Shute

Abstract

To provide a shute capable of suppressing attachment of transportation objects.SOLUTION: A shute 6 is to guide transportation objects discharged from an upstream side device 5 in a transportation direction of the transportation objects to a downstream side device 7 placed at a downstream side of the upstream side device 5 in the transportation direction, wherein a low friction part 10 with lower friction coefficient than a peripheral part thereof is arranged on a part where the transportation objects discharged from the upstream side device 5 collide.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a chute. [Background technology]

[0002] The expanded use of inexpensive coal with a high moisture content is being considered. When using coal with a high moisture content, for example, as a pre-treatment of the coal before loading into a coke oven, the moisture content of the coal is reduced to a preset moisture content using a coal moisture controller installed in the coal transmission line between the storage yard and the coke oven. Furthermore, because coal is stored in an outdoor storage yard, the moisture content of the coal increases with rainfall. When the moisture content of the coal increases due to rainfall, it is necessary to set the drying time of the coal using the coal moisture controller longer.

[0003] The coal feeding line is provided with a plurality of conveyors, and the coal is transported by transferring the coal from the upstream conveyor to the downstream conveyor in the coal transport direction. Specifically, a chute is provided between the upstream conveyor and the downstream conveyor. The coal discharged from the upstream conveyor is received in the chute, and the coal is transferred from the discharge opening of the chute to a predetermined location on the downstream conveyor.

[0004] Furthermore, because coal has adhesive properties, coal adhesion is likely to occur in the parts of the chute that come into contact with the coal. If the amount of coal adhering to the chute becomes excessive, the chute will be unable to accept the coal, which may hinder the transport of coal through the chute. Therefore, cleaning to remove coal adhering to the chute is performed periodically or according to the amount of coal adhering to the chute. However, the above-mentioned cleaning work necessitates stopping the transport of coal in the coal delivery line and halting the operation of the coal moisture control unit. For this reason, technologies to suppress coal adhesion to the chute have been studied.

[0005] An example of a technology for suppressing adhesion of coal to a chute is described in Patent Document 1. The chute described in Patent Document 1 has a ceramic sheet that collides with transported materials such as iron ore and coal discharged from an upstream transport conveyor. The ceramic sheet is attached to the inner wall surface of the chute so that it can swing around its upper part as a fulcrum. The transported materials discharged from the upstream transport conveyor collide with the ceramic sheet, causing it to vibrate. This vibration suppresses adhesion of the transported materials to the ceramic sheet. An angle adjustment device is provided on the ceramic sheet opposite the surface that collides with the transported materials, supporting the ceramic sheet from its back and adjusting the angle of the ceramic sheet. The angle of the ceramic sheet is adjusted by the angle adjustment device to adjust the drop position of the transported materials on the downstream transport conveyor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 10-279061 Summary of the Invention [Problem to be solved by the invention]

[0007] The main causes of adhesion of transported objects to the ceramic sheet are liquid bridging force and frictional force. The liquid bridging force varies depending on the moisture content of the transported object. For example, as the moisture content of the transported object increases, the liquid bridging force increases accordingly. Therefore, when a transported object with a high moisture content collides with the ceramic sheet, the high liquid bridging force caused by the moisture content causes the transported object to adhere to the ceramic sheet. On the other hand, the frictional force is determined by the friction coefficient and normal force of the ceramic sheet. The friction coefficient of the ceramic sheet is somewhat higher than that of other materials. Therefore, when a transported object collides with the ceramic sheet, the friction coefficient of the ceramic sheet causes the transported object to adhere to the ceramic sheet. As such, the chute described in Patent Document 1 still has room for improvement in terms of suppressing adhesion of transported objects to the ceramic sheet.

[0008] Furthermore, ceramic sheets are difficult to process, resulting in thick, large sheets. Therefore, using ceramic sheets can increase the construction load. Furthermore, because ceramic sheets are hard and brittle, repeated collisions with coal can cause them to break or crack during coal transport. If this occurs, large ceramic sheet fragments may fall onto the conveyor, damaging it. Furthermore, ceramic cannot be detected by metal detectors. Therefore, ceramic sheet fragments may enter the coal moisture control unit located downstream of the chute described in Patent Document 1 in the coal transport direction, potentially destroying or damaging the steam tube inside the coal moisture control unit.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a chute that can suppress adhesion of transported objects. [Means for solving the problem]

[0010] The means for solving the above problems are as follows. [1] A chute that guides an object released from an upstream device in the transport direction of the object to a downstream device downstream of the upstream device in the transport direction, wherein a low-friction portion having a lower friction coefficient than the surrounding area is provided at the portion where the object released from the upstream device collides. [2] The chute according to [1], wherein the coefficient of friction of the low-friction portion is 0.4 or less. [3] The chute according to [1] or [2], wherein the hardness of the low-friction portion is 60 HS or more. [4] A chute as described in any of [1] to [3], which is equipped with an angle adjustment device that adjusts the installation angle of the low-friction portion, which is the angle between the low-friction portion and a horizontal plane, and in which the installation angle of the low-friction portion is 70° or more. [Effects of the Invention]

[0011] According to the present invention, adhesion of transported objects to the chute can be suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a coal feeding line to which the chute according to the present embodiment can be applied. [Figure 2] FIG. 10 is a diagram showing an example of a shot according to the present embodiment. [Figure 3] FIG. 3 is a front view of the plate of the buffer section shown in FIG. 2. [Figure 4] This is a diagram explaining the relationship between the number of operating days of a coal transmission line equipped with a chute equipped with a liner of this embodiment and the thickness of coal adhering to the chute equipped with a liner of this embodiment on each operating day. [Figure 5] FIG. 3 is a diagram illustrating the change in thickness of a high-hardness liner with respect to the number of days of use of the chute when a liner with increased hardness is attached to the chute shown in FIG. 2. [Figure 6] FIG. 10 is a diagram showing the amount of coal adhesion on each liner having different dynamic friction coefficients. DETAILED DESCRIPTION OF THE INVENTION

[0013] An example of an embodiment of the present invention (hereinafter referred to as this embodiment) will be described below. Fig. 1 is a diagram showing an example of a coal feeding line to which a chute according to this embodiment can be applied. The coal feeding line 1 shown in Fig. 1 transports coal, which is the transported item of this embodiment, from a storage yard 2 that stores the coal to a coke oven 3. A coal pulverizer 4 is provided in the storage yard 2, and the coal is pulverized to a predetermined size by the coal pulverizer 4.

[0014] A plurality of transport conveyors 5 are provided on the coal feeding line 1, and these transport conveyors 5 transport the coal pulverized by the coal pulverizer 4 toward the coke oven 3. The transport conveyors 5 may be conventionally known, and examples of the transport conveyors 5 include a roller conveyor and a belt conveyor.

[0015] A chute 6 according to this embodiment is provided between the upstream conveyor in the coal conveying direction and the downstream conveyor adjacent to the upstream conveyor. The chute 6 guides coal discharged from the upstream conveyor to a predetermined location on the downstream conveyor. In the example shown in FIG. 1 , a coal moisture control device 7 that adjusts the moisture content of coal is provided midway along the coal feed line 1. The coal moisture control device 7 may be a conventionally known device. Another chute 6 is provided upstream of the coal moisture control device 7 in the coal conveying direction, and coal is supplied into the coal moisture control device 7 through the chute 6. The coal feed line 1 corresponds to the feed line in this embodiment. The feed conveyor upstream of the chute 6 corresponds to the feed conveyor and the upstream device in this embodiment. The feed conveyor downstream of the chute 6 corresponds to the other feed conveyor in this embodiment, and either the feed conveyor downstream of the chute 6 or the coal moisture control device corresponds to the downstream device in this embodiment.

[0016] Fig. 2 is a diagram showing an example of a chute according to this embodiment. The chute 6 shown in Fig. 2 is configured in a funnel shape, and an end of the upstream transfer conveyor is disposed inside and above the chute 6. Coal is discharged from the end into the chute 6. A discharge port is formed at the bottom of the chute 6 for supplying coal to the downstream transfer conveyor, and coal is supplied from the discharge port to a preset location on the downstream transfer conveyor.

[0017] A buffer section 8 is provided inside the chute 6 to prevent coal released from the upstream conveyor 5 from colliding with the inner wall of the chute 6 and being crushed. The buffer section 8 is provided between the end of the conveyor 5 and the opposing inner wall of the chute 6 in the direction of movement of the coal released from the conveyor 5. In other words, the buffer section 8 is provided closer to the end of the conveyor 5 than the inner wall of the chute 6. This is to reduce the kinetic energy of the coal when it collides with the buffer section 8. The buffer section 8 also includes a plate 9 against which coal released from the upstream conveyor 5 collides. The coal released from the upstream conveyor 5 collides with the front of the plate 9, i.e., the surface facing the upstream conveyor 5, between the center and the lower end in the height direction of the chute 6. A shock absorbing section (not shown) is provided on the back of the plate 9 to reduce or absorb the impact force when coal collides with the plate 9. The shock absorbing section may be, for example, a spring (not shown) or an air cylinder (not shown). A plate 9 is attached to the inner wall surface of the chute 6 via the shock absorbing portion.

[0018] The buffer unit 8 further includes an angle adjustment device (not shown). The angle adjustment device allows the mounting angle θ of the plate 9, which is the angle between the plate 9 of the buffer unit 8 and the horizontal plane, to be changed. By changing the mounting angle θ, coal that collides with the plate 9 is caused to fall toward a predetermined location on the downstream transport conveyor. The angle adjustment device may be a conventionally known one.

[0019] Figure 3 is a front view of plate 9 of buffer section 8 shown in Figure 2. A plurality of liners 10, which correspond to the low-friction section in this embodiment, are fastened by screws or bolts to the front of plate 9 shown in Figure 3 in a section between the center and lower end in the height direction of chute 6. The liners 10 are flat plate-shaped members, and in Figure 3, the attachment portion of the liners 10 on the front of plate 9 is shown surrounded by a two-dot chain line.

[0020] The above-mentioned liner 10 prevents coal from adhering to the plate 9 of the buffer section 8, and is preferably formed from a material with a lower coefficient of friction than the material forming the plate 9 and chute 6 to which the liner 10 is attached. Specifically, the plate 9 and chute 6 are preferably formed from stainless steel, and the liner 10 is preferably made from a synthetic resin material with a lower coefficient of friction than stainless steel. Examples of synthetic resin materials include PTFE (polytetrafluoroethylene) resin and polyethylene resin. The above-mentioned liner 10 is manufactured, for example, by filling a predetermined mold with powder of PTFE resin or polyethylene resin, compression molding, and then sintering. The peripheral parts of the liner 10, such as the plate 9 and chute 6 to which the liner 10 is attached, correspond to the peripheral parts in this embodiment.

[0021] Coal discharged from the upstream transfer conveyor 5 repeatedly collides with the liner 10. Therefore, in order to ensure the wear resistance and durability of the liner 10, it is preferable that the hardness of the liner 10 is relatively high and that the plate thickness of the liner 10 is relatively thick. For example, the hardness of the liner 10 is preferably 50 HS or more, and more preferably 70 HS or more, in Shore hardness. Note that if the hardness of the liner 10 is less than 50 HS, the liner 10 may be easily worn or broken due to collisions with coal, which may require more frequent replacement.

[0022] To increase the abrasion resistance and durability of the liner 10, for example, copper powder as a filler is mixed into PTFE resin powder when manufacturing the liner 10 made of PTFE resin. The copper powder content is preferably about 60% (by weight). This increases the hardness compared to when no filler is added, allowing for the manufacture of a liner with improved abrasion resistance and durability. For example, the Shore hardness of the PTFE resin liner 10 described above without copper powder as a filler is about 50 HS. By adding copper powder as a filler, the hardness can be increased to about 70 HS. The thickness of the liner 10 is preferably 10 mm or more. This is because the liner 10 is replaced in synchronization with major repairs of the coal moisture control unit 7, which are performed approximately every six months. In other words, this ensures that the replacement life of the liner 10 is 180 days or more. In addition to copper powder, carbon fiber and glass fiber can also be used as fillers. When a liner is manufactured by mixing carbon fiber as a filler into PTFE resin powder, the Shore hardness is about 60HS. When a liner is manufactured by mixing glass fiber as a filler into PTFE resin powder, the Shore hardness is about 63HS.

[0023] FIG. 4 is a diagram illustrating the relationship between the number of operating days of a coal feed line 1 equipped with a chute 6 equipped with the liner 10 of this embodiment and the maximum adhesion thickness of coal adhering to the liner 10 of this embodiment on each operating day. FIG. 4 also illustrates the relationship between the number of operating days of a coal feed line equipped with a conventional chute not equipped with the liner 10 described above (hereinafter referred to as the comparative example) and the maximum adhesion thickness of coal adhering to the coal collision area of ​​the conventional chute on each operating day. The chute of the comparative example is made of stainless steel. As shown in FIG. 4, in the comparative example, when the coal feed line was operated and coal transportation began, the maximum adhesion thickness of coal adhering to the coal collision area of ​​the conventional chute reached 700 mm, which is the target for chute cleaning, on the first day of operation. Therefore, in the comparative example, cleaning work to remove coal was performed every day, and each cleaning took approximately two hours.

[0024] In contrast, in the present embodiment, the maximum thickness of coal adhering to the liner 10 reached 700 mm on the seventh day of operation of the coal transmission line 1. Therefore, in the present embodiment, cleaning work to remove coal adhering to the liner 10 was performed once a week. Furthermore, in the present embodiment, the provision of the liner 10 made it easier to remove coal adhering to the chute 6, and the cleaning time per cleaning was approximately 40 minutes. As described above, the liner 10 is made of PTFE, and the kinetic friction coefficient of the liner 10 is smaller than that of the comparative example chute made of stainless steel. Therefore, the adhesion force of coal to the liner 10 is smaller than that of coal to the comparative example chute. As a result, it is believed that the present embodiment made it easier to remove coal compared to the comparative example, and the cleaning time was shorter than that of the comparative example.

[0025] FIG. 5 is a diagram illustrating the change in the thickness of a high-hardness liner with increased hardness (hereinafter referred to as a high-hardness liner) attached to the chute 6 shown in FIG. 2 over the number of days of use of the chute 6. Note that FIG. 5 also illustrates the change in the thickness of a pure PTFE liner with no increased hardness (hereinafter referred to as a pure PTFE liner) attached to the chute 6 shown in FIG. 2 over the number of days of use of the chute 6. In this embodiment, the high-hardness liner is a liner made of PTFE resin, and as described above, is formed by filling a predetermined mold with PTFE powder and copper powder, compression molding the liner, and then sintering the liner. The pure PTFE liner is formed by filling a predetermined mold with PTFE resin powder, compression molding the liner, and then sintering the liner. In other words, the pure PTFE liner is manufactured in a manner similar to that of the high-hardness liner, except that copper powder is not added as a filler when the PTFE resin powder is compression molded. The hardness of the high-hardness liner is, for example, 70 HS, and the hardness of the pure PTFE liner is 50 HS.

[0026] Because the hardness and abrasion resistance of the high-hardness liner are greater than those of the pure PTFE liner, the plate thickness of the high-hardness liner is less likely to decrease than that of the pure PTFE liner, as shown in Figure 5. Therefore, when the high-hardness liner is attached to the chute 6 shown in Figure 2 and used, the frequency of liner replacement due to liner wear and breakage can be reduced compared to when the pure PTFE liner is attached to the chute 6. In addition, it is possible to prevent the coal transmission line 1 from being stopped due to liner replacement, and accordingly, the operating time of the coal moisture control unit 7 can be increased more than ever before.

[0027] According to this embodiment, adhesion of coal to the chute 6 can be suppressed and the cleaning time of the chute 6 can be shortened more than ever before. Furthermore, the downtime of the coal feeding line 1 due to cleaning of the chute 6 can be shortened more than ever before, and the operating time of the coal moisture control unit 7 can be increased more than ever before. Therefore, for example, even if coal stored in the storage yard 2 becomes wet due to rainfall and the moisture content of the coal increases, the coal moisture control unit 7 can sufficiently reduce the moisture content of the coal to the desired moisture content. That is, the bulk density of the coal before being charged into the coke oven 3 can be increased more than ever before. This can suppress the occurrence of cracks in the coke produced in the coke oven 3 and the occurrence of coarse pores in the coke. As a result, even when coal whose moisture content has increased due to rainfall or inexpensive coal that is inherently high in moisture is transported via the coal feeding line 1 and carbonized in the coke oven 3 to produce coke, the strength of the coke can be increased more than ever before. That is, according to this embodiment, the use of inexpensive coal with a high moisture content can be expanded. The coke manufacturing method of this embodiment corresponds to the coke manufacturing method in which coal is transported using the chute 6 and coal delivery line 1 described above, charged into a coke oven, and carbonized to produce coke. The following describes what to do if the liner 10 of this embodiment is broken or cracked during coal charging. The liner 10 of this embodiment is made of a synthetic resin material, which is softer than ceramic or metal materials. Therefore, even if fragments of the liner 10 of this embodiment enter the coal moisture conditioner, damage to the coal moisture conditioner can be suppressed. [Example]

[0028] The present invention will be specifically described below with reference to examples. In Example 1, the relationship between the dynamic friction coefficient of a liner and the amount of coal adhesion was investigated. A sealable container was prepared, a liner was attached to the inner wall surface of the container, and coal was placed in the container. The container was rotated for a preset time to bring the coal into contact with the liner. After the preset time had elapsed, the rotation of the container was stopped and the amount of coal adhesion per unit area of ​​the liner was measured. This measurement of the amount of coal adhesion was performed for each liner with a different dynamic friction coefficient, and the rotation speed when rotating the container was changed. The above-mentioned container was rotated around a central axis of rotation that was approximately parallel to the horizontal plane.

[0029] Specifically, the liners used in the above-mentioned investigation were a high-hardness liner (i.e., a PTFE liner containing added copper powder), a wear-resistant PTFE liner with improved wear resistance, a polyethylene liner, and a stainless steel liner. These liners were attached to the inner wall of the vessel, and the amount of coal adhesion to each liner was measured as described above. Note that the thickness of each liner and the moisture content of the coal were approximately constant. The amount of coal adhesion to each liner was measured multiple times, and the average value was calculated. The results are summarized in Figure 6. As shown in Figure 6, it was found that the lower the kinetic friction coefficient of the liner, the more effectively coal adhesion was suppressed. [Example]

[0030] In Example 2, several liners with different dynamic friction coefficients and hardness were prepared, and the cleaning time required to remove coal adhering to these liners and the liner lifespan were investigated. Specifically, each liner was attached to a chute configured similarly to the chute shown in Figure 2, and coal was transported through the chute. Cleaning was then performed when the thickness of the coal adhering to the liner reached 700 mm, which is the target thickness for cleaning, and the time required for cleaning was measured. The number of days until the liner broke was also measured, and this number was defined as the liner lifespan. The dynamic friction coefficients, hardness, cleaning time, and lifespan of these liners are summarized in Table 1. The above-mentioned investigations of cleaning time and lifespan were conducted multiple times for each liner, and the average values ​​are summarized in Table 1.

[0031] [Table 1]

[0032] In Example 1, a polyethylene liner with a dynamic friction coefficient of 0.4 and a hardness of 55 HS was attached to the plate of the buffer section of a chute constructed in a manner similar to that shown in Figure 2. The attachment angle θ was set to 70°. Coal was transported using this chute, and the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated.

[0033] In Example 2, the time required to clean coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Example 1, except that a polyethylene liner with a dynamic friction coefficient of 0.3 was used. The dynamic friction coefficient can be adjusted by adjusting the surface roughness of the liner.

[0034] In Example 3 of the present invention, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Example 1, except that a polyethylene liner with a dynamic friction coefficient of 0.2 was used.

[0035] Inventive Example 4, the time required to clean coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Inventive Example 1, except that a pure PTFE liner with a dynamic friction coefficient of 0.1 and a hardness of 55HS was used.

[0036] Inventive Example 5, the time required to clean coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Inventive Example 1, except that a high-hardness liner with a dynamic friction coefficient of 0.2 and a hardness of 60 HS, i.e., a PTFE liner with added copper powder, was used.

[0037] Inventive Example 6, the time required to clean coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Inventive Example 1, except that a high-hardness liner with a dynamic friction coefficient of 0.2 and a hardness of 65HS was used.

[0038] Inventive Example 7, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Inventive Example 1, except that a high-hardness liner with a dynamic friction coefficient of 0.2 and a hardness of 70HS was used.

[0039] In Example 8 of the invention, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Example 1 of the invention, except that the installation angle θ of the polyethylene liner was set to 80°.

[0040] Inventive Example 9, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Inventive Example 1, except that the installation angle θ of the polyethylene liner was set to 90°.

[0041] (Comparative Example 1) Comparative Example 1 was conducted in the same manner as Invention Example 1, except that a stainless steel liner with a dynamic friction coefficient of 0.8 and a hardness of 55HS was used, and the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated.

[0042] In Comparative Example 2, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Invention Example 1, except that a stainless steel liner with a dynamic friction coefficient of 0.7 was used.

[0043] In Comparative Example 3, the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated in the same manner as in Invention Example 1, except that a stainless steel liner with a dynamic friction coefficient of 0.6 was used.

[0044] Comparative Example 4 was conducted in the same manner as Invention Example 1, except that a stainless steel liner with a dynamic friction coefficient of 0.5 was used, and the time required to clean the coal adhering to the liner and the lifespan of the liner were investigated.

[0045] As shown in Table 1, the dynamic friction coefficients of the liners of Examples 1 to 9 were smaller than those of Comparative Examples 1 to 4. Therefore, in Examples 1 to 9, adhesion of coal to the liner was suppressed compared to Comparative Examples 1 to 4, and the time required to clean the coal adhered to the liner was shortened due to the weak adhesion of coal to the liner. Furthermore, in Examples 5 to 7, which had a higher hardness than Examples 1 to 4, 8, and 9, the life of the liner was extended. Furthermore, in Examples 8 and 9, the mounting angle θ was increased compared to Example 1, which facilitated the removal of coal adhered to the liner. Therefore, as shown in Table 1, in Examples 8 and 9, the time required to clean the coal adhered to the liner was shortened compared to Examples 1 and 2 and Comparative Examples 1 to 4.

[0046] The present invention is not limited to the above-described embodiment. For example, instead of attaching multiple liners 10 to the plate 9 of the buffer section 8, a single liner may be attached to the plate 9. This reduces unevenness and gaps that can be the starting point for coal adhesion, compared to attaching multiple liners 10 to the plate 9, thereby further suppressing coal adhesion. Alternatively, the upper end of a lower liner located below the upper liner and adjacent to the upper liner may be placed between the lower end of the upper liner located above in the vertical direction and the plate. In other words, the liners may be attached to the plate in a scale-like manner. This also reduces gaps that can be the starting point for coal adhesion, thereby further suppressing coal adhesion. Furthermore, in addition to attaching the liner 10 to the plate 9, the above-described liner 10 may be attached to the inner wall surface of a chute with which coal released from the upstream conveyor 5 collides or comes into contact. These configurations can achieve substantially the same effects and advantages as the above-described embodiment. [Explanation of symbols]

[0047] 1 Coal transmission line 2 Storage Yard 3. Coke oven 4. Coal crusher 5. Transport conveyor 6 Shoot 7 Coal moisture control unit 8 Buffer 9 Plates 10 Liner

Claims

1. A chute that guides an object released from an upstream device in the transport direction of the object to a downstream device downstream of the upstream device in the transport direction, wherein a low-friction portion having a lower friction coefficient than the surrounding area is provided at the portion where the object released from the upstream device collides.

2. 2. The chute according to claim 1, wherein the low-friction portion has a coefficient of friction of 0.4 or less.

3. 3. The chute according to claim 1, wherein the low-friction portion has a hardness of 60 HS or more.

4. A chute as described in claim 1 or 2, which is equipped with an angle adjustment device that adjusts the installation angle of the low-friction portion, which is the angle between the low-friction portion and a horizontal plane, and the installation angle of the low-friction portion is 70° or more.

5. 4. The chute of claim 3, further comprising an angle adjustment device for adjusting the mounting angle of the low-friction portion, which is the angle between the low-friction portion and a horizontal plane, and the mounting angle of the low-friction portion is 70° or more.

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