High Mold Temperature Research Articles

Explicit Modelling of Slag Infiltration and Shell Formation during Mould Oscillation in Continuous Casting

A mathematical model of the continuous casting process, which explicitly incorporates the presence of slag, molten steel, heat transfer through the mould walls, and shell solidification, is presented. The model is based on the solution of the Navier–Stokes equations for the multiphase slag–steel–air system under transient conditions, including tracking of the interface between these phases. The use of an extremely fine mesh (100 μm) in the meniscus region allows, for the first time, the direct calculation of liquid slag infiltration into the shell-mould gap. Elsewhere, a coarser mesh is used to capture the influence of the metal flow on the overall solution. Predictions are compared with prior, cold model experiments and high temperature mould simulators. Excellent agreement was found for features such as slag film development and heat flux variations during the oscillation cycle. Furthermore, predictions of shell thicknesses and heat fluxes for a variety of simulated casting speeds are also in good agreement with plant measurements. These findings provide an improved fundamental understanding of the basic principles involved in slag infiltration and solidification inside the mould and how these affect key process parameters, such as powder consumption and shell growth. These parameters have a decisive effect on the formation of oscillations marks and transverse cracks, which are a major source of defects in the casting practice.

Molding Analysis of Multi-Cavity Aspheric Lens and Mold Designing

The key of qualities of optical lens created by injection molding are geometric errors and distribution of residual stress. This study analyses a mobile phone camera lens with aspheric optical lens created by one mold and 16 cavities. Mold flow analysis was used to simulate geometric shapes of different gates and design cooling systems to control mold temperatures. Mold temperature was controlled during the actual injection process and simulation results were used as the basis for mold design. The effects of cold-wall-mold on lens residual stress are discussed. The experiment result showed that higher mold temperatures are helpful to reduce residual stress. An aspheric mould measurement system was used to measure both the mold and the product. The results showed that the replicating capacity is satisfactory with a molding error of 3.604μm.

Surface morphology alignment of block copolymers induced by injection molding

Block copolymers are of increasing interest because of their nanometer-scale morphologies, which can be utilized in a range of applications, including nanolithography. Orientation of the domains can be controlled by part design and processing conditions in injection molding. In this work the surface morphology and alignment of block copolymers by mechanical flow fields from injection molding was investigated using a styrene–ethylene/butylene–styrene triblock copolymer (SEBS) and compared with the morphology induced by spin coating. Compared with the isotropic morphology found by spin coating and annealing, the surface domains were oriented in the flow direction. Increasing mold temperature and injection velocity enhanced the degree of orientation, whereas melt temperature had little effect. Smaller characteristic lengths were produced with higher mold temperatures and injection velocities.

Hot tearing behaviour of binary Mg–1Al alloy using a contraction force measuring method

Hot tearing (or hot cracking) is recognised in the foundry industry as a serious defect. Although it has been investigated for decades, understanding still stands at a qualitative level. In this work, investigations on hot tearing in the binary Mg–1Al (wt-%) alloy have been conducted, using a contraction stress measuring method which shows evidence of good repeatability. The results show that increasing mould temperature decreases hot tearing susceptibility for Mg–1Al due to a decreased cooling rate. The recorded contraction force curves also show that hot cracks initiate under all investigated mould temperatures; however, the crack propagation behaves differently. At lower mould temperatures, the crack propagates very fast, while at higher mould temperatures it propagates slowly. This indicates that a lower cooling rate allows a better chance for the retained liquid to refill the crack. Consequently this leads to partial or complete interruption of crack propagation.

Online Control for the Processing of Urea Resin Moulding Compounds

Urea resin moulding compounds belong to the class of thermosetting materials. They undergo a chemical crosslinking reaction in the mould, giving them outstanding heat resistance. In contrast to thermoplastic materials, thermosets need a critical cure time before the glass transition temperature shifts sufficiently for the hot parts to be stable enough to be demoulded. The cycle times are therefore significantly longer. One possible means of reducing the cycle time would be to increase the mould temperature. As is generally known, increasing the temperature by 10 K doubles the reaction rate. However, a faster reaction rate reduces the time window available for demoulding the cured parts, and the whole process becomes more vulnerable to variations in process parameters and compound composition. By the use of an online cure monitoring system it should be possible to control the process even at higher mould temperatures. In this article the dielectric cure monitoring method is tested in the manufacture of injection moulded parts and its potential for process control is discussed.

An experimental investigation on water penetration in the process of water assisted injection molding of polypropylene

The water penetration phenomenon in the process of water assisted injection molding (WAIM) of a semi-crystalline polymer i.e. polypropylene (PP) was investigated. WAIM has been developed for production of hollow plastic elements and for parts having separate internal void spaces or channels. It offers a cost-effective means of producing the large elements having a good surface finish, reduced weight, and relatively short cycle time. In this study three processing parameters were investigated, namely, water injection delay time, holding time and mold temperature. Their effects on water penetration length, part hollow core characteristic (e.g. wall thickness, core diameter) and shrinkage were explored. The mold cavity shaped a branched pipe (two-head) to be cored out via water penetration. The results indicated that an optimum product, namely, having longer water penetration, lower wall thickness difference, more uniform pipe diameter and low shrinkage could be produced at a higher holding time, a higher mold temperature and at an optimum delay time.

Visualizing analysis for weld line forming in micro injection molding by experimental method

In micro injection molding, the melt flow behavior is important for the final product quality. However, the current process monitoring and measurement technology are not adequate enough to provide a direct analysis access. In the presented study, a glass insert mold designed for performing the direct visual analysis for melt flow phenomena in micro injection molding is introduced. The micro tensile specimen with 0.1 × 0.4 mm2 (depth × width) cross section dimension is chosen as the objective part. The correlation between processing parameters (injection pressure, injection speed, mold temperature) and flow behavior was investigated and analyzed. The results show that the injection pressure put an obvious effect on the filling speed through micro cavity. Injection speed can influence the filling time dramatically also. Higher mold temperature brings positive influence with the flowing speed, due to the lower viscosity of polymers in higher mold temperature.

Injection molding of a nanostructured plate and measurement of its surface properties

This paper highlights recent research on the injection molding of a surface nanostructured substrate with super-hydrophobicity or dry adhesiveness. An anodic aluminum oxidation (AAO) membrane or layer on an Si wafer is used as a molding master for surface nanostructures. The AAO membrane or layer has closely packed nanoholes; depending on the AAO membrane used, the nanoholes have a diameter of around 200 nm and a depth that varies from a few hundred nanometers to 60 μm. This AAO master is installed directly in the injection molding tool, or the AAO holes are replicated on the nickel stamper by an electroforming process and installed in the injection molding tool. Either a high temperature (> T g of the molding material) mold or a rapid heating (up to 200 °C) and cooling (<70 °C) mold is used to fill the high aspect ratio nanoholes with thermoplastic melt for the injection molding. These high aspect ratio nanoholes are extremely difficult to fill with melt in a conventional injection molding process. This paper proposes a new simple and efficient rapid heating and cooling method that heats the stamper by means of the electrical resistance of the stamper itself. Depending on the aspect ratio of the structures and the type of master, a chemical etching or mechanical ejecting process is used to release the molded surface nanostructures. With the use of an AAO membrane and a high temperature mold, some polypropylene disks with a nanohairy surface and some polycarbonate plates with a nanopillar on the surface are injection molded at several different mold temperatures for the purpose of studying the replication of the surface nanostructures. In addition, the contact angle of the water and the adhesion force on the molded surfaces are measured to investigate the effect of the surface nanostructures on the hydrophobicity or dry adhesiveness.

Evaluation of molecular orientation in injection molded parts with microscale features by Raman spectroscopy

AbstractMolecular orientation of polycarbonate (PC) in injection‐molded parts with microscale features was characterized by means of polarized Raman spectroscopy, and the relationship between microstructure and replication was discussed. The microscale feature size of continuous v‐groove was 20 μm in depth and 50 μm in width. PC injection‐molded parts were molded with various molding conditions. The molecular orientation distribution along flow direction on the cross‐section of molding parts were evaluated by the intensity ratio of the bands at 635 to 703 cm−1 (I635/I703) in the Raman spectra. Molecular orientation along the flow direction inside the v‐groove was higher than that of the core and the opposite surface region. In particular, the highest molecular orientation was at the surface of the v‐groove. Among the injection molding conditions, the mold temperature showed significant effect on the molecular orientation and replication. Higher mold temperature caused high replication and low molecular orientation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effect of mold temperature on the mechanical durability of titanium casting clasp model

Titanium is widely used in dental applications. This study investigated the effects of casting conditions on the mechanical characteristics of cast titanium, with a special focus on mold temperature. As such, the mechanical characteristics of specimens prepared at various mold temperatures of 23, 200, 400, 600 and 800 degrees C were compared. On tensile strength, a significant decrease was observed at mold temperatures above 400 degrees C as well as an increase in the scattering of the measured values at higher mold temperatures. On the durability of cast titanium which was assessed by simulating the actual clasp movement during cyclic flexural test, it was found to decrease as the mold temperature increased. When compared with Type 4 dental gold alloy, titanium which was cast at room temperature exhibited equivalent or better durability. Based on the results of this study, it is recommended to perform casting at lower mold temperatures in order to produce highly fatigue-proof cast titanium clasps.

Relationship between processing method and microstructural and mechanical properties of poly(ethylene terephthalate)/short glass fiber composites

AbstractComposites of recycled poly(ethylene terephthalate) (PET) reinforced with short glass fiber (GF) (0, 20, 30, and 40 wt %) were compounded in a single‐screw extruder (SSE) and in a intermeshing corotating twin‐screw extruder (TSE). An SSE fitted with a barrier double‐flight screw melting section in between two single‐flight sections and a TSE with a typical screw configuration for this purpose were used. The composites were subsequently injection molded at two different mold temperatures (10 and 120°C), with all other operative molding parameters kept constant. The effects of processing conditions on composite microstructure, PET degree of crystallinity, and composite mechanical properties were evaluated. Appropriate dispersive and distributive mixing of the glass fiber throughout the PET matrix as well as fine composite mechanical and thermal‐mechanical properties were achieved regardless of whether the composites were prepared in the SSE or TSE. The performance of the SSE was attributed to the efficiency of the barrier screw melting section in composite mixing. The mold temperature influenced the mechanical properties of the composites, by controlling of the degree of crystallinity of the PET in the composites. For a good balance of mechanical and thermal‐mechanical properties, high mold temperatures are desirable, typically, 120°C for a mold cooling time of 45 s. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Identification of critical factors affecting shrinkage porosity in permanent mold casting using numerical simulations based on design of experiments

Vital process parameters affecting the size and location of a shrinkage pore defect in an aluminum alloy permanent mold casting of varying section thicknesses were sought. The aim was to either modify or eliminate the defect by manipulating those parameters so that the lower inlet manifold casting would pass a leak test. The study was carried out ‘off-line’ using numerical simulations of the casting process. This was because the just-in-time production schedule of the busy mass production automotive foundry involved did not allow for any interruptions to accommodate physical experimentation. In a relatively novel approach, the design of experiments (DOE) method was employed to limit the number of simulations required, realizing significant savings in both labor cost and the time spent to arrive at a solution. Mold coat thickness and mold temperature were identified as the vital two parameters from a field of five potential factors nominated by experienced foundry personnel. It was determined that a thicker mold coat and a higher mold temperature would modify temperature profiles in the casting in such a way as to move the shrinkage porosity away from the critical location to less critical regions in a dispersed form. This solution would assume greater importance in applications where there is only a limited supply of feed metal either due to geometric constraints or due to a conscious effort aimed at increasing material yield. As a consequence of incorporating the project recommendations, the foundry achieved a reduction of more than 13% in its annual scrap rate for the casting involved.

Effect of molecular weight and molding conditions on the replication of injection moldings with micro‐scale v‐groove features

AbstractInjection molded optical plastic parts require accurate replication of micro‐scale features. The effects of melt viscosity and molding conditions on replication of microscopic v‐groove features in injection molded parts were examined for PC with different molecular weight. The micro‐scale feature size was a continuous v‐groove with 20 μm in depth and 50 μm in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied in three levels. As the result, the mold temperature had significantly affected replication for all polymers with different molecular weight. Additionally, the molding conditions that lower melt viscosity led to improved replication. In the case of polymer with high molecular weight, the viscosity decreased with increasing melt temperature. It has been found that high replication of micro‐scale features could be achieved by higher mold temperature and higher melt temperature even with high viscosity PC. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Oriented morphology and enhanced mechanical properties of poly( l-lactic acid) from shear controlled orientation in injection molding

This study investigates the effect of operative parameters of shear controlled orientation in injection molding (SCORIM) on poly( l-lactic acid), PLLA, and compared with conventional injection molded (CIM) PLLA. The in situ structure development was carried out with systematic variations of mold temperature and shearing time. The energy at break and maximum stress of all the SCORIM processed PLLA are higher than the CIM processed PLLA without sacrificing the modulus. The overall increments in maximum stress and energy at break were 134% and 641%, respectively. Significant enhancements in ductility for the SCORIM processed PLLA are shown to be a consequence of preferential molecular orientation of large fraction of core. The orientation of core is more pronounced at low mold temperature conditions and was increased with increasing shearing time at both the low and high mold temperatures. The processing–morphology and morphology–mechanical property relationships were then established.

Study on Weld Characteristics of Thin-wall Injection Molded Polypropylene Plates

This paper deals with a fundamental study on the weld structure of thin-wall injection molded polypropylene plates. Effects of the mold temperature and plate thickness on the weld characteristics were investigated. In the experiment, several measurements were performed; distribution of the optical retardation, specific latent heat for fusion, V notch depth and width, and tensile strength of the specimen. The results indicated that the fountain flow of the melt occurred in the filling stage even with a plate thickness of 0.3 mm. It was also shown that molecular orientation in the weld region was relatively low. Thermal property measurement showed that crystallinity of the molded specimen was affected not only by the mold wall temperature but also by the plate thickness. Mechanical strength reduction by the existence of the weld was experimentally confirmed through the tensile test, and it was shown that the thin-wall polypropylene plate molded at high mold temperature broke from the weld region under small strain.

Study on Flow Imbalance during Filling a Multi-Cavity Mold Using a H-type Runners

This study reports the experimental investigation on the flow imbalance phenomena during filling symmetrical multi-cavity in injection molding of optic elements. There are two aspects in this study: First, the flow imbalance in the eight-cavity mold with normal H-type symmetric runners were observed and measured with aid of short-shot experiments. Second, the effects of three processing conditions including injection speed, melt temperature and mold temperature on flow imbalance were investigated. Flow imbalances are consistently observed and quantitatively measured. The results have shown that proper injection speed, high melt and high mold temperature can reduce the flow imbalance.

Rapid replication of nanostructures made with a polymer using simple injection molding

AbstractIt is possible to fabricate nanostructures of 25.5 nm by replication using injection molding. In this study, a silicon calibration grating was used as a mold insert to replicate high‐quality nanostructures with a simple custom‐made injection machine. The replicated grating with 25.5‐nm nanofeatures made with a polymer was of high quality when a high mold temperature was employed and the mold was evacuated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The Study of Surface Properties in Injection Moldings (Part-1)

Injection molding is used in various fields. Surface properties are an important subject and there are many reports on them. From the viewpoints of cost and productivity, the injection molding of multi-cavity injection die is used widely. However, there is no report on the research of surface properties in these injection moldings.In this study, we observed surface state and measured surface roughness for the injection molding with emboss form on the surface and compared with surface state about molding conditions. Moreover, we carried out the optimization of runner design in consideration of simultaneous filling using injection molding flow analysis and considered the influence of runner balance on the surface state. High mold temperature improves surface properties for the whole injection molding. Short filling time improves surface properties for the portions do not require much packing pressure. The optimized runner balance can realize uniform surface properties in multi cavity injection die.

Effect of nucleation and plasticization on the crystallization of poly(lactic acid)

In this paper, different strategies to promote PLA crystallization were investigated with the objective of increasing the crystalline content under typical polymer processing conditions. The effect of heterogeneous nucleation was assessed by adding talc, sodium stearate and calcium lactate as potential nucleating agents. The PLA chain mobility was increased by adding up to 10wt% acetyl triethyl citrate and polyethylene glycol as plasticizers. The crystallization kinetics were studied using DSC analysis under both isothermal and non-isothermal conditions. The isothermal data showed that talc is highly effective in nucleating the PLA in the 80–120°C temperature range. In the non-isothermal DSC experiments, the crystallinity developed upon cooling was systematically studied at cooling rates of 10, 20, 40, and 80°C/min. The non-isothermal data showed that the combination of nucleant and plasticizer is necessary to develop significant crystallinity at high cooling rates. The nucleated and/or plasticized PLA samples were injection molded and the effect of mold temperature on crystallinity was determined. It was possible to mold the PLA formulations using mold temperatures either below 40°C or greater than 60°C. At low temperature, the molded parts were nearly amorphous while at high mold temperatures, the PLA formulation with proper nucleation and plasticization was shown to achieve crystallinity levels up to 40%, close to the maximum crystalline content of the material. Tensile mechanical properties and temperature resistance of these amorphous and semi-crystalline materials were examined.

Double yielding in PA6: Effect of mold temperature and moisture content

AbstractIn this study we have investigated the effect of mold temperature and moisture content on double yielding of virgin polyamide 6 (PA6) uniaxially deformed at room temperature. The experimental results have revealed that, to a certain extent, a limited increment in both mold temperature and moisture content will make the second yield process become more apparent. However, the double yielding behavior will disappear totally in the case of much higher mold temperature and moisture content. Instead, a typical single sharp yield or brittle fracture will be present in the former case, while in the latter case the samples only display a very broad yield, similar to a rubber‐like deformation. Maybe two critical states will be in existence in PA6 exhibiting double yielding behavior, and the critical states are probably relevant with the concentration of the interlinks and intralinks, the lamellae perfection and the crystallite size. Particular emphasis should be placed on the role of interlinks and intralinks when considering the origin of double yielding of virgin PA6 since these links affect the stress transfer significantly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1217–1225, 2007