Incline hoist skips are classified into dumping and non-dumping ones. Non-dumping skips are of two types―rear discharging and bottom discharging. They are mainly used on the slopes of 40° or more. The dumping skips are used at inclination angles below 40°, and an auxiliary rail is installed to increase the inclination of the skip for a sufficient discharging angle.
The dumping skips are of two types―rear-discharging and front-discharging. The latter is widely used. The rear wheel of a front-discharging skip is bigger in width than the front wheel. When approaching the emptying point, the front wheel tilts forward along the main rail, while the rear wheel is lifted along the profile of the unloading curve to increase the discharge angle.
The main rails on which the front wheels are placed are generally straight, which often causes complete overturning of the skip. Skip winching facilities are subjected to overwinding in unloading sections for several reasons. If the skip is out of its unloading section by overturning, the skip will be completely overturned in the direction of movement due to the increase in the angle of inclination of the skip, which causes the forward movement of the center of gravity, and the increase in the drag force exerted on the front wheels. There is also a disadvantage of poor skip restoration due to the presence of the center of gravity in the front side of the skip.
To prevent such phenomena, the main rails can be set to be curved. The curved shape of the main rails can prevent complete overturning of skips and increase the possibility of restoration. There have been many studies on dumping skips with big dip angles used in manufacturing lines of factories and enterprises in the construction and building materials industry. However, they failed to consider the unloading properties of bulk materials in the skips.
Hong Ryo Myong, a researcher at the Faculty of Mining Engineering, has analyzed the unloading properties of the front-discharging skips by combining the analysis of bulk materials and motion. He proposed that the curved shape of main rails for front wheels can eliminate full overturning of skips, and proved it by analyzing the behavior of bulk materials and motion.
He proposed a method of evaluating the overturning possibility of skips. The overturning possibility of skips can be estimated by measuring the force acting on hoisting wire ropes. If the force on hoisting wire ropes remains unchanged at zero for a while, the skips can be completely overturned.
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