JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MINE MECHANIZATION - II Previous Question Paper (September - 2021 - R16)

The design of a headgear is critical for the safe operation of mine hoisting systems. The primary parameters to be considered include:

• Hoisting Load: The total weight of the cage or skip, payload, and the weight of the winding rope.
• Depth of Shaft: Determines the total length of the rope and the static load acting on the headgear structure.
• Type of Winder: Whether a drum winder or a friction (Koepe) winder is used, as this dictates the rope fleet angle and the positioning of the head sheaves.
• Head Sheave Diameter: Must be designed to minimize rope fatigue, typically based on the ratio of sheave diameter to rope diameter.
• Dynamic Forces: Acceleration and deceleration forces during the winding cycle, including shock loads during emergency braking.
• Environmental Loads: Wind pressure, snow loads, and seismic considerations depending on the geographical location.
• Safety Clearance: Adequate height for overwind protection devices and the installation of detaching hooks.

Flexible guides, typically made of steel wire ropes, are used to guide the conveyance in the shaft. Their performance depends on proper suspension and tensioning:

• Suspension: The guide ropes are suspended from the headgear structure using specialized clamps or rope sockets. The suspension point must be designed to withstand the total static weight of the rope plus the dynamic tension induced by the moving conveyance.
• Weighting (Tensioning): To ensure the guide ropes remain vertical and taut, they are weighted at the bottom of the shaft, usually in the sump. This is achieved by attaching heavy weights (cheese weights) to the lower end of each guide rope.
• Function of Tension: The tension ensures that the guide ropes do not deviate significantly due to the lateral forces exerted by the cage. The amount of weight is calculated based on the depth of the shaft and the required stiffness to prevent the conveyance from oscillating or colliding with shaft furniture.
• Safety Considerations: The tensioning weights must be housed in a secure area in the sump, often with guides of their own to prevent them from swinging, and must be inspected regularly for corrosion or rope wear at the suspension points.