so that it normally extends beyond he inner extremity of the shield, said sensing pin having a length so that when the shield is in engagement with the object to be cut, the outer extremity of the sensing pin extends above the breech, said breech block assembly including a breech block, said firing pin being slidably mounted in said breech block, a rotor plate pivotally mounted on said breech block, said rotor plate having a slot therein, a portion of said slot being sufiiciently large to permit the firing pin to pass therethrough and the remaining portion of said slot being of a size which prevents the firing pin from passing therethrough, and means carried by said rotor plate and engageable by the sensing pin for shifting the rotor plate to a position in which the firing pin can pass through the slot in the rotor plate when the breech block assembly is secured to said breech.

2. A cutting device as in claim 1 wherein said means carried by the rotor plate engageable by the sensing pin includes a recess in the rotor plate engageable by the sensing pin so that as the breech block assembly is rotated, said sensing pin cause aid rotor plate to be pivoted.

3. A cutting device as in claim 2 together with a base plate mounted on said breech block and underlying said rotor plate, said base plate having an arcuate slot therein adapted to receive said sensing pin and permitting movement of said breech block through a substantial angle with respect to said sensing pin.

4. A cutting device as in claim 1 together with a slider slidably mounted in said breech block, said slider having a slot therein, one portion of said slot being of a larger size to permit the firing pin to travel therehrough and the other portions of said slot being of a smaller size to prevent further travel of said firing pin through said slider, and remotely controllable means secured to said breech block assembly for causing movement of said slider block into a position in which the larger portion of said slot in said slider block is moved into registration with said firing pin to permit the firing pin to advance therethrough.

5. A cutting device as in claim 4 together with means secured to said firing pin and extending from the breech block to permit the firing pin to be raised, and means disposed within the breech block for yieldably urging said slider into a position in which the smaller portion of said slot in said slider is in general alignment with said firing pin to prevent further travel of the firing pin through the slider.

6. A cutting device as in claim 4 wherein said remotely operable means for moving said slider includes a flexible cable, a flexible sheath surrounding said cable, and means for causing relative movement between said cable and said sheath to cause movement of said slider.

7. In an explosive cutting device for cutting a tubular object, a linear shaped explosive charge, means for securing said linear shaped explosive charge to said tubular object so that the linear shaped explosive charge is in general alignment with the line on which a cut is to be made in the tubular object, a shield surrounding said tubular object and enclosing said linear shaped explosive charge, a breech mounted on said shield, a detonator assembly mounted in said breech, a breech block assembly removably secured to said breech, said breech block assembly including a breech block, a firing pin slidably mounted in said breech block, means including a slider mounted in said breech block for normally retaining said firing pin in a cocked position and for releasing said firing pin from a cocked position, means for actuating said slider to move the same to a position in which the firing pin is released, means in the breech block for urging the firing pin into engagement with the detonator assembly to detonate the the same, safety means carried by the breech and the breech block assembly and preventing said firing pin from detonating said detonator assembly unless said shield is in engagement with the tubular object to be cut, said safety means including a sensing pin slidably mounted in said breech, means carried by the breech for yieldably urging the sensing pin in a direction towards the tubular object, said sensing pin being of a sufficient length so that when the shield is in engagement with the tubular object, the sensing pin is disposed above the breech, a rotor plate pivotally secured to the breech block, said rotor plate having a slot therein, one portion of said slot being sufficiently large to permit further travel of said firing pin through the same, and the remaining portion of said slot being of a smaller size to prevent further travel of the firing pin through the slot, said rotor plate also having an additional arcuate groove engageable by said sensing pin, said breech block assembly being rotatable on said breech whereby upon movement of said breech block assembly, said sensing pin causes movement of said rotor plate to shift said rotor plate into a first position in which the larger portion of said first named slot is in alignment with said firing pin to permit the firing pin to travel therethrough.

8. A cutting device as in claim 7 wherein said rotor plate 1s provided with an mcllned surface ad acent said 5 slot, said surface being inclined upwardly from the larger portion of said slot to the smaller portion of said slot in said rotor plate, said firing pin having an enlarged portion adapted to engage said inclined surface of said rotor plate.

9. A cutting device as in claim 7 wherein said sections are provided with reinforcing webs which extend radially and are perpendicular to the sides and wherein said sections are provided with overlapping end portions.

10. In an explosive cutting device for cutting a tubular object, a holder adapted to encircle the tubular object, said holder having a linear shaped explosive charge mounted therein and adapted to substantially encircle the tubular object along the line at which the cut is to be made in the tubular object, a shield adapted to encircle said tubular object and overlying said linear shaped explosive charge carried by the holder, said shield being comprised of at least two sections which are generally U- shaped in cross-section with substantially parallel sides, mean interconnecting the sections to permit movement of the same to positions adapted to encircle the tubular object and to provide two free ends which are in relatively close proximity to each other, non-yieldable latching means secured to said free ends of said sections for removably securing said sections to said tubular object and means carried by the shield for detonating the linear shaped explosive charge within the shield, said shield being spaced from the linear shaped explosive charge so there is no direct contact between the linear shaped explosive charge and the shield, said shield being constructed so that it arrests the travel of substantially all of any solid particles within a limited distance in at least one direction which are propelled by the detonation of the linear explosive charge.

11. A cutting device as in claim 10 wherein said means for detonating a linear shaped explosive charge consists of a breech carried by the shield, a detonating assembly mounted in the breech and disposed adjacent the linearshaped explosive charge, a breech block assembly removably mounted on said breech, said breech block as sembly including a firing pin, and safety means carried by said breech and said breech block to prevent the firing pin from actuating the detonating assembly unless the shield is in engagement with the object to be cut.

12. A cutting device as in claim 10 wherein said nonyieldable latching means includes an over-center toggle mechanism.

13. A cutting device as in claim 12 wherein said overcenter toggle mechanism comprises a fitting, linkage means engaging said fitting, said fitting and said linkage means being of such a size and being positioned so that said linkage means cannot be removed from said fitting when said breech block assembly is in position on said breech.

References Cited UNITED STATES PATENTS 2,140,338 12/1938 Temple.

2,638,323 5/ 1953 Bannon.

2,846,968 8/1958 Tipton 113-402 3,089,417 5/1963 Beyer et al. 102-24 3,135,163 6/1964 Mechlin et al. 10224 3,169,479 2/1965 Bryan 102-24 3,336,868 8/1967 Rush et al. 10224 SAMUEL W. ENGLE, Primary Examiner.