Engineering plastics can be used as engineering materials and plastics that replace metal in manufacturing machine parts. Engineering plastics have excellent comprehensive properties, such as high rigidity, low creep, high mechanical strength, good heat resistance, and good electrical insulation. They can be used for a long time in harsh chemical and physical environments. They can replace metals as engineering structural materials, but they are more expensive and have smaller output.
Tag: amorphous plastics
Characteristics of plastic raw materials have a huge impact on deformation of molded products. Different raw materials have different molecular structures and intermolecular forces, which manifest themselves in different fluidity, orientation characteristics, shrinkage characteristics, mechanical and physical properties. Therefore, shrinkage rates produced cannot be same. Different molecular structures of plastic materials determine type of plastic material; and different internal additives determine different properties of same plastic, including fluidity, anti-degradation performance, flexibility, flame retardancy, and UV resistance. Although most of time, as mold factories and injection molding factories, we cannot decide which plastic materials to use, but understanding differences of plastic materials and their impact on product deformation is very helpful for us to analyze and solve problems. With this knowledge, we can predict deformation to a greater extent in the early stage. On the one hand, we can give customers reasonable suggestions (such as well-founded advice to customers to relax unrealistic shape and size tolerance requirements; suggest reasonable design structures to compensate for deformation). On the other hand we can design effective preventive measures on mold (such as targeted design of gating system and cooling system).
Engineering plastics have been widely used in our daily life mainly as engineering materials and to replace metal to manufacture machine parts. In automobile industry, lightweight, safety and environmental protection of automobiles have been realized by replacing steel with plastic. In selection of engineering plastics, material engineers must consider not only mechanical properties, aging resistance, etc. of material, but also its thermal properties. There are many thermal performance tests of engineering plastics, what do we need to know?
【Abstract】: This paper proposes a new online inspection method for plastic injection molding process. Ultrasonic attenuation behavior of amorphous plastics (GPPS) and crystalline plastics (PP) during injection molding was studied by using reflection and transmission behaviors of ultrasonic waves at heterogeneous interface, response characteristics to temperature and pressure, influence of process parameters (mold temperature and holding pressure) on ultrasonic attenuation behavior of amorphous plastics was discussed. Experimental results show that ultrasonic attenuation signal can accurately reflect information of injection, cooling, shrinkage and crystallization process of plastic melt, which can be used for on-line detection of injection molding process.
(1) Crystalline is a solid in which internal particles (molecules, atoms, ions) of minerals are arranged regularly to form a certain lattice structure, which is called crystalline (crystal). Result of regular arrangement of particles is shown as regular geometric shapes. Most minerals in nature are crystals. (2) Amorphous: Any solid with irregular arrangement of particles (molecules, atoms, ions) inside a mineral without a lattice structure is called non-crystalline (or non-crystalline). This type of minerals is not widely distributed, and there are few types, such as volcanic glass.
Generally speaking, for crystalline plastics, when processing temperature is higher than its melting point, its fluidity is better, cavity can be filled quickly, and its required injection pressure can also be smaller. Fluidity of amorphous plastics is poor, injection speed is slower, and injection pressure it needs is larger. Therefore, when designing mold, you can design a reasonable runner system size according to fluidity of plastic. On the one hand, it can avoid waste of material due to large size of runner system, at the same time extend injection molding cycle. On the other hand, it can avoid too small size of runner system, which causes filling and pressure holding difficulties. Of course, there are exceptions. For example, although polystyrene is an amorphous plastic, its fluidity is very good. Indicators that reflect fluidity usually have melt index (MFR) and apparent viscosity. MFR refers to mass of melt flowing out of standard capillary every 10min under a certain temperature and load in melt flow rate meter, its unit is g/10min. For high molecular polymers, under normal injection molding conditions, their flow behavior mostly does not obey Newton's law of flow and belongs to non-Newtonian fluids. Ratio of their flow shear stress to shear rate is called apparent viscosity. Apparent viscosity is not a constant at a certain temperature, but can change with shear stress, shear rate, and even some changes with time.
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