JPH0428624A - Removal of powder or its transportation - Google Patents

Abstract

PURPOSE:To improve efficiency by gaining a wind speed lower limit value to refly attached powder against wind speed acceleration for removal and transportation of powder attached to the wall of a powder equipment and by making ventilation, which changes its speed at set acceleration in the neighbourhood of higher or lower than its lower limit, work on the surface of a solid body. CONSTITUTION:Relativity between each acceleration of ventilation at which wind speed rises at a specific rate and the lower limit of the wind speed at which attached powder reflies by this ventilation are preliminarily gained. Thereafter, the wind speed lower limit against the set acceleration is gained in accordance with this relativity. Then, the attached powder is reflown by making the ventilation at the speed, which is changed at the set acceleration over the neightbourhood higher or lower than this wind speed lower limit, work on the surface of the solid body. In this constitution, it is possible to save energy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for removing powder adhering to a solid surface of a powder device or the like, or a method for transporting powder.

(Background of the invention and prior art) It is generally known that high-speed airflow is applied to remove powder adhering to equipment such as powder handling equipment, and also to prevent powder from adhering to equipment etc. It is known that high-speed airflow is used, and these methods prevent or prevent adhesion by increasing the separation force generated by the action of high-speed airflow than the adhesion force between powder particles or between powder and equipment. The principle is to separate the powder.

However, in the past, the details of how the above-mentioned adhering powder is removed by the action of high-speed airflow have not necessarily been clarified. In many cases, high-speed airflow is applied.

This is because the adhesion force of powder to the surface of equipment, etc. varies greatly depending on the particle size, composition, moisture content, humidity, shape of the solid surface, etc. of the powder, and is uniform across all types of powder. This is because it cannot be determined.

(Problems to be Solved by the Invention) By the way, the inventors of the present invention have conducted repeated studies with the aim of saving energy when removing adhering powder by the action of high-speed airflow, and found that The lower limit of the wind speed necessary to apply a high-speed airflow to separate the particles (hereinafter referred to as "re-entrainment wind speed" in this specification) is of course related to the absolute value of the airflow speed, but In addition to this, we discovered that there is a significant relationship with the acceleration (α) of airflow, which was previously not considered.

In other words, when a wind speed with a positive acceleration is applied to the adhered powder, the lower limit of the re-entrainment wind speed becomes more rapid than when a constant wind speed that does not substantially include an acceleration component is applied. On the other hand, we have found that when this acceleration exceeds a certain level, the lower limit value of the re-entrainment wind speed hardly decreases even if the acceleration is increased further.

Based on such knowledge, the present inventor has developed an energy-saving powder removal method that can remove adhered powder from a solid surface with a small wind speed by applying a wind speed with a predetermined acceleration, or The present invention has led to the development of a method for transporting powder that is less likely to adhere to the inner walls of powder transport pipes.

That is, an object of the present invention is to provide a powder removal method that can efficiently separate and remove powder adhering to a solid surface.

Another object of the present invention is to provide a method for transporting powder that can transport powder while reducing adhesion to solid surfaces as much as possible.

(Means and operations for solving the problem) The feature of the method of the present invention for realizing the above-mentioned object is that the adhering powder on the solid surface is detached and scattered (re-splattered) by the action of ventilation in which the wind speed increases and changes. A method in which each acceleration α of the draft is such that the wind speed increases at a constant rate. A certain acceleration α is determined based on a characteristic line determined in advance regarding the relative relationship between the adhering powder and the lower limit value uc of the wind speed when the adhering powder is re-dispersed by this ventilation. , the wind speed lower limit value U when setting t. 5t is determined, and ventilation whose wind speed changes at the set acceleration αeat above and below this lower limit value is applied to the solid surface.

Another feature of the method of the present invention is a ventilation method in which powder is transported within a powder transport pipe by ventilation whose wind speed changes, and the action of the ventilation whose wind speed increases and changes causes the powder to flow through the inner wall of the powder transport pipe. Each acceleration α of the ventilation that causes the wind speed to increase at a constant rate when the powder adhering to the air is re-dispersed. A certain acceleration α is determined based on a characteristic line determined in advance regarding the relative relationship between the adhering powder and the lower limit value uc of the wind speed when the adhering powder is re-dispersed by this ventilation. , t is set, and the set acceleration α is applied to the ventilation that fluctuates above and below this lower limit value.

, , is applied intermittently, and the powder is transported by this ventilation.

In the above method, the lower limit value uc of wind speed when applying ventilation having an acceleration α6 is set to zero acceleration α. Divided by the lower limit value u0 of the wind speed when applying ventilation of (u, /u,) (acceleration α. (u o / u o) = 1), the acceleration α. As will be explained in detail below, this relationship shows an approximate tendency in the case of powders with an acceleration of 0 to 0.15 m/s.
The above (u c / u o) decreases rapidly within a range of
On the other hand, when the acceleration exceeds 0.5 m/s,
(u c/u a) decreases extremely slowly.

Therefore, when achieving the above-mentioned purpose such as removing adhering powder, it is rather inappropriate to change the wind speed due to too large an acceleration in order to save energy. When changing 0.5 m/s”
In many cases, it is appropriate to select ventilation having an acceleration within a range where the change in (u e/u o) is about 0.15 or less. More specifically, the acceleration α of the ventilation. 0.17
~2 m/s", preferably 0.5-1.25 m/s',
Optimally, it is often desirable to set the speed within the range of 0.7 to 1.0 m/s.

The powder to be subjected to the method of the present invention is not particularly limited in terms of composition, particle shape, etc.;
Preferably, the target is about 30 μI or less.

In order to give acceleration to the ventilation as described above, there are no particular limitations, but for example, high-pressure gas may be jetted out through a valve for a certain period of time, or the rotation speed of a fan or blower serving as an air source may be increased for a certain period of time. There are ways to raise it internally.

In addition, in the above method, when changing the wind speed near the upper and lower limits of the lower limit when powder is re-dispersed, it is not necessarily necessary to change the wind speed from below the lower limit of the wind speed, but for wind speeds exceeding the lower limit, , it is necessary to carry out the process over a necessary and sufficient range for re-scattering of the powder.

The reason why the accelerated ventilation of the present invention allows efficient removal of adhering powder, etc. is considered to be as follows.

In other words, the phenomenon in which the re-dispersion wind speed of adhering powder changes due to accelerated ventilation can be explained by the effect of changes in airflow shear force,
Considering the effect of airflow turbulence and the effect of acceleration of the force acting on aggregated particles separately, first, changes in airflow shear force are caused by changes in pressure due to changes in airflow acceleration. /s, 20m/s, 30m/s
The pressure difference ΔP at the wind speed was measured and the shear stress tw was calculated. As can be seen from FIG.
In the acceleration range of ”, the change in shear stress is extremely small;
Therefore, the influence of airflow shear force can be virtually ignored.

Next, regarding the influence of airflow turbulence, it is known that the turbulence of particles tends to become smaller in accelerated airflow, so we do not think that this will reduce the re-dispersion wind speed of adhering powder. It will be done.

Furthermore, considering the influence of acceleration of the force acting on the aggregated particles, the general equation of motion of the particles in the granules is given by the following equation.

Here, the left side is the force necessary to accelerate the particle, the first term on the right side is the viscous drag force, the second term is the force applied to the particle due to acceleration, and the third term is the force (reaction force, The fourth term is a force related to the history of changes in fluid flow, and F is an external force.

When the agglomerated particle size is small, as is the case with the method of the present invention, the second and third terms can be ignored, and F is the interparticle adhesion force, so the separation force that acts on the particles is The first and second paragraphs above apply.

Further, considering the scattering model of the aggregated particles of the adhered powder as shown in Fig. 9, and assuming that the aggregated particles 2o are partially buried in the surface of the powder layer 21, the velocity gradient of the airflow near the wall surface will be as shown in the figure. (Since it can be considered to be constant, the bending stress is dominant in the separation force due to the first term and the second term above that acts on the aggregated particles, and the bending stress due to the viscous drag force in the first term is . The bending stress due to the binomial particle flow history is given by:

Since the adhesion force between particles is constant regardless of airflow,
Since the scattering limit bending stress of accelerated flow is equal to the scattering limit bending stress of steady flow, τ, ti4-4-1.257D -g (ρα/πu
) I/2 u e@/4=U,,. 7/4 is led.

When this D 111 is calculated by the least squares method, it becomes a value considerably larger than the actual aggregate particle diameter Dag, so
Introducing the experimental constant k and applying it to the experimental results, we get the following diagram:
Approximately corresponds to the experimental results.

This shows that even if there are differences in the state of adhesion of the powder to the solid surface or the type of powder, it can be explained using the scattering model shown in FIG. 9.

(Example) The method of the present invention will be explained below based on examples.

Example 1 The method of the present invention was carried out using the apparatus shown in FIGS. 2 to 4.
A characteristic line showing the relative relationship between each acceleration of ventilation at which the wind speed increases at a constant rate and the lower limit of the wind speed at which the adhered powder is re-dispersed by this ventilation was determined.

In FIG. 2, reference numeral 1 designates a long cylindrical test tube with a rectangular cross section in a concave wall filled with powder shown enlarged in FIG. An air flow supply pipe 2 having a flow rate regulating valve 5 which can adjust the flow rate by open circuit state control is connected through the air supply pipe 2, and the upstream side of this supply pipe 2 is connected to a compressor 7 via a buffer container 6. ing. Further, the state of air flow in the supply pipe 2 downstream of the buffer container 6 is detected by a mass flow meter 8 and sent to a recorder 9.

The above flow rate adjustment valve uses a DC motor (Oriental Motor Co., Ltd. 2GN1
00, 2GN10XK) was installed so that it could be used and changed.

Reference numeral 10 denotes a microscope (Model SH2 manufactured by Olympus) provided to observe the internal state of the test tube 1.

A powder detection device 11 placed in an electrically shielding box 12 is disposed downstream of the test tube 1, and an ammeter 13 electrically detects the scattering of powder from the test tube 1. , to send a signal to the recorder 9. The details of this powder detection device 11 are shown in FIG. 4, and will be described later.

The powder that has passed through the powder detection device 11 is exhausted to the outside through a filter 14, a buffer container 15, and a pump 16.

The details of the test tube 1 are shown in Figure 3, and are 3mm long x 10mm wide.
A tube 10 with a length of 400 mm and a passage with a rectangular cross section of mm
1, a filling cell 102 having a recess 103 with a depth of 1 mm and a length of 20 mm in the longitudinal direction centered at a position approximately 75+++ m from the downstream end is assembled so as to be flush with the inner wall of the pipe. There is.

Next, a description will be given of the powder detection device, which is shown in detail in FIG.

The powder detection device shown in this figure has a copper coiled tube 30 (with an inner diameter of 2.5 mm) connected to the downstream connecting tube I7 from the test tube 101.
6 mm in length and approximately 70 mm in length), and the powder particles scattered and discharged are provided so as to generate a pulsed current by contact charging when they come into contact with this inner wall. It has been experimentally confirmed that the current generated at this time is approximately proportional to the amount of scattered powder, and therefore, the amount of scattered powder can be calculated by detecting this generated current.

In the device shown in this figure, suction was performed from the downstream side at approximately 60 m/s to prevent powder from adhering to the inside of the coiled tube. Also 3
2.33 is an insulator that supports the coiled tube.

The following tests were conducted using the apparatus shown in Figures 2 to 4 above.

As a powder, 10 types of spherical fly ash dried at 110°C for 12 hours were allowed to fall naturally into the above-mentioned filling cell using a standard sieve (150 mesh for fly ash), and the filling rate of the powder was determined in a centrifugal field. After adjusting the temperature, the powder was cut using a thin-bladed stainless steel knife so that the powder layer surface was flush with the channel wall surface, and further dried at 110° C. for 12 hours.

Next, this filled cell was installed in a test tube, and the air flow was raised from the state of average U=O at a constant acceleration α. Thereafter, particles scattered by the air flow were electrically detected using a powder detection device, and the results were recorded on a recorder.

The above tests were conducted while changing the air flow acceleration. However, as a test corresponding to acceleration α=0, the presence or absence of scattering in a steady state was confirmed by increasing the flow velocity by 1 m/s every 5 minutes. The acceleration when increasing the flow velocity was set to approximately 0.02 m/s'' to reduce the influence of changes in air flow on scattering.

Figure 5 is a diagram showing the current generated by the scattered particles obtained above and the change over time in the flow velocity. It shows changes in current I.

From this figure, if the velocity of the airflow is increased by a constant acceleration,
It can be seen that the current begins to be generated from a certain region, and when it exceeds the average flow velocity at this time (the wind speed at which re-scattering starts), the current gradually increases.

In addition, it is known that the generated current and the flux of particles scattered from the powder bed surface (unit time, amount of scattered particles on the surface of the powder bed) approximately correspond, so as the flow rate increases, the scattered flux increases. I understand.

The figure also shows the results of two tests with different airflow accelerations (a =
0.22 m/s", a = 0.03 m/s"), but as the acceleration increases, the re-scattering start wind speed u
It can also be seen that c decreases.

Further, FIG. 6 shows the peak of the waveform of the generated current value with respect to the average wind speed i, and it can be seen that even if the flow speed is the same, the larger the airflow acceleration is, the more the scattered flux will be.

Having summarized the above, the relationship between each acceleration and the re-entrainment start speed uc is shown in FIG.

Also, the re-scattered wind speed U when the acceleration a=O. and each acceleration α
(u e/u
FIG. 7 shows the relationship between a) and each acceleration, and the relationship between the results based on the above-mentioned scattering model.

From the above results, in order to remove powder attached to the solid surface, the ventilation acceleration α is required. 0.17-2 m/s", preferably 0.5-1.25 m/s", optimally 0.7-1
．． It has been confirmed that it is desirable to set it within the range of 0+n/s.

Example 2 The relationship between the redispersion wind speed and each acceleration was determined in the same manner as in Example 1 except that 10 types of fly ash (φ: o, 30) were used as the powder, and the results are shown in Figure 7. .

Example 3 Powdered talc (φ = 0.15) was used, and a standard sieve (
The relationship between the re-encrusted wind speed and each acceleration was determined in the same manner as in Example 1, except that the talc mesh was used (100 mesh for talc), and the results are shown in FIG.

Example 4 A stainless steel plate with 10 g of titanium oxide adhered to the surface was prepared as a solid sample piece, and an increasing wind speed of 15 m/s was applied to the plate at an acceleration of 1.0 m/s2.
After increasing the temperature to s and spraying, the state of removal was observed using a microscope.

As a result, most of the titanium oxide deposited on the surface of the stainless steel plate was scattered and removed.

Comparative Example 1 The same sample piece as in Example 4 was blown with a wind speed increasing at an acceleration of 0.02 m/s to the same average air flow rate as in Example 4, but the adhering powder was not removed. There wasn't.

Example 5 A transportation vibrator made of stainless steel was made of powdered titanium oxide, and the wind speed inside the transportation vibrator was in the range of 12 m/s to 915 m/g, and the airflow acceleration was 1. When the titanium oxide was air-transported by changing the wind speed so that the air velocity was 0+Il/s, there was almost no adhesion inside the vibrator.

Comparative Example 2 In the same manner as in Example 5, four air transport was carried out at a constant wind speed of 15 m/s, and the amount of adhesion inside the vibrator increased immediately.

(Effects of the Invention) According to the method of the present invention, powder adhering to a solid surface can be efficiently separated and removed by ventilation at a relatively low wind speed with acceleration, which contributes to energy saving. effective.

Furthermore, according to the conveying method of the present invention, it is possible to convey the powder in a state where there is little adhesion to the solid surface, or even if it does adhere, it can be efficiently re-splattered, thereby preventing clogging of the powder conveying pipe. This has the effect of reducing problems such as.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship characteristic line between each airflow acceleration and re-entrainment wind speed in Example 1 obtained by applying the method of the present invention, and Figure 2 is a diagram showing the relationship between each acceleration of powder and re-entrainment wind speed. 3(a) and 3(b) are enlarged views of the same test tube portion, and FIG. 4 is a diagram showing details of the powder detection device. FIG. 5 is a diagram showing the relationship between the current detected by the powder detection device and the average wind speed, and FIG. 6 is a diagram showing the relationship between the current detected by the powder detection device and the average wind speed. FIG. 7 is a diagram showing the relationship between (u c/u o) and each acceleration in Examples 1 to 3. FIG. 8 is a characteristic diagram showing the relationship between each airflow acceleration and airflow shear stress, and FIG. 9 is a diagram showing a model for analyzing the bending stress due to the airflow acting on the adhered powder. 4 others

Claims (1)

[Claims] 1. A method for detaching and scattering adhering powder from a solid surface by the action of ventilation in which the wind speed increases and changes, the method comprising: each acceleration of the ventilation in which the wind speed increases at a constant rate; Based on a characteristic line determined in advance for the relative relationship with the lower limit of wind speed when the powder is desorbed and scattered, the lower limit of wind speed when a certain acceleration is set is determined, and the A method for removing adhered powder characterized by applying ventilation whose wind speed changes according to a set acceleration to the solid surface. 2. The method according to claim 1, characterized in that an increasing change in wind speed is repeatedly given according to a set acceleration. 3. A ventilation method in which powder is transported within a powder transport pipe using ventilation whose wind speed fluctuates, and the powder that adheres to the inner wall of the powder transport pipe is detached and scattered due to the action of the ventilation whose wind speed increases and changes. In this case, a certain acceleration is determined based on a characteristic line determined in advance regarding the relative relationship between each acceleration of ventilation in which the wind speed increases at a constant rate and the lower limit of wind speed when the adhered powder is detached and scattered by this ventilation. , the lower limit value of the wind speed is determined, the set acceleration is intermittently applied to the ventilation that fluctuates around the upper and lower limits of the lower limit value, and the powder is transported by the ventilation. Transportation method. 4. The method according to any one of claims 1 to 3, wherein the set acceleration for increasing the wind speed is in the range of 0.17 to 2 m/s^2.