US 3083817 A
Description (OCR text may contain errors)
y /N VEN TOR $2,225@ Eau/ads 2Mb 22 Y Amm/gm l @Nm/M AM ATTORNEY April 2, 1963 R. E. CAMPBELL 3,083,817
WIRE aoPEs /N VE N TOR ima@ Edam@ gwefl 6W' W" 1MM l TTORNE April 2, 1963 R. E. CAMPBELL 3,083,817
WIRE RoPEs Original Filed Sept. 10, 1954 5 Sheets-Sheet 3 /A/ VEN TOR` @eze-EZ Ympzell g5 IMIMy-m "cg-MM ATTORNEY April 2, 1963 LL 3,083,817
RRRRRRR ES @ad im@ @QZ BY @um /al/Jd'v l ATTORNEY United States Patent O 3,083,817 WlRE RGPES Robert Edward Campbell, Wheatley Hills, Doncaster, England, assigner to British Ropes Limited, Doncaster, England Continuatinn of abandoned application Ser. No. 455,3il0, Sept. 1i?, 1954. rEhis application Nov. 2, 1960, Ser. No. 65,76@ Claims priority, application Great Britain Nov. 18, 1953 Claims. (Cl. 265-2) My present application is a continuation of my application Serial No. 455,300, filed September 10, 1954 and now abandoned.
This invention relates to wire ropes and the method ot the invention may be applied to strands, steel cores and/or finished or partly finished rope, irrespective of the type of core used or whether the ropes are stranded or locked coil.
The invention is more specically, but not solely, applicable to steel wires which have been isothermally quenched (bringing them into the condition known as patented) and then cold drawn, It is also applicable to constructions in which, say, liller wires which have not been isothermally quenched, are incorporated into a strand or core, the other wires of which have been isothermally quenched. By -the term strand as used throughout the specification and claims is meant a combination of steel wires arranged around a central, or king wire, in one or more helically wound layers, each layer of wires having a specific lay length.
The invention consists of a method of treating steel wire strands, cores or ropes, by imparting thereto a controlled degree of plastic ow with uniform pressure all round.
Anyone versed in the rope-making art would expect that fatigue resistance would be decreased after such treatment, but extensive experiments have now shown the contrary to be the case, as an appreciable increase in the fatigue resistance has been tfound to occur.
The invention will be further `described with reference to the accompanying drawings.
FIGURE 1 is a cross-section of a 6/1 wire strand, prepared in accordance with the invention, with the strand in the untreated state indicated in phantom.
FlGURE 2 is a similar View of a 9/9/1 strand.
FIGURES 3 and 3a show a plan, and
FIGURES 4 and 4a a side elevation of an apparatus for carrying the invention into eect.
FIGURE 5 is a cross-section of a 6/1 strand illustrating a correct drafting A, with two phases of insufficient drafting B and C FIGURE 6 is a cross-section of a 12/6/1 strand prepared in accordance with the invention.
FIGURE 7 is a cross-section of a 12/6/1 strand with filler wires, prepared in accordance with the invention.
FIGURES 8, 9 and l() show diagrammatically, alternative apparatus layouts for carrying out the invention.
The basis of the preferred method of operation is the application of the combined resultant reactive force arising `from plastic iiow under compression, coupled with predetermined elongation of the strand, whilst passing through a die of tungsten carbide, hardened steel, ceramic or any other material capable of acting as a drawing medium.
Back tension is applied to the longitudinal axis of the strand as it passes to the die, of sufficient magnitude to initiate plastic flow prior to the strand entering the die,
whilst not exceeding the limit of proportionality of the i strand (that is, the point on a stress-strain curve at which the strain ceases to be proportional to the stress).
After treatment as described, it is found in a strand of 3,083,817 Patented Apr. 2, 1963 ICC round wires that the originally round wires making up the Strand have individually been reformed to a geometric pattern which, in the case of a layer of six round wires over the king, is as shown in FIGURE l.
When there is more than one layer of wires laid over the king Wire, each outer Wire cross-section is a pentagon, as illustrated in FIGURE 2. That is, the king wire becomes faceted according to the number of wires laid over it, the point of Contact of the next layer of overlying wires forming the base of a pentagon which abuts a corresponding facet on the polygonal king wire, the next layer being of reversed pentagons and so on.
In one method of operation the steel wires, which may be round wires in the plain state, galvanized or treated with any other form of anti-corrosive or anti-frictional agent, are laid up into the desired construction in a stranding machine, the strand so `formed being coiled on to a reel, preferably of steel or light alloy.
MACHINE SET-UP `In the arrangement of FIGURES 3, 3a, 4 and 4a, the reel 1 of the strand is inserted into the cradle 2 and the end taken through the fairlead 3. From thence it is led three times around the capstan wheel 4, forward again through the cooling unit S, then into the die 6 and finally on to the second capstan or surge wheel 7, where it is allowed to lap round until the surge pad is full, thus attaining maximum traction. From there it passes through a second fairlead 8 on to the take-up drum 9 and over traversing gear 9a.
Prior to passing into the die, the strand and the face oi the die are supplied with a copious stream of lubricant by means of a centrifugal pump 10; the lubricant then gravitates back to the return tank 11. The die 6 is watercooled, and it is advantageous to ft a snorter on the strand as it emerges from lthe Idie as a high degree of follow-through of the lubricant takes place.
The die-holder 12 of the die `6 is tted on a swivel in the horizontal plane, and can be moved by quadrant and worm 13 by handle 13a so that when required, kill can be imparted to the strand.
IIn operation, having threaded up, the electric power drive 14 :over gear box 14a to the surge wheel 7 is started, and tension applied by means of the friction brake 15 with handle 15a on the capstan 4 until a predetermined reading is procured on the :ammeter of the power drive 14, and the |arnmeter reading is kept steady by increasing or decneasing the back tension as required. This virtually ensures reactive drawing of the strand and greatly increases the life of the die as Well yas initiating plastic flow as the strand runs into the die.
Additional control may be obtained by employing any hydraulically operated recorder on the friction brake 15, also by la similar type of recorder behind the die, which can be used to record the `actual back tension in the strand.
If necessary, the requisite deviation of the die from its longitudinal axis is then set by the worm and quadrant 13, and the machine is opened up to full speed.
Rotation of the cradle 2 can -be effected las desired by means of the power drive 16 over the gears 17, and the reel 1 is braked by means of the lfriction brake 18 with brake band tension 19.
Whilst the die iand die-holder have been shown fixed during the operation, these two can be built up so that they -are capable of rotation around fthe longitudinal axis of the strand by an independent drive, whilst the strand is being drawn through the die.
The main advantage is that a considerable reduction in the horse power required to draw the strand through the die is effected, particularly when the die is revolved `at high speeds, in the order of 4,000 to 5,00() rpm. Further advantages are, that the life `of the die is prolonged due to the prevention of uneven wear of the effective drawing portion of the die, that ovality of the strand reduced, coupled with better follow-through of the lubricant used whilst drawing.
In place of a mechanically operated die, as described,
it is also possible to carry out the operation in a like manner, by threading the strand through :the center of a four jawed chuck fitted into roller bearings. y Between :the bearing :and the rear Iof fthe chuck, a toothed driving wheel is built in as an integral part of the chuck, .and geared lto a high speed motor, which imparts the required rotation to the chuck in either a clockwise or anti-clockwise direction.
'I'he jaws of the chuck are fitted with parallel or convexed surfaced hardened steel or tungsten carbide rollers.
In operation the jaws of the chuck are closed until the diameter between the roller faces the final diameter at which it is required to produce the strand. They are then locked in this position, and the tapered end of the strand fed through as in the case of a die, to the pullingin strap, and the chuck rotated at the requisite speed, with the lay of the strand.
The strand is then pulled forward through the rotating chuck, thus .attaining the requisite degree of drafting and internal geometric pattern in the individual wires.
IOINTING AND HAULING-IN THE STRAND Any method which will produce `a graduated taper at the end of the strand to allow its insertion into the die can be employed such las twisting the end of the strand While it is hot and then grinding Vto the requisite degree of taper; or alternatively by svn-aging.
The free end of the strand is inserted into the die until a sufficient length is available to .allow a pulling-in strap,
but also to 4'give satisfactory performance when in service .as Ia rope lubricant.
Whilst this lubricant is considered to give the most satisfactory results, owing to the factors detailed above, any material which :acts as a lubricant and permits off drawing, can be used to operate this process.
COOLING SETTING UP OF O'PTIMUM CONDITIONS In order to obtain the maximum efficiency from a drawn strand, the optimum controlling factors must be accurately established for each construction of strand to be treated and these factors are:
(l) The Percentage Redaction in Area of the Entire Strand (Drafting) Which Gives Correct Geometric Compactng of the Strand If the reduction is correct, in the case of -a strand with a single layer of wires over a king wire the outer wires deform to a wedge shaped cross-section, the base of which fits to the facet on the king wire, the crown being radiused to form a composite part of the circumference of the strand.
or rope, to be attached to it by means of grips, the pullingin strap being connected to the haul-off capstan.
The machine can then be operated until a sufficient length of strand has been drawn through the die to permit of lapping around the haul-off capstan, and on to the take-up reel.
vAs soon as the initial lengthkof strand has been run through the machine, as described above, and secured to .the take-up reel, the die box is set to the requisite angle with the quadrant control, and the necessary back tension applied -via the brake band on the first capstan near the pay-off reel. All the necessary factors are now under control, according to the pre-set conditions, and uninterrupted drawing can proceed.
DIESv The dies are conveniently :orthodox wire drawing dies of conventional pattern, made of tungsten carbide, and runs vofwell over .a ton with such dies, employing a 27% drafting on 10G/110 ton tensile material in the outer wires l ave `been successfully accomplished, without any deterioration of the die surface, and with the special lubricant used, fthe die should remain on size.
Although ydies made of tungsten carbide have been used, `any material capable of withstanding the bursting strains, coupled with the requisite hardness to take a high polish to draw, is suitable.
LUBRICANTS The lubrication is basically a highly refined mineral oilinto which additives have been incorporated to give:
(l) Good drawing properties. (2) Good lubricating properties. (3) High stability under compression.
(4) Maximum water repellency. (5 Resistance to dissociation at elevated temperatures.
The lubricant is one which is intended not only to enable the drawing to be done with maximum efficiency,
In section A FIGURE 5, we have the correctly compacted geometric shape attained by the optimum drafting. Failure to apply the requisite optimum drafting will result in cooking of the outer wires and tubing of the outer cover, the varying degrees depending upon the percentage drafting, with the formation of a bird-cage when drawn.
To clarify the importance of selecting the optimum draft, the following examples are quoted to demonstrate the resultant effect.
In section B FIGURE 5, we have a `case where too light a drafting has been employed and, under such circumstances, the outer wire has been unable to compress the king Wire, and consequently, is expanding to ran ellipse, with resultant tubing of the cover, or lifting of the outer wires away from the king Wire; the wire deforma- -tion then becomes inconsistent and finally a wire lifts right out and the whole strand bird-cages and malforrns.
In section C FIGURE 5, an intermediate phase is demonstrated; this takes place when a drafting lying between the correct one and one that produces the result described in the previous paragraph, is applied. In such an instance the wire is plastic-ally deformed to the requisite geometric shape, but is unstable upon its axis and it tilts tangentially to the circumference of the strand, producing two convergent planes on the crown or contact position ofthe outer wires.
The line D-E illustrates the .tangential flat which is produced on the surface of the individual Wires when an insufficient degree `of drafting has been employed. Consequently, in the wire marked C, instead of having a uniform radius on the external surface, or drawn position, a tangential flat is formed. This causes the deformed wire to tilt upon its 'axis and give the appearance of a worn strand, instead of allowing the wire to correctly defo-rm to its full geometric pattern and secure complete locking in the strand.
In FIGURE 5, reference 3x refers to the continuous black line at the base of the correctly formed wire at A and shows how, as a result of the king wire being faceted, the overlying wires have a correspondingly firm base upon which to rest. To illustrate the importance of correct drafting still further, it will be seen that the oval section B cannot form a flat surface, but a spessi? slightly concave depression, which allows of rolling or rocking of the wire about its axis on the king wire, instead of its being firmly seated.
FIGURE 6 shows the 12/6/ 1 construction cross-section without ller Wires, after drawing, `and shows that the wires of the intermediate layer `between the king wire and the outer wires become pentagonal.
FlGURl-E 7 shows the eifect of iiller wires (ie. the small diamond shaped wires) which add an extra side to the pentagonal shaped Wires over the king wire, also an extra side to the outer wedge shaped wires.
Any combination of iiller wires interposed between the round wires produces the diamond shape in the filler wire with the corresponding extra side on the pentagonal shaped wires.
(2) Adjustment of Drafting to Maintain Geometric Pattern, and Produce Selected Physical Characteristics Having determined the requisite drafting to produce the required geometric shape, it is then necessary to determine the drafting which not only maintains the correct geometric pattern but gives maximum physical characteristics, thus producing an increased service life in the strand and ultimately the completed rope.
in order to obtain positive assurance upon this point, it is advisable to vary the drafting on either side of the one selected to give the required geometric pattern, so that a series of sample lengths bracketing the required geometric configuration are obtained; the resultant sarnples are tested to destruction for tensile and fatigue resistance, whilst modulus, lay, loss in weight and increase in length per unit length, are also determined and plotted graphically.
By careful interpretation of the graphical trends on each plot, it is possible to adjust the drafting to give a maximum reading on all the physical characteristics at the selected draft.
it should be noted that when the drafting is at the optimum, all the graphical plots are in ratio to one an other and follow the same trends.
The prior drafting, namely that to which the rod has been subjected whilst being drawn into wire, can have a material eiiect upon the optimum strand drafting, 'therefore, typical graphical plots cannot be constructed to cover all wire supplies and consequently the procedure detailed above must be employed.
(3) Design of Strand in Relation to Tensile 0f Wire The physical characteristics of a strand, and the iinished rope, can be extended if the strand is designed with the various layers of wires not of one tensile, but each layer of a different range so that the amount of secondary drawing in the respective layers (ie, the drawing of the wires of the strand due to drawing of the strand as opposed to the primary or initial drawing of the Wires themselves in their manufacture) may be brought to the same degree in the iinished strand, or intentionally maintained at selected amplitudes; this has been found to have an important bearing upon increased resistance to fatigue.
(4) The Optimum Drafting Required for any Given Construction of Strand This is critical, the reason for this being due to the fact that as the drafting applied to any given strand is progressively increased, the following stages tak-e place:
(a) The existing air space between the individual wires in the strand begins to diminish;
(b) The point contact of the individual round Wires begins to increase, due to the resultant reactive force exerted by the compression through the die, on the circumference of the strand, and the back tension from the reactive capstan;
(c) The air space continues to diminish whilst the wires are rapidly commencing to flow plastically.
When the drafting is applied in the range of %-40%,
the full geometric pattern is attained, and the air space within the strand has disappeared. Except for the thin rtilm of oil, the strand has virtually become a solid bar proved by the modulus rising rapidly to a close approximation to the modulus of a solid steel bar.
Normally, ir" 30% drafting is exceeded, the strand lbegins to draw purely as if it is a solid bar, demonstrated by the fact that the geometric cross-section of the wires is not changed, but that the lay length increases. In certain types of strand particularly those in which filler wires are included, this elect is delayed until as much as .40% drafting is given.
The optimum drafting would appear, from experiments, to be around 271/2%. This iigure varies with thev different constructions, and even more so where the respective covers in a strand are built up with wires of different tensiles because the rates of plastic deformation are bound to vary.
(5) T he Optimum Back Tensioning Force According to the construction of the strand, and the tensile of the Wires employed, the back tensioning force will range from, say, 12% to 35% of the breaking load of the strand.
This would apply not only to the 9/9/1 strand, but to any construction, and initially would be ascertained by taking the breaking load of the strand before drawing, and then applying the requisite percentage of that breaking load, but always keeping it below the limit of proportionality. (See definition above.)
The back tension can be measured by means of any lydraulically operated recorder incorporated behind the TYPES OF STRANDS The process and equipment as described has dealt with the treatment of strand Where round wires have been concentrically disposed around a king wire. By substituting triangular or oval-sectioned dies for a round one, and the building up of suitably constructed strand to allow ofY geometric reorientation, flattened, triangular or oval strands of any desired degree can also be produced with the same equipment and basic principles.
It should also be noted that the method is applicable to armoured or independent wire rope cores, also to strands whose cores are composed of plastic, either in the -form of a solid rod or containing a conductor, when improved fatigue resistance results.
Selection of the requisite tension and twist to the strand whilst drawing enables the internal lubrication to be introduced into the strand and then sealed in by the plastic iiow on the crown of the outer Wires, of which the strand is composed.
Selection of an optimum overall reduction on the initial strand diameter in relation to the particular contruction used, results in an increase in the tensile strength of the strand, without loss of fatigue strength.
ROPES The strands prepared in the manner detailed above are loaded into a rope making machine and closed into the completed rope, over any selected type of core.
The completed rope may then, if desired, be passed through a die in a similar manner, thus a controlled degree of plastic flow is imparted to the crown of the strands with uniform pressure all around the circumference of the rope. By this means, initial bedding of the strands to the core occurs, so that when the rope is put to work, no settling period is necessary within its designed working load, and it is less liable to elongate within its working range, especially when preformed.
Alternative layouts for treating strand in accordance with the invention are shown in FIGURES 8, 9 and 10 of the accompanying drawings.
a In FIGURE 8 the strand on a pay-off swift 20 is drawn in exactly the same way as steel wire, except that the die 21 is not only water cooled but immersed inthe lubrieating medium in oil bath 22 and the strand before ventering the die passes around pulley 23 which is fitted with a braking device (not` shown) to `give the necessary back tension. The strand after drawing is taken up on the drawing block 24. n
. In FIGURFl` 9 the strand pays off the swift 2t), around pulley 23 which is again fitted with a braking device, but inthisV instance the tension applied is of sufficient magnitude to keep the strand taut. -In this method no back tension, in the true sense, is applied from this pulley. i
The st-rand is then lapped three or four times around the drawing block '25, led' through a lubricating bath 22 and die 21 on tothe second drawing block 2 6. l
`To Aopera-te the process, the two blocks and 26 are driven by variable speed motors and to attain the necessary back tension the drawing block at 25 is runat a specified number of revolutions per minute slower than block 26. This allows the initiation of lplastic flow under controlled conditions, 'prior to the strand entering the ldie 21.
In FIGURE 1'0, the strand comes ot the pay-off swift 20 over the capstan wheel 27 which is fitted with a braking device to apply back tension and is situated vertically over the haul-ofi capst-an at 28. 'Ihe die 21 and lubricating Ybath 22 are situated between the two capstans 27 and 28. From thence the strand progresses forward on to the haul- -olf reel 29.
It will be lappreciated that this method is virtually the same as that in FIGURES 3, 3a and 4, 4a but the strand is actually drawn, and back tension applied, in the Vertical plane as against the horizontal. This would conserve floor space.
As an alternative to the use of ardrawing die in the above described embodiments of my invention a swaging machine may be substituted therefor with all other factors remaining the same.
In this particular application, whilst the final form is th'e same as that obtained by pulling through a die, it is produced by the combined resultant reactive force arising from predetermined elongation of the strand, whilst subjected to vrapid cyclic compression around the circumferenceof thestrand by mechanical means, using segmental dies, i.e. swaging. 4 g, l
The process of lthe invention results in:
(l) 'Reduction to a minimum of the air space within the strand. n 1 I p (2) The production, around the longitudinal axis of the strand, of a natural correlated geometric shape in all the wires of which the strand is composed, including the king.
(3) Reduction of the interstices'between the wires com- 'H posing the strand,particularly the outer wires.
.( 4) An increase of the internal contact area ofthe wires 'inf the strand, and improved compressional resistance when 'spun into a rope.
The above factors, when applied to a steel strand, result in:
(l) A considerable increase in the breaking load of a ropesize for size-due to 'the increased volume of steel, `which is proportionate to the diminution of air space within the rope, the remainingsmall percentage of non-metallic material being the internal lubricant, forced into the Astrand when drawing.
'to their geometric shape, `which not only occurs in each individual cover, but the underlying and overlying covers too.
(b)` A plastically flowed surface film on the working or contact area of each strand which gives added fatigue resistance.
(c) The formation` of geometric helical wedges (see cross-sectional diagram FIGURE 6) which give the strand, and consequently the rope, high resistance to compression CIL and malformation, thus ensuring that differential working of the wires is minimized, with consequent elimination of premature fatigue in individual wires. Contrary to what might be anticipated, it is especially noticeable when strands, or 'the tinal'rope are subjected to fatigue tes't, that no premature failure of individual wires is experienced until the full expectation of fatigue life is obtained; at this stage progressive failure of the individual wires then ensues in the normal way, the outer wires failing by square-ended fatigue and 'the inner Wires by pure tensile, thus proving that when this condition does ultimately occur, it takes place externally not internally, giving adequate warning of impending inability to sustain a load. This is due to the increased bearing surface and inability of the wires to roll and the strand malform.
(d) Even bedding of the strand to the core, which produces 'a tighter spun, less lively rope with improved iiexibility, Whilst the strands themselves, if drawn to an optimum, exhibit what are virtually microinterstices of uniform consistency. That is, they are completely free from gappiness, and are of uniform diameter, whilst the smooth surface of the strand allows controlled movement without the development of frictional forces and possible damage to the strand itself, or the core.
Both the strands, and consequently the finished rope, have a smooth surface, and as a result are easy to handle, the above factors again adding to the fatigue resistance, due to the fact that the surface layer of the strands has been plastically flowed, and the notch sensitivity of the component wires reduced.
(3) Increased anti-corrosion properties, due to the drawing lubricant used, which not only has a high degree of efficiency as such, but 'has been designed to act as a rope lubricant of high order, to permeate the whole of the strand, thereby securing maximum water repellency.
1. A process of transforming `an `initial rope strand having a given diameter and cross-sectional area of metal and comprised of at least one layer of circular Wires helically laid around a circular king wire and having spaces therebetween into a finished rope strand of substantially solid metal cross-section of smaller diameter and smaller cross-sectional area than the initial rope strand and comprised of a king wire of polygonal cross-section having a number of iiat faces corresponding to the number of wires in said one layer of wires, the wires in said one layer of said finished rope 'strand being of the saine polygonal cross-section, 'each having one flat face coextensive with and engaging flush against a respective fiat face of the king wire of the `finished rope strand, and having side flat Vfaces extending radially of the axis of the king wire of the finished rope strand and coextensive with and engaging flush against the side flat faces of the wires adjacent there- .ceeding the limit of proportionality of said initial rope strand but sufficient to bring the same to a state of incipient plastic iiow, before the compressive load is applied whereby toL reduce thek diameter and the cross-sectional area of all `of the wires of said initial rope strand, and to shape all the wires'to mutually engaging polygonal cross-section as aforesaid and thereby/provide said finished rope'strand of substantially solid metal cross-section.
` 2. A process of transforming initial rope strand as set forth in 'claim 1,'wherein the tensile load imposed on said length of initial rope strand is at a `constant value which lies between about 12% to about 35% of the breaking load of the initial rope strand.
3. A process of transforming initial rope strand as set forth in claim 1, wherein the compressive load applied to said length of said initial rope strand is of an amount to reduce the cross-sectional area thereof by a xed value in a range of from about 20% to about 40% of its original cross-sectional area.
4. A process of transforming initial rope strand having a given diameter and cross-sectional area of metal and comprised of at least one layer of circular wires helically laid around a circular king wire and having spaces therebetween into a iinished rope strand of substantially solid metal cross-section of smaller diameter and smaller crosssectional area than the initial rope strand and comprised of a king wire of polygonal cross-section having a number of ilat faces corresponding to the number of wires in said one layer of Wires, the wires in said one layer of said iinished rope strand being of the same polygonal crosssection, each having one flat face coextensive with and engaging flush against a respective flat face of the king wire of the linished rope strand, and having side ilat faces extending radially of the axis of the king wire of the finished rope strand and coextensive with and engaging iiush against the side at faces of the wires adjacent thereto in said one layer of said finished rope strand, comprising the steps of moving the initial rope strand in one direc` tion through a path in one part of which a length of said initial rope strand extends along its lengthwise axis,
simultaneously applying a radially inwardly directed com- 30 pressive load at one portion only of said length of said initial rope strand in an amount to reduce its diameter to a xed value within the range of from about 20% to 40% of its original diameter while imposing an accurately controlled constant tensile non-compressive load axially on the part of said length of said initial rope strand approaching said one position of from about 12% to about 35% of the breaking load of the initial rope strand so as not to exceed the limit of proportionality of said initial rope strand but suicient to bring the same to a state of incipient plastic flow, said compressive and tensile loads together reducing the cross-sectional area of and shaping all the wires of the initial rope strand to mutually engaging polygonal cross-section as aforesaid and thereby provide said nished rope strand of substantially solid metal crosssection.
5. A process of transforming initial rope strand as set forth in claim 1 wherein the compressive load applied to said length of initial rope strand is of an amount to reduce the cross-sectional area thereof to a iixed value of about 271/2 of its original cross-sectional area.
References Cited in the le of this patent UNITED STATES PATENTS 1,943,087 Potter et al. Jau. 9, 1934 2,050,298 Everett Aug. 11, 1936 2,062,059 Hodson Nov. 24, 1936 2,095,461 Whyte Oct, 12, 1937 2,098,922 McKnight Nov. 9, 1937 2,156,652 Harris May 2, 1939 2,445,365 Reardon July 20, 1948 FOREIGN PATENTS 7,535 Great Britain 1905 14,121 Great Britain 1891 143,096 Australia Aug. 28, 1951 438,275 Germany Dec. 15, 1926