GB2019476A - Sprag Plates for Mine Roof Supports - Google Patents

Abstract

The sprag plate 21 of a mine roof support is pivoted between a generally vertical (operative) position and a generally horizontal (retracted) position as a cantilever extension 22 on which it is mounted is extended and retracted. This is achieved by a ram 48 connected at 44 to links 43, slidably guided within the extension 22 and to which are pivoted further links 61 which are also pivoted to the sprag plate 21. As the ram 48 is retracted the links 43 slide relative to the extension 22 to which the sprag plate 21 is pivoted, thus causing it to swing into a longitudinal position. Further retraction of the ram causes retraction of the extension 22 relative to the roof plate 1. On extending the ram 48 the links 43 slide in the opposite direction relative to the extension 22 and cause the sprag plate to swing back into a vertical position, and further extension of the ram causes the extension 22 itself to extend relative to the roof plate 1. The roof plate 1 also contains a conventional cantilever extension 17 which is operated by a ram 15. One of the guides 18b of thin extension engages a plate 35 on the sprag plate 21 when the extension 22 is fully retracted to hold it horizontal. <IMAGE>