tailieunhanh - Five Hundred and Seven Mechanical Movements Episode 8

Tham khảo tài liệu 'five hundred and seven mechanical movements episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Mechanical 252. A and B are two rollers which require to be equally moved to and fro in the slot c. This is accomplished by moving the piece D with oblique slotted arms up and down. 253. Centrifugal check-hooks forprevent-ing accidents in case of the breakage of machinery which raises and lowers workmen ores etc. in mines. A is a frame-work fixed to the side of the shaft of the mine and having fixed studs D attached. The drum on which the rope is wound is provided with a flange B to which the check-hooks are attached. If the drum acquires a dangerously rapid motion the hooks fly out by centrifugal force and one or other or all of them catch hold of the studs. D and arrest the drum and stop the descent of whatever is j attached to the rope. The drum ought besides this to have a spring applied to it i I otherwise the jerk arising from the sudden j stoppage of the rope might produce worse effects than its rapid motion. 254. A sprocket-wheel to drive or to be driven by a chain. Movements. 65 255. A flanged pulley to drive or be driven by a flat belt. j 256. A plain pulley for a flat belt. 257. A concave-grooved pulley fora round band. 258. A smooth-surface V-grooved pulley for a round band. i I 259. A V-grooved pulley having its groove notched to increase the adhesion of the band. I 260. A differential movement. The screw c works in a nut secured to the hub of the wheel E the nut being free to turn in a bearing in the shorter standard but prevent- I ed by the bearing from any lateral motion. The screw-shaft is secured in the wheel D. The driving-shaft A carries two pinions F and B. If these pinions were of such size as to turn the two wheels D and E with an equal velocity the screw would remain at rest but the said wheels being driven at unequal velocities the screw travels according to the difference of velocity. 1 Mechanical Movements. 261. A combination movement in which the weight w moves vertically with a reciprocating movement the down-stroke being shorter than .