附录1DEVELOPMENT OF THE CABLE BELT CONVEYORlan Main Thomson BSc (Eng.)Managing DirectorCable Belt LtdSummary The early development of belt Conveying is discussed showing how the Cable belt system developed from the same requirements. The various design concepts are compared with those of the troughed belt conveyor highlighting the areas of advantage and disadvantage. The areas of conveying where the Cable Belt system is most useful and the likely developments are outlined. These and other developments have led to many major conveyor installations including a 2 flight 52 km system being constructed to the Cable Belt design. Development of the Cable Belt ConveyorThe origin of the belt conveyor is not easy to clearly identify but there are references to simple forms as early as 1795. However it was not until the dramatic increase in the world trading of grain after 1850 that major improvements were made. The first form of conveyor was a flat belt running in a trough which was quickly improved by the introduction of straight idlers to replace sliding friction by rolling friction. The need to increase the capacity and centralise the material load led to the appearance at the same time of both of the most common forms of heavy duty belt conveyors, the troughed belt conveyor and the Cable Belt conveyor. In the late 1860s the use in troughed belt conveyors of straight rollers with conical or dished ends was obsolete until the early 1890s. The introduction in 1865 of inclined straight concentrator idlers led to the conveyor in the Thomas Robins Jnr. patent of 1896, which is regarded as the first troughed belt conveyor. Since that date whilst there have been many important improvements in the detail of the idler, belt and drive construction, the basic concept of the troughed belt conveyor is the same as outlined in the work completed in the early 1900s. The Cable Belt conveyor principle whilst of earlier origin was not developed in a truly successful form until 1952.One of the earliest forms was that developed in 1859 and shown in the sketch fig. 1. This consisted of two parallel endless leather or rubber belts to which were attached at intervals curved meta1 spreaders supporting a canvas trough. There were many other similar conveyors but they all suffered from the same basic defect that the carrying belt was rigidly attached to the driving belts. This led to the disadvantages that the drive belts do not stretch alike and that the spreader bars are stressed and eventually break free from the drive belts. The Cable Belt system successfully overcame these defects and since its introduction has generally been accepted in the conveyor field for Long distance applications. A substantial proportion of the single flight conveyors over 5 km long that have been installed are now of the Cable Belt design. The fundamental design differences made in the Cable Belt system were to use a round drive belt in the form of a wire rope, and not to attach the carrying belt to the drive belts. The first of these changes was aimed at getting over the difficulty of training to run in parallel a pair of flat belts by substituting positively located round cables running in grooved pulleys. Early Belt Conveyor Fig 1The second change was the point that allowed the Cable Belt system to operate successfully in contrast to the other earlier attempts. The carrying belt merely rests on the drive cables, these cables sitting within shoes which are moulded on the be1t surfaces. It may seem that depending on friction alone the Cable Belt is liable to have the belt slip backwards on the drive cables. However as all belt conveyors depend on friction between the belt and the material carried to allow them to operate at all, the only requirement is that the friction between the belt and the drive cables should be greater than between the belt and the material. This was achieved by shaping the belt shoes to grip the drive cables. It has been possible using Cable Belt belting with specially formed surfaces to run on slope conveyor systems where the overall grade is 21 and with particular sections of 28, without experiencing slipping of the belt on the drive cables. Whilst the Cable Belt conveyor was developed at a time when the powers available of up to 300 kW were regarded as outstanding the basic concept is still retained even when now, single conveyors of 30000 metre length and 8000 kW power are being built. The terminal units are similar to those in a conventional troughed conveyor except that they also serve to separate and rejoin the carrying belt and drive cables. A typical example of a head discharge unit is shown in fig. 6.Obviously the terminals other than the drive unit are more complex than in a conventional troughed conveyor and take up more space particularly in the case of the tensioning arrangements. This is not true of the drive as for a comparable power rating it is compact and has the ad