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The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Conference Proceedings
LIFETIME PREDICTION OF POLYETHYLENE PIPES BASED ON AN ACCELERATED EXTRAPOLATION CONCEPT FOR CREEP CRACK GROWTH WITH FATIGUE TESTS ON CRACKED ROUND BAR SPECIMENS
Fracture mechanics lifetime and safety assessment of pressurized polyethylene (PE) pipes is based on the knowledge of material specific creep crack growth (CCG). However, with common test methods the investigation of this failure mechanism is not possible in modern PE-pipe materials in a feasible time. For an accelerated generation of CCG an extrapolation concept based on fatigue tests with cracked round bar (CRB) specimens was developed. In the present work this concept was applied to a common PE-pipe material to generate the material specific CCG data within a few weeks. To evaluate these data a fracture mechanics lifetime prediction of the CRB test was compared to results from static tests. With the integration of the data into a lifetime prediction model for pressurized pipes a simulation of a real pipe was possible.
HEATING AND PLASTICIZING THERMOPLASTICS WITH ULTRASOUND FOR MICRO INJECTION MOLDING
Ultrasonic plasticizing allows the melting of very small amounts of polymers for micro injection molding. The ability to plasticize polymers with ultrasound arises from the effect that they heat up under cyclic deformation due to inner and outer frictional losses. This paper presents investigations on the course of heating during plasticization. The heating rate as well as the corresponding process data of the ultrasonic equipment is analyzed in dependence on the parameter settings. Example micro parts being molded show the possibility to use ultrasonic plasticizing as a production technology.
EFFECT OF CARBON NANO FIBERS ON THE PERMEABILITY OF FIBER REINFORCED POLYMERIC NANOCOMPOSITES
One of the most attractive environmentally friendly energy generation methods is wind power. In order for this technology to compete favorably with the cost of traditional energy generation methods, the wingspan needs to be greatly increased from current dimensions. For this to occur, we need to take advantage of new material developments such as nano-composites.In order to manufacture such large parts, we need to understand factors affecting flow. In the case of flow through porous media, the material properties are permeability and viscosity. In this work we present preliminary results on the effect of carbon nano fibers on permeability.
SIMULATING THE DEFORMATION BEHAVIOR OF THERMOPLASTIC PARTS UNDER THERMAL AND MECHANICAL LOADS
During service, thermoplastic parts are often subject to a combination of thermal and mechanical loads. Especially the temperature has a great influence on the stiffness and the specific volume. Consequently the thermal exposure has to be considered during the design process of thermoplastic parts.
This paper describes the modeling of the temperature-dependent viscoelastic material behavior. Because the determination of the required thermal and mechanical properties is cost- and time-intensive, a procedure is elaborated to depict the temperature-dependent long-term behavior on basis of short-time tensile tests. Finally the model is evaluated in a comparison with experimental results.
PREDICTING THE CYCLE TIME IN INJECTION MOLDING AS A FUNCTION OF THE FROZEN LAYER THICKNESS
In the current economic market, production efficiency is critical if manufacturers are to remain competitive. The largest part of the cycle in injection molding is the cooling time. Thus for injection molders, to be successful, it is extremely important that they minimize this part of the process without adversely affecting part quality. Predicting the minimum safe cycle time in injection molding is complicated by the cyclic nature of the process. The mold thermal state changes with continuous molding until a quasi steady state is achieved.In this work, we evaluate the minimum frozen layer thickness required before the part can be demolded and how the growth of this frozen layer is affected as the mold thermal state changes with continuous molding cycles. Experiments are used to relate the minimum frozen layer thickness to dimensional stability and to select an ejection criterion in order to obtain a minimum safe cooling time
A STUDY ON MATERIAL DISTRIBUTION AND MECHANICAL PROPERTIES IN CO-INJECTION MOLDING
In the co-injection molding process, sometimesreferred to as sandwich molding, two different polymermelts are either simultaneously or sequentially injectedinto a mold to form a part with a skin/core structure. Coinjectionmolding offers the flexibility of using the bestproperties of each material to reduce material cost andpart weight. Particularly, it allows, the use of recycledmaterial in the core without an adverse effect on surfacequality. The properties of a co-injection molded productdepend on the individual properties of the skin and corelayers, and the skin/core volume ratio. This paper presentsa study of the effect of molding parameters on materialdistribution and mechanical properties of co-injectionmolded plates. Two virgin materials were triedpolypropylene (PP), and thermoplastic polyolefin (TPO)as well as grinded TPO from plastic bumpers.
MODELLING THE STRUCTURAL PERFORMANCE OF STRETCH-BLOW MOULDED PET BOTTLES
The mechanical properties of PET bottles are significantly affected by the process. In order to precisely model the structural performance of these bottles, the wall thickness and the process dependent material properties have to be considered. This paper describes an approach to combine the structural analysis and the process simulation. The wall thickness distribution and the local stretch ratios of the blown bottle are calculated by a process simulation and are then transferred to the structural analysis. Thereby, the stretch ratios are correlated with stretch ratio dependent material properties. In cooperation with Nestl?? Waters M.T., Vittel, France, the approach is applied on an empty and filled 0.5 litre PET bottle. The investigations point out that the accuracy of the structural analysis is significantly improved by applying the integrative approach.
NUMERICAL SIMULATION OF THE FAILURE BEHAVIOR OF PE PRESSURE
PIPES WITH ADDITIONAL LOADS
Using linear elastic fracture mechanics concepts a
simulation methodology for the assessment of internally
pressurized pipe lifetimes was developed. The concept is
based on the numerical calculation of stress intensity
factors for pipes under different loading conditions and on
using experimentally generated creep crack growth
kinetics for lifetime calculations. Comparison of simulated
lifetimes with experimental data from tests with internally
pressurized pipes proved the principal applicability of the
concept but also identified major parameters affecting
pipe lifetime.
NUMERICAL SIMULATION OF THE FAILURE BEHAVIOR OF PE PRESSURE PIPES WITH ADDITIONAL LOADS
Using linear elastic fracture mechanics concepts a simulation methodology for the assessment of internally pressurized pipe lifetimes was developed. The concept is based on the numerical calculation of stress intensity factors for pipes under different loading conditions and on using experimentally generated creep crack growth kinetics for lifetime calculations. Comparison of simulated lifetimes with experimental data from tests with internally pressurized pipes proved the principal applicability of the concept, but also identified major parameters affecting pipe lifetime.
DEVELOPMENT OF A PERMANENT PLASMA-INDUCED RELEASE COATING AS A SURROGATE FOR NON-PERMANENT RELEASE AGENTS
In the production of polyurethane parts the use of nonpermanent release agents is still inevitable. The regular mold-cleaning of residua of the release agent reduces the efficiency of the production process considerably. This paper describes the development of a permanent plasma-induced release coating with high durability for the series production of PU-parts as a surrogate for conventional non-permanent release agents. Basis of the project is a plasma-polymeric gradient layer with highly crosslinked siloxane-compounds for the mechanical strength of the coating and a high density of methyl groups towards the PU-sided surface for excellent release properties.
VALIDATION OF AN ACCELERATED FRACTURE MECHANICS EXTRAPOLATION TOOL FOR LIFETIME PREDICTION OF PE PRESSURE PIPES
For a fracture mechanics lifetime assessment of pressurized polyethylene (PE) pipes the knowledge of the material specific creep crack growth (CCG) kinetics is essential. As testing of CCG with common test methods is not possible in feasible times, an accelerated extrapolation procedure based on fatigue tests with cracked round bar (CRB) specimens was developed previously. Within the present work this test procedure was used to characterize CCG of a PE material at elevated temperatures of 60?øC. In combination with a numerical simulation model for pressurized pipes, lifetimes were predicted and correlated to real pipe failure times of the same material.
SAVING MONEY USING INTELLIGENT PROCESS OPTIMIZATION SOFTWARE
Looking at the increasing quality requirements and
the potential for time and cost savings in almost all injection
molding processes the classical way of optimizing a
process has to be reviewed. New and innovative software
solutions for process optimization and quality forecasting
therefore plays an important role and helps to answer
common questions to the shop floor managers:
Is the current machine setting the best one in terms of
cycle time and process capability? Is there a potential to
save time material or energy? Which machine parameters
have the highest influence on the quality?
A new software solution using self generating neuronal
networks now respond to these questions and supports
users without requiring a deep mathematical background.
It offers a pragmatic solution to be used by all
participants on the shop floor level. Practical experience
confirmed that on average 10% reduction in cycle time
can be achieved.
SAVING MONEY USING INTELLIGENT PROCESS OPTIMIZATION SOFTWARE
Looking at the increasing quality requirements and the potential for time and cost savings in almost all injection molding processes the classical way of optimizing a process has to be reviewed. New and innovative software solutions for process optimization and quality forecasting therefore plays an important role and helps to answer common questions to the shop floor managers: Is the current machine setting the best one in terms of cycle time and process capability? Is there a potential to save time, material or energy? Which machine parameters have the highest influence on the quality? A new software solution using self generating neuronal networks now respond to these questions and supports users without requiring a deep mathematical background. It offers a pragmatic solution to be used by all participants on the shop floor level. Practical experience confirmed that on average 10% reduction in cycle time can be achieved.
STRUCTURAL ANALYSIS OF SEMI-CRYSTALLINE THERMOPLASTICS WITH REGARD TO THE LOCALLY DISTRIBUTED MATERIAL BEHAVIOR DUE TO VARYING INNER PROPERTIES
During its manufacturing cycle a thermoplastic injection-molded part can be exposed to heat at various times. This has an influence on the inner and therefore on the mechanical properties of the part. Regarding these effects an integrative simulation approach has been developed at the Institute of Plastics Processing at RWTH Aachen University. It includes the development of a user-defined non-linear material model which takes into account the local distribution of the inner properties depending on the processing conditions and heat treatment. This paper deals with the main aspects of the material model and with the linking of the process simulation and the structural analysis using a universal data format.
PERFORMANCE OF A HELIBAR® EXTRUDER USING A GROOVED BARREL
A new type of single-screw extruder with grooved
barrel in the feeding and the melting section called
“HELIBAR®” was successfully introduced in recent
years. The grooved feeding section is typically cooled
passively by ambient air. The performance of a 35 mm D.
34 L/D HELIBAR was evaluated by running PP PC and
ABS in pellet form HMW-HDPE in powder form and
HDPE as a blend of pellet and regrind. One barrier-type
single-stage screw was used for all resins. The output rates
of this extruder were 3-4 times higher than those expected
for the same size extruder with smooth barrel while the
specific output rates (output rate per RPM) were more
than twice and virtually independent of screw speed or
head pressure. Furthermore this extruder had excellent
stability of the output rate and the melt temperature.
PERFORMANCE OF A HELIBAR?? EXTRUDER USING A GROOVED BARREL
A new type of single-screw extruder with grooved barrel in the feeding and the melting section, called 'HELIBARR', was successfully introduced in recent years. The grooved feeding section is typically cooled passively by ambient air. The performance of a 35 mm D., 34 L/D HELIBAR was evaluated by running PP, PC and ABS in pellet form, HMW-HDPE in powder form, and HDPE as a blend of pellet and regrind. One barrier-type single-stage screw was used for all resins. The output rates of this extruder were 3-4 times higher than those expected for the same size extruder with smooth barrel, while the specific output rates (output rate per RPM) were more than twice and virtually independent of screw speed or head pressure. Furthermore, this extruder had excellent stability of the output rate and the melt temperature.
DEVELOPMENT OF AN ADAPTIVE PROCESS OPTIMIZATION OF HOT-TOOL WELDING USING AN INNOVATIVE ACTUATION CONCEPT
This paper is a continuation of work presented at
ANTEC 2009 [5]. It looks into the initial steps of the
development of a self-optimizing hot-tool welding
machine. A new machine concept permits the specimen to
be pulled in a direction opposite to the joining direction.
Using this feature it is possible to assess the strength of
the weld directly at the hot plate welding machine. The
strength was measured while the material was still in the
molten state. In order to use these results for a selfoptimization
it was necessary to establish a correlation
between the short-time strength of the parts in the cooled
state and their short-time strength in the still molten state.
Using this concept, the control system of the welding
machine can be adapted to find an optimum processing
window with just a few test welds. The results show that
the optimum of the parameter settings can be defined by
measuring the tear forces on the welding machine. Based
on these results a self-optimization and quality assurance
during the running hot-tool welding process can be
developed and tested.
WHY GRADIENT COPOLYMERS MAKE BETTER COMPATIBILIZERS OF IMMISCIBLE POLYMER BLENDS THAN BLOCK COPOLYMERS: DETERMINING CRITICAL MICELLE CONCENTRATIONS OF COPOLYMER IN HOMOPOLYMER
A fluorescence technique is used to determine critical micelle concentrations (CMCs) of styrene-containing block and gradient copolymers dispersed within a homopolymer. Block copolymer composition and molecular weight are varied to determine what factors impact the CMC. Gradient copolymers are shown to have higher CMCs than block copolymers due to the gradient in comonomer composition along the copolymer backbone. Gradient copolymers can be more effective as compatibilizing agents, as they are less likely to be trapped within micelles upon melt processing
IN-MOULD LAMINATION OF METAL SHEETS WITH INTEGRATED FORMING FOR METAL DECORATED PARTS
For high-class applications (e.g. automotive interior) metal decorated plastic parts impress the customers with a metallic look and cool-touch haptics. Producing these parts has been a highly complex process. The in-mould lamination process of metal sheets allows a shortened process chain. In the process the injected melt adheres to a primer system on the metal surface. Furthermore the pressurized melt causes a forming of the metal sheet. This new technology enables a one-step production of metal decorated plastic parts.
This paper describes design principles for metal (stainless steel and aluminum) decorated parts first. Then the effects of the injection molding process parameters on the forming quality are shown. An approach to simulate the forming process is presented and evaluated by test results.
THE MORPHOLOGY OF MICRO-INJECTION MOLDED POLYOXYMETHYLENE
A micro-injection molding machine was used to obtain micro-moldings of high density polyethylene, polyoxymethylene, and polycarbonate, in order to study the effects of processing conditions on the microstructural characteristics and mechanical properties. The samples were microtomed and examined using a polarized light microscope for evaluation of morphology. Various microstructural features, such as morphological layer thickness and crystalline polymorphs, were observed and analyzed, in light of the thermo-mechanical history. These features were also correlated with both macro and local mechanical properties.
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