Hydraulic technology has been introduced into the industrial field for more than 100 years. With the rapid development of industry, hydraulic technology is changing with each passing day. Along with the development of mathematics, control theory, computers, electronic devices and hydraulic fluidics, hydraulic servo systems have emerged and have matured as an applied science, forming their own systems and a set of effective analysis and design methods. The author takes the application of hydraulic system in injection molding machine as an example, and focuses on the method and application of hydraulic system design. Attention to the problem. The basis for designing the hydraulic transmission system of the injection molding machine (1) The overall layout and process requirements of the injection molding machine, including the type of movement of the injection molding machine completed by hydraulic transmission, the types and models of hydraulic actuators that may be used during mechanical design, and the actuators The size range of the location and its space, the degree of automation required, and so on. The steps of designing the hydraulic transmission system 1. Defining the working requirements of the hydraulic transmission system is the basis for designing the hydraulic transmission system, which is proposed by the use department in the form of a technical task book. Pay attention to the problem when designing the hydraulic transmission system. 1. When combining the basic circuits, pay attention to prevent mutual interference between the circuits and ensure a normal working cycle. Problems to be paid attention to when using the hydraulic system (1) The user should understand the working principle of the hydraulic system, be familiar with various operations and adjust the position and direction of the handle. Reasons for the creep of the working parts and the elimination method (1) Because the air is highly compressible, when the liquid containing the bubbles reaches the high pressure zone and is subjected to severe compression, the volume of the oil becomes small, and the working parts are crawled.
(2) The working cycle of the injection molding machine, the movement mode (moving, rotating or swinging) of the actuator, and the completed working range.
(3) Movement speed, speed range, working stroke, load nature and range of variation of hydraulic actuators.
(4) The sequence of operations and interlocking requirements of the various components of the injection molding machine, as well as the working environment and floor space of each component.
(5) The working performance of the hydraulic system, such as work stability, reliability, commutation accuracy, dwell time and flushing amount.
(6) Other requirements, such as pollution, corrosivity, flammability, and quality, dimensions and economy of hydraulic equipment.
2. Proposed hydraulic transmission system diagram (1) According to the movement form of the working part, the hydraulic actuator is reasonably selected;
(2) List the various basic circuits that may be implemented according to the performance requirements and sequence of actions of the working components. At this point, we should pay attention to selecting the appropriate speed regulation scheme, speed conversion scheme, determining safety measures and unloading measures, ensuring the completion and sequence of automatic work cycle and reliability.
After the hydraulic transmission plan is drawn up, the official schematic diagram should be drawn according to the graphical symbols specified in the national standard. The model specifications of each hydraulic component should be marked in the figure. There should also be an action cycle diagram of the actuator and an action cycle diagram of the electrical component. At the same time, a list of standard (or general) components and auxiliary components should be listed.
3. Calculate the main parameters of the hydraulic system and select the hydraulic components (1) Calculate the main parameters of the hydraulic cylinder;
(2) Calculate the flow required by the hydraulic cylinder and select the hydraulic pump;
(3) Selecting a tubing;
(4) Select component specifications;
(5) Calculate the actual working pressure of the system;
(6) Calculate the power and select the motor;
(7) Calculation of heat and tank volume;
4. Perform the necessary hydraulic system check.
5. Structural design of the hydraulic device.
6. Draw a working diagram of the hydraulic system and compile technical documents.
2. Improve the working efficiency of the system and prevent the system from overheating. For example, the power is small, and the throttle control system can be used; the power is large, and the volume control system is preferably used; the parking brake is often used, so that the pump can be unloaded in time; the system with large fuel consumption rate in each working cycle Efficient circuits such as accumulators or pressure-compensated variable pumps should be considered.
3, to prevent hydraulic shock, for high pressure and large flow system, should consider using hydraulic reversing valve instead of electromagnetic reversing valve to slow the commutation speed; using accumulator or adding buffer circuit to eliminate hydraulic shock.
4. Under the premise of satisfying the work cycle and productivity, the system should be simple, and the more complex the system, the more chances of failure. The system should be safe and reliable. For the actuators that do the vertical motion lifting weights, there should be a balance loop; for the actuators with strict sequence action requirements, the sequence control loops should be used. In addition, there should be interlocks and some safety measures.
5, try to achieve standardization, serial design, reduce the design of special parts.
(2) Before driving, check whether the adjustment handles and handwheels on the system are moved by unrelated personnel, whether the position of the electrical switch and the travel switch is normal, whether the installation of the tool on the main machine is correct and firm, etc., and then the guide rail and the piston rod Wipe the exposed part before driving.
(3) When driving, first start the hydraulic pump that controls the oil circuit. When there is no special control oil circuit hydraulic pump, the main hydraulic pump can be started directly.
(4) The hydraulic oil should be inspected and replaced regularly. For the newly used hydraulic equipment, the fuel tank should be cleaned and replaced with new oil after about 3 months. Clean and change oil every six months to one year later.
(5) Attention should be paid to the oil at work. During normal operation, the temperature of the oil in the tank should not exceed 60 °C. If the oil temperature is too high, try to cool and use a higher viscosity hydraulic oil. When the temperature is too low, preheating should be carried out, or intermittent operation should be carried out before the operation, so that the oil temperature is gradually increased, and then enter the official working state.
(6) Check the oil level to ensure that the system has sufficient oil.
(7) The system with exhaust should be exhausted, and the system without exhaust should be reciprocated multiple times to allow it to naturally vent gas.
(8) The fuel tank should be sealed and sealed. An air filter should be installed at the vent hole above the fuel tank to prevent the intrusion of dirt and moisture. When refueling, it should be filtered to make the oil clean.
(9) The system should be equipped with coarse and fine filters as needed. The filters should be inspected, cleaned and replaced frequently.
(10) For the adjustment of the pressure control element, firstly adjust the system pressure control valve----relieving valve, open the adjustment when the pressure is zero, gradually increase the pressure to reach the specified pressure value; then adjust the loops in turn. Pressure control valve. The adjustment pressure of the safety relief valve of the main oil circuit hydraulic pump is generally greater than 10% -25% of the required working pressure of the actuator. The pressure valve of a fast-moving hydraulic pump generally has a regulating pressure of 10%-20% greater than the required pressure. If the unloading pressure is supplied to the control oil circuit and the lubricating oil circuit, the pressure should be maintained within the range of 0.3--0.6 MPA. The adjustment pressure of the pressure relay should generally be lower than the oil supply pressure by 0.3--0.5MPA.
(11) The flow control valve should be adjusted from small flow to large flow and should be adjusted step by step. The flow control valve of the synchronous motion actuator should be adjusted at the same time to ensure the smooth movement: 1 system generates noise and vibration; 2 the moving parts crawl; 3 the system has insufficient pressure; 4 the moving parts speed is abnormal; 5 the oil temperature is too high; The commutation or start is not normal;
Take measures: Install an exhaust device at the high point of the system circuit to remove the air.
(2) Since the frictional resistance between the relatively moving parts is too large or the frictional resistance changes, the working parts are caused to crawl while moving.
Take measures: have certain requirements on the geometrical tolerances and surface roughness of hydraulic cylinders, pistons and piston rods; and ensure that the hydraulic system and hydraulic oil are cleaned to prevent dirt from being caught between the surfaces of the moving parts. Increase the frictional resistance.
(3) Poor lubrication between the surfaces of moving parts, forming dry friction or semi-friction, also easily lead to crawling.
Take measures: Always check the lubrication between the surfaces of the moving parts to keep them in good condition.
(4) If the piston of the hydraulic cylinder and the piston rod are sealed and centered, crawling may occur.
Take measures: The load should be removed, the hydraulic cylinder should be operated separately, and the frictional resistance should be measured to correct the centering.
(5) Due to serious leakage of the hydraulic cylinder, it causes crawling.
Take measures to reduce leakage losses or increase hydraulic pump capacity.