JP3915625B2 - Structure of nitrogen gas chamber of electron beam irradiation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a nitrogen gas chamber in an electron beam irradiation apparatus. An electron beam irradiator uses a filament heated in vacuum to generate thermoelectrons, accelerate electrons with an accelerating tube to form a high-speed electron beam, and then take it out into the atmosphere through the window foil of the irradiation window. This is a device that performs treatments such as polymer crosslinking, coating film curing, and sterilization by irradiating an electron beam. The electron beam irradiation apparatus includes a high-voltage power supply, an acceleration tube, a filament, an irradiation window, a transport mechanism, a metal casing, a cooling mechanism, and the like.
[0002]
When the acceleration energy is as high as 5 MeV to 500 keV, a tall and large scanning type is used. It is a scanning type because it scans one beam back and forth. In order to scan the beam, a scanning coil is provided at the end of the accelerating tube, followed by a scanning tube extending in a triangular shape. A thin electron beam accelerated to high energy is scanned vertically and horizontally to irradiate the workpiece.
[0003]
When the acceleration energy is as low as several tens keV to 500 keV, a non-scanning type is used. In the non-scanning type, a large number of parallel filaments are connected in parallel to the electrode rods, and an electron beam is emitted from the parallel filaments in a direction perpendicular to the surface. The effective area of the filament region is widened, and it is accelerated as it is toward the irradiation window. Since an electron flow of a large area is generated from the beginning, an electron beam is irradiated at once to a wide area of the object to be processed without scanning. Since the energy is low, the beam is likely to spread under the influence of Coulomb repulsion, and it is easy to obtain a uniform electron beam density.
[0004]
The accelerating power source converts a commercial power source into an appropriate voltage by a transformer, and converts the commercial power source into a desired high voltage by a voltage multiplying circuit in which a large number of capacitors and rectifiers are combined. The capacitors and rectifiers that handle these high voltages are mounted on a high voltage base and are insulated from the ground side. In the case of a scanning type with a high voltage, the power supply circuit is complicated and has a large volume. In the case of a non-scanning type with a low voltage, the power supply circuit is further simplified.
[0005]
The irradiation window is a window for partitioning the vacuum region with the filament and the atmospheric pressure region where the workpiece is present, and Ti and Al window foils are stretched. The irradiation window is attached to a large metal casing. X-rays are emitted when an electron beam hits the workpiece. In order to shield X-rays, a thick metal casing covers the transport mechanism, the object to be processed, and the irradiation window. A transport mechanism such as an endless circular conveyor travels in the metal casing, and carries the object to be processed from the entrance—immediately below the irradiation window (processing position) —outlet. It has also been devised to meander strongly up and down so that X-rays do not leak.
[0006]
[Prior art]
The problem in the present invention is the irradiated portion of the object to be processed directly under the irradiation window. X-rays are generated when an electron beam hits the workpiece. Cover the entire irradiated part and the entire transport mechanism with a heavy metal casing so that it does not leak outside. When X-rays hit oxygen in the air, the oxygen becomes ozone. Ozone has a unique odor. Depending on the type of object to be treated, it may not be desirable to have an ozone odor. In that case, air is replaced with nitrogen so that ozone is not generated. An inert gas such as nitrogen or argon is allowed to flow from the downstream side to the upstream side of the transport mechanism inside the housing. Then, oxygen is expelled and the atmosphere becomes inert gas, so ozone is not generated.
[0007]
Since filling the entire interior of the housing with nitrogen gas is uneconomical, only the area around the irradiation section that irradiates the object to be processed with an electron beam is surrounded by a narrow container. Surround it with a container and blow nitrogen gas only there. Even if an electron beam hits the object to be processed inside the container and X-rays are generated, there is no oxygen, so ozone cannot be generated. Enclosing with a container is not a sealed container. Since the object to be processed must move forward and forward, an inlet and outlet for the object to be processed are necessary. Although it cannot be completely sealed, it is a container that can primarily hold nitrogen gas at a high concentration. It will be called a nitrogen gas chamber. The present invention relates to a nitrogen gas chamber that provides space for confinement of the nitrogen gas.
[0008]
The requirements for the nitrogen gas chamber are that it is directly under the irradiation window, that the object to be processed passes through it, and that it is substantially blocked from most of the space inside the housing. FIG. 1 shows the structure of a conventional nitrogen gas chamber. This shows a non-scanning type (area type) electron beam irradiation apparatus, but the same applies to the scanning type.
[0009]
The cylindrical vacuum chamber 2 is sealed and evacuated. A large number of filaments 3 parallel to the central portion are connected in parallel to a power feed rod (electrode rod), from which thermoelectrons are generated. Below the vacuum chamber 2 is an opening, which is an irradiation window 4 for emitting an electron beam to the outside. A window foil 5 is stretched on the irradiation window 4. The irradiation window 4 of the cylindrical vacuum chamber 2 is fixed to the opening of a metal housing 6. A flat nitrogen gas chamber 7 is provided in the housing 6 immediately below the irradiation window. A workpiece 8 passes through the nitrogen gas chamber 7 horizontally. In this case, a state where the strip-shaped continuous workpiece 8 is wound and unwound at both ends and self-runs is shown. However, the workpiece may be conveyed by an endless conveyor.
[0010]
Within the nitrogen gas chamber 7 is a beam catcher 9 which receives a portion of the electron beam. An electron beam that has passed through the workpiece 8, an electron beam that has reached the workpiece without happening to be hit, and an electron beam that has been reflected or scattered by other parts. Under the beam catcher 9, a metal shielding material 10 such as lead is stretched. The current of the electron beam can be obtained by measuring the current flowing through the beam catcher 9.
[0011]
Although the nitrogen gas chamber 7 is a semi-closed space, an inlet 20 and an outlet 22 for allowing the workpiece 8 to pass therethrough are upstream and downstream. A low and wide space defined by a front plate 23, a bottom plate 24, a rear plate 25, an upper plate 26, a side plate 29, etc. made of metal (for example, stainless steel). The bottom plate 24 is fixed to the front plate 23, the rear plate 25, the side plate 29 and the like via the packing 28.
[0012]
There is a nitrogen gas inlet 27 on the downstream side. Thereby, the air inside the nitrogen gas chamber 7 is replaced. The nitrogen gas that has replaced the air exits from the downstream outlet 22 and the upstream inlet 20 into the housing 6. What exits from the outlet 22 is a loss, so it goes as far as possible to pass through the irradiation section and exit from the entrance 20.
[0013]
Below the nitrogen gas chamber 7 is a wide plate-shaped shield 30. This is a metal plate made of stainless steel, iron, lead or the like, and shields the electron beam and X-ray so as not to leak outside. It is a member different from the housing 6. The shield 30 can be moved up and down by force of an air cylinder, a motor or the like. This is a heavy metal plate because it blocks electron beams and X-rays, and is heavy and wide. This can be moved up and down because maintenance of the irradiation window is necessary. When the irradiation window is inspected, repaired, or repaired, the shielding plate 30 is lowered to the bottom.
[0014]
If there is no such thing as a nitrogen gas chamber, it is necessary to fill a wide space with nitrogen gas from the downstream side to the upstream side. It is undesirable because it boosts the consumption of nitrogen gas. When the nitrogen gas chamber 7 is provided, the amount of nitrogen gas can be reduced because the nitrogen gas can be localized in a narrow space temporarily or not.
[0015]
[Problems to be solved by the invention]
If the nitrogen gas chamber 7 is installed inside the housing, the amount of nitrogen gas used can be saved and the electron beam irradiation processing cost can be reduced. This is effective in the case of a sheet-like workpiece that can pass through a narrow inlet and outlet. If the vertical shaking of the sheet-like workpiece is reduced, the inlet 20 and outlet 22 can be narrowed, and the nitrogen gas loss can be further reduced.
[0016]
Only a few electron beam irradiation apparatuses are equipped with such a nitrogen gas chamber. Nevertheless, it has been found that there is room for improvement. One is that the packing used to connect the bottom plate, the side plates, and the front and rear plates is deteriorated by exposure to X-rays. As described above, X-rays are emitted when an electron beam hits an object. X-rays are emitted in all directions around the origin. It hits the packing and degrades it. When the packing made of rubber or resin is deteriorated, nitrogen gas leaks and the amount of necessary nitrogen gas increases.
[0017]
Another problem is that it is difficult to maintain the irradiation window. Since the irradiation window is covered with window foil and cooling water passes, it is easy to break down and there is a high need for maintenance and inspection. The shielding plate 30 can be lowered by operating a motor or an air cylinder. With a conventional electron beam irradiation apparatus without a nitrogen gas chamber, the irradiation window portion is immediately exposed, so that the window foil can be replaced or the cooling water pipe or the like can be repaired immediately.
[0018]
However, in the electron beam irradiation apparatus provided with the nitrogen gas chamber as a problem here, even if the shielding plate 30 is lowered, the irradiation window is not exposed by itself. This is because there is still a nitrogen gas chamber concealing the irradiation window. Furthermore, the irradiation window cannot be maintained unless the nitrogen gas chamber is removed. Therefore, it is necessary to remove the bolt of the portion where the upper plate 26 is attached to the housing, and to extract the entire nitrogen gas chamber.
[0019]
Since the nitrogen gas chamber is a heavy metal box, it is not easy. Even if this is not the case, the irradiation window needs to be inspected and repaired. Therefore, it is not desirable that the irradiation window be covered several times by a nitrogen gas chamber or the like.
[0020]
It is a first object of the present invention to provide a nitrogen gas chamber structure that prevents rapid deterioration of the packing. It is a second object of the present invention to provide a nitrogen gas chamber structure that facilitates maintenance of the irradiation window portion.
[0021]
[Means for Solving the Problems]
The present invention divides a nitrogen gas chamber into a fixed upper half fixed to a housing and a movable lower half that can be moved up and down together with a shielding plate, and the packing is protected from X-rays by the shielding bottom plate side plate portion of the lower half And The upper half is composed of an upper plate, a front plate, and a rear plate, and is fixed to the casing near the irradiation window. The lower half consists of a shield bottom plate fixed to the shield plate and having a recess and a packing protected from X-ray exposure by the recess. Place the beam catcher on the shielding bottom plate.
[0022]
When the shielding plate rises, the lower half shielding bottom plate closes the lower opening of the upper half. At that time, the packing is protected from X-rays by the side plate portion of the shielding bottom plate. The electron beam hitting the beam catcher generates X-rays, but the side surface of the shielding bottom plate gets in the way and the X-rays do not hit the packing. Thereby, deterioration of packing is suppressed.
[0023]
When the shielding plate is lowered, the shielding bottom plate forming the lower half is lowered and the opening of the upper half is opened. The window foil flange bolt of the irradiation window can be removed by inserting a hand through the opening. The tired window foil can be removed. A new window foil can be inserted through the opening, sandwiched between the window foil flange and the irradiation window flange, and bolted again to secure the window foil between the flanges. You can repair and check the cooling water system by putting your hands through the opening. It is not necessary to remove the bolt to open the nitrogen gas chamber. The nitrogen gas chamber is opened only by lowering the shielding plate, and the nitrogen gas chamber is closed only by raising the shielding plate. Therefore, the maintenance of the irradiation window becomes easier.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
An electron beam irradiation apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows a state in which the nitrogen gas chamber is closed, and FIG. 3 shows a state in which the nitrogen gas chamber is opened.
[0025]
A filament 3 to which a negative high voltage is applied is provided inside a cylindrical vacuum chamber 2. The filament is a parallel metal resistor, and 10 to 50 filaments are connected in parallel and parallel. The outer shell of the vacuum chamber 2 is at ground potential. Thermoelectrons e ⁻ are emitted from the filament 3 and accelerated downward by an acceleration voltage to become an electron beam. Below the vacuum chamber 2 is an opening. That is the irradiation window 4. Since the vacuum is above the irradiation window and the atmospheric pressure is below, the window foil 5 of Ti and Al is stretched over the opening of the irradiation window 4 in order to partition it. The electron beam travels in a vacuum from the filament, passes through the window foil 5, exits into the atmosphere, and strikes an object to be processed 8 that travels thereunder to perform a desired process.
[0026]
If oxygen is present, ozone is generated, which is not preferable. Therefore, a nitrogen gas atmosphere is provided immediately below the irradiation window. Therefore, a nitrogen gas chamber 7 is provided inside the housing 6 immediately below the irradiation window 4. The nitrogen gas chamber 7 is divided into upper and lower parts. The upper half and the lower half can be divided.
[0027]
The upper half includes an upper plate 26, a front plate 23, a rear plate 25, and a side plate 29 that are fixed to the housing 6. These form a rectangular frame. The front plate 23 has an inlet 20 for introducing the workpiece 8. The rear plate 25 has an outlet 22 for discharging the workpiece. The lower side of the front plate 23, the rear plate 25, and the side plate 29 forming a frame is a flange 38 bent outward. A packing 36 is bonded to the flange 38.
[0028]
The lower half can be raised and lowered and is fixed to a shielding plate 30 originally provided inside the housing 6 in order to shield X-rays. A leg 32 is attached on the shielding plate 30 and a heavy metal (stainless steel, lead) shielding bottom plate 33 is placed thereon. A beam catcher 37 is provided in the shielding bottom plate 33. The beam catcher 37 receives the electron beam that has penetrated the workpiece and extinguishes it. The electron beam current can also be measured by the current flowing through the beam catcher. The shielding bottom plate 33 has side plate portions 34 extending upward on four sides. A horizontal rib 35 is provided at the height of the outer half of the side plate portion 34. When the shielding plate 30 is raised, the packing 36 on the rib 35 of the side plate portion 34 suppresses the flange 38 of the upper half frame from below. Thereby, the nitrogen gas chamber 7 is closed. No engagement fittings such as bolts, screws, pins, and latches are required to connect the lower half and the upper half.
[0029]
With the nitrogen gas chamber 7 closed, the workpiece 8 (sheet-like) is run to perform electron beam processing. An electron beam hits the beam catcher 37 and X-rays are generated. However, since the side plate portion 34 of the shielding bottom plate 33 blocks X-rays, the packing 36 does not hit X-rays. That is, the side plate portion 34 protects the packing 36 against X-rays. Since the deterioration of the packing 36 is caused by X-rays, in the present invention, the packing hardly deteriorates.
[0030]
A state where the movable shielding plate 30 is lowered is shown in FIG. The shielding bottom plate 33, the beam catcher 37, the rib 35, and the packing 36 are lowered together with the shielding plate 30. The upper half remains at the position directly below the irradiation window. If you enter the inside of the case, you can see the installation part of the window foil of the irradiation window and the part of the cooling water system, so you can inspect and repair. There is no need to remove the bolts to disassemble the nitrogen gas chamber.
Since it has such a structure, maintenance of the irradiation window portion can be performed much more quickly and easily.
[0031]
【The invention's effect】
According to the present invention, since the nitrogen gas chamber is provided so as to surround a part of the object to be processed immediately below the irradiation window, the nitrogen gas can be temporarily retained in the part at a high concentration. Therefore, generation | occurrence | production of the reaction which dislikes oxygen can be accelerated | stimulated. Furthermore, ozone generation can be effectively prevented. It is useful in the case of an object to be treated that the ozone odor is not good. In addition, since there is a nitrogen gas chamber surrounding the irradiated part in addition to the housing, there is an effect that X-ray shielding is more complete and safety is enhanced.
[0032]
Furthermore, the nitrogen gas chamber of the present invention can be divided into upper and lower parts, and when a wide and heavy shielding plate is lowered and raised by electric or hydraulic pressure, the lower half part is lowered and raised as it is. When ascending, the lower half part contacts the upper half part by the force of the shielding plate, and the nitrogen gas chamber is closed. When descending, the lower half moves down with the shielding plate and the nitrogen gas chamber opens. So there is no need to tighten or loosen the bolts to open and close the nitrogen gas chamber. Since the nitrogen gas chamber is opened simply by lowering the shielding plate, the window foil of the irradiation window can be replaced more easily and quickly.
[0033]
Moreover, since the side plate part 34 of the shielding bottom plate 33 in the lower half part blocks the X-rays generated by the beam catcher, the X-rays do not directly hit the packing. Therefore, the deterioration of the packing due to X-rays can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a conventional apparatus provided with a nitrogen gas chamber for temporarily retaining nitrogen gas introduced from the downstream side in a non-scanning electron beam irradiation apparatus directly under an irradiation window.
FIG. 2 shows the apparatus of the present invention in which a vertically divided nitrogen gas chamber is provided so as to surround a part of the object to be processed directly under the irradiation window in order to temporarily retain the nitrogen gas introduced from the downstream side. Sectional drawing of a closed state.
FIG. 3 shows an apparatus according to the present invention in which a nitrogen gas chamber of an upper and lower split system is provided so as to surround a part of an object to be processed directly under an irradiation window in order to temporarily retain nitrogen gas introduced from the downstream side. Sectional drawing of an open state.
[Explanation of symbols]
2 Vacuum chamber 3 Filament 4 Irradiation window 5 Window foil 6 Housing 7 Nitrogen gas chamber 8 Object 9 Beam catcher 10 Shielding material 20 Nitrogen gas chamber inlet 22 Nitrogen gas chamber outlet 23 Front plate 24 Bottom plate 25 Rear plate 26 Upper plate 27 Nitrogen gas inlet 28 Packing 29 Side plate 30 Shield plate 32 Leg 33 Shield bottom plate 34 Side plate portion 35 Rib 36 Packing 37 Beam catcher 38 Flange

Claims (1)

A frame consisting of an upper plate, a front plate, a rear plate and a side plate, a flange formed under the frame, a fixed upper half fixed to the housing directly under the irradiation window, and a shielding bottom plate having side plates and outward ribs And a packing directly above the outward rib and a movable lower half that includes a beam catcher placed on the shielding bottom plate and can be moved up and down together with the shielding plate. By moving the shielding plate up, the packing of the movable lower half is the upper half The upper and lower halves are united, the lower half of the movable part is lowered by lowering the shielding plate, the irradiation window part is exposed, and X-rays generated from the beam catcher are packed by the side plate of the shielding bottom plate. The structure of the nitrogen gas chamber of the electron beam irradiation apparatus characterized by shielding with respect to.

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