plastic injection molding machine

In 1980, France produced the world’s largest screw injection molding machine, with an injection capacity of 170kg. From the 1980s to recent years, the development of injection molding machine is mainly concentrated in several aspects: namely, the application of precision automatic control system and various auxiliary equipment in automatic molding; Precision machinery and high performance hydraulic system; Various special injection molding machine development and computer aided design of complex shape parts plastic flow analysis to determine the best injection conditions; Application of various energy saving technologies in injection molding machine.

Working principle of injection molding machine

Injection molding machine referred to as injection molding machine, injection molding is the use of plastic thermophysical properties, the material from the hopper into the barrel, the barrel outside by heating ring heating, so that the material melt, in the barrel is equipped with external power motor drive rotation of the screw, the material in the double action of the screw shear gradually plasticized, melting and homogenizing, when the screw rotation, Material in the groove friction force and shear force under the action of the molten material pushed to the head of the screw, at the same time, the screw in the material reaction backward, so that the head of the screw to form a storage space, complete the plasticization process, and then the screw in the injection cylinder piston reasoning under the action of high speed, high pressure, the storage room of the molten material through the nozzle into the mold cavity, After the molten material in the cavity is kept under pressure, cooled and solidified, the mold is opened under the action of the mold closing mechanism, and the finished product is ejected from the mold and dropped through the ejecting device.

Composition structure of injection molding machine

Injection molding machine according to the injection molding process requirements is a mechanical and electrical integration of a strong machine, mainly composed of injection parts, closing parts, frame, hydraulic system, heating system, control system, feeding device and so on.

plastic injection molding machine

At present, the common injection molding device has single cylinder type and double cylinder type.

Plasticized parts have two kinds: plunger type and screw type. In the process of continuous rotation of the screw, the plastic realizes the change of physical state, and is finally injected into the mold cavity in a molten state. Therefore, the plasticized component is the core component to achieve uniform plasticizing and quantitative injection.

To provide customers with plastic products development, mold design, product manufacturing and injection molding, its products are widely used in every field of life today, such as household appliances, instruments, wires and cables, building equipment, communications electronics, automotive industry, aerospace, daily hardware and so on.

The overall production process of plastic products is: raw material selection – raw material coloring and matching – design casting mold – machine decomposition injection molding – printing – assembly detection of finished products – packaging factory.

Plastic products are made by injection molding or blow molding, so every time you design a sample, you have to open a new mold, and the mold is generally tens of thousands to hundreds of thousands of dollars, so in addition to the raw material price of plastic products, the cost of the mold is also very large. There may be many parts to make a finished product, and each part needs a separate mold. For example, the trash can is divided into: the barrel body — the lid, the liner, the handle several parts.

Generally speaking, the plastic factory refers to the processing of plastic products with plastic raw materials, semi-finished products and finished products, such as MP3 shell, telephone shell, mobile phone shell, computer monitor shell and other plastic accessories. And finished products such as plastic cups, plastic washbasins, plastic buckets, and other daily necessities. Its essence is called plastic processing plant.

1. Preventive maintenance of injection molding machine`s hydraulic system

Injection molding machine`s hydraulic oil introduction:

The hydraulic transmission of the injection molding machine uses hydraulic oil as the working medium, and uses the pressure energy of the hydraulic oil in the sealed working volume to transmit energy, pressure or power or signal. The quality of hydraulic oil and seals directly affects whether the hydraulic system can work stably for a long time, and indirectly affects the quality of products. In order to prevent and reduce the failure of the hydraulic system, reduce the wear and prolong the service life, the hydraulic oil should be strictly used and maintained.

In general, 70% of hydraulic unit failures are due to incorrect or improper use and maintenance of hydraulic fluid. Maintaining good maintenance habits and preventive maintenance is the easiest and most effective way to reduce and prevent hydraulic failures in your machine. Therefore, careful maintenance of hydraulic oil and hydraulic system is very important.

(1) Selection of hydraulic oil

When the machine we ordered from the injection molding machine manufacturer arrives at our workshop, please read the instruction manual of the injection molding machine provided by the manufacturer in detail, and strictly select the hydraulic oil model recommended by the manufacturer or the hydraulic oil with a higher specification.

The most important properties of hydraulic fluids are viscosity and cleanliness, as well as good resistance to oxidation, wear, foam, corrosion, and good lubricity.

The viscosity of hydraulic oil is expressed by the average kinematic viscosity at 40°C. Our commonly used No. 46 high-quality anti-wear hydraulic oil (46csT/40℃) means that the average kinematic viscosity of this hydraulic oil at 40℃ is 46m2/S.

The relationship between hydraulic oil viscosity and pressure and temperature is as follows: viscosity decreases with increasing temperature; while viscosity increases with increasing pressure.

1. Regularly test hydraulic oil performance. If the oil is contaminated or deteriorated, the life of the injection molding machine will be shortened and failure may occur. Therefore, regular oil testing is required to detect changes in oil properties. Based on this, it is possible to decide whether to change the oil. (If conditions permit, it is best to use the data value of professional laboratory testing) We can use a simple visual method to understand the state of the oil:

a). Appearance test: Put new oil samples and used oil samples into their respective test tubes, and compare their color, transparency, floating matter, and water sedimentation at the bottom of the test tubes.
b). Drop test: put the old oil drop on the filter paper (oil-absorbing paper) and observe it after one hour. Contamination is easy to observe if it is oily or visibly deteriorated.
c). Finger rubbing: Used oil can be rubbed on fingers. If the viscosity decreases and deteriorates, the hand feels rough and there is no sticky feeling. The oil droplets slide off the fingers smoothly with no sticky bounce.

Routine maintenance of the hydraulic system usually includes the following points (not limited to):

(2) Working temperature of hydraulic oil:

The working temperature of the hydraulic system of the injection molding machine should be between 45-50 °C. Since the hydraulic system is designed according to the viscosity of the oil and the selected pressure, the viscosity will vary with the oil. The liquid level changes, thus affecting the working components of the system, such as oil cylinders, hydraulic valves, etc., reducing the control accuracy and response sensitivity, which is more serious in precision injection molding machines.
Temperature will also accelerate the aging of the seal, making it harden and break;
If the temperature is too low, the processing energy consumption will be reduced and the working speed will be reduced.
Therefore, it is necessary to pay close attention to the working temperature of the hydraulic oil.

The shortage of hydraulic oil will cause the oil temperature to rise, and the air will easily merge into the oil and hydraulic oil, which will affect the normal operation of the system. The lack of fuel is usually caused by oil leakage. During maintenance, attention should be paid to check whether there is leakage on site, and replace the worn seals as soon as possible. parts, tighten the loose joints, and check the supply of hydraulic oil after repair.

There are various reasons for high oil temperature, but many are attributed to faulty or malfunctioning oil cooling system, etc.

(3) Replace the old hydraulic oil

In principle, change the hydraulic oil every 5000 hours of operation or at most once a year. No matter how good the hydraulic oil is, after a certain period of time, metal and rubber particles worn by moving parts such as pumps will enter the oil and form sludge and dirt. During normal maintenance, some contaminants can adhere to parts and be carried into the hydraulic fluid.

An important property of hydraulic fluids is their chemical stability, ie oxidative stability. Oxidation is the most important factor in determining the service life of hydraulic oil. The wood tar, sludge and insoluble substances such as carbon residue produced by oxidation will contaminate the hydraulic system, increase the wear of hydraulic components, reduce various gaps, block holes, and eventually lead to hydraulic system. Fault.
The oxidation rate depends on factors such as the hydraulic oil itself and working conditions, of which temperature is the main factor, so use appropriate hydraulic oil, and regularly check the degree of oxidation of the hydraulic oil (the color of the oil is determined by the depth), after a certain working hours An oil change is absolutely necessary to be proactive.

Even if the hydraulic oil is used correctly, its service life is generally considered to be one year, and it can be up to two to three years. Once spoiled, it must be replaced with new oil without hesitation. Good oil quality is the cornerstone to keep the hydraulic system stable.

Hydraulic oil is filled with a special oil filter truck, not a pumping unit with a pump. The author has seen many simple oil pump trucks with pumps, pumping waste water and waste oil, and adding new oil.

Pumps that have pumped waste water and oil have no strainers, and the dirtiest impurities lurk in the pump and pipeline, mixed with new oil and added to the tank. The author has used the box to observe many times, and the new oil that I just started to pump contains a lot of pollutants. These contaminants will only contaminate new oil and damage pumps and valves.

The filter accuracy of the professional oil filter car is usually 125um (micron), and there are generally two filters, which are double-protected and filtered to protect the cleanliness of the oil.

(4) Clean the inside of the fuel tank

Hydraulic maintenance is not as simple as pumping out old oil, or just adding some new oil. Not only to replace the new oil, but also to clean the hydraulic equipment.

After the old oil is drained, do not wipe the oil tank with a rag to prevent the thread from clogging the filter. Using professional cleaners is expensive and leaves residue. The experience taught by the 20-year-old mechanic: ordinary flour is added with an appropriate amount of water to form a dry dough, and then divided into several pieces to apply oil stains, impurities, and powder in the metal oil tank. Clean and economical with no residue.

The magnetic frame and screen in the tank can be cleaned with kerosene and a copper brush; after that, they can be cleaned and dried with an air gun.

(5) Clean the air filter

The air filter outside the tank makes it easy for the air in the tank to come in and out according to the change of the oil level in the tank. Every time the oil is changed and maintained, the air filter should be taken out, cleaned with kerosene, and dried with an air gun. If not cleaned, dirt may enter the fuel tank and affect the oil quality.

(6) Hydraulic oil filter cleaning:

The oil filter plays the role of cleaning the hydraulic oil. The oil filter should be cleaned every three months to keep the oil suction pipe unobstructed. At the same time, check whether the oil filter net is damaged.

(7) Clean the inner and outer walls of the oil-water cooler

The hydraulic oil cooler should usually be cleaned once a year, or the interval between cleaning should be increased or decreased according to its own working environment and ability. Blockage or scaling inside the cooler will affect the cooling efficiency of both, and the cooling water should be clean. Clean soft water (mineral free) is preferred.

Tips:
1). The scale inside and outside the cooler tube should be cleaned with weak hydrochloric acid solution, rinsed with water, and dried with an air gun.
2). The dirt on the baffle should be cleaned with a copper brush.

(8) Clean the oil valve

First, the dirt outside the valve can be cleaned with a waste cloth and an air gun. You can remove the plug and remove the oil valve. The sludge and debris on the valve core and valve body can be cleaned with a kerosene brush and dried with an air gun. Care should be taken to avoid upside-down spool installation and loss of O-rings.

(9) Cleaning the cylinder

After disassembling the clamping, thimble, base, and plastic injection cylinder, use kerosene to clean the cylinder block and piston, and replace the worn and damaged oil seal, dust seal, and O-ring. The reasons for dismantling the oil cylinder, checking the oil seal and replacing it are as follows:

1. The stability of the injection pressure is the main factor determining the quality of the finished product. The sealing and wear rings should be replaced every 20,000 hours of machine operation or a maximum of five years. Although the five-year-old oil seal is not seriously damaged, it must also be replaced. It cannot be repaired until there is an oil leak, carbonation or pressure relief, or the machine fails.
2. Check whether the piston rod is loose.
3. Cleaning equipment parts is also a maintenance method.

(10) Replace the bypass filter element.

(11) Check whether the tightening oil pipe joint is loose, and replace the oil pipe with aging oil leakage.

2. Preventive Maintenance of Injection Molding Machine`s Electrical System

1. Wire connector inspection Preventive Maintenance

The connector will not be tightened, and the wires at the connector will be damaged if there is heat or sparks, and bad connectors will also affect the transmission of signals;
The movement of the contactor joint is easier due to vibration and electromagnetic release, so the position and tightening of the cable joint need to be checked regularly.

2. Servo Motor Preventive Maintenance

General motors are air-cooled, and the accumulation of dust will cause heating problems, so they should be cleaned regularly every year. Usually, there is a motor overload cut-off device in the circuit. The current limit of the protection device is adjustable, and the power consumption should be based on needs. Appropriate selection, once the overload protection is activated, it should be checked whether there is a phase loss, poor contact, or the position switch is restored after the oil temperature is high.

Picture: sciencedirect.com

3. Heating tube and thermocouple:

The heating pipe should be tightened and checked to ensure effective heat transfer, and heat is generated invisibly in the normally burning barrel. Pay attention to the work of the thermostat and judge whether it is normal from the heat pipe.

Another common damage to the heating tube is the cable connection. Due to the poor joint, the contact resistance increases, so the connection to the local overheating causes the interface to be oxidized and damaged.

4. AC Contactor Preventive Maintenance:

The contactor acts more frequently on the electrical part, because its loss rate is also relatively fast. If the melting point of the main contactor is overheated, it may lead to poor control of the heating temperature of the bonding, so if the contactor is found to be overheated or broken, it will make a clicking sound. , then the damaged contactor will be replaced as soon as possible when the fire is large.

5. Computer control part Preventive Maintenance

With the application of computer control technology in injection molding machines, computer electronic board parts and related auxiliary components have put forward higher requirements for working power supply voltage fluctuations, temperature and humidity of the working environment, installation earthquake interference, and the outside world for high-frequency signals. The ventilation fan of the control box is used for the work, and it is powered by a high-precision voltage stabilizer.

To reduce external vibration of the control box, the Effectively address these issues and check them regularly.

3. Preventive maintenance of injection molding machine`s Mechanical System

1. Template parallel:

The template best reflects the clamping state of the parallel part, the template will not cause the failure of the product and increase the wear of equipment and tooling in parallel.
The parallelism of the template is a preliminary analysis reflected by the movement of the end of the pressing plate and the appearance of the product, but the specific situation such as equipment testing needs to be derived from the dial table.

The steps of the template should be adjusted in parallel by a person familiar with it, otherwise the machine will be more damaged by improper adjustment.

2. Adjustment of mold thickness

The mold thickness should be adjusted regularly using the system, and the module thickness should be adjusted from the thickest to the thinnest to ensure the smooth long-term production of the machine and the same mold. This inspection must be carried out to avoid failure.

3. All the mechanical moving parts of the central lubrication system need to be properly lubricated.

The central lubrication system is an indispensable part of injection molding. The central oil lubrication system should always check whether it is filled, and the lubricating oil used should be clean and free of impurities to ensure that Lubricating oil supply to all parts is normal.

If the water pipe is found to be blocked or leaking, it should be replaced or repaired immediately.

Most mechanical wear occurs due to lack of lubrication, so the importance of adequate lubrication is self-evident.

4. Keep running smoothly

Smooth motion or vibration may be caused by improper speed adjustment, inconsistent speed change and time, or mechanical and hydraulic adjustments.
Such shocks will accelerate the wear and loosening of mechanical components, and tightened screws should reduce and prevent vibration.

5. Bearing inspection

If the bearing makes different sounds during operation, or the internal temperature rises, it means that the bearing is worn. It should be checked or replaced in time, and the grease should be refilled.

6. Injection system

The injection screw, inspection ring and barrel constitute the heart of the injection molding machine, which determines the processing quality and efficiency of the injection molding machine, and we must keep them in good working condition.

First of all, it is necessary to take necessary measures to prevent non-plastic chips from mixing into the flow of plastic. When adding, pay attention to check the gap between the screw and the barrel, and check whether the gap between the ring and the barrel is correct. When the gap is normal, it should be able to return and generate the plasticizing shears required for sealing. When it is found that the melt is slow, the melt spots and black spots, the molding is unstable or the product is worn, the wear of the screw, ring and barrel should be checked.

Injection Molding Machine Preventive Maintenance Checklist

Monthly Maintenance Checklist for Injection Molding Machines

3 / 6 Month and One-year Maintenance Checklist for Injection Molding Machines

Common Faults Causes & Solutions for Injection Molding Machines

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Treatment of common faults of injection molding machine:

1. The oil pump motor and oil pump start, but no pressure.

A). The proportional valve wiring on the oil pump is loose or the coil is burned out ——> Check whether the proportional pressure valve is energized.

B). Impurities block the oil port of the proportional pressure valve on the oil pump ——> Remove the proportional pressure valve to remove the impurities.

C). The pressure oil is not clean, and the debris accumulates on the surface of the oil filter, preventing the pressure oil from entering the pump – clean the oil filter and replace the pressure device.

D). Oil leaks inside the oil pump, which is caused by excessive use, internal wear or unclean pressure oil -> Repair or replace the oil pump.

E). Oil leakage from the oil pump, oil pipes and joints ——> Eliminate the leakage.

F). The oil system is stuck ——> Check whether the oil system spool moves normally.

2. The temperature of the melt cylinder cannot be controlled

A). The temperature cannot be controlled, check whether the contacts of the electric heating contactor are stuck, and whether the wires of the thermocouple are loose or damaged.

B). If the temperature cannot rise, check whether the electric heating air switch in the electric box is adjusted, whether the contactor and relay are closed, whether there is voltage, whether the insurance is burned out, and whether the heating ring is burned out.

C). Whether the thermometer is damaged.

3. No mode locking

A). Whether the front safety door has been closed, whether the limiter of the safety door has been pressed and released by the safety door, and whether the wiring is loose or damaged.

B). The coil of the clamping solenoid may have moved into the valve, stuck with the spool –> Clean or replace the clamping and opening control valve.

C). The directional valve may not reset -> Clean the directional valve.

D). The thimble cannot be returned to reset ——> Check whether the thimble moves normally.

E). Check whether the origin of the computer controller for mold clamping and mold opening electronic ruler has been changed, and whether the mold clamping position has been terminated.

F). Check whether the pressure gauge operates.

G). Press the mode-locking key to see if the display screen shows the mode-locking signal or other signals and alarms.

H). Check whether the clamping position, speed and pressure are properly adjusted.

I ). Check whether the clamping piston rod is broken.

4. No plastic was injected or plastics was not shot out of barrel

A). The coil of the injection solenoid may be burnt, or foreign objects enter the directional valve and move with the spool stuck –> Clean or replace the injection valve.

B). The pressure is too low ——> increase the injection pressure.

C). The temperature of injection molding is too low – adjust the thermometer to raise the temperature to the required point. If the temperature cannot be raised by adjusting the thermometer, check whether the electric heating tube and fuse are burnt or loose. Replace in time. 4. The connection of the valve opening system of the injection combination is loose or has poor contact ——> Connect the combination switch wire properly.

5. The screw rotates, but the melt plastics does not enter the barrel

A). Sol back pressure is too high, the back pressure valve is damaged or improperly adjusted ——> Adjust or replace the sol back pressure valve.

B). Insufficient water transport, so that the temperature is too high, so that the glue particles are blocked when entering the screw ——> Adjust the water transport amount, and take out the glued glue block. See if the water ring is blocked or the water is not cooled.

C). There is no material in the drop bucket ——> Add material.

D). Whether the temperature of the melt barrel is too high.

6. The launcher does not move

A). The moving limit travel switch of the shooting platform is pressed by the adjustment striker ——> Adjust.

B). The coil of the solenoid valve for the moving platform may be burnt or foreign objects enter the directional valve and the valve core moves –> Clean or replace the solenoid valve.

C). Check the forward speed of the shooting platform and whether the pressure is properly adjusted.

D). Check whether the 1/0 board and the output voltage (DC+24V) of the directional valve are normal. If not, check whether the corresponding output transistor or relay is damaged.

E). Press the radio button to check whether the computer screen displays the pre-launch signal, or other signals and alarms.

F). Check whether the pressure gauge has movement.

7. Mould opening makes a sound

A). There is no brake or brake failure of the mold opening stroke switch ——> Adjust or replace the solenoid valve.

B). The fixing screw of the slow speed solenoid valve is loosened, or the valve core is stuck ——> Adjust to a significantly slow speed.

8. Pressure oil temperature is too high

A). The pressure of the oil pump is too high ——> It should be adjusted to the demand pressure of the rubber compound.

B). The oil pump is damaged and the pressure oil concentration is too low ——> Check the oil pump and oil quality.

C). Insufficient amount of pressure oil ——> Increase the amount of pressure oil.

D). The cooling system is faulty and the water supply is insufficient ——> Repair the cooling system.

9. Automatic action failure

A). The electric eye is out of order, the fixing screw is loose or the light is not condensed. ——> Make the electronic sensor work again.

B). The time system is out of order or damaged ——> Adjust or replace the time system.

C). The heating element is damaged ——> replace it.

D). Poor or damaged thermocouple wiring ——> Tighten or replace.

E). Thermometer damaged ——> replace the thermometer

F). Semi-automatic failure: The semi-automatic cycle is realized by the stroke of the mechanical action, triggering the switch system and time system of each electrical appliance, sending electrical signals, and controlling the oil system. If it is in the manual state, every action is normal, but semi-automatic If it fails, most of it is because the electrical switch and time switch do not send a signal. First, observe the failure of the semi-automatic action at that stage, and find out the corresponding control element according to the “action cycle diagram”, and check and solve it.

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The many styles of mobile phone cases seen on the market make many people love it. Not only can they protect their phones, but they can also make their phones look stylish and unique. Generally, mobile phone case manufacturers make mobile phones from raw materials to the end. The finished shell products need to go through the main steps of mold opening production, mold trial, sample confirmation, injection molding production, surface spraying treatment, and assembly. Generally, plastic mobile phone cases are produced by Phone Case Maker Machine – optimized injection molding machines.  What about the turnkey solutions for making phone cases?

Guanxin had launched 2 types of mobile cover making machine in the mobile back cover manufacturing industry. They are normal plastic mobile cover making machines and silicone phone case making machines. The traditional plastics like TPU, PP, PC, ABS will need the the normal mobile phone case making machines for production. But the silicone mobile cover will need different silicone injection molding equipment. It is called liquid silicone injection molding machine (Click for detailed introduction). This silicone phone case making machine requires the liquid silicone metering and dosing machine to work together. As the silicone mobile cover is made by liquid injection molding ( LIM ) process.

Mobile phone protective cases are mass-automated production using general precision level 5. The wall thickness of most mobile phone covers is about 1.5mm, and the protruding part inside the mobile phone case is less than 5%. In the current automatic production of mobile phone protective cases, forced demoulding is adopted. Then it is taken out by a robot arm for 24-hour non-stop automatic manufacturing production.

 

Name	Detailed Specification of Mobile Cover injection Mold
Cell Phone Case Application Brands:	Iphone, Huawei, Xiaomi, Oppo, Vivo, Samsung, Google Pixel Phones, Motorola, Lenovo,LG, Asus, Realme, Tecno Mobile, Sony,ZTE, Nokia,
Mobile Cover Injection Mold Cavities:	1 or 2, or 4 mostly, Now some manufacturer is running 6 ~ 8 cavity production line.
Ejection Method:	By hand or Auto-Robot
Mobile Phone Cover Making Materials:	TPU, PC, PP, ABS are mostly used, But some quality mobile back cover are made by liquid silicone.
Phone Back Cover Mold Steel:	S50C, 718H, 738, SKD61, SCM435, ETC
Phone Case Mold Manufacturing Processing:	CNC Machining, Wire Cut, Grinding, Drilling, Polishing, etc

Phone Case Maker Machine Introduction

Guanxin Mobile phone case maker machine is a dedicated optimized injection molding machine for mobile phone`s protector manufacturing application. This phone cases making machine is optimized with the injection screw and barrel with is bi-metallic material for PC, Silicone supplier for soft silicone phone case, hydraulic driving system, higher injection speed and pressure. This mobile cover maker machine is mainly used to manufacture cell phone case by PC, Elastomers and other raw material. We are trying to offer the phone case machine maker to have light weight, high precision mobile phone case and protector.

Plastic Mobile Phone Case Manufacturing Process

Mobile phone cover are usually made of PC (polycarbonate) or PC+ABS. Due to the poor fluidity of PC (physical properties are shown in the table below), the mobile cover making process usually uses high mold temperature and high material temperature to fill the mobile phone case cavity; The mobile phone cover injection mold usually is designed with a point gate. Grading injection is required for filling. Finding the position of the gate and the VP (injection-holding pressure) switching position will be great help in solving abnormalities such as gate gas marks and underfill flash.

The following are the key points of the molding conditions of mobile phone cover products, introducing the points of attention to the setting of molding parameters such as melt temperature, mold temperature, injection speed, back pressure, etc.

Phone Case Injection Molding Process	Plastic Phone Case Manufacturing Process Controlling Method
Melting temperature	The optimal molding temperature setting is related to many factors, such as the size of the phone cover making machine, screw configuration, mold and molded product design, and molding cycle time. Generally speaking, in order to gradually melt the plastic, a lower temperature is set in the rear section/feeding zone of the material pipe, and a higher temperature is set in the front section of the material pipe. However, if the screw design is improper or the L/D value is too small, the reverse temperature setting is also possible.
mold temperature	In terms of mold temperature, high-temperature molds can provide better surface appearance, with less residual stress, and are easier to fill for thinner or longer molded products. The low mold temperature can shorten the molding cycle.
Screw rotation speed	40 to 70 rpm is recommended, but it depends on the mobile back cover making machine and screw design.
Injection Pressure	In order to fill the mold as quickly as possible, the higher the injection pressure, the better, generally about 850 to 1,400kg/cm2, and the highest can reach 2,400kg/cm2.
Injection speed	The rate of fire has a lot to do with the gate design. When using direct gates or edge gates, a slower rate of fire should be used in order to prevent sun glare and wave flow marks. In addition, if the thickness of the finished product is above 5MM, slow injection will help avoid bubbles or dents. Generally speaking, the principle of the rate of fire is that the thinner is fast, and the thicker is slow. When switching from injection molding to holding pressure, the holding pressure should be as low as possible to avoid residual stress in the molded product. The residual stress can be removed or reduced by annealing; the condition is 120°C to 130°C for about 30 minutes to one hour.
Back pressure	Generally, the lower the setting, the better, but for uniform feeding, it is recommended to use 3 to 14 kg/cm2.

 

PlasticS Mobile Phones Case Injection Molding defects and Troubleshooting Solutions

 

Common defects / Injection Troubles	Reasons	Trouble Shooting Solutions
Short injection:		increase injection pressure, speed, increase material temperature, mold temperature, and increase the amount of glue.
Gas mark		Reduce the flow rate of the melt through the gate and increase the mold temperature.
Black spot	1. The proportion of raw materials is too high 2. The screw is not cleaned 3. Poor workshop environment	1. Control the proportion of inferior materials and prohibit the mixing of heterochromatic raw and inferior materials 2. Develop phone cover maker machine maintenance, refueling and cleaning check and audit 3. Change the workshop environment and improve the cleanliness of the workshop
Flashing, piping	1. The injection pressure is too high 2. Insufficient clamping force of mobile cover manufacturing machine 3. The accuracy of the mobile cover making machine is poor 4. Because the employees were not serious in their work and the product was not taken out, the stamper and mold were damaged, causing the product to run away.	1. Improve the accuracy of the mold, and use high-hardness steel as the mold profile to prevent flash. The quenched and ground precision mold (block-plate combined type) is more reliable against flash. If the hardness reaches about HRC60. Ordinary molds (45 steel) are about to be repaired for about 100,000 molds, and they have been seriously damaged after about 300,000 molds. 2. From the aspect of molding process, the process conditions are mainly set in the direction of reducing fluidity. Reduce injection pressure, lower melt temperature and mold temperature, reduce injection speed, and reduce feed volume.
Weld Line	If excessive release agent is used, the fusion line will become thicker, the release agent is pushed forward by the melt, and the release agent is mixed between the forwards of the two streams, blocking the fusion of the forwards and weakening the mechanical strength.	1. Control mold temperature and material temperature 2. Adjust the glue flow of each section and add exhaust.
Big gate	1. The mold temperature is too low; 2. The fluidity of the material is low. 3. The glue position of the product is thin and difficult to remove. 4. Poor mold exhaust	1. Increase the mold temperature 2. Improve material fluidity 3. Change the position of the gate, generally designed on the thick wall 4. Increase vent holes|
Deformed	1. Uneven temperature 2. Uneven pressure 3. Molecular orientation 4. Improper gate position	Control mold temperature to prevent mold temperature differences from occurring Shorten the uneven deformation, adjust the pressure after the process
shrink	A. Improper molding process conditions (when injection pressure is insufficient, mold cooling is insufficient) B. The wall of the product is too thick or uneven C. The shrinkage of the raw material is too large (material problem) D. Shrinkage caused by uneven wall thickness of the product: There is often shrinkage on the back of the stiffener. Due to the uneven wall thickness of the stiffener, when the thickness is less than 50% of the wall thickness of the adjacent material, the shrinkage situation is obviously improved, but the width of the stiffener is at least 1MM, otherwise the mold manufacturing will be difficult, and the boss in the plastic part will have a similar situation	1. Increase injection pressure 2. Extend the holding time (delay the sol backflow at the gate) 3. A lot of shrinkage is caused by the unreasonable design of runners and gates. To deal with such shrinkage, it is necessary to modify the mold to reduce the shrinkage. 4. For complex and thin-walled products, some need to use gas-assisted technology to control shrinkage when designing and manufacturing molds

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L/D ratio is the ratio of the length of injection molding screw (L) to it`s outer diameter (D). Frankly speaking, L/D ratio is a very important parameter to a plastic injeciton molding machine. As it affect a lot on the injection machine`s melting performence and final plastic injection molding products quality. As an professional plastic molding machines manufacturer, we would like to explain it more to help our customers to under plastic injeciton molding machines screw better.

What is L/D Ratio in Injection Moulding Machine

Length-to-diameter ratio or L/D ratio in injection molding machine is the nominal length of the screw divided by the nominal diameter in consistent units. Or we can simply say the L/D ratio is the flighted length of the screw to its outside diameter. The L/D ratio formula is very simple that you do not need the L/D ratio calculator. Plastic injection molding machine screw L/D ratio is calculated by dividing the screw`s flighted length by its nominal diameter. Today, most of injection molding machine manufacturers are offering mouling machines with the L/D ratio of 20:1 or around this ratio like in 19:1 or 21:1. And for some optimized plastic injection machines are have a bigger ratio like 24:1 to 26:1. Fewer injection screws are special to have a L/D ratio of 28:1.

So why some plastic injection molding machines have are have bigger length-to-diameter ratio? There mainly 3 reasons:

1. More shear heat can be uniformly generated in the plastic without degradation.
2. Greater the opportunity for mixing, resulting in a better homogeneity of the melt.
3. Greater the residence time of the plastic in the barrel possibly permitting faster cycles of larger shots.

Bigger L/D ratio in injection moulding machine are mostly used to produce products with a very high quality of appearance. Like cosmetic packing bottles and containers have smooth, bright, and clear to see what it`s packed in it.

And some medical plastic tools and containers and optical lenses will need this kind of plastic moulding machine as well.

Is Plastic Injection Molding Machine`s L/D Ratio the Bigger the Better?

As you know from above, bigger L/D ratio can bring many benefits to the plastics injection molding process. You may have the question about the what factors affect on the L/D ratio selection. Is it the bigger the better? The answer is NO. We should pick a right plastic injection machine with a science L/D ratio. For our standard plastic molding machines, there are 3 different screws with similar L/D ratio for your choice. And there are bigger L/D ratio for some other dedicated optimized machines for different applications.

For example, our PET preform injection making machine is with bigger L/D ratio but PVC/PPR pipe fitting molding machine is with smaller one comparing to the standard plastic injection machines. We pick the reasonal L/D ratio according to the plastics performance and characteristic. Our dedicated injection molding machines are optimized designed with the screws, nozzle, clamps, hydraulic parts, PLC controling system as well. That is why we will ask our customers for what materials they will run and what kinds of products planning to produce. Just to advise the most suitable injection moulding machine model to quote our best cost accordingly.

As one of leading injection machine manufacturing, Guanxin is always doing our best to provid our customer best quality machines and service. You are welcome to contact us to have your injection molding solution by filling below form.

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The minimum and maximum daylight in injection molding machine determines the sizes of the items it can make.
The maximum daylight has to accommodate height of moving half of mould, height of moulded part, minimum and enough clearance for removal of moulded part and height of fixed half of mould.

Formula to calculate the day light of the toggle injection molding machines:
Maximum daylight = Maximum mould height + mould open stroke.
Minimum daylight = Minimum mould height + mould open stroke.

With Hydraulic clamp machine, Maximum daylight = Minimum mould height + mould open stroke.
If shut mould height is more than minimum mould height of machine then the mould open stroke is reduced to the extent of difference in shut mould height of mould and minimum mould height of machine.

MAXIMUM DAYLIGHT
The shut mould height of the mould should be less than 1/3rd of maximum daylight so that there should be enough room for the ejection of part when mould platen is fully opened. If it is closer to 1/3rd of maximum daylight then the clearance between core and cavity of mould in fully open position should be verified on the drawing board.

The maximum daylight has to accommodate height of moving half of mould, height of moulded part, minimum and enough clearance for removal of moulded part and height of fixed half of mould.

In case of Toggle machine, Maximum daylight = Maximum mould height + Mould open stroke. Mould open stroke remains constant in toggle machine.

MAXIMUM DAYLIGHT AND MOULD OPEN STROKE
Maximum daylight as well as mould open stroke depends on toggle geometry whereas hydraulic clamp machine can be built easily for larger daylight by simply providing longer cylinder and longer tie bars. The longer mould open stroke can be provided by using longer clamp cylinder and ram. Therefor it is easier to satisfy special requirements of customers.

In hydraulic clamp machine

Mould open stroke = Maximum day-light minus Closed mould height.

SPECIAL PROMOTION

Before answering the question about clamping force calculation, we should make it clear for some basic definition of the injection machine`s molding tonnage and how it comes from and what it supports during the injection molding process.

What is tonnage in injection Moulding machine?

The “tonnage” is the maximum of clamping force that a injection molding machine can offer to keep the the injection tool tightly closed during the injection process.

This clamping force ensure the mold won`t apart or getting loose and having products with sharps.The tonnage size is one of the most important factor when you want to select a injection molding machine. As it will determinate what kinds or size of plastic products you can produce with this molding machine.

We normally use the tonnage size as the main index of a injection moulding machine. You may heard some of these sentence:
I have a 200 ton injection machine, the mold will need a 300 ton molding machine,is the product can be produce with a 120 ton moulding machine?

What size injection molding machine do I need?

Normally, most plastic injection engineers will rough calcualate the machine`s tonnage with the product`s surface multiply by a index number.

If you are using square inch as the surface, then you can make it 2.5 times (higher flow materials like PS, PE and PP) to 4 times (lower flow materials like PA, PC and PSU) as the index number.

While your are using square cm as the surface, then you should make it 0.48 times (higher flow materials like PS, PE and PP) to 0.72 times (lower flow materials like PA, PC and PSU) as the index number.

SPECIAL PROMOTION

What is the formula to calculate tonnage?

There are many clamping force formula are used for different people for some different applications.  Below we will try to explain you the popular clamping force calcution formula：

Empirical Formula 1
Clamping force (T) = Clamping Force Constant Kp * Product Projected Area S (CM * CM) * Safety Factor(1+10%)

To properly calculate necessary clamp tonnage, you must first know the projected area of the molded part/s plus any runners.
Area can be calculated by multiplying length times width, A = L x W or A=πr2.

Above clamping force empirical formula is most used for fast calulate with more easy to have a rough size.  Most engineers will pick a bit larger size from the result even.  As it still have so risk for the products which have complex construction or the thickness on different position have big changed, or there are many perpendicular runner/corners.

Kp experience value for square cm:
PS/PE/PP – 0.32;
ABS – 0.30~0.48;
PA – 0.64~0.72;
POM – 0.64~0.72;
Add glass fiber – 0.64~0.72;
Other engineering plastics – 0.64~0.8;
For example, a product has a projected area of 410 cm2 and material is PE, How to calculate clamping force in this project`s injection molding ?
Calculated by above formula: P = Kp * S = 0.32 * 410*1.1 = 141 (T), 150-170 ton injection molding machine should be selected.

Kp experience value for square Inch:

Most injection molders are make it 2.5 times(higher flow materials like PS, PE and PP) or 4 times (lower flow materials like PA, PC and PSU)
the surface square inches of the part and an additional 10% as a safety factor.

If you have a part that is 120 square inches, you would need a injection machine with 300 tons clamping tonnage for injection molding.

After added 10% safety factor, the required press size would be 330 tons of clamping force.Then you will need a 330-350 ton injection molding machine for your project.

Empirical Formula 2
Clamping force (T) = Material Molding Pressure * Product Projected Area S (CM * CM) * Safety Factor(1+10%)
350bar*S(cm^2)/1000 * (1+10%)
As above, 350*410/1000*1.1=160T, choose 160T injection molding machine.

Accurate Calculation Formula 3

Two important factors in calculating clamping force:
1. Projected area (S) is the largest area viewed along mold opening and closing.
2. Determination of cavity pressure (P)
Cavity pressure is affected by following factors
(1) Number and location of gates
(2) Gate size
(3) Wall thickness of product
(4) Viscosity characteristics of plastics used
(5) Injection speed

3.1 Grouping of thermoplastic flow characteristics
Group 1: GPPS HIPS TPS PE-LD PE-LLD PE-MD PE-HD PP-H PP-CO PP-EPDM
Group 2: PA6 PA66 PA11/12 PBT PETP
Group 3: CA CAB CAP CP EVA PEEL PUR/TPU PPVC
Group 4: ABS AAS/ASA SAN MBS PPS PPO-M BDS POM
Group 5: PMMA PC/ABS PC/PBT
Group 6: PC PES PSU PEI PEEK UPVC

3.2 Viscosity grade
Each of above groups of plastics has a viscosity (flow capacity) rating. Relative viscosity grades of each group of plastics are as follows:
Group multiplication constant (K)
Group 1 * 1.0
Group 2 * 1.3～1.35
Group 3 * 1.35～1.45
Group 4 * 1.45～1.55
Group 5 * 1.55～1.70
Group 6 * 1.70～1.90

3.3 Cavity pressure is determined by ratio of wall thickness, flow to wall thickness
Look up table P0*P=P0*K (multiplication constant)
clamping force

3.4 Determination of clamping force (F)
F=P*S= P0*K*S

For example, part: calculation of clamping force of polycarbonate (PC) lamp holder
As shown in figure is a round PC plastic lamp holder with outer diameter of 220mm, wall thickness range of 1.9-2.1mm, and pin-type center gate design. The longest process for parts is 200mm.
Place where flow resistance of melt is the largest occurs at position where wall thickness is thinnest (1.9 mm), so value of 1.9 mm should be used when calculating required injection pressure.

* Process / wall thickness ratio calculation
Process / wall thickness = longest melt process / thinnest part wall thickness = 200mm / 1.9mm = 105:1

* Application of cavity pressure/wall thickness curve
Relationship between cavity pressure and wall thickness, process/wall thickness ratio is provided. It can be seen from figure that cavity thickness of 1.9mm,
cavity pressure of flow/wall thickness ratio of 105:1 is 160Bar. Data is applied to the first group of plastics. For other groups of plastics,
we should multiply corresponding multiplication constant K.

* Determination of cavity pressure value of PC
Flow properties of PC belong to viscosity class of sixth group. Compared with the first group, viscosity of PC is 1.7-1.9 times of that,
different viscosities are reflected in cavity pressure, so cavity pressure of PC lamp holder should be 160 bar*K (the viscosity grade of PC). P = 160*1.9 bar = 304 bar for safety reasons, we take 1.9 times.

* Projection area value of PC lamp holder
S = π*lamp holder outer diameter 2 / 4 = 3.14* 22*22 / 4 (cm2) = 380cm2

* Clamping force of PC lamp holder
F=P*S=304bar*380cm2=304kg/cm2*380 cm2=115520Kg or 115.5Ton, so 120T~130T injection machine can be used.

All above clamping force calculation formula requires you know how to calculate projected area injection molding.  So you can see the projected area calcution is the key to the calcution clamping force in injection molding.

Accurate Calculation with CAE software (MOLDFLOW, etc.)
Main basis for classification of injection molding machines is clamping force. It is true that large machine has a large clamping force and small machine has a small clamping force.  Clamping force in injection molding is one of the most important factor while you try to select a suitable injection molding machine for your project`s application.

This is traditional idea. It seems that clamping force is main indicator for measuring size of machine. However, as market becomes more and more subdivided, clamping force of machine cannot fully evaluate size of machine, and more and more special optimized machines are beginning to appear.

For example, when I produce thick-walled products, I need a large amount of melt glue and a small clamping force.
This is different from design idea of traditional machine. Rigidity of equipment board can be low and clamping force can be small, screw can be thick, screw can be deep, mold opening distance is large, opening and closing speed is slow.

However, when you want to produce thin-walled products, you will need high clamping force, a small amount of melting glue, a small opening distance, and a short cycle time. At this time, design is different, rigidity of equipment board is high, clamping force should be high, screw should be small, mold opening distance should be small, opening and closing distance should be fast.

For example, when I made PVC, PA, PS products, screw design has its own characteristics. Production of precision products is very demanding on repeatability of equipment.

Therefore, clamping force is main parameter to measure machine, but when evaluating a machine, it is necessary to look at comprehensive evaluation of other parameters.

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Please feel free to contact us if you still have questions on how to calculate injection molding machine`s tonnage or how to pick up a right size injection machine for your application.

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