Patent GB-1194351-A (GB)
Title: Shielded Explosive Cutting Device.
Inventor: BURKDOLL FRANCIS BURCH
IPC: E21B29/02
Filed: 1967-05-24
Abstract: 1,194,351. Dividing. EXPLOSIVE TECHNOLOGY Inc. 24 May, 1967, No. 24162/67. Heading B3W. [Also in Division F3] A shielded explosive cutting device comprises a rigid wall-like shield having an open side adapted to be positioned adjacent an object to be cut, a linear explosive charge mounted so that it is adjacent the object to be cut, and charge detonating means, the shield being substantially non-fragmentable and being constructed so that it arrests any solid particles resulting from the explosion of the charge. A pipe cutting device comprises a split clamp 12, 13, hinged at 19 and looked around the pipe 21 by a toggle clamp 41. The clamp is of channel section and has a rubber lining 24. The linear charge 26 comprises an explosive cord 28 and a lead cover 27, and is held on to the pipe by a plastic band 31, which has a central groove 33 to receive the charge and two edge beads 32. The ends of the band are drawn together by a tongue and slot connector and may be sealed to make the band waterproof for underwater use. Welded on to the clamp is a breech 66 which receives a cartridge 71 containing a primer 72. A copper tube 73 inside a rubber sleeve 74 directs the flame to a safety-type blasting cartridge 76 immediately above the linear charge. The primer is fired by a spring loaded pin 83 which is released by withdrawing a pin 91 by means of a lanyard. Safety devices.-(a) The breech block 64 is looked to the breech 66 by an interrupted thread. The bolts 51 which form part of the toggle clamp pass under the breech block and unless these rods are in their lowest position indicating that the toggle lever is over-centre the block 64 cannot be engaged on its thread. (b) A spring-loaded safety cam rod 99, Fig. 6, is housed in a tube 96 which is welded to the breech 66. Unless the bar 58 of the toggle clamp is in its normal position the rod 99 will move so that its larger diameter portion lifts a pin 111, 114 which then projects out of a bore 116 in the breech 66 and prevents the breech block being assembled. (c) The movement of the firing pin 83 from the cocked position is prevented by a leaf spring 126, Fig. 3, which passes across an annular groove 127 in the firing pin. The spring is biased into the groove by a helical spring 128 and is displaced from the groove by an arming key (121), Fig. 5 (not shown). The arming key comprises a spindle carrying two axially spaced eccentrics. One of these eccentrics displaces the spring 126 sideways when the key is turned and the other eccentric 123 is then in line with a longitudinal groove 131 in the head 85 of the firing pin. After the charge has been fired the arming key cannot be removed until the firing pin has been raised clear of the eccentric 123 and the pin 91 inserted. (d) A leaf spring (132), Fig. 5 (not shown) prevents the arming key being inserted in the breech block unless the block is correctly assembled to the breech. A modification of the device is suitable for cutting a hole in pipe for a T-junction, Fig. 10 (not shown). In a further modification for cutting a hole in a flat plate, the device is not clamped to the plate but instead includes a second charge which is fired simultaneously with the shaped charge and provides a reaction in the opposite direction to hold the device against the plate, Fig. 12 (not shown).