The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Flow Behavior of Newtonian Fluid through Conveying Elements and Kneading Blocks
The flow behavior of a Newtonian fluid through conveying elements and kneading blocks in a co-rotating twin screw extruder was examined by drag and pressure flow experiments. These results are compared with existing computer models. Also the flow behavior of the different kneading blocks and the conveying elements are compared with each other. The results can guide when to decide which mixing elements to use and can help with future computer modeling.
Modeling of Polymer Drop Deformation and Breakup during Melting under Shear Flow Using Volume-Of-Fluid Method
Polyethylene (PE) or polycarbonate (PC) drop breakup process in PE melt under shear flow was investigated using volume-of-fluid method. Real properties of polymers, and temperature and shear rate dependent viscosity model were incorporated in the modeling. An erosion mechanism was found for both PE and PC drops. Local flow information, such as shear rate, viscosity and shear stress, was obtained from the simulation results. Highest shear stress was observed at the interface, which could explain the erosion breakup mechanism.
New Intermeshing Pin Mixer for Extrusion
It is well known that reorientation of interfaces is key to efficient distributive mixing. However, how to achieve reorientation is not well known. This paper describes how interfaces can be reoriented in screw extruders and which method leads to the most effective reorientation. A new mixing device was developed to achieve highly efficient reorientation by utilizing an intermeshing mixing action between the screw and a floating sleeve. Test results indicate that the intermeshing pin mixer can produce excellent mixing quality over a short axial length, as short as one diameter.
Polytetrafluoroethylene (PTFE) Paste Preforming: The Effects of Viscosity and Surface Tension of Lubricants
Conventional processing methods are not applicable to PTFE due to its high melting point (342°C). Therefore, PTFE is processed by means of paste extrusion (extrusion of a mixture of PTFE powder with a lubricant). The physical properties of this new phase (lubricant) influence both the preforming stage as well as the rheology of the paste. In this paper, the effects of the physical properties of lubricant (viscosity and surface tension) on the preforming and extrusion pressure of PTFE paste are examined.
Extrusion Characteristics of HDPE-Wood Composites
Extrusion characteristics, such as output, pressure profiles and melting profiles, were investigated in a Brampton Engineering single screw extruder with two screw geometries. It was found that for the wood-HDPE1 composite, the channels were not fully filled until the melting process was completed in both screw geometries. The actual experimental results were compared to those simulated using a commercially available software program. It was found that the current extrusion theories do not predict the pressure profiles generated even for the virgin HDPE1 material for one of the screw geometries.
Temperature Gradients in the Channels of a Single-Screw Extruder
A novel fluorescence analytical technique was used to measure the polymer temperature inside an operating extruder. The method allowed the temperature measurement of the polymer without interference from the surrounding metal parts. This paper will show some temperature data for molten polycarbonate in a single-screw extruder under processing conditions.
Design of a Soft Sensor for Polymer Extrusion
The application of closed-loop viscosity control to polymer extrusion is desirable to achieve a consistent quality product. However, incorporation of such techniques is limited by the difficulties in obtaining an accurate, real-time indication of the melt viscosity. This paper outlines the design of an in-line viscosity sensor based on a capillary die and the use of software algorithms generated from off-line data. The use of data acquisition software to analyse and correct for errors is explored.
Kinematics of Solids Conveying
Solids conveying is typically calculated using friction factors. The friction factors depend on material and conditions, are difficult to measure, and the calculation is extremely sensitive to their value. Kinematic analysis of solids conveying is shown to yield the “solids lead angle” for the resin solids plug that does not require friction factors. Solids lead angle for different polymers are shown, and the data are used to make predictions of solids conveying performance without evaluation of friction factors.
Troubleshooting Mixing Problems in Single-Screw Extruders
Mixing processes are very important for plasticating, single-screw extrusion operations. Numerous mixing processes can occur including pre-blending prior to feeding to the hopper, during melting, trapping and melting of solid fragments, mixing of fully molten resins, and mixing downstream from the extruder. This paper focuses on the mixing processes that occur during melting and the handling of solid fragments. Troubleshooting guidelines are presented to mitigate these mixing problems.
Troubleshooting Underwater Pelletization Processes
The fundamental parameters governing the underwater pelletizing process are proposed and confirmed based upon actual observations during process and mechanical troubleshooting of high capacity pelletizing systems.
Production of Compounds with High Filler or Fiber Loading on Screw Kneaders
The production of filled and reinforced compounds has a high economic importance mainly because fillers and reinforcing fibers render the final product to serve very specific applications. In order to understand such operations more the term “highly filled” will be explained and critical aspects analyzed. In essence two different type of compounding machines are utilized for such compounding tasks, the co-rotating twin-screw and the reciprocating single screw (kneader). Fundamental differences of these systems are analyzed and compared. Examples of compounding processes are described.
Basic Extrusion Models as Diagnostic Tools in Extrusion Trouble Shooting
Use of the basic mathematical expressions of the solids conveying, melting, metering and mixing theories for single screw extruders permits the rapid understanding of the functions of an extruder and the interrelationship of polymer properties and process conditions. Understanding the algebra of these models allows for the development of corrective actions and then interpreting the result of the changes permits a new insight into the root cause of the problem.
Effect of Xylene Solubles in Biaxially Oriented Polypropylene
Xylene soluble is an atactic polypropylene and usually produced as a by-product during the polymerization of an isotactic polypropylene. Some amount of xylene soluble polypropylene is known to play a role in orientation of polypropylene to produce film. In this study, isotactic polypropylenes with various amounts of xylene solubles were prepared. The characteristics of these polymers and their performance on the TM long film stretcher were determined, as well as some structure-processing-property relationships.
Matching of Vulcanization with Blowing Reaction in Sponge Rubber Compounds
Sponge rubber is a porous material, that is foamed by the decomposition of a chemical blowing agent. The blowing up of the profiles takes place inside the vulcanization unit parallel to the curing reaction. Both reactions are thermally activated processes, that interact regarding their kinetics. To simplify process design and optimization, a FEA model for the calculation of the local curing rate is presented and a new test method is introduced that enables a process oriented characterization of sponge rubber compounds.
Simultaneous Characterization of Dispersive and Distributive Mixing in a Single Screw Extruder
Simulation of the dispersion of solid agglomerates along their trajectories in a single screw extruder with sequential tracking of parents and fragments allow us to assess conditions appropriate for dispersive mixing and simultaneously account for the spatial distribution of all particles in the system. A new mixing index based on the calculation of Shannon entropy for different size fractions of the minor component present in the system and giving preference to smaller sizes was developed.
Extrusion of BaSO4 Filled Medical-Grade Thermoplastic Polyurethane
Extrudability of 20% (vol.) BaSO4 filled medical-grade (additive free) thermoplastic polyurethanes was investigated. Filled TPU exhibits decreased shear viscosity and elasticity in comparison to unfilled TPU, generating reduced pressure drop at the die and reduced pressurization in the extruder. The moisture remaining in the BaSO4 may hydrolyze the polymer. However, hydrolysis is not sufficient and air, entrained with the filler into the extruder, reduces the viscosity and elasticity of the compounded TPU.
An Analysis of the Effect of Elongational Viscosity on the Flow in a Flat Die
The flow of a low-density polyethylene in a flat die is simulated using the axisymmetric and planar elongational viscosities estimated in an earlier publication by Beaupre and Gupta. Elongational viscosity is found to have only a limited effect on the velocity distribution at the die exit. However, the predicted pressure drop in the die and temperature distribution at the die exit changed significantly when the effect of elongational viscosity is included in the simulation.
An Optimization-Based Approach to Compute Sheeting Die Designs for Multiple Operating Conditions
A simulation-based approach is presented to optimally design polymer sheeting dies to operate over a range of operating conditions. The computational approach incorporates finite element simulations to quantify the ’goodness’ of a die design and includes a gradient-based optimization algorithm to update the die’s geometry. Examples are provided to illustrate the methodology for the creeping flow of purely viscous fluids through thin cavities that may be modeled with the Generalized Hele-Shaw approximation.
Twin Screw Extruder and Continuous Mixer Rate Limitations
An overview and general description of the fundamental parameters that limit feed rates of twin screw extruders (TSE’s) and continuous mixers (CM’s) is presented. This paper also identifies relationships that can be used to identify the key rate limiting parameters for a given TSE/CM design and set of operating conditions.
Deconvolution of Residence Time Distribution Signals to Individually Describe Zones for Better Modeling
Kinematic modeling has been shown to be important for the understanding and control of co-rotating twin screw extruders. Past techniques of kinetic modeling have dealt with the extruder as either one unit or a series of screw element wise units. In this work, multiple sensors are used to characterize the residence time distribution of an extruder. Additionally, the uncoupled signals from these sensors are deconvoluted to produce signals representative of the individual extruder zones.
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