JNTU B.Tech III MINE MECHANIZATION II Previous Question Paper (October - 2020 - R16)

Safety devices are critical for the secure operation of cages in vertical shaft winding. The primary fixtures include:

• Detaching Hook: Installed between the winding rope and the cage suspension gear to automatically disconnect the rope and suspend the cage in the headframe if an overwind occurs.
• Cage Arrestors/Keps: Mechanical supports at the shaft collar that hold the cage stationary during loading and unloading operations.
• Safety Catches/Dogs: Mechanical devices designed to grip the shaft guides and bring the cage to a controlled stop in the event of a rope failure or sudden slack rope condition.
• Guide Shoes: Fixtures attached to the cage frame that ensure the cage remains aligned with the shaft guides, preventing oscillation and collision with shaft infrastructure.
• Overwind/Overspeed Protection: Limit switches and sensors that trigger emergency braking if the cage exceeds designated speed limits or travel boundaries.
• Suspension Gear: Chains and shackles designed with a high factor of safety to connect the cage to the winding rope, ensuring structural integrity during dynamic loading.

The head sheave, or pulley, is a vital component of the winding system located at the top of the headframe. Its design features are engineered to minimize rope wear and ensure structural stability:

• Diameter Ratio: The sheave diameter is typically maintained at a minimum of 80 to 100 times the rope diameter to minimize bending stresses and prevent premature fatigue of the wire rope.
• Groove Profile: The rim features a semi-circular groove lined with materials like rubber, nylon, or hardwood to provide a high coefficient of friction, reduce rope abrasion, and ensure proper rope seating.
• Construction Material: Sheaves are generally constructed from cast steel or fabricated steel plates to provide high tensile strength and durability under heavy dynamic loads.
• Spoke/Web Design: Designed with either heavy-duty spokes or a solid web to distribute the compressive and bending forces evenly toward the central hub.
• Bearing Assembly: Equipped with high-precision roller or ball bearings to ensure smooth rotation and minimize frictional resistance during high-speed winding cycles.
• Rim Flanges: Designed with sufficient depth to prevent the rope from jumping out of the groove during slack rope conditions or sudden changes in tension.