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February, 1945

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Previous sections of this history of winding have described various devices for ensuring safety. One of these devices was the detaching hook, and this, although serving a useful purpose, does not prevent overwinding but only reduces the damage done when an overwind occurs; it does not in any event safeguard the descending cage although it may prevent loss of life in the ascending cage.

Attempts were therefore made to produce devices which would take the control of the winding engine out of the engineman's hands in the event of dangerous conditions arising, and bring the winder to rest before an overwind occurs.

Two classes of automatic contrivances were adopted. In one a projecting lever was fixed above the pit mouth, which when struck by the cage, forced on the brake; this device was no more effective than detaching hooks, as it came into operation too late.

The second type was an appliance so arranged that in the event of the engineman not shutting off steam at the proper moment he was exactly in the same position as if no such appliance existed, as it did not come into action; if, however, at a determined point in the wind the speed was in excess of what it should be at that point, the steam was cut off from the engine, and a brake applied.

The first mention of such an automatic arrangement was that designed by John Wild in 1839, consisting of a device for cutting off the steam and applying the brake. This appliance was in operation at Gledwick Colliery, Lancashire, for some considerable time. A full description is given in the Transactions of the Manchester Geological Society, ii, 36, 53.

One of the earliest and really successful automatic contrivances designed automatically to control the winding system was that of Whitmore. A comparatively recent form of it is illustrated in Fig. 1. Essentially it consists of a governor and two vertical screws a. Each screw carries two nuts b, c, and matters are so arranged that as the nuts on one screw ascend, those on the other screw descend. As one of the cages reaches bank the nut b on the corresponding rod reaches the top of its travel. Should an overwind occur, a dog on the nut b engages a mating dog on a collar d fixed to the screw a. Nut b then rotates with screw a, disengages a locking lever e, and by knocking out trigger j releases catch g under the influence of h, causing the throttle to he closed and the brake to be applied.

During the latter half of the wind, nut c is shadowed by a toothed hook j, which is inclined forward by the governor. Should the speed during any part of the deceleration period become excessive, the rising nut c catches in the hook and gradually draws it up, this action first closing the throttle and then progressively applying the brake. When the cage is nearing bank, nut c has to pass behind a catch k which is also controlled by the governor. If the banking speed is excessive, catch k (known as the "third attachment") engages with teeth on nut c, releases trigger f and trips the throttle and applies the brakes as before.

In the latest designs an "anti-nibbler" device is incorporated to overcome any tendency of the teeth on nut c and catch k to "nibble" or slide over one another. The anti-nibbler is shown, at l, and consists of a small link normally held straight by the weight of a small arm. If nut c attempts to engage catch k, its upward movement causes arm l to swing upwards; the upper end of catch arm k is thus thrown outwards and the lower end cants inwards and immediately secures a full grip on nut c.

When the cage is lowered the rotation of the screw a is reversed, and the lower nut c is able to turn a quarter turn with it. This brings to the front another arm of the nut, carrying teeth which constitute the fourth attachment. These are longer than those just described and engage with the catch k however slow the winding speed. If then the cage is stopped and started in the wrong direction the winder is pulled up instantly.

In designing the slow banker two points have been kept in view, both with the object of obtaining an immediate and certain trip. In the first place, governor action has been eliminated in favour of an oil dashpot, which can he set to any required maximum rate of movement, and which trips the gear instantly if this rate is exceeded. Secondly, the principle of a catch engaging a catch is regarded as too slow for landing control, and the slow banker is arranged to operate by a direct release.

The dashpot is shown at m, and is suspended in a stirrup from an arm n which is pivoted by a link x to the main column. When nearing hank, arm n meets a cam o and gradually raises dashpot m. As this motion proceeds, the point of contact between arm n and cam o travels to the right, so that the lift of dashpot m becomes progressively faster, thus making the control more sensitive the nearer the approach to bank. Dashpot m has a piston p, and the leakage is adjusted so that at safe banking speeds the rising dashpot fails to lift the piston, but an excess of speed immediately raises the piston, raising link q and releasing catch r, which allows spring s to swing round arm t and knock out catch f, thus tripping the gear. A second line of defence is afforded by link q engaging a pin u on arm k and tripping the gear directly.

Nut b is made in two halves; the top half comes off the guide plate so that it can rotate for the overwind trip, but the lower half remains on the guide plate, and is always available for the dashpot control. The overwind trip is supplemented by a protection v on nut c which engages the bottom of catch arm k in the event of an overrun, and in addition, piston p is arranged to bottom on the dashpot cylinder m so that if an overwind occurs it is raised solid.

The men and coal gear when in the men position suspends a weight w from the governor arm so that the governor brings all governor-operated trips into action at lower speeds; also cam o is tilted to give dashpot m a quicker rise.

The Visor overwinder

A simple overwinder which has long been on the market is the Visor. Essentially the gear consists of two governors, covering high and low speeds respectively, which project catches into the paths of toothed cams which rotate on a camshaft in accordance with the motion of the winder. An overspeed causes one of the hooks to engage one of the cams and to trip the brake and throttle controls.

Referring to Fig. 2, governor a has a high-speed range whereas governor b has a low-speed range to control banking. Each governor, on rising, closes-in a pair of catches c or d towards the camshaft e. Camshaft e is geared to the winder, and its position is an indication of the positions of the cages. In the early designs this camshaft made only one revolution during the wind, but this afforded only a coarse and slow control. In the present design, therefore, the camshaft is given an endwise motion by means of the screw f, so that it is able to perform several revolutions before cams g h come into register with their respective catches. By this means the rotation of the camshaft e is much faster, and a quicker and finer control is possible.

As the engine nears the end of the wind, one of the cams g (according to which cage is coming to bank) comes opposite its catch c, which is controlled by the high-speed governor a, and, if the wind is to continue, its teeth, of which there are nine, must pass catch c. Immediately afterwards one of the cams h registers with its corresponding catch d, controlled by the low-speed governer b; cam h also has nine teeth which must pass catch d if the gear is not to trip before coming to bank. If the speed should be excessive during any part of the time that cams g and h are in register, one of the catches c or d will be projected far enough to foul one of the teeth on the corresponding cam. This causes finger j to be lifted, releasing bar k which slides to the right under the influence of a weighted lever, which in turn trips the brake and throttle controls. As this weighted lever descends, it throws over a hand-lever on the driver's platform, and the gear can be reset by restoring the hand-lever to its normal position.

Finger j can also be tripped by an overwind and wrong. direction control, taking the form of an arm l which makes nearly one revolution during the wind and comes to rest almost touching one or other side of the upper extremity of a weighted arm m. An overwind or a start in the wrong direction causes arm l to tilt arm m, sliding a bar n to right or left and raising finger j by means of pin o. As will be seen from the drawing, this pin normally rests in a recess in bar n. Bar n is also connected to trips in the headgear operated directly by the cages. Arm l can be adjusted to allow for changes in rope adjustment, and bar n is reset automatically by weighted arm m dropping back to the vertical as the winder is restored to normal.

A lower-speed control for winding men is procured very simply by weights p, one to each governor, which can be slid to the right or left along governor levers q. In the left-hand position the weights assist the governors to rise, and the governors consequently rise at lower speeds.

Overspeed during any part of the wind is guarded against by a toothed wheel r mounted on camshaft e and of sufficient axial length always to register with one of the catches c controlled by the high-speed governor a. At the predetermined maximum speed the arms of this governor meet an auxiliary spring, and if this speed is exceeded, the resistance of the auxiliary spring is overcome and one of the catches c engages with wheel r and trips the gear. To prevent a violent brake application under these conditions a slow-braking attachment is provided, consisting of a cataract cylinder attached to the brake engine, this cylinder being thrown out of action when the deceleration trips are brought in to register. The device controlling the cataract cylinder consists of an arm s which normally rests across the camshaft d, but towards the end of the wind is lifted by one of the cams t. In the lowered position of arm s the cataract cylinder is operative, but when arm s is raised the cataract cylinder is out of action.

A further development is a throttle interlock which prevents the throttle being opened after an overwind unless the engine is reversed. A connection to the throttle lever carries a notched bar u which slides down and up as the throttle is opened and closed. Facing the notches on this bar are two pawls v, one for each end of the wind, which are normally held out of engagement by slotted links w attached to arms x. These arms are normally dropped, but in the event of an overwind, one or other of these arms is lifted by cam y, allowing one of the pawls v to drop into the corresponding notch in bar u, thus locking the throttle. The throttle cannot be released until the reversing lever is thrown over; this reverses links z and withdraws the pawl. The notches in bar u are double stepped to permit a restricted throttle opening over a predetermined travel of the cage above banking level; above this point the second step keeps the throttle closed.

Many overwinders of the types previously described have been designed and given satisfactory. and efficient service. The principles upon which they have been based are those adopted in the construction of the Visor and Whitmore overwinders even if minor details are different.

Drawings and Photographs accompanying the article