Intermediate frequency furnace convenient to feed

Abstract

The intermediate frequency furnace comprises a machine frame, a furnace body used for heating metal, a feeding assembly used for feeding materials into the furnace body, a cover plate and a driving part used for driving the cover plate to move, the furnace body is arranged on the machine frame, and the feeding assembly is connected to the machine frame in a sliding mode in the length direction of the machine frame; the cover plate is connected to the furnace body in a sliding mode in the moving direction of the feeding assembly, the driving part comprises a mounting rack, a driving rack and a driving gear, the length direction of the driving rack is parallel to the sliding direction of the cover plate, the driving rack is arranged on the cover plate, the driving gear is arranged on the cover plate, and the driving rack is arranged on the driving gear. The driving rack is meshed with the driving gear, the mounting rack is arranged on a feeding assembly, and the mounting rack is used for being meshed with the driving gear. The device has the effect of protecting the safety of workers.

Description

Technical Field

[0001] The present application relates to the field of metal casting, and in particular to a medium frequency furnace which is convenient for charging. Background Art

[0002] The tail plate of the injection molding machine is an important part of the injection molding machine. Its structural simplification and lightweighting is already a development trend. It is necessary to reduce the wall thickness or change the structure to achieve the purpose of weight reduction. The lightweight design is achieved through the silicon solid solution strengthening process. The silicon solid solution strengthening process requires casting to make the tail plate casting. The raw materials need to be melted before casting. The smelting equipment is a medium frequency furnace.

[0003] A medium frequency furnace is a device that uses the principle of medium frequency induction heating to melt metal materials. A cover is generally provided on the medium frequency furnace to protect the loss of heat and the splashing of molten metal during the smelting process.

[0004] The process steps of medium frequency furnace smelting are: first melt about 15% of the steel briquettes, then start adding carburizer, and when 70% of the steel briquettes are dissolved, add ferrosilicon and ferromanganese until they are completely melted and in liquid state.

[0005] Since materials need to be added into the medium frequency furnace during the smelting process, and the temperature inside the medium frequency furnace is relatively high at this time, the workers are easily exposed to the high temperature inside the furnace when opening the furnace cover, and the safety of the workers cannot be ensured. Utility Model Content

[0006] In order to protect the safety of workers, the present application provides a medium frequency furnace that is easy to charge.

[0007] The present application provides a medium frequency furnace that is easy to charge, which adopts the following technical solution:

[0008] A medium frequency furnace that is easy to feed, comprising a frame, a furnace body for heating metal, a feeding assembly for feeding into the furnace body, a cover plate, and a driving member for driving the cover plate to move, wherein the furnace body is arranged on the frame, the feeding assembly is slidably connected to the frame along the length direction of the frame, the cover plate is slidably connected to the furnace body along the moving direction of the feeding assembly, the driving member comprises a mounting rack, a driving rack and a driving gear, the length direction of the driving rack is parallel to the sliding direction of the cover plate, the driving rack is arranged on the cover plate, the driving gear is arranged on the cover plate, the driving rack is meshed with the driving gear, the mounting rack is arranged on the feeding assembly, and the mounting rack is used to mesh with the driving gear.

[0009] By adopting the above technical scheme, the furnace body is used to melt metal. When materials need to be added during the smelting process, the staff can place the materials on the feeding assembly, and then the staff controls the feeding assembly to move toward the furnace body. The installed rack on the feeding assembly meshes with the driving gear and drives the driving gear to rotate. The rotation of the driving gear drives the driving rack to move, and the driving rack drives the cover plate to move. Then the staff controls the feeding assembly to put the materials into the furnace body for heating. Then the feeding assembly is controlled to move away from the furnace body. The driving rack will drive the driving gear to rotate in the opposite direction. The driving gear drives the driving rack to move, and the cover plate covers the furnace body again to cover it, thereby reducing the occurrence of metal splashing in the smelting state. During the feeding process, the staff does not need to approach the furnace body, and the cover plate can be linked under the movement of the driving assembly, and the staff does not need to open the cover, thereby protecting the safety of the staff.

[0010] Optionally, the feeding assembly includes a sliding seat, a translational drive, a charging barrel and a feeding piece, the sliding seat is slidably connected to the frame along the length direction of the frame, the translational drive piece includes a screw and a driving motor, the length direction of the screw is parallel to the sliding direction of the sliding seat, the screw is rotatably connected to the frame, the screw is threadedly connected to the sliding seat, the driving motor is used to drive the screw to rotate, the charging barrel is arranged on the sliding seat, and the feeding piece is used to feed the material in the charging barrel into the furnace body.

[0011] By adopting the above technical scheme, the driving motor drives the screw to rotate, the screw is threadedly connected to the sliding seat, the sliding seat can slide in the direction close to or away from the furnace body, the loading barrel is used to hold the material to be added to the furnace body, and the feeding piece is used to feed the material in the loading barrel into the furnace body. The translation driving part has a simple structure and is easy for the staff to operate. The feeding component has a clear division of labor and a reasonable structure.

[0012] Optionally, the feeding assembly also includes a lifting component, which includes a lifting platform and a connecting rod. The lifting platform is slidably connected to the sliding seat in a vertical direction, one end of the connecting rod is rotatably connected to the frame, and the other end of the connecting rod is rotatably connected to the lifting platform, and the loading barrel is arranged on the lifting platform.

[0013] By adopting the above technical scheme, since the position of the furnace body mouth is relatively high, the height of the barrel when it is put in is also relatively high, and it is difficult for the staff to place the materials to be put in the barrel. The lifting member can lower the height of the barrel, which is convenient for the staff to place the materials to be put in the barrel; the lifting platform is connected to the sliding seat by sliding in the vertical direction, and when the sliding seat moves toward the furnace body, the sliding seat gradually approaches the connecting rod and rotates to be connected to the frame, and the angle between the connecting rod and the horizontal plane gradually increases. The connecting rod drives the lifting platform to gradually rise until the height of the barrel is higher than the height of the furnace body. With the rise of the lifting platform and the translation of the sliding seat, the barrel moves in an inclined upward direction. The lifting platform utilizes the linkage with the sliding seat, and no additional power source is required. The height of the lifting platform can be controlled by the staff only operating the driving motor.

[0014] Optionally, the loading barrel includes a barrel and a bottom plate, the barrel is arranged on a lifting platform, the bottom of the barrel is penetrated, the bottom plate is rotatably connected to the lower end surface of the barrel along the horizontal direction, and the feeding piece is used to control the bottom plate to keep abutting against the lower end surface of the barrel.

[0015] By adopting the above technical solution, when the bottom plate abuts against the bottom of the cylinder, the staff can load the material into the loading barrel; when the loading barrel is located directly above the furnace body, the staff can rotate the bottom plate by controlling the feeding piece, and the bottom plate no longer abuts against the lower end surface of the cylinder, and the material enters the furnace body from the cylinder. The loading barrel has a simple structure, and the material is dumped cleanly and quickly.

[0016] Optionally, the feeding member includes a feeding cylinder and a sliding block, the feeding cylinder is arranged on the barrel, the sliding block is arranged on the piston rod of the feeding cylinder, and the sliding block is used to drive the bottom plate to rotate.

[0017] By adopting the above technical solution, when the charging barrel is located directly above the furnace body, the staff can control the feeding cylinder, the piston rod of the feeding cylinder contracts, the position of the sliding block on the piston rod of the feeding cylinder changes, the sliding block drives the bottom plate to rotate, the bottom plate separates from the bottom of the barrel, and the material enters the furnace body from the barrel. The feeding part has a simple structure and is easy for the staff to control.

[0018] Optionally, the lifting platform is also provided with a rotating part for the convenience of the staff to add materials into the loading barrel. The rotating part includes a rotating motor and a horizontal rod. One end of the horizontal rod is rotatably connected to the lifting platform along the vertical direction, and one end of the cylinder body is arranged on the horizontal rod. The rotating motor is used to drive the horizontal rod to rotate.

[0019] By adopting the above technical solution, the rotating part makes it easy to rotate the charging barrel to the side away from the screw. When the staff needs to load materials into the charging barrel, the staff can start the rotating motor, and the rotating motor drives the horizontal rod to rotate. The horizontal rod drives the charging barrel to rotate along the rotation axis of the horizontal rod, so that the charging barrel is away from the frame, the screw, and the sliding block, reducing the staff from dropping materials onto the screw and the sliding seat when adding materials into the charging barrel. The rotating part protects the service life of the equipment and reduces the occurrence of additional maintenance of the equipment.

[0020] Optionally, a dumping box is provided on the frame, a drainage trough for the molten material to flow out is provided on the furnace body, the furnace body is rotatably connected to the frame, and a dumping motor for driving the furnace body to rotate is provided on the frame.

[0021] By adopting the above technical scheme, when the furnace body completes smelting of the metal, the staff drives the dumping motor, and the dumping motor drives the furnace body to rotate. The molten metal in the furnace body is poured out through the drainage trough, and the molten metal enters the dumping box. After that, the staff can transfer the dumping box and use the molten metal in the dumping box for casting. The furnace body dumps the internal molten metal by rotating. The structure is reasonable and easy to operate.

[0022] Optionally, a seal for sealing the drainage groove is provided on the furnace body, and the seal includes a sealing cylinder and a sealing plate. The sealing cylinder is provided on the furnace body, and the sealing plate is provided on the piston rod of the sealing cylinder. The sealing cylinder is used to seal the drainage groove.

[0023] By adopting the above technical scheme, the drainage groove makes the inside of the furnace body connected with the outside, and the sealing component reduces the escape of heat inside the furnace body, thereby improving the heating effect of the furnace body. When the furnace body is heated, the piston rod of the sealing cylinder extends, and the sealing plate blocks the drainage groove, thereby reducing heat loss; when the molten metal in the furnace body needs to be dumped, the staff retracts the piston rod of the sealing cylinder, and the sealing plate moves away from the drainage groove. The furnace body rotates, and the molten metal in the furnace body can flow out of the drainage groove.

[0024] In summary, the present application includes at least one of the following beneficial technical effects:

[0025] 1. The driving member is used to slide the cover plate on the furnace body when the furnace body needs to be charged;

[0026] 2. The lifting parts make it easy for the staff to add materials into the loading barrel;

[0027] 3. The seal is used to seal the drainage groove on the furnace body to improve the sealing effect of the furnace body. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a medium frequency furnace which is convenient for charging.

[0029] Figure 2 This is a state diagram of the medium frequency furnace used to pour molten metal.

[0030] Figure 3 This is a diagram of the usage status of the medium frequency furnace when it is used for charging.

[0031] Figure 4 yes Figure 3 The enlarged view of point A in the middle is used to show the structure of the driving part.

[0032] Figure 5 yes Figure 1 Schematic diagram of the structure of the feeding component.

[0033] Figure numerals: 1, frame; 2, furnace body; 21, drainage trough; 22, sealing member; 221, sealing cylinder; 222, sealing plate; 3, feeding assembly; 31, sliding seat; 32, translation driving member; 321, screw; 322, driving motor; 33, charging barrel; 331, barrel; 332, bottom plate; 34, feeding member; 341, feeding cylinder; 342, sliding block; 343, sliding bar; 344, sliding trough; 35, lifting member ; 351, lifting platform; 352, connecting rod; 353, sliding rod; 36, rotating member; 361, rotating motor; 362, horizontal rod; 363, vertical rod; 364, first rotating gear; 365, second rotating gear; 4, cover plate; 5, driving member; 51, mounting rack; 52, driving rack; 53, driving gear; 6, dumping assembly; 61, dumping motor; 62, first bevel gear; 63, second bevel gear; 7, dumping box. DETAILED DESCRIPTION

[0034] The following is combined with Figure 1-4 This application is described in further detail.

[0035] The present application embodiment discloses a medium frequency furnace that is convenient for charging. Figure 1 A medium frequency furnace for convenient charging includes a frame 1, a furnace body 2 for heating metal, a charging assembly 3 for charging into the furnace body 2, two cover plates 4, a driving member 5 for driving the two cover plates 4 to move on the furnace body 2, a dumping assembly 6 and a dumping box 7. The furnace body 2 is connected to the frame 1 in a horizontal rotation direction, the charging assembly 3 is connected to the frame 1 in a sliding manner along the length direction of the frame 1, the rotating member 36 is arranged on the frame 1, the dumping assembly 6 is used to drive the furnace body 2 to rotate, the dumping box 7 is fixedly arranged on the frame 1, and the dumping box 7 is used to collect the molten metal after smelting.

[0036] refer to Figure 1 and Figure 2A drainage groove 21 is provided on the upper end surface of the furnace body 2, and the drainage groove 21 runs through the furnace body 2. A sealing member 22 is provided on the furnace body 2, and the sealing member 22 includes a sealing cylinder 221 and a sealing plate 222. The sealing cylinder 221 is parallel to the length direction of the furnace body 2, and the sealing cylinder 221 is fixedly arranged on the outer wall of the furnace body 2. One end of the sealing plate 222 is fixedly arranged on the piston rod of the sealing cylinder 221. The sealing plate 222 is slidably connected to the outer wall of the furnace body 2, and the sealing plate 222 is used to seal the drainage groove 21.

[0037] refer to Figure 2 and Figure 3 The dumping assembly 6 includes a dumping motor 61, a first bevel gear 62 and a second bevel gear 63. The first bevel gear 62 is coaxially arranged with the rotation axis of the furnace body 2. The first bevel gear 62 is fixedly arranged on the rotation axis of the furnace body 2. The dumping motor 61 is fixedly arranged on the frame 1. The second bevel gear 63 is coaxially arranged with the output shaft of the dumping motor 61. The second bevel gear 63 is fixedly arranged on the output shaft of the dumping motor 61. The first bevel gear 62 is meshed with the second bevel gear 63.

[0038] refer to Figure 3 and Figure 4 The two cover plates 4 are slidably connected to the upper end surface of the furnace body 2 along the radial direction of the furnace body 2. When the furnace body 2 is in a vertical state, the sliding direction of the two cover plates 4 is parallel to the length direction of the frame 1. The driving member 5 includes a mounting rack 51, two driving racks 52 and a driving gear 53. The rotation axis of the driving gear 53 is parallel to the axial direction of the furnace body 2. The driving gear 53 is rotatably connected to the upper end surface of the furnace body 2. The two driving racks 52 correspond to the two cover plates 4 one by one. The driving racks 52 are fixedly arranged on the cover plates 4. The length direction of the driving racks 52 is parallel to the sliding direction of the cover plates 4. The two driving racks 52 are respectively located on both sides of the driving gear 53, and the driving racks 52 are meshed with the driving gear 53.

[0039] refer to Figure 3 and Figure 5 The feeding assembly 3 includes a sliding seat 31, a translational driving member 32, a charging barrel 33, a feeding member 34, a lifting member 35 for changing the height of the charging barrel 33, and a rotating member 36 for driving the charging barrel 33 away from the frame 1. The sliding seat 31 is slidingly connected to the frame 1 along the length direction of the frame 1, and the mounting rack 51 is fixedly set on the sliding seat 31. The mounting rack 51 is used to engage with the driving gear 53. The translational driving member 32 includes a screw 321 and a driving motor 322. The length direction of the screw 321 is parallel to the sliding direction of the sliding seat 31. The screw 321 is rotatably connected to the frame 1. The screw 321 is threadedly connected to the sliding seat 31. The driving motor 322 is fixedly set on the frame 1. The driving motor 322 is used to drive the screw 321 to rotate.

[0040] refer to Figure 3 and Figure 5 The lifting member 35 includes a lifting platform 351, a connecting rod 352 and two sliding rods 353. The two sliding rods 353 are distributed along the width direction of the frame 1. The sliding rods 353 are vertically arranged. The lower end surface of the sliding rod 353 is fixedly arranged on the upper end surface of the sliding seat 31. The lifting platform 351 is slidably connected to the sliding rod 353. One end of the connecting rod 352 is rotatably connected to the frame 1 along the width direction of the frame 1. The other end of the connecting rod 352 is rotatably connected to the lifting platform 351 along the width direction of the frame 1. The height of the connecting rod 352 gradually decreases from the lifting platform 351 to the furnace body 2.

[0041] refer to Figure 3 and Figure 5 The rotating member 36 includes a rotating motor 361, a horizontal rod 362, a vertical rod 363, a first rotating gear 364 and a second rotating gear 365. The lower end surface of the vertical rod 363 is rotatably connected to the upper end surface of the lifting platform 351. The first rotating gear 364 is coaxially arranged with the vertical rod 363. The first rotating gear 364 is fixedly arranged on the vertical rod 363. The second rotating gear 365 is horizontally arranged. The second rotating gear 365 is arranged on the upper end surface of the lifting platform 351. The rotating motor The machine 361 is fixedly arranged on the upper end surface of the lifting platform 351, and the rotating motor 361 is used to drive the second rotating gear 365 to rotate. One end of the horizontal rod 362 is fixedly arranged on the upper end surface of the vertical rod 363. The loading barrel 33 includes a barrel body 331 and a bottom plate 332. The barrel body 331 is vertically arranged, and the barrel body 331 is fixedly arranged on the other end of the horizontal rod 362. The barrel body 331 is through-arranged, and the bottom plate 332 is rotatably connected to the lower end surface of the barrel body 331 along the width direction of the frame 1.

[0042] refer to Figure 4 and Figure 5 The feeding member 34 includes a feeding cylinder 341, a sliding block 342 and a sliding bar 343. The length direction of the sliding bar 343 is parallel to the radial direction of the bottom plate 332. One end of the sliding bar 343 is fixedly arranged on the side wall of the bottom plate 332. A sliding groove 344 is opened on the sliding bar 343. The sliding groove 344 extends along the length direction of the sliding bar 343. The feeding cylinder 341 is vertically arranged and fixedly arranged on the outer wall of the cylinder body 331. The sliding block 342 is fixedly arranged on the piston rod of the feeding cylinder 341, and the sliding block 342 is located in the sliding groove 344.

[0043] The implementation principle of the medium frequency furnace that is easy to add materials in the embodiment of the present application is as follows: when materials need to be added to the furnace body 2, the staff starts the rotating motor 361, the rotating motor 361 drives the second rotating gear 365 to rotate, the second rotating gear 365 drives the first rotating gear 364 to rotate, the first rotating gear 364 drives the vertical rod 363 to rotate, the vertical rod 363 drives the horizontal rod 362 to rotate, the horizontal rod 362 rotates the charging barrel 33 towards the staff, and then the staff puts the materials to be added into the charging barrel 33, and then starts the rotating motor 361. 61 turns the feeding barrel back to its initial position, and then the staff starts the driving motor 322. The driving motor 322 drives the screw 321 to rotate, and the screw 321 drives the sliding seat 31 to move toward the direction of the furnace body 2. During the movement of the sliding seat 31, the sliding rod 353 and the connecting rod 352 move the lifting platform 351 vertically upward until the barrel moves to the top of the furnace body 2. During the movement of the sliding seat 31, the installation rack 51 is engaged with the driving gear 53, and the driving gear 53 drives the two driving racks 52 to move, and the two cover plates 4 move away from each other, and the furnace mouth is exposed.

[0044] Afterwards, the staff retracts the piston rod of the feeding cylinder 341, and the sliding block 342 moves vertically upward. The sliding block 342 moves in the sliding groove 344, and the sliding block 342 drives the sliding bar 343 to rotate. The sliding bar 343 mobilizes the bottom plate 332 to rotate, and the bottom plate 332 no longer abuts against the bottom of the cylinder 331. The material originally located in the charging cylinder 33 enters the furnace body 2; then the staff makes the driving motor 322 rotate in the opposite direction, and the sliding seat 31 moves in the direction away from the furnace body 2. During the movement of the sliding seat 31, the rack 51 is installed to drive the driving gear 53 to rotate, and the driving gear 53 drives the two driving racks 52 to move, and the two cover plates 4 are driven by the driving rack 52 to approach each other until the furnace body 2 is sealed again.

[0045] When the material in the furnace body 2 is completely melted, the staff retracts the piston rod of the sealing cylinder 221, the sealing plate 222 moves downward, the drainage groove 21 is exposed, and the dumping motor 61 is started. The dumping motor 61 drives the second bevel gear 63 to rotate, the second bevel gear 63 drives the first bevel gear 62 to rotate, and the first bevel gear 62 drives the furnace body 2 to rotate. The molten metal in the furnace body 2 enters the dumping box 7 from the drainage groove 21, and the smelting of the metal is completed.

[0046] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A medium frequency furnace that is easy to charge, characterized by: The invention comprises a frame (1), a furnace body (2) for heating metal, a feeding assembly (3) for feeding material into the furnace body (2), a cover plate (4), and a driving member (5) for driving the cover plate (4) to move, wherein the furnace body (2) is arranged on the frame (1), the feeding assembly (3) is slidably connected to the frame (1) along the length direction of the frame (1), the cover plate (4) is slidably connected to the furnace body (2) along the moving direction of the feeding assembly (3), and the driving member (5) comprises an installation A rack (51), a driving rack (52) and a driving gear (53), wherein the length direction of the driving rack (52) is parallel to the sliding direction of the cover plate (4), the driving rack (52) is arranged on the cover plate (4), the driving gear (53) is arranged on the cover plate (4), the driving rack (52) meshes with the driving gear (53), and the mounting rack (51) is arranged on the feeding component (3), and the mounting rack (51) is used to mesh with the driving gear (53).

2. The medium frequency furnace that is easy to charge according to claim 1 is characterized in that: The feeding assembly (3) comprises a sliding seat (31), a translational driving member (32), a charging barrel (33) and a feeding member (34); the sliding seat (31) is connected to the frame (1) in a sliding manner along the length direction of the frame (1); the translational driving member (32) comprises a screw rod (321) and a driving motor (322); the length direction of the screw rod (321) is parallel to the sliding direction of the sliding seat (31); the screw rod (321) is rotatably connected to the frame (1); the screw rod (321) is threadedly connected to the sliding seat (31); the driving motor (322) is used to drive the screw rod (321) to rotate; the charging barrel (33) is arranged on the sliding seat (31); and the feeding member (34) is used to feed the material in the charging barrel (33) into the furnace body (2).

3. The medium frequency furnace that is easy to charge according to claim 2 is characterized in that: The feeding assembly (3) further comprises a lifting member (35), wherein the lifting member (35) comprises a lifting platform (351) and a connecting rod (352), wherein the lifting platform (351) is slidably connected to the sliding seat (31) in a vertical direction, one end of the connecting rod (352) is rotatably connected to the frame (1), and the other end of the connecting rod (352) is rotatably connected to the lifting platform (351), and the charging barrel (33) is arranged on the lifting platform (351).

4. The medium frequency furnace that is easy to charge according to claim 3 is characterized in that: The loading barrel (33) comprises a barrel body (331) and a bottom plate (332); the barrel body (331) is arranged on a lifting platform (351); a bottom of the barrel body (331) is penetrated; the bottom plate (332) is rotatably connected to the lower end surface of the barrel body (331) in a horizontal direction; and the feeding piece (34) is used to control the bottom plate (332) to remain in contact with the lower end surface of the barrel body (331).

5. The medium frequency furnace that is easy to charge according to claim 4 is characterized in that: The feeding member (34) comprises a feeding cylinder (341) and a sliding block (342); the feeding cylinder (341) is arranged on the cylinder body (331); the sliding block (342) is arranged on the piston rod of the feeding cylinder (341); and the sliding block (342) is used to drive the bottom plate (332) to rotate.

6. The medium frequency furnace that is easy to charge according to claim 4 is characterized in that: The lifting platform (351) is also provided with a rotating member (36) for facilitating the staff to add materials into the loading barrel (33). The rotating member (36) includes a rotating motor (361) and a horizontal rod (362). One end of the horizontal rod (362) is rotatably connected to the lifting platform (351) in a vertical direction. One end of the barrel (331) is provided on the horizontal rod (362). The rotating motor (361) is used to drive the horizontal rod (362) to rotate.

7. The medium frequency furnace that is easy to charge according to claim 1 is characterized in that: The frame (1) is provided with a dumping box (7), the furnace body (2) is provided with a drainage groove (21) for molten material to flow out, the furnace body (2) is rotatably connected to the frame (1), and the frame (1) is provided with a dumping motor (61) for driving the furnace body (2) to rotate.

8. The medium frequency furnace that is easy to charge according to claim 1 is characterized in that: A sealing member (22) for sealing the drainage groove (21) is arranged on the furnace body (2); the sealing member (22) comprises a sealing cylinder (221) and a sealing plate (222); the sealing cylinder (221) is arranged on the furnace body (2); the sealing plate (222) is arranged on a piston rod of the sealing cylinder (221); and the sealing cylinder (221) is used to seal the drainage groove (21).

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