Lubricated wire rope

A wire rope having extraordinary resistance to wear comprises a core strand and a plurality of outer strands oriented and nested in the same helical lay as the core strand, all the wires thereof being made of a molybdenum-containing steel and having been stress-relieved at a temperature of at least 675.degree. F., said rope being coated inside and outside with a suspension of finely divided molybdenum disulfide in a non-fluid state at room temperature.

BACKGROUND OF THE INVENTION 
Wire rope has long been manufactured to meet very demanding conditions--in 
its employment in cranes, hoists, drag lines, elevators, ski lifts, 
various marine environments and mining machinery, it is commonly exposed 
to the elements and frequently flexed, abraded and tensed under extreme 
loads. While wire rope intended for such uses has always been made as 
rugged as economics will permit, its expense is such that a constant 
search is underway for ways to increase the hours-in-use before it must be 
replaced. 
Various approaches have been employed in the past to reduce wear and 
increase the life of wire rope. 
For example, it is not new to orient the outer strands of the rope in the 
same lay (i.e. to make a complete 360.degree. helical turn in the same 
linear measure of rope) with the inner strands so that contact between 
wires of the inner and outer strands is linear rather than at particular 
points See U.S. Pat. 3,306,022. The basic idea of internally lubricating 
wire rope has also been disclosed--see U.S. Pat. Nos. 3,705,489; 
2,485,019; 3,824,777 and the prior art recited in U.S. Pat. No. 4,344,278. 
Stress-relieving has also been practiced at an intermediate stage of wire 
rope making: U.S. Pat. No. 3,240,570. Likewise it is known (see U.S. Pat. 
No. 3,718,442) to employ steel of a certain metallurgy, particularly 
containing a small amount of vanadium and an optional amount of molybdenum 
in order to improve ductility and other characteristics of the strands. 
Mixtures of thermoplastic materials and lubricants are disclosed to be 
useful in the interiors of certain wire ropes--see U.S. Pat. Nos. 
4,120,145; 4,123,894 and 2,372,142. For other disclosures generally in the 
art of making wire rope, see U.S. Pat. Nos. 3,075,344; 3,259,487; 
3,293,837; 3,271,944; 3,668,020; 3,374,619 and U.S. Pat. No. Re. 29,537. 
None of these combines the features of my invention.

SUBJECT OF THE INVENTION 
My invention is a wire rope having a core and an outer layer of strands, 
which is lubricated inside and outside with a normally thick, highly 
viscous lubricant having a high (at least about 5%) solids content 
comprising finely divided solid lubricant such as graphite or molybdenum 
disulfide, the core and outer strands being stress-relieved and in the 
same lay, and the wire being made of steel including about 0.03 to about 
0.3% vanadium, molybdenum, chromium, or mixtures thereof. 
While the concept of placing the outer strands on the core strands (which 
are also helically wound) in the same lay is not new, it is notable that I 
am for the first time combining the use of an intimately applied solid 
lubricant with the use of a lay wherein the outer strands are "nested" in 
the valleys of the core strand. As is known in the art, a core strand will 
exhibit helical "valleys" tracing the same general pattern as the wires or 
smaller strands which make up the helical configuration of the core. My 
invention includes the concept, along with the internal lubricant, of 
nesting the outer strands in the "valleys" in a manner similar to that of 
U.S. Pat. No. 3,306,022, to reduce the Hertzian (transverse) stresses and 
thus increase the strength of the rope. Wire rope wound in this manner, 
having somewhat less free interior space, tends to have a more stable 
outer diameter before and during use and thus will not wear as much in the 
sheaves or suffer unnecessary internal friction. 
The lubricant is applied during manufacture of the rope; specifically, it 
is preferably applied to each wire as the wires are wound into strands and 
to each strand as the strands are wound into rope. It will be about 3-5% 
of the weight of the finished rope. Since the lubricant is normally very 
thick or viscous, i.e. almost solid, it should have a melting point of at 
least about 130.degree. F. and must be heated to a molten state (typically 
about 180.degree. F.) in order to apply it to the wires. Any vehicle, such 
as tar or asphaltic materials, which is solid at ambient temperatures 
(will not leak out of the wire rope) and which will suspend, without water 
or solvent, a solid, finely divided lubricant such as graphite or 
molybdenum disulfide, may be used. The lubricant should be fluid enough 
under flexing and stress conditions that it will be "self-healing", i.e. 
it will move back into areas from which it has been forced. Preferably it 
will also be inhibited against its own oxidative and/or bacteriological 
deterioration, and will advantageously contain "extreme pressure" 
additives, rust inhibitors, and additives to improve the lubricant's 
adhesion to metal, such as are known in the art. 
The use of wire of conventional metallurgical composition may lead to 
disparate perlite spacing--a phenomenon which may be measured in Angstroms 
as the distance between microscopically observable lines or crystals of 
perlite. With conventional metallurgy and processing, the variations in 
perlite or lamellar spacing result in a relatively soft interior of the 
wire compared to the exterior portions, so that if wear begins at a 
particular point it will not only continue but actually accelerate with 
continuing pressure, contact or friction. The vanadium-molybdenum 
containing composition of U.S. Pat. No. 3,718,442 renders the perlite 
spacing more uniform throughout the wire and improves hardenability and 
tensile strength. Thus, the onset of wear at a particular point will not 
be aggravated because of increasing softness as the wear progresses. Small 
amounts of chromium may be used instead, and/or any mixture of molybdenum, 
vanadium, and chromium may be used in amounts from about 0.03% to about 
3.0%. 
The strands may advantageously be "stress-relieved" --that is, they are 
heated to a temperature of at least about 675.degree. F. (up to about 
900.degree. F.) and passed through a series of flexing devices to secure 
proper alignment and internal contact, resulting in neutralization of the 
residual tensile stresses due to winding of the strand, leaving only 
residual compressive stresses. It has been observed that the yield 
strength of a strand can be increased 40% by stress relieving, which has a 
noticeable and favorable effect on wear. If stainless steel is used, the 
temperature of the stress-relieving process should be about 
900.degree.-1150.degree. F. In either carbon or stainless steel, the time 
employed for cooling is not critical. 
Tests and comparisons of my rope with conventional ropes in the field have 
shown significantly improved life with my rope. The results of some other 
tests, however, have been obscured because the diameters of the comparison 
ropes were smaller and in the actual tests the new rope was subject to 
more sheave abrasion because of its slightly larger diameter. 
The following field test results were obtained with my invention on a 
particular mining machine: 
______________________________________ 
Avg. Service - 
Test Ropes 
Conventional Ropes 
(Invention) 
______________________________________ 
1st Drag Line Rope 
756.2 hrs. 1126.37 hrs. 
2nd Drag Line Rope 
756.2 hrs. 1051.32 hrs. 
Hoist Line 2031.2 hrs. 2475.2 hrs. 
______________________________________ 
These results are not entirely conclusive, since a fairlead configuration 
change was also made on the machine immediately prior to the test. Wear on 
the ropes was considered normal, however--that is, the wear on the test 
ropes was not significantly different from wear prior to the change and 
the contribution of the change the increased life of the test ropes is 
considered problematical.