Runner
Downstream channels after the sprue.
RunnerGlossary
What Is a Sprue? Injection Molding Explained
The sprue is the first channel plastic sees after it leaves the machine nozzle.
Glossary
The sprue is the first path from the machine nozzle
Stringing, pull marks, and drool often start here before the cavity ever fills.
Plastic leaves the injection unit through the nozzle and enters the mold sprue bushing. The sprue connects that entry to the runner system on cold runner tools.
Sprue pull quality shows up as roughness or material stuck in the bushing if temperatures or sizing mismatch the resin.
Hot runner systems may bypass a cold sprue slug, but the nozzle interface still needs alignment and heat management.
Glossary
How sprue shows up on real programs
Library photos illustrate molding and tooling context for this term.
- Use the term in RFQs with geometry and material context, not in isolation.
- Link to the design guide when the term affects steel or part design.
- Upload CAD when the term changes tooling scope or piece price.
Samples
Sprue related defects to photograph on T1
These photos shorten debugging threads with your molder.
Sprue stick or stringing on ejection from the bushing
Drool or leak at the nozzle tip between shots
Discoloration only in the sprue, suggesting heat history issues
Sprue length change after a material lot switch
Visual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
Injection molded production parts on a tray
Injection molded production parts on a tray
Engineer reviewing a molded part drawing
Engineer reviewing a molded part drawing
Plastic housing components from a steel tool
Plastic housing components from a steel tool
FAQ
Sprue questions
Is sprue weight included in part quotes?
Cold runner scrap belongs in resin planning even if buyers only count part weight.
Can sprue length affect cycle?
Indirectly, if sticking forces manual intervention or slows robot pick.
Does every tool have a visible sprue on the part?
No. Hot runner and some gate styles move or eliminate the cold sprue witness.
Next step
Keep feed path in the DFM thread
Upload CAD when material changes or gate moves are on the table.