| 摘要 |
This invention relates to a face sprag for mining equipment, to a mine roof beam incorporating such a sprag and to a mine roof support provided with such a beam. The face sprag comprises a sprag plate, a piston and cylinder unit pivotally attached at one end about a first pivot axis to the sprag plate and at the other end about a second pivot axis to a portion of a support member, a link means pivotally attached at one end about a third pivot axis to the piston and cylinder unit and at the other end about a fourth pivot axis to the support member at a location spaced from the second pivot axis, all the pivot axes being parallel, and activation of the piston and cylinder unit urging the sprag plate, in use, into an operative position in engagement with the mineral face.
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