Preventive Maintenance Of Injection Molding Machine – Hydraulic, Electrical And Mechanical


Injection molding machine is one of the widely used equipment in the plastic processing industry, usually it has to work for a long time. Therefore, how to ensure the normal and stable operation of the injection molding machine in continuous production is a problem worthy of attention and efforts to solve. From the perspective of users, regular preventive maintenance is an effective way to ensure the normal operation of the injection machine under the premise of correct selection of injection machine.

The preventive maintenance is a series of preventive work and inspection, so as to avoid machine failure and prolong the working life of various parts. In this article, we are going to cover how does the injection molding machine achieve preventive maintenance from three aspects: hydraulic, electrical and mechanical.


Preventive Maintenance Of Injection Moulding Machine

1. Hydraulic

1) Hydraulic oil quantity: Insufficient oil will cause the oil temperature to rise and the air to dissolve into the oil, which will affect the oil quality and the normal operation of the hydraulic system. The shortage of oil is usually caused by oil leakage or loss during repair. Therefore, it is necessary to pay attention to check whether there is leakage, replace the worn sealing parts as soon as possible, tighten the loose joints, etc. after maintenance, check the oil volume of the oil tank and replenish it in time.


2) Hydraulic oil temperature: The ideal working temperature of the hydraulic system should be between 45 ℃ and 50 ℃. The reason is that the hydraulic system is designed according to the viscosity of a selected pressure oil, but the viscosity will change with the oil temperature, which will affect the working components of the system, such as oil cylinder, hydraulic valve, etc., so as to reduce the control precision and response sensitivity, especially for precision injection molding machines. At the same time, too high temperature will accelerate the aging of the seal and make it hardened and cracked.

If the temperature is too low, the processing energy consumption is large and the running speed is reduced. Therefore, it is necessary to pay close attention to the working temperature of hydraulic oil. The causes of high oil temperature are various, but most of them are due to the failure of oil circuit or cooling system.


3) Hydraulic oil quality: One of the important properties of hydraulic oil is its chemical stability, namely oxidation stability. Oxidation is the most important factor to determine the effective service life of hydraulic oil. Insoluble substances such as wood tar, oil sludge and carbon residue produced by oxidation will pollute the hydraulic system, increase the wear of hydraulic components, reduce various gaps, plug small holes, and eventually cause the hydraulic system to fail.

The oxidation rate of hydraulic oil depends on its own and working conditions and other factors, among which temperature is one of the main factors. Therefore, it is absolutely necessary to use appropriate hydraulic oil and regularly check the oxidation degree of hydraulic oil (judging from the color of the oil itself). It is absolutely necessary to replace the oil 


4) Oil filter cleaning: The oil filter plays the role of cleaning hydraulic oil, so the oil filter should be cleaned every three months to keep the oil suction pipe unblocked, and check whether the oil filter net is damaged.


5) Cooler cleaning: The cooler should be cleaned once a year, or according to whether its working capacity is reduced or not. The cooling efficiency will be affected by the blockage or fouling inside the cooler. The soft cooling water should be selected.


2. Electrical 

1) Wire joint inspection: If the connector is not tight, the wire will be damaged by high temperature or spark, and the signal transmission will be affected by poor connector. The connector on the contactor is easy to loosen due to the vibration of electromagnetic action, so it is necessary to check the position and tightening of the line connector regularly.


2) Motor: Generally, motors are air-cooled, and dust accumulation will cause heat dissipation difficulties. Therefore, regular cleaning is carried out every year. The motor overload cut-off device is usually installed in the circuit. The limited current of the protection device is adjustable. Appropriate selection should be made according to the motor power. At the same time, once the overload protector is started, it is necessary to check whether there is phase shortage, poor contact or high oil temperature before pressing back Reset the switch.


3) Heater and thermocouple: It is not easy to detect the burning of the heater in normal production. Therefore, it is necessary to pay attention to the working condition of the temperature controller to judge whether the heater is normal. In addition, the common damage of the heater is the wire connection. Due to the poor joint and the increase of contact resistance, the local overheating of the connection leads to the oxidation of the interface and damage.


4) Electromagnetic contactor: The contactor used in the electric heating part operates frequently, and its loss speed is also fast. If the main contact is overheated and fused, the heating temperature may be out of control. Therefore, if the contact overheats, makes a sound or the fire is very big when breaking, it indicates that it is about to be damaged and should be replaced as soon as possible.


5) Computer control part: With the application of microcomputer control technology in the injection molding machine, the normal operation of the microcomputer part and its related auxiliary electronic board puts forward higher requirements for the fluctuation of power supply voltage, the temperature and humidity of the working environment, the anti-seismic performance of the installation and the interference of external high-frequency signals. Therefore, the fan for ventilation and heat dissipation in the control box shall be kept in normal operation, and the power supply voltage stabilizing device with high precision shall be used In order to reduce the influence of external vibration on the control box, we should solve these problems and check them regularly.


3. Mechanical 

1) Template parallelism: The parallelism of the template can best reflect the condition of the mold locking part, and the non parallelism will make the product unqualified and increase the wear of the equipment and die. The parallelism of the formwork can be preliminarily reflected by the movement of the tail plate and the appearance analysis of the product. Its adjustment must be carried out by familiar personnel step by step, otherwise improper adjustment will cause more damage to the machine.


2) Die thickness adjustment: The first mock exam system should be used regularly to adjust the thickness from the thickest to the thinnest to ensure smooth movement. The machine must be inspected for long term production with the same mold to avoid malfunction.


3) Central lubrication system: All mechanical moving parts need proper lubrication, and central lubrication system is one of the necessary parts of injection molding machine. The amount of oil in the central lubrication system should be regularly checked to see if it is full. The lubricating oil used must be clean and free of impurities, so as to ensure that there is lubricating oil supply at all lubricating positions. If the oil pipe is blocked or leaking, it should be replaced or repaired immediately.


4) Bearing inspection: Abnormal sound or temperature rise of bearing during operation indicates that the bearing has been worn. Timely inspection or replacement shall be conducted and lubricating grease shall be injected again.


5) Injection system: Injection screw, check ring and barrel constitute the heart part of the injection molding machine, which determines the quality and efficiency of processing, and must keep them in good working condition.

Firstly, necessary measures should be taken to prevent the non plastic debris from mixing into the plastic material flow. Secondly, attention should be paid to checking the correct clearance between the screw and barrel, and between the check ring and the barrel. The normal clearance should be able to seal the plastic backflow and produce the shear action needed for plasticization. When the melting glue moves slowly and the melting material has spots and black spots, the wear of screw, check ring and barrel should be checked.