Optimization of the injection molding technology for profiled high-performance thermoplastic sealing elements

Marian Janko

Research output: ThesisDoctoral Thesis


Progress in the design of valves for industrial reciprocating compressors have led to new challenges and requirements on the valve's sealing elements. These fiber reinforced thermoplastic elements are the centerpieces of the valves and are responsible for the valve's performance, efficiency, and lifetime. The introduction of optimized profiled sealing edges results in an increase of sealing element complexity, which made the common processing of sealing elements no longer feasible and profitable. The new generation of profiled sealing elements and their complex geometry are produced by injection molding of material-saving semi-finished products, which require less rework than the full molded disks of the common processing method. The new production process and the high demands on the material and behavior of the elements led to a broad research on thermal expansion, weld lines, warpage, and high cycle impact resistance of fiber reinforced high-performance thermoplastics. The influence of material and geometry of the sealing elements on the thermal expansion behavior was investigated and optimized to guarantee a good sealing characteristic of the valves at high temperatures. The complexity of the new molds led to a multiplicity of weld lines, which lower the structural integrity of the elements and further led to a reduction of lifetime and applicability. To avoid this a novel mold-based method was developed to modify the fiber orientation at the time of weld line formation and increase the strength up to almost flawless bulk behavior. The warpage of the elements was investigated by means of a special measurement system. The effects of sealing element geometry, weld line optimization and heat treatment were investigated and the resulting emerging warpage shape and total warpage amount was determined. The influence of basis polymer, fiber content, molecular mass, and impact modifier on the cyclic impact resistance, which is crucial for the application as sealing element material, was investigated and a high cyclic resistant material was found. The research findings are used to optimize process technology and product performance of the injection molded profiled sealing elements.
Translated title of the contributionOptimierung der Spritzgusstechnologie für profilierte Dichtelemente aus Hochleistungsthermoplasten
Original languageEnglish
  • O'Leary, Paul, Assessor B (internal)
  • Holzer, Clemens, Assessor A (internal)
  • Lucyshyn, Thomas, Supervisor (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until 20-04-2020


  • injection molding
  • mold technology
  • fiber reinforced thermoplastic
  • weld line

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