DTII（A）型带式输送机【说明书+CAD图纸】
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毕业设计外文资料与中文翻译外文资料：Design of High Speed Belt ConveyorsG. Lodewi jks, The Netherlands.SUMMARYThis paper discusses aspects of high-speed belt conveyor design. The capacity of a belt conveyor is determined by the belt speed given a belt width and troughing angle. Belt speed selection however is limited by practical considerations, which are discussed in this paper. The belt speed also affects the performance of the conveyor belt, as for example its energy consumption and the stability of its running behavior. A method is discussed to evaluate the energy consumption of conveyor belts by using the loss factor of transport. With variation of the belt speed the safety factor requirements vary, which will affect the required belt strength. A new method to account for the effect of the belt speed on the safety factor is presented. Finally, the impact of the belt speed on component selection and on the design of transfer stations is discussed.1 INTRODUCTIONPast research has shown the economical feasibility of using narrower, faster running conveyor belts versus wider, slower running belts for long overland belt conveyor systems. See for example I-5. Today, conveyor belts running at speeds around 8 m/s are no exceptions. However, velocities over 10 m/s up to 20 m/s are technically (dynamically) feasible and may also be economically feasible. In this paper belt speeds between the 10 and 20 m/s are classified as high. Belt speeds below the 10 m/s are classified as low.Using high belt speeds should never be a goal in itself. If using high belt speeds is not economically beneficial or if a safe and reliable operation is not ensured at a high belt speed then a lower belt speed should be selected.Selection of the belt speed is part of the total design process. The optimum belt conveyor design is determined by static or steady state design methods. In these methods the belt is assumed to be a rigid, inelastic body. This enables quantification of the steady-state operation of the belt conveyor and determination of the size of conveyor components. The specification of the steady-state operation includes a quantification of the steady-state running belt tensions and power consumption for all material loading and relevant ambient conditions. It should be realized that finding the optimum design is not a one-time effort but an iterative process 6.This paper discusses the design of high belt-speed conveyors, in particular the impact of using high belt speeds on the performance of the conveyor belt in terms of energy consumption and safety factor requirements. Using high belt speeds also requires high reliability of conveyor components such as idlers to achieve an acceptable component life. Another important aspect of high-speed belt conveyor design is the design of efficient feeding and discharge arrangements. These aspects will be discussed briefly.2 BELTSPEED2.1 BELT SPEED SELECTIONThe lowest overall belt conveyor cost occur in the range of belt widths of 0.6 to 1.0 m 2. The required conveying capacity can be reached by selection of a belt width in this range and selecting whatever belt speed is required to achieve the required flow rate. Figure 1 shows an example of combinations of belt speed and belt width to achieve Specific conveyor capacities. In this example it is assumed that the bulk density is 850 kg/m3 (coal) and that the trough angle and the surcharge angle are 35 and 20 respectively.Belt speed selection is however limited by practical considerations. A first aspect is the troughability of the belt. In Figure 1 there is no relation with the required belt strength (rating), which partly depends on the conveyor length and elevation. The combination of belt width and strength must be chosen such that good troughability of the belt is ensured. If the troughability is not sufficient then the belt will not track properly. This will result in unstable running behavior of the belt, in particular at high belt speeds, which is not acceptable. Normally, belt manufacturers expect a sufficiently straight run if approximately 40% of the belt width when running empty, makes contact with the carrying idlers. Approximately 10% should make tangential contact with the center idler roll.A second aspect is the speed of the air relative to the speed of the bulk solid material on the belt (relative airspeed). If the relative airspeed exceeds certain limits then dust will develop. This is in particular a potential problem in mine shafts where a downward airflow is maintained for ventilation purposes. The limit in relative airspeed depends on ambient conditions and bulk material characteristics.A third aspect is the noise generated by the belt conveyor system. Noise levels generally increase with increasing belt speed. In residential areas noise levels are restricted to for example 65 dB. Although noise levels are greatly affected by the design of the conveyor support structure and conveyor covers, this may be a limiting factor in selecting the belt speed.2.2 BELT SPEED VARIATIONThe energy consumption of belt conveyor systems varies with variation of the belt speed, as will be shown in Section 3. The belt velocity can be adjusted with bulk material flow supplied at the loading point to save energy. If the belt is operating at full tonnage then it should run at the high (design) belt speed. The belt speed can be adjusted (decreased) to the actual material (volume) flow supplied at the loading point. This will maintain a constant filling of the belt trough and a constant bulk material load on the belt. A constant filling of the belt trough yields an optimum loading-ratio, and lower energy consumption per unit of conveyed material may be expected. The reduction in energy consumption will be at least 10% for systems where the belt speed is varied compared to systems where the belt speed is kept constant 8.3 ENERGY CONSUMPTION3.1 TRANSPORT EFFICIENCYThere are a number of methods to compare transport efficiencies. The first and most widely applied method is to compare equivalent friction factors such as the DIN f factor. An advantage of using an equivalent friction factor is that it can also be determined for an empty belt. A drawback of using an equivalent friction factor is that it is not a pure efficiency number. It takes into account the mass of the belt, reduced mass of the rollers and the mass of the transported material. In a pure efficiency number, only the mass of the transported material is taken into account.The second method is to compare transportation cost, either in kW-hr/ton/km or in $/ton/km. The advantage of using the transportation cost is that this number is widely used for management purposes. The disadvantage of using the transportation cost is that it does not directly reflect the efficiency of a system.The third and most pure method is to compare the loss factor of transport 10. The loss factor of transport is the ratio between the drive power required to overcome frictional losses (neglecting drive efficiency and power loss/gain required to raise/lower the bulk material) and the transport work. The transport work is defined as the multiplication of the total transported quantity of bulk material and the average transport velocity. The advantage of using loss factors of transport is that they can be compared to loss factors of transport of other means of transport, like trucks and trains. The disadvantage is that the loss factor of transport depends on the transported quantity of material, which implies that it can not be determined for an empty belt conveyor.The following are loss factors of transport for a number of transport systems to illustrate the concept:3.2 INDENTATION ROLLING RESISTANCEIt is important to know how the indentation rolling resistance depends on the belt velocity to enable selection of a proper belt velocity, 11. load on the belt decreases with a factor 2 then the indentation rolling resistance decreases with a factor 2.52 (2 4/3). The bulk load decreases with increasing belt speed assuming a constant capacity. Therefore, the indentation rolling resistance decreases more than proportionally with increasing belt speed.Secondly, the indentation rolling resistance depends on the size of the idler rolls. If the roll diameter increases with a factor 2 then the indentation rolling resistance decreases with a factor 1.58 (2 2/3). In general the idler roll diameter increases with increasing belt speed to limit the bearing rpms to maintain acceptable idler life. In that case the indentation rolling resistance decreases with increasing belt speed.Thirdly, the indentation rolling resistance depends on the visco-elastic properties of the belts cover material. These properties depend on the deformation rate, see Figure 3. The deformation rate in its turn depends on the size of the deformation area in the belts bottom cover (depending on belt and bulk load) and on the belt speed. In general the indentation rolling resistance increases with increasing deformation rate (and thus belt speed), but only to a relatively small account.Fourthly, the indentation rolling resistance depends on the belts bottom cover thickness. If the bottom cover thickness increases with a factor 2 then the indentation rolling resistance increases with a factor 1.26 (2 1/3). if a bottom cover is increased to account for an increase in belt wear with increasing belt speed, then the indentation rolling resistance increases as well.It should be realized that the indentation rolling resistance, although important, is not the only velocity dependent resistance. The rolling resistance of the idler rolls for example depends on the vertical load as well as on their rotational speed. The effect of the vertical load, which directly depends on the belt speed, is large. The effect of the rotational speed is much smaller. Another resistance occurs due to acceleration of the bulk solid material at the loading point. This resistance increases quadratically with an increase in belt speed assuming that the bulk material falls straight onto the belt. This will affect smaller, in plant belt conveyors in particular.3.3 RUBBER COMPOUNDSThe indentation rolling resistance depends on the visco-elastic properties of the belts bottom cover as discussed in the preceding section. This implies that the rolling resistance can be decreased by selecting a special low indentation rolling resistance (rubber) compound that is available on the market today. A small premium has to be paid for this special compound, but costs can be limited by applying it for the bottom cover only and using a normal wear-resistant compound for the carrying top cover. In that case turnovers are required to fully use the energy saving function of the bottom compound.A Quantitative indication of the level of indentation rolling resistance is the indentation rolling resistance indicator tan/E 1/3, where tan is the loss angle and E the storage modulus of the compound. Compounds with a reasonable indentation rolling resistance performance have indicators below 0.1. Figure 8 shows these indicators for typical medium to good performing rubbers. As can be seen in that figure, the choice for a specific rubber compound affects the energy consumption of the belt conveyor, in particular as a function of the ambient temperature.One comment (warning) must be made. A special belt with low indentation rolling resistance compound should never be selected if only one conveyor belt manufacturer offers it. In that case the conveyor system can only perform in accordance with its design specifications when that specific belt is used. It is much better, also cost wise, to specify the upper limit of the resistance indicator as given above that can be met by more than one conveyor belt manufacturer.Figure 1: Indentation rolling resistance indicators for fourdifferent rubbers as a function of temperature.4. SAFETY FACTOR REQUIREMENTSFor design purposes, standards like DIN 22101, ISO 5048 and CEMA provide safety factors (SF) that limit the permissible belt loads. Two types of safety factors can be distinguished: safety factors on the steady-state running tensions and safety factors on the non-stationary tensions. standards like the DIN standard base the recommended safety factor on reduction factors. DIN 22101 uses three reduction factors. The first (r0) generally accounts for the reduction of the strength of the belt (splices) due to fatigue. The second (r1) accounts for the extra forces that act on the belt in transition zones and on pulleys etc. The third (r2) accounts for the extra dynamic stresses in the belt during starting and stopping. The required minimum safety factor can be calculated as follows:SF=1/(1-(r0+r1+r2) (1)The DIN standard also gives values for the three reduction factors. For example, for a steel cord conveyor belt under normal operational conditions the values are as follows: r00.665, r10.15, r20.06, which yields a safety factor SF8.Although much can be said about the applicability of the safety factor determined with the DIN standard for the design of long belt conveyor systems, the major drawback, keeping the belt speed selection in mind, is that the conveyor systems operational data and the real fatigue properties of the belt are not taken into account.It is possible to account for these factors and to achieve a tailor-made safety factor by taking the belts operational data into account. The reduction factors r1 and r2 are independent of the fatigue properties of the belt and thus constant with increasing number of load cycles. Lets assume that the reduction factor r0 varies linearly with the log1O of the number of load cycles (revolution of the belt through the total belt conveyor) from 0 to 0.665 at 10,000 load cycles (approximation of DIN standard):r0= 0.166 log10(N) (N0.665， r10.15， r20.06，产生安全因素SF8。依据DIN标准设计的长距离带式输送机系统设计是完全可以应用的。但主要缺点是传送带速度选择所依据的输送机系统操作的数据和传送带的真正的疲劳性质没有被考虑到。这些因素应该被考虑，为了达到传送带定制安全系数的要求，输送机系统操作的数据应该被考虑到。 随着装载周期的增加，因数r1和r2是独立于传送带的疲劳特性减少的。 假设，因数r0在10,000个载荷循环周期内随装载周期log1O线性地(传送带的发展随着皮带输送机发展的)从0到0.665减少 (DIN标准的略计) ：r0= 0.166 log10(N) (N10.000) (2)式中N为载荷的循环次数。 超过10,000载荷次数周期r0增加。 现在假设，在设计的输送机的长度10,000 m之下，输送机一年工作5000个小时，有5年的使用寿命。 载荷循环周期的总数可以用下式计算：N=(3600 V)/(2L)HY (3)式中V是输送带速度、L输送机长度， H每年工作的小时的数和Y是预计工作年限。因数ro的减少值可以用式(2) 确定，并且载荷循环周期在图1已给定。 结果如图3显示。图3：给定例子的DIN 22101标准中r0带式输送机的安全系数可以根据公式（1）和图2确定，结果如图4所示。图4 ： 所举的例子所需安全因素的极小值从图4可以知道要保证以2 m/s速度稳定运行的输送机的设计所需的最小的安全系数约为7.5，在传送带运行速度为20 m/s.安全系数扩大为10。在安全系数允许范围内考虑输送带的速度可以有效的防止高速设计时估价过低和低速设计时估计过高(也取决于输送机系统的长度)。以上给定的图表和数据仅说明这个过程。 这个过程可以通过考虑被测量的传送带拉伸运载的各组件(钢绳子或织品)和橡胶的疲劳特性的优化而被改善，还需要考虑传送带的实际载荷循环周期(空载，满载，稳定运行，开始和停止，夏天和冬天工作环境等)。5 皮带输送机动力学实质上皮带输送机的动力学性能不随着传送带速度改变。 然而，随着传送带速度的增加动力学的变化率增加，这也导致传送带连续运行稳定性的降低。 本文不打算充分谈论皮带输送机动力学。 在参考文献7中这个题目被广泛地讨论。 无论怎样，关于高速输送机的动力学的一些注释在这里需要提到。当二个托辊组之间的传送带被一个托辊碾压或在临近固托辊的固有频率运行时将产生振动，这将引起共鸣现象的发生。 共鸣产生将增加的滚筒轴承的磨损和使得传送带能量消耗的增加，随着横向振动振幅的增加，输送带引起颤动，所以必须避免共振。 在高速传送机系统中共鸣的作用将对输送机的结构产生很大的破坏，例如共振将引起输送带速度的降低、毁坏以及轴承的磨损。因此设计皮带输送机时，应该避免共振的，并且要最大的利用现有的静态设计方法，以便最经济的设计带式输送机。高速输送机的输送带的运行轨迹必须良好。如果传送带没有合适的运行轨迹输送带将会随着传送带速度的增加而跑偏，输送带向旁边位移和向旁边位移率随着速度的增加而增2.1部分。 并且传送带制造商应尽最大的努力做平直的传送带和制造更好的输送带接头。 另外，制作长距离的传送带会减少接头的数量而增加输送带平直性。对于水平运输的传送带曲线设计部分可以做出相似的结论。 随着托辊改变的传送带的位置的变化主要依赖于由于装货程度引起的皮带张力变化。在(被中止的)起飞和(紧急状态)停止时，特别是在大张力变
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