Injection molding machine is one of the equipment commonly used in the plastics processing industry. Usually it has to work for a long time. Therefore, how to ensure the normal and stable operation of the injection machine in continuous production is a worthy and important consideration for injection machine manufacturers and users. To solve the problem, from the user's point of view, on the premise of correct selection of injection models, 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 prevent machine failures and extend the working life of various parts. For example, the sudden occurrence of failures that cause production shutdowns can be turned into foreseeable and planned shutdown repairs or overhauls; it can be timely Discovery and replacement of damaged parts can prevent chain damage, etc., which are the purpose of preventive maintenance.

Preventive maintenance work

Hydraulic part

1. Hydraulic oil volume

Insufficient oil will cause the temperature of the oil to rise easily, and the air will easily dissolve into the oil, which will affect the oil quality and the normal operation of the hydraulic system. Insufficient oil is usually caused by oil leakage or loss during repairs. For this reason, check whether there is any leakage. Replace the worn-out seals and tighten loose joints as soon as possible. After maintenance, check the oil volume of the fuel tank and replenish it in time.

2. Hydraulic oil temperature

The ideal working temperature of the hydraulic system should be between 45℃-50℃. The reason is that the hydraulic system is designed according to a selected pressure oil viscosity, but the viscosity will change with the oil temperature, which will affect the work of the system. Components, such as oil cylinders, hydraulic valves, etc., reduce control accuracy and response sensitivity, especially for precision injection machines. At the same time, too high temperature will accelerate the aging of the seals and cause them to harden and crack; too low temperature will consume more processing energy and reduce the operating speed. Therefore, it is necessary to pay close attention to the working temperature of hydraulic oil. There are many 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, that is, oxidation stability. Oxidation is the most important factor that determines the effective service life of hydraulic oil. The insoluble matter such as wood tar, sludge and carbon residue generated by oxidation will contaminate the hydraulic system, increase the wear of hydraulic components, reduce various gaps, block small holes, and eventually cause The hydraulic system is malfunctioning. The oxidation rate of hydraulic oil depends on many factors such as itself and working conditions, among which temperature is one of the main factors. Therefore, it is necessary to use suitable hydraulic oil and regularly check the oxidation degree of the hydraulic oil (judged from the darker color of the oil itself) ), after a certain number of working hours (usually 2000 to 4000 effective working hours), it is absolutely necessary to actively change the oil.

4. Clean the oil filter

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

Electrical parts

1. Wire connector inspection

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

2. Electric motor

Generally, the motor is air-cooled. The accumulation of dust causes difficulty in heat dissipation. Therefore, it is cleaned regularly every year. A motor overload cutoff is usually installed in the circuit. The limit current of the protection device is adjustable and should be adjusted according to the motor power. At the same time, once the overload protector is activated, it should be determined to check whether there is phase loss, poor contact or high oil temperature before pressing the return position switch.

3. Heating cylinder and thermocouple

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

4. Electromagnetic contactor

The contactor used for the electric heating part has a faster loss rate because of its frequent action. If the main contact is overheated and melted and bonded, it may cause the heating temperature to run out of control. Therefore, if the contact is overheated, it makes a noise or is very hot when it is disconnected. Large, it means 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 to the injection molding machine, the normal operation of the microcomputer part and its related auxiliary electronic board has raised the influence of the fluctuation of the power supply voltage, the temperature and humidity of the working environment, the shock resistance of the installation and the interference of external high-frequency signals. In order to meet higher requirements, to maintain the normal operation of the fans for ventilation and heat dissipation in the control box, use high-precision power supply and stabilizer equipment to supply power, try to reduce the influence of external vibration on the control box, and solve these problems in a timely manner. an examination.

Mechanical part

1. Template parallelism

The parallelism of the template can best reflect the condition of the clamping part. The non-parallel 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 clamping and the appearance analysis of the product, but the exact situation needs to be detected with a dial indicator and other instruments. The adjustment of the parallelism of the template must be carried out by a familiar person in steps, otherwise improper adjustment will cause greater damage to the machine.

2. Mold thickness adjustment

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

3. Central lubrication system

All mechanical moving parts need to be properly lubricated, and the central lubrication system is one of the must-haves for the current injection molding machine. The amount of oil in the central lubrication system should be checked frequently to see if it is full, and the lubricating oil used must be clean and free of impurities to ensure that all lubricating positions have lubricating oil supply. If the oil pipe is blocked or leaking, it should be replaced or repaired immediately. Most mechanical wear occurs due to lack of lubrication, so adequate attention must be paid to lubrication.

4. Keep all movements smooth

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

5. Bearing inspection

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

6. Injection system

The injection screw, check ring and barrel constitute the heart of the injection molding machine, which determines the quality and efficiency of the processing and must be kept in good working condition.

First, take necessary measures to prevent non-plastic debris from mixing into the plastic material flow, and then pay attention to checking the correct gap between the screw and the barrel, and the check ring and the barrel. The normal gap should be able to seal the plastic backflow and produce plastic When it is found that the melting action is slow, the melting material has spots and black spots, or the product is unstable, check the wear of the screw, check ring and barrel. It is also necessary to focus on checking the reliability of various safety devices, including mechanical and electrical devices such as limit switches.

Causes and solutions of some common faults

Oil temperature is too high

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

1. The cooling system is abnormal

1) The supply of the cooling system is insufficient, such as the water switch is not fully opened, the water pressure is insufficient, or the flow of the water pump does not meet the requirements.

2) The pipeline is blocked, such as the filter screen, cooling tower or water pipe.

3) The cooling water temperature is too high, such as the cooling tower has insufficient heat dissipation capacity, or is damaged or the temperature is too high.

2. The hydraulic system generates high heat

1) The oil pump is damaged, and the internal parts are worn at high speed to generate high heat.

2) The pressure is not adjusted properly, and the hydraulic system has been under high pressure for a long time and overheated.

3) Internal leakage of hydraulic components, such as damage to the directional valve or damage to the sealing ring, causes heat to be generated when high-pressure oil flows through a small space.

Noise generation

Abnormal noise generation means that there are parts damaged or improperly adjusted, and the cause should be found out and repaired immediately according to the location of the noise.

1. Insufficient hydraulic oil in the oil tank, suction of air by the oil pump or obstruction of the oil filter will cause the oil pump to be short of oil, causing the air bubbles in the oil to discharge and hit the blades and produce noise. The solution is to check the oil level to prevent air intake and Clean the oil filter.

2. The hydraulic oil has high viscosity and increases the flow resistance. It is necessary to replace the appropriate hydraulic oil.

3. As the bearings or blades of the oil pump or motor are damaged, the concentricity deviation of the coupling causes noise, and the concentricity must be adjusted or parts replaced.

4. The directional valve does not respond properly but its function is still there. For example, the valve core is worn out, internal leakage, burr blockage, inflexible movement, and the solenoid valve malfunctions due to insufficient current and will also produce noise. The solution is to clean the valve core. If the valve core is worn out, new parts must be replaced, and the current must be stable and sufficient.

5. The damage of hydraulic components or the blockage of the oil pipeline causes noise when the hydraulic oil flows at high speed.

6. The mechanical part is faulty, the bearing is worn or the machine lacks lubricating oil or the parts are loose. Find out the reason and tighten or replace the parts to ensure that there is enough lubricating oil.

Product production is unstable or unqualified

In a stable production cycle, the quality of the finished product 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 internal leakage of the sealing ring in the injection cylinder is damaged.

3. The temperature control of the heating cylinder is unstable.

4. The pressure and speed control are partially abnormal.