Injection molding machine fault analysis and troubleshooting II

The diagnosis of the hydraulic system fault of the injection molding machine is often limited by the on-site conditions, and it is required to eliminate it as soon as possible after the failure occurs, so as not to affect the production schedule. Fault diagnosis methods for hydraulic system of injection molding machine commonly used in the field:
1. Visual inspection
For some simple faults, the parts can be inspected by sight, hand mold, ear hearing and smelling.
For example, visual inspection can detect faults such as cracks, oil leaks, loosening, and deformation, so that parts can be repaired or replaced in a timely manner, and when you hold the hose (especially the hose) with your hand, you will feel a vibration when there is pressure oil flowing, but not when there is no oil flowing or the pressure is too low. In addition, hand touch can also be used to judge whether the lubrication of hydraulic components with mechanical transmission parts is good, feel the temperature change of the component housing with your hands, if the component housing is overheated, it means that the lubrication is poor; Odors are caused by poor lubrication and cavitation, and the point of failure can be identified by smelling.
2. Replacement diagnostics
This method should be used when there is a lack of diagnostic instruments at the maintenance site or the inspected components are relatively precise and not suitable for disassembly. First, remove the suspected faulty components, replace them with new parts or other components of the same model that work normally on other machines for testing, and make a diagnosis to see if the fault can be eliminated. If the hydraulic system of an injection molding machine has no working pressure, it is suspected that the main safety valve is faulty according to experience, so the main safety valve on the injection molding machine of the same type on the site is replaced with the safety valve, and the test machine works normally, confirming that the suspicion is correct. Although it may be troublesome to use the exchange diagnostic method to check the fault, although it is limited by factors such as structure, on-site component reserve or inconvenient disassembly, it is more convenient to use this method for small and easy-to-disassemble components such as reversing valves, relief valves, and check valves. Replacement diagnostics can avoid the degradation of hydraulic components due to blind disassembly. If the suspect main safety valve is removed and dismantled without the replacement method for the above faults, if there is no problem with the component, its performance may be affected after installation.
3. Instrument measurement inspection method
The instrument measurement and inspection method is to judge the fault point of the system by measuring the pressure, flow rate and oil temperature of the hydraulic oil in each part of the hydraulic system. In the general on-site inspection, because the fault of the hydraulic system is often manifested as insufficient pressure, it is easy to detect, and the detection of the flow rate is more difficult, and the size of the flow can only be judged by the speed of the action of the executing components. Therefore, in on-site testing, more methods of detecting the pressure of the system are used.
The fault of an injection molding machine is that the melt pressure is low. During the test, it was found that when the pressure of the hydraulic motor was 5MPa, the screw did not move, that is, the motor did not rotate, which fully indicated that the internal leakage of the motor was serious. The dismantling and inspection of the motor found that the wear of the distribution plate and plunger pair was very serious, indicating that the judgment was correct. After grinding the distribution plate after assembly, everything returned to normal when the machine was tested.
4. Principle reasoning
The basic principle of the hydraulic system of the injection molding machine is to use different hydraulic components and match according to the combination of hydraulic system circuits, which can be analyzed and reasoned when there is a fault, and the location and cause of the fault can be preliminarily determined, and the right medicine can be prescribed to quickly eliminate it.
For the fault of the on-site hydraulic system, according to the working principle of the hydraulic system, the cause of the fault can be analyzed by forward reasoning on the system diagram according to the order of the power element→ the control element → the execution element. The possible factors that cause the pressure drop or flow rate decrease are: first, the oil tank, such as lack of oil, the oil suction filter is blocked, and the ventilation hole is not smooth; second, the hydraulic pump leaks; third, the pressure adjustment of the main safety valve is too low or the leakage is serious; fourth, the hydraulic cylinder leakage is serious. After taking these factors into account, some factors are eliminated based on the existing inspection results and the scope of the fault is narrowed down until the fault point is found and eliminated.
In the fault diagnosis of on-site hydraulic system, according to the working principle of the system, it is necessary to master some laws or common sense; one is to analyze whether the fault process is gradual or abrupt, if it is gradual, it is generally due to the change of the original size and fit caused by wear and tear and lose the original function; if it is a mutation, it is often caused by sudden damage to the parts, if the spring is broken, the seal is damaged, the moving parts are stuck or the dirt is blocked, etc. Second, it is necessary to distinguish whether it is a wearing part or a non-wearing part, or a moving part under high frequency and heavy load, or a hydraulic component that is prone to failure. The components that are at low frequency, light load or basically relatively stationary are not easy to fail, such as reversing valves, sequential valves, spool valves, etc. After mastering these rules, it can play a positive role in quickly judging the fault location.