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November, 1951

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The haulage of anhydrite, which has twice the specific gravity of coal, has proved the inadequacy of many of the standard safety devices used on rail haulage in coal mines, when these are applied to trains of 30-40 tons total weight operating on rope-haulage inclines. Recently at Billingham Mine a review of the many standard safety devices was made following the failure of a runaway switch and inclined warrick, made of a 6 x 5-in, joist, to stop a runaway set of 19 tubs weighing 31 tons after running free down 300 yards of a gradient of 1 in 14. As a result of this mishap a new form of derailing ramp was designed, and tested in the mine by deliberately allowing six full tubs of stone to run free for 200 yards down an incline of 1 in 14 to meet the derailing ramp. The ramp was effective in bringing all the tubs to rest from a speed of 29 miles per hour within a distance of 10 yards.

As far as is known, this test was unique in the history of mining since for the first time a slow-motion cinematograph film was taken of the test, with exposures at the rate of 64 per second in lighting absorbing 40 kW. For the protection of the camera men a special dugout was constructed of a 4 ft. packwall, steel joists let into roof and floor, a double row of sandbags and a ¼-in, sheet of Perspex protecting the camera lens.

Safety devices in use on rope haulage inclines in mines

Derailing switches (single). — In its simplest form this consists of the inside rail being cut and a single point or rail section installed that may be set to catch the inside of the wheel flange to deflect and drop the wheel off the rail the outside wheel will tend to move away from the other rail and drop off.

This is effectual for derailing slow-running trains only, which, however, can continue running for a considerable distance if the ground is hard.

Derailing switch (double or runaway switch). — The best form consists of a large-radius turn-out with both points rigidly coupled and operated by a weighted throw-over lever. The rail tracks of the turn-out may end just clear of the straight tracks leaving the train to run on a rough floor, or the turn-out may be directed to buffer stops. A variation to deal with very heavy trains is to continue the turn-out track up a steep incline or escape road.

This device is effectual only for deflecting a heavy train at moderate speed. Where the tracks are of broad gauge and the switch points carefully designed with a transition curve leading into a turn-out of large radius, and rail joints are held flush with bolted fishplates, such a switch should be at least partially effective except at the highest speeds, e.g., over 30 mph. It can be completely ineffectual if the wheel flange breaks out, or if a rail joint causes the wheel to jump the points.

All the above safeguards suffer in two respects: (1) an official can walk past them without receiving a clear impression as to whether the devices are set for safety or for danger unless he makes a deliberate examination (2) their operation to safety cannot he relied on when the mass and velocity of the runaway train is high.

Warrick. — This consists of a baulk of timber or a steel joist secured to the roof with the bottom end resting between the rail tracks, inclined at about 45°. In its best form the top end is set in a pocket cut in the roof and the bottom rests in a concrete recess.

For trains of moderate weight and speed a warrick can be a positive stop and gives a feeling of security to any men who have to work lower on the incline. It has the advantage of being obvious as to whether it is set for safety or not. To stop very heavy trains at high speed the weight of the warrick necessary would become excessive since the work done in bringing a train to rest, or its kinetic energy, increases as the velocity squared. (See Figs. 1 and 2.)

Dumpling or Wedge block. — This consists of a block of timber cut from a 12 x 12 in. baulk about 2 ft. long formed with an inclined face directed towards the approaching train. It may be placed loosely between the rail tracks or placed in a prepared concrete inset.

It is effectual for light trains at slow speed. It has the advantages of mobility and of being obvious when placed in the correct position. It is, however, too cumbersome to lift in and out of the tracks for men to do this frequently with a good will. It is ineffectual for trains of high weight and speed, when tubs may ride over the block, become uncoupled and land squarely on the tracks to continue on their way, or it may be split up by the force of the impact. (See Figs. 3 and 4.)

Counterweighted Drop Stops. — To safeguard the man-winding shaft pit bottom at Billingham a special form of tub stop has been designed to ensure that the tubs to he lowered are raised a few inches by the haulage rope before the stops can be released. The stop consists of a heavy steel angle that covers the buffers of the tubs, itself supported by steel struts pivoted in a concrete recess between the rail tracks.

This device has been effectual in preventing the release of tubs on the incline by a set-runner in the mistaken belief that they were coupled to the haulage rope, since it cannot be lowered until the tubs are pulled back by the haulage rope. It is completely positive for trains of any weight lowered against the stops at slow speed. It is, however, costly to install, and although it might well stop runaway sets at speed, the mechanical parts would be completely wrecked after one such accident.

Automatic overspeed tub stops. — These are devices by which tubs are intended to be pulled up automatically if they pass in excess of a very slow speed ; they are sometimes installed in coal mines at the bottom of an incline before a curve. The principle of operation is that where the first tub axle strikes one end of a weighted cantilever at a very slow speed, the weight will fall before being caught by the second tub axle. Where the tubs arrive at speed the weight will be thrown so high that it is caught by the second axle before it has time to fall and acts as an axle stop.

The only real good cause such a device serves is to make the haulage driver limit the speed of the tubs under his control. When strongly made and used with 8 to 10 cwt. coal tubs they can cause a single tub to somersault at the expense of a bent axle. The only hope when struck by a train of tubs at speed is for the first tub's axles to be ripped from their bearings so that the front tub acts as a derailer for the remainder of the train. There is a probability that the device will be smashed by the first few tubs, allowing the later tubs to follow through where the tubs are numerous and heavy. Such devices are wrong in principle in attempting to bring to rest in an instant of time a large mass moving at high speed, and most likely would be ineffectual in stopping even one tub of anhydrite weighing 33 cwt.

Spring wheel stops. — Wheel stops hinged at the side of the rail tracks are constructed on long slides with powerful springs for control of tubs at junctions.

Spring stops are sound in principle for arresting a train moving at moderate speeds on horizontal tracks. They are not intended for inclines but are mentioned as being better in principle than some of the devices mentioned previously.

Wheel skid shoes. — On steep inclines skid shoes may be used under tub wheels to control speed, but are only practical and economical for use with a few large-capacity rail trucks.

Used only with heavy locomotive haulage in American mines, they are effective in preventing any train reaching an excessive speed since the friction increases as the shoes become red hot and soft. The shoes may be cast off automatically at any point but no method has been devised to place them under a train at speed.

Brake car. — For control of man-riding trains on inclines in this country many forms of brake car have been designed working on the principle of a weighted car being raised off its wheels on to rail skids either by manual control or automatically under conditions of excessive speed.

This is an elaborate and costly piece of equipment necessary to safeguard man riding on rope-haulage inclines, but impractical and uneconomical for use with mineral haulage trains.

General comment

All the above devices suffer from one or other of the following disadvantages :—

1. They attempt to stop a moving mass in an instant of time, which is not possible in practice.
2. They cannot be relied on to remain intact and effectual up to the last tub of a long train.
3. They are too costly and elaborate for constant shift use in the haulage of mineral trains.
4. They are cumbersome to operate, which leads to evasion of their use.
5. They do not promise 100 per cent. certainty of stopping a runaway set of tubs within a few yards.

In the present transition period at Billingham, where rope and rail haulage is being replaced by diesel and electricar haulage on pneumatic tyres, there are places where a motor road intersects a rope-haulage incline. To safeguard personnel on the motor road the Inspectorate of Mines required that in addition to a runaway switch above the motor road, a 6 x 5-in, steel-joist warrick should be installed approximately 20 yards above the motor road and interconnected with red and green signal lights on the haulage incline and motor road, giving a clear indication as to whether the warrick was set at safety or danger. Much reliance had been placed on these two devices in their ability to prevent any runaway tubs reaching the motor road. On inclines approaching the working face the use of dumplings was relied on.

Billingham derailing ramp

Following the accident referred to above, the Billingham mine staff designed a cast-steel derailing ramp (see Fig. 5) and with the approval of H.M. Inspector of Mines made one up for test in the mine. The objectives of the new device were as follows :—

1. Positive in action in derailing and overturning tubs of large mass travelling at high speed, even to the last tub of a long set.
2. Requiring little manual effort to operate, thus encouraging regular use.
3. Position of safety to be obvious to any passer-by so that the attention of officials will be drawn to the derailer being left in the danger position.
4. Powerful enough not to be smashed up at the first time in action against runaway tubs.

The results of the test are shown in Figs. 7 and 8, and the results of a similar test on devices previously accepted as standard are shown in Figs. 1, 2, 3, 4 and 10.

For stopping heavy trains of tubs at speed the derailing ramp has been proved much more effective than devices relied on previously, and at Billingham all rail haulage inclines are being fitted with this new device.

* Manager and Agent, Billingham Anhydrite Mine.

Drawings and Photographs accompanying the article