Why does the pump truck hydraulic system heat up?How to solve it?
Reasons for heating of hydraulic system
A concrete pump is a construction equipment that transports concrete under pressure through a pipeline. The hydraulic system of the concrete pump is generally a high-pressure and large-flow system. 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 using for about 40 minutes, and the thermal equilibrium temperature of the hydraulic system can be as high as 70e or more after using for about 2 hours. The normal thermal equilibrium temperature should be around 50e. Therefore, the problem of excessively high oil temperature in the hydraulic system of the concrete pump, that is, the problem of heat generation, has occurred.
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. The damage caused by the heating phenomenon mainly includes the following points:
(1) After the temperature of the working fluid increases, the viscosity of the working fluid decreases, the leakage of the pump increases, and the actual flow rate of the pump decreases;
(2) The seals of the hydraulic system and components deteriorate at high temperatures, and the elastic denaturation ability decreases, which reduces the sealing performance, or even seals failure, and increases the leakage;
(3) When the valve core and valve body material of the hydraulic valve are different, and the coefficient of thermal expansion is different, the valve core is stuck due to thermal expansion between the valve core and the valve body, which makes the concrete pump unable to work;
(4) When the viscosity of the working fluid decreases, the lubrication performance of the working fluid is reduced, the wear of the hydraulic components is accelerated, the wear failure of the components is accelerated, and the service life of the components is shortened.
In order to avoid the occurrence of the above phenomenon as much as possible, some concrete pumps have to stop after a certain period of use to cool the system, thereby 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 according to the cause of the system heating.
3,Main reason for the heating of the hydraulic system of the concrete pump and its elimination method
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 or improper use of the hydraulic components. Obviously, the cause of fever is different, and its elimination method is also different.
3.1 Unreasonable design, resulting in heating of the hydraulic system and its elimination
(1) The 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 the increase in leakage also promotes the rise of oil temperature, forming a vicious circle of oil temperature. The solution is to select hydraulic oil with suitable viscosity according to the load of the system and the requirements of normal working temperature.
(2) The design of the oil tank is unreasonable, which reduces the heat dissipation effect of the hydraulic system. The main function of the heating oil tank of the system is to store hydraulic oil, but it also has the functions of heat dissipation, precipitation of impurities, and separation of water. The design of the fuel tank is unreasonable, mainly manifested in two aspects: First, the design of the fuel tank is too small. Because the concrete pump is a mobile hydraulic equipment, the fuel tank volume is generally about twice the flow rate of the hydraulic pump. Therefore, the heat dissipation area and oil storage capacity of the fuel tank Both are small; second, some fuel tanks are structurally unreasonable. The suction pipe and the return pipe are close, and there is no partition in the middle, which shortens the cooling cycle of the oil in the fuel tank and the path for precipitation of impurities, and even As a result, most of the return oil directly enters the suction pipe, reducing the heat dissipation effect of the fuel tank and increasing 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 suction pipe port and the return pipe port. A partition should be set between the suction and return pipes to ensure the fuel tank. Required heat dissipation power.
(3) The heat dissipation flow is small and the installation location of the cooler is unreasonable, which reduces the heat dissipation capacity of the system. The cooling methods of the concrete pump are air-cooled and water-cooled. Users can choose according to the actual situation, but generally use more air-cooling. Some concrete pumps, considering the pressure requirements of the cooler, set the cooler on the oil return path of the mixing system, and only cool the oil in the mixing system. Because the flow 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 install the cooler on the system's total oil return path 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 cannot 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 main oil return line to match the motor speed with the heat dissipation flow rate, and at the same time can solve the impact of the main circuit pressure shock on the pressure bearing capacity of the cooler; The second problem is that if a motor is used to drive the fan, the pressure impact of the main system will affect the pressure-bearing capacity of the cooler. At this time, a low-pressure overflow protection valve or a one-way valve can be installed in the oil return line and the cooler. The maximum pressure protection is carried out by the device.
(4) Improper selection of hydraulic components causes the system to generate heat. 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, overflow valve and sequence valve, are unreasonably selected and cannot meet the requirements Flow rate requirements, so that in use, the valve port fluid flow rate is too high, causing a greater pressure loss and increasing the oil temperature. Therefore, in the hydraulic system design, the hydraulic components must be selected and designed according to the hydraulic components The maximum working pressure, the maximum flow rate and the required pressure and flow adjustment range are used to select components to minimize valve port pressure loss, thereby reducing system heating caused by unreasonable selection of hydraulic component specifications.
(5) The pipeline design and installation are unreasonable, resulting in large pressure loss and converting pressure energy into heat energy. In the design of hydraulic system, the design and installation of pipelines cannot be ignored. The diameter of each pipeline should be strictly in accordance with its working pressure and passing The flow rate is designed to avoid that the design of the pipe diameter is too small, resulting in excessive flow rate, excessive pressure loss along the way, and heat generation. At the same time, attention should be paid to the installation of pipelines, not only to ensure a neat appearance, but also to avoid pipeline accumulation and sharp turns of pipelines, which affect the natural heat dissipation of the pipelines or cause excessive local pressure loss to cause heating.
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, always observe the oil level of the hydraulic oil in the oil tank and always keep the hydraulic oil level at the normal oil level. In order to ensure the heat dissipation effect of the fuel tank, when the hydraulic oil level in the fuel tank is lower than the minimum level, the fuel tank should be filled in time.
(2) The cooling effect of the cooler is reduced, the oil temperature rises, and the cooling effect of the system heat-generating cooler is reduced, which may be caused by the following reasons: a1 The internal blockage of the cooler or the surface dirt is too much, causing the cooler safety device to open, Overflow decreases, which reduces the heat dissipation flow, or poor ventilation of the cooler, which reduces the cooling heat transfer coefficient of the cooler and reduces the cooling effect. Therefore, the concrete pump must be checked regularly during use, the cooler should be cleared, and the surface of the cooler should be regularly checked. The dirt is removed to ensure that the inside of the cooler is unblocked and the outside is clean to ensure the cooling effect of the cooler. b1 The opening pressure of the cooler safety valve or one-way valve is lower than the standard value, so that the cooler safety protection device is opened when the cooler is not blocked, resulting in overflow and diversion, which reduces the heat dissipation flow of the cooler. Therefore, the cooler is used before , The opening pressure of the safety protection device must be adjusted correctly, and the opening pressure value of the safety protection device must be checked and corrected regularly during use.
(3) Improper adjustment of hydraulic system pressure causes system heating. In the concrete pump hydraulic system, due to performance requirements, the system is often equipped with safety valves, overflow valves, and sequence valves. If the pressure of the safety valve is adjusted too low, the safety valve will open frequently, resulting in overflow loss, causing system heat; if the pressure is adjusted too high, the leakage in the system will increase and the system will heat up. Therefore, the hydraulic system should be 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 pumping system is a closed system, the pumping system must be equipped with a heat exchange circuit. The set pressure of the relief valve in the heat exchange circuit should be paid attention to. If the set pressure is too low, it will pump hydraulic pressure. The impact of cylinder reversal increases and the set pressure is too high, which will cause excessive overflow loss and excessive system temperature rise. 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 replenishment circuit of the pumping system is 215 MPa. When the sequence valve is installed in the hydraulic system of the concrete pump, it is necessary 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 a pressure loss at the valve port of the sequence valve, which will cause temperature rise and cause the system to heat up. Determine the setting of the internal control sequence valve reasonably The pressure 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 opened, and there is basically no pressure loss at the valve port, thus avoiding the system heating caused by improper sequence valve setting pressure .
(4) The increase of internal leakage can increase the oil temperature, and the internal leakage of the hydraulic system of the concrete pump, including the internal leakage of hydraulic pumps, hydraulic cylinders, hydraulic motors and hydraulic valves. The pressure of the pressure oil will drop during the leakage process. The temperature rises. If the internal leakage of the system increases, it will cause the oil temperature to rise, the system overheats, and 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, these components should be checked regularly, the corresponding sealing components should be replaced regularly, and damaged or strained parts should be replaced or repaired in time, and even the corresponding hydraulic components should be replaced, so as to avoid system heating caused by component leakage.
The heating problem of the hydraulic system of the concrete pump has become one of the problems that cannot be ignored. The heating of the hydraulic system will cause many failures of the concrete pump. For the concrete pump manufacturer, it is important to start with the design and reduce the heating of its hydraulic system to the lowest value. This will not only increase the operating rate of the user's concrete pump and extend its service life, but also save energy and reduce maintenance costs; for concrete pumps Users should start with the use and maintenance, and use, debug, inspect, and maintain the concrete pump in strict accordance with the manufacturer's requirements to reduce the failure rate and reduce the system heat caused by improper use. In short, after taking certain measures for different causes of heat generation, the heat generation of the hydraulic system can be controlled or reduced, and the operating rate of the concrete pump can be improved and the service life of the concrete pump can be prolonged.