Suppression device of microwave dryer

Abstract

The utility model relates to the technical field of suppressors, and provides a suppressor of a microwave dryer, which comprises an isolation box, the isolation box is provided with an isolation channel, the isolation channel is used for materials to pass through, a plurality of wave absorbers are arranged, a plurality of suppression strips which are arranged in sequence form a group, and a plurality of groups of suppression strips are arranged. And the plurality of groups of suppression strips and the plurality of wave absorbers are alternately arranged on the wall of the isolation channel. By means of the technical scheme, the technical problem that in the prior art, microwave dissipation at the inlet and outlet of the microwave dryer is large is solved, microwave dissipation at the inlet and outlet of the microwave dryer is reduced, and safety of personnel and equipment is guaranteed.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of suppressor, specifically, relate to the suppressor of microwave drying machine. BACKGROUND

[0002] At present, most of the corrugated paper boxes on the market are formed by die cutting after pasting paper, because the moisture in the corrugated paper is greatly increased after the pasting paper process, if it enters the die cutting process immediately, the die cutting plate and the corrugated paper board cannot be effectively separated, thereby causing a large amount of waste. Therefore, in the actual production, the corrugated paper after the pasting paper process is static for a period of time, and then enters the die cutting process after the moisture inside is partially evaporated. The time required for this process is less than ten hours or more than one or two days, thereby greatly reducing the production efficiency of the customer. If this process is not handled properly, the corrugated paper board will be warped and deformed, not only reducing the efficiency of the die cutting process, but also affecting the appearance of the carton. Therefore, the importance of the microwave drying machine for drying the corrugated paper board is also increasing. The microwave drying machine is different from other machines, which uses microwave drying method. This method is fast, energy-saving and effective, but improper handling of the inlet and outlet of the drying machine will cause microwave leakage, which will have a bad effect on the operator's body. SUMMARY

[0003] In order to overcome the above defects, the utility model provides a suppressor of microwave drying machine, which solves the technical problem of large microwave emission at the inlet and outlet of the microwave drying machine in the prior art.

[0004] According to one aspect, at least one embodiment of the utility model provides a suppressor of microwave drying machine, which comprises:

[0005] The isolation box has an isolation channel for the passage of materials.

[0006] The wave absorber is a plurality of wave absorbers.

[0007] The suppression strips are arranged in a group, and the suppression strips are arranged in a plurality of groups. The plurality of groups of suppression strips and the plurality of wave absorbers are alternately arranged on the wall of the isolation channel.

[0008] For example, the suppressor of microwave drying machine provided by at least one embodiment of the present disclosure has a waveguide groove, which faces the isolation channel, and the waveguide groove has wave scattering holes perpendicular to the two side walls of the isolation channel, and the wave scattering holes are arranged along the length direction of the waveguide groove.

[0009] For example, the suppressor of microwave drying machine provided by at least one embodiment of the present disclosure further comprises:

[0010] A conveying belt is arranged in the isolation channel and under the sealing cloth.

[0011] A sealing cloth is arranged in the isolation channel and under the conveying belt.

[0012] Anti-blocking plates are arranged in the isolation channel, above the sealing cloth and on both sides of the conveying belt.

[0013] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure further comprises:

[0014] Two shielding curtains are arranged at the entrance and exit of the isolation channel.

[0015] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure, the inner wall of the isolation channel has annular wave suppression installation grooves and annular wave absorption installation grooves arranged in sequence, the wave suppression strips are arranged in the annular wave suppression installation grooves, and the wave absorption bodies are arranged in the annular wave absorption installation grooves.

[0016] A fixing plate is movably arranged in the groove wall of the annular wave absorption installation groove and abuts against the wave absorption body, and is used for fixing the wave absorption body.

[0017] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure, the wave scattering space is formed between two adjacent wave suppression strips, and the wave scattering holes and the wave scattering space are in communication.

[0018] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure, the annular wave absorption installation groove is a through groove, and further comprises:

[0019] Shielding cover plates are arranged at two groove openings of the annular wave absorption installation groove, and the wave absorption bodies face the isolation channel.

[0020] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure, the wave absorption space is formed between the shielding cover plates and the wave absorption bodies.

[0021] For example, the microwave dryer suppressor provided by at least one embodiment of the present disclosure, the shielding curtain is a metal soft curtain.

[0022] The embodiments of the present application have the following beneficial effects:

[0023] The isolation channel of the isolation box provides a dedicated transmission channel for the materials. It can effectively restrict the materials in a specific space, allowing them to flow in an orderly manner during the process of entering and exiting the microwave drying machine, and avoiding the materials from scattering or deviating from the predetermined path. The isolation box plays a certain physical isolation role, restricting the microwaves inside and reducing microwave leakage to the external environment, thereby ensuring the safety of the operators.

[0024] The multiple wave absorbers can absorb microwave energy, preventing the generation of reflection, standing wave and other adverse phenomena of microwaves in the isolation channel. When the microwaves encounter the wave absorbers during propagation in the channel, the wave absorbers absorb the microwave energy, thereby reducing the reflection of microwaves and avoiding damage to the equipment caused by microwave reflection, prolonging the service life of the equipment.

[0025] The sequentially arranged suppression strips further enhance the function of the suppressor. The suppression strips can regulate the propagation of microwaves, and can suppress the irregular propagation of microwaves, allowing the microwaves to be more uniformly distributed in the isolation channel, thereby improving the uniformity of material drying. At the same time, the suppression strips can also prevent the excessive concentration of microwaves in certain areas, avoiding local overheating or damage to the materials.

[0026] The suppressor of the microwave drying machine improves the performance of the microwave drying machine through the cooperative work of the isolation box, the wave absorber and the suppression strip. The isolation box provides a stable material transmission channel and a microwave isolation environment; the wave absorber effectively absorbs microwave energy, reduces reflection and prevents microwave overflow; and the suppression strip regulates the propagation of microwaves, allowing the microwaves to be more uniformly distributed, thereby ensuring that the materials can be dried by the residual waves. This design effectively solves the problems of reflection and standing wave of microwaves during propagation, improves the working efficiency and stability of the microwave drying machine, and ensures the safety of the operators and the normal operation of the equipment. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the present utility model. Obviously, the drawings in the following description are only some example embodiments of the present utility model. For those skilled in the art, other drawings can also be obtained according to the contents of the example embodiments of the present utility model and these drawings without paying creative labor.

[0028] Figure 1 is a structural schematic view of the present utility model;

[0029] Figure 2 is Figure 1 is another perspective view of the embodiment of the present utility model;

[0030] Figure 3 Figure 2 is an enlarged structural schematic view of A in the embodiment of the present utility model.

[0031] In the figure: isolation box-1, isolation channel-101, ring wave suppression installation groove-102, ring wave absorption installation groove-103, wave absorption body-2, suppression strip-3, wave guide groove-301, wave dispersion hole-302, wave dispersion space-303, conveying belt-4, sealing cloth-5, material containing space-501, anti-clamping plate-6, shielding curtain-7, fixed plate-8, shielding cover plate-9, wave absorption space-901. DETAILED DESCRIPTION

[0032] The utility model will be described in further detail below in connection with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the utility model, and not limited to the utility model.

[0033] In order to make the drawing simple, only the parts related to the utility model are shown in the drawings, which do not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, the same structure or function in some drawings is only schematically shown, or only one of them is marked. In this paper, "one" not only means "only one", but also means "more than one", and "several" includes "two" and "more than two".

[0034] In this paper, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication between two elements. For ordinary skilled in the art, the specific meaning of the above terms in the utility model can be understood according to the specific circumstances.

[0035] In the utility model, unless otherwise specified and limited, the first feature "on" or "below" the second feature can include the direct contact between the first and second features, or the indirect contact between the first and second features through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes the first feature above and oblique above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature includes the first feature below and oblique below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0036] In the description of this embodiment, terms such as "upper," "lower," "left," and "right" are based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of description and simplification of operation, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0037] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] like Figures 1-3 As shown, it illustrates a suppressor for a microwave dryer in one embodiment of the present invention.

[0039] like Figure 1 As shown, the isolation channel 101 of the isolation box 1 provides a dedicated transport channel for materials. It effectively confines the materials within a specific space, ensuring orderly flow during entry and exit from the microwave dryer and preventing material spillage or deviation from the predetermined path. The isolation box 1 provides a certain degree of physical isolation, confining microwaves internally, reducing microwave leakage to the external environment, and ensuring the safety of operators.

[0040] Multiple microwave absorbers 2 can absorb microwave energy and prevent microwaves from generating adverse phenomena such as reflection and standing waves within the isolation channel 101. When microwaves propagate within the channel and encounter microwave absorbers 2, the absorbers 2 absorb the microwave energy, thereby reducing microwave reflection and preventing damage to the equipment caused by microwave reflection, thus extending the service life of the equipment. The microwave absorbers 2 are long strip-shaped materials used to absorb microwaves.

[0041] The sequentially arranged suppression bars 3 further enhance the function of the suppressor. The suppression bars 3 can regulate the propagation of microwaves, suppressing irregular microwave propagation and ensuring a more uniform distribution of microwaves within the isolation channel 101, thereby improving the uniformity of material drying. Simultaneously, the suppression bars 3 also prevent excessive microwave concentration in certain areas, avoiding localized overheating or damage to the material.

[0042] The microwave dryer's suppressor enhances its performance through the coordinated operation of the isolation chamber 1, the microwave absorber 2, and the suppressor strip 3. The isolation chamber 1 provides a stable material transport channel and a microwave isolation environment; the microwave absorber 2 effectively absorbs microwave energy, reduces reflection, and prevents microwave leakage; the suppressor strip 3 regulates microwave propagation, making the microwave distribution more uniform and ensuring that materials can be dried by residual microwave waves. This design effectively solves the problems of reflection and standing waves that occur during microwave propagation, improving the working efficiency and stability of the microwave dryer, and ensuring the safety of operators and the normal operation of the equipment.

[0043] In some examples, such as Figure 3 As shown, the waveguide groove 301 faces the isolation channel 101, increasing the contact area between the suppression strip 3 and the microwaves. When microwaves propagate to the suppression strip 3, more microwave energy enters the waveguide groove 301. Compared to the suppression strip 3 without the waveguide groove 301, the waveguide groove 301 can more effectively capture and conduct microwaves, further reducing microwave reflection and standing wave phenomena within the isolation channel 101, improving the utilization rate of microwave energy, and allowing more energy to be used for material drying.

[0044] The presence of the waveguide groove 301 guides the propagation direction of microwaves. After entering the waveguide groove 301, microwaves undergo multiple reflections and absorptions within the groove. This reflection and absorption process helps to distribute microwave energy more evenly within the isolation channel 101. By changing the microwave propagation path, the waveguide groove 301 enables microwaves to be distributed more evenly around the material, thereby improving the uniformity of material drying and avoiding localized overheating or insufficient drying.

[0045] The wave-scattering apertures 302 are perpendicular to the two side walls of the isolation channel 101 and arranged along the length of the waveguide groove 301. When microwaves propagate within the waveguide groove 301, some microwave energy is scattered into the isolation channel 101 through the wave-scattering apertures 302. This scattering effect can more evenly distribute the microwave energy concentrated within the waveguide groove 301 to various areas of the isolation channel, further improving the uniformity of microwave distribution within the channel. By rationally setting the size, number, and arrangement of the wave-scattering apertures 302, the degree of microwave scattering can be precisely controlled to meet the microwave distribution requirements for drying different materials.

[0046] The diffuser aperture 302 effectively prevents excessive microwave concentration within the waveguide groove 301. Excessive microwave concentration within the waveguide groove 301 can lead to localized overheating, affecting the performance and lifespan of the suppression strip 3. Dispersing microwave energy through the diffuser aperture 302 reduces the microwave energy density within the waveguide groove 301, minimizing the risk of localized overheating and ensuring the normal operation of the suppression strip 3. It also contributes to improving the overall stability and reliability of the microwave dryer. The diffuser aperture 302 is perpendicular to the length of the waveguide groove 301, and the diffuser apertures 302 on the sidewalls of adjacent waveguide grooves 301 can be staggered to achieve a better diffuser effect.

[0047] The waveguide groove 301 and the scattering hole 302 of the suppression strip 3 cooperate with each other to further optimize the performance of the microwave dryer suppressor. The waveguide groove 301 enhances the wave absorption ability and the role of guiding microwave distribution, and the scattering hole 302 realizes the dispersion of microwave energy and prevents the concentration of microwave. They work together to make the distribution of microwave in the isolation channel 101 more uniform, reduce microwave reflection and standing wave phenomenon, improve the utilization rate of microwave energy, and thus improve the quality and efficiency of material drying. This structural design can better adapt to the drying needs of different materials, enhance the adaptability and practicality of the microwave dryer in actual application, and also prolong the service life of the suppressor and the microwave dryer.

[0048] In some examples, as shown in Figure 2 The conveying belt 4 circulates through the isolation channel 101 to provide a continuous and stable transmission path for the materials. It can uniformly send the materials into the working area of the microwave dryer and transport the materials out after drying. For materials of different shapes, sizes and weights, the conveying belt 4 can well carry and transport them to ensure the orderly movement of the materials in the isolation channel 101 and improve the efficiency and automation level of material processing. The material of the conveying belt 4 is selected to have good microwave transmittance to avoid excessive absorption of microwave energy during transmission, which affects the drying effect of the materials. At the same time, it can stably operate in the microwave environment without being damaged or performance degradation due to the effect of microwave, ensuring the reliability of material transmission.

[0049] The sealing cloth 5 is arranged in the isolation channel 101 and below the conveying belt 4. When the paperboard slightly deforms, the sealing cloth 5 can lift the paperboard to prevent the paperboard from jamming and maintain the support and protection of the paperboard.

[0050] The anti-jamming board 6 is arranged in the isolation channel 101, above the sealing cloth 5 and on both sides of the conveying belt 4, forming a material containing space 501 with the sealing cloth 5. The anti-jamming board 6 limits and guides the deformation of the paperboard. It can prevent the paperboard from deforming or lifting excessively to both sides during transmission, so that the paperboard maintains a relatively stable shape in the material containing space 501. By reasonably setting the position and shape of the anti-jamming board 6, the deformation range of the paperboard can be effectively controlled to ensure the flatness of the paperboard during drying and prevent the paperboard from jamming.

[0051] In some examples, as shown in Figure 2As shown, the shielding curtains 7 are respectively arranged at the entrance and exit of the isolation channel 101, and its main function is to effectively prevent microwave leakage from both ends of the channel to the external environment. When the microwave is used to dry the materials in the isolation channel, part of the microwave may escape through the entrance and exit without the blocking of the shielding curtains. The shielding curtains 7 are made of materials with good shielding performance, which can reflect and absorb microwaves as much as possible to limit the microwaves in the isolation channel, ensuring the safety of the operators and avoiding potential harm to human health caused by microwaves.

[0052] In some examples, as shown in FIG. 1, the microwave drying machine 1 comprises a microwave generator 4, a microwave drying channel 101, a microwave suppression strip 3, a microwave absorber 2, and a microwave shielding curtain 7. Figure 2 As shown, the annular wave suppression installation groove 102 provides a precise installation position for the suppression strip 3. By setting the suppression strip 3 in the groove, it can ensure that the suppression strip 3 is arranged neatly along the inner wall of the isolation channel 101, ensuring the consistency and stability of the suppression strip 3 in regulating the propagation of microwaves. This precise positioning helps to more effectively suppress the irregular propagation of microwaves, making the distribution of microwaves in the isolation channel more uniform, thereby improving the uniformity of material drying.

[0053] The existence of the installation groove makes the connection between the suppression strip 3 and the inner wall of the isolation channel 101 more firm. During the operation of the microwave dryer, the suppression strip 3 will be affected by microwaves and possible vibrations during material transmission. The annular wave suppression installation groove 102 can enhance the structural stability of the suppression strip 3, prevent it from loosening or shifting, and ensure that the suppression strip 3 continuously and effectively suppresses microwaves.

[0054] The annular wave absorption installation groove 103 is specially designed for installing the wave absorber 2, which provides a suitable installation space for the wave absorber 2, allowing it to closely adhere to the inner wall of the isolation channel 101. This maximizes the contact area between the wave absorber 2 and the microwaves, improving the efficiency of the wave absorber 2 in absorbing microwave energy, more effectively reducing microwave reflection and loss, and improving the utilization rate of microwave energy.

[0055] The wave absorber 2 will gradually wear out due to the absorption of microwave energy during long-term use and needs to be regularly maintained or replaced. The design of the annular wave absorption installation groove 103 makes it easier to install and remove the wave absorber 2. Technicians can relatively easily remove the wave absorber 2 from the groove for inspection, replacement, or repair, improving the maintainability of the equipment and reducing maintenance costs and time.

[0056] The fixed plate 8 is arranged through and movably arranged on the groove wall of the annular wave-absorbing installation groove 103 and abuts against the wave-absorbing body 2, which plays a role in fixing the wave-absorbing body 2. It can ensure that the wave-absorbing body 2 maintains a stable position in the installation groove and will not be displaced due to the action of microwaves, equipment vibration or other external forces. Stable installation of the wave-absorbing body 2 can ensure that it continuously and effectively absorbs microwave energy and maintains the normal operation of the microwave dryer.

[0057] Since the fixed plate 8 is movably arranged, when installing or adjusting the wave-absorbing body 2, the technician can fine-tune the position of the wave-absorbing body 2 by sliding the fixed plate 8, so that it better adapts to different working requirements. This flexibility makes the installation and adjustment of the wave-absorbing body 2 more convenient, and can optimize the working performance of the wave-absorbing body 2 according to actual conditions, improving the adaptability of the microwave dryer to different materials and working conditions.

[0058] The annular wave-suppression installation groove 102, the annular wave-absorbing installation groove 103 and the fixed plate 8 cooperate with each other to further optimize the structure and performance of the microwave dryer suppressor. They make the installation of the suppression strip 3 and the wave-absorbing body 2 more precise and stable, and are convenient for maintenance and adjustment.

[0059] In some examples, as shown in Figure 3 The wave-dispersion space 303 provides sufficient diffusion area for microwaves. When microwaves propagate between adjacent suppression strips 3, they first reflect, refract and interfere in the wave-dispersion space 303, preliminarily realizing energy dispersion. The wave-dispersion holes 302 connected with the wave-dispersion space 303 further guide the microwaves to scatter in different directions, so that the microwaves preliminarily dispersed in the wave-dispersion space 303 propagate to various places in the isolation channel 101 through the wave-dispersion holes 302 in a more complex path. The two cooperate to form a multi-stage scattering mechanism, effectively avoiding the concentration of microwaves and ensuring the uniform distribution of microwave energy in the isolation channel, providing uniform drying conditions for the materials.

[0060] In some examples, as shown in Figure 2 The through-slot design of the annular wave-absorbing installation groove 103, combined with the shielding cover plate 9 and the wave-absorbing body 2, forms a functional microwave management system. The through-slot facilitates the installation and maintenance of the wave-absorbing body, optimizes the absorption path, the shielding cover plate 9 enhances the protection performance, and the wave-absorbing body 2 efficiently absorbs microwaves. The three work together not only to improve the microwave absorption efficiency and energy utilization rate, but also to reduce the risk of microwave leakage, protecting the safety of equipment and personnel.

[0061] In some examples, as shown in Figure 3As shown, the presence of the absorbing space 901 provides an additional operating area for microwaves, extending their propagation path within that area. When microwaves enter the absorbing space 901, they undergo multiple reflections, refractions, and scatterings within the space, increasing the number of contacts and the contact area with the absorber 2. This allows the microwaves to be absorbed more fully by the absorber 2, further reducing microwave reflection and leakage, and improving the utilization rate of microwave energy.

[0062] In some examples, such as Figure 1 As shown, the metal flexible curtain, due to its metallic properties, effectively reflects and absorbs microwaves. Because microwaves are reflected when they encounter metal, the metal flexible curtain can reflect microwaves attempting to leak from the inlet and outlet of the isolation channel 101 back into the channel, reducing the possibility of microwave leakage into the external environment. Simultaneously, the metallic material can also absorb some microwave energy, further reducing the risk of microwave leakage, effectively ensuring the safety of operators, preventing potential harm to the human body from microwaves, and preventing microwave interference with the normal operation of surrounding electronic equipment.

[0063] It should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of the technical solution of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A suppressor for a microwave dryer, characterized in that, include: An isolation box (1) has an isolation channel (101) for the passage of materials; Wave absorber (2), wherein there are several wave absorbers (2); Suppression strips (3), a number of suppression strips (3) arranged in sequence form a group, the suppression strips (3) are in several groups, and several groups of suppression strips (3) and several absorbers (2) are alternately arranged on the wall of the isolation channel (101).

2. The suppressor for the microwave dryer according to claim 1, characterized in that, The suppression strip (3) has a waveguide groove (301) facing the isolation channel (101). The waveguide groove (301) has diffuser holes (302) on both sides perpendicular to the isolation channel (101). The diffuser holes (302) are arranged along the length of the waveguide groove (301).

3. The suppressor for the microwave dryer according to claim 1, characterized in that, Also includes: A conveyor belt (4) circulates through the isolation channel (101) for the passage of the material; A sealing cloth (5) is disposed within the isolation channel (101) and located below the conveyor belt (4); Anti-jamming plate (6) is set in the isolation channel (101), above the sealing cloth (5) and on both sides of the conveyor belt (4). The anti-jamming plate (6) and the sealing cloth (5) form a material holding space (501). The material holding space (501) is used to prevent jamming due to material deformation.

4. The suppressor for the microwave dryer according to claim 1, characterized in that, Also includes: Two shielding curtains (7) are provided, which are respectively set at the entrance and exit of the isolation channel (101).

5. The suppressor for the microwave dryer according to claim 1, characterized in that, The inner wall of the isolation channel (101) has annular wave-suppressing mounting grooves (102) and annular wave-absorbing mounting grooves (103) arranged in sequence. The suppression strip (3) is disposed in the annular wave-suppressing mounting groove (102), and the wave-absorbing body (2) is disposed in the annular wave-absorbing mounting groove (103). The channel also includes: A fixing plate (8) is provided through and movably disposed on the wall of the annular absorbing mounting groove (103) and abuts against the absorbing body (2) to fix the absorbing body (2).

6. The suppressor for the microwave dryer according to claim 2, characterized in that, A dispersion space (303) is formed between two adjacent suppression strips (3), and the dispersion aperture (302) is connected to the dispersion space (303).

7. The suppressor for the microwave dryer according to claim 5, characterized in that, The annular absorbing mounting groove (103) is a through groove and also includes: The shielding cover (9) and the absorber (2) are respectively disposed at the two slots of the annular absorber mounting groove (103), and the absorber (2) faces the isolation channel (101).

8. The suppressor for the microwave dryer according to claim 7, characterized in that, The shielding cover (9) and the wave absorber (2) form a wave absorbing space (901).

9. The suppressor for the microwave dryer according to claim 4, characterized in that, The shielding curtain (7) is a metal soft curtain.

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