The height adjustment system of the shearer is generally hydraulic height adjustment. The hydraulic system has a single pump and a double gear pump. The oil circuit system can be simplified into 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 required flow is large, and the required oil pressure 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, which requires less flow. The brake oil circuit uses oil to compress the brake pad to achieve braking efficiency, which also requires less flow. The oil pressure required by the oil circuit is about 2MPa. This paper compares the hydraulic system.
1. Oil tank heat dissipation:
When the hydraulic oil passes through the mesh block, due to the existence of elbows, joints, mesh openings and suddenly changed sections, the flow resistance in local areas caused by the velocity change of flow or flow direction will cause pressure loss, leading to the rise of oil temperature.
In the principle of the dual gear pump system, because there is no pressure drop in the main oil circuit, 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 that with a dual pump, which is unfavorable to the design of the shearer requiring a short fuselage.
2. Control valve life:
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. At the same time, large flow also means that more impurities may flow into the control oil circuit with the liquid, which is easy to cause blockage of the electromagnetic reversing network or pipeline, resulting in shutdown and maintenance accidents. In the dual 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, greatly reducing the occurrence of hydraulic system faults.
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 oil pump outlet. When the height is adjusted, the oil flows into the oil cylinder first and then into the control oil circuit. When the pump operates at full load (that is, the outlet oil pressure is 20MPa), the oil pressure supplied by the hydraulic pump to the hydraulic cylinder 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 flows directly 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 4mLhr small hydraulic pump. 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 main pump oil flows through the hydraulic cylinder, and the remaining oil is connected to the oil tank. When the load is full, the pressure drop is the set pressure of the high-pressure overflow stage (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 height adjustment system of the shearer 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
