US2207191A - Apparatus for blasting coal - Google Patents

Description

July 9, 1940. E. GEERTz y.APPARATUS FOR BLASTING COAL yFiled Dec. 27, 1957 l .x f, 4 l MN s NWA-:WWK

y Patented July 9, 1940 UNITED STATES PATENT. OFI-Ica 2.201.191 ArrAaarUs Fon BLAs'rING COAL Y- Eric Geertz, Aurora, Ill., assignor to Cardox Corporation, a corporation of Illinois Application December 27, 1937, Serial No. 181,886 4 Claims. (Cl. 11m-6) This invention relatesto new and 'useful improvements in apparatus for blasting coal by means of carbon dioxide.

The primary object ofthis invention is to pro- 5 vide 'improved apparatus for employing carbon dioxide as a blasting medium to break down materials, such as coal,v and wherein s uch improvements as increasing the quantity and improving A invention. Y

For the past several years, carbon dioxide has -been employed commercially as a blasting medium. Briefly, in this use of carbonv dioxide, it

, is coniined in its liquid phase in an indestructible cartridge or container which, at the time of use, is placed in a ,suitable blast or drill hole formed in the material-to be broken down. The mechanism of this type of blasting cartridge includes a suitable chemical heater unit which is positioned within the carbon dioxide receiving chamber of the cartridge. A suitable match-head is imbedded in the chemical heater composition and is energizedl at the'time of use of the heater unit by connecting the match-head to a suitable source of electricity, such as a conventional blasting magneto. When the blasting charge is to be released into the material to be -broken down,

the chemical heater unit is ignited and the burning of the same generates an intense heat sufli- 40 cient to quickly convert the carbon dioxide to its gaseous state. Each of the cartridges used in g this type of blasting is provided with a rupturable lwall section which is of proper construction to have a portion of the' same sheared from the remainder at the pressure desired for the particular Ablasting operation to be performed. l

Due to the great many different types and characters of coal encountered involving such characteristics as cleavage or natural parting planes both as to their occurrence and direction, friability, tenacity, elasticity, hardness, compressive strength and VWeight of over-burden, and due to the height or, thicknessofthe vein, which determines whether hand or power drilling can be employed, it has been necessary to use cartridges of different diameters and lengths. These diil'erent sized cartridges, naturally, possess different volumetric capacities insofar as the amount of carbon dioxide employed in the same is concerned.

Up to the time of development of the present 5 invention, it has been considered that the energy provided by a particular cartridge was measured theoretically by multiplying the release pressure of the charge by the volume of the charge. It has been the practice, therefore, to increase the 10 release pressure for the smaller sized cartridges. For example, the largest cartridge employed, the use of which was made ssible by the height or depth of the coal vein w ich permitted power drilling, had maximum capacity of f`cubic 15. inches. Such acartridge was customarily charged with 3 pounds of liquid carbon dioxide. 'Ihe average pressure at which this cartridge charge was released wasbetween 26,0009` and 30,000 pounds per square inch. Where the coal veins 20A were too thinto employ power drilling and hand drilling had to be resorted to, the smaller cartridges, having capacities ranging from 20 to 44 cubic inches were used. These smaller cartridges,

following the above referred to theory that the 25 product of the release pressure times the volume constituted the measure of energy provided by a cartridge charge, were discharged at an average release pressure of approximately 40,000 pounds per square inch. 30

Attempts were made from time to `time to inycrease the quantity of coal broken down with a single charge of carbon dioxide. It was found 0 that for a given quantity of carbon dioxide. the quantity of coal broken down could be increased 35 by raising the pressure at which the charge was released. Raising the release pressure, however, increased the shattering effect of the charge; i. e., the coal was broken down with a larger percentage of iines and the lump. which wereV 40 produced were less rm and therefore more easily broken during handling. This increased shattering effect was satisfactory under certain conditions, but it could not be tolerated generally in the use of carbon dioxide as profitsv obtained by the use of carbon dioxide as 55 blasting medium. i45V This was due to the fact that the use of carbon rio `types of explosives. 4 It was obvious, however, that increasing the quantity of yield at the expense of quality could not be favorably considered..

Attempts also were made to increase the productivenessof a chargeby increasing the quantity or volume of carbon dioxide in each cartridge. It was determined that this modication did not result in any appreciable increase in the amount of coal broken down. Apparently, therefore, it was impossible to' improve the quantity of coal broken down by a single cartridge charge over that which was being obtained. It was finally decided that attempts should be made tol improve the quality of yield without loss of quantity. Proceeding on the theory thatreducing the release pressure of a charge would result in improving the quality of yield and increasing the volume of the charge proportionately would `give an energy value which was equal to that of the cartridges then being used, experiments were conducted with larger volumes andlower pressures. A number -of cartridges having a 200 cubic inch capacity were preparedand discharged at release pres1 sures of approximate1y15,000 pounds per square inch. Comparingthese cartridges with lthe largest cartridges previously used, it will be noted that these cartridges had twice the volumetric capacity and were discharged at a release pres' sure approximately one-half that of the largestcartridges theretofore used. It was considered that these new cartridges would produce the same quantity of yield but would provide an improvement inthe quality because the product of release pressure times volume was the same for this new cartridge -and the largest cartridge previously used.

'rests with these new 20o cubic inch cartridges notonly demonstrated that the quality of the yield could be materially improved in this way, but that other improvements also resulted, the most surprising and unexpected of which. was a very material increase in the number of` tons of coal with respect to each other.

broken down per shot. Ir other words, a way of improving the productivex/iess of a cartridge had been unexpectedly discovered while attempting to improve the quality of the yield.

Naturally, additional tests were conducted ems ploying still lower release pressures and higher release pressures which fell-between the 15,000

With reference to acceptable release pressures,

-it was determined that the release pressure could l not fall below the fracturing strength of the coal to be broken down; i. e., the pressure at which the coal actually could be fractured or broken loose from the face of the seam. Although the characteristicsof the coal varied considerably, as lnoted'above, it was determined that most bitu- V minous coals could be fractured or broken loose with pressures ranging from 5,000 -to 10,000 jpounds per square inch.' The results obtained with these pressures naturally varied in diiferent a blasting medium compared favorably with other dition the coal for mechanical loading, with the entire fall of coal loose and requiring no digging, pressures ranging from- '15 per cent to 125 per cent in excess of the actual fracturing strength of the 'coal would produce the desired mechanical loading condition. The full range of pressures found to be most practical commercially was from. 8,000 to 19,000 pounds per square inch.

By maintaining the volume of the charge within a certain range of ratios relative to the release pressure, it was found that cartridges having. capacities fromV 50 to 200 cubic inches, which were capable of receiving charges of liquid carbon .dioxide weighing from 1 pound 9 ounces to 6 pounds, moreor less depending upon temperature conditions, -could be used and obtain all of these improved results. Attempts to increase seams. It was determined that to properly conthe volume of the charge above 200- cubic inches,

or approximately 6 pounds of carbon dioxide, at release pressures ranging from 8,000 to 19,000 [pounds per square inch failed to show any appreciable improvement either in the quantity or the quality of the yield. The maximum leil'ective volume, therefore. appeared to be 200 cubic inches when using this low range of'release pressures.

As stated above, the experiments -conducted with this new low pressure type of cartridge clearf ly showed that the ratio of the volume of the charge to the release pressure must be main. tained within a certain range of values to obtain the desired results. For the purpose of evaluating the volume-pressure ratio of cartridge charges,

the following formula has been found to provide accurate gures: l

' ,l FoauuLA No. 1

WFM-4(=vplume-pressure ratio #COz=pounds of carbon dioxide in charge. i 14,400=numb`er of cubic inches of space occupied by one pound of CO2 gas at normal atmospheric temperature and pressure. .P=pressure at which CO2 charge is. released measured in pounds per square inch.

(ne pound of liquid carbon dioxide occupies 33t/3 cubic inches of space under the conditions and practices prevailing in thev commercial use of carbon dioxide as a blasting medium. A charge of carbon dioxide weighs the same whether liquid or a gaseous state).

-Ezample The volume-pressure ratio values for all of the cartridge charges which have been found to proina this Formula No. 1 to the various high release pressure cartridges which have beenstandardized in commercial use, it was determined that their values all fell below 1.7 and extended as low as .20. This difference in the Avolume-pressure ratios of the two types of cartridge charges; Ji. e., the former high pressure charges and the new low pressure chargeais believed to be a clear indica- `vide the improved and vunexpected results of this invention range i'rom 1.7,to 10.8. In applying tion of the improvements effected bythe new lowl pressure type of cartridge.

As has been stated above, the only way it was found .to be possible to improve the quantity `of the yield, when operating in the high release pressure range was by yfurther increasing the release pressure. Increasing the volume of the charge that this failure to improve the quantity of the yield by increasing the volume of the charge was due to the fact that at such high release pressure, the coal surrounding the drill or blast holes failed so quickly that the added volume of carbon dioxide had no opportunity to perform any useful work. Just the reverse is found to be true with pressures falling within the new low pressure range. It has been determined that variations in the volume of the charge more eil'ectivelyproduce variations in the quantity of the yield than do variations inthe release pressures. In an effort to effect further improvements in the productiveness of a cartridge charge of the new low pres- 4 sure, large volume type,` tests were conducted to determine what. eiect the rate or speed of discharge of the blasting charge had on the work performed. It was ascertained that the speed of release of the charge is a factor which also governs the quantity and the quality of the work performed; that the effectiveness of variations in the speed of release to govern the work performed is dependent on the relationship or ratio of the speed of release to the release pressure and the volume of the charge; that the greater the speed of release of a low pressure, large volume charge, the greater its en'ectiveness to improve` the quantity and the quality ofthe yield, and that the rate or speed of release of a charge can be varied more effectively by varying the area of the discharge passage or outlet opening than by varying the release pressure.

As a result of these further tests, it was A denitely established that the true measure of the available energy or available work performing energy of a carbon dioxide cartridge is not the product of the charge volume times the release pressure, but is truly expressed by the following formula:

FORMULA No. 2

available energy #COz=pound of carbon dioxide in charge. tsec.=time in seconds required to exhaust the charge. 1000=an arbitrary ligure employed to enable the available energyto be expressed in terms of numerical unity. P=pressure at which C0: charge is released measured in Apounds per square inch.

(The time in seconds required to exhaust CO2 through a circular orifice from high pressure to atmospheric pressure may be calculated by the formula given by Schiile in his book, Technische f Thermodynamik von Prof. Dipl. Ing. W. Schiile,

. Berlin, Julius Springer, 1923, vol. 2.)

Example gbl-09M: 8 1 available energy 15,000 The various cartridges which have been adopted commercially in this new volume-pressure carbon dioxide blasting are provided with discharge orifices having areas ranging from .89 to 2.4 square inches. The t sec. rating for these various cartridges, calculated by Schles formula, range from .0475 second to .0760 second. The available energy ratings for these new cartridges, calculated by the above noted Formula No. 2 range from 2.0 to 10.0. The available energy ratings for all of the old high pressure, low volume cartridges, when calculated by Formula No. 2 are found to fall well below 2.0.

Naturally, the chemical heater unit employed to generate sumcient heat to eect gasification of the liquid carbon dioxide charge has been a cost item for this type of blasting. It has been determined that no greater quantity ofi heater compound need be employed with these new low pressure, large volume charges notwithstanding the fact that approximately twice the volume of carbon dioxide is used in eachI one of the new cartridges as compared with the old high pressure cartridges which have been displaced by the same. This is due to the fact that the final release pressure as well as the volume of the charge governs the amount of heater compound required to condition the charge for the desired blasting operation. For example, it requires substantially the same quantity of heater lcompound to raise 6 pounds of carbon dioxide to 15,000 pounds per square inch as it requires to raise 3 pounds of carbon dioxide to 30,000 pounds per square inch pressure.

The problem of formingY blast or drill holes to accommodate carbon dioxide cartridges has always been a controlling factor in determining the size of cartridge which can be used in a given coal vein. Where the coal predominates in the form of thin veins, hand drilling is necessary and the ,drill holes must be of comparatively small diameter. In high coal veins, power drilling is possible and larger drill hole diameters may be employed. After determining the advantages to be obtained bythe use of this new low pressure, large volume type of charge, it became necessary to devise ways and means of countering-undue drilling penalties.l The cartridge structure finally developed is illustrated in the drawing and will be described by reference to the same.

In the accompanying drawing, the reference character I0 designates the main body of the cartridge. This body is provided with a chamber II for receiving the charge of liquid carbon dioxide and the chemical heater unit I2. 'The rear or charging end of the cartridge has a charging cap or plug I3 threaded therein. A shoulderl is provided within the bored out end of the cartridge body to receive a gasket I5 which is compressed by the charging plug I3 when the latter is fully threaded into the body of the cartridge. This shoulder I4 also acts as a seat for the head I 8 of the chemical heater unit I2.

This chemical heater unit employs a matchhead I1' which includes the circuit wires I8 and I9. The wire or terminal I8 is arranged to have electric contact with the electrode 20 which is suitably mounted within the charging plug or cap I3 and is properly insulated therefrom. Ihe remaining lead wire I9 of the match-head is grounded to the cartridge body. This ground also includes the charging plug or cap I8. A suitably insulated socket 2I is formed transversely in the charging plug or cap I3 for receiving one lead or wire from a blasting magneto. This socket ZI permits the electrode 20 to make contact with the magneto wire detachably inserted in the said socket. A second socket 22 is formed in the charging plug I3 for the reception of the second lead wire from the magneto. This means of asuitable charging plant which is provided with a charging clamp or head that properly engages the plug 13. The adjustable valve 23 can be manipulated while the charging clamp or head is associated with the charging plug of the cartridge for making and breaking .communication between the charging plant and the chamber I l of the cartridge body.

The discharge end of the cartridge body is formed with a shoulder 24 against which seats va packing gasket 25 and a disc 26 which is adapted to have the central portion of the same sheared from the marginal portion by the blasting pressure developed within the chamber Il of the cartridge. This central portion of thedisc is sheared by the edge 21-of the discharge cap shank 28. The discharge cap is designated by the reference character 29.

VThe shearingv or rupturing of the disc eects Wcommunication between theY chamber yH of the cartridge and the interior of the cap 29. To per-- will be noted that these discharge ports are arranged at aproper angle to eect release of the blasting charge in a rearward direction. This controlled directional release of the blasting .charge very eil'ectively functions to retain the cartridge within a drill hole and to prevent the development of pressure between the inner `end of the cartridge and the inner end of the drill hole which is a very'desirable feature. vIt has' arranged at an angle of approximately 45 degrees4 and should each have a diameter of approxi.

mately H of an inch. In providing this large number of ports in a single cap, it has been found desirable to arrange the same in two series of six ports to a series with the ports of one series staggered with respect to the ports of the second series.

'Ihe cartridges normally used, i. e., the low volunie high pressure cartridges, were provided wiwi/outside diameters of 1% inches and 21/2 inches. The overall length for the cartridge bodies of the 1% inch cartridges varied from 20116 inches to 43% inches. The thickness of the side chamber wall for each of these cartridges was .25 inch. These cartridges hadl volumetric capacities ranging from to 44 cubic inches. The overall length of the 21/2 inch cartridges was 42% inches. The thickness of theA chamber wall for this type of cartridge was l of an inch. This typeof cartridge had a volumetric capacity of 100 cubic inches.

To provide the increased capacity for the low pressure cartridges, the old 13/4, inch outside diameter cartridge was increased to 2 inches outside diameter. The length of the different 2 inch cartridges ranged from 301/4 inches to 54% inches. The chamber wall thickness for A fewer number of this type of cartridge was reduced to .'18X. This reduction in wall thickness was made possible byu .metric capacities of 50,80 and 100 cubic inches.

The old 21/2 inch outside diameter cartridge was increased to 3 inches. The chamber wall thickness was reducedto .25 inch, which reduction was made possible by the reduction in re` 10 lease pressure. The overall length of the body portion of this 3 in ch cartridge was standardized at 46% inches. This cartridge had a volumetric capacity of 200 cubic inches.

To elect as rapid discharge of the blasting l5 medium as was possible, the inner wall surface ofthe cartridge chamber Il Vwasmade streamlined, as indicated at 3|. "The diameters ci' theoutlet openings were increased as much as pos-Y sible. The diameter of the outlet opening, of 20 course, is controlled by the outside diameter of the cartridge. The old 1% inch outside diameter cartridge had an outlet opening which was 3A of an inch in diameter. The new 2 inch outside diameter cartridge was provided with an outlet 25 opening which measures 11x, inches in diameter. The old 21/2 inch outside diameter cartridge was A provided with an outlet opening having a diameter of 1% inches. The new 3 inch cartridge was proyided with an outlet opening having a diameter of 1% inches. These increases in l outlet opening diameters and the streamlining of the discharge-end oi the cartridge chamber resulted in a much morerapid rate of discharge of the blasting medium. .36

As has been generally stated above, the use 'of the low pressure large volume cartridge resultedI in numerous improvements over the results obtained with the former high pressure cartridges. The shattering effect of the low pressure charge 40 was much less than with the high pressure charge. The yield possessed a higher percentage of lump coal over fine and the lumps produced were fully twice the s ize of the lumps formerly produced. 'Ihe larger lumps also were ilrmer and resulted in much less breakage during handling.' Due to the production of a larger quantity of lump and larger lump sizes, the coal dust produced by a blast was materially reduced. It was determined by visibility tests employing light sources .50

and an exposure meter, that 3 minutes after the ring of al low pressure charge, visibility was within 14 percent ot being normal and 10 minutes after iiring visibility had returned to normal. With high pressure charges visibility was 56 per cent below normal after '3v minutes had elapsed. i

An increase in tonnage of coal per shot was eiected which was very material. For example, the high pressure 100 cubic inch cartridge, released at an average of 30,000 pounds per square inch, broke down on an average of 5 tons of coal. The new 200 cubic inch cartridge released at a pressure of 15,000 pounds per square' inch broke down on an average of 8 tons per shot. This 65 increased yiel'd per shot naturally enables a Working -face to be brought down with fewer shots which reduces the cost by effecting a saving on drilling time. The cost of, breaking down a ton of coal by the low-pressure cartridge was found to be 20 per cent less than the cost with high pressure cartridges.

It also was determined that the large volume and .low pressure of the new type of cartridge rolls the coal out from the face in a substantially u better condition for easy and consequently lower cost mechanical loading. It also has an eiective spread to a much greater area resulting in breaking down more coal per shot, shearing straighter ribs, roof and face resulting in substantially eliminating overhanging coal on the ribs and face. Overhanging coal has always presented a real hazard to miners in cleaning out coal deposited close to the base of the ribs and face. The provision of straighter ribs, roof and i'ace also slightly increases the tonnage produced from a room of a. given size.

It is to be'understood that the forms of this invention herewith shown and described are tol be taken as preferred examples of the same, and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit oi' the invention or the scope of the subjoined claims.

Having thusdescribed the invention, I claim:

l. In apparatus employed ior breaking down coal in a mine by suddenly releasing into the coal a highly compressed gaseous charge oi' carbon dioxide which has been confined as a liquid and converted to its gaseous state by the application of intense heat at the time of eiecting release of the charge, the improvement which comprises a cartridge'having a charge receiving chamber possessing a volumetric capacity of 50 to 200 cubic inches and a discharge orifice having a diameter of from 1115 inches to 1% inches. means in said chamber for heating the carbon dioxide charge to eirect gasification ot the same, and a wall section closing said discharge oriilce and being of a character to rupture at the development oi a pressure within the chamber falling between 8,000 and 19,000 pounds per square inch.

2. In apparatus employed for breaking down coal in a mine by suddenly releasing into the coal a highly compressed gaseous charge oi' carbon dioxide which has been conned as a liquid and converted to its gaseous state by the application o'i intense heat at the time of effecting release of the charge, the improvement which comprises a cartridge having a charge receiving chamber capable of conining a liquid charge of from 1 pound, 9 ounces to 64 pounds o! carbon dioxide and a discharge orice having a diameter of from 111. inches to 1% inches. means operatively associated with the cartridge for gasitying the charge, and means for controlling said discharge orice to eflect discharge of the gasiiied charge at a pressure falling between 8,000 and 19,000 pounds per square inch.

3. In apparatus employed for breaking down coal in a mine by suddenly releasinginto the coal a highly compressed gaseous charge of carbon dioxide which has been confined as a liquid and converted to its gaseous state at the time of effecting release of the charge, the improvementY which comprises a cartridge having a charge receiving lchamber capable of confining a liquid charge from l pound 9 ounces to 6 pounds of carbon dioxide and a discharge orifice having a diameter of from 111.; to 1%, inches, means for heating the liquid carbondioxide charge to effect gasification of the same, and a wall section closing said discharge orifice and being of a character to rupture at the development of a pressure within the chamber falling between 8,000

and 19,000 pounds per square inch, the particular liquid charge, discharge oriiice diameter, and discharge pressure combination of the cartridge being such as to provide an available Work performingV energy value offrom 2.0 to 10.0 when calculated by Formula No. 2 appearing in the accompanying specication.

4. In apparatus employed for breaking down coal in a mine by suddenly releasing into the coal a highly compressed gaseous charge of carbon dioxide which has been conned as a liquid and converted to its gaseous state at the time oi effecting release of the charge, the improvement which comprises a cartridge having a charge receiving chamber capable of conning a liquidcharge of from l pound 9 ounces to 6 pounds of carbon dioxide and a discharge orifice having a diameter of from 1x1; inches to 1% inches, means operatively associated with the cartridge for gasiiying the charge. and means forcontrolling said discharge orice to effect discharge of the gasied charge at a pressure falling between 8,000 and 19,000 pounds per square inch. the particular liquid charge, orifice diameter, and discharge pressure combination of the cartridge being such as to provide an available work performing energy value of from 2.0 to 10.0 when calculated by Formula No. 2 appearing in the accompanying specification.

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