Polish the sprue in the draw direction. Cold Runner Design. When designing cold runner systems, use the same guidelines that apply to most engineering resins. Gates should be large enough with minimal sharp transitions to minimize gate blush and prevent premature gate freeze. Where part size and cooling allow, pinpoint gating may be from inside the part or into a recess to hide the vestige.
Many vendors have designs specifically for polyester-type polymers.
In general, the types that work well have heaters external to the melt stream with no spots for polymer hold-up. Also, drops with integral cooling around the gate give more consistent temperature control and vestige formation. Types of hot drops not recommended because of the potential for degradation are those that have heaters internal to the melt stream but no heaters or insulation external to the melt stream. Some polyester materials like PET tend to crystallize and whiten at the gates in hot runner systems. This may require gate placement into noncritical areas or into a post or tab that can be hidden or removed.