Injection molding machine has the ability to mold complex appearance, precise size or with metal inserts of dense texture of plastic products, is widely used in national defense, electromechanical, automotive, transportation, building materials, packaging, agriculture, education and health and people's daily lives in various fields. The injection molding process has good adaptability to the processing of various plastics, high production capacity, and easy to realize automation. In the rapid development of the plastics industry today, the injection molding machine, whether in terms of quantity or variety occupies an important position, the total production of plastic molding equipment accounted for the entire 20% -30%, thus becoming the fastest-growing plastics machinery, the production of one of the largest number of machine types. According to relevant statistics, 1996 - 1998 China's exports of injection molding machine 8383 sets (sets), imports of injection molding machine 42959 sets (sets), of which China's production of injection molding machine in 1998 reached 20,000 units, and its sales accounted for the total sales of plastic machine 42.9%. The working principle of the injection molding machine is similar to the syringe used for injection, it is with the help of the screw (or plunger) of the thrust, will have been plastified in a molten state (i.e., viscous flow state) of the plastic injected into the closed cavity of the mold, after curing and shaping to obtain the product of the process. Injection molding is a cyclic process, each cycle mainly includes: dosing - melting and plasticizing - pressure injection - mold cooling - open the mold to take parts. After removing the plastic part and then close the mold for the next cycle. Injection molding is a cyclic process, each cycle mainly includes: dosing - melting and plasticizing - pressure injection - mold filling and cooling - opening the mold to take the part. After removing the part, the mold is closed again for the next cycle.
General injection molding machine including injection device, mold closing device, hydraulic system and electrical control system and other parts.
Injection device: its main role is to make the plastic uniformly plasticized into a molten state, and with sufficient pressure and speed to inject the melt into the mold. It is mainly composed of plasticizing parts (barrel, screw or plunger, nozzle, etc.), hopper, screw drive (oil motor, etc.), injection cylinder, injection seat moving cylinder and so on.
Closing device: it is to ensure that the molding mold is reliably closed and realize the opening and closing of the mold action and take out the product parts. As the melt is injected into the mold cavity at high pressure, in order to lock the mold without causing the product to produce flying edge or affect the quality of the product, the mold should be sufficient to apply the locking force (i.e., clamping force). Closing device mainly includes fixed template, moving template, back wall plate, connecting the front and rear templates with the tie rod, mold clamping cylinder, ejector cylinder, mold adjusting device and other components.
Hydraulic system and electrical control system: it is to ensure that the injection molding machine according to the process of predetermined requirements (such as pressure, speed, temperature, time, etc.) and action procedures to carry out accurate and effective work and set the power and control system.
General screw injection molding machine molding process is: first granular or powdered plastic into the barrel, and through the rotation of the screw and barrel wall heating to make the plastic become molten, and then the machine for the mold and the injection seat forward, so that the nozzle close to the mold's gate channel, then to the injection cylinder through the pressure of the oil, so that the screw forward to a very high pressure and high speed will be the melt Injected into the closed mold at a lower temperature, after a certain period of time and pressure to maintain (also known as holding pressure), cooling, so that the solidification of the mold, you can open the mold to remove the product (the purpose of holding pressure is to prevent backflow of molten material in the mold cavity, to the cavity to supplement the material, as well as to ensure that the product has a certain density and dimensional tolerances). The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a prerequisite to achieve and ensure the quality of molded products, and in order to meet the requirements of molding, injection must ensure that there is sufficient pressure and speed. At the same time, due to the high injection pressure, the corresponding high pressure in the mold cavity (the average pressure in the mold cavity is generally between 20 ~ 45MPa), so there must be a large enough clamping force. Thus, the injection device and mold closing device are the key components of the injection molding machine.
The action program of the injection molding machine
Closing door→mold closing→nozzle advance→injection→pressure preservation→pre-molding→loosening retreat→nozzle retreat→cooling→mold opening→ejection→needle withdrawal→opening door.
Injection molding machine operation project: injection molding machine operation project includes control keyboard operation, electrical control system operation and hydraulic system operation in three aspects. Separately for the injection process action, feeding action, injection pressure, injection speed, ejector type selection, barrel temperature monitoring of the various segments, injection pressure and back pressure pressure adjustment, etc.
There are three main aspects of the evaluation of plastic products, the first is the appearance of the quality, including integrity, color, luster, etc.; the second is the accuracy of the dimensions and the relative position of the intersection; the third is the use of the corresponding physical properties, chemical properties, electrical properties and so on. The third is the physical properties corresponding to the use, chemical properties, electrical properties and so on. These quality requirements and according to the different occasions of product use, the scale of requirements are different. The defects of the products mainly lie in the design of the mold, manufacturing accuracy and wear and tear. But in fact, the plastic processing plant technicians are often faced with the process means to make up for mold defects brought about by the problem and the results of the difficult situation.
Production process adjustment is to improve the quality of products and production of the necessary way. Because the injection molding cycle itself is very short, if the process conditions are not good, scrap will be endless. When adjusting the process, it is best to change only one condition at a time, and observe a few times, if the pressure, temperature and time are all adjusted together, it is easy to cause confusion and misunderstanding, and do not know the reason for the problem. Adjustment process measures, means are various. For example: to solve the problem of product injection is not enough to have more than ten possible solutions, to choose a solution to the crux of the problem of one or two major programs, in order to truly solve the problem. In addition, should also pay attention to the solution of the discursive relationship. For example: the products appear concave, sometimes to increase the material temperature, sometimes to reduce the material temperature; sometimes to increase the amount of material, sometimes to reduce the amount of material. To recognize the feasibility of reverse measures to solve the problem.
On the maintenance of the injection molding machine
Injection molding machine is one of the commonly used equipment in the plastics processing industry, usually it has to work for a long time, so how to ensure that the injection molding machine in the continuous production of normal and stable work, no matter for the injection molding machine manufacturer or the user is a worthy of attention and efforts to solve the problem, as far as the user's point of view, in the correct selection of the injection molding machine type of premise. Regular preventive maintenance is an effective way to ensure the normal operation of the injection molding machine. The so-called preventive maintenance is a series of preventive work and inspection, so as to avoid machine failure and prolong the working life of all parts, such as the sudden emergence of faults leading to production stoppages into the foreseeable and can be planned for downtime repairs or overhaul; can be found in time to replace the damaged parts can be prevented from the chain of damages and so on is the preventive maintenance of the work of the purpose. At the same time, in order to achieve the best performance of the injection molding machine and extend the service life, improve the durability of the machine, the machine regularly check and make the corresponding repair and maintenance is completely necessary.
Preventive maintenance work is as follows:
Production efficiency: reduce downtime and maintain normal operating speed can improve productivity;
Machine accuracy; timely replacement of aged or worn parts can maintain the accuracy level of the machine;
Life of the parts: the regular replacement of wearing parts, proper adjustment and lubrication and appropriate environmental conditions (temperature, humidity, dust, etc.). conditions (temperature, humidity, dust adhesion) can extend the life of parts.
Preventive maintenance
The injection molding machine is a set of hydraulic, electrical, mechanical and other technologies in one of the equipment, with the maturity of the technology and development, the combination of the three more closely, so the injection molding machine preventive maintenance of the work of the hydraulic, electrical, mechanical tripartite to carry out a description.
Hydraulic part
Hydraulic oil quantity
Insufficient oil quantity will lead to easy rise of oil temperature, air is easy to dissolve into the oil and affect the quality of oil and the normal work of the hydraulic system, insufficient oil is usually caused by oil leakage or loss during repair, so you should pay attention to check whether there is leakage of the parts in the day-to-day, and change the worn out seals and tighten the loose joints as early as possible, and then check the oil level of the oil tank after repair. The oil volume of the tank should be checked after maintenance and replenished in time.
Hydraulic oil temperature
The ideal working temperature of the hydraulic system should be between 45 degrees -50 degrees, 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 affects the system components, such as cylinders, hydraulic valves, etc., so that the control accuracy and response sensitivity is reduced, especially for precision injection machines. Precision injection molding machine, especially for the situation. At the same time, too high a temperature will accelerate the aging of the seals to make it hardened, cracked; too low a temperature is the processing of energy consumption, so that the operating speed is reduced. Therefore, it is necessary to pay close attention to the working temperature of the hydraulic oil. Oil temperature is too high for various reasons, but more attributable to oil circuit failure or cooling system failure.
Hydraulic oil quality
One of the important properties of hydraulic oil is its chemical stability, that is, oxidative stability. Oxidation is the most important factor in determining the effective service life of hydraulic oil, oxidation of wood tar, sludge and charcoal residue and other insoluble matter will contaminate the hydraulic system and increase the wear and tear of the hydraulic components to reduce the various gaps, clogging the holes, and ultimately lead to the failure of the hydraulic system. Hydraulic oil oxidation rate depends on itself and working conditions and other factors, including temperature is one of the main factors, so use the appropriate hydraulic oil, and regularly check the degree of oxidation of the hydraulic oil (from the color of the oil itself to the judgment), more than a certain number of hours of work after the initiative to change the oil is absolutely necessary.
Injection molding machine in the use of the process, we must often check the level of pressure oil, oil pump pressure and the cleanliness of the pressure oil, when encountering wet weather, you must check the concentration of pressure oil on a daily basis, but also need to frequently check the water pipe, so as to avoid water mixed in the pressure oil, resulting in blockage of the oil filter. Check the oil tank frequently to keep it clean and prevent debris from falling into it. Replenish the pressure oil on time. For the lubrication of the moving parts, the trip switch, screws and the tightness of the oil pipe, joints part of the oil leakage, etc., should be routinely checked once a week to maintain a good condition, if loose, it will be replaced or tightened.
In addition, a pressure oil used for too long, can replace the pressure oil, so as to extend the life of the valves, pumps and seals.
Filter cleaning
The filter plays the role of clean hydraulic oil, so the filter should be cleaned every three months to keep the pump suction pipe smooth, and check whether the filter is damaged. Usually the specification of the filter shall not be larger than 200 mesh.
Cooler cleaning
The cooler should be cleaned every two years, or based on its ability to work whether or not to reduce the cleaning, the cooler internal clogging or accumulation of scale will affect the cooling efficiency, cooling water should be selected from the soft (non-mineral) is better.
Electrical parts
Wire connector check
The wire without tight connector will cause high temperature or sparks at the connector position and damage, and the poor connector will affect the signal transmission; the connector on the contactor will be easy to loosen due to the vibration of the electromagnetic action, so it is necessary to check the wire connector fastening condition regularly.
The injection molding machine circuit of the contact points must be maintained in a tight state, there shall be no loose phenomenon. In order to avoid affecting the cooling function of the electric box, we should always pay attention to the working performance of the exhaust fan, and timely clean up the dust on the dust screen and replace the dust screen.
In accordance with the specified time for all wires in the electrical box to check the joints once, to see whether the rubber casing of the wires are hardened, to prevent leakage.
Motor
General motor is air-cooled, dust accumulation will cause heat dissipation difficulties, so every year for regular cleaning, usually in the circuit equipped with motor overload cutoff, the limit current of the protective device is adjustable, should be based on the power of the motor to make the appropriate choice, and at the same time, once the overload protector start, should be sure to check whether the under-phase, poor contact or high oil temperature before pressing back to the reset switch. Only press the reset switch back.
Heating cylinder and thermocouple
Heating cylinder should be checked whether the period of fastening to ensure that effective heat transfer, in normal production of heating cylinder burn is not easy to detect, so pay attention to the temperature controller's work, from which to determine whether the heating cylinder is normal. In addition, the common damage to the heat cylinder is the wire connection, due to poor joints, contact resistance increases, so that the connection of local overheating leads to oxidation of the interface and destruction.
Often maintain the thermocouple contact point clean.
AC contactor
For electric heating part of the contactor because of the number of actions more frequently, the rate of loss is also faster, if the main contact overheating occurs melting bonding may cause the heating temperature out of control, therefore, if you find that the contactor has overheating phenomenon, loud noise or break off the fire is very big, it means that it will be damaged, should be replaced as soon as possible.
Computer control section
With the application of microcomputer control technology in the injection molding machine, the microcomputer part and its related auxiliary electronic board of the normal operation of the power supply voltage fluctuations, the working environment of the temperature, humidity, installation of seismic as well as outside the interference of high-frequency signals have put forward a higher demand for this to keep the control box ventilation and cooling with the normal operation of the fan, the use of high precision power supply regulator equipment power supply, and try to find ways of control box to keep the control box ventilation and cooling with a normal work, use the higher precision of the power supply regulator equipment power supply. The power supply voltage stabilization equipment power supply, try to reduce the control box by the influence of external vibration, etc. are the basic requirements of normal operation, should be effectively solve these problems and regular checks.
Mechanical parts
1, template parallelism
The parallelism of the template best reflects the condition of the clamping part of the template, the template is not parallel to make the product unqualified and increase the wear and tear of equipment and molds. The parallelism of the template can be initially reflected by the movement of the tail plate during mold clamping and the appearance of the product, but the exact situation needs to be detected with a percentage meter and other instruments. Adjustment of the template parallelism must be familiar with the personnel step by step, otherwise improper adjustment of the machine more damage.
2, mold thickness adjustment
should be used periodically to adjust the mold thickness system, the mold thickness from the thickest to the thinnest back and forth once to ensure smooth movement, the same mold for a long period of time with the production of the machine, you must carry out this check to avoid failure.
3, the central lubrication system
All mechanical activities require proper lubrication, the central lubrication system is currently one of the necessary injection molding machine. Central lubrication system should be careful to check the amount of oil is filled, the lubricant used must be clean and free of impurities to ensure that all lubrication position of the lubricant supply. When the oil pipe is found to be clogged or leaking, it should be replaced or repaired immediately. Most of the mechanical wear and tear is due to the lack of lubrication occurs, so we should pay enough attention to the lubrication.
4, keep the action of the smooth
Action vibration or not smooth may be due to improper speed adjustment, speed change and time does not match or mechanical, oil pressure adjustment caused. This kind of vibration will make the mechanical part of the accelerated wear and vibration has been tightened screws, so should be reduced and avoided.
5, bearing inspection
When the bearing part of the work of the strange sound, or temperature increases that is to say that the bearing has been worn out internally, it should be checked or replaced in time, and re-injected into the grease.
6, the injection system
The injection screw, check ring and barrel form the heart of the injection molding machine, determining the quality and efficiency of the processing, they must be kept in good working condition. First of all, take the necessary measures to prevent non-plastic debris mixed into the plastic raw materials, and then to pay attention to check the screw and barrel, the check ring and barrel of the correct gap, the normal gap should be able to seal the plastic back and produce the plasticization of the required shear effect, when found that the melting action is slow, the melt has a spot and the black spot, or the product shaping is unstable should be checked screw, check the ring and the barrel of the wear and tear situation.
In addition to keep the motor and the various valves clean, if the motor shell has dust and dirt, can lead to its heat dissipation function, should be checked on time, found that there is a problem in a timely manner to repair, so that it plays a role in ensuring that the machine operates normally. If the machine's seals are used for too long, they will naturally erode and lose their function, or play a bad function and generate oil leakage, they should be replaced according to the specifications. In addition, the machine stops being used for too long or to inject different plastics, you must first melt the remaining glue in the barrel finishing clean, so as to facilitate the smooth progress of the melting process.
The service life of the injection molding machine, not only to rely on the injection molding machine manufacturer's quality assurance, but also rely on the user's careful maintenance, in order to improve its reliability and durability.
Causes and solutions to some common failures
High oil temperature
An abnormal rise in oil temperature may be caused by an abnormal cooling system or high heat generated by the hydraulic components during operation.
1, the cooling system is not normal
1) the cooling system supply is insufficient, such as the valve is not fully open, water pressure is insufficient or the pump flow does not meet the needs.
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 insufficient, or damage or high temperature.
2, the hydraulic system produces high heat
1) oil pump damage, internal parts in the high-speed rotation of wear and tear to produce high heat.
2) pressure regulation is not appropriate, the hydraulic system is in a high-pressure state for a long time and overheating.
3) Hydraulic components of the internal leakage, such as directional valve damage or seal damage to the high-pressure oil flow through the small space generated heat.
Noise generation
Unusual noise generation indicates that parts are damaged or improperly adjusted, and the cause should be identified and repaired immediately according to the location of the noise.
1, insufficient hydraulic oil in the tank, oil pump air inhalation or oil filter dirt blockage will cause oil pump oil shortage, resulting in oil bubbles in the oil out of the impact of the blades and noise, the solution is to check the amount of oil, to prevent the inhalation of air and clean the oil filter.
2, high viscosity of hydraulic oil, increase flow resistance, need to replace the appropriate hydraulic oil.
3, due to the oil pump or motor bearings or vane damage, coupling concentricity deviation caused by noise, must adjust the concentricity or replacement parts.
4, the directional valve response failure but the function is still there, such as valve core wear, internal leakage, burr blockage, mobile inflexible, solenoid valve failure due to insufficient current will also produce noise. The solution is to clean the valve core, valve core wear shall be replaced with new parts, the current shall be stable and sufficient. 5、Hydraulic components are damaged or oil piping obstruction of the hydraulic oil flow at high speed noise.
6, the mechanical part of the failure, bearing wear or mechanical lack of lubricant or loose parts, should find out the reasons for the parts to be tightened or replaced, to ensure that there is enough lubricant.
Unstable or unqualified production
In a stable production cycle, the quality of the finished product is unstable, mostly due to wear and tear of mechanical parts or improper adjustment.
1. Wear and tear of screw, check ring and barrel.
2, damaged seals in the injection cylinder and internal leakage.
3, the temperature control of the heating cylinder is not stable.
4, pressure, speed control part of the malfunction.
Maintenance summary table
I. Daily maintenance
1. machine sanitation
2. oil temperature
3. machine hinge lubrication system
4. heating system
5. cooling water
6. emergency stop
7. the effect of the safety mechanism
2. Weekly maintenance
1. Checking of travel and proximity switch
2. Oil seepage
3. Grease lubrication
4. Loose screws
5. Oil quantity
3. Quarterly maintenance
1. Wire connectors
2. Electrical box hygiene
3. Oil pump, oil motor
4. Grease
5. Power supply
Four. Annual maintenance matters
1. Oil tank and pressure oil
2. Insulation degree of wires
3. Electric motor
4. Injection screw
5. Machine hinge
About the tuning of injection molding machine
Injection molding is an engineering technology, which involves the content is to transform the plastic into a useful and can maintain the original Products that can maintain the original properties. The important process conditions for injection molding are the temperature, pressure and the corresponding time of each action that affects the flow and cooling of plasticization.
A, temperature control
1, barrel temperature: injection molding process needs to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastic, while the latter temperature mainly affects the flow of plastic and cooling. Each kind of plastic has different flow temperature, the same kind of plastic, due to the source or brand name is different, its flow temperature and decomposition temperature is different, this is due to the average molecular weight and molecular weight distribution is different, plastic in different types of injection molding machine plasticization process is also different, and thus the choice of barrel temperature is not the same.
2, the nozzle temperature: the nozzle temperature is usually slightly lower than the maximum barrel temperature, which is to prevent the melt in the straight-through nozzle may occur "salivation phenomenon. Nozzle temperature can not be too low, otherwise it will cause early condensation of the melt and the nozzle blocked, or due to early condensation of the material injected into the mold cavity and affect the performance of the product
3, mold temperature: mold temperature has a great impact on the intrinsic properties of the product and the apparent quality. Mold temperature is determined by the presence or absence of plastic crystallinity, product size and structure, performance requirements, as well as other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).
Two, pressure control: injection molding process pressure including plasticizing pressure and injection pressure of two kinds, and directly affect the plasticization of plastic and product quality.
1, plasticizing pressure: (back pressure) the use of screw-type injection machine, the top of the screw melt in the screw rotation back pressure is called plasticizing pressure, also known as back pressure. The size of this pressure can be adjusted by the relief valve in the hydraulic system. In the injection, the size of the plasticizing pressure is with the screw speed are unchanged, then increase the plasticizing pressure that will increase the temperature of the melt, but will reduce the speed of plasticization. In addition, increasing the plasticizing pressure often makes the temperature of the melt uniform, the color mixing uniform and the discharge of the gas in the melt. General operation, the decision of plasticizing pressure should be in the premise of ensuring good quality products the lower the better, the specific value is with the variety of plastics used, but usually rarely more than 20 kg / cm2.
2, injection pressure: in the current production, almost all of the injection pressure of the injection machine is to the plunger or the top of the screw on the plastic applied pressure (converted from the oil pressure) shall prevail. Injection pressure plays a role in injection molding is to overcome the resistance to flow of plastic from the barrel to the cavity, to give the rate of molten material to fill the mold and compaction of molten material.