Concrete pump is a pipeline construction equipment rely on pressure delivery of concrete , concrete pump hydraulic system is generally high pressure and high flow system. From the use of concrete pump survey found that many types of concrete pump, the use of about 40min, the hydraulic system temperature up to 60e, after about 2h, the hydraulic system thermal equilibrium temperature can be as high as 70e above the concrete pump hydraulic system Normal heat balance temperature should be about 50e. Therefore, there has been a concrete pump hydraulic system, the problem of excessive heating oil temperature problem.
2 Concrete pump hydraulic system heating phenomenon hazards
Concrete pump hydraulic system heating, a direct impact on the normal operation of concrete pumps, fever caused by the hazards, mainly in the following points: (1) the working fluid temperature increases, the viscosity of the working fluid decreased pump leakage increased, The actual flow of the pump has decreased; (2) the hydraulic system and components of the seals metamorphism at high temperatures, elastic degeneration ability to reduce the sealing performance, or seal failure, so that leakage increases; (3) When the thermal expansion coefficient is different, the valve core is stuck due to thermal expansion between the valve core and the valve body, so that the concrete pump can not work. (4) When the viscosity of the working fluid drops, the lubrication of the working fluid Decreased performance, hydraulic components accelerated wear and tear accelerated wear and tear components, shortening the service life of components.
In order to avoid the occurrence of the above phenomena, some concrete pumps have to stop after being used for a certain period of time to cool down the system, thereby reducing the startup rate of concrete pumps and affecting the construction progress. Therefore, we should take into account the causes of system heat, take appropriate measures to control the temperature of the hydraulic system to ensure the normal use of concrete pumps.
3 concrete pump hydraulic system heating the main reason and rule out
The heating of the hydraulic system can be divided into two categories according to the causes of heat: one is the heat caused by the design; the other is the heat caused by the failure or improper use of hydraulic components. Obviously, different causes of fever, the exclusion method is not the same.
3.1 unreasonable design, resulting in the heating of the hydraulic system and its exclusion
(1) improper use of hydraulic oil number may cause heating of the hydraulic system The selected hydraulic oil at low oil temperatures, the system works normally, but the system is working for some time, the oil temperature increases, the viscosity of hydraulic oil decreased, resulting in Increased internal system leakage, with the increase in leakage also led to an increase in oil temperature, the formation of a vicious circle of oil temperature. The solution is: According to the system load and normal operating temperature requirements, select the appropriate viscosity of the hydraulic oil.
(2) The fuel tank design is unreasonable, and the heat dissipation effect of the hydraulic system is reduced . The main function of the system heating oil tank is to store hydraulic oil, but it also has the functions of dissipating heat, precipitating impurities and separating water. Fuel tank design is unreasonable, mainly in two aspects: First, the fuel tank volume design is too small, because the concrete pump is a mobile hydraulic equipment, the fuel tank volume is generally double the hydraulic pump flow, so the tank cooling area and oil reserves Second, some of the tanks in the structural design is not reasonable, the suction nozzle and the return pipe port closer, no separator in the middle, thus shortening the oil in the tank cooling cycle and the path of precipitation of impurities, or even Resulting in most of the return oil directly into the suction pipe, reducing the cooling effect of the fuel tank, increasing the oil temperature. The solution is to increase the volume of the fuel tank properly so that the volume of the fuel tank is (1125-115) Q, and try to increase the distance between the suction pipe port and the oil return pipe port. A partition plate should be provided between the suction pipe and the oil return pipe to ensure that the fuel tank Should have cooling power.
(3) smaller heat flux, cooler installation location is unreasonable, so that the cooling capacity of the system reduces the cooling capacity of concrete pumps are air-cooled and water-cooled two, users can choose according to the actual situation, but the general use of air-cooled more. Some concrete pumps consider the pressure requirements of the cooler, the cooler is set on the oil return line of the stirring system, and only the oil of the stirring system is cooled. Due to the smaller flow rate of the stirring system, the cooling effect of the entire system is poor, fever. Solution: First, an independent cooling circuit can be used to improve the cooling effect. The second is to set the cooler in the system total oil return to increase the heat flow, improve cooling effect, but this time should pay attention to two problems, the first issue is the cooling fan speed, cooling fan speed can not be too low, Otherwise it will reduce the cooling effect, you can use the motor to drive the fan, or in the total oil return road set a low-voltage drive motor, the motor speed and cooling flow to match, but also can solve the main circuit pressure impact on the cooler pressure capacity; The second problem is the use of motor-driven fan, the main system of the pressure impact on the cooler pressure capacity, this time, the return line and the cooler and installed a low pressure overflow protection valve or one-way valve for cooling The highest pressure protection device.
(4) improper selection of hydraulic components, resulting in system heating concrete pump hydraulic system is generally high pressure flow system, if the system of hydraulic components, the main valve, relief valve and sequence valve size selection is not reasonable, can not meet the large Flow requirements, which in use, so that the flow velocity of the valve port flow is too high, resulting in greater pressure loss and the oil temperature, therefore, hydraulic system design in the selection of hydraulic components design, must be based on hydraulic components The maximum working pressure to be sustained , the maximum flow rate passed, and the required range of pressure and flow adjustment to minimize the pressure loss at the valve port and to reduce the heating of the system due to the unreasonable selection of hydraulic components.
(5) pipeline design, installation unreasonable, resulting in large pressure loss, so that the pressure can be converted into heat energy in the hydraulic system design, piping design and installation can not be ignored, the pipeline diameter should be strictly according to their working pressure and through Flow design, to avoid too small diameter design, resulting in high flow velocity, along the pressure loss is too large, causing fever. At the same time, it should also pay attention to the installation of the pipeline, it is necessary to achieve the appearance of tidy, but also to avoid pipelines gather and the pipeline sharp turn, affecting the natural cooling pipe or cause local pressure loss caused by excessive heat.
3.2 due to improper use of hydraulic system or component failure, resulting in heating and eliminating the hydraulic system
(1) The hydraulic oil level in the fuel tank is lower than the minimum level to reduce the cooling power of the fuel tank. During the operation of the concrete pump, observe the oil level of the hydraulic oil in the tank at all times and keep the hydraulic oil level at the normal level Range, so as to ensure the cooling effect of the tank, when the tank hydraulic oil level below the minimum level, it is timely fuel tank.
(2) Cooler cooling effect is reduced, so that the fluid temperature rise, cooling system cooler cooling effect may be caused by the following reasons: a1 cooler internal blockage or surface dirt more, causing the cooler safety device is turned on, the cooler reduced flow through the cooling flow reduction, cooling or ventilation bad, the cooler of the cooling heat transfer coefficient is reduced, the cooling effect is reduced, and therefore, the concrete pump must be regularly checked, in use, and clear the cooler, the cooler surface regularly Dirt removal, to ensure smooth internal cooler and external cleaning, to ensure cooler cooling effect. b1 cooler relief valve or check valve opening pressure is lower than the standard value, so that the cooler safety protection device is open when the cooler is not blocked, resulting in overflow shunt, cooler cooling flow to reduce, therefore, the cooler before use , We must correctly adjust the opening pressure of the safety protection device, in the use of regular inspection to correct the safety protection device opening pressure value.
(3) improper adjustment of the hydraulic system pressure, resulting in system heat In the concrete pump hydraulic system, due to the performance requirements, the system often have safety valves, relief valves and sequence valves. If the safety valve pressure is too low, the safety valve will be frequently opened, resulting in overflow loss, resulting in system fever; if the pressure is too high, it will increase the system leakage, the system fever, therefore, should be hydraulic system Load requirements, correct calculation and adjustment of safety valves and pressure values â€‹â€‹to ensure that the system operates within the specified pressure range. When the main pump of the pump system is a closed system, the heat exchange circuit must be installed in the pumping system. The set pressure of the relief valve in the heat exchange circuit should be taken seriously. If the set pressure is too low, the pump hydraulic pressure Cylinder commutation increases, set the pressure is too high, will make the overflow loss is too large, the system temperature is too high. Therefore, should be reasonable to determine the heat exchanger circuit relief valve pressure adjustment value, the general adjustment value of the relief valve (1 ~ 115) MPa, pumping system working pressure of the oil circuit is 215MPa. When setting the sequence valve in the hydraulic system of the concrete pump, we must understand the working characteristics of the sequence valve and correctly adjust the working pressure of the sequence valve. If the internal control sequence valve to adjust the pressure is too high, when the working pressure of the working cylinder is lower than the pressure adjustment, there is a pressure sequence valve port loss, caused by temperature, resulting in heating systems, provided a reasonable determination of the internal control sequence valve Set the pressure, the working pressure of the working cylinder is higher than the opening pressure of the sequence valve, the sequence valve work, the valve port will be fully open, the valve port basically no pressure loss, thus avoiding the sequence valve set pressure caused by improper system fever.
(4) The internal leakage increases, the oil temperature can be raised, the system heat concrete pump hydraulic system of internal leakage, including hydraulic pump, hydraulic cylinder, hydraulic motor and hydraulic valve internal leakage, pressure oil in the leakage process, the pressure drop, Temperature rises. If the system increases the internal leakage, will cause the oil temperature to rise, the system overheated, serious, it will make the system pressure drop, poor pumping, pumping displacement decreased, stirring weak, mixing speed decline. Therefore, regular inspection of these components, the replacement of the corresponding sealing components on a regular basis, the timely replacement of damaged or injured parts replacement or repair, or even replace the corresponding hydraulic components, so as to avoid component leakage caused by the system heat.
Concrete pump hydraulic system fever in the course of the problem has become one of the problems can not be ignored, due to the heating of the hydraulic system will lead to many concrete pump failure occurred. For concrete pump manufacturers, should strive to start from the design, the heating system of its hydraulic system to a minimum, this will not only increase the user's concrete pump boot rate and extend its life, but also save energy and reduce maintenance costs; for concrete pump Users should strive to start from the use and maintenance, in strict accordance with the requirements of manufacturers, the proper use, commissioning, inspection, maintenance of concrete pumps to reduce the failure rate and reduce the system due to improper use of fever. In short, for different causes of fever, take some measures, you can control or reduce the heat of the hydraulic system to improve the boot rate of concrete pumps and extend the service life.
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