Meaning
A mathematical framework determines the cooling time of injection moulded parts by calculating the thermal diffusion through the polymer thickness. The norton bailey model assumes one dimensional heat transfer and constant material properties to predict the duration until the part core reaches a temperature safe for ejection. It defines the point where the centre temperature drops to the required demoulding level based on initial melt and mold wall temperatures.
Processing Limits
Engineers apply this calculation to establish cycle times for thermoplastic production. The norton bailey model uses the square of part thickness as the primary variable to estimate the required cooling phase. If the geometry drifts beyond the specified wall dimensions, the actual part temperature at ejection exceeds the calculated threshold, resulting in thermal deformation or surface distortion.
Datasheet values for thermal diffusivity guide this computation, yet moulders must adjust these constants for specific crystal structures or filler loads found in regrind batches.
Material Constants
Effective heat dissipation depends on the thermal properties of the specific resin grade. The norton bailey model treats the material as a uniform medium, ignoring the latent heat of fusion that occurs during the solidification of semi-crystalline polymers. Cooling rates calculated under this assumption frequently underestimate the actual time needed for semi-crystalline resins because of the energy released during phase changes.
Accuracy in the result relies on the thermal diffusivity value remaining stable throughout the cooling process.
Production Outcome
Deviations in cooling duration directly impact the dimensional stability of finished plastic components. When the norton bailey model underestimates the required time, internal stresses remain locked within the part, causing delayed warpage or sink marks as the piece settles after removal from the tool. Excess cooling time lowers production output without providing additional benefit to the mechanical properties of the component.
Precise thermal management allows for the optimization of the injection cycle while maintaining consistent part geometry.
