Single-shaft double-pipe mixing pile machine

Abstract

The invention relates to a single-shaft double-pipe mixing pile machine which comprises a pile frame and a power head, a drill rod connected with the power head is arranged on the pile frame, the single-shaft double-pipe mixing pile machine is characterized by further comprising an air compressor, the drill rod comprises an outer pipe and an inner pipe located in the outer pipe, an air channel is formed between the outer pipe and the inner pipe, and the air channel is communicated with the air compressor. The air channel is connected with the outlet end of the air compressor, a plurality of air injection holes are formed in the outer pipe, a cement paste input port is formed in one end of the inner pipe, a cement paste output port communicated with the outside of the outer pipe through a cement conveying pipe is formed in the other end of the inner pipe, and a stirring and smashing structure is arranged on the outer pipe. According to the single-shaft double-pipe mixing pile machine, cement can penetrate into a soil body, and the problem that the depth of cement sprayed by an existing mixing pile machine entering the soil body is small is solved.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation construction, in particular to a single-shaft double-tube mixing pile machine. Background Art

[0002] Cement-soil mixing piles are a method used to reinforce saturated soft clay foundations. They use cement as a curing agent and forcefully mix the soft soil and curing agent deep in the foundation through a special mixing machine. They use a series of physical and chemical reactions between the curing agent and the soft soil to harden the soft soil into a high-quality foundation with integrity, water stability and a certain strength. Cement and soft soil are mixed mechanically to form cement soil, which is based on a series of physical and chemical reactions between cement and soft soil.

[0003] Conventional ultra-deep cement-soil mixing piles are constructed by using a large high-tower cement-soil mixing pile machine with bottom spraying. However, due to site restrictions, only a small single-axis mixing pile machine can be used for construction. A large number of engineering practices have shown that the quality of the upper part of the cement-soil mixing pile body is significantly better than that of the lower part. When the cement mixing pile is constructed at the lower part of the pile, the sprayed cement slurry is not able to penetrate the soil, resulting in the cement slurry gathering near the drill bit.

[0004] In addition, when constructing soil in complex strata, cement mixing piles using traditional drill bits usually have the following problems: when there is a sand layer mixed in the clay layer, the cement slurry sprayed by the traditional drill bit is not fully mixed with the soil and then seeps through the sand layer and loses, resulting in slurry waste and reduced pile quality; the traditional drill bit is very easy to stick to the soil during the mixing pile construction process, resulting in the problem of drill sticking; the traditional drill bit cannot easily break up the soil blocks, resulting in larger soil blocks that cannot be mixed with the cement slurry; when constructing deep cement mixing piles, the traditional drill bit cannot drill easily, resulting in "drill stuck". Summary of the invention

[0005] The first object of the present invention is to provide a single-axis double-tube mixing pile machine that can make cement penetrate deeply into the soil, thereby solving the problem that the cement sprayed by the existing mixing pile machine penetrates shallowly into the soil.

[0006] The second purpose of the present invention is to further improve a single-axis double-tube mixing pile machine that can fully mix cement with soil to reduce the loss of cement when passing through the sand layer, solving the problem that the existing drill bit cannot fully mix and crush during construction, resulting in easy loss of cement when passing through the sand layer.

[0007] The above technical problems are solved by the following technical solutions: a single-axis double-tube mixing pile machine, the single-axis double-tube mixing pile machine includes a pile frame and a power head, the pile frame is provided with a drill rod connected to the power head, characterized in that it also includes an air compressor, the drill rod includes an outer tube and an inner tube located inside the outer tube, an air channel is formed between the outer tube and the inner tube, the air channel is connected to the outlet end of the air compressor, a plurality of jet holes are provided on the outer tube, one end of the inner tube is provided with a cement slurry input port, and the other end is provided with a cement slurry output port connected to the outside of the outer tube through a cement conveying pipe, and the outer tube is provided with a mixing and crushing structure. The shortcomings of only spraying grout during construction of the traditional drill bit are changed, and a cement slurry pipe and a high-pressure air pipe are set inside the drill bit, so that cement slurry and compressed air are sprayed out at the same time during construction. The spraying of compressed air can form a certain space between the drill bit and the soil during the mixing process, which is convenient for the spraying of cement slurry. At the same time, the compressed air can also separate the soil blocks attached to the blades, prevent the problem of holding the drill during mixing, and enable the soil to achieve the best mixing effect. The drill pipe is composed of inner and outer pipes to form a channel for conveying gas and cement slurry, and the installation is convenient.

[0008] Preferably, the outer end of the gas jet hole is provided with a conical outlet pipe head with a small outer end and a large inner end, the outer end of the cement delivery pipe is passed through and built into the conical outlet pipe head, and an outlet gap surrounding the outer periphery of the cement delivery pipe is formed between the outer end of the cement delivery pipe and the conical outlet pipe head, which can improve the patency of cement slurry output.

[0009] Preferably, the lower end of the inner tube is provided with a hollow connector, a connector sleeve is sealingly and rotatably connected to the connector, an air distribution groove is provided on the inner circumference of the connector sleeve, the cement slurry outlet is arranged on the connector and aligned with the air distribution groove, the cement delivery pipe is connected to the connector sleeve and communicated with the air distribution groove, the connector is fixed to the outer tube, the outer tube is connected to the power head and driven to rotate by the power head, and the inner tube remains stationary when the outer tube rotates. The power required for the rotation of the drill rod can be reduced.

[0010] Preferably, the opening shape of the jet hole is polygonal, the inner circumference of the end face of the jet hole is provided with an annular limiting step extending along the circumference of the jet hole, each side wall of the inner circumference of the jet hole is hinged with a cover plate connected to the radial outer end of the annular limiting step, all the cover plates close the jet hole when they are closed, a spring driving the cover plates to close is provided between the cover plates and the jet hole, and the cover plates are opened under the action of the airflow ejected from the jet hole. The jet hole can be automatically and synchronously switched with jetting, which can effectively avoid blockage.

[0011] Preferably, the stirring and crushing structure includes an upper horizontal blade, a lower horizontal blade and a spiral blade, which are arranged in sequence from top to bottom, and the two ends of the upper horizontal blade along the circumference of the outer tube are provided with upper horizontal blade cutting edges extending in the extension direction of the upper horizontal blade, the upper horizontal blade is connected to the upper ends of a plurality of upper vertical blades, and the upper vertical blades are distributed along the extension direction of the upper horizontal blade, the two ends of the upper vertical blade along the circumference of the outer tube are provided with upper vertical blade cutting edges extending in the extension direction of the upper vertical blade, the two ends of the lower horizontal blade along the circumference of the outer tube are provided with lower horizontal blade cutting edges extending in the extension direction of the lower horizontal blade, the lower horizontal blade is connected to the lower ends of a plurality of lower vertical blades, the lower vertical blade is distributed along the extension direction of the lower horizontal blade, the two ends of the lower vertical blade along the circumference of the outer tube are provided with lower vertical blade cutting edges extending in the extension direction of the lower vertical blade, and the lower end of the upper vertical blade extends downward beyond the upper end of the lower vertical blade. This technical solution, by providing vertical blades, overcomes the problem of insufficient blade mixing and loss of traditional drill bits when they pass through local sand layers during construction. At the same time, the vertical blades can better cut the soil, improve the mixing degree of cement slurry and soil, and enhance the uniformity and strength of piles. The drill bit of the present invention is provided with three types of blades, two different nozzles, and two types of drill bit lower end tips, which can more effectively solve the problems of slurry leakage, drill sticking, and difficulty in drilling in the construction of cement mixing piles in complex strata, thereby improving the construction quality and efficiency. The second invention purpose is achieved.

[0012] Preferably, the lower end surface of the outer tube is also provided with a plurality of drill bits distributed along the circumference of the outer tube, and the lower ends of all the drill bits are gathered together, so as to simultaneously cut the soil and assist the drill bit in drilling, thereby improving the construction efficiency when constructing in deep layers or hard soil.

[0013] Preferably, the grouting port is located between the upper horizontal blade and the lower horizontal blade, which can effectively prevent the cement slurry from being injected into the hole wall and then lost when passing through the sandstone layer.

[0014] Preferably, an air passage is provided inside the outer tube, and the air passage is provided with an exhaust hole penetrating the circumference of the outer tube. To change the deficiency of only spraying grout during the construction of the traditional drill bit, a cement slurry pipe and a high-pressure air pipe are provided inside the drill bit, so that cement slurry and compressed air can be sprayed out simultaneously during the construction. The spraying of compressed air can form a certain space between the drill bit and the soil during the mixing process, which is convenient for the cement slurry to be sprayed out. At the same time, the compressed air can also separate the soil blocks attached to the blades, prevent the problem of the drill bit sticking during mixing, and enable the soil body to achieve the best mixing effect.

[0015] Preferably, the exhaust hole and the grouting port are located on the same horizontal plane, which can improve the depth and efficiency of cement slurry mixing into the soil.

[0016] Preferably, when the outer tube rotates toward the direction of drilling into the soil, the exhaust holes and the grouting ports are distributed from front to back along the rotation direction of the outer tube, so that the airflow can form gaps in the soil slurry before the cement slurry is sprayed out, thereby facilitating the mixing of the cement slurry.

[0017] Preferably, the upper horizontal blade and the lower horizontal blade are arranged at intervals along the circumference of the outer tube, which can improve the cutting effect on the soil and facilitate slurrying.

[0018] Preferably, it also includes an isolation tube sleeved on the outer tube, the grouting port is located inside the space surrounded by the isolation tube, the isolation tube is connected to the suspension ring through a connecting rod, the suspension ring is sleeved on the outer tube, a supporting ring and a pressing ring located above the supporting ring are provided on the outer tube, the suspension ring is located between the supporting ring and the pressing ring, the supporting ring is used to push up the suspension ring when the outer tube moves upward, and the pressing ring is used to press down the suspension ring when the outer tube moves downward. The formed mixing pile hole can be isolated from the surrounding land, thereby preferably avoiding the loss of cement slurry through the sand and gravel layer, the isolation sleeve can be raised and lowered together with the outer tube without synchronous rotation, thereby ensuring the isolation of the dynamic grouting from the hole wall and avoiding the increase in the load that leads to an increase in the equipment power required to form the mixing pile.

[0019] Preferably, the lower horizontal blade is fixedly connected to the outer tube, the outer tube is sleeved with an inner gear ring and an outer gear ring, the outer gear ring is coaxially fixed to the outer tube, the inner gear ring is meshed with a plurality of intermediate gears, the intermediate gears are meshed with the inner gear ring, the intermediate gears are distributed along the circumference of the inner gear ring, the outer gear ring can be rotatably supported on a boss fixed to the outer tube, the upper horizontal blade is fixed to the outer gear ring, and the upper vertical blade and the lower vertical blade are staggered along the circumference of the outer tube. The connected outer tube enables the upper and lower vertical blades to rotate in opposite directions, which can make the relative speed of the vertical blades fast when the outer tube rotates, thereby improving the crushing and cutting effect on the soil.

[0020] The present invention has the following advantages: it can make cement slurry penetrate deeper into the soil; by setting a vertical blade, the invention overcomes the problem of insufficient blade mixing and loss when the traditional drill bit passes through the local sand layer during construction. At the same time, the vertical blade can better cut the soil, improve the mixing degree of cement slurry and soil, and improve the uniformity and strength of pile formation. The setting of spiral annular blades and double-tooth spiral tips at the bottom can simultaneously cut the soil and assist the drill bit in drilling, thereby improving the construction efficiency when constructing in deep layers or harder soils. To change the deficiency of only spraying slurry during construction of traditional drill bits, a cement slurry pipe and a high-pressure air pipe are set inside the drill bit, so that cement slurry and compressed air can be sprayed out at the same time during construction. The spraying of compressed air can form a certain space between the drill bit and the soil during the mixing process, which is convenient for the spraying of cement slurry. At the same time, compressed air can also separate the soil blocks attached to the blades, prevent the problem of holding the drill during mixing, and enable the soil to achieve the best mixing effect. The drill bit of the present invention is provided with three types of blade forms, two different nozzles and two types of drill bit lower end tips, which can more effectively solve the problems of slurry leakage, drill sticking, difficulty in drilling and so on in the construction of cement mixing piles in complex strata, and improve the construction quality and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of embodiment 1; Figure 2 is a cross-sectional schematic diagram of the lower portion of the drill rod in Example 1; Figure 3 It is a schematic diagram of the drill rod in the second embodiment; Figure 4 for Figure 3 A schematic cross-sectional view of the lower end of the drill pipe; Figure 5 for Figure 3 A local enlarged schematic diagram of point A; Figure 6 for Figure 3 A local enlarged schematic diagram of B; Figure 7 for Figure 3 C-C cross-sectional schematic diagram; Figure 8 for Figure 4 A local enlarged schematic diagram of point D.

[0022] In the figure: outer tube 1, cement slurry input channel 2, spraying port 3, air channel 4, exhaust hole 5, upper horizontal blade 6, lower horizontal blade 7, pile frame 8, upper vertical blade 9, lower vertical blade 10, power head 11, isolation tube 12, connecting rod 13, suspension ring 14, supporting ring 15, pressing ring 16, inner gear ring 17, outer gear ring 18, intermediate gear 19, boss 20, supporting ball 21, drill rod 22, inner tube 23, cement conveying pipe 24, cement slurry output port 25, stirring and crushing structure 26, conical air outlet pipe head 27, air outlet gap 28, connector 29, connecting sleeve 30, air distribution groove 31, annular limit step 32, cover plate 33, hinge shaft 34. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1, see Figure 1 and Figure 2 A single-axis double-tube mixing pile machine includes a pile frame 8 and a power head 11. The pile frame is provided with a drill rod 22 connected to the power head. It also includes an air compressor. The drill rod includes an outer tube 1 and an inner tube 23 located inside the outer tube. An air passage 4 is formed between the outer tube and the inner tube. The air passage is connected to the outlet end of the air compressor. The outer tube is provided with a plurality of air injection holes 5. One end of the inner tube is provided with a cement slurry input port, and the other end is provided with a cement slurry output port 25 connected to the outside of the outer tube through a cement delivery pipe 24 (see Figure 4 ), the outer tube is provided with a stirring and crushing structure 26. The stirring and crushing structure is a plurality of stirring rods. The inner space of the inner tube constitutes a grouting port 3. The port of the cement delivery pipe 24 constitutes a grouting port 3.

[0025] Embodiment 2 is different from Embodiment 1 in that: See also Figures 3 to 7The outer end of the jet hole is provided with a conical air outlet pipe head 27 with a small outer end and a large inner end. The outer end of the cement conveying pipe is inserted into and built into the conical air outlet pipe head. An air outlet gap 28 surrounding the outer periphery of the cement conveying pipe is formed between the outer end of the cement conveying pipe and the conical air outlet pipe head. A hollow connector 29 is provided at the lower end of the inner pipe. A connecting sleeve 30 is sealingly and rotatably connected to the connector. An air distribution groove 31 is provided on the inner circumference of the connecting sleeve. The cement slurry output port is provided on the connector and aligned with the air distribution groove. The cement conveying pipe is connected to the connecting sleeve and communicated with the air distribution groove. The connector is fixed to the outer pipe. The outer pipe is connected to the power head and is driven to rotate by the power head. When the outer pipe rotates, the inner pipe remains stationary. The opening shape of the jet hole is polygonal, and the inner circumference of the end face of the jet hole is provided with an annular limiting step 32 extending along the circumference of the jet hole. A cover plate 33 connected to the radial outer end of the annular limiting step is hinged on each side wall of the inner circumference of the jet hole through a hinge shaft 34. When all the cover plates are closed, the jet hole is closed. A spring for driving the cover plates to close is provided between the cover plates and the jet hole, and the cover plates are opened under the action of the airflow ejected from the jet hole.

[0026] The stirring and crushing structure includes an upper horizontal blade 6 and a lower horizontal blade 7 which are sequentially arranged on the outer tube from top to bottom. The upper horizontal blade is provided with upper horizontal blade portion cutting edges extending along the extension direction of the upper horizontal blade at both ends of the upper horizontal blade along the circumference of the outer tube. The upper horizontal blade is connected with the upper ends of a plurality of upper vertical blades 9. The upper horizontal blade exceeds the spiral blade in the radial direction of the outer tube. The upper vertical blades are distributed along the extension direction of the upper horizontal blade, and the upper vertical blade is provided with upper vertical blade portion cutting edges extending along the extension direction of the upper vertical blade at both ends of the upper vertical blade along the circumference of the outer tube. The lower horizontal blades are provided with lower horizontal blade cutting edges extending in the extending direction of the lower horizontal blades at both ends of the lower horizontal blades along the circumference of the outer tube, the lower horizontal blades are connected with the lower ends of a plurality of lower vertical blades 10, the lower vertical blades are distributed along the extending direction of the lower horizontal blades, the lower vertical blades are provided with lower vertical blade cutting edges extending in the extending direction of the lower vertical blades at both ends of the lower vertical blades along the circumference of the outer tube, and the lower ends of the upper vertical blades extend downward beyond the upper ends of the lower vertical blades. The spraying port is located between the upper horizontal blades and the lower horizontal blades. The upper horizontal blades and the lower horizontal blades are arranged at intervals along the circumference of the outer tube.

[0027] It also includes an isolation tube 12 sleeved on the outer tube, and the spraying port is located inside the space surrounded by the isolation tube. The isolation tube is connected to a suspension ring 14 through a connecting rod 13. The suspension ring is sleeved on the outer tube, and a supporting ring 15 and a pressing ring 16 located above the supporting ring are provided on the outer tube. The suspension ring is located between the supporting ring and the pressing ring. The supporting ring is used to push up the suspension ring when the outer tube moves upward, and the pressing ring is used to press down the suspension ring when the outer tube moves downward.

[0028] The lower horizontal blade is fixedly connected to the outer tube, and the outer tube is sleeved with an inner gear ring 17 and an outer gear ring 18, the outer gear ring is coaxially fixed to the outer tube, the inner gear ring is meshed with a plurality of intermediate gears 19, the intermediate gears are meshed with the inner gear ring, and the intermediate gears are distributed along the circumference of the inner gear ring. The outer gear ring can be rotatably supported on a boss 20 fixed to the outer tube, specifically: a boss annular groove extending along the circumference of the outer tube is provided on the upper surface of the convex strip, and a gear ring annular groove extending along the circumference of the outer tube is provided on the lower surface of the outer gear ring, the boss annular groove is aligned with the gear ring annular groove, and a plurality of support balls 21 supported in the Chongqing annular groove are provided in the boss annular groove. The upper horizontal blade is fixed to the outer gear ring, and the upper vertical blade and the lower vertical blade are staggered along the circumference of the outer tube.

[0029] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0030] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A single-axis double-tube mixing pile machine, comprising a pile frame and a power head, wherein the pile frame is provided with a drill rod connected to the power head, characterized in that: It also includes an air compressor. The drill pipe includes an outer tube and an inner tube located inside the outer tube. An air passage is formed between the outer tube and the inner tube. The air passage is connected to the outlet end of the air compressor. The outer tube is provided with a plurality of jet holes. One end of the inner tube is provided with a cement slurry input port, and the other end is provided with a cement slurry output port connected to the outside of the outer tube through a cement conveying pipe. The outer tube is provided with a stirring and crushing structure.

2. A single-axis double-tube mixing pile machine according to claim 1, characterized in that: The outer end of the air jet hole is provided with a conical air outlet pipe head with a small outer end and a large inner end. The outer end of the cement conveying pipe is passed through and built into the conical air outlet pipe head. An air outlet gap surrounding the outer periphery of the cement conveying pipe is formed between the outer end of the cement conveying pipe and the conical air outlet pipe head.

3. A single-axis double-tube pile mixing machine according to claim 1 or 2, characterized in that: The lower end of the inner tube is provided with a hollow connector, and a connecting sleeve is sealingly and rotatably connected to the connecting head. An air distribution groove is provided on the inner circumference of the connecting sleeve. The cement slurry outlet is arranged on the connecting head and is aligned with the air distribution groove. The cement conveying pipe is connected to the connecting sleeve and communicated with the air distribution groove. The connecting head is fixed to the outer tube, and the outer tube is connected to the power head and is driven to rotate by the power head. When the outer tube rotates, the inner tube remains stationary.

4. A single-shaft double-tube mixing pile machine according to claim 1 or 2, characterized in that: The opening shape of the jet hole is polygonal, and the inner circumference of the end face of the jet hole is provided with an annular limiting step extending circumferentially along the jet hole. A cover plate connected to the radial outer end of the annular limiting step is hinged on each side wall of the inner circumference of the jet hole. When all the cover plates are closed, the jet hole is closed. A spring for driving the cover plates to close is provided between the cover plates and the jet hole, and the cover plates are opened under the action of the airflow ejected from the jet hole.

5. A single-axis double-tube mixing pile machine according to claim 1 or 2, characterized in that: The stirring and crushing structure includes an upper horizontal blade, a lower horizontal blade and a spiral blade, which are arranged in sequence from top to bottom, and the two ends of the upper horizontal blade along the circumference of the outer tube are provided with upper horizontal blade cutting edges extending in the extension direction of the upper horizontal blade, and the upper horizontal blade is connected to the upper ends of a plurality of upper vertical blades, and the upper vertical blades are distributed along the extension direction of the upper horizontal blade, and the two ends of the upper vertical blade along the circumference of the outer tube are provided with upper vertical blade cutting edges extending in the extension direction of the upper vertical blade, and the two ends of the lower horizontal blade along the circumference of the outer tube are provided with lower horizontal blade cutting edges extending in the extension direction of the lower horizontal blade, and the lower horizontal blade is connected to the lower ends of a plurality of lower vertical blades, and the lower vertical blade is distributed along the extension direction of the lower horizontal blade, and the two ends of the lower vertical blade along the circumference of the outer tube are provided with lower vertical blade cutting edges extending in the extension direction of the lower vertical blade, and the lower end of the upper vertical blade extends downward beyond the upper end of the lower vertical blade.

6. A single-shaft double-tube mixing pile machine according to claim 1 or 2, characterized in that: The lower end surface of the outer tube is also provided with a plurality of drill bits distributed along the circumference of the outer tube, and the lower ends of all the drill bits are gathered together.

7. The single-shaft double-tube mixing pile machine according to claim 5, characterized in that: The upper horizontal blade strips and the lower horizontal blade strips are arranged at intervals along the circumference of the outer tube.

8. A single-shaft double-tube mixing pile machine according to claim 1 or 2, characterized in that: It also includes an isolation cylinder sleeved on the outer tube, the outlet end of the cement delivery pipe is located inside the space surrounded by the isolation cylinder, the isolation cylinder is connected to the suspension ring through a connecting rod, the suspension ring is sleeved on the outer tube, the outer tube is provided with a supporting ring and a pressing ring located above the supporting ring, the suspension ring is located between the supporting ring and the pressing ring, the supporting ring is used to push up the suspension ring when the outer tube moves upward, and the pressing ring is used to press down the suspension ring when the outer tube moves downward.

9. A single-shaft double-tube mixing pile machine according to claim 1 or 2, characterized in that: The lower horizontal blade is fixedly connected to the outer tube, and the outer tube is sleeved with an inner gear ring and an outer gear ring, the outer gear ring is coaxially fixed to the outer tube, the inner gear ring is meshed with a plurality of intermediate gears, the intermediate gears are meshed with the inner gear ring, the intermediate gears are distributed along the circumference of the inner gear ring, the outer gear ring can be rotatably supported on a boss fixed on the outer tube, the upper horizontal blade is fixed on the outer gear ring, and the upper vertical blade and the lower vertical blade are staggered along the circumference of the outer tube.

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