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Wire_Rope_MH_section - 332 Wire Diam(inch SPRINGS Table 23...

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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 br...
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