Comment
Author: Admin | 2025-04-28
With a consumption of between 120-140 m3/min, depending on grab size. Operational issues The cactus grab unit is mounted to the underside of the shaft sinking stage. This is seen as a significant disadvantage as heavier stage steelwork is required to support it. This, in turn, necessitates larger stage hoist ropes etc., which all add cost to the project. A further disadvantage is the space that the cactus grab occupies underneath the stage. This limits the distance that the stage can be lowered and so the shaft concrete lining may not come as close to the shaft bottom as is desirable. According to Martin and Harvey (1989) this, as well as the particular geology, was the reason that the cactus grab was not chosen as the lashing system for the sinking of the Asfordby shafts. An advantage of the cactus grab system, though, is that provided its hoist ropes are long enough it may operate reasonably independently of the stage position. Cactus grabs are suited to larger diameter shafts. Obert (1973) stated that cactus grabs may operate in shafts less than 6.7 m diameter, but they are economically suited to larger diameter shafts. He further stated that for shafts larger than 9.8 m diameter the cactus grab is the only economically viable option. The loading rates published in the literature vary. Dengler et al., (1992) stated that typical loading rates may be in excess of 100 t/h, Wakefield (2009) stated that 180 t/h is possible, while according to MacGillivray (1979) peak loading rates up to 250 t/h are possible with a large capacity grab (0.85 m3). MacGillivray (1979) further noted that 'A lashing unit with a pneumatic cactus grab is unequivocally the fastest shaft mucker in vertical shafts and is universally adopted for rapid sinking in large deep shafts'. Despite the high instantaneous loading rates that are quoted by MacGillivray and Wakefield, the data presented by Morgan (2015) indicates that the average loading rate was about 50 t/h, excluding blow-over, on the basis of an 8.1 m diameter shaft, 3.15 m advance per blast, estimated solid rock density of 2800 kg/m3, and lashing duration of 9 hours. In reality, instantaneous rates should be significantly higher, but Morgan's figures would be comparable to other types of loaders. In a similar manner to the Riddell mucker, the cactus grab relies on gravity for the tines to penetrate the muckpile. This has the
Add Comment