Hot runner molds have been successfully used for processing various plastic materials. Such as PP, PE, PS, ABS, PBT, PA, PSU, PC, POM, LCP, PVC, PET, PMMA, PEI, ABS/PC and so on. Any plastic material that can be machined with a cold runner mold can be machined with a hot runner mold. Therefore, the characteristics of plastics are particularly important. For example: ablative temperature, pressure, viscosity, specific heat... And so on must be noticed. Because the range of plastics is so broad, it cannot be studied further, but we will clarify based on their knowledge.
1. Plastic
The reason why plastic can be formed and processed is that it deforms under the action of temperature and pressure, and can be divided into four forms according to the heating temperature. The highly elastic form (rubber state), T1~T2, is not easy to form due to external deformation. Viscous flow state (plasticized form) : T2~T3, can be arbitrarily formed. Form of differentiation: T3, the plastic begins to divide, showing gas differentiation and even carbonization form.
2. Formation premise
The following is the forming premise of ordinary plastics. For each type of forked plastic, the opposite formation area can be forked, but the process analysis is the same. Therefore, a good mold designer should study the molding area and processing characteristics of each plastic.
3. Fluidity of molten plastic
Ordinary fluids (such as water, oil, etc.) behave according to Newtonian definitions. Plastic melt looks like a popular fluid, but is actually the length of a Newtonian fluid. In a Newtonian fluid, the shear stress changes, but the viscosity does not. As with plastic melt, when the shear stress fluctuates, the viscosity also changes significantly. For example, in a Newtonian fluid, when the pressure increases from 1 to 10, the outflow increases 10 times. When the same operation is performed on plastic melt, when the pressure is increased from 1 to 10, it can be increased by 100 times, 500 times, or even 1000 times (depending on the plastic).
4. Selection of plastic material
Plastic should be selected at the beginning of the final product design, but most molds are not considered. However, if possible, the selected information should make the manufacture of the mold brief. Dimensional accuracy with small molding shortening rate (PS, ABS, PC) is easy to obtain. The reduction rate (PP, PE, POM) is more difficult to achieve 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 large (ABS, etc.), the solution is not easy to flow into the crack, but even if the gap is small, the solution with small viscosity (such as PA, POM) is easy to enter.
Those with lower forming temperatures (PS, etc.) are easier to form and have faster forming cycles, but those with higher forming temperatures (PC) are slower.
When molding is not easy to deform or differentiate (PS, PE, PP, etc.), mass production is not easy to cause quality instability of defective products, but when molding is not easy to deform or differentiate (if there are no strict requirements) under the premise of molding (mold can be in the premise of fine control of molding) will not be able to mass production. This is especially problematic under hot runways.
