Effect of the heat treatment mode of high chrome iron rolling mills on chrome redistribution in the stress field

Heat treatment is an important stage in the technology of rolling rolls, due to the fact that the thermal stresses that occur during rapid or uneven heating summing up with the rather high residual stresses after casting, create a risk of cracking. Goal. The aim is improving the quality of rolling rolls by varying the modes of heat treatment. Therefore, it is important to assess the level of thermal stress. Method. Evaluation of thermal stresses arising in heating and cooling in the heat treatment process that summing up to the relatively high residual stresses after casting, creates the risk of fractures. The profile of the distribution of chromium in the cross section of the working layer at each time under the action of the stress gradient that occurs during heat treatment of the roll is obtained by calculation. Results To ensure a minimum temperature difference between the surface and the core, it is necessary to reduce the heating and cooling rate, as well as increase the duration of exposure at a given temperature. Reducing the cooling rate from 17 to 3.7°C/h decreases the temperature difference at the surface and in the center of the roll and the intensity of thermal stresses from 29 to 7 MPa. It is established that the rate of heating and cooling should not exceed 10– 15° C/h, and exposure to annealing should be at least 5–7 hours. Scientific novelty. The modes of heat treatment of rolling rolls with a high-chromium cast iron working layer are designed by estimating the level of thermal stresses. The profile of distribution of chromium after various modes of heat treatment is calculated analytically and its mode at which the most uniform distribution of chromium on section of a working layer remains is offered. Practical significance. The developed technique allows to calculate analytically the profile of distribution of chromium after various modes of heat treatment and to choose such a mode at which the most uniform distribution of chromium remains on the section of a working layer.

Automated system for design and calculation of heating devices for hot die forging

Methods of mathematical modeling, basic technologies and methods of modeling in various design systems of the stamping process are considered. The canonical equations of temperature stresses are obtained, which make it possible to obtain a picture of the temperature distribution over the workpiece area during heating. A mathematical model has been developed for a thin metal strip during heating; thermal stresses arising in it due to uneven heating have been described. Numerical modeling has been carried out on the basisof field data, which will allow verification of the automated environment for the selection of functional and design schemes and the calculation of the parameters of heating devices in hot volumetric stamping of workpieces in terms of speed, energy efficiency, heating quality: accuracy of achieving specified temperatures and maximum heating uniformity. By areas, ease of use and readjustment, resource, reliability and maintainability. The proposed system will include the following CAD elements: databases and rules for operating with them, calculation modules, modules for selecting and matching options.

The Effect of Uneven Heating On the Flow Distribution Between Parallel Microchannels Undergoing Boiling

As the size, weight, and performance requirements of electronic devices grow increasingly demanding, their packaging has become more compact. As a result of thinning or removing the intermediate heat spreading layers, non-uniform heat generation from the chip-scale and component-level variations may be imposed directly on the attached microchannel heat sink. Despite the important heat transfer performance implications, the effect of uneven heating on the flow distribution in parallel microchannels undergoing boiling has been largely unexplored. In this study, a two-phase flow distribution model is used to investigate the impact of uneven heating on the flow distribution behavior of parallel microchannels undergoing boiling. Under lateral uneven heating (i.e., the channels are each heated to different levels, but the power input is uniform along the length of any given channel), it is found that the flow is significantly more maldistributed compared to the even heating condition. Specifically, the range of total flow rates over which the flow is maldistributed is broader and the maximum severity of flow maldistribution is higher. These trends are assessed as a function of the total input power, degree of uneven heating, and the extent of thermal connectedness between the channels. These model predictions are validated against experiments for a representative case of thermally isolated channels subjected to even heating and extreme lateral uneven heating conditions and show excellent agreement.

Effect of different thawing methods on the quality of mackerel (Pneumatophorus japonicus)

Five thawing methods such as flow water thawing, ultrasonic flowing water thawing, air thawing, microwave thawing and low temperature thawing were used, and the physical, chemical properties and structure of mackerels after thawing were assessed. The results showed that the low temperature thawing had the best water retention, lower protein and fat oxidation. The microwave thawing had the shortest thawing time, but uneven heating leads to partial maturation. Air thawing prolonged exposure to air leads to high levels of protein and fat oxidation. The flow water thawing had better water retention than that of the ultrasonic flowing water thawing, only the thawing time was slightly longer than that of the ultrasonic flowing water thawing. In general, the low temperature thawing performed well after thawing. The flow water thawing used only 1/43 of the low temperature thawing's elapsed time after sacrificing some acceptable qualities. Thus, flow water thawing is more suitable for thawing frozen mackerel.

MODELING OF A SYSTEM FOR AUTOMATIC REGULATION OF THE TENSION MODE IN THE ROUGHING GROUP OF STANDS OF A CONTINUOUS SECTION MIL

The subject of the research is automatic control system modeling features for tensioning of stands roughing group, which takes into account changes in the rolling speed at exit of the previous stand and entrance to the next stand. Control systems for high-speed rolling on section mills are the most critical systems, since the trouble-free operation of rolling mill largely depends on their work. Rolling speed control is understood to mean tension regulation in the roughing group of stands and stabilization of the rolling loop in the finishing groups. The influence of such technological factors as uneven heating of blanks, change in the crimping mode in stands, etc. leads to the appearance of tension or back-up forces, deviation of rolled loop from the specified values. Tension rolling, in contrast to loop rolling, is a stable rolling mode. However, (at significant values of tension in the rolled products) such a rolling mode leads to different thicknesses of the finished product. The loop rolling mode is an unstable mode and is impossible without automatic control systems. Both in the tension rolling mode and in the free rolling mode with a loop, it is necessary to study automatic control systems in order to determine the possibilities of compensating for disturbing influences and obtaining rolled products of the given accuracy. Therefore, the main task of the automatic control system is to maintain the rolling mode with the lowest possible tension. To achieve this goal, direct control of the tension of the rolled strip with modern technical means is rather difficult, and the operation of tension control systems is based on indirect methods of measuring it, and the study of the system efficiency is reduced to modeling the process itself. The developed model consists of three stands and two inter-stand spaces, since it takes into account changes in rolling speed at the exit of previous stand and the entrance to the next stand. It is due to this that adequate simulation results are obtained that are close to the real rolling process. Keywords: automation, rolls, stand, inter-stand spacing, modeling, loop tension, rolling mill, roughing group.

Various Methods for Measurement of Resistive Leakage Current of Metal Oxide Surge Arrester

Metal Oxide Surge Arrester (MOSA) does not require any ordinary maintenance. But MOSA is get affected from ageing due to the effect of discharging impulse currents, uneven heating and internal partial discharges. A leading cause of deterioration is ingress of moisture. The degradation of MOSA also correlated with the ageing level of the arrester. This is called degradation under surge. The ageing level with the degradation of MO surge arrester or the leakage current of the surge arrester is related to each other. The leakage current is directly proportional to the ageing level. If the ageing level is raise, the leakage current also will increase. So, various methods for determination of the condition of ZnO surge arrester by means of measurement of the arrester leakage current are discussed. A MSCM method, which is based on leakage current of the surge arrester presented. The measuring instrument Leakage Current Monitor is also discussed.

ANALYSIS OF THE REASONS FOR CRACKING PIPES OF THE BOILER OF THE RECOVERY

8-381X Abstract. Formulation of the problem. One of the main tasks of production is reliable and trouble-free operation of equipment. In the oxygen-envelope process, when cast iron is purged, a large amount of carbon monoxide CO is emitted in the converter, which has a high temperature of more than 1 700 °С of the outgoing gases. The envelope gases in the waste heat boiler are cooled. Converter gas output is characterized by cyclic unevenness In this case, uneven heating of the walls of the boiler pipes occurs. By circulation pumps, chemically purified water is supplied for forced cooling of the boiler walls. When raising the outgoing gases, the cooling water is converted to pars by its subsequent supply to the consumer. The study is dedicated to solving the scientific and applied problem for the reasons for the formation of defects and the identification of cracks in the pipes of the recovery boiler.The purpose of the work. To investigate the causes of the development of transverse cracks in the pipelines of the recovery boiler by various methods of non-destructive testing, to use the methods of scanning microscopy to analyze the microstructure, mechanical tests, and the magnetic properties of structural carbon steel. Conclusions. One of the main reasons for the appearance of massive cracks in the pipes of cylindrical caissons is thermal fatigue caused by high thermal loads. Transverse cracks have the character of thermal fatigue failure, which is confirmed by changes in the ferrite-pearlite structure of the metal, resulting from uneven local cooling of the walls of the caisson. The reasons for the violation of the water circulation in the boiler are the pressure drop in the boiler and a sharp discharge, the load is the release of water from the boiler.

Analysis on the effect of polyetherimide on energy distribution of radio frequency heating of viscous sauce

Radio frequency (RF) sterilization of low-moisture, high-oil, high-protein, and viscous sauces for instant food (LHHVS) demonstrates many advantages, but uneven heating is a main problem that must be addressed. Main factors that affect heating uniformity are generally considered dielectric properties, shape and size of the sample and its position relative to the electrode plate, in addition the structure and voltage of RF electrode. A method based on texture characteristics of the solid–gel–liquid mixing system of LHHVS for adjustment and control of energy distribution in the RF field is proposed in this study to improve the heating uniformity. First, energy conversion principles and control equations of RF heating were analyzed on the basis of dielectric theory. Second, the influence of RF electromagnetic field-medium polyetherimide (PEI) on the RF heating of peanut butter (RHPB) was investigated on the basis of the numerical model of RHPB that was verified through experiments. Finally, the influence mechanism and its regulation and control effect were analyzed and discussed. The following conclusions can be drawn from this study: the increase of electrode gaps exerts minimal effect although it reduces the unevenness of the energy distribution. However, RF heating protocols must use the smallest possible electrode gap to heat agrifoods and increase the heating rate significantly. The energy distribution on the part of the sample close to PEI varies with the change of geometry and size of PEI when its placement is bias or symmetric. The area of energy enhancement continues to expand where the sample is in contact with PEI as PEI gradually increases. The area where the temperature increases under the influence of PEI will expand along the direction of the sample radius when the thickness of PEI remains unchanged and the radius gradually enlarges; otherwise, it will expand along the direction of the sample thickness. The influence of PEI on the energy distribution of RHPB demonstrates local characteristics. PEI significantly influences the energy distribution and heating mode of RHPB, which is easy to adjust and control, but does not reduce the processing speed and does not increases energy consumption. Hence, PEI is an effective means to interfere with energy distribution of RHPB. Uniform energy distribution can be obtained by selecting the appropriate PEI shape and size. Results of this study can help determine the experimental protocol for RHPB with the optimal uniform distribution and promote the fast commercial application of this technology.

Repair of a Cracked Historic Maryan Bell by Gas Welding

In this article, the range of works connected with the repair of a historical Maryan bell from 1639 are presented. The first attempts to repair damaged bells occurred in the 1930s in Poland. However, this process was stopped because of extensive technological difficulties. Welding and soldering-welding were the basic methods. There is one difference between these two methods—connecting surfaces are melted during the welding process but only heated until the melting temperature of the material added to the connection (that is the solder) during the soldering-welding process. It was important to heat the bell to the proper temperature during welding. Uneven heating causes the enlargement of existing cracks or the appearance of new ones, or even the complete destruction of the bell. Nowadays, a method of even heating using a special heating mat has been devised. Thanks to this method it is possible to control the heating and cooling process. The most important task during the whole operation of bell welding was obtaining the original sound. During this research, the chemical composition was examined to prepare a welding rod with a suitable chemical composition. After the repair process, an analysis of the sound of the bell was conducted. It was shown that the repair of bells is possible when correct thermal parameters are used. The most highly recommended technique for repairing bells is gas welding.

The Prospect of Microwave Heating: Towards a Faster and Deeper Crack Healing in Asphalt Pavement

Microwave heating has been shown to be an effective method of heating asphalt concrete and in turn healing the damage. As such, microwave heating holds great potential in rapid (1–3 min) and effective damage healing, resulting in improvement in the service life, safety, and sustainability of asphalt pavement. This study focused on the microwave healing effect on porous asphalt concrete. Steel wool fibres were incorporated into porous asphalt to improve the microwave heating efficiency, and the optimum microwave heating time was determined. Afterwards, the microwave healing efficiency was evaluated using a semi–circular bending and healing programme. The results show that the microwave healing effect is largely determined by the steel fibre content and the mix design of the porous asphalt concrete.. Besides, the uneven heating effect of microwave contributes to an unstable damage recovery in the asphalt mixture, which makes it less efficient than induction heating. However, microwaves exhibited the ability to penetrate further into the depth of the test specimen and heat beneath the surface, indicating deeper damage recovery prospects.