AU2001100469A4 - An inflatable bore hole plug having a heat exchange medium in the bag - Google Patents

Description

AN INFLATABLE BORE HOLE PLUG HAVING A HEAT EXCHANGE MEDIUM IN THE BAG FIELD OF THE INVENTION This invention relates to an inflatable bore hole plug assembly which has a heat exchange medium in the bag to facilitate a more rapid inflation of the bag.

BACKGROUND ART Bore holes are drilled so that explosive charges may be placed in the bore hole at a particular position. Sometimes, the bore hole is entirely filled with explosive, but other times an explosive charge must be placed somewhere along the bore hole length. For this type of use, a plug is lowered down the bore hole to the desired area to form a support platform for the explosive.

Inflatable bore hole plug assemblies are well-known. The assemblies comprise an inflatable bag which can be inflated to form the bore hole plug. Inside the bag is a pressurised can which contains the inflating substance. The can is provided with a valve which can be opened to expel the inflating substance into the bag to inflate the bag. The pressurised can has a one-way valve which can be locked into the open position to expel the inflating substance (typically hydrocarbons). The plug assembly is attached to a measured length of rope and is lowered down the hole to be supported by the rope until the plug inflates to be jammed against the wall of the bore hole.

In the past, the valve was opened and the plug assembly was quickly lowered down or pushed down the bore hole and it was hoped that the plug assembly could be positioned before the bag was inflated to the point where it formed the plug.

It is known to use reagents which, when mixed, create a gas which expands in the inflatable bag to create the plug. A major disadvantage with this arrangement is that the reaction rate varies depending on temperature and other climatic conditions which makes it difficult to ensure that the plug assembly is correctly positioned in the bore hole before substantial inflation takes place. Often, the inflation occurred too quickly which meant that the inflatable bag would plug the bore hole at an undesired position.

More recently, pressurised cans have been used to inflate the bag. As the bag can be lowered some considerable distance down the bore hole, it is necessary to actuate the can valve prior to lowering the bag down the bore hole. For this reason, various attempts have been made to provide some form of time delay between activating the can valve and substantial inflation of the bag.

One attempt involves a specially filled pressurised can which contains a quantity of water as well as the inflating substance (typically hydrocarbon). The water and the hydrocarbon do not mix and the water, being heavier than the hydrocarbon, settles at the bottom of the can. The can has an internal small diameter tube extending from the adjacent the bottom of the can and connected to the valve. When the valve is opened, the water will initially be expelled into the inflatable bag and, after the water has been expelled, the inflating substance will pass into the bag to cause inflation. The amount of water, the diameter of the internal tube, and other parameters can be varied to cause a time delay typically from between 10 to 40 seconds which is considered sufficient to lower the bag down the bore hole and to hold it by the rope until inflation is complete.

While this arrangement was more reliable and provided a more reliable time delay, it suffers from a number of disadvantages. The main disadvantage is that the can can only be used in the upright position. Should the can be tilted, the water will not completely pass out of the can before the inflating substance passes out of the can. This causes premature inflation. It should be appreciated that as the bag is lowered down the hole, the bag can catch on the sides of the bore hole and can be tilted or twisted. This can reduce the time delay provided by initial expulsion of the water from the can.

The bag also needs to be carefully held in the vertical position after opening the valve and before lower into the hole. A second disadvantage is that the pressurised can cannot be completely filled with the inflating substance which means that larger cans may be required. A third disadvantage is that specially designed and filled cans are required.

Another disadvantage with existing inflatable bag plug assemblies is that the bags need to be inflated fairly quickly in order to minimise the time taken to plug a bore hole. For this reason, the can contents are expelled as quickly as possible though the valve and into the bag. If the can contents contain butane or propane, volatisation of this material causes a large temperature drop in the bag. It is common for the bag temperature to drop below the boiling point of the propane or butane which causes a slow down in inflation.

There would therefore be a substantial advantage if it could be possible to use a low boiling liquid as the bag inflating medium, but to have some means to facilitate a more rapid vaporisation of the inflating medium.

OBJECT OF THE INVENTION The present invention is directed to an inflatable bore hole plug assembly which has an inflatable bag (which can be of conventional design), a means to inflate the bag (typically a conventional pressurised can), and a heat exchange medium in the bag which will more rapidly vaporise the can contents as the can contents are discharged into the bag.

It is an object of the invention to provide an inflatable bore hole plug assembly which may overcome the abovementioned disadvantages or provide the public with a useful or commercial choice.

In one form, the invention resides in an inflatable bore hole plug assembly which has an inflatable bag which can be inflated to form the plug, a pressurised can which contains the inflating substance to inflate the bag,, the can typically having some sort of valve which can be activated to cause the can to release the inflating substance into the inflatable bag, and a heat exchange medium which is in the inflatable bag and which functions to more rapidly vaporise any liquid portion of the inflating substance.

Suitably, the heat exchange medium is a liquid. The liquid may comprise an aqueous liquid, a non aqueous liquid, or a mixture of liquids.

Suitably, the liquid is non-toxic and non hazardous and is able to provide a good heat exchange with the inflating substance. It is considered that water or an aqueous mixture would be a suitable heat exchange medium. However, the heat exchange medium may also comprise liquids such as oils and the like. It is envisaged that the heat exchange medium may also be, or comprise a solid and preferably a flowable solid and this type of heat exchange medium may comprise sand or other suitable flowable solid material.

The amount of the heat exchange medium in the inflatable bag can vary depending into alia on the size of the bag, the type of inflating medium in the can and the like. For instance, if the inflating medium is of the type that will generate a reasonable amount of unvaporised liquid in the bag, it may be necessary to increase the amount of heat exchange medium in order to promote a more rapid and possibly a more uniform inflation. On the other hand, if the inflating medium is of the type that only a small amount of liquid will pool in the bag, a lesser amount of inflating medium may be required.

Suitably, the amount of heat exchange medium will be between 20-500 ml if the heat exchange medium is a liquid, or between 500 g if the heat exchange medium is a solid. Preferably, the amount will be between 50-100 ml or g.

Inflatable bags are already known in the art and it is envisaged that the inflatable bag of the invention can be similar to bags already known.

Typically, the inflatable bag comprise multi-layer plastic bags which are gas tight. These bags can be formed from suitable material such as plastics. As mentioned above, such bags are known in the art. The size and volume of the bag can also vary depending on the bore hole size, the weight of explosives to be supported by the plug and the like, and it is considered that this information is already public knowledge.

The pressurised can can be of a type already known in the art and already known to inflate bore hole plug bags. The valve is typically such that once opened, the valve stays open which means that the contents of the container will be totally released without interruption until the pressure in the container and the pressure in the bag equalises.

The inflating substance can vary to suit. The inflating substance is typically in the form of a volatile liquid which will expand and volatise once in the inflatable bag. Alternatively, the pressurised can can contain compressed gas, although a volatisable liquid is preferred as it will allow greater expansion of the bags.

Typical inflating substances may include, but need not be limited to hydrocarbons such as propane and butane, halohydrocarbons, low boiling point ethers; compressed gases such as nitrogen, carbon dioxide, mixtures thereof.

The pressure in the can is typically between 150 to 1000kPa and is usually within the range of about 150 to 500kPa.

A delay means may be provided to delay inflation of the bag until such time as the bag has been inserted into the bore hole. Various delay means are known in the art. The delay means can be of various basic types.

The time delay can be varied to suit and is typically between seconds to several minutes with a preferred time delay being between 20 to seconds.

The inflatable bag can contain a quantity of heat exchange medium, for instance water, before inflation occurs. As the bag inflates, some of the resultant temperature drop can be stabilised by heat exchange with the heat exchange medium which will facilitate a more rapid inflation of the bag.

In an embodiment, the heat exchange material is water which can be added to the bag during the manufacture of the plug assembly. It is found that the addition of water to the bag also moisturises and improves the shelf life of the bag and can reduce bag failure caused by the bag becoming brittle over time.

The heat exchange medium can be water which can be added to the bag during the manufacture of the plug assembly.

It can be seen that the inflatable bore hole plug assembly according to the invention has several advantages not hitherto realised DETAILED DESCRIPTION In a detailed description, the invention comprises an inflatable bore hole plug assembly which consists of an inflatable bag which can be inflated to form the plug, a pressurised can which has a valve and a heat ecxhange medium in the bag.

The inflatable bag can be of conventional design and a person skilled in the art would be able to manufacture the inflatable bag. Typically, the inflatable bag consists of two bags connected together to provide strength.

It is typical that the pressurised can is initially inserted into the inner bag through an open end, the open end then being sealed. The inner bag is then inserted into the outer bag and the open end of the outer bag is also sealed to form the bag.

The can is typically of conventional design and manufacture and is sized and holds enough inflating liquid to allow bag to be properly inflated in the bore hole. Of course, the size and the contents of the can will depend on the size of the bag. Typically, the can has a top valve which is connected to an internal tube through which the inflating substance can pass. The valve is usually provided with some form of lock down mechanism which can be easily manipulated via the outside of bag to lock the valve in the open position when required.

The can is filled with a suitable inflation substance which in the embodiment comprises a mixture of propane and butane. In the embodiment, the can does not need any additional internal ingredients such as water and the like.

If desired, a delay means can be provided to delay inflation of the bag until such time as the bag has been inserted into the bore hole. Delay means are known in the art.

A heat exchange medium is located or positioned within the bag prior to inflation of the bag. It is preferred that the heat exchange medium is water at ambient temperature and that a quantity of water is added to the bag during manufacture. The water inter alia prevents drying of the plastic parts which, over time, can go brittle and cause bag failure if not lubricated.

The water acts as a heat exchange medium. That is, once the optional time delay has passed, and the inflating liquid propane and butane) passes into the bag, the bag experiences a significant temperature drop which can dramatically slow the inflation rate of the bag The water acts as a heat exchange medium and will convert the cold inflating liquid into gas vapour.

It is found that the addition of water or similar heat exchange medium can give an exceptionally fast inflation of the bag. The amount of water added is typically between 50-100 ml.

The water is added to the bag prior to inflation.

This is critical for mine site charging operations to prevent double or triple charging passes of the explosives truck. Instead, the explosives truck can wait until the bag has been inflated, and can then pour explosives onto the bag. After that, a second bag can be lowered and inflated and more explosive charge can be placed on the second bag. Because of the short time interval between the two bags, the explosives truck can wait until all the bags have been inflated and charged.

It should be appreciated that various other changes or modifications can be made to the embodiments described without departing from the spirit and scope of the invention. For instance, anti-freeze additives may be required to regulate the time delay.

Claims (4)

1. An inflatable bore hole plug assembly which has an inflatable bag which can be inflated to form the plug, a pressurised can which contains the inflating substance to inflate the bag, and a heat exchange medium which is within the inflatable bag and which functions to facilitate vaporisation of the inflating substance.

2. The assembly as claimed in claim 1,wherein the heat exchange medium is a liquid, or a flowable solid.

3. The assembly as claimed in claim 1 or claim 2, wherein the heat exchange medium is water or an aqueous liquid.

4. The assembly as claimed in any one of the preceding claims, wherein the amount of the heat exchange medium is between 20-500 ml if the heat exchange medium is a liquid, or between 20-500 grams if the heat exchange medium is a solid. An assembly as claimed in any one of the preceding claims and substantially as hereinbefore described. DATED this 11 day of October 2001 M DE LUIS By his Patent Attorneys CULLEN CO.