Extrusion Dies Research Articles

Influence of the Geometry of the Extrusion Die on the Melt Strength of Polymers

Abstract In the past some studies have been carried out to investigate the melt strength of polymers with the purpose of comparing the results obtained with different materials and at different temperatures. In those experimental activities, once that the testing instrument had been chosen, the polymers were considered the object of the investigation and the attention was rarely focused on the testing geometry. The present work, instead, intends to analyze the influence that the geometry of the extrusion die has on the melt strength of polymers. In particular, attention is focused on the analysis of the differences produced on the melt strength of a material, when the extruded filament is subjected, via the use of two different dies specifically designed, to two distinct temperature profiles along the stretching axis. This investigation highlights that the testing geometry chosen for an experimental activity based on melt tension tests, via haul-off measurements, plays a fundamental role in the correct interpretation of the results. In fact it is demonstrated that the correct choice of the extrusion die allows one to obtain results much more similar to the real processing type that, using melt tension tests, has to be analyzed.

Scale‐Up in the Design of Extrusion Dies

AbstractThe similarity theory and the scale‐up procedure developed from it make it possible to convert a technical‐physical process from one scale to another – generally in the upwards direction. In the design of extrusion dies with an annular die gap, the die is broken down into basic geometric elements, and scale‐up rules are then drawn up for the individual elements. In this project, scale‐up rules were found that satisfy both full and partial similarity. The pseudoplasticity and elasticity of the melt were also taken into consideration. A comparison of the model laws obtained with the results of finite element calculations showed good conformity between the models and the production versions. Deviation in pressure difference between the model and the production version assuming flow behavior in accordance with the power law (Di = const. and L = const.).magnified imageDeviation in pressure difference between the model and the production version assuming flow behavior in accordance with the power law (Di = const. and L = const.).

Optimal Shape Design of an Extrusion Die Using Polynomial Networks and Genetic Algorithms

Designing the optimal shape for an extrusion die to produce a high-quality extrusion product is often required by industry. Design from experience is unsatisfactory for achieving the flexibility and precision requirements in die design. In this paper, a design method has been developed for the optimum shape design of extrusion die. The extrusion process was modelled and analysed by using the finite-element method to obtain the extrusion force and effective strain for different die shapes. A polynomial network was applied to identify the force and strain models in terms of the geometric parameters of the extrusion die. An improved genetic algorithm was used to optimise the identified model for optimal shape with minimum force and strain. It has been verified that the modelling error is extremely small. The designer can quickly and accurately access the optimal shape of an extrusion die through this new approach.

Analysis and Design of the Prestressed Cold Extrusion Die

Analysis and Design of the Prestressed Cold Extrusion Die

Effects of operation conditions and die angles on the pressure losses in capillary flow of polystyrene melt

The rheological properties of polystyrene (PS) melt were measured using a constant rate type of capillary rheometer over temperatures varied from 240 to 260°C and shear rates varied from 10 2 to 10 3 s −1. Dies with different entry angles were selected in order to identify the influence of the die angles on the pressure losses during extrusion of the melt. It was found that the end pressure losses increased non-linearly with increasing the piston speeds ( V), while the extrusion rate sensitivity of it was insignificant at higher temperature. The total pressure drop (Δ P) in the die extrusion of the melt also increased non-linearly with the increase of V, and decreased with a rise of temperature. In addition, Δ P decreased with increasing the die angle (2 α) and showed a minimum value when 2 α was about 75°.

Wear of surface treated dies for aluminium extrusion — a case study

Dies for extrusion of aluminium alloys are exposed to severe thermal, chemical and mechanical conditions. Extrusion dies are usually made from hot work tool steels such as AISI H13. In order to reduce wear they are almost always surface treated by various forms of nitriding. Surface-coating by physical vapour deposition (PVD) or chemical vapour deposition (CVD) is currently being introduced as a means to further improve the wear resistance. The present study aims at elucidating the life limiting wear mechanisms of gas nitrided tools, and duplex coated tools. The latter has been plasma nitrided and subsequently PVD coated with CrN in the same process. The duplex coating is included for its potential to effectively reduce the wear of extrusion dies. It is estimated that duplex coating prolongs the tool life at least five times as compared to conventional nitriding. The reason is that the superficial PVD-layer shows a combination of high resistance to mechanical wear and resistance to corrosive attack by hot aluminium. Eventually, the PVD-layer fractures and delaminates due to fatigue. When the nitrided substrate is exposed, the wear accelerates significantly.

Pressure effect of viscosity for polymer fluids in die flow

Pressure effect of steady shear viscosity for viscoelastic fluids during die extrusion flow has been analyzed and discussed. On the basis of simplified conditions, an expression for estimating the pressure coefficient ( β) has been proposed in the present article. The sensitivity of melt shear viscosity to pressure during the die extrusion flow of natural rubber (NR)/styrene–butadiene rubber (SBR) blend (a tread rubber), a low-density polyethylene (LDPE) and a polystyrene (PS), has been studied by using a capillary rheometer under testing conditions. The results show that values of β calculated using this equation based on the measured data from the samples are close to the values reported in literature. In addition, it is shown that β decreases with increasing extrusion flow rates and a rise in temperatures.

Adherent and slippery walls for extrusion of entangled polymer melts and compounds

AbstractA brief overview is given of the distortions observed when polymer melts or compounds are extruded. It appears that extrusion through steel dies can be done either with macroscopic slip or with no‐slip wall conditions.Recent experimental and theoretical progress made in understanding the various aspects of slip at the wall, and its measurement techniques, are presented. Boundary conditions for rubber compounds flowing through steel‐walled dies could be seen to be much more complex than those for melts. However many aspects of the methodologies developed are of common interest both for melts and rubber.It has already been suggested that advantages can be obtained from the use of slippery walls in extrusion. Such wall properties have already been used indeed for a long time with compounds, where processing additives are introduced.New experimental data are presented concerning two typical EPDM compounds series, obtained using several laboratory techniques at the same time. Constitutive equations for the bulk and for friction at the wall can be introduced at present and adjusted to experimental data. Die extrusion can be simulated numerically, and significant improvements can be expected in quality and productivity.

Development of a Mathematical Model for the Calculation of the Pressure Drop in Extrusion Dies

Analytical approaches for calculating the pressure drop in extrusion dies are limited because they are only applicable in ideal flow channel geometries. In finite element calculations the pressure drop in different flow channels was determined. Parallel the cross section of those geometries was calculated, transformed into the ideal form of a slit or circle and analytical calculations were done. From the results a correction function was derived. This enables realistic pressure drop calculation by applying simple analytical equations.

The Use of Three-Dimensional Computational Fluid Dynamics in the Design of Extrusion Dies

With the proper use of three-dimensional computational fluid dynamics (CFD), the design of extrusion dies can be taken from that of an art to a science. Although replacing simpler traditional one- and two-dimensional approaches with fully three-dimensional ones requires a much more in depth analysis and a large amount of computations, the design of most dies can be performed on a personal computer. This paper demonstrates how these techniques are being used to obtain optimized designs of extrusion dies.

Temperature Measurements in Extrusion Dies

Temperature Measurements in Extrusion Dies

Polymer processing: principles and design

Importance of Process Design. Isothermal Flow of Purely Viscous Non--Newtonian Fluids. Viscoelastic Response of Polymeric Fluids. Diffusion and Mass Transfer. Nonisothermal Aspects of Polymer Processing. Mixing. Extrusion Dies. Extruders. Postdie Processing. Molding and Forming. Appendices. Index.

Morphological studies on extruded films and filaments of polypropylene

AbstractIn the present work, an attempt has been made to study the development of morphology during extrusion and uniaxial stretching of polypropylene (PP) films and filaments at corresponding conditions. Dies for extrusion of films and filaments were designed to achieve similar extrusion velocity and shear rates. Orientation in films and fibers of PP produced from these dies was determined by birefringence and wide‐angle X‐ray diffraction (WAXD). The degree of crystallinity was determined by density and WAXD. The superstructure developed during extrusion was studied in films by small‐angle light scattering. It was inferred that films and fibers prepared under similar conditions would produce similar morphology. Hence, films can be characterized by optical techniques when it is difficult to study fibers. © 1994 John Wiley & Sons, Inc.

Three-Dimensional Analysis of Extrusion Process Utilizing the Physical Modeling Technique

The purpose of this study was to simulate the metal extrusion processes via three-dimensional physical modeling technique. Plasticine was utilized as the modeling material, while plexiglass was incorporated in the design and fabrication of a labscale extrusion apparatus. The extrusion setup was designed to accommodate dies of different semi-cone angle while also making it possible to change the extrusion ratio R = A0/Af. Cylindrical billets were prepared utilizing alternating layers of two colors of plasticine. Extrusion of cylindrical billets was conducted at three different reduction ratios and three different die angles for each reduction ratio. Dissection of the extruded billets along a centroidal plane revealed the internal deformation patterns which were subsequently utilized for determining the effect of the die angle and extrusion ratio on the state of strain in the final product as well as the required extrusion loads.

Software and hardware design of a robotic manipulator for the manufacture of complex shaped dies

Metal forming dies can be manufactured by various conventional and nontraditional methods. Dies for drawing and extrusion of complex cross-section components are usually difficult to manufacture by traditional methods, and in many cases Wire Electro Discharge Machining ( WEDM ) technique is found to be suitable. Currently WEDM machines with integral CNC systems are commercially available. However, these machines are very expensive and have limited angular machining facilities. A precision robotic manipulator, which is independent of the machine would be more versatile and cheaper. The present paper describes the design and commissioning aspects of such a manipulator. This four axes manipulator has two linear and two rotational movements facilitated by A.C. servomotors, which in turn are controlled using micro-computer based softwares. The complex shapes are generated by precision manipulation of the workpiece through appropriate software. Tests have been carried out using model materials and simulated WEDM. The principal application would be in machining of dies or components having 3-dimensional external and / or internal surfaces.

Software and hardware design of a robotic manipulator for the manufacture of complex shaped dies

Metal forming dies can be manufactured by various conventional and nontraditional methods. Dies for drawing and extrusion of complex cross-section components are usually difficult to manufacture by traditional methods, and in many cases Wire Electro Discharge Machining ( WEDM ) technique is found to be suitable. Currently WEDM machines with integral CNC systems are commercially available. However, these machines are very expensive and have limited angular machining facilities. A precision robotic manipulator, which is independent of the machine would be more versatile and cheaper. The present paper describes the design and commissioning aspects of such a manipulator. This four axes manipulator has two linear and two rotational movements facilitated by A.C. servomotors, which in turn are controlled using micro-computer based softwares. The complex shapes are generated by precision manipulation of the workpiece through appropriate software. Tests have been carried out using model materials and simulated WEDM. The principal application would be in machining of dies or components having 3-dimensional external and / or internal surfaces.

The Development of Cast Dies for Hot Direct Extrusion of Aluminum Alloys

The Development of Cast Dies for Hot Direct Extrusion of Aluminum Alloys

Flow of a Generalised Power-Law Fluid in Triangular Dies for Rubber Extrusion

Abstract A theoretical and experimental study of the flow of a rubber compound through dies of equilateral triangular cross-section is presented. To determine the pressure drop in these sections both the variational approach and the finite difference method are used. Velocity profiles for different non-Newtonian indices have been obtained under the assumption that rubber compounds conform to the generalised power-law equation of state. Comparisons between the two methods adopted and experimental data are made. Memory effects which contribute to extrudate swelling are also considered; and a quantitative analysis is carried out in which these effects are used to calculate a minimum die land or preform length. Experimental trials were carried out with an ethylene propylene ter polymer (EPDM) compound and a fair agreement was obtained with theoretical predictions. Also the assumed isothermal conditions were found to conform well with experimental results.

Computer Integrated Manufacturing for Flat Die Extrusion

This paper discusses Computer Integrated Manufacturing (CIM) as it would apply to Flat Die Extrusion. The extrusion environment is an ideal application for CIM because of the complexity of the process and the need to simultaneously improve quality and reduce costs.Several system design considerations required to successfully implement CIM are presented. A case study is used to document the benefits of CIM when applied to a multi-line flat die extrusion plant, and the importance of system design for achieving meaningful results.

Application of Flow Behavior to Design of Rubber Extrusion Dies

Abstract It is common in the tire industry to extrude profiles like treads using a hot-feed dual extrusion line. There is a need to extrude the profiles with zero drawdown in the extrusion line after exiting from the die. Also, the extrudate from the two extruders in a dual extrusion must knit together to form a well-defined and reproducible junction line. A contoured flow channel called a preform is customarily used to achieve a desired junction line and to roughly preshape the stream before passing it through the final die. In practice, several trials are usually required to arrive at an optimum die combination to obtain desired size and shape of extrudate after due allowance for extrudate swell, as well as uniform velocity across the width of the extrudate profile. It is helpful to eliminate some of these trials by developing calculation methods for estimating pressure profile, velocity and swell distribution. There are a number of articles on calculating pressure drop from flow rate for non-Newtonian fluids in odd shaped ducts and tapered channels. Also, many simple techniques are available for analyzing non-Newtonian flow of polymer melts in simple extrusion dies. Most of these calculations assume a one-dimensional flow. More recently, there has been much work on developing finite element and other numerical methods for computing complex die flows. This paper describes and tests the utility of a quick and easy method of estimating extrusion pressures and velocities in and at the exit of extrusion dies using material properties and geometry. This method allows for abrupt changes in geometry such as sudden contractions in the flow channel.