1. From the investigation of the use of concrete pumps, it is found that for many types of concrete pumps, the temperature of the hydraulic system can be as high as 60e after about 40 minutes of use, and the thermal equilibrium temperature of the hydraulic system can be as high as 70e after about 2 hours of use. The normal thermal equilibrium temperature of the system should be around 50e. Therefore, the oil temperature of the hydraulic system of the concrete pump is too high, that is, the problem of heat generation.
2. The harm of the heating phenomenon of the hydraulic system of the concrete pump
The heating of the hydraulic system of the concrete pump directly affects the normal operation of the concrete pump, and the harm caused by the heating phenomenon mainly includes the following points: (1) After the temperature of the working liquid increases, the viscosity of the working liquid decreases, and the leakage of the pump increases. The actual flow of the pump has decreased; (2) the seals of the hydraulic system and components are deteriorated at high temperatures, and the elastic denaturation ability is reduced, which reduces the sealing performance, and even the seal fails, which increases the leakage; (3) When the valve of the hydraulic valve When the material of the core and the valve body are different and 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 cannot work; (4) When the viscosity of the working fluid decreases, the lubrication of the working fluid is reduced. The performance is reduced, the wear of hydraulic components is accelerated, the wear and failure of components is accelerated, and the service life of components is shortened.
In order to avoid the above phenomenon as much as possible, some concrete pumps have to stop after using for a certain period of time to cool the system, thus reducing the operating rate of the concrete pump and affecting the construction progress. Therefore, corresponding measures should be taken to control the temperature of the hydraulic system to ensure the normal use of the concrete pump.
3. The main reasons for the heating of the hydraulic system of the concrete pump and the methods of elimination
The heating of the hydraulic system can be divided into two categories according to the heating reasons: one is the heating caused by the design; the other is the heating caused by the failure of the hydraulic components or the improper use. Obviously, the causes of fever are different, and the methods of elimination are also different.
3.1 The design is unreasonable, resulting in the heating of the hydraulic system and its elimination
(1) Improper selection of the oil number of the hydraulic oil may cause the heating of the hydraulic system. When the oil temperature of the selected hydraulic oil is low, the system works normally, but after the system works for a period of time, the oil temperature rises and the viscosity of the hydraulic oil decreases, causing The internal leakage of the system increases, and with the increase of leakage, the oil temperature rises, forming a vicious circle of oil temperature. The solution is: according to the load of the system and the normal working temperature requirements, select the hydraulic oil with the appropriate viscosity.
(2) The design of the oil tank is unreasonable, which reduces the heat dissipation effect of the hydraulic system. The main function of the system heating oil tank is to store hydraulic oil, but it also has the functions of heat dissipation, precipitation of impurities, and separation of water. The unreasonable design of the fuel tank is mainly manifested in two aspects: First, the volume of the fuel tank is too small. Since the concrete pump is a mobile hydraulic equipment, the volume of the fuel tank is generally about double the flow rate of the hydraulic pump. Therefore, the heat dissipation area of the fuel tank and the oil storage capacity Second, some fuel tanks are unreasonably designed in structure, the suction pipe mouth and the oil return pipe mouth are close, and there is no partition in the middle, which shortens the cooling cycle of the oil in the oil tank and the path for precipitation of impurities, and even As a result, most of the return oil directly enters the oil suction pipe, which reduces the heat dissipation effect of the oil tank and increases the oil temperature. The solution is: appropriately increase the volume of the fuel tank, so that the volume of the fuel tank is (1125~115)Q, and try to increase the distance between the oil suction pipe and the oil return pipe. The proper cooling power.
(3) The heat dissipation flow is small, and the installation position of the cooler is unreasonable, which reduces the heat dissipation capacity of the system. The cooling methods of the concrete pump include air cooling and water cooling. Users can choose according to the actual situation, but generally more air cooling is used. Considering the pressure bearing requirements of the cooler, some concrete pumps set the cooler on the oil return road of the mixing system, and only cool the oil in the mixing system. Because the flow rate of the mixing system is small, the cooling effect of the whole system is poor, which makes the system fever. Solution: First, an independent cooling circuit can be used to improve the cooling effect. The second is to set the cooler on the total oil return circuit of the system to increase the heat dissipation flow and improve the cooling effect. However, two problems should be paid attention to at this time. The first problem is the speed of the cooling fan. The speed of the cooling fan should not be too low. Otherwise, the cooling effect will be reduced. A motor can be used to drive the fan, or a low-voltage drive motor can be installed on the total oil return circuit to match the motor speed with the heat dissipation flow, and at the same time, it can also solve the impact of the main circuit pressure shock on the cooler's pressure bearing capacity; The second problem is that if a motor is used to drive the fan, the pressure shock of the main system will affect the pressure bearing capacity of the cooler. At this time, a low pressure relief valve or a check valve can be installed on the oil return road and the cooler in parallel to the cooling effect. device for maximum pressure protection.
(4) Improper selection of hydraulic components causes the system to heat up. The hydraulic system of the concrete pump is generally a high-pressure and large-flow system. If the hydraulic components in the system, mainly the reversing valve, relief valve and sequence valve are unreasonably selected, they cannot meet the requirements of large Therefore, in the hydraulic system design, when selecting and designing hydraulic components, the hydraulic components must be selected according to the hydraulic components. The components are selected according to the maximum working pressure, the maximum flow and the required pressure and flow adjustment range, so as to reduce the pressure loss of the valve port as much as possible, thereby reducing the system heating caused by the unreasonable selection of hydraulic components.
(5) Unreasonable design and installation of pipelines, resulting in large pressure loss and conversion of pressure energy into heat energy. In the design of hydraulic systems, the design and installation of pipelines cannot be ignored. The diameter of each pipeline should be strictly based on its working pressure and passage The flow rate is designed to avoid the design of the pipe diameter being too small, resulting in excessively high flow rate, excessive pressure loss along the process, and causing heat generation. At the same time, attention should also be paid to the installation of pipelines, not only to achieve a neat appearance, but also to avoid pipeline accumulation and sharp turns of pipelines, which will affect the natural heat dissipation of pipelines or cause excessive local pressure loss to cause heat generation.
3.2 The heating of the hydraulic system and its elimination due to improper use of the hydraulic system or component failure
(1) The oil level of the hydraulic oil in the oil tank is lower than the minimum liquid level, which reduces the heat dissipation power of the oil tank. During the use of the concrete pump, the oil level of the hydraulic oil in the oil tank should be observed at any time, and the oil level of the hydraulic oil should always be kept at the normal oil level. In order to ensure the heat dissipation effect of the fuel tank, when the oil level of the hydraulic oil in the fuel tank is lower than the minimum liquid level, oil should be filled into the fuel tank in time.
(2) The cooling effect of the cooler is reduced, the oil temperature rises, and the cooling effect of the system heating cooler is reduced, which may be caused by the following reasons: a1 The inside of the cooler is blocked or there is a lot of dirt on the surface, which causes the safety device of the cooler to open and the cooler The reduction of the overflow will reduce the heat dissipation flow, or the ventilation of the cooler will be poor, so that the cooling heat transfer coefficient of the cooler will be reduced, and the cooling effect will be reduced. The dirt is removed to ensure that the inside of the cooler is unblocked and the outside is clean, so as to ensure the cooling effect of the cooler. b1 The opening pressure of the safety valve or one-way valve of the cooler is lower than the standard value, so that the safety protection device of the cooler is opened when the cooler is not blocked, resulting in overflow and diversion, which reduces the cooling flow of the cooler. Therefore, before the cooler is used , the opening pressure of the safety protection device must be adjusted correctly, and the opening pressure value of the safety protection device should be checked and corrected regularly during use.
(3) Improper adjustment of the hydraulic system pressure, causing the system to heat up. In the hydraulic system of the concrete pump, due to performance requirements, there are often safety valves, relief valves and sequence valves in the system. If the pressure of the safety valve is adjusted too low, the safety valve will be opened frequently, resulting in overflow loss, causing the system to heat; if the pressure is adjusted too high, it will increase the leakage in the system and cause the system to heat up. Load requirements, correctly calculate and adjust the safety valve and pressure value, so as to ensure that the system works within the specified pressure range. When the main circuit of the concrete pump pumping system is a closed system, a heat exchange circuit must be set up in the pumping system, and attention should be paid to the set pressure of the relief valve in the heat exchange circuit. The cylinder reversing impact increases and the set pressure is too high, which will cause the overflow loss to be too large and the system temperature rise to be too high. Therefore, the adjustment pressure value of the relief valve of the heat exchange circuit should be reasonably determined. Generally, the adjustment value of the relief valve is (1 ~ 115) MPa, and the working pressure of the oil supply circuit of the pumping system is 215 MPa. When setting the sequence valve, be sure to understand the working characteristics of the sequence valve and adjust the working pressure of the sequence valve correctly. If the adjustment pressure of the internal control sequence valve is too high, when the working pressure of the working hydraulic cylinder is lower than its adjustment pressure, there will be pressure loss at the valve port of the sequence valve, which will cause temperature rise and cause the system to heat up. Reasonably determine the setting of the internal control sequence valve. The pressure of the working cylinder can make the working pressure of the working cylinder higher than the opening pressure of the sequence valve. When the sequence valve is working, the valve port will be fully open, and there is basically no pressure loss at the valve port, thus avoiding the system heating caused by the improper setting pressure of the sequence valve. .
(4) The increase of internal leakage can increase the oil temperature, and the internal leakage of the hydraulic system of the system heating concrete pump, including the internal leakage of the hydraulic pump, hydraulic cylinder, hydraulic motor and hydraulic valve, during the leakage process of the pressure oil, the pressure drops, temperature rises. If the internal leakage of the system increases, it will cause the oil temperature to rise and the system to overheat. In severe cases, the system pressure will drop, the pumping will be weak, the pumping displacement will be reduced, the stirring will be weak, and the stirring speed will drop. Therefore, it is necessary to check these components regularly, replace the corresponding sealing components regularly, replace or repair the damaged and strained parts in time, and even replace the corresponding hydraulic components, so as to avoid the system heating caused by the leakage of components.
The heating problem of the hydraulic system of the concrete pump during use has become one of the problems that cannot be ignored. Due to the heating of the hydraulic system, many failures of the concrete pump will occur. In short, after taking certain measures for the different causes of heat generation, the heat generation of the hydraulic system can be controlled or reduced, the operating rate of the concrete pump can be improved and the service life can be prolonged.
