If it is worn off-center, thereby forcing the rope to undercut or to rub against the flange, it then becomes necessary to correct the alignment of the reeving system, and to specify a harder material. When checking the grooves, the bearings of the sheaves and rollers should also be examined. They should turn easily. If not, each bearing must be properly lubricated. Bad bearings will set up vibrations in the wire rope that can cause rapid deterioration unless the condition is remedied.
Bad bearings also increase the force on the rope that is needed to move a given load, since friction forces will be greatly increased. Sheaves with broken flanges may allow the rope to jump from the sheave and become fouled in the machinery. When this happens, the rope is cut; curled, and the crowns of the wires in the strands are burred. There is ample evidence to support then. This condition helps to accelerate the fatigue breakage of wires.
Sometimes the reeving is such that the whip or wave is arrested by a sheave. In these circumstances. For example, plain-face smooth drums can develop grooves or rope impressions that will prevent the rope from winding properly.
Imprinting is. If this happens, the surface should be repaired by machining or replaced. The winding should be checked to make sure that the rope is winding "thread wound" Fig. Excessive wear in grooved drums should be checked for variations either in the depth or pitch of the grooves.
This condition is particularly critical when double drums are used because a differential force will be set up that can break the drum and shear the shaft.
No matter what type of drum is in use, excessive drum wear will usually result in rapid rope deterioration, This condition will accelerate rapidly when winding in multiple layers. If, however, the rope passes over acurved surface such asa sheave or pin its strength "is decreased. At smaller bid ratios, the loss in strength increases quite rapidly. Derived from standard test data. The curve is based on i i I i!
The schematic drawing Fig. The fleet angle Fig. There are left and right fleet angles. This illustration of wire rope running from a fixed sheave. Correct appraisal of the following will simplify the selection process: 1 Strength-resistance to breaking 2 Resistance to bending fatigue 3 Resistance 10 vibrational fatigue 4 Resistance to abrasion 5 Resistance to crushing 6 Reserve strength It is well-nigh impossible for any single rope to have top values in all of the above qualities. The first task is to make a careful analysis of the job requirements, establishing priorities among these requirements, and then selecting the rope on a trade-off basis.
This will provide the best possible balance by sacrificing the least essential advantages in order to obtain maximum benefits in the most important requirements. Following, are brief explanations ofthe six factors previously listed: 1 Strength-resistance to breaking. Thus, the very first consideration in choosing a "machine," is to determine the potential work load.
Stated in tenus of wire rope, this means establishing the actual16ad that is to be moved. To this known dead weight, there must be added those loads that are caused by abrupt starts acceleration , sudden stops, shock loads, high speeds, friction of sheave.
Another item in this equation is the loss of efficiency that occurs when the rope is bent over sheaves. All of these loads must be summed up in order to determine the true total load that will ultimately be handled. For an average operation, this figure is generaliy multiplied by a "design factor" of 5. For increased mobility or design space economy, a design factor of less than 5 is used at times.
A still larger factor is sometimes found to be desirable. The factored load is now used to choose the size, grade, and core of the wire rope to be considered. An extended discussion of Design Factors can be found on page If it is repeatedly bent back and forth at one point. The reason for this is a phenomenon called "metal fatigue. As for the rope, there is one governing overall rule: the greater the number of wires in each strand, the greater the resistance of the rope to bending fatigue.
The subject of metal fatigue is covered by a large and extensive body of literature. It is not the intent of this publication to discuss, even in broad terms, the theoretical concepts of the phenomenon.
It will simply be noted here that the concept of fatigue as a cause of metal "crystallization" is incorrect since all metals are at all times crystalline in structure. The crystalline appearancein many fractures is not indicative of "crystallization.
These waves are a form of energy that must be absorbed at some point. This point may appear at various places-'-the end attachment, the tangent where the rope contacts the sheave, or at any other place where the waves are arrested and the energy absorbed.
In the normal operation of a machine or hoist, wire ropes develop a Wave action that can be observed either as a low frequency or as a sharp, high frequency cycle. A good example of this is found in shaft hoists. When the cage is just starting up, the rope has a very slow swing within the shaft. But, by the time the cage reaches the top of the shaft, the initially low frequency has become a high frequency vibration.
The result is eventual breakage of the wires at the attachment of the cage. Another type of vibrational fatigue is found in operations where there is cyclic loading. Such loadings would be found, for example, in the boom suspension systems of draglines. Here, the energy is absorbed at the end fittings of the pendants or at the tangent point where the rope contacts the sheave.
In this case, the "vibration" is torsional as well as transverse. It will occur whenever a rope either rubs against or is dragged through any soil or other material. It happens whenever a rope passes around a sheave or drum.
And, it takes place within the rope itself whenever it is loaded or bent. Abrasive action weakens the rope simply by removing metal from both inside and outside wires. When excessive wear is encountered in an operation, the problem usually stems from faulty sheave alignment, incorrect groove diameters, an inappropriate fleet angle, or improper drum winding. There may, however, be other causes.
If, on investigation, none of these common conditions are found to be causative factors. In making such a change, it is helpful to remember that larger oliter wires alld lang-lay ropes are more abrasion resistant than regular-lay ropes.
See p. The pressure of rope against a sheave is determined by the sheave diameter and the load. Irregular or scramble winding is an even greater cause of damage. Obviously, in each of these cases, reducing the load will ease the condition. If, however, this is not feasible, offending sheaves should be replaced with sheaves that have larger tread diameters.
Otherwise, the rope will have to be replaced by one with a construction better designed to resist the abuse. If the original rope has a fiber core, the replacement should have a steel core because a steel core rope will provide greater physical support. And here it is well to remember that regular-lay ropes are better able to resist crushing than lang-lay ropes.
Check all equipment functions. Lower load blocks and check hooks for deformation or cracks. During lowering procedure and the following raising cycle, observe the rope and the reeving. Particular notice should be paid to kinking, twisting or. Drumwinding conditions should also be noted. Check wire rope and slings for visual signs of anything that can cause them to be unsafe to use, i.
Particular attention should be given to any new damage during operation. The Monthly Reports should include inspection of the following: a. All functional operating mechanisms for excessive wear of components, brake system parts and lubrication.
Limit switches. Crane hooks for excess 'throat opening or twisting along with a visual for cracks. Wire rope and reeving for conditions causing possible removal. All end connections suchas hooks, shackles, turnbuckles, plate clamps, sockets,'etc. Crane hook for cracks. Hoist drum for wear or cracks. Structural members for cracks, corrosion and distortion.
It is not, however, presented as a substitute for an experienced inspector. It is rather a user's guide to the accepted standards by which ropes must be judged.
This is not easy to determine and discovery relies upon the experience gained by the inspector in measuring wire diameters of discarded ropes. For an extended discussion of stretch, see pp. As rope deteriorates from wear, fatigue, etc. A "stretch" curve plotted for stretch vs. Initial stretch, during the early beginning period of rope service, caused by the rope adjustments to operating conditions constructional stretch.
Phase 2. Following break-in, there is a long period-the greatest part of the rope's service life-during which a slight increase in stretch takes place over an extended time. This results from normal wear, fatigue, etc.
On the plotted curve-stretch vs. Phase 3. Thereafter, the stretch begins to increase at a quicker rate. This secoridupturn of the curve is a warning indicating that the rope should soon be removed.
I I ::l: U This curve is plotted to show the relationship of wire rope stretch to the various stages of a rope's life. Such reduction may be attributed to: excessive external abrasion internal or external corrosion loosening or tightening of rope lay inner wire breakage rope stretch ironing or milking of strands In the past, whether or not a rope was allowed to remain in service depended to a great extent on the rope's diameter at the time of inspection.
Currently this practice has undergone significant modification. Previously, a decrease in the rope's diameter was compared with published standards of minimum diameters. The amount of change in diameter is, of course, useful in assessing a rope's condition. But, comparing this figure with a fixed set of values is, for the most part, useless.
These long-accepted minima are not, in themselves, of any serious significance since they do not take into account such factors as: 1 variations in compressibility between IWRC and Fiber Core; 2 differences in the amount of reduction in "j diameter from abrasive wear, or from core compression, or a combination of both; and 3 the actual original diameter of the rope rather than its nominal value.
As a matter of fact, all ropes will show a significant reduction in diameter when a load is applied. Therefore, a rope manufactured close to its nominal size may, when it is subjected to loading, undergo a greater reduction in diameter than that stipulated in the minimum diameter table.
As an example of the possible error at the other extreme, we can take the case of a rope manufactured near the upper limits of allowable size.
If the diameter has reached a reduction to nominal or slightly below that, the tables would show this rope to be safe: But it should, perhaps, be removed. Today, evaluations of the rope diameter are first predicated on a comparison bf the original diameter-when new and subjected to a known load-with the current reading under like circumstances. Periodically, throughout the life of the rope, the actual diameter should be recorded when the rope is under equivalent loading and in the same operating section.
This procedure, if followed carefully, reveals a common rope characteristic: after an initial reduction, the diameter soon stabilizes. Later, there will be.
Core deterioration, when it occurs, is revealed by a more rapid reduction in diameter and when observed it is time for removal. Deciding whether or not a rope is safe is not always a simple matter. A number of different but interrelated conditions must be evaluated. Because criteria for removal are varied, and because diameter, in itself, is a vague criterion, the table of minimum diameters has been deliberately omitted from this manual.
Usually, it signifies a lack of lubrication. Corrosion will often occur internally before there is any visible external evidence on the rope surface. Pitting of wires is a cause for immediate rope removal. Not only does it attack the metal wires. Usually, a slight discoloration because of rusting merely indicates a need for lubrication. When a rope shows more than one wire failure adjacent to a terminal fitting,,it should be removed immediately.
To retard corrosive deterioration, the rope should be kept well lubricated. In situations where extreme corrosive action can occur, it may be necessary to use galvanized wire rope. This is cause for rope replacement unless the affected portion can be removed.
During normal operations this wear is not visible. Drum cross-over and flange point areas must be carefully evaluated. All end fittings. Under these circumstances the rope should be replaced.
The cause should be sought out and corrected. The rope strikes against an object such as some'structural part of the machine, or it beats against a roller, or it hits itself. Often, this can be avoided by placing protectors between the rope and the object it is striking. Another common cause of peening is continuous passage-under high tension-over a sheave or drum. Where peening action cannot be controlled, it is necessary to have more frequent inspections and to be ready for earlier rope replacement.
Figure 36 shows the external appearance of two ropes, one of which has been abraded and the other peened. Also shown are the cross-section of both wires in these conditions. Note that a crack has formed as a result of heavy peening.
This, in turn, causes wear and displacement of wires and strands along one side of the rope. Corrective measures should be taken as soon as this condition is observed. Such failures can occur on the crown of the strands, or in the valleys between the strands where adjacent strand contact exists.
In almost all cases, these failures are related to bending stresses or vibration. If diameter of the sheaves, rollers or drum cannot be increased, a more flexible rope should be used. But, if the rope in use is already of maximum flexibility, the only remaining course that wiil help prolong its service life is to move the rope through the system by cutting off the dead end.
By moving the rope through the system, the fatigued sections are moved to less fatiguing areas of the reeving. This technique is most frequently used in rotary drilling. Frequent inspection will help determine the elapsed time between breaks.
Ropes should be replaced as soon as the wire breakage. Such action must be taken without;,;, regard to the type of fracture. On occasion, a single wire will break shortly after installation.
However, if no other wires break at that time, there is no need for concern. On the other hand, should more wires break, the cause should be carefully investigated. When two or more such conditions are found, the rope should be replaced immediately.
It is well to remember that once broken wires appear-,-in a normal rope operating under normal conditions-a good many more will show up within a relatively short period. Attempting to squeeze the last measure of service from a rope beyond the allowable number of broken wires Table 13 , will create an intolerably hazardous situation.
A wire that has broken under a tensile load in excess of itsstrength. The necking down of the wire at point of failure shows that failure occurred while the wire retained its ductility. Broken ends will appear grainy. All running rope if left in service long enough will eventually fail by fatigue.
Tension Wire break reveals predominantly cup and Check for overloads; sticky, grabby clutches; cone fracture with some 45 0 shear breaks. Check for too great a strain on rope after factors of deterioration have weakened it. Abrasion Wire break mainly displays outer wires Checkfor change in rope or sheave size; change worn smooth to knife edge thinness.
Mashing Wires are flattened and spread at broken ends. Check on all the above conditions for mechanical abuse, or either abnormal or accidental forces during installation.
Corrosion Wire surfaces are pitted with break showing Indicates improper lubrication or storage. Abrasion Reduced cross-section is broken off A long term condition normal plus Fatigue square thereby producing a chisel shape. Tensile to the operating process. An example of interstrand and core-to-strand nicking. A cork-screll' 'd rope: the condition Came about asa result of the rope being pulled. When a reel has been damaged in transit, it is a safe assumption that irreparable damage has b.
Wire rope abuses during shipment create serious problems. One of the more ," common causes is improper fastening of rope end to reel. An example of "high strand". The excessive wear of a single strand is caused by improper socketing. This rope was damaged by being rolled over some sharp object. These damages were the result of bad drum winding. This effect of drum crushing is evidence of bad winding conditions. A deeply corrugated sheave. This rope condition is called a dog leg. An occurrence that is called a popped core.
This is a typical bird cage condition. A very bad condition spiralling brought about when the rope jumped from the sheave. This is the appearance of a typical tension break; a result of overloading. A Serious wear resulting from excessive bending. This is an illustration of a seriolls condition where the rope slides over or against itself. Flexing the rope exposes broken wires hidden in valleys between strands.
It is always better to replace a rope when there is any doubt concerning its condition or its ability to perform the required task. The cost of wire rope replacement is quite insignificant when considered in terms of human injuries, the cost of down time, or the cost of replacing broken structures.
Wire rope inspection includes examination of basic items such as: 1 Rope diameter reduction 2 Rope lay 3 External wear 4 Internal wear 5 Peening 6 Scrubbing 7 Corrosion 8 Broken wires Some sections of rope can break up without any prior warning. Already discussed in some detail as to cause and effect, sections where this occurs are ordinarily found at the end fittings, and at the point where the rope enters or leaves the sheave groove of boom hoists, suspension systems, or other semi- operational systems.
Because of the "working" that takes place: at these sections, no appreciable wear or crown breaks will appear. Under such an operation, the core fails thereby allowing the strands to notch adjacent strands.
As soon as the first vaHey break is detected, the rope should be removed immediately. If preventive maintenance, previously described, is diligently performed, the rope life will be prolonged and the operation will be safer. Cutting off a given length of rope at the end attachment before the core deteriOI:ates and valley breaks appear, effectively eliminates these sections as a source of danger.
As a positive means of minimizing abuses and other-than-normal wear, the procedures here set forth should be adhered to. Every observation and measurement should be carefully recorded and kept in some suitable and accessible file. These warning labels were designed by the Wire Rope Technical Board for use with all wire rope products. A warning label should accompany all wire ropes and wire rope slings provided to the user.
For rope, these labels are available in packages of in either flat Tyvek, eyelet Tyvek or self-adhesive Mylar. The flat version is ideally suited for stapling to the flanges of wood reels, the eyelet version is ideal for tying to coils of wire rope or wire rope assemblies and the adhesive is ideally suited for attaching the warning tag to metal reels.
For wire rope slings, they are available in packages of in tractor feed fan fold Tyvek. The fan fold tags also have blanks for the sling fabricator to include the rated load information required by the ASME B One language is printed on each side.
See order form. This groove size is the minimum diameter of a sheave or drum groove where applicable standards recommend replacement or re-machining. At smaller bid ratios, the loss in strength increases quite rapidly. The angle of bend need not be I 80 0 90 0 , or even 45 0 ; relatively small bends can cause considerable loss.
Derived from standard test data. The curve is based on static loads only and applies to 6 x 19 and 6 x 17 class ropes. This illustration of wire rope running from a fixed sheave. Of all these factors,the one that exerts perhaps the greatest influence on winding characteristics. The schematic drawing Fig. The fleet angle Fig. The drum flange represents the farthest position to which the rope can travel across the drum. There are left and right fleet angles.
It is necessary to restrict the fleet angle on installations where wire rope passes over the lead or fixed sheave and onto a drum. For optimum efficiency and service characteristics. Fleet angles larger than these suggested limits can cause such problems as bad winding on smooth drums, and the rope rubbing against the flanges of the sheave grooves.
Larger angles also create situations where there is excessive crushing and abrasion of the rope on the drum. Correct appraisal of the following will simplify the selection process: 1 Strength-resistance to breaking 2 Resistance to bending fatigue 3 Resistance 10 vibrational fatigue 4 Resistance to abrasion 5 Resistance to crushing 6 Reserve strength It is well-nigh impossible for any single rope to have top values in all of the above qualities.
The first task is to make a careful analysis of the job requirements, establishing priorities among these requirements, and then selecting the rope on a trade-off basis. This will provide the best possible balance by sacrificing the least essential advantages in order to obtain maximumbenefits in the most important requirements.
Following, are brief explanations ofthe six factors previously listed: 1 Strength-resistance to breaking. Thus, the very first consideration in choosing a "machine," is to determine the potential work load. Stated in tenus of wire rope, this means establishing the actual16ad that is to be moved. To this known dead weight, there must be added those loads that are caused by abrupt starts acceleration , sudden stops, shock loads, high speeds, friction of sheave.
Another item in this equation is the loss of efficiency that occurs when the rope is bent over sheaves. All of these loads must be summed up in order to determine the true total load that will ultimately be handled.
For an average operation, this figure is generaliy multiplied by a "design factor" of 5. For increased mobility or design space economy, a design factor of less than 5 is used at times. A still larger factor is sometimes found to be desirable. The factored load is now used to choose the size, grade, and core of the wire rope to be considered.
An extended discussion of Design Factors can be found on page If it is repeatedly bent back and forth at one point. The reason for this is a phenomenon called "metal fatigue. But fatigue can be greatly reduced if sheaves and drums have, at the 49 very least, the recommended minimum diameter Table 9. As for the rope, there is one governing overall rule: the greater the number of wires in each strand, the greater the resistance of the rope to bending fatigue. The subject of metal fatigue is covered by a large and extensive body of literature.
It is not the intent of this publication to discuss, even in broad terms, the theoretical concepts of the phenomenon. It will simply be noted here that the concept of fatigue as a cause of metal "crystallization" is incorrect since all metals are at all times crystalline in structure. The crystalline appearancein many fractures is not indicative of "crystallization. These waves are a form of energy that must be absorbed at some point. This point may appear at various places-'-the end attachment, the tangent where the rope contacts the sheave, or at any other place where the waves are arrested and the energy absorbed.
In the normal operation of a machine or hoist, wire ropes develop a Wave action that can be observed either as a low frequency or as a sharp, high frequency cycle. A good example of this is found in shaft hoists. When the cage is just starting up, the rope has a very slow swing within the shaft. But, by the time the cage reaches the top of the shaft, the initially low frequency has become a high frequency vibration.
The result is eventual breakage of the wires at the attachment of the cage. Another type of vibrational fatigue is found in operations where there is cyclic loading. Such loadings would be found, for example, in the boom suspension systems of draglines. Here, the energy is absorbed at the end fittings of the pendants or at the tangent point where the rope contacts the sheave. In this case, the "vibration" is torsional as well as transverse. It will occur whenever a rope either rubs against or is dragged through any soil or other material.
It happens whenever a rope passes around a sheave or drum. And, it takes place within the rope itself whenever it is loaded or bent. Abrasive action weakens the rope simply by removing metal from both inside and outside wires. When excessive wear is encountered in an operation, the problem usually stems from faulty sheave alignment, incorrect groove diameters, an inappropriate fleet angle, or improper drum winding.
There may, however, be other causes. If, on investigation, none of these common conditions are found to be causative factors. In making such a change, it is helpful to remember that larger oliter wires alld lang-lay ropes are more abrasion resistant than regular-lay ropes.
See p. The pressure of rope against a sheave is determined by the sheave diameter and the load. Overwinding is also a cause of wear even when the winding is done in an ordeiIy thread-winding manner.
Irregular or scramble winding is an even greater cause of damage. Obviously, in each of these cases, reducing the load will ease the condition. If, however, this is not feasible, offending sheaves should be replaced with sheaves that have larger tread diameters.
Otherwise, the rope will have to be replaced by one with a construction better designed to resist the abuse. If the original rope has a fiber core, the replacement should have a steel core because a steel core rope will provide greater physical support. And here it is well to remember that regular-lay ropes are better able to resist crushing than lang-lay ropes. The foHowing listing Table 12 gives the percent of reserve strength for 6- or 8-strand wire rope relative to the number of outside wires ineach strand: TABLE12 Number of Outside Wires 3' 4 5 6 7 8 9 10 12 14 16 18 51 Percent of Reserve Strength o 5 13 18 22 27, 32 36 43 49 54 58 r.
Check all equipment functions. Lower load blocks and check hooks for deformation or cracks. During lowering procedure and the following raising cycle, observe the rope and the reeving.
Particular notice should be paid to kinking, twisting or. Drumwinding conditions should also be noted. Check wire rope and slings for visual signs of anything that can cause them to be unsafe to use, i. Particular attention should be given to any new damage during operation.
The Monthly Reports should include inspection of the following: a. All functional operating mechanisms for excessive wear of components, brake system parts and lubrication. Limit switches. Crane hooks for excess 'throat opening or twisting along with a visual for cracks. Wire rope and reeving for conditions causing possible removal. All end connections suchas hooks, shackles, turnbuckles, plate clamps, sockets,'etc. Crane hook for cracks. Hoist drum for wear or cracks.
Structural members for cracks, corrosion and distortion. It is not, however, presented as a substitute for an experienced inspector. It is rather a user's guide to the accepted standards by which ropes must be judged. This is not easy to determine and discovery relies upon the experience gained by the inspector in measuring wire diameters of discarded ropes.
For an extended discussion of stretch, see pp. As rope deteriorates from wear, fatigue, etc. A "stretch" curve plotted for stretch vs. Initial stretch, during the early beginning period of rope service, caused by the rope adjustments to operating conditions constructional stretch. Phase 2. Following break-in, there is a long period-the greatest part of the rope's service life-during which a slight increase in stretch takes place over an extended time.
This results from normal wear, fatigue, etc. On the plotted curve-stretch vs. Phase 3. Thereafter, the stretch begins to increase at a quicker rate. This means that the rope is reaching the point of rapid deterioration; a of prolonged subjection to abrasive wear, fatigue, etc. This secoridupturn of the curve is a warning indicating that the rope should soon be removed.
I I :;: '-. Vl I g This curve is plotted to show the relationship of wire rope stretch to the various stages of a rope's life. Such reduction may be attributed to: excessive external abrasion internal or external corrosion loosening or tightening of rope lay inner wire breakage rope stretch ironing or milking of strands In the past, whether or not a rope was allowed to remain in service depended to a great extent on the rope's diameter at the time of inspection.
Currently this practice has undergone significant modification. Previously, a decrease in the rope's diameter was compared with published standards of minimum diameters. The amount of change in diameter is, of course, useful in assessing a rope's condition. But, comparing this figure with a fixed set of values is, for the most part, useless.
These long-accepted minima are not, in themselves, of any serious significance since they do not take into account such factors as: 1 variations in compressibility between IWRC and Fiber Core; 2 differences in the amount of reduction in diameter from abrasive wear, or from core compression, or a combination of both; and 3 the actual original diameter of the rope rather than its nominal value.
As a matter of fact, all ropes will show a significant reduction in diameter when a load is applied. Therefore, a rope manufactured close to its nominal size may, when it is subjected to loading, undergo a greater reduction in diameter than that stipulated in the minimum diameter table. Yet, these circumstances, the rope would be declared unsafe although it may, in actuality, be safe.
As an example of the possible error at the other extreme, we can take the case of a rope manufactured near the upper limits of allowable size. If the diameter has reached a reduction to nominal or slightly below that, the tables would show this rope to be safe: But it should, perhaps, be removed. Today, evaluations of the rope diameter are first predicated on a comparison bf the original diameter-when new and subjected to a known load-with the current reading under like circumstances.
Periodically, throughout the life of the rope, the actual diameter should be recorded when the rope is under equivalent loading and in the same operating section. This procedure, if followed carefully, reveals a common rope characteristic: after an initial reduction, the diameter soon stabilizes. Later, there will be. Core deterioration, when it occurs, is revealed by a more rapid reduction in diameter and when observed it is time for removal. Deciding whether or not a rope is safe is not always a simple matter.
A number of different but interrelated conditions must be evaluated. It would be 54 dangerously unwise for an inspector to declare a rope safe for continued service simply because its diameter had not reached the minimum arbitrarily established in a table if, at the same time, other observations lead to an opposite conclusion.
Because criteria for removal are varied, and because diameter, in itself, is a vague criterion, the table of minimum diameters has been deliberately omitted from this manual. Usually, it signifies a lack of lubrication.
Corrosion will often occur internally before there is any visible external evidence on the rope surface. Pitting of wires is a cause for immediate rope removal. Not only does it attack the metal wires.
Usually, a slight discoloration because of rusting merely indicates a need for lubrication. When a rope shows more than one wire failure adjacent to a terminal fitting,,it should be removed immediately.
To retard corrosive deterioration, the rope should be kept well lubricated. In situations where extreme corrosive action can occur, it may be necessary to use galvanized wire rope. This is cause for rope replacement unless the affected portion can be removed. During normal operations this wear is not visible. Drum cross-over and flange point areas must be carefully evaluated. All end fittings. Under these circumstances the rope should be replaced. The cause should be sought out and corrected.
The rope strikes against an object such as some'structural part of the machine, or it beats against a roller, or it hits itself. Often, this can be avoided by placing protectors between the rope and the object it is striking.
Another common cause of peening is continuous passage-under high tension-over a sheave or drum. Where peening action cannot be controlled, it is necessary to have more frequent inspections and to be ready for earlier rope replacement. Figure 36 shows the external appearance of two ropes, one of which has been abraded and the other peened.
Also shown are the cross-section of both wires in these conditions. Note that a crack has formed as a result of heavy peening. This, in turn, causes wear and displacement of wires and strands along one side of the rope.
Corrective measures should be taken as soon as this condition is observed. Such failures can occur on the crown of the strands, or in the valleys between the strands where adjacent strand contact exists. In almost all cases, these failures are related to bending stresses or vibration. If diameter of the sheaves, rollers or drum cannot be increased, a more flexible rope should be used. But, if the rope in use is already of maximum flexibility, the only remaining course that wiil help prolong its service life is to move the rope through the system by cutting off the dead end.
By moving the rope through the system, the fatigued sections are moved to less fatiguing areas of the reeving. This technique is most frequently used in rotary drilling. Frequent inspection will help determine the elapsed time between breaks. Ropes should be replaced as soon as the wire breakage. Such action must be taken without;,;, regard to the type of fracture. On occasion, a single wire will break shortly after installation. However, if no other wires break at that time, there is no need for concern.
On the other hand, should more wires break, the cause should be carefully investigated. When two or more such conditions are found, the rope should be replaced immediately. It is well to remember that once broken wires appear-,-in a normal rope operating under normal conditions-a good many more will show up within a relatively short period. Attempting to squeeze the last measure of service from a rope beyond the allowable number of broken wires Table 13 , will create an intolerably hazardous situation.
A wire that has broken under a tensile load in excess of itsstrength. The necking down of the wire at point of failure shows that failure occurred while the wire retained its ductility.
Broken ends will appear grainy. Wire break reveals predominantly cup and cone fracture with some 45 0 shear breaks. Wire break mainly displays outer wires worn smooth to knife edge thinness. Wire broken by abrasion in combination with another factor will show a combination break. Wires are flattened and spread at broken ends. Wire surfaces are pitted with break showing evidence either of fatigue tension or abrasion. Reduced cross-section is broken off square thereby producing a chisel shape.
Reduced cross-section is necked down as in a cup and cone configuration. Tensile break produces a chisel shape. All running rope if left in service long enough will eventually fail by fatigue. Check for too great a strain on rope after factors of deterioration have weakened it. Checkfor change in rope or sheave size; change in load; overburden change; frozen or stuck sheaves; soft rollers, sheaves or drums; excessive fleet angle; misalignment of sheaves; kinks;..
Check on all the above conditions for mechimical abuse, or either abnormal or accidental forces during installation. Check on all the above conditions for mechanical abuse, or either abnormal or accidental forces during installation. Indicates improper lubrication or storage. A long term condition normal to the operating process, A long term condition normal to the operating process.
An example of interstrand and core-to-strand nicking. A cork-screll' 'd rope: the condition Came about asa result of the rope being pulled. When a reel has been damaged in transit, it is a safe assumption that irreparable damage has b. Wire rope abuses during shipment create serious problems. One of the more common causes is improper fastening of rope end to reel.
These photos show two acc 'prab! An example of "high strand". The excessive wear of a single strand is caused by improper socketing. This rope was damaged by being rolled over some sharp object. These damages were the result of bad drum winding. This effect of drum crushing is evidence of bad winding conditions. A deeply corrugated sheave. This rope condition is called a dog leg. An occurrence that is called a popped core. This is a typical bird cage condition. A very bad condition spiralling brought about when the rope jumped from the sheave.
This is the appearance of a typical tension break; a result of overloading. A B Figure A Serious wear resulting from excessive bending. This is an illustration of a seriolls condition where the rope slides over or against itself. Flexing the rope exposes broken wires hidden in valleys between strands. It is always better to replace a rope when there is any doubt concerning its condition or its ability to perform the required task.
The cost of wire rope replacement is quite insignificant when considered in terms of human injuries, the cost of down time, or the cost of replacing broken structures. Wire rope inspection includes examination of basic items such as: 1 Rope diameter reduction 2 Rope lay 3 External wear 4 Internal wear 5 Peening 6 Scrubbing 7 Corrosion 8 Broken wires Some sections of rope can break up without any prior warning.
Already discussed in some detail as to cause and effect, sections where this occurs are ordinarily found at the end fittings, and at the point where the rope enters or leaves the sheave groove of boom hoists, suspension systems, or other semi- operational systems.
Because of the "working" that takes place: at these sections, no appreciable wear or crown breaks will appear. Under such an operation, the core fails thereby allowing the strands to notch adjacent strands. As soon as the first vaHey break is detected, the rope should be removed immediately. If preventive maintenance, previously described, is diligently performed, the rope life will be prolonged and the operation will be safer.
Cutting off a given length of rope at the end attachment before the core deteriOI:ates and valley breaks appear, effectively eliminates these sections as a source of danger.
As a positive means of minimizing abuses and other-than-normal wear, the procedures here set forth should be adhered to. Every observation and measurement should be carefully recorded and kept in some suitable and accessible file. Make certain that the proper means of attachment is applied correctly, and that any safety devices in use are in satisfactory working order.
All bearings must be in good operating condition and furnish adequate support to the sheaves and rollers. Sheaves that are permitted to wobble will create additional forces that accelerate the deterioration rate of the rope. Be on the lookout for spots on the equipment that have been worn bright or cut into by the rope as it moves through the system.
Ordinarily, excessive abrasive wear on the rope can be eliminated at these points by means of some type of protector or roller. This in-process treatment will provide the finished rope with ample protection for a reasonable time if it is stored under proper conditions.
But, when the rope is put into service, the initial lubrication may be less than needed for the full useful life of the rope. Because of this possibility, periodic applications of a suitable rope lubricant are necessary. Following, are the important characteristics of a good wire rope lubricant: 1 It should be free from acids and alkalis, 2 It should have sufficient adhesive strength to remain on the ropes, 3 It should be of a viscosity capable of penetrating the interstices between wires and strands, 4 It should not be soluble in the medium surrounding it under the actual operating conditions, 5 It should have a high film strength, and 6 It should resist oxidation.
Immediately after it is cleaned, the rope should be lubricated. When it is normal for the rope to operate in dirt, rock or other abrasive material, the lubricant should be selected with great care to make certain that it will penetrate and, at the same time, will not pick up any of the material through which the rope must be dragged. Many techniques are used; these include the continuous bath, dripping, pouring, swabbing, painting, or where circumstances dictate, automatic systems can be used to apply lubricants either by a drip or pressure spray method Fig.
Lubricant application methods in general use today include continuous bath, dripping, pouring, swabbing, painting, and spraying. The arrows indicate the direction in which the rope is moving.
This lost strength is not available to lift the load, and in a multi-part tackle block system Fig. The load "seen" by the lead line fast Ilne under static no-movement conditions can be readily calculated if the load is divided by the number of parts of line as expressed in the following fbrmula: F 1 1 d Total load incl.
Static loading on the rope is: A equal to, B Y. D l,4 of. Schematic representation of a four-part reeving system. On the other hand, if the sheaves have plain bearings such as bronze bushings, the lead line load will increase to lb.
Derricks often use 8 or more parts in the boom support system. The schematic diagram Fig. This system has the same number of sheaves as there are parts of line.
The following procedure presumes this condition throughout. Provision for extra lead sheaves are given at the end of this discussion. When S exceeds N, refer to the text. Schematic representation of a 4-part reeving system with an extra idler sheave. Example: What is the lead-line factor for a plain bearing tackle block system of 5 parts of line and two extra lead-in sheaves? The tabulated value is. Since there are two additional sheaves, the computation is:. Systems in which both rope ends are attached to a drum such as may be founa in overhead cranes are not within the planned scope of this manual.
It is suggested, therefore, that information on such systems be obtained directly from a wire rope manufacturer. There is, moreover, a third source of elongation-under-Ioad: the rope's tendency to rotate and its associated lengthenings of the lay.
This rather complex process has potentially dangerous consequences and must be avoided. Constructional stretch occurs when the rope's elements are compressed, or pulled together, as the load is applied. The result is a slight decrease in diameter and increase in length. This may be likened to the familiar effect known as the "Chinese Finger Trap.
Usually, constructional stretch in IWRC or strand core ropes becomes permanent after several loadings leaving the rope with very little resiliency or recovery. However, fiber core ropes if lightly loaded elevator ropes may retain some degree of resiliency throughout most of their service life. The rope's construction, particularly its type of core and the. The load range will also influence the overall stretch. Note: A ft piece would stretch times this figure or. Tables 16 and 17 provide approximate modulus of elasticity and metallic area for a number of rope classifications and diameters.
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