PET injection molding machine is used to make 5 gallon PET preform.
An injection molding machine (also spelled injection moulding machine) also knowns as an injection press. It is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.
The PET preform injection molding machine is a special equipment for producing PET preforms. And it mainly uses to make polyethylene terephthalate (PET) materials into preforms through injection molding process. PET Preform Injection Molding Machine is an industrial equipment uses to process polyethylene terephthalate (PET) raw materials into preforms. Its basic definition is: by injection molding process, molten PET material injects into a mold to form preforms with specific shapes and sizes. And then they used for blow molding into final PET containers, such as beverage bottles, mineral water bottles, cosmetic bottles, etc.
In the manufacturing 5-gallon PET preforms process , the PET preform injection molding machine works as follows:
- material preparation
- injection molding
- Cooling and demoulding
- Post-processing
- Key technologies of PET preform injection molding machines
5 gallon PET preform machine: material preparation
PET materials need to be thoroughly dried before processing to remove the impact of moisture absorption. The drying temperature of PET is usually 145 ° C to 165 ° C, and the recommended duration is 5-9 hours. Among them, drying at 145 ° C for 9 hours. This considers the best solution to avoid material degradation.
PET material characteristics
- Excellent physical properties: PET has good compressive strength, creep resistance, impact resistance, and transparency, as well as good gas barrier performance, making it widely used in food and beverage packaging containers.
- Moisture absorption: PET is a hygroscopic material, and high humidity can cause it to hydrolyze at high temperatures, reducing its physical and mechanical properties and affecting the quality of preforms. Therefore, PET particles must dry to a moisture content below 0.05% before injection molding.
- Thermal sensitivity: PET is prone to thermal decomposition at high temperatures, producing aldehydes and reducing the quality of preforms. Therefore, the design of PET injection screws should have low shear characteristics to reduce the risk of thermal cracking.
- Crystallinity: PET is a crystalline resin with a melting point of approximately 245 ° C and a molding temperature typically between 290 and 315 ° C. To ensure good molding results, the temperature of PET preform molds controlls between 270 and 295 ° C.
5 gallon PET preform: injection molding
The neck size of 5-gallon PET preforms is usually 55mm. And the weight range is generally between 650g and 800g. Specifically, common weights include 700g, 730g, 750g, 780g, and 800g. These preforms are typically made of 100% fresh PET resin, which has high transparency and toughness.
The molten PET material injectes into the mold cavity. It has the pre-designed shape of the preform. The injection process requires control of PET preform injection molding machine injection speed, pressure and time. To ensure that the preform molds evenly and without defects.
The typical process of injection molding includes the following steps:
Mold closure
The two parts of the mold (fixed mold and moving mold) are closed to form a sealed cavity.
Plastic melting
Plastic particles melt into a molten state through a heating system (such as a drum heating belt).
Injection
Molten plastic injects into the mold cavity through the high-pressure push of a screw or plunger.
Pressure holding
Maintain a certain pressure inside the mold thus to ensure that the plastic fully fills and prevent shrinkage.
Cooling and demoulding
After injection, the mold closes and cools the preform to set its shape. Cooling time is an important factor affecting production efficiency. So an efficient cooling system (such as hot runner mold) is very important. After cooling, the preform demoulds from the mold and enters the next process.
Cooling water temperature
The temperature of the cooling water should control at 15-20 ° C to ensure rapid cooling of PET preforms and reduce haze.
Cooling water pressure
The pressure of the cooling water should be about 5 Bar to provide sufficient cooling effect.
Cooling time
The cooling time is usually 10-30 seconds, depending on the mold design and production requirements.
Cooling method
Water cooling is more efficient than air cooling and can better control the cooling rate.
Mold temperature
The cooling water temperature of the mold should be 6 ° C, combined with a sealed locking space and dry air with a dew point of 3 ° C to ensure cooling effect.
Cooling system: It recommends to use a water chiller to maintain the low temperature and stability of the cooling water.
Demoulding operation
Before demolding, it is necessary to ensure that the PET preform has been sufficiently cooled to around 80 ° C to prevent stress concentration caused by material shrinkage.
The mold opening stroke should be long enough to ensure that the preform can smoothly eject without damage. It usually recommends to have a mold opening stroke of 420mm or more to accommodate the length of 5-gallon preforms.
A margin of 1-2cm should be reserved for the ejection stroke to ensure stability during the demolding process.
During the demolding process, it should adopt a staged ejection method. With medium pressure and slow ejection first, followed by medium pressure and medium speed ejection, to reduce damage to the preform.
The demolding force should be large enough to overcome the crystallization shrinkage force of PET material, generally providing 1 ton of demolding force per hole.
Post-processing
The preform after demoulding may require further processing. Such as cleaning, drying, etc., to ensure its surface quality and hygiene standards.
Cooling and removal
After injection molding, PET preforms need to be cooled to room temperature in the mold. During the cooling process, the mold temperature is usually controlled by a cooling water system to ensure the stability of the pre formed shape. After cooling is completed, the preform is removed by a robotic arm or robot.
Quality inspection
Pre formed products need to undergo quality inspection after cooling to ensure that their size, transparency, and surface defects meet the requirements. For example, the RANSAC algorithm and grayscale consistency can be used to detect bottle mouth defects in PET preforms [47]. In addition, surface defects can also be identified and classified through multi stream deep convolutional neural networks (multi stream deep CNN).
Storage and transportation
Qualified preforms require appropriate storage and transportation to prevent deformation or contamination during subsequent processing. The storage environment typically requires temperature and humidity control to maintain the physical and chemical stability of the preform.
Re heating and blow molding
During the blow molding process, the preform needs to be heated again above the glass transition temperature for stretching and blow molding. The heating process usually uses infrared heating or hot air systems to ensure uniform heating of the preform [41]. The heated preform is stretched and blow molded to form the final PET bottle.
Post processing and optimization
After blow molding, PET bottles may require further post-processing, such as heat setting, cutting, and packaging.
Key technologies of PET preform injection molding machines
- Screw design: The corrugated screw can improve the plasticizing effect of PET and reduce the plasticizing time and energy consumption.
- Mold design: The use of hot runner molds can improve production efficiency and product quality.
- Control system: Modern injection molding machines usually equipp with advanced control systems. That can accurately control injection parameters and mold temperature to ensure the quality and consistency of the preforms.
Therefore, through the application of these technologies, the PET preform injection molding machine can efficiently produce 5-gallon PET preforms that meet the requirements and meet the needs of different industries for packaging containers.
Haichen PET injection molding machine
Haichen is one Chinese injection molding machine manufacturer in Ningbo. In addition, Haichen has more than ten years of rich experience in the production of plastic injection molding machines. All our servo energy saving injection molding machines quality are under CE safety standars certificate.
Haichen have rich experience of production PET preform injection molding machine. So we can supply suitable and complete PET preform production line as per client’s specific demand.
