Injection molding machine is one of commonly used equipment in plastic processing industry. It usually has to work for a long time. Therefore, how to ensure that injection machine works normally and stably in continuous production is a matter worthy of attention and attention for both manufacturer and user of injection machine. From user's perspective, regular preventive maintenance is an effective way to ensure normal operation of injection machine on premise of correctly selecting injection machine model.
So-called preventive maintenance is a series of preventive work and inspections to avoid machine failure and extend working life of various parts. For example, a sudden failure that causes production shutdown can be converted into a foreseeable and planned shutdown for repair or overhaul; purpose of preventive maintenance is to detect and replace damaged parts in time to prevent chain damage.

 

1.Hydraulic oil volume
Insufficient oil volume will cause oil temperature to rise easily and air to easily dissolve into oil, which will affect oil quality and normal operation of hydraulic system. Insufficient oil is usually caused by oil leakage or loss during repairs. For this reason, you should check daily for leaks, replace worn seals as soon as possible, tighten loose joints, etc. After maintenance, check amount of oil in tank and replenish it in time.
2. Hydraulic oil temperature
Ideal operating temperature of hydraulic system should be between 45℃ and 50℃. Reason is that hydraulic system is designed based on a selected pressure oil viscosity, but viscosity will change with oil temperature, which will affect working components in system, such as oil cylinders, hydraulic valves, etc., reducing control accuracy and response sensitivity, especially for precision injection machines.
At the same time, if temperature is too high, it will also accelerate aging of seal, cause it to harden and crack; if temperature is too low, processing energy will be consumed and operating speed will be reduced. Therefore it is necessary to pay close attention to operating temperature of hydraulic oil. There are many reasons for excessive oil temperature, but they are mostly attributed to oil line failure or cooling system failure.
3. Hydraulic oil quality
One of important properties of hydraulic oil is its chemical stability, that is, oxidation stability. Oxidation is the most important factor that determines 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 gaps, block small holes, and ultimately cause hydraulic system to malfunction.
Oxidation rate of hydraulic oil depends on many factors such as itself and working conditions. Temperature is one of main factors. Therefore, it is necessary to use appropriate hydraulic oil and regularly check oxidation degree of hydraulic oil (judged from darker color of oil itself). It is absolutely necessary to actively change oil after exceeding a certain number of working hours.
4. Oil filter cleaning
Oil filter plays a role in cleaning hydraulic oil, so oil filter should be cleaned every three months to keep oil suction pipe smooth, and check whether oil filter screen is damaged.
5. Cooler cleaning
Cooler should be cleaned once a year, or according to whether its working capacity has been reduced. Blockage or fouling inside cooler will affect cooling efficiency. Soft (mineral-free) water should be used for cooling.

1. Wire joint inspection
Wires with loose joints will cause high temperatures or sparks at joints and cause damage. 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 regularly check position of wire connector and tighten it.
2. Electric motor
Generally, motors are air-cooled. Dust accumulation will cause heat dissipation difficulties, so they must be cleaned regularly every year. Usually, a motor overload cutout is installed in circuit. Limited current of this protection device is adjustable and should be appropriately adjusted according to motor power. At the same time, once overload protector is activated, you should make sure to check whether there is a lack of phase, poor contacts, or oil temperature is too high before pressing return switch.
3. Heating cylinder and thermocouple
Heating cylinder should be checked regularly to see if it is fastened to ensure effective heat transfer. In normal production, burning of heating cylinder is not easy to detect. Therefore, attention should be paid to working condition of temperature controller to determine whether heating cylinder is normal. In addition, common damage to heating cylinder is at wire connection. Due to poor joints, contact resistance increases, causing local overheating of connection, leading to oxidation of interface and damage.
4.Electromagnetic contactor
Contactors used in electric heating parts move more frequently and wear out faster. If main contacts are overheated, melted and bonded, heating temperature may be out of control. Therefore, if contact is found to be overheated, makes a sound, or has a strong fire when it is broken, it means that it is about to be damaged and should be replaced as soon as possible.
5. Computer control part
With application of microcomputer control technology in injection molding machines, normal operation of microcomputer part and its related auxiliary electronic boards has put forward higher requirements for power supply voltage fluctuations, temperature and humidity of working environment, shock resistance of installation, and even interference of external high-frequency signals. To this end, keep fan used for ventilation and heat dissipation in control box working normally, use high-precision power supply voltage stabilizing equipment for power supply, and try to reduce impact of external vibration on control box. These problems should be effectively solved and checked regularly.

1. Mold plate parallelism
Parallelism of mold plate can best reflect condition of mold clamping part. Non-parallel mold plates will cause product failure, increase equipment and mold wear. 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 with a dial indicator and other instruments. Adjustment of parallelism of mold plate must be carried out step by step by familiar personnel, otherwise improper adjustment will cause greater damage to machine.

 

2. Mold thickness adjustment
Mold thickness adjustment system should be used regularly to adjust mold thickness from the thickest to the thinnest once to ensure smooth movement. For machines that have been produced with same mold for a long time, this check must be performed to avoid malfunctions.
3. Central lubrication system
All mechanical moving parts need to be properly lubricated, and a central lubrication system is one of the must-haves for current injection molding machines. Amount of oil in central lubrication system should be checked frequently to see if it is full. 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 clogged 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.
4. Keep all movements smooth
Vibration or sluggish movement may be caused by improper speed adjustment, uncoordinated speed changes and time, or mechanical or hydraulic adjustments. This kind of vibration will accelerate wear of mechanical parts and loosen tightened screws, so vibration should be reduced and avoided.
5. Bearing inspection
If bearing makes abnormal noise during operation or temperature rises, it means that inside of bearing is worn. It should be checked or replaced in time, and grease should be re-injected.
6. Injection system
Injection screw, check ring and barrel form heart of injection molding machine, which determines quality and efficiency of processing. They must be kept in good working condition. First, necessary measures should be taken to prevent non-plastic debris from being mixed into plastic material flow. Secondly, attention should be paid to checking correct gaps between screw and barrel, between non-return ring and barrel. Normal gap should be able to seal plastic backflow and produce shearing action required for plasticization. When it is found that melt moves slowly, melt has spots and black spots, or product is unstable, wear of screw, check ring and barrel should be checked.

 

Abnormal rise in oil temperature may be caused by abnormal cooling system or high heat generated by hydraulic components during operation.
1. Cooling system is abnormal
1) Supply of cooling system is insufficient, such as water switch is not fully opened, water pressure is insufficient, or water pump flow does not meet needs, etc.
2) Pipes are blocked, such as filters, cooling towers or water pipes.
3) Cooling water temperature is too high, such as cooling tower has insufficient heat dissipation capacity, is damaged, or temperature is too high.
2. Hydraulic system generates high heat
1) Oil pump is damaged, internal parts wear and generate high heat when rotating at high speed.
2) Improper pressure adjustment, 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 high-pressure oil to generate heat when it flows through a small space.

Occurrence of abnormal noise indicates that parts are damaged or improperly adjusted. Cause should be identified according to location of noise and repaired immediately.
1. There is insufficient hydraulic oil in oil tank. If oil pump sucks air or oil filter is blocked by dirt, it will cause oil pump to be short of oil, causing bubbles in oil to be discharged and hit blades to produce noise. Solution is to check oil volume, prevent air inhalation and clean oil filter.
2. Viscosity of hydraulic oil is high and increases flow resistance, so it is necessary to replace hydraulic oil with a suitable one.
3. Due to damage to bearings or blades of oil pump or motor, concentricity deviation of coupling causes noise, and concentricity must be adjusted or parts must be replaced.
4. Directional valve fails to respond but still functions, such as valve core wear, internal leakage, burr obstruction, inflexible movement, and solenoid valve failure due to insufficient current, which will also produce noise. Solution is to clean valve core. If valve core is worn, it must be replaced with a new one. Current must be stable and sufficient.
5. Damage to hydraulic components or blockage of oil pipelines causes hydraulic oil to flow at high speed, causing noise.
6. If mechanical part fails, bearing is worn or machine lacks lubricating oil or parts are loose, cause should be found out and parts should be tightened or replaced to ensure sufficient 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. Sealing ring in injection cylinder is damaged and causes internal leakage.
3. Temperature control of heating cylinder is unstable.
4. Pressure and speed control parts are abnormal.