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  • Articles  (166)
  • 1990-1994  (166)
  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 2 (1993), S. 171-175 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 2 (1993), S. 75-106 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The design of extrusion lines deals with the extruder and the die as well as with the down stream equipment, especially the cooling section. This paper aids in the design of these three units, regarding different aspects. The scale-up of extruders by means of the model theory is demonstrated in its practical use with examples. Emphasis is laid on the design of series of single screw extruders with mixing-pins and of twin-screw extruders (scale-up). There the adequate selection of the necessary restrictions for the compilation of model laws is discussed in detail. This is an approach to the safe machine design on the basis of model theory.The present standard of the calculation of threedimensional flow patterns in extrusion dies by means of the finite-element-method (FEM) is shown in order to point out how design-aids for the die-designer are derived from these calculations. After a discussion of application-criteria for the FEM, examples will show possible ways of using FEM-results.For the shaping of Y-branches in twin-screw machines the FEM-results point to possible plate-out areas and to their avoidance by geometrical modifications. The calculation of a die for a T-profile helps to design the passages between entry and exit sections. Finally, flow coefficients for the calculation of pressure losses in different cross sections are given.The design and optimization of cooling sections, as it can be done with the aid of the actual cooling models, is shown for some important extrusion processes. Heat transfer coefficients for practical cases (film-sheet-, pipe- and parison extrusion) are presented. Examples show, how diagrams for the design and optimization of cooling sections (for example the reduction of internal stresses and warping) can be made, using a microcomputer.
    Additional Material: 31 Ill.
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  • 3
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Mechanical tests of prestressed and nonprestressed specimens show that prior stressing often significantly changes the stress-strain curve of amorphous and partly crystalline thermoplastics.1-3 Specimens subjected to a prior mechanical stress show a flatter stress-strain curve (even with a “kink”) than those not previously stressed. The original properties of prestressed specimens can be restored by tempering (at least in the range of small elongations). Specimens made of ABS react differently: After certain longterm prior stresses, followed by short-term tensile tests, brittle fracture occurs.
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 13-21 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The SMC process has reached a new level of quality with the recent generation of compression presses. SMC ply preheating has allowed shorter cycle times and improved flow properties. Cycle times of less than 1 min are now possible. Surface quality is improved with accurate press-velocity control and accurate parallelism control of the movable platen. When mold vacuum is used, the surface quality can approach the auto-maker's Class A finish standards without the use of time-consuming in-mold coating. The parallelism control allows tighter tolerances on the shear edge of the mold. If this is combined with accurately controlled press-force profile, a substantial reduction in flash can be achieved. The never presses are equipped with microprocessor controls. On-line quality control is possible, since all relevant parameters can be stored or closed-loop controlled. Statistical process control (SPC) can therefore be achieved without the need for additional hardware.
    Additional Material: 11 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 23-30 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper, the approach of biodegradation to reduce the environmental impact of plastic wastes is reviewed. The mechanism of biodegradation and the processing and applications of these materials are also discussed in relation to the structural characters of their molecules. The synthetic biodegradable materials such as starch based biodegradable materials are compared with naturally occurring biodegradable materials such as poly(hydroxy butyrate) (PHB) in terms of their applications, processing difficulty, and degradation mechanism. The future trends of these materials are anticipated.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 55-59 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Assuming that the solid moves in consequence of wall friction and friction of the material, transport equations have been established by means of a force and momentum balance on the volume element. These equations serve as a basis for describing the material feeding. That is, transition of the polymer from the feed hopper, or the feeding device, into the filling region of screws and the transport and compression of the solid polymer, i.e., the movement of the feed towards the plasticating zone, with simultaneous decrease of porosity. Depending on the geometry of the screws and on technological and material parameters, the model gives information on degree of filling, compression, pressure buildup, throughput of solids transport zone, and power consumption. The process model is suited for the design of the solids transport zone.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Knit lines in reaction injection molding (RIM) are formed when a fluid flow front passes through the mold cavity and must pass around objects in its path. Factors were ordered in importance of their effects on the deterioration in mechanical strength associated with knit lines. In order of decreasing importance, reactant temperature, mold temperature, and relative location (from the product) of the knit line sample were found to affect the knit line strength.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 75-76 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Additional Material: 2 Ill.
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  • 9
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element simulation of viscoelastic flows in double-layer coextrusion of polymer melts has been performed. The constitutive equation used is a realistic integral model of the K-BKZ type which can describe the viscoelastic memory characteristics of polymer melts. Viscosity and first normal stress data of typical PS and HDPE melts at 200°C are employed along with a feed ratio used in actual experiments found in the literature. Our results reveal important viscoelastic effects that could not be predicted by previous inelastic simulations. In particular, when the outer layer is more elastic than the inner layer, an enhanced extrudate swell is observed relative to the opposite configuration at the same flow rate, even if the outer layer is less viscous than the inner layer. In terms of a dimensionless stress ratio SR measured on the die wall, the more elastic material at the outer layer results in a higher SR value than that of the opposite configuration at the same flow rate. On the other hand, when the outer layer is less elastic than the inner layer, a reduced extrudate swell is observed relative to the opposite configuration at the same flow rate even if the outer layer is more viscous than the inner layer. When compared at the same SR value, however, our results show that the inelastic swell mechanism proposed by Tanner still applies qualitatively, i.e., a more viscous outer layer will result in larger extrudate swell than the opposite configuration.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 79-81 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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