Fume hoods with forced downward air flow

Abstract

A fume hood capable of forced downward air supply, comprises a test support platform and a cabinet cavity arranged above the support platform; characterized in that it also comprises a lower air supply device, the lower air supply device comprises an air passageway through which supply air can flow, the air outlet of the air passageway extends along the edge direction x of the support platform, the air passageway is used to supply air from the outside of the cabinet cavity to the nearby area on the support platform surface, the lower air supply device also comprises a partial channel wall forming the air passageway and an upper shell body located above the air passageway, on the flow path of the supply air, the upper shell body comprises a first shell portion and a second shell portion arranged in sequence, so that the air passageway also correspondingly comprises a first section and a second section corresponding to and connected to the first shell portion and the second shell portion.

Description

Technical Field

[0001] The invention relates to ventilation equipment for a laboratory, in particular to a fume hood capable of forcibly supplying air downward. Background Art

[0002] Various harmful gases are generated during chemical experiments. In order to immediately exhaust the harmful gases nearby, fume hoods are often used. Fume hoods are common local exhaust systems in chemical laboratories. They can exhaust a large amount of harmful gases with a small air volume, control the diffusion of harmful gases, and ensure the health and safety of experimenters. Fig.10 The first common fume hood structure is shown. The common fume hood mainly includes a test support platform 2, a cabinet cavity 3 arranged above the support platform 2 for experimental operation, and an exhaust fan (not shown in the figure) connected to the cabinet cavity 3. When the exhaust fan is working, a negative pressure is formed in the cabinet cavity 3, so as to reduce the amount of harmful gas leaking from the cabinet cavity 3 to the outside, and to extract the harmful gas from the cabinet cavity 3. An operation window 30 is arranged on the cabinet cavity 3, and a lower air supply channel 10 and a channel upper shell 1 for forming an upper channel wall of the lower air supply channel 10 are arranged at the threshold position of the operation window 30. The channel upper shell 1 includes a front shell 11, an intermediate shell 12 and a rear shell 13, which are respectively in the shape of a flat plate. The front shell 11 is arranged horizontally, and the rear shell 13 is arranged vertically. The intermediate shell 12 is obliquely connected between the front shell 11 and the rear shell 13. An air outlet 15 of the lower air supply channel 10 is formed between the front shell 11 and the support platform 2, and an air inlet 14 of the lower air supply channel 10 is formed between the rear shell 13 and the support platform 2. When the exhaust fan is working, the air outside the cabinet cavity 3 enters the lower air supply channel 10 through the air inlet 14, and then enters the cabinet cavity 3 through the air outlet 15. A water blocking boss 21 is also provided on the support platform 2. In addition, as Fig.11 The second common fume hood structure is shown in the figure. The channel upper shell 1a shown in the figure includes a front shell 11a and a rear shell 12a connected together. The front shell 11a is a flat plate, and the rear shell 12a is an arc plate. The other structures are the same as Figure 1 After multiple airflow tests, it was found that the above two fume hoods were not ideal in cleaning the relatively heavy harmful gases deposited on the support platform. Summary of the invention

[0003] There are many factors that affect the fume hood's ability to clean heavier harmful gases that are deposited on the support platform. Technical personnel can easily think of factors such as insufficient exhaust fan power and poor guide structure of the guide back plate. A particularly common technical solution is to increase the amount of air flowing through the lower guide groove of the guide back plate to solve the above technical problem, but the fume hood's air supply mechanism is often ignored, thinking that as long as enough air can be supplied to the fume hood, it will be sufficient. The supply air volume is certainly important, but the flow path of the supply air will also affect the fume hood's ability to capture harmful gases. Figure 1 and Figure 2 A careful analysis of the disclosed air supply structures revealed that they all have one thing in common, that is, they are all provided with a flat front shell portion. Under the guidance of the front shell portion, part of the airflow blown out from the air outlet will flow horizontally, and part of the airflow will flow upward, while the airflow flowing downward and swooping down onto the support platform is seriously insufficient, and cannot effectively flush and clean the heavier harmful gases deposited on the support platform, resulting in some harmful gases remaining on the support platform and escaping to the external space after the fume hood stops operating. It can be seen that it is necessary to further improve the air supply structure of the fume hood.

[0004] In view of the shortcomings of the prior art, the present invention first proposes a fume hood capable of forced downward air supply, comprising a test support platform and a cabinet cavity arranged above the support platform; characterized in that it also includes a lower air supply device, the lower air supply device includes an air passage through which supply air can flow, the air outlet of the air passage extends along the edge direction x of the support platform, the air passage is used to supply air from the outside of the cabinet cavity to the vicinity of the support platform surface, the lower air supply device also includes a partial channel wall forming the air passage and an upper shell located above the air passage, on the flow path of the supply air, the The upper shell includes a first shell portion and a second shell portion arranged in sequence, so that the air passage also correspondingly includes a first section and a second section corresponding to the first shell portion and the second shell portion and connected, wherein external air enters from the first section and flows out from the second section; viewed from the cross-sectional direction perpendicular to the direction x, the height position of the edge of the support platform is lower than the height position of the second shell portion, and the inner side wall of the second shell portion extends downward at an angle along the airflow direction, so as to force at least part of the airflow entering the second section to flow from top to bottom and then pass through the air outlet and dive onto the support platform.

[0005] The inner cavity of the cabinet is an operating space for conducting various experimental activities. With the help of the inner cavity of the cabinet, harmful gases generated during the experiment can be temporarily collected therein to prevent them from running around.

[0006] The air outlet of the air passage is arranged to extend along the edge direction x of the support platform. The above feature defines that the extension direction of the air outlet of the air passage is substantially consistent with the extension direction of the edge of the support platform. In actual applications, the extension length of the air outlet of the air passage in direction x can reach the position of the left and right cavity side walls of the cabinet cavity and be directly connected to the left and right cavity side walls, and of course, can also be directly connected to the support platform.

[0007] Among them, the air passage is used to supply air from the outside of the cabinet cavity to the nearby area on the support table surface, that is, the air passage is an air supply passage connecting the cabinet cavity with the external space, and the air passage is used to introduce the external air of the cabinet cavity into the cabinet cavity, so as to replenish the gas for the cabinet cavity.

[0008] Among them, the height position of the edge of the support platform is lower than the height position of the second shell portion, that is, in the up and down direction, the edge of the support platform is located below the second shell portion, for example, the edge of the support platform extends to directly below the upper shell portion, specifically, it can be located directly below the second shell portion, or directly below the intermediate transition shell portion, at which time the edge of the support platform is also located obliquely below the second shell portion; the edge of the support platform can also be located outside directly below the upper shell portion, as long as it can receive at least part of the airflow blown out from the air outlet.

[0009] Among them, from the perspective of appearance and structure, the first shell portion and the second shell portion may have no obvious boundary and are integrated, for example, the first shell portion and the second shell portion are both inclined downward and are in the shape of a straight plate; the first shell portion and the second shell portion may also have a clear boundary, for example, the first shell portion and the second shell portion have an angle between them and are combined into a shell in the shape of a mountain.

[0010] According to the above technical scheme, compared with the prior art, the beneficial technical effect of the present invention is that: since the inner side wall of the second shell part extends downwardly along the direction of the airflow, most of the airflow entering the second section can be forced to flow from top to bottom and then pass through the air outlet and dive onto the support platform. In this way, the amount of airflow blown out from the air outlet and diving from top to bottom and the impact force of the airflow can be relatively increased. The diving airflow can relatively strongly flush and clean the harmful gas deposited on the surface of the support platform, and use the board guide effect of the support platform to push the harmful gas toward the inner direction of the cabinet cavity and away from the lower air replenisher. Further, the rebound effect of the support platform surface on the airflow can also be used to expand the flow range of the airflow, and the harmful gas that is scattered within a certain height range from the support platform surface can be pushed toward the inner direction of the cabinet cavity. It can be seen that the structure in which the inner side wall of the second shell part extends downwardly along the direction of the airflow effectively and with a very simple structure optimizes the fume hood's ability to capture harmful gases and reduces the amount of harmful gases leaking out.

[0011] Secondly, further analysis of the first and second more common fume hood structures disclosed in the above background technology section reveals that they also have a common structural feature, that is, the water-blocking boss is provided at the air outlet, and the water-blocking boss will hinder the airflow from scouring the support table surface, resulting in a large amount of harmful gas remaining on the support table surface. In view of this, a further technical solution can also be that a water-blocking boss extending along the direction x is provided on the support table, and a reference line extending along the inclined direction of the inner side wall of the second shell portion enters the inner space of the water-blocking boss. According to the above technical solution, under the guidance of the inner side wall of the second shell portion, at least part of the airflow in the air passage can pass over the water-blocking boss in a downward dive mode to enter the inner space of the water-blocking boss to scour and push the harmful gas deposited on the support table surface. In addition, the water-blocking boss can prevent the liquid spilled on the support table from dripping onto the ground.

[0012] A further technical solution may be that the inner side wall of the second shell portion is a plane wall. That is, the inner side wall of the second shell portion is not a curved wall, which is more conducive to strengthening the impact force of the airflow diving from top to bottom, and further improving the flushing and cleaning ability of the diving gas on the harmful gas deposited on the surface of the support platform; secondly, the processing process of the inner side wall of the second shell portion can be simplified.

[0013] In some cases, part of the external air will enter the inner cavity of the cabinet after flowing through the outer wall of the second shell part. In order to be able to use this part of the air to enhance the flushing and cleaning ability of the harmful gases deposited on the surface of the support platform, a further technical solution may also be that the outer wall of the second shell part extends downwardly along the direction of the airflow. In this way, part of the external air dives from top to bottom onto the support platform under the guidance of the outer wall of the second shell part to form a second airflow, and then can merge with the airflow blown out from the air outlet and swooping from top to bottom onto the support platform to coordinately push the harmful gases deposited on the surface of the support platform, thereby enhancing the cleaning ability of the harmful gases deposited on the surface of the support platform. Furthermore, the outer wall of the second shell part is a plane wall, which is more conducive to enhancing the flushing ability of the swooping airflow.

[0014] A further technical solution may be that the upper shell further includes an intermediate transition shell arranged between the first shell and the second shell, so that the wind passage further includes an intermediate section corresponding to the intermediate transition shell and connecting the first section and the second section; from the cross-sectional direction perpendicular to the direction x, the inner side wall of the intermediate transition shell is an arc wall, and the inner side wall of the first shell and the inner side wall of the second shell are smoothly transitioned and connected through the inner side wall of the intermediate transition shell. In this way, it is beneficial to optimize the smoothness of the airflow flowing from the first section to the second section, and reduce the vortex amount and vortex intensity formed in the wind passage.

[0015] A further technical solution may be that the upper shell covers at least part of the edge of the support platform, and the support platform becomes at least part of the lower wall of the air passage, thereby simplifying the lower air supply structure of the fume hood.

[0016] A further technical solution may be that the upper shell also includes a tail plate connected to the lower end of the first shell, the tail plate extends vertically in the up-down direction, and an air inlet of the air passage is formed between the tail plate and the edge of the support platform, and the air inlet is connected to the external space of the cabinet cavity. According to the above technical solution, the air inlet is arranged downward, and when the experimenter stands beside the lower air replenishment device to perform experimental operations, the air inlet will not be easily blocked by the experimenter's body to destroy the air replenishment effect.

[0017] A further technical solution may be that the lower air supply device further includes an air guide vane extending along the flow path of the supply air, and the air guide vane is arranged in the air passage. In this way, the air flow in the air passage is guided by the air guide vane, so that the number and intensity of vortices formed in the air passage can be reduced.

[0018] A further technical solution may be that the cavity wall body of the cabinet cavity includes a left cavity side wall and a right cavity side wall which are arranged on the left and right sides and a cavity back wall located therebetween, and also includes an operation window constructed opposite to the cavity back wall, the operation window is used to form an inlet and outlet passage for conducting experiments on the support platform; the lower air supply device is arranged at the door sill position of the operation window, and a movable cabinet door is arranged on the operation window, and the cabinet door abuts against the upper shell when it falls. In this way, when the cabinet door completely closes the operation window, the air outside the cabinet cavity can still be guided to the nearby area on the support platform surface for air supply through the air passage.

[0019] Since the present invention has the above characteristics and advantages, it can be applied to a fume hood capable of forced downward air supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a three-dimensional structural schematic diagram of a fume hood to which the technical solution of the present invention is applied;

[0021] Figure 2 This is a structural schematic diagram of a fume hood in the main viewing direction to which the technical solution of the present invention is applied;

[0022] Figure 3 yes Figure 2 Schematic diagram of the cross-sectional structure in the AA direction;

[0023] Figure 4 yes Figure 3 The enlarged view of the C part in FIG.

[0024] Figure 5 3 is a schematic structural diagram of the guide back plate in the main viewing direction, wherein the left and right dotted line parts respectively represent the left cavity side wall 31 and the right cavity side wall 32, and the dotted line part below represents the support platform 2;

[0025] Figure 6 yes Figure 3 A magnified view of part B in FIG.

[0026] Figure 7 is a schematic diagram of the three-dimensional structure of the fixing seat 8;

[0027] Figure 8 is a structural schematic diagram of the lower air supply device in the main viewing direction;

[0028] Fig. 9 is a schematic diagram of the three-dimensional structure of the lower air replenisher after it is turned over to the back;

[0029] Fig.10 This is the first and more common fume hood structure diagram;

[0030] Fig.11 This is the second most common fume hood structure diagram. DETAILED DESCRIPTION

[0031] The structure of the fume hood using the technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0032] like Figure 1 to Figure 3 and Figure 5 As shown, the present invention relates to a fume hood, comprising a test support platform 2, a cabinet cavity 3 arranged above the support platform 2, and a cavity wall body configured as the cabinet cavity 3, wherein the cavity wall body comprises a left cavity side wall 31, a right cavity side wall 32, and a cavity back wall 34 and a cavity top wall 33 arranged between the left cavity side wall 31 and the right cavity side wall 32. It also comprises an operation window 30 constructed opposite to the cavity back wall 34, the operation window 30 extends left and right along the front side edge 22 of the support platform 2, and the operation window 30 is used to form an inlet and outlet channel for conducting experiments on the support platform 2, and the hands of the experimenter can pass through the operation window 30 to extend into the cabinet cavity 3 to conduct various experimental operations, and the harmful gases generated during the experiment will be temporarily collected in the cabinet cavity 3 to avoid running around. A total exhaust port 330 is also provided on the cavity top wall 33, and the total exhaust port 330 is used to exhaust the air in the cabinet cavity 3; in other embodiments, the total exhaust port 330 can also be provided at a suitable place on the left cavity side wall 31, the right cavity side wall 32 or the cavity back wall 34, and the specific setting position can be reasonably determined according to the flow field design of the entire airflow of the fume hood.

[0033] An exhaust passage 6 connected to the main exhaust port 330 is provided in the cabinet inner cavity 3. An exhaust fan (not shown in the figure) connected to the main exhaust port 330 is also installed above the fume hood, and the exhaust fan is used to form a negative pressure in the cabinet inner cavity 3. When the exhaust fan is running, the harmful gas accumulated in the cabinet inner cavity 3 is sucked into the exhaust passage 6 and then discharged through the main exhaust port 330.

[0034] The basic goal of safe use of fume hoods is that, under the suction force of the exhaust fan, the design of the airflow field in the entire cabinet should ensure that the surface wind speed at the position of the operating window 30 is stable and uniform, the gas in the cabinet cavity 3 will not flow back from the position of the operating window 30, and the large molecular harmful gases deposited at the bottom of the cabinet cavity 3 can be removed in time and cannot flow back. Of course, there are many specific schemes to achieve the above basic goals, and the scheme proposed in the present invention is not the only one; secondly, to achieve the above basic goals, it is necessary to improve various local structures so that they can play their role in a fume hood product. For this reason, the present invention also mainly improves the local structure of the fume hood in order to achieve the corresponding technical effect. The corresponding local improvement schemes will be explained one by one in the following statements.

[0035] In order to achieve the above basic objectives, the present invention first improves the wind passing structure at the bottom of the guide back plate 5. Figure 3 As shown, the guide back plate 5 is provided in the cabinet inner cavity 3, and the guide back plate 5 and the cavity wall body of the cabinet inner cavity 3 are a split structure. The guide back plate 5 is located in front of the cavity back wall 34 and there is a distance between them to form the exhaust duct 6. For this reason, the guide back plate 5 actually also faces the operation window 30.

[0036] like Figure 5As shown, the guide back plate 5 includes a first guide back plate 51 disposed above the support platform 2 and close to the support platform 2. The first guide back plate 51 and the cavity back wall 34 are arranged substantially parallel to each other. Of course, in other embodiments, the first guide back plate 51 may be arranged obliquely relative to the cavity back wall 34. The first guide back plate 51 is located in front of the cavity back wall 34 and there is a distance between them to form a first exhaust duct 61 extending up and down, and the first exhaust duct 61 forms a partial channel of the exhaust duct 6. The left and right side edges of the first air guide back plate 51 extend close to the left cavity side wall 31 and the right cavity side wall 32 in the left and right directions, respectively. However, the two side edges of the first air guide back plate 51 located in the lower area of ​​the cabinet inner cavity 3 and the left cavity side wall 31 and the right cavity side wall 32 respectively have a gradually expanding air opening 71 and a gradually expanding air opening 71a, that is, the gradually expanding air opening 71 and the gradually expanding air opening 71a are located on the left and right sides of the lower area of ​​the cabinet inner cavity 3, and the gradually expanding air opening 71 and the gradually expanding air opening 71a are expanding air openings. The gradually expanding air opening 71 and the gradually expanding air opening 71a are in a geometric shape that gradually increases from the top to the bottom. In one preferred embodiment, the maximum width W of the gradually expanding air opening 71 and the gradually expanding air opening 71a in the left-right direction is 35 mm to 45 mm, for example, 35 mm, 40 mm or 45 mm. In addition, the two sides of the upper area of ​​the first air guide back plate 51 are spaced from the left cavity side wall 31 and the right cavity side wall 32 by a suitable spacing that does not need to be too large, specifically including an upper side gap 76 and an upper side gap 76a with uniform gap width, the upper side gap 76 is located above the gradually expanding air opening 71, and the upper side gap 76a is located above the gradually expanding air opening 71a. The gap width W4 of the upper side gap 76 and the upper side gap 76a is smaller than the width of the gradually expanding air opening 71 and the gradually expanding air opening 71a. The gap width W4 of the upper side gap 76 and the upper side gap 76a is also smaller than the gap height H of the bottom spacing 7 to be discussed below. The gap width W4 is generally 1mm to 20mm, for example, 1mm, 10mm, 20mm. The specific gap size is determined according to other specific air inlet structures of the fume hood, the exhaust power of the exhaust fan, the applicable scope of the fume hood, etc. The gaps with uniform width in the left and right directions between the two sides of the second guide back plate 52 and the third guide back plate 53 to be discussed below and the left cavity side wall 31 and the right cavity side wall 32 are also of the same width W4.

[0037] According to the above technical scheme, compared with the prior art, the beneficial technical effects are: first, since the two side edges of the first guide back plate 51 located in the lower area of ​​the cabinet cavity 3 and the left cavity side wall 31 and the right cavity side wall 32 respectively have gradually expanding air openings 71 and gradually expanding air openings 71a, that is, relatively large air guide gaps arranged continuously from top to bottom are formed on the left and right sides of the first guide back plate 51, respectively, so that a flow channel can be provided for the relatively heavy macromolecular gases deposited in the left and right corners of the lower area of ​​the cabinet cavity 3 to be discharged into the first exhaust duct 61 in time, and it is also beneficial to reduce the resistance of airflow and the formation of vortices, thereby increasing the airflow speed. Secondly, when the fume hood is configured with an inhaled airflow as the control airflow and a pressure gradient that gradually increases from bottom to top is formed in the cabinet cavity 3, there will be a certain inhaled air velocity gradient between the highest point and the lowest point of the gradually expanding air opening 71. The shape change of the gradually expanding air opening 71, that is, the geometric shape that gradually increases from the top to the bottom, is conducive to forming a basically uniform inhaled air volume (air volume) on the gradually expanding air opening 71, so that the distribution state of the airflow field at the left and right corners of the lower area of ​​the cabinet cavity 3 can be optimized, and the generation of eddy currents can be further reduced. In addition, compared with the gaps with uniform widths from top to bottom in the prior art, the lower part of the gradually expanding air opening 71 has a relatively larger air flow area, so that the lower part of the gradually expanding air opening 71 has a relatively larger air flow volume, so that more relatively heavy macromolecular gases deposited in the left corner of the lower area of ​​the cabinet cavity 3 can be captured. The gradually expanding air opening 71a can achieve the same technical effect as the gradually expanding air opening 71, and will not be discussed again here.

[0038] like Figure 5As shown, the first guide back plate 51 is close to the support platform 2 and is provided with a spacing, so that there is a bottom spacing 7 between the first guide back plate 51 and the support platform 2 for passing wind, and the gap width W4 of the upper side gap 76 and the upper side gap 76a are respectively smaller than the gap height H of the bottom spacing 7. In one preferred embodiment, the gap height H is generally 30 mm to 150 mm, such as 30 mm, 68 mm, 88 mm or 150 mm, and the specific gap height is determined according to other specific air inlet structures of the fume hood, the exhaust power of the exhaust fan, the applicable scope of the fume hood and other factors. According to the above technical solution, the bottom air guide passage is formed by the bottom spacing 7, which is conducive to capturing the heavier macromolecular gas that sinks into the lower area of ​​the cabinet cavity 3. In other embodiments, the bottom spacing 7 can be set to be close to zero, that is, the bottom end surface of the first guide back plate 51 stands on the support platform 2. Furthermore, the gradually enlarged air opening 71 and the gradually enlarged air opening 71a respectively extend downward through the bottom end surface of the first guide back plate 51 and are combined with the bottom spacing 7. In this way, the gradually enlarged air opening 71 and the gradually enlarged air opening 71a and the bottom spacing 7 form a U-shaped bottom total air space, which can better capture the relatively heavy macromolecular gas deposited in the lower area of ​​the cabinet inner cavity 3. In addition, it is also convenient to process the gradually enlarged air opening 71 and the gradually enlarged air opening 71a on the first guide back plate 51.

[0039] In order to form the gradually expanding air opening 71 and the gradually expanding air opening 71a, the following technical solutions may be further selected. The first technical solution is: Figure 5 As shown, the two side edges of the first air guide back plate 51 located in the lower area of ​​the cabinet cavity 3 are inclined and narrowed towards each other, and the left cavity side wall 31 and the right cavity side wall 32 are upright. In this embodiment, the first technical solution is adopted, and the gradually expanding air opening 71 and the gradually expanding air opening 71a are right-angled triangles, and their vertex angles Q are 3°~13°, for example, 3°, 6°, and 13°. The second technical solution (not shown in the figure): the lower areas of the left cavity side wall 31 and the right cavity side wall 32 are respectively in a shape that is gradually concave outward from top to bottom, and the two side edges of the first air guide back plate 51 located in the lower area of ​​the cabinet cavity 3 are upright.

[0040] In order to achieve the above basic objectives, the present invention proposes another improved solution for the structure of the guide back plate 5, which can be used alone or in combination with the gradually expanding air opening 71 and the gradually expanding air opening 71a in the fume hood product. Specifically, Figure 5As shown, a guide structure capable of guiding the airflow in the front space 35 into the exhaust channel 6 is provided on the guide back plate 5, that is, a lower air guide passage 72 extending left and right is provided only on the plate body located in the lower area of ​​the cabinet inner cavity 3 on the first guide back plate 51, and the air flow area of ​​the lower air guide passage 72 is not greater than the air flow area of ​​the bottom spacing 7, that is, the air flow area of ​​the lower air guide passage 72 can be equal to or less than the air flow area of ​​the bottom spacing 7. In this way, the lower air guide passage 72 is also located in the lower area of ​​the cabinet inner cavity 3, so that the relatively heavy macromolecular gas deposited in the lower area of ​​the cabinet inner cavity 3 can be discharged in time. In addition, compared with the case where multiple rows of air guide slots are provided on the lower area of ​​the first air guide back plate 51, the air flow rate of the lower air guide passage 72 is relatively stronger, which can not only better capture the harmful gases that drift to the vicinity thereof, but also provide conditions for configuring the appropriate air flow rate of the gradually expanding air flow opening, and can greatly simplify the air guide structure of the first air guide back plate 51, reduce the damage to the original structural strength of the first air guide back plate 51, and facilitate the processing of the first air guide back plate 51. Further, the lower air guide passage 72 includes at least three first sub-aisles, that is, there can be 3, 4 or other multiple first sub-aisles. In this embodiment, three first sub-aisles are provided, namely, the first sub-aisle 72a, the first sub-aisle 72b, and the first sub-aisle 72c, the three first sub-aisles are arranged left and right, and each of the first sub-aisles is in the shape of a long strip extending in the left-right direction. According to the above technical solution, the first guide plate 51 can still maintain a suitable structural strength when the lower air guide passage 72 is formed.

[0041] In order to achieve the above basic objectives, the present invention proposes another improved solution for the structure of the guide back plate 5, which can be used alone or in combination with the gradually expanding air opening 71 and the gradually expanding air opening 71a in the fume hood product. Specifically, Figure 3 and Figure 5As shown, the guide back plate 5 also includes a second guide back plate 52 which is separately arranged from the first guide back plate 51, the second guide back plate 52 is located above the first guide back plate 51 and arranged close to the first guide back plate 51, the second guide back plate 52 is located in front of the cavity back wall 34 and is arranged roughly parallel to each other and there is a spacing between them to form a second exhaust duct 62 extending up and down, and the second exhaust duct 62 also forms a part of the exhaust duct 6 (in other embodiments, the second guide back plate 52 can also be arranged obliquely relative to the cavity back wall 34). It also includes a middle air guide passage 73 extending left and right, the middle air guide passage 73 is composed of the inter-plate spacing 73 between the first guide back plate 51 and the second guide back plate 52, and the middle air guide passage 73 is roughly located in the central area of ​​the cabinet inner cavity 3 viewed in the up and down direction in the up and down direction, and the wind passing area of ​​the middle air guide passage 73 is smaller than the wind passing area of ​​the lower air guide passage 72. Compared with the prior art, the beneficial technical effects of the above technical solution are: first, since there is a bottom spacing 7 between the first guide back plate 51 and the support platform 2 for air to pass through, the bottom spacing 7 can be used to timely discharge the heavier macromolecular gases deposited in the lower area of ​​the cabinet cavity; secondly, since the lower air guide passage 72 is located in the lower area of ​​the cabinet cavity 3 and above the bottom spacing 7, the heavier macromolecular gases that escape from the bottom spacing 7 and continue to drift upward can be captured by the airflow flowing through the lower air guide passage 72 and brought into the air duct behind the guide back plate 5; furthermore, since only one lower air guide passage 72 is provided on the first guide back plate 51, and the lower air guide passage 72 The wind passing area of ​​72 is not greater than the wind passing area of ​​the bottom spacing 7. Thus, compared with the case where multiple rows of air guides are arranged on the first guide back plate 51, the wind passing volume of the lower air guide passage 72 is relatively stronger, and can better capture the harmful gases that drift to its vicinity, and can make the bottom spacing 7 have a suitable wind passing volume; again, the middle air guide passage 73 is composed of the inter-plate spacing between the first guide back plate 51 and the second guide back plate 5. Thus, it is very convenient to control the size of the inter-plate spacing to make the middle air guide passage 73 have a suitable wind passing area, especially to form a narrow air guide gap in a very simple way. The ventilation area of ​​the middle air guide passage 73 is not limited by the size specifications of the milling tool and can be flexibly configured. The relatively light harmful gases that escape from the lower air guide passage 72 and continue to drift upward can be captured by the airflow flowing through the middle air guide passage 73 and brought into the air duct behind the guide back plate 5.Based on this, it can be found that by setting the bottom spacing 7, the lower air guide aisle 72, and the middle air guide aisle 73 in sequence from bottom to top, and configuring them with appropriate ventilation areas, quantities and layout positions, not only can the harmful gases of different weights be effectively captured, but the guide structure of the guide back plate 5 can also be greatly simplified, reducing the damage to the original structural strength of the guide back plate 5, and facilitating the processing of the guide back plate 5.

[0042] like Figure 5 As shown, the guide back plate 5 also includes a third guide back plate 53 located above the second guide back plate 52, and the third guide back plate 53 is located in front of the cavity back wall 34 and can be arranged substantially parallel to each other between the cavity back wall 34. In other embodiments, the third guide back plate 53 can also be arranged obliquely relative to the cavity back wall 34. There is a spacing between the third guide back plate 53 and the cavity back wall 34 to form a third exhaust duct 63 extending up and down, and the first exhaust duct 61, the second exhaust duct 62 and the third exhaust duct 63 are connected front and back to form an exhaust channel 6 leading to the total exhaust port 330. The lower end of the third guide back plate 53 is connected to the upper part of the second guide back plate 52, and the third guide back plate 53 is arranged below the total exhaust port 330 in an inclined upward structure so that the third exhaust duct 63 is connected to the total exhaust port 330. A joint seam 74 is provided between the second guide back plate 52 and the third guide back plate 53, and the wind passing area of ​​the joint seam 74 is not greater than the wind passing area of ​​the inter-plate spacing 73, and no wind hole groove is provided on the second guide back plate 52 and the third guide back plate 53. According to the above technical scheme, compared with the scheme of providing wind hole grooves on both the second guide back plate 52 and the third guide back plate 53, it is beneficial to increase the wind passing volume of the bottom spacing 7, the lower guide channel 72, the middle guide channel 73 and the gradually expanding wind opening, so that the ability to capture harmful gases deposited in the lower area and the central area of ​​the cabinet cavity 3 can be maintained while simplifying the guide structure on the guide back plate 5. Among them, the wind passing area of ​​the splicing seam 74 is not greater than the wind passing area of ​​the middle air guide passage 73, that is, the wind passing area of ​​the splicing seam 74 is less than or equal to the wind passing area of ​​the middle air guide passage 73, and the wind passing area of ​​the splicing seam 74 can even be zero, for example, when sealed with the aid of a seal. In addition, a top spacing 75 is formed between the upper end of the third air guide back plate 53 and the cavity top wall 33 of the cabinet cavity 3. According to the above technical solution, the top spacing 75 is actually located in the upper area of ​​the cabinet cavity 3, so that the harmful gases that escape from the bottom spacing 7, the lower air guide passage 75, and the middle air guide passage 73 in sequence and continue to drift upward can be captured by the airflow flowing through the top spacing 75 and brought into the third exhaust duct 63 and then discharged from the cabinet cavity 3.

[0043] like Figure 3 , Figure 6 and Figure 7 As shown, in order to fix the guide back plate 5, a fixing seat 8, a fixing seat 8a and a fixing seat 8b are arranged between the guide back plate 5 and the cavity back wall 34. The structures of the fixing seats 8, 8a and 8b are the same, and the fixing seat 8 is taken as an example for description below. The fixing seat 8 is U-shaped, including a top support wall 83 and a left support wall 81 and a right support wall 82 arranged on the left and right sides of the top support wall 83. An interlayer cavity 80 is formed between the top support wall 83 and the left support wall 81 and the right support wall 82. A connecting column 85 is arranged on the top support wall 83, and the tail of the connecting column 85 extends into the interlayer cavity 80. The fixing seat 8 is locked on the cavity back wall 34 by screws. The fixing seat 8 is located between the second guide back plate 52 and the cavity back wall 34, the second guide back plate 52 is pressed against the top support wall 83, and the fastener 86 passes through the second guide back plate 52 and is connected to the connecting column 85 to fix the second guide back plate 52 to the fixing seat 8; an oblique slot 84 is provided on the top support wall 83, and the lower end of the third guide back plate 53 is inserted into the oblique slot 84 to connect to the upper part of the second guide back plate 52. The fixing seat 8a is provided between the first guide back plate 51 and the cavity back wall 34, the first guide back plate 51 is pressed against the top support wall of the fixing seat 8a, and the fastener passes through the first guide back plate 51 and is connected to the connecting column of the fixing seat 8a to fix the first guide back plate 51 to the fixing seat 8a. In this way, the installation, disassembly and replacement of the first guide back plate 51, the second guide back plate 52 and the third guide back plate 53 are simplified.

[0044] like Figure 2 , Figure 3 and Figure 4 As shown, the cabinet is also provided with a lower air supply device, the lower air supply device includes an air passage 10 capable of circulating air supply, and the air outlet 15 of the air passage 10 is arranged along the edge 22 of the support platform 2 in the direction x (wherein the direction x is Figure 2In the direction of the middle X-axis), the air passage 10 is used to supply air from the outside of the cabinet cavity 3 to the nearby area on the surface of the support platform 2, and the lower air supply device also includes an upper shell 1 that forms a partial channel wall of the air passage 10 and is located above the air passage 10. On the flow path of the supply air, the upper shell 1 includes a first shell portion 11, an intermediate transition shell portion 13 and a second shell portion 12 that are arranged in sequence, so that the air passage 10 is also correspondingly divided into a first section 101, an intermediate section 103 and a second section 102 that correspond to the first shell portion 11, the intermediate transition shell portion 13 and the second shell portion 12 and are connected, wherein the external air enters from the first section 101 and flows through the intermediate section 103 and then flows out from the second section 102; viewed from the cross-sectional direction perpendicular to the direction x (i.e. Figure 4 As shown in the figure), the inner side wall 11a of the first shell portion 11 is a plane wall extending upwardly along the airflow direction, and the inner side wall 13a of the intermediate transition shell portion 13 is an arc wall. The inner side wall 11a of the first shell portion 11 and the inner side wall 12a of the second shell portion 12 are smoothly transitioned and connected through the inner side wall 13a of the intermediate transition shell portion 13.

[0045] Among them, the air outlet 15 of the air passage 10 is arranged to extend along the direction x of the edge 22 of the support platform 2. The above characteristics define that the extension direction of the air outlet 15 of the air passage 10 is substantially consistent with the extension direction of the edge 22 of the support platform 2. Secondly, the air passage 10 is used to guide the air outside the cabinet cavity 3 to the nearby area on the surface of the support platform 2 to replenish air, that is, the air passage 10 is an air replenishment channel connecting the cabinet cavity 3 with the external space, and the air passage 10 is used to introduce the external air of the cabinet cavity 3 into the cabinet cavity 3, so as to replenish the gas for the cabinet cavity 3. In addition, the inner side wall 11a of the first shell part 11 is a plane wall extending in an inclined upward direction along the air flow direction, that is, the inner side wall 11a of the first shell part 11 is not a curved wall, and the inner side wall 11a of the first shell part 11 not only extends straightly from bottom to top, but also extends from outside to inside (from the outside direction of the cabinet cavity 3 to the inside direction of the cabinet cavity 3). The plane wall can not only guide the flow but also easily form a stable flow. The inner side wall 11a of the first shell 11 and the inner side wall 12a of the second shell 12 are smoothly transitioned and connected through the inner side wall 13a of the intermediate transition shell 13, so that the intermediate transition shell 13 can minimize the damage to the flat and stable flow formed by the plane wall.

[0046] Compared with the prior art, the beneficial technical effects of the above technical solution adopted by the lower air replenisher are: first, since the air passage 10 is used to replenish air from the outside of the cabinet cavity 3 to the nearby area on the surface of the support platform 2, it is beneficial to blow the harmful gases deposited in the nearby area on the surface of the support platform 2 toward the inside of the cabinet cavity 3, thereby reducing the amount of harmful gases leaking outward. Second, since the inner wall 11a of the first shell 11 is a plane wall extending upwardly along the direction of the airflow, at least part of the airflow entering the first section 101 can flow not only from bottom to top but also from outside to inside under the guidance of the inner wall 11a of the first shell 11, that is, at least part of the airflow under the guidance of the inner wall 11a of the first shell 11 has not only the kinetic energy of the movement trend flowing from bottom to top but also the kinetic energy of the movement trend flowing from outside to inside; secondly, the inner wall 11a of the first shell 11 is a plane wall, which is easy to form a steady flow; In addition, since the inner side wall 13a of the intermediate transition shell 13 is an arc wall, the inner side wall 11a of the first shell 11 and the inner side wall 12a of the second shell 12 are smoothly transitioned and connected through the inner side wall 13a of the intermediate transition shell 13, so that on the flow path from the first section 101 to the middle section 103, at least part of the gas can smoothly enter the second section 102 from the first section 101 under the guidance of the inner side wall 13a of the intermediate transition shell 13, effectively improving the undesirable phenomenon of a large number of vortices formed in the middle section 103. Because the inner side wall of the upper shell 1 has the above-mentioned structural improvement, the external airflow can enter the air passage 10 relatively more, so that more airflow can be added to the cabinet cavity 3, reducing the formation of a large number of vortices near the air outlet 15.

[0047] The structure of the inner side wall 12a of the second shell portion 12 can be various, and can be selected from the following three technical solutions according to actual needs: The first technical solution of the second shell portion 12: Figure 4As shown, the height position of the edge 22 of the support platform 2 is lower than the height position of the second shell part 12, and the inner side wall 12a of the second shell part 12 extends downward along the airflow direction, so as to force at least part of the airflow entering the second section 102 to flow from top to bottom and then pass through the air outlet 15 and dive onto the support platform 2. In this way, the amount of airflow blown out from the air outlet 15 and diving from top to bottom and the impact force of the airflow can be relatively increased. The diving airflow can relatively strongly flush and clean the harmful gas deposited on the surface of the support platform 2, and use the board surface guide effect of the support platform 2 to push the harmful gas toward the inner direction of the cabinet cavity 3 and away from the lower air replenisher. Furthermore, the rebound effect of the surface of the support platform 2 on the airflow can also be used to expand the flow range of the airflow, and the harmful gas that is scattered within a certain height range from the surface of the support platform 2 is pushed toward the inner direction of the cabinet cavity 3. It can be seen that the structure of the inner side wall 12a of the second shell 12 extending downward along the airflow direction effectively and with a very simple structure optimizes the fume hood's ability to capture harmful gases and reduces the amount of harmful gases leaking outward. Furthermore, a water-blocking boss 21 extending along the direction x is provided on the support platform 2, and a reference line A extending along the inclined direction of the inner side wall 12a of the second shell 12 enters the inner space of the water-blocking boss 21. In this way, under the guidance of the inner side wall 12a of the second shell 12, at least part of the airflow in the air passage 10 can pass over the water-blocking boss 21 in a downward dive manner to enter the inner space of the water-blocking boss 21 to flush and push the harmful gases deposited on the surface of the support platform 2. In addition, the water-blocking boss 21 can prevent the liquid spilled on the support platform 2 from dripping onto the ground. In order to simplify the processing of the second shell 12 and optimize the smoothness of the airflow in the air passage 10, the inner side wall 12a of the second shell 12 is a plane wall. This is more conducive to strengthening the impact of the dive airflow and further improving the fume hood's ability to capture harmful gases.

[0048] The other two technical solutions of the second shell 12 are: the inner side wall 12a of the second shell 12 extends upward along the direction of the airflow so that the airflow blown out from the air outlet 15 can be blown from bottom to top. In this way, even if the water blocking boss 21 is higher than the inner side wall 12a of the second shell 12, the airflow blown out from the air passage 10 can still enter the vicinity of the surface of the support platform 2 under the guidance of the inner side wall 12a of the second shell 12. Alternatively, the inner side wall 12a of the second shell 12 extends horizontally, so that the airflow blown out from the air outlet 15 can be blown horizontally.

[0049] like Figure 4As shown, the outer side wall 12b of the second shell 12 is a plane wall extending in an oblique downward direction along the airflow direction. In this way, part of the external air dives from top to bottom onto the support platform 2 under the guidance of the outer side wall 12b of the second shell 12 to form a second airflow, which can then merge with the airflow blown out from the air outlet 15 and swooping down onto the support platform 2 to coordinately push the harmful gas deposited on the surface of the support platform 2, thereby enhancing the cleaning ability of the harmful gas deposited on the surface of the support platform 2. Moreover, the outer side wall 12b of the second shell 12 is a plane wall, which is more conducive to strengthening the impact force of the second airflow and further improving the fume hood's ability to capture harmful gases. In addition, the outer side wall 11b of the first shell 11 is a plane wall extending in an oblique upward direction along the airflow direction, and the outer side wall 13b of the intermediate transition shell 13 is an arc wall, and the outer side wall 11b of the first shell 11 and the outer side wall 12b of the second shell 12 are smoothly transitioned and connected through the outer side wall 13b of the intermediate transition shell 13. In this way, part of the external air is blown from bottom to top under the guidance of the outer wall 11b of the first shell 11, so that the harmful gas floating at a certain height from the surface of the support platform 2 can be pushed forward away from the lower air replenishment device. Accordingly, under the guidance of the outer wall of the upper shell 1, the external air flow can be divided into tributaries flowing upward and downward, increasing the cleaning range of the air flow for harmful gases. In this embodiment, in order to simplify the structure and manufacturing process of the upper shell 1, the upper shell 1 can be made of a thin plate.

[0050] like Figure 4 As shown, the upper shell 1 covers at least a portion of the edge 22 of the support platform 2, and the support platform 2 becomes at least a portion of the lower wall of the air passage 10. This simplifies the lower air supply structure of the fume hood. The upper shell 1 also includes a tail plate 16 connected to the lower end of the first shell 11, and the tail plate 16 extends vertically in the up and down directions. An air inlet 14 of the air passage 10 is formed between the tail plate 16 and the edge 22 of the support platform 2, and the air inlet 14 is connected to the external space of the cabinet cavity 3. According to the above technical solution, the air inlet 14 is arranged downward, and when the experimenter stands beside the lower air supply device for experiment, the air inlet 14 will not be easily blocked by the experimenter's body to destroy the air supply effect.

[0051] In order to reduce the formation of eddy currents in the wind passage 10, Fig. 9As shown, the lower air supply device further includes an air guide vane 17 extending along the flow path of the supply air, and the air guide vane 17 is arranged in the air passage 10. In this way, the air flow in the air passage 10 is guided by the air guide vane 17 to reduce the generation of vortex. It also includes a wing connector 171, one end of which is connected to the air guide vane 17, and the other end is connected to the upper shell 1. The wing connector 171 and the air guide vane 17 can be a split structure or an integrated structure.

[0052] like Figure 1 , Figure 8 and Fig. 9 As shown, the lower air supply device is arranged at the door threshold position of the operating window 30 (the door threshold position of the operating window 30 refers to the bottom position of the operating window 30), and the front and rear ends of the air outlet 15 of the lower air supply device are respectively close to the left cavity side wall 31 and the right cavity side wall 32 of the cabinet inner cavity 3. The air outlet 15 includes a front end air outlet expansion port 151, a rear end air outlet expansion port 152 and a middle air outlet narrowing port 153 located therebetween, and the height H2 of the front end air outlet expansion port 151 relative to the support platform 2 and the height H3 of the rear end air outlet expansion port 152 relative to the support platform 2 are respectively greater than the height H4 of the middle air outlet narrowing port 153 relative to the support platform 2. In the direction x, the width W1 of the front end air outlet expansion port 151 and the width W2 of the rear end air outlet expansion port 152 are smaller than the width W3 of the middle air outlet narrowing port 153. In this way, within the unit length range in the direction x, the amount of air blown out from the front end air outlet expansion port 151 and the rear end air outlet expansion port 152 is greater than the amount of air blown out from the middle air outlet narrowing port 153, so that the strong airflow on both sides is used to regulate the airflow in the middle area, so that the airflow blown out from the air outlet 15 flows smoothly and concentratedly as a whole, effectively improving the airflow's ability to capture and clean harmful gases in the vicinity of the surface of the support platform 2. In addition, the airflow blown out from the front end air outlet expansion port 151 and the rear end air outlet expansion port 152 has a larger flow range in the up and down directions and a relatively larger flow rate than the middle air outlet narrowing port 153, so that the heavy molecular gases corresponding to the front and rear ends of the air outlet 15 that are located at the corners on both sides of the cabinet cavity 3 can be blown away more quickly. The head end wind outlet expansion port 151 and the tail end wind outlet expansion port 152 can provide appropriate air volume for the gradually expanding wind opening 71 and the gradually expanding wind opening 71a respectively, so as to help maintain a uniform surface wind speed.

[0053] Secondly, in the process of supplying air through the operation window 30 of the fume hood, the relevant technical standards generally require that the operation window 30 has a uniform and stable surface wind speed (about 0.5 m / s). Since the middle air outlet narrowing port 153 roughly corresponds to the central area of ​​the operation window 30, and the central area of ​​the operation window 30 itself has the largest air supply volume, and the head end air outlet expansion port 151 and the tail end air outlet expansion port 152 roughly correspond to the left and right sides of the operation window 30, the air supply volume of the left and right sides relative to the central area of ​​the operation window 30 is relatively small. In the above-mentioned layout structure, it is possible to further utilize the characteristics that the height of the head end air outlet expansion port 151 and the tail end air outlet expansion port 152 relative to the support platform 2 is respectively greater than the height of the middle air outlet narrowing port 153 relative to the support platform 2, to make up for the problem that the left and right sides of the operation window 30 are relatively insufficient in air supply and the central area of ​​the operation window 30 is excessive in air supply, which greatly improves the uniformity and stability of the surface wind speed of the operation window 30.

[0054] The front and rear ends of the upper shell 1 are respectively close to the left cavity side wall 31 and the right cavity side wall 32 of the cabinet inner cavity 3. The lower air supply device also includes a plug 18 arranged at the front end of the upper shell 1 and a plug 18a arranged at the rear end of the upper shell 1. The plug 18a has a similar structure to the plug 18. The plug 18 is used as an example for introduction below. The plug 18 includes a plug body 181 for blocking the end of the air passage 10 and a plug connection part 182 for fixing the plug body 181 to the upper shell 1. The screw passes through the plug body 181 of the plug 18 to fix the plug 18 to the left cavity side wall 31, and the screw passes through the plug body of the plug 18a to fix the plug 18a to the right cavity side wall 32. In this way, the plug 18 and the plug 18a can not only block the end of the air passage 10, but also be used to fix the lower air supply device. In addition, a movable cabinet door 4 is provided on the operating window 30, and the upper shell 1 can limit the lowest limit position of the cabinet door 4, that is, the cabinet door 4 can be pressed against the upper shell 1 when it falls. In this way, when the cabinet door 4 completely closes the operating window 30, the air outside the cabinet cavity 3 can still be guided to the nearby area on the surface of the support platform 2 through the air passage 10. In another embodiment, the air passage 10 of the present invention can also be applied to a structure in which a blower is installed at its inlet or a pipe connected to its inlet, and the lower air supply device can also be directly connected to the support platform 2.

Claims

1. A fume hood capable of forced downward air supply, comprising a test support platform and a cabinet cavity arranged above the support platform; characterized in that: The cabinet further comprises a lower air supply device, wherein the lower air supply device comprises an air passage through which supply air can flow, and the air outlet of the air passage extends along the edge direction x of the support platform, and the air passage is used to supply air from the outside of the cabinet cavity to the nearby area on the support platform surface, and the lower air supply device also comprises an upper shell body which forms a part of the channel wall of the air passage and is located above the air passage, and on the flow path of the supply air, the upper shell body comprises a first shell part and a second shell part which are arranged in sequence, so that the air passage also correspondingly comprises a first section and a second section which correspond to the first shell part and the second shell part and are connected, wherein external air enters from the first section and flows out from the second section; viewed from the cross-sectional direction perpendicular to the direction x, the height position of the edge of the support platform is lower than the height position of the second shell part, and the inner side wall of the second shell part extends downward obliquely along the air flow direction, so that at least part of the airflow entering the second section can be forced to flow from top to bottom and then pass through the air outlet and dive onto the support platform.

2. The fume hood capable of forced downward air supply according to claim 1, characterized in that: A water blocking boss extending along direction x is arranged on the support platform, and a reference line extending along the inclined direction of the inner side wall of the second shell portion enters the inner space of the water blocking boss.

3. The fume hood capable of forced downward air supply according to claim 1, characterized in that: The inner side wall of the second shell portion is a plane wall.

4. The fume hood capable of forced downward air supply according to claim 1, characterized in that: The outer side wall of the second shell portion extends obliquely downward along the air flow direction.

5. The fume hood capable of forced downward air supply according to claim 4, characterized in that: The outer side wall of the second shell portion is a plane wall.

6. The fume hood capable of forced downward air supply according to any one of claims 1 to 5, characterized in that: The upper shell covers at least a portion of the edge of the support platform, and the support platform becomes at least a portion of the lower wall of the air passage.

7. The fume hood capable of forced downward air supply according to claim 6, characterized in that: The upper shell also includes a tail plate connected to the lower end of the first shell, the tail plate extends vertically in the up and down directions, and an air inlet of the air passage is formed between the tail plate and the edge of the support platform, and the air inlet is connected to the external space of the cabinet cavity.

8. The fume hood capable of forced downward air supply according to any one of claims 1 to 5, characterized in that: The lower air supply device also includes an air guide vane extending along the flow path of the supply air, and the air guide vane is arranged in the air passage.

9. The fume hood capable of forced downward air supply according to any one of claims 1 to 5, characterized in that: The cavity wall body constructed as the inner cavity of the cabinet includes a left cavity side wall, a right cavity side wall and a cavity back wall located therebetween, and also includes an operation window constructed opposite the cavity back wall, and the operation window is used to form an entry and exit channel for conducting experiments on the support platform; the lower air replenisher is arranged at the door sill position of the operation window, and a movable cabinet door is arranged on the operation window, and the cabinet door abuts against the upper shell when it falls.

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