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A computational design optimization environment is developed, handling, for the first time, streamline dies used for profiles in unplasticized polyvinyl chloride (uPVC) having multiple complex features, as well as simpler designs. Die cavity cross sections are described by planar contours, such as the cutting paths for wire electrical discharge machining of the plates from which streamline profile dies are constructed. Contours are parameterized using key points, and by joining the contours with ruled surfaces, the three-dimensional geometry can be reconstructed. For the optimization a developed flow analysis on each die cross section is used with the avoid-cross-flow strategy. Cross sections are partitioned and the die is balanced to obtain the required flow rate through each. A robust and efficient parallel decoupled optimization strategy is developed. In application to a uPVC window profile, five cross sections were optimized. The number of design variables on each ranged from 2 to 46, and the cross section optimizations converged within one to seven cycles. Compared with the work of an experienced designer making manual changes to the computer-aided design model, guided by computational fluid dynamics analyses, the design quality was comparable or better and computational demands similar; however, the time required from the designer was reduced seven times. POLYM. ENG. SCI., 53:189-203, 2013. [C] 2012 Society of Plastics Engineers, INTRODUCTION Profile Extrusion Profile extrusion of thermoplastics and rubber is an important processing sector, dominated by unplasticized polyvinyl chloride (uPVC), used widely in the building industry, and by compounded rubber [...]

A charge-coupled device (CCD) camera was used to observe n-butane-blown low-density polyethylene (LDPE) foams at the extrusion die exit. The effects of butane content, nucleating-agent (talc) content, aging modifier (glycerol monostearate), die temperature, and die geometry on the initial expansion behavior of the foam extrudate were studied. A transparent section of the foam extrudate was found at certain die temperatures. The reasons for the existence of this transparent section and its effect on the processing conditions and material formulations are discussed. POLYM. ENG. SCI., 51:492-499, 2011. [C]2010 Society of Plastics Engineers, INTRODUCTION Visualization has been widely utilized in polymer science. Many rheological phenomena, such as die swelling and melt fracture, for example, have been investigated using this technology (1). However, this [...]

This article presents a procedure to achieve a uniform outlet flow of molten polymer for a complex die profile with various thicknesses in die outlet cross section. According to a specific optimization methodology, the die was optimized based on varying die land length. The scope of this article includes: 3D flow simulation, optimization of the die velocity outputs based on the results of simulation process, and comparison of numerical predictions with the experimental data. Finally a significant result obtained by this work indicates higher ratio of the land length to the height of the zone with cross flow rather than the zones that are directly fed by the extruder. POLYM. ENG. SCI., 50: 2417-2424, 2010. [C] 2010 Society of Plastics Engineers, INTRODUCTION Nowadays, polymer extrusion process has been widely used in industries. In this process, design of the dies is usually based on the trial and error and empirical efforts, because [...]

Coextrusion is widely used to fabricate multilayered products with each layer providing a separate functionality, including barrier resistance to gases, strength, and printability. Here an analytical model of the coextrusion die flow of two incompressible, viscoplastic fluids in a slit die, subject to nonlinear wall slip and under fully developed and isothermal conditions, is developed to allow the prediction of the steady-state velocity and shear stress distributions and the flow rate versus pressure gradient relationship. The resulting model is applied to the coextrusion of two layers of viscoplastic fluids in a thin rectangular slit die (slit gap, h ≪ slit width, W). The analytical solution recognizes a number of distinct flow conditions (eleven cases) that need to be treated separately. The solutions for all eleven cases are provided along with an apriori identification methodology for the determination of the applicable case, given the shear viscosity and wall slip parameters of the two viscoplastic fluids, the slit geometry and the flow conditions. Simplifications of the model would provide the solutions for the fully developed and isothermal coextrusion flows of any combination of Hershel-Bulkley, Bingham, power-law and Newtonian fluids with or without wall slip at one or both walls of the slit die. POLYM. ENG. SCI., 50:652-664, 2010. [C] 2009 Society of Plastics Engineers, INTRODUCTION Multilayered coextrusion involves the bringing together of two or more fluids (1) to generate layered products with structural distributions and ultimate properties that depend on the properties of the [...]

This article presents an experimental study on the flow balance of an extrusion die for various wood flour (WF)/high-density polyethylene (HDPE) compositions. Flow balancing, in the design of a thermoplastic extrusion die, is dependent on the material rheological properties so that a change in the material, in some cases, may result in a total redesign of the die. To investigate the importance of this particular effect, the flow balance of an extrusion die, with a U-shaped profile having uneven wall thicknesses, was undertaken. The main feature of the die was an adjustable restrictor implemented for fine balancing similar to that employed in the slit dies. The rheological influence of wood plastic composites (WPCs) on the flow balance of the die via loading various WF contents, 40, 60, and 70% by weight, was experimentally investigated; flow balancing was performed via varying the height of the restrictor bar. Interestingly, the results showed that, for a high WF content (above 60%), the issue of flow balancing for an uneven wall thickness profile is much less complicated because of the plug flow behavior of the composite. POLYM. ENG. SCI., 50:543-549, 2010. [C] 2009 Society of Plastics Engineers, INTRODUCTION The most important function of a polymer extrusion die is flow balancing, namely to distribute the flowing polymeric melt so that a uniform velocity profile at the die exit [...]

A forum to improve communication and relationships between industry and institutions and to discuss the latest technologies in extrusion, drying, and food processing systems was held by Wenger Manufacturing (Sabetha, KS), in 11/00 in Kansas City, KS. New developments discussed included a single-screw extruder, a twin-screw extruder, a vacuum microwave dryer, and a phase transition analyzer.

This paper is concerned with an attempt to find an upper bound solution for the problems of steady-state extrusion of asymmetric polygonal section bars through rough square dies. A class of kinematically admissible velocity fields is examined, reformulating the SERR technique, to get the velocity field that gives the lowest upper bound. This velocity field is utilized to compute the non-dimensional average extrusion pressure at various area reductions for different billet aspect ratios.

A fluid dynamics analysis package (FIDAP), using the finite element method, was implemented to simulate the 3-D isothermal flow patterns in the conveying element of a ZSK-53 co-rotating twin screw extruder. The fluid was described by a power-law model. The dynamics of distributive mixing was studied numerically by tracking the motion of particles in the mixer. The extent of distributive mixing was characterized in terms of length and area stretch as well as strain distributions. The length stretch reflects the overall capability of the mixing device to spread minor component particles away from their neighbors originally present in the same cluster. The area stretch reflects the evolution of intermaterial area when mixing two fluids with a passive interface. We observed an oscillatory behavior for the average intermaterial area stretch, which was explained in terms of a stretching and folding mechanism. Folding occurs during material takeover from one screw to the other. Operating at higher rotational speeds enhances distributive mixing efficiency., INTRODUCTION Twin screw extruders have been used for processing of viscous materials for several decades. Significant applications in the plastics industry started in the 1930s and 40s with the efforts [...]

Extensive experimental studies of a starved flow modular tangential screw extruder are described. Die pressures and fill factor profiles along the screw axis are measured and used to determine screw characteristic curves Q vs. ΔP/L for individual screw elements of varying designs in a Leistritz twin screw extruder. Superior pumping characteristics of matched as opposed to staggered elements is found. The experimental screw characteristic curves are compared with the results of mathematical simulations of the flow. Agreement is generally good., INTRODUCTION Tangential counter-rotating twin screw extruders have a long history (1, 2). There have, however, been limited published experimental studies of these machines. Measurement of the pumping characteristics of forward [...]

The flow distribution of slowly reacting polymeric materials inside an extrusion die was analyzed by lubrication theory. The viscosity of the polymeric liquid was assumed to be time-dependent owing to chemical reaction. Three types of extrusion dies were considered: a T-die, a linearly tapered coat-hanger die with a choker bar, and a curvilinearly tapered coat-hanger die. It was found that the T-die is not suitable to deliver the polymeric liquid films, whereas the two coat-hanger dies can deliver the polymeric liquid films with acceptable flow uniformity and residence time distribution., INTRODUCTION Extrusion dies are extensively employed to deliver wide and thin liquid layers. After solidification these thin liquid layers can become products such as polymer packaging films, adhesive tapes, magnetic [...]

A flow visualization technique was employed to observe the flow fields at the entrance region inside extrusion dies. Four types of solutions, i.e., Newtonian, shear-thinning, Boger, and viscoelastic fluids, were used as test fluids. Entrance flows inside center-fed and end-fed dies of different configurations were examined. It was found that, even though the swirling motions appear in the entrance region of center-fed dies, no vortex develops. Shear-thinning behavior tends to enhance swirling, but fluid elasticity suppresses the swirling. On the other hand, vortices exist at certain end-fed die geometries, and vortices will grow if the fluid exhibits shear-thinning, yet fluid elasticity reduces the size of vortices. Several inlet designs effective for eliminating vortices were studied., INTRODUCTION Film or sheet extrusion is a major polymer processing operation, and extrusion dies are indispensable for this operation. Extrusion dies are also widely used in various coating operations. Ever [...]

A simulation of slit dies in operation is described. Two-dimensional finite element analyses are used for the pressure field in the die (based on Hele-Shaw flow assumptions), and for the deflection of the die body resulting from this internal pressure (using Mindlin thick plate theory). These analyses are coupled in an iterative scheme, which converges to give results for the dynamic operating performance of the die. Predictions of deflections and pressure drops agree closely with experimental data. Post-processing of primary pressure results yields the stream function, melt residence time, total melt strain, and wall shear stresses. The calculation routines are enclosed within a graphical user interface in the MS-Windows operating environment, running on PCs, and providing a powerful and convenient computational aid for the designer and process operator., INTRODUCTION The primary requirement in the process design of slit extrusion dies is to ensure uniform melt distribution across the width of the die, leading to an extrudate of a [...]

This study investigates deformation of a thermotropic liquid crystalline polymer (TLCP) in different die geometries. Blends of a TLCP with a thermoplastic elastomer of EPDM were made in a twin-screw extruder. Morphological observation of the extruded blends demonstrates the complimentary effect of shear in the die exit on dispersed phase deformation and fibril formation. Shear strain can affect fibril formation for a relatively large dispersed phase in the region close to the die wall. However, the main role of shearing is in breaking up the larger particles and initial polydomain structure. A strong elongational deformation on the blended melt after the die exit is required, and free microfibrils normally observed in in situ composites were not easily formed by shear deformation only in the die., INTRODUCTION Thermotropic liquid crystalline polymers have attracted attention during the past two decades because of their characteristic properties (1-5), one of which is their ability to form self-reinforced blends with [...]

It is of great importance in designing extruders to predict the screw characteristics, that is, the throughput in terms of the screw speed and the pressure gradient along the down-channel direction. The screw characteristics depend on the extruder geometry, the operating conditions, and material properties of non-Newtonian fluids. This paper suggests a simple approach to determining the screw characteristics for a three-dimensional flow in a channel with a finite aspect ratio (ratio of a width to a depth, W/H) by introducing a Total Shape Factor ([F.sub.t]) to correct a two-dimensional flow analysis for a channel with an infinite aspect ratio. In the present study, the Total Shape Factor ([F.sub.t]) was defined as a ratio of a net flow rate obtained by the three-dimensional analysis to that by the two-dimensional analysis. In the proposed approach, the quantity, Δ[F.sub.t]/Δ(H/W), which turns out to be almost constant, offers important information for understanding the effects of the flights. Therefore, Δ[F.sub.t]/Δ(H/W) is extensively reported in this paper in terms of several dimensionless parameters. This simple approach with such a database will be very useful for extruder designers to predict screw characteristics., INTRODUCTION The present paper concentrates on the relationships among the throughput, screw speed, and the pressure gradient along the down-channel direction, namely, screw characteristics, especially as regards the flight effects [...]

The effect of the screw configuration of a closely intermeshing co-rotating twin-screw extruder on residence time and mixing efficiency was studied for an uncompatibilized immiscible PA6/PP (80:20) bend. Alternative screw configurations were investigated systematically. The residence time distribution (RTD) was found to be a poor indicator of the total mixing efficiency, whereas the mixing intensity function yielded considerably better information. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good dispersion of the minor phase. The evolution of morphology along the screw axis depended strongly on the screw configuration. The downstream flow characteristics after the screw end determined the final morphology of the blend., INTRODUCTION The predominant commercial method of blend preparation is melt blending in an extruder. The co-rotating twin-screw extruder (co-TSE) has outstanding distributive mixing efficiency and self-wiping characteristics (1). In general, [...]

Factors to consider when you're buying a gear pump include the pump design in relation to the application, its drive system and controller, and the support capability of the gear [...]

Co-rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co-rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time-dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package - FIDAP - using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-30 co-rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter lambda quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristics was analyzed.

A novel substrate micromachining step is presented for wafer front-to-backside alignment. The single-etch, single-mask process uses resist-patterned etch control to produce various final thicknesses on a single-crystal silicon wafer. It was employed to simplify the fabrication of wafers with two-sided alignment as thin film microphones. The new approach may also be implemented on other microdevices manufactured by integrated circuit technology.

The design of a microfabricated floating-element sensor is presented. Fabricated via wafer-bonding technology, the sensor measures liquid shear stresses at high levels and at high pressure. An analytical and finite element analysis of the device's operation in a cone and plate viscometer is described alongside test results of its mechanical strength in high pressure surroundings. The sensor was developed for application in the industrial extrusion process.