• Document: CO-EXTRUSION BLOW MOLDING With A Continuously or Sequentially Foamed Layer
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CO-EXTRUSION BLOW MOLDING With A Continuously or Sequentially Foamed Layer Wolfgang Meyer W. Müller USA, Inc. Annual Blow Molding Conference October 6-7, 2014 Chicago, IL W. Müller GmbH, Troisdorf, Germany W. Müller USA, Agawam, MA Manufacturing Engineering R&D Customer Service W. Müller USA, Agawam, MA Field Service Sampling up to 7 Layers Parts Service W. Müller USA, Agawam, MA • More than 1,200 extrusion heads installed in North, Central and South America S18/35-80 P-PE, ReCo 3 S5/35-85 P-PE, CoEx 6 S1/160 RV-PE, CoEx 3 Accumulator Presentation • Topics  Foam Blow Molding • Existing Technologies • Our Objective  Pilot Project: Foaming of Preform  Trilayer Co-Extrusion with Foam  Trilayer Sequential Co-Extrusion with Foam Foam Blow Molding • Why ? • Foam Blow Molding is not a new technology • Commercial application are not widespread • Reasons for Foam Blow Molding  Light-weighting  Lower part weight while maintaining rigidity  Increased rigidity without adding weight  Thermal insulation  Noise reduction (from airflow) Foam Blow Molding • Existing Technolgy ... • … is based on continuous extrusion blow molding with chemical or physical blowing agents or a combination thereof.  Chemical blowing agents are often unacceptable for food/beverage packaging and automotive applications.  Physical blowing agents are preferred. • … uses nucleating agents to achieve a uniform microcellular structure.  Adds cost Foam Blow Molding • Existing Technology ... • … allows gas to escape to the surface causing open pores  Not ideal for food and beverage packaging  Not suitable for exhaust and fluid carrying ducts  Can be solved with trilayer co-extrusion • … introduces blowing agents in the extruder barrel  … does not adequately control gas volume injected in each parison of a multi-parison extrusion head • … tries to make do with existing extrusion heads, seldom designed with flow channels to avoid pressure drop. • … not suitable for sequential foaming of a parison or a layer Foam Blow Molding • Our Overall Objective • Develop a multi-parison trilayer extrusion head • for discontinuous/sequential extrusion of a center foam layer • with a controllable and consistently repeatable cellular structure in each parison • without the use of nucleating agents. • Explore potential applications in the industrial/automotive sector • Apply expertise gained for applications in the packaging sector Pilot Project: Foaming of Preform • First Steps: • Inject gas in the extrusion head instead of in extruder • Produce a monolayer foamed preform with a consistently fine cellular structure • Push out preform via an accumulator in preparation for sequential foam extrusion. • Evaluate  Impact of blowing agent on viscosity and melt temperature  Length of mixing section  Effect of gas pressure and compressor Pilot Project: Foaming of Preform • Equipment: S1/25 T-PE Extrusion Head Pilot Project: Foaming of Preform • Effect of Mixer Length and Gas Pressure (w/ PA) Picture 1 Picture 2 Picture 3 # of Mixing Elements 2 4 4 Melt Pressure – Elbow 53 bar 103 bar 192 bar Gas Pressure 45 bar 105 bar 390 bar Melt Pressure – Mixer Entry 37 bar 80 bar 171 bar Pilot Project: Foaming of Preform • First Results • Nitrogen blowing agent is least costly, environmentally friendlier than CO2 and suitable for many resins. • Blowing agent reduces melt viscosity, material dependant; run with up to 50⁰F lower than normal melt temperatures. • Suitable mixers are not commercially available, determined required minimum length of a static mixer • Compressor must generate up to 600 bar / 8,700 PSI. The higher the pressure, the finer the cell structure. • Flow channel must remain unchanged in size from point of gas injection to extrusion die. Avoid 90⁰ turns. Pilot Project: Foaming of Preform • Pressure Drop  To avoid premature expansion, gas must be kept in solution in plastic melt from point of introduction to the bottom of the die  Soda bottle example:

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