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2026
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09
Sprue Bushings and Locating Rings: The Entry Point of Every Mold
Author:
Timould
Not sure whether you're dealing with sprue bushings or locating rings? These two small parts sit at the very entrance of every mold, guiding molten plastic from the machine nozzle into the mold cavity.
What They Do
Locating ring centers the mold on the injection machine platen, making sure the machine nozzle and the sprue bushing align perfectly every time.
Sprue bushing (also called sprue bushing or gate bushing) carries the melt from the nozzle through the mold plate into the runner system. Its tapered bore feeds plastic into the cavity while keeping flow smooth and pressure loss low.
Common Types
Locating rings come in standard diameters (e.g., 100 mm, 125 mm, 150 mm) to match common machine brands like Nissei, Engel, or Haitian — always check your machine's specification.
Sprue bushings vary mainly by bore design:
- Straight taper — the most common, suits standard thermoplastics
- Stepped / multi-stage taper — for large parts or long flow paths
- Extended / long type — reaches through thick mold plates
- Insulated or heated types — for heat-sensitive materials or to prevent premature cooling
Material is usually hardened tool steel with a polished, wear-resistant bore. Brass or beryllium copper versions are used where rapid heat transfer matters.
Why Matching Matters
A wrong locating ring size means the mold won't center on the machine — leading to nozzle misalignment, leakage, and damage to both parts.
A worn or poorly polished sprue bushing causes:
- Stringing / drooling — melt sticking at the nozzle
- Cold slugs — solidified plastic entering the cavity, causing defects
- Excessive pressure loss— short shots and uneven filling
Quick Tips
- Match the locating ring OD to your machine platen, not just the mold.
- Keep the sprue bushing bore polished — it directly affects demolding and cycle time.
- Check for wear at the nozzle contact area regularly; replace before scoring starts.
- Use a sprue puller or cold slug well to keep the first bit of cold plastic out of the cavity.
Every mold starts at the sprue bushing. Choose the right one, and the rest of the process runs smoother.
sprue bushings,locating rings,mold components,injection molding
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