Band 21, Heft 4

There are still some difficulties in injection molding a super thin plate with micro through holes. Nozzle or filter plates are some examples of typical products. Conventional processes to manufacture nozzle plates of ink jet printer heads are electroplating or laser machining. In order to reduce the production cost and improve the performance of nozzle plates, a new approach, micro injection molding, is introduced to manufacture nozzle plates in this study. The micro mold was made by integration of the LIGA and M-EDM technology to improve the positioning and alignment accuracy. After assembling the micro mold, micro injection molding technique was applied to produce four nozzle plates in one shot. There are sixty micro through-holes on each plate and their diameters have been inspected and met the specification, 101 ± 1 microns, under a proposed vario-thermal molding process. The flow hesitation problem for molding a thin film of 50 microns was then solved. Experimental and simulation results indicated that the most significant factor for molding these nozzle plates is the initial mold temperature. This work recommends that the best initial mold temperature for molding such a thin film with the nozzle array is about 150°C for PP. The manufacturing procedures proposed here are believed to be more accurate and economical, and can be applied to mold similar micro parts.

Carbon black (CB) was added into a matrix of poly(ethylene terephthalate) (PET) by melt processing to prepare electrically conductive master batch (ECMB) for fiber applications. The amount of CB required to achieve a desired electrical property often results in poor mechanical properties of the final fibers. To solve this problem, a type of ECMB with a lower percolation threshold was designed by incorporating titanate coupling agent treated CB and using a matrix blend (adding polyethylene (PE) into PET). The effects of titanate coupling agent treatment and the matrix blend on the percolation threshold of ECMB are discussed and the effect of lower percolation threshold on the mechanical properties of final melt-spun fibers was investigated. The results indicated that titanate coupling agent treatment and a matrix blend are able to reduce the percolation threshold and thereby minimize problems with the mechanical properties of the final fibers, yet maintain the desirable electrical property.

In order to evaluate the tip-clearance effect on mixing, 3-D numerical simulations were applied to kneading block section of co-rotating twin screw extruders. The software we used was originally developed for non-Newtonian and non-isothermal flow analysis based on the finite element technique. The marker-particle tracking analysis was also developed in order to estimate the particle path, residence time distribution, stress and strain history, and so on. The stress distribution obtained by the above-mentioned simulations suggested the following mixing mechanisms. The kneading block with the small tip-clearance (TC) caused the bimodal stress distribution which had peaks in both high and low stress level. The marker-particles which overpassed the TC formed the peak at the high stress level and the other particles contributed to the peak at the low stress level. In other words, a large number of particles evaded the TC and it caused heterogeneous stress induced mixing. On the other hand, the large tip-clearance caused the narrow and sharp stress distribution because most of the particles passed over the TC. The stress level was not high, however, homogeneous stress induced mixing was expected. Since the tip-clearance applied a significant effect to the dispersive mixing, it should be optimised in accordance with the material design.

An experimental study of melt spinning and cold drawing of polyethylene and its Dow Chemical INSITE Ø catalyst octene copolymers was carried out. The structure and morphology of both melt spun and cold drawing fibers were investigated using wide angle x-ray diffraction (WAXD), small angle x-ray scattering (SAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and birefringence. Up to 5.9 mol.% octene, the fibers exhibit only the Bunn orthorhombic crystal structure. Fibers with 9.7 mol.% and 13.3 mol.% octene, whose DSC crystallinity is 0.23 and below, have an additional reflection at about 0.45nm. The Hermans-Stein orientation factors for the melt spun fibers were determined and correlated with spinline stress. Cold drawn polyethylene fibers exhibited additional reflection at 0.45, 0.38 and 0.35nm which may be associated with the Tanaka-Seto et al. monoclinic unit cell. The copolymers contained a decreased monoclinic level which disappears at about 5.9 mol.%. However, a broad reflection at 0.45nm, reappears at 9.7 mol.% octene. This reflection is also present at the 13.3 mol.% level. It is surmised that a pseudohexagonal or mesomorphic structure is developing. The Hermans-Stein orientation factors were determined for the drawn fibers as a function of cold draw ratio. Drawing results in high crystalline orientation and fibrillation for polyethylene fibers. For copolymers, with higher octene content, the fibrillation decreases.

The effect of distributor geometry on crimp contraction in the melt spinning and drawing of polyethylene terephthalate (PET) side-by-side bicomponent fibers was studied. Three different distributors located on top of the spinneret were designed to change curvature ratio of a side-by-side cross-section of bicomponent fibers. Regular and modified PET were selected to make latent crimp yarns. Spinning and drawing conditions were changed to choose the effective variables heat set temperature and draw ratio. Crimp contraction increased with increasing draw ratio and decreasing heat set temperature. Die geometry had a significant effect on crimp contraction by changing the curvature ratio of the cross-section. Under the same spinning and drawing conditions, the crimp contraction with higher curvature ratio was larger.

Thermal and rheological properties of various blends of gelatinized starch and biodegradable polyester, polycaprolactone (PCL) or poly(butylene succinate adipate) (PBSA), were studied by DSC, TGA and rheometry. Methylenediphenyl diisocyanate (MDI) was used as a compatibilizer and was distributed in different phases through controlled processing. The addition of MDI showed a stronger effect on thermal and rheological properties when it was mainly distributed in the polyester phase prior to blending. Starch was shown to increase the shear viscosity of both types of polyesters. The two blends, starch/PCL and starch/PBSA, showed a similar pattern of a power law dependence of viscosity on shear rate. MDI was shown to enhance the effect of starch on the melting and decomposition temperatures, especially when distributed in the polyester phase.

In this work, a three-dimensional finite element flow analysis code is used to study the flow behavior during sequential co-injection molding. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, continuity and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. Solutions are presented for the filling of a spiral-flow mould for which experimental measurements are available. The numerical approach is shown to predict the core advance stage during which the core flow front catches up on the skin flow front and the core expansion phase when the flow fronts of core and skin materials advance together without breakthrough. The breakthrough phenomenon is also predicted and the numerical solution is in good agreement with the experiment. Those phenomena are hard to predict numerically and to our knowledge this is the first attempt at simulating the three-dimensional melt behavior during core expansion and core breakthrough. The predicted flow front behavior is compared to the experimental observations for various skin/core melt temperature, skin/core viscosity ratio, and core injection delay. Simulation results are in good agreement with experimental data and indicate correctly the trends in solution change when processing parameters are changing.

This study investigated the effects of processing conditions on the shrinkage and warpage behavior of a box-shaped, polypropylene part created using a special microcellular co-injection molding process. Results were compared to the shrinkage and warpage of conventional and microcellular injection molded parts. A preliminary study was performed to determine processing condition limits and the steady state conditions for each combination of molding parameters. A 2 6-1 fractional factorial design of experiments (DOE) was performed utilizing the previously determined processing conditions. The molded parts were measured using an optical coordinate measuring machine (OCMM), which had previously been examined with a repeatability and reproducibility (R&R) study. These measurements were analyzed to determine the processing parameters that had the greatest effect on the shrinkage and warpage (S&W). The results of this analysis indicated that the supercritical fluid content and core-to-skin volume ratio had the greatest effect on the shrinkage and warpage of microcellular co-injection molded parts. The results of the experiment were that a considerable reduction in shrinkage and warpage could be achieved by utilizing microcellular co-injection molding.

Semi-crystalline polymers exhibit broad and multiple peaks in their melting traces. Thus, the melting temperature characteristics of polymers should consider both melting peak positions and melting temperature polydispersity. In this work, the effective melting temperature and temperature polydispersity are defined and calculated from DSC traces, using the crystal size number distribution and the melting temperature equation. Three methods are proposed for calculating melting temperature characteristics. These methods are based on: (i) average crystal size, (ii) the crystal stem number distribution function, and (iii) the monomer structural unit distribution function. They were employed to analyze the isothermal and non-isothermal experimental results for polyethylene polymers, especially linear low-density polyethylene copolymers. The first method, based on the value of average crystal size, gives the most reasonable results, taking into consideration agreement with experimental observations and structural data.

Advection of material volumes in a three-dimensional cavity flow is analyzed by using an experimental setup and a collection of computational tools. The experimental setup for the lid-driven cavity flow makes it possible to study the advection of drops for a wide range of flow parameters. The location of unmixed regions for a specific mixing protocol is predicted by means of the mapping method, which are then used to determine the initial location of the dyed drops in the experiments. Finally, an adaptive front tracking method is used to computationally follow the drops during flow in a precise way. In most cases, a qualitative comparison between the experiments and the simulations is found. In addition, the mapping method proves to be well suited to quickly predict unmixed regions in mixers.

Composite friction materials used in the braking system of vehicles are composed of different ingredients (typically up to 20 materials). The overall physical properties of these products are determined by the type and percentage of the individual ingredients in the final composition and consequently, may differ from one product to another. This paper studies the cure characteristics of railroad composite brake blocks during compression molding. Numerical simulations using the control volume/finite element method (CV/FEM) are utilized to predict temperature fields and cure conversion during the process. As railroad brake blocks are normally thick-sectioned parts, a three-dimensional modeling routine is developed. The model combines heat conduction and mass balance equations employing an appropriate cure kinetics equation. The required material data for the numerical simulation is obtained experimentally for a brake block available commercially. The effect of processing parameters and material properties on cure is studied by performing numerical simulations for different molding conditions and materials with different thermophysical properties. The effect of the heat of reaction on the thermal events of cure is also investigated using the numerical simulation in absence and in presence of that parameter, and assuming different values. For a rubber-based friction material, temperature distribution and molding time are not influenced by the heat of reaction released during cure. Moreover, the results indicate that the thermophysical properties of the brake blocks are much more effective than molding conditions in reducing the cycle time. Since the thermophysical properties are governed by the ingredients of the friction material, these properties can be improved in the formulation designing stage by including the appropriate ingredients. The results obtained by numerical simulation can be helpful to the designer of the compound, in order to achieve a brake block with both good braking performance and suitable processing properties.