Introduction
Brief overview of hydraulic systems
The hydraulic system is a transmission system that uses liquid as a working medium and uses the internal pressure of the liquid to transfer, convert and control power (or energy) based on Pascal's principle in fluid mechanics.
The hydraulic system is the key to controlling mechanical equipment to perform various actions, and its technical level and product performance will directly affect the automation level and reliability of mechanical equipment.
Characteristics of hydraulic systems:
Benefits:
1. The hydraulic transmission device operates smoothly and can move steadily at low speeds. When the load changes, its movement stability is relatively stable, and it can easily achieve continuous speed regulation during movement, and the regulation ratio is large, generally up to 100:1, and the maximum can reach 200:1.
2. Under the same power, the hydraulic transmission device has a small volume, light weight and compact structure, so its inertia is small and the switching rate is high.
3. The control and regulation of the hydraulic transmission device is relatively simple and easy to operate.
Disadvantages:
1. The hydraulic transmission device uses liquid as the energy transfer medium, and there will be inevitable leaks between the relative moving parts, causing volume loss.
At the same time, due to the compressibility of the body, it is generally not easy to use in the case of very strict requirements for the transmission ratio (such as thread and gear processing).
To reduce leaks, the manufacturing precision of hydraulic components must be high.
2. The flow of oil in pipelines and through relevant hydraulic components will result in loss of pressure, loss of mechanical friction and loss of viscosity friction between moving parts and flowing oil molecules, and loss of volume caused by leaks, the which will reduce the overall efficiency of the hydraulic system. system.
3. Changes in oil temperature will cause changes in oil viscosity, which will affect the stability of the hydraulic system, so it is difficult to use hydraulic transmission in low and high temperature environments.
4. Due to the small clearance between the hydraulic device and relative motion parts, the hydraulic system is sensitive to oil pollution, and there must be facilities to prevent oil pollution and good filtration.
Importance of hydraulic systems in various industries
1. Application of Hydraulic Technology in Industry
Hydraulic technology is generally applied to heavy, large and very large equipment, such as rolling mill hydraulic systems and continuous casting hydraulic systems in the metallurgical industry, and high-speed response scenarios in the military industry, such as aircraft rudder control, ship rudder and high-speed response tracking systems.
2. Application of Hydraulic Technology in Wind Energy Generation
The hydraulic system is mainly used to regulate the blade moment, damping, stopping and braking status of the wind turbine.
The wind turbine in wind power generation has many rotating components. The nacelle rotates in the horizontal plane and rotates with the wind wheel along the horizontal axis to generate power.
In the variable blade wind turbine, the blades of the wind wheel must rotate around the central axis of the root to adapt to different wind conditions. When the wind turbine is stopped, the tip of the blade must be released to form a cushion.
3. Application of Hydraulic Technology in the Military Field
Modern warfare is local warfare under high-technology conditions. High technology is widely used in military fields, and various new technological weapons and weapons are placed on the battlefield, causing the rapidity and destructiveness of warfare to increase unprecedentedly, and the dependence of warfare on hydraulic technology to increase even further.
4. Application of Hydraulic Technology in the Field of Engineering Machinery
High frequency variable impact hydraulic hammers have a very good application prospect in geological exploration and oceanic fields.
The excitation frequency of high-frequency variable hydraulic impact hammers is 10 to 20 Hz, while the latest high-frequency variable hydraulic impact hammers recently introduced in Japan can reach 60 Hz.
And in construction, the excitation frequency and amplitude can be changed according to the actual site situation, and the optimization of vibration and working conditions can be realized.
5. Application of Hydraulic Technology in the Field of Underwater Operations
With the deepening of human exploration of the seabed in today's society, the development of underwater robot technology is also rapid and its functions are no longer limited to simple types of observation.
People's eyes are on operational underwater robots, which are obviously more development and market space. In the entire operation, the mechanical hand is the most used and complicated component.
The flexible mechanical hand helps the underwater operating robot complete various underwater operation tasks with excellent results.
6. Application of Hydraulic Technology in the Field of Mining Machinery
The new hydraulic excavator not only has the advantages of light weight, small size, compact structure, etc., but also has a series of advantages in the transmission process, such as stability, easy operation and easy stepless speed regulation and automatic control.
Furthermore, performance is developing in the direction of high efficiency, high reliability, safety, energy conservation, and automation and intelligence.
7. Application of Hydraulic Technology in Elevators
Hydraulic elevators have the advantages of large load capacity and smooth operation, but the way they operate is different.
The R-layer stacked guide rail is suitable for the movement form of the hydraulic stair lift, and the composite pulley group is suitable for the movement form of the hydraulic stair lift.
Principles of Hydraulic Systems
1. Getting started
All electromagnets are turned off and the oil output from the main pump passes through the intermediate discharge of valves 6 and 21.
2. Rapid descent of the main cylinder
Electromagnets 1Y and 5Y are energized, valve 6 is in the correct position, and control oil passes through valve 8 to open solenoid-controlled one-way valve 9.
Inlet path: pump 1 valve 6 right position valve 13 main cylinder upper chamber.
Return path: main cylinder lower chamber valve 9 valve 6 right position valve 21 middle position oil tank.
The slide of the main cylinder quickly descends under the action of its own weight, and the pump 1, although in the state of maximum flow, still cannot meet its needs, so the oil in the upper chamber of the oil tank 15 enters the upper chamber of the main cylinder through charging valve 14.
3. Slow approach to the workpiece and increase in pressure of the main cylinder
When the main cylinder slide descends to a certain position and actuates the stroke switch 2S, 5Y is de-energized, valve 9 closes and the oil in the lower chamber of the main cylinder returns to the oil tank through the back pressure valve 10, valve 6 in the right position and valve 21 in the middle position.
At this time, the pressure in the upper chamber of the main cylinder increases, valve 14 closes, and the main cylinder slowly approaches the workpiece under the action of pressurized oil supplied by pump 1.
After contacting the workpiece, the resistance suddenly increases and the pressure increases further, causing the output flow of pump 1 to automatically decrease.
4. Pressure maintenance
When the pressure in the upper chamber of the main cylinder reaches the predetermined value, the pressure switch 7 sends a signal, causing 1Y to be de-energized, valve 6 to return to the intermediate position, the upper and lower chambers of the main cylinder to be closed , and the tapered surfaces of the one-way valve 13 and the charging valve 14 to ensure a good seal, thus maintaining the main cylinder pressure.
The pressure maintenance time is adjusted by the time relay. During pressure maintenance, the pump is unloaded through the intermediate position of valves 6 and 21.
5. Pressure release, main cylinder return and end of pressure maintenance
When the time relay sends a signal, solenoid 2Y is energized and valve 6 is in the left position.
Due to the high pressure in the upper chamber of the main cylinder, the hydraulic pilot valve 12 is in the upper position and the pressurized oil opens the external control sequence valve 11, allowing the output oil from pump 1 to return to the oil tank through the valve 11 .
Pump 1 operates under low pressure, which is not sufficient to open the main valve core of the charge valve 14, but instead opens the discharge valve core of the valve, allowing oil into the upper chamber of the main cylinder. be released back into the upper oil tank through opening the discharge valve and the pressure gradually decreases.
When the pressure in the upper chamber of the main cylinder drops to a certain level, valve 12 returns to the lower position, valve 11 closes, and pump 1 pressure increases, causing valve 14 to open fully. At this time, the oil entry route is:
pump 1 to valve 6 in the left position to valve 9 to the lower chamber of the main cylinder. The oil return route is:
upper chamber of the main cylinder to valve 14 to the upper oil tank 15, performing the rapid return of the main cylinder.
6. Master cylinder stops in place
When the master cylinder slider rises to actuate travel switch 1S, solenoid 2Y loses power and valve 6 is in the middle position, sealing the lower chamber of the main cylinder with hydraulic one-way valve 9, causing the main cylinder to stop in place and do not move, with the oil output from pump 1 being discharged through valves 6 and 21 in the middle position.
7. Lower Cylinder Extrusion and Retraction
When 3Y is energized, valve 21 is in the left position. Oil enters the lower cylinder through the following path: pump 1, valve 6 in the center position, valve 21 in the left position and the lower cavity of the lower cylinder.
The oil returns to the oil tank via the following route: upper cavity of the lower cylinder, valve 21 in the left position. The lower cylinder floating sleeve rises, causing extrusion.
When 3Y loses power, 4Y is energized and valve 21 is in the correct position, causing the lower cylinder piston to descend and retract.
8. Floating pressure edge
Key components of hydraulic systems
A hydraulic system typically consists of the following components:
Power supply:
This component converts the mechanical energy of an electric motor into pressure energy in a fluid, such as various types of hydraulic pumps.
Actuators:
This includes various hydraulic cylinders and motors, which convert fluid pressure energy into mechanical energy to drive working components.
Control and Regulation Components:
This includes various pressure valves, flow valves and directional valves, which regulate and control the pressure, flow and direction of flow of fluid in the hydraulic system to meet the working component's requirements for force (torque), speed (rotation ) and direction of movement (motion cycle).
Auxiliary Components:
All other components outside the above three components are known as auxiliary components, including oil tanks, oil pipes, pipe joints, oil filters, accumulators, pressure gauges, heaters (coolers) and more.
These play an important role in ensuring the reliability and stability of the hydraulic system.
In addition, there is hydraulic oil, which is the transmission medium.
Hydraulic Systems Applications
Hydraulic technology has greatly improved work efficiency by iterating and upgrading traditional equipment.
At present, hydraulic technology has been integrated into machinery renovation and has gradually replaced traditional technology as the core part, indicating the future development of the machinery industry.
In which industries is the hydraulic system used? Let's take a look together.
1. Machine tool industry
In the machine tool industry, hot work machine tool hydraulic systems include die casting machines, injection molding machines, hydraulic presses, punches, and rapid forging machines.
Cold working machine tools include combination machine tools, lathes and various profile machine tools.
2. Construction machines
Hydraulic transmission (hydraulic system) is widely used, such as excavators, tire loaders, automobile cranes, crawler excavators, tire cranes, self-propelled dump trucks, flatbed machines, vibratory rollers, etc.
3. Automotive industry
Hydraulic technology (hydraulic system) is used for hydraulic off-road vehicles, hydraulic dump trucks, hydraulic aerial work vehicles and fire trucks.
4. Agricultural and forestry machines
Hydraulic systems control agricultural implements in combines and tractors. Hydraulic systems control various wood movements in wood container machines. Artificial plate hot presses are also operated with hydraulic systems.
5. Chemical and textile machines
In chemical and textile machinery, hydraulic systems are used for plastic injection molding machines, rubber machines, paper machines, leather straightening machines, soap grinding machines, ceramic waste molding machines, machines spinning machines and textile machinery spinning machines.
6. Energy industry
Machines with hydraulic systems used in the energy industry include drilling rigs, underwater oil extraction machines, drills, winches, coal mining machines, mining machines, hydraulic supports for mining, power generation equipment, etc.
7. Metallurgical industry
In the metallurgical industry, hydraulic systems are used for blast furnace feeding machines, steel furnace control systems, ladle tower machines, rolling mill low pressure systems, roller bending balance systems, strip deviation control, etc.
8. Shipbuilding Industry
Hydraulic technology (hydraulic system) is widely used in the shipbuilding industry, such as fully hydraulic dredgers, salvage ships, pile driving ships, oil production routes, water wings, air cushion ships, auxiliary equipment. ships, etc.
9. Small and medium-sized machine parts processing technology
For example, various small and medium-sized metal parts designed for the metal parts industry.
Hydraulic presses are commonly used for pressure molding of these metal machine parts, including extrusion forming, die pressing, cold and hot die forging, and free forging of metal profiles.
10. Non-metallic materials pressing technology
This process belongs to the manufacturing of specific products, such as rubber product processing technology, SMC molding technology and thermal forming of automobile interior parts.
The advantages of hydraulic presses in these devices are also very obvious.
Maintenance and troubleshooting
Pressure loss
Due to the viscosity of the liquid and the inevitable frictional forces in the pipeline, a certain amount of energy will inevitably be lost as the liquid flows. This loss of energy manifests itself mainly as a loss of pressure. There are two types of pressure loss: along the path and local.
Pressure loss along the way is the loss of pressure due to friction as liquid flows through a straight tube of constant diameter for a certain distance.
Local pressure loss is caused by a sudden change in the cross-sectional shape of the pipeline, a change in the direction of liquid flow, or other forms of liquid resistance.
The total pressure loss is equal to the sum of the pressure losses along the path and the local pressure loss. As pressure loss is inevitable, the pump's nominal pressure should be slightly higher than the maximum working pressure required by the system.
Generally, the maximum working pressure required by the system is multiplied by a factor of 1.3-1.5 to estimate the nominal pressure.
loss of flow
In a hydraulic system, there are relative moving surfaces between each compressed component, such as the inner surface of a hydraulic cylinder and the outer surface of a piston. Since there must be relative movement, there is a certain gap between them.
If one side of the gap is high-pressure oil and the other side is low-pressure oil, the high-pressure oil will flow through the gap into the low-pressure area, causing leakage.
At the same time, due to the imperfect sealing of hydraulic components, some oil will also leak to the outside. The actual flow rate is reduced due to this leakage, which is what we call flow loss.
Loss of flow affects the speed of movement, and leakage is difficult to avoid completely, therefore, the nominal flow rate of the pump in the hydraulic system should be slightly higher than the maximum flow rate required during system operation.
Typically, the maximum required system flow can be multiplied by a factor of 1.1-1.3 to estimate the nominal flow.
Hydraulic Shock
Cause: When liquid flows in a hydraulic system, switching of executor components and closing of valves can cause an instantaneous pressure spike due to inertia and insufficiently sensitive reaction of some hydraulic components, which is called hydraulic shock. Its maximum value can exceed the working pressure several times.
Damage: May cause vibration and noise; cause pressure components such as relays and sequence valves to produce incorrect actions and even damage some components, sealing devices and piping.
Measures: Find out the cause of the shock and avoid a sudden change in flow. Delay the time for the change in speed, estimate the value of the peak pressure and take corresponding measures.
For example, the combination of flow switching valves and solenoid switching valves can effectively prevent hydraulic shock.
Cavitation
Phenomenon: If air infiltrates the hydraulic system, the bubbles in the liquid will burst quickly under high pressure when they flow into the high pressure area, causing local hydraulic shock and generating noise and vibration.
Additionally, as bubbles destroy continuity of liquid flow, the ability of oil to flow through the piping is reduced, causing fluctuations in flow and pressure and affecting the life of hydraulic components.
Cause: Hydraulic oil contains a certain amount of air, which can be dissolved in the oil or mixed in the form of bubbles.
When the pressure is lower than the air separation pressure, the air dissolved in the oil separates and forms bubbles.
When the pressure drops below the saturated vapor pressure of the oil, the oil will boil and produce a large number of bubbles. These bubbles mixed with the oil form a discontinuous state, called cavitation.
Location: It is easy to form air pockets in the oil suction port and oil suction pipe below atmospheric pressure.
When oil flows through small openings such as choke holes, the pressure drops due to the increase in speed, which can also cause air pockets.
Damage: Bubbles move with the oil to the high pressure area and explode quickly under high pressure, causing a sudden decrease in volume.
The surrounding high-pressure oil flows to supplement it, causing local instantaneous shock, a rapid increase in pressure and temperature, and producing strong noise and vibrations.
Measures: The structural parameters of the hydraulic pump and oil suction piping must be designed correctly to avoid narrow oil passages and sharp bends and prevent the formation of low pressure zones.
Reasonable selection of mechanical materials, increasing mechanical strength, improving surface quality and increasing corrosion resistance.
Cavitation erosion
Cause: Cavitation is often accompanied by cavitation erosion, and the oxygen in the bubbles produced in the air pockets can corrode the surface of metal components.
We call this corrosion caused by cavitation cavitation erosion.
Location: Cavitation erosion can occur in oil pumps, pipelines and other devices with throttling devices, especially in oil pump devices where this phenomenon is most common.
Cavitation erosion is one of the causes of several failures in hydraulic systems, especially in high-speed and high-pressure hydraulic equipment, where special attention must be paid.
The damages and measures are the same as for cavitation.
Future Developments in Hydraulic Systems
1. Emergence of the Trend of Import Substitution with High-Quality Hydraulic Products
Although China's hydraulic industry has developed rapidly, most hydraulic component manufacturing enterprises are small-scale and have limited innovation capabilities.
Hydraulic products are mainly concentrated in the medium to low-cost market, and there is significant excess capacity of common hydraulic components, leading to fierce competition in low-price and low-end products.
Due to the delay in the development of high-quality hydraulic components compared with downstream equipment manufacturing industries, domestic mainframe manufacturers have long depended on importing high-quality hydraulic components.
In recent years, with the development of the industry and the technological innovation of companies, domestic hydraulic component manufacturers have gradually made advances in technology and processes, resulting in better product performance.
Some high-quality companies in the hydraulic industry have gradually broken the dependence of domestic mainframe manufacturers on international brands with their high cost-performance ratio and regional advantages, continuously expanding their market share.
With the outbreak of the COVID-19 pandemic in 2020, international trade was hampered to a certain extent, and domestic mainframe manufacturers actively sought out domestic companies for matching, promoting the process of import substitution and providing new opportunities for domestic mainframe manufacturers. hydraulic components.
2. Integration of Hydraulic Technology with High-Tech Achievements”
In recent years, the integration of hydraulic technology with new technologies such as computer information technology, microelectronic technology and automatic control technology has promoted the development level of hydraulic systems and components.
In the short term, the possibility of radical changes in hydraulic technology is low, but hydraulic technology will continue to improve, specifically in terms of: miniaturization, light weight and modularization of hydraulic components; greening of production processes; integration and integration of hydraulic systems.
1) Miniaturization, weight reduction and modularization of products
Miniaturization, weight reduction and modularization are inevitable trends throughout the hydraulic industry.
Miniaturization can be achieved by redesigning the layout and structure of components and helps improve the response speed of hydraulic systems.
Weight reduction of hydraulic components can be achieved through material selection and technological upgrades, reducing energy consumption of downstream equipment, extending service life and improving production efficiency.
Modularization of hydraulic products refers to the integration of multiple functions that were previously achieved by several separate components into a single module.
Modularization can improve the assembly efficiency and sealing performance of hydraulic products.
2) Green Manufacturing Process
The manufacturing process of hydraulic components and parts has always faced important challenges, such as process pollution, product vibration and noise, material loss and media leakage.
In the future, green production technology should be applied to the entire life cycle of product design, process, manufacturing, use and recycling.
Vibration and noise from hydraulic products and systems can be reduced through structure optimization and the use of active control principles.
Harmful manufacturing processes must be phased out and replaced with environmentally friendly processes and equipment to improve the efficiency of resource and energy use in the manufacturing process.
The development of new materials that reduce friction and reduce wear on hydraulic components can improve the efficiency of material use.
The development of new hydraulic pipeline connection technologies, research of new sealing materials, optimization of sealing structures and precision machining processes can improve the sealing performance of products and reduce leakage and medium pollution.
The development of recycling and reuse processes for fluid media, as well as specialized processes for disassembly, recycling and remanufacturing of hydraulic components can improve product recyclability.
3) Integration and Integration of Hydraulic Systems
The integration and integration of hydraulic systems can realize the flexibility and intelligence of hydraulic systems, fully exercising the advantages of hydraulic systems such as high transmission power, low inertia and fast response.
With the development of new energy technologies and intelligent equipment, hydraulic transmission technology and electronic control technology must be combined effectively, and the traditional control way must be changed to improve the system's response performance.
The industry needs to break through traditional restrictions, promote the development of intelligent and integrated systems, and satisfy the future demand for hydraulic products in the Chinese market. The integration and integration of hydraulic systems is the future development direction of the hydraulic industry.
Conclusion
This article presents the definition, principle, main components, applications, troubleshooting and future development of hydraulic systems.
By reading this article, it is believed that you have gained a lot of knowledge. Your valuable feedback is also welcome in the comments section.
