Processing Technology

Institut für Kunststofftechnik

Research topics

Describing a machine, a tool or a processing method appropriately is essential to increasing efficiency. Possibly, suitable measurement systems and methods have to be invented first. For predicting the behavior of machines and tools during processing, the IKT researches on exemplary and, if possible, universally appicable mathematical descriptions of the respective processes, enabling a realistic simulation.

Current research

Single-screw extrusion

Initial Situation

  • Increasing demands on production speed and product quality in extrusion
  • No high-speed extruders with small screws (D = 20-40 mm) at the moment
  • Conventional grooved sleeve extruders: high melting temperatures, throughput fluctuations and increased wear due to pressure peaks
  • Helibar® system: combination of barrier screw and grooved plasticizing zone --> high specific throughputs with gentle pressure build-up without overheating of the melt

Challenges

  •   high throughputs lead to short dwell times in the high-performance extruder and to poorer melt homogeneity

Approach

  • Variation of screw, barrel and groove geometry
  • Development of new, objective methods for the evaluation of mixing quality
  • Adaptation of design criteria for high-speed extruders
  • Optimization of process parameters

Initial Situation

  • Process engineering processes in single-screw extruders with grooved plasticizing zone are not yet fully understood
  • The design of these extruder systems is still largely based on empirical values and complex trial-and-error tests.

Objectives

  •  Analytical modelling of the melting zone of extruders with grooved plasticizing zone for simple and cost-effective design of energy-efficient high-performance extruders

Approach

  • experimental investigations on a longitudinal folding cylinder
  • Further development of the existing analytical model based on experimental investigations
  • Validation of the newly or further developed model for calculating grooved plasticizing cylinders

 

 

Initial Situation

  • until now, three-dimensional modelling of the feed and melting zone of single-screw extruders is only possible by separate investigation of each zone
  • application of 3D CFD flow simulation is not widespread

Objectives

  • coupling of particle simulation (discrete- element-method) und flow simulation (finite-volume-method)
  • prediction of throughput and melting performance, pressure and temperature profile
  • knowledge gained will be used to optimize the design of the cylinder and the screw

Challenges

  • no melting model describing the transition of the plastic granulate from solid particles to liquid phase
  • difficult modelling and simulation

Initial Situation

  • Often shearing devices are used during processing polymer-blends
  • Usually they are designed empirically
  • no information about the quantity of the shear and strain deformation acting on the polymer melt

Objectives

  • Design and construct a novel experimental setup to investigate the droplet deformation and breakup in polymer melts
  • Model the droplet sizes
  • Optimize the shearing devices

Challenges

  • Droplet size and shape are not considered at the preliminary design
  • Wrong choice of design leads to poor melt homogeneity as well as unsatisfactory dispersion
Poincaré-maps through a mixing element

Initial Situation

  • Because of the highly specific throughputs of advanced high-speed extruders, mixing elements are applied at the end of the screw to ensure thermal and material homogeneity of the melt
  • A great challenge is the design of these mixing elements under consideration of varying requirements

Challenge

  • Computational Fluid Dynamics are used for the description of the mixing behavior
  • Current statistical mixing quality measures have numerical limits

Objectives/Approach

  • After the flow field is calculated, the particle tracking method is applied on two particle clouds at the inlet
  • Between these two clouds an interface can be reconstructed by means of a novel interface recontruction algorithm
  • A new mixing quality measure, the interface enlargement, has been introduced

Initial Situation

  • design of extrusion dies with empirical or simple analytical methods
  • highly time and cost intensive
  • especially in case of new materials or process parameters

Challenges

  • Reduce the pressure drop in the extrusion die
  • homogeneuos velocity profile at the die outlet is required
  • application of accurate flow models

Objectives/Approach

  • Implementation of the new viscosity model CARPOW-model in OpenFOAM®
  • 3D-simulation of extrusion dies
  • Example: spiral mandrel distribut

Initial Situation

  • Co-Kneaders meet the highest mixing requirements
  • Process design currently only by empirical knowledge and based on trial-and-error method

Objectives

  • Enhanced understanding of the process conditions using experimental data and numerical simulations
  • Development of both an analytical model for Co-Kneaders and a simulation tool

Approach

  • Comprehensive experimental investigations of the operation conditions of Co-Kneaders
  • Development of a 3D numerical simulation and 1D analytical simulation

 

Injection Molding

Initial Situation

  • Injection molded parts have a low thermal conductivity due the thickness
  • Potential of thermal conductive additives are not used yet

Challenges

  • Lower share of high cost additives
  • Lower fillpressure and mold temperature

Approach

  • Add of additives for a better polymer flowability
  • Add of additves for a slower crystallization rate

Initial Situation

  • Injection molding cycle times are often too long and are based on experience
  • Material characterizations take place in laboratories, independent of the actual process

Objectives

  • Material and additive characterization directly in the injection molding process
  • Creating new parameters in order to gain a process time optimized injection molding cycle

 Approach

  • Automated evaluation of ejection forces
  • Investigation of a correlation between viscosity data and flow path length
  • Use of these developments in order to optimize the process parameters

Initial Situation

  • Intensive maintenance is necessary for signs on trees (e.g. by means of nails)
  • Alternatively high costs for signs with posts and foundation

Objectives

  • Variable, cheap and low-maintenance fastening system for signs
  • Development of a material and specific test methods to meet the new requirements

 

Approach

  • Intelligent component design
  • Development of suitable materials
  • Development of specific testing methods, e.g. to simulate the growing of the part with the trees

 

Initial Situation

  • Reducing CO2-emission by lightweight design and construction
  • New manufacturing concepts for continuous fiber reinforced thermoplastics

Challenge

  • Long cycle time and high energy usage do not allow for high volume production

Objectives /Approach

  • New heating concepts for CRP sheets during handling utilizing electric conductivity of carbon fibers
  • High automation, low processing costs

Initial Situation

  • Limitations to convective drying due to poor heat and mass transfer within in the polymer
  • Thermo-oxidative damage due to long-time exposure to high temperatures
  • High energy consumption

Approach

  • Using microwaves for volumetric heating
  • Better mass transfer through partial pressure gradient
  • Combination of complementary drying mechanisms for improved mode of action

Objectives

  • Reduction of thermal and oxidative damage to polymers
  • Improvement of energy and time efficiency in polymer drying

Initial Situation

  • Potential for design of resource and energy efficient light weight structures
  • Possibility of recycling due to thermoplastic matrix

Challenges

  • Production of structural parts in high quantities
  • Recycling and reuse of materials used in the Process

Objectives

  • High amount of recycled fibers and recycled matrix material
  • Perserving the mechanical properties of the part

Thermoforming

Initial Situation

  • The quality of thermoformed parts is highly influenced by sheet quality. Due to alternating sheet quality, especially in multi-layer-sheets, the thermoformed part‘s quality decrease and processing is made difficult.

Challenges

  • Because of alternating sheet quality the processability of multi-layer-sheets is difficult

Approach

  • The IKT develops a testing apparatus for the characterization of incoming goods quality. The testing apparatus characterizes and quantifies the thermoformability of multi-layer-sheets and thereby improves communication between sheet producer and processer.

Initial Situation

  • The challenge during manufacturing thermoformed parts is the control of the wall thickness distribution of the final part

Challenge

  • High stretching and material thinning on angles, edges and roundings can lead to waste

Approach

  • The IKT develops a new heating strategy using a special heating element, that enables the generation of temperature profiles on the sheet surface with higher resolutions than commercial systems do. With this temperature profiles the temperature depending stretching behavior of the sheet is influenced in such a manner that a more uniform wall thickness distribution of the final part is achieved.

Pultrusion

Initial Situation

  • increasing importance of continuous fiber or fabric-reinforced thermoplastics
  • so far frequently plate shaped semi-finished products --> "organic sheet"
  • high-fibre profiles for highly stressed lightweight structures
  • Manufacture of fibre-reinforced thermoplastic solid profiles

Challenges

  • Difficult to impregnate and wet the fibre fabrics with viscous thermoplastic matrix
  • Flow path severely limited compared to low-viscosity monomers of duromers
  • No large-scale production
  • No integrated flame retardant for thermoplastic matrix available on the market this time
  • No fibre-reinforced tube profiles with thermoplastic matrix available

Solution

  • continuous anionic polymerisation of PA6
  • low-viscosity monomers: simple fibre impregnation
  • Tool reaction to a thermoplastic matrix
  • Manufacture of fiber-reinforced thermoplastic tubes on a novel pultrusion line

Initial Situation

  • currently petrochemical products  are mainly used for wooden constructions (pultrusion process)
  • biobased resin with better flame retarding and strength properties shall replace them

Challenges

  • highly viscous raw materials
  • organic content higher than 90% to reach
  • no statement about fiber impregnation possible by using simulation methods

Objectives

  • process development for production of reinforcement ribs with cellulosic fibres for wooden constructions
  • simulation of the fiber impregnation for precess design

Rheology

viscosity curves of an unfilled and a filled polymer

Initial Situation

  • increased applications of filled polymers in the industry
  • previous viscoity models lead to mistakes in the approximation

Challenges

  • simulation of the stream is usually inaccurate
  • viscosity behavior at low shear rates is not considered usually

Objectives

  • development of a new vicsosity model with physical based parameters
  • quantification of the network structure based on the fractal dimension
  • forming a network structure in dependence on the deformation

Initial Situation

  • increased application of PA66 produced by blow forming and thermoforming

Challenges

  • simulation of the stream usually inaccurate
  • viscosity behavior at low shear rates is not considered usually

Objectives

  • development of a PA66 melt with higher viscosity
  • development of a PA 66 melt with a strain hardening effect

Contact

This image shows Alptekin Celik

Alptekin Celik

Dr.-Ing.

Research associate

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