WO2000058047A1

WO2000058047A1 - Gas-powered rescue power cutter

Info

Publication number: WO2000058047A1
Application number: PCT/SE2000/000558
Authority: WO
Inventors: Sten Sundberg; Göran Olofsson
Original assignee: Bofors Carl Gustaf Ab
Priority date: 1999-03-31
Filing date: 2000-03-22
Publication date: 2000-10-05
Also published as: AU4157100A; SE513758C2; SE9901169L; SE9901169D0

Abstract

The present invention relates to an improved type of gas-powered cutting tool of the general type whose tool section with its cutting blade (24) operates against a bucker (2a) that consitutes a fixed part of a body (1) in which a piston-cylinder arrangement for powering the cutting blade (24) of the tool against the bucker (2a) is integrated. The present invention more exactly constitutes a re-design of previous cutting tool designs that when implemented means that such cutting tools in the future will better withstand the overloads caused by being fired when empty or when the quantity of material to be cut is significantly less than that for which the cutting tool was designed. The distinguishing feature of the present invention is that the rear piston (12) which powers the cutting blade (24) has been provided with an internal damper (16) that prevents the cutting tool from becoming overloaded.

Description

GAS-POWERED RESCUE POWER CUTTER

The present invention relates to an improved type of gas-powered cutting tool of the general type whose tool section with its cutting blade operates against a reaction arm that constitutes a fixed part of a body housing a piston-cylinder arrangement for driving the cutting blade towards the reaction arm. The present invention is a re-design of earlier tool designs. This new design means that such tools in the future will be much better at withstanding overloads resulting from blind firings without any object to be cut, or when the quantity of material to be cut is considerably less than the tool was designed for.

The type of gas-powered tool in the present invention comprises three main components, namely a body, a piston-cylinder assembly with related cutting blade which performs the actual cutting function, and a propellant charge with inherent ignition function and which emits gas during combustion to power the piston-cylinder assembly that enables the cutting operation. The last mentioned of these three main components — the one with a propellant charge with inherent ignition function and which emits gas during combustion — is not affected by the present invention as it is based entirely on known technology and will thus not be discussed in any more detail other than to state that it is incorporated in the appended figure.

The body of the present tool, which should preferably be entirely forged in high-tensile steel in one piece, consists of a reaction arm that constitutes the bucker, a holder arm parallel to the axis of actuation of the tool housing the piston-cylinder assembly and related components located at a distance from the reaction arm dependent on the desired length of the cutting action, and a spacer section uniting the reaction arm and holder arm. The length of the spacer section is also dependent on the desired length of the cutting action. It may be appropriate to arrange a guide groove for one end of the cutting blade along the inside of the body extending along the spacer section to the reaction arm. The piston-cylinder assembly incorporates a cylinder mounted in the power cutter body and in which there is a slidable piston and piston rod. This piston rod, which is integral with the cutting blade, extends outside the cylinder with its outer end — which incorporates the cutting blade— pointing towards the reaction arm. The opposite end of the cylinder has an intake for entry of the gases emitted by the propellant charge during combustion. These gases in turn power the piston, piston rod and integral cutting blade with great force against the reaction arm whereby the cutting blade through interaction with the reaction arm cuts through all material located between the cutting blade and the reaction arm when the tool was actuated, provided the quantity and hardness of the material to be severed does not exceed the maximum capacity of the tool. Generally, however, tools of this type have a high capacity. Until now it has been more common for such tools to be damaged by overloading when being fired while empty or with very little material to be cut through, rather than being damaged by trying to sever more material than they have the capacity to cut through.

Power cutters of the type described briefly above have shown themselves to be highly effective in releasing traffic accident victims when the time factor is vital, and where there may often be spilled fuel preventing the use of spark generating tools such as cross-cutting saws. -Another application for these tools is the cutting of various types of heavy duty cables, where in an emergency situation it is even possible to cut live cables as the tool can be rigged up and fired remotely.

As previously mentioned there have been a number of problems with tools of this type being overloaded and damaged when fired without any cutting object between the cutting blade and the reaction arm, or when the quantity of material to be cut has been altogether too small. A serious attempt to resolve this problem is described in United States Patent Number 5,465,490 (EP 0686077) in the form of such a tool equipped with a compression chamber located at the opposite side of the cutting blade piston compared with the combustion gas powered side of the piston, and in this compression chamber a certain volume of air is compressed at the same time as the piston powers the cutting blade against the reaction arm, and this air compression decelerates the piston to a certain degree. At the same time the side of the piston facing the compression chamber functions as a base stop so that when it strikes the transfer shoulder of the cylinder it transfers at least some of its kinetic energy to the cylinder. This is in turn mounted movably within certain limits in the axis of actuation in the power cutter body by a deceleration spring fixed between an own shoulder and the power cutter body, which deceleration spring in turn can assimilate some of the remaining excess kinetic energy in the piston which is not dissipated when severing the object to be cut.

Theoretically this design appears to be satisfactory since the magnitude of the kinetic energy remaining after severing the object to be cut is partially dissipated when compressing the air in the compression chamber, partially is transferred as kinetic energy in the complete piston-cylinder assembly, and finally is assimilated by the deceleration spring to the maximum of its capacity.

In practice, however, these improvements have not made it possible to fabricate the gas-powered cutting tool within reasonable material dimensions so as to prevent it being damaged when fired to cut small objects or when fired empty. In reality the power cutter must withstand practice use while training operators and be usable without the operator needing to decide whether the object to be cut will provide sufficient resistance. The most common type of damage experienced with power cutters incorporating the above mentioned deceleration spring is rupture of the piston rod, deformation of the threads securing the various parts of the power cutter, and swelling of the part of the cylinder affected by the propellant gases.

The purpose of the present invention is to offer such improvements as to enable the general type of gas-powered cutting tools in question to withstand a number of consecutive blind firings in the future without suffering damage. The type of gas-powered cutting tool referred to herein comprises a body, a piston-cylinder assembly axially slidable to a certain degree in the axis of actuation that is mounted against a spring force in the body opposite the reaction arm with associate piston rod whose outer end incorporates a cutting blade for implementation of the desired cutting function, and finally a small propellant charge containing a substance whose combustion generates gas and with an associate ignition function, which substance when initiated forms combustion gases that are fed into a space behind the piston in the piston- cylinder assembly to power the piston in the direction of the reaction arm to enable the cutting blade in interaction with the reaction arm to perform the desired cutting function. The piston-cylinder assembly also incorporates an air compression chamber in front of the slidable piston around the initial position of the piston rod in which some of the air originally filling the chamber is compressed when the piston slides in the direction of the termination of the compression chamber and where the piston at full stroke bottoms out. As claimed in the present invention the piston unit of the piston-cylinder assembly is supplemented with a double-acting built-in damper whose task is both to increase the friction against the inner wall of the cylinder in conjunction with the piston striking the transfer shoulder of the cylinder and to dampen the impact of the piston against the transfer shoulder of the cylinder. This twin function has been achieved by designing the piston unit with a fixed rear piston actuated by the combustion gases and a front piston that is axially movable in the direction towards the fixed rear piston, plus an internal damper located between the front and rear pistons in the form of an elastically deformable material with a good capability for re-assuming its original shape, and whereby the original dimension of this internal damper does not exceed the inner dimension of the cylinder. When the movable front piston is subjected to load on impact the internal damper is subjected to a compressive pressure in the direction of the piston rod whereby the sides of the internal damper are pressed outwards by the elastic deformation of the material against the side-wall of the cylinder where it first fills any gap between the outside of the internal damper and the inside of the cylinder. Consequently, there is an increase in the friction of the front piston against the inside of the cylinder that has a decelerating effect. When the front piston finally bottoms out in the cylinder the elastic properties of the internal damper limit the hardness of the impact against the transfer shoulder of the cylinder. The front external damper located between the cylinder and the body of the power cutter is designed to assimilate some of the motion of the front piston when it bottoms out in the cylinder, and we have found that an elastic damper material of the same type as the internal damper in the cylinder is suitable for the external damper. In this development of our design we thus have an interaction between the internal piston unit damper and the external damper that further reduces stresses on the complete power cutter when it is fired when empty or is used to cut a small cutting object.

The present invention is defined in the subsequent Patent Claims and shall now be described in further detail with reference to the appended figure which shows a longitudinal section of a preferred form of execution of the invention.

The gas-powered cutting tool as claimed in the present invention thus comprises a body 1 preferably entirely forged in one piece and comprising a reaction arm 2 with an integral bucker 2a, a holder 3 located at a distance from the reaction arm 2 dependent on the desired cutting stroke A, and a spacer section 4 uniting the reaction arm 2 and the holder 3. The holder 3 has an axial bore 5 in which the cylinder is mounted. The cylinder 6 incorporates a reduced external section 7 extending from the outside of the holder through the axial bore 5 and secured on the inside of the said bore by a screwed-on locking ring 8. An external damper 10 made of polyurethane rubber is located between a stop flange 9 on the cylinder and the holder 3. The slidable piston unit 11 is the active component located in the cylinder 6. The piston unit 11 comprises a rear piston 12 with seal 14 that move in the axis of actuation and that are secured on a piston rod 13 which interacts with the said piston unit 11 , a front piston 15 on the piston rod 13 which front piston 15 is axially slidable towards the rear piston 12, and an internal damper 16 located between the said front and rear pistons 15 and 12. The internal damper 16 is made of a relatively hard polyurethane rubber with good elasticity and very good form memory. In front of the piston unit 11 there is a confined space 17 confined by the inside wall 18 of the cylinder 6, the outside surface 19 of the piston rod 13, and by the transfer shoulder 20 of the confined space 17 and the front face 21 of the front piston 15. The cylinder 6 is closed by a cylinder head 22 fixed to the said cylinder by a threaded joinder. The cylinder head 22 incorporates a cartridge chamber 23 to accommodate a gas-generating propellant cartridge. The front end of the piston rod 13 terminates in a cutting blade 24 directed at the reaction arm 2.

When the cartridge in the cartridge chamber 23 is fired the piston unit 11, piston rod 13, and the cutting blade 24 are propelled towards the bucker 2a. The velocity imparted to these movable parts is thus partly dependent on the quantity and hardness of the object to be cut that is located within the cutting stroke A. When the piston unit 11 is propelled forwards through the confined space 17 the air contained therein is compressed. When the front piston 15 of the piston unit 11 bottoms out in the cylinder 6 and impacts with the transfer shoulder 20 of the said cylinder the internal damper 16 is compressed whereby the friction against the inside wall 18 increases. At the same time as damping is provided by the compression of the rubber material of the said internal damper there is additional damping provided by the external damper 10. The interaction between these two dampers has been proved to provide such good combined damping as to enable the operational life of a power cutter of the type described herein to be extended many times over.

Claims

PATENT CLAIMSWe hereby claim and desire to secure by Letters Patent the following.

1. A gas-powered cutting tool of the type whose active tool part consists of a movable cutting blade (24), which is powered in the cutting direction by a slidable piston unit (11) with which the said cutting blade is connected by a piston rod (13) and whereby the piston unit (11) is in turn driven by the combustion gases generated during combustion of a gas-emitting cartridge and whereby the said piston unit powers the cutting blade (24) in the direction towards the bucker (2a) opposite the initial position of the said cutting blade, mounted in a tool-interconnecting body (1) in which a cylinder (6) incorporating the piston unit (11) is mounted and whereby at the rear of the said cylinder relative to the direction of actuation of the said piston unit there is a feed chamber (23) for the said combustion gases while in front of the said piston unit in its initial position there is a confined space (17) around the piston rod (13) between its outside surface (19), the front face (21) of the front piston (15), the inside wall (18) of the cylinder (6) and the transfer shoulder (20) of the cylinder (6) in which the enclosed volume of air is subjected to compression when the piston unit (11) is actuated towards the bucker (2a) and this said air compression achieves a partial deceleration of the piston unit (11) wherein the said piston unit (11) comprises a rear piston (12), securely attached on the piston rod (13), and directly actuated by the combustion gases and, facing the confined space (17), a front piston (15) which is axially movable along the piston rod (13) in the direction of the rear piston (12) but whose movement in this direction is limited by a central internal damper (16) made of an elastically deformable material with good form memory located between the rear -piston (12) and the front piston (15) and occupying all the space between these said two pistons.

2. A gas-powered cutting tool as claimed in Claim 1 wherein the internal damper (16) is made of polyurethane rubber.

3. A gas-powered cutting tool as claimed in Claim 1 or Claim 2 wh erein the central internal damper (16) of the piston unit (11) has an original outer diameter when not subjected to load that does not exceed the internal diameter of the cylinder (6).

4. A gas-powered cutting tool as claimed in Claims l, 2 or 3 wherein the cylinder (6) in which the piston unit (11) is slidable is in turn displaceable in the body (1) in the same direction as the piston unit (11) and that to counteract this motion there is an external damper (10), fabricated from the same type of material as the internal damper (16) of the piston unit (11), located between a stop flange (9) on the cylinder (6) and the body (1).