Injection molding machine is one of equipment commonly used in plastic processing industry. Usually it needs to work for a long time. Therefore, how to ensure normal and stable operation of injection machine in continuous production is a problem worthy of attention and efforts to solve for manufacturer or user of injection machine. From perspective of users, regular preventive maintenance is an effective way to ensure normal operation of injection machine under premise of correct selection of injection mold.
So-called preventive maintenance is a series of preventive work and inspections to prevent machine failures and prolong working life of various parts. For example, purpose of preventive maintenance is to turn sudden occurrence of failure that caused production stoppage into foreseeable and planned shutdown repair or overhaul; to detect and replace damaged parts in time to prevent chain damage.

 

Insufficient oil 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 is usually caused by oil leakage or loss during repairs. For this reason, you should pay attention to checking for leaks, replace worn seals as soon as possible, tighten loose joints, etc., check oil volume of fuel tank after maintenance, and replenish it in time.

Ideal working temperature of hydraulic system should be between 45℃-50℃. Reason is that hydraulic system is designed according to 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., reduce control accuracy and response sensitivity, especially for precision injection machines. At the same time, if temperature is too high, it will 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 working temperature of hydraulic oil. There are many reasons for high oil temperature, but most of them are due to failure of oil circuit or failure of cooling system.

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 matter such as wood tar, sludge and carbon residue generated by oxidation will contaminate 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, among which temperature is one of main factors. Therefore, it is necessary to use suitable 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 a certain number of working hours.

Oil filter plays a role in cleaning hydraulic oil, so oil filter should be cleaned every three months to keep oil suction pipe unblocked, 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. Blockage or fouling inside cooler will affect cooling efficiency. Cooling water should be soft (mineral-free).

Unfastened wires in connector will cause high temperature or sparks at connector location and damage. A poor connector will also affect signal transmission; connector on contactor will be easier to loose due to vibration of electromagnetic action, so it is necessary to check position of line connector and tighten it regularly.

Generally, motor is air-cooled. Accumulation of dust causes difficulty in heat dissipation. Therefore, it is cleaned regularly every year. A motor overload cutoff is usually installed in circuit. Limit current of protection device is adjustable. It 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, a bad contact or oil temperature is too high before pressing return position switch.

Heating tube should be checked regularly to ensure that it is fastened to ensure effective heat transfer. Burning of heating tube is not easy to detect in normal production. For this reason, pay attention to working condition of temperature controller and judge whether heating tube is normal. In addition, common damage of heating cylinder is wire connection. Due to poor joint, contact resistance increases, local overheating of connection causes interface to be oxidized and damaged.

Contactor used for electric heating part has a faster loss rate because of its frequent action. If main contact is overheated, melted and bonded, it may cause heating temperature to run out of control. Therefore, if it is found that there is overheating in contact, noise or fire when breaking, it means that it is about to be damaged and should be replaced as soon as possible.

With application of microcomputer control technology to injection molding machine, normal operation of microcomputer part and its related auxiliary electronic board puts 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. For this reason, keep fan for ventilation and heat dissipation in control box working normally, use high-precision power supply and stabilized equipment to supply power, try to reduce influence of external vibration on control box, solve these problems and check regularly.

 

Parallelism of mold plate can best reflect condition of clamping part. Non-parallel mold plate will make product unqualified, increase wear of equipment and mold. 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 a dial indicator. Adjustment of parallelism of mold plate must be carried out by a familiar person in steps, otherwise improper adjustment will cause greater damage to machine.

Mold thickness adjustment system should be used regularly to adjust mold thickness from the thickest to the thinnest to ensure smooth movement. For machines that use same mold for a long time, this inspection must be performed to avoid malfunctions.

All mechanical moving parts need proper lubrication, and central lubrication system is one of must-haves for current injection molding machine. 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 blocked or leaking, it should be replaced or repaired immediately. Most mechanical wear occurs due to lack of lubrication, so sufficient attention must be paid to lubrication.

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

When bearing is working, there are abnormal noises, or temperature rises, it means that inside of bearing has been worn out, it should be checked or replaced in time, and grease should be refilled.

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

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

1) Supply of cooling system is insufficient, such as water switch is not fully opened, water pressure is insufficient, or flow of water pump does not meet requirements, etc.
2) Pipeline is blocked, such as filter screen, cooling tower or water pipe.
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 are worn at high speed to generate high heat.
2) Pressure is not adjusted properly, hydraulic system has been overheated under high pressure for a long time.
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 generation means that there is damage to parts or improper adjustment, cause should be found out and repaired immediately according to location of noise.
1. Insufficient hydraulic oil in oil tank, suction of air by oil pump or clogging of oil filter will cause oil pump to be short of oil, causing air bubbles in oil to discharge, hit blades and generate noise. Solution is to check oil volume, prevent air intake and clean oil filter. .
2. Hydraulic oil has high viscosity and increases flow resistance, so it needs to be replaced with a suitable hydraulic oil.
3. As bearings or blades of oil pump or motor are damaged, concentricity deviation of coupling causes noise, concentricity must be adjusted or parts must be replaced.
4. Directional valve does not respond to failure but its function is still there. For example, valve core is worn, internal leakage, burr blocked, movement is not flexible, solenoid valve fails due to insufficient current and will cause noise. Solution is to clean spool. If spool is worn out, new parts must be replaced, current must be stable and sufficient.
5. Damage of hydraulic components or blockage of oil pipeline causes noise when hydraulic oil flows at a high speed.
6. Mechanical part is faulty, bearing is worn or machine lacks lubricating oil or parts are loose. Find out reason and tighten or replace parts to ensure that there is enough lubricating oil.

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