JPH11201925A - Powder-ignition testing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder-ignition testing apparatus in which a dust cloud of uniform density is formed to find the minimum ignition energy of a powder simply and with good accuracy, by which an ignition test can be performed continuously a plurality of numbers of times and in which time and labor spent for the ignition test can be reduced sharply. SOLUTION: When an ignition container 1 and its fixation part 2 are vibrated by a vibrating device 3, a sample container 40 which is installed inside the ignition container 1 is vibrated. As a result, a powder to be tested (a sample) which is filled into the sample container 40 falls through a wire net 41, and a dust cloud is formed. An ignition test of the dust cloud is performed by a discharge spark generated by a high voltage applied to a discharge electrode. When the dust cloud is not ignited, discharge energy is increased stepwise. The ignition test is performed repeatedly until its ignition is confirmed. In succession, the control switch 33 of the vibrating device 3 is turned, and the amplitude of its vibration is increased. The ignition test is performed repeatedly until the ignition is confirmed. When the ignition test is repeated, the minimum ignition energy of the powder to be tested is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder ignition test device for testing the ignition characteristics of combustible powder due to static electricity.

[0002]

2. Description of the Related Art A powder ignition test apparatus for testing the ignition characteristics of combustible powder due to static electricity, particularly its minimum ignition energy, has been known. Here, the ignition test is specifically performed by changing the concentration of the dust to obtain the minimum required discharge energy between the discharge electrodes for igniting the dust cloud, that is, the minimum ignition energy.

[0003] As a conventional powder ignition test device for performing such an ignition test, devices called a blow-up type ignition test device and a hammer drop type ignition test device are known.

The former includes a cylindrical ignition vessel having a volume of about 2 liters, and a predetermined amount of test powder (for example, Ishimatsuko (beard spores)) is placed in the bottom of the ignition vessel, and this is placed in the container. This is a device that forms turbulent floating dust (dust cloud) in an ignition container by blowing it up with compressed air. The latter has a wire mesh on its upper part and a diameter of 15 mm.
cm of a cylindrical ignition container, place the test powder on this wire mesh, hit it once with a hammer to drop the test powder, and create a dust cloud of uniform concentration in the ignition container for a certain period of time. The device to form.

[0005]

However, any of the above conventional ignition test apparatuses has the following problems.

That is, in the former blow-up type ignition test apparatus, 1) since the dust cloud is formed in a turbulent flow, the dust concentration is not uniform, and the distribution state of the dust changes with time. The timing of ignition of the dust cloud (ignition is usually performed by applying an electric spark generated by applying a predetermined high voltage to the discharge electrode, so the ignition timing is the discharge timing) affects the test results. Influence, and
The evaluation of the discharge timing was difficult because the distribution state of the dust and its time change depended on the properties and particle size distribution of the test powder. 2) For each blow-up of the test powder, the ignition test can be performed only once. In addition, since the test powder adheres to the wall surface of the ignition container by blowing up, it is necessary to clean the ignition container every time blowing up regardless of whether or not ignition has occurred, and a great deal of time and labor is spent on the ignition test. 3) Since the entire amount of the test powder is dispersed in the ignition container, the amount of the sample is large, and therefore, the explosion pressure when ignited increases. Therefore, a robust device is required, and the sound of the explosion is large.
Combustion products (such as soot) also increased.

Further, in the latter hammer drop type ignition test apparatus, 1) the dust concentration is not uniform due to the single-shot dropping type, and depending on the accumulation state of the test powder on the wire mesh. Since the dust concentration at the time of drop changes, it is difficult to continuously supply dust at a constant concentration.Moreover, since the distribution state of the dust changes with time, the discharge timing affects the test results, and In addition, it was difficult to evaluate the timing of the discharge because the distribution state of the dust and its time change depended on the properties and the particle size distribution of the test powder. 2) For each drop of the test powder, an ignition test was performed once. In addition to this, it is necessary to clean the ignition container every time an ignition occurs in this device, and a great deal of time and effort was spent on the ignition test. 3) Fine adjustment of the dust concentration was difficult, and the test was difficult. 4) Dispersion of the entire amount of the test powder in the ignition container increases the amount of the sample, thus increasing the explosion pressure. Therefore, a robust device is required, the sound of the explosion is large, and the combustion products ( Soot).

The present invention has been made in view of this point, and forms a dust cloud having a uniform concentration, which is necessary for improving the accuracy of ignition energy measurement, and conducts an ignition test continuously plural times. It is another object of the present invention to provide a powder ignition test apparatus capable of performing the above-described method and further greatly reducing the time and labor spent for the ignition test.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention tests the ignition characteristics of a combustible powder by igniting a dust cloud formed by mixing the combustible powder with air. An ignition container to which the dust cloud is supplied; a powder storage container provided in the ignition container for loading the combustible powder; and a bottom portion of the powder storage container. A wire net having a predetermined shape provided with a mesh having a size through which the loaded combustible powder passes, and a discharge electrode provided in the ignition container, having a predetermined electrode interval. A discharge spark is generated between the electrodes by applying a high voltage to the discharge electrode to ignite the dust cloud, and the loaded combustible powder is dropped from the wire mesh. The ignition to form the dust cloud The vibrating means for vibrating the vessel, and having a capable change its oscillation mode.

Preferably, the wire mesh has a shape such that the formed dust cloud falls in a sheet shape near the space between the electrodes.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing an entire configuration of a powder ignition test apparatus according to one embodiment of the present invention.

Referring to FIG. 1, a powder ignition test apparatus according to the present embodiment includes a cylindrical ignition container 1, a fixing portion 2 for fixing the ignition container 1, and a vibration for vibrating the ignition container 1 and the fixing portion 2. The device 3 is mainly configured, and components other than the vibration device 3 are shown in a cross-sectional view for convenience of explanation.

The ignition container 1 is composed of a tubular portion 11 made of, for example, acrylic, and an upper lid portion 12 and a lower lid portion 13 for closing the inside of the tubular portion 11. 13 is pressed by a spring 21b.

The upper end 11a and the lower end 11 of the cylindrical portion 11
The inner and outer radii of b are shorter than the other inner and outer radii, and the upper surface of the upper end 11a, that is, the annular surface, is a cone for loading the test powder (sample). A trapezoidal sample container 40 is supported.

FIGS. 2A and 2B are sectional views showing the vicinity of the sample container 40, FIG. 2A is a front sectional view, and FIG. 2B is a side sectional view.

As shown in FIG.
A wire mesh 41 having a U-shaped cross section is joined to 0a. The wire mesh 41 is for dropping the sample from the sample container 40, and has a mesh (for example, in the case of Ishimatsuko, the mesh interval is 63 μm (230 mesh)) enough to allow the sample to pass through. The wire mesh 41 is formed by a discharge electrode 50
The U-shape of the front cross section is a gentler curve than the U-shape of the side cross section so that only the vicinity of the gap between a and 50b falls in a sheet shape.

Further, the sample container 40 is covered with a wire mesh 41 to protect the wire mesh 41 and the remaining sample therein from flames and combustion products of the ignited sample.
2 are also joined. In other words, the protective wire mesh 42 cools the flame of the ignited dust to extinguish the flame, thereby preventing damage to the wire mesh 41 due to the flame and clogging of the mesh due to the adhesion of combustion products, and the remaining sample in the wire mesh 41. It serves to prevent inflammation.

Returning to FIG. 1, the discharge electrodes 50a and 50b are provided at predetermined positions of the cylindrical portion 11 so as to penetrate the side wall of the cylindrical portion 11. The distance between the discharge electrodes 50a and 50b is set to, for example, 4 mm, and the shape of the wire net 41 is determined so that the sample (dust cloud) falls in a sheet shape in or near this electrode distance. Here, the sample is dropped in a sheet shape because of the discharge electrodes 50a, 50a.
This is because a sheet-shaped dust cloud having a stable and uniform concentration is continuously supplied when the sample is ignited by discharging b, and the ignition is easily caused to improve the test accuracy. That is, when the sample is dropped not in the form of a sheet but in the form of a spot, it is difficult not only to drop the sample stably and continuously, but also to ignite because the dust concentration between the discharge electrodes and in the vicinity thereof is not sufficient. This is because ignition may not occur despite the application of only discharge energy.

The fixing portion 2 fixes the ignition container 1 in both horizontal and vertical directions.

In the horizontal direction, the ends 50a1 and 50b1 of the discharge electrodes 50a and 50b are connected to the electrodes 22a and 22b, respectively.
It is fixed by pressing inward with. The electrode 2
2a is grounded (GND), and the electrode 22b is connected to a high voltage capacitor (not shown) via a series resistor and a high voltage relay.

On the other hand, the vertical direction is the vibration table 3 of the vibration device 3.
1 and the beam portion 20 of the fixed portion 2
Is fixed by being brought into pressure contact with a damper 21 provided at the bottom. The damper 21 is mainly constituted by a pressure contact plate 21a for pressing the upper lid portion 12 of the ignition container 1 and a plurality of springs 21b for urging the pressure contact plate 21a vertically downward. The function of fixing the ignition container 1, the effect of releasing the pressure by lifting the upper lid portion 12 of the ignition container 1 upward when the pressure in the ignition container 1 rises to a certain level or more due to the ignition, and the necessity of the ignition container 1 It has the function of absorbing the above vibration.

The vibrating device 3 includes an ignition container 1 and a fixing portion 2
And a vibration table 31 that vibrates both 1 and 2 and an actuator 32 that vibrates the vibration table 31.

On the panel surface of the actuator 32, a control switch 33 for changing the vibration intensity, that is, the vibration amplitude, is provided. The scale value "1" indicating the minimum amplitude is changed to "10" indicating the maximum amplitude. ", The vibration intensity can be changed in ten steps. In the present embodiment, the frequency of the vibration is fixed at, for example, 50 Hz, but is not limited to this, and the frequency may be changed according to the operation of the control switch 33.

Hereinafter, an ignition test method performed by the powder ignition test apparatus configured as described above will be described.

First, the urging of the damper 21 against the ignition container 1 is released, the upper lid portion 12 of the ignition container 1 is removed from the cylindrical portion 11, and an appropriate amount of the sample is put into the sample container 40.

Next, the upper lid part 12 is attached to the cylinder part 11,
The upper lid 12, that is, the entire ignition container 1 is urged and fixed by the damper 21.

The capacity of the high-voltage capacitor and the magnitude of the high voltage (supply voltage) supplied thereto are set to predetermined values, and then a discharge energy measuring device (not shown) (for example, a digital oscilloscope, a personal computer, (A plotter or the like) is set in a measurable state (hereinafter referred to as “reset”).

After confirming that the scale of the control switch 33 of the vibration device 3 indicates a predetermined initial value, when the power is turned on, the vibration table 31 is set in advance in accordance with the scale. Vibrates with amplitude. As a result, the ignition container 1 vibrates, and the sample container 40 therein also vibrates, so that the sample passes through the wire net 41 and falls in the form of a sheet near the area between the discharge electrodes 50a and 50b as described above. .

After the sample starts dropping, the discharge electrode 50
After a time period in which the dust concentration in the vicinity of a and 50b converges to a predetermined value has elapsed, the discharge electrode 50
a, a high voltage is applied to 50b to generate a discharge spark,
Check if the dust cloud ignites. At this time, if the dust cloud is not ignited, the discharge energy measuring device is reset again, and then it is checked whether or not the dust cloud is ignited by generating a discharge spark as described above. The operation is usually repeated 10 times. If the ignition still does not occur, the setting of the high-voltage capacitor or the supply voltage is changed so that the discharge energy increases stepwise, and the above operation (1) is performed.
0 times). Hereinafter, the same operation is repeated until the dust cloud is ignited. In this way, when ignition of the dust cloud is confirmed, the discharge energy measured at that time is the minimum ignition energy at this dust concentration. Subsequently, the scale of the control switch 33 is adjusted to the next scale in order to change the dust concentration, and the vibration intensity (amplitude) of the vibration table 31 is increased.

After waiting for the time for the dust concentration to converge to the next predetermined value elapses,
The minimum ignition energy at this dust concentration is determined. The above operation is repeated by changing the scale of the control switch 33 one after another to obtain the minimum ignition energy at each dust concentration. The smallest minimum ignition energy among these is the minimum ignition energy of the test powder to be obtained. The above-described dust concentration, that is, the mass of the dust per unit volume is calibrated based on the size of the mesh of the wire net 41 and the size of the vibration of the vibrating device 3 (that is, the value of the scale indicated by the control switch 33). It can be calculated by experiment.

FIG. 3 is a diagram showing a measurement result of how the amount of drop of the sample per unit time changes when the vibration intensity of the vibration device 3 is changed. Indicates the amount of drop of the sample per unit time, and the horizontal axis indicates the scale position indicated by the control switch 33.

In FIG. 3, three measurement results are shown, and each of the measurement results r1 to r3 indicates a measurement result when the vibration direction is changed. That is, the measurement result r1 shown by the solid line shows the result when the sample is vibrated in the vertical direction, and the measurement result r2 shown by the broken line shows the result when the
a and 50b when vibrated at right angles to the longitudinal direction, and a measurement result r3 indicated by a dashed line indicates a case when vibrated in the horizontal direction and in the longitudinal direction of the electrodes 50a and 50b. .

As shown in the figure, the amount of drop of the sample is increased by increasing the intensity of the vibration of the vibrating device 3, and fine adjustment can be made by appropriately selecting the vibration direction. . Thereby, the dust concentration is changed according to the vibration intensity of the vibration device 3, so that the dust concentration can be adjusted easily and accurately.

As described above, in the powder ignition test apparatus of the present embodiment, a dust cloud having a constant concentration can be continuously supplied into the ignition container 1 for a predetermined time (for example, several minutes). (For example, about 10 to 20 times) An ignition test by electrostatic discharge can be performed, thereby making it possible to shorten the test time and reduce the labor.

In addition, a wire mesh 4 is selected according to the particle size distribution of the test powder.
In addition to coarsely adjusting the dust concentration by selecting the size of the first mesh, it is possible to finely adjust the dust concentration continuously within a certain range by changing the vibration mode such as the amplitude and frequency of the vibration device 3. Therefore, it is possible to adjust the dust concentration necessary for the ignition test comprehensively.

Further, a dust cloud having a predetermined concentration can be continuously supplied into the ignition container 1 only for a predetermined period of time in the vicinity of the discharge electrodes 50a and 50b. When the pressure rise is small, the size of the ignition container 1 can be reduced and simplified, and the emission of combustion products is reduced and the noise is reduced.

Further, by making the shape of the wire net 41 into a predetermined shape (for example, a U-shape), sheet-like dust having a stable and uniform concentration can be continuously supplied to the ignition container 1, The minimum ignition energy can also be determined accurately.

[0039]

As described above, according to the present invention,
When the ignition container is vibrated by the vibrating means, the flammable powder in the powder storage container passes through a wire mesh to form a dust cloud, and an ignition test is performed on the dust cloud by a discharge spark generated by the high voltage applied to the discharge electrode. When the ignition is not performed, the ignition test is repeatedly performed until the ignition mode is confirmed by changing the vibration mode, so that a dust cloud having a uniform concentration can be formed, and the ignition test can be continuously performed a plurality of times. Further, there is an effect that the time and labor spent for the ignition test can be significantly reduced.

Preferably, the shape of the wire mesh is determined so that the dust cloud falls in the form of a sheet near the electrode, so that the sheet-shaped dust cloud having a stable and uniform concentration is continuously placed in the ignition container. , So that the minimum energy can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of a powder ignition test apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of the vicinity of a sample container of FIG.

FIG. 3 is a diagram showing a measurement result obtained by measuring how a drop amount of a sample per unit time changes when a vibration intensity of the vibration device of FIG. 1 is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ignition container 3 Vibration device (vibration means) 40 Sample container (powder storage container) 41 Wire mesh 50a, 50b Discharge electrode

Claims (2)

[Claims] 1. A powder ignition test device for igniting a dust cloud formed by mixing flammable powder with air to test the ignitability of the flammable powder, wherein the dust cloud is supplied. An ignition container, a powder storage container provided in the ignition container for loading the combustible powder, and a wire net having a predetermined shape provided at the bottom of the powder storage container, And a discharge electrode provided in the ignition vessel having a predetermined electrode spacing, wherein a high voltage is applied to the discharge electrode. Generating sparks between the electrodes to ignite the dust cloud; and vibrating the ignition container to drop the loaded combustible powder from the wire mesh to form the dust cloud. The vibration mode Powder ignition test apparatus characterized by having a capable change. 2. The powder ignition test device according to claim 1, wherein the wire mesh has a shape such that the formed dust cloud falls in a sheet shape near the space between the electrodes.