Improving the compact heat exchangers with profiled tubes for marine power plants

The design features of heat exchangers with flat tubes are considered. The stages of creating a new flat tube and its prototypes are analyzed. An oil refrigerator is chosen as a prototype of the heat exchanger because of the previous use of flat tubes with wells, now replaced with new flat profiled tubes. Thermal and hydraulic tests of a refrigerator made of such tubes are carried out at the stand. During the testing, the hydraulic resistance of the cavities of the cooled and cooling media and thermal parameters are determined: heat power, heat transfer coefficient and heat transfer coefficient from the cooled medium in the inter-tube cavity with the transverse flow of tubes to the tube wall. A satisfactory correspondence of the actual power values determined for both working environments has been established. The discrepancy does not exceed (-7.6%)-(+5%) with an average value of +0.2%. A satisfactory correspondence of the actual and calculated values of the refrigerator power has been obtained. The discrepancy does not exceed (-15%)-(+9%) with an average value of -2.8%. The calculation of the capacity of the refrigerator during its operation in the design mode of oil cooling is carried out. The oil flow is considered both through the pipe and through the inter-pipe space. A good convergence of the calculations with the experimental results has been revealed.

Effect of Forging Deformation and Cooling on Mechanical Properties of Martensitic Stainless Steel

Stainless steel has good mechanical properties compared to other materials for strength and hardness, usually it will increase in hardness after hardening or forging. The purpose of this study was to obtain information about: The value of hardness and tensile strength of martensitic stainless steel forging with various deformations and cooling. The research method used is an experimental method, namely by forging on martensitic stainless steel with variations in deformation and cooling rate. Variations of forging deformation used are 25%, 50%, and 75%. The cooling media used are water, oil and air. The results of forgings with various cooling media were tested for tensile strength and tested for hardness using the Rockwell C (HRC) method. It was found that the higher the value of forging deformation, the higher the value of strength and hardness of martensitic stainless steel. This is because more and more martensite structures are recrystallized. In addition, it was also found that water and air cooling media gave an increase in the hardness of martensitic stainless steels. This is influenced by the cooling rate, where the higher the cooling rate, the more martensite structures formed, thus increasing the hardness value. The increase in hardness value is proportional to the increase in yield strength and tensile strength.

Analisis Struktur Mikro dan Kekerasan Paduan Aluminium ADC 12 Hasil Proses Pengecoran Semi Solid dengan Proses Perlakuan Panas

This research aims to analyze the effect of providing additional heat treatment and artificial aging with variations in temperature of quenching and variations in aging time of ADC12 semi-solid casting result which include hardness and microstructure values. The Selected quenching temperature variations are 10°C, 30°C and 50°C. While the aging time variations are 0 h, 1 h, 3 h, 5 h, 7 h, 9 h, 11 h and 13 h. The tests carried out are hardness testing as well as microstructure that will be used to calculate the grain size values and structural density. The highest hardness value was at 180°C, 10°C cooling media variation with 5 h aging time is 83.10 HB. While the smallest grain size value was at the temperature of 10°C cooling media with an aging time of 5 h is 42.797 µm. The optimal value lies at a temperature of 10°C with an aging time of 5 h resulting hardness 83.7911 HB, the average of grain size is 13.5995 µm and the grain density value is 0.8892 with desirability reaching 0.920.

STUDY ON THE EFFECT OF COMPOSITION AND VARIATION OF Sn/Zn COOLING MEDIA ON NICKEL ALLOY STEEL THROUGH HOT FORGING AND AUSTEMPERING

STUDY ON THE EFFECT OF COMPOSITION AND VARIATION OF Sn/Zn COOLING MEDIA ON NICKEL ALLOY STEEL THROUGH HOT FORGING AND AUSTEMPERING. Laterite steel with nickel content is expected to be a solution to overcome the lack of domestic steel availability and dependence on imports. This research was conducted to develop Nickel-Chromium-Molybdenum alloy steel used Grinding ball for cement industrial applications. Grinding ball is the one of imported steel products needed to be crushing and size reduction the ores or cement. In addition to import issues, grinding balls have a significant problem: their mechanical properties that do not meet SNI 1049 require the material to have a minimum hardness value of 45 HRC. In this study, the characteristics of Nickel alloy steel were investigated further through heat treatment of forgings heated at the austenitizing temperature of 950 °C and austempering with variations in the cooling medium of Sn/Zn solution. The cooling medium was chosen because it has a melting temperature in the phase diagram area to form the bainite microstructure with complex and challenging characteristics, both of which are required in material for grinding ball applications. In particular, the hardness value that passed the SNI 1069 standard was the use of samples with a Cr-Mo alloy of 1%-wt with a hardness value of 45.92 HRC for Sn Austemper and 48.07 HRC for Zn austemper.

Analisis Struktur Mikro dan Kekerasan Paduan Aluminium ADC 12 Hasil Proses Pengecoran Semi Solid dengan Proses Perlakuan Panas

This research aims to analyze the effect of providing additional heat treatment and artificial aging with variations in temperature of quenching and variations in aging time of ADC12 semi-solid casting result which include hardness and microstructure values. The Selected quenching temperature variations are 10°C, 30°C and 50°C. While the aging time variations are 0 h, 1 h, 3 h, 5 h, 7 h, 9 h, 11 h and 13 h. The tests carried out are hardness testing as well as microstructure that will be used to calculate the grain size values and structural density. The highest hardness value was at 180°C, 10°C cooling media variation with 5 h aging time is 83.10 HB. While the smallest grain size value was at the temperature of 10°C cooling media with an aging time of 5 h is 42.797 µm. The optimal value lies at a temperature of 10°C with an aging time of 5 h resulting hardness 83.7911 HB, the average of grain size is 13.5995 µm and the grain density value is 0.8892 with desirability reaching 0.920.

Study of the process of rolling steel balls in skew rolling mill – metallographic analysis

This paper presents the results of metallographic research studies carried out for stock materials as well as the samples collected from the balls formed in the rolling process in a skew rolling mill. The stock material was bearing steel 100Cr6 and the steel from rail scrap. The rolling process was carried out in parallel for the two assumptions: the conventional method (hereinafter referred to as conventional rolling) and the modified method (hereinafter referred to as modified rolling). After the rolling process, three cooling media were used: air, water and oil. The pictures below, which depict microstructures, were taken using the bright-field and the dark-field microscopy technique, the samples were etched with a 4% solution of picral.

Analisis Kekerasan Hasil Pengelasan Gas Tungsten Arc Welding pada Baja ST 37 dengan Variasi Media Pendingin

Cooling media is a substance that increases the hardness value of a materialthrough a heat-treatment process. This study aims to determine the effect of cooling media on the hardness of ST 37 steel due to Gas Tungsten Arc Welding (GTAW). The method used is an experimental method using the independent variables, namely water cooling media, seawater cooling media, and oil cooling media, while the dependent variable is the hardness test result. In specimens using water cooling media, the hardness in the weld area is 47.19 kg/mm2, in the HAZ area the it is 54.6 kg/mm2, and the base metal gets a value of 40.87 kg/mm2. While the specimens with seawater cooling media get a value in the weld area of 76.37 kg/mm2, in the HAZ area it gets a value of 83.89 kg/mm2 and the base metal gets a value of 70.13 kg/mm2. The specimens with oil cooling media the value in the weld area is 40.77 kg/mm2, in the HAZ area it gets a value of 43.32 kg/mm2 and the base metal gets a value of 36.09 kg/mm2 . From the hardness values obtained, specimens immersed in seawater cooling media have the highest hardness values compared to water and oil cooling media.

Fatigue Characteritics of Medium Carbon Steel after Heat Treatment Using Sand as Cooling Media

Stress concentrations cause many machine element failures. Failure will occur more rapidly if the machine elements obtain repeated and fluctuating loading. For this reason, the material for machine elements must have better fatigue life. There are various attempts made to increase material life and other mechanical properties. In this study, the research sample used is AISI 4140 steel. The samples obtain hardening followed by cooling and tempering. The hardening temperature is 8500C with a holding time of 17 minutes. The cooling media in this research are dry sand, semi-wet sand, and wet sand. Wet measurements based on volumetric ratios. Semi-wet sand with a ratio of sand and water 4: 1, sandy sand 4: 2. The final process is tempering treatment, with a temperature of 2500C. The material fatigue test refers to the JIS Z 2274 Standard. From this study, the heat treatment given can reduce the fatigue life of the material, even though the hardness increases. The higher the cooling rate, the hardness of the material increases, but the fatigue life is low.