What Are the Fixed-Point Settings for Hot Runner Systems?

The core principle behind hot runner fixed-point settings lies in the combination of "axial limitation + radial positioning + thermal expansion compensation." Through the use of structural components such as spacer pads, locating seats, and point-contact supports, the system remains stable during both room-temperature assembly and high-temperature operation, thereby preventing leaks or seizing caused by thermal deformation.

I. Key Fixed Points and Their Functions

1. Axial Positioning: The distance L from the mold parting line to the axial locating face of the hot nozzle.

This dimension is defined as L = L' + ΔL, where:

L' represents the actual length of the nozzle at room temperature;

ΔL represents the axial elongation due to thermal expansion at the mold's operating temperature (calculated based on the material's coefficient of linear thermal expansion).

Function: To ensure that, during high-temperature operation, the nozzle tip seats precisely against the cavity gate, thereby preventing damage to the mold (caused by excessive elongation) or poor sealing.

2. Spacer Pad-The Core Axial Limitation Component

Installed above the top of the nozzle, it works in conjunction with the nozzle's own axial locating face to restrict its movement.

A clearance of 0.025 mm is left at room temperature; this ensures that once the mold heats up and expands, the spacer pad becomes firmly compressed, thereby achieving a state of "thermal pre-loading."

The material typically selected is a high-temperature-resistant alloy steel with a hardness of ≥50 HRC to prevent crushing under pressure.

3. Locating Seat and Locating Pin-Radial and Overall Position Control

The locating seat and the stationary mold plate require a specific radial fit tolerance (Dimension D2)* to ensure the precise positioning of the hot runner manifold within the mold assembly.

When used in conjunction with locating pins, this arrangement achieves precise 3-axis (X/Y/Z) positioning, preventing assembly deviations that could lead to runner eccentricity or stress concentration.

4. Connection Method Between the Hot Runner Manifold and the Mold Plate

Point-Contact Support: The interface between the hot runner manifold and the mold plate utilizes localized point contact (with a contact area of ≤10%) or incorporates a 2–3 mm air gap. This design minimizes heat transfer from the manifold to the mold plate while simultaneously allowing for unrestricted thermal expansion. Screw Locking: In mold designs where the A-plate features an insert-style structure, screws are used to directly fasten the hot runner manifold plate to the A-plate; this method is suitable for simplified installation configurations.

5. Radial Fit between Nozzle and Stationary Mold Plate (D1)

A precise radial fit (dimension D1-typically H7/g6 tolerance) is required between the nozzle and the stationary mold plate to ensure nozzle perpendicularity and prevent eccentric loading.

The length of this fitted section should generally be ≥ 15 mm to enhance guiding stability and stability.

6. Fit between Nozzle Tip and Stationary Mold Insert (d)

A sealing fit (dimension d) is required between the nozzle tip and the stationary mold insert to prevent molten material from leaking into areas outside the mold cavity.

The stationary mold insert is required to be hardened to approximately 50 HRC to withstand erosion caused by high temperatures and high pressures.

II. Summary of Key Design Points

Nozzle Tip–d Fit | Prevent material leakage | Sealing fit; insert hardness: 50 HRC.

Practical Tip: In multi-cavity molds or large-scale molds, it is recommended to provide independent adjustment shims and locating structures for each individual hot runner nozzle to prevent localized deformation from compromising the overall reliability of the system.