Z-Pin vs. Ejector-Pin vs. Fixed-Side Runner Change Pins: How to Choose

Three Configuration Overview

Z-Pin Type

A Z-pin runner change pin is a cylindrical pin with a through-bore or cross-bore that creates a vertical flow channel between two runner channels on different plate surfaces. The name comes from the Z-shaped flow path the resin follows — horizontal in one runner, vertical through the pin, then horizontal in the second runner.

Use Z-pins when:

• The primary runner on one plate surface must connect to a branch runner on the opposite plate surface
• The flow channel must cross from the fixed plate runner to the runner plate runner at a specific location
• Multiple parallel runner planes are used to increase cavity count within the mold footprint

Z-pins are the simplest change pin type but require separate runner ejector sets for runner removal, since the Z-pin itself has no ejection function.

Ejector-Pin Type

The ejector-pin configuration combines flow redirection with a spring-loaded ejection mechanism. During injection, resin flows through the pin's bore to transfer between runner levels. During mold opening, the spring-loaded pin pushes the solidified runner out of the channel.

This dual-function design reduces the total number of components in the mold — you don't need a separate runner ejector set at the same location. However, the combined mechanism is more complex and has more parts that can wear or fail.

Use ejector-pin type when:

• Space in the mold is limited and you cannot fit both a Z-pin and a separate ejector set at the same location
• The runner change point coincides with where an ejector set would naturally be placed
• Reducing total component count is a design priority

Fixed-Side Type

Fixed-side runner change pins are installed in the fixed plate (A plate) and redirect the runner flow before it enters the runner plate. They are used when the runner path on the fixed plate must change direction or connect to the runner plate at a non-collinear point.

Unlike Z-pins and ejector-pin types (which transfer flow between plates), fixed-side pins redirect flow within the same plate — typically by creating an angled or L-shaped flow path.

Use fixed-side type when:

• The sprue location on the fixed plate does not align with the runner entry point on the runner plate
• The mold has an offset sprue design where the injection nozzle axis is not centered on the runner layout
• Runner flow must be redirected before entering the runner plate channels

Selection Decision Guide

Answer these questions to select the right configuration:

• Does the flow need to transfer between two plates? → Z-pin or ejector-pin type
• Is space available for a separate ejector set at the transfer point? → Yes: Z-pin (simpler). No: ejector-pin type (combined)
• Does the flow direction change occur entirely in the fixed plate? → Fixed-side type
• Is runner ejection needed at the transfer point? → Ejector-pin type (built-in ejection)

According to ScienceDirect's three-plate mold design reference, runner change pin bore diameter should match the runner channel diameter within ±0.1 mm to prevent flow restriction or material hang-up at the transition point.

Bore and Sizing Considerations

According to JIS B 5111 standards, runner change pin bore surfaces must be polished to the same finish as the runner channel to prevent flow disruption and material degradation at the transition.