STEEL CORE BELT REDUCES CONVEYOR FLIGHTS IN AUSTRALIAN DRIFT COAL MINE
A special vulcanising method is used to joint this belt, providing a consistent strength throughout its length.
Reproduced from International Mining Equipment (Vol. 15, No. 12-December 1964) with kind permission of the publishers – The Certificated Engineer July 1965.
A Single flight conveyor, constructed of longitudinal steel cords embedded in natural rubber is doing work that would have required the services of four conventional high-strength belts at Appin Colliery, New South Wales.
Operating at a speed of 632 f.p.m. with a full capacity of 600 long tons of coal an hour tie 1-in the thick belt is 6 270 feet long and over 3 feet width, with a breaking strain of more than 550 long tons. Each foot of belt weighs about 33 lb.
Its installation was designed to haul coal to the surface from a seam 8 feet to 10 feet wide running between 1 550 and 1 800 feet underground. Openings to the seam are two concrete-lined ventilation shafts and parallel tunnels sloping at 16° from the horizontal. The larger tunnel is 8 feet 4-in high by 11 feet 6-in wide and contains a 60 H.P. direct rope haulage driven through radio signals by a man riding in a car on the end of the haulage rope. It is used to transport men, materials, equipment and refuses. The other tunnel, normally 7 feet high and 8 feet 6-in wide, houses the main slope conveyor carrying coal to the surface.
When it was decided to develop Appin Colliery as a slope mine the engineers were faced with something of a problem. The strongest conveyor belting which was economically acceptable was thought to need a conveyor system of four flights. Design and development were in fact based on an installation of this type, although widespread enquiries were continued in the hope that a belt suitable for single flight installation could be found. Finally, a specification and design for a suitable steel-cord belt of very great strength were obtained and the belt ordered.
The belting, of the type used in the brown coal fields of Germany, was made by Franz Clouth A.G., Cologne, and supplied by Barrow, Hepburn and Gale Ltd., Mitcham, England, in conjunction with their Australian agents, Greendale Engineering and Cables Pty. Ltd. Due to the size and number of its steel wire ropes, and the amount of abrasion-resistant natural rubber necessary to form them into an efficient belt. it is about four times the weight of belting of similar width used in the mine.
It is installed on a single-head pulley, snubbed to give sufficient wrap. for the adequate transmission of the driving force to the belt. Two motors, each coupled to its gearbox, drive the head pulley. Braking is achieved by brakes on each motor coupling and by a large emergency brake on the main shaft.
The belting was supplied in sixteen rolls, each about 800 feet long. Each length was lowered by winch into the tunnel and clamped off, and another length joined to it. This was repeated until there were two sections, each of eight lengths, joined together and lying on rollers on the conveyor structure-one on the top rollers and one on the return rollers. The two ends at the top were joined and lowered on to the head pulley, and the final splice was made underground at the tail.
The principle of splicing the lengths of the belting together is based upon the load being transferred from the ropes in one length to the ropes in the following length by laying them next to one another with sufficient overlap to ensure that the strength of the rubber bonding them is not less than that of the ropes. Where there is insufficient room to lay all the ropes in between each other they are cut, and the length of the splice increased.
Form of construction
Although belts embodying steel in the form of plates or cords were developed in Sweden and the U.S.A. some years ago, it was in Germany in the 1950's that Franz Clouth A.G., of Cologne, developed a belt con-taining steel cords in the warp direction but without any fabric, duck insert whatever. By 1961 the company had produced over 300 miles of this belt said to have given satisfactory service under arduous duties on conveyor centres never before attempted.
The Mitcham Steel Cord Belt is based on the principles of the Clouth belt and has been produced under licence in Britain at the Barrow Hepburn & Gale factory since last year.
It dispenses entirely with the fabric of any type and is an all-rubber construction with steel cords for the transmission of the requisite strength and the cords are of special patented cast steel, corrosion-resistant and highly-elastic wire. Flame-resistant neoprene and certain heat-resisting materials are also available.
The cords are placed in the warp direction of the belt only and are generally situated equidistant from the top and bottom of the belt. If specific duties demand a greater-than-normal abrasion resistance, this can be provided, but there are no covers in the usual meaning of belt construction, the rubber on and around the steel cords being vulcanised inseparably into a solid mass. This form of construction is said to offer several important advantages for the conveying of heavy materials such as metallic or granite, sandstone rock, limestone, in large lumps and quantities.
It can be supplied in any width from 30 in up to 118 in and in varying thicknesses from ?-in up to 1-in.
Working tensions of the belt range from 560 lb per inch width to over 3 000 lb per inch width, and breaking tensions are from 5 600 up to 33 000 lb per inch width.
In a Steel Cord belt of about ?-in thick, the tensile strength of the rubber in the weft direction is approximately 3 000 lb per inch width. This means that when a severe impact occurs on the steel cord belt, it can stretch in the weft direction about thirty-five times as much as a fabric type belt. This, according to the makers means that the cords would have to increase their spacing up to about 1-in before the connecting rubber between them would break.
Tear resistance is provided by combining rubber layers which have varied tear resistances in several planes.
The flexibility of the belt is reported to be high so that it can work satisfactorily on pulley diameters "much smaller than is usually appreciated for such a high tensile," and (in the weft direction) offer good troughing: troughing angles of 55° are quite common and higher angles are possible where needed. Its flexibility helps the steel cord belt to trough evenly on the idlers with maximum contact with the centre rolls which ensures straight running whether empty or loaded.
This feature also allows the use of much higher speeds than is possible with fabric belts; some conveyors are running at 1 200 f.p.m. With perfect training on the idlers.
Jointing
The steel cord belt is joint by a special vulcanised method. The basis is that the tensile strength of the steel cords is maintained in the joint by overlapping the cords in the joint area and vulcanising produces a bond of rubber which carries the tensile pull through the surrounding area from cord to cord. The resultant strength of the joint is about 95% that of the actual belt. Apart from the increased number of steel cords in the joint, the construction is the same as the remainder of the belt. An emergency type of mechanical joint is also available which needs no vulcanising.
Barrow Hepburn & Gale say that the Mitcham Steel Cord belt is working on conveyors of over 2 000 h.p., and carrying tonnages of up to 20 000 tons per hour.