High-pressure inner-cooling center-outlet secondary filtering mechanism

CN224911955UActive Publication Date: 2026-10-30CHONGQING DAHONGXING PRECISION MASCH MFG CO LTD
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Patent Information

Application Number
CN202522467050.7
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2025-11-20
Publication Date
2026-10-30
Estimated Expiration
2035-11-20

AI Technical Summary

Benefits of technology

[0017]综上所述,本实用新型具有结构设计合理,操作使用方便,能够对切削液进行二级过滤,能够提高切削液的洁净度等优点。

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Abstract

The utility model discloses a kind of secondary filtering mechanism for high-pressure inner-cooling center water outlet, it is characterized in that, including secondary water tank, the top vertical of secondary water tank is provided with bag filter, the bag filter includes the outer cylinder body of cylinder, the lower end of the outer cylinder body is communicated with the secondary water tank, and internally provided with the filter bag support frame of cylinder, replaceable filter bag is provided on the filter bag support frame, and the upper end edge of the filter bag is sealed with the inner wall of the outer cylinder body It is matched;Second liquid inlet is provided on the outer cylinder body, and the second liquid inlet is located above the filter bag. The utility model has the advantages of reasonable structure design, easy operation and use, can carry out secondary filtration to cutting fluid, and can improve the cleanliness of cutting fluid.
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Description

Technical Field

[0001] This utility model relates to the field of machine tool chip removal and cutting fluid purification devices, and in particular to a two-stage filtration mechanism for high-pressure internal cooling center water outlet. Background Technology

[0002] During CNC machine tool spindle cutting, one of the main functions of cutting fluid is to effectively remove cutting heat from the machining area of ​​the machine tool, thereby reducing the temperature rise in the cutting area and improving tool durability and workpiece machining accuracy. Another function of cutting fluid is lubrication. After entering the cutting area, cutting fluid penetrates into the contact surface between the tool and the workpiece and adheres to the metal surface to form a lubricating film, which reduces friction, reduces the adhesion of chips to the tool, and helps improve the surface quality of the workpiece. Cutting fluid also assists in chip removal. It can flush small chips away from the workpiece or tool, thereby improving the machining accuracy of parts and the service life of tools.

[0003] Existing metal machining centers use spindle center water outlet and a chip flushing port at the spindle to discharge cutting fluid for tool cooling. However, spindle center water outlet has higher requirements for the cleanliness of the cutting fluid. Usually, the cutting fluid that has been filtered once needs to be filtered with higher precision to meet the requirements. Therefore, how to perform secondary filtration of cutting fluid has become an urgent problem to be solved. Utility Model Content

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by this utility model is: how to provide a high-pressure internal cooling center outlet water two-stage filtration mechanism with reasonable structural design, convenient operation and use, capable of two-stage filtration of cutting fluid, and capable of improving the cleanliness of cutting fluid.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A two-stage filtration mechanism for high-pressure internal cooling center outlet water is characterized by comprising a two-stage water tank, a bag filter vertically disposed on the top of the two-stage water tank, the bag filter comprising a cylindrical outer cylinder, the lower end of the outer cylinder being connected to the two-stage water tank, and an internal cylindrical filter bag support frame; a replaceable filter bag is disposed on the filter bag support frame, the upper edge of the filter bag forming a sealing fit with the inner wall of the outer cylinder; a two-stage liquid inlet is disposed on the outer cylinder, the two-stage liquid inlet being located above the filter bag.

[0006] Furthermore, a centrifugal filter is connected to the secondary inlet. The centrifugal filter includes an upper cylindrical body and a lower funnel-shaped body. The upper cylindrical body has a centrifugal inlet arranged tangentially. The centrifugal inlet is connected to a secondary water pump for extracting cutting fluid through a pipeline. The top of the upper cylindrical body has a coaxially connected outlet pipe. The upper end of the outlet pipe is connected to the secondary inlet through a pipeline, and the lower end extends downward into the upper cylindrical body to form a centrifugal separation pipe.

[0007] Furthermore, the inner wall of the outer cylinder has a support ring arranged in an annular shape, the outer diameter of the filter bag support frame matches the inner diameter of the support ring, and the upper end has a limiting ring that protrudes radially outward, and the filter bag support frame is hung on the support ring through the limiting ring.

[0008] Furthermore, the filter bag support frame is covered with a disc-shaped filter bag pressure plate, the diameter of which matches the inner diameter of the outer cylinder; the filter bag pressure plate has through-holes for liquid passage.

[0009] Furthermore, multiple liquid passage holes are evenly distributed along the circumference of the filter bag pressure plate, and the axial projection of all the liquid passage holes is located within the filter bag support frame.

[0010] Furthermore, the upper end of the outer cylinder is sealed with a detachable cylinder cover; the filter bag pressure plate has a handle arranged radially along the side facing the cylinder cover, the handle being made of elastic sheet material bent in an arc shape; the height of the handle matches the distance between the support ring and the cylinder cover, so that the cylinder cover abuts against the handle.

[0011] In this way, since the handle is made of elastic sheet material, when the cap is sealed and installed on the outer cylinder, pressure is first applied to the handle, causing the handle to deform elastically and apply the elastic force to the filter bag pressure plate. The filter bag pressure plate can then firmly press the opening of the filter bag on the filter bag support frame, ensuring that the cutting fluid is reliably filtered through the filter bag.

[0012] Furthermore, a pressure gauge for detecting the pressure inside the cylinder is provided on the cylinder cover.

[0013] Furthermore, the secondary water tank has a vertically arranged overflow baffle, the height of which is lower than the height of the secondary water tank, and the secondary water tank is divided into a first tank and a second tank; the bag filter is located in the first tank, and the secondary overflow outlet is located in the second tank and is lower than the overflow baffle.

[0014] In this way, the cutting fluid filtered by the bag filter enters the first tank, where denser impurities settle, making the upper layer of cutting fluid cleaner. It then flows into the second tank through the overflow baffle. The second tank controls the water level through a secondary overflow port, allowing excess cutting fluid to flow back into the filter tank through the secondary overflow port, thus achieving cutting fluid circulation.

[0015] Furthermore, the second chamber has a vertically arranged overflow pipe, the lower end of which penetrates the bottom of the second chamber, and the secondary overflow port is the top opening of the overflow pipe.

[0016] Furthermore, the second housing is provided with a liquid level detection mechanism, which includes a stand installed on the second housing, a slide rod that can slide vertically through the stand, a float ball at the lower end of the slide rod, and a proximity switch at the upper end of the stand.

[0017] In summary, this utility model has the advantages of reasonable structural design, convenient operation and use, ability to perform secondary filtration of cutting fluid, and ability to improve the cleanliness of cutting fluid. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present utility model.

[0019] Figure 2 This is a schematic diagram of the overall structure of the primary filtration mechanism.

[0020] Figure 3 This is a cross-sectional structural diagram of the primary filtration mechanism.

[0021] Figure 4 This is a schematic diagram of the filter mechanism.

[0022] Figure 5 This is a schematic diagram of a centrifugal filter.

[0023] Figure 6 This is a cross-sectional view of a centrifugal filter.

[0024] Figure 7 This is a schematic diagram of the overall structure of the secondary filtration mechanism.

[0025] Figure 8 This is an exploded view of a bag filter.

[0026] Figure 9 This is a cross-sectional structural diagram of a bag filter and a secondary water tank.

[0027] Figure 10 This is a schematic diagram of the internal structure of the secondary water tank.

[0028] Figure 11This is a schematic diagram of a stainless steel belt degreasing machine and an oil-water separation tank. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to a composite scraper chip conveyor that employs the structure of the present invention.

[0030] In practical implementation: such as Figures 1 to 11 As shown, a composite scraper chip conveyor includes a filtrate tank 1, on which a primary filtration mechanism 2 and a secondary filtration mechanism 3 are installed. The primary filtration mechanism 2 includes a horizontally arranged housing 21, one end of which has a main liquid inlet, and the other end extends upward at an angle to form a chip discharge port, which is higher than the housing 21. A scraper mechanism 23 for scraping and removing chips is provided inside the housing 21, and the scraper mechanism 23 extends along the bottom of the housing 21 to the chip discharge port. The housing 21 has a main outlet connected to the filtrate tank 1, and a filter screen mechanism 24 is provided at the front end of the main outlet; the secondary filtration mechanism 3 includes a secondary water tank 31 installed above the filtrate tank 1, the secondary water tank 31 is provided with a secondary inlet and a secondary overflow outlet 311, the secondary overflow outlet 311 is connected to the filtrate tank 1, a secondary water pump 32 is installed on the filtrate tank 1, and a centrifugal filter 33 is provided between the secondary water pump 32 and the secondary inlet. Figure 5 and Figure 6 As shown, the centrifugal filter 33 includes a cylindrical upper cylinder 331 and a funnel-shaped lower cylinder 332. The upper cylinder 331 has a centrifugal inlet arranged tangentially, which is connected to the outlet of the secondary water pump 32 via a pipeline. The top plate of the upper cylinder has a coaxially connected centrifugal outlet pipe 333, the upper end of which is connected to the secondary inlet, and the lower end extends downward into the upper cylinder 331 to form a centrifugal diversion pipe 334. Specifically, the bottom end of the lower cylinder 332 is provided with a centrifugal chip discharge port, which is equipped with an openable ball valve. The other end of the ball valve is connected to the main inlet via a pipeline.

[0031] like Figure 3As shown, the scraper mechanism 23 includes a drive sprocket assembly 231 and a driven sprocket assembly 232, which are respectively located at the chip discharge port and the main liquid inlet, and are connected by two parallel chains (not shown in the figure). The inclined part of the housing 21 also has a chain guide plate 234, and the two chains are respectively fitted on the corresponding chain guide plates 234 to keep the distance between the lower half of the chain and the bottom plate of the housing 21 consistent. A scraper (not shown in the figure) is connected between the two chains, and the scraper located on the lower half of the chain contacts the bottom plate of the housing 21. A chain plate drive mechanism 233 is connected to the drive sprocket assembly 231.

[0032] like Figure 4 As shown, the filter mechanism 24 includes a cylindrical support cage 241, the two ends of which are rotatably mounted on the side wall of the housing 21, and the outer circular surface is covered with a filter screen; the main liquid outlet is located on the side wall of the housing 21 and within the rotation area of ​​the support cage 241; the two ends of the support cage 241 have sprocket teeth 244 arranged circumferentially, which respectively cooperate with the corresponding chains.

[0033] The filter mechanism 24 further includes a water spray pipe 242 arranged axially along the support cage 241. The water spray pipe 242 is located inside the support cage 241 and its two ends are fixedly connected to the housing 21. The water spray pipe 242 has upward-facing water spray holes, and multiple water spray holes are evenly distributed along the axial direction of the water spray pipe 242. One end of the water spray pipe 242 is closed, and the other end is connected to a backwash water pump 243 through a pipeline. The backwash water pump 243 is installed on the filtrate tank 1. A Y-type filter is connected between the backwash water pump 243 and the water spray pipe 242.

[0034] During operation, cutting fluid containing chips enters the primary filtration unit through the main inlet. After being filtered by the filter screen at the front of the main outlet, the cutting fluid flows into the filtrate tank. The chips filtered by the filter screen remain in the tank and are scraped along the bottom of the tank by a scraper mechanism to the chip discharge port for collection. The cutting fluid in the filtrate tank is then pumped by the secondary water pump into the centrifugal filter. Because the centrifugal inlet is tangentially positioned along the upper cylinder, the cutting fluid forms a high-speed rotating flow along the inner wall of the upper cylinder. Higher density impurities in the cutting fluid move towards the outer wall under centrifugal force, making the cutting fluid in the middle cleaner. The clean cutting fluid is then diverted through the central centrifugal distributor into the secondary water tank, which provides even cleaner cutting fluid for the machine tool. Once the cutting fluid level in the secondary water tank exceeds the secondary overflow outlet, it flows back into the filtrate tank from the secondary overflow outlet, thus achieving cutting fluid circulation.

[0035] like Figure 7 As shown, a bag filter 34 is provided on the top of the secondary water tank 31. The bag filter 34 includes a cylindrical outer cylinder 341, the lower end of which is connected to the secondary water tank 31, and a cylindrical filter bag support frame 342 is provided inside. A replaceable filter bag is provided on the filter bag support frame 342, and the upper edge of the filter bag forms a sealing fit with the inner wall of the outer cylinder 341. The secondary liquid inlet is provided on the outer cylinder 341 and is located above the filter bag.

[0036] By installing a bag filter between the centrifugal filter and the secondary water tank, the cutting fluid can be further filtered. Since the bag support frame inside the outer cylinder allows for replacement of the filter bags, liquid is injected into the filter bags from above through the centrifugal outlet. The filtered liquid then flows into the secondary water tank through the lower end of the outer cylinder. Maintenance is achieved by replacing the filter bags when they become clogged. This improves the cleanliness of the liquid while facilitating maintenance.

[0037] Specifically, the upper end of the outer cylinder 341 is sealed with a removable cylinder cover 343, and the cylinder cover 343 is equipped with a pressure gauge for detecting the internal pressure. When the filter bag inside the bag filter becomes clogged, the internal pressure will change. By checking the pressure value on the pressure gauge, it can be determined whether the filter bag needs to be replaced, so as to facilitate maintenance and replacement.

[0038] In this embodiment, as Figure 8 and Figure 9 As shown, the inner wall of the outer cylinder 341 has a ring-shaped support ring 344. The outer diameter of the filter bag support frame 342 matches the inner diameter of the support ring 344, and the upper end has a radially outward protruding limiting ring. The filter bag support frame 342 is hung on the support ring 344 through the limiting ring. Simultaneously, a disc-shaped filter bag pressing plate 345 is provided on the filter bag support frame 342. The diameter of the filter bag pressing plate 345 matches the inner diameter of the outer cylinder 341 and presses against the limiting ring. The filter bag pressing plate 345 has through-holes. Multiple through-holes are evenly distributed along the circumference of the filter bag pressing plate 345, and the axial projection of all through-holes is located within the filter bag support frame 342.

[0039] Specifically, the filter bag pressing plate 345 has a handle 346 arranged radially along the side facing the cylinder cover. The handle 346 is made of elastic sheet material bent in an arc shape. The height of the handle 346 matches the distance between the support ring 344 and the cylinder cover 343, so that the cylinder cover 343 abuts against the handle 346.

[0040] In this way, since the handle is made of elastic sheet material, when the cap is sealed and installed on the outer cylinder, pressure is first applied to the handle, causing the handle to deform elastically and apply the elastic force to the filter bag pressure plate. The filter bag pressure plate can then firmly press the opening of the filter bag on the filter bag support frame, ensuring that the cutting fluid is reliably filtered through the filter bag.

[0041] When implementing, such as Figure 10 As shown, the secondary water tank 31 has a vertically arranged overflow baffle 312, the height of which is lower than the height of the secondary water tank 31, dividing the secondary water tank 31 into a first tank 313 and a second tank 314. The bag filter 34 is located in the first tank 313, and the secondary overflow port 311 is located in the second tank 314, and is lower than the overflow baffle 312. Specifically, the second tank 314 has a vertically arranged overflow pipe, the lower end of which penetrates the bottom of the second tank 314, and the secondary overflow port 311 is the top opening of the overflow pipe.

[0042] In this way, the cutting fluid filtered by the bag filter enters the first tank. The denser impurities settle in the first tank, making the upper layer of cutting fluid cleaner. It then flows into the second tank through the overflow baffle. The second tank controls the water level through a secondary overflow port, and allows excess cutting fluid to flow back into the filter tank through the secondary overflow port, thus realizing the circulation of the cutting fluid.

[0043] The second housing 314 is provided with a liquid level detection mechanism 4. The liquid level detection mechanism 4 includes a stand 41 provided on the second housing 314. A vertically sliding slide rod 42 is provided on the stand 41. A float ball 43 is provided at the lower end of the slide rod 42. A proximity switch is provided at the upper end of the stand 41.

[0044] In addition, a central water supply pump 7 is installed on the secondary water tank 31, and the central water supply pump 7 is located inside the second tank. A cutting fluid supply pump 8 is installed on the filter tank. In this way, the cutting fluid supply pump 8 and the central water supply pump 7 can respectively provide cutting fluid with different filtration precision to the machine tool.

[0045] like Figure 11As shown, a stainless steel belt oil separator 5 is installed on the filtrate tank 1, and the stainless steel belt of the stainless steel belt oil separator 5 extends into the filtrate tank 1. An oil-water separation tank 6 is connected to the oil outlet of the stainless steel belt oil separator 5. The oil-water separation tank 6 has a vertically arranged partition plate 61, which divides the oil-water separation tank 6 into an oil filtering zone 62 and a reflux zone 63. The oil filtering zone 62 is connected below the oil outlet of the stainless steel belt oil separator 5, and the top of the side wall has an oil filtering notch. The oil filtering notch has a downwardly inclined oil guide groove 64, and an oil storage tank 65 is connected below the oil guide groove. The upper end of the partition plate 61 is higher than the oil filtering notch, and the bottom has a channel connecting the oil filtering zone 62 and the reflux zone 63. The reflux zone 63 has a vertically through reflux pipe 66, and the height of the reflux pipe 66 is lower than the oil filtering notch.

[0046] In the composite scraper chip conveyor of this embodiment, during operation, the contaminated cutting fluid containing a large amount of chips first enters the primary filtration unit through the main inlet. Chips and large particles are trapped inside the unit. The chain in the scraper mechanism rotates, driving the scrapers to push the deposited chips forward along the bottom of the unit, ultimately lifting them to the chip discharge port for collection. Simultaneously, the liquid cutting fluid inside the unit undergoes preliminary filtration through the filter screen mechanism (i.e., the filter screen on the outside of the support cage) at the front of the main outlet, removing larger particles. The filtered cutting fluid then flows into the lower filtrate tank for temporary storage. During this process, a backwash pump pumps liquid through a Y-type filter into a spray pipe, spraying it outwards from inside the support cage to backwash the filter screen, preventing clogging. The washed-off impurities fall back to the bottom of the unit and are carried away by the scrapers.

[0047] The cutting fluid, after primary filtration, accumulates in the filtrate tank and is then pumped by the secondary pump through pipelines to the centrifugal filter. The cutting fluid enters the upper cylinder at high speed tangentially, creating a strong rotating flow within the cylinder. Under centrifugal force, denser fine impurities in the cutting fluid are thrown against the cylinder wall and settle down to the lower cylinder, ultimately returning to the main inlet through the centrifugal chip discharge port and ball valve pipeline to participate in primary filtration again. The cleaner cutting fluid located at the center of rotation is discharged through the top centrifugal outlet pipe and centrifugal diversion pipe, directly entering the bag filter above the secondary water tank.

[0048] Cutting fluid enters the bag filter through the liquid passage holes on the filter bag pressure plate and flows into the filter bag inside the outer cylinder. The liquid undergoes fine filtration through the filter bag, effectively trapping tiny suspended particles. The filtered, high-purity cutting fluid flows from the lower end of the outer cylinder into the first tank of the secondary water tank. At this stage, the cap on the top of the outer cylinder, with its elastic handle, firmly presses the filter bag pressure plate against the filter bag support frame, ensuring a tight seal and forcing all liquid to pass through the filter bag. If the filter bag becomes clogged, causing an increase in internal pressure, the pressure gauge will display an abnormal reading, prompting personnel to replace and maintain the filter.

[0049] The cutting fluid entering the first tank of the secondary water tank undergoes further settling and sedimentation. The clear liquid on top then overflows through the overflow baffle and flows into the second tank. The cutting fluid in the second tank is delivered to the machine tool via a central water supply pump to meet the cooling requirements of high-precision machining. When the fluid flow rate in the secondary water tank exceeds the machine tool's capacity, the excess cutting fluid automatically flows back to the filter tank through the secondary overflow port (overflow pipe) in the second tank, forming a closed-loop circulation of the cutting fluid. Simultaneously, a stainless steel belt degreasing machine on the filter tank scrapes off floating oil to an oil-water separation tank. The separated cutting fluid flows back to the filter tank, ensuring the cleanliness and quality of the cutting fluid throughout the entire circulation system. The primary filtrate in the filter tank is then pumped by the cutting fluid supply pump for routine rinsing.

[0050] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A two-stage filtration mechanism for high-pressure internal cooling center water outlet, characterized in that, The system includes a secondary water tank (31), on which a bag filter (34) is vertically mounted. The bag filter (34) includes a cylindrical outer cylinder (341), the lower end of which is connected to the secondary water tank (31), and a cylindrical filter bag support frame (342) is provided inside. A replaceable filter bag is provided on the filter bag support frame (342), and the upper edge of the filter bag forms a sealing fit with the inner wall of the outer cylinder (341). A secondary liquid inlet is provided on the outer cylinder (341), and the secondary liquid inlet is located above the filter bag.

2. The two-stage filtration mechanism for the outlet water of the high-pressure internal cooling center as described in claim 1, characterized in that, A centrifugal filter (33) is connected to the secondary inlet. The centrifugal filter (33) includes an upper cylindrical body (331) in the shape of a cylinder and a lower cylindrical body (332) in the shape of a funnel. The upper cylindrical body (331) has a centrifugal inlet arranged along the tangential direction. The centrifugal inlet is connected to a secondary water pump (32) for extracting cutting fluid through a pipeline. The top of the upper cylindrical body (331) has a coaxially through outlet pipe (333). The upper end of the outlet pipe (333) is connected to the secondary inlet through a pipeline, and the lower end extends downward into the upper cylindrical body (331) to form a centrifugal separation pipe (334).

3. The two-stage filtration mechanism for the outlet water of the high-pressure internal cooling center as described in claim 1, characterized in that, The inner wall of the outer cylinder (341) has a support ring (344) arranged in an annular shape. The outer diameter of the filter bag support frame (342) matches the inner diameter of the support ring (344), and the upper end has a limiting ring that protrudes outward in a radial direction. The filter bag support frame (342) is hung on the support ring (344) through the limiting ring.

4. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 3, characterized in that, The filter bag support frame (342) is covered with a disc-shaped filter bag pressure plate (345), the diameter of which matches the inner diameter of the outer cylinder (341); the filter bag pressure plate (345) has a through-hole for liquid passage.

5. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 4, characterized in that, The liquid passage holes are evenly distributed along the circumference of the filter bag pressure plate (345), and the axial projection of all the liquid passage holes is located within the filter bag support frame (342).

6. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 4, characterized in that, The upper end of the outer cylinder (341) is sealed with a removable cylinder cover (343); the filter bag pressure plate (345) has a handle (346) arranged radially along the side facing the cylinder cover, the handle (346) is made of elastic sheet material bent in an arc shape; the height of the handle (346) matches the distance between the support ring (344) and the cylinder cover (343), so that the cylinder cover (343) abuts against the handle (346).

7. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 6, characterized in that, The cylinder cover (343) is equipped with a pressure gauge for detecting the pressure inside the cylinder.

8. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 1, characterized in that, The secondary water tank (31) has a vertically arranged overflow baffle (312) inside. The height of the overflow baffle (312) is lower than the height of the secondary water tank (31), and the secondary water tank (31) is divided into a first tank (313) and a second tank (314). The bag filter (34) is located in the first tank (313), and the second tank (314) is provided with a secondary overflow port (311), which is lower than the overflow baffle (312).

9. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 8, characterized in that, The second housing (314) has a vertically arranged overflow pipe inside, the lower end of which penetrates the bottom of the second housing (314), and the secondary overflow port (311) is the top opening of the overflow pipe.

10. The two-stage filtration mechanism for high-pressure internal cooling center outlet water as described in claim 8, characterized in that, The second housing (314) is provided with a liquid level detection mechanism (4). The liquid level detection mechanism (4) includes a stand (41) provided on the second housing (314). A slide rod (42) that can slide vertically is provided on the stand (41). A float ball (43) is provided at the lower end of the slide rod (42). A proximity switch is provided at the upper end of the stand (41).