The Mechanical Handling and Storing of Material

8 THE MECHANICAL HANDLING OF MATERIAL which are one and all intended to reduce or break the fall of the material, thus bringing it into the hold of the vessel in as whole and sound a condition as possible. In order to save trimming in the hold, ships have been specially built with a great number of hatchways, but as yet no satisfactory appliance has been found which will trim coal mechanically in the hold of an ordinary ship. An important subject is the service of large boiler-houses and gasworks. Here mechanical means are used for filling and discharging bunkers, bins, or silos, and two essential features in such installations are the automatic feeding of the boilers and retorts, and the removal of the ashes and coke. Much attention has also been devoted to the coaling of railway engines and the feeding of blast furnaces. The subject as a whole is a very extensive one, and is here divided into— Appliances and installations which deal with the material continuously—that is, receive and deliver it in uninterrupted stream—such plant, for instance, as is suitable for factory yards, coal and other mines, gasworks, power stations, etc. Such installations as serve to handle material intermittently and for longer distances, as light railways, ropeways, and telphers, in conjunction with grabs and other unloading devices. A number of complete installations in which these appliances are used are illustrated and described in the course of this work. In dealing with machines of the continuous type it will be evident that the material which is being handled is evenly distributed over the entire length of the elevator or conveyor; thus the apparatus is only burdened with a comparatively moderate weight, a fact which permits of a relatively light construction of the mechanism and its supports. For this reason appliances of this type have often a distinct advantage over machines which must lift a considerable load at one point, because in the latter case the load, consisting of the material under treatment and the receptacle in which it is being carried, is concentrated in one place, and necessarily requires machinery and structure of a heavy description and of more solid construction. Again, in what may be termed the intermittent conveying of material, as for instance in the use of cranes, there is the operation of charging and discharging, to say nothing of the loss of time, sometimes unavoidable, from the return of the empty receptacle, whereas there is no loss of the kind with machinery of the continuous type. The capacity of a crane is really limited, because its speed is not capable of any considerable increase, on account of the heavy weight to be dealt with. To greatly increase the load carried at each lift is often impracticable, because the bucket or skip becomes more awkward to handle, and smart brisk work is then out of the question, whereas with a continuous conveyor it is perfectly possible to enhance the capacity by simply increasing the width of the conveyor as well as the speed within certain limits, always, of course, provided that the supply of the material being handled keeps pace with the increased capacity of the conveyor. When it is a case of handling „large and heavy lumps, cranes are undoubtedly in place, especially where it is a question of quickly clearing barges or railway trucks. Most important factors in the choice of machinery for given purposes are general local conditions and the adaptation of the machinery to the space available. The material should be handled as gently as possible if it be liable to deteriorate through breakage, as in the case of coal, which may easily lose from 5 to 10 per cent, of its value through rough handling, and this consideration is even more urgent in the case of coke, as coke dust is almost worthless. To minimise the cost of upkeep, as the constant renewal of parts of the machinery