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  • 1990-1994  (3)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 495-501 
    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 knowledge of how welding parameters affect the mechanical properties of welds is important. However, the mechanical properties of welds cannot be characterized by nondestructive testing methods. Because of its sensitivity to process conditions, extrusion welding of polypropylene-homopolymer (PP-H) was used to investigate the effects of welding parameters on the resulting mechanical properties of welds. Overall optimization of the welding process to obtain stable conditions during welding, which required a redesign of the welding shoe and the welding geometry, resulted in improved weld properties through better build-up of critical weld areas and suppression of void formation. Investigation of material heating characteristics led to a new air nozzle design. The effect of air temperature and welding velocity on the temperature and thickness of the molten layer was determined. The effects of individual process parameters on the structure and mechanical behavior of welds were established, thereby making it possible to specify narrow limits on the values of the weld parameters for producing high-quality welds. The quality of these joints cannot be determined by short-time tests because, even with severe testing conditions, cracks occur in the bulk material. Polarized optical microscopy was used to correlate crack behavior with the build-up of a specific multilayer structure in the weld area. Long-term tests demonstrated that, in both the time-to-crack and crack behavior, the joining area is not the weakest link in an extrusion weld when the welding parameters are chosen correctly.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 11 (1991), S. 91-98 
    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 recent years, efforts aimed at producing high-strength polymers have intensified noticeably. In addition to additive-based reinforcement, self-reinforcement without additives represents a way to increase material strength. In this study, the effects of self-reinforced polyethylene during extrusion with a conventional single-screw extruder are investigated. High extrusion pressure and controlled flow conditions at a low stock temperature, in conjunction with a longitudinal flow gradient in the die, permit the production of high-strength, extremely rigid profiles from high-density polyethylene (HDPE). The reinforcement is due to the shish-kebab structure, which is responsible for the improvement of thermal and mechanical properties. The growth of shish-kebab structures with an extended chain crystal axis and the radially lamellar structure, originated by flow-induced crystallization, depends on the orientation of the macromolecules in the melt. Compared to a conventional extruded profile, the high-strength profile exhibits molecular chain orientation largely parallel to the direction of extrusion, homogeneous transparency, and an approximately tenfold increase in Young's modulus, as well as improved thermal properties and good dimensional stability.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: By specificly influenced processing substantial effects of self-reinforcement can be obtained with PE and PP. Stiffness, strength and resistance to wear will increase by the factors of five (injection moulding) and nearly twenty (extrusion) compared with the normally processed materials. The effect of reinforcement is caused by the shish-kebab structure. It is multiaxial, which is of real importance for functional parts. This structure is favoured by a flow-and pressure-induced crystallization. The solidification of the polymer does not occur in the normal way by cooling but by pressure. The process can be on conventional machines. The morphology is a very stable one.
    Notes: Durch gezielte Beeinflussung der Verarbeitungsprozesse können besonders bei PE, aber auch bei PP erhebliche Selbstverstärkungseffekte erreicht werden. Die Steifigkeit, die Festigkeit und der Verschleißwiderstand werden bis zum 5-fachen (Spritzguß), sogar teilweise bis zum 20-fachen (Extrusion) gegenüber normal verarbeitetem Material angehoben. Die Verstärkungswirkung wird durch Shish-Kebab-Strukturen erreicht. Sie ist mehrachsig, was für Bauteile grundsätzlich wichtig ist. Erreicht wird dieses durch Begünstigung einer strömungs- und druckinduzierten Kristallisation. Die Verfestigung des Materials erfolgt nicht wie üblich durch Abkuhlen sondern ebenfalls druckinduziert. Das Verfahren ist auf konventionellen Verarbeitungsmaschinen realisierbar. Die Strukturen sind sehr stabil.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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