US2256298A - Blasting device - Google Patents

Description

"sept, 1'6, 1941. J.. TAYLOR 2,256,298

v BLASTING DEVICE v Filed OG'C. 27, 1957 MMF-...J

James Taylor INVENToR.

ATTORNEY Patented Sept. 16, 1941 '2,256,298 l l l LAsrINc DEVICE James Taylor, Saltcoats, Scotland, assgnor to Imperial Chemical Industries Limited, a corporation of Great Britain Application October 27, 1937, Serial No. 171,391

In Great Britain October 29, 1936 claims.

.This invention relates to blasting devices, par- Vticularly to those of the kind comprising a pres" sure-resistance reutilisable container, a charge of a solid material capable of undergoing a non- Vdetonatingv gas-evolving decomposition when locallyl initiated, `and'means for locally initiating the decomposition of the said charge.

Blasting devices of this kind have been proposed in which the container is charged at atmospheric pressure with a solid material of the kinddescribedvand is tted with avvalve or rupturable disc seal of high tensile strength material adapted to release the products of decomposition ofthe charge when the internal pressure has attained a" predetermined and considerable value sufficient to produce a blasting leffect when the device has been suitably located in a borehole.

Blasting devices of this latter kind rhave beenvr` .compositions is that their rates of exothermic decomposition, and hence their rates of development of gas pressure ywhen confined, do notv become great enough to produce a blasting efl fect until the decomposition is taking place under an already considerable pressure. This property is desirable in that the unconfined compositions may be handled with safety; but hithertothey have not been considered suitable for use as blasting explosives, except when in proper associationy with a pressure-resistant venting container, since if they are loosely tamped in a borehole, or if the borehole has breaks or fissures, any gas pressure developed by their initial decomposition will leak away too rapidly for the complete decomposition of' the charge to produce an eiective blast.

In the devices used hitherto, in which the charged container is adapted to vent when the y internal pressure reaches a value lsuitable for blasting, the considerable pressure mentioned above is built up by the gas evolved during the relatively slow decomposition of the charge imi mediately after its initiation at substantially norprolonged time static pressures up to the venting pressure.

The provision of a release valve'or of view of economy and simplicity, but also with a view to a more efficient use of the energy of discharge of the gases and the elimination of deterioration of the apparatus due to erosion at the venting end of the device.

This invention has as an object to provide a blasting device which does not require any screwed unions or detachable venting cap. A

further object is to provide a blasting device L which shall be more'simple and economical than known'blasting devices. Further objects will appear hereinafter.

These objects are accomplished by the-follow` ing invention. lI have vfound vthat blasting de-` .vices of the kind venting at a predetermined arid considerable pressure may be constructed, without any necessity for the provision of a seal of which the materialis capableY of prolonged resistance to pressures less than the Venting pressure, by lmaking use of 'the pressure-resisting properties of a column'of granular or like material supported in a rigid tube, if adequate support is given to the column' of granularA material within a pressure-resistant tube, preferably byra gas-tight supporting and sealing member. The support need only withstand a static pressure that is small relative to the pressure at which the container is intended to vent, al-

though it must be capable of withstanding presn sure substantiallyv greater than atmospheric. Thus for example the support alone must be vcapable of withstanding an internal pressure of square inch. When such support is used in conjunction with a column 4of sand thatis short relative 'to the length of sand tamping hitherto employed with safety explosives to ensure a safe blast in a dangerous atmosphere, the assembly can withstand pressures exceeding 30tons per square inch.

Referring generally .to the drawing there is depicted therein a view in vertical cross-section of a blasting device according to thepresent ninvention. y

In greater detail theicylindrical steel tube l is depicted as closed at one end. Adjacent to said closed end is a charge 2 of sodium nitrite l Embedded in said Y and ammonium chloride. charge is an electric igniter 3, the leadsv 4 of which pass downward and out through `the otherk end of said steel tube. Belowl the aforesaid charge 2 is a column of sand 5 supported by a plaster of Paris plug l retained inplace by means Aquired in each case to dislodge the assembly from the tube is given in the following table. The pressure required to dislodge the plaster of Paris plug alone was approximately-V2 ton per square inch.

Heght of Breakdown sand pressure column Tana per Inches square inch 1 0. 53 Z 0. 87 3 4. 07 3% 1l. 7 4 14Y 5 The usual'venting pressure of a 11/4" internal diameter blasting device of the kind described is 12 tons per square inch.

According to the present invention, a blasting device comprises a pressure-resistant reutilisable container provided with a seal adapted to yield under an internal pressure substantially higher than atmospheric pressure, but considerably less than the pressure at which the device is intended to vent; a charge of a solid material capable of undergoing a non-detonating gas-producing exothermic decomposition after being locally initiated; means for local initiation of the charge; and a quantity of a granular or like substance having the property of packing under pressure, completely lling the free space between the charge and the seal, and in amount such that the device vents at a pressure suiicient to exert a blasting effect, but insuilicient to cause any deformation or other damage to the container. The actual magnitude of the venting pressure will be a function of the length of the column of sand or like granular material; and it will be under- Weight of Length of Length of Maximum charge tube sand pressure Tous per Grams Inches Inches square meh 150 17 t-8 12 30 12-15 l5 200 l5 2-4 855 20 -S 12 25 12-14 15 250 22 7-9 l5 28 10-15 2O The following examples illustrate but do not limit the invention. Example 1 A cylindrical high-tensile steel tube, 11A; inches internal diameter, 1% inches external diameter, 20 inches long and closed at one end, is charged with 200 gm. of a mixture of sodium nitrite and ammonium chloride, granulated 24-100 mesh, containing 1.5% light magnesium oxide as stabiliser. A suitable igniter, such as a 30-grain powder fuze or a safety igniter, is embedded in the charge, and the leads are brought forward through the open end of the tube. The charge occupies approximately 11 inches of the tube. The remainder of the tube up to 2 inches from the mouth is filled with sand, well shaken down but not rammed hard. A plug of plaster of Paris is then cast into the remaining two-inch space at the open end of the tube, which is provided with grooves or holes to assist in keying the plaster of Paris plug to theV tube. When initiated in `the usual manner, the charge vents-at an internal pressure of approximately 9 tons per square inch; and when the device is well tamped in a borehole, a satisfactory blasting effect is obtainable.

Example 2 A tube 29 inches long is charged with 300 gms. of a mixture as in Example 1. The tamping consists of 12 inches of dry sand and a 2 inch Aplaster 0I Paris plug. The means of initiation is a safety igniter of the type described in copending application Serial No. 758,317, led January 19, 1934, situated at the base of the tube. When initiated, the charge vents at a pressure of 16 tons per square inch.

A type of pressure-resistant container suitable for use according to the invention is a plain cylindrical steel tube closed at one end and if desired otherwise free from constructions, screwed fittings, or any other device likely to ,prevent free egress of the contents of the tube. Tubes open at both ends, and having the charge placed more or less evenly between two columns of granular packing material and two sealing plugs, may also be used: but the single-open-.end tube is preferred.

Another suitable type of container is a cylindrical steel tube hemispherically closed at both ends and provided with lateral venting apertures near one end. In a device of this kind the blast does not produce such a reaction tending to cause the tube to be moved in an axial direction as may ,happen when a simple open-ended tube is used.

As charges I may use the gas-producing compositions described and claimed in U. S. Patents 2,038,772, 712,052, 2,048,827, copending applications Serial Nos. 68,143? and 96,121, led March 10, 1936, and August 14, 1936, respectively, and in co-pending application Serial-No. 162,221, filed September 2, 1937; or any other suitable composition having the properties described.. The lnvention is best applied however, when used with charges that do not produce a blasting effect,l

when used under comparable borehole conditions, except when contained in a pressure-resistant enclosure adapted to confine the products' of their decomposition during its initial stages.

As means of initiating the charges I may use electrically-fired powder fuzes or detonators, or safety igniters.

Thepacking material used is preferably sand, or a similar material, the essential property being that it must pack" under the application of rapa plug of plaster of Paris, castinto place; but an oversize wooden or like plug driven into the mouth of the tube will a1so serve, although its resistance is more diicult torgauge. When using seals cast into place, I prefer to use sealing materials that expand on solidication, of which'.`

plaster of- Paris is the most convenient. The seal may be, if desired, formed afterthe device has been loaded in the borehole, for example by soaking the granular tamping at the mouth of the tube With Water and tamping the borehole next to the tube with solid carbon dioxide so that `a plug of ice is formed.

This invention is useful in the art as it provides new and 'effective blasting devices which are easy and economical to make.

Certain blasting devices constructed according to the invention are safe foruse in ery and gassy mines, and may even be vassembled, with` safety at the working face.

For example, devices of the foregoing type vmay and provided with an initiating device of thev twype described in co-pending application Serial As manyapparently Widely different embodi- Y ments of this invention may be made without departing from the spirit and scope thereof it is to be understood that I do not limit myself to the device comprising a non-destructible re-usable pressure-resistant container, a charge of nondetonating gas-producing material disposed in said container, igniting means disposed adjacent to said charge, venting means confining said charge in said container comprising a column of inert granular 'material and a supporting member located in the end of said contaner adjacent to said inert granular material.

2. A non-detonating gas-generating blasting device comprising a non-destructible re-usable pressure-resistant container, a charge of nondetonating gas-producing material disposed in said container, igniting means disposed adjacent to said charge, venting means confining said charge in said container comprising a column of inert granular vmaterial and a cast plug of material having the property of expansion on solidication disposed in the end'oi said container and supporting said column of inert granular material.

,3.A non-detonating gas-generating blasting device comprising a non-destructible re-usable pressure-resistant container, a charge of nondetonating gas-producing Ymaterial disposed.- in

said container, igniting means disposed adjacent to said charge, venting means confining said charge in said container comprising a column of inert granular material and a plug of plasterv of Paris cast into place in the venting end of said container supporting said column of inert granular material..

4. A non-detonating gas-generating blasting device comprising a non-destructible re-usable pressure-resistant' container, a charge of nondetonating gas-producing material disposed in said container, igniting means disposed adjacent' to said charge, venting means confining said charge in said container comprising a column of sand and a plug member disposed in the end of said container suuporting said sand.

5. A non-detonating gas-generating blasting device .comprising a re-usable*pressure-resistant container consisting of a cylindrical steel tube closed at one end, a charge of non-detonating gas-producing material disposed Within said tube adjacent to the closed end thereof, an igniter embodied in said charge, a column ofsandfdisposed in said tube between the locus of said charge and the opened end of said tube, keying means in the mouth of said tube, and a plug of plaster of Paris cast into place closing saidmouth and co-operating with said keying means.

JAMES TAYLOR.

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