Silicon carbide crystal sawing machine

Abstract

The invention discloses a silicon carbide crystal sawing machine, which belongs to the technical field of silicon carbide crystal cutting devices, and is characterized in that the silicon carbide crystal sawing machine comprises a rack, a cutting mechanism and a feeding mechanism, the cutting mechanism comprises a first band saw support, a second band saw support, a driving wheel, a driven wheel, an annular band saw blade and a tensioning assembly; the first band saw bracket is in sliding fit with the second band saw bracket; a motor is installed at the upper end of the first band saw support and connected with a rotating shaft of the driving wheel, and a tensioning assembly is installed in the second band saw support. Compared with the prior art, the self-adaptive tensioning device has the characteristic of self-adaptive tensioning.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide crystal cutting devices, in particular to a silicon carbide crystal sawing machine. Background Art

[0002] Silicon carbide, as one of the most critical and widely used base materials in the semiconductor manufacturing industry, plays a vital role in promoting the development of semiconductor technology with its excellent high purity characteristics and unparalleled electronic performance. In the complex process of precision manufacturing of single-crystal silicon carbide substrates, a crucial step is to accurately cut and finely process the silicon carbide rod crystals in order to achieve a specific particle size or perfect wafer morphology, which is crucial to the performance and reliability of subsequent semiconductor devices.

[0003] At present, the industry generally uses annular band saws as tools for cutting silicon carbide rods. However, the efficient operation of the annular band saw cutting machine is inseparable from a core component - the tensioning assembly, which is responsible for applying appropriate tension to the annular band saw blade during the cutting process to ensure that the saw blade can cut the material stably and accurately, thereby achieving the ideal cutting effect.

[0004] However, the tensioning assembly of the existing circular band saw cutting machine has a problem that cannot be ignored: even when the cutting machine is not in operation (such as standby, maintenance or night rest period), the tensioning assembly continues to apply tension to the circular band saw blade. Although the original intention of this uninterrupted tensioning state is to keep the saw blade taut so that it can be used at any time, it actually causes long-term mechanical stress accumulation on the circular band saw blade. Over time, this continuous tension will gradually cause the saw blade material to undergo microscopic deformation, or even gradually relax, which will not only weaken the original tightening effect of the tensioning assembly, but also greatly shorten the service life of the circular band saw blade. The deformation and relaxation of the saw blade will not only increase the cutting error and affect the product quality, but also increase the production cost and reduce the production efficiency due to the frequent replacement of the saw blade. Summary of the invention

[0005] The purpose of the present invention is to provide a silicon carbide crystal sawing machine in view of the deficiencies of the above-mentioned prior art, so that the tensioning assembly can automatically tension the annular band saw blade when the device is working, and the tensioning assembly will not play a tensioning role when the device is not working.

[0006] A silicon carbide crystal sawing machine provided by the present invention is characterized in that it includes a frame, a cutting mechanism and a feeding mechanism, wherein a support frame and a feeding mechanism are respectively installed on the upper end of the frame, and the support frame and the cutting mechanism are slidably matched; the cutting mechanism includes a first band saw bracket, a second band saw bracket, a driving wheel, a driven wheel, an annular band saw blade and a tensioning assembly, the driving wheel is rotationally matched with the first band saw bracket, the driven wheel is rotationally matched with the second band saw bracket, and the annular band saw blade is sleeved on the driving wheel and the driven wheel; the first band saw bracket is slidably matched with the second band saw bracket; an electric motor is installed on the upper end of the first band saw bracket, the motor is connected to the driving wheel, and a tensioning assembly is installed inside the second band saw bracket.

[0007] Furthermore, a slide plate is installed on the first band saw bracket, and a slide is provided on the slide plate. A slide rail is installed on the second band saw bracket, and the slide rail is slidably matched with the slide of the slide plate.

[0008] Furthermore, the first band saw bracket and the second band saw bracket are respectively provided with guide plates, the guide plates are provided with guide grooves, and the slide rail is also provided with guide grooves. One side of the annular band saw blade passes through the guide grooves on the two guide plates, and the other side passes through the guide grooves on the slide rail. The part of the annular band saw blade located between the two guide plates is the cutting part, which is exposed to the outside of the first band saw bracket and the second band saw bracket.

[0009] Furthermore, the inner walls on both sides of the guide groove of the guide plate and the slide rail are respectively rotatably matched with a plurality of first guide rollers.

[0010] Furthermore, wheel grooves are respectively provided on the outer peripheral surfaces of the driving wheel and the driven wheel, and the annular band saw blades are placed in the wheel grooves.

[0011] Furthermore, the support frame is rotatably matched with the first lead screw, the upper end of the first lead screw is connected to the motor shaft of the motor, first guide rails are respectively provided on both sides of the first lead screw, the first lead screw nut and two first sliders are fixedly installed on the back of the slide plate, the first lead screw nut is matched with the first lead screw, the first slider is provided with a slide groove, and the first guide rail is slidably matched with the slide groove of the first slider.

[0012] Furthermore, the feeding mechanism includes a base plate, a sliding frame and a three-jaw chuck. The base plate is fixedly installed on the upper end of the frame. The base plate and the sliding frame are slidably matched. The sliding frame is fixedly connected to the motor, and the motor shaft of the motor is connected to the three-jaw chuck.

[0013] Furthermore, the base plate is rotatably matched with the second lead screw, one end of the second lead screw is connected to the motor shaft of the motor, the base plate is located on both sides of the second lead screw and second guide rails are installed respectively, the lower end of the sliding frame is fixedly installed with a second lead screw nut and two second sliders, the second lead screw nut is matched with the second lead screw, the second slider is provided with a slide groove, and the second guide rail is slidably matched with the slide groove of the second slider.

[0014] Furthermore, a guide mechanism is installed on the frame, and the guide mechanism is installed between the cutting mechanism and the feeding mechanism. The guide mechanism includes a bidirectional screw, a clamping block, a connecting frame and a second guide roller. An elongated guide groove is provided at the upper end of the frame, and the bidirectional screw is rotatably matched in the elongated guide groove. One end of the bidirectional screw is connected to the motor, and a threaded hole is provided at the lower end of the connecting frame. The lower end of the connecting frame slides with the elongated guide groove, and two sections of the thread of the bidirectional screw are respectively threadedly matched with the threaded holes at the lower end of the corresponding connecting frame; the upper end of the connecting frame is fixedly connected to the clamping block, and a V-shaped clamping groove is provided on the clamping block. The V-shaped clamping grooves of the two clamping blocks are correspondingly arranged, and the two V-shaped clamping grooves are respectively rotatably matched with the second guide roller, and the center of the clamping groove formed by the two V-shaped clamping grooves is on the same straight line as the center of the circle of the three-jaw chuck.

[0015] Furthermore, the tensioning assembly includes a friction wheel, a driving gear, a driven gear and a rack. The driving wheel and the driven wheel are respectively provided with a rotating shaft at the center of the circle. The rotating shaft of the driving wheel is rotationally matched with the first band saw bracket, and the rotating shaft of the driven wheel is rotationally matched with the second band saw bracket. The friction wheel is installed on the rotating shaft of the driven wheel, and the driving gear is installed on the outer side of the friction wheel; the rotating shaft of the driven wheel is slidingly matched with the gear hole of the driving gear, and a spring is installed on the outer side of the driving gear. The spring is sleeved on the rotating shaft, one end of the spring is connected to the second band saw bracket, and the other end is against the driving gear, pressing the driving gear onto the friction wheel; the two inner side walls of the second band saw bracket are respectively rotationally matched with the driven gear through shafts, and the driven gear is meshed with the driving gear. Two symmetrically distributed racks are installed at the end of the slide plate, and the racks extend into the interior of the second band saw bracket and mesh with the corresponding driven gear.

[0016] Compared with the prior art, the present invention has the following outstanding beneficial effects: 1. The tensioning assembly of the present invention can automatically tension the annular band saw blade when the device is working. When the device is not working, the tensioning assembly does not tension the annular band saw blade, thereby preventing the annular band saw blade from being deformed due to long-term tension or even gradually loosening, which affects the service life of the annular band saw blade. 2. A guide mechanism is installed on the frame of the present invention. When the three-jaw chuck clamps one end of the bar, the second guide rollers on the two clamping blocks can be made to contact the outer wall of the bar by rotating the bidirectional screw of the guide mechanism. At this time, the second guide roller does not clamp the bar, and the bar can drive the second guide roller to rotate during the feeding process. Therefore, the second guide roller can not only play an auxiliary guiding role for the bar, but also radially limit the bar during the cutting process to prevent shaking during the cutting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the present invention; Figure 2 It is a schematic diagram of the internal structure of the present invention; Figure 3 It is a right side view of the present invention; Figure 4 is a top view of the present invention; Figure 5 The internal structure of the cutting mechanism in the present invention is shown in FIG. Figure 1 ; Figure 6 The internal structure of the cutting mechanism in the present invention is shown in FIG. Figure 2 ; Figure 7 It is a front view of the cutting mechanism in the present invention; Figure 8 yes Figure 7 Cross-sectional view of the AA section; Fig. 9 yes Figure 7 Cross-sectional view of the middle BB part; Fig.10 It is a structural schematic diagram of the clamping block part of the present invention; Among them, 1. frame; 11. support frame; 12. material box; 13. material guide plate; 14. first lead screw; 2. cutting mechanism; 21. first band saw bracket; 22. tensioning assembly; 221. rack; 222. driven gear; 223. driving gear; 224. friction wheel; 23. second band saw bracket; 24. driving wheel; 25. driven wheel; 26. guide plate; 261. first guide roller; 27. annular band saw blade; 28. slide plate; 29. ​​slide rail; 3. guide mechanism; 31. bidirectional lead screw; 32. connecting frame; 33. clamping block; 331. second guide roller; 4. feeding mechanism; 41. three-jaw chuck; 42. sliding frame; 43. bottom plate; 44. second lead screw. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0019] like Figures 1 to 4 As shown, the present invention includes a frame 1, a cutting mechanism 2 and a feeding mechanism 4.

[0020] A support frame 11 and a feeding mechanism 4 are respectively installed on the upper end of the frame 1 . The support frame 11 is slidably matched with the cutting mechanism 2 , and the feeding mechanism 4 is located at one side of the cutting mechanism 2 .

[0021] like Figures 5 to 8As shown, the cutting mechanism 2 includes a first band saw bracket 21, a second band saw bracket 23, a driving wheel 24, a driven wheel 25, an annular band saw blade 27 and a tensioning assembly 22. The driving wheel 24 and the driven wheel 25 are respectively provided with a rotating shaft at the center of the circle. The driving wheel 24 is installed inside the first band saw bracket 21 and is rotatably matched with the first band saw bracket 21 through its rotating shaft. The driven wheel 25 is installed inside the second band saw bracket 23 and is rotatably matched with the second band saw bracket 23 through its rotating shaft.

[0022] The annular band saw blade 27 is sleeved on the driving wheel 24 and the driven wheel 25, and the saw teeth of the annular band saw blade 27 face upwards. The annular band saw blade 27 is driven to run by the driving wheel 24 and the driven wheel 25. A slide plate 28 is installed on the first band saw bracket 21, and a slide is provided on the slide plate 28. A slide rail 29 is installed on the second band saw bracket 23, and the slide rail 29 is placed in the slide of the slide plate 28, and the slide plate 28 and the slide rail 29 are slidably matched. The first band saw bracket 21 and the second band saw bracket 23 are respectively installed with guide plates 26, and the two guide plates 26 on the first band saw bracket 21 and the second band saw bracket 23 are arranged correspondingly. The two guide plates 26 are respectively provided with guide grooves, and the slide rail 29 is also provided with guide grooves. One side of the annular band saw blade 27 passes through the guide grooves on the two guide plates 26 in sequence, and the other side passes through the guide grooves on the slide rail 29. The part of the annular band saw blade 27 located between the two guide plates 26 is the cutting part, which is exposed outside the first band saw bracket 21 and the second band saw bracket 23.

[0023] The first band saw bracket 21 and the slide plate 28 may be an integrated structure or a split structure.

[0024] In the optimization scheme, Fig. 9 As shown, the inner walls on both sides of the guide groove of the guide plate 26 and the slide rail 29 are respectively rotatably matched with a plurality of first guide rollers 261, so that during the movement of the annular band saw blade 27, the friction with the inner wall of the guide groove can be reduced.

[0025] Wheel grooves are respectively provided on the outer circumferential surfaces of the driving wheel 24 and the driven wheel 25 . The width of the wheel grooves is greater than the width of the annular band saw blade 27 . The annular band saw blade 27 is placed in the wheel grooves of the driving wheel 24 and the driven wheel 25 .

[0026] An electric motor is installed at the upper end of the first band saw bracket 21, and the motor shaft of the electric motor is connected to the rotating shaft of the driving wheel 24. A tensioning assembly 22 is installed inside the second band saw bracket 23, and the tensioning assembly 22 includes a friction wheel 224, a driving gear 223, a driven gear 222 and a rack 221. Friction wheels 224 are fixedly installed on the rotating shafts on both sides of the driven wheel 25, and a driving gear 223 is installed on the outer side of the friction wheel 224. The rotating shafts on both sides of the driven wheel 25 pass through the corresponding gear holes of the driving gear 223 respectively, and the driving gear 223 is slidably matched with the rotating shaft. A spring is installed on the outer side of the driving gear 223, and the spring is sleeved on the rotating shaft. One end of the spring is connected to the second band saw bracket 23, and the other end is pressed on the driving gear 223, so that the driving gear 223 is pressed on the friction wheel 224.

[0027] The two inner side walls of the second band saw bracket 23 are respectively rotatably matched with the driven gear 222 through shafts, and the driven gear 222 is meshed with the corresponding driving gear 223. Two symmetrically distributed racks 221 are installed at the end of the slide plate 28. The racks 221 extend into the interior of the second band saw bracket 23 and mesh with the corresponding driven gear 222. When the driven wheel 25 rotates, it can drive its rotating shaft to rotate, and the rotating shaft drives the friction wheel 224 to rotate. The friction wheel 224 drives the driving gear 223 to rotate through friction, and the driving gear 223 drives the driven The gear 222 rotates, and the driven gear 222 moves along the rack 221, so that the driven wheel 25 and the driving wheel 24 move in opposite directions, thereby tensioning the annular band saw blade 27. When the annular band saw blade 27 is tensioned to a certain extent, the friction force between the friction wheel 224 and the driving gear 223 is less than the resistance of the driven wheel 25 and the driving wheel 24 moving in opposite directions. At this time, the friction wheel 224 no longer drives the driving gear 223 to rotate, and the driven wheel 25 and the driving wheel 24 no longer move in opposite directions, thereby avoiding excessive tensioning force and damaging the annular band saw blade 27.

[0028] The support frame 11 is rotatably matched with the first lead screw 14, the upper end of the first lead screw 14 is connected to the motor shaft of the motor, and first guide rails are respectively provided on both sides of the first lead screw 14. The back of the slide plate 28 is fixedly installed with a first lead screw nut and two first sliders, the first lead screw nut is matched with the first lead screw 14, and a slide groove is provided on the first slider, and the first guide rail is slidably matched with the slide groove of the first slider.

[0029] The feeding mechanism 4 includes a base plate 43, a sliding frame 42 and a three-jaw chuck 41. The base plate 43 is fixedly installed on the upper end of the frame 1. The base plate 43 and the sliding frame 42 are slidably matched. The sliding frame 42 is fixedly connected to the motor, and the motor shaft of the motor is connected to the three-jaw chuck 41.

[0030] In the optimization scheme, the base plate 43 is rotatably matched with the second lead screw 44, one end of the second lead screw 44 is connected to the motor shaft of the motor, the base plate 43 is located on both sides of the second lead screw 44 and second guide rails are installed respectively, and the lower end of the sliding frame 42 is fixedly installed with a second lead screw nut and two second sliders, the second lead screw nut is matched with the second lead screw 44, and a slide groove is provided on the second slider, and the second guide rail is slidably matched with the slide groove of the second slider.

[0031] A guide mechanism 3 is installed on the frame 1, and the guide mechanism 3 is installed between the cutting mechanism 2 and the feeding mechanism 4. The guide mechanism 3 includes a bidirectional screw 31, a clamping block 33, a connecting frame 32 and a second guide roller 331. An elongated guide groove is provided at the upper end of the frame 1, and the bidirectional screw 31 is rotatably matched in the elongated guide groove. One end of the bidirectional screw 31 is connected to the motor, and a threaded hole is provided at the lower end of the connecting frame 32. The lower end of the connecting frame 32 is slidably matched with the elongated guide groove, and the two sections of the thread of the bidirectional screw 31 are respectively threadedly matched with the threaded holes at the lower end of the corresponding connecting frame 32.

[0032] like Figures 1 to 4 As shown in FIG. 10 , the upper end of the connecting frame 32 is fixedly connected to the clamping block 33, and a V-shaped clamping groove is provided on the clamping block 33. The V-shaped clamping grooves of the two clamping blocks 33 are arranged correspondingly, and the two V-shaped clamping grooves are respectively rotatably matched with the second guide rollers 331, and the center of the clamping groove formed by the two V-shaped clamping grooves is located on the same straight line as the center of the circle of the three-jaw chuck 41. When the three-jaw chuck 41 clamps one end of the bar material, by rotating the bidirectional lead screw 31, the second guide rollers 331 on the two clamping blocks 33 can be brought into contact with the outer wall of the bar material, thereby guiding and limiting the bar material.

[0033] The frame 1 is provided with an opening at the position of the cutting mechanism 2, and a slanted material guide plate 13 is provided at the lower end of the opening. A material box 12 is placed below the guide plate 26, and the cut wafers can enter the material box 12 through the material guide plate 13.

[0034] The operation process is as follows: when using the present invention, when using the three-jaw chuck 41 to clamp one end of the bar, by rotating the bidirectional screw 31, the second guide rollers 331 on the two clamping blocks 33 can contact the outer wall of the bar, thereby playing a guiding and limiting role, and the second guide rollers 331 will not clamp the bar. Rotate the second screw 44 to allow the feeding mechanism 4 to drive the bar to move to the position of the cutting mechanism 2. During the movement of the bar, the second guide roller 331 is driven to rotate, and the second guide roller 331 plays an auxiliary guiding role for the bar. The cutting thickness is adjusted by adjusting the position of the bar and the annular band saw blade 27; the cutting mechanism 2 is started, the motor drives the driving wheel 24 to rotate, the driving wheel 24 and the driven wheel 25 drive the annular band saw blade 27 to move, the driven wheel 25 rotates to drive the tensioning assembly 22 to work, so that the driving wheel 24 and the driven wheel 25 tension the annular band saw blade 27, and the first lead screw 14 is started to drive the cutting mechanism 2 to rise, and the bar is cut, and the cut wafer enters the material box 12 through the guide plate 13.

[0035] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes to the present invention without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A silicon carbide crystal sawing machine, characterized in that: The invention comprises a frame (1), a cutting mechanism (2) and a feeding mechanism (4), wherein a support frame (11) and a feeding mechanism (4) are respectively mounted on the upper end of the frame (1), and the support frame (11) and the cutting mechanism (2) are slidably matched; the cutting mechanism (2) comprises a first band saw bracket (21), a second band saw bracket (23), a driving wheel (24), a driven wheel (25), an annular band saw blade (27) and a tensioning assembly (22), wherein the driving wheel (24) and the first band saw bracket (21) are rotationally matched, and the driven wheel (25) and the second band saw bracket (23) are rotationally matched, and the annular band saw blade (27) is sleeved on the driving wheel (24) and the driven wheel (25); the first band saw bracket (21) and the second band saw bracket (23) are slidably matched; an electric motor is mounted on the upper end of the first band saw bracket (21), and the electric motor is connected to the driving wheel (24); and the tensioning assembly (22) is mounted inside the second band saw bracket (23).

2. A silicon carbide crystal sawing machine according to claim 1, characterized in that: The first band saw bracket (21) is provided with a slide plate (28), the slide plate (28) being provided with a slideway, and the second band saw bracket (23) is provided with a slide rail (29), the slide rail (29) being slidably matched with the slideway of the slide plate (28).

3. A silicon carbide crystal sawing machine according to claim 2, characterized in that: The first band saw bracket (21) and the second band saw bracket (23) are respectively provided with guide plates (26), the guide plates (26) are provided with guide grooves, and the slide rail (29) is also provided with guide grooves. One side of the annular band saw blade (27) passes through the guide grooves on the two guide plates (26), and the other side passes through the guide grooves on the slide rail (29). The portion of the annular band saw blade (27) located between the two guide plates (26) is a cutting portion, which is exposed outside the first band saw bracket (21) and the second band saw bracket (23).

4. A silicon carbide crystal sawing machine according to claim 3, characterized in that: The inner walls on both sides of the guide groove of the guide plate (26) and the slide rail (29) are respectively rotatably matched with a plurality of first guide rollers (261).

5. The silicon carbide crystal sawing machine according to claim 1, characterized in that: Wheel grooves are respectively provided on the outer peripheral surfaces of the driving wheel (24) and the driven wheel (25), and the annular band saw blades (27) are placed in the wheel grooves.

6. The silicon carbide crystal sawing machine according to claim 1, characterized in that: The support frame (11) is rotatably matched with the first lead screw (14), the upper end of the first lead screw (14) is connected to the motor shaft of the motor, first guide rails are respectively provided on both sides of the first lead screw (14), a first lead screw nut and two first sliders are installed on the back of the slide plate (28), the first lead screw nut is matched with the first lead screw, a slide groove is provided on the first slider, and the first guide rail is slidably matched with the slide groove of the first slider.

7. The silicon carbide crystal sawing machine according to claim 1, characterized in that: The feeding mechanism (4) comprises a bottom plate (43), a sliding frame (42) and a three-jaw chuck (41). The bottom plate (43) is fixedly mounted on the upper end of the frame (1). The bottom plate (43) and the sliding frame (42) are slidably matched. The sliding frame (42) is fixedly connected to the motor. The motor shaft of the motor is connected to the three-jaw chuck (41).

8. The silicon carbide crystal sawing machine according to claim 7, characterized in that: The base plate (43) is rotatably matched with the second lead screw (44), one end of the second lead screw (44) is connected to the motor shaft of the motor, the base plate (43) is respectively provided with second guide rails on both sides of the second lead screw (44), a second lead screw nut and two second sliders are installed at the lower end of the sliding frame (42), the second lead screw nut is matched with the second lead screw (44), a slide groove is provided on the second slider, and the second guide rail is slidably matched with the slide groove of the second slider.

9. The silicon carbide crystal sawing machine according to claim 1, characterized in that: The frame (1) is provided with a guide mechanism (3), which is installed between the cutting mechanism (2) and the feeding mechanism (4). The guide mechanism (3) comprises a bidirectional lead screw (31), a clamping block (33), a connecting frame (32) and a second guide roller (331). The upper end of the frame (1) is provided with a long guide groove, in which the bidirectional lead screw (31) is rotatably matched. One end of the bidirectional lead screw (31) is connected to the motor. The lower end of the connecting frame (32) is provided with a threaded hole for connecting the two-way lead screw (31). The lower end of the frame (32) is slidably matched with the long strip guide groove, and the two sections of the thread of the bidirectional lead screw (31) are respectively threadedly matched with the threaded holes at the lower end of the corresponding connecting frame (32); the upper end of the connecting frame (32) is connected to the clamping block (33), and the clamping block (33) is provided with a V-shaped clamping groove. The V-shaped clamping grooves of the two clamping blocks (33) are arranged correspondingly, and the two V-shaped clamping grooves are respectively rotatably matched with the second guide roller (331), and the center of the clamping groove formed by the two V-shaped clamping grooves is located on the same straight line with the center of the circle of the three-jaw chuck (41).

10. The silicon carbide crystal sawing machine according to claim 1, characterized in that: The tensioning assembly (22) comprises a friction wheel (224), a driving gear (223), a driven gear (222) and a rack (221); a rotating shaft is respectively provided at the center of the driving wheel (24) and the driven wheel (25); the rotating shaft of the driving wheel (24) is rotationally matched with the first band saw bracket (21); the rotating shaft of the driven wheel (25) is rotationally matched with the second band saw bracket (23); the friction wheel (224) is mounted on the rotating shaft of the driven wheel (25); the driving gear (223) is mounted on the outer side of the friction wheel (224); the rotating shaft of the driven wheel (25) is slidably matched with the gear hole of the driving gear (223); A spring is installed on the outer side of the driven gear (223), and the spring is sleeved on the rotating shaft. One end of the spring is connected to the second band saw bracket (23), and the other end is pressed on the driving gear (223), so that the driving gear (223) is pressed on the friction wheel (224); the two inner side walls of the second band saw bracket (23) are respectively rotatably matched with the driven gear (222) through the shaft, and the driven gear (222) is meshed with the driving gear (223); two symmetrically distributed racks (221) are installed at the end of the slide plate (28), and the racks (221) extend into the interior of the second band saw bracket (23) and mesh with the corresponding driven gears (222).

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