Hot Chamber Research Articles

Prediction of die casting process parameters by using an artificial neural network model for zinc alloys

Pressure die casting is an important production process. In pressure die casting, the first setting of process parameters is established through guess work. Experts use their previous experience and knowledge to develop a solution for a new application. Due to rapid expansion in the die casting process to produce better quality products in a short period of time, there is ever increasing demand to replace the time-consuming and expert-reliant traditional trial and error methods of establishing process parameters. A neural network system is developed to generate the process parameters for the pressure die casting process. The system aims to replace the existing high-cost, time-consuming and expertdependent trial and error approach for determining the process parameters. The scope of this work includes analysing a physical model of the pressure die casting filling stage based on governing equations of die cavity filling and the collection of feasible casting data for the training of the network. The training data were generated by using ZN-DA3 material on a hot chamber die casting machine with a plunger diameter of 60 mm. The present network was developed using the MATLAB application toolbox. In this work, the neural network was developed by comparing three different training algorithms: i.e. error backpropagation algorithm; momentum and adaptive learning algorithm; and Levenberg-Marquardt approximation algorithm. It was found that the Levenberg-Marquardt approximation algorithm was the preferred method for this application as it reduced the sum-squared error to a small value. The accuracy of the developed network was tested by comparing the data generated from the network with those of an expert from a local die casting industry. It was established that by using this network the selection of process parameters becomes much easier, so that it can be used by a novice user without prior knowledge of the die casting process or optimization techniques.

Determination of Heat Transfer Coefficients Using a 1-D Flow Model Applied to Irregular Shaped Cooling Channels in Pressure Diecasting

A mesh partitioning strategy is presented which facilitates the application of boundary conditions to irregular shaped cooling channels in the pressure diecasting process. The strategy is used to partition a boundary element mesh, but can also be applied to the surface of a cooling channel bounded by a finite element mesh. The partitioning of the mesh into a series of element packs enables a one-dimensional flow model to be applied to the coolant. The flow model is used in conjunction with a steady-state thermal model which initially assumes that no boiling is taking place on the die/coolant interface. Values of bulk temperature, pressure, and velocity in the coolant are thus ascertained. This information, together with die temperatures, is then used in empirical relationships which model the various heat transfer mechanisms, including nucleate and transitional film boiling, between die and coolant. Effective heat transfer coefficients are calculated and applied at the die/coolant interface. The steady-state thermal code and the empirical boiling model are then used iteratively until stable values for the effective heat transfer coefficients are obtained. The models are tested by casting a small thin component using a die with conventional cooling channels and also using a novel die with irregular shaped cooling channels running on a hot chamber proprietary die casting machine. Simulation results are shown and experimental results using the hot chamber pressure die casting machine are reported. [S1087-1357(00)02302-9]

Observation of nanometer silicon clusters in the hot-filament CVD process

Currents of 0.2–5 μA were measured in the hot filament CVD chamber for deposition of silicon. In such a highly ionizing atmosphere with the appreciable supersaturation for precipitation of silicon, it is highly probable that the charged clusters should be formed in the gas phase by ion-induced or photo-induced nucleation. The predicted nanometer silicon clusters were observed by TEM on a carbon membrane, which was placed in the hot-filament CVD chamber in the Si–Cl–H system. The clusters for the filament temperatures of 1800 and 1600°C were ∼2 nm and 5–7 nm, respectively. The film grown by the deposition of these clusters did not show any identity of the individual clusters, making the film indistinguishable from that grown by the atomic unit. In the case of the halogen lamp heating instead of the hot filament, however, the film consists of the large clusters of ∼50 nm and the morphology is similar to the cauliflower structure. The morphological difference between the two heating sources was explained by Fujita's concept of the magic size.

Transient thermal model for the hot chamber injection system in the pressure die casting process

This paper describes a three-dimensional numerical model that is used to predict the transient thermal behaviour of the metal injection system of a hot chamber pressure die casting machine. The behaviour of the injection system is considered in conjunction with that of the die. The Boundary Element Method (BEM) is used to model the transient thermal behaviour of the injection system elements and the die blocks. A perturbation approach is adopted. By adopting this approach, only those surfaces over which a significant transient variation in temperature occurs need be considered. The model assumes that a corresponding steady-state analysis has first been performed so that time-averaged thermal information is available. A finite element based technique is used to model the phase change of the liquid metal in the die cavity and in the injection system. At injection the nozzle and die are assumed to be instantly filled with liquid metal, however, a procedure is presented that attempts to model the heat transfer associated with the flow through the nozzle, gate, and runner regions during injection. Model predictions are compared against thermocouple readings and thermal images obtained from experimental tests. Good agreement is obtained between predicted and measured temperatures. The transient thermal behaviour of an existing hot chamber injection system is investigated in detail and recommendations for improved performance are made. In an attempt to improve the solidification pattern of the casting and the thermal behaviour of the injection system, a redesign of the experimental die is considered. The numerical predictions indicate that the redesign will have a beneficial effect on the solidification pattern of the casting, and on the performance of the injection system.

Influence of chamber temperature on properties of the corona discharge system

This paper investigates the influence of the chamber temperature on properties of the corona discharge system. It is found that the critical voltage Vc required for the corona discharge breakdown is inversely proportional to the chamber temperature T. The electrical energy wc required for corona discharge breakdown is inversely proportional to the square of the chamber temperature T. Thus, the electrical energy consumption for the corona discharge system decreases significantly as the temperature increases. The plasma generation by corona discharge in a hot chamber is much more efficient than that in a cold chamber.

Coupled simulation of gas flow and heat transfer in an RTP-system with rotating wafer

In this study the concept of a lamp heated RTP-system with rotating wafer is considered. Using the fluid-flow-simulation software Phoenics-CVD, we investigated the cooling of the wafer by a process gas flow which is injected at room temperature into the hot process chamber through an inlet pipe in the side wall. In a full 3D-simulation of the gas flow and of the heat transfer in the gas and in the wafer the Navier–Stokes equations and the energy equation are solved. The radiative power consumption and the energy loss of the wafer have been modeled by the Stefan–Boltzmann law. Simulations without wafer rotation show a strong drop in the temperature distribution at the wafer near the inlet pipe. In contrast to this, simulations with rotation show an axisymmetric temperature distribution with a considerably smaller temperature gradient over the wafer. Comparisons with oxidation experiments showed good agreement with the simulation results.

Steady state thermal model for the hot chamber injection system in the pressure die casting process

Abstract This paper describes a three-dimensional numerical model that is used to predict the steady state thermal behaviour of the metal injection system of a hot chamber pressure die casting machine. The behaviour of the injection system is considered in conjunction with that of the die. The boundary element method (BEM) is employed, as surface temperatures are of primary importance. The model yields time-averaged injection system and die temperatures and the heat input from localised heating arrangements (injection system). This is valuable information that can be used in the optimisation of the process. The die model utilised is based on that presented by Davey and Hinduja (Int. J. Numer. Methods Eng. 30 (1990) 1275–1299). A number of novel techniques that improve the efficiency and performance of this model are presented. An efficient scheme is presented for modelling the flow of heat through the melt. A procedure is developed to account for the thermal effects of flow in the nozzle, gate and runner regions. An iterative procedure is developed that enables the average amount of energy supplied per cycle by the heater band, to be calculated. The coupled injection system–die model is verified using thermal data obtained from experimental work. The predicted and the measured temperatures are shown to be in good agreement. Based on the numerical predictions and the experimental data obtained, recommendations are made for improving the thermal behaviour of the existing hot chamber injection system and the die used in the experimental tests.

Transverse bias-enhanced nucleation of diamond in hot filament chemical vapor deposition

The nucleation density of diamond films was greatly enhanced by inserting a transverse bias into hot filament vapor deposition chamber, which differs from the conventional used longitudinal bias method. In-situ Optical Emission Spectroscopy (OES) technique was used to investigate the diamond deposition process. The relative optical emission intensities of the atomic hydrogen and CH radical to argon near the substrate were calculated. The results show that the improvement of the nucleation density is due to the product of much more atomic hydrogen and CH radicals.

Bias enhanced nucleation and bias textured growth of diamond on silicon(100) in hot filament chemical vapor deposition

A four-step process, i.e. pretreatment, heating, bias nucleation and bias growth, was developed to enhance diamond nucleation and to grow textured diamond(100) on Si(100) in a hot filament chemical vapor deposition chamber. A polycrystalline diamond film was optimally nucleated on Si(100) during the period of nucleation enhancement via a bias of −250 V for approximately 30 min, with 1% of methane concentration in hydrogen flowing into the chamber. The nucleation density of diamond is approximately 10 7 cm −2. The uniform nucleation area is as large as 1.5 in. in diameter. A textured diamond(100) film was grown on the nucleated polycrystalline diamond film, simply by adding a bias of −50 V at the growth step. The capability of using negative bias to control the orientation of diamond grains in the hot filament chemical vapor deposition system is new to the diamond community.

Analysis and avoidance of pre-ignition in S.I. gasoline engines

In spark ignition gasoline engines, efforts to improve performance and exhaust emissions have resulted in increased compression ratios and methods of maintaining stoichiometric air-fuel ratio even at high engine load. This paper analyzes the pre-ignition phenomena under such tight conditions, and proposes a new method for avoiding pre-ignition. As a result of the analysis, it was shown that knocking occurred very frequently in the early stage of pre-ignition, which was caused by overheated spark plug or extremely hot combustion chamber deposits. It was also verified that the pre-ignition could be avoided by adding logic to the KCS (knocking control system) for screening high-frequency knocking to detect pre-ignition, and by quickly enriching the charged air fuel mixture after the detection.

Physiological effects of wearing heavy body armour on male soldiers

The effect of wearing two widely used body armours (BA) weighing 9.0 kg and 11.0 kg by the security personnel in India was evaluated. Six male soldiers underwent treadmill exercise in the laboratory (26–28°C) at a fixed speed of 2.2 m · sec −1 for 10 minutes with and without wearing the 11.0 kg BA over their regular uniform. Six other soldiers were exposed to a hot humid climatic chamber (34°C Wet Bulb Globe Temperature/60% relative humidity) with and without 11.0 kg BA for one hour with light physical exercise. Pulmonary function test was conducted on 16 soldiers with 9.0 kg, 11.0 kg BA and without it. The heart rate (HR), minute ventilation (V̇ E) and oxygen uptake (VO 2) on wearing the 11.0 kg BA increased significantly ( p < 0.01) as compared to the values of without wearing it in treadmill exercise. The difference in magnitude being 15 beats · min −1, 9.4 1 · min −1 and 6.0 ml · kg −1 min −1 respectively, for HR, V̇ E, and VO 2. In hot humid exposure the HR and mean skin temperature ( T S ) with 11.0 kg BA also increased significantly ( p < 0.05) as compared to without wearing it during exercise. Pulmonary functions deteriorated significantly with wearing BA and recorded further decrease with increase in weight of the armour. The significant increase in energy cost of physical task, increase cardiovascular strain in hot humid exposure and increase restrictive ventilatory effect which have been found when BA is worn have important practical implications. It is expected that the BA wearer would develop early onset of fatigue if they are to carry out the same task at the same rate as before without wearing BA. These factors need due consideration when planning work/rest cycles of BA wearer placed in demanding and/or endurance type of tasks.

Efficacy of Hot Air as a Postharvest Disinfestation Treatment Against Thrips on Cut Chrysanthe-Mums, Hawaii, 1996

Abstract Efficacy trials were conducted at the University of Hawaii at Manoa, Waiakea Agricultural Research Station in Hilo, HI. Flowers were harvested on 2 Apr from a commercial planting in Mt. View, HI, and transported to the Experiment Station for subsequent tests. Flower stems were divided into 18 groups arranged in 6 treatments with 3 replicates of 10 stems each and held in 19 liter buckets containing 11 liters of tap water. Flowers were treated on 3 Apr (rep 1) and 8 Apr (reps 2 and 3). Treatment consisted of placing the bucket of flowers in the hot air chamber at 44.4 °C, 60% r.h., 0.23 m3 s-1 fan circulation at 26 °C (measured) for 1-5 h at 1 h interval. The check was not treated. Immediately after treatment, flowers were enclosed in bags made from spunbonded polyester (Reemay 2006 UV [20 g/m2], DuPont Wilmington, DE) to prevent cross contamination. Twenty-four hours after treatment, thrips were extracted from 10 flowers (1 flower per stem) using Berlese funnels heated with a 60 watt incandescent light bulb. Thrips were collected in a 8:2:1:1 solution of ethanol, distilled H2O, acetic acid and glycerin. The number of adults and nymphs were counted and pooled for analysis. Data were subjected to ANOVA and means separated by Waller Duncan k-ratio t test k = 100.

Assessment of soyabean as partial or complete replacement for groundnut in coating meals for suya

AbstractFive vegetable protein suya coating meals were formulated to contain 100:0, 75:25, 50:50, 25:75 and 0:100% groundnut: soyabean in addition to a mixture of spices and seasonings used in traditional preparation of tsire‐type suya. Slices of beef loin muscles were coated with the formulated meals and roasted at 175 °C for 15 min. Samples of the hot freshly cooked tsire were held in heated (68 °C) dry or humidified holding chambers for 90 or 180 min. The amount of coating meals bound by the beef slices decreased significantly (P &lt; 0.05) while cook yield was not affected (P &gt; 0.05) as more soyabean replaced groundnut in the coating meals. Protein, fat and ash contents of the raw tsire, and moisture, protein and ash contents of the cooked tsire were not affected (P &gt; 0.05) by variations in coating meal. However, moisture content in the raw tsire increased (P &lt; 0.05) with increasing proportion of soyabean in the coating meals. Sensory qualities of tsire declined significantly (P &lt; 0.05) only when the groundnut was completely replaced. Weight losses associated with hot chamber holding of the cooked tsire was significantly (P &lt; 0.05) reduced by humidifying the chamber. Increased proportions of soyabean in coating meals reduced (P &lt; 0.05) weight losses by tsire only after an extended holding period.

The impact of transmutant helium on weldability of austenitic steel

The results of the investigation of 0.05–0.15 dpa neutron irradiation impact on the Cr16Ni11Mo3Ti austenitic steel weldability are presented. Samples were irradiated to doses of 10 20 n/cm 2 and 3 × 10 20 n/cm 2 ( E > 0.1 MeV) in the RBT-10 reactor, thus providing helium accumulation of 1 appm and 2.5 appm, respectively. Flat samples, 1 mm in thickness, were welded by an automatic device for argon arc welding in a hot chamber. Low-cycle fatigue (LCF) testing in bending was used to assess impact of helium on the degradation of welded joint properties. LCF tests showed that the transmutant helium accumulation resulted in a decrease in the number of cycles to failure at T test = 20°C and 350°C. It is concluded that repeated welding will present in the repair of ITER materials.

Dynamic simulation of one-stage G-M refrigerator and comparison with experiment

In this paper a mathematical model of a one-stage G-M refrigerator has been made to simulate its dynamic performance. A set of governing equations has been solved by a numerical method. Some P- V diagrams under different refrigeration temperatures have been tested. The calculated results show good agreement with experiment, especially in the hot chamber. The greatest deviation in the cold chamber is about 11%.

Reactive processing of thermoset/thermoplastic blends: A potential for injection molding

AbstractPoly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) is an engineering plastic with high heat distortion temperature. Melt processing of neat PPE is usually accompanied with thermal degradation. The degradation problem is solved by blending with polystyrene to reduce the processing temperature. We propose an alternative using triallylisocyanurate (TAIC). TAIC is a low viscosity liquid that can be cured by peroxide, e.g. α,α′‐bis(t‐butylperoxy‐m‐isopropyl)benzene (PBP), to provide a thermoset. The PPE/TAIC mixture was shown to have the upper critical solution temperature (UCST) type phase behavior. At the single‐phase regime above UCST and below the cure temperature (∼180°C for PBP), the mixture had a low viscosity, less viscous than a conventional thermoplastic such as PC and PP. That is, a nice window for injection molding was available, e.g., at 100°C to 160°C for a 50/50 blend. After injecting into a hot mold set at cure temperature, the blend cured in a short time (∼80% conversion in 5 min). Then the molded and partly cured material kept its shape and dimensions during post‐cure in a hot chamber at higher temperature (e.g. 250°C). Using transmission electron microscopy and dynamic mechanical analyses, it was shown that the cured blend had a bicontinuous two‐phase structure with periodic spacings of ∼30 nm, suggesting a structure formation via a spinodal decomposition driven by the increase in molecular weight of TAIC during cure. The cured material showed excellent flexural strength and high chemical resistance.

Two-step diamond growth for reduced surface roughness

A two-stage growth process proposed by Wild et al. (Diamond Relat. Mater., 2 (1993) 158–168) and demonstrated in earlier work (C. Nørgård, A. Matthews and S. Eskildsen, Surf. Coat. Technol., 74–75 (1995) 358–361) has been used to obtain smooth {100}-faceted diamond films. By controlling the growth parameter x, i.e. the ratio of the growth rates on 11001 and {111} faces, during deposition, it is possible to obtain smooth diamond films with a minimum film thickness for complete coverage of {100} faces which is considerably thinner than for conventional <100>-textured films. The deposition method utilized is a hot filament CVD chamber with a CH4-H2 gas mixture.In the first stage, a highly <100>-textured diamond film is grown, which results in a relatively rough surface with small {100} faces compared with the film thickness. The second stage involves subsequent diamond deposition with growth parameters which increase the growth rate of the inclined {111} planes of the <100>- textured film. The {100} faces of the diamond crystal then expand and eventually grow together to form a smooth surface. Due to a poor <100> texture after the first step, only a limited decrease in surface roughness is observed.

Parametric investigation for direct chemical vapour deposition of magnetite films

Abstract A direct growth of magnetite (Fe 3 O 4 ) phase has been obtained by a low-pressure chemical vapour deposition (LPCVD) technique using metal-organic ferric dipivaloylmethanate (Fe(DPM) 3 ) as precursor. On oxidation these films are converted to γ-Fe 2 O 3 phase which give superior magnetic coercivity values. Crystallographic structures are determined by small-angle XRD analysis. As deposited magnetite and oxidized γ-Fe 2 O 3 films are reported with coercivity values of 93 and 122 kA/m, respectively. Squareness ratios of 0.80 are observed for both as-deposited Fe 3 O 4 and oxidized γ-Fe 2 O 3 films with remanent magnetization values of 101 and 102 mT, respectively. Deposition conditions of the as-deposited films along with a growth mechanism involving a gas phase reaction, as promoted by a hot wall type reactor chamber, are described.

Experimental Study of Coke Deposition under Gas Turbine Combustor Conditions

Abstract Abstract–The formation of carbonaceous deposits in gas turbine combustion chambers has been studied at the Institute for Thermal Turbomachinery at the University of Karlsruhe. The deposits show differing chemical and physical properties over wide ranges. Consequently, different mechanisms of formation are considered. In investigating the dominant parameters for coke deposition the chosen approach was to study the formation process under well defined test conditions. These bench tests were followed by comparison with deposits derived from operating combustors using elementary analysis, gaschromatography, infrared spectroscopy as well as electron microscopy. The development of the deposits by fuel droplet impingement on the hot combustion chamber wall is simulated. In using both gas turbine fuels as well as pure hydrocarbons the influence of wall temperature and fuel composition is examined. As a result of the analysis, a characteristic temperature range for the coke deposition is found. In addition, the deposition-causing fraction of the fuel can be determined. Two different groups of deposits are identified under combustion chamber operation conditions. Deposit formation by droplet impingement accompanied with chemical reactions at the combustor wall is found in the primary zone of the combustor. This is confirmed by identical chemical characteristics between deposits of the bench tests and the combustion chamber deposits. Another typical deposit build-up is formed by adhesion of small particles formed in the reaction zone of the combustor. Based on our results, a scheme for the formation of deposits from the liquid fuel is formulated.

Diamond Doping by Low Energy Ion Implantation During Growth

ABSTRACTA novel method of implanting dopant material in diamond using low energy ions during growth is described. In this method, relatively low energy (∼10 KeV) dopant ions are directed through an aperture into a hot filament chemical vapor deposition growth chamber and onto the growing diamond sample. Collisions with the gas molecules in the growth chamber (∼10 Torr of a 99.5% H2 - 0.5% CH4 gas mixture) partially neutralize the ion beam and slow the dopant atoms down to a few hundred electron volts before striking the growing diamond crystal. The residual energy is large enough to embed the dopant atoms a few layers deep in the crystal but not large enough to cause significant lattice damage. Continued doping during growth yields uniformly doped material throughout the implanted region. Results for sodium, rubidium, and phosphorus atom doping are presented with sodium found to be a p-type dopant and phosphorus a deep n-type dopant.