US1905863A - Blasting cartridge - Google Patents

Description

Aprifi 25, 1933. A. HARRIS v BLASTING CARTRIDGE 4 Sheets-Sheet l Filed Oct. 11

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P 5 1 mm M Aprifi 25, 1933. A. HARRIS BLASTING CARTRIDGE 4 Sheets-Sheet 2 Filed Oct. 11 1930 April 25, 3933. HARRls I 1,905,863

BLAST IN G CARTRIDGE Filed Oct. '11. 1930 4 Sheets-Sheet 3 Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE ALLYN HARRIS, OF W'HEATON, ILLINOIS, ASSIGNOR TO SAFE'IY MINING COMPANY, A

- CORPORATION OF ILLINOIS BLASTING CARTRIDGE Application filed October 11, 1930. Serial No. 488,143.

This invention relates to blasting cartridges of the well known type wherein a highly compressed or liquefied gas is employed as the blasting medium. In this type of cartridge, the desired energy is developed by subjecting the gas to intense heat generated by an electrically energizable heater unit, thus causing the gas to expand and increase in pressure. When the desired energy has been developed, the cartridge is automatically vented to liberate the gas into the material on which it is to act.

One of the particular problems involved in cartridges of this type is to devise an entirely suitable means for conducting electricity from the exterior to the interior of the cartridge for energizing the heater. This, of course, involves some form of electrode accessible to the interior of the cartridge for engagement with the heater circuit and to the exterior thereof for engagement with a source of electricity. The electrode must, of course, be completely insulated from the cartridge and at the same time, must afford a gas tight seal at the point or points where it extends or is made accessible to the exterior of the cartridge. The two factors which make this problem particularly difiicult are, the extremely high pressures involved in cartridges of this type, often approximating 40,000 pounds per square inch, and the comparatively low compressive strength of available materials possessing the necessary insulating and sealing qualities.

The present invention is, in part, concerned with this problem and aims to provide an improved means for conducting electricity from the exterior to the interior of cartridges of the type indicated. More particularly, it is an object of the invention to provide an electrode so constructed and arranged with reference to a cartridge that the pressure acting on the electrode is not transmitted in substantial amount to the material which insulates and seals it.

Under present practice, the automatic venting of the cartridges involves the destruction of a replaceable steel disc at each discharge. This, of course, is an appreciable item of expense, not only in the cost of the discs, but

also in the labor involved in the preparation of cartridges for action. Accordingly, it-is an object of the invention to provide an improved and less costly means for automatically venting cartridges of this type.

Another item which contributes largely to the cost of operation of this form of blasting means is the combustible heater unit. Of course, this unit is destroyed at each discharge and must be replaced before the cartridge can be used again. This involves a considerable labor cost in addition to the cost of the heater unit. It is an object of this invention to further reduce operating costs by providing a substantially permanent heater unit which will not be affected by discharge of the cartridge and which need not be renewed or replaced after each discharge.

in addition to the foregoing, it is an object of the invention to generally improve cartridges of the type indicated and, particularly, to provide a simplified method and means for governing the admission of gas into the cartridges.

Referring to the drawings,

Figure 1 is a view in longitudinal section, with parts in elevation, illustrating a cartridge embodying certain features of the inventlon.

Figure 2 is a view in longitudinal section illustrating the construction of the portions shown in elevation in Figure 1.

. Figure 3 is a longitudinal sectional view of a modified form of the invention.

Figure 4 is a top plan view of aportion of the structure shown in Figure 3.

Figure 5 is a view in longitudinal section illustrating a slightly modified form of the construction shown in Figures 3 and 4.

Figure 5a is a plan view of a portion of Figure 5.

Figure 6 is a view in longitudinal section illustrating a third modification of the invention.

Figure 7 is a view similar to Figure 6, but showing a fourth modification.

Figure 8 is a view in transverse section taken on line 8-8 of Figure 7.

Figure 9 is a longitudinal sectional view illustrating another form of electrode and an im rovcd charging means.

igure 10 is a view in longitudinal section illustrating a duplex electrode'arrangement. V Figure 11 is an end view of the device of Fi ure 10.

igure 12 is an end view of the device of Figure 13.

i are 13 is a view in longitudinal section illustrating a new type of heater unit.

Figure 14 is an enlarged detail view in section, illustrating a contact plug for the cartridge of Figure 17.

Figure 15 is a longitudinal sectional view of the improved venting device, taken along line 1515 of Figure 16.

Figure 16 is a top plan view of the device shown in Figure 15. V

Figure 17 is a transverse sectional view taken on line 17-17 of Figure 15.

Figure 18 is a detail view illustrating certain modifications of the device shown in Figure 15.

The complete cartridge with one form of the invention applied thereto is shown in Figure 1. It consists of a substantially cylindrical metallic body 1 having duplicate internally threaded ends 2 and 3, sealing surfaces 4 and 5, and a gas chamber 6. A standard form of venting device consisting of a re laceable metal disc 7 and a discharge cap 8 is applied to the threaded end 2 of the cartridge body. 'A ecial form of shell top 9 is applied to the t readed end 3 of the cartridge body. The shell top embodies means for introducing gas into the chamber 6 of the cartridge and also carries or cooperates with a heater unit 10, by which the cartridge may be energized. It will be understood, of course, that the cartridge is automatically vented by rupture or failure of disc 7 in response to a predetermined pressure in cham her 6, thus permitting the gas to pass out through ports 11 in discharge cap 8 and into the material on which it is to act.

The construction of shell top 9 and associated parts is shown in Figure 2. The shell top has threaded engagement with the part 3 of the cartridge body and is adapted to have sealing engagement with the surface 5 through the medium of a gasket 12, preferably of copper; On the inner end of the shell top is an extension 13, of reduced diameter, in which is centrally threaded a bolt 14, the head of which is of the same diameter as extension 13. Surrounding the bolt 14 and interposed between the head thereof and the end face of extension 13 is a disc 15, which isseparated from the bolt and extension by fibre or other insulators 16. The inner face of bolt 14 and the adjacent face of disc 15, and the end face of extension 13 and the adjacent face vof disc 15 are sealing surfaces which are effectively sealed by the interposed insulating washers 16, due to pressure exerted thereon by suitably tightening bolt 14. Thus, disc 15 is an electrode accessible to the interiorof the cartridge for cooperation with the heater circuit, completely insulated from the cartridge, and reliably sealed to prevent escape of gas where it enters the interior of the cartridge. It is apparent that this electrode must also be accessible to the exterior of the cartridge for cooperation with a source of electricity, and this is accomplished by extending a lead or contact element through the sealed surfaces on the end of extension 13 and the adjacent face of electrode 15. This element is in the form of a rod 17 which extends through the shell top from the outer end thereof through the end face of extension 13 and has threaded engagement with the electrode 15. An insulating sleeve 18 separates the rod 17 from the shell to It will be understood that since rod 1 extends through the face of extension 13, insulating disc 16, and the adjacent face of electrode 15 within the sealed area thereof, the rod and surrounding insulating sleeve will not be exposed to the pressure existing within chamber 6 and cons uently will not present a possibility of lea age.

The most important feature of the elec trode arrangement above described is that the pressure in chamber 6 acts upon it in relatively opposite directions, thus producing substantial neutralization of forces and practically eliminating the transmission of force to the relatively weak insulating and sealing elements. It will be noted that the exposed portions of the opposite sides of electrode 15' are of substantially equal area and for this reason, the force tending to move the electrode in one direction cannot be sub stantially greater than the force tending to move it in the opposite direction. This not only removes the danger of damaging the insulating and sealing elements, but also greatly simplifies the sealing problem, due to the fact that there are no unbalanced forces tending to separate the sealed surfaces.

For the purpose of connecting the electrode 15 to the heater circuit there is shown a sleeve-like member 19 having threaded engagement with the periphery of electrode 15 and also having a flange 20 for engagement with the flanged head of plug 21 of heater unit 10. The match head or squib 22 of the heater unit has one lead extending through the center of wood plug 21 and forming a.

contact for engagement with the end of bolt 14, and a second lead extending between the plug and heater casing and terminating be- 1,eos,aes

This particular means of connecting the electrode to the heater is by no means essential and it is to be understood that this type of electrode may be used in any way desired.

Figure 2 also illustrates a very simple valve for governing the admission of gas into the cartridge. The shell top is provided with a cylindrical bore 24 in which is threaded a flanged sleeve 25 which is adapted to be sealed on the shell top as indicated at 26. Threaded through the center of this sleeve is a valve stem 27 having a head 28 in which is formed a pocket for reception of a fibre or soft metal insert 29. A passage 30 extends from the nozzle seat 31 into the lower portion of bore 24, and a second passage 32extends from the center of the bottom wall of the bore to the inner face of the shell top. A raised seat 33 is formed on the bottom wall of the bore around passage 32. Packing discs 34 surround valve stem 27 and are arranged to be compressed between valve head 28 and the'end of sleeve 25 when the valve is screwed outwardly to permit charging, thus preventing leakage of gas around the threads in sleeve 25 and on valve stem 27.

A modified electrode arrangement is shown in Figure 3 in connection with a cart-ridge and shell top of substantially the same construction as that of Figure 2. In this form, the shell top 35 is formed with an extension 36 of reduced diameter, which extension is formed with two parallel chordal flats 37. Substantially at the center of these flats and extending at right angles to the surfaces thereof is a bore 38 which extends through from the surface of one flat to the other. On each fiat, and concentric with bore 38 is a countersink or depression 39, designed to receive insulating and sealing discs 40. A bolt 41 extends through concentric openings in discs 40 and is thus concentrically positioned in the substantially larger bore 38. The bolt is provided with a head 42 of substantially greater diameter than bore 38, butslightly less than washers 40. A screw cap 43, which is'the same size as head 42, engages the end of bolt 41. Thus, by suitably tightening cap 43 on bolt 41, the bore 38 is completely and dependably sealed from the interior of the cartridge and. at the same time, the bolt and its cap are effectively insulated from the cartridge. Therefore, the bolt assembly constitutes an electrode whichv is accessible to the interior of the cartridge and which is reliably sealed against the escape of gas at the point where it enters the pressure chamber. For the purpose of connecting the electrode to a source of electricity there is provided a small conductor 44 extending entirely through the shell top from the exposed end thereof and having threaded connection with bolt 41 within the bore 38. The conductor 44 is surrounded by an insulating sleeve 45. A contact member 46 is threaded into the bolt head 42 and arranged for contact with a termirtal 47 of an electrically energizable heater uni It is apparent that the construction of Figure 3 affords the same balanced relation as to pressures as that of Figure 2. The bolt head 42 and screw cap 43 have the same areas exposed to the pressure within chamber 6 and, since the head andcap are directly connected, the pressure exerted on one is neutralized or offset by an equal and oppositely directed pressure exerted on the other. For this reason, the insulating and sealing washers 40 are not subjected to substantial pressures and the sealed relation is effectively maintained since there are no unbalanced forces tending to separate the sealng surfaces. It is also apparent that there is no necessity of sealing around conductor 44, since the bore 38 which it enters is itself entirely sealed from the gas chamber 6.

The construction shown in Figures 5 and 5a is very similar to that of Figure 3, the chief difference being that the electrode is so arranged as to have direct contact with the terminal of a heater unit, instead of employing an intermediate contact member, such as member 46 in Figure 3. Referring to Figures 5 and 5a, it will be noted that the shell top extension 48 is of a width substantially equal to the diameter of the sealing and insulating washers 49, and that its end portion conforms to the contour of said washers. The bolt head 50 and screw cap 51 are slightly larger in diameter than the washers and consequently overhang the washers and the rounded end of extension 48, thus permitting direct contact with the metallic terminal 52 of heater unit 53. Otherwise, the construction and. arrangement of the electrode and associated parts are the same as, and present all of the advantages of the construction of Figure 3.

The construction shown in Figure 6 is a slight modification of that shown in Figure 2. The disc like electrode 15 is replaced in Flgure 6 by a cup like electrode member 54 which is arranged for direct abutting contact with the metallic terminal 55 of heater unit 56. Otherwise, the construction is substantially the same as that of Figure 2.

Referring now to Figures 7 and 8, there is shown a construction which difi'ers considerably from those hereinabove described, but which embodies the chief characteristics and advantages of such other structures. In this form of the invention, the electrode is in the form of an annular or ring like member 57 which'is supported by the ledge or shoulder 58 formed in the cartridge body, but separated therefrom by an insulating and sealing washer 59. The periphery of theelectrode 57 is maintained out of contact with the cartridge body by an insulating sleeve 60, and a second insulating and sealing washer 61 is terposed between the outer face of the elec- 7 1n trode and the inner end of shell top 62. Thus, the electrode is comdpletely insulated from the as regards the balancing of forces as do the cartridge body an shell top and is alsoeffectively sealed on its opposite faces with the cartridge bodyand shell top by washers 59 and 61, respectively. In order to make the electrode accessible to the exterior of the cartridge, the body is provided with an opening 62' through which extends a contact element 63 having threaded engagement with the electrode. As shown, opening 62 is substantlal- 1y larger than contact element 63 in order to permit slight movement of the latter and yet maintain the same out of contact with the cartridge body.- Obviously, an insulating sleeve could be provided for element 63 if necessary.

The electrode arrangement above described serves both as a contact for one terminal of a heater circuit and as a support for the heater unit. The central opening in the electrode is of such diameter as to receive a heater unit 64 and to support the same by engagement with the flanged head of plug 65. A match head or squib 66 has the end of one lead d1sposed beneath the flange of plug 65 and in contact with the electrode, while the other lead ertends through the center of the plug and has direct contact with the shell top 62. Referring to Figure 8, it will be noted that the electrode is provided with a plurality of slots 67 which permit free passage of gas from oneside to the other thereof.

In the operation of a cartridge according to Figures 7 and 8, the first step is to remove the shell top 62 in order that a new heater unit may be inserted in the position shown.

vIt will be understood that the electrode and its insulators remain in thecartridge at alltimes. After a new heater has been inserted and the shell top replaced and sufliciently tightened to seal both faces of the electrode, gas may be introduced into the cartridge by applying a chargin nozzle to the nozzle seat 67 and o ning va ve 68.. In order to (11$- charge t e charged cartridge it is merely necessary to.connect a source of electricity to some ortion of the shell top or cartridge body an to member 63.

The electrode construction of Figures 7 and 8 presents substantially the same advantages preceding forms.

Figure 9 discloses a cartridge embodying improved charging means, together with a slight modification of electrode arrangement of Figure 2. Referring first to the charging means, the threaded portion 69 of the cartridge body is adaptedto receive a nut 70, the inner end surface of which is designed for sealing engagement with the surface of shoulder 71 through the medium of a suitable gasket 72, preferably of fibre or copper. A nozzle seat 73 is formed in the cartridge body,

and a charging passage 74 leads from the lower part of this seat to a mid-point on the sealing surface of shoulder 71. Thus, by screwing the nut outwardly a fraction of a turn or more, the opening of passa e 74 on the surface of shoulder 71 is unseale and gas may be introduced into the cartridge. Of course, passage 74 may be again sealed by screwing the nut inwardly, thus confining the gas charged into the cartridge. The normal pressure of the gas usually employed in cartridges of this type is approximately 1,000 pounds per square inch and for this reason it is necessary to provide some means for preventing the escape of gas around the threads of the nut during the charging operation. This is accomplished by providing a second nut 75 threaded into the portion 69 of the cartridge body and having an integral flange adapted to have sealing engagement with the end surface of said body through the medium of a suitable gasket 76. Another sealing gasket 77 is interposed between the outer end surface of nut 70 and the adjacent end surface of nut 75. Figure 9 illustrates the parts in their normal relative positions, nut 70 being sealed on the surface of shoulder 71, and there being a slight clearance between the adjacent surfaces of nuts 70 and 75 and gasket 77. In the charging position, nut 70 is screwed outwardly until its outer end surface is effectively. sealed on the adjacent surface of nut 75, through the gasket 77. Thus, gas may be introduced into the cartridge through passage 74, and the escape of gas around the threads of the nuts is prevented by the sealed relation atgaskets 76 and 77. Nut 75 is permanently sealed on gasket 76 and the end of the cartridge. Suitable wrench sockets 78 and 79 may be provided in nuts 70 and 75, respectively.

The electrode construction carried by nut 70 of Figure 9 differs from that shown in Figure 2 only in that the bolt 14 of the latter figure is replaced by an integral threaded extension 80 on nut 7 0, which extension is adapted to receive a screw cap 81. The conductor 82 which is threaded into electrode 83 terminates at the bottom of wrench socket 78 of the nut.

In all of the electrode arrangements hereinabove described, it is necessary to ground one branch of the heater circuit on the cartridge body or on some part having electrical contact therewith, thus including the entire metallic cartridge in the heater circuit. This givesrise to a rather remote possibility of sible with electrode designs heretofore known, since such designs have necessarily involved relatively large parts to withstand the severe pressure conditions hereinabove outlined, and which, due to size, could not 'be practically duplicated in a cartridge of reasonable dimensions. According to the present invention, the several forms of electrode are so designed as to achieve balance or neutralization of forces .and, for this reason, the parts involved may be made relatively small, thus permitting duplication within practical limits, if desired. An example of this is illustrated in Figure 10,, and will now be described.

This'particular example is a duplication of the type of electrode arrangement shown in Figure 2. Referring to Figure 10, it will be noted that the bolt 84 carries an electrode 85, which corresponds to electrode 15 of Figure 2, and a second electrode 86, of slightly'smaller diameter than electrode 85. A conductor 87 makes electrode 85 accessible to the exterior of the cartridge in the same manner as in Figure 2. A second conductor 88 and insulating sleeve 89 extend through electrode '85, and the second conductor has threaded engagement with the second electrode 86. Thus, electrodes .85 and 86 are accessible to both the interior and exterior of the cartridge. The opposite exposed surfaces of electrode 85 are of equal area, and the same is true of electrode 86. Any desired means may be employed for connecting the two electrodes to the two contacts of the heater unit.

. One such means may consist of a cup like member 90 screw threaded on electrode 86, and a flanged sleeve 91 screw threaded on electrode 85. The flange of sleeve 91 may serve to draw and hold the heater plug 92 into contact with the member 90 and match head 93 may have its leads arranged in the manner shown, one in contact with the end of cup like member 90, and the other in con-.

tact with the flange of sleeve 91. A plurality of holes 94 may be provided in members 90 and 91 to permit gas to flow therein, thus maintaining equalization of pressures.

While the duplex electrode arrangement of Figure 10 is shown in connection with a cartridge of the general construction shown in Figure 9, it is to be understood that the same is applicable to any of the types of construction shown, or other types. It should also be understod that the duplex electrode idea can be very easily carried out in connection with the other types of electrode shown.

Figure 13 illustrates one application of a permanent electric heater unit to a cartridge of the type under consideration. As here shown, the cartridge is substantially the sion 96 adapted to receive the internally threaded end of an electric heater casing 97. This casing has a wall thickness designed to withstand the'maximum pressure which may exist in the cartridge chamber, and in order to prevent the entrance of gas to the interior of the casing, its open end is securel sealed on nut 95 by means of gasket98. resistance coil 99 is disposed within the casing on insulator 100. Lead 101 of the coil extends outwardly through the center of the insulator 100 and through a central bore in nut 95. The other end 102 of the coil has contact with the flange of metallic sleeve 103, which isins'ulated from lead 101 and the nut by fibre sleeves 104. Referring to Figure 14, sleeve 103 may be internally threaded at its outer end to receive a threaded contact plug 105 which has a central insulated terminal 106.

An importantfeature of this permanent electric heater is the security against damage by the destructive discharge pressures generated in cartridges of this t e. Since the heater casing is substantially indestructible and is permanently sealed on the inner surface of the nut, the internal parts are fully protected. Moreover, this arrangement greatly simplifies the matter of making the heating element accessible to theexterior of the cartridge for connection to a source of electricity, since pressure is not involved.

While a particular construction of electric heater has been illustrated and described, it is to be understood that many other forms may be employed without departing from the spirit of the invention. A permanent electric heater for cartridges of this type will result in very substantial savings in the costs of operation and maintenance Cartridges of the type under consideration have usually employed a venting device of the general form illustrated in Figure 1, involving a metal disc designed to rupture or shear out at a predetermined pressure. This device materially contributes to the cost per discharge, not only the cost of the discs, but also the labor cost involved in removing the parts of the sheared disc, replacing it with a new disc and gasket, and again sealing the discharge end of the cartridge at surface 4 by screwing the discharge cap tightly into the cartridge. Considerable thought has been given to the problem of providing a pres sure responsive discharge device not involving destruction of a part or parts. Owing to the extremely high discharge pressures, it has been thought impossible to devise any form of practical mechanical venting device capable of withstanding or absorbing the tremendous discharge shock. According to the present invention, such a device is provided, embodying a unique and very useful method of dissipating the shock energy.

Referring to Figures 15 to 17 inclusive, the venting device is embodied in a somewhat end of'a cartridge 109, vof the usual construcformed with an axial bore 111, one en tion. The inner end of cap 107 may be securely sealed on surface 110 ofthe cartridge by means of a suitable gasket. The ca 1? which is in open communication with the interior of the cartridge and the other end of which communicates with a pair of transversely directed discharge ports 112. the purpose ofsealing these openings there is provided a pair of members 113 ofshght- 1y, greater-width than the diameter'of said ports and adapted to overlie them in the manner shown. These members are pivotally mounted-in thecap as indicated at 114. A wall 115 closes theend of bore 111 just beyond the discharge ports 112. Referring to Figures 16 and'lf, it will be noted that slots 116 are formed in cap 107, said slots being designed to receive and snugly fit the members 113. It will also be noted that-the outer .4

ends'of discharge ports 112 terminate at the bottom surfacesof said slots.

For the purpose of exerting a sealing pressure on the ends'of members 113 which over lie discharge ports 112, the opposite ends of 3d said members are connected by a toggle mech anism, consisting of a pair of pivotallycon nected links 117. The knuckle or pivotal 'joint'l18 ofthe toggleis acted upon by a sliding member 119, which is under the infiuenceof a spring 120. The member 119 and spring 120 are disposed within a bore 121 in the cap, said bore being provided with screw threads designed to receive a nut 122 for adjusting the compression of the spring.

In the use of this improved ventin device, the cap 107 remains in the CflI'tIl( ge at all times and may be permanently sealed on surface 110 thereof. Suitable gaskets or sealing strips are preferably employed around or over the discharge ports 112 for cooperation with the sealing surfaces of members 113. Assuming the parts to be in the relative positions shown in full lines in Figare 15, it will be appreciated that an appro priate spring 120 will exert a tremendous force on the outer ends of the pivoted mem-' bers 113 through the medium of the toggle, thus forcing the opposite ends of said members 113 into effective sealing engagement with the surfaces immediately surrounding discharge ports 112. Now, assuming that the cartridge is fully charged and positioned in a drill hole of a diameter slightly greater than that of the cartridge, energization of the cartridge results in the rapid development of a working pressure therein, which acts on those portions of members 113 which are exposed by the discharge ports. When the effective force exerted on members 113 through discharge ports 112 exceeds that ex erted on said members through the toggle,

For

it is apparent that said members will be moved outwardly into the materialsurrounding the cartridge, thus opening the discharge ports and permitting the gas to escape into estroy the valve or, atleast, render-it unfit v for further use, With this in mind, it will be noted that during the initial stage of opening of members 113, the force exerted thereon by the discharge is'opposed or counteracted both by the resistance of the material to'the entry of members 113 thereinto, and the constantly increasing pressure of spring 120.

This stage extends from the full line position to the dotted line position a. This is the dead center position, wherein the toggle links 117 are in substantial alignment with their respective members 113. i From this point the spring 120 tends to assist the further outward movement of members 113 to the limit posi tion 5. Of course, the coal, or other material in which the cartridge isused, offers consid erable resistance to movement of members 113 throughout the entire range, and'this resistance is a highly important'factor in the successful absorption or dissipation of the discharge shock. Thus a successful pressure responsive mechanical venting device is provided by combining the functions of valve and anchoring device, the latter serving its own very useful purpose and at the same time serving to absorb or dissipate the destructive energy which would otherwise be fatal to a valve structure.

In Figure 18 is shown a modified form of combined valve and anchoring members, together with a different toggle arrangement. According to this form, the members 123 are substantially right angular and are pivoted at approximately the center of the cap as indicated at 124. Obviously, this arrangement permits greater strength in the pivotal mounting. The toggle consists of pivotally connected links 125, the knuckle of which is adapted to be acted upon by a spring in the same manner as in Figure 15. It will be noted, however, that the action of this toggle is somewhat dilferent from that of Figure 15 in that the knuckle progressively moves toward the end of the cap, thus compressing the spring, throughout the entire range of movement from the full line position to the dotted line position 0.

Although the various phases of the invention have been described in some detail, and

particular structures are illustrated, it is to be understood that they involve new ideas capable of embodiment in a variety of struc-- tural forms. Therefore, the invention is not to be regarded as limited to the particular disclosure.

I claim: i

1. A blasting cartridge comprising a metallic body having a gas chamber therein, an electrode subject to the gas pressure within said chamber and insulated with respect-to said body and accessible to the interior thereof for cooperation with a heater circuit and to the exterior thereof for cooperation with a source of electricity, said electrode being constructed and arranged so that the forces acting thereon resulting from the gas pressure are'substantially balanced.

2. A blasting cartridge comprising a metallic body having a pressure chamber therein, an electrode within said chamber, subject to the gas pressure therein and insulated with respect to said body and having a connection extending to the exterior of said cartridge, said electrode being constructed and arranged to be in a state of substantial equilibrium in relation to the forces imposed thereon by said gas pressure.

3. A blasting cartridge comprising a metallic body having a pressure chamber therein, an electrode disposed within said chamher, subject to the gas pressure therein and insulated with respect to said body and sealed against the escape of gas where it enters said chamber, said electrode having opposed surfaces of substantially equal area exposed to said gas pressure within said pressure chamber, thus placing said electrode in substantial equilibrium in relation to said gas pressure and means for connecting said electrode to an external source of electricity.

4. A blasting cartridge comprising a metallic body having a pressure chamber therein, an electrode disposed within said chamber and insulated from said body, cooperating sealing surfaces on said electrode and cartridge, and a conductor extending from said electrode to the exterior of said cartridge and protected from the pressure in said chamber by the sealed relation of said surfaces.

5. A metallic body having a gas chamber therein, an electrode within said chamber subject to the gas pressure therein and insulated with respect to said body, said electrode being so constructed and arranged that the forces imposed thereon by said gas pressure are substantially neutralized.

6. The combination with a metallic cylinder adapted to contain a quantity of highly compressed gas, of an electrode extending into said cylinder and accessible to the exterior thereof for the purpose of introducing an electric current into said cylinder, said electrode comprising a substantially circular disc having one surface in sealing and insuof October 1930.

lating engagement with a surface on the interior of said cylinder, a member having adj ustable connection with said cylinder and having insulating and sealing engagement with an equal area of the opposite surface of said disc, and a member extending from the exterior of said cylinder and projecting through the first said pair of engaging sealed and insulated surfaces and having electrical contact with said electrode, said member being insulated with respect to said cylinder.

7. A metallic cylinder adapted contain a quantity of highly compressed gas, closures for the ends of said cylinder, one of said closures having an inward projection with op-.

posed flat surfaces and a bore extending through said extension, an electrode comprising a shank portion extending through said bore and a head portion having sealing and insulating engagement with one 0f Sa1d iiat surfaces and a second head portion havmg adjustable engagement with said shank portion and having insulating and sealingengagement with the other of said flat surfaces, and a member extending from the exterior of 'said cylinder into said bore and having electrical contact with said electrode, said member being insulated with respect to said cylinder and closure.

Signed at Chicago, Illinois this 6th day ALLYN- HARRIS.

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