METHOD FOR BENDING A TENSION ELEMENT OVER A PULLEY

Abstract

Method of cooling a pulley, comprising a step of decreasing the temperature of the pulley by using a closed cooling system that is in contact with the pulley comprising a cooling medium in the range of −60 to 70° C.

Claims

1. A method of cyclic bending a tension element over a pulley, the tension element comprising high performance fibers and having a core temperature not exceeding 70° C., the method comprising a step of decreasing the temperature of the pulley by using a closed cooling system that is in contact with the pulley comprising a cooling medium in the range of −60 to 70° C.

2. The method according to claim 1, wherein the tension element is a strip, a strap, a belt, a cord, a ribbon, a cable, a wire, a rope, a strand, a tube, a hose, a wire rope, a tape, a chain and/or combinations thereof, and preferably the tension element is a rope.

3. The method according to claim 1, wherein the high performance fibers are ultrahigh molecular weight polyethylene fibers.

4. The method according to claim 1, wherein the pulley is a wheel, a sheave, gliding shoe, bitts or a drum, and preferably the pulley is a sheave.

5. The method according to claim 1, wherein the closed cooling system comprises a cooling device, a channel located inside the pulley and a cooling medium, the cooling device being connected to the channel, forming together a closed circuit suitable for recirculating the cooling medium through the pulley.

6. The method according to claim 1, wherein the cooling device comprises an outlet by which the cooling medium is fed to the channel and an inlet by which the cooling medium is fed into the cooling device, the inlet and the outlet forming together with the channel located inside the pulley a closed loop.

7. The method according to claim 1, wherein the pulley is connected with the closed cooling system via a swivel connector.

8. The method according to claim 1, wherein the swivel connector inlet part is static and the swivel connector outlet part is dynamic.

9. The method according to claim 1, wherein the cooling medium is fed from the cooling device into the pulley via the inlet of the pulley through an internal channel located underneath the groove surface of the pulley.

10. The method according to claim 1 whereby the method increases the cyclic bending over sheave lifetime of the tension element, preferably wherein the bending cycles to failure value of the tension element is more than 100% higher than the bending cycles to failure value of a non-cooled tension element.

11. Use of the method according to claim 1 for lifting and hoisting, preferably for cranes, marine platforms, robotics, mining, deep-sea-installation and recovery, transportation.

Description

[0076] FIG. 1 herein schematically illustrates the side view cross section of a sheave used according to the present invention, wherein: 1=groove of the sheave; 2=back disc for covering the sheave for sealing the cooling medium; 3=internal channel located at back side of the sheave; 4=internal channel connecting inlet and back side of the sheave; 5=sheave; 6=internal channels connecting front side and back side of the sheave; 7=front disc for covering the sheave for sealing the cooling medium; 8=cooling media outlet; 9=internal channel located at front side of the sheave; 10=cooling medium inlet; 11=symmetry axis.

EXAMPLES

Methods

[0077] Dtex: yarn's or filament's titer was measured by weighing 100 meters of yarn or filament, respectively. The dtex of the yarn or filament was calculated by dividing the weight (expressed in milligrams) to 10. [0078] Heat of fusion and peak melting temperature have been measured according to standard DSC methods ASTM E 794 and ASTM E 793 respectively at a heating rate of 10K/min for the second heating curve and performed under nitrogen on a dehydrated sample. [0079] IV: the Intrinsic Viscosity is determined according to method ASTM D1601 (2004) at 135° C. in decalin, the dissolution time being 16 hours, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/I solution, by extrapolating the viscosity as measured at different concentrations to zero concentration. [0080] Tensile properties of UHMWPE fibers: tensile strength (or strength) and tensile modulus (or modulus) are defined and determined on multifilament yarns as specified in ASTM D885M, using a nominal gauge length of the fibre of 500 mm, a crosshead speed of 50%/min and Instron 2714 clamps, of type “Fibre Grip D5618C”. On the basis of the measured stress-strain curve the modulus is determined as the difference between 0.3 and 1% strain. For calculation of the modulus and strength, the tensile forces measured are divided by the titer, as determined above; values in GPa are calculated assuming a density of 0.97 g/cm.sup.3 for the UHMWPE. [0081] Tensile properties of fibers having a tape-like shape: tensile strength, tensile modulus and elongation at break are defined and determined at 25° C. on tapes of a width of 2 mm as specified in ASTM D882, using a nominal gauge length of the tape of 440 mm, a crosshead speed of 50 mm/min. [0082] Number of olefinic branches per thousand carbon atoms was determined by FTIR on a 2 mm thick compression moulded film by quantifying the absorption at 1375 cm-1 using a calibration curve based on NMR measurements as in e.g. EP 0 269 151 (in particular pg. 4 thereof). [0083] Breaking strength of the tension element was measured according to method ISO2307. For the rope comprising UHMWPE used in the examples, the spliced breaking strength was 400 kN, measured according to ISO2307. [0084] Cyclic bend-over-sheave (CBOS) test: the bend fatigue of the rope was tested by bending the rope over a sheave. The rope was placed under load and cycled back and forward over the sheave, at a stroke speed of 210 m/min, until the rope reached failure. Each machine cycle produced two straight-bent-straight bending cycles of the exposed rope section, the double bend zone. The force applied to the rope was 30% of the average breaking strength of the tested rope. The ratio D/d was 20, wherein D is the diameter of the sheave and d is the diameter of the rope. The test-load was 24 metric tons for the machine. The test-load was 12 metric tons for the load in the rope applied during testing. The double bend zone was 14 times the diameter of the rope. The bending cycle time was 12 seconds. The pause was 1 second between each cycle reversal. The total machine cycle time was 14 s. The pre-load for bedding in the rope was 5 times 14.5 metric tons.

Sample 1

[0085] A rope having an essentially circular cross-section with an effective diameter of about 21 mm was braided from 12 principal strands, each principal strand containing 7 laid secondary strands, each secondary strand containing a bundle of 15 yarns having 1880 dtex and comprising UHMWPE fibers. The yarns were sold by DSM Dyneema, NL, under the commercial name of Dyneema® DM20 XBO. The primary strands were braided with a braiding period of 150 mm. The secondary strands were twisted to form a primary strand with a twist factor of 15 twists per m. The yarns were twisted to form a secondary strand with a twist of 13 twists per m. The rope was unwound from a coil and pulled through a tank containing a rope coating commercially available under the name ICO-DYN 10. The coating was diluted before application on the rope with water (in ratio of 1:1) in order to obtain the proper amount of coating weight on the rope (12% dry coat weight), after which the rope was dried by air. The rope was configured in an endless loop construction, meaning both rope ends have been connected with use of a splice termination. The loop had a circumference of about 6.5 m. The splice termination (often referred also to as a tucked splice) had an amount of tucks of 9 per rope side. Both splice-ends were not tapered.

Example 1

[0086] A sheave of 420 mm in diameter made of a steel type known as RVS 303 was connected by means of a Ring Feder conical coupling to the lower shaft of a cyclic bend-over-sheave fatigue test apparatus. The feed and return channels in the sheave were connected to a swivel connector (manufactured by DSTI) by using a pair of silicon hoses, each end of both hoses being fixed with hose clamps to either the sheave inlet and swivel outlet and vice versa. The swivel connector was then coupled to both the inlet and outlet hoses of a closed cooling system by using a snap tight quick release coupling at the end of each hose. The closed cooling system was connected to the swivel connector such that one side of the swivel connector that connected to the sheave was dynamic, i.e. was able to rotate freely along with a shaft, while the other side of the swivel connector that connected to the cryostat side was static (i.e. does not rotate). Thus, the swivel inlet was static and the swivel outlet was dynamic, rotating together, in the same direction and with the same velocity with the sheave and the shaft. The closed cooling system contained a cryostat as being the cooling device, the cryostat and the internal channels of the sheave forming together a closed circuit suitable for recirculating tap water used as the cooling medium through the sheave and enabling cooling of the sheave and consecutively of the rope.

[0087] A Lauda Cryostat TT-19 of type Ultra Kryomat RUK50 was used. The cryostat had an outlet (or feed) by which tap water having a temperature of 5° C. was fed to the sheave with a flow rate of about 15 l/min and an inlet (or return) by which water was fed (or returned) to the cryostat with a flow rate of about 15 l/min and temperature of more than 5° C. The cryostat set temperature for cooling the bending sheave was set and maintained at about 5° C.

[0088] The water was fed via the inlet of the sheave (i.e. by pumping it using an electrical pump) with a flow rate of about 15 l/min and at a temperature of about 5° C. from the cryostat directly into the sheave through internal channels milled underneath the groove surface of the sheave. At both sides (front and back side) of the bending sheave, two stainless steel plates having disc shape were mounted for reasons of sealing the sheave. Both plates manufactured by RVS 303 were provided with a rubber seal for water sealing purposes.

[0089] The temperature of the sheave was measured by using a type K thermocouple taped to the side (at groove end) of the sheave and the temperature of the circulated water at the outlet of the cryostat (i.e. the feed of the sheave) was controlled/maintained at the chosen set temperature of about 5° C. For means of reproducibility, the flow rate was kept constant, at about 15 l/min.

[0090] During the experiments, the rope center temperature, i.e. the center of the double bending zone (i.e. the core temperature) was continuously monitored and logged. For this, a type K parallel thermocouple has been inserted in the center of the rope at the double bending zone. The thermocouple was, together with the thermocouple used to measure the sheave temperature, connected to a Picotech TC-08 data logger device that was connected to a computer via an USB connection and the live temperature being displayed and logging initiated or configured.

[0091] The bend fatigue of the rope was tested by bending the rope over the sheave according to the CBOS test conditions as detailed herein above. The temperature in the single bend zone of the rope at contact surface of the rope with the sheave was about 10 K less than the temperatures in the double bend zone. The temperature difference between the sheave and the double bend zone of the rope at contact surface of the rope with the sheave before cooling was 17 K. After the water cooling was initiated (by tap water circulation in the sheave), the temperature difference between the sheave and the double bend zone of the rope remained the same, however the absolute temperature level of both dropped around 26K. The core temperature of the rope in the double bend zone at contact surface with the sheave before cooling stabilized at about 58° C., and after the water cooling was initiated the temperature decreased rapidly to about 33° C. in less than 1000 s. The sheave temperature measured on the sheave near the groove in which the rope is fitted before cooling stabilized at about 40° C., and after the water cooling was initiated the temperature decreased rapidly to about 16° C. in less than 10 min. The rope failed after 26064 bending cycles. The bending cycles to failure was increased by 211% compared to below Comparative Example 1.

Comparative Experiment 1

[0092] A sheave of 420 mm in diameter machined out of a steel type known as RVS 303 was connected by means of a Ring Feder conical coupling to the lower shaft of a cyclic bending over sheave fatigue test apparatus. The bend fatigue of the rope obtained as Sample 1 was tested by bending the rope over the sheave according to the CBOS test conditions as detailed herein above. The rope and/or the sheave were not actively cooled but there was a cooling effect given by exposing the rope over the sheave into the air at ambient temperature (about 23° C.). The temperature in the single bend zone of the rope at contact surface with the pulley was 10K less than the temperatures in the double bend zone of the rope. The temperature difference between the sheave and the double bend zone of the rope at the contact surface with the sheave was 17K, remaining thus the same as in Example 1, however the absolute temperature level of the sheave and the double bend zone of the rope was significantly higher than their temperature as described in Example 1. The core temperature of the rope in the double bend zone at contact surface with the sheave during the test at air exposure was about 58° C. The rope failed after 12368 bending cycles.

[0093] It can be thus observed that a tension element with increased life time (i.e. double value of the resulting bending cycles to failure) when subjected to bending under high load and high frequency cycles of bending during prolonged times was achieved according to the present invention.