A, classification and properties of nylon classification:
1, according to the number of carbon atoms of diamine and dibasic acid, composed of two monomer synthetic nylon: 46, 66, 610, 66, 613, 1010, 1313,
2, according to the monomer containing named in the number of carbon atoms: nylon 4, 5, 6, 7, 8, 9, 11, 12, 13
1, nylon has good toughness, self lubrication and wear resistance, chemical resistance, gas permeability, and oil resistance, non-toxic, and the advantages of easy coloring, so the nylon is widely applied in industry.
The technological characteristic of the rheological properties of nylon, nylon: most for crystalline nylon resin, when the temperature exceeds its melting point, the melt viscosity is small, the melt liquidity is wonderful, should prevent excessive edge. Due to the melt condensation speed at the same time, should prevent material blocking the nozzle, runner and gate products caused by insufficient phenomenon. Mould overflow boundary value of 0.03, and the melt viscosity are sensitive to temperature and shear stress change, but is more sensitive to temperature, lower viscosity of the melt from the cylinder temperature first.
Four, nylon nylon absorbent, water absorption and the dry wet nylon in molding process, characterized by viscosity fell sharply and mixed with surface silver bubble products, the products obtained mechanical strength decreased, so the material must be dry before processing.
Crystalline: in addition to the transparent nylon, nylon mostly for the crystallization of polymer, high crystallinity and tensile strength, abrasion resistance, hardness, lubricity, and so on a performance improvement, thermal expansion coefficient and water tends to decline, but bad for transparency and impact resistance. Had a greater influence on the mold temperature on the crystallization, mould temperature high crystallinity, die temperature bottom end of crystallinity.
Shrinkage: similar to other crystalline plastics, nylon resin shrinkage rate larger problems, the maximum nylon with crystallization of contraction, when products crystallinity big products shrinkage increases, in the process of forming lower mold temperature, increasing injection pressure, lower temperature will decrease the contraction, but the internal stress of products is more easy to deformation. PA66 shrinkage rate of 1.5 to 2%
Molding equipment: nylon molding, mainly pay attention to prevent "nozzle flow delay phenomenon", so the nylon material processing generally choose the self-locking type nozzle.
Products and moulds:
1, the products of wall thickness Do so than for 150-200 between nylon, nylon products wall thickness below 0.8 mm generally between 1-3.2 mm, and the products of contraction associated with products of wall thickness, the thicker the thickness contraction.
2, exhaust nylon resin overflow boundary value is about 0.03 mm, so the vent groove should be controlled below 0.025.
3, mold temperature products thin wall molding mould heating control or require high crystallinity, required products have certain flexibility of general use cold water temperature control.
Third, molding technology of nylon
Cylinder temperature: as nylon is a crystalline polymer, so obvious, melting point of nylon polymer in the injection molding of the selected material barrel temperature with the performance of the resin itself, equipment and products of shape factors. Nylon 6 melt temperature is 225 ℃ at the bottom, nylon 66 is 260 ℃. * due to the poor thermal stability of nylon, should not be so high temperature for a long time to stay in the cylinder, lest cause the material color is yellow, due to the liquidity of nylon is better at the same time, the temperature over flow quickly after its melting point.
Injection pressure: nylon low melt viscosity, good fluidity, but the cooling speed faster, the complex shape and wall thickness thinner products are easily appear shortage problem, so still need high injection pressure. Pressure is too high, usually products will overflow edge problems; Pressure is too low, products can produce corrugated, bubble, obvious welding scar or lack of product defects, most varieties of nylon injection pressure does not exceed 120 mpa, the general selection within 60-100 mpa is meet the requirements of most of the products, as long as the products don't appear bubbles, defects such as dents, generally do not want to use high pressure maintaining pressure, so as not to cause internal stress increased.
Injection speed: for nylon, injection speed for quick profit, can prevent the ripples caused by too fast cooling, molding shortage problem. Fast injection speed impact on the performance of the products is not prominent. Mold temperature mold temperature on the crystallinity and the molding shrinkage has certain influence, anti-embrittlement high crystallinity, wear resistance, hardness and elastic modulus increased, decreased water imbibition, products molding shrinkage rate increase; Low mold temperature low crystallinity, good toughness and elongation is higher.