Papers by Keyword: Heating

Abstract: The weakening of the behavior of reactive powder concrete (RPC) under high temperature is a major drawback; therefore, it is necessary to find an ingredient that improves their resistance under rising temperatures. The present work involves the use of metakaolin as a substitute for sand in a reactive powder concrete (RPC) in order to assess its effect on the mechanical strength at high temperatures. The test specimens are preheated up to 100°, 300°, 500°, 700° and 900°C, respectively following a well-defined cycle, thereafter subjected to a three-point bending followed by compression tests. Samples of the tested specimens were used for thermal, mineralogical and microstructural analyses using the thermogravimetric and differential thermal analysis (TG / DTA), the X-ray diffraction (XRD) and the scanning electron microscopic Analysis (SEM).The heating tests revealed that all the specimens exploded before reaching 500°C. However, they can withstand 300°C before exploding for different exposure durations depending on the metakaolin substitution ratio. Therefore, the mechanical tests were applied only on unheated specimens and those heated up to 100°C. The results showed that the use of metakaolin improves the mechanical strength of the RPC, both at room temperature (25°C±1°C) and at 100°C. This result is confirmed by the microstructure analysis, which revealed the absence of portlandite. The latter did react with the metakaolin silica to form new calcium silicate hydrates (CSH) enhancing the mechanical strength.

Abstract: The main problem of shaping threaded holes in sheet blanks with a thickness of less than two millimeters is to obtain a threaded surface that provides the necessary strength of the threaded connection. The method of forming holes with flanges in sheet blanks by rotating punch (thermal drilling) has wide technological capabilities. The rotational speed of the punch, as well as its axial feed, affect the shape, size and properties of the material of the resulting hole, which in its turn affects the length of the screwing and the strength of the threaded joint.

Abstract: The article describes a heat and power complex utilizing internal sources of consumer heat, as well as using renewable energy sources. The power complex also includes heat accumulators, cold accumulators and a cascade heat pump plant. This heat pump plant has a high conversion factor of electrical energy due to optimization of heat flows. In this article, a method for determining the energy efficiency of the heat-energy complex under consideration is disclosed.

Abstract: Various heat sources effect on the contact tip of the welding torch for MIG/MAG welding has been considered. Factors affecting heating rate and contact tip temperature during welding have been described. Experiments on heating rate and contact tip temperature for various welding conditions have been presented. Sources of heat, exerting maximum influence on contact tip heating have been identified.

Abstract: This paper discusses the mathematical model of powder material particles heating in the gas flow when applying plasma gas and thermal coatings. It has been assumed that while moving in the plasma, the particle is heated by convective heat transfer and radiative heat transfer. To ensure accuracy and validity of calculation, two characteristic regions have been outlined: Core, where the temperature, density, and viscosity of plasma, as well as the other parameters are assumed as constant; and the region from the core to the coated surface (substrate), where these parameters are the functions of the plasma flow coordinates. One of the assumptions is that the shape of the particles is near-spherical, and the thermal flow’s action to the particles’ surface is uniform. Special attention has been paid to correct selection of criteria , which allowed to simplify the solution and reduce it to the ordinary first-order differential equation derived from the particle heat balance equation.

Abstract: Single Point Incremental Forming (SPIF) is a recent technology of forming sheet in several decades. Nowadays, SPIF technology is still continued to be studied, applied and ameliorated in sheet manufacturing in industry. However one of the difficulties of the technology is the forming angle is still small (smaller than 80⁰ according the properties of metal sheets). This paper recommends a measure of increasing the plasticity of the sheet by heating in time of forming by SPIF technology. Naturally, the plasticity of metal sheet increases by the temperature of the material in forming process with its limitation and constraint. The paper represents the effect of heating metal sheet through the empirical process of SPIF technology directed by the design of experiment (DOE). The analyses of the results of experimental process is applied to show the effect of heating to the precision of Titanium sheet. Finally, some private opinions about the heating in SPIF are also mentioned as a very tiny contribution of the research for the new technology.

Abstract: In several last decades, Single Point Incremental Forming named as SPIF, a branch of Incremental Sheet Forming (ISF), is an advanced flexible manufacturing process to produce complex 3D sheet products especially for unique models such as personal cranium, cheek-bone,…applied in surgery. Presently, the SPIF technology has been continuously studied, applied and perfected for metal sheet manufacturing, especially Titanium and its alloys in some industrial sectors like aerospace, chemical engineering, and medical surgery. However, the formability of Titanium alloys is limited at room temperature that causes so many failures and tears of sheet workpiece when forming. This paper recommends a measure of increasing the plasticity of the formed metal sheet by heating. This paper studies on the effect of the control of temperature to increase the plasticity of the sheet workpiece. The accuracy of dimensions of the products under the effect of springback phenomenon in forming process at normal and high temperature of workpiece is also studied to show the effect of hot SPIF. The design of experiment (DOE) is also mentioned in this paper to select a set of suitable input parameters for the empirical process.

Abstract: Drying masonry building structures using high-frequency electromagnetic radiation, so-called microwave technology in construction practice is becoming more common. It is an innovative method which can be used to remove excess moisture with significant speed. This article focuses on the description of physical phenomena that occurs during drying and compares the most commonly used processes for drying buildings. This article describes the heating of building materials (basement spaces built from full burnt bricks) using microwave radiation. It assesses the depth of the heating process achieved under different conditions while taking account of various moisture content of irradiated material and varied length of heating.

Abstract: Natural ventilation is currently widely used in existing buildings in order to assure the fresh air needed by occupants. The low investment and operational costs are the most important advantages of this type of ventilation. However, the dependency on the meteorological parameters has to be considered as disadvantage of the natural ventilation. In case of buoyancy-driven ventilation, the variation of the outdoor temperature results in the variation of the infiltrated air flow, CO₂ concentration in the indoor air and energy demand of the ventilation. The air inlet and outlet orifices have to be properly chosen in order to meet the indoor air quality and energy requirements at the same time. In this paper the CO₂ concentration and energy aspects of gravitational ventilation are discussed in case of a typical block of flats.

Abstract: In this research evolution of austenite grain size in Nb-microalloyed steels X65÷X120 grades during slab reheating and roughing rolling was studied. A mathematical model has been development to obtain the target temperature and soaking time in furnace, which ensure a uniform austenite structure and maximum possible dissolution of the carbonitride particles prior to roughing rolling. The Hot Rolling Recrystallization Model (HRRM) has also development to predict the austenite microstructure evolution during roughing rolling. The model is based on empirical equations and organized following a tree-structure. A validation of the model has been carried out in the laboratory by multipass compression tests. The models jointly have been used to create new strategies of processing technology of rolled plates on rolling mill 5000 for the South Stream pipeline. The industrial application has confirmed a great benefit of the models in point of cold resistance of rolled plates.