Influence of temperature in the production process filament
The source of heat causing the temperature rise heater is disposed on the cylinder. In addition, material is mixed intensively in the channel, which is accompanied by a process of internal friction of the replaced heat which increases the temperature of the material.
Depending on the temperature change in the nature of flow, with a view to plastic flow at lower temperatures and for Newtonian flow at higher temperatures. The inverse of liquidity is the viscosity. The viscosity of the polymer decreases with increasing temperature, which results from the increased mobility of macromolecules and free volume between them.
At elevated temperatures and at low strain rates thermoplastic polymeric materials they behave as a viscous liquid. This viscoelastic behavior of the polymer makes it possible to transmit the desired shapes utility products from thermoplastic polymeric materials. As the temperature increase is reduced because the viscosity of the polymer which is easier to deform under such conditions. With a reduction in viscosity is related to the creep rate as polymers, which increases as the increase of stress and temperature. However, at too high a temperature may overheat and thermal degradation of the material. Upon reaching a certain temperature called the decomposition temperature is a polymer destruction (they break chemical bonds).
Due to the performance of the extrusion process should be applied so the highest possible temperature, but below the temperature limit. The temperature dependence of the viscosity is stronger for amphoteric materials (ABS, SAN, PC), than for the semi-crystalline polymers (HDPE, LDPE, PP, PE).
Temperature also affects the amount of heat shrinkage . The shrinkage is defined as the reduction in volume or size reduction . The higher the temperature the greater the shrinkage as it sets. This means that by varying the temperature can control the diameter of the extruded filament . A higher temperature causes a reduction in diameter, while a decrease in temperature causes an increase in the diameter of the extruded filament .
Effects on the resulting filament diameter is also a phenomenon called Barus effect . It involves swelling stream plasticized polymer leaving the extruder head . As a result, the occurrence of this effect, the filament cross-sectional area is larger than the sectional area of the nozzle orifice extrusion.
The numerical value Barus effect is defined as the ratio of the characteristic quantity of the material stream leaving the passageway to the corresponding characteristic quantity of such a channel eg . the ratio of the diameter df of filament diameter dk channel :
β= df / dk x 100%
This value depends on many factors, primarily on the shear rate , pressure, plastic material residence time in the channel, the channel dimensions , eg . Its length.
Temperature also has a big impact on the value of the numerical effect Barus . When the temperature rises , this value decreases. So the diameter of the filament decreases. Also decreases with increasing residence time of the material in the channel and the channel length . In contrast, increased with increasing shear rate and pressure.
