Quarries.
201. Quarrying, crushing and screening of "Hong Kong Granite" continued throughout the year at Hok Un and Tsat Tze Mui Quarries. These two plants, operated by the Roads Office, supplied the bulk of the requirements of the Department for aggregate. In addition the production of 11/2″ and 3″ premixed bituminous macadam formed a major item of the Quarry production during the year.
202. At both quarries the rock is produced from primary blasting by benching and subjected to secondary blasting either by pop-holing or by plaster shooting. Gelignite with a 62% content of nitro-glycerene is the normal explosive used and the yield over the year averaged 6.58 tons of rock per pound of explosive, including both primary and secondary blasting.
203. Before the rock is fed to the primary crushers it undergoes a further reduction in size by stone breakers (masons) with spalling hammers. Stone is then loaded into steel side-tipping wagons on 24″ gauge light railway and pushed by hand to the primary crushers, the actual output of which depends on the number of stone breakers. The demand of stone of all sizes continued to rise, and in October the number of stone breakers in each Quarry was increased to 50 with the result that daily production of stone rose from a previous 275–300 tons to 400 tons from each quarry and total production of crushed stone to double that for 1951/52. Both Quarries were operated in two 8-hour shifts, this system having been introduced during the previous year.
204. On the Island, the primary crushing capacity at Tsat Tze Mui was increased when the old 20″ × 10″ Edgar Allen jaw crusher was replaced by a new 24″ × 13″ Hadfield Crusher. The primary stage at Tsat Tze Mui then consisted of two 24″ × 13″ Hadfield machines, which exactly duplicated the equipment at Hok Un Quarry on the Mainland.
205. Two 75 h.p. electric motors were installed to drive the two "Broomwade" Type EH 330 cu. ft. per min. twin cylinder stationary air compressors at Tsat Tze Mui. The supply of
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Quarries.
201. Quarrying, crushing and screening of "Hong Kong Granite" continued throughout the year at Hok Un and Tsat Tze Mui Quarries. These two plants, operated by the Roads Office, supplied the bulk of the requirements of the Department for aggregate. In addition the production of 15′′ and 3′′ premixed bituminous macadam formed a major item of the Quarry pro- duction during the year.
202. At both quarries the rock is produced from primary blasting by benching and subjected to secondary blasting either by pop-holing or by plaster shooting. Gelignite with a 62% content of nitro-glycerene is the normal explosive used and the yield over the year averaged 6.58 tons of rock per pound of explosive, including both primary and secondary blasting.
203. Before the rock is fed to the primary crushers it under- goes a further reduction in size by stone breakers (masons) with spalling hammers. Stone is then loaded into steel side-tipping wagons on 24" gauge light railway and pushed by hand to the primary crushers, the actual output of which depends on the number of stone breakers. The demand of stone of all sizes continued to rise, and in October the number of stone breakers in each Quarry was increased to 50 with the result that daily production of stone rose from a previous 275-300 tons to 400 tons from each quarry and total production of crushed stone to double that for 1951/52. Both Quarries were operated in two 8-hour shifts, this system having been introduced during the previous year.
204. On the Island, the primary crushing capacity at Tsat Tze Mui was increased when the old 20′′ × 10′′ Edgar Allen jaw crusher was replaced by a new 24" x 13" Hadfield Crusher. The primary stage at Tsat Mui then consisted of two 24" x 13" Hadfield machines, which exactly duplicated the equipment at Hok Un Quarry on the Mainland.
205. Two 75 h.p. electric motors were installed to drive the two "Broomwade" Type EH 330 cu. ft. per min. twin cylinder stationary air compressors at Tsat Tze Mui. The supply of
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