CN215214714U - Mechanical sealing device of reaction kettle - Google Patents

Abstract

The utility model discloses a mechanical sealing device of a reaction kettle, which comprises an equipment rotating shaft, a machine seal outer cover sleeved outside the equipment rotating shaft, and a machine seal fixed bottom plate arranged between the machine seal outer cover and the equipment rotating shaft and used for fixing the equipment rotating shaft, wherein a sealing device is arranged between the machine seal fixed bottom plate and the outside of the equipment rotating shaft; the mechanical seal device comprises a mechanical seal outer cover, an air outlet and an air exhausting device, wherein a cavity is formed between the mechanical seal outer cover and the equipment rotating shaft, the air outlet communicated with the cavity is formed in the mechanical seal outer cover, and the air exhausting device used for exhausting air pressure in the cavity is connected to the air outlet. The utility model discloses a sealing device is sealed, and gas leaks to the machine in sealing the dustcoat in the reation kettle, then discharges the workshop exhaust tuber pipe through the gas of exhaust apparatus in with the machine sealing dustcoat, adopts this kind of mode to exhaust reation kettle, solves in the reation kettle malleation and prevents that the outside air from getting into reation kettle, and the normal clear sealed problem of reaction that goes on of influence, and makes waste gas get into workshop exhaust tuber pipe to outdoor absorption tower, and then improves workshop production environment.

Description

Mechanical sealing device of reaction kettle

Technical Field

The utility model relates to a reation kettle's technical field especially relates to a reation kettle mechanical seal device.

Background

In the preparation process of the ternary precursor, oxygen enters the kettle due to poor sealing of the reaction kettle, so that the reaction materials are oxidized; therefore, nitrogen protection is needed in the ternary precursor reaction kettle, nitrogen is injected into the kettle in real time through the guide pipe, a reaction system reacts under ammonia complexation, ammonia gas is formed in the reaction process, the pressure in the kettle is increased, the ammonia gas in the kettle needs to be removed, and otherwise the ammonia gas overflows outside the kettle to influence the workshop site environment. At present, the reaction kettle body is generally sealed, and the stirring rotating shaft part is sealed through installation, water seal or self-pressure mechanical seal to ensure the reaction tightness. The water seal is that the upper cover rotating body rotating along with the shaft is installed on the stirring rotating shaft, a set of U-shaped water tank is installed on the kettle body, water is added into the U-shaped water tank, the upper cover rotates along with the rotating shaft at a high speed to drive the water in the tank to rotate so as to form a water film, and the sealing effect is achieved through the water in the U-shaped tank. For example, CN201821299199.2, a dual-end-face cartridge mechanical seal device in the prior art, the self-pressing mechanical seal includes a shaft sleeve, a fastening ring, a water jacket, a non-medium-end snap spring, a moving ring seat, a medium-end snap spring, a stationary ring gland, a non-medium-end stationary ring, a non-medium-end moving ring, a spring pad, a spring, a medium-end stationary ring, and a medium-end moving ring, and achieves a sealing effect by sealing between the self-pressing moving ring and the stationary ring.

However, the above solution has the following disadvantages:

1) oxygen in the air enters the reaction through the stirring shaft and reacts with the metal salt, so that the oxidation of the product is unqualified; 2) the existing exhaust is that there is an exhaust port on the cover plate of the reaction kettle, but because the reaction in the kettle is changed in real time, the existing conditions can not reach the self-control real-time regulation to reach the gas balance in the kettle, the material oxidation will be caused when the valve opening is large, when the valve opening is small, the gas (ammonia gas) in the kettle will overflow to the production environment through the stirring shaft, and the environment is polluted; 3) due to the fact that the pressure in the reaction kettle is too high, materials overflow from the shaft seal along the stirring paddle, and pollution and loss are caused; 4) when the water seal and the mechanical seal are replaced, replacement and maintenance personnel need to enter a limited space (in the reaction kettle) to disassemble the stirring paddle, so that the operation is dangerous, the replacement period is long and the operation is complicated; 5) the gas in the kettle body is alkaline, and the contact end face of the movable ring and the static ring of the existing mechanical seal can be attached with alkali, so that the seal is not tight; 6) the deviation of the concentricity of the stirring paddle is large, and the failure rate of mechanical sealing is high.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The to-be-solved technical problem of the utility model is to provide a reation kettle mechanical seal device, it is sealed through sealing device, reach preliminary sealed effect, under the pressure-fired circumstances in guaranteeing reation kettle, let gaseous in the reation kettle leak to the machine in sealing the dustcoat, then it is sealed continuous with workshop exhaust tuber pipe through the collection of machine sealing the dustcoat, adopt this kind of mode to exhaust reation kettle, in solving reation kettle malleation and preventing that the outside air from getting into reation kettle, and influence the normally gone on sealed problem of reaction, simultaneously at the exhaust port department installation exhaust apparatus of machine sealing dustcoat both sides, make waste gas get into workshop exhaust tuber pipe to outdoor absorption tower through the pipeline, and then improve workshop production environment.

(II) technical scheme

The utility model provides a solution to the above technical problem is a mechanical sealing device for a reaction kettle, comprising an equipment rotating shaft, a machine seal cover sleeved outside the equipment rotating shaft, and a machine seal fixing bottom plate arranged between the machine seal cover and the equipment rotating shaft and used for matching the equipment rotating shaft, wherein a sealing device is arranged between the machine seal fixing bottom plate and the outside of the equipment rotating shaft; the mechanical seal device comprises a mechanical seal outer cover, an equipment rotating shaft and an exhaust device, wherein a cavity is formed between the mechanical seal outer cover and the equipment rotating shaft, an exhaust port communicated with the cavity is formed in the mechanical seal outer cover, and the exhaust port is connected with the exhaust device used for exhausting air pressure in the cavity.

Specifically, the machine seal fixing bottom plate is sleeved outside the equipment rotating shaft in a matching mode, and when the machine seal fixing bottom plate operates, the equipment rotating shaft rotates along the inner wall of the machine seal fixing bottom plate.

Specifically, adopt indirect mode (peripheral hardware exhaust apparatus bleeds) to advance the exhaust to reation kettle, gas is through the interior malleation overflow of reation kettle and comes out, then discharges gas through the gas vent, and indirect exhaust volume is greater than reation kettle overflow volume, can supply through the clearance between machine seal dustcoat up end and the equipment pivot, and then reaches the air volume balance in the machine seal dustcoat.

By adopting the scheme, the sealing device is used for sealing, the primary sealing effect is achieved, under the condition that micro-positive pressure in the reaction kettle is ensured, gas in the reaction kettle is enabled to be discharged into the machine seal outer cover, then the gas is connected with the workshop exhaust air pipe through the collection sealing of the machine seal outer cover, the reaction kettle is exhausted by adopting the mode, the sealing problem that the normal reaction is influenced by positive pressure in the reaction kettle and the fact that external air enters the reaction kettle is solved, meanwhile, the exhaust devices are arranged at the exhaust ports on the two sides of the machine seal outer cover, and waste gas enters the workshop exhaust air pipe to the outdoor absorption tower through the pipeline, so that the workshop production environment is improved; the problem of in the synthetic reaction process of precursor reation kettle, need guarantee the reation kettle in the pressure-fired condition, direct cauldron in air exhaust leads to the product to oxidize is solved.

Further, the exhaust device comprises an exhaust valve connected with the exhaust port, and the exhaust valve is detachably mounted on the machine seal housing.

Preferably, two ball valves are arranged on the exhaust port, so that the exhaust volume can be adjusted.

Furthermore, one end of the exhaust valve, which is far away from the exhaust port, is connected with an exhaust connecting pipe, and the other end of the exhaust connecting pipe is connected with an exhaust air pipe of the workshop.

Preferably, the lower end of the exhaust valve is detachably mounted on the mechanical seal housing through a first fastening bolt and a first nut, and the upper end of the exhaust valve is detachably connected with the exhaust connecting pipe through a second fastening bolt and a second nut.

Specifically, the top of machine seals the dustcoat is provided with the gas vent with the air vent valve is connected, the air vent valve passes through the exhaust connecting pipe with workshop exhaust tuber pipe is connected to carry gas to outdoor absorption tower in, adopt above-mentioned mode to exhaust to reation kettle, can effectively prevent in the reation kettle that ammonia from spilling over to the workshop.

Furthermore, the sealing device comprises a sealing ring arranged between the mechanical seal fixing bottom plate and the equipment rotating shaft and a plurality of sealing packing positioned above the sealing ring.

Preferably, a groove for mounting a sealing packing is formed in one end, close to the equipment rotating shaft, of the machine seal fixing bottom plate, and four sealing packings with the size larger than that of the sealing packing are arranged above the sealing packing; and one end of each of the four sealing packing contacts with the outer wall of the equipment rotating shaft, and the other end of each of the four sealing packing contacts with the inner side of the mechanical seal fixing bottom plate.

More preferably, the sealing packing and the sealing ring are disconnected by adopting the bevel opening, and the cutting openings are installed in a staggered mode during installation, so that the sealing effect is enhanced.

By adopting the scheme, the concentricity deviation is large and the shaking is large when the rotating shaft of the equipment runs; the sealing packing is sealed by the sealing ring, the application compensation capability is strong, and the sealing performance and the reliability are stable on a station with frequent high-temperature and high-pressure fluctuation; the problem of because of equipment pivot concentricity is poor, rock big unable installation of self-compression mechanical seal and unable applicable phenomenon to solve equipment main shaft concentricity deviation big, the liquid level height installation space is limited in the reation kettle, water seal and conventional mechanical seal can't avoid the stirring to rock the mechanical wear phenomenon that arouses.

Furthermore, a sealing gland is detachably mounted above the sealing packing.

Preferably, the sealing gland is manufactured in a split mode by adopting a central dividing line.

Furthermore, the sealing gland is detachably mounted on the mechanical seal fixing bottom plate through an adjusting bolt.

By adopting the scheme, the equipment rotating shaft is sealed by the sealing ring and the sealing packing, the air seal forms air flow seal with the gap between the PTFE through the rotation of the equipment rotating shaft, the primary sealing effect is achieved, and the sealing performance can be adjusted through the adjusting bolt on the sealing gland so as to achieve the proper sealing effect; the problem of in the reation kettle under the pressure-fired condition, water-tight seal can't guarantee to seal tightly, alkaline gas (ammonia) can be excessive through the clearance between equipment pivot and the machine seal dustcoat in the cauldron simultaneously, and then influence the interior reaction atmosphere of reation kettle and workshop operational environment (the ammonia is heavy).

Furthermore, the machine seal outer cover is arranged above the machine seal fixing bottom plate, and an equipment top cover plate is arranged below the machine seal fixing bottom plate.

Further, the machine seal outer cover, the machine seal fixing bottom plate and the equipment top cover plate are connected through fixing bolts.

Preferably, a bolt gasket is arranged between the fixing bolt and the machine seal outer cover to enhance the sealing property.

Furthermore, the machine seal fixing bottom plate is manufactured to be in a split type by adopting a central dividing line.

By adopting the scheme, a sealed split mode is adopted, the stirring is not required to be dismantled in a reaction kettle during installation, and the disassembly and the assembly are convenient and the installation is convenient; the problem of when water-tight and conventional sealed change, need get into the reation kettle in with the stirring disassemble, go into reation kettle danger and loaded down with trivial details phenomenon is solved.

(III) advantageous effects

Compared with the prior art, the utility model designs a mechanical sealing device of a reaction kettle,

(1) the gas in the reaction kettle is discharged to the machine seal outer cover under the condition of ensuring the micro-positive pressure in the reaction kettle, then the gas is connected with a workshop exhaust air pipe through the collection seal of the machine seal outer cover, the reaction kettle is exhausted by adopting the mode, the sealing problem that the normal running of the reaction is influenced by the positive pressure in the reaction kettle and the external air is prevented from entering the reaction kettle is solved, meanwhile, the exhaust devices are arranged at the exhaust ports on the two sides of the machine seal outer cover, the waste gas enters the workshop exhaust air pipe to an outdoor absorption tower through a pipeline, the workshop production environment is further improved, and the problem that the product is oxidized due to the fact that the exhaust air in the kettle is directly exhausted tightly in the reaction kettle under the condition of ensuring the micro-positive pressure in the reaction kettle in the synthesis reaction process of the precursor reaction kettle is solved;

(2) the concentricity deviation is large when the rotating shaft of the equipment runs, so that the shaking is large; the sealing packing is sealed by the sealing ring, the application compensation capability is strong, and the sealing performance and the reliability are stable on a station with frequent high-temperature and high-pressure fluctuation; the phenomenon that the self-compaction mechanical seal cannot be installed and cannot be applied due to poor concentricity of a rotating shaft of the equipment and large shaking is solved, the phenomenon that the concentricity deviation of a main shaft of the equipment is large, the installation space of the liquid level in a reaction kettle is limited, and the mechanical abrasion phenomenon caused by stirring and shaking cannot be avoided due to water seal and conventional mechanical seal is solved;

(3) the equipment rotating shaft is sealed by a sealing ring and a sealing packing, the air seal forms airflow seal with a gap between the tetrafluoro membrane through the rotation of the equipment rotating shaft, so as to achieve a primary sealing effect, and the sealing performance can be adjusted through an adjusting bolt on the sealing gland so as to achieve a proper sealing effect; the problem that the water seal cannot guarantee tight seal under the condition of micro-positive pressure in a reaction kettle is solved, and meanwhile, alkaline gas (ammonia gas) in the kettle overflows through a gap between an equipment rotating shaft and a machine seal outer cover, so that the reaction atmosphere in the reaction kettle and the workshop working environment (heavy ammonia smell) are influenced;

(4) a sealed split mode is adopted, the stirring is not required to be dismantled in a reaction kettle during installation, and the disassembly and the assembly are convenient and the installation is convenient; the problem of when water-tight and conventional sealed change, need get into the reation kettle in with the stirring disassemble, go into reation kettle danger and loaded down with trivial details phenomenon is solved.

Drawings

FIG. 1 is a sectional view of a mechanical seal device of a reaction vessel according to the present embodiment;

FIG. 2 is an enlarged view of FIG. 1 at I;

fig. 3 is a schematic view of a mechanical sealing device of a reaction kettle according to the present embodiment.

Description of reference numerals: 1. a machine seal fixing bottom plate; 2. a seal ring; 3. a machine seal housing; 4. fixing the bolt; 5. a bolt washer; 6. sealing the packing; 8. a sealing gland; 9. adjusting the bolt; 10. an exhaust port; 11. a device rotating shaft; 12. a top cover plate of the device; 13. an exhaust valve; 14. a first fastening bolt; 15. a first nut; 16. an exhaust connecting pipe; 17. a second fastening bolt; 18. a second nut; 19. workshop exhaust tuber pipe.

Detailed Description

The following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings and examples. The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In this embodiment:

as shown in fig. 1, the mechanical sealing device for the reaction kettle of the embodiment includes an equipment rotating shaft 11, a machine seal housing 3 sleeved outside the equipment rotating shaft 11, and a machine seal fixing bottom plate 1 arranged between the machine seal housing 3 and the equipment rotating shaft 11 and used for matching the equipment rotating shaft 11, wherein a sealing device is arranged between the machine seal fixing bottom plate 1 and the outside of the equipment rotating shaft 11; a cavity is formed between the machine seal outer cover 3 and the equipment rotating shaft 11, an exhaust port 10 communicated with the cavity is formed in the machine seal outer cover 3, and an exhaust device used for exhausting air pressure in the cavity is connected to the exhaust port 10. Specifically, the machine seal fixing base plate 1 is sleeved outside the equipment rotating shaft 11 in a matching manner, and when the machine seal fixing base plate operates, the equipment rotating shaft 11 rotates along the inner wall of the machine seal fixing base plate 1. Specifically, adopt indirect mode peripheral hardware exhaust apparatus to bleed and advance the exhaust to reation kettle, gas is through the interior malleation overflow of reation kettle and comes out, then discharges gas through gas vent 10, and indirect volume of airing exhaust is greater than the reation kettle overflow volume, can supply through the clearance between 3 up end of machine seal dustcoat and the equipment pivot 11, and then reaches the air volume balance in the machine seal dustcoat 3. By adopting the scheme, the sealing is realized through the sealing device, the primary sealing effect is achieved, under the condition of ensuring the micro-positive pressure in the reaction kettle, the gas in the reaction kettle is discharged into the mechanical seal outer cover 3, and then the gas is connected with the workshop exhaust air pipe 19 through the collection sealing of the mechanical seal outer cover 3, the reaction kettle is exhausted by adopting the mode, the sealing problem that the normal reaction is influenced by the positive pressure in the reaction kettle and the external air entering the reaction kettle is solved, meanwhile, the exhaust devices are arranged at the exhaust ports 10 at the two sides of the mechanical seal outer cover 3, and the waste gas enters the workshop exhaust air pipe 19 to the outdoor absorption tower through the pipeline, so that the workshop production environment is improved; the problem of in the synthetic reaction process of precursor reation kettle, need guarantee the reation kettle in the pressure-fired condition, direct cauldron in air exhaust leads to the product to oxidize is solved.

As shown in fig. 1, further, the exhaust device includes an exhaust valve 13 connected to the exhaust port 10, and the exhaust valve 13 is detachably mounted on the enclosure housing 3. Preferably, two ball valves are installed at the exhaust port 10, so that the exhaust amount can be adjusted. Furthermore, one end of the exhaust valve 13, which is far away from the exhaust port 10, is connected with an exhaust connecting pipe 16, and the other end of the exhaust connecting pipe 16 is connected with a workshop exhaust air pipe 19. Preferably, the lower end of the exhaust valve 13 is detachably mounted on the mechanical enclosure 3 through a first fastening bolt 14 and a first nut 15, and the upper end of the exhaust valve 13 is detachably connected with the exhaust connecting pipe 16 through a second fastening bolt 17 and a second nut 18. Specifically, the top of the mechanical seal housing 3 is provided with the exhaust port 10 and the exhaust valve 13, the exhaust valve 13 is connected with the workshop exhaust air pipe 19 through the exhaust connecting pipe 16, and conveys gas to the outdoor absorption tower, and the reaction kettle is exhausted by adopting the above mode, so that ammonia gas in the reaction kettle can be effectively prevented from overflowing to the workshop.

As shown in fig. 1-2, further, the sealing device includes a sealing ring 2 disposed between the mechanical seal fixing bottom plate 1 and the equipment rotating shaft 11, and a plurality of sealing packing 6 located above the sealing ring 2. Preferably, a groove for mounting a sealing packing 6 is formed in one end, close to the equipment rotating shaft 11, of the machine seal fixing bottom plate 1, and four sealing packing 6 with the size larger than that of the sealing packing 6 are arranged above the sealing packing 6; and one end of each of the four sealing packing 6 is contacted with the outer wall of the equipment rotating shaft 11, and the other end is contacted with the inner side of the mechanical sealing fixed bottom plate 1. More preferably, the sealing packing 6 and the sealing ring 2 are disconnected by adopting inclined openings, and the cutting openings are installed in a staggered mode during installation, so that the sealing effect is enhanced. By adopting the scheme, the concentricity deviation is large and the shaking is large when the rotating shaft 11 of the equipment runs; the sealing packing 6 is sealed by the sealing ring 2, the application compensation capability is strong, and the sealing performance and the reliability are stable on a station with frequent high-temperature and high-pressure fluctuation; the problem of because of equipment pivot 11 concentricity is poor, rock big self-compaction mechanical seal and can't be suitable for the phenomenon because of unable installation to solve equipment main shaft concentricity deviation big, the liquid level height installation space is limited in the reation kettle, water seal and conventional mechanical seal can't avoid the stirring to rock the mechanical wear phenomenon that arouses. Furthermore, a sealing gland 8 is detachably mounted above the sealing packing 6. Preferably, the gland 8 is made to be split using a central split line. Further, the sealing gland 8 is detachably mounted on the mechanical seal fixing bottom plate 1 through an adjusting bolt 9. Preferably, a bolt gasket 5 is installed between the fixing bolt 4 and the mechanical seal housing 3 to enhance the sealing performance. By adopting the scheme, the equipment rotating shaft 11 is sealed by the sealing packing 6 through the sealing ring 2, the air seal forms air flow seal with a gap between the tetrafluoro through the rotation of the equipment rotating shaft 11, the primary sealing effect is achieved, and the sealing performance can be adjusted through the adjusting bolt 9 on the sealing gland 8 so as to achieve the proper sealing effect; the problem that the water seal cannot guarantee tight seal under the condition of micro-positive pressure in the reaction kettle is solved, and meanwhile alkaline gas ammonia in the kettle overflows through a gap between the equipment rotating shaft 11 and the machine seal outer cover 3, so that the reaction atmosphere in the reaction kettle and the workshop working environment are influenced.

As shown in fig. 1 and fig. 3, further, the machine seal housing 3 is disposed above the machine seal fixing bottom plate 1, and an equipment top cover plate 12 is disposed below the machine seal fixing bottom plate 1. Further, the machine seal outer cover 3, the machine seal fixing bottom plate 1 and the equipment top cover plate 12 are connected through fixing bolts 4. Further, the machine seal fixing bottom plate 1 is manufactured to be split by adopting a central dividing line. By adopting the scheme, a sealed split mode is adopted, the stirring is not required to be dismantled in a reaction kettle during installation, and the disassembly and the assembly are convenient and the installation is convenient; the problem of when water-tight and conventional sealed change, need get into the reation kettle in with the stirring disassemble, go into reation kettle danger and loaded down with trivial details phenomenon is solved.

The above is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, a plurality of improvements and decorations can be made without departing from the technical principle of the present invention, and these improvements and decorations should also be regarded as the protection scope of the present invention.

Claims (9)

1. The utility model provides a reation kettle mechanical seal device which characterized in that: the mechanical seal device comprises an equipment rotating shaft (11), a mechanical seal outer cover (3) sleeved outside the equipment rotating shaft (11), and a mechanical seal fixing bottom plate (1) which is arranged between the mechanical seal outer cover (3) and the equipment rotating shaft (11) and used for being matched with the equipment rotating shaft (11), wherein a sealing device is arranged between the mechanical seal fixing bottom plate (1) and the outside of the equipment rotating shaft (11); the mechanical seal device comprises a mechanical seal outer cover (3) and an equipment rotating shaft (11), wherein a cavity is formed between the mechanical seal outer cover (3) and the equipment rotating shaft (11), an exhaust port (10) communicated with the cavity is formed in the mechanical seal outer cover (3), and an exhaust device used for extracting air pressure in the cavity is connected to the exhaust port (10).

2. The mechanical seal device of the reaction kettle according to claim 1, characterized in that: the exhaust device comprises an exhaust valve (13) connected with the exhaust port (10), and the exhaust valve (13) is detachably mounted on the mechanical seal outer cover (3).

3. The mechanical seal device of the reaction kettle according to claim 2, characterized in that: one end, far away from the exhaust port (10), of the exhaust valve (13) is connected with an exhaust connecting pipe (16), and the other end of the exhaust connecting pipe (16) is connected with an exhaust air pipe (19) of a workshop.

4. The mechanical seal device of the reaction kettle according to claim 1, characterized in that: the sealing device comprises a sealing ring (2) arranged between the mechanical seal fixing bottom plate (1) and the equipment rotating shaft (11) and a plurality of sealing packing (6) positioned above the sealing ring (2).

5. The mechanical seal device of the reaction kettle according to claim 4, characterized in that: and a sealing gland (8) is detachably arranged above the sealing packing (6).

6. The mechanical seal device of the reaction kettle according to claim 5, characterized in that: the sealing gland (8) is detachably mounted on the mechanical seal fixed bottom plate (1) through an adjusting bolt (9).

7. The mechanical seal device of the reaction kettle according to claim 1, characterized in that: the machine seal outer cover (3) is arranged above the machine seal fixing bottom plate (1), and an equipment top cover plate (12) is arranged below the machine seal fixing bottom plate (1).

8. The mechanical seal device of the reaction kettle according to claim 7, characterized in that: the machine seal outer cover (3), the machine seal fixing bottom plate (1) and the equipment top cover plate (12) are connected through fixing bolts (4).

9. The mechanical seal device of the reaction kettle according to claim 1, characterized in that: the machine seal fixing bottom plate (1) is manufactured to be split by adopting a central dividing line.

Images