Polymer Melt Instability Limits in High Speed Profile Extrusion
Polymer melt instability limits define the maximum line speed in profile extrusion before surface fracture and wall slip destroy yield and drain cash flow.
Profile Line Speed Optimization
Meaning
Throughput adjustments aimed at maximizing the linear output of an extrusion line determine the hourly profitability of a manufacturing plant. Profile line speed optimization is the process of finding the highest velocity at which a part can be produced while still meeting all dimensional and aesthetic tolerances. This balance is limited by the cooling capacity of the downstream water baths.
Velocity Ceiling
Maximum output is reached when the material can no longer be cooled fast enough to maintain its shape. Profile line speed optimization requires a step-by-step increase in speed followed by a full quality check.
Cooling Speed
Heat removal must be efficient to prevent the center of the profile from remaining molten. During profile line speed optimization, the temperature of the cooling water is monitored to ensure it stays within the range required for part stability.
Dimension Control
Stretching of the melt front can lead to thinning of the walls as the speed increases. Profile line speed optimization is successful when the line reaches a steady state where the scrap rate is minimized and the production volume is maximized. Calling the speed too early results in a high volume of rejected parts that do not meet the customer’s specifications.