Liftable spiral-flow aerator

Abstract

The utility model provides a liftable spiral-flow aerator, which belongs to the technical field of sewage aeration, and structurally comprises an aeration tank and an aeration cylinder, the aeration cylinder is suspended above the bottom of the aeration tank, and the aeration cylinder is vertically arranged; spiral blades which are vertically arranged along the axial direction are arranged in the main body section of the inner cavity of the aeration cylinder, and each spiral blade divides the cylindrical inner cavity of the aeration cylinder into two spiral flow channels; every two adjacent spiral blades have opposite rotation directions and are alternately arranged in the vertical direction of the inner cavity of the aeration cylinder; an air inlet pipe is communicated with the cylinder wall of the main body at the bottom of the aeration cylinder in a penetrating manner, an aeration pipe network main pipe is arranged above the aeration tank, and an air path of a downlink lower branch pipe is communicated with the air inlet pipe; and the aeration pipe network main pipe, the descending upper branch pipe, the descending lower branch pipe, the aeration cylinder and the aeration tank form a lifting type aeration system. The aeration device can be overhauled without stopping production, stopping water and discharging water, is convenient to overhaul and good in aeration effect, and saves energy.

Description

Technical Field

[0001] The utility model relates to the technical field of sewage aeration, in particular to a liftable cyclone aerator. Background Art

[0002] Generally, the main functions of an aerator in a sewage treatment plant’s aerobic tank are: (1) oxygenation, transferring oxygen from the air into the mixed liquid to meet the respiration needs of microorganisms in the activated sludge; and (2) stirring and mixing, so that the mixed liquid is in a violent mixing state, allowing the activated sludge, dissolved oxygen, and organic matter to fully contact each other, while preventing sludge from settling.

[0003] The jet aeration blind area is large, which can easily cause serious mud accumulation at the bottom of the pool. The jet aerator is prone to scaling and clogging the aeration head, resulting in a decrease in oxygen utilization, uneven distribution of dissolved oxygen, increased energy consumption, and the fixed type is not easy to repair and clean. The jet pump and pipeline are seriously eroded and cavitated, with many leakage points. The aeration head needs to be stopped and the pool needs to be drained before entering the maintenance. There are problems such as uncontrollable gas in the confined space, high safety risks for maintenance, and high costs.

[0004] The principle of microporous aeration is to squeeze the air and escape from the micropores of the rubber diaphragm to form tiny bubbles that diffuse into the water. The oxygen utilization rate can reach more than 30% in 6 meters of clean water, which is the aerator with the highest oxygen utilization rate. Microporous aerators are more suitable for use in low-concentration wastewater such as domestic wastewater. They are easy to clog and break in industrial wastewater and have a short lifespan. Because there is no stirring function, sludge deposition is easy to occur.

[0005] The principle of traditional cyclone aerators is that the airflow is ejected at high speed, mixed with sewage in the cylinder, and cut into tiny bubbles by the collision of the mushroom head during the rotating upward process. At the same time, negative pressure is formed at the bottom to suck up the sludge at the bottom of the pool.

[0006] Cyclone is a new type of aeration process that has emerged in recent years. The oxygen utilization rate of 6-meter clean water is about 18%-22%. Because it can be installed without stopping production, is not easy to be blocked, has a service life of more than ten years, and has moderate energy consumption, it has been widely used in industrial wastewater in recent years. Summary of the invention

[0007] The technical task of the utility model is to solve the deficiencies of the prior art and provide a liftable cyclone aerator.

[0008] The technical solution of the utility model is implemented in the following manner: a liftable cyclone aerator of the utility model comprises an aeration tank and an aeration cylinder, the aeration cylinder is suspended above the bottom of the aeration tank, and the aeration cylinder is vertically arranged;

[0009] The upper and lower ends of the main body wall of the aeration cylinder are respectively provided with end flanges;

[0010] The main body section of the inner cavity of the aeration cylinder is provided with spiral blades arranged vertically along the axial direction, and the overall diameter of each spiral blade is equal to the cavity diameter of the inner cavity of the aeration cylinder; the lateral edge of each spiral blade is fixedly connected to the inner wall of the aeration cylinder;

[0011] Each spiral blade divides the cylindrical inner cavity of the aeration cylinder where it is located into two spiral flow channels;

[0012] In the vertical direction, the rotation directions of each two adjacent spiral blades are opposite: one is a left-hand spiral blade, and the other is a right-hand spiral blade, and the two are arranged alternately in the vertical direction of the inner cavity of the aeration cylinder;

[0013] Each spiral blade has a flat starting edge at its starting end and a flat ending edge at its ending end;

[0014] The spiral rise height of each spiral blade adopts half the pitch;

[0015] The flat start edge of each spiral blade and the flat end edge of the body are parallel to each other, and the two are respectively located on the inner cavity diameter of the aeration cylinder;

[0016] For every two adjacent spiral blades: the flat end edge of the first spiral blade and the flat start edge of the adjacent second spiral blade intersect vertically in the same plane; the two spiral flow channels of the flat end edge of the first spiral blade are cut by the flat start edge of the second spiral blade;

[0017] An air inlet pipe is intersected and connected on the main body wall at the bottom of the aeration cylinder. The air inlet pipe is perpendicular to the aeration cylinder. The inner end of the air inlet pipe is connected to the inner cavity at the bottom of the aeration cylinder. An air inlet pipe flange is arranged at the outward end of the air inlet pipe.

[0018] An aeration pipe network main pipe is arranged above the aeration tank, a downward upper branch pipe is connected to the diversion node of the aeration pipe network main pipe, a downward lower branch pipe is connected in series downstream of the downward upper branch pipe, a pipe body of the downward lower branch pipe extends downward to above the bottom of the aeration tank, and a terminal end of the downward lower branch pipe is connected to an air inlet pipe flange of an air inlet pipe through an elbow; an air path of the downward lower branch pipe is connected to the air inlet pipe;

[0019] The aeration pipe network main pipe, the downward upper branch pipe, the downward lower branch pipe, the aeration cylinder and the aeration tank constitute a liftable aeration system.

[0020] The main body wall of the aeration cylinder is composed of two semi-cylindrical walls which are relatively sealed and fixedly connected to form a cylindrical structure that penetrates from top to bottom.

[0021] The length span of each spiral blade in the inner cavity of the aeration cylinder is the same.

[0022] The body of the aeration cylinder is provided with a fixing ear, and a clamping hoop is provided between the fixing ear and the bottom section of the lower branch pipe.

[0023] The hanging height of the aerator is 200±20 mm from the bottom of the aeration tank to the bottom of the aeration tank.

[0024] The aeration tank adopts an open top aeration tank or a fully enclosed steel concrete aeration tank;

[0025] A process hole is opened on the top of the fully enclosed steel concrete aeration tank, a cover plate is arranged on the process hole, and a downward branch pipe penetrates the cover plate and extends into the bottom of the space in the aeration tank to communicate with the air inlet pipe of the aeration cylinder.

[0026] The air inlet pipe is connected to the inner cavity of the aeration cylinder in radial or tangential direction;

[0027] The connecting position of the air inlet pipe is located below the lowest spiral blade in the aeration cylinder.

[0028] Each spiral blade in the aeration cylinder has the same characteristics except the direction of rotation, such as the spiral diameter, lead, and angle of rise.

[0029] Each spiral blade in the aerator has different characteristics except the direction of rotation.

[0030] The air inlet pipe is provided with an extended end section in the inner cavity of the aeration cylinder. The extended end section of the air inlet pipe extends toward the center of the aeration cylinder and bends upward in the direction of the central axis of the aeration cylinder. The bent end opens toward the flat starting edge of the spiral blade.

[0031] Compared with the prior art, the utility model has the following beneficial effects:

[0032] The utility model discloses a liftable cyclone aerator, the structural design of which is combined with fluid mechanics to realize efficient and energy-saving aeration. The installation method of the liftable cyclone aerator is convenient for future maintenance, and the maintenance can be performed without stopping production, stopping water, or draining water. The maintenance is convenient, the aeration effect is good, and energy is saved.

[0033] The gas-liquid foam entrainment at the bottom of the aeration cylinder rises, and is cut by the flat starting edge of the first spiral blade to form a two-way spiral turbulent flow channel for mixing, and then rises to the second spiral blade. The two-way spiral turbulent flow channels just after leaving the flat ending edge of the first spiral blade are cut into four-way gas-liquid foam entrainment by the flat starting edge of the second spiral blade. The four-way gas-liquid foam entrainment is merged into two in the two-way spiral flow channels of the second spiral blade and continues to be disturbed under the guidance of the counter-rotating spiral blade, rising in the counter-rotating direction. In this way, it is cut and disturbed in the counter-rotating direction every time it passes through a spiral blade. Until it rises and leaves the aeration cylinder. After rising to the liquid surface of the aeration tank with the gas-liquid foam entrainment, it sinks to the bottom of the tank and enters the aeration cylinder with the flow, forming a circulating aeration.

[0034] The spiral blades not only play a cutting role, but also play a spiral turbulence role in achieving radial mixing in the channel, which increases the gas-liquid contact time and the gas-liquid contact route. The design of alternating positive and reverse spirals also greatly increases turbulence and disturbance. The gas and liquid collide, cut and mix with each other, and the gas-liquid contact area continues to increase, which increases the aeration effect.

[0035] The utility model adopts underwater aeration and cooperates with complex disturbance aeration to increase the transfer speed of oxygen in the aeration process. Since the aerator is close to the bottom of the pool, the flow rate at the bottom of the pool is fast, and sludge precipitation can be prevented in a relatively large range.

[0036] The air intake method of the aeration pipe network main pipe is compressed air delivery.

[0037] The characteristics of cyclone aeration are:

[0038] (1) The air release port has a large diameter, small resistance, small pressure loss, and is not easy to be blocked.

[0039] (2) The air spirals upward and creates a pressure drop through the aerator. Due to the air lift effect, about 1.3 times the amount of water enters the aerator.

[0040] (3) Air and water swirl vigorously and rise upward.

[0041] (4) The internal structure of the aerator uses strong centrifugal force to mix and cut air and water, turning the air into micro bubbles.

[0042] (5) The fully mixed air and water rush upward with great force.

[0043] (6) Strong circulating water flow causes the air and water to rush to the bottom of the pool, allowing the bottom sludge to participate in the circulation.

[0044] (7) Small bubbles move downward, increasing the time they stay in the water and improving the efficiency of dissolved oxygen.

[0045] The utility model has a wide application range and can be used for various waste waters such as municipal and industrial waste waters, and is particularly suitable for papermaking, chemical, printing and dyeing, and food industries.

[0046] Reduce the maintenance frequency of the aeration tank. The probability of aeration system blockage will be greatly reduced, and the frequency of operation and maintenance by on-site operators will also be greatly reduced. If there is no large volume of garbage (such as garbage bags, etc.) in the pool, it can be never blocked and maintenance-free for life.

[0047] Reduce the failure rate of the blower. Under the condition of the same air supply volume, due to the extremely low resistance loss of this aerator, the current of the fan operation will be significantly reduced compared with other aeration methods, so the actual operating energy consumption of the fan is reduced, and the long-term stable operation of the fan can be guaranteed.

[0048] Save the cost of pool cleaning, installation and maintenance. The lifting suspension installation method can be adopted, which is simple and convenient to install, and can achieve the goal of not cleaning the pool and draining, and installing and replacing the aeration equipment with water; and the lifting cyclone aerator can stir up the sludge accumulated at the bottom of the pool and discharge it into the aeration pool, playing the role of cleaning and expanding the aeration pool; after being put into operation, there will be no sludge accumulation at the bottom of the aeration pool, thus saving the cost of pool cleaning and maintenance.

[0049] Improve the stability of the aeration tank's treatment capacity. Its structure is mainly composed of three parts: the outer cylinder, the air inlet pipe, and the spiral blade. All of them are fixed parts, and there are no running parts. Imported PA66+30GF material can be used, which has the advantages of light weight, high strength, and strong corrosion resistance, which can bring ultra-long service life and constant performance.

[0050] The utility model has a designed service life of more than 10 years. For normal water quality without strong acid or strong alkali, the service life can generally reach more than 15 years. During use, its performance remains constant and will not decay with the increase of use time, thereby greatly improving the stability of the aeration tank's treatment capacity.

[0051] No silt deposition: After 1.3 times the amount of air is sucked in, the water flow circulates vigorously throughout the pool, improving the metabolic efficiency of microorganisms and eliminating silt accumulation at the bottom of the pool.

[0052] Abandoning the design idea of ​​burying the aeration main pipe under the pool bottom or laying it on the pool bottom, the aeration main pipe is arranged above the aeration tank. On the one hand, the air gas pipeline above is easy to inspect and maintain, and the corrosion resistance of the pipeline is easy to maintain; on the other hand, the layout of the pipeline in the aeration tank is completely omitted, almost no silt precipitation is generated, and dredging is basically unnecessary.

[0053] The utility model adopts an integral hanging type, is easy to install, and can be installed with water without stopping production.

[0054] The utility model discloses a liftable cyclone aerator which has reasonable design, simple structure, safety and reliability, convenient use and easy maintenance, and has good promotion and use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Attached Figure 1 It is a structural schematic diagram of the utility model;

[0056] Attached Figure 2 It is a three-dimensional structural schematic diagram of the aeration cylinder of the utility model;

[0057] Attached Figure 3 The utility model is a schematic diagram of the top process hole structure of a fully enclosed steel concrete aeration tank.

[0058] The symbols in the accompanying drawings represent:

[0059] 1. Aeration tank, 2. Aeration cylinder,

[0060] 3. Semi-cylindrical wall, 4. End flange, 5. Inner cavity of aeration cylinder, 6. Spiral blades,

[0061] 7. Spiral flow channel,

[0062] 8. Left-hand spiral blade, 9. Right-hand spiral blade,

[0063] 10. Flat start edge, 11. Flat end edge,

[0064] 12. Intake pipe, 13. Intake pipe flange,

[0065] 14. Aeration pipe network main pipe, 15. Diversion node, 16. Downward upper branch pipe, 17. Downward lower branch pipe,

[0066] 18. Tightening hoop, 19. Elbow,

[0067] 20. Process hole, 21. Cover plate, 22. Top of the fully enclosed steel concrete aeration tank. DETAILED DESCRIPTION

[0068] The following is a detailed description of a liftable cyclone aerator of the utility model in conjunction with the accompanying drawings.

[0069] As shown in the attached drawings, a liftable cyclone aerator of the utility model comprises an aeration tank 1 and an aeration cylinder 2, wherein the aeration cylinder 2 is suspended above the bottom of the aeration tank 1 and is vertically arranged;

[0070] The upper and lower ends of the main body wall of the aeration cylinder 2 are respectively provided with end flanges 4;

[0071] The main body of the inner cavity of the aeration cylinder 2 is provided with spiral blades 6 arranged vertically along the axial direction, and the overall diameter of each spiral blade is equal to the cavity diameter of the inner cavity of the aeration cylinder; the lateral edge of each spiral blade is fixedly connected to the inner wall of the aeration cylinder;

[0072] Each spiral blade divides the cylindrical inner cavity of the aeration cylinder where it is located into two spiral flow channels 7;

[0073] In the vertical direction, the rotation directions of each two adjacent spiral blades are opposite: one is a left-hand spiral blade 8, and the other is a right-hand spiral blade 9, and the two are alternately arranged in the vertical direction of the inner cavity of the aeration cylinder;

[0074] Each spiral blade has a flat starting edge 10 at its starting end and a flat ending edge 11 at its ending end;

[0075] The spiral rise height of each spiral blade adopts half the pitch;

[0076] The flat start edge 10 of each spiral blade and the flat end edge 11 of the body are parallel to each other, and the two are respectively located on the inner cavity diameter of the aeration cylinder;

[0077] For every two adjacent spiral blades: the flat end edge of the first spiral blade and the flat start edge of the adjacent second spiral blade are perpendicular to each other in the same plane or perpendicular to each other in different planes (when they are perpendicular to each other in different planes, the two adjacent spiral blades are arranged at intervals); the two spiral flow channels of the flat end edge of the first spiral blade are cut by the flat start edge of the second spiral blade;

[0078] An air inlet pipe 12 is intersected and connected to the main body wall at the bottom of the aeration cylinder. The air inlet pipe is perpendicular to the aeration cylinder. The inner end of the air inlet pipe is connected to the inner cavity at the bottom of the aeration cylinder. An air inlet pipe flange 13 is provided at the outward end of the air inlet pipe.

[0079] An aeration pipe network main pipe 14 is arranged above the aeration tank 1, and a downward upper branch pipe 16 is connected to the diversion node 15 of the aeration pipe network main pipe, and a downward lower branch pipe 17 is connected in series downstream of the downward upper branch pipe 16. The pipe body of the downward lower branch pipe 17 extends downward into the top of the bottom of the aeration tank, and the end of the downward lower branch pipe is connected to the intake pipe flange 13 of the intake pipe through an elbow 19; the gas path of the downward lower branch pipe is connected to the intake pipe;

[0080] The aeration pipe network main pipe, the downward upper branch pipe, the downward lower branch pipe, the aeration cylinder and the aeration tank constitute a liftable aeration system.

[0081] The main body wall of the aeration cylinder is composed of two semi-cylindrical cylinder walls 3 which are relatively sealed and fixedly connected to form a cylindrical cylinder structure that penetrates from top to bottom.

[0082] The length span of each spiral blade in the inner cavity of the aeration cylinder is the same.

[0083] The aeration tube body is provided with a fixing ear, and a clamping hoop 18 is provided between the fixing ear and the bottom section of the lower branch pipe body.

[0084] The hanging height of the aerator is 200±20 mm from the bottom of the aeration tank to the bottom of the aeration tank.

[0085] The aeration tank adopts an open top aeration tank or a fully enclosed steel concrete aeration tank;

[0086] A process hole 20 is provided on the top of the fully enclosed reinforced concrete aeration tank, a cover plate 21 is provided on the process hole 20, and a descending lower branch pipe 17 penetrates the cover plate and extends into the bottom of the space in the aeration tank to communicate with the air inlet pipe of the aeration cylinder.

[0087] The air inlet pipe is connected to the inner cavity of the aeration cylinder in radial or tangential direction;

[0088] The connecting position of the air inlet pipe is located below the lowest spiral blade in the aeration cylinder.

[0089] Each spiral blade in the aeration cylinder has the same characteristics except the direction of rotation, such as the spiral diameter, lead, and angle of rise.

[0090] Each spiral blade in the aerator has different characteristics except the direction of rotation, such as the diameter, lead, and angle of rise of the spiral.

[0091] The air inlet pipe is provided with an extended end section in the inner cavity of the aeration cylinder. The extended end section of the air inlet pipe extends toward the center of the aeration cylinder and bends upward in the direction of the central axis of the aeration cylinder. The bent end opens toward the flat starting edge of the spiral blade.

[0092] An extended design of the utility model: the aeration cylinder is provided with a plurality of channel cavities, each of which is provided with spiral blades arranged alternately in rotational directions; and the channel cavities are parallel to each other, and the end of the air inlet pipe faces the plurality of channel cavities.

[0093] The spiral blade of the utility model is a fixed spiral blade twisted by 180°, which is divided into two types: left-handed and right-handed. The spiral blades in two adjacent sections rotate in opposite directions and staggered by 90°. In order to facilitate the installation of the spiral blades, the cylinder is made into two semicircles, both ends of which are connected by end flanges, and the gaps between the cylinders are bonded with epoxy resin to ensure the sealing requirements.

[0094] The spiral blades in the pipeline are fixed, and the direction of the fluid passing through it changes, causing turbulence, thereby improving mixing efficiency and increasing the dissolved oxygen rate. In addition to producing pressure reduction, this cyclone aerator does not require external energy.

[0095] During the operation of the aerator, gas enters from the bottom. Due to the gas lift effect, the mud, water and gas mixture circulates inside and outside the cylinder. During the rising process of the mixed liquid, it is cut multiple times by the spiral blade internal parts of the cylinder, realizing the lifting, stirring and crushing of the gas-liquid-solid mixture, and continuously circulating convection, which enhances the oxygen transfer rate and utilization rate.

[0096] The aerator is installed in a hanging style, which can be installed with water without stopping production, and can be lifted for easy maintenance. If the biochemical pool is a fully enclosed steel concrete structure, a hole with a size of Ø250 needs to be opened on the top of the pool during installation. After the aerator is installed, a steel cover is made to seal it;

[0097] The aerator is suspended, the vertical pipe does not touch the bottom, and the bottom of the aerator is about 200 mm away from the bottom of the pool. When the plan is implemented, the suspension height of the aerator can be adjusted slightly as a whole based on the data measured on site.

Claims

1. A liftable cyclone aerator, Features It includes an aeration tank and an aeration cylinder, wherein the aeration cylinder is suspended above the bottom of the aeration tank and is vertically arranged; The upper and lower ends of the main body wall of the aeration cylinder are respectively provided with end flanges; The main body section of the inner cavity of the aeration cylinder is provided with spiral blades arranged vertically along the axial direction, and the overall diameter of each spiral blade is equal to the cavity diameter of the inner cavity of the aeration cylinder; the lateral edge of each spiral blade is fixedly connected to the inner wall of the aeration cylinder; Each spiral blade divides the cylindrical inner cavity of the aeration cylinder where it is located into two spiral flow channels; In the vertical direction, the rotation directions of each two adjacent spiral blades are opposite: one is a left-hand spiral blade, and the other is a right-hand spiral blade, and the two are arranged alternately in the vertical direction of the inner cavity of the aeration cylinder; Each spiral blade has a flat starting edge at its starting end and a flat ending edge at its ending end; The spiral rise height of each spiral blade adopts half the pitch; The flat start edge of each spiral blade and the flat end edge of the body are parallel to each other, and the two are respectively located on the inner cavity diameter of the aeration cylinder; For every two adjacent spiral blades: the flat end edge of the first spiral blade and the flat start edge of the adjacent second spiral blade intersect vertically in the same plane; the two spiral flow channels of the flat end edge of the first spiral blade are cut by the flat start edge of the second spiral blade; An air inlet pipe is intersected and connected on the main body wall at the bottom of the aeration cylinder. The air inlet pipe is perpendicular to the aeration cylinder. The inner end of the air inlet pipe is connected to the inner cavity at the bottom of the aeration cylinder. An air inlet pipe flange is arranged at the outward end of the air inlet pipe. An aeration pipe network main pipe is arranged above the aeration tank, a downward upper branch pipe is connected to the diversion node of the aeration pipe network main pipe, a downward lower branch pipe is connected in series downstream of the downward upper branch pipe, a pipe body of the downward lower branch pipe extends downward to above the bottom of the aeration tank, and a terminal end of the downward lower branch pipe is connected to an air inlet pipe flange of an air inlet pipe through an elbow; an air path of the downward lower branch pipe is connected to the air inlet pipe; The aeration pipe network main pipe, the downward upper branch pipe, the downward lower branch pipe, the aeration cylinder and the aeration tank constitute a liftable aeration system.

2. A liftable cyclone aerator according to claim 1, Features: The main body wall of the aeration cylinder is composed of two semi-cylindrical walls which are relatively sealed and fixedly connected to form a cylindrical structure that penetrates from top to bottom.

3. A liftable cyclone aerator according to claim 1, Features: The length span of each spiral blade in the inner cavity of the aeration cylinder is the same.

4. A liftable cyclone aerator according to claim 1, Features: The body of the aeration cylinder is provided with a fixing ear, and a clamping hoop is provided between the fixing ear and the bottom section of the lower branch pipe.

5. A liftable cyclone aerator according to claim 1, Features: The hanging height of the aerator is 200±20 mm from the bottom of the aeration tank to the bottom of the aeration tank.

6. A liftable cyclone aerator according to claim 1, Features: The aeration tank adopts an open top aeration tank or a fully enclosed steel concrete aeration tank; A process hole is opened on the top of the fully enclosed steel concrete aeration tank, a cover plate is arranged on the process hole, and a downward branch pipe penetrates the cover plate and extends into the bottom of the space in the aeration tank to communicate with the air inlet pipe of the aeration cylinder.

7. A liftable cyclone aerator according to claim 1, Features: The air inlet pipe is connected to the inner cavity of the aeration cylinder in radial or tangential direction; The connecting position of the air inlet pipe is located below the lowest spiral blade in the aeration cylinder.

8. The liftable cyclone aerator according to claim 1, Features: Each spiral blade in the aerator has the same characteristics except for the direction of rotation.

9. The liftable cyclone aerator according to claim 1, Features: Each spiral blade in the aerator has different characteristics except the direction of rotation.

10. The liftable cyclone aerator according to claim 1, Features: The air inlet pipe is provided with an extended end section in the inner cavity of the aeration cylinder. The extended end section of the air inlet pipe extends toward the center of the aeration cylinder and bends upward in the direction of the central axis of the aeration cylinder. The bent end opens toward the flat starting edge of the spiral blade.

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