Production of Pipe with Uniform Wall Thickness: How to Compensate for Gravity Sag
-
J. F. T. Pittman
Abstract
A detailed simulation of the cooling process in the production of plastic pipes has been used to gain insights into the problem of gravity flow or sag, which can lead to troublesome wall thickness variations in thick walled pipes. It is shown how the simulation can be used in an iterative, forward-backward calculation, based on the time reversibility of the creeping gravity flow problem, to calculate the initial extru-date wall thickness profile that the die must deliver to precisely compensate for sag. For pipes with particularly thick walls, this calculation shows that no compensating initial profile exists whilst conventional cooling arrangements are used. Reduction of the cooling rate of the lower part of the pipe promotes wall thickness uniformity and the existence of a compensating profile. Means for achieving the required initial profiles are discussed, and the need for an integrated view of the design and operation of the die and cooling line in understanding and overcoming the effects of sag is emphasised.
© 2000, Carl Hanser Verlag, Munich
Articles in the same Issue
- Editorial
- Third of a Series: Pioneering Polymer Industry Developments — The First Successful Mathematical-Computer Modeling of A Complex Industrial Process: Toyobo and Melt Spinning
- Screw Extrusion / Mixing
- Polymer Flow Velocity in the Helical Channel in Dependence of a Coordinate System
- Non-Isothermal Transient Startup of A Starved Flow Modular Co-Rotating Twin Screw Extruder
- Numerical Simulations and Experiments in a Double-Couette Flow Geometry
- Dynamic Analysis of Melting in Injection Extruder
- Extrusion Die
- Production of Pipe with Uniform Wall Thickness: How to Compensate for Gravity Sag
- Fiber and Film
- Assessment of LDPE Melt Strength by Use of Rheotens Mastercurves
- Molding
- Analysis of Flow and Heat Transfer in Liquid Composite Molding
- Solidification Criterion on Shrinkage Predictions for Semi-crystalline Injection Moulded Samples
- Polymer Melt Rheology at High Shear Rates
- Factors Affecting the Stability of Gas Penetration in Gas Assist Injection Molded Bifurcation Parts
- Transient Polymer Flow Rate in Injection Mold Filling
- Flow Analysis of Injection-Press Molding Process
- Properties of Injection Molded In Situ Composites Based on PPS and a Melt Processable Glass
- A New Approach in Offline-Optimization of the Injection Molding Process
Articles in the same Issue
- Editorial
- Third of a Series: Pioneering Polymer Industry Developments — The First Successful Mathematical-Computer Modeling of A Complex Industrial Process: Toyobo and Melt Spinning
- Screw Extrusion / Mixing
- Polymer Flow Velocity in the Helical Channel in Dependence of a Coordinate System
- Non-Isothermal Transient Startup of A Starved Flow Modular Co-Rotating Twin Screw Extruder
- Numerical Simulations and Experiments in a Double-Couette Flow Geometry
- Dynamic Analysis of Melting in Injection Extruder
- Extrusion Die
- Production of Pipe with Uniform Wall Thickness: How to Compensate for Gravity Sag
- Fiber and Film
- Assessment of LDPE Melt Strength by Use of Rheotens Mastercurves
- Molding
- Analysis of Flow and Heat Transfer in Liquid Composite Molding
- Solidification Criterion on Shrinkage Predictions for Semi-crystalline Injection Moulded Samples
- Polymer Melt Rheology at High Shear Rates
- Factors Affecting the Stability of Gas Penetration in Gas Assist Injection Molded Bifurcation Parts
- Transient Polymer Flow Rate in Injection Mold Filling
- Flow Analysis of Injection-Press Molding Process
- Properties of Injection Molded In Situ Composites Based on PPS and a Melt Processable Glass
- A New Approach in Offline-Optimization of the Injection Molding Process
