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Encyclopedia Britannica - Main :: RON-SAC |
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ROPE AND ROPE-MAKING. All varieties of cordage having a circumference of an inch or more are known by the general name of " rope." Twisted cordages of smaller dimensions are called cords, twines and lines, and when the sectional area is still smaller, the article is known as thread or doubled yarn. All these varieties of cordage are composed of a number of separate yarns, each of which is made from some kind of textile fibre by preparing and spinning machinery. The number of separate yarns which ultimately form the rope or cord depends upon the fineness of the yarn, and also upon the circumference of the finished article. From thread and fine twine upwards the whole art of manufacture is that of twisting together fibres and yarns; but the comparative heaviness and coarseness of the materials operated on in rope-making render necessary the adoption of heavy machinery and modified processes which clearly define this manufacture as a distinct calling. The modern trade of rope-making is again divided into two distinct branches dealing with vegetable fibres and metallic wire. Many different vegetable fibres are used for rope-making, but for the combined qualities of strength, flexibility and durability, none can compete with the common hemp, which is consequently the staple of the rope-maker. Cotton
A rope is composed of a certain number of " strands," the strand itself being made up of a number of single threads or yarns. Three strands laid or twisted together form a " hawser-laid " rope, and three such hawsers similarly laid make a " cable-laid " rope or " cable." A " shroud-laid " rope usually consists of four strands laid around a central strand or core. The prepared fibre is twisted or spun to the right hand to form yarn; the required number of yarns receive a left-hand twist to make a strand; three strands twisted to the right make a hawser; and three hawsers twisted to the left form a cable. Thus the twist in each operation is in a different direction from that of the preceding one, and this alternation of direction serves, to some extent, to preserve the parallelism of the fibres. The primary object of twisting fibres together in a rope is that by mutual friction they may be held together when a strain is applied to the whole. Hard twisting has the further advantage of compacting the fibres and preventing, to some extent, the penetration of moisture when the ropes are exposed to water; but the yield of rope from a given length of yarn diminishes in proportion to the increase of twist. The proper degree of twist given to ropes is generally such that the rope is from three-fourths to two-thirds the length of yarn composing it. Rope-walk Spinning.The sequence of operations in this method of working is as follows: (r) hackling the fibre; (2) spinning the yarn; (3) tarring the yarn when necessary; (4) forming the strands; (5) laying the strands into ropes. Hackling differs but slightly from the hand-hackling process used in the preparation of flax. The hackle board consists of a wooden block
sharp
series of such hackle boards is used in the progressive hackling operation, the prongs diminishingin size and being more closely set together. For the commoner kinds of ropes, however, hackling through the coarsest board is found to be sufficient, while in most other cases two hacklings are adopted. The hackler takes up a handful or " streak "1 of hemp from the bundle, wraps one end firmly round his hand, and with his fingers distributes a little oil over the hemp. The oil softens the material, keeps the hackle pins in good condition, and facilitates generally the splitting up of the fibre as the streak is drawn
drawn
The spinning is done in what is termed the " rope-walk," and from the nature of hand-spinning, and the length of the rope required, it is necessary that this walk should be from 300 to 400 yds. in length. It is sometimes completely covered in with walls and roof; at other times only a roof is built; while in exceptional cases the whole of the walk, with the exception of a small hut at each end, is without shelter of any kind. The operation of spinning is very important, as the weight of the yarn and the appearance of the finished product depend upon it. A description of spinning and laying as per-formed by the aid of the hand-wheel will perhaps be the best means of giving an idea of this useful branch of manufacture. The front and end elevations of one variety of spinning-wheel are shown in figs. i and 2. The apparatus is fixed to some convenient part of the' building, or to special
' See note in the article on JUTE for variations of spelling. hooks B, C or D ; the assistant at the wheel begins to turn, and thus a certain amount of twist is imparted to the material between the spinner and the hook. The spinner now walks backwards down the walk, drawing out the fibre with his left hand and adjusting it with his right. A piece of flannel
At convenient intervals in the length of the walk, and projecting from posts, are short horizontal
original
Fig. 3 shows one form of top, the three yarns being shown in distinctive marks so that the path of each may be more easily followed by the reader; a plan of the thick end of the top appears to the left of the figure. If four yarns of strands are required, the top would contain four grooves, as well as a hole through the centre to admit of a core when such a thing is required. As soon as the spinner, who carries the top, arrives at the wheel, the assistant takes the yarns off hooks B, C and D (figs. I and 2), and puts them all on hook E. The other ends of the strands are removed from the looper and attached to a block
If the strands require tarring before they are laid, they are separately taken off the hooks, after they have been spun, and tied at both ends to pegs to keep them taut until a sufficient number has collected to be conveniently handled at the tarring tank. The tar is heated to about 220 F., and the strands are then passed through it at a speed not greater than 15 ft. per minute. Before emerging from the tank, the strands pass between squeezing rollers which remove all superfluous tar. In a short time the strands are dry, while in the space of a few days the tar is hard enough to allow the strands to be formed into ropes. Such is, in general, the hand process of forming ropes when they are composed of only three or four single yarns. It very often happens, however, that a number of single yarns are required to form each strand of the rope. The single yarns may be spun by hand, as described above, or by machinery. In the former case a group of yarns is usually termed a " haul," while the machine-spun yarns are formed into what is known as a " warp " or " chain." In any case, the group of yarns is stretched down the rope-walk, at each end of which is a " jack " twister. A few of the yarns taken from the groupthe number depending upon the size of the yarn and also upon the required diameter of the strandare then placed on a hook of the jack twister and twisted together. When three such strands are made they are laid into a rope in a similar manner to that explained above. A simple form of hand jack twister is illustrated in figs. 4 and 5. The wheel A gears with pinions B on the shafts of the hooks or whirls, and this imparts the necessary motion to the latter. At the other end of the walk is a similar machine which moves upon rails as the twist is put into the strands. When the hooks are empty, pinions B and wheel A (fig. 4) are out of gear, but those hooks carrying yarn are drawn out, as shown at C, until the pinion B gears with wheel A, when the hooks are rotated. The C End of Article: ROPE AND If you wish, you can link directly to this article.
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