GB1572156A

GB1572156A - Shot stemming ampoules

Info

Publication number: GB1572156A
Application number: GB5161475A
Authority: GB
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1975-12-17
Filing date: 1975-12-17
Publication date: 1980-07-23
Also published as: DE2657323A1; FR2335822A1; FR2335822B1

Description

(54) IMPROVEMENTS IN OR RELATING TO SHOT STEMMING AMPOULES (71) We, UNILEVER LIMITED, a com- pany organised under the laws of Great Britain, of Unilever House, Blackfriars, London, E.C.4, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in or relating to shot stemming ampoules for use in bore holes as stemming either before or after the insertion of an explosive charge, and particularly to gel filled stemrning ampoules.

It has been proposed in British Patent Specification No. 972 504 to provide a shot stemming ampoule filled with plastic or gelatinous tamping material which is inserted into the bore hole and then caused to burst by pressure applied by a tamping rod to allow the plastic or gelatinous tamping material to escape before the blasting charge is exploded. It is however not considered good mining practice to have to tamp so hard as to burst the ampoule in the bore hole because of the risk of damaging the detonators and/or dislodging the wires connecting the detonator to the firing device. British Patent Specification No.

1 223 326 discloses a synthetic plastics shot stemming ampoule for tamping a borc hole which contains a gelatinous tamping material and is provided with a tab formed integrally with a tear-off strip in the tube wall so that the user, before inserting the ampoule in a bore hole can, by pulling on a tab, tear off or partially tear off a strip to leave a slit in the tube wall. This construction can be incorporated in a shot stemming ampoule made by moulding but is not applicable to ampoules made from welded calendered, extruded or cast film, welded lay flat tubing or by extrusion.

According to the present invention there is provided a shot stemming ampoule comprising a closed tube of flexible plastics material containing a gelatinous tamping material, one or more tear-off strips being secured by welding to the outside of the tube along a respective weld forming lines of weakness in the tube and each having at one end grip a portion unattached to the tube. Pulling the grip portion removes the tear-off strip by tearing the tube along the lines of weakness and removing that part of the tube which is welded to the tear-off strip to form a slit in the tube. The gelatinous material can flow through the slit in the tube when pressure is applied to the tube. There is thus provided an ampoule construction enabling the ampoule to be pre-opened before inserting in the bore hole which construction can be incorporated in ampoules which are not manufactured by moulding.

The ampoule is conveniently manufactured from flat sheet material to form a tube having at least one longitudinal heat sealed or welded seam, the tube being closed by transverse heat-sealed or welded seams, The securing of the tear-off strip can conveniently be incorporated in such a manufacturing process with little additional expense and without requiring further handling in a second operation. Preferably the weld does not extend to any of the edges of the tear-off strips. This facilitates securing the tear-off strip to the tube since the risk of damage to the tube should the heat sealing or welding tool extend beyond the tearoff strip is avoided and furthermore when the tear-off is removed a cleaner end is formed to the slit in the tube and any tendency of the slit to tear beyond the predetermined weld length is minimised.

Conveniently the tear-off strip is formed of material identical with but of greater thickness than the material from which the tube itself is formed. This avoids firstly the necessity of providing any special antistatic treatment for the ampoule. It also facilitates the welding operation in that it is easier to ensure that the thinning of the material which occurs during the welding operation does not leave any part of the tear-off strip thinner than the tube. Pulling on the grip portion of the tear-off strip causes tearing along lines of weakness caused by the welding and it will be appreciated that to avoid the tear-off strip simply being torn from the tube without the tube being torn the weakest points must be in the tube and not in the tear-off strip.

Alternatively the tear-off strip can be of a different stiffer material than that of the tube and in this case the tear-off strip may be thinner than the tube material provided that the weakest points after welding are in the tube wall and not in the tear-off strip.

Clearly the shape of the welding jaws or electrodes, their temperature and the pressure applied, can all be varied as is well known in the art to ensure that whatever materials or combinations of material are employed the desired weakening of the tube material is effected whilst not weakening the tear-off strip so that it tears when being pulled away from the tube.

The tear-off strip can be secured to the tube by a single line weld but where the width of the slit in the tube requires it the welding can be by two or more parallel weld lines.

The width of slits produced by removal of the tear-off strip is substantially the measurement between the two outermost edges of the weld or welds, the welding jaws or electrodes being arranged such that the tear-off strip and tube are welded together between the welds sufficient to ensure that the tube material between the welds is entirely removed with the tear-off strip.

The plastics material of the tube can be PVC, PVdC polyethylene, polypropylene or an ethylene vinyl acetate copolymer. The tear-off strip, whilst being preferably of plastics material, can be of any other suitable material weldable to the tube material such as coated or impregnated paper or coated metal foil.

The invention will now be more particularly described with reference to the accompanying diagrammatic drawings in which Figure 1 is a front elevation of an ampoule; Figure 2 is a side elevation of the ampoule of Figure 1; Figure 3 is a sectional elevation of an enlarged scale along the line Ill-Ill in Figure 1; Figure 4 is a sectional elevation similar to Figure 3 of an alternative construction; and Figure 5 is a sectional elevation to Figure 3 showing another alternative construction.

Referring to Figures 1 and 2 there is shown an ampoule formed by welding two sheets of plasticised PVC to form a tube 1, the material being welded along two longitudinal edges 2 enclosed at each end by transverse welds 3. One end of the tube is provided with additional inclined welds 4 to avoid the "pilllow-case effect" produced when a transverse weld alone is used.

The tube is filled with a gelatinous tamping material.

Secured to opposite sides of the tube are two tear-off strips i of rigid PVC each having grip portions 6 unattached to the tube wall so they are free to be gripped by hand.

The tear-off strips are secured to the tube wall along a weld line 7 which does not extend to any of the edges of the tear-off strip.

As shown in Figure 3 the welding operation results in a thinning of both the tearoff strip and the tube material. The tear-off strip and the tube wall are welded together over a distance A between points B and C which are the outermost longitudinal edges of the weld and from lines of weakness in the tube. The welding conditions are arranged such that the plasticised PVC of the tube softens to a greater extent than the rigid PVC tear-off strip so that the thinning is greater in the tube material. Thus the tear strength of the tear-off strip, even where it has been thinned by the welding operation, is greater than the tear strength of the lines of weakness of the tube along the outermost edges B and C of the weld.On pulling at the grip portion 6 to remove the tear-off strip from the tube and open the ampoule the tube wall 1 tears longitudinally along the edges B and C of the weld to form a slot or slit in the tube of width A and length corresponding to the length of the weld. The width A of the weld and hence of the slot is chosen according to the rheological properties of the tamping material so that after opening the ampouled tamping material can be caused to exude by the application of external pressure to the ampoule. Thus the ampoule can be opened by removing the tear-off strips, inserted into a bore hole and the necessary gentle pressure applied with a tamping rod to cause the tamping material to escape from the ampoule and stem the bore-hole as necessary without any danger of damaging the detonator or the wires to the detonator.

Although the maximum thinning of the bag and the tear-off strip occurs at the centre of the weld there is no tendency for tearing of either the tear-off strip of the tube material along the line of maximum thinning when the grip portion of the tearoff strip is pulled. This is because the weld does not extend into the grip portion and pulling on the grip portion pulls the tearoff strip on both sides of the weld. Furthermore the welding can be effected so that the tear strength of this thinnest part of the tearoff strip is nevertheless greater than the tear strength of the tube along the lines B and C.

By varying the angle of inclination a of the weld in Figure 3 the width A can be varied. Further variation in the width A of the slit can be achieved by welding the tearoff strip to the tube along two or more parallel weld lines as shown in Figure 4. On pulling on the grip portion of the tear-off strip of Figure 4 the bag tears along the lines B1 C, at the outermost edges of the welds to remove a portion of the bag of width At. Even if the tear-off strip and the tube are not fully welded together between the two weld lines, e.g. at 8 if for example the weld lines are spaced far enough apart, the bag still tears along lines B1 C1 since tearing along any other line of weakness in the bag is prevented by the greater tear strength of the tear-off strip.

In the embodiments shown in Figures 3 and 4 the thickness of the tear-off strip is equal to the thickness of the tube. The tearoff strip may however be thinner than the tube provided that the welding is carried out to produce lines of weakness at the edges of the weld in the tube wall which have a lower tear strength than the tear-off strip thereby ensuring that removal of the tear-off strip tears the tube in the desired manner.

When the tear-off strip is of the same material as the tube the softening and thinning of the tear-off strip and the tube during the welding are substantially the same which could lead to the tear-off strip not tearing away part of the tube wall as desired. For this reason a tear-off strip of the same material as the tube should preferably be thicker than the tube. Similarly when the tear-off strip is of a softer material than that of the tube the thickness of the tear-off strip must be greater than the thickness of the tube. Such an embodiment is shown in Figure 5 in which the tear-off strip Si is li- times the thickness of the tube wall 1.

The tear-off strip Si has thinned at the weld to a greater extent than the tube wall 1.

Nevertheless the minimum thickness of the tear-off strip at the edges of the weld is greater than the thickness of the tube wall at the edges of the weld so that the tear strength in the tube wall at the edges B2 C2 of the weld is less than the tear strength of the tear-off strip thereby ensuring that it is the tube and not the tear-off strip which tears when the grip portion of the tear-off strip is pulled.

WHAT WE CLAIM IS: 1. A shot stemming ampoule comprising a closed tube of flexible plastics material containing a gelatinous tamping material, one or more tear-off strips being secured by welding to the outside of the tube along a respective weld forming lines of weakness in the tube and each having at one end a grip portion unattached to the tube.

2. A shot stemming ampoule according to Claim 1 in which the weld does not extend to any of the edges of the tear-off strip.

3. A shot stemming ampoule according to Claim 1 or Claim 2 in which the tube is manufactured from a flat sheet material having at least one longitudinal heat sealed or welded seam and closed by transverse heat sealed or welded seams.

4. A shot stemming ampoule according to any one of the preceding claims in which the tear-off strip is formed of material identical with but of greater thickness than the material of the tube itself.

5. A shot stemming ampoule according to any one of Claims 1 to 3 in which the tear-off strip is of a different stiffer material than that of the tube itself.

6. A shot stemming ampoule according to Claim 5 in which the tear-off strip is thinner than the tube material.

7. A shot stemming ampoule according to any one of the preceding claims in which the weld is formed by two parallel weld lines.

8. A shot stemming ampoule substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 4 or Figure 5 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. varied. Further variation in the width A of the slit can be achieved by welding the tearoff strip to the tube along two or more parallel weld lines as shown in Figure 4. On pulling on the grip portion of the tear-off strip of Figure 4 the bag tears along the lines B1 C, at the outermost edges of the welds to remove a portion of the bag of width At. Even if the tear-off strip and the tube are not fully welded together between the two weld lines, e.g. at 8 if for example the weld lines are spaced far enough apart, the bag still tears along lines B1 C1 since tearing along any other line of weakness in the bag is prevented by the greater tear strength of the tear-off strip. In the embodiments shown in Figures 3 and 4 the thickness of the tear-off strip is equal to the thickness of the tube. The tearoff strip may however be thinner than the tube provided that the welding is carried out to produce lines of weakness at the edges of the weld in the tube wall which have a lower tear strength than the tear-off strip thereby ensuring that removal of the tear-off strip tears the tube in the desired manner. When the tear-off strip is of the same material as the tube the softening and thinning of the tear-off strip and the tube during the welding are substantially the same which could lead to the tear-off strip not tearing away part of the tube wall as desired. For this reason a tear-off strip of the same material as the tube should preferably be thicker than the tube. Similarly when the tear-off strip is of a softer material than that of the tube the thickness of the tear-off strip must be greater than the thickness of the tube. Such an embodiment is shown in Figure 5 in which the tear-off strip Si is li- times the thickness of the tube wall 1. The tear-off strip Si has thinned at the weld to a greater extent than the tube wall 1. Nevertheless the minimum thickness of the tear-off strip at the edges of the weld is greater than the thickness of the tube wall at the edges of the weld so that the tear strength in the tube wall at the edges B2 C2 of the weld is less than the tear strength of the tear-off strip thereby ensuring that it is the tube and not the tear-off strip which tears when the grip portion of the tear-off strip is pulled. WHAT WE CLAIM IS:

1. A shot stemming ampoule comprising a closed tube of flexible plastics material containing a gelatinous tamping material, one or more tear-off strips being secured by welding to the outside of the tube along a respective weld forming lines of weakness in the tube and each having at one end a grip portion unattached to the tube.