1. Project Overview

The Caojie Avionics Junction Project is located on the section of the Jialing River near Caojie Town in Hechuan, Chongqing. It is the second stage of the bottom-to-up cascade development of the section from Hechuan to the mouth of the main stream of the Jialing River. The normal water level is 203.00m and the design flood level is 217.56 m. m, the check flood level is 220.81m. It is a comprehensive utilization project of water resources with the main purpose of developing shipping and other benefits such as power generation, sediment retention and silt reduction, and irrigation. The width of the orifice of the sand flushing gate is 14.8m, and the height of the arc-shaped working gate is 25.5m. The gate adopts the structure of three main beams and three inclined arms. The radius of curvature of the panel is 31m, and the height of the hinge is 22m. The gate leaf is made in 8 sections, which are welded as a whole at the installation site. When the gate is at a maximum opening height of 27 m, the bottom edge of the gate is still underwater at 14.18 m (checking the water level), which means that it is in a partially open state when the water level is being checked for leakage. The purchase of the gate hinge bearing of the sand flushing system is subject to domestic public bidding. Due to the large force on the hinge bearing, the high downstream water level and the complex water flow pattern, the gate hinge is affected by the impact of the positive water flow and the flooding of the backwater. The pivot bearing adopts the self-lubricating spherical sliding bearing with sealing ring of international famous brand, the inner diameter is 630mm.

2. Technical conditions

Table of force characteristics of self-lubricating spherical plain bearings for hinges

1) The working environment of the bearing: Usually, the gate is closed in a water-retaining state, and the working environment of the bearing is dust and humid atmosphere; when the gate is opened to flush the sand and release the flood, the bearing works underwater.

2) Under normal operating conditions, the radial load of the bearing is 32000kN, and the axial load is 2200kN. The operation mode of the bearing is reciprocating motion, the angle of each operation is 62.5o, and the speed of the hoist piston of the gate is 0.6m/ min. The operating temperature of the bearing is -20℃～+150℃.

3) The bearing consists of an inner ring with an outer spherical surface and an outer ring with an inner spherical surface, and the outer ring is longitudinally split (axially separable).

4) If there is relative sliding between the inner ring and the outer ring of the bearing, self-lubricating anti-friction materials should be provided, and the dry friction coefficient of the friction pair material should not exceed 0.11.

5) Self-lubricating spherical sliding bearings should have maintenance-free functions, no oil or other lubricating materials are required during the use of the bearings, and the working life is not less than 30 years.

6) Bearings work underwater and should have a double-sided watertight function.

3.The check of the performance indicators of the bearing

1. Bearing selection:

1) Bearing model: choose GEW630HFZB056-2RS bimetal inlaid self-lubricating spherical plain bearing;

2) Bearing form:

-(1) The outer ring adopts an axially separated type (double half outer ring), and the material is bimetal self-lubricating material: the surface layer is high-strength copper alloy of Sanhuan Company, the steel base material is GCr15SiMn normalizing treatment, and the friction surface is inlaid with solid lubricant . The surfacing process is adopted between the copper alloy surface layer and the steel substrate, and the two are metallurgically bonded.

-(2) The inner ring is an integral structure, the material is GCr15SiMn, the hardness after heat treatment is HRC58-64, the spherical surface is plated with hard chrome, and the thickness of the coating is 0.05 (after processing) mm.

-(3) There are built-in O-rings on both sides of the outer ring of the bearing to achieve double-sided water sealing.

3) Bearing size: inner diameter φ630mm, outer diameter φ900mm, inner ring width 450mm, outer ring width 425mm.

2. Mechanical properties of bearing materials:

See the table below Physical properties of bearing O-ring seal: see the table below

3. Check of bearing characteristic index:

1) Bearing static load capacity: The surface layer material of GEW630HFZB056-2RS bearing is three-ring high-strength copper alloy, and the yield limit is 500Mpa. If the yield limit is taken as the allowable static load and calculated according to 35% of the inlaid area, the allowable static load of the bearing is 500×(1-35%)=325Mpa. Since the force at each point of the spherical bearing is unbalanced, the maximum pressure is 1.334 times the average pressure, so the maximum allowable pressure is 325/1.334=243.6Mpa. According to the allowable static load specific pressure of 243.6Mpa, the effective bearing projected area of GEW630HFZB056-2RS (excluding the sealing grooves at both ends) is 313480mm2, then the allowable static load of the spherical plain bearing is 243.6Mpa×313480mm2=76373KN.

2) Bearing dynamic load capacity: According to the conditions of use, the radial load is Fr=32000kN, the axial load is Fa=2200kN, Fa/Fr=0.07, and the equivalent load factor is 1.07, so the equivalent load is 1.07×32000kN=34240KN. The allowable dynamic load specific pressure of the bimetal bearing material whose surface material is high-strength copper alloy is 160Mpa, and the allowable dynamic load is 160Mpa×313480mm2=50157KN. Compared with the equivalent load, the safety factor is 50157KN/34240KN=1.46, which is obviously safe and reliable.

3) Bearing dry friction coefficient: On December 30, 2006, the performance test of bimetal self-lubricating spherical plain bearings was carried out on the CZS-4000 CNC self-lubricating bearing testing machine at the Vibration and Strength Testing Center of Dalian University of Technology (MA certification testing unit), under the conditions: load 83Mpa, line speed 16mm/s, the sliding distance is 1000m (equivalent to 50 years of real machine operation), the result is: the friction coefficient is 0.045-0.075, the radial wear amount is 0.065-0.11mm, the surface condition is good and a uniform and continuous solid lubricating film is formed . In addition, in 2005, the GEW220XFZ5 spherical plain bearing produced for the fast gate fixed wheel of the Three Gorges Right Bank Underground Power Station was subjected to running-in and working condition (destructive) tests on a large-scale multi-functional testing machine. The test results are: The dry friction coefficient is 0.086-0.091. The above tests show that: GEW630HFZB056-2RS meets the requirement that the dry friction coefficient is less than 0.11. The tests are all carried out under dry friction conditions. Except for the pre-coating of a solid lubricating film during the installation process, no oil or other lubricating materials are required during the use of the bearing. It has a maintenance-free function and has a working life of not less than 50 years.

4) Bearing tolerance and radial clearance: Radial clearance: 0.35—0.45mm. The above tolerances and clearances comply with ISO12240-1:1998 (equivalent to GB/T9163-2001).

5) Others: (1) The roughness of the mating surface and end face of the bearing is within Ra1.6μm; (2) Residual magnetic strength: Since the demagnetization treatment must be carried out after the bearing is ground, it is in line with the relevant national standards; (3) Since the bearing works underwater, not only the outer ring of the bearing should be provided with a built-in seal, but also the glands at both ends of the bearing should be provided with sealing devices to avoid water immersion into the bearing as much as possible.

4. Conclusion

Through the above analysis of the dynamic load capacity, static load capacity, friction coefficient and life test analysis of GEW630HFZB056-2RS bearing, it fully meets the various technologies of the arc-shaped working gate of the Chongqing Caojie Aviation Power Project. requirements, are reliable. In 2005 and 2006, GEW530HFZB056 joint bearings were used in the supporting hinges of the arc gates in the Shidi and Youxu projects in Chongqing, and the results were good. In 2006, GEW220XFZB056 spherical plain bearings were used in all the quick gates of Goupitan. In 2007, the Dedingshan project also adopted domestic GEW440HFZB056 spherical plain bearings. The Caojie project adopts the largest domestic bimetal self-lubricating bearing, which indicates that the technical performance and process technology of the bearing have matured and have entered the stage of large-scale promotion.