Property of friction between macromolecules when molten plastic flows is called plastic viscosity. Coefficient of this viscosity is called viscosity, so viscosity is a reflection of fluidity of molten plastic. The greater viscosity, the stronger viscosity of melt, the worse fluidity and the more difficult processing. In industrial applications, comparing fluidity of a plastic is not based on its viscosity value, but on its melt flow index (called MFI): so-called MFI means that at a certain melting temperature, melt is subjected to a rated pressure, weight of melt passing through standard die per unit time (usually 10 minutes). It is expressed in g/10min, such as injection molding grade PP material, grade is different, MFI value can vary from 2.5 to 30. Viscosity of plastic is not static. Change of characteristics of plastic itself, influence of external temperature, pressure and other conditions can all contribute to change of viscosity.
Tag: Melting temperature
POM (also known as Saigang, Trane). It is obtained by polymerization of formaldehyde as raw materials. POM-H (polyoxymethylene homopolymer) and POM-K (polyoxymethylene copolymer) are thermoplastic engineering plastics with high density and high crystallinity. Has good physical, mechanical and chemical properties, especially excellent friction resistance. POM is a crystalline plastic with obvious melting point. Once it reaches melting point, melt viscosity drops rapidly. When temperature exceeds a certain limit or melt is heated for too long, it will cause decomposition. Copper is a catalyst for POM degradation, copper or copper materials should be avoided in parts in contact with POM melt.
Polyphenylene sulfide, full name of polyphenylene sulfide, English name polyphenylene Sulfide (PPS for short), is a thermoplastic engineering plastic with a phenyl sulfide group on main chain of molecule. Polyphenylene sulfide has excellent heat resistance, and long-term use temperature is 200℃; it has good chemical resistance, and has excellent chemical properties similar to polytetrafluoroethylene; it also has special rigidity and good blendability with various fillers and other polymer materials. At present, it is the lowest price among high temperature engineering plastics and can be molded by general thermoplastic processing methods.
Problem:Â Cavity is not filled
Reasons: Melting temperature is too low; injection pressure is too small; gate is too small; hot nozzle is too small; mold temperature is too low; nozzle opening of melt cylinder is too small; hot nozzle is blocked.
Treatment: Increase temperature of hot nozzle and manifold, increase injection pressure, expand gate, increase mold temperature, install a large-size hot nozzle, increase discharge port of melt cylinder, and remove blockage.
Temperature Temperature measurement and control are very important in injection molding. Although it is relatively simple to make these measurements, most injection molding machines do not have enough sampling points or lines.On most injection molding machines, temperature is sensed by an electric thermocouple. A thermocouple is basically formed by connecting ends of two different wires. … Continue reading Injection parameters and control
Melt glue usually flows from nozzle into nozzle, but in some molds, nozzle is part of mold because it extends to bottom of mold. There are also two main types of nozzles: open nozzles and closed nozzles. In injection molding, open nozzles should be used more because they are cheaper and less likely to stay. If injection molding machine is equipped with a pressure-removing device, this nozzle can be used even for low-viscosity melts. Sometimes a closed nozzle must be used. This nozzle acts as a stop valve to block plastic in injection cylinder. Make sure that nozzle is correctly connected to nozzle sleeve. Top hole is slightly smaller than nozzle sleeve. This makes nozzle easier to withdraw from mold. Hole of nozzle sleeve is 1mm larger than that of nozzle, that is, radius of nozzle is 0.5mm smaller than radius of nozzle sleeve.
Temperature in brackets is recommended as basic setting value, stroke utilization rate is 35% and 65%, ratio of module flow length to wall thickness is 50:1 to 100:1
Comparing fluidity of a plastic is not based on its viscosity value, but on its melt flow index (called MFI): So-called MFI is that melt is weight of melt that passes through a standard die per unit time (usually 10 minutes) under a certain melting temperature and action of rated pressure of melt. Expressed in g/10min, viscosity of plastics is not static. Changes in characteristics of plastics, effect of external temperature, pressure and other conditions can all contribute to changes in viscosity.
Property of friction between macromolecules when molten plastic flows is called viscosity of plastic, and coefficient of this viscosity is called viscosity, so viscosity is a reflection of fluidity of molten plastic. The larger viscosity, the stronger viscosity of melt, the worse fluidity, the more difficult processing. Comparing fluidity of a plastic is not based on its viscosity value, but on its melt flow index (called MFI): So-called MFI is weight of melt that passes through standard die per unit time (Typically 10 minutes) under a certain melting temperature and melt is subjected to rated pressure. Expressed in g / 10min, viscosity of plastics is not static. Changes in characteristics of plastics, influence of external temperature, pressure and other conditions can all contribute to changes in viscosity.
PC/ABS polycarbonate and acrylonitrile-butadiene-styrene copolymers and mixtures Typical applications: computer and commercial machine housings, electrical equipment, lawn gardening machines, automotive parts dashboards, interior finishes, and wheel covers. Injection Molding Process Conditions : Drying: Drying before processing is a must. Humidity should be less than 0.04%. Recommended drying conditions are 90~110C for 2~4 hours.
Gud Mould 