US2040581A

US2040581A - Mine blasting and similar operations

Info

Publication number: US2040581A
Application number: US23105A
Authority: US
Inventors: Voortmann Walter
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-02-16
Filing date: 1935-05-23
Publication date: 1936-05-12
Anticipated expiration: 1953-05-12
Also published as: GB449268A; BE409119A; DE727397C; FR47175E; BE414203A; FR804012A

Description

w. VORTMANN MINE BLASTING AND SIMILAR OPERATIONS Filed May 23, 1955 g Ww@ Fatenteel i12, E @'i attesti eterea Walter Voortman, Dortmnrid, Germany Ripphcation Eday 23, i935, Serial No.. 23,1195 lin Germany February lid, i934 3 Claims. l((l'll., Mge-5) The present invention relates to a method of and means for mine blasting both above ground (quarrying) and under ground. Hitherto, the tamping of blasting holes has been based solely 5 on practical experience and has not taken into account the effect of rock pressure and the nature of the strata to be blasted. Consequently, for

v example, in coal mining, the coal has been largely shot to coal dust by the wrong tamping method and by too heavy an explosive charge.`

In the art o shot-firing, it has been appreciated for some time that if the utmost useful work is to be performed bythe explosive, the high pressure gases released on ring the charge must be conned in the bore hole and must be made to exert their maximum pressure on the rock, coal or other containing strata to be blasted. ,For this reason, stemming is used to conne the gaseous products in the bore hole until the pres- 20 sure generated is sufficient to burst the containing strata. Pressure also is important in effecting complete combustion of the solid explosive, there-r by reducing the possibility of the production of fumes. Therefore, the stemming should be sumciently rigid to prevent it being blown out of the bore hole and the more rigid the-stemming, the more eiective is the explosive.

Although these desiderata have known, they have not been achieved in practice 30 with the methods of stemming known up to the present, since with all these known methods the stemming at the beginning, immediately .nearest to the charge, has been relatively loosely tamped 5 in order to avoid damage to the priming cartridge and it has been only remote from the charge, near the mouth 'of the bore hole, that the stemming has been at all tightly tamped. Consequentiy, when the charge is ired the high pres-* sure gases dissipate some of their energy in 1 40. performing useless work in forcing back the beginning ci the stemming and very often the l stemming is unable to resist this pressure and is blown out of the bore hole.y Even when the stemming resists the pressure of the' gases some part of the charge has been wasted in performing this uselesswork of compressing the steming it throughout the air space, instead of it being localized at one spot. It has been found and isfully realized that, for most emcient resuits, the length of the air cushionA should be varied according to the nature of the strata to be blasted, but with the present known practical methods of stemming, it has not been possible to control this length with any reasonable degree of accuracy. As yet, there is no known easy practical method of accurately controlling cushion firing.

The present invention has for its main object 10 to provide a new method of and means for tamping stemming;- and further objects of the invention are a method of and means for accurately controlling cushion ring; a method and means whereby a saving in the quantity of explosive 15 used is eiected and an improved output of materlal is obtained by reducing the amount of dust formed; the elimination of flame; to render it practically impossible to have a. blown-out shot; to eliminate almost entirely the reek produced 20 by the explosive; to render it impossible for the detonator to be exploded when the stemming is being tamped. l

These objects are achieved by introducing into 25 the bore hole, after the charge has been inserted in the bottom of the bore hole, a stemming plug oi incombustible material provided with a pulling member which extends outside the bore hole. The stemming plug is rst pushed up against the priming cartridge of the charge by means of the tamping tool which is inserted in the bore hole, then, while holding the pulling member attached to the plug against the tamping tool, the pulling member, i! a cushion is required, is pulled 35 to withdraw the plug to leave a blasting space between the priming cartridge and the stemming plug. lihe length of this space or air cushion, if provided, is predetermined according to the nature of the rock or the like to be blasted and is measured o by the distance 4by which the pulling member is withdrawn from the mouth of the borehole. lThe tamping tool is then removed and a quantity of stemmingv inserted in the bore hole'and is tamped tightly against the plug with 45 the stemming tool while at the same time the v pulling member is held to maintain the plug in its correct position and afterwards pulled to force the stemming round the base of the plug, thereby forming a gas-tight seal across the bore hole. The bore hole is then tamped with stemming in the normal manner. Afterwards the stemming is tested by pulling'hard on the pulling member. s If the latter moves at all, thereby giving'an indication that the plug has moved, more stemthe plug is firm the this stemming plug and pulling member. Furthermore, by means ofthe pulling member controllable from outside the bore hole, the stemming can be made completely rigid and ga'stight at the beginning and without any risk of the cartridge and detonator being crushed or damaged while the stemming is tamped. Thus, the advantages of accurately controlled ring are obtained.

It is an important feature of the invention that the plug may be firmly held by means of the pulling member at any definitely required distance from the end priming cartridge. When employing cushion firing, this distance is variable and depends upon the nature of the rock or the like to be blasted. The distance will, for instance, be greater with soft rock than with hard rock.

Also, the cartridges of the explosive charge will preferably be arranged directly one behind the other Without intervening spaces so that they reach to the bottom of the bore hole.

'Ihe result will then be obtained that all the cartridges will be ignited. The gases from the explosive, which act in the cavity or air space between the end priming cartridge and plug, will than blast olf a large coherent mass, which can easily be reduced as desired.

'I'he invention also comprises a stemming plug for use in the above method, a preferred construction of which comprises a substantially cylindrical body of incombustible material of somewhat smaller diameter than the internal width of the bore hole in which it is to be used, the said plug having a central b'ore for accommodating a non-inammable pulling cord or the like and having one or more lateral grooves through which pass the ignition wires or fuse of the priming cartridge.

A constructional example of the invention is i1- lustrated diagrammatically, by way of example, in the accompanying drawing, in which Fig. 1 shows a lay-out of the charge in a bore hole according to the method of the invention.

Fig. 2 illustrates, on a larger scale, a stemming plug according to the invention adapted to be inserted in the bore hole.

Fig. 3 shows a view of the left end of the plug according to Fig. 2, also on a larger scale.

Fig; 4 shows, on a larger scale, cords of diEerent lengths in combination with plugs according to the invention.

Fig. 5 shows, on a smaller scale, an arrangement of bore holes for carrying out the method according to the invention when blasting in a mine.

With reference to Fig. 1, a borehole is bored into the' rock to be blasted, the closed end of which bore hole accommodates explosive cartridges I. As can be seen from the figure, the end cartridge at the left is located in the bottom of the bore hole and the other cartridges are so positioned as to succeed the latter without intervening spaces. The end cartridge at the right is the priming cartridge, from which ignition wires 2 lead to the open end of the bor'e hole. A plug 3, which is made of 4incombustible material, or of salt, and the length of which is about one and a half times its diameter, is introduced into the bore hole from the right in such a manner that a cavity H is left free between the end of abacus;

the priming cartridge and the left-hand end of the plug 3. 'I'he diameter of the plug is somewhat less than the internalwidth of the bore hole. f

As can be seen from Figs. 2 and 3, the plug 3 is of substantially cylindrical form. It is provided with an axial bore, through which a cord 4 is passed. I'his cord is provided at the end located in the plug withva knot 4 which lies in a corresponding cavity 5 of the plug, said cavity being curved (for instance, semi-spherical) The cylindrical outer surface of the plug is provided with a groove 6, through which pass the ignition wires 2.

Once the plug has been inserted 4in the' bore ole in the manner illustrated in Fig. 1, part of the stemming B is rst tamped against the plug, the plug being rmly held by the cord. The remainder of the stennning can then be tamped.

'Ihere is no danger whatever of the striking priming cartridge being damaged by the tamping of the stemming, because after tamping the rst part thereof, the plug is stationary. It can be checked from outside the bore hole by an inspection of the cord whether the plug has moved or i.

not and also whether the stemming has been cor.. rectly tamped by pulling hard at the cord. If the cord and plug move at all, more stemming is required. If firm, the tamping is complete.

The cord consists of incombustible material" and is supplied in various lengths, in order to be able to use it for bore holes of diierent lengths. Preferably the end of the cord is coloured. For example, the different useful lengths such as 1.50 m., 1.6i) m., 1.70 m., etc., are distinguished by different colours.

As can be seen from Fig. 4, for instance, the vcord of the topplug is longer than the rest. The colour of this cord is indicated by the interruption of the left-hand end of the cord. The diierent marking of the cord of the centre plug is indicated by a chain-dotted line and the marking of the cord of the lower plug by a dotted line. When an electric current flows through the ignition wires 2, the priming cartridge is ignited, the

ignition flame is propagated with certainty up to the cartridge lying at the end of the bore hole. owing to the compact assemblage of the individual cartridges, the explosion wave of the powder gases returns to the cavity H and then acts in the direction of least resistance. Any expulsion of gases is prevented by the tamping of the stemming. The stemming, particularly at the beginning, is also tamped so firmly in the bore hole that ejection of the stemming or the plug is avoided.

Since the bore hole is sealed so.as to be gastight neither gases or particles of explosive can escape when the explosion of the charge takes place. The whole of the explosive charge is used up. Consequently the occurrence of the so-called after fumes is also prevented. The mine or quarry at which the blasting takes place can be entered again shortly after the explosion. Moreover, a coal dust explosion or ignition of explosive gases is prevented since the llame does not reach the exterior.

'I'he size of the cavity H depends on the nature of the rock. 'Ihe harder the rock, the smaller the size of the cavity. In Fig. 5, for example, 1 denotes diagrammati- I cally a mine being worked. 8 is a gallery in which a shaking conveyor 9 is arranged. At the right of the gallery 8 is a coal seam to be worked. In-

clined blast hoies lo, le and lz are nrst bored and by blasting, a. recess or niche is worked out, as indicated by the chain-dotted line N. After the coal has been removed from this niche, blastholes I3 and I4 are respectively bored. By further blasting of the seam with the explosive charge introduced into the bore hole I3, the block situated between the bore hole I3 and the wall of the niche is pushed out as a whole towards the niche and relieved of the rock pressure, so

that only very little coal dust arises. Since the block shows ne fissures, it can be further reduced very easily. In the same manner the' block of coal situated between thegibpre hole It and the niche is pushed out towards' the niche by blasting. In this manner, by using a lreduced quantity of explosive charge, coal may be obtained with a much smaller quantity of coal dust than hitherto, thus ensuring improved mining operations over those hitherto practised.

I claimz- 4 1. In blasting operations, the method of laying a blasting charge in a bore hole in which an incombustible plug having a diameter slightly less than that of the bore hole and a flexible holding member attached thereto is utilized, which comprises the steps of inserting the blasting charge into the bore hole, inserting said plug into the bore hole, tamping stemming material tightly against said plug while the latter is firmly held by said ilexible holding means against movement toward the charge, and then pulling the said plug outwardly by said holding means in order to insure the compactness of the inner portion of the stemming material.

2. In blasting, the method of laying a blasting charge in a bore hole in which an incombustible cylindrical plug having a diameter slightly less than that of the bore hole and a flexible holding member attached thereto is utilized,

which comprises the steps of inserting .a blasting charge into the inner end of a bore hole, inserting said plug into abutting relationship with said blasting charge, withdrawing said plug a predetermined distance by said flexible holding member so as to lea've an air space between said charge and said plug and tamping a quantity of stemming material `tightly against said plug while the latter is rmly held by said holding means against movement toward the charge, whereby a gas-tight and firm seal is formed.

3. The method of laying a blasting charge in a bore hole in which an incombustible cylindri cal plug having a diameter slightly less than that of the bore hole and an elongated exible holding member attached thereto is utilized, which comprises the steps of inserting the blasting charge into the inner end of the bore hole, inserting the plug into abutting relationship with said charge, drawing out the plug a predetermined distance from the blasting charge so as to leave a cushioning air space, forcing tamping material tightly against thefplug while holding it rmly in place, and then pulling it outwardly by means of the flexible holding member so as to insure the compactness of the inner portion of the tamping.

` WALTER. VOORTMANN.