April 28, 1916. THE COLLIERY GUARDIAN. 803 Table III.—Permissible Rates of Acceleration for Certain Hoisting Speeds and Safety Factors. Maximum Minimum Speed. accelera- time of tion. acceleration. Feet per min. Feet per sec. Seconds. 500 or less 4*16 2 750 : 4*16 . . 3 1,000 5-55 3 1,250 5*95 3| 1,500 6*25 4 2,000 8*33 4 2,500 8*33 5 3,000 8*33 6 3,500 8*33 7 Diameter of Sheave. The figures take care of the variables of depth of shaft, hoisting speed, and acceleration stresses. The question of bending stresses is not considered, nor is it in section 34. The bending stress, of course, increases as the diameter of the sheave or drum decreases. It could be kept from becoming too great by specifying minimum permissible ratios between sheave and rope diameters. The increase in stress caused by running a rope over too small a sheave is unimportant, compared with the result- ing increase in rope wear, and as explained in the foot- note to section 34, considerations of economy can be trusted to prevent the use of sheaves and drums too small for the ropes. If the other provisions of section 34 are followed, the question of size of sheave will take care of itself. The economical ratio between rope and sheave dia- meters varies with the character of the wire in the rope and the type of construction. A pliable rope can run economically and safely over a smaller sheave than can a stiffer rope. The committee has reports of excellent results from the use of a in. rope over an 84 in. sheave, which gives a ratio of 66, whereas, in many cases, especially in the case of deep shafts and long ropes which usually are of necessity stiffer, a ratio of 100 has been recognised as not too high. In connection with the question of sheave diameters, one point should be noted, namely, that it is possible to make the ratio too high under certain conditions, or, more correctly stated, it is possible to make the sheave too heavy. This is the case frequently with turn-sheaves, guide pulleys, rollers, etc., on which the arc of contact and the compression between sheave and rope may be so little as to allow excessive slip, the rope failing to rotate the sheave easily. Of course, such a condition would cause wear, and tend to deteriorate the rope faster than would the use of a smaller, lighter sheave. To decide'on a suitable size of sheave under such con- ditions, the following rule is serviceable. Suppose that a ratio between sheave and rope diameters of 72 is con- sidered permissible. Then, when the deflection angle of the rope is less than 90 degs., that is, when it has less than 90 degs. of contact arc on the sheave, the diameter of the sheave shall be eight-tenths of the deflection angle times the diameter of the rope. Thus, as the deflection angle or arc of contact becomes less, the size of the sheave decreases. For a 45 degs. deflec- tion angle, a 3 ft. sheave is required for a 1 in. rope, and for zero degree no sheave is required, a rubbing board alone being sufficient. Permissible Deterioration of Rope in Use. There may be said to be five ways in which deteriora- tion of a rope proceeds. First, there is frictional wear; second, there is breakage of wires due to inequalities in even the best material; third, there is the breakage caused by the stress of bending over sheave and drum; fourth, there is corrosion inside and out; fifth, there is fatigue of the steel caused by its passing its elastic limit and accelerated by bending and by rapid hoisting. All of these effects finally take the 'form of broken wires. For this reason the committee considers the appearance of broken wires the best single sign to follow in deciding when to discard a rope. The number of such wires permitted is intended to correspond to a reduction in strength of about 25 per cent., but as stated, this corre- spondence is only approximate and probably exists only in ropes of standard construction. There are two difficulties in the way of expressing quantitatively by the number of broken wires a percentage reduction in strength. The first is that the position of the broken wires in the rope is of the greatest importance in deter- mining their effect on the rope’s strength. The second is that ropes of a great variety of construction are in use and in each type the effect of the breaks is different; this is especially true when the wires are of different diameters. As regards the different types of rope, whereas those used for hoisting are generally made of 6 strands with 19 wires to the strand, there are sometimes used ropes with strands consisting each of 7, 12, 13, 14, 15, 16, 19, 37, and 61 wires. Of the 6 by 19 construction, as it is called, there are again several different types. What is commonly considered standard is that in which the strand is composed of 7 inside wires with the 12 outside wires laid around these, alternating in the size of their diameters. In this construction the twist of both outside and inside groups is the same, and the alternation in size of outside wires is necessary to prevent 6 of them from sinking into the valleys between the inside wires and making a rough-surfaced strand. Tn another method of construction the wires are all of the same size, but the twist is made different. In the “ scale ” construction 9 small inside wires are sur- rounded by 9 large outside wires of uniform size, about twice the diameter of those inside. In a fourth type the valleys of the inside group of wires are filled with 6 very small annealed filler wires, and the 12 outside wires are all of one size. There are further to be con- sidered ropes of flattened and triangular strands which use wires of various shapes and sizes, non-twisting ropes, steel-clad ropes, and many ropes of special constructions. As regards the effect of the position of the broken wires, it is evident in the first place that the binding action of the twist is such that if a number of breaks occur separated some distance from one another, the diminution in strength may" be only that due to the elimination of one wire. Therefore the committee has specified that the breaks are to be counted within the distance of one “ lay ” or turn of the rope, within which distance the binding action need not be considered. A greater difficulty arises from the fact that the disposition of the breaks in the strand and their occurrence in one or several strands modifies their effect on the strength of the rope. In connection with this matter of the location of the breaks, some tests made under the auspices of the manufacturers committee are of interest and value. They are not at all conclusive, but serve excellently to illustrate how complicated the problem is. The tests were made on a plough-steel rope of standard 6 by 19 construction, 1 in. in diameter. The results with explanations are presented in Table 4. Table 4.—Tests of Hoisting Rope with Cut Wires. o £ No. of wires cut in a strand. Strands broken. O bJD ce .5 ce o ® PsA A £ 1.., . 6 . .. 1 .. . — ...93*02...74,441...74,100.. 92*60.. . 3 ..Centre 2... . 6 . .. 1 .. . 1 .'..89*56...71,887...72,390...90'46... . 2 ... Centre 3.. . 6 . .. 2 .. . 1 ...82*62...66,119...67,640 . 84*50.. . 1 ... Centre 4.. . 6 . .. 2 .. . 2 ...79*20...63,375...67,010...83*74... , 3 ...Centre 5... 6 . .. 3 .. . 2 ...72*23...57,798...62,020.. 77*51... , 2 ...Centre 6... 6 .. .. 3 .. . 3 ...68*79...55,046...59,620...74*51.. . 2 ...End 7... . 6 . 4 .. . 3 ...61*83...49,474 ..55,575...69*45... . 2 ...End 8... 1 . .. 6 .. . 6 ...89*56...71,807...60,090...75*09... 1 ... Centre 9... 6 .. .. 4 .. . 3 ...61*83...49,474...58,180...72'71... 2 ... Centre 10... 2 .. .. 6 .. . 6 ...79*20...63,375...54,090...67*60.. 2 ...Centre n... 6 .. .. 4 .. . 3 ...61*83...49,474...58,850...73*54... 3 ...Centre 12... 2 .. .. 6 .. . 6 ...79*20...63,375...72,250...90*29... 2 , ...Centre 13... 1 .. . 6 .. . 6 ...89*56...71,837...76,700...95*85 1 1 ... Centre ...End # Strength before cutting was about 80,0001b. Notes. Test 1.—One large wire cut from each strand. Each wire cut three times. End cuts a distance of two rope lays from centre cut. Each series of cuts in same circumference. Test 2.—One large and one small wire cut in each strand on same axis. Each wire cut three times. End cuts a distance of one rope lay from centre cut. Test 3.—Two large wires and one small wire cut in each strand in same manner as in test 2. Test 4.—Two large and two small wires cut in each strand, same manner as in test 2. Test 5.—Three large and two small wires cut in each strand, same manner .as in test 2. Test 6.—Three large and three small wires cut in each strand, same manner as in test 2. Test 7.—Four large and three small wires cut in each strand, same manner as in test 2. Test 8.—Three sets of four wires each or all outside wires in one strand only cut. Wires cut only once. Each set of four wires cut were a distance of one strand lay from each other. Test 9.—Same as test 7, except each wire cut only once. Test 10.—Same as test 8, except two strands were cut. Test 11.—Four large wires and three small outside wires in each strand cut. One large wire in each strand cut in centre in same circumference. One end cut, two large and one small wires; other end cut two small and one large. Distance from centre to end cuts one strand lay. Each wire cut only once. Test. 12.—Same as test 10, except that each set of cuts was a distance of one rope lay apart. Test 13.—Same as test 8, except that each set of cuts was a distance of one rope lay apart. It should be noted that the rope tested was new, and the diminution in strength is purely that from cuts or breaks, corrosion and abrasion not entering in. Furthermore, the tests were static, the effect of passing over sheave or drum being neglected. The 13 tests can be divided roughly into two classes. Nos. 1 to 7, 9, and 11 had the cuts symmetrically located by strands, that is, there were wires cut in each of the six strands. Nos. 8, 10, 12, and 13 had the cuts unsymmetrically located by strands, that, is, one or two strands had wires cut, the other strands being left intact. Those of the first class gave results about as might have been expected, that is, the more cuts the less strength. Those of the second class gave results that seem discordant until analysed. In test 8, for instance, only one strand had wires cut, and these cuts being one strand lay apart, the binding action was not enough to prevent the strand from elongating, so that an undue share of the stress was put on the other five strands, which were thrown out of their position of strength, the shape of, the section being altered. Before they could re-form into a position of' uniform tension, the wires were attacked severally and rupture resulted at a point below the calculated strength of the section, evidently because part of the wires were momentarily out of commission. In test 13, on the other hand, the cuts were also all in one strand, but they were a whole rope lay apart, and. therefore the binding action was such as to give an ultimate strength above that calculated for the uncut wires. Although many of the difficulties evidenced by the apparent discrepancies in these tests may be overcome by specifying that the breaks and worn wires lie within the limits of one rope lay, as in section 34, it is never- theless evident that the relation between broken and worn wires and ultimate strength is dependent on a host of variables, and it must be repeated that the requirements of section 34 for discarding are not intended to be strictly quantitative. They merely con- stitute a useful criterion for determining when a rope is no longer safe. The manner in which breaks occur is of significance. Thus, when a new rope is installed there is likely to be a short period, while the rope is taking its set and equalising tension, during which breaks are relatively frequent. These breaks are of no importance and do not indicate that the rope is wearing out. After the period of their occurrence, the rope will run for some time without more wires breaking. Toward the end of the life of the rope, however, it may happen that the number of breaks begins' to increase rapidly. Thus inspection on one day may show one wire broken at a certain point. The next day two may appear there, and the third day, three or four. This condition arising is a sign that the rope is going to pieces and should be taken off forthwith. It may also happen that breaks occur before any great wear is visible—this, of course, after the period of initial breaking. Breakage without wear indicates faulty installation of some kind; either the rope is made of brittle wires or it is being bent over too small a drum or sheave. Rope Fastenings. Involved with the question of selecting and caring for a hoisting rope is that of the proper method of fastening it to the conveyance in the shaft. There are two types of fastening in common use, that in which the end of the rope is held in a socket by metal poured in the molten state, the socket being arranged for easy attachment to the shaft conveyance, and that in which the rope is doubled around .a thimble, brought back and fastened to itself by clamps or clips. , The latter method is probably most widely used in this country, although the former is extremely popular in certain districts, for instance, the copper region of Lake Superior. When the socket fastening is employed, it is customary to use babbitt or some similar alloy for fastening the rope in the socket, the wires in the end of the rope being “ broomed out ” and doubled back a short distance. Many operators have a profound distrust of this method of fastening, a distrust based partly on records of poor performance, partly on the apparent insecurity of the fastening, and partly on the fact that the essential parts are concealed and it is impossible to know what is going on inside the socket. The committee was, in fact, strongly urged to prohibit this type of fastening altogether. It was unwilling to do so, because the fastening properly made is a good one, because it prevails in many important mining districts, and because it possesses certain advan- tages, being economical of headroom, a matter of some importance, especially in preliminary operations where buckets are used. This decision of the committee received entire vindication through the conference with the rope manu- facturers, who are strongly opposed to the thimble-and- clamp method of fastening, and recommend the socket method under all conditions. The socket fastening which they recommend, however, differs from that in ordinary use in that instead of some metal of the babbitt class, zinc is used to hold the wires, and the wires themselves are not doubled back inside the socket, but are merely “ broomed out.” It has been estab- lished beyond question of doubt that this is the strongest fastening that can be made. The wires having been previously cleaned with acid, the zinc makes a perfect bond with the steel just as in galvanising; the wires can not pull out. As final proof of the efficiency of this fastening there is adduced the fact that in testing ropes in machines for ultimate strength, the zinc-filled socket is used, and when properly made never fails. The manufacturers urge against the thimble-and- clamp method of fastening that it is practically impos- sible to develop by it more than 85 per cent, of the strength of the rope, and that the maintenance of even 85 per cent, efficiency is difficult. As a rope takes tension, it tends to compress the hemp centre and become reduced in diameter; this loosens the clamps or clips that hold it to itself. It is therefore necessary to keep tightening the clamping bolts to prevent the fastening from becoming unsafe. On the other hand, it must be said that the thimble-and-clamp fastening is easy to make and not easy to make wrong, and that it is constantly exposed to view and therefore subject to' easy inspection, whereas the zinc joint must be made with care and like the babbitt joint is not readily inspected so far as its internal condition is concerned. Directions for Making a Socket Joint with Zinc. The following directions for making a socket joint with zinc are given by the manufacturers’ committee :— (1) The rope should be securely seized at the end before cutting off, and an additional seizing placed at a distance from the end equal to the length of the basket of the socket. In the case of large ropes, this seizing should be several inches long, and wrapped on securely with a special seizing iron. This is very important in order that the lay of the rope may not become untwisted, otherwise the tension in the strands may not be uniform when the socket is applied. (2) Take the end seizing off the rope, leaving the other seizing on. Then cut out the hemp centre back to this latter seizing, and broom out the wires; they should be all untwisted but not necessarily straightened. (3) Clean the wires thoroughly in benzine, naphtha, or gasoline for the distance that they are to be inserted in the socket, and then dip them in a bath of commercial muriatic acid for a period of about 30 to 60 seconds, or until the acid has thoroughly cleaned each wire. (4) Dip the wires in boiling hot water to which has been added a small amount of soda to neutralise the acid, and insert the wires in the basket of the socket. Be sure that the socket lies with the axis of the rope. If the temperature is below 65 degs. Fahr., warm the socket before pouring the zinc. (5) Seal the base of the socket basket with putty, clay, or similar substance and pour the molten zinc into the basket until it is full. The zinc must not be too hot, or it will anneal the ends of the wires, especially of small ropes. About .700 degs. to 800 degs. Fahr, should be sufficiently hot. After the zinc is solidified, the socket can be plunged into cold water to cool off. If the socketing is properly done, the rope when tested will break one or more strands between the sockets in a testing machine.