WO2019237135A1

WO2019237135A1 - Pumpable explosives density measurement

Info

Publication number: WO2019237135A1
Application number: PCT/ZA2019/050029
Authority: WO
Inventors: Selwyn Peter Pearton
Original assignee: Selwyn Peter Pearton
Priority date: 2018-06-04
Filing date: 2019-06-04
Publication date: 2019-12-12
Also published as: ZA202007929B

Abstract

A device suitable for providing a reading, which is a measure of a density of an explosive' the device including an expansible chamber for receiving a sensitised emulsion through an inlet to the chamber, an indicating member which is actuated by the expansion of the chamber due to a reaction of the sensitised emulsion, the indicating member thereby providing the reading, and an outlet from the chamber through which air can be displaced form the expansible chamber as the sensitised emulsion is introduced into the chamber.

Description

PUMPABLE EXPLOSIVES DENSITY MEASUREMENT

BACKGROUND OF THE INVENTION

[0001]This invention relates to the measurement of the density of a pumpable explosive.

[0002] Pumpable explosives, e.g. emulsions, water gels or slurries, are in widespread use. The benefits which are associated with this type of explosive are significant but, nonetheless, in order to achieve optimal blast performance and to meet safety regulations it is important to manage the density of the explosive prior to sensitization and subsequently, i.e. when a blasthole is loaded.

[0003] During the loading of a blasthole with a pumpable explosive a sample is drawn and tested for consistency if the final density (the density once the explosive has been sensitised fully) falls within predetermined limits the quality of the explosive is correct. If the density falls outside the predetermined limits the quality is not acceptable.

[0004]A pumpable explosive can be supplied to an operation site in a final cap sensitive form i.e. as a pre-sensitised explosive that is manufactured to the correct blasting density. For a pre-sensitised explosive the density is confirmed by filling a cup of a pre-determined volume with the explosive and then weighing the cup and the explosive to determine the mass of the sample. After compensating for external factors the mass of the explosive is divided by the volume of the cup to obtain the density of the explosive.

[0005] For a non-sensitized explosive one of two methods is used to determine the density of the explosive during the loading process. The first method is essentially the same as that described for a pre-sensitised explosive in that a cup of a pre-determined volume is filled with a sample of a mixture of the explosive matrix and an activating agent (sensitizer). As the matrix reacts with the sensitizer, gas bubbles are formed and the density of the sample decreases, increasing the volume of the sample in the cup. After the reaction has been completed, that quantity of explosive that has risen above the top of the cup is removed, leaving behind a predetermined sample volume in the cup. The density of the sample is then determined in the manner which has been described. [0006] In a second approach use is made of a cup of predetermined volume and a sliding ring that can be lifted to a fixed height above a rim of the cup. Once the cup has been filled with the explosive matrix and activating agent the ring is lifted, thereby forming a specific volume into which the explosive can expand, to obtain an indication of the density of the product. If the explosive does not rise to meet the height of the raised ring, the density of the explosive is too high, whereas if the explosive rises above the ring, the density of the sample is too low.

[0007] In implementing the aforementioned techniques, it is important to handle each sample with care to ensure that the integrity of the sample is not adversely affected. Excess explosive must be scraped away from the cup which contains the sample of the sensitized explosive - this can be a difficult exercise to carry out accurately particularly in a harsh working environment of the kind encountered at a blast site. Operator error can result in an incorrect subtraction of the mass of the cup from the combined mass of the cup and sample, and this error then directly translates into a miscalculation of the density. Each sample must be protected by an operator for the duration of the reaction period (± 30 minutes) so that the sample is preserved in the cup for the measurement process. If a sample is damaged prior to the completion of the reaction, or should the operator fail to measure the sample, no density reading would be obtained for the sample.

[0008] An object of the present invention is to address, at least to some extent, the aforementioned difficulties. SUMMARY OF INVENTION

[0009] The invention provides a device for use with a bulk explosive delivery system, the explosive being a combination of an emulsion and a sensitizer, the device including an expansible chamber of an initial known volume, an inlet to the chamber, an outlet from the chamber, and an indicating member, actuatable by the expansion of the volume of the chamber, wherein a sample of a predetermined mass of the explosive, which is sufficient to fill the volume, is introduced into the chamber via the inlet, immediately after the combination has been mixed, displacing gas (air) within the chamber via the outlet and closing the outlet when the volume is filled, thereby to allow a reaction between the emulsion and the sensitizer to take place within the expansible chamber, causing the volume of the chamber to expand and actuate the indicating member so that, when the reaction is complete, a reading is taken from the indicating member, which reading provides a measure of a density of the explosive.

[0010] The outlet may be used to release the sample from the chamber after the reading has been taken.

[0011]The expansible chamber may comprise a piston and a cylinder arrangement wherein the piston is positioned relative to the cylinder to form the known volume and the piston is displaceable relative to the cylinder, once the volume has been filled by the sample, as the reaction takes place. [0012] The indicating member may be defined by a portion of the piston that is driven from the cylinder during the displacement thereof.

[0013] A protruding portion of the piston may be calibrated or marked to allow for reading to be taken.

[0014] The inlet and the outlet may each be regulated by a respective valve. [0015] Expansion of the chamber may be limited so that the reaction causes a pressure of the emulsion to increase within the chamber. The pressure or a rate of pressure increase may be measured in any suitable way. Preferably, the chamber is equipped with a sensor for measuring the pressure or the rate of pressure increase. [0016] In one form of the invention, a hollow piston defines the known volume. The inlet is in an external formation of the piston. The external formation is configured sealingly to connect to a delivery pipe to a of a bulk explosive delivery system to receive the sample to fill the volume. Once the volume is filled, the reaction drives the cylinder relative to the piston to expose the calibrated portion of the piston to an extent which is dependent on the degree to which the size of the volume has been increased by the reaction, thus allowing for a reading to be taken therefrom.

[0017] In an alternative embodiment, the inlet is at one end of the cylinder and the piston, having a calibrated rod, is at an opposed end of the cylinder. A biasing member may be used to bias the piston into a position relative to the cylinder thereby to define the initial known volume between the piston and the inlet. An outlet may be formed in a wall of the cylinder to allow air to be displaced from the known volume as the sample is introduced into the volume. Once the volume is filled, the reaction drives the piston relative to the cylinder, driving the rod out of the end of the cylinder, to the extent that the volume is expanded, thereby allowing a reading to be taken off the calibrated rod. [0018] The device may be configured to integrate temporarily or permanently with the bulk explosive delivery system, to receive the sample via the inlet and return the sample to the system via the outlet.

BRIEF DESCRIPTION OF THE DRAWINGS [0019] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a representation of apparatus according to one form of the invention, for measuring the density of a sensitised explosive;

Figure 2 is a flow chart illustrating a sequence of operations, based on the use of the apparatus of Figure 1 , for measuring the density of a sensitised explosive;

Figure 3 illustrates a device according to the invention for obtaining a density measurement of a sensitised explosive;

Figure 4 shows the device of Figure 3 in use; and

Figure 5 illustrates a different device according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] Figure 1 illustrates, in block diagram form, apparatus 10, according to the invention, which includes a load cell 14 which is connected to a micro-controller or processor 16. A memory unit 20, in data communication with the processor 16, holds data relating to one or more of a plurality of sample cups 24A, 24B . 24N. Each sample cup has a known mass and a known volume and data relating thereto is held in the memory unit 20. The processor 16 is connected to an output mechanism 30 which includes a display screen 32 and a storage device 34 and, optionally, a printer, not shown.

[0021]The measurements are taken under conditions wherein the temperature and pressure are constant. Preferably the conditions are ambient.

[0022] Figure 2 depicts a sequence of operations which are carried out when the apparatus 10 of Figure 1 is used.

[0023JA sample cup 24N is selected and an operator pumps or diverts a sample 36 of an emulsion explosive 38 into the cup 24N. The sample 36 expands due to the action of a sensitizer. After about 30 minutes, the sensitising process is complete. At that time, excess emulsion 40, protruding above a rim 42 of the sample cup 24N is scraped from the cup leaving behind a predetermined volume of the emulsion 36A in the cup 24N. The cup 24N with the sample 36A is then placed onto the load cell 14 which produces a measurement 44 of the combined mass, M1 , of the cup 24N and the sample 36A. The memory unit 20, which is previously loaded with data detailing the mass M2 of the sample cup 24N and the volume V of the sample cup 24N, is accessed to direct data detailing M2 and V to the processor 16.

[0024]The processor 16 subtracts the mass M2 from the mass M1 to derive a measurement of the mass M3 of the explosive sample 36A. In a subsequent step 46, M3 is divided by the volume V to produce a calculated density value D of the sample 36A, which is displayed on the display screen 32 and, if required, data relating to the density measurement is stored in the memory unit 20. Additional data such as the date, time, identity of the operator, the identity of the measurement cup, the nature of the explosive composition, the location of the blast bench at which the emulsion is being used, and the like, can be stored in the memory unit 20 for subsequent access and for record keeping purposes.

[0025] Improved techniques for obtaining the density measurement of an emulsion sample are described hereinafter with reference to Figures 3 and 4, and to Figure 5, respectively.

[0026] In order to obviate the scraping of excess emulsion from each sample cup during the testing process as well as to protect the explosive sample during the sampling process it is beneficial to make use of an inline density measurement. [0027] Figure 3 depicts a device 50 according to one form of the invention prior to a sampling process being carried out.

[0028] Figure 4 shows the device 50 following the reaction of the emulsion and the sensitising agent and indicates how an initial volume of a known size of the device 50 is increased.

[0029] The device 50 includes an outer tubular sleeve 52 and an inner tubular sleeve 54 which is slidably located inside the outer sleeve 52. The inner sleeve 54 at one end has an inlet non-return valve 56 secured to it. This valve is located inside a conical cap 58. An end 60 of the inner sleeve 54, which is located inside the outer sleeve 52, is open. The inner sleeve 54(conical cap) protrudes from an open end 62 of the outer sleeve. An opposing end 64, of the outer sleeve, carries an outlet non-return valve 66. The inner sleeve in effect comprises an elongate hollow piston. The outer sleeve thus comprises a cylinder.

[0030]An emulsion delivery pipe 70 (Figure 3) is connected to a main pipeline, not shown, in an explosive delivery system used to direct emulsion to a blasthole.

[0031]The conical cap 58 is designed to be engaged in a leak-proof manner with an open mouth 74 of the emulsion delivery pipe 70. The emulsion then flows from the delivery pipe 70 through the inlet non-return valve 56 and fills an interior volume 76 of the inner sleeve 54. Air can escape from the inner sleeve 54 during the filling process via the outlet valve 66. When emulsion starts leaving the inner sleeve via the outlet valve 66 this is indicative that the inner sleeve 54 has been filled completely with emulsion. At this stage the valve 66 is closed.

[0032]The volume 76 of the inner sleeve 54, when the inner sleeve 52 is pushed fully into the outer sleeve 52, defines an expansion chamber 76 of known dimension which is completely filled with emulsion in the manner which has been described. As the sensitizer reacts with the emulsion gas bubbles are produced which expand the emulsion inside the expansion chamber 76. The effect of the expanding emulsion is to drive the inner sleeve 54 out of the outer sleeve 52, as shown in Figure 4, to a position which is determined by the extent to which the emulsion expands. The inner sleeve 54, see Figure 4, carries gradations or markings 78 on an outer surface which have previously been applied to the inner sleeve during a calibrating exercise. These markings directly indicate the density of the emulsion.

[0033] The device 50 in the Figure 3 configuration has an expansion chamber 76 of known volume and the emulsion is injected into the expansion chamber to fill the expansion chamber i.e. a known mass of the emulsion is placed into the chamber. The expansion of the chamber 76 due to the expansion of the emulsion is directly measurable by means of the gradations 78 on the inner sleeve and this, in turn, allows the density of the emulsion to be determined immediately. There is little room for operator error. After the measurement process has been completed the emulsion inside the expansion chamber 76 is displaced and the device 50 is then ready for re-use.

[0034] The extent to which the inner sleeve (the hollow piston) moves relative to the outer sleeve (the cylinder) can also be measured by means of one or more sensors. This feature allows the density measurement process to be substantially automated. [0035] In an alternative embodiment, volumetric expansion of the chamber 76 is restricted so that the sensitising reaction causes a pressure of the emulsion to increase. The rate of pressure increase is detected by a suitable sensor located in the chamber. The pressure increase can be used as an indication of the density of the emulsion. [0036] Figure 5 depicts a density measuring device 84 which is configured to be connected directly to an emulsion delivery pipeline 86. Optionally this is a permanent connection.

[0037]The device 84 includes a tubular body 88 which includes an elongate defining an emulsion expansion chamber 90. An inlet 92 to the chamber 90 has connected to it a control valve 94. An outlet valve 96 is connected to a port 98 leading from the chamber 90. Optionally, the valve 96 has an outlet 100 which is coupled to an extension of the pipeline 86.

[0038]The body 88 at an end 02 which opposes the inlet 92 has an opening 104 through which extends a piston rod 106. An outer surface 108 of the piston rod is gradated with calibrated markings 110. A piston 112 at an inner end of the piston rod 106 is in sealing and sliding contact with an inner surface 114 of the tubular body 88. The piston 112 is retained in a relative position in respect of the tubular body 88 by means of a spring 113.

[0039] The valves 94 and 96 can be manually actuated or they can be operated by means of pneumatic or electrical connections. The scope of the invention is not limited in this respect.

[0040]The expansion chamber 90 is initially devoid of any emulsion i.e. it is completely empty. The piston 112 is moved to a pre-determined position and locked there so that a known volume, bounded by the piston 112, is defined inside the expansion chamber 90. At this point, the valve 94 is opened so that emulsion of know size, from the line 86 can enter the expansion chamber 90. Air inside the chamber is allowed to escape through an outlet mechanism which preferably is incorporated in the valve 96. Once the expansion chamber 90 is filled with emulsion the air outlet is closed. At this stage a pre-determined volume of emulsion is held in the chamber 90. The piston 112 is then unlocked from its predetermined position and is then free to move relative to the body 88 as the emulsion inside the chamber 90 expands due to the action of the sensitising agent on the emulsion.

[0041] The extent to which the piston rod 106 protrudes from the expansion chamber 90 is an indication of the density of the emulsion. A reading of the position of the piston rod can be taken manually or automatically through the use of appropriate sensors. Using data previously generated, the density of the explosive inside the expansion chamber 90 is directly determined simply by reading the gradation or marking on the piston rod.

[0042] The device 84 may be adapted to restrict actuation of the piston 112 so that the sensitising reaction increases the pressure of the emulsion. The rate of pressure increase is then detected by a pressure sensor in the chamber.

[0043] In this configuration, the spring 113 acts as a linear actuator which, when activated opens valves 94 and 96 to allow fluid flow of the emulsion through the body 88. The device 84 the uses the pressure sensor in the chamber to measure the rate of pressure increase due to controlled volumetric expansion. [0044] After the measurement process has been completed the emulsion in the expansion chamber 90 is directed through the outlet valve 96 into an extension 120 of the pipeline 86 or, as the case may be, can be dumped to waste. The device 84 is then ready for re-use.

[0045] The apparatus and devices of the invention remove the human element from the measurement of pumpable explosives density. The accuracy and efficiency of a measurement process are enhanced, and emulsion waste is reduced. In the devices respectively shown in Figures 3 and 4, and in Figure 5, the emulsion sample remains enclosed in the expansion chamber for the duration of the measuring process. This means that the sample is protected from damage. The sample can be transported and stored for quality control purposes if a detachable device is used such as that shown in Figures 3 and 4. With the inline process shown in Figure 5 the density measuring device can be re-used without previously purging the expansion chamber. In this regard it is pointed out that once a density measurement has been made, emulsion can then be directed into the expansion chamber 90. If the valve 96 is open the emulsion which at that time is in the chamber is expelled through the valve 96. During this process the piston and piston rod are moved to the predetermined initial measurement position so that the expansion chamber can again be filled with a predetermined and known volume of the emulsion.

Claims

1. A device, for use with a bulk explosive delivery system, the explosive being a combination of an emulsion and a sensitizer, the device including an expansible chamber of a known initial volume, an inlet to the chamber for receiving a sample of an unreacted known mass of the combination, an outlet from the chamber through which air is displaced, by the sample, and an indicating member that is actuable by the expansion of the volume of the chamber, wherein the chamber is caused to expand by a reaction between the emulsion and the sensitizer and a reading, related to the extent of such expansion, is taken from the indicating member, once the reaction is complete, which reading provides a measure of the density of the explosive.

2. A device according to claim 1 wherein the outlet is used to release the sample from the chamber after the reading has been taken.

3. A device according to claim 1 or claim 2 wherein the expansible chamber is formed by a piston and a cylinder arrangement, the initial known volume is defined by relative positions of the piston and the cylinder, and the volume of the chamber is expanded by displacement of the piston relative to the cylinder.

4. A device according to claim 3 wherein the indicating member comprises at least a portion of the piston.

5. A device according to claim 4 wherein the portion of the piston is calibrated to allow for the reading to be taken.

6 A device according to any one of claims 1 to 5 wherein expansion of the chamber is restricted.

7. A device according to claim 6 wherein a pressure sensor is located in the chamber.

8. A device according to any one of claims 3 to 7 wherein the piston is a hollow cylinder.

9. A device according to claim 8 wherein the piston includes an external formation in which the inlet is located.

10. A device according to any one of claims 3 to 7 wherein the calibrated portion of the piston is a piston rod.

11. A device according to claim 10 which includes a biasing member which is biases the piston to a position relative to the cylinder thereby to form the initial known volume.

12. A device according to claim 10 or claim 11 wherein the outlet is located in a portion of a wall of the cylinder between the piston and the inlet and wherein expansion of the volume displaces the piston relative to the cylinder.

13. A device according to any one of the aforementioned claims which is integrated with the bulk explosive delivery system to receive the sample via the inlet and, after completion of the reaction, to return the sample to the system via the outlet.