PASTE TYPE LUBRICATION

Abstract

In a paste type lubrication between a steel wire rope and a rope groove of a pulley, is applied a paste lubricant which contains oil and small solid particles. Solid particles could be of a wide variety sizes and they are small enough to at least partly fit into the valleys between the peaks of surface roughness of the ropes or the rope groove.

Claims

1. A paste lubricant between a steel wire rope and a rope groove of a pulley, wherein the paste lubricant comprises oil and small solid particles, the small solid particles being of a wide variety of sizes, and being small enough to at least partly fit into valleys between peaks of surface roughness of the steel wire rope or the rope groove.

2. A paste lubricant applied in a contact between a steel wire rope and a rope groove of a pulley, the paste lubricant comprising particles and oil, a surface structure of steel wires of the steel wire rope comprises a wire surface asperity and a surface of the rope groove comprises a groove surface asperity, the paste lubricant compressed in a space between the steel wires and the rope groove, the particles transmitting at least part of a shear force resulting from slip between the surface of the rope groove and the surface structure of the steel wires of the steel wire rope, wherein particles in the lubricant substantially are smaller than 5 times of an Ra-value of a rougher one of the surface structure of the steel wires and the surface of the rope groove, and wherein at least 80 percent of a total mass of the particles in the lubricant consists of particles larger than one tenth ( 1/10) of an Ra-value of a smoother one of the surface structure of the steel wires and the surface of the rope groove.

3. The paste lubricant according to claim 1, wherein a major part of the particles is harder than a softer one of the surface structure of the steel wires and the surface of the rope groove.

4. The paste lubricant according to claim 1, wherein the paste lubricant comprises particles having an internal aspect ratio of at most about 5.

5. The paste lubricant according to claim 1, wherein a shape of the particles is substantially spherical or almost spherical.

6. The paste lubricant according to claim 1, wherein an elastic modulus of the particles is in a range of from 50 GPa to 420 GPa.

7. The paste lubricant according to claim 6, wherein that the elastic modulus of the particles is in a range of from 80 GPa to 160 GPa.

8. The paste lubricant according to claim 1, wherein at least 5 percent of a total mass of the particles in the paste lubricant consists of particles smaller than one tenth ( 1/10) of an Ra-value of a smoother one of the surface structure of the steel wires and the surface of the rope groove.

9. The paste lubricant according to claim 1, wherein an Ra-value of roughness of the surface structure of the steel wires and/or the surface of the rope groove is in a range of 0.3-2.5 m.

10. The paste lubricant according to claim 1, wherein a particle size in the paste lubricant is in a range of 0.1-8 m, and particles of the paste lubricant are of different sizes.

11. The paste lubricant according to claim 1, wherein a median of a particle size distribution in the paste lubricant is in a range of 0.3-4 m.

12. The paste lubricant according to claim 1, wherein, in the paste lubricant mass portions as a function of particle size follows Weibull distribution or normal distribution.

13. The paste lubricant according to claim 2, wherein a major part of the particles are harder than a softer one of the surface structure of the steel wires and the surface of the rope groove.

14. The paste lubricant according to claim 1, wherein the paste lubricant comprises particles having an internal aspect ratio of at most about 5, and less than 2.

15. The paste lubricant according to claim 1, wherein the paste lubricant comprises particles having an internal aspect ratio of at most about 5, and less than 1.5.

16. The paste lubricant according to claim 1, wherein the paste lubricant comprises particles having an internal aspect ratio of at most about 1.2.

17. The paste lubricant according to claim 1, wherein an elastic modulus of the particles is in a range of from 70 GPa to 200 GPa.

18. The paste lubricant according to claim 1, wherein an Ra-value of roughness of the surface structure of the steel wires and/or the surface of the rope groove is in a range of 0.8-1.6 m.

19. The paste lubricant according to claim 1, wherein a median of a particle size distribution in the paste lubricant is in a range of 1-3 m.

20. The paste lubricant according to claim 2, wherein the paste lubricant comprises particles having an internal aspect ratio is at most about 5.

Description

[0050] In the following, the invention will be described in detail by the aid of an example of its embodiment with reference to the attached drawing, wherein

[0051] FIG. 1 presents a diagrammatic and simplified view of a traction sheave elevator with its rope tension chart as viewed from the side of the traction sheave,

[0052] FIG. 2 presents a cross-section of one metal rope, such as a suspension rope of an elevator, lubricated with a lubricant,

[0053] FIG. 3 presents a graph, compiled on the basis of measurement results, of the wearing of an elevator rope lubricated according to the invention,

[0054] FIG. 4 presents a graph, compiled on the basis of measurement results, of the ratio of the slip percentage of two elevator ropes lubricated in different ways and also of the friction factor between the elevator rope and the rope groove, and

[0055] FIG. 5 presents an enlarged cross-section of a metal rope, such as a suspension rope of an elevator, in a rope groove of a traction sheave, and lubricated with a lubricant according to the invention.

[0056] FIG. 1 presents a diagrammatic and simplified view of a typical traction sheave elevator, which comprises an elevator car 1, a counterweight 2 or balance weight and, fixed between these, elevator roping formed of elevator ropes 3 that are parallel to each other. The elevator ropes 3 are guided to pass over the traction sheave 4 rotated by the hoisting machine of the elevator in rope grooves dimensioned for the elevator ropes 3. As it rotates, the traction sheave 4 at the same time moves the elevator car 1 and the counterweight 2 in the up direction and down direction, due to friction.

[0057] Owing to the difference between the counterweight 2 and the elevator car 1 plus the load at any given time in the car, the rope forces T.sub.CTW and T.sub.CAR exerted on the elevator ropes 3 are of different magnitudes on different sides of the traction sheave 4. When the elevator car 1 contains less than one-half of the nominal load, the counterweight is generally heavier than the elevator car 1 with load. In this case the rope force T.sub.CTW between the counterweight 2 and the traction sheave 4 is greater than the rope force T.sub.CAR between the elevator car 1 and the traction sheave 4. Correspondingly, when the elevator car 1 contains over one-half of the nominal load, the counterweight 2 is generally lighter than the elevator car 1 with load. In this case the rope force T.sub.CTW between the counterweight 2 and the traction sheave 4 is smaller than the rope force T.sub.CAR between the elevator car 1 and the traction sheave 4. In the situation presented in FIG. 1, the rope force between the elevator car 1 and the traction sheave 4 is T.sub.CAR>T.sub.CTW. As a consequence, the rope tension acting on the elevator ropes 3 that is produced by the rope forces T.sub.CTW and T.sub.CAR in the rope grooves of the traction sheave 4 is not constant, but instead increases when going from the counterweight 2 side to the elevator car 1 side. This growing rope tension is diagrammatically presented in the tension chart 5 drawn in FIG. 1. As explained earlier, this tension difference tries to cause slipping of the elevator ropes 3 in the rope grooves. It is endeavored to compensate for the tension difference across the traction sheave 4 with a controlled slip, which can be implemented e.g. owing to the larger friction.

[0058] FIG. 2 presents a cross-section of a metal rope, such as a suspension rope 3 of an elevator for suspending and moving the elevator car. The suspension rope 3 of the elevator comprises strands 7 laid together around a core 6, which strands 7 for their part are laid e.g. from metal wires, such as from steel wires 9. The elevator rope 3 is lubricated with a lubricant 8 in connection with the manufacture of the rope. The lubricant 8 is between the strands 7 and also between the wires 9 of the strands, and the lubricant 8 is arranged to protect the strands 7 and the wires 9 from rubbing against each other. The lubricant 8 of the elevator rope 3 according to the invention also acts on the friction factor between the elevator rope 3 and the traction sheave 4 of the elevator, increasing the friction compared to elevator ropes lubricated with lubricating oil or lubricating grease according to prior art.

[0059] The lubricant 8 of a suspension rope 3 of an elevator according to the invention comprises at least some base oil suited to the purpose, some thickener, i.e. solid powder-like additive, that is preferably non-organic, and later referred as powder substance, and also if necessary some binder agent, such as poly-isobutene or some other suitable organic compound. The base oil, more briefly referred to as oil, is e.g. some suitable synthetic oil that contains various additives, such as e.g. wear resistance agents and corrosion resistance agents. The task of the oil is, among other things, to prevent water from entering the rope 3 and to protect the rope from corrosion and wear. Anti-fretting and possibly also anti-seize types of lubricants are applicable to the purpose according to the invention as a lubricant of an elevator rope 3, even though there are restrictions caused by the application.

[0060] The powder substance of the lubricant 8 comprises one or more fine-grained solid substances comprising small particles of different sizes. At least a part of the particles, preferably a majority of the particles are suitably hard. The hardness of those particles on the Mohs scale is about equal to the hardness of the steel of the wires 9 of the rope, or greater than the hardness of the steel of the wires 9. Preferably the solid powder substances belong to the spinel group of minerals where common crystal forms are cubic or isometric, for instance octahedral.

[0061] Steel wires most usually used in elevators belong to strength classes 1370 N/m.sup.2, 1570 N/m.sup.2, 1770 N/m.sup.2 and 1960 N/m.sup.2, where the strength is calculated as nominal tensile strength. However, even stronger steel wires are used. Commercial elevators are provided even with steel wires whose nominal tensile strength is between 2000-3000 N/m.sup.2. Usually stronger steel wires are also harder than steel wires with smaller strength.

[0062] The particles in the powder substance have a high specific weight. Thus, the specific weight of the particles is many times greater than the specific weight of the used oil. For that reason, the particles tend to descent onto the bottom of lubricant 8 at least in a long term storage. Preferably the lubricant 8 comprises additives that slow that kind of precipitation down or even prevent it.

[0063] The binder agent is arranged to keep the other materials of the lubricant 8, i.e. the oil, and the powder substance better together. The binder agent is e.g. an organically-based mass, such as a butene compound or some other substance suited to the purpose, e.g. a resin-based or wax-based substance.

[0064] The lubricant 8 is manufactured simply by mechanically mixing its different constituent parts with each other. The mixing ratios of the different constituents of the lubricant 8 are e.g. approx. 10-40%, preferably approx. 15-30%, suitably approx. 20%, oil; e.g. approx. 60-95%, preferably approx. 70-85%, powder substance; and e.g. approx. 0-5%, preferably approx. 0.2-3%, suitably approx. 0.3-0.6%, e.g. 0.4%, binder agent. The aforementioned percentage figures are percentages by weight. Owing to the large amount of powder substance, the structure of the lubricant 8 is a paste. With the help of the binder agent and powder substance, the lubricant 8 stays on the rope well and does not detach easily.

[0065] The lubricant 8 according to the invention differs from conventional lubricating grease in that, among other things, preferably the lubricant comprises a very high proportion of powder substance and less oil. The powder substance can account for e.g. at most 95%, in which case the proportion of base oil remains at 5% at the highest. Whereas with lubricating greases according to prior art the proportion of base oil in the grease is 80-90%, in which case the proportion of powder substance and other substances remains only at 10-20%.

[0066] FIG. 3 presents a graph compiled on the basis of the measurement results obtained in tests, of the wearing of elevator ropes lubricated in different ways. The curve p1 presents a rope lubricated with paraffin according to prior art, and the curve n1 presents a rope lubricated with the lubricant 8 according to the invention. The wearing of the ropes was tested with test equipment such that the rope was driven back and forth in a groove of a rope sheave and wearing of the rope was diagnosed from the reduction in diameter of the rope.

[0067] Both the ropes had the nominal diameter of 8 mm. The rejection limit in the tests was set to the value where the diameter of the ropes had become 6% thinner from the nominal diameter. In that case the rejection limit was 8*0.94=7.52 millimeters.

[0068] It can be seen from FIG. 3 that the rope p1 that were originally about 8.05 mm thick and lubricated with paraffin-based lubricant has thinned after approx. one million test cycles to become 7.54 millimeters thick in its diameter. The rejection limit 7.52 millimeters was reached before 1.2 million test cycles. Then the rope p1 seems to have essentially lost its fitness for purpose. On the other hand, the rope n1 that was lubricated with the lubricant 8 according to the invention has not really worn at all after the initial operational period even during the 10 million test cycles and is fit for use up till about 14 million test cycles. This is about 12 times more than with the rope p1.

[0069] FIG. 4 presents a graph, compiled on the basis of the results of measurements made in a laboratory, of the relationship between the friction factor of the rope groove of the traction sheave 4 and the slip percentage of a steel rope p1 lubricated with a paraffin-based lubricant according to prior-art and a steel rope n1 lubricated with the lubricant 8 according to the invention. The case shown here is thus the empirically obtained effective friction factor between two objects that slide against each other, and not the specific friction factor for an individual material.

[0070] It can be seen from the graph that in the case of a steel rope lubricated with a paraffin-based lubricant according to prior art, which is represented by the curve p1 in FIG. 4, the effective friction factor rises linearly and relatively fast in the initial phase of slip. When the slip is approx. 0.2%, the increase in the effective friction factor has slowed down, being in this phase now approx. 0.08. After this when the slip increases, the rise in the effective friction factor slows down even faster and does not increase over the approx. 0.09 limit here, even if the slip were to grow more. In this case, the situation is that the grip of the elevator rope in the groove of the traction sheave 4 has been lost.

[0071] Correspondingly, in the case of a steel rope lubricated with the lubricant 8 according to the invention, which is represented by the curve n1 in FIG. 4, the effective friction factor again rises linearly and relatively fast in the initial phase of slip. As the slip increases, the effective friction factor now also continues its increase, essentially linearly to a higher value of effective friction factor than with the rope represented by the curve p1. With the rope n1 lubricated with the lubricant 8 according to the invention, as the slip increases, the effective friction factor reaches a value of about 0.13. In this case considerably more grip reserve remains for the traction sheave 4 in case of unexpected situations, and larger values than 0.1, e.g. values about 0.13, can be used for the effective friction factor in the dimensioning. This enables a higher ratio T.sub.CAR/T.sub.CTW of rope forces, in which case it is possible to achieve smaller moving masses, a further consequence of which is smaller acceleration forces, lower energy consumption and smaller losses.

[0072] In addition, savings can be made in materials. Instead of making the elevator car lighter the better friction factor or friction grip can be utilized in several ways. For instance, it is not necessary to reduce acceleration because of slipping, and in addition it is possible to reduce under cutting in rope grooves and to increase rope force because surface pressure is now not a hindrance. That means in practice that the number of suspension ropes 3 can be reduced. And further, the better working lubrication makes it possible to use smaller rope pulleys.

[0073] FIG. 5 presents a greatly enlarged cross-section of a metal rope, such as a steel suspension rope 3 of an elevator, in a rope groove of a traction sheave 4, and lubricated with the lubricant 8 according to the invention. As mentioned earlier the lubricant 8 comprises a special powder substance that is powder like and comprises small solid particles 10 of different sizes. Preferably the particles 10 are rather round, advantageously in form of a sphere or chunk or an oval. Advantageously the ratio of the longest dimension to the shortest dimension of the particle 10 is close to one. This ratio is called the internal aspect ratio as mentioned earlier.

[0074] Besides the round or almost round shape, the hardness of at least a part of the particles 10, preferably a majority of the particles 10 on the Mohs scale is about equal to the hardness of the steel of the wires 9 of the rope, or greater than the hardness of the steel of the wires 9. One possible type of substances to be used are solid substances belonging to the spinel group of minerals which have crystal forms that are cubic or isometric, for instance octahedral, and therefore the particles of these substances can approximately resemble spherical particles. For example, classified manganese (II, III) oxide, Mn.sub.3O.sub.4, is a substance that can be used as a powder substance in the lubricant 8 according to the invention. The hardness of Mn.sub.3O.sub.4 on the Mohs scale is about 5.5, which value corresponds to the hardness of the cutting edge of a good carbon steel blade of a knife.

[0075] It is also possible that manganese (IV) oxide or manganese dioxide, MnO.sub.2 is used as a powder substance in the lubricant 8 according to the invention. The hardness of MnO.sub.2 on the Mohs scale is about 5. In that case the hardness of MnO.sub.2 is also greater than the hardness of the steel of the most commonly used wires 9.

[0076] Preferably the hardness of the particles 10 of the main substance of the powder substance is greater than 4, for instance between 4 and 6, and suitably between 5 and 5.5 on the Mohs scale.

[0077] FIG. 5 shows in a greatly enlarged view how the mainly round or almost round solid particles 10 of the powder substance in the lubricant 8 are located between the surfaces of the suspension rope 3 and the rope groove of the traction sheave 4. Between the solid particles 10 the lubricant 8 has synthetic oil 11 and binder agents, the amounts of them has been mentioned earlier. The thickness of the layer of the particles 10 between the two adjacent steel surfaces is greater than the surface roughness of each of the steel surfaces. In that case the particles 10, being harder or at least as hard as the steel surfaces, prevent the two steel surfaces from touching each other. That reduces the wear of the suspension rope 3 and also the rope grooves of the traction sheave 4. The slip plane 12, which actually represents a slip surface in this cross-sectional view, between the two surfaces is more or less curvilinear somewhere between the particles 10, and can change all the time. Instead two steel surfaces there could be other kind of metal pairs, for example a steel surface and a cast iron surface. The teaching of FIG. 5. is schematic and thus there should not be direct conclusions from the dimensions of the particles, asperities of the surfaces or their distances or slip line. Also should be understood that there actually could be several slip lines between the surfaces.

[0078] The inventor believes that the lubrication performance of the lubricant 8 according to the invention is that the more or less spherically shaped hard particles 10 of the powder substance form a layer between the sliding and/or rolling surfaces of the suspension rope 3 and traction sheave 4, which layer prevents the contact between surface asperities. At the same time the particles 10 form a complex slip plane 12, which is not easily sheared and thus increases the friction but at the same time reduces wear of the surfaces. Due to their more or less spherical shape the hard particles 10 do not cause abrasive wear. Because of the different sizes of the particles 10 they can lock each other effectively in a dynamic contact situation between the contact surfaces.

[0079] The powder substance of the lubricant 8 should be rather fine. Advantageously the particle size of the powder substance is below 75 m. Preferably at least 50% of mass of the powder substance of the lubricant 8 belongs to the particle size range from 1 to 10 m.

[0080] The size distribution of the particles 10 is preferably such that a part of the particles 10 are greater than the asperity of the surfaces of the suspension rope 3 and the groove of the traction sheave 4. For example, one possible size distribution of the particles 10 is as follows: the powder substance contains 0% particles greater than 63 m, 1% particles between 20 and 63 m, 16% particles between 6.3 and 20 m, 63% particles between 2 and 6.3 m, and 20% particles smaller than 2 m. Other size distributions with other particle sizes and percent distributions are also possible. A part of the particles 10 are smaller than the asperity of the surfaces of the suspension rope 3 and the groove of the traction sheave 4. In case of greater proportion of small particles, the total surface area of the particles being in contact with oil is larger.

[0081] It is clearly verified by the tests described above that, owing to the high proportion of powder-like powder substance with hard and more or less spherical particles 10 contained in the lubricant 8, the lifetime of an elevator suspension rope 3 lubricated with the lubricant 8 is considerably longer than the lifetime of elevator ropes lubricated with prior-art lubricants, and in addition the friction factor between the rope 3 and the traction sheave 4 is greater than when using conventional lubricants, which enables more advantageous dimensioning.

[0082] One characteristic aspect, among others, of the elevator according to the invention is that the elevator is provided with suspension ropes 3 that are lubricated with the lubricant 8 that contains the powder substance with hard solid particles 10 mentioned above, and the load-bearing material of the suspension ropes 3 is metal, e.g. steel. The whole mass of the lubricant 8 comprises a suitable aforesaid percentage of the powder substance with the substantially hard and substantially spherical particles 10. In addition, the lubricant 8 can contain the aforementioned binder agents and other additives.

[0083] The use of the aforementioned lubricant 8 that contains powder substance for lubricating a rope laid from metal wires 9 is further characteristic for the solution according to the invention.

[0084] It is obvious to the person skilled in the art that different embodiments of the invention are not only limited to the examples described above, but that they may be varied within the scope of the claims presented below. Thus, for example, the composition of the lubricant and the mixture ratio of the different constituents can also be different to what is described above.

[0085] Likewise, it is obvious to the person skilled in the art that instead of synthetic oil, mineral oils or vegetable oils suited to the purpose can also be used as an oil in the lubricant.

[0086] Further, the invention would easily be carried out within the teaching of the following items:

[0087] Item 1. Steel wire rope comprising one or more strands composed of steel wires and a lubricant, which lubricant comprises oil and an amount of a powder substance, the lubricant is in a form of paste and the powder substance in the lubricant comprises particles whose internal aspect ratio is at most about 5, preferably less than 2, more preferably less than 1.5, even more preferably at most about 1.2, most preferably as close to one as possible.

[0088] Item 2. Steel wire rope of item 1, in which the shape of the particles is substantially spherical or almost spherical.

[0089] Item 1a. Steel wire rope comprising one or more strands composed of steel wires and a lubricant, which lubricant comprises oil and an amount of a powder substance, the lubricant is in a form of paste and the powder substance in the lubricant comprises particles whose hardness is greater than 4 on the Mohs scale.

[0090] Item 2a. Steel wire rope of item 1a, in which the hardness of the particles is about equal to the hardness of the steel of the wires of the strands, or greater than the hardness of the steel of the wires of the strands.

[0091] Item 3. Steel wire rope of item 1, in which the powder substance in the lubricant (8) comprises particles (10) whose hardness is greater than 4 on the Mohs scale.

[0092] Item 4. Steel wire rope of item 1, in which the hardness of the particles is about equal to the hardness of the steel of the wires of the strands, or greater than the hardness of the steel of the wires of the strands.

[0093] Item 5. Steel wire rope of item 1 or item 1a, in which the powder substance comprises particles that belong to the spinel group of minerals, which has crystal forms that are cubic or isometric, for instance octahedral.

[0094] Item 6. Steel wire rope of item 1 or item 1a, in which the powder substance comprises classified manganese (II, III) oxide, Mn.sub.3O.sub.4 and/or manganese (IV) oxide, MnO.sub.2.

[0095] Item 7. Steel wire rope of item 6, in which the powder substance is classified manganese (II, III) oxide, Mn.sub.3O.sub.4 and/or manganese (IV) oxide, MnO.sub.2.

[0096] Item 8. Steel wire rope of item 1 or item 1a, in which the powder substance comprises glass balls and/or glass beads, and/or other substantially spherical or almost spherical material particles, such as ceramic particles.

[0097] Item 9. Steel wire rope of item 1 or item 1a, in which the particle size of at least some of the particles is greater than the asperity of the contact surface of the suspension rope and the counter contact surface of the suspension rope.

[0098] Item 10. Steel wire rope of item 1 or item 1a, in which advantageously the size of particles of the powder substance in the lubricant is smaller than 75 m.

[0099] Item 11. Steel wire rope of item 9 or item 10, in which preferably at least 50% of the mass of the powder substance belongs to the particle size range from 1 to 10 m.

[0100] Item 12. Steel wire rope of item 9 or item 10 or item 11, in which the more or less spherically shaped hard particles (10) of the powder substance are arranged to form a layer between the sliding and/or rolling contact surface of the suspension rope (3) and the counter contact surface of the suspension rope (3), which layer prevents the contact between surface asperities, and that the particles (10) are arranged to form a complex slip plane (12), which increases the friction but at the same time reduces wear of the contact surfaces.

[0101] Item 13. Steel wire rope of item 1 or item 1a, in which the lubricant comprises a binder agent, the proportion of the binder agent being in the range of 0-5 weight-%, preferably in the range of 0.2-3 weight-%, even more preferably in the range of 0.3-0.6 weight-%, and more suitably about 0.4 weight-% of the amount of the lubricant.