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The complexity of blow molded parts grows steadily. Accordingly the technology must keep space with the raised requirements of the market. Thus to improve the thickness distribution of complicated blow molded parts such as tanks for cars it becomes necessary to alter the thickness distribution of the parison not only in axial direction but also in circumferential direction. Encouraged by the success of the introduction of Membrane Dies for film and sheet extrusion the idea was born to design also dies with an extreme flexible outer wall for blow molding machines. This flexible wall can be locally deformed by adjusting screws which are located around the circumference of the die. The basic steps to reach this goal and the possibilities of the new technology are described.
Rapid tooling (RT) has been surveyed, talked about, praised and condemned by users, promoters and bystanders since the development of alternative tooling methods debuted. However, RT processes are improving, with newer direct metal deposition and spray metal methods addressing concerns by plastic molders about size, durability, and molded materials. This paper outlines the state of RT industry for users already familiar with prototyping and RT. Setting the group of commercialized RT products which can be used in standard injection molding machines against P20 CNC produced tooling standards for density, cosmetics, thermal conductivity, cost and lead-time, feature definition, and others shows the evolving technology and the gaps that persist. By and large, the RT industry has been redefining acceptable boundaries for rapid tooling, and listening more to customer concerns. Several experimental technologies and limited use technologies exist that may be used to produce molded plastic parts, but are not available for placement on a conventional injection molding machine. Experimental and noncommercial technologies are not covered in this paper, and discussion is limited to three commercialized processes that show more commercial and mainstream acceptance by custom molders, KelTool™, LaserForm™, and DMD™.
This paper discusses the use of ethylene octene (EO) copolymers made with metallocene catalysts in thermoplastic polyolefin (TPO) compounds designed for single-ply roofing. The performance of two neat EO copolymers is first compared with a polypropylene (PP) based Reactor TPO (RTPO) currently used in single-ply roofing. The more crystalline EO copolymer displays superior thermal and physical properties compared to RTPO. Formulations comprising the EO polymers were designed and optimized using mixture design of experiments. The optimal compounds contain about 50 % EO, 20 % PP and 30 % magnesium hydroxide (MH), a flame retardant additive.
Influence of processing conditions, part thickness and residual stress on the structure performance of 3C thin-wall injection molded parts were investigated. Thin-wall tensile test specimens were molded. A computer dictionary (CD), with 1.6 mm thick housings, was also used for structure evaluation of bending strength and drop-impact performance. It was found that as part becomes thinner, residual stress becomes higher and affects both part tensile strength and weld-line strength more significantly. Higher melt temperature and mold temperature, lower packing pressure and faster injection speed would reduce residual stresses, increase weld-line strength and improve associated properties. When CD housings were redesigned to 1 mm thick keeping sidewall 1.6 mm, both its bending strength and drop-impact performance were only slightly decreased.
Ultra sonic sensors have proven to provide valuable information on the thermoplastic foaming process in polymers. Measurement of the attenuation of the ultrasonic signal can be easily related to the nucleation process, i.e. the onset of bubble formation in the foam matrix. The ultrasonic sensors can be installed in-line, on the extrusion line, and thus allow direct access to the prevailing processing conditions. In this work, the degassing conditions (pressure and temperature) of a mixture of polystyrene and a physical blowing agent, HCFC 142b, are determined for two different nucleating agents. The resulting cellular structure of the extruded foams is correlated to the degassing conditions determined by the ultrasounds. The results are discussed in light of other observations on the nucleation process.
The falling weight impact test is a common method to evaluate mechanical properties of rotomoulded parts. This is because the resistance to impact of rotationally moulded articles is very sensitive to variations in resin, processing conditions, etc. More information could be obtained from an instrumented falling weight impact test, such as impact force/time and failure mode variation. In this work, these relationships are studied. Also, the effects of material properties, processing parameters, such as temperature and introducing pressure, are discussed.
During cure of a thermoset resin, the material exhibits three distinct phases: liquid, gel, and solid. Each of these material states is marked by dramatic changes in the thermomechanical properties of the resin. The glass transition temperature and the elastic modulus of the thermoset materials are two examples of the material properties that are of great interest to processors in the thermoset resin industry. The ability to predict the progression can give insight into the performance and optimisation of processing methods for thermoset resins.
The falling-weight impact test in injection-molded plates is simulated in a finite element based computer code (FORGE2®). The effect of processing is introduced on the material constitutive model through the dependence of its coefficients upon the thermomechanical indices computed from mold filling simulations. Two plate-like moldings (a box and lateral gated disk) were injected with arbitrary sets of processing conditions. In the impact simulations, two extreme conditions of contact between the impactor and the plates are considered: frictionless and adhesive contacts. The simulated force-deflection curves are compared with the experimental ones. Good agreements are obtained providing the different strain-rate sensitivities of the microstructural parameters are taken into account The results also evidence the role of the viscoelastic coefficient on the initial deformation stages. Moreover, the contact conditions have a strong effect on the mode of rupture of the plates and consequently on the maximum sustained strength levels.
The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene copolymer was used as the compatibilizer in high-density polyethylene-wood flour composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing elements with low intensity of shearing. A suitable combination of processing variables, including screw rotation speed, throughput rate, and barrel temperatures, was necessary for limiting the thermal degradation and the darkening of the wood filler. However, tensile properties of the composites were not affected much.
The effects of various types of compatibilizers on the mechanical properties of high-density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated linear low-density polyethylene, polypropylene, and styrene-ethylene/butylene-styrene copolymer were incorporated to reduce the interfacial tension between polyethylene matrix and wood filler. It was found that LLDPE-g-MA gave maximum tensile and impact strength of the composite presumably due to better compatibility. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for SEBS-g-MA system. Whereas, notched impact strength decreased with increasing loadings of PP-g-MA. A scanning electron microscopy study was employed to reveal the interfacial region and confirm these findings.
Step shear strain experiments were performed using several entangled polystyrene (PS) solutions to investigate factorability requirements of the non-linear relaxation modulus, G(t,?) [? ?12(t,?)/?]. A phase modulated flow birefringence apparatus was used to measure optical equivalents of shear stress (n12) and first normal stress difference (n11-n22) in a plane-Couette shear flow geometry. For all polymers studied, a separability time ?k was identified beyond which the optical equivalent of G(t,?) [B(t,?) ? n12/? ? G(t,?)×C] could be factorized into separate strain and time dependent functions. In every case, ?k exceeded longest Rouse relaxation time ?R and found to be of the order of terminal relaxation time ?d0. These findings could help explain previous experimental observations of delayed factorability and non-factorable relaxation moduli in well entangled polymer solutions and melts.
The cohesive properties of many engineering plastics are difficult to determine experimentally, as the polymers are frequently insoluble, have high Tg's, and are sometimes poorly characterized. Molecular modeling can provide useful information of higher quality than might be obtained by other methods for these difficult polymers. A series of simulations on Ultem® and related molecules have been performed to evaluate the cohesive energy density of the polymer and determine interfacial interactions with small molecules. These methods yield a value near 22.0(MPa)½ for the solubility parameter of the polymer, and it is shown that benzyl alcohol has the most favorable interactions.
The melting of polymer caused by friction before the solid plug is formed is an important phenomenon in the plastic injection process. To analyze the melting process caused by solid particles sliding against the bellow, an analytical method that can simulate behavior of each particle during the calculation should be used. Particle element numerical method is hence adopted in the analysis for this research to take into consideration the behavior of each particle. In the review of literatures in this area, no publication has reported success in the analysis of the transient close-contact melting process caused by friction. In this paper an analytical expression for the transient melting process is derived by assuming friction against flight and screw as friction against adiabatic walls.
In plug-assisted thermoforming, the interaction between the sheet and the plug strongly affects the final part thickness distribution due to sheet cooling and slippage on the plug surface. The type of plug material and surface finish has to be carefully selected. The amount of slip on the plug surface depends on the rheology of the polymer sheet and on the friction coefficient. Both properties are temperature dependent. In this work a non-isothermal friction coefficient model is evaluated for its potential in predicting the amount of slip in plug-assisted thermoforming. The model has been implemented in a finite element analysis software for predicting the consecutive steps of the thermoforming process. The model has been applied to simulate industrial scale plug-assisted thermoforming and the predictions are compared to experimental measurements.
Four series of coatings were prepared by using a soybean oil based isocyanate prepolymer and two types of the soybean oil based polyols as the crosslinkers. Water (humidity from the air ) was also used as a co-crosslinker. The isocyanate prepolymer and the polyols were prepared according to the original, proprietary methods. Varying the hydroxyl number of the polyol and polyol/ water ratio in the crosslinker varied the structure and properties of the coatings. The coatings were tested for hardness, elasticity (bending test), scratch resistance and adhesion. DSC, TGA, TMA, tensile strength and swelling were used to assess the glass transition and crosslinking density of the films.
Thermotropic liquid crystalline polymer (TLCP) reinforced thermoplastic polymer (TP) strands were spun and used in injection molding to form wholly thermoplastic composite materials. While keeping the strand size suitable for injection molding, effort was made to increase the orientation and aspect ratio of the TLCP fibril that would remain in the final product as reinforcement. The pelletized strand can be injection molded without disturbing the TLCP reinforcing fibrils. The samples have similar mechanical properties, lower density and smoother surfaces compared with glass fiber reinforced samples.
In the wire and cable industry the speed of the insulated copper wire through the die is very fast. In 1963 a 24 gage wire was coated with plastic with a clearance in the die of only 5 mils (1 mm = 40 mils, i.e., 5 mils = 0.125 mm) at a speed that exceeded 2500 feet/min (almost 1 kilometer/minute). The shear rate calculates to be in excess of one million reciprocal seconds (actually this is 4 x 106 sec-1). Drastic changes were discovered in the molecular structure of the plastic. Shearing the polymer chain causes changes in the molecular structure that can be advantageous or severely detrimental. These running conditions and the effect on the PVC is the concern of this paper.
Long-stroke shuttle machines have developed a well-defined role in the extrusion blow molding of calibrated neck bottles. However, these machines have limitations due to factors such as the long axial length of the stroke and the need for large multiples of tooling, knives, dies, punches and In-Mold Labeling (IML) tooling sets per the number of mold sets. Many of these limitations have been overcome through the incorporation of an indexing rotary motion. The end result is a technologically advanced, small footprint machine that can produce IML bottles with very little cycle time penalty. Further, the multi-layer containers are de-flashed before exiting the machine with positive bottle transfer between stations with a true single-point product discharge. All of this is accomplished using fewer die pins, bushing sets, cut-off knives, trim dies, punches, and IML deployment heads than typically required. This paper discusses the technical hurdles that were overcome to re-invent" the shuttle machine and open up new possibilities in extrusion blow molding."
Styrene Maleic Anhydride (SMAH) / Polytetramethylene Ether Glycol (PTMEG) blends were produced in a batch mixer in the presence or absence of hydrated zinc acetate catalyst. The oscillatory shear properties in the melt state and the Fourier Transform Infrared Spectra (FTIR) of the blends were studied. The SMAH/PTMEG/zinc acetate blend had higher storage modulus, G', loss modulus, G and complex viscosity ?* than the blend without the catalyst. The distribution of relaxation times was calculated by using the oscillatory shear data and a generalized Maxwell Model. In comparison to pure SMAH for all the blends higher relaxation strengths at longer relaxation times were obtained due to chain extension and branching. The FTIR spectra of the SMAH/PTMEG blend indicated ester formation confirming the existence of chain extension / branching reactions in batch mixing."
Models produced by rapid prototyping (RP) allow the validation of a parts design with respect to its geometry. Beyond this, the rapid prototyping technique Stereolithography (SL); when used to manufacture moulding cavities, has shown itself to be capable of rapidly and economically producing low volumes of plastic injection moulded parts prior to commitment to hard tooling. These parts are more complete prototypes, they imitate parts that would be produced by a hard tooling manner with respect to their material, geometry and production process. A major drawback of the SL injection moulding process is that the tools are susceptible to producing only a small number of parts before failure. SL tools may break under the force exerted by part ejection when the friction between a moulding and a core is greater than the tensile strength of the core resulting in tensile failure. Very few justified recommendations exist concerning the choice of mould design variables that can lower the part ejection force experienced and reduce the risk of SL tool failure. This research investigates the ejection forces resulting from injection moulding polypropylene (PP), acrylonitrile-butadiene-styrene (ABS) and polyamide 66 (PA66) parts from SL tools which are identical in all respects except for their build layer thickness (a process variable when generating the SL tooling cavities) and incorporated draft angles (a tooling design variable). This work attempts to identify appropriate evidence for recommendations with respect to these variables and SL injection moulding. The results show that linear adjustment of draft angle results in a fairly minor linear change of part ejection force according to the moulding material. A linear adjustment of the build layer thickness results in a greater change in part ejection force as a more non-linear relationship. In both cases greater ejection forces were experienced by PA66, then ABS and then PP parts, respectively. The results also show that the s
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