conveyor belt

Abstract

A conveyor belt, including: a band nucleus body; and a rubber cover that covers the core of the tape; wherein the cover rubber is formed with an impact resistance performance rating index value which is a product of an elongation at break Eb, a tensile strength TSb and a loss tangent tan δ of a predetermined value or greater; and wherein a measurement condition of the loss tangent tan δ is determined on the basis of a velocity of an impact applied under an operating condition of the conveyor belt, where the loss tangent tan δ is a ratio between a memory module and a loss modulus calculated from a voltage when vibrations of a predetermined frequency are applied to the cover rubber; the measurement condition is the predetermined frequency; and The predetermined frequency is determined by adjusting the speed of an impact exerted under the operating conditions of the conveyor belt to a maximum vibration speed. where if the shock resistance performance rating index value, calculated using the loss tangent tan δ at the predetermined frequency of 10 kHz, is 6000 or greater.

Description

Technical field

[0001] The present invention relates to a conveyor belt comprising a belt core body and a cover rubber that covers the belt core body. State of the art

[0002] In the prior art, indicators for mechanical strength such as elongation at break Eb and tensile strength TSb are used as performance evaluation indicators for rubber elements such as conveyor belts.

[0003] For example, when a conveyed item is loaded onto a conveyor belt, it can impact a rubber cover over a core body with considerable force, causing cuts on the surface of the cover. To reduce these cuts, rubber with high mechanical strength (elongation at break Eb and tensile strength TSb) has been developed.

[0004] A well-known method for evaluating this type of rubber material includes a DIN abrasion test in which a test piece made of rubber material is pressed onto a cylindrical element around whose outer circumferential surface an abrasive cloth is wrapped, the cylindrical element makes a predetermined number of rotations and the amount of wear on the test piece is measured.

[0005] Furthermore, a known method for evaluating the durability of a rubber material for a conveyor belt involves assessing the material's durability based on the reduction in weight of a test specimen by grinding and blasting the specimen for a predetermined period (see Patent Document 1 below). As described in Patent Document 1, a large impact force is exerted on the surface of the test specimen when the granules collide with it, and the surface is abraded by the repeated impact. In other words, the test specimen can be subjected to wear similar to that experienced by an actual conveyor belt, thus making it possible to simulate the durability of a real conveyor belt.

[0006] WO 2017 / 051 566 A1, JP 2016- 204 159 A, DE 698 30 206 T2, US 2017 / 0 240 730 A1, EP 2 610 301 A1, JP 2004- 346 220 A and EP 2 116 569 B1 also apply to conveyor belts. List of literature on patent literature

[0007] Patent Document 1: JP 2008-224510 A Brief description of the invention: Technical problem

[0008] There is a need for the development of rubber element products, such as conveyor belts, that can withstand impacts and shocks during operation and exhibit high abrasion resistance and high impact strength. Impact strength depends on both the mechanical strength, as described above, and the energy-absorbing properties of the rubber (hysteresis loss due to viscosity). However, quantitative assessments of these properties are rare, and there is potential for improvement.

[0009] For example, the loss tangent tan δ, which is an indicator of the viscoelastic properties of a rubber element, uses the value at room temperature and a few tens of Hz for the sake of simplification. However, the viscosity of the rubber element depends on the speed, and therefore the viscosity properties of a speed range (frequency range) should be evaluated according to the application. Development policy is preferably based on the evaluation results.

[0010] In light of the foregoing, it is an object of the present invention to provide a conveyor belt with improved impact resistance performance. Solution to the problem

[0011] To solve the problem described above, a conveyor belt according to claim 1 of the invention comprises the following: a band nucleus body; and a cover rubber that covers the belt core body; wherein the cover rubber is formed with an impact resistance performance rating index value that is a product of an elongation at break Eb, a tensile strength TSb and a loss tangent tan δ of a predetermined value or greater; and a measurement condition of the loss tangent δ is determined on the basis of a velocity of an impact, which is applied under an operating condition of the conveyor belt.

[0012] In a conveyor belt according to the invention, the loss tangent tan δ is a ratio between a storage modulus and a loss modulus, which is calculated from a voltage when vibrations of a predetermined frequency are applied to the cover rubber; The measurement condition is the predetermined frequency; and the predetermined frequency is determined by adjusting the speed of an impact exerted under the operating condition of the conveyor belt to a maximum speed of vibrations.

[0013] In a conveyor belt according to the invention, if the shock resistance performance rating index value, calculated using the loss tangent tan δ at the predetermined frequency of 10 kHz, is 6000 or greater. Advantageous effects of the invention

[0014] According to claim 1 of the invention, the conveyor belt is formed with an impact resistance performance rating index value, i.e., the product of an elongation at break Eb, a tensile strength TSb, and a loss tangent δ of a predetermined value or more. As can be seen by unifying and comparing the index values ​​that were conventionally evaluated separately, the conveyor belt can be provided with improved impact resistance performance. Additionally, the measurement conditions of the loss tangent tan δ, which are used to evaluate the impact resistance performance, are determined based on the impact velocity applied under the operating conditions of the conveyor belt.As a result, the impact resistance performance can be evaluated using the value of the loss tangent tan δ, which corresponds to an actual impact exerted on the rubber element, and it is possible to improve the accuracy of the impact resistance performance evaluation. According to the invention, the measurement frequency (a predetermined frequency) of the loss tangent tan δ is determined by adjusting the velocity of the impact exerted under the operating conditions of the conveyor belt to the maximum velocity of the vibrations. Thus, the impact resistance performance can be evaluated by representing the viscosity of the cover rubber, which changes depending on the velocity of the impact.

[0015] According to the invention, it is possible to provide a conveyor belt that has sufficient impact resistance performance in its intended operating environment. Brief description of the drawings Fig. 1A and 1B are explanatory diagrams illustrating a configuration of a conveyor belt 10 according to one embodiment. Fig. Figure 2 is an explanatory diagram of a procedure for determining an evaluation frequency based on the velocity of an impact. Fig. Figure 3 is an explanatory diagram of a procedure for determining an evaluation frequency based on the velocity of an impact. Fig. Figure 4 is a graph showing a principal curve of a loss tangent tan δ. Fig. Figure 5 is a graph showing the impact resistance performance rating index (Eb × TSb × tan δ) of samples A to C. Fig. Table 6 lists performance evaluation values ​​and performance evaluation test results for samples A to C. Fig. Images 7A to 7C are surface photographs of a conveyor belt cover rubber after use for a predetermined period of time. Description of embodiments

[0016] Conveyor belts according to preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0017] Fig. 1A and 1B are explanatory diagrams illustrating a configuration of a conveyor belt 10 according to one embodiment.

[0018] Fig. 1A is a perspective view of the use of conveyor belt 10, and Fig. 1B is a cross-sectional view along line AA of conveyor belt 10.

[0019] The conveyor belt 10 is used in a belt transport system 20 which includes a drive roller 22, a driven roller 24 and the conveyor belt 10 wound on it.

[0020] The belt conveyor system 20 transports conveyed items that are loaded onto the conveyor belt 10 and moves the conveyor belt 10 in the direction of the arrow over the drive roller 22 and the driven roller 24 to move the conveyed items.

[0021] As shown in FIB. 1B, the conveyor belt 10 has a belt core body 14 with several layers of sailcloth and a cover rubber 12 that covers the belt core body 14. Various known materials can be used as the sailcloth forming the belt core body 14, including organic fibers such as nylon fibers, polyester fibers, aramid fibers, and the like.

[0022] The cover rubber 12 can withstand cuts or similar damage caused by the impact of the conveyed objects. Therefore, improving the impact resistance of the cover rubber 12 leads to an improvement in the durability of the conveyor belt 10.

[0023] In the present embodiment, an impact resistance performance rating index (Eb × TSb × tan δ), i.e. the product of an elongation at break Eb, a tensile strength TSb and a loss tan δ of the cover rubber 12, is set to a predetermined value or higher, for example 6000 or higher.

[0024] Additionally, the measurement conditions for the loss tangent tan δ, used to evaluate the impact resistance performance rating index, are determined based on the impact velocity applied under the operating conditions of the conveyor belt 10. In other words, the loss tangent tan δ of the cover rubber 12 is a ratio between the dynamic storage modulus and the dynamic loss modulus, calculated from the stress when the cover rubber 12 vibrates at a predetermined frequency. By adjusting the impact velocity applied under the operating conditions of the conveyor belt 10 to the maximum vibration velocity, the frequency (rating frequency) of the loss tangent tan δ, used in calculating the impact resistance performance rating index, is determined. Each parameter that constitutes the impact resistance performance rating index (Eb × TSb × tan δ) is described below. Elongation at break Eb and tensile strength TSb

[0025] First, the elongation at break Eb and the tensile strength TSb of the cover rubber 12 are described.

[0026] The elongation at break Eb and the tensile strength TSb are measured using a procedure that involves pulling a test specimen of the cover rubber 12, which is to be subjected to performance evaluation. The elongation at break Eb is the elongation at which the test specimen fails due to being pulled and is expressed as a percentage relative to an initial distance between reference lines. The tensile strength TSb is the tensile force recorded when the test specimen fails due to being pulled, divided by an initial cross-sectional area of ​​the test specimen.

[0027] The exact process of measuring the elongation at break Eb and the tensile strength TSb is determined by the process specified in JIS K6251: Vulcanized rubber and thermoplastic rubber - Tensile properties. Loss tangent tan δ

[0028] Next, the loss tangent tan δ of the cover rubber 12 is described.

[0029] The loss tangent, tan δ, is the ratio between the storage modulus and the loss modulus, calculated from the stress exerted when vibrations of a predetermined frequency are applied to the cover rubber 12. This is the ratio of the loss modulus to the storage modulus in dynamic viscoelasticity measurements. Higher values ​​indicate higher viscosity and correspondingly higher efficiency in converting kinetic energy into heat. Furthermore, high viscosity increases the apparent hardness at the point of impact, which has the effect of distributing stress in the surrounding area and reducing the amount by which the object sinks into the rubber element.

[0030] Thus, a high loss tangent tan δ of the cover rubber 12 indicates a high impact resistance performance.

[0031] The measurement of the loss tangent tan δ of the cover rubber 12 is generally carried out with a device for dynamic viscoelasticity measurement.

[0032] In a device for dynamic viscoelasticity measurement, a sample of the cover rubber 12 is clamped in the measuring head, and stress is applied to the sample from the load-generating section via a probe. This stress is applied as a sinusoidal force at a frequency defined as one of the measurement conditions, such that the stress amplitude of the sample remains constant. The extent of the deformation (distortion) of the sample caused by this sinusoidal force is detected by a displacement sensing unit, and various types of viscoelastic quantities, such as the loss tangent tan δ, are calculated from the stress applied to the sample and the detected distortion and output.

[0033] If the temperature is constant, as in Fig. As illustrated in Figure 4, a main curve is obtained with a frequency on the x-axis and tan δ (alternatively, storage modulus or loss modulus are also possible) on the y-axis.

[0034] Fig. Figure 4 shows the loss tangent tan δ of three types of cover rubbers 12 (samples A to C).

[0035] Specimen A is an internally developed impact resistance example. Specimen B is a rubber type H compliant product (JIS-H compliant) as specified in JIS K6369. Specimen C is a rubber type S compliant product (JIS-S compliant) as specified in JIS K6369.

[0036] The loss tangent tan δ of each cover rubber 12 increases overall from a low frequency band to a high frequency band, but the frequency characteristics differ from each other.

[0037] It should be noted that the thickness of the conveyor belt's cover rubber is typically 5 mm to 25 mm. In this embodiment, a sample with a thickness of 10 mm was used. Additionally, the temperature condition was set to 20 °C.

[0038] Furthermore, in practice, in a case where a main curve has a frequency axis as in Fig. As illustrated in Figure 4, the measurement is performed by changing the temperature of the sample instead of changing the frequency of the vibrations. The reason for this is that the frequency characteristic, which shows the relationship between the loss tangent tan δ and the frequency of the vibrations, and a temperature characteristic, which shows the relationship between the loss tangent tan δ and the ambient temperature at which the measurement is performed, can be converted into each other.

[0039] A known method for converting the frequency response curve and the temperature response curve can be used; therefore, its description is omitted. However, a loss tangent tan δ at low temperatures corresponds to a loss tangent tan δ in a high frequency band, and a loss tangent tan δ at high temperatures corresponds to a loss tangent tan δ in a low frequency band. Evaluation frequency of the loss tangent tan δ

[0040] Next, the frequency (evaluation frequency) of the loss tangent tan δ, which is used in the evaluation of impact resistance performance, is described.

[0041] As in Fig. As shown in Figure 4, the value of the loss tangent, tan δ, is obtained as a frequency characteristic derived from the frequency on the horizontal axis. The value of the loss tangent, tan δ, used in evaluating impact resistance performance is determined from the main curve.

[0042] In particular, the evaluation frequency, which is the frequency of the loss tangent tan δ used to evaluate the impact resistance performance, is determined by adjusting the velocity of the impact exerted under the operating conditions of the cover rubber 12 to the maximum velocity of the vibrations.

[0043] A method for determining the assessment frequency based on the impact velocity is used. Fig. 2 and Fig. 3 described.

[0044] The impact exerted under the operating conditions of the cover rubber 12 is an impact when the conveyed item is loaded. Generally, items conveyed on a conveyor belt are dropped from a position higher than the conveyor belt surface (cover rubber surface) via a chute or the like and loaded onto the conveyor belt.

[0045] The discharge velocity Vf, when the conveyed object lands on the conveyor belt, is determined based on the discharge height H of the conveyed object. In other words, V = √2gH (g: gravitational acceleration).

[0046] Fig. Figure 2 is a graph showing the relationship between the drop height H of the conveyed item and the drop velocity Vf when it reaches the conveyor belt. For example, if the conveyed item on the conveyor belt is ore or the like, the drop height H is high and approximately 8 m. In this case, the drop velocity Vf when the conveyed item reaches the conveyor belt is approximately 12.5 m / s.

[0047] In the case that the drop height H is relatively low, for example at about 0.5 m, the drop velocity Vf when the conveyed object reaches the conveyor belt is approximately 3.1 m / s.

[0048] Next, the maximum velocity of the vibrations in the dynamic viscoelasticity measurement is considered in order to determine the relationship between the ejection velocity Vf and the measurement conditions of the loss tangent tan δ.

[0049] As in Fig. As shown in Figure 3, for a sine wave with an amplitude A and a frequency f (angular frequency ω = 2nf) there is a displacement U = Asin(ωt) and a velocity V = Aωcos(ωt).

[0050] A maximum velocity Vx is obtained at cos0° = 1 and Vx = Aω = 2nAf.

[0051] If the above-discussed launch velocity Vf is used instead of the maximum velocity Vx, then f = Vf / 2nA.

[0052] If the amplitude A of the sine wave is 0.1 mm and the drop velocity Vf described above is set to 3.1 m / s (drop from a height of 0.5 m) to 12.5 m / s (drop from a height of 8 m), the frequency f of the sine wave corresponds to 5 kHz (drop from a height of 0.5 m) to approximately 20 kHz (drop from a height of 8 m). This range corresponds to the shaded section (logf = approximately 3.7 to 4.3) of the graph of tan δ in Fig. 4. In this range, the tan δ of sample A is the highest, then sample C, then sample B.

[0053] To prevent damage to the rubber cover when objects are dropped (conveyed items) onto it, the mechanical strength should be high at the point where the dropped object sinks deepest into the cover. Since the dropped object has a velocity of 0 in one direction, it is reasonable to use the laboratory-measured elongation at break Eb and tensile strength TSb as indicators of mechanical strength without modification.

[0054] However, since the energy-absorbing properties during the initial impact time are influenced by the initial velocity at which the dropped object comes into contact with the cover rubber, it is useful to determine the tan δ, which represents the viscosity of the cover rubber 12, taking into account the velocity of the impact exerted under the operating conditions of the cover rubber 12.

[0055] For example, if the cover rubber is used in an environment where the conveyed item is dropped from a height of 0.5 m, the evaluation frequency is preferably 4.9 kHz, and if the cover rubber is used in an environment where the conveyed item is dropped from a height of 8 m, the evaluation frequency is preferably 19.9 kHz. However, as described below, in the present embodiment, 10 kHz is used as a representative value for the evaluation frequency of the cover rubber, which requires impact resistance performance.

[0056] It should be noted that a principal curve of the loss tangent tan δ, such as the one in Fig. 4 cannot be measured, and instead the loss tangent tan δ of the frequency can be measured precisely after setting the weighting frequency.

[0057] Furthermore, as described above, if the temperature characteristic is converted into a frequency characteristic, a temperature corresponding to the weighting frequency can be calculated based on the relationship between the lines, and the loss tangent tan δ can be calculated by precisely measuring the stress when vibrations are applied to the cover rubber 12 at this temperature. Impact resistance performance rating index (Eb × TSb × tan δ)

[0058] As described above, the elongation at break Eb, the tensile strength TSb, and the loss tangent tan δ are used to evaluate the impact resistance performance of the cover rubber 12. Specifically, the impact resistance performance rating index (Eb × TSb × tan δ), i.e., the product of the elongation at break Eb, the tensile strength TSb, and the loss tangent tan δ of the cover rubber 12, is set to a predetermined value or greater.

[0059] In the present embodiment, the evaluation frequency of the cover rubber 12 is defined as 10 kHz when calculating the impact resistance performance rating index. This is because a cover rubber with an evaluation frequency of less than 10 kHz, i.e., a cover rubber with a low impact velocity in the operating environment, has a low demand for impact resistance performance and therefore a low need for evaluation using an impact resistance performance rating index. As in Fig. As illustrated in Figure 4, the value of the loss tangent tan δ increases with increasing frequency. However, by using 10 kHz as a representative value for the evaluation frequency of the cover rubber, which requires impact resistance performance, the impact resistance performance can be evaluated simply and accurately.

[0060] Additionally, in the present embodiment, the impact resistance performance is rated as high if the impact resistance performance rating index, calculated using the loss tangent tan δ at a rating frequency of 10 kHz, is 6000 or higher. In other words, the cover rubber 12 according to the present embodiment is designed with an impact resistance performance rating index of 6000 or higher, calculated using the loss tangent tan δ at a rating frequency of 10 kHz.

[0061] Fig. Figure 5 is a graph showing the impact resistance performance rating index (Eb × TSb × tan δ) of samples A to C. Fig. Table 6 lists the performance evaluation values ​​and performance evaluation test results for samples A to C. It should be noted that each in Fig. The 6 listed values ​​are an average of values ​​measured in a large number of samples of the same type.

[0062] In Fig. 5 is the vertical axis of the impact resistance performance rating index (Eb × TSb × tan δ) and the horizontal axis is the frequency (logarithmic display).

[0063] As in Fig. As stated in Figure 6, the tensile strength TSb for specimens A, B and C is 22.3, 28.2 and 20.9 respectively, the elongation at break Eb is 572, 562 and 530 respectively, and the tensile energy index, i.e. Eb x TSb, is 12761, 15848 and 11077 respectively. The tan δ at each frequency (see Figure 6) is 22.3, 28.2 and 20.9 respectively. Fig. 4) was multiplied by Eb × TSb to obtain the graph of Fig. to generate 5.

[0064] As in the Fig. 5 and Fig. Figure 6 shows that the impact resistance performance rating index value (Eb × TSb × tan δ) of samples A, B and C at 10 kHz (Logf = 4) is 6543, 5901 and 4944 respectively, and sample A has an impact resistance performance rating index value (Eb × TSb × tan δ) of 6000 or higher.

[0065] The performance evaluation test was carried out by means of a drop impact test, a DIN abrasion test and a surface observation of the conveyor belt's cover rubber after use for a predetermined period of time.

[0066] The drop impact test was performed by dropping a needle from a predetermined height onto the surface of the sample and measuring the needle's penetration depth. The results were determined to be 17.2 mm and 19.9 mm for samples A and B, respectively (the test was not performed on sample C), indicating that sample A was more resistant to drop impact than sample B.

[0067] The DIN abrasion test was performed according to the procedure specified in JIS K6264-2, with results of 122, 117, and 167 for specimens A, B, and C, respectively. Accordingly, specimens A and B exhibited high and approximately equal DIN abrasion resistance, while the DIN abrasion resistance of specimen C was lower than that of specimens A and B. Fig. Images 7A to 7C are surface photographs of conveyor belt cover rubbers of samples A to C, made of the same materials, after use for a predetermined period. Sample A showed very little cut damage on the surface of the cover rubber. Sample B showed more cut damage than Sample A, but had relatively few cuts. In contrast, Sample C showed a large amount of cut damage.

[0068] These results show that the impact resistance performance rating index (Eb × TSb × tan δ) using the elongation at break Eb, the tensile strength TSb and the loss tangent tan δ accurately reflects the impact resistance performance of the actual rubber element.

[0069] As described above, according to one embodiment, the conveyor belt 10 is formed with an impact resistance performance rating index value, i.e., the product of an elongation at break Eb, a tensile strength TSb, and a loss tangent δ of the cover rubber 12 with a predetermined value or greater. As can be seen by unifying and comparing the index values, which were conventionally evaluated separately, the conveyor belt 10 can be provided with improved impact resistance performance.

[0070] Additionally, the measurement conditions for the loss tangent tan δ, used to evaluate the impact resistance performance, are determined based on the impact velocity applied under the operating conditions of the conveyor belt 10. Thus, the impact resistance performance can be evaluated using the value of the loss tangent tan δ corresponding to an actual impact exerted on the conveyor belt 10, thereby improving the accuracy of the impact resistance performance evaluation. Furthermore, the measurement frequency (a predetermined frequency) of the loss tangent tan δ is determined by adjusting the impact velocity exerted under the operating conditions of the conveyor belt 10 to the maximum vibration velocity. This allows the impact resistance performance to be evaluated by representing the viscosity of the cover rubber 12, which changes depending on the impact velocity.

[0071] By designing the cover rubber 12 such that the impact resistance performance rating index value calculated using 10 kHz as the evaluation frequency of the loss tangent tan δ is 6000 or more, it is also possible to provide the conveyor belt 10 with sufficient impact resistance performance in the intended operating environment. List of reference symbols 10 Conveyor belt 12 Cover rubber 14 band nucleus bodies 20 belt conveyor system 22 Drive roller 24 Driven roller

Claims

[1] A conveyor belt comprising: a tape core body; and a cover rubber covering the tape core body; wherein the cover rubber is formed with an impact resistance performance evaluation index value which is a product of an elongation at break Eb, a tear strength TSb, and a loss tangent tan δ of a predetermined value or greater; and wherein a measurement condition of the loss tangent tan δ is determined based on a speed of an impact applied under an operating condition of the conveyor belt, where the loss tangent tan δ is a ratio between a storage module and a loss modulus calculated from a stress when vibrations of a predetermined frequency are applied to the cover rubber; the measurement condition is the predetermined frequency; and the predetermined frequency is determined by adapting the speed of an impact exerted under the operating condition of the conveyor belt to a maximum speed of the vibrations, where when the shock resistance performance evaluation index value calculated using the loss tangent tan δ at the predetermined frequency of 10 kHz is 6000 or greater.

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