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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Optimization of Parts with Rib Using Gas Assisted Injection Molding Technique
Gas-assisted injection molding (GAIM) offers a cost effective means of production of plastic parts and a solution to the problems associated with conventional injection molding (CIM). GAIM process utilizes compressed gas as the packing medium, hence a lower injection/packing pressure and clamp force are required than CIM. Especially, GAIM has less residual stress and warpage, and better surface finish than CIM in produce plastic parts with ribs geometry.So, A shell of embroider-machine with lots of rids across its bottom was used to analysis by CIM and GAIM numerical simulation software. In order to gain a set of optimize processing condition for GAIM, a L9(34) experimental matrix design based on the Taguchi method was conducted. The results show GAIM effectively lessen weight of the part, significant reduce the packing pressure, and provide a good surface finish. So GAIM has shown considerable advantages in the production of parts with ribs in the industry.
Blend Compatibilization via the Use of Sodium Neutralized Ionomers
An ethylene-methacrylic acid copolymer partially neutralized with sodium (Na-EMAA), was successfully used to compatibilize nylon 6 (Ny6) and low-density polyethylene (LDPE) blends. The phase morphology and thermal behavior of these blends were investigated over a range of compositions using a variety of analytical techniques. The addition of small amounts (0.5 phr) of Na- EMAA improved the compatibility of Ny6/LDPE blends as evidenced by a significant reduction in dispersed phase sizes. TGA measurements demonstrated an improvement in thermal stability when Na-EMAA was added to either LDPE or Ny6. DSC results of Ny6/Na-EMAA binary blends showed that with increasing Na-EMAA content, the crystallization temperature of Ny6 phase decreased indicating that Na-EMAA retarded crystallization of Ny6. TGA and DSC results indicate that chemical reactions might have taken place between Ny6 and Na-EMAA, a hypothesis confirmed by the Molau test.
Study of the Optical Performance of Injection Molded Light Guide Plates
Display panels of various sizes are important components for many 3C devices. However, their optical performances are sensitive to optical design, material selection, molding conditions. In the present study, optical design software (Trace Pro™) is used to simulate the optical performance of light guided plate designed with the micro-featured circle array so that the light distribution characteristics within the plate from the side LED source light can be understood in a better manner. PMMA and PC were used as materials for injection molded light-guide plate. For PMMA parts, the measured optical performance is quite consistent with simulated prediction due to the lower value of residual stress and birefringence. The optical property in PC plate shows deviation from prediction due to high level of birefringence. By properly modified the micro-featured array via the aid of simulation, optimum light uniformity are improved in both PMMA and PC light-guide plate.
Micro Injection Molding of Micro Fluidic Platform
In this study, micro injection molding was applied to mold micro fluidic platform used for DNA/RNA test. LIGA like process using UV light aligner was applied to prepare silicon based SU-8 photoresist followed by electroforming to make Ni-Co based stamp be the mold insert. The micro features in the stamp with a size of 80 mm by 40 mm by 0.4mm includes 30?m by 100?m micro-channel size and 50?m pitch size. COC, PC and PS were utilized as molding materials. Micro channel depth and width in stamp can achieve an accuracy of about +1.5?m (+5%) and -14.1?m -14.1% . For micro injection molded parts, the dimensional accuracy are about -0.58?m (1.8%) and +1.16?m (+1.4%) for depth and width , respectively. Vacuum during melt filling provide a better replication of micro features. Among injection processing parameters, the mold temperature and holding pressure are found to affect the molding accuracy significantly.
Study on the Rheological Behavior of Polymer Melt for Micro Molding
Determination of polymer melt rheological behavior within micro structured geometry is very important for the accurate simulation of micro molding. Yet its investigation is difficult due to the lack of commercial equipment. In this study, melt viscosity measurement within micro channel was established using a micro channel embedded mold operated at a mold temperature as high as the melt temperature. From measured pressures drop and volumetric flow rate both capillary flow model and slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the measured viscosity values in the test ranges are significantly lower (about 30% to 90% lower) than those obtained from macroscopic rheometer. As micro channel size decreases, the derivation in viscosity is increases. This may be attributed to the melt slip occurs on the micro channel wall and the extend of wall slip increases when size of micro channels decreases. In addition, the higher the melt temperature, the effect of wall slip also becomes more significant. The result indicates that current simulation packages are not suitable for micro molding simulation without considering this effect.
Variable Mold Temperature on the Part Qualities of Injection Molded Parts
In this study, electromagnetic induction heating is utilized to achieve a rapid mold surface heating. Mold surface temperature was raised to above glass transition temperature instantly within few seconds (2 to 3 seconds) then mold is closed for melt injection and cooled down to regular mold temperature before the next cycle starts. Varied mold temperature was applied to injection molding and the associated part qualities including weld line appearance, weld line strength and residual stress were examined. It was found that surface appearance of weld line can be eliminated and the associated weld line strengths are enhanced for molding double-gated tensile test parts. For thin-wall parts, applying variable mold temperature also reduces the injection molding pressure and the part residual stress. The rapid heating and cooling of mold surface temperatures using induction technology combined with low coolant temperature cooling was successfully illustrated.
Breathing Tube Failures
Polysulphone is a useful high-temperature resistant material but demands high quality moulding methods. It was chosen for use as the transparent tube of breathing apparatus for use by hospitals with patients, but the first prototypes were rejected by the manufacturer for defects found in the tube. The manufacturer initiated proceedings against the toolmaker, claiming that the tool was poorly designed for its intended purpose. However, detailed examination of many such tubes showed that the defects were caused by faulty moulding. The case went to a full trial but failed when the plaintiff could not withstand cross-examination. Documents produced in his case against the toolmaker had also been doctored, and the judge ordered the original copies, which were never produced. The case exonerated the toolmaker, who won his full costs.
Orientation, Structure and Properties of Double-Bubble Oriented LLDPE Films
Biaxially oriented linear low density polyethylene films were produced using the double-bubble process with different machine direction (MD) orientation levels and the same transverse direction (TD) blow-up ratio. Their mechanical behavior was characterized in terms of the tensile strength and tear resistance. The microstructure and orientation were characterized using microscopy, Xray diffraction and Fourier Transform Infra Red spectroscopy. The results indicate that MD tensile strength increases with MD stretching ratio while TD one decreases. Tear resistance remained mainly constant in TD and decreased in MD with draw ratio. Morphology analysis revealed that over stretching lamellae tend to align perpendicular to machine direction with an increase of their lamellar dimensions. c-axis orientation in MD direction increases with draw ratio while a- and b-axes orient towards normal and transverse direction respectively. A good correlation was observed between caxis orientation and MD tear resistance and tensile strength.
Studies of Creep and Fatigue Crack Growth in HD-PE Pipe Materials
An experimental observation and an approach to thermodynamic modeling of creep and fatigue crack growth (CCG and FCG) in High Density Polyethylene (HDPE) is reported in this work. The experimental investigation was carried out at elevated temperatures (80 °C) using the Tapered Double Cantilever Beam (TDCB) test specimen allowing the observation of crack growth at constant stress intensity factors (SIF). Both, stepwise and continuous crack growth was recorded with a regular and highly reproducible pattern of crack growth after initiation. The continuous vs. discontinuous crack growth is observed to be dependent on R-ratio. The observations provide the basic data for thermodynamic analysis and application of crack layer (CL) approach to modeling of the fracture propagation process. The thermodynamic forces responsible for process zone (PZ) formation and crack growth are computed as the derivative from Gibbs potential of loaded TDCB specimen with respect to PZ and crack characteristic sizes respectively. A comparative analysis of CCG and FCG suggests a rather complex relation between the two that is not as simple as commonly assumed.
Study on the Weld Line Strength of Injection Molded Nylon6 Nanocomposites
Nanocomposites have been attracted great attentions in recent years. However, most efforts are focused on the preparation and layer structure modification and very few mentioned about the properties of molded parts. In this study, molding conditions including melt temperature, mold temperature, packing pressure and injection speed on the mechanical properties particularly the weld line strength of injection molded Nylon6/Fluoromica nanocomposites were investigated. It is found that with the addition of nano-fluoromica particles the weld line strength becomes significantly weakens as compared to that of pure Nylon6 parts and non-welidline Nylon6/Fluoromica nano- composites. As melt temperature, mold temperature, packing pressure and injection speed increases the weld line strength of molded nanocomposites also increases. Among processing conditions, packing pressure exhibits most significant effect on weld line strength.
Beam Shaping with Diffractive Optics for Laser Micro-Welding of Plastics
This paper reviews the use of diffractive optics for beam shaping of high-power lasers (100 W) for micro-welding of plastics. By using Fourier transformations on twodimensional complex arrays, spatial domain images were transformed into phase domain images. These images were then used to produce a mask for the microlithography etching of a glass diffractive optical element (DE). A 40 W YAG laser with a wavelength of 1064 nm was coupled in air to the lens to shape the beam into predetermined patterns. These patterns were then reduced with standard optics to a desired size. The images were focused at the faying surface of two plastic components in a through-transmission weld configuration. Weld quality was assessed on fidelity. In both cases, reasonably good results were obtained.
A Novel Approach to Manufacture Formaldehyde-Free Wood Based Biocomposites
This study examined the differences between wood composite panels made with maleated polyethylene (MAPE) and maleated polypropylene (MAPP) binding agents. Specifically, the study investigated the contrasts of (i) base resin type, PE or PP, (ii) molecular weight and maleic anhydride content in MAPP binding agents, and (iii) the manufacturing methods (reactive extrusion vs. hot press) on the physico-mechanical properties of the composites. Results showed that while extruding the particles before panel pressing gave better internal bond strength, superior bending properties were obtained through compression molding alone. MAPP based panels outperformed MAPE based panels in stiffness, likely due to the higher stiffness of the PP base resin. MAPE enhanced the IB strength compared to MAPP, attributed to better melting and flow of the polyethylene. Polymer base resin had no effect on MOR or screw holding capacity. Differences between the two maleated polypropylene compounds were not significant for any of the mechanical properties tested. Formaldehyde-free wood based biocomposite panels manufactured in this study often outperformed standard requirements for conventional particleboard, regardless of material composition or manufacturing method used.
Rotational Molding Cycle Time Reduction via Exterior Mold Modification
Production cycle times for rotational molding are limited by the time required to heat up and cool down the mold and the product. Consequently, efforts have been made to enhance heat transfer to and from molds, ultimately reducing cycle times. The application of pins and roughened textures to molds has been investigated with several techniques being employed to predict the enhancement of heat transfer. To validate these predictions a series of rotomolding trials have been carried out using surface enhanced molds. Excellent cycle time reductions in the order of 30 and 20% have been achieved for the pin and roughness enhanced molds respectively, demonstrating the significant benefits mold exterior modification can provide to the industry.
Analysis of Interface of Two Layer Molded Product by Simultaneous Composite Injection Molding
Simultaneous Composite Injection Molding (SCI) is a injection molding technique to impart two layered injection molded composites, which consists of top and bottom layers, by simultaneously feeding two resins through independent cylinders. We have previously reported that low cylinder temperature and low injection speed were key parameters for producing excellent two-layered specimens, preventing commingling between the layers.In this study, the focus shall be on the interface structure in two layer molding in a molding parameter under which a desirable two layered specimen can be obtained. The used materials consist of blend of PC+ABS, a weight ratio of 6 to 4. According to high magnification SEM photos, internal structure was not observed in a region near the interface of the resin layers. Although elongated structure was observed near the mold wall, round shape was seen near the interface. The thickness of interface region was measured.
The Influence of Meeting Angle on the Weld Line Strength in Injection Molded Short-Fiber-Reinforced Polyamide 66
In this report, an experimental investigation has been conducted to examine the effect of meeting angle on the tensile strength of weld line in commercial available 33% glass-fiber-filled PA66 composites. A film gated rectangular plaque mold with circular, square and diamond inserts was used to generate weld line, and the diameter of circular insert has four sizes viz. 30,25,20,15 centimeters. The meeting angles were obtained by filling simulation package. The results showed that the strength of weld line varied linearly with meeting angle during two domains, and the critical angle was about 100°. The larger the meeting angle, the higher the strength of weld line.
Fast BEA for Cooling Analysis in Injection Molding
Boundary element analysis (BEA) is a commonly used method for the cooling analysis in injection molding. However, how to solve the BEA equation is a challenging problem when the number of elements becomes very large. With the ability of current personal computers, it seems no way to obtain accurate solution. A fast BEA solver is studied in this paper. Considering the coarse mesh is good enough in most cases, an indirect method to make dense mesh coarse is suggested, in which the elements are classified into some groups. The element-group temperature is firstly solved, and then the result is used to further calculate element temperature. The method tremendously shortens the computing time. The given example shows the result by the method is very reasonable.
Effect of Element Geometry in the Processing of Highly Filled Materials in High-Speed Deep-Flighted Twin-Screw Extruders
It is well known that deeper flights lead to improved efficiencies in a twin-screw extruder. The deeper flights result in the reduction of shear rates. This is taken advantage to increase the screw speed thereby maintaining the mixing rates and increasing the volumetric capacity of the machine. An improvement in process efficiency is realized due to the reduction in viscous dissipation per unit mass of material.The localized increase in melt temperature due to the working of the kneading elements at high speeds is still a problem. Fractional lobed element geometry with unequal tip angles can be used to solve these problems. These new geometry can easily replace standard kneading elements. These fractional three and four lobed geometry are used in the processing of highly filled LLDPE with TiO2. Melt Temperatures and Dispersive Mixing effectiveness by in-line melt filtration data are discussed while processing with the known “Erdmenger” geometry and the new Fractional geometry.
Meeting Application Requirements with Conductive Carbon Black
High structure or so-called conductive carbon blacks (CCB’s) constitute the major family of conductive additives. They enable to make polymers permanently conductive at ‘low’ to ‘very low’ loadings, for technical applications involving i.e. the transport of energy, the protection against arching or discharge. Designing conductive parts requires certain know-how as many parameters influence the final electrical conductivity, and many other requirements have to be fulfilled. This paper highlights the impact of the carbon black (CB) type and loading, the polymer type and the compounding conditions on the conductive, mechanical, dispersion and flow properties of various plastics compounds. The study especially positions a unique family of ‘low surface area (LSA)’ CCB’s, suggests means to make conductive parts with compounding and transformation ease, and points out that the more conductive additive does
Performance of Polymer Composite Gears - Effect of Tooth Deflection
Unreinforced nylon 6/6, 20 % short glass fiber reinforced nylon 6/6 and 20 % short carbon fiber reinforced nylon 6/6 materials were used for understanding the effect of tooth deflection on gear performance. Test materials were injection molded into spur gears of 2 mm module, 200 pressure angle, 17 number of teeth and 6 mm face width. A test rig is designed and developed in the laboratory to quantify the hysteresis loss of test gear with the measurement of single tooth deflection during static loading and unloading. The performance test is conducted using a power absorption type gear test rig at a constant rotational speed of 1000 rpm and at 0.8 and 1.5 Nm torque conditions. Temperature of test gears during performance tests is continuously measured using non-contact infrared temperature sensors. The net surface temperature measured in reinforced gear during testing is less than that measured in unreinforced gears. A better heat dissipation and less amount of heat generation contributes to improved gear performance.
The Effect of Gamma Sterilisation on Colour and Mechanical Performance of Medical Rigid PVC Compounds
A range of commercially available gamma sterilisable medical rigid PVC (clear) compounds were characterized for hardness, specific gravity, Vicat softening, heat stability and rheological properties. In addition, the effect of exposure to gamma irradiation at 25 and 40 kGy on the colour, mechanical performance and dynamic mechanical response of the various PVC compounds was investigated. The results show no significant difference in hardness of the materials tested. However, significant differences in heat stability, Vicat softening temperature and rheological properties were evident. The results showed that exposure to gamma irradiation had only a slight effect on the mechanical performance of the PVC compounds tested. However, the results show exposure to gamma irradiation had a significant effect on the colour of PVC compounds B, C and D. All three compounds showed significant increases in b-value (yellowness/blueness index) following exposure to gamma radiation. PVC compound A showed superior gamma resistance, with only slight changes in b-value recorded after exposure to gamma irradiation.
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