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Characterization of spray lubricants for the high pressure die casting processes
Abstract
During the high pressure die casting process, lubricants are sprayed in order to cool the dies and facilitate the ejection of the casting. The cooling effects of the die lubricant were investigated using thermogravimetric analysis (TGA), heat flux sensors (HFS), and infrared imaging. The evolution of the heat flux and pictures taken using a high-speed infrared camera revealed that lubricant application was a transient process. The short time response of the HFS allows the monitoring and data acquisition of the surface temperature and heat flux without additional data processing. A similar set of experiments was performed with deionized water in order to assess the lubricant effect. The high heat flux obtained at 300°C was attributed to the wetting and absorbent properties of the lubricant. Pictures of the spray cone and lubricant flow on the die were also used to explain the heat flux evolution.
... This advancement significantly reduces the number of components required to manufacture the body-in-white (BIW) structure of a vehicle, optimizing production and enhancing efficiency [16]. The high ductility required for these components is normally achieved by using primary alloys with a reduced Fe content [16][17][18]. However, this low Fe content significantly increases the affinity of the aluminum alloy for the steel of the die, decreasing the die's lifespan [17,19]. ...
... To prevent premature failure of the HDPC dies, the die surface is sprayed with a release agent after the part solidifies and the die is opened [18]. This step is performed before closing the die again for the next injection of molten alloy, delivered at high temperature, speed and pressure. ...
... This step is performed before closing the die again for the next injection of molten alloy, delivered at high temperature, speed and pressure. Release agents in HPDC serve two primary purposes: (1) cooling the die surface, especially in regions where the internal cooling channels are insufficient and (2) protecting the die with a lubrication film acting as a release agent that prevents damaging mechanisms, such as die soldering or oxidation, and enabling the extraction of the casted parts [5,18]. However, the high temperatures of the die during the casting production, make it challenging for the lubricant to effectively reach the die surface due to the Leidenfrost effect. ...
The high-pressure die-casting process is growing since it is a cost-effective solution in the production of lightweight parts for a variety of industries. Nevertheless, the harsh working conditions of the die lead to premature failing and poor quality of the produced parts. Lubricants are applied to cooling the die surface and create a protective film to minimize die wear. However, the high temperature of the die during the casting production makes it difficult for the lubricant to reach the die surface due to the Leidenfrost effect. In this study, the effectiveness of newly developed ester-based lubricants designed to address Leidenfrost phenomenon in high-pressure die-casting is evaluated at laboratory and pilot plant scale. The new lubricants are based on the same ester solution; however, one of them includes a specially formulated anti-Leidenfrost additive to optimize performance at the temperature ranges typically encountered in industrial aluminum high-pressure die-casting processes. The results show a correlation between lubricant heat-transfer capability and aluminum adhesion. Additionally, a pilot plant methodology for testing newly formulated lubricants has been established while the experimental methodology developed for assessing heat-transfer capability is validated as a rapid and cost-effective approach for evaluating lubrication alternatives for high-pressure die-casting applications. Finally, the efficiency of environmentally friendly ester-based lubricants for high-temperature applications has been demonstrated.
... After the casting ejection, die lube is used to cool the die to enhance the productivity [4]. Meanwhile, a lubricating film is created at the surface of the die that facilitates the extraction of the casting from the molds [5][6][7][8]. Moreover, a protection film to resist die soldering with aluminum is also formed, using either the lubricating film or a surface oxide layer that forms on the die surfaces when the lube is in contact with the hot dies. ...
... While it is arguable how effective the lube is in terms of providing lubrication and soldering prevention, the cooling effect of the lube is vital to the efficiency of the HPDC process. Sufficient cooling is important not only for shortening cycle times but also for reducing soldering tendency and die dissolution [8][9][10][11][12], because both are affected by the surface temperature of the die. ...
This article examined the cooling efficiency of pulse spray under different pressures, duty cycles, and frequencies. The cooling curves of the surface temperature were measured, and the cooling efficiency was evaluated by the temperature drop and the recovery temperature at the die surface. Meanwhile, the lube usage and runoff associated with each condition were measured to evaluate the lube consumption. The results suggest that the lube spray at pressure in the range of 0.2 to 0.4 MPa produces identical cooling curves and cooling efficiency. The cooling efficiency of pulse spray is mainly affected by the duty cycle, while the pulse frequency affects temperature fluctuation at the surface of the hot plate. The pulse spray can achieve identical cooling efficiency as continuous spray with a pulse frequency of 100 Hz and a duty cycle of 50% when the pressure is higher than 0.2 MPa. Moreover, the use of pulse spray can reduce the consumption of lube and runoff by several times during lube spray, leading to significant cost saving, decreased environmental footprint, and leaner work environment.
... In contrast to this, numerous research groups have investigated the heat transfer coefficient during solidification of the casting 20-26 and during the spraying process. [27][28][29] An evaluation of the available literature revealed that both heat transfer processes are strongly influenced by the surface temperature, geometry and process parameters. In some cases, the peak values for the heat transfer vary by almost an order of magnitude. ...
High-pressure die casting dies are produced in most cases by conventional subtractive manufacturing processes. In this case, a massive design of the die usually ensures high stability during the casting process. However, at the same time, it leads to low flexibility in casting production and high material costs. The basic approach in the present work is to reduce the conventional subtractive production process of a die casting die in favor of a flexible, modular design, where only a few contour elements of the die have to be replaced for achieving different castings. In order to pave the way for this design principle, basic thermal and structural properties of a lightweight design die casting die were analyzed. The finite element calculations carried out showed that the modular lightweight die casting die consumes considerably less energy for preheating and during operation. Due to the reduced stiffness and material, however, calculated deformations and stresses in the die are considerably higher during the casting process. Although the initial calculation results look very promising, further knowledge must be gained in order to ensure the future success of modular lightweight die casting dies.
... The use of an IR camera has previously been studied to evaluate the spray pattern of lubricant application in the die casting process (Sabau and Dinwiddie, 2008) and indoor air temperature measurements (Fokaides et al., 2016). This is the first study that uses an IR Table 2 Advantages of an infrared camera over traditional thermocouples to determine the spray characteristics of the emitted plume from pMDIs. ...
Plume characteristics, such as temperature and velocity, emitted from pMDIs could significantly affect the dose delivered to the lung. Currently, high speed cameras and thermocouples are used separately to evaluate these parameters. We used a low-noise infrared camera to evaluate both the temperature and velocity of the emitted plume from pMDIs. Additionally, we investigated whether the fine particle fraction (FPF) is affected when time between actuations is varied. We tested three different albuterol sulfate pMDIs: ProAir® HFA, Proventil® HFA, and Ventolin® HFA. The plume and aerodynamic characteristics from these pMDIs were evaluated, after varying the time between actuations (15, 30, 60, and 120 s), using the infrared camera and a next generation impactor, respectively. The aerodynamic characteristics were evaluated with and without a valved holding chamber (VHC). ProAir HFA had the softest plume followed by Proventil HFA and Ventolin HFA. Further, Ventolin HFA was slightly cooler and had significantly lower FPF than ProAir HFA and Proventil HFA. All inhalers had higher FPF when used with VHC. Further, we observed that the time between actuations affected the FPF across pMDIs. Moreover, generalized guidelines suggesting one-minute interval between actuations for pMDIs should be reconsidered, with and without a VHC.
... In order to maintain a stable die temperature, cooling and tempering circuits are employed, but to obtain a good quality part the lubrication of the die should also be adjusted to the selected alloy, working temperatures, and cycle time. They are several types of lubricants (water-based, oil-based, or dry lubricants), that should be selected for a determined application [8][9][10]. The quantity and percentage of lubricant should also be adjusted to the process for avoiding quality defects. ...
Nowadays, fuel consumption and carbon dioxide emissions are two of the main focal points in vehicle design, promoting the reduction in the weight of vehicles by using lighter materials. The aim of the work is to evaluate the influence of different aluminium foams and injection parameters in order to obtain compound castings with a compromise between the obtained properties and weight by high-pressure die cast (HPDC) using aluminium foams as cores into a magnesium cast part. To evaluate the influence of the different aluminium foams and injection parameters on the final casting products quality, the type and density of the aluminium foam, metal temperature, plunger speed, and multiplication pressure have been varied within a range of suitable values. The obtained compound HPDC castings have been studied by performing visual and RX inspections, obtaining sound composite castings with aluminium foam cores. The presence of an external continuous layer on the foam surface and the correct placement of the foam to support injection conditions permit obtaining good quality parts. A HPDC processed magnesium-aluminium foam composite has been developed for a bicycle application obtaining a suitable combination of mechanical properties and, especially, a reduced weight in the demonstration part.
... For many parts, post-machining can be totally eliminated or very light machining may be required to bring dimensions to size [4][5][6][7]. The process cycle for hot chamber die casting process [4,[8][9][10][11] is shown in Fig. 1. ...
Hot chamber die casting process is designed to achieve high dimensional accuracy for small products by forcing molten metal under high pressure into reusable moulds, called dies. The present research work is aimed at study of some parameters (as a case study of spring adjuster) on cast component properties in hot chamber die casting process. Three controllable factors of the hot chamber die casting process (namely: pressure at second phase, metal pouring temperature and die opening time) were studied at three levels each by Taguchi’s parametric approach and single-response optimization was conducted to identify the main factors controlling surface hardness, dimensional accuracy and weight of the casting. Castings were produced using aluminium alloy, at recommended parameters through hot chamber die casting process. Analysis shows that in hot chamber die casting process the percentage contribution of second phase pressure, die opening time, metal pouring temperature for surface hardness is 82.48, 9.24 and 6.78 % respectively. While in the case of weight of cast component the contribution of second phase pressure is 94.03 %, followed by metal pouring temperature and die opening time (4.58 and 0.35 % respectively). Further for dimensional accuracy contribution of die opening time is 76.97 %, metal pouring temperature is 20.05 % and second phase pressure is 1.56 %. Confirmation experiments were conducted at an optimal condition showed that the surface hardness, dimensional accuracy and weight of the castings were improved significantly.
Die soldering is challenging issue on die life and casting quality in High Pressure Die Casting (HPDC) Industry. It
increases die down time which causes increasing production cost per piece. Die soldering can be tackled by surface
heat treatment operations like gas nitriding and other PVD coatings. Used and scraped die is selected from the die
casting industry for investigation of die soldering issue. Chemical distribution of elements and surface condition of
affected die soldering zone is investigated. The study reveals that, there are abundant micro cracks, micro holes and
micro cavities at soldering portion. The radius of micro holes is about 0.25 μm and the radius of macro holes is
about 8μm. The die inserts are made up of H13 die steel and LM24 Aluminum alloy is used for casting operation. At
the die soldering cross section region, distribution of aluminum and die soldering mechanism and its causes studied.
The die soldering mechanism is classified as chemical, physical, mechanical and mixed soldering. The soldering
phenomena have been researched based on die temperature and its chemistry, metal temperature and its chemistry,
injection pressure and its velocity, and die surface roughness. The spread and formation of die soldering on used and
scraped die is also discussed in this article.
Different damaging phenomena such as erosion, wear, and thermal fatigue characterize the surfaces of dies for high pressure die‐casting. The aim of this study is the development of a test rig able to reproduce thermal stresses and contact with molten aluminum alloy, typical of high pressure die‐casting dies. During the test a hot work tool steel sample (AISI H11) is cyclically heated by the contact with molten aluminum alloy (EN‐AC 46100 – AlSi11Cu2(Fe)) and then cooled by the spraying of a water‐diluted silicone‐based lubricant. A FEM simulation was set up to determine the temperature at different depth beneath the sample surface during thermal cycling and was experimentally validated to design the proper sample geometry aimed at reproducing the stress/strain conditions experienced by a die‐casting die insert. A tensile – compressive stress state is achievable on the surface of the sample by machining a notch with a suitable radius, able to produce a plastic strain comparable to the insert one. A thermally induced stress – strain fatigue loop was determined for both the sample and the component. Temperatures are monitored discontinuously by IR thermography after heating and continuously by thermocouples placed at a reference depth of 5,5 mm. Finally the optimized testing conditions were validated experimentally: both thermal cracking and soldering phenomena were successfully reproduced on a lab‐scale test rig. This article is protected by copyright. All rights reserved.
A method for the estimation of the die release force of die castings of JIS-ADC12 aluminum alloy manufactured through high-pressure die casting was examined. The die release force was evaluated by the strain in the axial direction of the extrusion pin when releasing the die castings. In this research, it was assumed that the factors that influenced the die release force were the thermal deformation of the die and die castings and the reaction layer of Al and Fe generated during the solidification process in the die. These factors in the resistance of the die release were evaluated by the friction coefficient. The die and die castings temperature in the die release process were simulated, and calculation results were mapped onto an FE model, and a coupled analysis of the thermal structure was performed. The calculated value of the mold release force was approximately the same as the actual value, and the friction coefficient was estimated to be approximately 0.5.
Die-casting processes are commonly employed in the automotive area to cast aluminum alloys. These processes involve the use of steel dies, typically realized in AISI H11 or H13, with or without a coated surface. Mechanical and chemical stresses and thermal cycles act producing stresses, plastic deformation, corrosion and metallization on the mold surfaces. Particularly, the interaction between the die and the molten aluminum causes the nucleation of intermetallic compounds at the interface. In this work the interaction between the hot work steel AISI H13 and the aluminum alloy EN–AB 46000 were evaluated in terms of adhesion strength for different roughness of the die surface. Two of the tested roughness were finally applied on the surface of die inserts; the use of injection pressure in a high pressure die casting (HPDC) machine, led to observe the possible variations in terms of soldering severity on the surface of the die in real operating conditions. The comparison between casting tests carried out in laboratory conditions (aluminum alloy casted on the steel surface) and in real-work conditions (aluminum alloy injected with a certain pressure on the steel surface) allowed to evaluate the effect of surface-roughness on soldering mechanisms.
Hot chamber (HC) die casting process is one of the most widely used commercial processes for the casting of low temperature metals and alloys. This process gives near-net shape product with high dimensional accuracy. However in actual field environment the best settings of input parameters is often conflicting as the shape and size of the casting changes and one have to trade off among various output parameters like hardness, dimensional accuracy, casting defects, microstructure etc. So for online inspection of the cast components properties (without affecting the production line) the weight measurement has been established as one of the cost effective method (as the difference in weight of sound and unsound casting reflects the possible casting defects) in field environment. In the present work at first stage the effect of three input process parameters (namely: pressure at 2nd phase in HC die casting; metal pouring temperature and die opening time) has been studied for optimizing the cast component weight ‘W’ as output parameter in form of macro model based upon Taguchi L9 OA. After this Buckingham’s π approach has been applied on Taguchi based macro model for the development of micro model. This study highlights the Taguchi-Buckingham based combined approach as a case study (for conversion of macro model into micro model) by identification of optimum levels of input parameters (based on Taguchi approach) and development of mathematical model (based on Buckingham’s π approach). Finally developed mathematical model can be used for predicting W in HC die casting process with more flexibility. The results of study highlights second degree polynomial equation for predicting cast component weight in HC die casting and suggest that pressure at 2nd stage is one of the most contributing factors for controlling the casting defect/weight of casting.
Based on the identification of the main process variables in die casting, the correlation of die-casting defects and the process variables were analyzed, and the model framework of the process-oriented die casting control system was constructed. The function and main features of the system was briefly reviewed, and the measures of optimizing die casting process control were discussed. It is proposed to take the technical characteristics of die casting and their quality requirements as the target, and based on the process control and continuous improvement of the process, to optimize the casting process control, make real-time adjustments and improve die-casting process; therefore the quality of the casting will be under control.
In this study, the composite heat treatment for SKD61 by gas Nitriding and Carbon coating was researched. Hardness profile was measured by Vickers hardness tester at 100g and 10 (s) dwell time. The case depth was up to 40μm and surface hardness was 1200Hv. The growth configuration of carbon coating was observed by scanning electron microscope (SEM). At first, CNTs was grown on the surface, and finally it became high density layer by CNTs clumped together. This layer was analyzed by Raman spectroscopy and X-ray diffraction meter. It shows that the carbon layer is amorphous structure and it includes sp2 and sp3 bonds. To compare friction coefficient with only gas Nitriding, boll on disk wear tester was used in 10N weight. The friction coefficients of only Nitriding and composite treatment samples showed between 0.6-0.8 and 0.2-0.4 respectively. It revealed that the carbon coating decreasing the friction coefficient.
Hot chamber die casting (HCDC) process is designed to achieve high dimensional accuracy and surface hardness (SH) for industrial applications (like machine tool components). In the present study, outcome of Taguchi model has been used for developing a mathematical model for SH; using Buckingham’s π-theorem for HCDC process. Three input parameters namely pressure at 2nd phase; metal pouring temperature and die opening time were selected to give output in form of SH. This study will provide main effects of these variables on SH and will shed light on the casting hardness mechanism in HCDC process. The comparison with experimental results will also serve as further validation of model.
The paper reports an experimental study of die-casting dies with conformal cooling fabricated by direct-metal additive techniques. The main objective is to compare the benefits and limitations of the application to what has been widely discussed in literature in the context of plastics injection molding. Selective laser melting was used to fabricate an impression block with conformal cooling channels designed according to part geometry with the aid of process simulation. The tool was used in the manufacture of sample batches of zinc alloy castings after being fitted on an existing die in place of a machined impression block with conventional straight-line cooling channels. Different combinations of process parameters were tested to exploit the improved performance of the cooling system. Test results show that conformal cooling improves the surface finish of castings due to a reduced need of spray cooling, which is allowed by a higher and more uniform cooling rate. Secondary benefits include reduction of cycle time and shrinkage porosity.
Spray cooling of a hot surface was investigated to ascertain the effect of nozzle-to-surface distance on critical heat flux (CHF). Full cone sprays of Fluorinert FC-72 and FC-87 were used to cool a 12.7 x 12.7 mm(2) surface. A theoretical model was constructed that accurately predicts the spray's volumetric flux (liquid volume per unit area per unit time) distribution across the heater surface. Several experimental spray sampling techniques were devised to validate this model. The impact of volumetric flux: distribution on CHF was investigated experimentally. By measuring CHF for the same nozzle flow rate at different nozzle-to-surface distances, it vas determined CHF can be maximized when the spray is configured such that the spray impact area just inscribes the square surface of the heater Using this optimum configuration, CHF data were measured over broad ranges of flow rate and subcooling, resulting in a new correlation for spray cooling of small surfaces.
The die spray cooling is discussed. Die spray cooling is especially critical for jobs where sufficient internal water cooling is not possible. The ability of the die lubricant to cool the die quickly is a key performance factor that affects cycle time, solder and die lubricant consumption.
A systematic experimental study was conducted to examine the heat transfer characteristics from the hot die surface to the water spray involved in high pressure die casting processes. Temperature and heat flux measurements were made locally in the spray field using a heater made from die material H-13 steel and with a surface diameter of 10 mm. The spray cooling curve was determined in the nucleate boiling, critical heat flux, as well as the transition boiling regimes. The hydrodynamic parameters of the spray such as droplet diameters, droplet velocities, and volumetric spray flux were also measured at the position in the spray field identical to that of the test piece. Droplet size and velocity distribution were measured using a PDA system. A new empirical correlation was developed to relate the spray cooling heat flux to the spray hydrodynamic parameters such as liquid volumetric flux, droplet size, and droplet velocity in all heat transfer regimes. The agreement between experimental data and predicted results is satisfactorily good.
Wall heat fluxes can be derived from time resolved measurements of the surface temperature. This paper describes an analytical approach to calculate the heat flux from an analytical solution of the one-dimensional transient energy equation with transient boundary conditions using the Laplace transformation. The results are compared to simple test cases for which the heat fluxes are given in literature. The method is used to calculate the heat flux from a fuel spray to a wall at diesel engine conditions.
Spray cooling is an integral part of many manufacturing processes and is particularly relevant to high-temperature process. It may be used to simply allow the survival of a unit or to insure that a unit operates at an acceptable temperature. A more recent trend is to use spray cooling to control the final properties of the product. Particular problems are experienced when cooling from the high temperature, stable film boiling regime through Leidenfrost to nucleate boiling. In this case, the published relationships between spray impact density (liters/s/sq meter) and heat transfer coefficient (HTC) are of little use, becoming very inaccurate as cooling proceeds. Mathematical models of cooling are well developed and reliable but need accurate information on the heat removal conditions at the surface of the stock. A test apparatus using a stainless steel specimen cooled from 1,200 C to ambient has been used to investigate the HTC`s from various types of spray, both pressure atomized and air mist, by a transient method. The temperature history is supplied to a mathematical model which works in a reverse iterative manner but with a convergence function. This gives a relationship between HTC and stock temperature over the entire temperature range. Relationships between impact density and HTC are presented for various nozzles and suggestions for further work are made.
We conducted experiments on the effect of dissolving three different salts sodium chloride (NaCl), sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 90°C to 220°C. We photographed droplets as they evaporated, and recorded their evaporation time. At surface temperatures that were too low to initiate nucleate boiling all three salts were found to reduce droplet evaporation rates because they lower the vapor pressure of water. In the nucleate boiling regime, low concentrations (<0.1 mol/l) of Na2SO4 and MgSO4 enhanced heat transfer because they prevented coalescence of vapor bubbles and produced foaming in the droplet, significantly reducing droplet lifetimes. Increasing the salt concentration further did not produce a corresponding increase in droplet boiling rate. Dissolved salts prevent bubble coalescence because they increase surface tension and stabilize the liquid film separating bubbles, and because electric charge that accumulates on the surfaces of bubbles produces a repulsive force, preventing them from approaching each other. Na2SO4 and MgSO4, which have high ionic strengths, produced a large amount of foaming in droplets and increased their boiling rate significantly. NaCl, which has low ionic strength, had little effect on droplet boiling.
This paper deals with a new method for the evaluation of the kinetic parameters from thermogravimetric measurements with a general temperature program. The procedure assumes the use of a computer or calculator. In principle, it is an integral method with two variants. The kinetic parameters can be determined from a single and/or from two general temperature programs. This method is free of the shortcomings that the existing method has, i.e. the self-heating and/or self-cooling, resulting in errors in measurements and the limitation of the weight of sample. The two variants of the submitted method have been tested by evaluation of the experimental data of the thermal decomposition of CaCO2.
This paper concerns a quantitative assessment of the heat and mass transfer behavior of spray droplets, downward oriented prior to their impact on a heated horizontal surface. An experimental and theoretical investigation of the coupling effects between a downward oriented spray and a rising saturated buoyant jet that results from evaporation of the spray an a heated surface has been successfully completed. A model describing the coupled thermal and hydrodynamic behavior of both the spray and the saturated buoyant jet has been developed. An experimental set-up involving a high speed photographic apparatus has been used to observe in-flight monodispersed sprays and to measure the diameter and the velocity of droplets as they approach the heated surface. The theoretical and experimental results indicate that the temperature of the saturated buoyant jet is highly affected by the presence of a subcooled spray and small droplet sprays, vertically projected, experience high condensation rates as they pass through the saturated buoyant jet, reaching the saturation temperature before impacting on the heated surface, as well as experience acceleration as a consequence of an increase in mass due to the condensation.
Lubricant spray application experiments were conducted for the die casting process. The heat flux was measured in situ using a differential thermopile sensor for three application techniques. First, the lubricant was applied under a constant flowrate while the nozzle was held in the same position. Second, the lubricant was applied in a pulsed, static manner, in which the nozzle was held over the same surface while it was turned on and off several times. Third, the lubricant was applied in a sweeping manner, in which the nozzle was moved along the die surface while it was held open. The experiments were conducted at several die temperatures and at sweep speeds of 20, 23, and 68 cm/s. The heat flux data, which were obtained with a sensor that was located in the centre of the test plate, were presented and discussed. The sensor can be used to evaluate lubricants, monitor the consistency of die lubrication process, and obtain useful process data, such as surface temperature, heat flux, and heat transfer coefficients. The heat removed from the die surface during lubricant application is necessary for (a) designing the cooling channels in the die, i.e. their size and placement, and (b) performing accurate numerical simulations of the die casting process.
During the die casting process, lubricants are sprayed in order to cool the dies and facilitate the ejection of the casting. In this paper, a new technique for measuring the heat flux during lubricant application is evaluated. Data from experiments conducted using water spray are first presented. Water spray experiments were conducted for different initial plate temperatures. Measurements were conducted for the application of two different lubricants, of dilution ratios of 1/15 and 1/50 of lubricant in water. The measurement uncertainties were documented. The results show that the surface temperature decreases initially very fast. Numerical simulation results confirmed that the abrupt temperature drop is not an artifact but illustrates the thermal shock experienced by the dies during the initial stages of lubricant application. The lubricant experiments show that the sensor can be successfully used for testing die lubricants with typical dilution ratios encountered in the die casting process.
It is known that the insulating ability of powder lubricant is higher than that of conventional oil-soluble or water-soluble lubricants. This will be effective to prevent the formation of scattered chill structure. Influence of the components and composition of powder lubricants on insulating ability and lubricating ability were investigated. Furthermore, the interaction between powder lubricants and molten alloy was observed with high-speed video system. In the binary components powder lubricants, which include inorganic (talc or Al(OH)3) and polyethylene wax, the wax content was changed from 10 to 60 mass%. Maximum heat insulation was found in the composition of talc (or Al(OH)3)—15–25 mass% of wax. The result of in-situ observation revealed that superior insulating ability at 25 mass% of wax was due to formation of thin gaseous film between molten alloy and die by vaporized wax. Regarding the lubricating ability, when castings were released from mold, the ejection force of ejector pin decreased with increasing the wax content. Thus, it was found that the lubricant contains 40 mass% or more of wax that will be appropriate for die lubricant. On the other hand, the high insulating lubricant contains 25 mass% of wax that will be suitable for sleeve lubricant.
With electronic packages becoming more dense and powerful, traditional methods of thermal energy removal are reaching their limits. One method of direct contact cooling capable of removing high heat fluxes while still being compact in size is spray impingement cooling, but its heat transfer behavior is not understood well enough to enable systematic, practical system design. This work presents the results of a large parametric study of spray cooling using a number of different nozzle patterns. It was found that nozzles that use the fluid most efficiently to remove thermal energy were limited by low peak heat fluxes and that the highest peak heat fluxes were obtained when phase change was avoided. Multiple nozzle arrays allowed for higher peak heat fluxes but used fluid inefficiently due to interactions between neighboring sprays. In general, the geometric pattern of the nozzle arrays had little effect on overall heat transfer performance.
An experimental study was made in the first of two papers to determine the effect of liquid sprays used to cool a hot surface. Both pure water and R-134a were served as a working medium sprayed from a single circular nozzle onto a Cu (oxygen free) metal of an electrically heated surface which was heated to an initial temperature with a range of wall superheat for steady-state nucleate boiling experiments using thermocouples for heat transfer measurements. Cooling characteristics (boiling curves) were obtained over a range of spray mass flux, Weber number, wall superheat and degree of subcooling. Boiling visualization was also conducted with varied heat flux levels at a specified We for R-134a and water.
Spray cooling of a hot surface was investigated in the second of two papers to determine the effect of mass flux, Weber number, and degree of subcooling on two different working fluids such as pure water and R-134a. Full cone circular sprays were used to cool a circular surface of diameter 80 mm with an initial temperature about 250/70 °C for pure water/R-134a, respectively. Both the transient liquid crystal technique (only for R-134a) and thermocouple wire temperature measurements were conducted. Cooling curves were obtained in a wide range of the above-mentioned parameters.
An investigation into single nozzle spray cooling heat transfer mechanisms with varying amounts of dissolved gas was performed using two powerful techniques. Time and space resolved heat transfer distributions produced by a single nozzle were measured using an array of individually controlled microheaters, while visualization and measurements of the liquid–solid contact area and the three-phase contact line length were made using a total internal reflectance technique. The presence of dissolved gas increased the effective subcooling of the liquid, and shifted the spray cooling curves to higher wall temperatures, but CHF was also increased. The phase-change heat transfer contribution was found to correlate directly with the contact line length for the experimental conditions tested.
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