Injection molding machine is one of commonly used equipment in plastics processing industry. Usually it has to work for a long time. Therefore, how to ensure normal and stable operation of injection molding machine in continuous production is a worthy and important consideration for both manufacturer and user of injection molding machine. Problem that we are trying to solve, from user's point of view, on the premise of correct selection of injection machine, regular preventive maintenance is an effective way to ensure normal operation of injection machine.
So-called preventive maintenance is a series of preventive work and inspections to avoid machine failures and prolong working life of various parts, such as turning sudden failures that cause production stoppages into foreseeable and planable shutdown repairs or overhauls; Purpose of preventive maintenance is to detect and replace damaged parts in time to prevent chain damage.

 

Insufficient oil quantity will cause oil temperature to rise easily, and air will easily dissolve into oil, which will affect oil quality and normal operation of hydraulic system. Insufficient oil quantity is usually caused by oil leakage or loss during repair. For this reason, daily attention should be paid to check whether there is any leakage, replace worn seals as soon as possible, tighten loose joints, etc. After maintenance, check oil volume of fuel tank and timely supply.

Ideal working temperature of hydraulic system should be between 45℃ and 50℃, because hydraulic system is designed according to a selected pressure oil viscosity, but viscosity will change with oil temperature, which will affect work in system. Components, such as oil cylinders, hydraulic valves, etc., reduce control accuracy and response sensitivity, especially for precision injection machines.
At the same time, if temperature is too high, aging of seal will be accelerated, causing it to harden and crack; if temperature is too low, processing energy will be consumed and running speed will be reduced. Therefore, it is necessary to pay close attention to working temperature of hydraulic oil. There are various reasons for high oil temperature, but most of them are due to oil circuit failure or cooling system failure.

One of important properties of hydraulic oil is its chemical stability, i.e. oxidative stability. Oxidation is the most important factor determining effective service life of hydraulic oil. Insoluble substances such as wood tar, oil sludge and carbon residue generated by oxidation will pollute hydraulic system, increase wear of hydraulic components, reduce various clearances, block small holes, and eventually cause hydraulic system to fail.
Oxidation rate of hydraulic oil depends on many factors such as itself and working conditions, among which temperature is one of main factors. Therefore, it is necessary to use suitable hydraulic oil, regularly check degree of oxidation of hydraulic oil (judged from color of oil itself), and it is absolutely necessary to change oil actively after a certain number of working hours.

Oil filter plays role of cleaning hydraulic oil, so oil filter should be cleaned every three months to keep oil gas suction pipe unobstructed, and at the same time check whether oil filter screen is damaged.

Cooler should be cleaned once a year, or according to whether its working capacity is reduced or not. Blockage or fouling inside cooler will affect cooling efficiency. Cooling water should be soft (mineral-free).

Wires with loose joints will cause high temperature or sparks to damage joints. Poor joints will also affect signal transmission; joints on contactor will be easily loosened due to vibration of electromagnetic action, so it is necessary to check position of wire connector and tighten it.

Generally, motors are air-cooled. Dust accumulation will cause difficulty in heat dissipation. Therefore, regular cleaning is carried out every year. Usually, a motor overload circuit breaker is installed in circuit. Limited current of this protection device is adjustable and should be adjusted according to motor power. At the same time, once overload protector is activated, it should be determined to check whether there is a lack of phase, bad contacts or high oil temperature before pressing reset switch.

Heating tube should be checked regularly to ensure that it can effectively transfer heat. In normal production, burning of heating tube is not easy to detect. Therefore, pay attention to working condition of temperature controller, and judge whether heating tube is normal. In addition, common damage to heating tube is wire connection. Due to poor connection, contact resistance increases, which causes local overheating of connection to cause interface to oxidize and damage.

Contactor used for electric heating part operates more frequently, and its loss speed is also faster. If main contact is overheated, melted and bonded, it may cause heating temperature to run out of control. If it is large, it means that it is about to be damaged and should be replaced as soon as possible.

With application of microcomputer control technology in injection molding machine, normal operation of microcomputer part and its related auxiliary electronic boards has put forward higher requirements on fluctuation of power supply voltage, temperature and humidity of working environment, shock resistance of installation and interference of external high-frequency signals. To this end, keep fans for ventilation and heat dissipation in control box working normally, use high-precision power supply voltage stabilizers to supply power, try to reduce influence of external vibration on control box. These problems should be effectively solved and checked regularly.

 

Parallelism of mold plate can best reflect condition of clamping part. If mold plate is not parallel, product will be unqualified, equipment and mold wear will be increased. Parallelism of mold plate can be initially reflected by movement of tail plate during mold clamping and appearance analysis of product, but exact situation needs to be detected by instruments such as dial indicators. Adjustment of parallelism of mold plate must be carried out by familiar personnel according to steps, otherwise improper adjustment will cause more damage to machine.

Mold thickness adjustment system should be used regularly to adjust mold thickness from the thickest to the thinnest once to ensure smooth operation. For machines produced with same mold for a long time, this inspection must be carried out to avoid failure.

All mechanical moving parts need to be properly lubricated, and a central lubrication system is one of the must-haves for injection molding machines today. Amount of oil in central lubrication system should be checked frequently to see if it is filled up. Lubricating oil used must be clean and free of impurities to ensure that all lubricating positions are supplied with lubricating oil. If oil pipe is found to be blocked or leaking, it should be replaced or repaired immediately. Most mechanical wear occurs due to lack of lubrication, so sufficient attention should be paid to lubrication.

Vibration or unsmooth movement may be caused by improper speed adjustment, uncoordinated speed change and time, or mechanical and oil pressure adjustment. This kind of vibration will accelerate wear and tear of mechanical parts, loosen fastened screws, so vibration should be reduced and avoided.

If bearing makes abnormal noise during operation, or temperature rises, it means that inside of bearing has been worn. It should be checked or replaced in time, and grease should be refilled.

Injection screw, check ring and barrel form heart of injection molding machine, which determines quality and efficiency of processing, and must be kept in good working condition.
First, take necessary measures to prevent non-plastic debris from mixing into plastic flow, then pay attention to checking correct clearance between screw and barrel, check ring and barrel. Normal clearance should be able to seal plastic backflow and produce plastic. When it is found that melting action is slow, melt has spots and black spots, or product is unstable in forming, wear of screw, check ring and barrel should be checked.

 

Abnormal rise of oil temperature may be caused by abnormal cooling system or high heat generated by oil pressure components during operation.

1) Cooling system supply is insufficient, such as water valve is not fully opened, water pressure is insufficient or water pump flow does not meet needs, etc.
2) Blocked pipes, such as filters, cooling towers or water pipes.
3) Cooling water temperature is too high, such as cooling tower has insufficient heat dissipation capacity, or is damaged or temperature is too high.

1) Oil pump is damaged, and internal parts wear and generate high heat when rotating at high speed.
2) Pressure adjustment is not appropriate, hydraulic system is in a high pressure state for a long time and overheats.
3) Internal leakage of hydraulic components, such as damage to directional valve or damage to sealing ring, causes heat to be generated when high-pressure oil flows through a small space.

Abnormal noise is generated, indicating that parts are damaged or improperly adjusted, cause should be identified according to location of noise and repaired immediately.
1. Hydraulic oil in oil tank is insufficient, air sucked by oil pump or blockage of oil filter will cause oil pump to be short of oil, which will cause air bubbles in oil to be discharged, hit blades and generate noise. Solution is to check amount of oil, prevent air inhalation and clean oil filter.
2. Hydraulic oil has high viscosity and increases flow resistance, so it is necessary to replace appropriate hydraulic oil.
3. Due to damage of bearings or blades of oil pump or motor, concentricity deviation of coupling causes noise, and concentricity must be adjusted or parts should be replaced.
4. Directional valve fails to respond but still functions, such as valve core wear, internal leakage, burr blockage, inflexible movement, and failure of solenoid valve due to insufficient current will also produce noise. Solution is to clean valve core, valve core must be replaced with new parts when worn, current must be stable and sufficient.
5. Hydraulic components are damaged or oil pipeline is blocked, so that hydraulic oil flows at a high speed and generates noise.
6. Mechanical part is faulty, bearing is worn or machine lacks lubricating oil or parts are loose, reasons should be found to tighten or replace parts to ensure that there is enough lubricating oil.

In a stable production cycle, quality of finished products is unstable, which may be caused by wear or improper adjustment of mechanical parts.
1. Wear of screw, check ring and barrel.
2. Internal leakage occurs due to damage to sealing ring in injection cylinder.
3. Temperature control of heating cylinder is unstable.
4. Pressure and speed control parts are abnormal.