Wire_Rope_MH_section

Wire_Rope_MH_section - 332 Wire Diam(inch SPRINGS Table 23 Arbor Diameters for Springs Made from Music Wire Spring Outside Diameter(inch Arbor

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Unformatted text preview: 332 Wire Diam. (inch) SPRINGS Table 23. Arbor Diameters for Springs Made from Music Wire Spring Outside Diameter (inch) Arbor Diameter (inch) Spring Outside Diameter (inches) Arbor Diameter (inches) mm— mwmmmmai , ,. . WIRE ROPE 333 STRENGTH AND PROPERTIES OF WIRE ROPE Strength and Properties of Wire Rope Wire Rope Construction—Essentially, a wire rope is made up of a number of strands laid helically about a metallic or non-metallic core. Each strand consists of a number of wires also laid helically about a metallic or non-metallic center. Various types of wire rope have been developed to meet a wide range of uses and operating conditions. These types are distinguished by the kind of core; the number of strands; the number, sizes, and arrangement of the wires in each strand; and the way in which the wires and strands are wound or laid about each other. The following descriptive material is based largely on information supplied by the Bethlehem Steel Co. Rope Wire Materials: Materials used in the manufacture of rope wire are, in order of increasing strength: iron. phosphor bronze, traction steel, plow steel, improved plow steel, and bridge rope steel. Iron wire rope is largely used for low-strength applications such as elevator ropes not used for hoisting, and for stationary guy ropes. Phosphor bronze wire rope is used occasionally for elevator govemor-cable rope and for certain marine applications as life lines, clearing lines, wheel ropes and rigging. Traction steel wire rope is used primarily as hoist rope for passenger and freight elevators of the traction drive type, an application for which it was specifically designed. Ropes made of galvanized wire or wire coated with zinc by the electrodeposition process are used in certain applications where additional protection against rusting is required. As will be noted from the tables of wire—rope sizes and strengths, the breaking strength of gal— vanized wire rope is 10 per cent less than that of ungalvanized (bright) wire rope. Betha- nized (zinc-coated) wire rope can be furnished to bright wire rope strength when so specified. Galvanized carbon steel, tinned carbon steel, and stainless steel are used for small cords and strands ranging in diameter from igto 31, inch and larger. Marline clad wire rope has each strand wrapped with a layer of tarred marline. The clad- ding provides hand protection for workers and wear protection for the rope. Rope Cores: Wire-rope cores are made of fiber, cotton, asbestos, polyvinyl plastic, 3 small wire rope (independent wire-rope core), a multiple-wire strand (wire-strand core) or a cold-drawn wire-wound spring. Fiber: (manila or sisal) is the type of core most widely used when loads are not too great. It supports the strands in their relative positions and acts as a cushion to prevent nicking of the wires lying next to the core. Cotton: is used for small ropes such as sash cord and aircraft cord. Asbestos cores: can be furnished for certain special operations where the rope is used in oven operations. Polyvinyl plastics cores: are offered for use where exposure to moisture, acids, or caus- tics is excessive. A wire-strand core: often referred to as WSC, consists of a multiple-wire sn'and that may be the same as one of the strands of the rope. It is smoother and more solid than the indepen- dent wire rope core and provides a better support for the rope strands. The independent wire rope core, often referred to as IWRC, is a small 6 x 7 wire rope with a wire-strand core and is used to provide greater resistance to crushing and distortion of the wire rope. For certain applications it has the advantage over a wire-strand core in that it stretches at a rate closer to that of the rope itself. Wire ropes with wire-strand cores are, in general, less flexible than wire ropes with inde- pendent wire-rope or non-metallic cores. 334 ' WIRE ROPE Ropes with metallic cores are rated 7% per cent stronger than those with non-metallic cores. Wire-Rope Lay: The lay of a wire rope is the direction of the helical path in which the strands are laid and, similarly, the lay of a strand is the direction of the helical path in which the wires are laid. If the wires in the strand or the strands in the rope form a helix similar to the threads of a right-hand screw, i.e., they wind around to the right, the lay is called right hand and, conversely, if they wind around to the left, the lay is called left hand. In the reg- ular lay, the wires in the strands are laid in the opposite direction to the lay of the strands in the rope. In right-regular lay, the strands are laid to the right and the wires to the left. In left- regular lay, the strands are laid to the left, the wires to the right. In Lang lay, the wires and strands are laid in the same direction, i.e., in right Lang lay, both the wires and strands are laid to the right and in left Lang they are laid to the left. Alternate lay ropes having alternate right and left laid strands are used to resist distortion and prevent clamp slippage, but because other advantages are missing, have limited use. The regular lay wire rope is most widely used and right regular lay rope is customarily furnished. Regular lay rope has less tendency to spin or untwist when placed under load and is generally selected where long ropes are employed and the loads handled are fre- quently removed. Lang lay ropes have greater flexibility than regular lay ropes and are more resistant to abrasion and fatigue. In preformed wire ropes the wires and strands are preshaped into a helical form so that when laid to form the rope they tend to remain in place. In a non-preformed rope, broken wires tend to “wicker out” or protrude from the rope and strands that are not seized tend to spring apart. Preforming also tends to remove locked-in stresses, lengthen service life, and make the rope easier to handle and to spool. Strand Construction: Various arrangements of wire are used in the construction of wire rope strands. In the simplest arrangement six wires are grouped around a central wire thus making seven wires, all of the same size. Other types of construction known as “filler- wire,” Warrington, Seale, etc. make use of wires of different sizes. Their respective pat- terns of arrangement are shown diagrammatically in the table of wire weights and strengths. Specifying Wire Rope.—In specifying wire rope the following information will be required: length, diameter, number of strands, number of wires in each strand, type of rope construction, grade of steel used in rope, whether preformed or not preformed, type of cen— ter, and type of lay. The manufacturer should be consulted in selecting the best type of wire rope for a new application. Properties of Wire Rope.—Important properties of wire rope are strength, wear resis- tance, flexibility, and resistance to crushing and distortion. Strength: The strength of wire rope depends upon its size, kind of material of which the wires are made and their number, the type of core, and whether the wire is galvanized or not. Strengths of various types and sizes of wire ropes are given in the accompanying tables together with appropriate factors to apply for ropes with steel cores and for galvanized wire ropes. WearResistance: When wire rope must pass back and forth over surfaces that subject it to unusual wear or abrasion, it must be specially constructed to give satisfactory service. Such construction may make use of 1) relatively large outer wires; 2) Lang lay in which wires in each strand are laid in the same direction as the strand; and 3) flattened strands. The object in each type is to provide a greater outside surface area to take the wear or abrasion. From the standpoint of material, improved plow steel has not only the highest tensile strength but also the greatest resistance to abrasion in regularly stocked wire rope. WIRE ROPE 335 Flexibility: Wire rope that undergoes repeated and severe bend' ‘ ' mg, such as 1n assm around small sheaves and drums, must have a high degree of flexibility to preventfprem: ture breakage and failure due to fatigue. Greater flexibility in wire rope is obtained by 1) using small wires in larger numbers; 2) using Lang lay; and 3) preforming, that is the wires and strands of the rope are sha ed durin man f tu ' ’ ' assume in the fiIfiShed rope. p g u ac re to fit the posrtion they wrll Resistance to Crushing and Distortion: Where wire rope is to be subjected to transverse loads that may crush or distort it care should be ' , taken to select a of co ‘ W111 stand up under such treatment. type nsmcnon that Wire rope designed for such conditions may have 1) large outer wires to spread the load Per Wire over a greater area' and 2) an independent wire core 0 ' . ' r a hl h-carbo - wound sprmg core. g 1'1 001d drawn Standard Classes of Wire Rope.—Wire ro is commonl de ' the first indicating the number of strands and Eh: second, the nyiimtféfgfisggypgguigidrzz: 6 x 7,-a Six—strand rope having seven wires per strand, or 8 X 19, an eight-strand rope havin . 19 w1res per strand. When such numbers are used as designations of stande wire ro g classes, the second figire in the designation may be purely nominal in that the numbergef Wires per strand for various ropes in the class may be slightly less or slightly more than the nominal as w1ll be seen from the following brief descriptions. (For ropes with a wire strand core, a second group of two numbers may be used to indi ‘ ‘ cate the constru core, as 1 x21, 1 X43, and so on.) cuon Ofme wue 6.x 7 Class (Standard Coarse Laid Rope): Wire ropes in this class are for use where resrstance to wear, as in dragging over the ground or across rollers, is an important require- ment. Heavy hauling, rope transmissions, and well drilling are common applications These w1re ropes are furnished in right regular lay and occasionally in Lang lay. The cores may be of fiber, independent wire rope, or wire strand. Since this class is a relatively stiff type of construction these ropes should be used with lar , ' ge sheaves and drums. B the small number of Wires, a larger factor of safety may be called for. ecause 0f Fig. la. Fig. lb. Fig. 1c. Fig. 1d. 6X7withfiberc0re 6X7with1X7WSC 6X7with1Xl9WSC 6x7withIWRC As shown in Figs. la through Figs. 1d, this class includes a 6 x 7 construction with fiber core: a 6 x 7 construction with l x 7 wire strand core (sometimes called 7 x 7); a 6 x 7 con- struction with 1 x 19 wire strand core' and a 6 x 7 construction with ' ' o , inde d t core. Table l provrdes strength and weight data for this class. pen en Wire rope Two special types of wire rope in this class are: aircraft cord, a 6 x 6 or 7 x 7 Bethanized wire rope of high tensile strength and sash cord a 6 x 7 iro ‘ . , n to e used for a vane - poses where strength 15 not an important factor. p ty 0f pm Ana-1a.. 336 WIRE ROPE Table 1. Weights and Strengths of 6 x 7 (Standard Coarse Laid) Wire Ropes, Preformed and Not Preformed Breaking Strength. Breaking Strength. Tons of 2000 Lbs. Tons of 2000 Lbs. Approx. Impr. Mild Weight Impr. Plow Plow per FL, Plow Steel Steel Pounds Steel For ropes with steel cores, add 7VZ per cent to above strengths. For galvanized ropes, deduct 10 per cent from above strengths. Source: Rope diagrams, Bethlehem Steel Co. All data, U.S. Simplified Practice Recommendation 198—50. 6 x 19 Class (Standard Hoisting Rope): This rope is the most popular and widely used class. Ropes in this class are furnished in regular or Lang lay and may be obtained pre- formed or not preformed. Cores may be of fiber, independent wire rope, or wire strand. As can be seen from Table 2 and Figs. 2a through 2h, there are four common types: 6 X 25 filler wire construction with fiber core (not illustrated), independent wire core, or wire strand core (1 x 25 or 1 x 43); 6 x 19 Warrington construction with fiber core; 6 X 21 filler wire construction with fiber core; and 6 x 19, 6 X 21, and 6 x 17 Scale construction with fiber core. Table 2. Weights and Strengths of 6 x 19 (Standard Hoisting) Wire Ropes, Preformed and Not Preformed Breaking Strength, Tons of 2000 Lbs. Breaking Strength, Tons of 2000 Lbs. Impr. Plow Impr. Mild Plow Plow Dia., Steel Steel lnches Steel The 6 x 25 filler wire with fiber core not illustrated. For ropes with steel cores, add 7 )3 per cent to above strengths. For galvanized ropes, deduct 10 per cent from above strengths. Source: Rope diagrams, Bethlehem Steel Co. All data, U.S. Simplified Practice Recommendation 198-50. 337 Fig. 2a. Fig. 2b. Fi .2c. ' 6x 25 filler wire 6 x 25 filler wire 6 x 1E9 Scale 6 f Sgale w1th WSC (l X 25) with IWRC with fiber core with fiber core Fig. 2e. Fig 2f Fig 2 ' . . _. . g. F1 . 2h. 6x 25 filler Wire 6 X 19 Warrmgton 6 x 17 Scale 6 X 21 fgiller wire w1th WSC (1 X 43) With fiber core with fiber core with fiber core 6x 37 Class ( Extra lexible Hoisting Rope): For a given size of rope, the component Wires are of smaller drameter than those in the two classes previously described and hence have less resistance to abrasion. Ropes in this class are furnished in regular and Lang lay w1th fiber core or mdependent wire rope core, preformed or not preformed. Table 3. Weights and Strengths of 6 X 37 (Extra Flexible Hoisting) Wire Ropes, Preformed and Not Preformed ' Breaking Strength, Tons of 2000 Lbs. Impr. Plow Plow Steel Steel Breaking Strength, Tons of 2000 Lbs. Impr. Plow Plow Steel Steel For ropes with steel cores, add 7%per cent to above strengths. For galvanized ropes, deduct 10 per cent from above strengths. 1 9.Séotgace: Rope diagrams, Bethlehem Steel Co. All data, U. S. Simplified Practice Recommendation As shown in Table 3 and Figs. 3a through 3h, there are four common types: 6 x 29 filler Wll'e construction w1th fiber core and 6 x 36 filler wire construction with independent wire Adina. 338 WIRE ROPE ' ro for construction equipment; 6 X 35 (two operations) construction :25: 33:1: gsgemla >321 Warrington Seale construction with fiber core, a standard crane rope in this class of rope construction; 6 x 41 filler Wire construction With fiber ggre 2; independent wire core, a special large shovel rope usually furnished in Lang lay, an 11X 1 filler wire construction with fiber core or independent Wire rope core, a speCial arge s ove and dredge rope. ' ' Fi . 3c. Fig. 3d. 6 x zigligiififiwire fig 3b. g 6 x 41 Wamngton-Seale with fiber core with IWRC with fiber core I ‘ ' Fig. 3h. F' . 3 . Fig. 3f. Fig. 3g. . p 6 x 41%“; wire 6 x 41 filler wire 6 X 46 filler Wire 6 X filler \Eire with fiber core with [W RC With fiber core W1 IW R ' ' ‘ ' ' ‘ ' ble and smooth-running, 8 X 19 Class (S ectal F lextble Horstmg RopeTlus rope is sta ‘ . and is especiallypsuitable, because of its fleXibility, for. high speed operation With reverse bends. Ropes in this class are available in regular lay With fiber core. As shown in Table 4 and Figs. 4a through 4d, there are four common types: 8 X 25 filler ' ' ‘ ' f the four types; War- onstruction, the most flexrble but the least wear res1stant rope o I zilirgign type in 8 X 19 construction, less flexible than the 8 X 25; 8 X 21 filler Wire construc- tion, less flexible than the Warrington; and Scale type in 8 X 19 construction, which has the greatest wear resistance of the four types but is also the least flexrble. Table 4. Weights and Strengths of 8 X 19 (Special Flexible Hoisting) Wire Ropes, Preformed and Not Preformed ‘ Breaking Strength, gynfligztsxt)‘; Tons of 2000 Lbs. Impr. Plow Plow Steel Steel lmpr. Plow Steel 2.04 3.18 For ropes with steel cores, add 7%per cent to above strengths. For alvanized ro s, deduct 10 per cent from above strengths. . I I Sourgce: Rope diagrams, Bethlehem Steel Co. All data, U. S. Simplified Practice Recommendation 198-50. 4“ . WIRE ROPE 339 Fig. 43. Fig. 4b. Fig. 4c. Fig. 4d. 8 x 25 filler wire 8 X 19 Warrington 8 X 21 filler wire 8 X 19 Scale with fiber core with fiber core with fiber core with fiber core Also in this class, but not shown in Table 4 are elevator ropes made of traction steel and iron. 18 X 7Non-rotating Wire Rope: This rope is specially designed for use where a mini- mum of rotating or spinning is called for, especially in the lifting or lowering of free loads with a single-pan line. It has an inner layer composed of 6 strands of 7 wires each laid in left Lang lay over a fiber core and an outer layer of 12 strands of 7 wires each laid in right reg- ular lay. The combination of opposing lays tends to prevent rotation when the rope is stretched. However, to avoid any tendency to rotate or spin, loads should be kept to at least one-eighth and preferably one-tenth of the breaking strength of the rope. Weights and strengths are shown in Table 5. Table 5. Weights and Strengths of Standard 18 X 7 Nonrotating Wire Rope, Preformed and Not Preformed Recommended Sheave and Drum Diameters: Single layer on drum 36 rope diameters. Multiple layers on drum 48 rope diameters. Mine service 6O rope diameters. Breaking Strength, Breaking Strength, Tons of 2000 Lbs. Approx. Tons of 2000 Lbs. Weight. Impr. Weight Impr. per Ft., Plow Plow per FL, Plow Pounds Steel Steel Pounds Steel 8 For galvanized ropes, deduct 10 per cent from above strengths. Source: Rope diagrams, sheave and drum diameters, and data for 3/16, '4 and 5/16-inch sizes, Bethle- hem Steel Co. All other data, U. S. Simplified Practice Recommendation 198-50. F lattened Strand Wire Rope: The wires forming the strands of this type of rope are wound around triangular centers so that a flattened outer surface is provided with a greater area than in the regular round rope to withstand severe conditions of abrasion. The triangu- AIJRII a. 340 WIRE ROPE lar shape of the strands also provides superior resistance to crushing. Flattened strand wire rope is usually fumished in Lang lay and may be obtained with fiber core or independent wire rope core. The three types showu in Table 6 and Figs. 6a through 6c are flexible and are designed for hoisting work. Fig. 6a. Fig. 6b. Fig. 6c. 6 X 25 with fiber core 6 x 30 with fiber core 6 x 27 with fiber core Table 6. Weights and Strengths of Flattened Strand Wire Rope, Preformed and Not Preformed Breaking Strength, Tons of 2000 Lbs. Breaking Strength. Tons of 2000 Lbs. Impr. Mild Impr. Mild Plow Plow Plow Plow Steel Steel Steel Steel ‘ These sizes in Type B only. Type H is not in US. Simplified Practice Recommendation. Source: Rope diagrams, Bethlehem Steel Co. All other data, U.S. Simplified Practice Recommen- dation 198-50. Flat Wire Rope: This type of wire rope is made up of a number of four-strand rope units placed side by side and stitched together with soft steel sewing wire. These four-strand units are alternately right and left lay to resist warping, curling, or rotating in service. Weights and strengths are shown in Table 7. Simplified Practice Recommendations—Because the total number of wire rope types is large, manufacturers and users have agreed upon and adopted a US. Simplified Practice Recommendation to provide a simplified listing of those kinds and sizes of wire rope which are most commonly used and stocked. These, then, are the types and sizes which are most generally available. Other types and sizes for special or limited uses also may be found in individual manufacturer's catalogs. Sizes and Strengths of Wire Rope—The data shown in Tables 1 through 7 have been taken from US. Simplified Practice Recommendation 198-50 but do not include those wire ropes shown in that Simplified Practice Recommendation which are intended prima- rily for marine use. Wire Rope Diameter: The diameter of a wire rope is the diameter of the circle that will just enclose it, hence when measuring the diameter with calipers, care must be taken to obtain the largest outside dimension, taken across the opposite strands, rather than the smallest dimension across opposite “valleys” or “flats.” It is standard practice for the nom- inal diameter to be the minimum with all tolerances taken on the plus side. Limits for diam- WIRE ROPE 341 eter as well as for minimum breaking strength and maximum itch are iven ' F (1 a1 Specification for Wire Rope, RR-R—57 la. p g m 6 er Wire Rope Strengths: The strength figures shown in the accompanying tables have been obtained by a mathematical derivation based on actual breakage tests of wire rope and rep- resent from 80 to 95 per cent of the total strengths of the individual wires, depending upon the type of rope construction. Table 7. Weights and Strengths of Standard Flat Wire Rope, Not Preformed eeeeeeeaee Flat Wire Rope Breaking Strength. , Tons of 2000 Lbs. This rope consists of a number of 4—strand rope units placed side by side and stitched together with soft steel sewing wire. Breaking Strength. Tons of 2000 Lbs. Approx. Mild Weight Mild Plow- per FL, Plow Steel Pounds Steel lgiousrge: Rope diagram, Bethlehem Steel Co.; all data, U.S. Simplified Practice Recommendation Safe Working Loads and Factors of Safety.——The maximum load for which a wire rope Is to used should take into account such associated factors as friction, load caused by bending around each sheave, acceleration and deceleration, and, if a long length of rope is to be used for horstmg, the weight of the rope at its maximum extension. The condition of the rope —— whether new or old, worn or corroded — and type of attachments should also be considered. Factors of safety for standing rope usually range from 3 to 4; for operating rope, from 5 to 12. Where there is the element of hazard to life or property, higher values are used. Installing Wire Rope.—The main precaution to be taken in removing and installing wire rope is to av01d kinking which greatly lessens the strength and useful life. Thus, it is pref- erable when removing wire rope from the reel to have the reel with its axis in a horizontal pos1t10n and, if possible, mounted so that it will revolve and the wire rope can be taken off Adina. 342 WIRE ROPE straight. If the rope is in a coil, it should be unwound with the coil in a vertical position as by rolling the coil along the ground. Where a drum is to be used, the rope should be run directly onto it from the reel, taking care to see that it is not bent around the drum in a direc- tion opposite to that on the reel, thus causing it to be subject to reverse bending. On flat or smooth-faced drums it is important that the rope be started from the proper end of the drum. A right lay rope that is being overwound on the drum, that is, it passes over the top of the drum as it is wound on, should be started from the right flange of the drum (looking at the _ drum from the side that the rope is to come) and a left lay rope from the left flange. When the rope is underwound on the drum, a right lay rope should be started from the left flange and a left lay rope from the right flange, so that the rope will spool evenly and the turns will lie snugly together. CENTER FLEET LINE WIRE ROPE I Sheaves and drums should be properly aligned to prevent undue wear. The proper posi- tion of the main or lead sheave for the rope as it comes off the drum is governed by what is called the fleet angle or angle between the rope as it stretches from drum to sheave and an imaginary center-line passing through the center of the sheave groove and a point halfway between the ends of the drum. When the rope is at one end of the drum, this angle should not exceed one and a half to two degrees. With the lead sheave mounted with its groove on this center-line, a safe fleet angle is obtained by allowing 30 feet of lead for each two feet of drum width. Sheave and Drum Dimensions: Sheaves and drums should be as large as possible to obtain maximum rope life. However, factors such as the need for lightweight equipment for easy transport and use at high speeds, may call for relatively small sheaves with conse- quent sacrifice in rope life in the interest of overall economy. No hard and fast rules can be laid down for any particular rope if the utmost in economical performance is to be obtained. Where maximum rope life is of prime importance, the following recommenda- tions of Federal Specification RR—R-571a for minimum sheave or drum diameters D in terms of rope diameter d will be of interest. For 6 x 7 rope (six strands of 7 wires each) D = 72d; for 6 x19 rope, D = 45d; for 6 x 25 rope, D = 45d; for 6 X 29 rope, D = 30d; for 6 x 37 rope, D = 27d; and for 8 x19 rope, D = 31d. Too small a groove for the rope it is to carry will prevent proper seating of the rope in the bottom of the groove and result in uneven distribution of load on the rope. Too large a groove will not give the rope sufficient side support. Federal specification RR-R-57 1 a rec- ommends that sheave groove diameters be larger than the nominal rope diameters by the following minimum amounts: For ropes of X,- to 546-inch diameters, V64 inch larger; for 3/3- to X—inch diameter ropes, V32 inch larger; for 13/16- to Mar-inch diameter ropes, 3/64 inch larger; for 13/16- to llg-inch ropes, V16 inch larger; for 19/16- to ZZ-inch ropes, V32 inch larger; and for 25/16 and larger diameter ropes, lginch larger. For new or regrooved sheaves these values should be doubled; in other words for Z,- to 5/16-inch diameter ropes, the groove diameter should be V32 inch larger, and so on. Drum or Reel Capacity: The length of wire rope, in feet, that can be spooled onto a drum or reel, is computed by the following formula, where A =depth of rope space on drum, inches: A = (H — D — 2Y) + 2 B = width between drum flanges, inches D = diameter of drum barrel, inches WIRE ROPE 343 H = diameter of drum flanges, inches K = factor from Table 8 for size of line selected Y = depth not filled on drum or reel where winding is to be less than full capacity L = length of wire rope on drum or reel, feet. L = (A+D)XA><B><K Table 8. Table 8 Factors K Used in Calculating Wire Rope Drum and Reel Capacities . Note: The values of “K” allow for normal oversize of ropes, and the fact that it is practically impos- sible to “thread-win ” ropes of small diameter. However, the formula is based on uniform rope wind- ing and Will. not give correct figures if rope is wound non-uniformly on the reel. The amount of tension applied when spooling the rope will also affect the length. The formula is based on the same number of wraps of rope in each layer, which is not strictly correct, but which does not result in Eplpreciable error unless the width (B) of the reel is quite small compared with the flange diameter Example: Find the length in feet of 9/16-inch diameter rope required to fill a drum having the followmg dimensions: B = 24 inches, D = 18 inches, H = 30 inches, A = (30—18—0)+2 = 6inches L = (6+ 18) X6X24x0.741 = 2560.0 or 2560 feet The above'formula and factors K allow for normal oversize of ropes but will not give cor- rect figures 1f rope lS wound non-uniformly on the reel. Load Capacity of Sheave or Drum: To avoid excessive wear and groove corrugation, the radial pressure. exerted by the Wire rope on the sheave or drum must be kept within certain maxrmum lirmts. The radlal pressure of the rope is a function of the rope tension, rope diameter, and tread diameter of the sheave and can be determined by the following equa- tron: where P = Radial pressure in pounds per square inch (see Table 9) T = Rope tension in pounds D = Tread diameter of sheave or drum in inches d = Rope diameter in inches ..._..._.. , ,,,.i ...... ,,A,_._____mmm~mmmm___wa Adina. 344 WIRE ROPE Table 9. Maximum Radial Pressures for Drums and Sheaves Drum or Sheave Material Cast Cast Manganese Iron Steel Steel‘ Recommended Maximum Radial Pressures, Pounds per Square Inch 300” 1500” 500“ Type of Wire Rope 6 x 7 550b 6 x 19 9005 2500” 6 x 37 600 1075 6 x 8 Flattened Strand 450 850 6 X 25 Flattened Strand 1450 6 X 30 Flattened Strand 1450 ‘ l l to 13 per cent manganese. b These values are for regular lay rope. For Lang lay rope these values may be increased by 15 per cent. According to the Bethlehem Steel Co. the radial pressures shown in Table 9 are recom- mended as maximums according to the material of which the sheave or drum is made. Rope Loads due to Bending: When a wire rope is bent around a sheave, the resulting bending stress 5,, in the outer wire, and equivalent bending load Pb (amount that direct ten- sion load on rope is increased by bending) may be computed by the following formulas: sb = Edw + D; Pb = sbA, where A = dZQ. E is the modulus of elasticity of the wire rope (varies with the type and condition of rope from 10,000,000 to 14,000,000. An average value of 12,000,000 is frequently used), d is the diameter of the wire rope, dw is the diameter of the component wire (for 6 X 7 rope, dw = 0.106d; for 6 x 19 rope, 0.063d; for 6 x 37 rope, 0.045d; and for 8 X 19 rope, dw = 0.050(1). D is the pitch diameter of the sheave in inches, A is the metal cross-sectional area of the rope, and Q is a constant, values for which are: 6 X 7 (Fiber Core) rope, 0.380; 6 X 7 (IWRC or WSC), 0.437; 6 x 19 (Fiber Core), 0.405; 6 x 19 (IWRC or WSC), 0.475; 6 X 37 (Fiber Core), 0.400; 6 x 37 (IWRC), 0.470; 8 x 19 (Fiber Core), 0.370; and Flattened Strand Rope, 0.440. Example: Find the bending stress and equivalent bending load due to the bending of a 6 x 19 (Fiber Core) wire rope of Vz-inch diameter around a 24-inch pitch diameter sheave. dw = 0.063 x0.5 = 0.0315 in. A = 0.52XO.405 = 0.101 sq. in. sb = 12,000,000X0.0315+24 = 15,750 lbs. per sq. in. Pb = 15,750x0.101 = 1590 lbs. Cutting and Seizing of Wire Rope—Wire rope can be cut with mechanical wire rope shears, an abrasive wheel, an electric resistance cutter (used for ropes of smaller diameter only), or an acetylene torch. This last method fuses the ends of the wires in the strands. It is important that the rope be seized on either side of where the cut is to be made. Any annealed low carbon steel wire may be used for seizing, the recommended sizes being as follows: For a wire rope of if; to l-§’16-inch diameter, use a seizing wire of 0.054—inch (No. 17 Steel Wire Gage); for a rope of 1- to 15/g-inch diameter, use a 0.105-inch wire (No. 12); and for rope of 132- to 3 Vz-inch diameter, use a 0.135-inch wire (No. 10). Except for preformed wire ropes, a minimum of two seizings on either side of a cut is recommended. Four seizings should be used on either side of a cut for Lang lay rope, a rope with a steel core, or a non- spinning type of rope. The following method of seizing is given in Federal specification for wire rope, RR-R- 571a. Lay one end of the seizing wire in the groove between two strands of wire rope and wrap the other end tightly in a close helix over the portion in the groove. A seizing lI'OIl WIRE ROPE 345 (round bar lg to V8 inch diameter by 18 inches long) should be used to wrap the seizing tightly. This bar is placed at right angles to the rope next to the first turn or two of the seiz- ing wire. The seizing wire is brought around the back of the seizing iron so that it can be wrapped loosely around the wire rope in the opposite direction to that of the seizing coil. As the seizing iron is now rotated around the rope it will carry the seizing wire snugly and tightly into place. When completed, both ends of the seizing should be twisted together tightly. Maintenance of Wire Rope.—Heavy abrasion, overloading, and bending around sheaves or drums that are too small in diameter are the principal reasons for the rapid dete- rioration of wire rope. Wire rope in use should be inspected periodically for evidence of wear and damage by corrosion. Such inspections should take place at progressively shorter intervals over the useful life of the rope as wear tends to accelerate with use. Where wear is rapid, the outside of a wire rope will show flattened surfaces in a short time. If there is any hazard involved in the use of the rope, it may be prudent to estimate the remaining strength and service life. This assessment should be done for the weakest point where the most wear or largest number of broken wires are in evidence. One way to arrive at a conclusion is to set an arbitrary number of broken wires in a given strand as an indica- tion that the rope should be removed from service and an ultimate strength test run on the worn sample. The arbitrary figure can then be revised and rechecked until a practical work- ing formula is arrived at. A piece of waste rubbed along the wire rope will help to reveal broken wires. The effects of corrosion are not easy to detect because the exterior wires may appear to be only slightly rusty, and the damaging effects of corrosion may be confined to the hidden inner wires where it cannot be seen. To prevent damage by corrosion, the rope should be kept well lubricated. Use of zinc coated wire rope may be indicated for some applications. Periodic cleaning of wire rope by using a stiff brush and kerosene or with compressed air or live steam and relubricating will help to lengthen rope life and reduce abrasion and wear on sheaves and drums. Before storing after use, wire rope should be cleaned and lubricated. Lubrication of Wire Rope—Although wire rope is thoroughly lubricated during manu- facture to protect it against corrosion and to reduce friction and wear, this lubrication should be supplemented from time to time. Special lubricants are supplied by wire rope manufacturers. These lubricants vary somewhat with the type of rope application and operating condition. Where the preferred lubricant can not be obtained from the wire rope manufacturer, an adhesive type of lubricant similar to that used for open gearing will often be found suitable. At normal temperatures, some wire rope lubricants may be practically solid and will require thinning before application. Thinning may be done by heating to 160 to 200 degrees F. or by diluting with gasoline or some other fluid that will allow the lubri- cant to penetrate the rope. The lubricant may be painted on the rope or the rope may be passed through a box or tank filled with the lubricant. Replacement of Wire Rope.——When an old wire rope is to be replaced, all drums and sheaves should be examined for wear. All evidence of scoring or imprinting of grooves from previous use should be removed and sheaves with flat spots, defective bearings, and broken flanges, should be repaired or replaced. It will frequently be found that the area of maximum wear is located relatively near one end of the rope. By cutting off that portion, the remainder of the rope may be salvaged for continued use. Sometimes the life of a rope can be increased by simply changing it end for end at about one-half the estimated normal life. The worn sections will then no longer come at the points that cause the greatest wear. Wire Rope Slings and Fittings—A few of the simpler sling arrangements or hitches as they are called, are shown in the accompanying illustration. Normally 6 X 19 Class wire rope is recommended where a diameter in the 11—inch to lig-inch range is to be used and 6 x 37 Class wire rope where a diameter in the 1 Z—inch and larger range is to be used. However, 15.7mm. ‘W'WWYWMM 346 WIRE ROPE the 6 x 19 Class may be used even in the larger sizes if resistance to abrasion is of primary importance and the 6 x 37 Class in the smaller sizes if greater flexibility is desired. Wire Rope Slings and Fittings 2000 lb Straight Leg Vertical Straight Lift Basket Hitch Basket Hitch One leg Vertical. Load capacity Two legs vertical. Load capacity Two Legs at 30 deg with the ver- is 100 pct of a single rope. is 200 pct of the single rope in the tical. Load capacity is 174 pct of ' Straight Lift Hitch (A). the single rope in the Straight Lift Hitch (A). Choker Hitch Two legs at 60 deg with the verti- One leg vertical, with slip- cal. Load capacity is 100 pct of through loop. Rated capacity is the single rope in the Straight the single rope in the Stright Lift 75 pct of the single rope in the Lift Hitch (A). Hitch (A). Straight Lift Hitch (A). The straight lift hitch, shown at A, is a straight connector between crane hook and load. The basket hitch may be used with two hooks so that the sides are vertical as shown at B or with a single hook with sides at various angles with the vertical as shown at C, D, and E. As the angle with the vertical increases, a greater tension is placed on the rope so that for any given load, a sling of greater lifting capacity must be used. Basket Hitch Basket Hitch Two legs at 45 deg with the verti- cal. Load capacity is 141 pct of WIRE ROPE 347 The choker hitch shown at F is widely used for liftin ’ . . ,. . , g bundles of items such b poles, pipe, and Slmllal' objects. The choker hitch holds these items firmly as am, but the load must be balanced so that it rides safel ' ' ' ‘ ' I I y. Since additional stress is 1m osed o the rope due to the choking action, the capacity of this type of hitch is 25 per cent IlJess thaitl that of the comparable straight lift If two choker hitches are used at an . . an 1 , th must also be taken into consideration as with the basket hitches. g e 686 angles Industrial Types w IW Round Eye R 0 d Eye st-Hook W]: I; :— Button-Stop Threaded Stud \\\Vl Swaged Closed Socket Swaged Open Socket Aircraft Types Single-Shank Ball Double-Shank Ball m Eye Fork Strap-Eye Strap-Fork Wire Rope Fittings Wire Rope Fittings.—Many varieties of swaged fittin s are available for ' ' rope and seyeral industrial and aircraft types are showngin the accompanyinlgsicllilvsltil'hat‘ilclihe Swaged fittings on wire rope have an efficiency (ability to hold the wire rope) of approxi: mately 100 per cent of the catalogue rope strength. These fittings are attached to the end or body of the Wire rope by the application of high pressure through special dies that cause the Afilh 34s WIRE ROPE material of the fitting to “flow” around the wires and strands of the rope to form a union that is as strong as the rope itself. The more commonly used types, of swaged fittings range from lg- to ég-inch diameter sizes in industrial types and from the V16- to 9/3-inch sizes in air- craft types. These fittings are furnished attached to the wire strand, rope, or cable. Applying Clips and Attaching Sockets.—In attaching U-bolt clips for fastening the end of a wire rope to form a loop, it is essential that the saddle or base of the clip bears against the longer or “live” end of the rope loop and the U-bolt against the shorter or “dead” end. The “U” of the clips should never bear against the live end of the rope because the rope may be cut or kinked. A wire-rope thimble should be used in the loop eye of the rope to prevent kinking when rope clips are used. The strength of a clip fastening is usually less than 80 percent of the strength of the rope. Table 10 gives the proper size, number, and spacing for each size of wire rope. Table 10. Clips Required for Fastening Wire Rope End 2 F I: a: a O m .2 I" E m a In V OOOOOOQOGO‘LII 2 2 2 2 3 3 4 4 4 In attaching commercial sockets of forged steel to wire rope ends, the following proce- e . dure is recommended. The wire rope is seized at the end and another seizing is applied at a distance from the end equal to the length of the basket of the socket. As explained in a pre- vious section, soft iron wire is used and particularly for the larger sizes of wire rope, it is important to use a seizing iron to secure a tight winding. For large ropes, the seizing should be several inches long. The end seizing is now removed and the strands are separated so that the fiber core can be cutback to the next seizing. The individual wires are then untwisted and “broomed out” and for the distance they are to be inserted in the socket are carefully cleaned with benzine, naphtha, or unleaded gasoline. The wires are then dipped into commercial muriatic (hydro- chloric) acid and left (usually one to three minutes) until the wires are bright and clean or, if zinc coated, until the zinc is removed. After cleaning, the wires are dipped into a hot soda solution (1 pound of soda to 4 gallons of water at 175 degrees F. minimum) to neutralize the acid. The rope is now placed in a vise. A temporary seizing is used to hold the wire ends together until the socket is placed over the rope end. The temporary seizing is then removed and the socket located so that the ends of the wires are about even with the upper end of the basket. The opening around the rope at the bottom of the socket is now sealed with putty. A special high grade pure zinc is used to fill the socket. Babbit metal should not be used as it will not hold properly. For proper fluidity and penetration, the zinc is heated to a tem- perature in the 830- to 900—degree F. range. If a pyrometer is not available to measure the temperature of the molten zinc, a dry soft pine stick dipped into the zinc and quickly with- drawn will show only a slight discoloration and no zinc will adhere to it. If the wood chars, the zinc is too hot. The socket is now permitted to cool and the resulting joint is ready for use. When properly prepared, the strength of the joint should be approximately equal to that of the rope itself. Single Leg, 6 x [9 Wire Rope TWO-Leg Bridle or Basket Hitch, 6 X 19 Wire Rope Sling ,‘ wan-me nun—nu 2 e U 3. e a: E B H s: d) '1: r: U a. 0 c s: 1 m E é N “- e E 3 .E V a Q) 8‘ r: O .‘.: 1: t: N 0 a. O M Q .'.: E 8 m B 2 91 E S L: E I- 8 m .2 .7: i a U '5 i3 :4 Rope Diameter (In ) um. 4-Hn- . re Rope and Wire Rope Slings (in tons of 2,000 lbs)—Fiber Core 6 x 19 Wire Rope Single Leg. i TWO—Leg Bridle or Basket Hitch, 6 X 37 Wire Rope Sling Rated Capacities for Improved Plow Steel W A—socket or swaged terminal attachment; B—mechanical sleeve attachment; C—hand-tucked splice attachment. Data taken from Longshoring Industry, OSHA Safety and Health Standards Digest, OSHA 2232, 1985. “ma-MW__, , CRANE CHAIN AND HOOKS 351 CRANE CHAIN AND HOOKS Material for Crane Chains.——The best material for crane and hoisting chains is a good grade of wrought iron, in which the percentage of phosphorus, sulfur, silicon, and other impurities is comparatively low. The tensile strength of the best grades of wrought iron does not exceed 46,000 pounds per square inch, whereas mild steel with about 0.15 per cent carbon has a tensile strength nearly double this amount. The ductility and toughness of wrought iron, however, is greater than that of ordinary commercial steel, and for this rea- son it is preferable for chains subjected to heavy intermittent strains, because wrought iron will always give warning by bending or stretching, before breaking. Another important reason for using wrought iron in preference to steel is that a perfect weld can be effected more easily. Heat-treated alloy steel is also widely used for chains. This steel contains car- bon, 0.30 per cent, max; phosphorus, 0.045 per cent, max; and sulfur, 0.045 per cent, max. The selection and amounts of alloying elements are left to the individual manufacturers. Strength of Chains—When calculating the strength of chains it should be observed that the strength of a link subjected to tensile stresses is not equal to twice the strength of an iron bar of the same diameter as the link stock, but is a certain amount less, owing to the bending action caused by the manner in which the load is applied to the link. The strength is also reduced somewhat by the weld. The following empirical formula is commonly used for calculating the breaking load, in pounds, of wrought-iron crane chains: W = 54,000D2 in which W= breaking load in pounds and D = diameter of bar (in inches) from which links are made. The working load for chains should not exceed one-third the value of W, and, it is often one-fourth or one-fifth of the breaking load. When a chain is wound around a cast— ing and severe bending stresses are introduced, a greater factor of safety should be used. Care of Hoisting and Crane Chains.—Chains used for hoisting heavy loads are subject to deterioration, both apparent and invisible. The links wear, and repeated loading causes localized deformations to form cracks that spread until the links fail. Chain wear can be reduced by occasional lubrication. The life of a wrought-iron chain can be prolonged by frequent annealing or normalizing unless it has been so highly or frequently stressed that small cracks have formed. If this condition is present, annealing or normalizing will not “heal” the material, and the links will eventually fracture. To anneal a wrought-iron chain, heat it to cherry-red and allow it to cool slowly. Annealing should be done every six months, and oftener if the chain is subjected to unusually severe service. Maximum Allowable Wear at Any Point of Link Sourcelongsharing Industry, OSHA 2232, 1985. Chains should be examined periodically for twists, as a twisted chain will wear rapidly. Any links that have worn excessively should be replaced with new ones, so that every link will do its full share of work during the life of the chain, without exceeding the limit of safety. Chains for hoisting purposes should be made with short links, so that they will wrap closely around the sheaves or drums without bending. The diameter of the winding drums should be not less than 25 or 30 times the diameter of the iron used for the links. The accompanying table lists the maximum allowable wear for various sizes of chains. \ Adi-1a.. ...
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This note was uploaded on 10/01/2009 for the course MEGR 2144 taught by Professor Sharpe during the Fall '08 term at UNC Charlotte.

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Wire_Rope_MH_section - 332 Wire Diam(inch SPRINGS Table 23 Arbor Diameters for Springs Made from Music Wire Spring Outside Diameter(inch Arbor

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