CN115010249A

CN115010249A - Aerator for industrial wastewater treatment

Info

Publication number: CN115010249A
Application number: CN202210947780.5A
Authority: CN
Inventors: 伦晓中; 袁桂兰
Original assignee: Shandong Beiweize Environmental Protection Technology Co ltd
Current assignee: Shandong Beiweize Environmental Protection Technology Co ltd
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-09-06
Anticipated expiration: 2042-08-09
Also published as: CN115010249B

Abstract

The invention is suitable for the field of sewage treatment devices, and provides an aerator for industrial wastewater treatment, which comprises a fixed shell, a rotating head and a plurality of telescopic pieces, wherein the rotating head is rotatably sleeved at the upper end of the fixed shell and is driven by a rotating head driving assembly to rotate, and the telescopic pieces are arranged on the rotating head and can extend and contract; each telescopic piece is provided with a plurality of oxygen injection ports; the lower end of the fixed shell is provided with an air inlet which is communicated with a plurality of oxygen injection ports; one end of each telescopic piece is hinged to the rotating head and is driven by a driving disc to be subjected to telescopic switching, the moving block moves to reset in the process and drives the telescopic pieces to contract under the matching action of the resetting pieces, therefore, the telescopic oxygen diffusion device can utilize the telescopic pieces to perform auxiliary diffusion on oxygen, and the device can automatically detect concentration change to realize switching of working states.

Description

Aerator for industrial wastewater treatment

Technical Field

The invention relates to the field of sewage treatment devices, in particular to an aerator for industrial wastewater treatment.

Background

Most aeration tanks in the prior art adopt an activated sludge process for sewage treatment, and the specific working principle is as follows: activated sludge is discharged into the aeration tank, a large number of aerobic microorganisms capable of degrading pollutants in sewage are contained in the activated sludge, then oxygen is charged into the aeration tank by utilizing an aerator, and the process is carried out on one hand so as to meet the oxygen quantity required by the aerobic microorganisms, and on the other hand, the discharge of the oxygen can promote the full mixing of the sewage and the activated sludge.

Referring to fig. 1 and 2, the spray head of the conventional aerator is generally fixed, and the following defects are exposed in the normal use process: when activated sludge is discharged into the aeration tank, the local concentration of the aeration tank near the sludge discharge pipe is greatly increased, the resistance inside the fluid is increased due to the increase of the fluid concentration, and the range covered by oxygen during the spraying is reduced (the range shown by the dotted line in fig. 1 and 2, fig. 1 is the gas diffusion range in a low concentration state, and fig. 2 is the gas diffusion range in a high concentration state), even a diffusion fault 100 (shown in fig. 2) is formed between the aerators, and the uneven distribution of the oxygen greatly reduces the working efficiency of aerobic microorganisms.

In view of the above, the prior art is obviously inconvenient and disadvantageous in practical use, and needs to be improved.

Disclosure of Invention

In view of the above-mentioned drawbacks, an object of the present invention is to provide an aerator for industrial wastewater treatment, which can assist in oxygen diffusion by using a telescopic member that is extended and contracted, and which can automatically detect a change in concentration to switch operating states.

In order to achieve the aim, the invention provides an aerator for industrial wastewater treatment, which comprises a fixed shell, a rotating head and a plurality of telescopic pieces, wherein the rotating head is rotatably sleeved at the upper end of the fixed shell and is driven by a rotating head driving assembly to rotate, and the telescopic pieces are arranged on the rotating head and can extend and contract; each telescopic piece is provided with a plurality of oxygen injection ports; the lower end of the fixed shell is provided with an air inlet which is communicated with a plurality of oxygen injection ports; one end of each telescopic piece is hinged to the rotating head and is driven by a driving disc to perform telescopic switching; the driving disk is rotatably arranged in the rotating head and is driven by a rotating driving component to rotate by a preset angle; the end face of the telescopic piece is provided with a guide groove, and the driving disc is provided with a moving block matched with the guide groove; a reset piece for driving the rotating head to reset is movably arranged in the rotating head; the rotation driving assembly drives the driving disc to rotate by a preset angle, and in the process, the moving block moves along the guide groove and drives the telescopic piece to extend out in a rotating mode around the hinge point; the rotation driving assembly drives the driving disc to rotate reversely and reset, and the moving block moves to reset in the process and drives the telescopic piece to contract under the matching action of the resetting piece.

According to the aerator for industrial wastewater treatment, the fixed shell comprises a fixed base with a cavity arranged therein and a fixed cylinder fixedly arranged at the upper end of the fixed base; the rotating head driving assembly comprises a transmission cylinder, a driving motor and a driving gear, wherein the transmission cylinder is rotatably arranged in the fixed cylinder, the outer wall of the transmission cylinder is provided with a gear structure, the driving motor is fixedly arranged on the fixed base, and the driving gear is arranged at the output end of the driving motor and is meshed with the gear structure; the upper end of the transmission cylinder is fixedly connected with the rotating head.

According to the aerator for industrial wastewater treatment, the rotation driving component comprises a gear ring arranged at the center of the driving disc, a reversing gear arranged on the inner wall of the rotating head and a switching piece which is arranged at the upper end of the fixed cylinder and can not rotate relative to the fixed cylinder, wherein the outer wall of the switching piece is provided with an incomplete gear structure; the incomplete gear structure can be meshed with a reversing gear; and a torsion spring for driving the driving disc to reset is arranged between the driving disc and the inner wall of the rotating head.

According to the aerator for industrial wastewater treatment, the reset piece comprises a cylinder body filled with buffer fluid and a piston rod arranged in the cylinder body; a damping hole is formed in a piston pad of the piston rod; a return spring for driving the piston rod in the extending state to retract into the cylinder body is arranged in the cylinder body; the end of the cylinder body is hinged inside the rotating head, and the end of the piston rod is hinged with the telescopic piece.

According to the aerator for industrial wastewater treatment, the upper end of the fixed cylinder is provided with a supporting sleeve; the switching piece is sleeved on the supporting sleeve, and the switching piece and the supporting sleeve are rotationally positioned through a key structure; the switching piece is driven by a switching structure to move up and down along the axial direction of the transmission cylinder; the switching piece at the lower end position is meshed with the reversing gear; the switching piece in the upper end position is disengaged from the reversing gear.

According to the aerator for industrial wastewater treatment, the switching structure comprises a connecting seat arranged at the upper end of the rotating head and a resistance fan rotatably arranged on the connecting seat; the lower end of the resistance fan is provided with a plurality of extrusion blocks, the connecting seat is provided with a plurality of extrusion grooves filled with driving fluid corresponding to the extrusion blocks, and a plurality of telescopic cylinders communicated with the extrusion grooves are fixedly arranged in the rotating head; an extrusion block return spring for driving the extrusion block to return is arranged in the extrusion groove; the output end of the telescopic cylinder is connected with the switching piece through the end face bearing.

The invention provides an aerator for industrial wastewater treatment, which comprises a fixed shell, a rotating head and a plurality of telescopic pieces, wherein the rotating head is rotatably sleeved at the upper end of the fixed shell and driven by a rotating head driving assembly to rotate, and the telescopic pieces are arranged on the rotating head and can extend and contract; each telescopic piece is provided with a plurality of oxygen injection ports; the lower end of the fixed shell is provided with an air inlet, the air inlet is connected with external oxygen supply equipment through a conveying pipeline, the air inlet is communicated with a plurality of oxygen jet orifices, and the conveyed oxygen is jetted into the aeration tank through the oxygen jet orifices. One end of each telescopic piece is hinged to the rotating head and is driven by a driving disc to perform telescopic switching; each telescopic part rotates out of the rotating head around a hinge point when the telescopic part performs extension work, and is opposite to the rotating head, and the telescopic part rotates into the rotating head around the hinge point when the telescopic part performs contraction work. The device utilizes the telescopic and retractable telescopic piece to carry out auxiliary diffusion on oxygen, and can automatically detect the concentration change to realize the switching of the working state.

Drawings

FIG. 1 is a schematic view of the gas diffusion range in a low concentration state; FIG. 2 is a schematic view of the gas diffusion range at high concentration; FIG. 3 is a schematic structural view of the present invention; FIG. 4 is a cross-sectional view of FIG. 3; FIG. 5 is a connection diagram of a resistance fan and an extrusion block; FIG. 6 is a view showing the configuration of the extensible member and the guide groove formed at the upper end thereof; FIG. 7 is a block diagram of the drive plate of FIG. 4; fig. 8 is a top view of the switch; FIG. 9 is a top cross-sectional view taken along section line A-A of FIG. 4; FIG. 10 is a top cross-sectional view taken along section line B-B of FIG. 4; fig. 11 is an internal structural view of the restoring member; fig. 12 is an enlarged view of portion D of fig. 4; in the figure, 100-diffusion fault, 1-fixed shell, 11-fixed base, 12-fixed cylinder, 121-supporting sleeve, 2-transmission cylinder, 21-gear structure, 22-driving gear, 23-driving motor, 3-rotating head, 31-driving disk, 311-gear ring, 32-reset piece, 321-cylinder body, 322-piston rod, 323-damping hole, 324-reset spring, 33-reversing gear, 34-switching piece, 36-air chamber, 37-rotating ring, 371-connecting port, 4-telescopic piece, 41-moving block, 411-guiding groove, 412-oxygen injection port, 43-extrusion groove, 44-extrusion block, 46-flow hole, 47-resistance fan, 48-extrusion block reset spring, 5-air inlet, 6-telescopic cylinder, 200-rotating component.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and embodiments, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

Referring to fig. 3, the present invention provides an aerator for industrial wastewater treatment, which comprises a fixed housing 1, a rotating head 3 rotatably sleeved on the upper end of the fixed housing 1 and driven by a rotating head driving assembly to rotate, and a plurality of extensible members 4 capable of extending and contracting and arranged on the rotating head 3; each telescopic part 4 is provided with a plurality of oxygen injection ports 412; the lower end of the fixed shell 1 is provided with an air inlet 5, the air inlet 5 is connected with an external oxygen supply device through a conveying pipeline, the air inlet 5 is communicated with a plurality of oxygen injection ports 412, and the conveyed oxygen is injected into an aeration tank through the oxygen injection ports 412.

Referring to fig. 3 and 4, one end of each telescopic member 4 is hinged to the rotating head 3 and is driven by a driving disc 31 to perform telescopic switching; each telescopic part 4 rotates out of the rotating head 3 around a hinge point when the extension work is performed, and the telescopic parts 4 rotate into the rotating head 3 around the hinge point when the contraction work is performed.

Referring to fig. 4, 6, 7 and 10, the driving disc 31 is rotatably mounted in the rotating head 3 and driven by a rotating driving assembly to rotate by a predetermined angle; a guide groove 411 (shown in fig. 6) is arranged on the end surface of the telescopic member 4, and a moving block 41 (shown in fig. 7) matched with the guide groove 411 is arranged on the driving disc 31; a reset piece 32 (shown in fig. 10) for driving the telescopic piece 4 to reset is movably mounted in the rotating head 3; when the extensible member 4 is driven to extend, the rotary driving assembly drives the driving disc 31 to rotate by a predetermined angle, the moving block 41 moves along the guide groove 411 (from one end to the other end) and drives the extensible member 4 to rotate around the hinge point to extend; when the telescopic member 4 is driven to contract, the rotation driving assembly drives the driving disc 31 to rotate reversely and reset, and the moving block 41 moves and resets and drives the telescopic member 4 to contract under the matching action of the resetting member 32.

When the device works, the rotating head driving assembly drives the rotating head 3 to rotate, and meanwhile, the rotating driving assembly drives the driving disc 31 to switch forward and reverse rotation within a preset angle range, so that the expansion of the expansion piece 4 is realized, and the expansion piece 4 which repeatedly expands and contracts is utilized to realize auxiliary diffusion of oxygen.

Referring to fig. 10 and 11, it is preferable that the restoring member 32 of the present invention includes a cylinder 321 containing a buffer fluid therein and a piston rod 322 installed in the cylinder 321; a damping hole 323 is formed in a piston pad of the piston rod 322; a return spring 324 which can drive the piston rod 322 in the extending state to retract into the cylinder 321 is arranged in the cylinder 321; the end of the cylinder 321 is hinged inside the rotary head 3, and the end of the piston rod 322 is hinged with the telescopic part 4 (shown in fig. 10). When the telescopic member 4 extends, the piston rod 322 extends from the cylinder 321 (at this time, the return spring 324 is compressed), when the telescopic member 4 is to retract (loses external force), the return spring 324 resets and drives the piston rod 322 to retract in the process of resetting the moving block 41, and the piston rod 322 further drives the telescopic member 4 to retract. The cylinder body 321 is filled with buffer fluid, the buffer fluid is matched with the damping hole 323 arranged on the piston rod 322 in the extension process of the piston rod 322, so that the motion buffer of the piston rod 322 is realized, the extension piece 4 can retract according to a preset speed when retracting, the activity detention time of the extension piece 4 is increased, and the oxygen diffusion effect is optimized.

In this example, the fixed casing 1 includes a fixed base 11 having a cavity therein and a fixed cylinder 12 (shown in fig. 3) fixed to an upper end thereof; the rotating head driving assembly comprises a transmission cylinder 2 which is rotatably arranged in the fixed cylinder 12 and provided with a gear structure 21 on the outer wall, a driving motor 23 which is fixedly arranged on the fixed base 11, and a driving gear 22 which is arranged at the output end of the driving motor 23 and is meshed with the gear structure 21, and the transmission cylinder 2 can be used for conveying gas and transmitting power; the top of transmission section of thick bamboo 2 carries out the rigid coupling with rotating head 3 (C department in the rigid coupling position figure 12), fixed 12 tops of section of thick bamboo are equipped with an air chamber 36, the upper end of transmission section of thick bamboo 2 is equipped with the through-hole and the position department that is located

air chamber

36, 36 outer fringe cover in air chamber has rotating ring 37, is equipped with a plurality of connectors 371 on this rotating ring 37, and this connector 371 communicates through a hose and the inside of extensible member 4, because air chamber 36 sets firmly on fixed section of thick bamboo 12 (so air chamber 36 is fixed), through rotating ring 37 can guarantee that the hose is normally connected and not influenced by rotating head 3 pivoted state. When the rotating head 3 rotates, the driving motor 23 drives the transmission cylinder 2 to rotate through the meshing transmission of the gear structure 21 and the driving gear 22, and the transmission cylinder 2 rotates to further drive the rotating head 3 to rotate. The oxygen flows through the process that the oxygen enters the device from the air inlet 5, passes through the transmission cylinder 2, the through hole, the air bin 36 and the hose in sequence, finally enters the expansion piece 4, and is discharged from the oxygen jet 412.

Referring to fig. 4 and 12, in addition, in order to achieve the compact structure and the saving of power source, the driving disk 31 is also driven by the transmission cylinder 2 (although the present application is not limited to this embodiment, the present application can also achieve this function by using dual power source drive), the rotation driving assembly of the present invention includes a gear ring 311 (shown in fig. 7 and 12) installed at the center of the driving disk 31, a reversing gear 33 installed on the inner wall of the rotating head 3 and engaged with the gear ring 311, and a switching member 34 (shown in fig. 4 and 8) installed on the upper end of the fixed cylinder 12 and being non-rotatable relative to the fixed cylinder 12, and an incomplete gear structure is provided on the outer wall of the switching member 34; the incomplete gear structure is capable of meshing with the reversing gear 33. During operation, the rotating head 3 drives the reversing gear 33 to rotate around the switching piece 34, when the incomplete gear structure is meshed with the reversing gear 33, transmission is formed, and the rotating reversing gear 33 drives the driving disc 31 to rotate. A torsion spring (not shown) for driving the driving disc 31 to return is installed between the driving disc 31 and the inner wall of the rotating head 3, the torsion spring is installed at the rotating connection position of the driving disc 31, and one end of the torsion spring is fixedly connected to the driving disc 31, and the other end of the torsion spring is fixedly connected to the inner wall of the rotating head 3. When the incomplete gear structure and the reversing gear 33 do not form transmission (the reversing gear 33 enters a toothless area of the incomplete gear structure), the driving disc 31 rotates under the resetting action of the torsion spring.

The high concentration change in the aeration tank only occurs in a period of time each time the activated sludge is discharged into the aeration tank, so that the expansion piece 4 does not need to be in an expansion switching working state all the time when working, and in this state, on one hand, high load is caused to the driving motor 23, and on the other hand, unnecessary resource waste is caused. Therefore, a switching mechanism for switching the working state is arranged inside the device, and specifically, referring to fig. 4 and 12, a supporting sleeve 121 is arranged at the upper end of the fixed cylinder 12; the switch member 34 is sleeved on the support sleeve 121 and the switch member and the support sleeve 121 are rotationally positioned by a key structure, the key structure is a protrusion (shown in fig. 8) arranged on the switch member 34, and the protrusion enables the support sleeve 121 and the fixed cylinder 12 to only move relative to the axial direction but not to rotate relative to each other; the switching piece 34 is driven by a switching structure to move up and down along the axial direction of the transmission cylinder 2; when the fluid in the aeration tank is in a high-concentration state, the switching piece 34 is in a lower end position and is meshed with the reversing gear 33, and the telescopic piece 4 can enter an auxiliary telescopic working state; when the fluid in the aeration tank is in a low concentration state, the switching piece 34 is in the upper end position and is disengaged from the reversing gear 33, and in this state, the driving motor 23 only drives the rotating head 3 to rotate, so that the load of the driving motor 23 is small, and the resource saving is realized.

Referring to fig. 4, 5 and 9, the switching structure includes a connecting base disposed at an upper end of the rotating head 3 and a resistance fan 47 rotatably mounted on the connecting base, wherein the resistance fan 47 is used for detecting resistance (concentration) of fluid in the aeration tank; a plurality of squeezing blocks 44 (shown in fig. 5) are arranged at the lower end of the resistance fan 47, a plurality of squeezing grooves 43 (shown in fig. 9) filled with driving fluid are arranged on the connecting seat corresponding to the squeezing blocks 44, a plurality of telescopic cylinders 6 with internal cavities communicated with the squeezing grooves 43 are fixedly arranged in the rotating head 3, and specifically, the squeezing grooves 43 are communicated with the insides of the telescopic cylinders 6 through flow holes 46 arranged in the squeezing grooves 43; a pressing block return spring 48 for driving the pressing block 44 to return is installed in the pressing groove 43, and the pressing block return spring 48 can also provide an initial critical value for the resistance fan 47 (details will be described later); the output end of the telescopic cylinder 6 is connected to the switching member 34 through a rotating member 200, in this example, the rotating member 200 is an end face bearing, one end of the end face bearing is welded to the end face of the switching member 34, and the other end face is welded to the output end of the telescopic cylinder 6. When the fluid in the aeration tank is in a high-concentration state, the rotating resistance fan 47 bears resistance and rotates relative to the rotating head 3, the extrusion block 44 is further driven to move in the extrusion groove 43, the driving fluid in the extrusion groove 43 is extruded to the telescopic cylinder 6 in the moving process of the extrusion block 44, the output end of the telescopic cylinder 6 extends out and drives the switching piece 34 to move downwards, and the switching piece 34 enters a lower end position (can be meshed with the reversing gear 33 in the state); when the fluid in the aeration tank is in a low concentration state, the resistance fan 47 cannot rotate relative to the rotating head 3 due to insufficient fluid resistance (mainly because the pretightening force generated by the pressing block return spring 48 is much larger than the rotating force generated by the resistance fan 47 due to the fluid resistance), and in this state, the output end of the telescopic cylinder 6 is in a retraction state because the driving fluid cannot enter the telescopic cylinder 6, so the switching piece 34 is in an upper end position (in this state, the switching piece cannot be meshed with the reversing gear 33).

In summary, the present invention provides an aerator for industrial wastewater treatment, which comprises a fixed housing, a rotating head rotatably sleeved on the upper end of the fixed housing and driven by a rotating head driving assembly to rotate, and a plurality of extendable and retractable telescopic members arranged on the rotating head; each telescopic piece is provided with a plurality of oxygen injection ports; the lower end of the fixed shell is provided with an air inlet, the air inlet is connected with external oxygen supply equipment through a conveying pipeline, the air inlet is communicated with a plurality of oxygen jet orifices, and the conveyed oxygen is jetted into the aeration tank through the oxygen jet orifices. One end of each telescopic piece is hinged to the rotating head and is driven by a driving disc to perform telescopic switching; each telescopic part rotates out of the rotating head around a hinge point when the telescopic part performs extension work, and is opposite to the rotating head, and the telescopic part rotates into the rotating head around the hinge point when the telescopic part performs contraction work. The invention utilizes the telescopic and contractible telescopic pieces to carry out auxiliary diffusion on oxygen, and the device can automatically detect the concentration change and realize the switching of the working state.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An aerator for industrial wastewater treatment is characterized by comprising a fixed shell, a rotating head and a plurality of telescopic pieces, wherein the rotating head is rotatably sleeved at the upper end of the fixed shell and driven by a rotating head driving assembly to rotate, and the telescopic pieces are arranged on the rotating head and can extend and contract; each telescopic piece is provided with a plurality of oxygen injection ports;

the lower end of the fixed shell is provided with an air inlet which is communicated with a plurality of oxygen injection ports;

one end of each telescopic piece is hinged to the rotating head and is driven by a driving disc to perform telescopic switching;

the driving disk is rotatably arranged in the rotating head and is driven by a rotating driving component to rotate by a preset angle; the end face of the telescopic piece is provided with a guide groove, and the driving disc is provided with a moving block matched with the guide groove;

a reset piece for driving the rotating head to reset is movably arranged in the rotating head;

the rotation driving assembly drives the driving disc to rotate by a preset angle, and in the process, the moving block moves along the guide groove and drives the telescopic piece to rotate around the hinged point to extend out;

the rotation driving assembly drives the driving disc to rotate reversely and reset, and the moving block moves to reset in the process and drives the telescopic piece to contract under the matching action of the resetting piece.

2. The aerator of claim 1, wherein the stationary housing comprises a stationary base having a cavity therein and a stationary cylinder fixedly mounted on an upper end thereof;

the rotating head driving assembly comprises a transmission cylinder, a driving motor and a driving gear, wherein the transmission cylinder is rotatably arranged in the fixed cylinder, the outer wall of the transmission cylinder is provided with a gear structure, the driving motor is fixedly arranged on the fixed base, and the driving gear is arranged at the output end of the driving motor and is meshed with the gear structure;

the upper end of the transmission cylinder is fixedly connected with the rotating head.

3. The aerator for industrial wastewater treatment as claimed in claim 2, wherein the rotation driving assembly includes a gear ring installed at the center of the driving disc, a reversing gear installed at the inner wall of the rotating head, and a switching member installed at the upper end of the fixed cylinder and being non-rotatable with respect to the fixed cylinder, and an incomplete gear structure is provided on the outer wall of the switching member; the incomplete gear structure can be meshed with a reversing gear;

and a torsion spring for driving the driving disc to reset is arranged between the driving disc and the inner wall of the rotating head.

4. The aerator of claim 1, wherein the reset piece comprises a cylinder body containing the buffer fluid therein and a piston rod installed in the cylinder body; a damping hole is formed in a piston pad of the piston rod; a return spring for driving the piston rod in the extending state to retract into the cylinder body is arranged in the cylinder body;

the end of the cylinder body is hinged inside the rotating head, and the end of the piston rod is hinged with the telescopic piece.

5. An aerator as claimed in claim 3, wherein a supporting sleeve is provided at the upper end of said fixed cylinder; the switching piece is sleeved on the supporting sleeve, and the switching piece and the supporting sleeve are rotationally positioned through a key structure; the switching piece is driven by a switching structure to move up and down along the axial direction of the transmission cylinder;

the switching piece at the lower end position is meshed with the reversing gear;

the switching piece in the upper end position is disengaged from the reversing gear.

6. The aerator of claim 5, wherein the switching structure comprises a connecting base provided at an upper end of the rotating head and a resistance fan rotatably mounted on the connecting base; the lower end of the resistance fan is provided with a plurality of extrusion blocks, the connecting seat is provided with a plurality of extrusion grooves filled with driving fluid corresponding to the extrusion blocks, and a plurality of telescopic cylinders communicated with the extrusion grooves are fixedly arranged in the rotating head; an extrusion block return spring for driving the extrusion block to return is arranged in the extrusion groove;

the output end of the telescopic cylinder is connected with the switching piece through the end face bearing.