Page:The Kinematics of Machinery.djvu/211

 CHAIN-CLOSURE AT DEAD POINTS.

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�at right angles the guides themselves be placed 90 apart (Fig. 147), a single crank may serve for both mechanisms. This is frequently * used for screw-steamers, and has also been applied to land-engines. In this case, as in the former, the driving force (steam-pressure) in the chain is assumed to act upon the bodies c and c'.

Another mechanism which is carried over its dead points by chain-closure is sketched in Fig. 148. Two equal and parallel cranks a and c are connected by a link ~b having a length equal to that of the fixed link d. The figure 1234 is therefore a

��FIG. 147.

parallelogram having dead points in the positions 1 2' 3' 4 and 1 2" 3" 4, and this whether the driving force be applied to a or c. The dead points may be passed by the addition to the first chain of a second one a! V c' df similar to it, in such a way that a has a common axis with of, c with c', and that each pair of cranks encloses an angle of 90, and further that d is connected with d', i.e., that both are made stationary (Fig. 149). Locomotives with coupled wheels give familiar illustrations of this arrangement.

little used for marine engines, at least for many years, in this country : I have seen it applied to oscillating cylinders. One of its most recent applications has been at the Panteg Steel Works, Pontypool, where it forms the driving mechanism of large direct-acting Eolling Mill Engines (see Engineering, vol. xix. p. 249). The same mechanism has lately been used for large compound engines in the Guyoii
 * The arrangement with cylinders equally inclined to the vertical has been very

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