1 Introduction to the production of plastic injection molding machine
Injection molding machine (referred to as injection machine or injection molding machine) is the main molding equipment for making thermoplastics or thermosets into plastic products of various shapes using plastic molding molds.
Injection molding is achieved through injection molding machines and molds. Although there are many types of injection molding machines, no matter what kind of injection molding machine, its basic functions are two: (1) to heat the plastic to make it melt, (2) to apply high pressure to the molten plastic so that it can be injected and fill the mold cavity.
2. Structure and function of injection molding machine
In the injection molding process, the molten thermoplastic is injected from a heated barrel into a closed mold by pressure, and after a period of cooling, the mold is separated and the finished product is taken out. The re-closing of the mold is combined with the injection of plastic to form an orderly operation process, which is repeated over and over again. The injection molding machine is usually composed of an injection system, a mold clamping system, a hydraulic conveying system, an electrical control system, a lubrication system, a heating and cooling system, and a safety monitoring system.
(1) Injection molding system
The role of the injection system: the injection system is one of the most important components of the injection molding machine, and there are generally three main forms: plunger type, screw type, and screw preplastic plunger injection type. At present, the most widely used is the screw type. Its function is that in a cycle of the plastic injection machine, a certain amount of plastic can be heated and plasticized within a specified time, and the molten plastic is injected into the mold cavity through a screw under a certain pressure and speed. At the end of the injection, the melt injected into the mold cavity is kept in shape.
Composition of the injection system: The injection system consists of a plasticizing device and a power transmission device.
The plasticizing device of the screw injection molding machine is mainly composed of a feeding device, a barrel, a screw and a nozzle. The power transmission device consists of an injection cylinder, an injection seat moving cylinder, and a screw drive (melt motor).
(2) Mold clamping system
The function of the clamping system: The function of the clamping system is to ensure that the mold is closed, opened and ejected products. At the same time, after the mold is closed, the mold is given enough clamping force to resist the cavity pressure generated by the molten plastic entering the mold cavity, so as to prevent the mold from opening and causing the undesirable status quo of the product.
Composition of mold clamping system: The mold clamping system is mainly composed of mold clamping device, mold adjusting mechanism, ejection mechanism, front and rear fixed template, moving template, mold clamping cylinder and safety protection mechanism.
(3) Hydraulic system
The function of the hydraulic transmission system is to realize the injection molding machine to provide power according to the various actions required by the process, and to meet the requirements of pressure, speed, temperature and other requirements of each part of the injection molding machine. It is mainly composed of various hydraulic components and hydraulic auxiliary components, among which the oil pump and motor are the power source of the injection molding machine. Various valves control oil pressure and flow to meet the requirements of the injection molding process.
(4) Electrical control system
The electrical control system and the hydraulic system are reasonably coordinated, which can realize the process requirements (pressure, temperature, speed, time) and various program actions of the injection machine. It is mainly composed of electrical appliances, electronic components, meters, heaters, sensors, etc. Generally, there are four control modes, manual, semi-automatic, fully automatic, and adjustment.
(5) Heating/cooling system
The heating system is used to heat the barrel and the injection nozzle, and the barrel of the injection molding machine generally uses an electric heating ring as a heating device, which is installed on the outside of the barrel and detected by thermocouple segments. The heat conducts heat through the cylinder wall to provide a heat source for the plasticization of the material, and the cooling system is mainly used to cool the oil temperature, and the oil temperature must be controlled because the oil temperature is too high and will cause a variety of faults. Another position that needs to be cooled is near the discharge port of the barrel to prevent the raw materials from melting at the discharge opening, resulting in the failure of the raw materials to be discharged normally.
(6) Lubrication system
The lubrication system is a circuit that provides lubrication conditions for the parts with relative movement such as the moving platen, the mold adjusting device, and the connecting rod hinge of the injection molding machine, so as to reduce energy consumption and improve the life of the parts.
(7) Security protection and monitoring system
The safety device of the injection molding machine is mainly used to protect the safety of people and machines. It is mainly composed of safety doors, hydraulic valves, limit switches, photoelectric detection components, etc., to achieve electrical-mechanical-hydraulic interlocking protection.
The monitoring system mainly monitors the oil temperature, material temperature, system overload, and process and equipment failures of the injection molding machine, and indicates or alarms when abnormal conditions are found.
3. The working process of the injection molding machine
The plastic injection molding machine is to use different states of plastics, with the help of injection molding machines and molds, to mold the required plastic products. Although the injection molding machines used are different, the process content and basic process to be completed are still the same, and the processing process of the horizontal screw injection molding machine is explained below.
*Clamping and locking
On the one hand, it is to ensure that the mold is smoothly clamped, reduce the impact, and prolong the service life of the mold; on the other hand, when the moving mold is in contact with the fixed mold, it is transformed into a high-pressure clamping stage, and the role of this stage is to ensure that the mold has enough clamping force, so as to avoid flashing and other phenomena during injection and pressure holding.
*The injection base is moved forward
When the clamping mechanism is closed and locked, the injection seat moves the cylinder as a whole to work, so that the injection device moves forward, ensures that the nozzle fits the mold sprue, and prepares for the injection stage. After completing the above working process, the injection cylinder of the injection device pushes the screw of the injection molding machine forward, so that the molten material in the front of the barrel is injected into the mold cavity at a certain pressure and speed. At this time, the pressure of the screw head acting on the melt is called the injection pressure. After the melt is injected into the mold cavity, the volume of the material in the mold cavity shrinks due to the cold and heat conduction of the mold. In order to ensure the compactness, dimensional accuracy, strength and stiffness of plastic products, the injection system must apply a certain pressure to the mold for feeding, until the plastic of the gating system (the key is the gate) is frozen, and the pressure of the screw acting on the melt is called the holding pressure.
(1) Product cooling and pre-plasticization (melting)
With the further cooling of the mold, the melt in the mold pouring system gradually tends to freeze, especially when the gate is frozen, the holding pressure has lost the role of feeding, at this time, the holding pressure can be removed, so that the product is fully cooled and shaped in the mold. At the same time, the screw transmission device drives the screw to rotate, and the plastic in the hopper is conveyed forward through the screw, and under the external heating of the barrel heating system and the shearing and mixing of the screw, the plastic is gradually melted and plasticized in turn, and is transported to the end of the barrel by the screw, and a certain pressure is generated. This pressure is established according to the properties of the plastic and products being processed, adjusting the back pressure valve of the hydraulic system of the injection molding machine and overcoming the movement resistance of the screw retreat, which is collectively referred to as the pre-plastic back pressure (melt back pressure). The aim is to ensure the quality of plastic plasticization. It is a key process in injection molding. Because the screw keeps rotating, the melt is also continuously conveyed to the end of the barrel, and when the melt at the end of the screw has met the next injection amount, the pre-molding time is generally required not to exceed the cooling time of the product due to the cooling of the product and the pre-molding at the same time, so as not to affect the molding cycle.
*The injection device is set back
Whether the injection unit advances or retreats depends on the process of the plastic being processed. Sometimes in the pre-plastic (melting), some are returned before melting, and the temperature of the material in the nozzle of the injection device is too low to affect the quality of the next injection and the product. Sometimes it is easier to clean the material, and often the injection device is returned.
* Mold opening and ejection products
After the product in the mold is cooled and set, the mold clamping mechanism opens the mold. Under the joint action of the ejection system of the injection molding machine and the ejection mechanism of the mold, the product will be automatically jacked down to prepare for the next molding process.
Cycle Process:
Mould clamping - (injection table forward) - glue injection - pressure holding - melting (cooling at the same time) - (injection table retreat) - mold opening - ejection - ejection - clamping
4. Peripheral auxiliary equipment
Peripheral auxiliary equipment refers to the general term of the mechanical devices used to directly install the injection molding machine or set up in front and rear of the injection molding machine and other related equipment to automate, labor-saving and process quality requirements of various related operations of the injection molding machine. Nowadays, the peripheral machines generally used can be divided into the following categories according to their functions:
(1) Handling and supply of molding materials;
(2) Removal and post-processing of molded products;
(3) Temperature adjustment of the mold;
Hot air dryer
The hot air dryer is to dry the molding material before it is supplied to the injection molding machine to remove the moisture in the raw material. The working principle of the hot air dryer is to transport the dry hot air to the raw materials through the fan and take away the moisture in the raw materials.
mill
The pulverizer crushes the nozzle or defective products that appear in the injection molding process and crushes them into remoldable pellets.
Color mixer
The color mixer mixes different raw materials or adds various toners, masterbatches and additives to the raw materials to improve the quality of the product, reduce the cost and reduce the manpower.
Automatic Filler
The suction machine is to cooperate with various reserve devices to input raw materials into the cylinder to ensure the cleanliness of raw materials, reduce manpower, and ensure the safety of high-altitude feeding.
Chiller
The chiller is used to reduce the water temperature and control the mold temperature (3-50 °C) to ensure the molding needs of the product.
Thermostat
The thermostat is used to stabilize the water temperature or oil temperature, control the temperature of the mold (30-300 °C), and ensure the molding needs of the product
manipulator
The manipulator takes out the molded products from the mold cavity, saves manpower, improves production efficiency, and improves product molding quality.
Conveyor belts
The conveyor belt is to transport the products to the place where the products are concentrated, saving manpower, thereby improving automated production and improving production efficiency.
5. Correct operating procedures for injection molding machines
Preparation before operation
(1) Prepare appropriate tools;
(2) Check the means of production and correct the parameters such as temperature and pressure;
(3) Turn on the dryer to dry and preheat the plastic.
Check the safety device
(1) Whether the low-pressure mold protection action is normal;
(2) Check whether the safety door protection device is normal;
(3) Check other safety protection devices.
Boot program
(1) Check whether the waterway is fully opened;
(2) Check whether each power supply is normal.
(3) Turn on the power of the motor, open the mold, clean the mold and lubricate the mold.
(4) Check the safety device.
(5) Open the hopper when the temperature reaches the set value. Remove overheated plastic from the barrel;
(6) Clamping, injection table forward, manual, semi-automatic or fully automatic production.
Shutdown procedure
1. Close the switch and continue the operation until the product is incomplete, that is, the plastic in the barrel is used up.
2. If working in fully automatic or semi-automatic. You need to switch to manual when the work in progress is incomplete.
3. Clean the mold surface, spray the protective agent, and the mold can not be closed with high pressure, and the injection table will be withdrawn.
4. Turn off the power supply and main power supply of each part of the machine, and clean the body and position.
Semi-automatic operating procedures
Before the semi-automatic operation, manual operation can be used several times, and when the quality of the product meets the requirements, it can be converted to semi-automatic production.
Fully automatic operating procedures
Before fully automatic production, manual and semi-automatic production must be carried out. First of all, it is necessary to check whether the product meets the conditions of automatic production, and if it does, it can be used after the semi-automatic production of several molds is normal.
Mold-loading procedure
(1) Turn on the power supply, water transportation and temperature control power supply of the injection molding machine;
(2) Select raw materials and put them into the hopper;
(3) Check whether the mold can be installed in the injection molding machine for adjustment;
(4) Check whether the thimble of the mold is consistent with the top stick of the injection molding machine;
(5) Check whether the tools required for the mold are complete;
(6) The mold is equipped with the width and thickness of the hanging mold, and the motor is started for mold adjustment;
(7) Measure the width and thickness of the mold, and start the motor for adjustment;
(8) Put the mold carefully into the injection molding machine and cancel the high pressure for operation.
(9) Fix the mold, check the position of the safety rod, and connect the mold to transport water;
(10) Adjust the appropriate clamping force;
(11) After the temperature reaches the temperature, start the manual operation. The mould is finished.
Proper use of the crane
(1) Pay attention to the maximum weight of the crane, and clearly determine the function of each button of the crane before it can be used.
(2) The crane should not be subjected to lifting weight load for a long time to avoid danger;
(3) When loading and unloading the mold, the crane may be suspended, but remember to turn off the power to ensure safety.
Mold adjustment
(1) Select the adjustment mode, cancel the high-voltage position point, straighten the hinge of the machine, and adjust the mold thickness device to the mold surface to fit;
(2) Adjust the clamping stroke, the position of the thimble, and the position of the mechanical protection rod;
(3) Enter the required pressure parameters, and adjust the appropriate clamping force before or after mold adjustment;
(4) Accurately adjust the mold protection point and mold protection parameters. The mold adjustment is complete.
Die down program
(1) First remove the water pipe, let go of the water, clean the mold cavity, spray the protective agent in the mold, and close the mold.
(2) Cut off the power supply of the motor, hang the mold with a crane, and remove the code mold clamp.
(3) Turn on the power of the motor and hang the mold down at a slow speed.
(4) Cut off the power supply, carefully hang the mold down, and store the mold in the appropriate position.
(5) Turn off the entire power supply of the injection molding machine, and clean the machine position and body.
6. Correct adjustment procedures for injection molding machines
When adjusting the injection molding part, it is necessary to follow the correct procedure in order to achieve the desired effect and efficiency.
The basic procedures for tuning are as follows:
(1) Before starting to adjust, the hopper should be cleaned, filled with raw materials, and the variety of raw materials and whether the raw materials need to be dried;
(2) Adjust the appropriate barrel temperature from low to high.
(3) Adjust the appropriate injection pressure and injection speed according to the product and raw materials.
(4) Estimate the amount of material and reserve more. (After the adjustment is completed, adjust the amount of material to the appropriate level, and reserve some pad positions appropriately according to the different raw materials of the product)
(5) Enter the preliminary time, and the product molding process should be modified to ensure that the product quality is qualified.
(6) Enter the appropriate mold cold water or hot mold temperature. It is mainly according to the needs of raw material molding. After confirming that the above items have been pre-adjusted, injection molding can be carried out. It can be further adjusted in the semi-automatic production process, and can be transferred to fully automatic production after the product is qualified.
How to set the injection time
There are two basic settings for the injection time. The first is to identify the quality of the product from the appearance and know its injection time. The second is to know the injection time from the weight of the product. When the injection time begins, the runner and cavity are continuously injected with molten compound. When the product is completely full and the weight is the heaviest, when the weight of the product does not increase when the injection time is added, this time is the best injection time
7. Plastic injection process
The injection temperature of commonly used plastics
Type of plastic: Mold temperature: C, barrel temperature: °C
The starting segment, the middle segment, the anterior segment to the nozzle
PS 10-75 150-160 200-260 200-280
HIPS 10-75 150-160 190-260 200-280
ABS 10-80 150-160 190-260 220-270
LDPE 20-60 130-200 220-300 230-310
HDPE 20-60 130-200 220-300 230-310
PP 10-80 140-180 220-290 220-325
PC 70-115 230-270 280-340 300-350
PMMA 30-70 140-170 190-220 190-240
PA6 50-80 200-210 210-230 210-230
PA66 50-80 190-250 250-280 250-280
POM 60-90 160-180 175-210 190-210
PPO 40-80 250-290 300-320 300-330
PU 40-80 170-200 180-210 190-240
CP 30-80 160-180 190-220 180-210
Commonly used plastic injection molding conditions
Plastic pressure injection
Injection pressure
Kg/cm2 Holding pressure Back pressure
Kg/cm2 injection speed
PS does not require high pressure 30-60% 100-200 depending on the shape of the product
ABS 1000-1500 30-60% 100-250 Slow first and then fast
PE does not require high pressure 30-60% 150-250 depending on the shape of the product
PP 1200-1800 50-70% 120-200 high-speed injection
PVC 1000-1600 can't be too high and less than 50 can't be too fast
PC 1300-1800 40-60% 60-150 Depends on the shape of the product
PMMA High Pressure Injection Longer 150-400 depending on the shape of the product
The PA should not be too high and the 50-150 injection should be rapid
POM 1200-1500 depends on the artifact situation 100-200 can't be too slow
8. Factors affecting product quality
The factors affecting product quality are mainly divided into: 1. Injection molding machine mechanical factors, 2. Mold factors, 3. Raw material factors, 4. Human factors, 5. Environmental factors.
(1) Injection molding mechanical factors
Time, temperature, pressure
The time of the screw advance heater temperature and the pressure of the injection rod
The cooling time of the rubber Nozzle temperature The injection glue into the mold cavity is insufficient
Mold opening time, raw material drying temperature, pressure holding
Injection compound speed The heat generated by the rotation of the screw
(2) Mold factor
Time control, pressure control, temperature control
Injection time Design of main sprue and sub-sprue Design of the streamline length of the melt in the mold cavity
Cooling time The design of the length of the melt in the mold cavity
The design of the streamline length of the melt in the mold cavity Whether the design of the cooling pipe in the mold is uniform and reasonable
Venting of the mold
(3) Raw material factors
Flow Characteristics Thermal Properties Colloidal particles
Melt viscosity during injection molding, thermal conductivity, particle size and shape
Change in viscosity under different flow particles (i.e. shear force is affected by viscosity) The time it takes for the compound to cool down to the start of crystallization Large lubricity of the compound
Resin formulation
(4) Human factor: The human factor refers to the operator's own professional skills. The human factor is the most critical factor in determining the quality of the product.
(5) Environmental factors: the temperature or humidity of the injection molding operation environment is too high or the injection molding machine is carrying out injection molding of other pigments nearby, and this pigment floats into the mold or raw materials in the air, causing shortcomings. High-quality products have very strict requirements for environmental factors.
9. Procedures for improving the shortcomings of injection molded parts
Analysis of the causes of plastic part problems
Based on the operator's experience, an approximate molding cycle is determined. Check the results of the injection molded product, and if there is a problem, start with the injection molding machine, and adjust the variable one by one according to the time, temperature, and pressure. If it still doesn't work, it may be a problem with the mold design or the raw material itself, but these two types of cases are rare, especially in the mold.
There are five project principles that must be adhered to to to solve problems
(1) Make a plan, (2) Only one variable can be changed at a time, (3) One variable can be changed at a time, (4) Clearly record the operation of each time, (5) Record the appropriate operation or store it for the next operation.
10. Analysis and treatment methods of common plastic parts
Causes of molding defects and how to improve them
Molding Raw Materials Injection Molding Machine, Injection Conditions Product Mold Design
01 Insufficient filling Example 1: The product is not completely filled
The end part of the work-in-progress is incomplete
Insufficient fluidity of raw materials. Use raw materials with better flow first 1, the temperature is too low 1, and the design of the water inlet is poor
2. Insufficient injection pressure
3. The injection is too fast to maintain pressure 2. The water inlet is too small or too long
4. The holding pressure is too low 3. The runner is too thin
5. The injection speed is too slow 4. The process is too long
6. The mold temperature is too low 5. The cold material well is insufficient
7. The check ring is worn or the action is abnormal 6. The gate is too thin and long
Example 2: There is no problem with the number of products, but one of them is poorly filled
The exhaust in the mold is poor, and the air in the cavity cannot be discharged
1. The decomposition of raw materials produces air 1. The injection speed is too fast 1. Add exhaust gas to the mold
2. The material temperature is too high
02 Shrinkage/rib line Example 1: The thick part of the work-in-progress shrinks
The surface of the finished product is wavy, the molding shrinkage rate is too large 1, the injection pressure is too low 1, and the water inlet is too thin and long
2. The holding pressure is not enough
3. The injection speed is too slow 2. The design position of the water inlet is incorrect
4. The mold temperature is too high, and the part with high temperature in the mold shrinks
3. The runner is too thin
4. The product is too thick
5. The material temperature is too high 5. The flow resistance is large
6. The action of the check ring is not smooth or worn 6. The rib line and the protruding part are too large
Example 2: Wave phenomenon on products of average thickness
1. The action of the check ring is not smooth or worn
03 Rotten glue 1, raw materials or additives react keenly to heat 1, and the material temperature is too high
2. The injection pressure is too high
3. The injection speed is too fast 1. The water inlet is too thin or too long
Mold exhaust bad gas volume
Discoloration of a part of the product
04 Black streaks 1, raw materials or additives react keenly to heat 1, the material temperature is too high 1, and the water inlet is too thin and long
The product extends out from the black bar from the water inlet 2. The raw material stays in the barrel for too long
2. The lubrication of raw materials is not enough 3. The barrel of the injection molding machine is damaged and the raw materials accumulate
05 Cloud fog 1, the stability of the plastic is not enough 1, the material temperature is too high 1, the mold polishing is too poor
The surface finish of the product is poor 2. The mold temperature is too low
3. The raw materials stay in the barrel for too long
4. Improper use of release agent
06 Silver bars 1, raw materials are not dry enough 1, and the drying hopper is wet
Silver lines appear in the flow direction of the work-in-process rubber 2, and the material temperature is too high
2. The thermal stability of the raw material is not enough 3. The back pressure is insufficient
4. The raw material stays in the barrel for too long
07 Flow marks 1, the movement of raw materials is not enough 1, the material temperature is too low
2. The mold temperature is too low 1. There is no or insufficient cold material well
The ripple amplitude is formed at the center of the WIP water inlet
08 Welding line 1, raw material fluidity is not enough 1, material temperature is too low
2. The rate of fire is too slow
3. The mold temperature is too low
4. The injection pressure is too low
5. Mold release agent has been used
1. The inlet is too thin or too long
2. The location and method of the water inlet are inappropriate
3. The material well is not enough
4. Gas addition and exhaust equipment
5. The local price cold material well that appears in the welding line
Weld line marks will occur where there are holes in the product, and it is difficult to completely eliminate them
09 Jet stream 1, insufficient fluidity of raw materials 1, material temperature is too low
2. The injection speed is inappropriate
3. The mold temperature is too low 1. The position of the water inlet is poor
2. The cold material well is not enough
3. Add a blocking needle to the place where the raw material flows into the water inlet
An earthworm-like line is formed at the inlet
10 Top white 1, the injection pressure is too high
2. The injection speed is too fast
3. The ejection speed is too fast 1. The mold buckle slope is not enough
2. There is a groove in a certain part of the mold
3. The ejection structure is inappropriate
Ejector contact bleaching such as HLPS and ABS is prone to occur
11 Rupture 1. The molecular weight of the raw material is too low
2. The strength of the raw material is not enough 1. The injection pressure is too high
2. The injection speed is too fast
The ejection speed is too fast, the cooling time is too short, 1, the buckle slope is not enough, 2, and there is a groove in a certain part of the mold
3. The ejection structure is inappropriate
4. The setting and position of the water inlet are improper
Cracks appear on the product
Air bubble Example: A hole appears in the center of a thick piece
Due to excessive inflation or poor exhaust in the melt, the residual gas in the plastic parts is formed into holes or a series of holes To be cleared on the transparent products, but non-transparent products do not need to be removed, but must not affect the strength of the product itself
12 1. The plastic flow is too high 1, the injection pressure is too low 1, and the diameter of the injection port, runner and gate is too small
2. The screw is returned earlier
2. The molding shrinkage is too large 3. The holding pressure is too low 2. The mold exhaust is poor
4. The injection speed is too slow 3. The runner is poor and there are dead ends
5. The mold temperature is too low
Example 2: Small bubbles appear on the product
1. The raw material is sensitive to heat
2. The raw material is not dried enough 1. The back pressure of the screw is too low
2. The temperature of raw materials is too high
3. The raw material stays in the barrel for too long
The flash is too large 1, the fluidity of the plastic is too high 1, the injection pressure is too high 1, and the hardness of the mold is insufficient
13. Due to poor clamping, the gap is too large, the plastic fluidity is too large, the feeding is too much, and the plastic parts are used to have excess thin fins along the edge 2, and the injection speed is too fast
3. The injection time to pressure holding time is too long 2. The plane of the mold is not close to each other
4. The clamping force is insufficient, and the projection area is greater than the clamping force of the injection surface, forming a mold expansion
14 Changes in injection amount 1. The fluidity of raw materials is too high 1. The material temperature is too high
2. The check ring is worn or the action is smooth
15
It is difficult for the product to stick to the mold and remove the mold 1, the molding shrinkage is too large 1, the injection pressure is too large 1, and the mold buckle slope is insufficient
2. The injection is slow to be protected 2. There are grooves in the mold
2. The flow of raw materials is too large 3. The holding pressure is too high 3. The mold is poorly polished
4. The material temperature is too high 4. The ejection method is improper
5. Use a release agent
11. General handling of equipment production failures
The oil pump motor is out of order
(1) There is abnormal noise. You should check:
fuses and wiring;
Check whether the three-phase power supply is average;
whether the motor steering is normal;
whether the oil pump is normal;
Whether the working pressure of the hydraulic system exceeds the rated maximum value;
(2) The fruit motor suddenly stops working, it should be checked;
Whether the motor is overloaded.
Whether the relay or other safety of the starting motor has burned out.
Whether the motor burns out or not.
Check whether the overload protector reply button pops up.
Check whether the emergency stop button and other related wiring are normal.
(3) The oil pump rotates, but there is no pressure:
Check if the motor steering is working properly.
Whether the oil pump is installed in the correct position after repair.
The proportional valve works and fails, check the proportional valve.
If the electronic board of the control proportional valve is faulty or improperly adjusted, check the electronic board.
There is a lot of air in the oil circuit, so check the exhaust gas.
Failure to lock the mold, including the inability to apply high pressure:
Check whether the contact of the safety door travel switch is normal and whether the hydraulic protection is normal.
Check if the mode lock button is invalid or the control system is broken.
When the high pressure cannot be raised, the low pressure setting parameters should be checked for too low, improper or jammed low pressure valves and too small clamping force.
Improper mold adjustment.
If you use an electric eye to work, you need to check whether the electric eye is normal.
The thimble does not recede or the clamping directional valve is working normally.
Cannot open the mold:
Check whether the position of the end of the mold opening is appropriate;
Check whether the proportional valve and the mold opening direction valve are working normally;
If the mold can not be opened after a period of shutdown, it is necessary to increase the pressure and flow rate of the mold, if the mold can not be opened, it has been reversed, and it needs to be handled carefully.
Loss of high pressure
Readjust the mold thickness
Check that the low pressure end (i.e., high voltage start) position is normal
Check if the oil temperature is too high. Normal oil temperature is 30--55°C
Check that the proportional valve is working properly
Check if the low-pressure valve is stuck or leaking badly
The ejection action is out of order
When semi-automatic or fully automatic, whether the forward kill switch of the shooting table is touched
Check the injection directional valve and see if it is working properly. Whether the circuit control signal is normal
Check whether there is a problem with the computer I/O board and whether the injection parameters are set normally.
3. Causes and prevention of failures in the structure of the shooting platform
Wear of the plug ring:
The function of the plug ring (also known as the check valve) is to prevent the plastic from flowing back into the melt cartridge when the glue is injected, so that the injection volume is unstable. Insufficient injection volume caused by the wear of the plug rubber ring is a fault that is difficult to find in the injection table structure. The main reason is that the plastic is related to the combination of the plastic and the plug rubber ring material: the material used in the plug rubber ring is generally alloy steel and nitriding, and the hardness is about HRc56-59. Under normal use, the average working life is about three years or more. However, when used in plastics containing glass brazing or mineral reinforcements, the rate of wear increases and the working life is shortened. In addition, the above-mentioned phenomenon also exists in the melt screw, in the past, the wear of the melt screw is not easy to find, unless the screw is removed for inspection, therefore, when the bolt rubber ring is found to be a problem, the melt cartridge screw should be checked at the same time whether there is also a problem. Under normal circumstances, the service life of the melt cartridge is twice that of the screw.
Fault Prevention:
When using plastics containing glass brazing, mineral reinforcements or corrosive substances, it is necessary to consider the selection of melt screws and their supporting parts with strong corrosion resistance and wear resistance, so as to avoid serious wear and tear of parts that affect the injection molding effect and increase waste.
To judge whether the bolt rubber ring (check ring) is worn, you can stop the screw melt in the middle of the process, block the iron plate from the nozzle for injection, and observe the position of the screw. If the screw stops, the plug ring is normal, and if it keeps moving forward, it proves that the plug ring has lost its efficacy. When judging this method, do not use materials that are easy to decompose such as POM to avoid accidents, such as using PE, ABS, PP and other raw materials.
Partial maintenance of the shooting table
1. Keep the surface of the injection table and the guide rail of the injection table clean
2. Do not put anything other than plastics, pigments and additives into the hopper, and add a magnetic frame to the hopper to prevent metal from entering the melt cylinder.
3. Before the temperature of the melt cartridge is reached, it is strictly forbidden to shoot glue and melt/extract glue
4. Tighten the loose part during the cycle check and add lubricating oil regularly. Regularly remove the lubricating grease from the bearing assembly of the transmission shaft part and replace it with new grease.
5. When the temperature of the melt barrel is normal and black spots or discoloration are constantly found, please check the screw barrel assembly. And please use which screw is more suitable for this kind of plastic.
6. When using special plastics, consult the plastic supplier for corrosiveness.
Causes and prevention of failures in hydraulic systems
1. One of the most common faults in hydraulic systems is the loss of pressure in the system. When in normal use, the maximum pressure of the system is 140bar, if the cyclic action of the injection molding machine is suddenly slow and the pressure cannot be increased, and the control signals are normal, it means that there is a problem with the components in the system. There are two groups of components in the hydraulic system that affect the system pressure: one is the pressure and flow proportional valve, and the other is the oil pump and motor.
2. The main function of the pressure and flow proportional valve is to control the pressure of the system and the output displacement of the oil pump. When the component fails, it is mainly due to the unclean hydraulic oil, which causes individual blockages and causes abnormal operation. In addition, water infiltration into the hydraulic oil causes oxidation of the oil, which may cause rust inside the components, increase or decrease the wear of the components and pollute the hydraulic system. Component failures can also be caused by internal leaks.
3. The oil pump and motor are another group of components that affect the pressure of the system. The oil pump continuously outputs the hydraulic oil while the motor rotates and thus creates system pressure. If the rotation of the oil pump is affected or the hydraulic oil cannot be output internally, the system pressure cannot be increased. The reason for the problem of oil pump rotation may be a problem with the rotation of the motor, or a problem inside the oil pump, and the problem of the motor is mainly caused by the failure of the power supply or the motor itself. The main reason for the problem inside the oil pump is related to the hydraulic oil. When there is dirt in the oil or the oil has been oxidized, it will lead to serious wear and tear of the rotor and blades of the oil pump, which will affect the hydraulic oil delivery work.
fault prevention;
In order to prevent the failure of hydraulic components, it is necessary to pay attention to the cleaning of the hydraulic oil, to filter the dirt in the oil as much as possible and to prevent water from seeping into the oil. Keep the oil equipment and oil tank clean and tidy when changing the oil. Seal the fuel tank cap immediately after changing the oil to prevent debris and water from entering the tank. In addition, when storing and placing the hydraulic oil, attention should be paid to tilting the oil drum slightly to allow the water on the lid to flow away. Avoid water accumulation on the barrel and seepage into the oil from the oil cap. When the hydraulic oil is found to contain water or dirt, the pressure oil should be replaced immediately or the oil tank should be cleaned to avoid the problem from worsening. Pressure oil should be replaced once a year under normal use.
Hydraulic Actuator Failure:
Hydraulic actuators can be divided into linear and rotary: hydraulic cylinders are linear actuators, while hydraulic motors are rotary actuators. The main failure of hydraulic cylinders is damage or failure of seals, resulting in oil leakage and reduced efficiency.
Seal damage or failure can be attributed to the following reasons: the oil temperature is too high to accelerate the aging of the seal, if the working oil temperature of the injection molding machine has been too high, the seal will accelerate the aging, and can not be deformed and the gap is sealed when pressurized, causing the hydraulic cylinder to leak. The normal oil temperature of the injection molding machine should be maintained between 30°C-55°C is optimal. If the oil temperature is too low, it is easy to affect the normal service life of the oil pump and related hydraulic components. Dirt and moisture in hydraulic fluids can also cause seals to wear.
The piston rod is connected to other parts in a deviation, which causes the seal to wear out and cause oil leakage. When the equipment is working for a long time, the fixing screws or fixing parts may be loose or repaired, and the piston rod position of the hydraulic cylinder will be deviated, resulting in long-term compression deformation and wear of the seals. In addition, a serious leak in the hydraulic cylinder can also lead to functional failure.
The same problems are also experienced in hydraulic motors, where high temperatures accelerate the aging of seals and oil contaminants damage them.
Fault Prevention:
In order to avoid premature deterioration of the seals, the oil temperature must be properly controlled. On computerized injection molding machines, the oil temperature must be properly controlled. On computerized injection molding machines, the maximum setting of oil temperature is generally 60°C. Outside of this range, an alert is issued and the automatic operation is stopped. At this time, you should check whether the cooling system is working properly. If the injection molding machine is digitally controlled, and there is no built-in oil temperature display in the system, in this case, you need to pay close attention to the oil temperature change and the thermometer to measure the oil temperature, or choose to install an oil temperature gauge with an over-temperature alarm to display the oil temperature and sound the alarm. The oil temperature should not be allowed to exceed the 60°C limit and the workpiece should continue to accelerate the aging of the seal.
In the installation of hydraulic cylinders, attention should be paid to whether the fixing screws and fixing parts are loose, and whether there is any deviation in the connection of other parts.
In South China, we recommend our customers to use ISOVG46 viscosity anti-wear hydraulic fluids.
In East China, we recommend that customers use ISOVG68 viscosity lubricants.
