Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/878

Rh 844 K P E the strength of the rope. lu a bundle of fibres, equal in length and strength, fastened at the ends, each fibre will, upon a strain being applied to the bundle, bear its proper share of the stress; and the strength of the bundle will evidently be measured by adding together the strength of the separate fibres. But if this bundle is twisted so as to form a thread, the strain will no longer be equally distributed among the fibres, for, by the tor- sion, the external fibres of the bundle will be wound round those that lie nearest to the centre^ and, in proportion to their distance from the heart of the bundle and the amount of twist given, will form spirals more or less inclined from the axis of the thread. The external fibres will in consequence be longer than the internal ones, and the greatest share of the strain will be borne by the latter. The depreciation in strength from twist- ing of hard woody fibres is greater than is the case with fine soft flexible fibres, such as common hemp of good quality. To prevent the decay of ropes which are frequently exposed to water, the yarns of which they are composed are soaked in hot Archangel tar before they are formed into strands. Tarring, it is found, also seriously diminishes the strength of the .rope, but no other means of preventing water from penetrating and rotting the fibre has yet been found. M. Duhamel, from a series of investigations made in 1741-46, came to the conclusion that, apart from exposure to wet, untarred cordage in constant service was about one-third more durable than tarred, that it retained its strength for a longer period when kept in store, and that it resisted the ordinary influences of the weather better than when it was tarred. Subsequent experience has fully borne out these conclusions, and now that Manila hemp, which withstands the influence of Avater well, is so extensively used for heavy cordage, tarring is no longer so generally practised in rope-making as was at one time the case. Ropewalk Spinning. The sequence of operations in this ancient but still greatly used method of working is (1) heckling the fibre ; (2) spinning the yarn ; (3) tarring the yarn (when neces- sary) ; (4) forming the strands ,- (5) laying the strands into ropes. Heckling differs in no way from the hand-heckling process used in the preparation of flax (see vol. xiv. p. 604-5). The heckle- board consists of a wooden plank, studded with strong tapered and sharp-pointed steel prongs. A series of such heckle-boards is used in the progressive heckling operation, the prongs diminishing in size and being closely set together. In drawing his " stricks " of fibre through these gradually diminishing heckles the workman not only combs out and disentangles the material, separating "tow" from "line," but he also splits up and makes finer the fibres upon which he operates. A little oil is sprinkled on the heckles in course of the process. The spinning is done in a covered and enclosed walk from 300 to 400 yards in length, at both ends of which the machines are placed. These (one variety of which is shown in fig. 1) consist of a series of " whirls " d, d, generally twelve in number, set in a semicircular frame e. The whirls are set in rapid rotation by a belt which passes over them from a wheel bb ; or, what is now more usual, they are driven by the direct friction of the wheel itself pressed hard against them. The point of the prolonged axis of the whirl is bent into a hook, on which the ends of the fibre are hung for spinning. Each spinner carries around his waist a quan- tity of heckled fibre, and, fasten- ing an end on the whirl hook, he walks backward down the walk giving out even proportions of fibre all the while and regulating his pace so that the amount of. twist communicated to the yarn ' is uniform. He draws the fibre from hia waist with the left hand and lets it slip between the thumb and finger of the right, which, protected by a piece of woollen cloth, compresses and moulds into cylindrical form the yarn as it is spun. At intervals in the length of the walk there are posts and rails supplied with hooks into which the spinner throws the yarn to keep it off the ground. The spinners commonly work from both ends in sets of six, and as each set arrives at the end of the walk the yarns spun by them are unhooked from the whirls, tied together at the ends, and collected in large hooks along the side of the walk till a haul of about four hundred yarns is accumulated. When tarred rope is to be made the haul of yarn is at this stage passed through a kettle of tar heated to about 212 Fahr., from which it is drawn through a nipping apparatus which squeezes out superfluous tar, leaving the yam a bright brown colour soaked with about one-fourth its weight of tar. For "forming" strands the spun yarn is wound, each yarn separately, on bobbins and placed in a bobbin frame. From their bobbins the yarns are conducted through a concentric circle of holes in a steel register plate, behind which they come together and are pressed. through a trumpet-mouthed tube, which varies in diameter according to the diameter of the strand being formed ; and they are attached to the hooks of the forming machine or traveller. This machine travels down the ropewalk on rails moved by an endless rope passing over a grooved pulley, the hooks being at the same time set in rotation by gearing connected with the pulley. "When the machine has reached the end of the walk and sufficient "twist" is given to the three strands, they are un- hooked and hung together on the centre hook of the machine. A grooved conical block of wood called a "top" is inserted between the strands, one of which lies in each of the three equidistant con- centric grooves. The strands at the fore-end are cut away and attached separately to three other hooks. The laying of the three strands into a hawser is now proceeded with by giving a reverse rotation to the central hook on which at the lower end they are hung. As twist is communicated to the strand between the top and the machine, the former is forced away towards the fore-end, and on the uniform motion outwards of the top depends the even and regular character of the lay. While the hook at the lower end is rotating in one direction to lay the strands, the time; hooks holding the strands at the upper end are correspondingly revolved in the opposite direction to keep up the amount of twist in them which they would otherwise lose by the unwinding effect of the revolution of the laying hook. As the laying pro- ceeds, the forming machine is gradually dragged up the rails owing to the shortening of the strands caused by twisting them into a hawser. The formation of a cable from three hawsers is effected in a similar manner ; but the great weight of material dealt with necessitates some modified operations to ensure uniformity of laying. In many rope-works distinct machinery is used for the strand lay- ing and rope-forming operations. Machine <rr Factory Rope-Making. The ropewalk system of manufacture has several inconveniences, among which, in towns, the most serious is the difficulty and expense of obtaining the long narrow strips of ground it requires. Hand-made ropes are also subject to certain irregularities of twist, and the yarns are less uniform than can be obtained from the operations of automatic machinery. Moreover in machine-spinning it is possible so to form the strands and lay the finished rope that any strain can be more equally distributed over all the fibres than can be done with hand-spinning and twisting. The essential feature of the factory system consists in having yarns, strands, and ropes wound upon bobbins or drums in each successive stage, the material being drawn direct from the reel to be twisted and immediately wound up again. The length of rope made is only limited by the carrying capacity of the drum on which it is finally wound. The earliest practical attempt to introduce machine rope-spinning was made by Cartwright, the famous inventor of the power loom, who, in 1792, obtained a patent for a machine called by him a "Cordelier." Cartwright's cordelier, as improved in 1805 by Captain Huddart, became the basis of modern laying and forming machines. Numerous modifications and improved combinations have been introduced, but the principle on which they are worked is essentially the same. A complete set of rope and twine making machinery includes heckling machines, spreading and drawing frames for line yarns, and carding engines and drawing frames for tow. These machines do not differ from the ordinary preparing machinery in flax manufactures, nor is there any essential ditterence in the spinning frames for the smaller counts of yarns. The heavier yarns for rope-making are spun upon a gill-spinning frame, such as Goode's automatic spinner, which is fitted with a self-feeding motion by which when the sliver is presented in large quantity the rate of motion and spinning is proportionally increased, when the sliver becomes attenuated the motion is correspondingly slow, and when the sliver is broken the spinner stops. Thus a yarn well laid and uniform in thickness is secured by automatic machinery. For spinning heckled yarn such as is used in the ropewalk a machine of simple construction, Ronald's patent (fig. 2), is now extensively used. The yarn in this machine has the advantage of being hand-spun, as the spinner draws out, compresses, and feeds the fibre from a supply round his or her waist just as on the rope-