AU2009100883B4

AU2009100883B4 - Blast hole plug and propellant therefor

Info

Publication number: AU2009100883B4
Application number: AU2009100883A
Authority: AU
Inventors: Koen Alixe Mauritz Dhooge
Original assignee: Riplog Pty Ltd
Current assignee: RIPLOG Pty Ltd
Priority date: 2009-09-04
Filing date: 2009-09-04
Publication date: 2010-02-18
Anticipated expiration: 2017-09-04
Also published as: AU2009100883A4

Description

P/00/0 11 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Blast hole plug and propellant therefor The following statement Is a full description of this Invention, including the best method of performing it known to us: -1 BLAST HOLE PLUG AND PROPELLANT THEREFOR BACKGROUND OF THE INVENTION THIS invention relates to a blast hole plug and to a propellant used in a blast hole plug to inflate it in use. Blast hole plugs are known which comprise an inflatable plastic body in which is contained a canister of gas. A reinforcing sleeve surrounds the inflatable body and acts to restrain the body against distension thereof when the body is pressurised. An example of a blast hole plug of this kind is described in International Patent Publication WO 01/04565. To operate the blast hole plug, an actuator on the gas canister is operated by a user, as described in Australian patent no. 2008100509, which starts the release of the gas from the canister and the inflation of the device. The device is then lowered down a blast hole to a desired or pre-determined position. As the blast hole plug inflates, the distension of the plug is restrained until the restraining means fails at a predetermined pressure, after which the blast hole plug lodges in the blast hole and effectively provides a deck for stemming and explosives. It is an object of the invention to provide an alternative blast hole plug of the above general kind, and a propellant therefor.

2 Summary of the invention According to the invention there is provided a blast hole plug comprising an inflatable body and a container of pressurized propellant associated with the inflatable body and operable to release the propellant without any time delay effect to inflate the inflatable body in use, the 5 propellant being a two phase composition, comprising upper and lower separate liquid propellant phases each including a mixture of dimethyl ether and water, with the percentage of dimethyl ether by weight being greater than 34 wt%, but no more than 93 wt%, and the percentage of water by weight being less than 66 wt%, but no less than 7 wt%, wherein the lower propellant phase comprises a lesser % by weight dimethyl ether than the upper propellant 10 phase. Preferably, the percentage of dimethyl ether by weight is in the range of 35 wt% to 55 wt% and the percentage of water by weight is in the range of 65 wt% to 45 wt%. More preferably, the percentage of dimethyl ether by weight is in the range of 40 wt% to 50 wt% and the percentage of water by weight is in the range of 60 wt% to 50 wt%. 15 The propellant may include an anti-corrosive agent in an amount less than 1.0 wt%. For example, the anti-corrosive agent may comprise sodium nitrate. In a preferred embodiment the propellant comprises 44.83 parts by weight of dimethyl ether, 54.87 parts by weight of water, and 0.3 parts by weight of an anti-corrosive agent. Further according to the invention there is a provided a blast hole plug propellant, the propellant 20 being a two phase composition releasable without any time delay effect from a container to inflate an inflatable body in use, the propellant comprising upper and lower separate liquid propellant phases each including a mixture of dimethyl ether and water, with the percentage of dimethyl ether by weight being greater than 34 wt%, but no more than 93 wt%, and the percentage of water by weight being less than 66 wt%, but no less than 7 wt%, wherein the 25 lower propellant phase comprises a lower % by weight dimethyl ether than the upper propellant phase.

-3 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Is a perspective view of a blast hole plug in an un-inflated configuration thereof; Figure 2 is a perspective view of the blast hole plug of Figure 1 with a pressure tube thereof removed, showing how the blast hole plug is folded; Figure 3 is a perspective view of the blast hole plug in its fully inflated configuration, outside of a blast hole; Figure 4 is a cross sectional view on the line 4-4 in Figure 3, showing a gas canister within the inflatable body of the blast hole plug; Figure 5 is a first pictorial view from above of an actuator for a container of pressurized gas within the body of the blast hole plug; Figure 6 is a perspective view from below of the actuator of Figure 5; Figure 7 is a sectional side view of the actuator mounted on a canister of pressurized gas, prior to use thereof; Figure 8 is a similar view to that of Figure 7, showing the actuator latched into a release position thereof; Figure 9 is a cross sectional view of a blast hole with the blast hole plug of the invention; and Figure 10 is a cross sectional plan view on the line 10-10 in Figure 9.

-4 DESCRIPTION OF A PREFERRED EMBODIMENT The blast hole plug shown in Figures 1 to 4 is similar in its physical configuration to that described in WO 01/04565. The blast hole plug 10 includes an inflatable gas impervious plastic bladder 12, a paper sleeve 14, and a plastic sleeve 16 which are all folded up and contained within a plastic bag 18. In some embodiments either the plastic sleeve or the paper sleeve could be omitted. The inflatable bladder 12 consists of a co-extruded and weldable material with good gas barrier properties. An aerosol canister 24 containing a pressurized two phase propellant is located in an upright position within the bladder 12, oriented so that it is upright in use. The two phase propellant is a United Nations classified non-flammable composition that includes dimethyl ether and water, with the percentage of dimethyl ether by weight being greater than 34 wt%, but no more than 93 wt%, and the percentage of water being less than 65 wt%, but no less than 7 wt%. A small percentage by weight of an anti-corrosive such as sodium nitrate, typically less than 1.0 wt%, is included as a rust inhibitor. The preferred aerosol propellant composition is: Dimethyl ether 44.83 parts by weight Water 54.87 parts by weight Sodium nitrate 0.3 parts by weight Dimethyl ether (DME) is of a polar, water miscible nature. To form a single clear phase aerosol composition, a maximum of 34 wt% DME is miscible with water and a maximum of 6 wt% water is miscible with DME. Thus, mixing a higher wt% of DME with water will result in a composition having two separate liquid phases.

-5 For example, in a propellant formula made up of, say, 45% DME and 55% water, two separate phases will be formed in the aerosol canister. As DME is absorbed 34% by water, the lower phase will consist of 34% DME and 66% water and the upper phase will consist of 6% water and 94% DME. In use, on actuation of the aerosol canister, the lower phase is first discharged from the canister and then the upper phase is discharged, in a continuous discharge process. When the aerosol canister is activated the bladder 12 will immediately begin to inflate due to the 34% dimethyl ether present in the lower phase of the propellant in the canister, without any time delay effect. The described two phase propellant has a number of advantages compared with known propellants. * A smaller aerosol canister is required, compared with a propellant comprising a single phase, below 34 wt% of dimethyl ether and water. " The described propellant is non-flammable when tested according to the United Nations testing procedures on aerosol flammability " No shaking of the canister before use is required. " The smaller aerosol canister results in lower product cost, freight and transportation cost as well as packaging cost. The paper sleeve 14 consists of three layers of paper. Each layer is 100 microns thick and is not treated with a non-flammable or flame resistant substance. The prime function of the paper sleeve 14 is that of an insulator. It acts as a heat barrier which prevents the heat of a blast from melting the plastic bladder. If the plastic bladder melts it will deflate and the blast plug will not be able to contain the blast within a blast hole 32. Thus it can be appreciated that the heat barrier could be made of other suitable non-stretchable materials which should not soften and elongate in hot conditions. An example of such a material is aluminium foil, which is -6 also flexible and which can reflect the heat of the blast away from the plastic bladder. Thus the heat barrier must not melt, or must at least have a substantially higher melting point than the plastic bladder 12 and the plastic sleeve 16, so that it protects the plastic bladder 12 and prevents the plastic bladder from being melted by the heat of the blast. The plastic sleeve 16 is made of woven polypropylene. The function of the plastic sleeve 16 is to contain the plastic bladder 12 against over-expansion if the paper sleeve 14 ruptures. The paper sleeve 14 can rupture if water dissolves the adhesive which forms a seam 30 between two overlapping ends of the paper. In situations where water is not present, the plastic sleeve 16 is not necessary since the paper sleeve 14 is strong enough by itself to contain the plastic bladder 12, and to prevent the plastic bladder 12 from being punctured by sharp portions of the sidewall of the blast hole 32. In normal low temperature blast holes, the plastic sleeve 16 can be used without the paper sleeve 14. The plastic bag 18, the plastic sleeve 16 and the paper sleeve 14 have apertures 32 through which the canister 24 can be seen and activated. The function of the plastic bag 18, other than to store the folded plastic bladder 12, paper sleeve 14 and plastic sleeve 16, is to restrict the size of the bladder 12 for a limited period of time whilst it is being inflated. This limited period of time provides a user with sufficient time to activate the aerosol canister 24 and to insert the blast hole plug 10 into a blast hole 32 before the plastic bag 18 ruptures and the bladder 12 becomes too large to insert into the blast hole 32. A charge of explosive 34 and a fuse 36 are first placed into the blast hole 32. The blast plug 10 is then inserted into the blast hole 32 after the aerosol canister has been activated. Once the blast hole plug 10 has inflated sufficiently to plug the blast hole 32, stemming 38 is poured into the blast hole 32 onto the top of the blast plug 10.

-7 Figures 5 to 8 show an actuator 50 which is associated with the propellant canister 24. The actuator is intended to be clipped firmly onto a ridge or rim 48 at the upper end of the canister 24, as best shown in Figures 7 and 8. The actuator 50 comprises a body defining a mounting ring 52 with an inwardly extending lip 54. The lip 54 has an inclined surface 56 which allows the actuator to be pushed over the rim 48 and maintained in position by the lip on the top of the canister. Formed integrally with the mounting ring 52 is an actuator member comprising an upstanding central portion 58, an operating tab 60 extending radially outwardly beyond the ring 52, and a bridge portion 62 joining the tab to the mounting ring 52. As best shown in the sectional views of Figures 7 and 8, the upstanding central portion 58 of the actuator has a stepped bore 64 which is formed with a slight taper for engaging the stem 74 of the canister 24 with a gas tight seal. The bore 64 has a widened mouth portion 66. At the extreme inner end of the bore 64 is a nozzle 68 through which the contents of the canister are expelled in use. As best seen in Figures 6, 7 and 8, a clip or latch member 70 is formed integrally with the actuating tab 60 and extends below the tab. On its outer edge, the catch has a chamfer allowing it to ride over the inner edge of a complemental catch formation 72 formed at an edge of an opening in the mounting ring 52. When the tab 60 is depressed as indicated by the arrow in Figure 8, the catch members 70 and 22 ride over one another and lock the actuator member in its depressed position, operating the canister and causing its contents to be expelled via the nozzle 68. The tapered construction of the bore 64 ensures a gas-tight fit over the stem 74 of the canister, so that fluid does not leak from the actuator in use, but is expelled only from the nozzle 68. The actuator is moulded from acetal plastics material, which maintains its shape and physical properties over a wide temperature range, and helps to -8 ensure that gas does not leak from the joint between the stem 74 and the bore of the actuator member in use. The blast hole plug 10 performs two functions. Firstly, it contains the blast within the blast hole 32. In this regard the blast hole plug 10 provides sufficient time for the gas pressure to build up in the air gap 40 in the blast hole 32 before the plug 10 is shattered by the blast. Secondly, the blast hole plug 10 acts as a deck upon which the stemming 38 is supported.

Claims

1. A blast hole plug comprising an inflatable body and a container of pressurized propellant associated with the inflatable body and operable to release the propellant without any time delay effect to inflate the inflatable body in use, the propellant being a two phase 5 composition, comprising upper and lower separate liquid propellant phases each including a mixture of dimethyl ether and water, with the percentage of dimethyl ether by weight being greater than 34 wt%, but no more than 93 wt%, and the percentage of water by weight being less than 66 wt%, but no less than 7 wt%, wherein the lower propellant phase comprises a lesser % by weight dimethyl ether than the upper 10 propellant phase.

2. A blast hole plug according to claim 1 wherein the percentage of dimethyl ether by weight is in the range of 35 wt% to 55 wt% and the percentage of water by weight is in the range of 65 wt% to 45 wt%.

3. A blast hole plug according to claim 2 wherein the percentage of dimethyl ether by 15 weight is in the range of 40 wt% to 50 wt% and the percentage of water by weight is in the range of 60 wt% to 50 wt%.

4. A blast hole plug according to claim 3 wherein the propellant comprises 44.83 parts by weight of dimethyl ether, 54.87 parts by weight of water, and 0.3 parts by weight of sodium nitrate. 20

5. A blast hole plug propellant, the propellant being a two phase composition releasable without any time delay effect from a container to inflate an inflatable body in use, the propellant comprising upper and lower separate liquid propellant phases each including a mixture of dimethyl ether and water, with the percentage of dimethyl ether by weight being greater than 34 wt%, but no more than 93 wt%, and the percentage of water by 25 weight being less than 66 wt%, but no less than 7 wt%, wherein the lower propellant phase comprises a lower % by weight dimethyl ether than the upper propellant phase.