Mold Best Assurance Company Limited
New rapid mold-temperature control technology allows molder to eliminate cosmetic defects like knit lines or sink marks in parts that require a glossy finish or feature texturing.
To conclude, traditional machined vents, sintered vents, and porous pins and plugs all have their place, depending on the part, flow path, and plastic material.
As an alternative to machining, mold components such as vent plugs can be produced from sintered metals (Fig. 4). The conventional approach is to compact and sinter metal powder around an array of copper wires. After sintering, the wires are pulled out, leaving tiny tubular “pores” straight through the sintered plugs.
One of the most common ways of adding venting is by manually machining it into the mold (Figs. 1-3). A parting-line vent is the most common type of machined vent. In this setup, the best location for a vent is opposite the gate, where the part gets filled last.
Venting is a small part of tool design that has a large effect on part quality, and the number of vents and their locations are therefore critical. But not all plastics designers and processors pay close enough attention to this crucial design aspect.
Wear due to the abrasiveness of the material adds to the maintenance frequency a tool requires. Filler and additives are commonly used today to enhance part performance. In these cases, preventative maintenance frequency should be increased beyond the normal recommendation.
Not only injection mold temperature determines melt temperature as it moves quickly through the mold. The melt temperature itself as it starts its journey through the injection mold (self-evidently) is the reference point. Speed of injection, particularly in thin sections, is of huge influence, as it will determine the degree of shear heating.
Many engineering materials like PBT (Polybutylene terephthalate) have a tendency of out-gassing. The best practices that I have to date are: Add 10mm wide vents spaced 30mm from each other all the way around parting line. Always follow the recommendations of the material company for vent depth.
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