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  • 1
    Electronic Resource
    Electronic Resource
    A linear viscoelastic model for solid polyethylene (1997)
    Springer
    Rheologica acta 36 (1997), S. 462-471 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polyethylene ; viscoelastic solid ; time ; temperature superposition ; stress relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Stress relaxation tests have been carried out on a blue, pipe grade PE80 medium density polyethylene (BP Chemicals), to provide thermo-viscoelastic rheology for use in calculating thermal stresses in pipe production. Stresses up to 4MPa were used, with strains up to about 2%, in tests at temperatures from 23° to 90°C. Within this range a linear viscoelastic model was applicable, provided the initial ramp strain rate was less than 7×10–5s–1. The stress relaxation data was fitted directly by a model incorporating an elastic response to volumetric strains, and a generalised linear solid model, consisting of two Maxwell elements and a purely elastic element in parallel, for deviatoric strains. Arrhenius type temperature dependence of relaxation times and shear moduli is found, and within experimental accuracy the temperature dependence of all these model parameters is the same. As a consequence, and provided that the duration of the strain ramp is sufficiently short relative to relaxation times, the model leads to time-temperature superposition of the relaxation moduli, using the same shift factor on both the response magnitude and time axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396331
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  • 2
    Electronic Resource
    Electronic Resource
    Wall thickness uniformity in plastic pipes: Computer simulations of the effectiveness of die mandrel offsetting and pipe rotation in combatting sag (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 921-928 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A computer simulation, based on a thermoviscous model of cooling and gravity induced flow (sag) in plastic pipe manufacture, which has previously been described in detail and validated against experimental results, is here used to investigate the effectiveness of die mandrel offsetting and pipe rotation in combatting sag. SDR11 MDPE pipes of 315, 560, 800, and 1000 mm diameter are considered. Results are examined in terms of a waste percentage, representing polymer used in excess of that corresponding to the minimum wall thickness. With a concentric mandrel, waste is predicted to be 4.3, 14.0, 17.9, and 18.7% for the four sizes, respectively. Optimum offsets and minimum waste percentages are found to be: 2 mm, 0.8%; 15 mm, 4.6%; 42 m, 9.8%; 63 mm, 12.7%, respectively. For the largest pipe this corresponds to a wall thickness variation of 19.6 mm. Simulations of rotation of the 800 mm pipe show waste falling rapidly to 5% at 1 revolution/4800s, then a slower decrease, reaching 1.6% at 1 revolution/600s. The simulation is equally applicable to all grades and sizes of pipe, and provides a valuable computer aid for the design and operation of pipe cooling lines.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351106
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation of aligned discontinuous fiber pre-pregs by deposition from a suspension (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 787-797 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In a process for production of aligned short fiber pre-pregs, fiber suspension passes through a converging channel to emerge as a thin free-surf ace sheet which is laid down onto a reciprocating horizontal filter surface. Following our previous work on fiber alignment in the channel, detailed studies are reported of the suspension sheet falling under gravity, and of the deposition stage. Close agreement is found between computed and experimental velocity profiles for sheets of fiber-free liquid. Modification of the velocities resulting from the presence of fibers aligned in the flow direction is taken into account using an increased extensional viscosity. This is evaluated using pre-existing theory which is tested experimentally and found satisfactory. A simple relationship between velocity and fiber alignment change in the falling sheet is derived and tested experimentally. Alignment is marred by surface disturbances to the sheet. Comments are made on the stability of the free-surface sheet. An experimental study is made of alignment changes as fibers are deposited on the filter, and the results related qualitatively to operating conditions. In general there is little difference in alignment before and after deposition, except close to the leading edge of the filter where alignment loss occurs. Previous work is reviewed and recommendations made on optimum operating conditions.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760201205
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  • 4
    Electronic Resource
    Electronic Resource
    Flow and heat transfer in screw extruders: I. A variational analysis applied in helical co-ordinates (1973)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 13 (1973), S. 209-215 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A variational analysis is applied in helical co-ordinates to the problem of a developed, steady-state flow in a screw extruder. The functional involves only two dimensionless coordinates and is suitable for minimisation, e.g. by the finite element method. It is applicable to non-isothermal, purely viscous flows and contains terms representing effects of inertia, convective and conductive transport of heat, pressure gradient, and viscous dissipation. The analysis takes account of the true helical geometry and involves assumptions only in taking the fluid density, specific heat and thermal conductivity of the fluid to be constant, in regarding the fluid to be homogeneous and isotropic, and in simplifying the pressure distribution.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760130307
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  • 5
    Electronic Resource
    Electronic Resource
    Finite element solutions for flow in a single-screw extruder, including curvature effects (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 339-348 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Slow developed flow in an extruder channel has been set up as a two-dimensional, variational problem using a helical coordinate system, thus avoiding the usual geometrical simplification. Continuity is enforced by an integral form of constraint, and solutions for isothermal, Newtonian flow are obtained by a finite element method for both shallow and deep, highly curved channels. The performance of the solution procedure as a function of Lagrangian multiplier is discussed. Convergence to correct solutions is demonstrated for the shallow channel case. Deep channel results are compared with analytic predictions, curvature corrected according to Booy. Further testing of deep channel results will be made against experimental data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760200505
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  • 6
    Electronic Resource
    Electronic Resource
    Finite element solutions for flow in a single-screw extruder, including curvature effects (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 983-983 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760201412
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental deep-channel velocity profiles and operating characteristics for a single-screw extruder (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 982-982 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760201411
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental deep-channel velocity profiles and operating characteristics for a single-screw extruder (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 349-356 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Data have been obtained on the operation of a deep-channel single-screw extruder, pumping a Newtonian liquid under isothermal, developed flow conditions. Flow rate, screw speed, and pressure gradient characteristics were measured, and a tracer particle technique was employed to determine channel velocity profiles. The data were required for the testing and development of a computer model for flow in the extruder, which takes into consideration channel curvature. Results confirm the correctness of the computer solutions previously reported.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760200506
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  • 9
    Electronic Resource
    Electronic Resource
    Bending and breaking fibers in sheared suspensions (1981)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 23-31 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An experimental study was made of single fibers rotating and bending in Couette flow of a Newtonian liquid. A previous result for critical fiber buckling was re-tested and found satisfactory, and the transition between ‘springy’ and ‘snake’ rotation was delineated. The minimum radius, of curvature achieved during rotation in the “snake orbit” regime was measured as a function of fiber aspect ratio, Young's modulus, and fluid shear stress. Two correlations are presented which are constrained to satisfy limiting conditions for very stiff and very flexible fibers. Together with a result from thin rod theory, these correlations may be used to predict breaking conditions for fibers of known Young's modulus and ultimate tensile strength. Predictions are tested in experiments where two types of glass fiber are broken in suspension and found satisfactory. Results show that several reinforcing materials will probably break within the range of conditions covered by our experiments, or in a region which can be treated by extrapolation from our results.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760210105
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  • 10
    Electronic Resource
    Electronic Resource
    Deep channel operating characteristics of a single screw extruder: Finite element predictions and experimental results for isothermal non-Newtonian flow (1981)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 100-104 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Finite element solutions are presented for developed, isothermal, power-law flow in an extruder channel, based on a variational formulation in helical co-ordinates. The success of the method in handling non-Newtonian flow in a deep, highly-curved channel is tested by comparison with experimental results. Operating characteristics were determired under virtually isothermal conditions for a screw with depth to diameter ratio 0.25 pumping an aqueous glucose solution containing high molecular weight hydroxyethyl cellulose. Shear stress and first normal stress differences of this solution were determined in a rheogoniometer. It was both highly shear-thinning and elastic. Computed and experimental screw operating characteristics agree well, except near closed discharge, where effects due to viscous heating and elasticity are tentatively suggested.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760210208
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