Transcript
WIRE ROPES
WHAT ARE WIRE ROPES?
Are intricate vital machine elements that are used to transmit FORCES or MOTION.
Or are simply used to support WEIGHTS/ LOADS.
THEIR SERVICE CATEGORY COULD BE CLASSIFIED INTO TWO (2): 1. STATICS (Stationary
applications)
2. DYNAMICS (Moving applications)
1. STATICS -- as tower supports, guy wires, suspension bridge supports, and electrical power transmission lines.
2. DYNAMICS -- as for pulling or lifting applications. These include elevators, cable cars, cranes, hoists, dredges, and control cables.
Small wire sizes are better suited to being bent sharply over small sheaves (pulleys) while large wire ropes are preferred when the cable/ wire rope will be rubbed or dragged through abrasives.
HISTORY:
Initially starting out as ropes made up of nylon or fiber but later on develop into strands of wires. Wire ropes were eventually invented by a german engineer for mining haulage purposes.
Fiber/ nylon strands of a typical rope
Before steel chains were commonly used for hauling purposes but had numerous mechanical failures due to its design but not necessarily on the material used.
Weak steel chain portion of a single link.
Wire ropes on the other hand, due to their design/ physical make-up and construction corrects the flaws encountered by steel chains.
WIRE ROPE PARTS:
WIRE ROPE CONSTRUCTION:
The individual wires are first twisted into strands and then the strands are twisted around a hemp or steel center to form the rope.
Often the central element is an independent wire rope core. The twisting or laying (lay) of the wire rope describes the manner in which either wires in a strand or the strands in the rope are laid in a helix.
WIRE ROPE TYPES:1. PREFORMED WIRE ROPE
Has its wires and strands “PRESHAPED” to the curvature they are made as a ROPE.
2. NON-PREFORMEDis the opposite of the
preformed wire rope. There is no preshaping of the wires and strands. All wires in a strand are twisted afterwhich, the individual strands along with the core are again twisted to form the rope.
ADVANTAGE OF PREFORMING:
1. ELIMINATES LOCKED-UP STRESS AND STRAIN existing in non-preformed wire ropes.
2. PREVENTS THE ROPE FROM FLYING APART when “CUT or BROKEN” and resists “KINKING”.
3. ELIMINATES THE TENDENCY OF THE ROPE ROTATING ABOUT ITS AXIS.
4. Are easily “SPLICED”.5. ARE USED AS “OPERATING ROPES” (failure
is due to fatigue) with small safety factors.
DISADVANTAGE OF PREFORMING:1. DIFFICULTY OF TUCKING.2. HAS NO ADVANTAGE WHEN USED
FOR “STATIONARY OPERATION” (Failure is due to corrosion)
3. COSTS MORE.
WIRE ROPE TYPE ACCORDING TO LAY:
1. LEFT HAND LAY -- strands are twisted in a counterclockwise (CCW) direction.
LEFT REGULAR LAY WIRE ROPE
2. RIGHT HAND LAY -- strands are twisted in a clockwise (CW) direction.
RIGHT REGULAR LAY WIRE ROPE
WIRE ROPE TYPES ACCORDING TO THE LAYING OF WIRES THAT MAKE-UP
THE STRAND:
1. ORDINARY LAY (REGULAR LAY): The laying of wires in each
strand is in opposite direction of the laying of strands that form the wire.
LEFT REGULAR LAY WIRE ROPE
RIGHT REGULAR LAY WIRE ROPE
2. LANG’S LAY (ALBERT’S LAY): the lay of wires in each strand
is in the same direction as the lay of the strands that form the wire.
RIGHT LANG LAY WIRE ROPE
LEFT LANG LAY WIRE ROPE
Such type is able to flex over sheaves easier but has this disadvantage of untwisting or loosening-up when subjected to high torques. This would be dangerous to its core as the load would be diverted into the core itself instead of the strands primarily.
3. ALTERNATE LAY(REVERSE LAY): Strands alternate equally between LANG’S LAY and ORDINARY LAY.
Say a six (6) strand wire rope:three (3) Ordinary Laythree (3) Lang’s Lay
RIGHT ALTERNATE LAY WIRE ROPE
CONSTRUCTION ACCORDING TO STRAND:
The design arrangement of a strand is called “CONSTRUCTION”. The wires in the strand maybe of the same size or a mixture of sizes. The most common strand construction are:
1. ORDINARY STRAND the wires making-up the
strand are all of the same sizes.
2. SEALE uses a large diameter of wires on the outside of the strand to resist abrasion and uses smaller wires inside to provide flexibility.
3. WARRINGTON alternates large and small wires to
combine great flexibility with resistance to abrasion.
4. FILLER is where small wires fill the valleys
between the outer and inner rows of wires to provide good abrasion and fatigue resistance.
WIRE ROPE CORE CONSTRUCTION:
The CORE is where the strands of wire are laid or twisted about and either allows FLEXIBILITY or ADDITIONAL STRENGTH combined with the strands.
1. FIBER CORE Maybe a hard fiber such as
manila, hemp, plastic, paper, or sisal. Offers the advantage
of “GREAT FLEXIBILITY “ while serving as a cushion to reduce the effects of sudden strain as well as an “OIL RESERVOIR” to lubricate the wires and
strand.
2. WIRE STRAND CORE resists more heat than a
fiber core while adding about 15% of additional strength. It has this
disadvantage of making the rope less flexible than a fiber core.
3. INDEPENDENT WIRE ROPE CORE A separate wire rope strand
over which the main strands are laid. The core strengthens the wire, providing support against, while being much
more resilient to heat.
WIRE ROPE MATERIAL:
There are three (3) primary grades / materials used in the construction of the wires in the strands of the wire rope.
1. MILD PLOW STEEL (MPS) Is tough and pliable
withstanding repeated strain and stress (TENSILE STRENGTH OF 200 – 220 KSI.
These characteristic makes it desirable for cable tool drilling and other purposes where abrasion is encountered.
2. PLOW STEEL (PS) Is unusually tough and
strong with a tensile strength of 200 – 240 ksi and is suitable for hoisting, hauling, and logging.
3. IMPROVED PLOW STEEL One of the best grades
available and is the most common force used in Naval Construction.
This material is stronger, tougher, and more resistant to wear than either MPS or PS. It has a tensile strength of 240 – 260 ksi and is therefore used for heavy duty service such as cranes.
OTHER MATERIALS:
4. Wrought Iron 5. Cast Steel 6. Alloy Steel 7. Stainless Steel 8. Copper 9. Bronze
VARIOUS SIZES AND APPLICATIONS:
6 x 7 haulage, tramways, guy wires 6 x 19 general purpose rope, hoists,
cranes, drilling, elevators
6 x 37 high speed elevators, cranes, hoists
8 x 19 extra flexible hoisting rope applications
WIRE ROPE CODING SYSTEM:
A wire rope uses an accepted coding system, consisting of a number of abbreviations for its material composition and wire strand sizes and arrangements.
6 x 19 FC RH OL FSWR
No. of strandsNo. of wires per strands Type of Core
Laying of strands
Laying of wires on strand
Wire material
WIRE ROPE DATA TABLE:
WIRE ROPE DATA TABLE:
Type of Service: Factor of Safety:
Elevators 8 – 12
Mine Hoists 2.5 – 5
Cranes, motor- driven
4 – 6
Hand- driven
3 – 5
Derricks 3 - 5
FACTORS TO CONSIDER IN WIRE ROPE SELECTION:
There are several factors to consider in choosing the proper wire rope type to be used in a particular type of operation such as if it could be able to withstand the type of wear and stress in that particular type of operation. However selecting a wire rope is a matter of compromise. That is you have to sacrifice one quality over the other to meet the urgently needed characteristic.
1. TENSILE STRENGTH Is necessary to withstand
the possible maximum load that could be applied. It includes a reserve of strength measured in a so-called factor of safety.
2. CRUSHING STRENGTH: Is the necessary strength
to resists the compressive or squeezing forces that distort the cross-section of a wire rope as it runs over sheaves, rollers, and hoists drums when under a heavy load.
Regular lay ropes distorts less in theses situations than lang lay.
3. FATIGUE RESISTANCE : Is the ability to
resist constant bending and flexing that runs continuously on sheaves and hoists drums.
It is an important factor when a rope is running at high speeds.
3. ABRASION RESISTANCE: Is the ability to resist
gradual wearing away of the outer material as the ropes run across sheaves and hoists drums.
The rate of abrasion depends upon the load carried upon by the rope and the running speed.
3. ABRASION RESISTANCE: Wire ropes made from
harder steel such as IPS has considerable resistance to abrasion.
Ropes having larger wires forming their outer strands are more resistant to wear that those having smaller wires that wear away more quickly.
4. CORROSION RESISTANCE:Is the ability to withstand dissolution
of the wire metal that results from chemical attack by moisture in the atmosphere or elsewhere in the working environment.
Ropes in static applications are protected by insulating a special dressing or by galvanizing the wire itself.
In dynamic applications, the ropes lubrications also serve as their protection against corrosion.
HOW IS IT TO MEASURE A WIRE ROPE?
A wire rope is designated by its diameter, in inches. The correct method of measuring a wire rope is to measure from the top of one strand directly opposite it. The wrong way is to measure across two strands side by side.
HOW IS IT TO MEASURE A WIRE ROPE?
To ensure accurate measurement of the diameter of a wire rope, always measure the rope at three (3) places, at least five (5) feet apart then use the averaged diameter of the rope.
WIRE ROPE ATTACHMENTS:
Since wire ropes do have numerous strands of wire, attachments are necessary to clip their ends and prevent them from lossening-up.
Such is the use of WIRE ROPE ATTACHMENTS to also connect it to other “ropes” such as chains and equipments.
1. END FITTINGS: Are types of detachable wire rope attachments that allow the rope greater flexibility thus allowing the wire rope to be made into numerous different arrangements.Ex. Wire Rope Clips, Clamps, Thimbles, and Basket Sockets.
1.A WIRE ROPE CLIPS Are used in tandem with thimbles to make eye sockets and are made-up of a U-bolt and a “saddle”(lock).
FORMULAS USED IN DETERMINING THE NUMBER OF WIRE ROPE CLIPS:
Number of CLIPS
= 3 x wire rope diameter + 1
Spacing Between CLIPS= 6 x wire rope diameter
1.A.1 TWIN BASE CLIP: Often referred to as the universal or two
clamp. Both parts of this clip are shaped to fit the wire rope; therefore, the clip cannot be attached incorrectly. The twin based clip allows a clear 360 degree swing with the wrench when the nuts are being tightened.
2. WIRE ROPE CLAMPS: Are used to make an eye in the rope with or
without a thimble. The eye will have approximately 90% of the strength of the rope. The two end collars should be tightened with wrenches to force the wire
rope clamp to a good snug fit. This squeezes the rope securely against each other.
3. THIMBLE: When an eye is made in a wire rope,
a a metal fitting called a “thimble” is usually placed in the eye to protect it from wear and tear. Wire rope eyes with thimbles and wire rope clips can hold approximately 80% of the wire
rope strength.
4. WEDGE SOCKET: Is used in situations that require the fitting to be changed
frequently and are normally used for smaller wire ropes.
5. BASKET SOCKET: Is normally attached to the end of the
rope with either molten zinc or babbitmetal; therefore it is a permanent endfitting. In all circumstances, dry or
poured, the wire rope should lead from the
socket inline with the axis of the socket.
BASKET SOCKET using DRY METHOD:
BASKET SOCKET using POURING METHOD:
6. OVAL SLEEVE: A sleeve where there are two
(2) holes for the wire rope to be inserted to create an eye or eye splice. Initially one end of the wire rope is inserted until a loop is formed by inserting again the same end. When the desired eye is obtained, the oval sleeve is then pressed to create a
sealing action.
BASIC WIRE ROPE PRACTICES:
UNREELING & UNCOILING
When uncoiling a wire rope from a reel on which it is received, it is imperative that the “reel” or “coil” rotates as the rope unwinds.
Attempts to unwind rope from stationary coil or reels will result in “kinking” (condition in which some of the fibers/ wires that composes the strands get damaged due to “looping”) .. That once a “kink” is formed, the rope at that point is ruined beyond repair.
KINKING from a LOOP FORMATION:
METHODS OF UNREELING/ UNCOILING:1. The reel maybe set upon two (2) jacks
enabling the reel to rotate as the wire rope is unreeled.
The wire rope’s end at this point should be held by an individual who casually walks away from the reel as the reel rotates.
2. The reel may also be mounted on a turn table. It is then unreeled in the same manner as that of the reel mounted on two (2) jacks. Again care must be taken to make sure that the tension is kept on all the wire rope to prevent any “slack” unstraightening of the wire rope that may become a cause “kinking” in it while
unreeling.
3. It is also possible to uncoil without any mounting supports. As such two (2) individuals serve as accomplices. One should hold the end of the wire rope while the other slowly “rolls” the reel away from the other individual.
4. Never unreel a wire rope with the reel placed or laid on its side and then the wire rope being pulled-off. Such method will either put a twist or take-out a twist in the rope producing a kinky, curly rope frequently forming “doglegs” (a condition in which certain cross-sections are no longer equal) eventually reducing rope service.
5. When re-reeling a wire rope from one horizontal reel to a second horizontal reel, the rope should travel from the top of the full reel to the top of the empty reel, or from the bottom of the full reel to the bottom of
the empty .
6. When winding the first layer of wire rope on a smooth drum, it should be started from the side which causes the coils to hug together. This tends to produce a uniform and close wound first layer providing uniformity to the succeeding layers . If there is uneven spacing in between the ropes, the reel would spin faster than the rope when pulled-off. As such succeeding turns of
ropes would simply loosen-up.
7. Ropes should come from the top of the reel. If the rope comes from beneath and the reel overruns, it may form loops that could eventually form
into doglegs.
8. Like reels, coils of wire unwound/ unreeled from the reel should also be rotated to form a common coil of the same diameter so that uncoiling it once again would prevent it from kinking. In doing so, it should be rotated on the ground.
9. Do not flop a coil on its side on the ground.
This will put in or take-out a twist in the rope for every loop pulled from the coil.
10.You could use another turntable with a
protruding portion as it is easy, quick, and eliminate possible
twisting.
11. A loop that has not been pulled tight enough to set the wires or strands of the rope permanently can be removed by turning the rope at either end in the proper direction to restore the lay. If this is
not done and instead
the loop was pulled tight to set the wires, the spot in question will be damaged irreparably.
12. Never nail through the rope as this will
seriously injure a rope.
13. To secure a rope to the reel, you must use a U-bolt through the side of the reel or fasten a tie wire to the rope and then nailing this tie wire to the reel side.
SEIZING AND CUTTING A ROPE:
The proper cutting procedure should be observed for wire rope. Improper cutting technique would lead to spoilage of the rope translating into additional costs. When a rope is to be cut, it should be thoroughly seized (by wires) so that there maybe no displacement of the strands.
A SEIZING IRON shown could also be used instead with the seizing wire in tandem as shown.
When cutting, a wire rope should be seized on each side of the place where the rope is to be cut.
** As a general rule lang lay ropes, 18 x 7 ropes, ropes with independent wire rope core or a wire strand core, and all ropes larger than 1” in diameter should not have than four (4) seizings on each side.
Other ropes should not have less than three (3) seizings on each side.
Tools such as cable cutters, bolt clippers, hacksaw, cold chisel ,and oxy-acetylene torch are used as a means of cutting.
WIRE ROPE LUBRICATION:
To get more “SERVICE”or to “PROLONG” the life or wire ropes, proper lubrication should be made. In terms of:
1. Scheduling2. Type of lubrication (oil) to
be used3. Way of applying lubrication
All portions of the WIRE ROPE should be properly be lubricated from the outer portion to the innermost portion.
If not properly lubricated, a rope will fail not because of the WEAR and TEAR but mainly due to “CORROSION”.
There are no clear time tables for the lubrication of wire ropes but can be specified upon the type of load and frequency of work.
If a wire rope had been under great work load for a week, then the wire should be lubricated. If the cable has not been used for heavy work for six (6) months, then its previous lubrication is still sufficient enough.
TYPICAL PROBLEMS ENCOUNTERED BY WIRE ROPES:
1. POOR OR NO LUBRICATION
2. WORN SHEAVES or DRUMS
3. SHEAVES TOO SMALL
4. HEAT (WORKING CONDITION)
5. KINKS and BENDS
CONDITIONS REQUIRING FREQUENT LUBRICATION:
1. HEAVY LOADS/ WEIGHTS.
2. GREAT NUMBER OF BENDS3. SMALL SHEAVE DIAMETER
4. HIGH CABLE SPEEDS
5. MOISTY OR CORROSIVE ENVIRONMENT
PROCEDURE IN LUBRICATING WIRE ROPES:
1. The rope should be thoroughly be cleaned from grit and old lubrication and then dried. A jet of air (compressed air) or by brushing would help in this ordeal.
2. Applying lubrication by means of brushing the oil into the wire rope repeatedly could be done. Or applying the
lubricant itself by means of gloves immersed in a lubricant would also do the trick.
3. Lubricants could also be poured onto cables moving over sheaves. With the cable bending/ flexing, the inner core also gets lubricated aside from the outermost strands.
END OF DISCUSSION..
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