GB1601661A - Gas generating charge for open chamber gas powered tool - Google Patents

Description

(54) GAS GENERATING CHARGE FOR OPEN CHAMBER GAS POWERED TOOL (71) I, DAVID DARDICK, a citizen of the United States of America, of 211 East 70th Street, New York, New York 10021, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to ignitible gas generating charges for powering tools for home and industry, and more particularly is concerned with a charge for an open chamber gas powered tool, such as a fastener driving tool for driving nails, studs and the like into workpieces.

Propellant gas powered fastener driving tools are well shown in the art. One class of such tools fires fasteners, such as studs, directly into a workpiece at high velocity in much the same way as a gun fires a bullet into a target. Another class of tools for driving fasteners are gas powered percussion tools. These tools have a breech mechanism for firing gas generating charges, and a plunger which is propelled through a working stroke by the gas generated by each fired charge. The driven plunger in the tool is, in turn, utilized to drive a fastener, such as a nail or stud; or to deliver an impact to a workpiece; or to perform some other work operation. Examples of gas powered percussion tools are disclosed in earlier patents of the present inventor, including U.S. patents nos. 3,514,026 and 3,283,657 and British patents nos. 1,036,224 and 1,074,195.

The present inventor is the originator of the "open chamber" type of weapon and gas percussion tool as is disclosed in U.S. patent no. 3,514,026. This tool provides for a "repeater" type of action, wherein a succession of open chamber charges are successively fed into the firing chamber and each is ignited to actuate the tool for one cycle of operation. This patented tool is relatively simple to construct and operate and may be manufactured at relatively low cost, yet provides the "repeater" action that is not only labor saving over the "single shot" tools of the prior art but permits a wide variety of high rate uses, such as driving fasteners in the building construction trades.

However, one of the most serious problems applicable to all presently available types of ignition type gas powered fastener driving tools is the relatively high cost of the gas generating charges. One of the reasons for this high cost is the cost of manufacturing the conventional types of closed end metal casings. Another is the relatively high cost of producing the gunpowder propellant.

As a result of the high cost of the cartridges, ignition type gas powered tools are primarily limited for use at present to various industrial purposes, such as for driving studs into concrete and the like, where the high cost of the cartridges is economically justified.

To avoid the high costs of processed propellant for both gun and tool use, various kinds of less expensive propellant have been attempted in the past. For example, in the 1870's, ordinary gun cotton in natural fibrous form was used in closed cartridges for rifles. However, this material was soon abandoned because of its excessively high burning rate that produced excessive peak pressures that often ruptured the gun barrels. To reduce this too rapid burn rate, the gun cotton fibres were at a later time compressed into solid shapes and pellets, to reduce the excessive surface burning area and accordingly reduce the excessive peak burning pressures. However, this practice made it difficult to ignite the compressed material, necessitating the use of a primer explosive to break up the compressed material and ignite the then expanded material.

In a later evolutionary step, the gun cotton fibres were combined with various binder materials to provide structural integrity and to permit control of the burning rates and peak burning pressures. However it was found to be difficult to obtain uniform ballistic performance by this type of binder processing, and the cost of producing this propellant was considerably increased due to the processing steps. A primer explosive was also required to break up the solidified propellant in the binder and permit ignition.

In still later methods of making propellant, the gun cotton, or nitrocellulose obtained from other vegetable fibres, was ground into particles of uuiform size and colloidally suspended in suitable binders that were molded or extruded into shaped charges or small "grains". This process, of course, provided the virtue of ensuring uniformity of the charges, and of permitting the process to yield propellant charges of controlled and uniform burning characteristics and pressures. Accordingly, variations of this manner of making propellants have been used up to and including the present time. However, the cost of producing this propellant is relatively high, and the cartridges or charges also necessitate the use of a built-in or combined primer charge for breaking apart the propellant and igniting the particles.

Thus it is seen that gun cotton, or other nitrocellulose product, in the form of relatively loose fibres or otherwise expanded, was discontinued for use as a propellant over one hundred years ago, because of its too rapid burning and too high peak pressure. lts use at latter periods was in more expensive processed form, either colloidally suspended in a binder and molded or shaped, compressed in the form of compacted particles with a combined primer charge, or otherwise processed in such manner as to control its too rapid rate of burning and peak pressures.

In the prior art specifically concerned with ignition type gas pressure producing charges for tools, efforts have been made to use caseless charges employing pelletized gun cotton (compressed particles) containing a primer explosive to break up the pellet and ignite the particles. However such charges were found to be relatively expensive as discussed above, as well as not uniform in ignition, and to leave a residue after burning.

Additionally, efforts have been made to reduce the high cost of cartridges by employing conventional closed cylindrical cartridge cases of plastics instead of metal.

However, these efforts were discontinued for the most part due to the difficulty of removing the cases after firing as a result of excessive deformation of the plastics walls.

Still further efforts have been made to use liquid propellants to power such tools.

However this has been found to greatly increase the cost of the tool, requiring the provision of added machinism for storing, metering, and igniting the liquid propellant.

According to the present invention, there is provided an open chamber gas generating charge for an open chamber gas powered tool, the charge comprising a plastics jacket of non-circular section defining an opening therethrough open at both ends and a substantially unprocessed nitrocellulose fibre propellant disposed in the opening, the propellant being sufficiently loosely packed to be ignitible by a spark or heated wire.

The propellant can be a felted mass. Since the propellant is not tightly compressed or combined with a binder, it requires no primer explosive to break it up and ignite it, but instead it is easily ignited by a separate spark or electrical igniter, either hot wire or spark, that may be provided as a built-in part of the firing chamber of the tool.

Because of the open-ended construction of the (preferably triangular section) jacket or case, combined with the characteristics of the "open chamber" construction of the tool, the excessive peak pressures that were heretofore generated by loose gun cotton, or loose nitrocellulose fibres or particles in a closed end cartridge, are considerably lowered. The cost of charges according to the invention can be low due to the use of substantially unprocessed nitrocellulose fibres instead of processed gunpowder.

The invention is illustrated, by way of example only, by the accompanying drawings, in which: Fig. 1 is a perspective view of a gas generating charge according to the invention Fig. 2 is a longitudinal section through the charge; Fig. 3 illustrates belted or attached charges according to the invention; Fig. 4 illustrates a modified version of the belted charges; Fig. 5 illustrates a magazine for holding the belted charges; Fig. 6 is a perspective view of a modified charge; Fig. 7 illustrates a gas powered tool; Fig. 8 is a section taken on a line 8-8 in Fig. ;and Fig. 9 illustrates one firing means for the tool.

Figs. 1 and 2 illustrate an open chamber gas generating charge 10 according to the invention for the gas powered open chamber tool 12 of Figs. 7 through 9.

Charge 10 has an outer hollow plastics jacket 14 of uniform non-circular cross-section suitable for an open chamber breech action.

In this instance, the jacket has the preferred generally equilateral triangular cross-section described in the above mentioned patents and includes three side walls 16 which are externally cylindrically curved to the same radius. As will appear from the ensuing description, however, an open charge according to the invention may have any other cross-section, suitable for an open chamber breech action.

Extending longitudinally through the jacket 14, on its central longitudinal axis, is a propellant chamber 18. The illustrated chamber is circular in cross-section, although the chamber may be triangular in cross-section as shown in Fig. 6, or have any other desired cross-section. Propellant chamber 18 opens through the ends of the jacket 14, as illustrated. Filling the propellant chamber is a propellant 20, such as substantially uncompressed nitrocellulose fibres.

The open ends of the propellant chamber 18 may be left uncovered. However, the chamber ends may be covered by combustible seals of paper or other flammable material which are adhesively bonded or otherwise secured to the ends of the jacket 14.

The outer jacket or casing 14 is suitably made of inexpensive plastics material that can be rapidly formed in large quantity by extruding its cross-section lengthwise in long lengths and transversely cutting into individual units. For the propellant, it is preferred to employ substantially noncompressed, or lightly compressed, fibrous nitrocellulose, for example ordinary gun cotton fibres, as discussed above, whose use was abandoned in the 1800's; advantage can also be taken of many other plentifully available kinds of vegetable fibre that can be similarly treated cheaply by known chemical nitrating processes so as to be as highly inflammable, in the manner of gun cotton.

As is well known, such fibres, when dry and only loosely compressed, provide an extremely large exposed surface area and are therefore highly inflammable. In fact, the extremely high rate of burning and correspondingly high peak pressures produced by burning such loose gun cotton were the very reasons for discontinuing its use as a propellant in conventional closed end type cartridges, since such early use resulted in fractunng and cracking of gun barrels as discussed above. However, according to the present invention the facts that the jackets 14 of the charges are open at both ends, rather than closed at one end like a conventional cartridge case, and that such charges are employed in an open firing chamber instead of a conventional closed member, enables this inexpensive and plentiful propellant to be used with safety.

The substantially uncompressed form of the propellant enables it to be igniated, without a primer, by means of an easily generated spark, hot wire, or arc produced within the tool in the firing chamber. The elimination of the need for an explosive primer and the simplification of the ignition mechanism further reduce the cost of both the charge and the driving tool enhancing the economic utility of the invention for both industrial and home tool uses.

As will be appreciated by those skilled in the propellant arts, the mass or total quantity of fibres provided in the propellant charge determines its total energy and heat content available upon combustion, whereas the degree of compression of the fibres 20 within the opening of jacket 14 determines the burnable surface area and accordingly the rate of burning and peak pressures produced. Accordingly, both the mass of the propellant 20 used in the charge as well as the degree of its compression or looseness will be varied to some extent depending upon the size of the tool and driven element, as well as the nature and material of the workpiece. However, as will be appreciated from the foregoing, the propellant will always be employed in a relatively uncompressed or lightly compressed form that is ignitible by separately produced spark or hot wire.

As noted above, the gas generating charge 10 is adapted for use in the open chamber gas powered tool 12 of FIGS. 7 to 9. Except for the charge firing means and a fastener magazine embodied in the tool 12, the latter is identical to that described in my earlier mentioned Patent No. 3,514,026 which, as noted in the latter patent, embodies a breech mechanism like that of my prior Patent No. 2,865,126. Accord is it is unnecessary to describe the tool 12 in elaborate detail.

Suffice it to say that the tool has a rear open chamber breech mechanism 24 in which the charges 10 are fired to generate a pressurized propellant gas and a forward cylinder or barrel 26 containing a plunger 28 which is driven through a forward working stroke in the barrel by the propellant gas pressure. A spring 30 returns the plunger to the rear end of its working stroke after firing. Plunger 28 has a forward reduced shank 32 which slides in a forward sleeve portion 34 of the barrel 26. The front end of this sleeve portion is open.

Referring to FIG. 8, the breech mechanism 24 has a breech cylinder 36 rotatable in a breech frame 38 including a handgrip 40 and a firing strap 42. Cylinder 36 contains chambers 44 which open laterally through the cylinder circumference and endwise through the front and rear cylinder ends.

These chambers have a cross-sectional shape matching that of the gas generating charge 10: Within the handgrip 40 are magazines 46,48 for containing a number of the charges 10. The upper ends of these magazines have infeed openings to the cylinder 36 through which the charges are urged against the cylinder by springs 50 in the lower ends of the magazines. The magazines have upper access openings, closed by hinged covers 52, 54 through which the charges 10 are inserted into the magazines.

Each cylinder chamber 44 is rotatable in the direction of the arrow in FIG. 9, through infeed, firing, and ejection positions. In the infeed position, the chambers register with the infeed openings to the magazines 46,48, as do the two lower chambers in FIG. 8, to permit infeed movement of charges 10 from the magazines into the chambers, in the manner described in my prior Patent No.

2,865,126. Each cylinder chamber 44, when in a firing position, is located under and has an open side closed by the firing strap 42, as illustrated by the upper chamber in FIG. 8.

In this firing positon, each cylinder chamber is axially aligned with and opens forwardly to a passage 56 leading to the rear end of the tool plunger barrel 6. Rotation of each chamber 44 from firing to infeed positions occurs through the ejection position, wherein the chamber registers with an ejection opening 58 in the breech frame 38.

Embodied in the breech mechanism 24 is a conventional trigger actuated mechanism (not shown) including a trigger 60 for rotatin the cylinder 36 stepwise through the cylinder chamber infeed, firing and ejection positions. Each actuation of the trigger 60 rotates one chamber, containing a charge 10, from infeed to firing positions where the charge is fired in the manner to be explained, and another chamber from firing position, through ejection position where the jacket 14 of the fired charge is ejected back to infeed position to receive a fresh charge.

The tool 12 may have an electrical firing means 60 (fig. 9) for firing the charges 10 in the firing position. This firing means includes an electrical propellant igniter 62 mounted in the breach frame 38, at the rear of the breech cylinder 36 and on the axis of the breech passage 56, so as to be disposed in ignition relation to the propellant 20 of a charge located in firing position within the cylinder chamber 44. thins igniter is effective, when energized, to ignite the expanded propellant of the charge in firing position through the rear open end of the jacket 14 of the charge. Igniter 62 may be a spark, hot wire, or other ignition means capable of igniting means capable of igniting the prop ellant of the charge and, in this description, is assumed to be a hot wire.For example, the igniter may be a spark generator of a non-electrical type.

The hot wire igniter 62 of fig. 9 is energized by a firing circuit 64 including a trigger switch 66, safety switch 68, and battery 70 connected in electrical series with the igniter, as shown in FIG. 10. Trigger switch 66 is a normally open switch which is mounted in the breech frame 38 for closure by depression of the trigger 60 to rotate a breech cylinder chamber 44 to firing position in such a way that the switch closure occurs after arrival of the chamber in firing position. Safety switch 68 is a normally open switch mounted at the front end of the tool barrel 26 and includes a work engaging member 72 projecting forwardly of the barrel. The safety switch is closed by pressing the tool against a workpiece to depress the switch member 72 rearwardly relative to the barrel.Battery 70 is mounted in the breech frame 38 and is accessible for replacement by removing a threaded battery retaining cap 74.

From the description to this point, it will be understood that each actuation or depression of the trigger 60 rotates a breech chamber 44 and its contained gas generating charge 10 to firing position. Assuming that the safety switch 68 is closed by pressing the tool against a workpiece, depression of the trigger also energizes the igniter 62 to fire the charge in firing position by closure of the trigger switch 66. The pressurized gas genera ted by the fired charge enters the rear end of the tool barrel 26 through the passage 56 and drives the plunger 28 through a forward working stroke in the barrel. After firing, the plunger is returned rearwardly by its spring 30. The plastics jacket 14 of the charge seals the breech during firing. After firing sufficient leakage space exists to permit return of the plunger by its spring.

As indicated earlier, the tool may be designed for various uses. The particular tool shown is a fastener driving tool, specifically a nail driver, mounting on its barrel 26 a replaceable nail magazine 76. This nail magazine feeds a nail to a nail positioning means (not shown) in the barrel in front of the plunger 28 each time the plunger retracts for driving of the nail into a workpiece by the plunger during its next working stroke. This nail magazine and nail positioning means are conventional and hence need not be further described.

In some cases, a tool according to the invention may be designed for use with belted or attached gas generating charges.

FIG. 3 illustrates such belted charges. In this case, the charges 10 described eariler are adhesively bonded to a feed belt or web 78 constructed of paper or other suitable material. The charges are spaced along the belt in accordance with the circumferential spacing between the breech cylinder chambers of the tool.

As noted earlier, the open ends of the propellant chambers of the charges 10 may be closed by seals. FIG. 4 illustrates modified belted charges wherein the feed belt or web 80 has integral flaps 82 along its edges which may be folded against and bonded to the ends of the charges to form the propellant chamber seals.

The belted charges of FIGS. 3 and 4 may be stored in a magazine 86 (FIG. 5) adapted for attachment to a tool. The belted charges are preferably placed in the magazine in aligned arrangement with the propellant openings all facing in the same direction for purposes of safety. The belt 80 with its attached charges 10 may be withdrawn from the magaazine through an exit opening 88 in the magazine. This opening may be sealed bya strip of pressure sensitive tape 90 or the like which also anchors the leading end of the belt to permit feeding of the belt into the tool.

Production of charges according to the invention best involves filling the jacket openings with the propellant whilst it is in a moist non-ignitible condition. For safety purposes the charges are preferably fabricated and packaged in a storage container, such as magazine 86, all while their propellant is still in moist state and the propellant is then dried in its jacket or case which is inside in the container, after which the latter is hermetically sealed. Fabrication of the charges may be accomplished, for example, by extruding a long tube of plastics having the desired cross-section of the charge jackets, filling the tube with lightly compressed or substantially uncompressed nitrocellulose propellant fibres in a moist state, and then slicing the tube into individual charges.

Alternatively, the jackets may be formed first by extruding and slicing a long tube of plastics or by injection molding the jackets, after which the jackets may be filled with the moist propellant fibres. The propellant may be in other expanded forms, such as porous felt, but in all cases it is sufficiently loosely packed in the dry product to provide the large surface area in contact with air necessary for direct ignition by a spark or electric ignition.

After packaging of the completed but still moist charges in the storage container, the propellant is dried by placing the container in a suitable drying atmosphere. The container is provided with one or more vent openings 106 (FIG. 5) to permit escape of the moisture released from the propellant.

After drying, the container is hermetically sealed, as by sealing the vent openings with tape 108. This safe method of handling the charges virtually eliminates any possibility of ignition of the highly inflammable propellant during the fabricating and packaging operations. The storage container will be sized to receive the charges with a close fit in their endwise direction such that even if ignition of the propellant of a charge somehow occurs in the container, its jacket will prevent ignition of the other charges.

U.K. Patent No. 1,466,401 describes and claims a gas generating charge for an open chamber gas powered tool, comprising a jacket of non-circular cross-section containing a propellant chamber extending longitudinally through and opening through the ends of the jacket, and a propellant within said chamber.

WHAT I CLAIM IS: 1. An open chamber gas generating charge for an open chamber gas powered tool, the charge comprising a plastics jacket of non-circular section defining an opening therethrough open at both ends and a substantially unprocessed nitrocellulose fibre propellant disposed in the opening, the propellant being sufficiently loosely packed to be ignitible by a spark or heated wire.

2. A charge according to claim 1 wherein the propellant comprises a felted mass of nitrocellulose fibres.

3. A charge according to claim 1 or 2 wherein the jacket is of generally triangular external cross-section.

4. A method of making a charge according to claim 1 in which the opemng in the jacket is filled with the propellant while the propellant is in a non-ignitible moist state.

5. An open chamber gas powered percussion tool for driving fasteners, and a gas generating charge therefor according to any of claims 1 to 3, wherein the charge is fed into and removed from the chamber in a lateral direction by means of a laterally moving feed mechanism and wherein the firing chamber of the tool includes a firing strap for retaining the charge jacket and a zone for communication with the rear portion of the propellant opening in the jacket and containing a spark or hot wire firing mechanism for directly igniting the propellant within the jacket.

6. A method of powering an open chamber gas powered tool which comprises loading the tool with a charge according to any of claims 1 to 3 and igniting the propellant of the charge directly with a spark or heated wire.

7. A gas generating charge substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying draw ings.

8. A gas generating charge substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

9. A method according to claim 6 and substantially as hereinbefore described with reference to Figures 7 to 9 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. aligned arrangement with the propellant openings all facing in the same direction for purposes of safety. The belt 80 with its attached charges 10 may be withdrawn from the magaazine through an exit opening 88 in the magazine. This opening may be sealed bya strip of pressure sensitive tape 90 or the like which also anchors the leading end of the belt to permit feeding of the belt into the tool. Production of charges according to the invention best involves filling the jacket openings with the propellant whilst it is in a moist non-ignitible condition. For safety purposes the charges are preferably fabricated and packaged in a storage container, such as magazine 86, all while their propellant is still in moist state and the propellant is then dried in its jacket or case which is inside in the container, after which the latter is hermetically sealed. Fabrication of the charges may be accomplished, for example, by extruding a long tube of plastics having the desired cross-section of the charge jackets, filling the tube with lightly compressed or substantially uncompressed nitrocellulose propellant fibres in a moist state, and then slicing the tube into individual charges. Alternatively, the jackets may be formed first by extruding and slicing a long tube of plastics or by injection molding the jackets, after which the jackets may be filled with the moist propellant fibres. The propellant may be in other expanded forms, such as porous felt, but in all cases it is sufficiently loosely packed in the dry product to provide the large surface area in contact with air necessary for direct ignition by a spark or electric ignition. After packaging of the completed but still moist charges in the storage container, the propellant is dried by placing the container in a suitable drying atmosphere. The container is provided with one or more vent openings 106 (FIG. 5) to permit escape of the moisture released from the propellant. After drying, the container is hermetically sealed, as by sealing the vent openings with tape 108. This safe method of handling the charges virtually eliminates any possibility of ignition of the highly inflammable propellant during the fabricating and packaging operations. The storage container will be sized to receive the charges with a close fit in their endwise direction such that even if ignition of the propellant of a charge somehow occurs in the container, its jacket will prevent ignition of the other charges. U.K. Patent No. 1,466,401 describes and claims a gas generating charge for an open chamber gas powered tool, comprising a jacket of non-circular cross-section containing a propellant chamber extending longitudinally through and opening through the ends of the jacket, and a propellant within said chamber. WHAT I CLAIM IS:

1. An open chamber gas generating charge for an open chamber gas powered tool, the charge comprising a plastics jacket of non-circular section defining an opening therethrough open at both ends and a substantially unprocessed nitrocellulose fibre propellant disposed in the opening, the propellant being sufficiently loosely packed to be ignitible by a spark or heated wire.

2. A charge according to claim 1 wherein the propellant comprises a felted mass of nitrocellulose fibres.

3. A charge according to claim 1 or 2 wherein the jacket is of generally triangular external cross-section.

4. A method of making a charge according to claim 1 in which the opemng in the jacket is filled with the propellant while the propellant is in a non-ignitible moist state.

5. An open chamber gas powered percussion tool for driving fasteners, and a gas generating charge therefor according to any of claims 1 to 3, wherein the charge is fed into and removed from the chamber in a lateral direction by means of a laterally moving feed mechanism and wherein the firing chamber of the tool includes a firing strap for retaining the charge jacket and a zone for communication with the rear portion of the propellant opening in the jacket and containing a spark or hot wire firing mechanism for directly igniting the propellant within the jacket.

6. A method of powering an open chamber gas powered tool which comprises loading the tool with a charge according to any of claims 1 to 3 and igniting the propellant of the charge directly with a spark or heated wire.

7. A gas generating charge substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying draw ings.

8. A gas generating charge substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

9. A method according to claim 6 and substantially as hereinbefore described with reference to Figures 7 to 9 of the accompanying drawings.