date：2019-12-24view：797
hot runner mold has been successfully used in processing various plastic materials. such as pp, pe, ps, abs, pbt, pa, psu, pc, pom, lcp, pvc, pet, pmma, pei, abs/pc, etc. any plastic material that can be machined with a cold runner mold can be machined with a hot runner mold. therefore, the properties of plastics are particularly important. for example: ablation temperature, pressure, viscosity, specific heat... and so forth must be noticed. the scope of plastics is so wide that further study is not possible, but we will clarify it according to its knowledge.
1. the plastic
plastic can be formed and processed because it deforms under the action of temperature and pressure, and can be divided into four forms according to the heating temperature. high elastic form (rubber state), t1 ~ t2, due to external deformation, not to reach the molten form is not easy to form. viscous flow state (plasticized form) : t2 ~ t3, can be arbitrarily shaped. differentiation form: t3, plastic begins to split, showing gas differentiation and even carbonization.
2. form the premise
the following are the general plastic forming requirements. for each bifurcated plastic, bifurcations can be made relative to the area of formation, but the process analysis is the same. therefore, good mold designers should study the molding area and processing characteristics of each plastic.
3. fluidity of molten plastic
ordinary fluids (such as water, oil, etc.) move in newtonian ways. plastic melt looks like a popular fluid, but it's actually the length of a newtonian fluid. in a newtonian fluid, the shear stress changes, but the viscosity does not. like plastic melt, the viscosity also changes obviously when the shear stress fluctuates. for example, in a newtonian fluid, when the pressure increases from 1 to 10, the outflow increases 10 times. the same can be done for plastic melts, where the pressure increases from 1 to 10 by a factor of 100, 500, or even 1,000 (depending on the plastic).
4. selection of plastic materials
plastic should be chosen at the beginning of the final product design, but most molds are not considered. however, if possible, the selected information should keep the mold manufacturing brief. shape shortening rate is small (ps, abs, pc) size accuracy is easy to obtain. the pressing rate (pp, pe, pom) is more difficult to achieve the dimensional accuracy (the public service amount of the mold is 1/6 of the public service amount of the molding product). when the viscosity is relatively high (abs, etc.), the solution is not easy to flow into the crack, but even if the gap is small, the solution with low viscosity (such as pa, pom) is easy to enter.
hose with lower forming temperatures (ps, etc.) are easier to form and have a faster forming cycle, but those with higher forming temperatures (pc, etc.) are slower.
when molding is not easy to deformation or differentiation (ps, pe, pp, etc.), mass production is not easy to cause defective quality instability, but when molding is not easy to deformation or differentiation (if there is no strict requirements) in the premise of molding (the mold can be in the premise of molding fine control) will not be able to mass production. this problem is especially serious under hot runner.
