CONVEYOR BELT AND BELT CONVEYOR SYSTEM

Abstract

Conveyor belt (1), comprising: a core layer (2) having a plurality of metal cords (2a) extending in the belt longitudinal direction, arranged in parallel in the belt width direction; an upper cover rubber (3) and a lower cover rubber (4), each arranged to sandwich the core layer (2) from above and below; a plurality of loop coils (5) embedded in the lower cover rubber (4) at intervals in the belt longitudinal direction; and a plurality of protective layers (6) arranged between the core layer (2) above and each of the loop coils (5) below and embedded in the lower cover rubber (4) at intervals in the belt longitudinal direction, characterized in that each of the protective layers (6) is arranged in the vertical direction at intervals from the core layer (2) and each of the loop coils (5), and each of the loop coils (5) is embedded at a position of 30% to 80% of the rubber thickness (T) of the lower cover rubber (4) from the lower surface of the core layer (2).

Description

Technical FieldThe present invention relates to a conveyor belt and a belt conveying system, and more particularly to a conveyor belt that further improves durability of loop spools embedded in the conveyor belt to detect vertical cracks in the conveyor belt; and a belt conveying system using this conveyor belt.Prior ArtIn order to detect a vertical crack of a conveyor belt (cracks continuous in the belt longitudinal direction), a conveyor belt in which loop coils are embedded is known (see JP 2014-031241 A, JP 2015-071493 A, and U.S. Pat. No. 2015-0203299 A1). In such a conveyor belt, a sensor disposed adjacent the conveyor belt senses the induction current occurring in loop coils passing near the sensor. When a sharp object or the like to be conveyed pierces the conveyor belt and a vertical crack is generated, the loop coils are damaged, so that no induction current is generated in the loop coils. In this case, the sensor does not detect the induction current even though the loop coils have passed in the vicinity. Thus, depending on whether the induction current is detected by the sensor, it may be determined whether a vertical crack has occurred in the conveyor belt. When it is determined that a vertical crack has occurred based on the detection of the sensor, the operation of the conveyor belt is stopped to prevent the vertical crack from expanding.By loading objects to be conveyed or the like, local impact forces and external forces are exerted on conveyor belts. Even if no vertical crack occurs in the conveyor belt due to the impact force or the external force, the loop coils may be damaged. When loop coils are damaged in this manner, the sensors do not detect the induction current even when the loop coils pass in the vicinity. Thus, when it is judged based on the detection of the sensor, it is erroneously recognized that vertical cracks occur in the conveyor belt.JP 2015-071493 A proposes loop coils comprising a metal part and a stretchable conductive material. In this proposal, the durability of the loop coils is improved by alleviating the impact force or the like applied to the conveyor belt with the stretchable conductive material. However, when a large impact force or stress is locally applied to the conveyor belt, it is difficult to avoid damage to the loop coils even if a part of the stretchable conductive material is provided. In addition, when a large impact force or stress is directly applied to the metal member, the mitigating effect of the stretchable conductive material can hardly be obtained and damage to the loop coils cannot be prevented. Therefore, there is an improvement potential in improving durability of loop coils.US 2015 0203299 A1, which is considered as the closest prior art, discloses a conveyor belt in accordance with the features specified in the preamble of independent claim 1.SUMMARY OF THE INVENTIONTechnical ProblemThe object of the present invention is to provide a conveyor belt that can further improve durability of loop bobbins embedded in the conveyor belt and detect vertical cracks of the conveyor belt; and a belt conveying system using this conveyor belt.Solution of the ProblemTo achieve the object, the conveyor belt according to the present invention includes: a core layer having a plurality of metal cords extending in the belt longitudinal direction and arranged in parallel in the belt width direction; an upper cover rubber and a lower cover rubber respectively arranged to sandwich the core layer from above and below; a plurality of loop coils embedded in the lower cover rubber at intervals in the belt longitudinal direction; a plurality of protective layers disposed between the core layer above and each of the loop coils below and embedded in the lower cover rubber at intervals in the tape longitudinal direction, each of the protective layers being disposed vertically at intervals from the core layer and each of the loop coils, and each of the loop coils being embedded at a position of 30% to 80% of the rubber thickness of the lower cover rubber from the lower surface of the core layer.The belt conveying system according to the present invention comprises: the aforementioned conveyor belt; a magnetic field generating unit disposed adjacent to the lower cover rubber and generating a magnetic field for generating an induction current in each of the loop coils; and a sensor disposed adjacent to the lower cover rubber for detecting the induction current.Advantageous Effects of the InventionAccording to the present invention, since the protective layers are disposed between the core layer above and each of the loop coils below and embedded in the lower cover rubber, the protective layers absorb and alleviate a localized impact force or an external force of articles to be conveyed acting on the conveyor belt. In particular, since the metal cords arranged in parallel are limited by the protective layers, the impact force and the external force acting are widely dispersed in the metal cords. Even if a large impact force or an external force locally acts on the conveyor belt, the loop coils are hardly damaged and their durability is further improved. Accompanying this, it is advantageous to avoid the situation that the loop bobbins are damaged even when vertical cracks do not occur in the conveyor belt.In addition, since the respective protective layers are embedded in the lower cover rubber at intervals in the belt longitudinal direction, an increase in the weight of the conveyor belt due to the provision of the protective layers can be further suppressed, and deterioration of flexibility can also be avoided.Brief Description of the DrawingsFIG. 1 is a cross-sectional view illustrating a conveyor belt according to an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating the internal structure of the conveyor belt of FIG. 1 in a plan view as viewed from the upper cover rubber side. FIG. 3 is an explanatory diagram illustrating a belt conveying system according to the present invention in a side view. FIG. 4 is a cross-sectional view taken along A-A of FIG. 3. FIG. 5 is an explanatory diagram schematically illustrating the state of the metal cords when the conveyor belt in FIG. 1 is subjected to an impact force from the upper cover rubber side in a plan view as viewed from the upper cover rubber side. FIG. 6 is an explanatory diagram schematically illustrating the state of the metal cords when a conveyor belt without embedded protective layers is subjected to an impact force from the upper cover rubber side in a plan view as viewed from the upper cover rubber side.DESCRIPTION OF EMBODIMENTSA conveyor belt and a belt conveying system according to the present invention will be described below with reference to the drawings.A conveyor belt 1 according to the invention is illustrated in Figs. 1 and 2. The conveyor belt 1 is provided with a core layer 2 and an upper cover rubber 3 and a lower cover rubber 4 which are arranged to sandwich the core layer 2 from above and below. These components are formed integrally with each other by a vulcanization process. The conveyor belt 1 may also include edge rubber disposed at each end portion in the belt width direction, or other constituent members as appropriate.In the core layer 2, a plurality of metal cords 2 a(for example, steel cords) extending in the tape longitudinal direction are arranged parallel to each other in the tape width direction. Specifically, the core layer 2 is covered with buffer rubber, and the buffer rubber is bonded to the upper cover rubber 3 and the lower cover rubber 4 by vulcanization bonding.For the upper cover rubber 3 and the lower cover rubber 4, a rubber composition containing at least a diene rubber including natural rubber and carbon black may be used to achieve good abrasion resistance. The film thicknesses of the upper cover rubber 3 and the lower cover rubber 4 are determined according to the required performance of the conveyor belt 1 in a range of, for example, 5 mm to 30 mm as required. The buffer rubber is a rubber having excellent adhesiveness.A plurality of loop coils 5 are embedded in the lower cover rubber 4 at intervals in the tape longitudinal direction. The loop coils 5 are, for example, a conductive wire 5 aformed in an annular shape, and a known wire may be used. The conductive wire 5 amay be formed in a wavy shape or a non-wavy shape. The loop coils 5 are not limited to a double square shape, and various shapes such as a circular shape and an elliptical shape may be used. The in-plane embedded position of the loop coil 5 is located within a range including the center portion in the tape width direction.The position of the embedding depth of each of the loop coils 5 is preferably 30% to 80% of the rubber thickness T of the lower cover rubber 4 from the lower surface of the core layer 2, more preferably 50% to 60% (rubber thickness t=from 30% to 80% of T). The upper-to-lower distance between the lower surface of the core layer 2 and the upper surface of the loop coils 5 (rubber thickness t) may be 5 mm or more.The protective layers 6 are disposed between the core layer 2 above and each of the loop coils 5 below. That is, the protective layers 6 are embedded in the lower cover rubber 4 at intervals in the tape longitudinal direction. The protective layers 6 are designed to have less elongation (higher modulus) than the rubber used for the conveyor belt 1 under the same conditions. The thickness of the protective layers 6 may be 0.2 mm to 3.0 mm.The protective layers 6 are each disposed so as to cover the entire area of the respective loop coils 5 (loop coils 5 disposed closest to the respective protective layer 6) in a plan view as viewed from the upper cover rubber 3 side. It is possible to set the protective layers 6 so as to cover at least the central portion of the respective loop coils 5 in the tape width direction in a plan view as viewed from the upper cover rubber 3. However, in order to reliably protect the loop coils 5, it is preferable that the specification is such that the protection layers 6 are arranged so as to cover the entire range of the loop coils 5 as in the present embodiment. Moreover, although the metal cords 2a are indicated by dot-dash lines at the center of Fig. 2 in order to facilitate understanding of the internal structure of the conveyor belt 1, they are omitted from the illustration of the first and second protective layers 6 from above. Moreover, in FIG. 2, the second protective layer 6 is partially cut out from above and the third protective layer 6 is omitted from above.The protective layers 6 may be formed of various materials including natural fibers, resins, metals, and the like. Various structures such as a woven structure and a coating shape may be used for the protective layers 6. As the woven structure, a plain woven structure, a cord woven structure, a twill weave structure, a satin woven structure or the like can be exemplified.In this embodiment, the protective layers 6 are formed by a plurality of wires 6a. As the wires 6 a, any wires 6 asuch as natural fibers, resin fibers, metal fibers, or the like can be used. These protective layers 6 have a simple woven structure, and thus a plurality of wires 6 aextending in the tape width direction are arranged in parallel in the tape longitudinal direction. Consequently, the wires 6a extending in the tape width direction intersect with the metal cords 2a arranged in parallel in the tape width direction.Although the metal cords 2a arranged in parallel are connected by the buffer rubber interposed therebetween in the mutual gap, the buffer rubber elastically deforms so that the force for restricting the displacement of the metal cords 2a in the tape width direction is weak. However, the protective layers 6 in the present embodiment are arranged to cover the metal cords 2 aarranged in parallel, so that the protective layers 6 confine and bundle the metal cords 2 aarranged adjacently to each other in the tape width direction. Thus, in the present invention, the displacement of the metal cords 2a in the belt width direction is suppressed as compared with a prior art conveyor belt.As illustrated in FIG. 3, a belt conveying system 7 of the present invention is provided with the conveyor belt 1, a magnetic field generating unit 10, and a sensor 11. The conveyor belt 1 is stretched between the pulleys 8, 8. As illustrated in FIG. 4, the carrier-side conveyor belt 1 is supported in a downward trough shape by support rollers 9, so that the loaded articles C to be conveyed are disposed mainly in the middle in the belt width direction.The magnetic field generating unit 10 is disposed adjacent to the lower cover rubber 4. The magnetic field generation unit 10 transmits, for example, an electromagnetic wave to each of the loop coils 5 passing in the vicinity of the magnetic field generation unit 10. An induced current is induced in each of the loop coils 5 due to this electromagnetic wave. When the loop coils 5 are separated, no induction current is induced.The sensor 11 is disposed adjacent to the lower cover rubber 4. The sensor 11 is disposed slightly downstream of the magnetic field generation unit 10 in the forward direction of the conveyor belt 1. The sensor 11 detects whether induction current is generated for each of the loop coils 5 passing in the vicinity of the sensor 11. Detection data from the sensor 11 is transmitted to a control unit 12. Based on the detection data from the sensor 11, the control unit 12 determines that a vertical crack has not occurred in the conveyor belt 1 when an induction current is generated, and when no induction current is generated, the control unit 12 determines that a vertical crack has occurred in the conveyor belt 1. When it is determined that a vertical crack occurs in the conveyor belt 1, the operation of the conveyor belt 1 is stopped, and a warning or the like is output.As illustrated in FIG. 6, when an object for conveyance C is supplied from a hopper part 13 onto a conveyor belt 14 in the related art in which the protective layers 6 are not embedded, the metal cords 2 aexpend to be displaced in the belt width direction due to the impact force caused by the object for conveyance C and the external force. Specifically, in the local portion of a conveyor belt 14 subjected to an impact force or an external force, the distance between the metal cords 2a in the belt width direction is widened. Thus, the impact force or the external force is easily transmitted to the loop coils 5 embedded below the core layer 2. That is, in the structure of the prior art conveyor belt 14, a local impact force or an external force received by the conveyor belt 14 greatly acts on the loop coils 5, so that the loop coils 5 are easily damaged.On the other hand, in the conveyor belt 1 of the present invention illustrated in FIG. 5, the metal cords 2a arranged in parallel are restricted by the protective layers 6, so that displacement of the metal cords 2a in the belt width direction is suppressed even if a local impact force or an external force acts on the conveyor belt 1 due to an article for conveyance C. Thereby, the impact force and the external force acting are widely distributed among the metal cords 2a. In addition, the impact force and the external force are absorbed or decreased by the protective layers 6. Even if a large impact force or an external force locally acts on the conveyor belt 1, the loop coils 5 are not easily damaged, and their durability is further improved. The advantage is therefore that damage to the loop spools 5 is avoided even if vertical cracks do not occur in the conveyor belt 1, thereby making it possible to detect vertical cracks in the conveyor belt 1 more accurately. In addition, the protective layers 6 are omitted in FIG. 5.When the article for conveyance C is loaded on the conveyor belt having the same specifications from the side of the upper cover rubber 3 under the same conditions except for the presence or absence of the protective layers 6 illustrated in FIGS. 1 and 2, the main stress generated in the loop coils 5 and the degree of deformation were simulated. The protective layers 6 were embedded at a position of 60% of the thickness T of the lower cover rubber 4 from the lower surface of the core layer 2 and applied to a plain woven structure of nylon fibers. As a result, it was found that, in the presence of the protective layers 6, the main stress generated in the loop coils 5 and the degree of deformation are about 60% of those in the absence of the protective layers 6.In addition, since the respective protective layers 6 are embedded in the lower cover rubber 4 at intervals in the belt longitudinal direction, the weight increase of the conveyor belt 1 due to the provision of the protective layers 6 can be suppressed, and it is also possible to avoid deterioration of flexibility (ease of bending when traveling around the pulley 8). These facts are mainly effective in reducing the energy required for the operation of the conveyor belt 1, which contributes to energy saving.In addition, in order to meet the specification in which the protective layers 6 are embedded in the lower cover rubber 4 at intervals in the belt longitudinal direction, each loop bobbin 5 may be disposed together with each protective layer 6 in the lower cover rubber 4 in the molding process for the conveyor belt 1. Thus, it is not necessary to substantially increase the number of steps in manufacturing according to this specification, compared to the case of the specification in which the protective layers 6 are not embedded.When the protective layers 6 have a specification in which a plurality of wires 6 aextending in the tape width direction are arranged in parallel in the tape longitudinal direction, the displacement of the metal cords 2 ain the tape width direction can be further suppressed by the wire 6 a. Thus, it is advantageous to avoid damage to the loop coils 5.When a cord fabric structure (woven structure in which the wires 6a in one direction have a substantially lower arrangement density than the perpendicular wires 6a in another direction) is used for the protective layers 6, the wires 6a having a higher arrangement density extend in the tape width direction. Thereby, it is possible to achieve the effect of preventing the flexibility of the conveyor belt 1 from being deteriorated and the effect of suppressing the displacement of the metal cords 2 in the belt width direction at a high level.When the loop coils 5 are embedded at a position of 30% to 80% of the rubber thickness T of the lower cover rubber 4 from the lower surface of the core layer 2, more preferably at a position of 50% to 60%, it is advantageous to protect the loop coils 5 from an impact force or an external force due to an object to be loaded for conveyance C. When the loop coils 5 are embedded at a position of less than 30% of the rubber thickness T from the lower surface of the core layer 2, an impact force or an external force is easily transmitted to the loop coils 5, which is disadvantageous in preventing damage to the loop coils 5. In addition, when the loop coils 5 are embedded at a position of more than 80% of the rubber thickness T from the lower surface of the core layer 2, since the distance between the loop coils 5 and the surface of the lower cover rubber 4 becomes too small, the impact force or the external force is easily transmitted from the lower cover rubber 4 side to the loop coils 5, which is not preferable.List of Reference Numerals1 Conveyor belt 2 Core layer 2 aMetal cord 3 Upper cover rubber 4 Lower cover rubber 5 Loop coil 5 a Leitfähiger wire 6 Protective layer 6 aWire 7 Belt conveying system 8 Pulley 9 Support roller 10 Magnetic field generating unit 11 Sensor 12 Control unit 13 Shaft part 14 Prior art conveyor belt C Object for conveying

Claims

A conveyor belt (1) comprising: a core layer (2) having a plurality of metal cords (2a) extending in the belt longitudinal direction arranged in parallel in the belt width direction; an upper cover rubber (3) and a lower cover rubber (4) respectively arranged to sandwich the core layer (2) from above and below; a plurality of loop coils (5) embedded in the lower cover rubber (4) at intervals in the belt longitudinal direction; and a plurality of protective layers (6) disposed between the core layer (2) above and each of the loop coils (5) below and embedded in the lower cover rubber (4) at intervals in the tape longitudinal direction, characterized in that each of the protective layers (6) is disposed vertically at intervals from the core layer (2) and each of the loop coils (5), and each of the loop coils (5) is embedded at a position of 30% to 80% of the rubber thickness (T) of the lower cover rubber (4) from the lower surface of the core layer (2).The conveyor belt (1) according to claim 1, wherein each of the protective layers (6) is arranged to cover the entire area of the respective loop coils (5) in a plan view as viewed from the side of the upper cover rubber (3).The conveyor belt (1) according to claim 1 or 2, wherein the protective layers (6) are formed by arranging a plurality of metal wires (6a) extending in the belt width direction parallel in the belt longitudinal direction.The conveyor belt (1) according to any one of claims 1 to 3, wherein each of the loop coils (5) is embedded at a position of 50% to 60% of the rubber thickness (T) of the lower cover rubber (4) from the lower surface of the core layer (2).A belt conveying system (7) comprising: the conveyor belt (1) according to any one of claims 1 to 4; a magnetic field generating unit (10) disposed adjacent to the lower cover rubber (4) and generating a magnetic field for generating an induction current in each of the loop coils (5); and a sensor (11) disposed adjacent to the lower cover rubber (4) for detecting the induction current.

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