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April, 1944

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It is not intended to describe the mine car constructed solely of timber. This type of car is gradually being replaced, but in those countries where wood is in ample supply, and transport is difficult, the wooden mine car often holds sway.

Composite mine cars

Where wooden cars have been in use for some time, a rapid and complete change-over to the steel type would mean a considerable capital outlay. It is, therefore, frequently advisable, in order to obtain some of the advantages of the steel car, to have a composite one of wood and steel. The capital outlay is reduced, and the change-over from timber to steel can take place gradually over a number of years, the complete replacement being effected as and when desired.

A further advantage is that a modern dust-proof car is obtained from steel components supplied by the manufacturer only, the car walls being built from timber taken from old cars, the completed structure being erected and maintained by the mining undertaking's own employees. Fig. 1 illustrates the composite general service tub or car, which generally consists of a pressed steel bottom with an all-round vertical flange two inches deep, to which any type of underframe can be mounted.

It is usual to fit pressed steel end plates and a five-inch vertical flange at the sides: a beaded top edge and two deep section hot-pressed corrugations greatly improve the strength of the car. The channel section pressed steel sideboard protectors are designed not only to prevent rapid wear of the timber during filling and emptying, but they also give maximum resistance to endway shocks on the car. Centre bars keep the side boards rigid, and the provision of inside and outside stiffening flats ensures that all bolts and nuts are tightened on steel to steel.

Whilst there is a saving in original capital cost and the advantage of gradual replacement of cars in service, the change-over to all-steel cars should be as rapid as possible. This particularly applies to cars carrying wet material which tends to rot the wood where it is in contact with metal, and especially in proximity and around the bolts; wooden sides are also more readily smashed. The mixed use of composite and steel cars underground often introduces tare difficulties.

Steel cars

The general service type is constructed so as to carry loads of from 5 to 25 cwt. It has been previously stressed that the actual size of the car is dependent upon the height of roadways, daily output and the capacity of the cage. Certain general types available are discussed

A flat-bottomed car, shown in Fig. 2, is manufactured from five steel parts only. The bottom consists of an unbreakable solid steel plate with radius corners of 2½ in. and vertical flanges all the way round.

The side and end plates forming the body have top and, what is of importance too, bottom tubular edges, filled solid with ¾ in. dia. steel bars. Double all-round corrugations provide additional strength, and the special corner shaping ensures rigidity at the seams. Fig. 3 indicates the five steel parts, the ease with which the car can be assembled and which is made possible by the use of socket and spigot joints. The bottom is easily attached to the body and the whole structure is held together by means of 16 bolts only. The diagram also gives some indication of the facility with which the car can be assembled or dismantled and the ease in renewing a damaged part. Consideration will also show that the design of the car is such that assembly can be effected by unskilled labour.

To permit this car to carry from 10 to 15 per cent. greater load, instead of having the flat bottom fitted, a well bottom can be attached which does not in any way interfere with existing creepers, car stops, cages or other handling equipment. It has been found from experience, that the bottom of a car wears out more rapidly than any other portion and it is, therefore, apparent that the provision of an easily renewable bottom plate (Fig. 4) reduces replacements to a minimum and provides a definite economy. It will be noticed that the edges are rounded, which means there is reduced risk to the men getting injured. The corrugations give rigidity and strength in combination with lightness.

Fig. 6 indicates a further type of steel car having many of the advantages of types previously described. The main difference is in the construction of the corners, which are interlocking, the sliding joints obviate bolting or riveting, and the four thickness "flat roll" top belt provides a rigid band right round the car.

The diagrams in Fig. 5 indicate the types of joints and other features which are used in the manufacture of the general service steel car to ensure freedom from accidents and to ensure rigidity and strength.

The all-steel underframe, Fig. 7, is built up of pressed and welded construction, and it will be observed that one of the most noticeable features is the absolute rigidity of the buffers, obviating the use of caps and the loosening of bolts. The design is such that it is capable of withstanding maximum buffeting shocks.

Drawings and Photographs accompanying the article