Application of double gear pump in shearer height adjusting system
The height adjustment system of the shearer is generally hydraulic height adjustment. The hydraulic system has single pump and dual gear pump.
The height adjustment system of the shearer is generally hydraulic height adjustment. The hydraulic system has single pump and dual gear pump. The oil circuit system can be simplified as the main oil circuit, control oil circuit and brake oil circuit. The main oil circuit controls the lifting rocker arm of two hydraulic cylinders. The flow required is large, and the oil pressure required is slightly less than the oil pressure of the high-pressure overflow valve. The control oil circuit only controls the action of the manual hydraulic steering network, and the required flow is small. The brake oil circuit uses oil to compress the brake pad to achieve braking efficiency, and the required flow is also small. The required oil pressure in the oil circuit is about 2MPa. This paper compares the hydraulic systems.
1. Heat dissipation of oil tank:
When the hydraulic oil passes through the mesh block, due to the existence of elbows, joints, mesh ports and suddenly changed sections, the flow resistance in local areas due to the flow or flow direction speed changes will cause pressure loss, resulting in oil temperature rise.
In the principle of double gear pump system, there is no pressure drop in the main oil circuit, so the power waste is mainly in the control oil circuit. From the calculation results, in order to meet the heat dissipation requirements of the oil tank, the oil tank with a single pump is larger than the oil tank with a double pump, which is unfavorable to the design of the shearer requiring a short fuselage.
2. Service life of control valve:
In the hydraulic system of a single pump, the oil in the main oil circuit enters the control oil circuit as a whole with a large flow, so a thicker hydraulic pipe must be used in the control. At the same time, during the control, the oil passes through many small holes and the pressure loss is serious. Large flow also means that more impurities may enter the control oil circuit with the flow of liquid, which is easy to cause the blockage of the electromagnetic reversing network or pipeline, resulting in shutdown and maintenance accidents. In the duplex pump system, since the control oil circuit is a relatively separate circuit, the small pump absorbs oil through the main oil return pipe, enters the pump body, and passes through the fine filter to ensure the quality of oil, which greatly reduces the occurrence of hydraulic system failures.
3. Power loss:
The oil enters the control oil circuit after passing through the middle position (H) of the left and right rocker arm hydraulic cylinder network group through the pump. When not in operation, the oil returns to the oil tank through a low-pressure overflow network (2MPa) without passing through the electromagnetic reversing network. There is a high pressure overflow network (20MPa) at the outlet of the oil pump. When the height is adjusted, the oil enters the oil cylinder first and then the control oil circuit. When the pump operates at full load (that is, the outlet oil pressure is 20MPa), the oil pressure supplied to the hydraulic cylinder by the hydraulic pump is 18MPa, which shows that 10% of the power is wasted.
This problem does not exist in the dual gear pump system. When the height is not adjusted, the main pump oil directly flows through the middle position (H) of the left and right rocker arm hydraulic cylinder network groups and returns to the oil tank directly. The control system is controlled by a small hydraulic pump of 4mLhr. There is a low-pressure overflow network (2MPa) in the control oil circuit to ensure the oil pressure of the control system and the braking system. When the height is adjusted, the oil of the main pump passes through the hydraulic cylinder, and the remaining oil is connected with the oil tank. When the load is full, the pressure drop is the set pressure of the high-pressure overflow vane (20MPa). It can be seen that there is no power waste in this system.
From the above analysis, it can be seen that the application of the double gear pump system in the shearer height adjustment system can significantly reduce the waste of power, reduce the rise of oil temperature, shorten the length of the machine body, and increase the service life of hydraulic components.