Working principle of gear rack of ship lift for Three Gorges Dam

The ship lift of the Three Gorges project is located on the left bank of the Three Gorges Project and on the right side of the two-way five level ship lock. It is a fast passage for passenger ships to cross the dam. The joint operation with the two-way five level ship lock can greatly improve the navigation capacity of the project. The ship lift of the Three Gorges project adopts the gear rack climbing balance weight vertical ship lift, with a designed ship passing capacity of 3000 t and a maximum lifting height of 113 m. It is characterized by a large lifting height, a large lifting quality, a large variation of Upstream Navigation water level and a fast change rate of downstream water level. It is the largest and most technically difficult ship lift in the world [1-2].

The ship chamber of the Three Gorges ship lift is driven by four sets of open gear mechanism, and it rises and falls vertically along the four racks laid on the concrete column wall. The height of each rack is 127.5 m, the bottom installation elevation is 51.45 mm, and the top installation elevation is 178.98 M. The rack is manufactured and installed in sections. The module of rack is 62.667 mm, the width of gear is 810 mm, and the length of single section is 4705 mm. The material is g35crnimo6. The process of casting blank + induction hardening of gear is adopted. Each rack is composed of 26 sections. The total weight of the four racks is approximately 2692 t. The design life of the gear rack of the Three Gorges ship lift is 35 years, 18 times a day, 335 days a year, and the total number of cycles is 4.22 × 105. The gear rack is one of the key components of the Three Gorges ship lift, which has the characteristics of large quantities, large scale, high processing accuracy requirements and difficult replacement. At present, there is a lack of test data accumulation and Test Method Research of this kind of rack at home and abroad, and there is no ready-made test device that can carry out performance test and quality evaluation on the large module and large size rack of the lifting system of the Three Gorges ship lift. Therefore, it is very necessary to carry out reliability quality evaluation and test on the large rack of the Three Gorges ship lift, This will also fill in the blank of no test equipment or test method for large rack test in China. For this reason, led by Zhengzhou Institute of machinery, in combination with China’s second Heavy Machinery Group Corporation (Three Gorges rack manufacturer), General Institute of mechanical science, Shanghai Jiaotong University, Henan University of technology and other units, Zhengzhou Institute of machinery is carrying out life test, material limit stress test, reliability research and quality assessment of rack, The completion of the work will provide reference for the installation and commissioning of the Three Gorges ship lift, provide scientific guidance for the operation and maintenance of the Three Gorges ship lift, and provide important technical support for the safe operation of the ship lift.

The analysis and Research on the force direction and load size of the gear rack of the Three Gorges ship lift is the basis for the quality assessment work, which has the same guiding significance for the manufacture, installation and operation of Xiangjiaba ship lift, and has important reference value for the design and manufacture of large module gear rack drive devices (such as lifting system of offshore oil drilling platform) in other application fields.

The ship lift of the Three Gorges project is a rack and pinion climbing fully balanced vertical ship lift, as shown in Figure 1, which is mainly composed of tower column, ship chamber, steel wire rope, pulley, balance weight, balance chain and four sets of rack and pinion driving devices. When the ship lift works, the weight of the equipment, ship and the 3.5m deep water in the cabin is completely balanced by the same weight. The load on the rack is mainly related to the unbalanced weight caused by the water depth of the wrong load, which is not related to the quality of the equipment. The ship chamber and the balance weight are connected by steel wire rope. The steel wire rope turns after the pulley set at the top of the tower column to realize the reverse movement of the balance weight and the ship chamber. The imbalance caused by the length change of the steel wire rope on both sides of the pulley is finally compensated by the balance chain. In the design of the Three Gorges ship lift, the ship chamber lifting is fully balanced.

The Three Gorges ship lift is driven by rack and pinion climbing. The rack is fixed on the tower, and the shaft gear drive system is installed on the cabin, which works through the relative movement of rack and pinion. The ship lift of the Three Gorges project is a fully balanced vertical ship lift. Theoretically, the weight of the balance weight is equal to that of the ship’s cabin in 3.5 m water depth. The rack and pinion drive device only needs to exert a small amount of force to overcome the resistance of motion, so that the ship’s cabin can move up and down. However, due to the existence of false loading depth in the application, there is imbalance between the balance weight at both ends of the wire rope and the cabin, which becomes the main load of the gear rack.