US2738162A

US2738162A - Method and apparatus for forming blasting holes in rock

Info

Publication number: US2738162A
Application number: US339301A
Authority: US
Inventors: Robert B Aitchison
Original assignee: Union Carbide and Carbon Corp
Current assignee: Union Carbide Corp
Priority date: 1953-02-27
Filing date: 1953-02-27
Publication date: 1956-03-13
Anticipated expiration: 1973-03-13

Description

March 13, 1956 R. B. AITCHISON 2,738,162

ETHOD AND APPARATUS FOR FORMING BLASTING HOLES IN ROCK Filed Feb. 27, 1953 2 Sheets-Sheet l Z7 INVENTOR ROBBYERT B AITCHISON ATTORNEY March 13, 1956 R. B. AITCHISON METHOD AND APPARATUS FOR FORMING BLASTING HOLES IN ROCK Filed Feb. 27, 1953 2'Sheets-Sheet 2 INVENTOR ROBERT B. AITCHISON ATTORNEY procedure.

METHOD AND APPARATUS FOR FORMING BLASTING HOLES IN ROCK Robert B. Aitchison, Jackson Heights, N. Y., assignor to Union Carbide and Carbon Corporation, a corporation of New York Application February 27, 1953, Serial No. 339,301

11 Claims. (Cl. 255-13) The present invention relates to a novel method and apparatus for forming blasting holes in rock. More particularly, it concerns such a method and apparatus for thermally enlarging a bore in a'body of rock. The invention can be used successfully on such rocks as quartzite, dolomite, trap-rock, the low-grade iron ore known as taconite, and others.

Deep blasting holes have been bored successfully in rock bodies by the flame piercing method and apparatus described in United States Reissue Patent Re. 22,964, granted January 20, 1948, to C. J. Burch. Mechanical devices such as churn drills also have been .used, particularly on the softer rocks. As the diameter of the holes desired has increased, larger and heavier equip ment and more powerhave been required to operate it. For example, the flame piercing of blasting holes having a minimum diameter of 6% inch and a depth of 30 feet in taconite iron ore has required a blowpipehaving a diameter of 4% inches and weighing about a ton; and the direct piercing of holes having a larger diameter would require an even larger and heavier blowpipe.

Naturally the amount of explosive which can be loaded into a hole or small diameter is strictly limited. Heretofore it has been customary to spring the bottom portion of such a small hole by repeatedly exploding small charges of explosive at the bottom and clearing out the detritus to form an enlarged chamber for receiving the final charge of explosive. This procedure is slow, laborious, uncertain, dangerous, and expensive; and is limited to forming a chamber at the bottom of a bore.

Among the objects of the present invention are to produce thermally in rock a blasting hole having at least a portion of larger diameter than could be obtained efficiently by direct flame piercing with equipment of the same size, weight, and power; and to increase thermally over all or any part of its length the diameter of a blasting hole previously formed in rock by any known Other objects are to provide novel 'apparatus for thermally enlarging a blasting hole'over all or any part of its length; and to provide such apparatus which operates to increase the diameter of a blasting hole beyond that which can be efficiently obtained directly by flame piercing equipment of the same size, weight, and power.

The above and other objects will become apparent from the following description, having referenceto the annexed drawings, wherein:

Fig. l is a schematic side elevational view, partly in section, showing apparatus including a blowpipe for thermally increasing the diameter of a blasting hole in accordance with the invention;

Fig. 2 is an enlarged longitudinal sectional view of the lower end of the blowpipe shown in Fig.1;

Fig. 3 is sectional view taken along the line 3-3 in Fig. 2;

Fig. 4 is a longitudinal sectional view through the lower end of a blowpipe which can be used for directly piercing a blasting hole in a body of rock;

A United States Patent fiice 2,738,1fl2 Patented Mar. 13, 1956 Fig. 5 is a schematic view showing the lower portion of a blowpipe when enlarging a bore in a single pass;

Fig. 6 is a sectional view of the lower end of a modified blowpipe embodying the present invention; and

Fig. 7 is a schematic view showing the lower portion of the blowpipe of Fig. 6 when enlarging a bore in a single pass.

' In accordance with the present invention there is provided a novel method for increasing the diameter of a blasting hole or bore in a body of rock by directing a high (supersonic) velocity flame jet having a radial component against a peripheral zone of the side wall of the bore to loosen and remove material therefrom, and traversing the high velocity flame jet in a direction axially of the bore to remove material or detritus from successive peripheral zones of the side wall. The detritus is promptly and continuously cleared from the bore, as by ejection with a flowing stream of ejection fluid. The high velocity flame jet removes material predominantly by spalling it oif as unfused particles, but in some rocks there is also some melting; e. g. in quartzite the material is removed almost entirely by spalling, whereas in taconite iron ore there is noticeable melting. Other rocks melt more or less than taconite.

In the embodiment of the invention shown in Figs. 1-5 of the drawings, the high veloctiy flame jet is provided as one or more individual radial flame jets which are rotated around the longitudinal axis of the bore so that they impinge against a peripheral zone of the side wall. Thus, each flame jet follows a helical path. as it traverses the bore axially. Additionally, as the flame removes material, jets of water are injected into the bore adjacent the flame jet to quench the hot material and solidify any molten part, and this water flashes to steam when heated by the flame and the hot detritus. The steam joins with the gaseous products of flame combustion to form the ejection fluid for blowing detritus out of the bore so promptly that there is no time for detritus to accumulate and melt. Furthermore, since some quite large particles of material are spalled oif by the high velocity flame jet or are formed when molten material is quenched, it has been found advantageous to mechanically disintegrate such particles in the bore to permit their ejection.

It has been found that rock formations which cannot be effectively spalled by conventional low velocity flames, such as granite which contains many high melting point constituents, are easily spalled and sprung in accordance with the present invention. This is believed to be attributable to the fact that the high (supersonic) velocity flame jets employed in the present invention are capable of delivering heat at a higher transfer rate and are accompanied by a mechanical force which aids in disintegrating the rock formation to which the flame jet is applied. In addition, spalling, being a thermal surface effect, does not require deep heat penetration such as is accomplished through the use of low velocity flames. Thus, the action of the high velocity jet is more eflicient in thermally spalling formations which cannot be effectively spalled by the action of a conventional low velocity, heat soaking type of flame. Referring to Fig. 1 of the drawings, there is shown an elongated blowpipe 11 which is suspended within a vertical bore 13 in a body of rock 14 by a cable 15 passing over a pair of sheaves 17 and 19 on the top of a vertical mast 21 which is mounted on a mobile platform 23. Cable 15 is wound on a drum 25, also mounted on platform 23, for raising and lowering the blowpipe.

Blowpipe 11 has a nozzle 27 at its front end provided with a pair of oppositely disposed radial flame jet ports 29 and 31 (Figs. 2 and 3) having their axes at right angles to the longitudinal axis of the blowpipe for directing a pair of horizontal high velocity flame jets radially against the side wall 33 of the bore. A burning combustible fluid, such as a mixture of oxygen and kerosene, enters

ports

29 and 31 from an internal combustion chamber 32 which is supplied with oxygen and kerosene by passage 34 and injector 36, respectively.

The high velocity flame jets from

ports

29 and 31 are rotated around the longitudinal axis of the bore 13 by rotating the whole blowpipe 11 by means of a mechanism 35 operated by a gear reducer and electric motor set 37 controlled by start and stop switches and 41. Mechanism 35 may be of any suitable type, such as that described in United States Patent 2,338,093, issued January 4, 1944, to W. T. Caldwell. The rotating mechanism there described is constructed with keys sliding in longitudinal grooves such as the groove 38 on the blowpipe, so that the blowpipe can be rotated and also moved longitudinally up or down simultaneously.

Longitudinal movement of the blowpipe up or down is accomplished by the drum 25 which is operated by a gear reducer 39 and electric motor 42 controlled by

electrical switches

43, 44 and 45. When the operator wishes to raise the blowpipe in the hole he presses the switch 43 which causes the motor 42 to rotate the drum 25 counterclockwise to wind up cable 15. When the operator wishes to lower the blowpipe in the hole he presses the stop switch 44 and then the switch 45 which reverses the rotation of motor 42 and causes drum 25 to rotate clockwise and pay out cable.

Sometimes the diameter of an approximately cylindrical bore 13 is to be enlarged locally to form an approximately cylindrical chamber 48 for receiving a larger quantity of explosive than otherwise could be loaded. Then the blowpipe 11 is lowered into the bore 13 with the high velocity flame jets burning until the nozzle 27 is at the bottom of the desired chamber, and rotation of the blowpipe is begun to cause the radial flame jets from

ports

29 and 31 to impinge against the side wall 33. At the same time or shortly thereafter the operator starts the drum motor 42 to cause the blowpipe to be raised slowly. The radial high velocity flame jets thus impinge against successive peripheral zones and remove material for enlarging the diameter of the bore. When the nozzle 27 has reached the top of the desired chamber the operator then reverses the drum motor 42 and lowers the blowpipe slowly to enlarge the diameter still more. This back-and-forth movement of the blowpipe is continued for any number of cycles, as experience may dictate, until the desired enlargement has taken place. Obviously if the nozzle 27 is first positioned at the top of the desired chamber, the first step is to lower the nozzle slowly to its bottom. The size of the chamber can be controlled much more effectively than in the previous procedure of exploding successive small explosive charges to spring the hole.

During the operation of the blowpipe 11 cooling water is supplied to an annular chamber in the nozzle 27 and jets of this water are discharged radially from a plurality of circumferentially arranged ports 46 in the nozzle slightly to the rear of the

flame ports

23 and 31. A single jet of water also is discharged axially through an axial port 46a. These jets of water are vaporized to steam by the heat of the high velocity flame jet and by contact with the hot detritus, and the steam cooperates with the gaseous products of flame combustion to eject detritus from the bore.

Since some of the material removed from the side wall of the bore may be overly large for ejection, four or more radially extending longitudinal teeth 47 are provided on a removable sleeve near the front end of blowpipe 11 just to the rear of water ports 46 so as to rotate with the blowpipe and disintegrate such large particles. Water from ports 46 cools the teeth 47 to protect, them from deterioration by the heat.

The bore 13 shown in Fig. 1 has been locally enlarged tained by fully loading such a hole.

at the bottom providing a large chamber 48 to receive an explosive. One or more similar chambers can be formed any where along the length of a bore singly or as a series separated from one another by portions of the bore having the original diameter. Charging an explosive charge into a chamber located near the top of a blasting hole causes greater fragmentation than heretofore, which reduces the amount of secondary piercing and blasting necessary.

It is also frequently desirable to enlarge the diameter of a bore over its entire length by generally following the procedure described above, by extending the back-andforth traversing movement of the blowpipe over the entire bore. The maximum explosive effect can be ob- Such procedure is of particular importance where the explosive charge to be used is contained in an inflexible metallic cannister.

A predetermined minimum bore enlargement can be obtained in a single pass by starting at the top and lowering the blowpipe slowly into the bore. In this case the over-all diameter of the blowpipe teeth should be about the same as the desired minimum hole diameter, so that the teeth'will hang up on any undersize protuberances in the bore until they are removed by the high velocity flame jet and the blowpipe can drop to the next protuberant zone, as shown in Fig. 5. All or any part of the length of the bore can be enlarged in this way.

The nozzle 27 has been shown in Figs. 1-5 with radial high velocity flame jets having their axes at right angles to the longitudinal axis of the blowpipe and the bore, but successful operation has been achieved when these radial high velocity flame jets are directed upwardly or downwardly at a small angle to the blowpipe axis. In fact, a slight upward, or swept back, inclination of the flame jets assists in ejecting detritus from the bore. A blowpipe having such upward inclination of flame jets is shown in Figs. 67 of the drawings. As there shown, elements have been assigned primed numerals corresponding to the numerals of equivalent elements of the apparatus shown in Figs. 1-5. Furthermore, while two radial flame jets have been shown by way of illustration, successful operation has been achieved with a single radial port; and more than two flame jets also can be used successfully.

While the original bore which is enlarged by the method of the invention may be produced in any desired way, as by mechanical drilling or by flame piercing, the present method has been found particularly valuable when used in conjunction with a flame piercing procedure. In flame piercing the bore the same blowpipe 11 is used but, instead of the nozzle 27 having radial high velocity flame jets, the blowpipe is provided with a nozzle 49 (see Fig. 4) having a longitudinal flame jet 51 arranged to impinge an intensely hot high velocity flame jet on the body of rock in the direction of piercing. This flame jet first produces a shallow depression in the rock which rapidly deepens to form a bore. The blowpipe is advanced into the bore as it deepens to remove more material until a bore of a desired depth, such as 30 feet, has been obtained. During its advance the blowpipe is rotated and is lowered downwardly in the manner described for enlarging the hole diameter.

The detritus which is loosened from the rock body is ejected from the bore by the gaseous products of combustion and the steam from evaporating water jets which are injected into the bore from ports 53. Any overly large particles are disintegrated by the rotating teeth 47. When a bore has been completed the blowpipe 11 is withdrawn, and nozzle 49 is removed from the blowpipe and replaced by a nozzle 27 having radial or swept back flame jet, ports, as shown in Figs. 2 and 6. Then the lighted blowpipe is re-inserted in the bore and. the diameter is increased in the manner previously described. Of course, when, the bore. is. to be enlarged by a single downward pass, the sleeve 50 also should be replaced by a sleeve SShaving teeth 57 thereon of about the sam over-all diameter as desired in the final hole.

The method and apparatus of the invention have been used successfully in hard taconite iron ore which had been flame pierced originally ;with bores having a depth of 30 feet, and a minimum diameter of 6% inches. One hole was enlarged over its entire lengfli in a single downward pass to a minimum diameter of 7 /2 inches at a rate of 60 linear feet per hour. Another hole-was enlarged to a minimum diameter of 8 /2 inches oyer'its entire length in a single downward pass at a rate of 30 linear feet per hour. Still another'hole was cnlarged to a minimum diameter of 9% inches over its entire length in a single downward pass at a rate of 22 /2 linear feet per hour. Enlargement was accomplished with the same equipment as had been used for the original flame piercing of the bores, except for the substitution of a two-flame jet nozzle of the general type shown in Figs. 2, 3, 6 and 7 for the nozzle of the general type shown in Fig. 4. Oxy-kerosene high velocity flame jets were used.

In other examples of how the method of the invention has been performed, three bores were flame pierced in a body of traprock and were then enlarged in the manner described above, using a blowpipe nozzle having a single radial high velocity flame jet in place of the piercing nozzle. One hole having a minimum diameter of 3 /2 inches was enlarged over a 13 /2 inch length to a minimum diameter of 6 inches by traversing an oxykerosene flame jet back and forth for 10 cycles at a rate of 18 inches per minute while rotating at 20 revolutions per minute. Another hole having a minimum diameter of 5 inches was similarly enlarged to a minimum diameter of 6 inches over a 14 /2 inch length in cycles. Still another hole having a minimum diameter of 4 inches was similarly enlarged to a minimum diameter of 7 inches over an 8-inch length in 7 cycles.

It is to be understood that in the forming and enlarging of bores by the method of the invention, natural rock, such as iron ore, is often so formed that an absolutely uniform diameter cannot be obtained by a flame process. This is true both in the piercing and the enlarging of a bore.

It is also to be understood that the method of the invention can be performed on bores extending in directions other than vertically down, for example on horizontal bores. Apparatus of the general type disclosed in the aforementioned U. S. reissue patent Re. 22,964 can then be used for manipulating the blowpipe.

Further, it is to be understood that by the words high velocity jet of burning gases, high velocity flame jet, and flame jet, as employed herein, is meant a flame having a linear velocity exceeding the velocity of sound in the combustible mixture (approximately 3000 linear feet per second) at thattemperature and pressure. Tests have indicated that flame velocities of about 4000-5000 linear feet per second are obtainable with the apparatus of the present invention.

This is a continuation-in-part of my copending application Serial No. 188,508, now abandoned.

What is claimed is:

1. The method for increasing the diameter of a bore in a body of rock which comprises directing from an internal combustion burner against a peripheral zone of the side wall of said bore a jet of burning gases having a linear velocity greater than sonic velocity, the axis of said jet forming, in the region between said jet and the open end of said bore, an angle of less than 90 degrees with the longitudinal axis of said bore; traversing said jet axially of said bore to remove material from successive peripheral zones of said side wall; and ejecting said material from said bore at least in part by the action of said jet.

2. The method for increasing the diameter of a bore in a body of rock which comprises directing from an internal combustion burner against a peripheral zone of the side wall of said bore a jet of burning gases having a linear velocity greater than sonic velocity, the axis of said jet forming, in the region between said jet and the open end of said bore,-an angle of less than degrees with the longitudinal axis of said bore; rotating said jet around the longitudinal axis of said bore to remove material from a peripheral zone of said side wall; and ejecting said material from said bore at least in part by the action of said jet.

3. The method for increasing the diameter of a bore in a body of rock which comprises directing from an internal. combustion burner against a peripheral zone of the side wall of said bore a jet of burning gases having a linear velocity greater than sonic velocity, the axis of said jet forming, in theregion between said jet and the open end of said bore, an angle of less than 90 degrees with the longitudinal axis of said bore; rotating said jet around the longitudinal axis of said bore to impinge said flame jet against a peripheral zone of said side wall; traversing said rotating flame jet back and forth axially of said bore to remove material from successive peripheral zones of said side wall; and ejecting said material from said bore at least in part by the action of said jet.

4. The method in accordance with claim 3, wherein said rotating flame jet is traversed back and forth along substantially the full length of said bore.

5. The method in accordance with claim 3, wherein said rotating flame jet is traversed back and forth along a portion of the length of said bore to form an enlarged chamber therein.

6. The method in accordance with claim 3, wherein said rotating flame jet is traversed along a plurality of axially-spaced portions of the length of said bore to form a series of enlarged chambers therein separated from one another by portions of said bore having substantially the original diameter thereof.

7. A blowpipe for removing rock comprising an enlarged tubular member including a nozzle at the front end thereof, said nozzle having an internal combustion chamber, at least one radial flame jet port means for providing a flame jet of supersonic velocity and a diverging passage between said internal combustion chamber and each of said flame jet ports, wherein the axis of said flame jet port means is positioned so as to discharge flame jets having a rearward directional component forming an acute angle with the longitudinal axis of said nozzle; and means for supplying combustible fluid to said internal combustion chamber.

8. A blowpipe for removing rock comprising an enlarged tubular member including a nozzle at the front end thereof, said nozzle having an internal combustion chamber, at least one radial flame jet port means for providing a flame jet of supersonic velocity, and a diverg ing passage between said internal combustion chamber and each of said flame jet ports, wherein the axis of said flame jet port means is positioned so as to discharge flame jets having a rearward directional component form ing an acute angle with the longitudinal axis of said nozzle; means for supplying combustible fluid to said internal combustion chamber; and said tubular member having a plurality of circumferentially-arranged ports positioned near said front end and to the rear of said flame jet port means for discharging jets of water.

9. A blowpipe in accordance with claim 8, which also comprises radially extending teeth secured thereon near said front end in position for breaking up large particles of rock loosened by said flame jet.

10. Apparatus for thermally increasing the diameter of a bore in a body of rock comprising an elongated blowpipe adapted to be inserted in said bore, said blowpipe having a nozzle at the front end thereof provided with an internal combustion chamber, at least one flame jet port means for directing a flame jet of supersonic velocity against the side wall of said bore to remove material therefrom and a diverging passage communicating between said internal combustion chamber and each of said flame jet port means, the axis of said flame jet port means being positioned so as to discharge flame jets having a rearward directional component formingv an acute angle with the longitudinal axis of said nozzle; said blowpipe also having radially extending teeth secured thereon near said front end in position to break up large particles of said removed material; means for rotating said nozzle and said teeth to impinge said flame jet against a peripheral zone of said side wall to cause said teeth to break up said large particles; and means for traversing said blowpipe back and forth longitudinally thereof to impinge said supersonic velocity flame jet against successive peripheral zones of said side wall.

11. Apparatus in accordance with claim 10, wherein said blowpipe is additionally provided with ports positioned near the front end of said nozzle for discharging water into said bore adjacent said flame jet.

Refesences Cited in the file of this patent UNITED STATES PATENTS 2.195,384 Zobel et a1 Mar. 26, 1940 2,286,782 Aitchison Tune 16, I942 2,327,482 Aitchison et a1. Aug. 24, 1943 2,327,496 Burch Aug. 24, 1943 2327,492 Burch Aug. 24, 1943 2,367,119 Hess Jan. 9, 1945 2,628,817 Wyland, J'r. Feb. 17, 1953 2,675,993 Smith et a1. Apr. 20, 1954

Claims

1. THE METHOD FOR INCREASING THE DIAMETER OF A BORE IN A BODY OF ROCK WHICH COMPRISES DIRECTING FROM AN INTERNAL COMBUSTION BURNER AGAINST A PERIPHERAL ZONE OF THE SIDE WALL OF SAID BORE A JET OF BURINING GASES HAVING A LINEAR VELOCITY GREATER THAN SONIC VELOCITY, THE AXIS OF SAID JET FORMING, IN THE REGION BETWEEN SAID JET AND THE OPEN END OF SAID BORE, AND AN ANGLE OF LESS THAN 90 DEGREES WITH THE LONGITUDINAL AXIS OF SAID BORE; TRAVERSING SAID JET AXIALLY OF SAID BORE TO REMOVE MATERIAL FROM SUCCESSIVE PERIPHERAL ZONES OF SAID SIDE WALL; AND EJECTING SAID MATERIAL FROM SAID BORE AT LEAST IN PART BY THE ACTION OF SAID JET.