Air-cooling Process Research Articles

Intercritical tempering enables nanoscale austenite/ε-martensite formation in low-C medium-Mn steel: A pathway to control mechanical properties

In a 0.05C-5.4Mn-0.2Si-0.8Cr-wt% steel intercritically tempered at 700 °C for 50 min a new hexagonal closed-packed phase (ε-martensite) appears on former reversed austenite by an air-cooled process. The tensile strength of the tested steel increased from ~ 840 MPa after intercritical tempering at 650 °C for 50 min to ~ 1002 MPa with the tempering temperature increased to 700 °C, and the product of strength and elongation was improved from 19.9 GPa % to 21.6 GPa %; moreover, the impact energy at − 40 °C was decreased from 143 J to 68 J, and the yield ratio was reduced from 0.84 to 0.50. This result was attributed to the weakening of TRIP effect in existence of ε-martensite. The partitioning of alloying elements at different intercritical tempering conditions and the calculation of SFE (stacking faults energy) indicated that ε-martensite was produced in the ~ 50–100 °C temperature range while cooling in air after tempering at 700 °C for 50 min ε-Martensite affected the stability of the reversed austenite and the fracture mode. The fracture mode was changed with the increased tempering temperature. The results reveal that a multiphase low-C medium-Mn steel can be produced via intercritical tempering accompanied by a unique phase transformation process. A high-temperature and long-time tempering condition will lead to a thermally-induced ε-martensite transformation due to lower SFE possibly associated with more homogenized (or less amount of) alloying elements in austenite, and affects the mechanical behaviors of medium Mn steel.

Effect of controlled cold air distribution on temperature profile and phase transformation of wire loops in the Stelmor air-cooling process

Wire rods produced by the Stelmor air cooling process were found to have the problem of microstructure non-uniformity. The proper distribution of cold air from the nozzle of the plenum chamber can adjust the convection heat transfer intensity at the different positions of wire loops, and further control the dynamic distribution of temperature and phase transformation on wire rods. A three-dimensional mathematical model incorporating the turbulent flow of air, heat transfer and the JMAK phase transform model in the Stelmor process has been developed. Two types of air nozzle were applied in our study, and Type B nozzle which blocked the center portion applied more air to the side region of wire loops than the Type A nozzle. Compared to the unblocked nozzle, the type B nozzle can effectively reduce the temperature difference between the low dense zone and high dense zone on the wire loops from 69.7 K to 18.4 K. The simulated temperature results of wire loop agreed well with the measured one in the industry trials. The present study has demonstrated that these models can be useful tool for optimizing cooling condition in the Stelmor process and predicting the temperature profile and microstructure evolution of the wire rods.

A three-dimensional mathematical model to predict air-cooling flow and temperature distribution of wire loops in the Stelmor air-cooling system

Controlling the forced air cooling conditions in the Stelmor conveyor line is important for improving the microstructure and mechanical properties of steel wire rods. A three-dimensional mathematical model incorporating the turbulent flow of the cooling air and heat transfer of the wire rods was developed to predict the cooling process in the Stelmor air-cooling line of wire rolling mills. The distribution of cooling air from the plenum chamber and the forced convective heat transfer coefficient for the wire loops were simulated at the different locations over the conveyor. The temperature profiles and cooling curves of the wire loops in Stelmor conveyor lines were also calculated by considering the convective heat transfer, radiative heat transfer as well as the latent heat during transformation. The calculated temperature results using this model agreed well with the available measured results in the industrial tests. Thus, it was demonstrated that this model can be useful for studying the air-cooling process and predicting the temperature profile and microstructure evolution of the wire rods.

Air-cooling analysis of AZ31B magnesium alloy plate: Experimental verification, numerical simulation and mathematical modeling

The air-cooling transport process of AZ31B magnesium alloy plate was investigated and carried out under different initial cooling temperatures and different sample sizes at a transport velocity of 0.3 m/s. In order to provide the theoretical basis for the actual industrial rolling production, a detailed analysis of the temperature distributed along both the width direction and the thickness direction under different conditions was performed. Through the processing of the experimental data, the emissivity of AZ31B plate in the air-cooling transport process, as an important heat transfer parameter, was modeled accurately. After that, based on the establishment of the emissivity calculation model, the empirical formula of Stefan-Boltzmann was modified and optimized to be the temperature control model for the air-cooling process in consideration of the heat transfer characteristics of magnesium alloy. Finally, combining the finite element numerical simulation and the experimental results, comprehensive heat transfer coefficient between the AZ31B plate and the external environment during the transport process was accurately defined and further fitted about the experimental parameters.

Investigations on servicing damage mechanisms of Cr35Ni45Nb alloy under complex conditions

Abstract

INVESTIGATION OF LINING PARAMETERS IMPACT ONTO METAL AIR-COOLING PROCESS IN CHAMBER FURNACE

The appropriate mathematical model was created for the investigation of lining parameters impact onto metal air-cooling process in chamber furnace. Numerical computing for various lining composition was conducted: fully dense refractory material, made from chamotte brick; refractory ceramic fi bers on the wall and arch with fully dense refractory of hearth; conceptual lining of entire chamber furnace with refractory ceramic fi bers. Processing of the results allowed to illustrate the impact of the lining type on the length of aircooling process, thereby showing possible reserves for accelerating of this process step.

Mathematical model for studying of metal air-cooling process in furnaces

A mathematical model is developed for the air cooling of massive metallic billets in furnaces. The model permits calculation of the temperature field in the metal, lining, and also the air temperature within the furnace. The rate of calculation on the basis of the model considerably exceeds real-time requirements. Hence, the model may be used in predictive control systems.

Reducing water and energy consumption in chemical industry by sustainable production approach: a pilot study for polyethylene terephthalate production

In this study, a polyethylene terephthalate manufacturing plant was subjected to environmental performance evaluation and analyses/benchmarking of water consumption. The objective was to determine processes/practices where significant water and related energy saving potential was present. Based on evaluations and analyses, a technology change was realized in heat transfer systems from water-to air-cooled process. As a result of the applications, soft cooling water consumption of the company was reduced by 46.7% which corresponds to water saving of 151,428 m3/year. Moreover, 117,848 kWh/year of energy was saved due to electricity saving in electric motors of pumps of heat transfer systems as well as pumps/fans of cooling towers. Owing to the improved energy efficiency, total carbon emissions of the company was reduced by 69,530 kg CO2/year. Auxiliary material consumption was also reduced since the maintenance requirements of heat transfer pumps were minimized. The total cost saving was 104,905 $/year, while the payback period was calculated as 6 months. This study was conducted to be used as a successful model to increased water and energy efficiency in manufacturing industries based on systematic environmental performance evaluations and benchmarking. Furthermore, it could serve as a building block in Turkey for the integration of cleaner and sustainable production approach into national agenda which is currently being structured by the European Union harmonization efforts of this country.

Machining Parameters Evaluation During a Wet, Lubricated, and Air-cooled Turning Process

AbstractIn this paper, there is an attempt to derive an observation and study of specific machining parameters after turning process of a DIN 34CrNiMo6 nickel-chromium stainless steel in a conventional center (lathe). The machining parameters concerned are the temperatures developed on cutting tools and the workpiece, the surface roughness of the workpiece after process, the level of vibrations of cutting tool, the noise levels of the process, and the current of the lathe motor. Four different experimental scenarios completed namely wet, dry and air-cooled process. An optimally designed sensor network installed to monitor and record the measurements of the examined machining parameters. The experimental data considered for examination with statistical analysis of developed charts which presented interesting research findings. In dry cutting, the machining temperatures and the amount of removed material, observed with the highest values among other experimental scenarios. The surface roughness found its smallest value after the end of the lubricated cutting and the machining process with minimum vibrations observed during the operation of the Airgun. However, the study also brought out an interesting and useful observation for future consideration in the area of a Life Cycle Assessment. The chips taken at the end of experimental scenarios will be used for an LCA analysis in relation to the initial material and machining process. This will give an opportunity of an interesting approach that can be applied to assess the environmental impacts throughout a product's life cycle.

A facile approach to fabricate a stable superhydrophobic film with switchable water adhesion on titanium surface

A simple process of thermal oxidation and self-assembly modification was developed to fabricate a stable superhydrophobic film with controllable adhesion on titanium surface. Pure titanium plate was first heat treated in atmospheric environment at 900°C, 1000°C and 1100°C respectively for a certain time, then air cooled. The subsequent air-cooling process separated the flaky yellow oxide layer formed on titanium plate during the oxidation from the substrate and a rough titanium oxide surface with micrometer and nanometer-scale hierarchical structures was obtained. The following immersion process in N-octadecyltrichlorosilane solution endowed the surface with excellent water repellence, raised its contact angle up to 166° and reduced its slide angle as low as 2°. What's more, by controlling heat temperature and time, the surface's superhydrophobicity switched from sticky state to sliding state. Field-emission scanning electron microscopy (FE-SEM) and contact angle measurement were used to characterize the morphological features and wettability of the as-prepared surface respectively. Immersion test in corrosive liquids and abrasion test with sandpaper have a further exhibition of its chemical stability and mechanical durability. The result is meaningful to a wider range of future applications of superhydrophobic titanium surface in industry and real life.

Casted Strip Character of Twin-Roll Casted High Strength Non-Oriented Electrical Steel

A twin-roll casting process was used to produce high strength non-oriented electrical steel casted strips. The typical character in chemical composition is the adding of Ni and Cr.The main role of Ni and Cr is solution strengthening. MEM, SEM, and TEM were used to observe microstructure, texture, and precipitate characteristics of a casted strip. The casted strip character under different secondary cooling process was compared. The results show that water-cooled as-cast strip is composed of the equiaxed grains, air-cooled as-cast strip is characterized by a mixture of the quiaxed and columnar grains. The texture of water-cooled as-cast strip is weaker and diffuser than air-cooled as-cast strip. Precipitates mostly are AlN and MnS, which mostly precipitate in the grain. The precipitates of Ni and Cr is not observed. The size distinction of MnS between two secondary cooling process is not remarkable. The size of AlN in water-cooled process is smaller than in air-cooled process.

Modeling and analyzing the effects of air-cooled turning on the machinability of Ti–6Al–4V titanium alloy using the cold air gun coolant system

This study provides the mathematical models for modeling and analyzing the effects of air-cooling on the machinability of Ti–6Al–4V titanium alloy in the hard turning process. A cold air gun coolant system was used in the experiments and produced a jet of compressed cold air for cooling the cutting process. The air-cooling process seems to be a good environment friendly option for the hard turning. In this experimental investigation, the cutting speed, feed rate and cutting depth were chosen as the numerical factor; the cooling method was regarded as the categorical factor. An experimental plan of a four-factor (three numerical plus one categorical) D-optimal design based on the response surface methodology (RSM) was employed to carry out the experimental study. The mathematical models based on the RSM were proposed for modeling and analyzing the cutting temperature and surface roughness in the hard turning process under the dry cutting process and air-cooling process. Tool wear and chip formation during the cutting process were also studied. The compressed cooling air in the gas form presents better penetration of the lubricant to the cutting zone than any conventional coolants in the cutting process do. Results show that the air-cooling significantly provides lower cutting temperature, reduces the tool wear, and produces the best machined surface. The machinability performance of hard turning Ti–6Al–4V titanium alloy on the application of air-cooling is better than the application of dry cutting process. This air-cooling cutting process easily produces the wrinkled and breaking chips. Consequently, the air-cooled cutting process offers the attractive alternative of the dry cutting in the hard turning process.

Research on the Temperature Distribution near the Surface of Long-Shaft Heavy Forging

The precise edges of forging should be extracted from the image when measuring the dimensions of high temperature forging based on the non-contact image measurement technique. It is difficult to distinguish the forging boundary precisely due to the continuous variation of the air temperature near the forging. The two-dimensional simplified cross-section models, including the squaring, chamfering and rounding models, were established by the symmetrical modeling method. The air-cooling process from 1200°C to 800°C of high temperature long-shaft heavy forging was simulated based on ANSYS software. The variation regularities of temperature with the distance and time were obtained, which provides a theoretical basis to determine the edges of high temperature objects in non-contact measurement.

Research on the Temperature Distribution near the Surface of Long-Shaft Heavy Forging

The precise edges of forging should be extracted from the image when measuring the dimensions of high temperature forging based on the non-contact image measurement technique. It is difficult to distinguish the forging boundary precisely due to the continuous variation of the air temperature near the forging. The two-dimensional simplified cross-section models, including the squaring, chamfering and rounding models, were established by the symmetrical modeling method. The air-cooling process from 1200°C to 800°C of high temperature long-shaft heavy forging was simulated based on ANSYS software. The variation regularities of temperature with the distance and time were obtained, which provides a theoretical basis to determine the edges of high temperature objects in non-contact measurement.

Numerical Analysis and Experimental Study on Temperature Field of Brake Disc during the Air-Cooling Process

Numerical study established by using ANSYS 12.0 has been performed by considering convective and radiative heat transfer to predict the transient thermal behavior of a brake disc during air-cooling process of heat treatment. Though the model based on the numerical study, temperature distribution maps at different time delays and variation in the temperature at different parts of the brake disc are given. Additionally, experimental results demonstrate the validity of the simulation analysis through comparing with the results obtained from the transient analysis. It is shown that the air-cooling numerical model of brake disc is verified and has the rather accurately temperature prediction ability.

Change in Yield Strength of Ultra Low Carbon Steels with Cr Addition

The relationship between ferrite grain diameter and upper yield strength was investigated for cold-rolled and annealed ultra low carbon steel sheets containing various chromium contents from 0 to 23%. The upper yield strengths were dropped with annealing temperature and the tangent of the change in the yield strength was decreased with increasing in chromium content. The coefficient in Hall–Petch equation decreased linearly with chromium content. This is attributed to lowering solute carbon content at grain boundaries with precipitation of chromium carbide since the decrease was not due to ferrite region hot-rolling nor to α′ phase precipitation in high chromium steel. While friction stress (σ0) in Hall–Petch equation of air-cooled sheets after annealing showed the minimum at chromium content of 5%, σ0 of the lower chromium content steels increased and became to show linear relationship for chromium content after 150°C aging. This result indicates that σ0 increases with chromium content by solid solution strengthening. The reason why the minimum σ0 is exhibited in the 5% chromium steel air-cooled after annealing is that the amount of decrease in σ0 by retardation of aging during air-cooled process is larger than that of solid-solution strengthening by chromium.

Crystallization Behaviors Concerned with TTT and CCT Diagrams of Blast Furnace Slag Using Hot Thermocouple Technique

Currently, the most of slags are recycled and reused by taking the advantages of the feature of respective slags (e.g. the BF slag is used for cement and roadbed material, LD slag is also used for the roadbed material and marine resources, etc.). The quality and quantity of recycle of slags changed greatly within recent ten years and it will be expected as an important resource in the future. Whereas there is a remained possibility on the recycle of slags, most of slags have a high temperature more than 1 500, when it was exhausted.In general, there are two cooling processes adopted into the slag treatment, one is an air-cooling process and the other is a water quenching process. However, those slag cooling processes does not utilize the sensible and the latent heat related to high temperature melt. If there were a TTT (Time-Temperature-Transformation: isothermal transformation) diagram and a CCT (Continuous-Cooling-Transformation: continuous cooling curve) diagram, the property of the final slag could be estimated by the designed cooling path. Furthermore, it could be possible or easier to recover the sensible and the latent heat through a given cooling path.In the present study, using SHTT (Single Hot Thermocouple Technique), TTT and CCT diagrams of BF slags were measured. Crystallization behavior in the TTT and CCT diagrams of BF slag were clarified by XRD analysis, SEM observation and EDS analysis together with the in situ observation. Crystal phases in the TTT diagram for BF slag used were Gehlenite (2CaO·Al2O3·SiO2) and Merwinite (3CaO·MgO;·2SiO2). The Merwinite precipitated faster than the Gehlenite. The nose position of Merwinite was 4 s at 1 090 and the nose of Gehlenite was 8 s at 1 230. CCT diagram had wider glass region than TTT diagram and the temperature of crystal region decreased to 1 340 at 1 000 s and 1 160 at 14 s.

Effect of steel manufacturing process and atmospheric corrosion on the corrosion-resistance of steel bars in concrete

This paper presents results of a study conducted to evaluate the effect of steel manufacturing process and the surface condition of reinforcing steel on their corrosion-resistance when embedded in concrete. Steel bars produced by water quenching and air-cooling were utilized. The corrosion-resistance of fresh bars, i.e., those that were clean and shiny, and those exposed to atmosphere and accelerated salt spray, when embedded in concrete, was evaluated. The corrosion-resistance of the clean and corroded reinforcing steel bars was assessed by measuring corrosion potentials and corrosion current density. Accelerated impressed current technique was also utilized to evaluate the corrosion-resistance of clean and corroded reinforcing steel bars in concrete. A longer time-to-initiation and lower rate of reinforcement corrosion was noted in the concrete specimens prepared with water-quenched steel bars compared to similar bars manufactured by the hot-rolling process. Similarly, the rate of reinforcement corrosion in the concrete specimens prepared with corroded steel bars, exposed to atmosphere for 12 months and salt spray, was less than that on the unexposed bars. The data developed in this study also indicate that the surface layer formed on the water-quenched steel bars, due to the cooling process, provides protection to the metal substrate as against the loose mill scale formed on the steel bars produced by the air-cooling process.

Assessment of the hygienic performances of an air-cooling process for lamb carcasses and a spray-cooling process for pig carcasses

The air-cooling process for carcasses at a lamb slaughtering plant and the blast-plus-spray-cooling process for carcasses at a pig slaughtering plant were examined. Temperature histories were collected from the deep leg, the aitch bone pocket surface and randomly selected surface sites of carcasses passing through each process. For each process, sets of 25 temperature histories were collected for each type of site, with a single history being collected from each of 75 randomly selected carcasses. A swab sample was obtained from a randomly selected site on each of 25 randomly selected carcasses entering and 25 leaving each process. Total aerobic counts, coliforms and Escherichia coli were enumerated in each sample. Lamb carcasses resided in the chiller for between 17.5 and 66.8 h, and pig carcasses for between 14.8 and 24.5 h. All the lamb carcasses attained deep leg and aitch bone pocket surface temperatures <7°C as did most pig carcasses. However, those temperatures remained >13°C in 8% of pig carcasses. Such inadequate cooling of pig carcasses was not apparent in temperature histories from randomly selected surface sites as such sites on both pig and lamb carcasses all attained temperatures <7°C. Proliferation values for E. coli and psychrotrophic pseudomonads calculated for the temperature history from each randomly selected surface site indicated that growth of E. coli on either lamb or pig carcasses would be undetectable, but that increases in the log numbers of total aerobic counts of >1 and <1 during the cooling processes could be expected for lamb and pig carcasses respectively. Enumerations of bacteria showed that bacteria on pig carcasses behaved much as would be expected from the temperature histories from randomly selected sites. However, on lamb carcasses the log numbers of bacteria were reduced by about 0.5, 1.5 and 2 for total aerobic counts, coliforms, and E. coli, respectively. The findings indicate that microbiological data are required to properly assess the microbiological effects of carcass cooling processes because, in some, factors other than temperature determine the behavior of the microflora.

Prediction of hot-fill-air-cool sterilization processes for tomato paste in glass jars

A mathematical model to predict heat transfer and integrated sterilization values during the hot-fill process of double concentrated tomato paste in glass jars was developed. The model was capable of predicting satisfactorily the time-temperature relationships during the air-cooling process following the hot-fill process. Integrated sterilization values after hot-filling were calculated as a function of the retention time. A hot-filling temperature of 85°C was not adequate to sterilize properly this product for any of the jar sizes studied and for the initial and final population levels established, for the target microorganism employed ( B. coagulans). Hot-filling temperatures of at least 94, 92 and 90°C are recommended for jar sizes of 200, 500 and 4000 cm 3, respectively. As jar size increased, the hot-filling temperature and the retention time required to achieve the desired integrated sterilization value decreased. Larger retention times were obtained as the hot-filling temperatures decreased.