Hot Runner Expansion Calculator
Calculate the thermal expansion of a hot runner manifold and the required compensation gap. Correctly accounting for thermal expansion prevents leaks, distortion and damage to the hot runner system.
Input Parameters
Results
Fill in the data and click Calculate
ARGUS automatically accounts for thermal expansion when designing the hot runner system
Thermal expansion can cause leaks and damage — ARGUS monitors and compensates dimensional changes automatically.
How do we calculate hot runner expansion?
The hot runner manifold operates at 180–400°C, while the surrounding mold is at 20–120°C. This temperature difference causes thermal expansion of the manifold that must be compensated by appropriate gaps and centering systems. Without compensation the result is leaks, material seepage and mechanical damage.
The calculator applies the linear thermal expansion model with the expansion coefficient of the manifold material.
ΔT = Twork − Tambient
ΔL — elongation [mm]
L — manifold length [mm]
α — expansion coefficient [1/K]
ΔT — temperature difference [°C]
Thermal expansion coefficients: steel (12×10⁻⁶/K), stainless steel (16×10⁻⁶/K), brass (19×10⁻⁶/K), titanium (9×10⁻⁶/K), copper (17×10⁻⁶/K). For a steel manifold 400 mm long at an operating temperature of 280°C the expansion is approximately 1.25 mm — enough to cause a leak without compensation.
Thermal Expansion Compensation
Expansion compensation systems in hot runners:
Compensation gaps — clearance mounting holes
Insulating pads — spacers made of insulating material
Belleville springs — maintain contact pressure during dimensional changes
Critical points: nozzle–manifold and manifold–mold seals. The compensation gap should be 10–15% larger than the calculated expansion to account for uneven heating during start-up. Thermal stresses in the manifold can reach 50–150 MPa.
Hot Runner System Start-Up
During start-up the manifold heats unevenly — zones closer to the heaters reach operating temperature faster. This requires gradual heating (ramp 5–10°C/min) and temperature equalization before production begins. Temperature monitoring in all zones is critical for preventing leaks.
ARGUS monitors thermal expansion and automatically controls hot runner parameters
See it for yourself — book a presentation and watch hot runner monitoring in ARGUS.