US2704515A - Method of loading for liquid oxygen explosives - Google Patents

Description

Marchv2r2, 1955 L.. P. BARLow 2,704,515

METHOD OF LOADING FOR LIQUID OXYGEN EXPLOSIVES Filed Sept. l5. 1954 [IOR-rn zrzlennvm Zon:

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I N VENTORL rs1-:n 7.) .Banca ATTORNEY' United States Patent O METHOD OF LOADING FOR LIQUID OXYGEN EXPLOSIVES Lester P. Barlow, Stamford, Conn.

Application September 15, 1954, Serial No. 456,099

11 Claims. (Cl. 102-23) The present invention relates to explosive compositions and methods of making and loading explosives.

Commercial blasting operations such as those involved in mining, open cut excavations, submarine operations and the like present different problems due to the nature of the material to be blasted, the condition to which the material is to be reduced, the conditions under which the blasting is to be done (submarine, open cut, tunnel etc.) and various otherfactors known to persons skilled in the explosives art. The ideal commercial explosive is one which will satisfactorily perform the different operations under the diverse conditions encountered in commercial blasting. The properties which the ideal commercial explosive should have, have long been known and the art has tried unsuccessfully for many years to produce an explosive having all of those properties.

The ideal commercial explosive should have the following properties: First, it should be absolutely safe with detonation possible only at the will of the operator; Second, it should have power and speed which can be varied from low power and low speed to high power and high speed to suit condition: Third, vit should be inexpensive: Fourth, it should be such that blast holes may be quickly, safely and eiticiently loaded: Fifth, it should become inert if it fails to explode at the will of the operator: Sixth, it should be inert during transit: Seventh, the explosive should be such that it will fill even irregular blast holes without substantial space for `free g LOX explosives which consist of a combustible material and liquid oxygen have been known for more than4 sixty years and possess several of the characteristics of the ideal explosive such as readily variable speed and power, and low cost. Because of their high power and other desirable characteristics LOX explosives have been extensively investigated (c. f. U. S. Bureau of Mines Bulletin No. 472 entitled Safety and Performance Characteristics of Liquid-Oxygen Explosives) but LOX explosives have been regarded as very unstable, too sensitive and hazardous for use as a blasting agent in mine and quarry operations and the Federal Bureau of Mines does not recognize LOX as a permissible blasting agent.

Heretofore, LOX explosives have usually consisted of a bag or container of canvas, paper or the like filled with particles of carbonaceous material which was soaked in liquid oxygen just prior to inserting it in the blast hole. Many accidents occurred during loading and after about 35 minutes, the cartridge lost its maximum explosive power due to oxygen evaporation. Because of the rapid loss of oxygen, only a few blast holes may be loaded at a time and the blast holes must be detonated immediately after loading.

Efforts were made to pour LOX explosives into blast holes but the rapid evaporation of the liquid oxygen due to contact with the walls of the hole caused such violent action within the hole as to increase the hazard of explosion from sparks or impact from dislodged stones or rock. Efforts to introduce the carbonaceous material first and then pour in the liquid oxygen were also unsuccessful for the further reason the heat of the hole and the carbonaceous material caused such rapid and violent evaporation and expansion of the oxygen gas as to blow most of the carbonaceous material out of the hole. To feed the liquid oxygen into a carbon filled blast hole at a rate slow enough to avoid free gas pressure is not practical in blasting operations as the time of charging will be too long, the period of maximum danger will be extended and too much oxygen will be lost.

I have found that all of the conditions for the ideal commercial explosive can be met and one of the objects of the present invention is to provide an explosive meeting those conditions.

Another object is to provide an explosive which is formed in situ in the blast hole.

Another object is to provide an explosive which may be introduced into a blast hole in uid form.

Another object is to provide a safe method of loading blast holes with an explosive of the liquid oxygen carbon type.

Another object is to provide a method of conditioning blast holes to receive explosives fof the liquid oxygen carbon type.

Another object is to provide a method of detonating a loaded blast hole at a predetermined location in the explosive.

Another object is to provide a new composition for placing combustible material in a blast hole and conditioning the blast hole to receive liquid oxygen to form a LOX type explosive.

These and other objects and advantages reside in novel features and combinations and in steps and processes as will hereinafter be more fully set forth and pointed out in the appended claims.

In the drawing, the figure is a vertical sectional illustration of a blast hole loaded in accordance with the present invention.

The explosive of the present invention is of the type generally known as LOX explosives and consists of a combustible material such as carbon and liquid oxygen. A large variety of ingredients has been used in these LOX explosives. The oxygen component has ranged from liquid air which contains about 21% oxygen to substantially pure oxygen and the combustible material has included wood pulp, cotton, lamp black, carbon black, chars, hydrocarbons, metal powders, sulphur and the like.

I prefer to use carbon as the combustible material for my explosive and either activated or non-activated carbon may be used. Activated carbon is preferred because it gives faster detonation and more power. Generally speaking, finer particle sizes of carbon give greater explosive speeds and when the carbon is non-activated, the particle size should be very small to present the maximum surface area to the oxygen. When using non-activated carbon, I prefer particle sizes of the order of 400 mesh and with activated carbon, particle sizes of the order of 200 to 250 mesh are entirely satisfactory. The particle size of the carbon is not critical but the sizes mentioned give excellent results. If desired, the carbon may be "fireproofed with acid as described in my copending application Serial No. 351,035, tiled April 24, 1953, now abandoned in favor of application Ser. No. 466,652, tiled November 3, 1954, but this is not necessary in the present invention.

According to the present invention, the combustible material is mixed with a liquid gas having a boiling point no higher and preferably lower than that of liquid oxygen. The gas should be inert and various gases such as helium (B. P. -452 F.) could be used. However, since liquid oxygen (B. P. -297 F.) is obtained by fractional distillation of liquid air, and since this process also yields liquid nitrogen (B. P. 321 F.) economy practically compels the use of nitrogen as the inert liquid gas. The combustible material and the inert liquid gas are mixed to the consistency of a uid mud or slurry which is inert and can be handled like any inert liquid gas.

The carbon-liquid nitrogen slurry is poured or extruded into the blast hole to the desired depth and the nitrogen, due to its extreme low temperature, freezes the earth to a substantial distance outward from the hole. After the nitrogen evaporates, liquid oxygen preferably commercially pure liquid oxygen, is poured into the hole and the carbon and liquid oxygen then forms the explosive in situ in the blast hole. The use of activated carbon improves the absorption of oxygen into the combustible at this stage.

During manufacture, shipping and loading none of the materials is explosive and the explosive is formed .only after the components are in place and after the major hazards such as cartridge sticking, sparks from dislodged rocks and the like are past. The earth surrounding the hole and the carbonaceous material are s thoroughly chilled by the liquid nitrogen that the oxygen will remain liquid for hours.

"I'he present invention has a Wide variety of uses and applications and various techniques would be used in applying the invention in different conditions as will be apparent to those skilled in the art. It would be irnpractical to describe in detail all of the various modifications and techniques to be employed in dierent situations so, for the purpose of describing and illustrating the invention, one particularly difficult use and technique will be described. It is to be understood however, that that particular use is merely illustrative.

The high grade iron ores of the Mesabi Range have been depleted to such an extent that their exhaustion is in sight. There remains however, in the Mesabi Range an almost inexhaustible supply of iron ore in the form of taconite. Taconite is one of the hardest rocks in America, and, while economic methods are known for producing iron from taconite, the blasting and reducing 0f the taconite ore to a size useful for further processing has been so expensive as to seriously impede the cornmercial production of iron from taconite. As late as June 1953 the Federal Bureau of Mines found that the recognized problems in mining taconite had not been resolved and that special blasting methods were needed.

When conventional modern methods of blasting are employed, the taconite tends to break into tabular blocks too large for handling by conventional shovels or conventional crushers so that secondary blasting of these blocks has been required. This secondary blasting adds greatly to the cost of mining. The explosive of the present invention is so rapid and powerful that in a test blast on November 18, 1953 in taconite, substantially all of the taconite blasted was shattered to usable size without the need for secondary blasting.

The taconite is so hard that ordinary methods .of drilling are slow and costly and blast holes are frequently formed by oxygen-oil burning, jet piercing rigs. Since the taconite rock is frequently non-uniform throughout its structure, the jet-pierced blast hole usually has irregular walls and frequently has chambers where the flame encounters fissures or soft spots. These irregularities and chambers increase the danger and difficulty of loading with known solid or LOX explosives and also decreases the eciency of such explosives due to the free air space around the explosive which acts as an elastic cushion.

The drawing illustrates the invention as applied to a jet-pierced blast hole in a taconite deposit. After the hole is formed, a tube 12 about one or two inches in diameter and formed of suitable material is inserted so that it extends to or near the bottom of the hole. The tube 12 is preferably formed of reproof material such as aluminum or other metal but a paper or cardboard tube may be used. A metal tube is preferable because A a tube of paper or other combustible material might become saturated with liquid oxygen and become an LOX explosive. The bottom of the tube 12 is preferably closed and the lower portion of Vthe tube up to about the height the operator wishes the explosive charge to come is provided with perforations 14 which face in all directions. The upper end of the tube extends above the top of the hole.

The carbon-liquid nitrogen slurry is poured or extruded into the hole around the tube to the desired depth. desired, a cloth cover may be placed around the tube to prevent clogging of the perforations with carbon, stones or other particles. The liquid slurry lls the hole regardless of irregularities and, when the slurry is iirst introduced, the heat of the hole causes rapid evaporation of some of the liquid nitrogen which violently agitates the slurry to further insure complete filling of irregularities and elimination of air pockets. This violent agitation also tends to free any loose stones or gravel which might fall and cause an accidental explosion after the oxygen is introduced. The hole is then iilled above the slurry charge with loose gravel or the like which is suiiiciently porous to permit gas to escape freely from the hole.

The vaporization and expansion of the liquid nitrogen draws heat from the walls of the 119.16 Until the earth for some distance out from the holeis at or near the temperature of liquid nitrogen (-321 F.). Depending upon the size of the hole and other factors, the evaporation of all of the nitrogen will take several hours and a suitable thermometer in the slurry will indicate when the liquid nitrogen has all evaporated. If all of the liquid nitrogen evaporates before the hole is ready for charging .with liquid oxygen, further liquid nitrogen can be added through tube 12 to keep the hole at the proper temperature. Thus, all of the holes in a large field may be kept in condition for loading for long periods of time.

When the liquid nitrogen has evaporated, liquid oxygen is poured into the hole through the tube 12, and, since the hole and the carbon are at a temperature below the boiling point of the liquid oxygen, the introduction of the oxygen is quiescent and not accompanied by the violent liberation of oxygen gas.

Oxygen and carbon combine in the ratio of 2.66 pounds of liquid oxygen to l pound of carbon to form CO2 and give the maximum explosive eiect. Generally it is preferable to add some excess oxygen to provide for evaporation and I prefer to use from about 2 to 4 or 5 pounds of liquid oxygen for each pound of carbon depending upon conditions. Unless detonation is to be delayed for an excessive time, the adding of excess liquid oxygen is not essential because the hole and the carbon are at such a low temperature that the vaporization of the liquid oxygen is very slow and the hole will remain charged with liquid oxygen for many hours. Vaporization of the liquid oxygen also tends to cool the hole to even lower temperatures and, should firing be delayed too long, more liquid oxygen can be added prior to tiring. However, in the event of a misre, the charge can be quickly rendered harmless by forcing Warm air down the tube and accelerating vaporization of the oxygen.

While any suitable detonator may be used, some commercial detonators become undependable at the very low temperatures involved and, when the combustible material is fireproofed carbon, a detonator of high power is required. For certain and dependable detonation, I prefer to use a detonating type of explosive such as the commercial detonator known as Primacord This detonator must be in the explosive itself and the present invention permits locating the detonator at any desired place in the explosive to control the explosion.

As shown in the drawing, a Primacord detonator 15 passes down through the tube 12 and its lower end extends out through a perforation 14 into the body of the explosive. The Primacord within thev tube will not detonate the carbon-liquid oxygen mass outside the tube and only the end of the Primacord which passes through the tube into the body of the explosive causes detonation. Ordinary the tube 12 is formed of short sections secured together and the Primacord can be positioned or secured in place as the tube is assembled. The Primacord may be detonated through its top end by a second detonator such as a blasting cap, electrical detonator or the like. v

By locating the lower end of the Primacord detonator at different places in the body of the explosive, different effects can be obtained. For example, when the detonator is near the center of the explosive mass as shown, the explosion proceeds in both directions simultaneously and the explosion toward the mouth of the hole forces the remainder of the explosive toward the bottom of the hole to give maximum shattering effect.

The present method of loading is not only safer, more etcient and more effective than prior methods but is also less expensive. Liquid nitrogen is inexpensive, costing about one cent per pound to produce, and the amount of liquid nitrogen used to condition a hole under normal circumstances costs substantially less than the bags used for conventional LOX cartridges. Also the liquid nitrogen substantially reduces the vaporization of oxygen and thus results in a further saving.

From the foregoing it is apparent that l am able to attain the objects of my invention and provide a new system for producing, loading and detonating explosives. The present invention meets the conditions for an ideal commercial explosive and its flexibility is such that its use for diterent purposes and under dilerent conditions will be apparent to persons skilled in the art.

What is claimed and desired to be secured by United States Letters Patent is:

l. The method of loading a blast hole with an LOX type explosive which comprises, positioning combustible material in the blast hole, chilling the combustible material and blast hole with an inert liquid gas to a temperature not substantially higher than the boiling point of liquid oxygen and then introducing liquid oxygen into the blast hole.

2. The method of loading a blast hole as defined in claim 1 including pre-positioning a detonator within the blast hole in predetermined position before positioning thc combustible material.

3. The method of loading a blast hole with an LOX type explosive which comprises, forming a slurry of a finely divided mass of combustible material and an inert liquid gas having a boiling point not substantially higher than that of liquid oxygen, introducing the slurry into the blast hole, permitting the inert liquid gas to vaporize and introducing liquid oxygen into the blast hole and the combustible material after substantially all of the inert liquid gas has evaporated and while the temperature of the combustible material is not substantially above the boiling point of liquid oxygen.

4. The method of loading a blast hole as defined in claim 3 including the pre-positioning a detonator within the blast hole in predetermined position before positioning the combustible material.

5. The method ot' loading a blast hole with a liquid oxygen-carbon explosive which comprises, forming a slurry comprising particles of activated carbon and liquid nitrogen, introducing the slurry into a blast hole, permitting the liquid nitrogen to vaporize and introducing liquid oxygen into the blast hole and the carbon after substantially all of the liquid nitrogen has evaporated and before the carbon has risen to a temperature substantially above the boiling point of liquid oxygen.

6. The method defined in claim 5 in which between two and tive pounds of liquid oxygen is introduced for each pound of carbon.

7. The method defined in claim 5 including closing the blast hole and covering the slurry with a layer of porous material to permit the escape of nitrogen gas prior to introduction of the liquid oxygen and in which the liquid oxygen is introduced directly into the carbon mass.

8. The method defined in claim 7 including pre-positioning a detonator at a predetermined position before introducing the slurry.

9. The method of loading a blast hole with an explosive of the liquid oxygen combustible material type which comprises inserting into said hole a hollow tube having a plurality of openings in its lower portion, forming a slurry comprising a mass of particles of combustible material and a liquid inert gas having a boiling point not substantially higher than the boiling point of liquid oxygen, partially filling the hole with said slurry to a point above the openings in said tube, iilling the remainder of the hole around said tube with a porous inert material, permitting the inert liquid gas to vaporize, introducing liquid oxygen through said tube into said hole and combustible material after vaporization of the inert liquid gas and before the combustible material and the inner surface of the hole have reached a temperature substantially above the boiling point of liquid oxygen.

l0. The method of safely loading a blast hole with a liquid oxygen combustible material explosive which comprises inserting into said hole a hollow tube having a plurality of openings in its lower portion, passing a det- ,onator through said tube and outward through one of said openings, forming a slurry of particles of carbonaceous material and liquid nitrogen, partially filling the hole with said slurry to a point above said detonator, filling the remainder of the hole around said tube with a pervious inert material to permit the liquid nitrogen'to vaporize and leave the hole, introducing liquid oxygen through said tube into said hole and carbonaceous material after vaporization of the liquid nitrogen and before the carbonaceous material and inner surface of the hole have reached a temperature substantially above the boiling point ot' liquid oxygen.

ll. The method of precooling a blast hole to be charged with a liquid oxygen-carbon explosive which consist of mixing particles of carbonaceous material and liquid nitrogen to the consistency of a fluid slurry, introducing the slurry into the blast hole and allowing sufiicient time for substantially all of the liquid nitrogen to evaporate before charging the blast hole with liquid oxygen to form liquid oxygen-carbon explosive.

OTHER REFERENCES Blasters Handbook, published by E. I. DuPont de Nemours & Co., Wilmington, Del., 1939, pages 66-7. (Copy in Scientific Library.)

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