t it is mobile and capable of moving along with the face. Therefore, the unloading end [18] of a stage loader where it dumps coal into the entry belt conveyor is raised and can be pushed to overlap [19] the entry belt conveyor. Stage loaders are 30-150 ft (9-46m) long.
Powered roof supports [20] are used to support the roof at the face. They work in several steps, mostly, in the immediate forward support (IFS)[21] type in order to support the newly exposed roof as soon as possible. In normal supporting condition, the canopy [22] of the support is set tightly against the roof strata by the supporting resistances [23] of the hydraulic legs. When the cutting machine cuts and passes several support units beyond the support in question, the support legs are lowered and pulled forward [24] for a distance equal to the width of cut (web) by retracting the hydraulic advancing ram [25]. The advancing ram acts against the face conveyor panline, whose position is held unchanged by the advancing rams’ forces of the supports that are set on both sides of the support to be advanced. As soon as the support has been advanced to the designed position, the support is immediately reset against the roof. Finally, the advancing ram of the support in question is extended to push the conveyor forward and becomes ready for the next cut.
The sequential steps described are for the advance of an individual support in the direction perpendicular to the faceline. But along the faceline direction, the conveyor cannot be advanced in a sharp step immediately after the shearer has passed it, due to the rigidity [26] of the panline. Thus the fourth step is usually sometime after the shearer’s pass, resulting in a curved or snaked section [27].
During panel development [28], the panel entries are roof bolted as usual. But in the tailentry one or two rows of cribs [29] are erected to supplement the roof bolting[30]. During retreating mining, the roof at the headentry T-junction area [up to 500 ft (152m) outby the face] is generally reinforced with supports of some type to increase support density [30] to cope with the moving front and side abutment pressures.
NOTES TO THE TEXT
[1] Longwall mining techniques：长壁采煤工艺
[2] production capacities：生产能力
[3] the drilling and blasting mining：打眼放炮采煤
[4] millisecond blasting：毫秒爆破
[5] individual hydraulic props：单体液压支柱
[6] mechanized mining：机械化采煤
[7] plow：刨煤机
[8] fully mechanized mining：综合机械化采煤
[9] armored face conveyor (AFC)：工作面铠装输送机
[10] stage loader：转载机
[11] belt conveyor：胶带输送机
[12] panline：输送机溜槽
[13] faceline：工作面线
[14] self-contained motorized winch：整装的带电动机绞车
[15] cutting force：截割力
[16] guide channel：导向槽
[17] T-junction：T形连接
[18] unloading end：卸载端
[19] overlap：重叠，搭接
[20] Powered roof supports：液压顶板支架
[21] immediate forward support
