US 2812712 A
Description (OCR text may contain errors)
T. ASH URST Nov. 12, 1957 STEMMING OF SHOT HOLES IN BLASTING OPERATIONS Filed Feb. 5, 1954 rT .ms R 1S A S A M O m MQ/w; A2M@ Attorney 3 sraMMmGl or snor Horns IN BLASTING oPEnArroNs Thomas Ashurst, BulawayoSouthern Rhodesia, assignor to International Trublast Stemming Corporation (Proprietary) Limited, Johannesburg, Umon of South Africa, a cnipany of the Union of South Africa Application February 3, 1954, Serial No. 407,994
Claims priority, application nion of South Africa February 5, 1953 1 Claim. (Cl. 102-30) This invention relates to the stemming of shot holes in blasting operations and more particularly provides a stemming plug suitable for general use whether in underground or surface workings. It provides a plug intended to replace the usual plugging of the shot hole behind the explosive charge and detonator with pieces of socalled dagga or clay pushed into the hole and tamped solid and to obviate such methods which take considerable time to complete, depend upon a form of plugging which is aiected by water and therefore unsuitable for closing wet holes, and in the case of misres, is ditiicult, time wasting and dangerous to remove as with compressed air and water, for recovery of the charge, and in which the plugging, during the blasting, is subjected -to blowing out, with consequent or other wastage of a considerable percentage of the potential rock-shattering energy of the charge.
According to the invention there is provided a shot hole stemming device of the kind consisting of two solid wedge-shaped members of material which is unaffected by water, comprising opposed wedging surfaces and collectively constituting a cylindrical plug dimensioned to occlude the shot hole, characterized in that at least one of the members comprising a formation suitably provided for engagement by a tool adapted to be inserted in the hole for withdrawing the members therefrom one after the other, even after they have been wedged in position in said shot hole.
The plug member intended for insertion rst into position in the hole may be provided with a leading end of preferably concave form and friable character, and/or, in its wedging surface, with a recessed formation, hook or other means suitable for engagement by the said tool.
The member intended for insertion last into position in the shot hole and for endwise engagement with the other in the wedging surfaces, is provided with a recessed end formation or equivalent means for engagement by the said tool.
Furthermore grooves are formed along the exterior of the members which, when the latter are mutually orientated for co-engagement of their sloping or Wedge surfaces, combine to provide a channel for the passage of a fuse or of wires to the detonator or the like associated with the explosive charge.
In the accompanying drawings which refer to a preferred embodiment of the invention:
Figure l is a side view of the two-member plug;
Figure 2 is a view of the inner or leading end of the plug; and
Figure 3 is a sectional View of a shot hole containing an explosive charge and stemmed by a plug as shown in Figures l and 2.
The plug member 1 has a concave inner or leading end part 2 and its opposite end finishes in an oblique flat surface 3 to provide the required wedge or taper formation; a simple recess 4 in the surface 3 suflicing as a forma- '2,812,712 Patented Y Nov. l2, 1957 Z tion' by which the member may be pushed or' pulled into and out of the shot hole.
The other, or outer, plug member 5 has its inner or leading end tapered arid shaped asl the complement of thevv outer end of the iirst member, whereby the face 6 may be engaged against the face 3 in the coaxial assembly of the two members shown in Figure 3. The opposite orvouter end of the member 5 is given a stepped formation at '7, including a simple recess as 4 for the like purpose to the recess 4 in the member 1,
Additionally' like, simple longitudinal groove 8, 8 is provided in each member 1 and 2, which grooves come into line, when the faces 3 and 6 are arranged parallel or' in Contact asin Figure 3, to admit leads or fuse as 9 from the outer end of the shot hole to the charge or the like 10 at its inner end.
When the plug has been inserted over the fuse or leads 9 and into place as shown in Figure 3, with the outer portion or member 5 gently pressed home against the other 1, the stemming is completed. On detonation of the charge the preferably concave nose or inner end 2 of the plug may be subjected to a more or less localized disintegrating action assisting effective sealing between the periphery of the plug and the bore of the shot hole. The forward portion 1 of the plug is driven outwardly against the other portion with a wedge action which thus tightens the tit of the plug in the hole to retain it therein with a force proportional-to the intensity of the explosion, and totally obviating the blow-out and wastage of the explosive force which is thus concentrated in front of the plug for effective rock shattering.
Misres are dealt with easily and safely by withdrawing the plug members or portions one after the other with the aid of a suitably elongated non-ferrous metal tool having an end hook or the like for co-engagement in turn with the recessed formations 4 and 4 aforesaid whereby the plug portions may be extracted; the charge being then exposed for extraction in its turn without danger.
The plug is preferably made of concrete or the like, but may be made of any other suitable material, e. g. wood, plastic, baked clay, or brick; wood and plastic, however, like other inflammable materials, not being suitable for use in ery mines.
The length of a standard plug for normal use, i. e. for shot holes drilled for normal charges, is conveniently about eight inches, although of course no xed dimensions can be laid down owing to the diiferent sizes of drill bits used, and the different weights of explosive placed in different kinds of holes. The plug diameter s conveniently about one-eighth of an inch less than the gauge of the drill used, the clearance being sealed as a first consequence of the explosion, as already explained.
When the plug is made of concrete or the like and if a disintegration, more especially in the region of the front end of the plug should be desired, it suilices to make the plug or its nose portion from a weak mixture and thus more or less friable under the force of the explosion; but such a provision is not essential in all circumstances, owing to the highly effective wedge action between the two plug members.
A shot hole stemming device comprising two solid wedge-shaped members having opposed complementary wedging surfaces and in the position with the wedging surfaces against each other, said device forming a cylindrical plug for occluding a shot hole, one of said members having a recess in the wedging surface thereof, said recess being engageable by a tool for withdrawing said member from a shot hole, and the end of the other of said wedge-shaped members opposite the wedging surface of said other wedge-shaped member having a stepped notch therein with one surface substantially longitudinally and diametrically of said cylindrical plug and the other surface substantially'transversely of said cylindrical plug,
said one surface having a recess therein with the said other surface extending unbroken into and forming a part of the interior wall dening .said recess, said recess also engageable by a tool for withdrawing said other wedge-shaped member from a shot hole, whereby said wedge-shaped members may be inserted into Va'shot hole with the wedging surfaces engaged and driven into the shot hole until the device abuts an explosive charge in the shot hole and the other end having the stepped notch therein is wholly within the shot hole, and in case of a misfire the two wedge-shaped members may be successively withdrawn from the shot hole by inserting the withdrawing tool into the shot hole until it strikes said other surface of said notch and can easily be guided 1 into the recess in the one surface of said notch for pulling said other wedge-shaped member from the shotrhole, and the tool may again be inserted into the shot hole until it strikes the wedging surface of said one of said wedge- Y shaped members and can easily be guided into the recess therein for pulling said one wedge-shaped member from the .shot hole.
References Cited-in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Paul Litwin et al.: Stemming With the Voortmann Safety Stemming Plug, pages 2-12 (1935).