How much do you know about preventive maintenance of injection molding machines?

The injection molding machine is one of the widely used equipment in the plastic processing industry. It usually works 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 effort for both the manufacturer and the user of the injection molding machine. From the perspective of the user, on the premise of correct selection of the injection molding machine, Regular preventive maintenance is an effective way to ensure the normal operation of the injection machine.
The so-called preventive maintenance is a series of preventive work and inspections to avoid machine failure and extend the service life of all parts, for example, to turn the sudden failure that leads to shutdown into a foreseeable and planned shutdown repair or overhaul; The purpose of preventive maintenance is to find and replace damaged parts in time and prevent chain damage.
1、 Preventive maintenance work
（1） Hydraulic part
1. Hydraulic oil quantity
Insufficient oil quantity will cause the oil temperature to rise easily, and the air is easy to dissolve into the oil, which will affect the normal operation of the oil quality and hydraulic system. Insufficient oil quantity 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 seals as soon as possible, tighten the loose joints, etc., check the oil quantity of the oil tank after repair, and make timely replenishment.
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 based on a selected pressure oil viscosity, but the viscosity will change with the oil temperature, which will affect the working elements in the system, such as oil cylinders, hydraulic valves, etc., and reduce the control accuracy and response sensitivity, especially for precision injection machines. At the same time, too high temperature will also accelerate the aging of the seal and make it harden and crack; If the temperature is too low, the processing energy consumption will be large and the operating speed will be reduced. Therefore, it is necessary to pay close attention to the 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.
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 that determines the effective service life of hydraulic oil. The insoluble substances such as wood tar, oil sludge and carbon residue generated by oxidation will pollute the hydraulic system, increase the wear of hydraulic components, reduce various clearances, block small holes, and finally cause the hydraulic system to fail.
The oxidation rate of hydraulic oil depends on itself and working conditions, among which temperature is one of the main factors. Therefore, it is 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 change the oil after a certain number of working hours.
4. Oil filter cleaning
The oil filter plays the role of cleaning the hydraulic oil. Therefore, the oil filter should be cleaned every three months to keep the oil suction pipe of the oil reservoir unblocked, and check whether the oil filter screen is damaged.
5. Cooler cleaning
The cooler should be cleaned once a year, or according to whether its working capacity is reduced. The internal blockage or scaling of the cooler will affect the cooling efficiency. The cooling water should be soft (mineral free).
（2） Electrical part
1. Wire connector inspection
Wires with loose connectors will cause high temperature or spark damage at the connector location, and poor connectors will also affect signal transmission; The connector on the contactor is easy to loosen due to the vibration of electromagnetic action, so it is necessary to regularly check the position and tightening of the wire connector.
2. Motor
Generally, motors are air-cooled, and dust accumulation will cause heat dissipation difficulties. Therefore, regular cleaning shall be carried out every year. Usually, motor overload cut-out is installed in the circuit. The limited current of the protective device is adjustable, and appropriate selection shall be made according to the motor power. At the same time, once the overload protector is started, it shall be determined to check whether the phase is out, the contact is poor, or the oil temperature is too high before pressing the reset switch.
3. Heating cylinder and thermocouple
Check whether the heating cylinder is fastened regularly to ensure effective heat transfer. It is not easy to detect the burning of the heating cylinder in normal production. Therefore, pay attention to the working condition of the temperature controller to judge whether the heating cylinder is normal. In addition, the common damage of the heating cylinder is the wire connection. Due to the poor connection and the increased contact resistance, the local overheating of the connection leads to the oxidation and damage of the interface.
4. Electromagnetic contactor
The contactor used for the electric heating part acts frequently, and its loss rate is also fast. If the main contact is overheated and fused, it may cause the heating temperature to be out of control. Therefore, if the contact is overheated, makes a noise or has a large fire 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 associated auxiliary electronic board puts forward higher requirements for the fluctuation of power supply voltage, the temperature and humidity of the working environment, the seismic resistance of the installation and the interference of the external high-frequency signals. To this end, the fan for ventilation and heat dissipation in the control box should be kept in normal operation, and the power supply should be powered by the power stabilizer with higher accuracy, Try to reduce the influence of external vibration on the control box, solve these problems and check regularly.
（3） Mechanical part
1. Parallelism of formwork
The parallelism of the template can best reflect the condition of the locking part. The non-parallelism of the template will make the product unqualified and increase the wear of the equipment and mold. The parallelism of the template can be initially reflected by the movement of the tail plate during mold locking and the appearance analysis of the product, but the exact situation needs to be detected by the dial indicator and other instruments. The adjustment of formwork parallelism must be carried out by familiar personnel according to the steps, otherwise the improper adjustment will cause greater damage to the machine.
2. Die thickness adjustment
The die thickness adjustment system shall be used regularly to adjust the die thickness from the thickest to the thinnest to ensure smooth operation. For machines produced with the same die for a long time, this inspection must be carried out to avoid failures.
3. Central lubrication system
All mechanical moving parts need to be properly lubricated, and the central lubrication system is one of the necessary parts of the injection molding machine at present. The oil quantity of the central lubricating system should be checked regularly to see if it is full. The lubricating oil used must be clean and free of impurities to ensure that all lubricating positions have lubricating oil supply. Replace or repair the oil pipe immediately in case of blockage or leakage. Most mechanical wear occurs due to lack of lubrication, so enough attention should be paid to lubrication.
4. Keep all movements smooth
Vibration or unsmooth movement may be caused by improper speed adjustment, speed change and time incongruity, or mechanical and oil pressure adjustment. Such vibration will accelerate the wear of mechanical parts and loosen the fastened screws, so vibration should be reduced and avoided.
5. Bearing inspection
When the bearing is working, the abnormal sound or the temperature rise indicates that the bearing has been worn inside. It should be checked or replaced in time, and the lubricating grease should be refilled.
6. Injection system
The injection screw, check ring and barrel form the heart of the injection molding machine, which determines the quality and efficiency of processing, and must be kept in good working condition.
First of all, take necessary measures to prevent non-plastic debris from mixing into the plastic material flow, and then pay attention to checking the correct clearance between the screw and the barrel, and between the check ring and the barrel. The normal clearance should be able to seal the plastic backflow and produce the shear effect required for plasticization. When it is found that the melt action is slow, the melt has spots and black spots, or the product formation is unstable, check the wear of the screw, the check ring and the barrel.
2、 Causes and solutions of some common faults
（1） The oil temperature is too high
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 is abnormal
1) The cooling system supply is insufficient, such as the water switch is not fully opened, the water pressure is insufficient, or the water pump flow does not meet the requirements.
2) The pipe is blocked, such as filter screen, cooling tower or water pipe.
3) The cooling water temperature is too high, for example, the cooling tower has insufficient heat dissipation capacity, or is damaged or the temperature is too high.
2. High heat generated by hydraulic system
1) The oil pump is damaged, and the internal parts wear and produce high heat when rotating at high speed.
2) The pressure is not adjusted properly, and the hydraulic system is under high pressure for a long time and overheats.
3) The internal leakage of the oil pressure element, such as the damage of the direction valve or the damage of the sealing ring, makes the high pressure oil generate heat when it flows through the small space.
（2） Noise generation
Abnormal noise indicates that parts are damaged or improperly adjusted. Find out the cause according to the location of the noise and repair it immediately
1. Insufficient hydraulic oil in the oil tank, air suction by the oil pump or dirt blockage in the oil filter will cause the oil pump to be short of oil, which will cause the bubbles in the oil to discharge and impact the blades and generate noise. The solution is to check the oil volume, prevent air suction and clean the oil filter.
2. The viscosity of hydraulic oil is high and the flow resistance is increased. It is necessary to replace the appropriate hydraulic oil.
3. Because the bearing or blade of the oil pump or motor is damaged and the concentricity deviation of the coupling causes noise, the concentricity must be adjusted or the parts replaced.
4. The directional valve responds to failure but its function is still active, such as valve core wear, internal leakage, burr blockage, inflexible movement, and solenoid valve failure due to insufficient current will also generate noise. The solution is to clean the valve core, replace the worn valve core with a new one, and ensure that the current is stable and sufficient.
5. The hydraulic components are damaged or the oil pipeline is blocked, which causes the noise when the hydraulic oil flows at high speed.
6. In case of mechanical part failure, bearing wear, lack of lubricating oil or loose parts, find out the reason and fasten or replace the parts to ensure sufficient lubricating oil.
（3） The product production is unstable or unqualified
In a stable production cycle, the quality of finished products is unstable, which may be caused by the wear of mechanical parts or improper adjustment.
1. Wear of screw, check ring and barrel.
2. The inner seal ring of the injection cylinder is damaged, resulting in internal leakage.
3. The temperature control of the heating cylinder is unstable.
4. Pressure and speed control parts are abnormal.