TECHNICAL FIELD

The invention concerns a rock cracker cartridge comprising a first, outer sleeve with an end wall in a first end and a central opening in a second end which in other respects is closed by a closure member; a substantially cylindrical, second sleeve which is coaxial with the first, outer sleeve and with said central opening and communicates with said central opening and is connected to and extends from said closure member in a main chamber in said first, outer sleeve; and a rock cracker cartridge which fills the space in the main chamber between said first and second sleeves and between the end wall in said first end and the closure member in the second end.

The invention also concerns an ignition capsule for igniting the rock cracker cartridge, which ignition capsule in combination with a surrounding ignition assembly sleeve defines an explosive ignition assembly in the rock cracker cartridge which is prepared for ignition, said ignition assembly sleeve being an integrated member of the rock cracker cartridge, when the rock cracker cartridge is not yet prepared for ignition, as well as of the rock cracker cartridge when the rock cracker cartridge is prepared for ignition. BACKGROUND OF THE INVENTION

A rock cracker cartridge of the type mentioned in the preamble is disclosed in WO 2009/120139. This cartridge represents a significant contribution to the technical progress within its specific technical field; cracking major stones, usually called boulders, blocks of rock, minor bedrock sections and the like, in such a mode that it can be carried out even very close to buildings or in other environments which normally would require considerable measurements of precaution. It is also an objective of the invention to bring this technical progress a further step forwards. More specifically, it is ab purpose to provide ignition means for the rock cracker cartridge, which satisfy the requirements of lowest Swedish classification for transportation of explosives, transportation class 1,4. This means that the rock cracker cartridge shall be able to be fired without use of a detonator containing any detonating explosive, such as PENT or the like, which conventional ignition capsules do. These and other objectives of the invention can be achieved by means of a rock cracker cartridge and an ignition capsule which are characterized by what is stated in the appending patent claims.

Other characteristic features and advantages of the invention will be apparent from the following description of a preferred embodiment. BRIEF DESCRIPTION OF DRAWINGS

In the following description of a preferred embodiment, reference will be made to the accompanying drawings, in which

Fig. 1 is perspective view of a sleeve, in this context termed ignition unit sleeve, Fig. 2 shows an end view of the ignition unit sleeve according to Fig. 1,

Fig. 3 shows the ignition unit sleeve in a longitudinal cross-section along the line III-III in Fig. 2,

Fig. 4 shows the ignition unit sleeve in a transversal cross-section along the line IV-IV in Fig. 2,

Fig. 5 shows a complete ignition capsule including the ignition unit sleeve in

longitudinal cross-section as in Fig. 3,

Fig. 6 shows an insert of mainly known design,

Fig. 7 shows the insert according to Fig. 6 in a longitidunal, axial cross-section, Fig. 8 shows the rock cracker cartridge of the invention before priming as viewed obliquely from above,

Fig. 9 shows the rock cracker cartridge of the invention primed in a bore in a piece of rock that shall be cracked, and

Fig. 10 shows the primed rock cracker cartridge in cross-section along a line X-X in Fig. 9.

DESCRIPTION OF A PREFERRED EMBODIMENT

The unprimed cracker cartridge 1, Fig. 8, comprises a first, outer plastic sleeve 2 and an insert unit 25, Fig.6 and Fig.7, which in turn consists of a plug 4 and a second, inner sleeve 7. The plug 4 and the inner sleeve 7 consist, according to the embodiment, of a hard plastic material, more specifically an acetal plastic material, and still more specifially of an acetal (POM)- copolymer and are mould jointly to form an integrated unit.

The outer sleeve 2 is, according to the embodiment, made of a so called ABS-plastic, which also is a hard plastic material, and has the shape of an elongated circular- cylindrical tube with a flat end wall. The interior of the outer sleeve 2 forms a main chamber 5 which is filled with a cracking powder charge 6, preferably a nitro powder charge (NC-powder), Fig. 9.

The plug 4 has a circular-cylindrical outer wall 19, a flat annular end wall 20, which faces the main chamber 5 and is pressed against the powder charge 6, and a tubular portion 31 which defines a through hole 8, which is coaxial with the outer sleeve 2. Radial beams 24 extend between the tubular portion 21 and the cylindrical wall. Wedge- shaped, material saving recesses between the beams 24 are designated 23, and an upper flange is designated. On said upper flange there are provided three spacer members 19a, which protrude in the axial direction.

The second, inner sleeve 7, which is coaxial with the first, outer sleeve 2, and defines an ignition assembly sleeve 7a in the primed cracker cartridge 1 , extends from the flat end wall 20 of the plug 4 into the cracking powder charge 6 in the outer sleeve 2 to a significant depth in the powder charge, as is shown in Fig. 9. The sleeve 7, 7a has a comparatively thin wall 13. According to the embodiment, it is about one millimetre thick. It may optionally, in order to make it stiffer, be provided with longitudinal, external stiffeners. According to the preferred embodiment, however, the outer surface as well as the main portion of the inner surface are quite smooth, which nevertheless affords the ignition assembly sleeve 7a an adequate stiffness but at the same time not a greater rupture resistance than what it maximally may have in order certainly to be broken up when that ignition capsule which shall be described in the following, is ignited, and which in the primed cracking cartridge 1 is accommodated in the space 9 of the ignition assembly sleeve 7a which is denominated priming chamber. The pointed nose portion or tip 12 is conical, forming an acute angle. Close to the nose portion 12, the sleeve 7a has an internal constriction 26, which is about 0.2 mm thick in the radial direction and about 5 mm long in the axial direction.

The plug 4 is pressed with some force into the mouth section of the outer sleeve 2 so far that the flange 22 abuts the upper edge of the outer sleeve 2 and the flat end wall 20 will be pressed against the cracking powder charge 6. In connection with the insert 25 being entered, the inner sleeve, 7, 7a, will be pressed into the cracking powder charge 6, which is facilitated by its pointed edge portion or tip 12. The quantity of powder in the cracking powder charge 6 is adapted so that the insert 25 can be pressed into the outer sleeve 2 such that the cracking powder charge is compacted to a certain degree, which is advantageous because that prevents the powder from moving to any significant degree during transportation, however, is not compacted so much that the thin wall 13 of the inner sleeve is damaged or is pressed together to any significant degree.

In the thus assembled cracker cartridge 1 , the interior of the ignition assembly sleeve 7a forms a direct continuation of the through hole 8 in the plug 4 and it also has the same cross section as the hole 8. The hole 8 and the inner space in the ignition assembly sleeve 7a in other words are integrated and form said priming chamber 9.

With reference now also to Fig.1 - Fig. 5, the ignition capsule is generally designated 30. The ignition capsule 30 consists of an ignition unit sleeve 31, Fig. 1- Fig. 4, and, in said sleeve 31 an ignition unit 32 consisting of an igniter 33a which can be activated electrically, an ignition powder charge 29 consisting of the same type of NC -powder as the cracking powder charge 6, and an igniter socket 34, to which ignition cables 37 are connected. The igniter is of the type which has its normal use in the pyrotechnical field for firing pyrotechnical articles. Igniters of that type are manufactured e.g. by the Czech company META-PYRO, s.r.o., Brno.

The ignition unit sleeve 31 consists of a hard plastic material, preferably of the same type of ABS-plastic as the outer sleeve 2. The thickness, according to the embodiment is the same as of the ignition assembly sleeve 7a, about one millimetre. The ignition unit sleeve 31, however, is provided with a number, according to the embodiment of four external grooves 35 which extend from the cupped end portion 36 of the sleeve in the axial direction towards the mouth of the sleeve all the way to at level with the front end of the igniter 33a which is accommodated in the priming chamber 9. As to the rest the ignition unit sleeve 31 has a smooth circular-cylindrical outside surface 38. The depth of the grooves 35 exceeds half the wall thickness of the ignition unit sleeve 31, more specifically, the depth is 0.7 mm. The mean width of the grooves, which widen in the outwards direction, approximately equals the wall thickness of the ignition unit sleeve. The outer diameter of the ignition unit sleeve 31 is slightly - about 0.2 mm - smaller than the inner diameter of the ignition assembly sleeve 7a. Its cylindrical length equals the cylindrical length of the ignition assembly sleeve 7a, i.e. it extends all the way to the conical nose portion 12 of the ignition assembly sleeve 7a. This means that, when priming the cracker cartridge 1, the ignition capsule 30 can be entered into the ignition assembly sleeve 7a with close fit against the inside surface of the ignition assembly sleeve but without jamming. The gap 39 between the two sleeves 31 and 7a amounts to about 0.1 mm according to the embodiment but it may also be slightly smaller or larger. Preferably, however, the width of the gap should be within the range 0.05 - 0.2 mm. As has been mentioned in the foregoing, the ignition assembly sleeve 7a, however, has a constriction 26 quite close to the conical nose portion 12, which constriction has an extension in the radial direction which is greater than the width of the gap 39. In the preferred embodiment, the radial extension is about twice as large as the width of the gap or 0.2 mm. By, in the last phase of the entering operation of the ignition capsule 30 into the ignition assembly sleeve 7a, pressing the ignition unit sleeve 31 of the ignition capsule 30 into said constriction 26, the ignition capsule is fixed in the priming chamber 9, which prevents it from coming loose unintentionally and fall out when the rock cracker cartridge 1 is handled. The ignition unit sleeve 31 is provided with an outwardly directed flange 40 around its mouth 36, which sets a limit for its entering into the ignition assembly sleeve 7a.

The ignition unit sleeve 31 has a mouth section 41, Fig. 3, with an inner diameter which is slightly larger than the main portion of the sleeve 31 and a length adapted to the diameter and length of the socket 34 of the igniter 33a, so that the igniter 33a is secured in the charged ignition capsule 30 through press-fit between the socket 34 and the ignition unit sleeve 31 in the region of the mouth section 41. The igniter 33a extends in the ignition capsule 30 from its socket 34 into the ignition powder charge 29 all the way to where the grooves 35 have their rear ends on the outer side of the ignition

capsule/ignition unit sleeve. The igniter 33a thus is surrounded by and is in intense contact with ignition powder, which, lightly compressed, occupies essentially all available space between the cupped bottom portion 36 of the ignition unit sleeve 31 and the igniter socket 34. Therefore, the contact between the igniter 33a and the ignition powder charge 29 is very good, which promotes a safe ignition of the ignition powder charge when the ignition unit 32 is ignited electrically by means of the igniter 33a.

It is an important principle of the present invention that the ignition capsule 30 is not an explosive product "in free state", such as for example during transportation and storage, but that it shall be able to explode in a space which is closed by walls, such as in the ignition assembly sleeve 7a in the primed rock cracker cartridge 1. More specifically, the combustion of the ignition powder charge 29 and of the cracking powder charge 6 take place through that form of explosion which is called deflagration , in which the reaction zone proceeds during the process of combustion of the powder at a velocity which is lower than the velocity of sound in the powder charge, in contrast to detonation in detonative explosives. In this mode the desired effect can be achieved, namely, according to the invention, to crack the boulder or rock portion in which the cracker cartridge has been primed in a boring, but not to fragment it into a lot of pieces which would run the risk to be thrown widely around. In the above description, a number of terms have been used for the various components of the rock cracker cartridge of invention. These terms have been chosen in order that they as far as possible shall describe the function of the various components. How the various components are defined and how they work shall be summed up as follows:

The rock cracker cartridge 1 is a cartridge which is filled with an explosive agent for the purpose of cracking large boulders, minor rock sections and the like through deflagration of the explosive agent which consists of (gun) powder. The ignition capsule 30 consists of an ignition unit sleeve 31 and an ignition unit 32

The ignition unit 32 consists of an igniter 33a on a socket 34, electrical ignition cables 37 and ignition powder charge 29.

- The ignition capsule 30 can explode only if it is accommodated in a closed space which is limited by walls of adequate strength. The ignition unit sleeve 31 does not have such strength because its wall is thin and consists of a plastic material of limited rupture strength, and also because it is provided with said rupture strength reducing grooves 35. If the ignition unit 32 would be ignited in "the open air", the powder in the ignition powder charge would catch fire, the ignition unit sleeve 31 would be widened and possibly break as the powder successively is burnt but it would not explode. This means that the burning is not developed in a dramatic, explosion like mode, which, however does not mean that the ignition capsule may be handled carelessly. It shall be handled like a flammable product in the same class as various pyrotechnical articles.

The sleeve 7 of insert unit 25 which is pressed into the cracking powder charge 6 is termed ignition assembly sleeve 7a in order to mark that it is an element of the integrated ignition assembly which comprises the ignition capsule 30 and the sleeve 7, 7a. In said assembly, in which the ignition capsule 30 is inserted in the ignition unit sleeve 31 , the strength of the wall of the sleeve 7/the ignition assembly sleeve 7a is added to the wall strength of the ignition unit sleeve 31 , so that said two sleeves in combination, and possibly also in cooperation with support from the surrounding cracking powder charge 6, get a sufficient resistance against rupture in order to afford explosive features to the assembly, so that the ignition powder charge 29 as well as the cracking powder charge 6 will explode and be combusted through deflagration, see above.

When priming the rock cracker cartridge 1 , which is carried out on the blasting site where a large boulder or a section of the bedrock shall be cracked, the ignition capsule 30 is entered into the priming chamber 9 of the insert 25 in the rock cracker cartridge 6 so far as the flange 40 on the ignition unit sleeve 31 permits, and so that it is fixed in that position by means of the constriction 26, into which the front section of the cylindrical part of the ignition unit sleeve 31 is pressed in during the final phase of the entering procedure. Then the cartridge 1 is brought, upside down, all the way down into the bore 42 that has been made in the boulder or section of the bedrock to be cracked, such that the protruding spacer members 19a will rest against the bottom of the bore. If the rock cracker cartridge 1 is oriented in that way it can be hauled up again by means of the ignition cables 37, if one would wish to break off the cracking operation. If the rock cracker cartridge 1 instead were oriented with the protruding spacer members 19a directed upwards, and if one in that case would haul up the ignition cables 37, there would be a risk that the socket 34 with the igniter 33a or the entire ignition capsule 30 comes loose.

When the igniter 33a is electrically ignited, it ignites the ignition powder charge 29 causing the ignition powder charge to explode through deflagration type of combustion. The ignition unit sleeve 31 is widened by the pressure developed by the explosion so far as is possible due to the narrow gap 39 and ruptures in the regions of the strength reducing grooves 35. Which will take place first; the widening or the rupture is difficult or impossible to say but has on the other hand no significant importance. Probably, the widening and the rupture occur as good as

simultaneously. On the other hand, it is not unimportant that the ignition unit sleeve 31 ruptures in the region of the grooves 35, because that may contribute to a radially directed development of the pressure that almost simultaneously is transferred to the surrounding sleeve 7 - the ignition assembly sleeve 7a - so that also that one will rupture. The violent flame of fire which is developed in the ignition powder charge 29 now is transferred to the cracking powder charge 6 causing also that one to explode through deflagration type of combustion, which provides a desired radial development of pressure in the bore 42 and hence the intended cracking of the boulder or corresponding 43.

Also by means of the rock cracker cartridge 1 and of the ignition capsule 30 which have been improved according to the invention, delay ignition of ignition capsules and of rock cracker cartridges set at intervals may be applied according to the principles which have been disclosed in said WO 2009/120139. These principles therefore shall not be repeated in this text but are instead incorporated by reference to the said WO-document.