Patent Description:
A prior art cleaner for a conveyor belt is disclosed in <CIT> wherein the belt cleaner includes a plurality of cleaner means disposed thereon in the transverse direction of the conveyor belt at the return running side thereof. Each cleaner means has a scraping portion thereof which intends to come into contact with the belt surface, while all the scraping portions are arranged in linear relationship. More specifically, said cleaner means, which includes a scraper having said scraping portion formed with a tip at uppermost end thereof, is yieldingly supported by a resilient member of rubber so that the scraping portion thereof becomes in contact with the belt surface under pressure by the resilience of said resilient member.

It is known that an endless conveyor belt, which is fitted for running in a circle between a drive pulley and an idler pulley, is supported at the forward running side thereof by a plurality of guide rollers arranged at "trough" angles so as to be curved in an arcuate shape in cross section in order to carry the transferring material in a stable manner. In other words, at the forward running side of the belt where the material is transferred forward, the belt is supported so that the lengthwisely extending central region thereof can arcuately be deflected downward. The transferring materials are consecutively transferred generally on the central region of the belt, which will result in intensive wear on the central region of the belt surface rather than on both side regions of the same.

Because of the tendency to deflection (termed generally as a "trough" tendency), the belt is deflected arcuately upward at the return running side of the belt where the belt runs backward after discharging the transferring material therefrom. In such an arrangement of the known cleaner, the scraping portions of the cleaner means arranged in linear relationship are prevented from matching the belt surface when coming into close contact with the same. More specifically, there is a clearance between the scraping portions arranged linearly and the central region of the belt surface. The clearance becomes greater when the amount of wear on the central region of the belt surface is increased. Consequently, the leavings of material on the central region of the belt surface cannot positively be scraped off by the scraping portions of the cleaner. Since the leavings of material adhered to the belt are substantially greater in amount at the lengthwisely extending central region of the belt surface than the side regions of the same, some of the scraping portions disposed in the center get worn intensively in proportion to the amount of scraped material. This allows said clearance to become greater gradually.

Under the circumstances, an improved type of belt cleaner was developed by the present applicant under the product name "U-Type Cleaner" which is disclosed in <CIT> (<CIT>), <CIT> (<CIT>), <CIT> and <CIT> (<CIT>).

<FIG> show said prior art "U-Type Cleaner" developed by the present applicant. The belt cleaner includes a scraper <NUM> for removing the leavings stuck on a belt surface at the return running side of a conveyor belt <NUM>, a holder <NUM> for holding said scraper, and pushing-up tension means (not shown).

The holder <NUM> is provided with a pair of rotary shafts <NUM> having an axis (A) extending in the transverse direction of the belt, and a pair of holding rails 6a, 6b which form a holding groove <NUM> curving from its both ends toward the center in the return running direction (F) of the belt. As shown in <FIG> and <FIG>, the bottom of the holding groove <NUM> is formed by a bottom member <NUM> which is welded to the holding rails 6a, 6b in the holding groove <NUM>. As a result, claddings 8a, 8b of weld overlays are formed on the bottom of the holding groove <NUM>. Both ends of the inner side holding rail 6b are bent and extended to form supporting walls <NUM>, <NUM>. The supporting walls <NUM> and both ends of the bottom member <NUM> are connected by seat plates <NUM> respectively, and said rotary shafts <NUM> comprising pipe members are fixedly secured to the supporting walls <NUM> and the seat plates <NUM> respectively.

As shown in <FIG>, the scraper <NUM> comprises a blade <NUM> of a resilient member <NUM> in which supporting plates <NUM> of metal such as iron are embedded in parallel with each other, and thin plate-like tips <NUM> of wear-resistant material such as carbide alloy are fixedly mounted on the back top of the supporting plates <NUM> respectively. As disclosed in the patent documents mentioned above, the blade <NUM> is manufactured by such a process that arranging said supporting plates <NUM>, on which the tips <NUM> are mounted respectively, in parallel in a mold together with un-vulcanized rubber material, and vulcanizing said rubber material in the mold. On the opposite side of the tips <NUM>, the vulcanized rubber material is adhered to cover the side faces of the supporting plates <NUM>, and a leg portion 15a and a jaw portion 15b projecting from the upside of the leg portion are integrally formed. On the side beneath the tips <NUM>, a sheet <NUM> made of another rubber is provided to extend downward from a fixed portion 16a secured to the supporting plates <NUM>.

As shown in <FIG>, the tip <NUM> has a tooth 11a projecting upward from the top end of the supporting plate <NUM> for purpose of effectiveness of scraping the leavings. The projecting tooth 11a, however, may be broken if it is bumped by some kind of object when carrying the scraper <NUM> itself or when installing the belt cleaner with the scraper <NUM> held in the holder <NUM> at the lower side of conveyor belt. In order to protect the tooth 11a, a covering filler <NUM> is provided in such manner that a part of rubber material of the jaw portion 15b is filled into a gap between the teeth 11a and the top end of supporting plate <NUM>, and vulcanized together with the jaw portion 15b in the mold.

The blade <NUM> providing the scraper <NUM> can be yieldingly deformable in such manner as to be curved from the linear state as shown in <FIG> to the substantially arcuate shape as shown in <FIG>. The blade <NUM> is curved with the tips <NUM> positioned inside, and inserted in the holding groove <NUM> by inserting the leg portion 15a and the supporting plates <NUM> therein, and then held in the holding groove by using bolts screwed through the holding rails 6a, 6b.

As shown in <FIG>, the blade <NUM> covers the top end of the outer side holding rail 6a by means of said jaw portion 15b, and covers the inner side holding rail 6b by means of said sheet <NUM>. However, an interspace (S) is made between the jaw portion 15b and the top end of the outer side holding rail 6a since the lower end of the blade is placed on the claddings 8a, 8b in the holding groove <NUM>.

The belt cleaner is installed at the lower side of the belt <NUM> by mounting the rotary shafts <NUM> of the holder <NUM> on bearing means provided on frames, as not shown, where pushing-up tension means are provided on the frames. Such frames and pushing-up tension means are disclosed in the patent documents mentioned above, the description thereof is omitted here.

Said pushing-up tension means exerts resilient forces to the rotary shafts <NUM> in the rotating direction to lift up the center of the holder <NUM>. As a result, the scraper <NUM> shifts up the posture of the tips <NUM> from the posture perpendicular to the belt surface to the posture inclined at an angle θ1 with respect to the belt surface as shown in <FIG>, and the tips <NUM> are made to contact with the belt surface with pressure. Under the state that the curved portion of the scraper <NUM> is directed upward, a row of the tips <NUM> comes in contact with the belt surface with pressure across the full width thereof without causing an interspace between them so that the leavings on the belt surface may be scraped off efficiently even when the belt <NUM> has a trough tendency of an arcuate shape in cross section, or when the center portion of the belt surface has been worn.

According to the discovery by the present inventors, however, the prior art belt cleaner includes the following defects.

The present invention provides a belt cleaner which does not damage the belt surface by the tips of the scraper, and makes the scraper easy to be pulled out the holding groove of the holder in the future when it is to be exchanged.

The present invention provides a belt cleaner which removes the leavings of conveying material on the surface of a conveyor belt at the return running side thereof comprising a scraper, a holder holding said scraper and pushing-up tension means.

Said holder is provided with a pair of rotary shafts having an axis extending in the transverse direction of the belt, and a pair of holding rails which form a holding groove curving from its both ends toward the center in the return running direction of the belt.

Said scraper is comprised of a blade of a resilient member in which supporting plates are embedded in parallel with each other, and thin plate-like tips are fixedly mounted on the back top of the supporting plates respectively.

Said blade is formed to be curved from a linear state to a substantially arcuate shape and inserted to be held in the holding groove.

Said pushing-up tension means exerts resilient forces to rotate the rotary shafts so that the tips are moved up and pressed against the belt surface in an inclined posture at an angle θ1 from the perpendicular to the belt surface.

Said scraper is provided with a flat slope to be contacted with the belt surface in a manner of surface-contact connection which extends from the top edge of each tip toward the belt running direction (F) in parallel with the belt surface when the tips are held in said inclined posture.

A width (W) of said flat slope in the belt running direction with respect to the thickness (t) of said tip is formed under the condition of t<W.

Preferably, said flat slope is formed to incline downward at an angle θ2 in the belt running direction (F) about a reference line (L) perpendicular to the side face of the tip under the condition of θ1=θ2.

Preferably both the top edge of the tip and the top end face of the supporting plate are arranged in alignment mutually, and said flat slope is provided on the top end face of the supporting plate.

In a preferred embodiment according to the present invention, said resilient member in which the supporting plates are embedded to form the blade comprises a first resilient member and a second resilient member which are formed and secured to the front and back faces of the supporting plates respectively with respect to the belt running direction (F).

The first resilient member provides a leg portion to be inserted in the holding groove of the holder together with the supporting plates, and a first jaw portion of a block shape which comes in contact with the top end face of the outside holding rail of the holder.

The second resilient member provides a second jaw portion of a block shape which comes in contact with the top end face of the inside holding rail of the holder.

Said first and second jaw portions are formed integrally and connected by connecting portions filled in connecting apertures through the supporting plates.

Preferably, the top edge of the tip, the top end face of the supporting plate and the top end face of the first jaw portion are arranged in alignment mutually, and said flat slope is formed by both the top end face of the supporting plate and the top end face of the first jaw portion. Thereby the blade is provided with the flat slope extending along the upper edge thereof.

According to the present invention, the belt cleaner is installed at the lower side of conveyor belt, and the leavings on the belt surface are scraped off by the tips <NUM> of the scraper <NUM> which are shifted to the inclined posture at an angle θ1 from the perpendicular posture via pushing-up tension means. During the scraping operation, the flat slope having the width (W) is made to contact with the belt surface with pressure in a manner of surface-contact connection.

The tips <NUM> which are inclined to oppose the belt running direction (F) have tendency to bite the belt surface, however, the resilient rotational force exerted to the scraper <NUM> by the pushing-up tension means is stationary caught by the surface-contact connection between the flat slope <NUM> and the belt surface. As a result, the tips <NUM> are prevented from biting the belt surface so as not to damage the belt surface.

Since the scraper <NUM> is unified integrally with the holding rails 6a, 6b of the holder <NUM> by means of the first jaw portion <NUM> and the second jaw portion <NUM> provided on the both front and back sides of the supporting plates <NUM>. Upon receipt of shocks and impacts applied to the tips <NUM> from the belt surface, the scraper <NUM> and the holder <NUM> as unified may move back from the belt surface and absorb the shocks and impacts. As a result, a partial deflective wear of the flat slope <NUM>, which may be caused if the blade <NUM> vibrates vigorously, is prevented. The surface-contact connection between the flat slope <NUM> and the belt surface is maintained for a long time.

Preferred embodiments of the present invention will be described in detail in conjunction with the accompanying drawings.

In the embodiments described hereinafter, a belt cleaner according to the present invention includes a scraper <NUM> for removing the leavings stuck on a belt surface at the return running side of a conveyor belt <NUM>, a holder <NUM> supporting said scraper, and pushing-up tension means (not shown).

Said holder <NUM>, which has substantially the same structure as the holder of prior art belt cleaner mentioned above according to <FIG>, is provided with a pair of rotary shafts <NUM> having an axis (A) extending in the transverse direction of the belt, and a pair of holding rails 6a, 6b which form a holding groove <NUM> curving from its both ends toward the center in the return running direction (F) of the belt. As mentioned above, the bottom of the holding groove <NUM> is formed by a bottom member <NUM> which is welded to the holding rails 6a, 6b in the holding groove <NUM>. As a result, claddings 8a, 8b of weld overlays are formed on the bottom of the holding groove <NUM>. Both ends of the inner side holding rail 6b are bent and extended to form supporting walls <NUM>, <NUM>. The supporting walls <NUM> and both ends of the bottom member <NUM> are connected by seat plates <NUM> respectively so that said rotary shafts <NUM> comprising pipe members are fixedly secured to the supporting walls <NUM> and the seat plates <NUM> respectively.

Said scraper <NUM> comprises a blade <NUM> of a resilient member <NUM> in which supporting plates <NUM> of metal such as iron are embedded in parallel with each other, and thin plate-like tips <NUM> of wear-resistant material such as carbide alloy or ceramic are fixedly mounted on the back top faces of the supporting plates <NUM> respectively. The blade <NUM> can be yieldingly deformable in such manner as to be curved from the linear state to the substantially arcuate shape. The blade <NUM> is curved with the tips <NUM> positioned inside, and inserted in the holding groove <NUM> of the holder <NUM> and held therein by using bolts screwed through the holding rails 6a, 6b.

The belt cleaner is installed at the lower side of the belt <NUM> by mounting the rotary shafts <NUM> of the holder <NUM> on bearing means provided on frames. The rotary shafts <NUM> are rotated by resilient forces of pushing-up means, of which illustration is omitted, to lift up the center of the holder <NUM>. As a result, the scraper <NUM> shifts up the posture of the tips <NUM> from a vertical posture to an inclined posture at an angle θ1 with respect to the belt surface so as to be brought into contact with the belt surface with pressure. The scraper <NUM> directs the curved portion upward and makes a row of the tips <NUM> contact with the belt surface with pressure over whole width thereof without causing an interspace therebetween so that the leavings on the belt surface may be scraped off efficiently even when the belt <NUM> has a trough tendency of an arcuate shape in cross section, or when the center portion of the belt surface has been worn.

The foregoing features and operations are substantially same to those of the prior art, and embodiments of the present invention are described as follows.

<FIG> and <FIG> show a first embodiment of the belt cleaner according to the present invention.

With respect to the belt running direction (F) as shown in <FIG>, the front side (the right side in the figure) of the supporting plate <NUM> is referred to as "the front face", and the back side (the left side in the figure) of the supporting plate <NUM> is referred to as "the back face" hereinafter. The tip <NUM> is secured to the upper end of the back face of each supporting plate <NUM> by means of brazing or the like so as to both the top edge of the tip <NUM> and the top end face of the supporting plate <NUM> are aligned to form a flush surface. In other words, there is no tooth 11a as described about the prior art.

Said resilient member <NUM> of the blade <NUM>, in which the supporting plates <NUM> are embedded, comprises a first resilient member 23a formed on the front faces of the supporting plates <NUM>, and a second resilient member 23b formed on the back faces of the supporting plates <NUM>. In the process of manufacturing the blade <NUM>, the supporting plates <NUM> with the tips <NUM> secured are inserted in parallel in a mold, a first rubber material and a second rubber material are arranged on the front and back faces of the supporting plates <NUM> in the mold, and these rubber materials are vulcanized to form the first resilient member 23a and the second resilient member 23b respectively. Since a connecting aperture <NUM> is formed through the portion beneath the tip <NUM> in each or some of the supporting plates <NUM>, said rubber materials are filled in the aperture <NUM> and vulcanized to form a connecting portion 23c which connects the first resilient member 23a and the second resilient member 23b integrally with each other.

The first resilient member 23a is provided with a thick leg portion <NUM> and a first jaw portion <NUM> of a block shape projecting from the upside thereof. The leg portion <NUM> covers over the front faces as well as the lower ends of the supporting plates <NUM> and is inserted in the holding groove <NUM> of the holder <NUM>, and the first jaw portion <NUM> covers the top end of the outside holding rail 6a of the holder <NUM>.

The leg portion <NUM> has a tapered surface 26a which makes the thickness thereof reduce downward, and cutouts 26b, 26b are provided by chamfering or rounding the lower end corners of the leg portion so as not to be placed on the claddings 8a, 8b. As a result, the leg portion <NUM> is inserted in the holding groove <NUM> in such manner that the bottom surface 26c comes in contact with the bottom member <NUM> and the first jaw portion <NUM> fits on the top end face of the holding rail 6a without causing any interspace. As shown, a tapered surface 27a may be formed preferably on the first jaw portion <NUM> by reducing the thickness thereof upward.

The second resilient member 23b provides a second jaw portion <NUM> of a block shape on the back faces of the supporting plates <NUM> beneath the tips <NUM>. The second jaw portion <NUM> is connected integrally to the first jaw portion <NUM> by the connecting portion 23c, and covers and fits on the top end face of the inside holding rail 6b of the holder <NUM>. A tapered surface 28a may be formed preferably on the second jaw portion <NUM> by reducing the thickness thereof upward.

The blade <NUM> is provided with a flat slope <NUM>. When the tips <NUM> are held in the inclined posture at an angle θ1 as mentioned above, the flat slope <NUM> extends from the top edges of the tips <NUM> toward the belt running direction (F) in parallel with the belt surface, and contacts with the belt surface in a surface-contact connection manner. In other words, as shown in <FIG>, the flat slope <NUM> is inclined downward at an angle θ2 toward the belt running direction (F) with respect to a reference line (L) perpendicular to the side face of the tip <NUM>, and preferably the condition is made to be θ1=θ2.

In the first embodiment as shown in <FIG>, the flat slope <NUM> is formed by both the top end faces 22a of the supporting plates <NUM> and the top end face 27b of the first jaw portion <NUM> so that the flat slope extends along the upper edge of the blade <NUM>. A width (W) of said flat slope <NUM> in the belt running direction (F) with respect to the thickness (t) of the tip <NUM> is formed under the condition of t<W.

As shown in <FIG>, the belt cleaner installed at the lower side of the belt <NUM> lifts up the center of the scraper <NUM> together with the holder <NUM> by rotating the rotary shafts <NUM> of the holder <NUM> via resilient forces, and the tips <NUM> are tilted to shift up the posture from the vertical posture to the inclined posture at an angle θ1 with respect to the belt surface so that the tips <NUM> come in contact with the belt surface with pressure and scrape the leavings on the belt surface during the running operation of the belt. The dropping objects caused from the leavings scraped off fall down while guided by the tapered surface 28a of the second jaw portion <NUM> so as to be prevented from entering in the holding groove <NUM> through the top end of the inside holding rail 6b. Some small amount of the leavings passed through the tips <NUM> without being scraped thereby may be peeled off at the end of the flat slope <NUM> and dropped, however, such dropping objects are fell down while guided by the tapered surface 27a of the first jaw portion <NUM> so as to be prevented from entering in the holding groove <NUM> through the top end of the outside holding rail 6a. As a result, a difficulty of pulling out the scraper <NUM> from the holding groove <NUM> in the future exchange thereof is avoided.

The second jaw portion <NUM> which receives a large quantity of dropping objects is formed in a block shape and connected to the first jaw portion <NUM> by the connecting portion 23c. As a result, the function of the second jaw portion may be maintained for a long term without being easily peeled or fatigued as seen in the sheet <NUM> of the prior art.

Since the holding groove <NUM> is protected against invasion of the dropping objects as mentioned above, the leg portion <NUM> can be provided with the tapered surface 26a which makes the blade <NUM> easy to be inserted in or pulled out the holding groove <NUM>.

When the tips <NUM> are brought in contact with the belt surface with pressure by shifting up the posture from a vertical posture to an inclined posture at an angle θ1 as mentioned above, a whole surface of the flat slope <NUM> together with the tips <NUM> comes in contact with the belt surface as shown in <FIG>. The tips <NUM> which are inclined to oppose the belt running direction (F) have tendency to bite the belt surface, however, the resilient rotational force exerted to the scraper <NUM> by the pushing-up tension means is stationary caught by the surface-contact connection between the flat slope <NUM> and the belt surface. Accordingly, the tips <NUM> are prevented from biting the belt surface so that no damage of the belt surface may be caused.

The leavings are adhered unevenly on the belt surface, the tips <NUM> receive downward impulsion. Such impulsion may be absorbed by the backward movement of the holder <NUM> against the resilient force of the pushing-up tension means. In this connection, the supporting plates <NUM> receiving the impulsion at the tips <NUM> are supported by the second jaw portion <NUM> on the inside holding rail 6b. As a result, the plates <NUM> are prevented from being rattled back and forth, and the prevention of causing vigorous vibrations is achieved.

The scraper <NUM> is unified integrally with the holding rails 6a, 6b of the holder <NUM> by means of the first jaw portion <NUM> and the second jaw portion <NUM> provided on the both sides of the supporting plates <NUM>. The scraper <NUM> moves back from the belt surface in a unified manner with the holder <NUM> to absorb said impulsion. It makes possible to maintain for a long time the surface-contact connection of the flat slope <NUM> to the belt surface without causing a partial deflective wear thereof. Then, such object of the invention as not to form an exposed projecting tooth of the tip <NUM> against the belt surface may be achieved.

<FIG> and <FIG> show a second embodiment of the belt cleaner according to the present invention.

In the second embodiment, a plate member <NUM> is fixedly secured to the front face at the upper end of each supporting plate <NUM>. In the illustrated embodiment, the plate member <NUM> is made of metal such as iron, and the lower end is secured by welding to the supporting plate <NUM>. The plate member <NUM>, however, may be made of material other than metal, such as ceramic.

The flat slope <NUM> is provided to extend from the top edge of the tip <NUM> toward the belt running direction (F) to contact with the belt surface in a surface-contact connection manner. As shown in <FIG>, the flat slope <NUM> is inclined downward at an angle θ2 toward the belt running direction (F) with respect to a reference line (L) perpendicular to the side face of the tip <NUM>. The condition of the angle, θ2 is made to be θ1=θ2 in a similar way mentioned about the first embodiment.

As shown in <FIG> with respect to the second embodiment, the flat slope <NUM> is comprised of the top end faces 22a of the supporting plates <NUM> and the top end faces 30a of the plate members <NUM> so that the flat slope <NUM> extends along the upper edge of the blade <NUM>. A width (W) of said flat slope <NUM> in the belt running direction (F) with respect to the thickness (t) of the tip <NUM> is formed under the condition of t<W.

<FIG> shows an operation of the belt cleaner of the second embodiment. Since the operation is almost same to that of the first embodiment mentioned above with reference to <FIG>, the description thereof is omitted here.

<FIG> and <FIG> show an example of a belt cleaner not part of the present invention.

In the example, although the general construction of the scraper is almost same to that of the first embodiment mentioned above, the scraper <NUM> is provided with no flat slope <NUM> before it is use.

As shown in <FIG>, the blade <NUM>, which has not yet been used, provides a flat surface <NUM> extending from the top edge of the tip <NUM> toward the belt running direction (F). The flat surface <NUM> is formed on the reference line (L) perpendicular to the side face of the tip <NUM> as shown in <FIG>. In the illustrated example, the flat surface <NUM> is comprised of the top end faces 22a of the supporting plates <NUM> and the top end face 27b of the first jaw portion <NUM> so that the flat slope <NUM> extends along the upper edge of the blade <NUM>. A width (W) of the flat surface (W) with respect to the thickness (t) of the tip <NUM> is formed under the condition of t<W as shown in <FIG>.

In the example, as shown in <FIG>, the belt cleaner installed at the lower side of the belt <NUM> lifts up the center of the scraper <NUM> together with the holder <NUM> by rotating the rotary shafts <NUM> of the holder <NUM> via resilient forces, and the tips <NUM> are tilted to shift up the posture from the vertical posture to the inclined posture at an angle θ1 with respect to the belt surface. In this state, the flat surface <NUM> is placed above the top edges of the tips <NUM>, and the flat surface <NUM> comes in contact with the belt surface with pressure as shown in <FIG>.

When the belt <NUM> begins running, said flat surface <NUM> is worn gradually by the friction with the belt surface. After the predetermined time has passed, the flat surface <NUM> comprising the top end faces 22a, 27b is worn to become inclined surfaces 22x, 27x respectively so that a flat slope <NUM> having a width (W) and extending from the top edge of the tip <NUM> in the belt running direction (F) in parallel with the belt surface may be formed as shown in <FIG>.

Claim 1:
A belt cleaner which removes the leavings of conveying material on the surface of a conveyor belt at the return running side thereof comprising a scraper (<NUM>), a holder (<NUM>) holding said scraper and pushing-up tension means;
wherein said holder (<NUM>) is provided with a pair of rotary shafts (<NUM>) having an axis extending in the transverse direction of the belt, and a pair of holding rails (6a,6b) which form a holding groove (<NUM>) curving from its both ends toward the center in the return running direction (F) of the belt, and
wherein said scraper (<NUM>) is comprised of a blade (<NUM>) of a resilient member (<NUM>) in which supporting plates (<NUM>) are embedded in parallel with each other, and thin plate-like tips (<NUM>) are fixedly mounted on the back top of said supporting plates (<NUM>) respectively, said blade (<NUM>) being formed to be curved from a linear state to a substantially arcuate shape and inserted to be held in said holding groove (<NUM>), and said pushing-up tension means exerting resilient forces to rotate said rotary shafts (<NUM>) so that said tips (<NUM>) are moved up and pressed against the belt surface in an inclined posture at an angle θ1 from the perpendicular to the belt surface,
characterized in that:
said scraper (<NUM>) is provided with a flat slope (<NUM>) to be contacted with the belt surface in a manner of surface-contact connection which extends from the top edge of each tip (<NUM>) toward the belt running direction (F) in parallel with the belt surface when said tips are held in said inclined posture, and
a width W of said flat slope (<NUM>) in the belt running direction (F) with respect to the thickness t of said tip (<NUM>) is formed under the condition of t<W.