The molding process with PET preform injection machine is one of the most important technologies for plastic processing. This article systematically introduces the processing of PET by preform PET injection machine. This content includes PET features, characteristics, injection molding process, PET preform injection machines, process conditions, processing methods, etc., and helps PET manufacturing plants gain useful knowledge in minutes.
Do you know about the molding process with PET preform injection machine?
Plastic injection molding process is one of the most important technologies for plastic processing and preform PET plastic bottles, most plastic packaging factories adopt the production process with pneumatic plastic machine, but the PET preform injection molding process It has unique processing advantages. For injection molding, technical personnel must consider many factors.
Introduction of PET plastic
The chemical name of PET is polyterephthalate alcohol ester, also known as polyester. Currently, the most used by customers is GF-PET, mainly for the production of bottle preforms.
The rheological properties of PET are better in the melt state, and the effect of pressure on viscosity is greater than that of temperature. Therefore, the flow properties of melts are mainly changed by pressure.
specifications of PET used in preform PET injection machine
The conversion temperature of PET is about 165 ℃ and the material temperature range is 120 ~ 220 ℃. PET has strong hygrometry at high temperature. For glass fiber reinforced PET materials, bending deformation at high temperature is very easy.
The crystallinity of the material can be improved by adding a crystal enhancing agent. Transparent products made with PET have gloss and heat distortion temperature. Special additives such as mica can be added to PET to minimize bending deformation. Clear products can be obtained using unfilled PET materials if lower mold temperatures are used.
Molding process with PET preform injection machine
PET preform injection machine is mainly used for PET molding. To prevent wear after long-term use, the auger should usually be made of reinforced material. The length of the nozzle hole of the injection device should be as short as possible, and the diameter of the injection device should be controlled to about 3 mm.
The melting point of reinforced PET is up to 260℃. A higher power heater should be installed to prevent the nozzle from clogging. In addition, the tip of the nozzle hole should be processed as an inverted cone, so that the molten material in the flow channel and the nozzle can be cut off easily.
PET preform injection machine
PET can be generally molded by PET preform injection machine.
It is better to choose a reinforced spiral that has surface hardness and wear resistance with a ratio of length to diameter L/D = (15~20):1 and compression about 3:1
Too much material stays in the hopper for too long, too much heat can cause degradation and affect product performance. The compression ratio is too small for less heat generation, easy plasticization and poor performance. On the other hand, breakage of glass fibers increases and the mechanical properties of fibers decrease. When the glass fiber reinforced PET is reinforced, the inner wall of the hopper is highly abraded, and the barrel must be made of wear-resistant material or coated with wear-resistant material.
Since the nozzle is short, the inner wall needs to be polished and the aperture is as large as possible. Good hydraulic valve type nozzle. The nozzle must have heat preservation and temperature control to ensure that the nozzle does not freeze or block. But the temperature of the nozzle is not too high, otherwise it will cause the material to discharge. Before starting molding, low pressure PP material should be used and the barrel should be cleaned.
The main conditions of molding with PET preform injection machine
1, hopper temperature. The temperature range of PET formation is small, and the temperature directly affects the performance of the product. If the temperature is too low, it becomes hard to make plastic parts and causes dents and defects in production. On the other hand, too high temperature causes leakage, discharge of material from the nozzle, deep color change, reduction of mechanical strength, even destruction. Usually, the temperature of the hopper is controlled at 240~280℃, and the temperature of the glass fiber reinforced PET hopper is 250~290℃. The temperature of the nozzles should not exceed 300℃, and the temperature of the nozzles is generally lower than the temperature of the hopper.
2, mold temperature. The temperature of the mold has a direct effect on the cooling speed and crystallinity of the melt, and its crystallinity is different and the properties of plastic parts are different. Usually, the mold temperature is controlled at 100~140°C. When thin-walled plastic parts are formed, it is less important, but when thick-walled plastic parts are formed, more temperature control is recommended.
3. Injection pressure. PET melts have good fluidity and are easily formed. Medium pressure is usually used, the pressure is 80~140MPa, and the injection pressure of glass fiber reinforced PET is 90~150MPa. To determine the injection pressure, the viscosity of PET, the type and amount of filler, the location and size of the opening, the shape and size of the plastic piece, the temperature of the mold, the type of PET preform injection machine, etc. should be considered.
How much do you know about the production of PET plastic products?
1, plastic pet
Because the PET macromolecule contains a lipid base and has a certain hydrophilicity, the pellets are sensitive to water at high temperatures. When the moisture content exceeds the permissible limit, the molecular weight of PET decreases and the products become colored and brittle. In this case, the material must be dried before processing. The drying temperature is 150, 4 hours, which is generally 170, 3-4 hours. The air evacuation method is used to test whether the material is completely dry or not.
2. Selection of PET preform injection machine
Due to the short processing time after the melting point and the high melting point, it is necessary to choose an injection system with more temperature control part and less self-heating during plasticization. The actual weight of the product cannot be less than 2.3 grams. The injection volume of the device based on these requirements, in recent years, Pars Company has developed a series of special PET plasticizing systems in small and medium sizes. The clamping force is selected with more than 6300 tons per square meter.
3. Mold and nozzle design of preform PET injection machine
PET bottle preform is usually molded by hot runner mold. The insulation between the mold and the PET injection machine is best insulated with a thickness of 12 mm, and the thermal insulation plate can withstand high pressure. The outlet should be sufficient to prevent overheating or fragmentation, but the depth of the port is usually not more than 0.03 mm, otherwise it will lead to the production of waste.
4. Melting temperature
It can be measured by the air bounce method. At 270-295 ℃, the improvement level of GF-PET can be adjusted to 290-315 ℃.
5. Injection speed of preform PET injection machine
The general injection speed is fast, which avoids initial freezing of the injection. But too fast injection increases the cutting rate of the material and makes it brittle. The injection is usually completed in 4 seconds.
The lower the better, usually no more than 100 times and usually not used.
7. Molding time
Do not use too long molding time to prevent molecular weight loss. Try to avoid temperatures above 300 degrees Celsius.
8. Precautionary measures
If the mold temperature control is not good or the material temperature control is not suitable, the production of “white and dull” products will happen. The mold temperature should be low and uniform, the cooling rate should be fast, so the crystallization is less and the product is transparent.
Purchase preform PET injection machine
The price of preform PET plastic injection machine can be very diverse according to the features and options. For example, the production speed and the daily production rate of the product are among the influencing factors in the price of the PET injection machine. To know the prices and get guidance and advice, contact our experts.