In the manufacture of parts, there are high technical requirements for sealing and durability. At present, rolling technology has been widely used in the manufacture of hydraulic components, which has solved the problems of roundness and roughness well. Especially in that manufacture of hydraulic cylinder.
Definition of hydraulic pressure
A complete hydraulic system consists of five parts, namely, power component, executive component, control component, auxiliary component and hydraulic oil. The function of the power element is to convert the mechanical energy of the prime mover into the pressure energy of liquid, which refers to the oil pump in the hydraulic system and provides power for the whole hydraulic system. The structural forms of hydraulic pump generally include gear pump, vane pump and plunger pump. The function of executive components (such as hydraulic cylinder and hydraulic motor) is to convert the pressure energy of liquid into mechanical energy and drive the load to do linear reciprocating motion or rotary motion. Control elements (i.e. various hydraulic valves) control and adjust the pressure, flow and direction of liquid in the hydraulic system. According to different control functions, hydraulic valves can be divided into pressure control valves, flow control valves and directional control valves. Pressure control valves are divided into safety valves (safety valves), pressure reducing valves, sequence valves and pressure relays. The flow control valve includes throttle valve, regulating valve, shunting and collecting valve, etc. Directional control valves include one-way valves, hydraulically controlled one-way valves, shuttle valves, reversing valves, etc. According to different control methods, hydraulic valves can be divided into on-off control valves, fixed value control valves and proportional control valves. Auxiliary components include oil tank, oil filter, oil pipe and pipe joint, sealing ring, pressure gauge, oil level and oil temperature gauge, etc. Hydraulic oil is the working medium to transfer energy in hydraulic system, including various mineral oil, emulsion and synthetic hydraulic oil.
Hydraulic components:
Hydraulic components can be divided into three categories: power components, control components and executive components. Although they are all hydraulic components, their functions and technical requirements for installation and use are not the same. They are introduced as follows:
1. What is the power element?
Power components refer to various hydraulic pumps.
1, gear oil pump and series pump (including external meshing and internal meshing).
2. Vane pumps (including single-stage pumps, variable-displacement pumps, two-stage pumps and two-stage pumps).
3. Piston pumps are divided into axial piston pumps and radial piston pumps. Axial piston pumps include quantitative pumps, variable pumps and variable pumps.
Metering pumps are divided into manual variables, pressure compensation variables and servo variables. ) Structurally, it is divided into two oil distribution modes: end face oil distribution and valve oil distribution. The oil distribution mode of radial piston pump is basically valve oil distribution.
Classification of hydraulic components
Power components: gear pump, vane pump, plunger pump and screw pump;
Executive components: hydraulic cylinder, piston hydraulic cylinder, plunger hydraulic cylinder, oscillating hydraulic cylinder and combined hydraulic cylinder;
Hydraulic motors: gear hydraulic motors, vane hydraulic motors and plunger hydraulic motors;
Control elements: directional control valve, one-way valve and reversing valve;
Pressure control valve: overflow valve, pressure reducing valve, sequence valve, pressure relay, etc.
Flow control valve: throttle valve, speed regulating valve and diverter valve;
Auxiliary components: accumulator, filter, cooler, heater, oil pipe, pipe joint, oil tank, pressure gauge, flowmeter, sealing device, etc.
The hydraulic system consists of five parts: power component (oil pump), executive component (oil cylinder or hydraulic motor), control component (various valves), auxiliary component and working medium.
1, power component (oil pump) whose function is to use the mechanical energy of the prime mover to convert liquid into hydraulic energy; It is the power part of hydraulic transmission.
2. Actuator (oil cylinder, hydraulic motor) It converts the hydraulic energy of liquid into mechanical energy. Among them, the oil cylinder moves linearly and the motor rotates.
3. Control elements include pressure valve, flow valve and directional valve. Their function is to adjust the rotating speed of the hydraulic motor steplessly as needed, and to adjust and control the pressure, flow and flow direction of the working liquid in the hydraulic system.
4. Auxiliary components other than the above three parts, including pressure gauge, oil filter, energy storage device, cooler, pipe fittings (mainly including: various pipe fittings (flare, welding, clamping sleeve, sae flange), high-pressure ball valve, quick-change connector, hose assembly, pressure measuring connector, pipe clamp, etc. ) and fuel tank are also important.
5. Working medium Working medium refers to hydraulic oil or emulsion that realizes energy conversion through oil pump and hydraulic motor in various hydraulic transmissions.
hydraulic valve
It is a kind of automation components operated by pressure oil and controlled by pressure oil of pressure distribution valve. Usually used with electromagnetic pressure distribution valve, it can be used to remotely control the on-off of oil, gas and water pipeline system of hydropower station.
Used to reduce and stabilize the oil pressure of a branch in the system, often used for clamping, control, lubrication and other oil circuits. There are direct-acting type and pilot type, and the pilot type is mostly used.
Classification of hydraulic pipe joints
Hydraulic hose, high-pressure ball valve, strange quick connector, casing connector, welded pipe connector, high-pressure hose.
Difference between hydraulic pipe joint and ordinary pipe joint
The biggest and most remarkable difference is that the hydraulic pressure is amazing, and the sudden bursting of the hydraulic oil pipe has a great impact.
When I say this, I definitely can't use ordinary joints instead of special joints, because the hydraulic ones can bear a lot of pressure, and the ordinary ones with the maximum atmospheric pressure of 0.5 are dying. Now our hydraulic pipe joint technology is far behind foreign countries. Hydraulic talent network reminds friends in the hydraulic field to exchange and develop their own hydraulic pipe joint technology in China.
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The principle of hydraulic pressure is composed of two liquid cylinders of different sizes, which are filled with water or oil. Water-filled is called "hydraulic press"; Oil-filled ones are called "oil presses". Each of the two hydraulic cylinders has a slidable piston. If a certain pressure is applied to the small piston, according to Pascal's law, the small piston will transfer this pressure to the big piston through the pressure of the liquid and push the big piston upward. Let the cross-sectional area of the small piston be S 1 and the downward pressure on the small piston be F 1. Therefore, the pressure of small piston on liquid is P=F 1/SI, which can be transmitted in all directions by liquid with constant size. "The pressure on the big piston must also be equal to p. If the cross-sectional area of the big piston is S2, the upward pressure F2 generated by the pressure P on the big piston is equal to pXS2, and the cross-sectional area is a multiple of the cross-sectional area of the small piston. As can be seen from the above formula, if a small force is added to the small piston, a large force will be obtained on the large piston. So use hydraulic press to press plywood, squeeze oil, extract heavy objects, forge steel and so on.
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The development history of hydraulic transmission Hydraulic transmission and pneumatic transmission are collectively called fluid transmission, which is a new technology developed according to the hydrostatic transmission principle put forward by Pascal in the17th century. Braman (1749- 18 14) used water as working medium in London and applied it to industry in the form of hydraulic press, thus giving birth to the world's first hydraulic press. 1905, the working fluid water is replaced by oil, which is further improved.
After World War I (1914-1918), hydraulic transmission was widely used, especially after 1920. Hydraulic components began to enter the formal industrial production stage from the end of 19 to the beginning of the 20th century. 1925, F.Vikers invented the pressure balance vane pump, which laid the foundation for the gradual establishment of modern hydraulic component industry or hydraulic transmission. Constantine in the early 20th century? Newcastle (g? Constantimsco) conducted theoretical and practical research on energy fluctuation transmission; 19 10's contribution to hydraulic transmission (hydraulic coupling, hydraulic torque converter, etc. ) these two fields have been developed.
During World War II (194 1- 1945), 30% of machine tools in the United States used hydraulic transmission. It should be pointed out that the development of hydraulic transmission in Japan is nearly 20 years later than that in Europe and America. Around 1955, Japan developed hydraulic transmission rapidly, and 1956 established the "Hydraulic Industry Association". In recent 20~30 years, Japan's hydraulic transmission has developed rapidly and occupied a leading position in the world.
Hydraulic transmission has many outstanding advantages, so it is widely used, such as general industrial plastic processing machinery, pressure machinery, machine tools, etc. Construction machinery, construction machinery, agricultural machinery, automobiles, etc. In mobile machinery; Metallurgical machinery, lifting device, roller adjusting device, etc. Used in steel industry; Flood control dam device, river bed lifting device, bridge control mechanism, etc. Used in civil and hydraulic engineering; Turbine speed regulating devices in power plants and nuclear power plants. Deck crane (winch), bow door, bulkhead valve, stern propeller, etc. For ships; Giant antenna control device for special technology, measuring buoy, lifting turntable, etc. Gun control device for military use, ship anti-rolling device, aircraft simulation, aircraft landing gear retracting device, rudder control device.
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Advantages and disadvantages of hydraulic transmission Advantages of hydraulic transmission Compared with mechanical transmission and electrical transmission, hydraulic transmission has the following advantages:
1. Various components of hydraulic transmission can be conveniently and flexibly arranged as required.
2. Light weight, small volume, small motion inertia and fast reaction speed.
3. The operation and control are convenient, and a wide range of stepless speed regulation can be realized (the speed regulation range is 2000: 1).
4, can automatically realize overload protection.
5. The working medium is generally mineral oil, and the relatively moving surface can be lubricated by itself, with long service life.
6. It is easy to realize linear motion.
7. It is easy to realize the automation of the machine. When electro-hydraulic combined control is adopted, not only a high degree of automatic control process can be realized, but also remote control can be realized.
Disadvantages of hydraulic pressure 1. Because of the large fluid flow resistance, many leaks and low efficiency. If not handled properly, the leakage will not only pollute the site, but also cause fire and explosion accidents.
2. Because the working performance is easily affected by temperature changes, it is not suitable for working under very high or low temperature conditions.
3. The manufacturing accuracy of hydraulic components is high, and the development of shearing machine industry makes it more expensive.
4. Due to the leakage and compressibility of liquid medium, strict transmission ratio cannot be obtained.
5. When the hydraulic transmission fails, it is not easy to find out the reason; Use and maintenance require a high level of technology.
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Composition and function of hydraulic system A complete hydraulic system consists of five parts, namely, power component, executive component, control component, auxiliary component and hydraulic oil.
The function of the power element is to convert the mechanical energy of the prime mover into the pressure energy of liquid, which refers to the oil pump in the hydraulic system and provides power for the whole hydraulic system. The structural forms of hydraulic pumps generally include gear pumps, vane pumps and plunger pumps. See 1- 1 for their performance comparison.
The function of executive components (such as hydraulic cylinder and hydraulic motor) is to convert the pressure energy of liquid into mechanical energy and drive the load to do linear reciprocating motion or rotary motion.
Control elements (i.e. various hydraulic valves) control and adjust the pressure, flow and direction of liquid in the hydraulic system. According to different control functions, hydraulic valves can be divided into pressure control valves, flow control valves and directional control valves. Pressure control valve is divided into beneficial flow valve (safety valve), pressure reducing valve, sequence valve, pressure relay, etc. The flow control valve includes throttle valve, regulating valve, shunting and collecting valve, etc. Directional control valves include one-way valves, hydraulically controlled one-way valves, shuttle valves, reversing valves, etc. According to different control methods, hydraulic valves can be divided into on-off control valves, fixed value control valves and proportional control valves.
Auxiliary components include oil tank, oil filter, oil pipe and pipe joint, sealing ring, pressure gauge, oil level and oil temperature gauge, etc.
Hydraulic oil is the working medium to transfer energy in hydraulic system, including various mineral oil, emulsion and synthetic hydraulic oil.
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Three major problems in hydraulic system 1, fever. Due to the different flow rates in different parts of the conveying medium (hydraulic oil), there is some internal friction in the liquid, and there is also friction between the liquid and the inner wall of the pipeline. These are the reasons for the temperature rise of hydraulic oil. The increase of temperature will lead to the increase of internal and external leakage and reduce its mechanical efficiency. At the same time, due to the high temperature, hydraulic oil will expand, resulting in increased compressibility, so that the control action can not be transmitted well. Solution: heating is an inherent characteristic of hydraulic system, which cannot be eradicated and can only be minimized. Use high-quality hydraulic oil, avoid elbows in hydraulic pipeline layout, and use high-quality pipelines, pipe joints, hydraulic valves, etc.
2. Vibration of vibration hydraulic system is also one of its chronic diseases. The vibration of the system is caused by the impact caused by the high-speed flow of hydraulic oil in the pipeline and the impact caused by the opening and closing of the control valve. Strong vibration will lead to errors in the control actions of the system, as well as errors in some more precise instruments in the system, leading to system failures. Solution: Fix the hydraulic pipeline as far as possible to avoid sharp bends. Avoid changing the direction of liquid flow frequently, and take vibration reduction measures when it is inevitable. The whole hydraulic system should have good vibration reduction measures and avoid the influence of external vibration sources on the system.
3. The leakage of hydraulic system is divided into internal leakage and external leakage. Internal leakage refers to the leakage process occurring inside the system, such as the leakage on both sides of the piston of the hydraulic cylinder and the leakage between the valve core and the valve body of the control valve. Although internal leakage will not lead to the loss of hydraulic oil, it may affect the established control actions until the system fails. External leakage refers to the leakage between the system and the external environment. The direct leakage of hydraulic oil into the environment will not only affect the working environment of the system, but also lead to the failure caused by insufficient system pressure. Hydraulic oil leaking into the environment is also in danger of fire. Solution: Use better quality seals to improve the machining accuracy of the equipment.
In addition, for the three major ills of the hydraulic system, some people summed it up as "fever and diarrhea in an ostentatious manner" (the summoner is from the Northeast). Hydraulic system is used in elevators, excavators, pumping stations, dynamic compactors, cranes and other large industries, buildings, factories and enterprises, as well as elevators, lifting platforms, boarding bridges and other industries.
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Ways to find hydraulic faults. When analyzing and troubleshooting the hydraulic system diagram, the main method is to "grasp both ends"-that is, grasp the power source (oil pump) and the actuator (oil cylinder and motor), and then "connect the middle", that is, the pipeline and control elements passing between the power source and the actuator. When "grasping both ends", it is necessary to analyze whether the fault lies in the oil pump, cylinder and motor itself. When "connecting the middle", we should not only pay attention to analyzing whether the fault is caused by the hydraulic components on the connecting line, but also pay special attention to figuring out which control mode is adopted when the system switches from one working state to another, whether the control signal is wrong, and check the objects one by one, and pay attention to whether there is interference between the main oil circuits and between the main oil circuits and the control oil circuits. If there is interference, it is necessary to analyze how to use the adjustment error.
Second, use causality diagram to find hydraulic fault.
Using causality diagram (also known as fishbone diagram) analysis method to analyze the faults of hydraulic equipment can not only quickly find out the primary and secondary causes of faults, but also accumulate experience in troubleshooting.
Causality diagram analysis can closely combine maintenance management with fault finding, so it is widely used.
Thirdly, ferrography technology is applied to diagnose and monitor the faults of hydraulic system.
Ferrography technology is based on the wear of mechanical friction pairs. Wear particles and other pollution particles in hydraulic oil are separated by ferrography technology, and ferrography is made, and then observed under ferrography microscope or scanning electron microscope. Common faults and solutions of CNC bending machine are stored in glass tubes in turn according to size, and quantitative detection is carried out by optical method. Through the above analysis, we can accurately obtain the important information about wear in the system. According to this, the wear phenomenon is further studied, the wear state is monitored, the fault precursors are diagnosed, and finally the system fault prediction is made.
Ferrography technology can be effectively applied to the detection, monitoring, wear process analysis and fault diagnosis of hydraulic system of construction machinery, which has the advantages of intuition, accuracy and large amount of information. Therefore, it has become a powerful tool for diagnosing and analyzing hydraulic system faults in mechanical engineering.
Fourthly, use the correlation analysis table between fault phenomena and fault causes to find hydraulic faults.
According to the working practice, the relationship table between fault phenomena and fault causes (or provided by manufacturers) is summarized, which can be used to find and deal with general hydraulic faults.
Five, the use of equipment self-diagnosis function to find hydraulic fault.
With the continuous development of electronic technology, many large and medium-sized construction machinery are controlled by electronic computers, and their hydraulic systems are self-diagnosed through interface circuits and sensing technology, and displayed on the fluorescent screen. Users and maintenance personnel can troubleshoot according to the displayed fault content.
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Oil cylinder 1 unpacking for installation operation: the gasified rust inhibitor is sealed in the oil cylinder, so do not pull out the plug at the inlet before assembly. If the plug is removed, it must be installed on the body immediately and the oil cylinder should be filled with oil.
2 Rust prevention: After the oil cylinder is installed on the engine body, if the piston is in the extended state, the exposed part of the piston rod must be coated with grease.
3 Speed: When the running speed of the oil cylinder with general specifications exceeds 2m/s, the service life of the frame cold bending machine will be affected. When 0.3m/s is the end of the trip, for the sake of mechanism protection and safety, it is suggested to install a buffer mechanism inside. In addition, when the cylinder stops, in order to protect the cylinder mechanism and safety, we must also consider preventing the line from being greatly impacted. In order to increase the oil return of the oil cylinder, special attention should be paid to the circuit design. When running at a low speed below 0.5m/min, the maneuverability (especially vibration) will be affected. Therefore, the negotiation should be carried out at low speed.
4 Operation: At the initial stage of operation, the air in the oil cylinder must be completely removed. In the case of residual air, take low-speed full operation to eliminate air. If the residual air in the cylinder is pinched violently, the sealing ring may be burnt out due to the action of hydraulic oil. In addition, if negative pressure is generated inside the cylinder during operation, abnormality may occur due to cavitation.
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The motor in hydraulic system refers to the energy conversion device that outputs rotary motion and converts hydraulic energy provided by hydraulic pump into mechanical energy.
Characteristics and classification of hydraulic motors From the perspective of energy conversion, both hydraulic pumps and hydraulic motors are reversible hydraulic components, and any kind of hydraulic pump can be transformed into a hydraulic motor state by inputting working fluid. On the contrary, when the main shaft of the hydraulic motor is driven by external torque, it can also become a hydraulic pump state. Because they have the same basic structural elements-closed and periodically changing volume and corresponding oil distribution mechanism.
However, there are still many differences between hydraulic motors and the same type of hydraulic pumps because of their different working conditions and different performance requirements. First of all, the hydraulic motor should be able to rotate forward and backward, so its internal structure is required to be symmetrical; The speed range of hydraulic motor needs to be large enough, especially its minimum stable speed. Therefore, rolling bearings or hydrostatic sliding bearings are usually used; Secondly, because the hydraulic motor works under the condition of input pressure oil, it is not necessary to have self-priming ability, but it needs a certain initial seal to provide the necessary starting torque. Because of these differences, hydraulic motors and hydraulic pumps are similar in structure, but they cannot work reversibly.
Hydraulic motors can be divided into gear type, vane type, plunger type and other types according to their plum blossom type. According to the rated speed of hydraulic motor, it can be divided into two categories: high speed and low speed. Those with rated speed higher than 500r/min belong to high-speed hydraulic motors, and those with rated speed lower than 500r/min belong to low-speed hydraulic motors. The basic types of high-speed hydraulic motors are gear type, spiral type, vane type and axial plunger type. Their main features are high rotational speed, small moment of inertia, easy starting and braking, and high sensitivity of adjustment (speed regulation and commutation). Usually, the output torque of high-speed hydraulic motor is not large, so it is also called high-speed small torque hydraulic motor. The basic type of low-speed hydraulic motor is radial plunger type, and there are also axial plunger type, vane type and gear type low-speed structure types. The main characteristics of low-speed hydraulic motor are large displacement, large volume and low rotation speed (sometimes up to several revolutions per minute or even several tenths), so it can be directly connected with the working mechanism, which greatly simplifies the transmission mechanism. Usually, the output torque of low-speed hydraulic motor is large, so it is also called low-speed high-torque hydraulic motor.
Hydraulic motor 1 working principle, vane hydraulic motor
Due to the action of pressure oil, the unbalanced force makes the rotor produce torque. The output torque of the vane hydraulic motor is related to the displacement of the hydraulic motor and the pressure difference between the oil inlet and the oil outlet of the hydraulic motor, and its rotating speed is determined by the flow input to the hydraulic motor. Because the hydraulic motor generally requires positive and negative rotation, the blades of the vane hydraulic motor should be placed radially. In order to make the blade root always full of pressure oil, one-way valves should be set on the oil return cavity and the channel between the oil pressure cavity and the blade root. In order to ensure that the blade hydraulic motor can start normally after the pressure oil is filled, the top of the blade must be in close contact with the inner surface of the stator of the bending machine to ensure a good seal, so a pre-tightening spring should be set at the root of the blade. Vane hydraulic motor has small volume, small moment of inertia and sensitive action, and can be used in occasions with high commutation frequency, but it has large leakage and is unstable when working at low speed. Therefore, the vane hydraulic motor is generally used in high speed, low torque and sensitive action requirements.
2. Radial plunger hydraulic motor
The working principle of the radial plunger hydraulic motor is that when the pressure oil enters the bottom of the plunger in the cylinder through the window of the fixed oil distribution shaft 4, the plunger extends outward and tightly abuts against the inner wall of the stator, because there is eccentricity between the stator and the cylinder. At the contact between the plunger and the stator, the reaction force of the stator to the plunger is. Force can be divided into two components: sum. When the oil pressure acting on the bottom of the plunger is P, the diameter of the plunger is D, and the included angle between the force and the force is X, the force generates a moment on the cylinder, which makes the cylinder rotate. Then the cylinder outputs torque and speed through the transmission shaft connected with the end face.
In the case that one plunger generates torque as analyzed above, because there are multiple plungers acting in the oil pressure area, the torque generated by these plungers makes the oil cylinder rotate and output torque. Radial plunger hydraulic motors are mostly used in low-speed and high-torque situations.
3 Axial plunger motor
In principle, the axial piston pump can be used as a hydraulic motor except the distribution valve, that is, the axial piston pump and the axial piston motor are reversible. The working principle of axial plunger motor is that the oil distribution plate and swash plate are fixed, and the motor shaft is connected with the cylinder body to rotate together. When the pressure oil enters the plunger hole of the cylinder through the window of the oil distribution plate, the plunger extends out under the action of the pressure oil, and the swash plate clings to the plunger to generate a normal reaction force P, which can be decomposed into an axial component and a vertical component Q..Q to balance the hydraulic pressure on the plunger, and Q causes the plunger to generate a moment in the center of the cylinder to drive the motor shaft to rotate counterclockwise. The instantaneous total torque generated by the axial plunger motor is pulsating. If the input direction of motor pressure oil changes, the motor shaft rotates clockwise. The change of swash plate inclination angle α, that is, the change of displacement, not only affects the torque of the motor, but also affects its speed and steering. The greater the inclination of the swash plate, the greater the torque and the lower the rotational speed.
4. Gear hydraulic motor
In order to meet the requirements of positive and negative rotation in the gear motor structure, the oil inlet and the oil outlet are equal and symmetrical, and there is a separate oil outlet to guide the oil leakage of the bearing part out of the shell; In order to reduce the starting friction torque, rolling bearings are used; In order to reduce torque ripple, the gear hydraulic motor has more teeth than the pump.
The gear hydraulic motor has poor dry seal, low rental efficiency, and the input oil pressure cannot be too high to produce large torque. And the instantaneous rotational speed and torque change with the position of the meshing point, so the gear hydraulic motor is only suitable for high-speed and low-torque occasions. Eight telephoto cameras with high cost performance are recommended. Generally used in dry construction machinery, agricultural machinery and mechanical equipment with low requirements for torque uniformity.