JP7081033B1 - Mixing liquid separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mixed liquid separating device capable of realizing a higher recovery rate than before. SOLUTION: The inner member 2 has a cylindrical outer member 1, a rod-shaped inner member 2 coaxially arranged in the outer member 1 and relatively rotatable, and a driving means 3 for rotating the inner member. The outer peripheral side has two spiral guide walls 211 and 212, and the guides separated and paralleled by sending a specific substance along the guide walls 211 and 212 by the relative rotation of the outer member 1 and the inner member 2. The valley width Vw (mm), which is the distance between the walls 211 and 212, is 1.0 or more based on the mountain width Mw (mm), which is the width of the guide walls 211 and 212, and has an outer diameter D (mm). The relationship is that n · (Vw + Mw) / πD is 0.01 or more and 0.27 or less. [Selection diagram] Fig. 2

Description

The present invention relates to a mixed liquid separating device that separates a predetermined substance from a mixed liquid in which immiscible different components are mixed by being used for cleaning or lubrication in factory equipment such as a machine tool.

In manufacturing industries such as machining, coolants containing industrial water as the main component are used for various purposes such as lubrication and cooling during processing, cleaning and degreasing after processing. Various components such as cutting agents and cleaning agents are added to these coolants according to the purpose of use, and after use, they are collected in the state of drainage mixed with foreign substances such as chips and oil supplied for lubrication. Ru. The collected waste liquid is circulated and used after removing foreign substances. Various devices have been conventionally used as equipment for such drainage treatment (see, for example, Patent Documents 1 and 2).

In the prior art shown in this patent document, a rod-shaped inner member that rotates relative to the outer member is coaxially arranged inside the cylindrical outer member, and a spiral guide wall provided on the outer periphery of the inner member is placed on the outside. A screw pipe type liquid separation mechanism is adopted, which is configured to be in sliding contact with the inner peripheral surface of the member. Then, at the time of operation, the outer member and the inner member are relatively rotated with the lower portion of the screw pipe immersed in the mixed liquid to be separated. As a result, the guide wall rotates while sliding in contact with the inner peripheral surface of the outer member, and the substance to be separated such as oil suspended on the liquid surface of the mixed liquid is transferred upward by the spiral surface of the guide wall and separated and recovered.

Republished WO2005 / 038408 Gazette Japanese Unexamined Patent Publication No. 2014-050775

By the way, although the conventional mixed liquid separating device has high performance, it is required to reduce the operating amount of the device and aim for a long life by achieving further high performance. If the mixed liquid separation device fails due to a failure, the coolant will not be able to exert its original effect, and there is a risk of adverse effects on other devices in a chain reaction, so it is required to be able to operate without problems for a long period of time.

The present invention has been made in view of such a problem, and it is a problem to be solved to provide a mixed liquid separating device capable of realizing a higher recovery rate than before.

As a result of diligent studies for the purpose of solving the above problems, the present inventors have found that the recovery speed can be improved by adopting a specific form for the spiral guide wall provided on the outer periphery of the inner member. Completed the invention. That is, the mixed liquid separating device of the present invention is a mixed liquid separating device that separates and takes out a specific substance from a mixed liquid of at least two kinds of immiscible liquid substances having different entrainment characteristics.
An outer member that is cylindrical and has a suction port for sucking the mixed liquid at one end thereof and a discharge port for discharging the specific substance separated at the other end portion.
A rod-shaped inner member that is coaxially arranged with the outer member and can rotate relative to the outer member,
A driving means for relatively rotating the outer member and the inner member,
Have,
The outer peripheral side of the inner member has a plurality of spiral guide walls that guide the specific substance from one end to the other end by the relative rotation of the outer member and the inner member.
The specific substance is separated by being sent to the other end portion along the guide wall by the relative rotation of the outer member and the inner member.
The valley width Vw (mm), which is the distance between the plurality of parallel guide walls, is 1.0 or more based on the mountain width Mw (mm), which is the width of the guide walls, and has an outer diameter D (mm). The relationship with n · (Vw + Mw) / πD is 0.01 or more and 0.27 or less.

n · (Vw + Mw) / πD is preferably 0.16 or less, and preferably 0.05 or more. The valley width Vw is preferably 6.3 mm or more.

The mixed liquid separating device of the present invention can realize a high recovery rate by having the above configuration.

It is a schematic diagram explaining the position to measure the mountain width Mw of the guide wall in the mixed liquid separating apparatus of this invention. It is a front schematic diagram of the mixed liquid separating apparatus of this invention. It is a partially enlarged view of the front of the mixed liquid separating apparatus of this invention. It is a graph which shows the n · (Vw + Mw) / πD dependence of the recovery rate in the mixed liquid separating apparatus of this Example. It is a graph which shows the Vw / Mw dependence of the recovery rate in the mixed liquid separating apparatus of this Example.

Hereinafter, embodiments of the mixed liquid separating device of the present invention will be described. The numerical range described in the present specification can be set to any range by using the value described in the specification as the upper limit or the lower limit, and the upper limit and / or the lower limit of the set range is included or not included. May be.

The mixed liquid separating device of the present invention is a mixed liquid separating device that separates a specific substance from a mixed liquid composed of at least two kinds and immiscible substances having different traveling characteristics. The mixed liquid separating device of the present invention is a device that separates a specific substance from a mixed liquid of two or more substances having different turning characteristics with respect to an inner member such as a guide wall described later. The amount recovered from the mixed solution is affected by the carrying characteristics of the specific substance and the abundance / abundance ratio of the specific substance. Factors that affect the carrying characteristics include viscosity and affinity. The higher the viscosity and the higher the affinity, the more difficult it is to fall off from the inner member and the easier it is to move around. In particular, the high viscosity has a great effect on the ease of traveling.

Therefore, as the mixed liquid that can be separated by the mixed liquid separating device of the present invention, a mixed liquid containing a liquid having a low viscosity and a liquid having a high viscosity is desirable. For example, water and oil, oils with different viscosities, and so on. In particular, it is preferable to use oil having a high viscosity as a specific substance. As the oil having a high viscosity, an oil having a high viscosity of VG32 or higher (VG46, VG68, VG100, VG150, etc.) is preferable. Further, the mixed solution may be sludge containing metal chips such as chips and cutting powder, hedro, and water-soluble and water-insoluble liquids.

For example, the mixed liquid assumed by the mixed liquid separating device of the present embodiment includes a coolant and oil mixed in the coolant. In particular, as a specific substance, oil having a high viscosity is assumed. Therefore, the difference in viscosity is much larger than that of the coolant, and the speed at which the oil is recovered by the rotation is much higher than the speed at which the coolant is recovered. The recovery speed can be improved by having the configuration described later in the mixed liquid separating device of the present embodiment.

The mixed liquid separating device of the present invention comprises an outer member, an inner member, and a driving means.
The outer member is cylindrical and has a suction port for sucking the mixed liquid at one end thereof and a discharge port for discharging a specific substance separated at the other end. Further, the inner member is arranged coaxially with the outer member and has a rod shape that can rotate relative to the outer member.

The material of the outer member and the inner member is not particularly limited, but a material that is stable even when immersed in the separated mixed liquid for a long period of time or in contact with the mixed liquid is desired. Therefore, the material needs to be appropriately selected according to the type of the mixed solution, and for example, a metal or resin material is preferable. Further, the sizes of the outer member and the inner member depend on the type and amount of the mixed liquid to be separated, and may be appropriately determined. Of the axial lengths of the inner member, the longer the portion above the liquid surface, the lower the separation speed, but the higher the separation accuracy can be.

The shape and size of the suction port of the outer member are not particularly limited as long as the mixed liquid can be sucked into the outer member. For example, it preferably consists of one open end of a cylindrical member or an opening formed on the outer peripheral surface. It is preferable that the suction port is immersed in the mixed solution, and the mixed solution is continuously sucked from the suction port by the accompanying force with respect to the outer member and the inner member. Further, when the substance to be separated floats on the liquid surface, it is preferable that the opening is an opening extending in the axial direction. If the opening extends in the axial direction, if the mixing liquid separator is installed so that the axial direction intersects the liquid level, the vicinity of the liquid level will be located at the opening even if the liquid level fluctuates. It becomes possible to continuously inhale the mixed liquid containing the substance floating on the liquid surface from the opening. In the case of an opening extending in the axial direction, the size may be the entire axial direction of the outer member. For example, the opening shall be a range in the total length in the axial direction in which a fluctuating liquid level may exist. Can be done.

The type of the discharge port of the outer member is not particularly limited as long as the separated specific substance can be discharged to the outside of the outer member. For example, it preferably consists of one open end of a cylindrical member or an opening formed on the outer peripheral surface. In particular, a discharge port having an opening opened on the outer peripheral surface of the outer member can efficiently discharge a specific substance to the outside of the device. The size and shape of the discharge port are not particularly limited, and a tubular member or the like extending from the opening toward the outside of the device may be provided to convey a specific substance to a collection box or the like.

In addition, a specific substance receiving part formed at the other end of the outer member to receive a specific substance discharged from the discharge port, and a specific substance discharging part formed in the specific substance receiving part to discharge the specific substance accumulated in the specific substance receiving part. If it is a mixed liquid separating device having a discharge means including a unit and a unit, a specific substance can be efficiently discharged to the outside of the device.

The specific substance receiving portion is not particularly limited in shape and size as long as it can receive the specific substance discharged from the discharge port, but has, for example, a bottomed cylindrical portion coaxially fixed to the outer member. By doing so, it is possible to prevent the outflow from a place other than the specific substance discharge part. Further, since the cylindrical part is easy to process and inexpensive, it is easy to obtain. Further, when a plate-shaped body is used as the transfer means in the discharge means described later, it is preferable that the specific substance receiving portion has a cylindrical shape. As will be described later, since the plate-shaped body rotates with respect to the specific substance receiving portion, if the specific substance receiving portion is not cylindrical (for example, square shape), there will be a place where the plate-shaped body cannot reach, and the specific substance that will not be discharged will be generated. It can occur.

Further, the specific substance discharging unit is not particularly limited in its form as long as it can discharge the specific substance accumulated in the specific substance receiving unit. For example, if an opening is formed in the specific substance receiving portion as the specific substance discharging portion, the specific substance accumulated in the specific substance receiving portion is sequentially discharged to the outside of the device from the point where the opening is reached. Therefore, for example, an opening may be provided in the bottom portion or the outer peripheral surface of the specific substance receiving portion having the bottomed cylindrical portion. Further, when the device is installed, if the specific substance discharge part is open in the direction of gravity action, the specific substance accumulated in the specific substance receiving part is efficiently discharged by its own weight, which is preferable. .. In addition, if the discharge port is open in the direction of gravity, it becomes difficult for specific substances and dust to stay on the side surface of the discharge port, so that the specific substance solidifies and solidifies at the discharge port, and dust and sludge collect. It is possible to reduce the clogging of the discharge port caused by slackening.

Further, it is preferable that the discharge means further includes a transfer means for transferring the specific substance accumulated in the specific substance receiving portion to the discharge port. As a transfer means, it is fixed to the inner member and rotates relative to the specific substance receiving part due to the relative rotation between the outer member and the inner member to push the specific substance accumulated in the specific substance receiving part to the specific substance discharging part. It is preferably a plate-like body. In the mixed liquid separating device of the present invention, since the outer member and the inner member rotate relative to each other, the plate-shaped body fixed to the inner member rotates relative to the specific substance receiving portion and the discharging portion formed on the outer member. By rotating the plate-shaped body with respect to the specific substance receiving portion, the specific substance accumulated in the specific substance receiving portion can be pushed by the plate-shaped body and collected in the discharging portion, and the plate-shaped body can be efficiently discharged. Further, even if the specific substance is a substance that is easily solidified by being left for a long time, it is flown by the plate-like body, so that it can be prevented from solidifying in a state of being accumulated in the specific substance receiving portion.

The size and number of the plate-shaped body are not particularly limited as long as they have a surface on which a specific substance can be pressed. Further, the plate-shaped body may be an elastic body such as a metal plate, a resin plate having a certain degree of rigidity, or a rubber plate that comes into contact with a specific substance receiving portion.

Further, the outer member and the inner member are not particularly limited in the installation direction, but it is preferable that the axial direction thereof is the action direction of gravity. If it is installed so that the axial direction is the direction of gravity, the number of installation locations can be reduced. In addition, the rotation of the outer member and the inner member is less likely to be eccentric due to gravity. At this time, it is preferable that the suction port is located on the lower side and the discharge port is located on the upper side. When the axial direction of the outer member and the inner member is installed at an angle with respect to the action direction of gravity, the outer member and the inner member can be provided by using a support that supports both members coaxially and relatively to rotate. It is possible to prevent the rotation of the shaft from being eccentric due to gravity.

The driving means rotates the outer member and the inner member relative to each other. The rotating means preferably comprises a motor. Further, a circuit for controlling the motor may be provided so that the rotation speed of the device can be changed according to the type of the mixed liquid. Further, bearings may be provided so that the rotation of the outer member and the inner member is not eccentric.

In addition, the mixed liquid separating device of the present invention rotates relative to each other at a rotation speed at which a specific substance in the mixed liquid can be carried around to the outer member and the inner member. The rotation speed depends on the dimensions of the apparatus, the type of the mixed solution, and the processing capacity, but is preferably 10 to 200 rpm. The centrifugal force generated at this time is as weak as 0.002 to 0.9 G. Therefore, the rotation is not so fast as to generate a strong centrifugal force that pushes the substance toward the inner peripheral surface side of the outer member or keeps the substance away from the inner member. However, considering the recovery capacity of the substance and the durability of the device, 30 to 120 rpm is preferable.

The outer peripheral side of the inner member has two or more spiral guide walls that guide a specific substance from one end to the other end of the outer member by the relative rotation of the outer member and the inner member. Then, the specific substance is sent to the other end along the guide wall by the relative rotation of the outer member and the inner member to separate them. If the valley width Vw (mm) is the axial distance between the parallel guide walls and the mountain width Mw (mm) is the axial width of the guide walls, Vw / Mw is 1.0 or more. ..

Further, assuming that the outer diameter of the guide wall is D (mm), n · (Vw + Mw) / πD is 0.01 or more and 0.27 or less. For n · (Vw + Mw) / πD, the lower limit is preferably any of 0.05, 0.08, 0.10, 0.13, and the upper limit is 0.22, 0.16, 0.15, It is preferably either 0.14 or 0.135.

The valley width Vw is preferably 5.0 mm or more, more preferably 6.3 mm or more, and further preferably 9.0 mm or more. The upper limit of Vw is not particularly specified, but 11.5 mm, 11 mm, 10 mm and the like can be exemplified. The Mw is preferably 3.0 mm or less, more preferably 2.0 mm or less, and further preferably 1.2 mm or less. As D, it is preferable that the lower limit values are 10 mm, 15 mm and 20 mm, and the upper limit values are 150 mm, 100 mm and 50 mm. The larger the D, the higher the separation speed, and the smaller the D, the smaller the size of the mixed liquid separating device.

The valley width Vw is the distance between the adjacent guide walls among the guide walls having two or more rows arranged side by side. The values of Mw and Vw can be evaluated over the entire guide wall, but it is particularly preferable to evaluate them as the values in the vicinity of the liquid surface and the portion located above the vicinity thereof. Further, when the values of Mw and Vw are not the same over the entire evaluation range of the guide wall, it can be evaluated by the average value. In addition, it is preferable that the values of Mw and Vw fall within the range of 50 to 150% when the average value is 100% in an arbitrary 90% or more portion of the length of the range to be evaluated in the axial direction. More preferably, it falls within the range of 50-150% over the entire range to be evaluated. 70% and 90% can be adopted as the lower limit of this range, and 130% and 110% can be adopted as the upper limit.

The measurement of the mountain width Mw is the width at a portion 0.1 mm from the outermost circumference (the point located in the outermost direction at each position in the axial direction) of the guide wall (FIG. 1). For example, when the cross-sectional shape of the guide wall is rectangular as shown in FIG. 1 (a), Mw has the same width as the width of the outermost peripheral portion, and as shown in FIG. 1 (b), the guide wall When the cross-sectional shape is wavy, it is the width at the portion moved to the center side by 0.1 mm from the outermost circumference. Vw is a value measured at the site where Mw was measured. Therefore, the value obtained by subtracting Mw from the pitch P of the spiral constituting the guide wall is Vw.

It is preferable that the outer member and the inner member have a property of more strongly accommodating a specific substance in the mixed solution. For example, substances that are physically or chemically likely to adhere to the outer and inner members are taken to the outer and inner members.

Further, the outer member and the inner member are not particularly limited as long as they have a shape having a spiral guide wall on at least one of the inner peripheral side of the outer member and the outer peripheral side of the inner member. That is, it is preferable that the outer member has a cylindrical shape on the inner peripheral side thereof, and the inner member has a spiral guide wall on the outer peripheral side thereof. The inner member having a spiral guide wall on the outer peripheral side may be a spring or a spirally wound wire rod in addition to a male screw. At this time, the specific substance is taken to the cylinder-shaped inner peripheral surface of the outer member and the guide wall (male screw) of the inner member due to its adhesive force, frictional force, and the like. If it is desired to further improve the turning characteristics, the inner peripheral side of the outer member or the outer peripheral side of the inner member may be a raised or brush-like uneven surface. In particular, powder such as metal scrap is preferable because it easily adheres to the uneven surface. Further, at least one of the inner peripheral side of the outer member and the outer peripheral side of the inner member may be a hydrophilic or hydrophobic surface, or may be a surface having a magnetic force.

Then, the mixed liquid sucked from the suction port sends a specific substance of the mixed liquid to the other end along the guide wall by the relative rotation of the outer member and the inner member. At this time, since it is difficult for substances other than the specific substances in the mixed solution (hereinafter referred to as "other substances") to be taken to the outer member and the inner member, other substances are sucked together with the specific substances from the suction port. Also, while the specific substance is sent from one end to the other end of the outer member, it is detached from the outer member and the inner member. Further, even when the uneven surface is formed, if the uneven surface is formed of an elastic material, the specific substance adhering to the uneven surface is scraped off by the spiral guide wall, and the scraped specific substance is removed. It can be smoothly fed from one end to the other end of the outer member along the guide wall.

Even a mixed liquid made of a liquid having a small difference in viscosity between the mixed liquids can be separated by adjusting the width of the gap between the outer member and the inner member and the rotation speed of the rotating means. In addition, even if the same mixed solution is used, the amount of separation and the amount of other substances contained in the specific substance after separation may change by adjusting the width of the gap and the rotation speed of the rotating means. Since there is a difference in processing capacity, it is advisable to adjust according to the intended use of the specific substance after separation.

At least one of the mixed liquid separating devices of the present invention may be installed in, for example, a tank in which the waste liquid recovered in the metal processing step is recovered. If the specific recovered substance contains other substances, use a mixed liquid separator with different conditions such as the carrying characteristics of each member, the width of the gap between the members, and the rotation speed. It is also possible to separate them.

Hereinafter, the mixed liquid separating apparatus of the present invention will be described in detail based on the following examples. The drawings used in the following description are schematic views, and the relative positions, sizes, etc. are not necessarily exact.

The mixed liquid separating device of this embodiment will be described with reference to FIGS. 2 and 3. FIG. 2 is a front view of the mixed liquid separating device of this embodiment, and FIG. 3 is a partially enlarged view of FIG.

The mixed liquid separating device of this embodiment includes an outer member 1, an inner member 2, and a driving means 3.
The outer member 1 includes an outer cylinder main body 10 and a connecting portion 15. The outer cylinder body 10 is made of resin and is a cylindrical piping material. A suction port 11 is formed on the outer peripheral surface of the outer cylinder body 10. The suction port 11 is a 180 ° opening formed by being cut in the axial direction from one end of the outer cylinder main body 10. The suction port 11 is partitioned by an axial opening end surface 111, 113 extending in the axial direction and a circumferential opening end surface 112. Here, when an opening is formed on the outer peripheral surface of the cylindrical member, the axial cutting is usually cut in the radial direction. However, the cut surface 111 faces in a direction that obstructs the flow of the mixed liquid to be sucked. Therefore, the 180 ° opening is provided with an edge portion (not shown) having a thin tip on the side where the mixed liquid is sucked. By forming the edge portion with the axial opening end surface 111 as an inclined surface inclined toward the inner peripheral surface side, the flow of the mixed liquid becomes smooth.
A discharge port 16 is connected to the other end of the outer cylinder body 10.

The connecting portion 15 is made of the same resin as the outer cylinder main body 10, and has a cylindrical shape having a flange portion 151 at one end. The bottom surface of the other end of the connecting portion 15 is the surface to be installed 150 when it is installed in a mixed liquid tank or the like. Since the connecting portion 15 is shorter in the axial direction than the outer cylinder main body 10, the suction port 11 side of the outer cylinder main body 10 protrudes from below the installed surface 150 of the connecting portion 15.

The inner member 2 is made of a metal trapezoidal double-threaded screw. The inner member 2 is arranged coaxially with the outer member 1 (outer cylinder main body 10). At this time, the gap provided between the outer member 1 and the inner member 2 was arranged so as to be 1 mm or less. The outer peripheral side of the inner member 2 has two spiral guide walls 211 and 212, and the outer member 1 and the inner member 2 are separated by sending a specific substance along the guide walls 211 and 212 by relative rotation. .. A valley width Vw (mm), which is the distance between the guide walls 211 and 212 in parallel, and a mountain width Mw (mm), which is the width of the guide walls 211 and 212, are defined.

The drive means 3 includes a geared motor (not shown) and a case 31 for accommodating the geared motor. The case 31 has a flange portion 315 on the opening side, and the flange portion 315 and the flange portion 151 of the outer member 1 (connecting portion 15) are fixed by bolts 313. The geared motor 30 is connected to one end of the inner member 2 and rotationally drives the inner member 2.

Further, an inverter can be incorporated in the circuit for controlling the geared motor 30, the frequency of the motor can be controlled, and the rotation speed of the inner member 2 can be arbitrarily set.

《Measurement of oil recovery》
The recovery rate of a specific substance was evaluated using the mixed liquid separating device of the example. In the mixed liquid separating device of the present invention, it is expected that the recovery speed will be improved by changing the form of the inner member. Therefore, in this example, it was decided to examine the recovery rate instead of the separation rate. Since it is not essential to use a mixture in order to evaluate the recovery rate, VG68 oil as a specific substance was used alone instead of the mixture. The test was conducted by changing the morphology of the inner member as shown in Table 1. The inner member was rotated at 60 rpm and evaluated by the amount of specific substance recovered per 10 minutes.

Guide walls with leads shown in Table 1 were provided at pitch intervals as many as the number of rows. The width of the peaks and valleys of the guide wall was also changed. The axial length of the inner member is 150 mm, and a specific substance is lifted and recovered from the liquid surface to a portion 100 mm. The diameter D of the inner member was 36 mm.

From Table 1, the relationship between n · (Vw + Mw) / πD and the recovery rate is examined. As shown in FIGS. 7, 12, 13, 18, 20 in which the number of guide walls is 2, the range of 0.10 to 0.16 was found to be particularly high. Further, it was clarified that the test example having 2 rows tended to have a higher recovery rate than the test example having 1 strip.

When the relationship of Vw / Mw was examined, it was found that the result was n = 1, but as is clear from FIG. 5, a high recovery rate was exhibited when Vw / Mw was 1.0 or more. It was found that the recovery rate was almost constant even if it exceeded 3.0. Even when n = 2, the recovery rate tends to improve as Vw / Mw increases. The recovery rate is maximized when Vw / Mw is around 6.5, and the range of Vw / Mw is preferably 4 to 9, more preferably 5 to 8, and even more preferably about 6 to 7. ..

Claims (3)

It is a mixed liquid separating device that separates and takes out a specific substance from a mixed liquid of at least two kinds of immiscible liquid substances having different traveling characteristics.
An outer member that is cylindrical and has a suction port for sucking the mixed liquid at one end thereof and a discharge port for discharging the specific substance separated at the other end portion.
A rod-shaped inner member that is coaxially arranged with the outer member and can rotate relative to the outer member,
It has a driving means for relatively rotating the outer member and the inner member.
The outer peripheral side of the inner member has a plurality of spiral guide walls (n rows) that guide the specific substance from one end to the other end by the relative rotation of the outer member and the inner member.
The specific substance is separated by being sent to the other end portion along the guide wall by the relative rotation of the outer member and the inner member.
The valley width Vw (mm), which is the distance between the plurality of parallel guide walls, is 5 or more and 8 or less , and the outer diameter D (mm), based on the mountain width Mw (mm), which is the width of the guide walls. ), N · (Vw + Mw) / πD is 0.10 or more and 0.16 or less .
Mixing liquid separation device. The mixed liquid separating device according to claim 1, wherein n · (Vw + Mw) / πD is 0.1061 or more and 0.14 or less. The mixed liquid separating device according to claim 1 or 2, wherein the valley width Vw is 6.3 mm or more.

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