1902 Encyclopedia > Rope

Rope




ROPE. 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 dimensions are still smaller the article becomes thread or doubled yarn. All these varieties of cordage are composed of at least two, and in most cases of very many separate yarns, which are textile fibres drawn out and twisted into a uniform compact line. From thread and fine twine upwards the whole art of manufacture is simply that of twisting together fibres and yarns, but the comparative heaviness and coarse-ness of the materials operated on in rope-making render necessary the adoption of strong machinery and modified processes which clearly define this manufacture as a distinct calling. The modern trade of rope-making is again divided into two branches dealing respectively with certain vegetable fibres and with metallic wire. Silk cords and hair lines and ropes do not come within the scope of rope-making proper.

Vegetable fibres fit for rope-making are numerous, but ordinarily not many are employed. Speaking generally, for the prime requisites of strength, suppleness, flexi-bility, and durability, none can compete with the common HEMP (q.v.), which consequently is the staple of the rope-maker. MANILA HEMP (q.v.) is a fibre of the most remarkable tenacity, of unapproached value for heavy cordage, but too stiff and woody for small cords and twines. After these in utility come sisal hemp of Central America (Agave sisalana), phormium hemp of New Zealand (Phormium tenax, see vol. xviii. p. 812), and the sunn hemp of the East Indies (Crotalaria juncea, see vol. xi. p. 647)—all fibres of great strength, and largely used by rope-makers. Among fibres more rarely seen in rope-works are Jubbulpore hemp (Crotalaria tenuifolia), bowstring hemp (Sameviera zeylanica), and other "hemps" of the East Indies, and plantain fibre (Musa paraclisica) and agave fibre (Agave americana) of America. Ropes and twine of cotton are extensively made, especially for driving-bands for machinery. JUTE (q.v.) is now in considerable use by rope-makers, on account of its cheapness, but it is very deficient in strength and durability. COIR (see vol. vi. p. 917) is also largely employed, and many other fibres are used, principally in the localities of their production.

A rope is composed of a certain number of " strands," the strand being itself made up of many "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 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 yield a cable. Thus the twist in each successive operation is in a different direction from the preceding, and this alternation of direction serves to some extent to preserve the parallelism of the fibres.

The primary object ol 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 pre-venting the penetration of moisture when the ropes are exposed to water. The proper degree of twist is a matter of considerable importance, as all twisting injuri-ously affects the strength of the individual fibres, and indeed it is possible to twist a cord so hard that it will break under the action. The degree of twist given to ropes is generally such that the rope is from three-fourths to two-thirds the length of the yarn composing it, and the lighter the twist the greater in proportion is the strength of the rope. In 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 water 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 o' 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 wdieel 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 yam is uniform. He draws the fibre from his 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 yarn 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 jdaced 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 three 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 or 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 difference in the spinning frames for the smaller counts of yarns. The1 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-walk. In this way the strength, evenness, and other good qualities of hand-spun yarn are secured.

Twine Manufacture.—The making of twines and small cords forms a distinct branch of the rope trade, the whole of the opera-tions being carried out on a series of machines in which a large Dumber of twines and cords are twisted and otherwise prepared simultaneously, while in rope-making the machines deal only in general with the material of one rope at a time. Common twines are twisted from prepared yarns on a twine-twisting frame, the same in principle as the doubling spindle frames of the ordinary textile trade. The bobbins of yarn are placed on pegs in the creel above the twisting spindles, from two to five bobbins being placed over each spindle according to the number of yarns which go to make tip the twine. These yarns are passed round a pair of rollers, which pull them off the bobbins and deliver them evenly and with regularity to the flyer of the spindle, by which they are twisted and wound on the bobbin round which they rotate. By a recent improvement the required number of yarns, instead of being drawn from separate bobbins, are first wound together upon one bobbin in a " doubling winding frame." A series of bobbins so filled are placed on spindles in a twisting frame and twisted by inverted flyers; the twisted twine is drawn oil' by pairs of conical grooved twist rollers round which it passes, and is wound on taking-up bobbins. Cord or cable laid twine—that is, twine twisted first as above and then in strands of three, cabled or twisted in the reverse direction—is prepared on cabling machines. At the back of the machine the yarns receive their first twist as above described, and thence the strands from three spindles are drawn off together-over a pair of cone rollers, by which they are laid, and thence they pass to the front of the machine, where there is a range of powerful flyers and spindles by which they are twisted and wound upon a large bobbin. Twines and cords at this stage are rough and bristly in appearance, and for finishing them they undergo a dressing, sizing, and polishing operation in a special polishing machine. From the bobbins they are unwound and passed through a trough of hot water, thence in parallel order over the surface of a set of rubbing rollers covered with strong card cloth revolving at high speed in a contrary direction to that in which the twine is travel-ling. The friction of the strong card wires shaves and smooths the twine, which then passes through the sizing trough contain-ing a hot paste, usually of potato farina. The superfluous paste is squeezed out by passing the twine between rollers, and it is next passed over rollers covered with rough coir, which presses in all fibres yet protruding from the twine, and finally it is dried by passing round a range of steam-heated cylinders, running parallel with which are coir-covered polishing rollers which smooth the twine wdiile it is being dried. The finished twine is wound into balls of a definite weight on a balling machine.





Rope-Spinning.—The machines required for making ropes from spun yarn consist of a forming flyer for forming the strands and a laying machine for twisting the strands into rope. A cabling machine for uniting three-strand hawsers into a cable is only a second, laying machine of larger and heavier dimensions ; but it is still a common practice to lay the heavy cable on the ropewalk. The two operations of forming strands and laying rope may be per-formed on one combined machine, especially in dealing with light ropes composed of a few yarns ; but as a rule separate machines are preferred for each operation. In a simple machine designed only for a single twisting operation there must be one fixed and one revolving section. If the section .vhich contains the bobbins of yarn to be twisted is fixed, then the section in which is placed the bobbin for receiving the twisted product must be made to revolve. A machine in which the two operations of forming strands and laying rope are combined is of necessity cumbrous in proportion and complex in gearing. It must embrace three form-ing flyers, to form simultaneously three strands which in another part of the machine are laid into one rope. The forming flyers re-volve in one direction to twist the strands, wdiile they move in the opposite direction as a whole with the revolution of the laying section which gives the finishing twist to the rope, and such com-plex inter-revolutions within one frame are somewhat unwieldy. Finally, the machines may he made with their axis of revolution either vertical or horizontal. With all these alternatives there is considerable room for modification in the twisting arrangements.

The ordinary form of strand-laying machine is a vertical flyer (fig. 3). It consists of two or more upright frames or creels a, a, capable of holding ranged above each other a certain number of bobbins, from which the yarn may be easily run off and carried upward to be formed into a strand. The creels are fixed above and below in a stout circular plate and framework bb, to which motion of rotation is given by gearing c, placed on the under side. At the upper end of the revolving framework the yarns from the various bobbins are passed through a register plate d, a circular piece of metal pierced with concentric holes corresponding in number with the bobbins which the creels are fitted to hold. Beyond the register plate d the yarns come together in the trumpet-shaped mouth of the stranding tube. The stranding tube itself varies in gauge according to the diameter of the strand being made, and in it the yarns are caught, rounded, compressed, twisted, ami

Fi"
and the yarns are drawn through the register plate and twisted in the stranding tube by the revolution of the entire framework in which are placed the drawing-off gear and the large drum or spool on which the finished strand is wound. The advantages claimed for this apparatus are facility of replacing bobbins as the yarns run out, and increased production owing to the rapid and uninter-rupted rotation of the flyer.

In the ordinary laying machine there are only three bobbins of strand to deal with ; but, from the fact that it is necessary to give a certain amount of "forehard" or twisting to the strands them-selves while they are being twisted together in an opposite direction for laying, the machine is not without complexity. The three bobbins revolve together within a strong iron frame, and that motion forms the strand into a rope. But each bobbin is at the same time revolving in a contrary direction on its own axis at the rate tempered to the amount of forehard it is desired to put on the rope in laying. Moreover, in order to deliver evenly and in equal quantities the heavy and intractable strands from each bobbin to the laying top, it is necessary to have within each bobbin frame a drawing-off motion, and thus we have three distinct sets of motions in an ordinary laying machine. Fig. 5, in which only one bobbin frame is shown, will make plain one method of communicating these three motions, which in this case are controlled by a series of three shafts, placed one within the other. The external shaft gives motion to the entire apparatus, and its revolution in one direction forms the rope, which passes away over a pulley. The second shaft controls the spur wheel a, which, geared into the spur-wheel «' attached to the bobbin frame, turns it in a direction contrary to the motion of the whole. The internal shaft gears into a spur-wheel b, which again is centred on a tubular shaft c passing into the bobbin frame, and by a pair of bevel wheels controlling the rate of motion of the " drawing-off" pulley d, around which the strand is once wound, and from which it is conveyed by the tubu-lar shaft to a small guide pulley on the upper part of the revolving frame.

An American rope-laying machine is in use, similar in principle to the form-ing machine fig. 4, from which it differs only in having the strand bobbins mounted in flyers to give the strand the necessary amount of forehard in laying.

Wire Rope. —Ropes made of wire have only come into use in the course of the
present century, but now their employment is very extensive, and they play an important part in connexion with traction railways, mines, collieries, hoists, steam ploughing, and many other modern developments of industry. In the year 1822 a suspension bridge of wire was erected at Geneva. The wire used in this ease, however, was not twisted, but consisted of parallel bundles bound with wire and other coverings wrapped spirally around them to compact and keep the whole together. A bundle of small wires so treated presents the maximum of strain-resisting power combined with great rigidity, but it is obviously unsuited for most of the uses to which rope is put. Formed wire rope, consisting of strands laid in the manner of ordinary rope, began to be made about 1837; and now wire ropes of many kinds and dimensions are made from char-coal iron wire of fine quality, from mild steel, and from fine crucible steel. Copper wire and brass wire are also used for rope-making.

Wire ropes are stranded and laid or closed in machines which do not differ in essential features from the ordinary rope-making machinery. Both vertical and horizontal forms of revolving machines are used ; but, as the rope-closing machine has sometimes to carry as many as nine bobbins of strand, each with about two tons of wire, a vertical machine is best for enormous weights. An ingenious wire-rope machine has been invented by Mr Archibald Smith, in which the bobbins of wire are suspended, and only the framework around them and the wire drawn off are rotated for the forming and laying operations, and thus the necessity for rotat-ing these enormous weights at a high speed is obviated.

The number of wires in a wire-rope strand are few—generally from six to nine, and never more than eighteen. They are lightly twisted in the stranding machine, and they receive no foretwist in the rope-closing apparatus. The strands, on the other hand, which go to form a rope are numerous—from six to nine and up-wards ; and they are always wound round a core, which is generally of hemp, but sometimes a wire core is used. A wire rope thus forms a series of gentle spirals arranged continuously round a core. A large proportion of the wire is galvanized, to protect it from rusting.

The following table shows the relative circumference, weight, and strength of hemp, charcoal iron wire, and steel wire round ropes:—

== TABLE ==

(J. PA.)



The above article was written by: James Paton, Curator, Corporation Galleries of Art, Glasgow.



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