PET Preform Mould Hardness And Wear Resistance
PET Preform Mould injection molding process is a very important plastic processing technology, one for PET plastic bottles, in most cases, plastic packaging plant will be used to blow molding the way of processing, but the injection molding process is particularly unique Processing advantages, for PET Preform Mould injection molding, the technical staff need to consider many factors, as follows.
PET Preform Mould PET plastic Description: PET chemical called polyethylene terephthalate, also known as polyester. Currently used in the customer is the most GF-PET, mainly to play the preform. PET has good rheological properties in the molten state, and the effect of pressure on the viscosity is greater than the temperature. Therefore, the flowability of the melt is mainly changed from the pressure.
PET chemical and physical properties: PET glass transition temperature of 165 ℃ or so, the material crystallization temperature range is 120 ~ 220 ℃. PET has a strong hygroscopicity at high temperatures. For glass fiber reinforced PET materials, bending deformation is very prone at high temperatures. The degree of crystallization of the material can be increased by the addition of a crystallization enhancer. Transparent products processed with PET have gloss and thermal distortion. Special additives such as mica can be added to PET to minimize bending deformation. If a lower mold temperature is used, transparent products can also be obtained using non-filled PET material.
Injection molding process: injection molding method is mainly used to enhance the molding of PET. Usually using screw-type injection machine. Screws are generally required to be hardened to avoid abrasion after prolonged use. The length of the injection nozzle hole should be as short as possible, its diameter should be controlled at about 3mm. Enhance the melting point of PET up to 260 ℃, in order to prevent nozzle clogging, should install a larger power heater. In addition, the tip of the nozzle hole is preferably machined into an inverted cone type as shown in Fig. 1, so that the molten material in the flow path and the nozzle can be easily cut off.
Injection molding machine: injection molding is mainly used to enhance the molding of PET. PET under normal circumstances can only use screw-type injection molding machine. It is best to use a mutant screw with a reverse ring at its top, with a high surface hardness and wear resistance. The aspect ratio is less than L / D = (15 ~ 20): 1 The compression ratio is about 3: 1. L / D too much material in the barrel to stay too long, excessive heat easily lead to degradation, affecting product performance. Compression ratio is too small shear heat less, easy to plastic poor, poor product performance. The glass fiber will be more broken, mechanical properties decline. Processing of glass fiber reinforced PET, the barrel wall wear more powerful, the use of wear-resistant materials, the use of wear-resistant materials or lining with wear-resistant materials. The nozzle is short as well, the inner wall requires polished, the aperture is as large as possible. It is better to use hydraulic brake valve type nozzle. The nozzle must be kept warm and the temperature is controlled to ensure that the nozzle does not freeze. But the nozzle temperature can not be too high, otherwise cause salivation. Before the start of molding must use low-pressure PP material, the barrel clean.
PET's main injection molding conditions: 1, barrel temperature. PET molding temperature range is narrow, the level of temperature will directly affect the performance of products. If the temperature is too low, the plasticization is not good, so that plastic parts depression, lack of material and other defects; the other hand, the temperature is too high, will cause overflow, nozzle salivation, color deepening, mechanical strength decreased, and even cause degradation. Usually, the cylinder temperature is controlled at 240 ~ 280 ℃, the glass fiber reinforced PET cylinder temperature is 250 ~ 290 ℃, shall not exceed 300 ℃, the nozzle temperature is generally lower than the cylinder temperature 10 ~ 20 ℃ .2, mold temperature. Mold temperature directly affect the melt cooling rate and crystallinity, crystallinity is different, the plastic parts of different performance. Usually, the mold temperature control in the 100 ~ 140 ℃, when forming thin-walled plastic parts, may take a small value; forming thick-walled plastic parts, the choice of large value. 3, injection pressure. PET melt flow is good, easy to shape, usually using medium pressure, the pressure of 80 ~ 140MPa, glass fiber reinforced PET injection pressure of 90 ~ 150MPa. Injection pressure should be determined, should consider the viscosity of PET, the type and number of fillers, gate location and size, plastic parts shape and size, mold temperature, injection molding machine type.