US2154221A - Charge for gas pressure operated blasting devices - Google Patents

Description

Patented Apr. 11, 1939 UNITED STATES PATENT OFFICE CHARGE FOR GAS PRESSURE OPERATED BLAST'ING DEVICES No Drawing. Application September 2, 1937, Se-

rlal No. 162,221. In Great Britain September Claims.

This invention relates to pressure operated blasting devices and in particular to charges for such devices.

There are now on the market blasting devices which consist of a cylinder having at one end a seal which gives way when the pressure inside the cylinder reaches a certainvalue. The cylinder is charged with a composition or a liquid such as liquid carbon dioxide which evolves gas on being heated and a heater is placedin contact with the charge. The whole cylinder is placed in a bore hole and the heater ignited. When suflicient gas has evolved to bring the pressure to the desired value, the seal gives way and the pressure is released into the bore hole with explosive violence.

In my specification Serial No. 68,143 filed March 10, 1936, I use, as a charge for a gas-pressure operated device, a gas-evolving composition consisting essentially or largely of ammonium nitrate sensitised by the presence of a suitable chromium compound so as to be capable of undergoing a self-sustained decomposition without detonation when ignited locally at ordinary pres- 25 sure, and a suitable local and limited nondetonating igniting element. The igniting element is insumcient in itself to produce any appreciable rise in temperature of the whole of the ammonium nitrate composition, but heats a portion 30 of the composition in its immediate vicinity sufflciently to start its exothermic decomposition. the heat evolved from the exothermic decomposition being sufiicient to raise more of the composition in its immediate vicinity from ordinary temperature to the point of decomposition, and so forth; so that the decomposition is propagated throughout the whole composition. For blasting purposes the charge is contained in a pressure-resistant vessel sealed with a pressure-re- 40 sponsive venting device; and owing to the eflect of the confinement on its rate of propagation, the decomposition becomes rapid, so that the blast due to the escape of the gases through the venting device takes place at only a short inposition in order to avoid this objectionable formation of acid fumes.

The increased exothermicity of a mixture containing an oxldisable material over that of a mixture' of only the ammonium nitrate and the chromium compound naturally depends on the amount and nature of the oxidisable material. The tendency is for the sensitiveness to ignition and selfsustained decomposition on local heating in the unconfined state to increase with an increase in the proportion of carbonaceous material in the mixture from the amount resulting in the formation of carbon dioxide to that resulting in the formation of carbon monoxide.

According to my said specification there are used combustible carbonaceous ingredients. Such normally incombustible oxidisable carbonaceous materials as ammonium carbonate or bicarbonate, which on thermal decomposition absorb heat and evolve unobjectionable gaseous products are also used according to my said specification as materials capable of oxidation by the ammonium nitrate, although only in conjunction with normally combustible carbonaceous ingredients.

For the purpose of blasting in fiery or dusty mines it is obviously necessary that the products of combustion vented from the blasting device should not be capable of igniting a fiery or dusty atmosphere, and that no flame should accompany their ejection.

For blasting purposes in general it is preferred that the proportions of ammonium nitrate and oxidisable material should be such that little or no carbon monoxide is formed among the products of combustion, and according to my said specification it is therefore. considerable particularly desirable for the purposes of blasting in fiery or dusty mines that the proportions of ammonium nitrate and oxldisable material should be so adjusted that the carbonaceous materials present are practically completely burnt to carbon dioxide and water, in addition to the requirements that the charge should cause no ignition on ejection.

As regards the ignition of fiery or dusty atmospheres it is not merely necessary that the products of complete combustion should be incapable of igniting the atmosphere, but it is also necessary that no such ignition should occur as a result of the election of flaming gases or only partlylreacted portions of the mixture in a state of excessive temperature or liability to burst into flame on election. The failure to ful fll these conditions may thus lead to an ignition if a charge in excess of that necessary to effect venting is employed.

On a superficial examination of the problem it might appear that these objects can be accomplished while avoiding on the one hand the inconvenience of excessive evolution of hot oxides of nitrogen or nitric acid and on the other hand the inconvenience of excessive evolution of carbon monoxide with a mixture consisting of ammonium nitrate and combustible carbonaceous materials merely by accurately adjusting the quantities of the ingredients of the mixture so that there would be present neither so much ammonium nitrate as to give rise to nitric acid or nitrous fumes, or so much combustible carbonaceous material as to give rise to carbon monoxide.

While a mixture of sensitised ammonium nitrate and combustible carbonaceous ingredients in such proportions is capable of complete reaction under confinement to form products of combustion objectionable even from the point of view of ignition of fiery or dusty atmospheres, such a mixture burns in the open with flame. There is thus a danger that some of the still incompletely reacted or unreacted mixture will be vented in a flaming condition with the blast. The fact that the above mixture burns in the open with flame constitutes a further disadvantage in that it would not be premissible to keep a supply of such a mixture in the fiery or dusty atmosphere of the mine since an accidental local rise in temperature might bring about the initiation and the propagation of a decomposition through the material and thus would, on account of the fact that the mixture burns with flame, lead to an ignition in the mine.

The present invention has as an object to provide a charge which will avoid on the one hand the inconvenience of excessive evolution of hot oxides of nitrogen and nitric acid from the blasting device and on the other hand the inconvenience of excessive evolutionof carbon monoxide, while at the same time avoiding the danger of igniting a fiery or dusty atmosphere. Further objects of the invention include the provision of an improved charge for operating blasting devices of the type described which comprise sensitised ammonium nitrate mixture which do not burn with flame even in the open, the provision of charges comprising sensitised ammonium nitrate compositions of satisfactory utility in blasting in conjunction with a complementary charge element but which are not themselvescapable of propagating their decomposition in the open on subjection to limited and local application of heat. Further objects will appear hereinafter.

In my specification 68,143 I indicated that the combustible carbonaceous ingredient of a sensitised ammonium nitrate combustible carbonaceous ingredient mixture might be subjected to a flreproofing treatment. The advantage thatthe mixture so prepared was nolonger liable to burn with flame in the open would. in this case depend entirely on the eifectiveness' of the flreproofing treatment, and local imperfections .might have exceedingly serious consequences in the case of a quantity of the material in the mine locally subjected to an accidental application of heat so as to bring about propagation of the decomposition through the material in the open mine. Moreover, the ejection during the blast of the extremely hot particles. of solid inorganic flreproofing agent mightin itself tend to cause the ignition of inflammable gases, apart from any question of the failure of the flreproofing process to be effective throughout each and every particle of carbonaceous ingredient, which would not only render it inadvisable to keep the material in the open mine for the reasons given in the preceding sentence, but would also constitute a risk during the ejection of partly; reacted material.

I therefore considered it necessary to employ some material as oxidisable ingredient which did not yield so high an evolution of heat as combustible carbonaceous ingredients. I found it convenient to make use according to my said specification of such materials as ammonium carbonate or bicarbonate as were oxidisable by ammonium nitrate, incombustible under ordinary circumstances, and yielded a smaller evolution of heat on their oxidation with ammonium nitrate than that yielded by normally combustibleif used in excess of the amount capable of oxi dationby the ammonium nitrate, would further function as active cooling agents. Mixtures consisting entirely of ammonium nitrate and such normally incombustible ingredients however even when sensitised by the presence of the chromium compound are insufliciently sensitive to undergo a self-propagating decomposition when subjected to the action of the igniting element.

This disadvantage I proposed to overcome in specification 68,143by still keeping in the mixture a sufllcient percentage of normally combustible carbonaceous material, the greater heat evolution of which on oxidation by the ammonium nitrate naturally increased the sensitiveness of the mixture to ignition. A compromise was thus effected between insuflicient sensitiveness and the risk of causing ignition of fiery or dusty atmospheres.

The inclusion of small proportions of fixed alkaline materials in the sensitised ammonium nitrate mixture was also shown in specification "bustible carbonaceous material suflicient to render it selfvpropagating.

Although by application of the principles indicated in the preceding paragraphs in a meticulous fashion it was possible to strike a compromise and so v prepare satisfactory blasting charges for use in fiery or dusty mines according to my said specification, I have now found that by the application of a newer different principle it is possible toensure certainty of propagation of :the charge in the blasting device and a freedom from the risk of igniting a fiery or dusty atmosphere independent of flreproofing processes, which is not merely suflicient to ensure that a properly charged blastingdevice will effect a blast without the risk of ignition, but

such that the ammonium-nitrate mixture is itselfincapable of burning with a flame. The

.range .ofavailable ammonium-nitrate compositions is now greatly increased, and the present invention has the advantage that it is possible to employ as ammonium-nitrate mixtures not merely mixtures which do not burn with flame in the open, but mixtures which do not even propagate their decomposition outside the blasting device in the open when subjected to a local and limited application of heat. This constitutes an efiicae cious safeguard against the possibility of an accidental local rise in temperature in a quantity of the mixture kept in the mine leading to any mishap.

The principle on which my present invention depends is that the combustible carbonaceous ingredients of a sensitised ammonium nitrate charge for a blasting device of the kind described need not of necessity be evenly scattered throughout the whole of the charge, but will perform their functions if they are segregated in one part of it. According to my invention at least a portion of the combustible carbonaceous ingredient is segregated from the remaining mixture in coherent integral form, as contrasted with the disintegrated form in which it is present in the mixture, and at least partly in the neighborhood of the igniter.

The principle of the present invention is compatible in application with the principles applied according to my specification 68,143. Thus in putting my invention into effect the segregated or unsegregated carbonaceous material may be fireproofed; the mixture may contain a proportion of fixed alkaline material; and normally incombustible oxidizable ingredients such as ammonium carbonate and bicarbonate may be present in the mixture as part of the material oxidizable by the ammonium nitrate or as a cooling agent. Thus the mixture and the segregated carbonaceous ingredient function in the closed blasting device in complementary fashion, but the ammonium nitrate mixture itself contains too little carbonaceous combustible ingredient to render it capable of burning with flame in the open irrespective of any fireproofing treatment, and need not possess the property of being of itself capable of propagating its decomposition when enclosed with a local and limited igniter in the absence of the complementary segregated carbonaceous combustible material. The segregated carbona ceous material may conveniently be associated with the igniter as a unit and it is convenient to form the segregated carbonaceous material as a paper tube or the like in which the igniter itself may be located. It is preferable to locate the igniter some distance away .from both ends of the blasting device, that is to say from the venting' end and from the end most remote therefrom. Thus there may be used a paper tube of considerable length within which the igniter is positioned about half way along-the blasting device. This prevents the igniter hurling the whole of the mixture against the seal, which might prematurely break it.

In adjusting the quantities of the ingredients so that neither excess of oxidizable or oxidizing agent is present, account should be taken of the oxidizable ingredients of both the igniter, and the segregated carbonaceous ingredient as well as the oxidizable ingredients in the mixture.

Since it is desirable that the amount of oxidizable material in the charge should be restricted so that little or no free carbon monoxide is formed, the nature of the igniting element should be taken into account in the determination of the weight of carbonaceous material that must be included as a charge constituent segregated from the sensitised ammonium nitrate composition. For example, in the case of a IOU-grain powder fuse the products of combustion of the black-powder are capable of reducing about 9 grams ammonium nitrate, and the sealing material, employed and the paper container and its waterproofing material also consume an amount of ammonium nitrate dependent upon their nature and weight. A typical 30-grain electric fuse, provided with polychlor-naphthalene plugs amounting to 1.4 grams and a waxed paper container weighing about 1.1 grams, consumes in all about 18.5 grams ammonium nitrate;but as it would normally be constructed a local and limited igniting element would not consume more than 30 to 35 grams ammonium nitrate. According to the present invention it may be necessary in the case of large charges to segregate an amount of carbonaceous material equivalent to as much ammonium nitrate again as will oxidise an igniter of such construction in order to preserve a satisfactory margin of safety; and even in the caseof smaller charges the segregation of an amount of carbonaceous material from the composition equivalent to a greater amount of ammonium nitrate than could be reduced by such an igniter alone renders possible the use of compositions having a greater margin of safety than those in which the same proportion of carbonaceous ingredient, excluding the igniter, is distributed throughout the composition.

In putting my invention into effect, I may use the segregated carbonaceous material in the form of a paper or thin cardboard structure, as for instance a tube, and this may be impregnated with wax or the like. If desired, the structure may be made up integral with an igniting element such as an electric powder fuse by attachment of the latter thereto so that it projects for some distance into the blasting device; and one or both of the lead-wires may conveniently be passed through the tube from the igniter to their terminals in the device. An extended tube of the carbonaceous material suitably sealed may also be employed wholly or in part as a container for the active charge in the igniting element. For example, we may employ, in conjunction with the sensitized ammonium nitrate composition, a 100- grain powder fuse made up in an extended paper or thin cardboard container, suitably sealed and waterproofed, which itself provides the necessary weight of segregated carbonaceous material. As waterproofing agent, paraflln wax or the like may be employed; and if desired the cementitious ingredient employed for insulating the leads to the fusehead and for sealing the active composition within the igniting element may consist of an organic insulating material, for example a chlorinated naphthalene wax, instead of sulphur. The

segregated carbonaceous material may also be,

constructed in forms other than tubular, and may consist of materials other than paper or cardboard capable of effective segregation from the sensitized ammonium nitrate composition, so that it will not be distributed to any substantial extent through the latter by the slight disruptive action of the igniting element. As a further precaution, the segregated carbonaceous material may if desired be subjected to a flameproofmg treatment. When the segregated carbonaceous material is made up under these conditions in the form of a container for the active composition of the igniting element, any fragmentation incidental to the actuation of the igniting element does not in practice render any sensitized ammonium nitrate composition ejected from the blasting device after venting capable of causing an ignition in fiery or dusty atmospheres; and 1' have also been able to include at least a part of the segregated carbonaceous material in the form of small pieces of wood, charcoal, cardboard or the like, along with the active composition of the igniting element in its container without detriment to the safety of the charge as a whole.

The invention is further illustrated but not limited by the following examples, in which the parts are parts by weight unless otherwise stated.

Example 1 The blasting device used has a capacity of 680 cc., and vents at an internal pressure of 12 tons per square inch. The charge consists of 140 grams of a composition containing a mixture of ammonium nitrate, ammonium dichromate, starch and china clay in the proportions :5:2 :3; and an extended igniter containing grains of blackpowder, which is made from a tube of waxed fireproof paper 22" long weighing 13.8 grams, the cementing ingredient used for sealing and insulating being a. wax-like chlorinated naphthalene and weighing 2.4 grams. About half the length of the tube forms the actual container for the powder charge, the remainder enclosing the lead-wires. The above weight of composition is in excess of the amount required to generate the venting pressure. On ignition, the blast takes place without the development of objectionable nitrous fumes, and when the device is vented into a 9% methane-in-air atmosphere no ignition of the gas takes place, The amount of ammonium nitrate in the composition which is not reduced by the starch amounts to 106 grams, and the ammonium nitrate consumption of the igniter assembly containing the segregated carbonaceous material is in all 110 grams.

Example 2 The blasting device has a capacity of 660 cc. and vents at 21 tons per square inch internal pressure. The composition used in the charge consists of 280 grams of a mixture of ammonium nitrate, ammonium dischromate, starch, charcoal, china clay, basic magnesium carbonate and ammonium bicarbonate in the proportions 80:6:2:1:1:5:20. The segregated carbonaceous material is in the form of an igniter tube 9% inches long of fireproofed paper waterproofed with Wax and weighing 6.8 grams, into which a fusehead and 100 grains of blackpowder are sealed with 2.4 grams of a chlorinated naphthalene wax. The ammonium nitrate in the composition not reduced by the starch and ammonium bicarbonate amounts to approximately 67 grams, the total ammonium nitrate consumption of the igniter .assembly being 70 grams; this charged device is also safe when operated in gas and evolves no offensive nitrous fumes. I

Example 3 The blasting device has a capacity of 680 cc. and vents at 12 tons per square inch internal pressure. The composition consists of 210 grams of a mixture of ammonium nitrate, ammonium dichromate, starch, ammonium bicarbonate, basic magnesium carbonate and china clay in the proportions 80:6:3:20:3:1. The segregated carbonaceous material takes the form of a tube 9 inches long of flreproofed paper weighing 2.8 grams, into which a fusehead and 100 grains blackpowder are sealed with 2.4 grams of a chlorinated naphthalene wax. The igniter has a total ammonium nitrate consumption of about 45 grams. The ammonium nitrate unreduced in the composition amounts to 59 grams, No objectionable nitrous fumes are however produced, and the charged device is safe when operated in gassy and fiery atmospheres.

In addition to the oxidisable ingredients according to my said specification small proportions of inorganic materials such as magnesium carbonate, chalk, silica, china clay or the like which influence the decomposition of ammonium nitrate may be included, and any combustible organic ingredients present in the mixture may be fireproofed in order to minimise the risk of any such ingredients being vented while unconsumed or only partly consumed.

Suitable igniting elements are: an electric powder fuse as used for igniting blackpowder pellets, a safety electric igniter as described in specification 431,950, or a small smokeless powder or cordite charge ignited in turn by a fuse head or percussion cap, and the use of 30 to 100 grain powder fuses is illustrated.

The total quantity of carbonaceous ingredients in the charge and igniter taken together depends on the quantity of noncombustible ingredients which are oxidisable with ammonium nitrate and will vary with the chemical composition of such ingredients.

The proportion of combustible carbonaceous ingredients admixed in the ammonium nitrate should never exceed 4% and I prefer to keep it below 3% of the weight of ammonium nitrate and the remainder should be segregated. The total amount together with the other oxygen us- 'ing ingredients should be, as has been stated,

such that neither nitrous fumes nor carbon mondevices of the type which comprises an igniter and ammonium nitrate sensitised with a chromium compound, carbonaceous substances which combine exothermically with oxygen, cooling salts in a quantity consistent with certain propagation of the decomposition of the ammonium nitrate, and in which the total quantities of all the ingredients present both in the igniter and in the rest of the charge are adjusted substantially to the theoretical quantities necessary to their decomposition without the formation of oxides of nitrogen, nitric acid, and carbon monoxide and without there being left any unburnt carbonaceous material; the modification that the quantity of carbonaceous substances, which combine exothermically with oxygen, distributed 3. The modification as claimed in claim 1 in which the carbonaceous substances are fireproofed. I

4. A modified charge as claimed in claim 1 in which the segregated carbonaceous substances comprise a blackpowder igniter enclosed in P p 5. The modification as claimed in claim l in which the segregated carbonaceous material is placed in the neighborhood of the igniter.

6. The modification as claimed in claim 1 in which the segregated carbonaceous material is placed away from the vent hole.

'7. The modification as claimed in claim 1 in which the segregated carbonaceous material is included in the igniter,

8. The modification as claimed in claim 1 in which the segregated carbonaceous material is partly included in the igniter and the remainder is segregated in coherent form.

9. In a charge for pressure-operated blasting devices of the type which comprises an igniter and ammonium nitrate sensitized with a chromium compound, carbonaceous substances which :ombine exothermically with oxygen, cooling salts in a quantity consistent with certain propagation of the decomposition of the ammonium nitrate, and in which the total quantities of all the ingredients present both in the igniter and in the rest of the charge are adjusted substantially to the theoretical quantities necessary to their decomposition without the formation of oxides of nitrogen, nitric acid, and carbon monoxide and without there being left any unburnt carbonaceous material; the modification that a substantial portion of saidcarbonaceous substances is segregated from the remainder of the charge.

to their decomposition without the formation of oxides of nitrogen, nitric acid, and carbon monoxide and without there being left any unbumt carbonaceous material; the modification that a substantial portion of said carbonaceous substances is segregated from the remainder of the charge.

JAMES TAYLOR.

April 11, 1959.

JAMES TAYLOR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follower Page 2, first column, line 22, for the word objectionable read'unobjectionable; page 1 first column, line hh, for "dischromte" read dichrbniate; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this th day of June, A. D. 19 9.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.