Electro-hydraulic proportional pressure injection

Date：2014/8/19 11:03:29

With the rapid development of the plastics industry, injection molding machinery manufacturing increasing attention has been paid. For large injection molding machines, the hydraulic drive is the main drive, but the traditional hydraulic system does not fully meet the conditions of injection molding machines and energy requirements, people have been looking for a new system to replace the traditional hydraulic injection molding machine Hydraulic system. In recent years, with the electro-hydraulic proportional control technology matures, electro-hydraulic servo control technology, the pressure - flow control system complex proportional system has become commonly used in large injection molding machine, it will not only be able to meet the requirements of the injection molding machine operating conditions, and also it has a good energy saving effect. Since the electro-hydraulic proportional control system for the working medium cleanliness no special requirements, lower manufacturing costs, lower energy loss, steady-state and dynamic characteristics of engineering controls sufficient to meet most of the requirements, it has won more extensive than the electro-hydraulic servo system applications.
1 system program and adjust principle
1.1 System program
        Injection molding machine hydraulic system is a typical multi-level pressure - flow systems. Process injection molding machine is generally divided into mold, injection, Paul several stages, cooling, etc., pressure and flow is required at all stages of each are not identical. The traditional quantitative pump injection molding machine hydraulic system, in a work cycle injection molding machine, since the output flow of the pump is always the same, so there is a big throttling and overflow losses. Since the injection molding machine products are different, so asking them to hold pressure can be adjusted.
        According to the conditions of injection molding machines and energy requirements, designed electro-hydraulic proportional pressure - flow system plan, compared with traditional quantitative pump hydraulic system, which can change adaptive load pressure and flow requirements, the pump output power load to match the required power and greatly reduce the energy loss.
1.2 System Regulation principles
        Proportional throttle valve 5 and the load sensing valve 7 constitutes a flow control loop systems, front-throttle D, proportional pressure valve 8 and the constant pressure valve 6 constitute a control loop system. Between the closest vat of constant variable valve A-T path, connected in parallel with a liquid passage resistance R1 and the corresponding path with liquid path resistance R2 and R3. With this arrangement, for variable control and system operation and many have beneficial effects in rapidity and stability.
        Flow adjusted to the actual output of the pump flow rate control target, this time except in certain input signal proportional throttle valve, pump output corresponding flow without being affected by the load pressure changes, but also by changing the ratio of the throttle valve input signal, the output of the pump flow rate changes in accordance with certain rules, in order to adapt to the load speed. Perform load pump provides pressure and flow to match hydraulic system does not generate excess pressure and flow, so the system has a significant energy savings.
        When the system is in flow control conditions, load changes, the proportion of the differential pressure ΔP 5 at both ends of the throttle valve to increase or decrease, thus promoting the load sensing valve 7 spool right or left, so that the pump output flow is reduced or increased large, the final output of the pump to maintain a constant flow. After adjusting proportional throttle valve opening set, the system is in constant state of change does not affect the system load flow. Pump output pressure proportional throttle up only 5 at both ends of the load pressure than the pressure difference ΔP.
        When the injection molding machine into the packing finished state, the role of front-restrictor D, the constant pressure valve body 6 is shifted to the right, the variable displacement pump is rapidly reduced to close to zero, the system at high pressure small flow of work, thus avoiding the conventional hydraulic system pressure overflow losses. At the same time, the pump output pressure does not rise, avoiding damage to the equipment, the protection of the system components. In order to set the working pressure and flow values, pressure and motion transition time can be controlled by a computer.
2 system simulation model and related parameter settings
Build 2.1 System Simulation Model
        The system program, use AMESiM software to build electro-hydraulic proportional pressure injection - Flow System Simulation Model. Wherein the load sensing valve, constant pressure valves, variable-cylinder from the HCD (hydraulic component design library module) is built.
Set 2.2 related parameters
        Through repeated testing simulation model, which optimization parameters are as follows: motor rated speed 1000R / MiN, variable pump maximum displacement 100L / MiN, proportional throttle set pressure 1.5MPA, constant pressure valve spool diameter 6.5MM, load sensitive valve spool diameter 6.5MM, load sensing valve spring preload 49.75N, constant pressure valve spring preload 5N, vats variable diameter 50MM, variable small cylinder diameter 20MM, hydraulic oil temperature 40 ℃, the hydraulic oil density of 850kg / M3.
3 System Simulation
3.1 System Simulation research analysis ratio adjustment
        Shows the proportion of the throttle input signal, which ranges from 0 to 1, 0 indicates the proportion of the throttle opening is fully closed, a represents the proportion of the throttle valve port is fully opened. When the proportion of the throttle valve opening is fully open, the flow through of 100L / MiN. It can be seen from the output flow of the pump can according to proportional throttle input signal proportionally adjusted so that the output flow of the pump according to the load almost desired output, avoiding the waste flow.
        First load pressure regulating valve is provided, so that the load pressure increases linearly from the 0 ~ 20MPA set proportional pressure valve opening pressure (holding pressure) is 15MPA, set the proportional throttle valve opening is fully opened. Proportional pressure valve opening pressure of the injection molding machine can produce different products, in proportion to the setting. The output pressure of the pump according to changes in load pressure changes, but before the load pressure reaches holding pressure, the pump output pressure is always more than a little pressure fixed value (1.5MPA) load, so the system is throttling loss small. When the load pressure is greater than the holding pressure, the pump output pressure is constant. When the load pressure is greater than the holding pressure, the pump delivery rate rapidly drops to near zero, then the system is in a state holding pressure of high pressure low flow.
Simulation Research 3.2 holding pressure adjustable
        General injection molding machine production of different products, thus requiring its holding pressure can be based on product requirements and adjusted accordingly. Batch simulation capabilities AMESiM use simulation software, set proportional pressure valve opening pressure (holding pressure) is 10MPA, 15MPA and 18MPA, set the proportional throttle valve opening is fully opened. It can be seen holding pressure system can be set according to specific requirements, to meet the injection molding machine holding pressure adjustable requirements. As can be seen, when the load pressure is greater than the proportional pressure valve opening pressure, the pump output flow rapid decline in short time to close to zero, the system is under high pressure low flow, thus avoiding the traditional high-pressure injection molding machine hydraulic system overflow flow loss, while the output pressure of the pump is no longer rising, avoiding damage to the equipment, the protection of the system components.
3.3 Effect of constant pressure valve spring stiffness of packing process
        Injection molding machine operation, the holding pressure is important for the stability of product quality, thus requiring the injection molding machine in packing process mediator-pressure fluctuations do not occur, otherwise it will affect the quality of products.
        Batch simulation capabilities AMESiM use simulation software, set the spring stiffness constant pressure valves were 5N / MM, 10N / MM, 15N / MM, 30N / MM, set the proportional throttle valve opening is fully opened. System packing process, constant pressure valve spring stiffness from small to large, from the pump output flow becomes unstable steady, stable flow from the pump conducive to the stability of the system hold pressure, but the time spring rate increases reaction It becomes lag.
        1,2,3,4 curve represents the corresponding constant pressure valve spring stiffness 5N / MM, 10N / MM, 15N / MM, when 30N / MM, change the pump output pressure. As can be seen, the system packing process, the constant pressure valve spring stiffness from small to large, the system pressure becomes stable from the unstable, spring stiffness constant pressure valve should not be chosen too small.

【Return】