Twenty Kinds of Plastics and Their Properties—(2) PA6
2.PA6 polyamide 6 or nylon 6
Typical application range:
It is widely used in structural parts because of its good mechanical strength and stiffness. Because of its good wear resistance, it is also used to make bearings.
Injection molding process conditions:
Drying process: because PA6 is easy to absorb water, so the drying before processing should be paid attention to. If the material is supplied in a waterproof material, the container shall be kept closed. If the humidity is greater than 0.2%, it is recommended to dry for 16 hours in the hot air above 80 °C. If the material has been exposed to the air for more than 8 hours, it is suggested that a vacuum drying at 105 and more than 8 hours is recommended.
Melting temperature: 230~280 °C, for the enhanced variety 250~280 °C.
Mold temperature: 80~90 °C. The mold temperature greatly affects the crystallinity, and the degree of crystallinity affects the mechanical properties of the plastic parts. The crystallinity of the structural components is very important, so it is suggested that the mold temperature be 80~90 °C. For the thin-walled, the longer flow of the plastic parts also recommend the application of higher mold temperature. Increasing the mold temperature can improve the strength and stiffness of the plastic, but it reduces the toughness. If the wall thickness is more than 3mm, it is suggested to use a low temperature mold at 20~40 °C. For glass reinforced material, the mold temperature should be more than 80 °C.
Injection pressure: generally between 750~1250bar (depending on material and product design).
Injection speed: high speed (slightly reduced to reinforced material).
Runner and gate: the location of the gate is very important because of the short solidification time of the PA6. The gate diameter of the gate should not be less than 0.5*t (here t is the thickness of the plastic part). If the hot runner is used, the gate size should be smaller than the conventional channel, because the hot runner helps prevent the premature solidification of the material. If the subsurface gate is used, the minimum diameter of the gate should be 0.75mm.
Chemical and physical properties:
The chemical properties of PA6 are very similar to that of PA66. However, the melting point is low and the range of process temperature is very wide. Its impact resistance and solubility are better than that of PA66, but the hygroscopicity is stronger. Because many of the quality properties of the plastic parts are affected by the hygroscopicity, it is necessary to take this into full consideration when using PA6 to design the product. In order to improve the mechanical properties of PA6, a variety of modifiers are often added. Glass is the most common additive, and sometimes in order to improve the impact resistance also added to synthetic rubber, such as EPDM and SBR. For products without additives, the shrinkage rate of PA6 is between 1% and 1.5%. Adding glass fiber additives can reduce the shrinkage to 0.3% (but a little higher in the direction perpendicular to the flow). The shrinkage rate of the formed assembly is mainly influenced by the crystallinity and hygroscopicity of the material. The actual shrinkage rate is also related to the function of the plastic part design, wall thickness and other technological parameters.