When using an injection molding machine, possible failures of hydraulic system of injection molding machine are diverse. It is result of a combination of many factors, dispersion is relatively large. Therefore, when performing fault diagnosis, it is necessary to analyze factors that cause fault one by one, pay attention to their internal connections, find out main contradictions, so that they can be resolved relatively easily.
Under normal circumstances, failure of hydraulic system of injection molding machine is not accidental. Any failure will be accompanied by various abnormal signs before it evolves into a major failure. These signs can be summarized as:
(1) There are abnormal sounds, such as pumps, motors, and thermostatic valves.
(2) Operating speed of hydraulic motors for slewing, walking, and hoisting, as well as hydraulic cylinders of various working devices, is reduced and weak.
(3) Oil tank level drops and oil deteriorates.
(4) Oil leakage occurred on outer surface of hydraulic components.
(5) Oil temperature is too high.
(6) Pipeline damage, looseness and vibration occur.
(7) Smell of focal nucleus appears and so on.

 

Above phenomena can be discovered by naked eye observation, hand touch, and nose smell as long as you pay careful attention during use. In actual work, people use this on-site method as the first-hand information to analyze failure, then based on experience, synthesize these first-hand information to analyze actual problem, find out cause of failure, and solve it as soon as possible. However, in actual work, it is often impossible to accurately diagnose cause of failure at one time. At this time, several iterations are required, that is, repeated analysis and repeated inspections until cause of failure is found.
In actual work, engineering and technical personnel often follow following steps to deal with faults in hydraulic system.
(1) Understand system. When a certain injection molding machine has a hydraulic failure, you should first understand hydraulic system. It is to be familiar with relevant technical data and reports, understand working principle of liquefied pneumatic system, understand basic structure of various components and specific functions in system, be able to find out liquid flow process under various working conditions. Before inspecting equipment, observe working conditions of system and record necessary technical data, such as working speed, pressure, flow, cycle time, etc.
(2) Ask operator. Interrogate operator operating malfunctioning injection molding machine. Ask about characteristics of equipment and its functional characteristics; ask about basic phenomena when equipment fails, such as whether hydraulic pump can be started, whether system oil temperature is too high, whether system noise is too large, whether hydraulic cylinder can drive load, etc.
(3) Verify phenomenon provided by operator and check carefully. Phenomenon proposed by operator is further verified by observing meter readings, working speed, listening to sound, checking oil and actuators for malfunctions, etc.; then follow fluid flow in system to search carefully along circuit from oil tank in turn, record and observe results on time. During inspection, carefully check oil in fuel tank to determine whether dirt enters system. It affects normal operation of components of system; touch it by hand to check whether oil inlet pipe and high-pressure oil pipe are proliferated, softened, leaked, or damaged; check that pipe joints of each control element and mounting screws of housing are loose; finally check oil and piston rod of hydraulic cylinder. In each step of inspection, attention should be paid to whether there is improper operation or maintenance to find cause of failure.
(4) List possible causes of failure based on information obtained from understanding, inquiry, verification and inspection. At this time, it should be kept in mind that a failure phenomenon may be caused by two or more reasons. For example, speed of actuator may be reduced, which may be due to wear of hydraulic pump parts, or internal leakage of hydraulic cylinder may increase; for example, If oil temperature is too high, it may be that amount of oil in oil tank is not enough, or that oil pollution blocks heat dissipation surface, or pressure of overflow valve is adjusted too high.
(5) Make a conclusion. According to list of failure causes, inspection sequence is arranged according to principle of "easy first and then difficult". First select those that can be restored to normal after a simple inspection or repair, so that inspection work can be completed in the shortest time.
(6) Verification conclusion. Once through above steps, find out cause of failure of injection molding machine, start troubleshooting. Troubleshooting includes checking pressure and flow with appropriate test equipment, disassembling casing cover, inspecting pumps, motors and other components. These test inspections are basis for judging replacement of parts and hydraulic components. In actual work, there is often no suitable test device to carry out inspections. At this time, it is necessary to replace pump, motor, hydraulic valve and other component assemblies as an effective means of troubleshooting.
In process of finding and troubleshooting faults, you should be careful, cautious, and strive to be accurate, avoid blindly disassembling parts, or use improper methods to deal with faults, so as to avoid new damages caused by this. Except when necessary, do not easily disassemble hydraulic components, because unnecessary and premature disassembly and assembly will reduce service life of these components.