JP2001318200A - Electron beam irradiator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of energy increased due to the extension of the travel distance of an electron beam in the air caused by the great distance between an irradiation window and a trough by shortening the travel distance of the electron beam in the air though it is necessary to widen the distance between the trough and the irradiation window in a section where the electron beam is generated in anticipation of the irregularly high amplitude of a vibration trough during a stopping or actuating action in an electron beam irradiator where a vibrating conveyer is used for a conveying means. SOLUTION: The height of the trough of the vibrating conveyer can be adjusted by setting up an elevation retainer on the vibrating conveyer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam irradiation apparatus for irradiating an electron beam while rotating a granular material.
In particular, the present invention relates to a device that can solve the problem of irregular large amplitude generated in the transport mechanism at the time of stopping and starting.

An electron beam irradiator generates thermoelectrons in a vacuum, accelerates the electrons, takes them out into the atmosphere through a window foil of an irradiation window, and irradiates an object to be processed. Although the window foil is a metal foil of Ti or Al, it is necessary to maintain a vacuum in the electron beam generation acceleration part. A strong tension acts on the lower surface of the window foil because atmospheric pressure is applied. The electron beam penetrates the window foil, at which time it loses kinetic energy. Since the window foil is heated, it is cooled by means such as water cooling or air cooling.

[0003] Applications of electron beam irradiation are diverse. Irradiates wire coating and rubber to promote polymer crosslinking. Irradiate printed materials and coatings to cure. Irradiate and sterilize medical device components.
We have a track record of polymer cross-linking, coating curing, and sterilization of medical components. The present invention proposes a contrivance for a transport system for electron beam processing of powder and granules. The prior art will be described later, but it is difficult to irradiate only the surface of the granular material with an electron beam, and it has not been practiced on an industrial scale. In order to apply an electron beam to all surfaces of the granule, the granule must be rotated. When the granular material is transported by the vibrating conveyor, the granular material can be rotated. The present invention has a problem of abnormal amplitude at the time of stopping and at the time of starting when the granular material is conveyed by the vibrating conveyor.

[0004]

2. Description of the Related Art An electron beam irradiation apparatus mainly treats a tangible solid such as an electric wire or a printed material as an object to be processed. A promising application of the electron beam irradiation device is powder processing. Granules are amorphous solids that are different from tangible solids. The transport system also needs to be different from conventional tangible solids. There are various types of powders such as grains, plastic pellets, foodstuffs, drugs, and fertilizers.

[0005] Although there is a concept of treating particles with an electron beam, there is almost no object implemented as described above. Although there is no track record, some proposals have been made for electron beam irradiation of grains and the like. In each case, the granular material is rolled and rotated in order to irradiate only the surface of the granular material with an electron beam. The granular material is rotated by wind or vibration.

(1) Japanese Patent Application Laid-Open No. H10-215765 discloses a method of sterilizing grain and a grain rotating device used for the same. A tray mounting table is placed on a vibrator and a shaker, and an electron beam irradiation device is provided thereon. We propose a grain sterilizer. Put cereals such as brown rice, wheat, red beans and soybeans in a tray. The vibrator vibrates in the vertical direction (z direction) and the shaker moves in the horizontal direction (xy
Direction).

(2) Japanese Patent Application No. 10-142873 "Electron beam irradiation apparatus" is an electron beam irradiation apparatus in which a grain is placed on a water-cooled vibrating conveyor having a flat surface and a weak electron beam is applied while being carried by vibration. Has been proposed.

(3) Japanese Patent Application Laid-Open No. 1-192362 discloses a device for radiation treatment of powder, such as flour and spices, for conveying and suspending powdered and granular foods and sterilizing it with radiation.

(4) Japanese Patent Application Laid-Open No. 8-52201 "Electron Beam Sterilizer for Powder" is provided with a slightly inclined pipe section in a huge processing chamber having a thick concrete wall, and is axially parallel to the middle of the pipe section. A perforated plate is provided, air is blown in from underneath, a powdered object is charged from above the perforated plate, the object is lifted by air, and the object is conveyed obliquely downward and an electron beam is emitted from the side. Bathe.

(5) Japanese Patent Application No. 11-61327, entitled "Electron Beam Irradiation Apparatus, Electron Beam Irradiation Method and Object to Be Treated", has a horizontally extending perforated plate at the front end and at the bottom and top of a horizontal transfer space. Provide a vertical perforated plate, blow up gas from the lower perforated plate,
The gas is transported by blowing down the gas from the upper perforated plate and blowing the gas from the front perforated plate. It is a skillful method of irradiating an electron beam while transporting gas.

(6) In Japanese Patent Application No. 11-14312, "Electron Beam Irradiation Apparatus and Granule Sterilization Method", grains are conveyed by a vibrating conveyor having a large number of projections and depressions. The grains of the grain are turned over and flipped by the projections and irregularities.
Since all surfaces are likely to face upward and the entire surface is thinly irradiated with electron beams, the surfaces can be sterilized.

[0012]

When an electron beam is irradiated while conveying a granular material by a vibrating conveyor, the granular material is rotated, and the entire surface can be irradiated with the electron beam. The conventional examples (2) and (6) use a vibrating conveyor. The vibrating conveyor itself is a well-known transport mechanism. The object moves in one direction by slightly vibrating the plate surface (trough) up and down and back and forth. Some vibratory conveyors use inclined troughs. Some vibratory conveyors use horizontal troughs. Even in the horizontal direction, it can be selectively sent in one direction due to the anisotropy of vibration. The trough is moved in a direction of, for example, 45 degrees by combining the up-down movement (y-direction movement) and the back-and-forth movement (x-direction movement). Then, the workpiece on the trough advances in that direction. There is a moment when the whole surface is directed in the direction from which the electron beam comes because it advances while rolling and jumping, not just progressive. Therefore, the entire surface of the powder can be exposed to the electron beam.

It is assumed that the vertical amplitude of the vibration conveyor is D. The problem is that the amplitude at the time of stop and the amplitude at the time of start-up are larger than the amplitude at the time of steady operation. The term “stop” refers to a transition from when the power supply to the vibration conveyor motor is turned off to when the vibration stops. It means the time of change from movement to stillness. It does not mean when you are still. It should be noted that such usage will be continued thereafter. It may be referred to as a stop operation, but simply referred to as a stop operation. When stopped, the amplitude of the vibrating conveyor increases. For example, the vertical amplitude of the vibration conveyor during steady operation is 3 mm to 4 mm. When stopped by the same vibration conveyor, the amplitude becomes as large as 30 to 40 mm. At startup, the amplitude is as large as about 20 mm to 30 mm. Amplitude abnormalities at the time of stop and start are common in vibrating conveyors.

Although the cause is not clear, it is thought to be due to resonance. The AC motor of the vibration conveyor is rotated by a commercial power supply of 60 Hz and 50 Hz. In the case of a two-pole motor, the steady speed f ₀ is 60 Hz and 50 Hz, and in the case of a four-pole motor, the steady speed f ₀ is 30 Hz and 25 Hz. Since the vibration is obtained by eccentrically rotating the weight, the vibration frequency f of the vibration conveyor is equal to the number of rotations of the motor.

The trough is elastically supported by a spring. If the trough mass is M and the spring constant is K, the natural frequency F is given by (1 / 2π) (K / M) ^1/2 . The trough is forcibly vibrated by rotating the weight eccentrically by a motor. If the natural frequency F _c is lower than the rotational speed of the steady state, at the time of stop since frequency drops to zero from the steady value f _0, there is a case where although f is momentarily becomes f = F _c. At that time, the amplitude becomes abnormally large. Since startup also slide into increased gradually f starting from same a f = 0 becomes a moment f = F _c, the abnormally large amplitude at that time. For this reason, it is estimated that the amplitude will abnormally increase at the time of stopping and starting.

The occurrence of such abnormal amplitude is stopped,
It's just a moment of startup. For example, start time is 5
Seconds, steady operation 1 day to 1 week, stop time 15 seconds to 2
Time distribution such as 0 seconds. It is considered that the abnormal amplitude is more remarkable at the time of stopping than at the time of starting, probably because the time required for stopping is longer.

The trough of the vibrating conveyor and the irradiation window of the electron beam irradiation device must not be in contact with each other. Don't let them approach.
If they are approached, the window foil may be broken by hitting the trough and the object to be processed due to abnormal vibration at the time of stop. The window foil is a thin and weak metal foil, is heated by a pressure difference of 1 atm (0.1 MPa) above and below, and is in a very weak state. It is extremely dangerous that a trough hits this. Taking into account abnormal vibrations, the lower end of the irradiation window and the trough must be separated by 30 to 40 mm. In the irradiation window, the window foil is fixed by holding it with a frame. Since the thickness of the window foil holding frame is also required, the gap G between the window foil and the trough becomes as large as 50 mm.

An electron beam does not lose energy when traveling in a vacuum, but when it goes out into the atmosphere, the gas (nitrogen,
Oxygen) and quickly loses energy.
It is better that the range to the object to be processed in the air is as short as possible. In the case of the above vibrating conveyor, the range of the electron beam in the atmosphere is about 50 mm. Predetermined energy is required for the treatment of the granular material. The electron beam is accelerated to a speed that is the sum of the energy lost in the atmosphere and the loss in the window foil.

It is wasteful that an electron beam has a range of 50 mm in the atmosphere. There are more subtle problems besides simply wasting acceleration energy. There is a problem that the loss in the atmosphere differs depending on the acceleration energy (electron kinetic energy). Fast electrons have less loss because they interact with gas atoms for a short time. The electron beam accelerated to 1 MeV has almost no loss in the air range of about 50 mm. 300 keV is quite slow, so the loss is large.
In the case of an electron beam having a low energy of 120 keV, there is also a passage loss in the window foil, so that if the range in air is as large as 50 mm, it may not reach the target. Although the acceleration energy varies depending on the type of treatment, in the case of powder and granular material treatment, it is often desired to irradiate only the surface with an electron beam, so the energy is low. At low energies, atmospheric losses are significant. It is inconvenient that the low energy electron beam may be absorbed and disappear by the object to be processed.
It is troublesome that low-energy electron beams are absorbed by the atmosphere and become ineffective.

It is desirable that the object to be treated (granules) be encountered immediately after leaving the window foil. It is a first object of the present invention to provide an electron beam irradiation apparatus in which the distance between the window foil and the vibration conveyor is shortened to reduce the loss of electron beam energy in the atmosphere.
Is the purpose. It is a second object of the present invention to provide an electron beam irradiation apparatus capable of stably irradiating a granular material with a low energy electron beam.

[0021]

According to the present invention, there is provided an electron beam irradiation apparatus comprising: an electron beam generator for generating an electron beam; a vibrating conveyor for transporting a powdery material; including. The trough of the vibrating conveyor can be held at an optimum height by the lifting and lowering mechanism.

During normal operation, the trough is set high.
By lowering the trough at the time of startup, loss of electron energy can be prevented, and damage to the window foil, the trough, and the like can be avoided.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electron beam irradiation apparatus of the present invention is characterized in that the trough height of a vibrating conveyor can be freely adjusted. Therefore, the electron beam irradiation apparatus of the present invention
It can be said that the device includes an electron beam generator, a vibration conveyor, and a lifting and lowering mechanism.

The electron beam generator includes a hot filament for emitting thermoelectrons and an accelerating electrode for accelerating electrons.
There are two types of electron beam irradiators regarding the electron beam generator, one of which is a scanning type and the other is an area type. The scanning type scans a thin electron beam with an alternating magnetic field. The area type (non-scanning type) is a type in which a large-area electron beam is generated from a filament having a large effective area and accelerated by one stage. In each case, thermoelectrons are generated in a vacuum and accelerated by an appropriate voltage. The present invention can be similarly applied to a scanning type and a non-scanning type.

The terminal opening of the electron beam generator is an irradiation window, and a window foil is stretched here. The window foil is cooled by cooling water and cooling air. The outside of the irradiation window is a portion for irradiating an object to be processed with an electron beam at atmospheric pressure. The entire irradiating section is surrounded by a housing made of a thick metal wall for preventing radiation. X-rays are generated by electron beam irradiation.
Enclose it in a housing so that the wires do not leak outside.

Since the object to be processed moves in the housing, a transport mechanism is required. The transport mechanism transports the workpiece between the entrance, the irradiation window, and the exit. When the object to be processed is a tangible solid, an endless orbiting conveyor is used. However, since the present invention is intended for granular materials, a static endless orbiting conveyor is not suitable. Since it is necessary to expose the entire surface to electron beams, a vibrating conveyor is used. The vibrating conveyor can advance an object on the conveyor by synchronizing the vertical vibration and the front-back vibration. Speed can also be adjusted by tilting the conveyor. Even if the conveyor is horizontal, it can be fed in a certain direction. Instead of being sent statically, it is flipped and moved forward, so that the particles rotate and the electron beam hits all surfaces.

The most characteristic feature of the present invention is a lifting and lowering holding mechanism for holding the vibrating conveyor so as to be able to move up and down. Thereby, the distance between the window foil and the conveyor trough can be adjusted to an optimum gap. At the time of stop and start, resonance occurs, and the amplitude of the conveyor becomes abnormally large. Therefore, at the time of stopping and starting, the vibration conveyor is lowered by the lifting and lowering mechanism, and at the time of steady operation, the vibration conveyor is raised by the lifting and lowering mechanism.

At the time of stopping and starting, the gap between the irradiation window frame and the trough is set to 30 mm to 50 mm. Because of the wide gap, even when resonated, the trough and the object do not hit the frame or window foil of the irradiation window.

In the steady state, the vibrating conveyor trough is raised, and the gap between the trough and the irradiation window is reduced to about 10 mm to 20 mm. In the case of steady vibration, the amplitude is 3 to 4 mm.
If the opening is 0 mm, the trough does not hit the irradiation window. Since the range in the air after exiting the window foil is shortened, electron beam energy loss is reduced. Efficiency is improved because energy loss is reduced. The feature of the present invention is to change the height of the trough between the stop / start and the steady state. A hydraulic cylinder such as an air cylinder or a hydraulic cylinder can be used as the lifting and lowering mechanism. In addition, a mechanical elevating device combining a motor and a speed reducer (worm, worm gear) may be used. An elevating device combining a spring and a magnet may be used. The type and mechanism of the lifting and lowering holding mechanism are arbitrary.

[0030]

FIG. 1 shows an electron beam irradiation apparatus according to an embodiment of the present invention. The electron beam generator includes a filament 1, a shield 2, a vacuum chamber 3, and the like. Although not shown, there is an acceleration power supply, a filament power supply, and the like. The filament is biased to a negative voltage, a current flows through the filament to generate thermoelectrons, and an electron beam is accelerated between the filament and the electrode. The accelerated electrons become parallel downward beams (electron beams) EB. The lower opening of the vacuum chamber 3 is the irradiation window 4. A window foil 5 is attached to the irradiation window 4. A vibration conveyor as a transport mechanism is provided directly below the electron beam generator.

A trough 6 is provided above the vibrating conveyor, and is vibrated diagonally forward by a vibration source 7.
In this example, as shown by an arrow 14, the amplitude is set to be 45 degrees diagonally forward. The trough 6 is supported by several feet 11. A spring 8 is provided in the middle of the foot 11. The spring 8 is an essential member for enabling the trough to vibrate. The spring 8 allows the trough to move up and down and back and forth. A vibration source 7 provides vibration power. The vibration source 7 only needs to apply vibration in an oblique direction, and may use a piezoelectric phenomenon. Here, a vibration source that turns an eccentric weight by a motor is used. Vibrating conveyors are known per se, and a number of vibration sources are also known. The trough of the conveyor may be inclined or, as such, may be horizontal. Tilt forward can accelerate, lean backward can slow down. Even if the trough is horizontal, the granular material (object) can be moved in a certain direction.

An elevating device 9 is provided in the middle of the foot 11.
The foot 11 can be extended and contracted by the lifting device 9. That is, the trough 6 goes up and down. There is an elevating device 9 for adjusting the height of the trough. The gist of the present invention lies in that the height of the vibrating conveyor is controlled by the lifting device 9. At the time of stop (at the time of transient movement toward stop) and at the time of start-up, the trough is lowered because the amplitude of the vibration conveyor abnormally increases. When the amplitude is stabilized during the steady motion, the trough is raised to bring the trough closer to the irradiation window. Since the amplitude is only 3 mm to 4 mm in a stable steady state, the gap between the trough and the irradiation window can be set to about 10 mm.

The lifting and lowering device 9 is, for example, an air cylinder, which moves the piston up and down by sending compressed air. A long cylinder is reminded of an air cylinder, which is a case where a long stroke is required. Here, the lifting stroke is 50m
It is not necessary to use a long cylinder because m is sufficient. Here, a square air cylinder of about 100 mm × 100 mm × 100 mm is used. There is a piston that can move up and down inside the box-shaped cylinder. If air is sent into one of the upper space and the lower space of the piston and the air is removed from the other space, the piston can be moved up and down freely. The lifting device 9 is provided with compressed air pipes 12 and 13 for introducing and discharging compressed air into the upper space and the lower space. The piston can be moved up and down by introducing compressed air from one of the pipes and removing it from the other.

In the steady state, the trough is raised upward to reduce the distance between the trough and the irradiation window as shown in FIG. Thereby, the electron beam is hardly scattered by the air. At the time of the stop operation and the start-up, the trough is lowered as shown in FIG. 2 so that the vibration conveyor and the electron beam generator do not come into contact with each other.

[0035]

According to the present invention, since the vibrating conveyor is used, the electron beam can be irradiated while the granular material is sowed and rolled. Since the electron beam can be uniformly applied only to the surface of the granular material, electron beam irradiation can be used for sterilization of granular foods and the like. In a vibration conveyor, when the vibration source stops (when stopped) and when it starts moving (when started), the amplitude becomes abnormally large.
In the present invention, the height of the trough of the vibrating conveyor can be freely adjusted because of the lifting mechanism. At the time of stopping and starting with a large amplitude, the trough is lowered to widen the gap between the trough and the irradiation window. During steady motion with small amplitude, the trough is raised to narrow the gap between the irradiation window and the trough. Since the distance (range) in which the electron beam flies in the air is shortened, energy loss is reduced. Since there is no need to accelerate further by the energy loss, the acceleration energy can be reduced. The power for electron beam irradiation can be saved and the efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an electron beam irradiation apparatus according to an embodiment of the present invention when a trough is at a raised position.

FIG. 2 is a schematic sectional view of the electron beam irradiation apparatus according to the embodiment of the present invention when the trough is at a lowered position.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Filament 2 Shield 3 Vacuum chamber 4 Irradiation window 5 Window foil 6 Trough 7 Vibration source 8 Spring 9 Lifting device 10 Base plate 11 Feet 12 Compressed air piping 13 Compressed air piping 14 Vibration direction B Particles EB Electron beam

Claims (1)

[Claims] 1. An electron beam irradiation apparatus comprising: an electron beam generator for generating an electron beam; a vibrating conveyor for transporting powdery and granular materials; and a lifting and lowering holding device for holding the vibrating conveyor up and down.