JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year MINE MECHANIZATION II Previous Question Paper (February - 2022 - R16)

A headgear is a robust structural frame, typically made of steel, erected directly over the mine shaft. It serves as the primary support system for the winding operations, housing the headgear pulleys at its summit to guide the winding ropes from the winding engine to the shaft compartments.

The primary functions of the headgear include supporting the weight of the winding ropes, the cages or skips, and the payload, while also providing a platform for the detaching hook to operate in the event of an overwind. It must be designed to withstand high static loads and dynamic forces during acceleration and deceleration.

The headgear pulley, or sheave, is a large-diameter wheel mounted at the top of the headgear. Its function is to change the direction of the winding rope from the horizontal or inclined path coming from the winder house to the vertical path required for the shaft. The pulley diameter is typically specified to be at least 80 to 100 times the diameter of the winding rope to minimize bending stresses and prevent premature fatigue of the rope wires.

Key components of the headgear structure include:

• Main legs: The primary vertical or inclined members that carry the main compressive loads.
• Back stays: Inclined members that provide stability against the horizontal pull exerted by the winding ropes.
• Cross-beams: Horizontal members supporting the pulley shafts and bearings.
• Pit-top landing: The platform where material and personnel are loaded or unloaded.

In a diagrammatic representation, the headgear is depicted as an A-frame or four-legged tower. The winding rope passes from the winder drum, over the headgear pulley, and hangs vertically into the shaft. The pulley is mounted on a central shaft supported by heavy-duty pedestal bearings on the headgear platform. The design ensures that the resultant force of the rope tension is directed towards the center of the foundation to maintain structural stability.

The selection of wire ropes for mining operations is critical for safety and efficiency. The primary factors to consider include:

• Load and Safety Factor: The rope must be selected based on the maximum static load, dynamic loads (acceleration/deceleration), and the required factor of safety as per statutory regulations.
• Rope Construction: The number of wires and strands determines flexibility and wear resistance. A higher number of wires provides better flexibility, while fewer, thicker wires offer better abrasion resistance.
• Operating Conditions: Factors such as the presence of corrosive mine water, high temperatures, or acidic environments dictate the need for galvanized or stainless steel wires and specific core types (fiber vs. steel).
• Drum and Sheave Diameter: The ratio of the drum/sheave diameter to the rope diameter (D/d ratio) must be sufficient to prevent excessive bending stresses and fatigue.
• Type of Lay: Regular lay is generally preferred for stability, while Lang's lay offers better wear resistance but is more prone to unlaying.

Care and maintenance are essential to extend the service life of wire ropes and ensure operational safety:

• Lubrication: Regular application of suitable lubricants is necessary to reduce internal friction between wires and to prevent corrosion. The lubricant must penetrate the core and reach the inner wires.
• Inspection: Ropes must be subjected to regular visual and non-destructive testing (NDT) to check for broken wires, diameter reduction, corrosion, or distortion. Statutory inspections must be documented in a rope record book.
• Handling and Storage: Ropes should be stored in a dry, well-ventilated area, protected from moisture and chemicals. During installation, care must be taken to avoid kinking or twisting the rope.
• Operational Practices: Avoid sudden jerks or shock loads. Ensure that the rope is correctly seated on pulleys and drums, and prevent the rope from rubbing against stationary objects.
• Discard Criteria: Ropes must be removed from service immediately if they reach the statutory limit for broken wires, excessive wear, or significant loss of strength as defined by safety regulations.