How to maintain injection molding machine?

Therefore, how to ensure the normal and stable operation of injection machines in continuous production is a problem worthy of attention and effort for both injection machine manufacturers and users. From the user's point of view, regular preventive maintenance is an effective way to ensure the normal operation of injection machines under the premise of the correct selection of injection machines.

The so-called preventive maintenance is a series of preventive work and inspection to avoid machine failure and prolong the working life of various parts, such as the sudden occurrence of failures that lead to production stoppages to foreseeable and planned downtime repair or overhaul; the timely detection and replacement of damaged parts can prevent chain damage, etc. are the purpose of preventive maintenance work.
 

A. Preventive maintenance work

A. Hydraulic part

1. Hydraulic oil quantity

Insufficient oil will cause the oil temperature to rise easily, the air is easy to dissolve in the oil and affect the oil quality and the normal work of the hydraulic system, insufficient oil is usually caused by oil leakage or repair loss, so daily attention should be paid to check whether there is leakage parts, early replacement of worn seals, tighten the loose joints, etc., after maintenance to check the amount of oil in the tank, timely replenishment.

2. Hydraulic oil temperature

The ideal operating temperature of the hydraulic system should be between 45 ℃ -50 ℃, the reason is that the hydraulic system is based on a selected pressure oil viscosity and design, but the viscosity will change with the oil temperature, which will affect the work of the system components, such as cylinders, hydraulic valves, etc., so that the control accuracy and response sensitivity is reduced, especially in the case of precision injection machines.

At the same time, high temperature will also accelerate the aging of the seals so that they harden and crack; too low a temperature will consume a lot of processing energy and reduce the operating speed. Therefore, it is very necessary to pay close attention to the working temperature of hydraulic oil. Oil temperature is too high for a variety of reasons but mostly attributed to the failure of the oil circuit or cooling system failure.

3. Hydraulic fluid oil quality

One of the important properties of hydraulic oil is its chemical stability, i.e. oxidation stability. Oxidation is the most important factor to determine the effective service life of hydraulic oil. The insoluble materials such as wood tar, sludge, and carbon residue generated by oxidation will pollute the hydraulic system and increase the wear of hydraulic components, reduce various gaps, block small holes and eventually cause the hydraulic system to fail.

The oxidation speed of hydraulic oil depends on itself and working conditions and other factors, of which temperature is one of the main factors, so use suitable hydraulic oil, and regularly check the degree of oxidation of hydraulic oil (judging from the color of the oil itself turns dark), more than a certain number of working hours after the initiative to change the oil is absolutely necessary.

4. Oil filter cleaning

The oil filter plays the role of cleaning hydraulic oil, so the oil filter should be cleaned every three months to keep the oil Ga suction pipe open and check whether the oil filter is damaged.

5. Cooler cleaning

The cooler should be cleaned once a year or according to whether its working capacity is reduced.
 

B. Electrical part

1. Wire connector inspection

The wire with unfastened joints will cause high temperature or sparks to damage the joints, and poor joints will also affect the transmission of signals; the joints on the contactor will be easier to loosen due to the vibration of electromagnetic action, so it is necessary to check the position of the wire joints and tighten them regularly.

2. Motor

Generally, the motor is air-cooled, dust accumulation will cause heat dissipation difficulties, so every year for regular cleaning, usually in the circuit is equipped with a motor overload cut-off device, the protection device is adjustable limited current, should be based on the motor power for appropriate selection, at the same time once the overload protector start, should be sure to check whether the under-phase, poor contact or oil temperature is too high before pressing the reset switchback.

3. Heating cylinder and thermocouple

The heating cylinder should be checked periodically for tightness to ensure effective heat transfer. In normal production, it is not easy to detect the burning of the heating cylinder, so pay attention to the work of the temperature controller to determine whether the heating cylinder is normal. In addition, the common damage to the heating cylinder is the wire connection, due to poor joints, contact resistance increases so that the local overheating of the connection leads to oxidation and destruction of the interface.

4. Electromagnetic contactor

Contactor used for the electric heating part because the action is more frequent, the loss of speed is also faster, if the main contacts overheating melting bonding may cause the heating temperature out of control, so if the contact is found to have overheating phenomenon, a loud sound or fire when breaking is very large, it is said to be damaged, 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 work of the microcomputer part and its related auxiliary electronic board on the fluctuations of the power supply voltage, the temperature and humidity of the working environment, the installation of shock resistance, and external high-frequency signal interference have put forward high requirements, in order to maintain the normal operation of the fan for ventilation and heat dissipation in the control box, the use of high-precision power supply regulator, trying to reduce the control box by external vibration, these aspects should be effectively addressed and regularly checked.
 

C. Mechanical parts

1. Parallelism of the template

The parallelism of the mold plate can reflect the condition of the clamping part, and the non-parallelism of the mold plate will make the product unqualified and increase the wear and tear of the equipment and mold. The parallelism of the mold plate can be reflected by the movement of the tail plate and the appearance of the product during clamping, but the exact situation needs to be tested with a percentage meter and other instruments. The adjustment of the parallelism of the mold plate must be carried out by familiar personnel according to the steps, otherwise, the damage to the machine will be greater if the adjustment is not done properly.

2、Die thickness adjustment

Should regularly use the mold thickness adjustment system, the mold thickness from the thickest to the thinnest back and forth once to ensure smooth action, the same mold production machine for a long time, this check must be carried out to avoid failure.

3、Central lubrication system

All mechanical moving parts need to have a proper lubrication, and the central lubrication system is one of the necessities of an injection molding machine. The oil quantity of the central lubrication system should be checked frequently to see if it is full, and the lubricant used should be clean and free of impurities to ensure that all lubrication positions are supplied with lubricant. The oil pipe should be replaced or repaired immediately if it is found to be blocked or leaking. Most of the mechanical wear and tear is due to the lack of lubrication and occur, so to have enough attention to lubrication.

4、Keep the smoothness of each action

Motion vibration or smooth may be due to improper speed adjustment, speed change and time are not coordinated or mechanical, oil pressure adjustment caused. This kind of vibration will make the mechanical part accelerate wear and loosen the tightened screws, so should reduce and avoid vibration.

5、Bearing inspection

Bearings in the work of a strange sound, or temperature rise that the internal bearing has been worn, should be timely inspection or replacement, and re-inject grease.

6、Injection system

The injection screw, stop ring and barrel form the heart of the injection molding machine and determine the quality and efficiency of processing. First of all, take necessary measures to prevent non-plastic debris from mixing into the plastic material flow, and then pay attention to check the correct clearance between the screw and the barrel, and between the stop ring and the barrel, the normal clearance should be able to seal the plastic reflux and produce the shearing effect required for plasticization, when the melt is found to be slow, the melt has spots and black spots, or the product forming is not stable, the screw, stop ring and barrel should be checked for wear.

Second, the cause of some common failures and solutions

A. Oil temperature is too high

The oil temperature may rise abnormally because the cooling system is not normal or the oil pressure components in the work of high heat caused by.

1、Cooling system is not normal

1）Insufficient supply of the cooling system, such as water valve not fully opened, insufficient water pressure or pump flow does not meet the needs, etc. 2）Pipe blockage, such as filter, cooling tower or water pipe blockage.

(3) cooling water temperature is too high, such as cooling tower cooling capacity is not enough, or damaged or the temperature is too high.

2、Hydraulic system generates high heat

(1) oil pump damage, internal parts wear at high-speed rotation generated high heat.

(2) improper pressure adjustment, the hydraulic system in a long-term high-pressure state, and overheating.

(3) internal leakage of hydraulic components, such as damaged directional valves or damaged seals, so that the high-pressure oil flow through the small space generated heat.

B. Noise generation

Abnormal noise generation, indicating that there are parts damaged or improperly adjusted, should be issued according to the location of the noise to identify the cause of immediate maintenance.

1, the hydraulic oil in the tank is not enough, the oil pump inhalation air or filter dirt blockage will cause the oil pump lack of oil, resulting in the discharge of bubbles in the oil hitting the vane and generating noise, the solution is to check the amount of oil, to prevent the inhalation of air and clean the oil filter.

2, the high viscosity of hydraulic oil, increases the flow resistance, needs to replace the appropriate hydraulic oil.

3, due to the oil pump or motor bearing or vane damage, the concentricity of the coupling deviation caused by noise, must adjust the concentricity or replace parts.

4, the directional valve response failure but still functional, such as valve core wear, internal leakage, burr blockage, inflexible movement, solenoid valve failure due to insufficient current will also generate noise. The solution is to clean the spool, spool wear must be replaced with new parts, the current must be stable and sufficient.

5, hydraulic components damage or oil pipeline blockage so that the hydraulic oil flow at high speed when the noise.

6, mechanical part failure, bearing wear, or mechanical lack of lubricant or lose parts, should find the cause of the parts to tighten or replace, to ensure that there is sufficient lubricant.

C. Product production is unstable or unqualified

In a stable production cycle, the quality of the finished product is unstable, which may be due to the wear of mechanical parts or improper adjustment.

1、The wear of screw, stop ring, and barrel.

2、Inward leakage due to damage of the seal ring inside the injection cylinder.

3、The temperature control of the heating cylinder is not stable.

4、The pressure and speed control part is out of order.