Transportation of coal inside the mine can be described by two types of haulage locomotives. The first being a main haulage locomotive, the second is a gathering locomotive. Let’s look at the properties of each locomotive.
1. Main Haulage Locomotives
Locomotives of this type are the heaviest of those used anywhere in the mine. The type of work they perform requires high traction effort and a speed rating of six to eight miles per hour. Such locomotives range in size from 6 to 8 tons minimum to 25 tons maximum. The majority of the locomotives are of the electrically driven type receiving their power from an overhead trolley wire carrying either 250 or 500 volts DC. These locomotives have two sets of driving wheels, with each set driven through gearing by a motor. Locomotive size will be determined by haulage problems in the mine. This can be a number of things not limited to: rail size and weight, radius of rail curvature, road bed conditions, physical size of the tunnel, haulage distance, power requirements and so on. A few locomotives are of the storage battery type. Storage battery main haulage locomotives are designed primarily for operation in gassy mines where conditions are so hazardous that even trolley wire on a main haulageway must be excluded as a possible source for ignition. Their design differs from electric type locomotives in that the battery carried with the chassis gives a weight greatly in excess of that possible with electric type locomotives with the same drawbar pull. Use of this type of locomotive requires small trains and numerous trips, but work performance when this is done compares favorably with that of electric locomotives of higher drawbar pull. Where graded favor loads the great weight of these locomotives allows them to haul and keep under control trips equal in size to those which would be handled by electric locomotives. Storage battery haulage locomotives have a speed rating of six miles per hour and battery voltage ranges from 80 to 250 volts.
Main haulage locomotive service consists in hauling loaded cars from the sidetracks where they have been stored to the shaft bottom or landing, foot of slope, or to the outside in the case of a drift or tunnel. On the return trip the locomotive hauls empty cars to replace the loads taken away from the side tracks. Most efficient main haulage is obtained when, after the haulage has been planed and the track and equipment are of the proper size, a dispatching system is put into effect. By this means locomotive overloading is prevented since all trips can be limited to the proper number, the flow of coal is regulated and should additional help be needed at any point a dispatcher can send an extra locomotive to help out. Dispatching is possible at mines of such size that the haulage problem demands such a system. It might not be economically beneficial at small mines.
2. Gathering Locomotives
Gathering haulage involves the collection of individual cars at the faces of rooms or entries, or at other points where loading is done. Then bringing them to suitable sidings where they are made into trains for the main haulage locomotives. Gathering may be considered as follows:
A. Room gathering. This is where the locomotive handles the cars in the rooms and hauls them to the main sidetrack.
B. Entry Gathering. This is where men handle the cars in the rooms or mechanical loading devices deliver the coal to the entry, or the cars are loaded from chutes and the locomotive handles the cars between the entry and the side track.
Locomotives in these classes include cable reel, storage battery or combination locomotives. Gathering locomotives benefit from not needing a trolley wire ran into the tunnels where the work will take place.
Cable Reel Locomotives
These are light weight locomotives that get their power from the trolley wire either by the use of a trolley pole and wheel or with the cable. They may be of the single or double motor type. They range in size from 4 up to as much as 10 tons in places where the cars are of high capacity. The cable is held on a reel which may be of the Long Horizontal Type or the Flat Vertical Type. and usually pays out over the motorman’s end. The reel may be either operated by a motor or by a mechanical friction drive. A throw over switch is operated when changing from trolley pole to cable so the motors may obtain power from either source. If the cable is of the single conductor type a hook is thrown over the trolley wire while the return current from the locomotive motors passes through the track. Double conductor type uses the second conductor as a return and requires a ground hook to be placed over the rail at the entry at the same time as the cable hook is placed on the trolley wire before the locomotive can operate on the cable.
Selection of cable reel locomotives is based on car sizes, grades, radius of room curves, rail size and seam height. Control and speed are also important with many locomotives designed with a speed rating of four miles per hour. Room travel is usually over uncertain track and the low speed locomotive can negotiate such track with safety and enjoy the following advantages over locomotives rated at six miles per hour:
A. Able to exert greater drawbar pull with smoother starting and less wheel slippage, thereby reducing sand use and wear on tires.
B. Less cable maintenance due to lower current consumption and less liability to being over run.
C. Use of controller at maximum speed point reduces wear on controller and resistance grids, and less current is lost through less running “on point”. Motors are usually cooler after a shift of work.
D. Less need of brakes and better control of locomotive and loads on critical grades.
Storage Battery Locomotives
These are locomotives designed to operate entirely on storage battery power and thus eliminate the use of trolley wires in working sections. The battery which furnishes the power may be of either the lead acid type of alkaline types. Number of cells of either type in any one battery should be sufficient to give an average of 80 volts. Charging stations are necessary to charge the battery at the end of a shift. Extra batteries and facilities for changing battery boxes are necessary where locomotives are double shifted. Storage battery locomotives may vary in size from four to eight tons with a speed rating of three and a half miles per hour. These locomotives are termed “permissible” for use in gassy mines and in many cases are flame proof. These locomotives can be used with safety in any part of any gassy mine since even the hazard of a cable reel has been eliminated. Latest developments in battery locomotives stressing large batteries assure the operator of sure, steady power throughout the shift without loss of time due to power failure. This type of locomotive can equal or exceed the production of the cable reel locomotive in the same territory due to the gain in time from no necessity of handling the cable and is more economical of power due to its lower speed rating and other features of this design.
Combination trolley and battery locomotives consist of an ordinary electrical locomotive equipped with a storage battery. While operating at the entry, the locomotive operates on the trolley wire through use of a trolley pole. When it is necessary to operate in the rooms, the trolley pole is lowered and the locomotive operates on the battery. In many cases the battery is connected to the trolley pole lead and charging takes place while the locomotive is operating on the trolley wire. Whether this is the case or not, it is best to provide a charging station to recharge the batteries at the end of a shift. This type of locomotive can cover more ground than straight storage battery locomotives due to its higher speed ratings when operating on the trolley wire but the service is harder on the battery and the life is shortened considerable due to the constant charging.