Page:The American Cyclopædia (1879) Volume XIV.djvu/445

 ROPE 425 over a drum to cool it, when each separate yarn is led to, and evenly wound upon, its appropriate bobbin. After tarring, the yarn should before use be allowed a few hours to harden, and attach more closely to the fibre. Should it be made into rope immediately after tarring, the tar would press through to the surface, giving it an unsightly appearance, and decay would soon set in at the centre of the rope. The passing of the yarn through the boiling hot tar at a certain rate is necessary to enable it to take up a sufficient quantity of tar, the rollers pressing out and returning to the trough the superfluity. Enough of the tar is retained in the yarn to coat over the fibre and preserve it from decay. Tarring protects cordage from injury by exposure to rain and immersion in water ; but it makes its fibre rigid and impairs its strength. This fact has long been known, and many efforts have been made, hitherto unsuccessful, to improve the tar or find a substitute for it. It has been shown by experiment : 1, that white cordage in con- tinual service is one third more durable than tarred ; 2, that it retains its strength much longer when kept in store ; 3, that it resists the ordinary injuries of the weather one fourth longer. Manila is judged by inspection, and is not tested by strain. It is neither hackled nor tarred, with the single exception. of the case of outside yarns of large hawsers, which are tarred. Having a harsher fibre, it is oiled before running through the preparation ma- chines, the oil softening the fibre and relieving the machinery of much of the work it would otherwise have to perform. Care must be exercised, however, not to use too much oil, lest the manila turn yellow and the yarn be- come gummy. It should be well prepared before being taken to the spinners, as all the work required of them should be to put the twist into the yarn and wind it on the bobbin. The yarn having been spun of the size desired and wound up on bobbins, it is taken to the laying ground, where each bobbin is placed on an iron rod in frames convenient for reel- ing off in the process of forming the strands. The frames hold from 200 to 300 bobbins, one, two, or three frames being used, according to the size of the rope to be made. The number of yarns required for a strand are passed each through its proper hole in a metallic plate, brought together through a closely fitting iron tube in the tube board, and attached to the proper hook in the "former," a machine so called because it forms and equalizes the twist of the strand. The holes in the plate are made on concentric circles. The tube inserted in the tube board opposite the centre of the plate is so made as to compress the yarns of each strand into a solid mass as they are drawn through and twisted into a strand. Each strand has a sepa- rate plate and tube. The " former " is drawn down the ropewalk by steam power, and is so constructed with "whelps" on drums, and gears, that at whatever rate it may travel the proper rotary motion is always given to the spindle to twist the yarns into strands. Pow- er is applied to the former by means of an endless rope passing from one end of the walk to the other. The tube board is heated du- ring cold weather by steam pipes, thus warm- ing the tubes and keeping the tarred yarns soft and pliable. The next step is to put the strands into a rope, termed " closing." Two machines are used for this purpose, one at each end of the walk. The one at the lower end is termed a layer, as it lays up or closes the rope. The upper machine is stationary, and is used to keep the proper twist in the strand while laying. The strands are attached to the hooks of the machines separately. The ma- chines being put in motion, the strands are brought to a proper degree of tension by means of a press attached to the lower or laying ma- chine. As the tnrn or twist is put into the strands they shorten in length ; this is termed " hardening." After the strands become hard, they are placed on one hook of the laying machine, but kept separate in front by the insertion of the ''top," a wooden cone with grooves cut in its surface of a size to admit the strands. The top has attached to it "rope tails," which are applied to the rope during the process of closing for the purpose of cre- ating friction. The more turns taken with the tails, the more twist is given the rope, and consequently the harder it becomes. The ma- chines are so geared that the lower one makes two revolutions to one of the upper ; that is to say, it requires two revolutions of the rope to one of the strands, the additional revolu- tion being requisite to overcome the friction caused by the top, tails, and stake heads, which are placed at every five fathoms to support the strands and the rope. To obviate the ne- cessity for long ropewalks, a machine has been devised for reeling up the rope as it is made. In private establishments rope is made on these layers as large as 10-inch. They are known as " Woodworth's laying machines." The gov- ernment ropewalk, in Boston, Mass., is 1,360 ft. long. Rope can be made there, without re- sorting to unusual means, 170 fathoms (1,020 ft.) in length. The Quality of Rope. The strength of rope depends mainly upon the quality of the material of which it is made. Hemp fibres vary from 3 to 3 ft. in length ; the manila averages over 6 ft., and is often found as long as 12 ft. To make rope, these fibres must be overlapped among themselves, and compressed so as not to be drawn apart. This compression is obtained by twisting, the fibres being contin- uously drawn out from a bundle in quantities sufficient to produce the thread or yarn, as already described. It is customary to spin the yarn right-handed. Yarns are then combined by twisting, and form a strand which becomes left-handed, the twist being reversed at each successive step. Three or more strands are then combined by twisting, forming a rope, which in its turn becomes right-handed ; and