Advanced Materials Research Vol. 837

Abstract: The main transportation pipelines are subjected to complex stresses resulting from the nature and state of the transported material, the operating conditions, and the environmental factors and so on. Thus, the stress in the pipe wall is generated and influenced by the pressure, the temperature and the mass of the transported fluid, by the weight of the pipe, the ambient temperature and in certain periods of time by the wind speed. In this paper are presented dynamic phenomena generated by wind flow and their effect on the magistrate transportation pipelines. The content of the paper presents an detailed analysis regarding the regimes in which is developing the force generated by Karman vortex and the situation when resonance phenomena are developed. The study presents a mathematical model that describes the dynamic phenomena generated by the wind action, determining the mathematical expression of the aerodynamic force that act on the normal direction to the wind speed. This force is having a periodic variation, its size and the frequency variation is dependent on the wind speed. Some methods are proposed in order to decrease the wind influence on the lifetime of transportation pipelines. The main results of the study are: determination of the speed range for which the dynamic phenomena have a high influence on the pipeline lifetime; determination of the real conditions that can lead to sharp rises of the pipe deformations; determination of the pipeline lifetime reduction under development of dynamic loads.

Abstract: This paper presents the measurements of the residual stresses for polymeric parts using different methods. The residual stresses are usually introduced during manufacturing and are caused by processes such as molding. In order to optimize injection molding process with polymeric material, it is important to predict the internal stress development during molding. The residual stresses are caused mainly by non-uniform temperature profile in the cavity during filling, packing and cooling stages. This research offers information and a methodology which may be applied in practical conditions for a large number of parts manufactured from the different polymeric materials and for several technological constraints. The author confirmed that all this methods which measure the residual stresses can be applied to injection molded parts.

Abstract: This paper presents a case study regarding use the laser XL 80 to check the linearity movement of the Z-axis to horizontal machining center, TMA-AL 550. This machining center has been upgraded to the possibility of processing to 3 CNC linear axes and 2 CNC rotary axes (up to 5 CNC simultaneous axes) and also 1 PLC axis (the index table), as well the including of the machine into to the flexible manufacturing cell. This work paper presents the linearity accuracy at machining centre on the Z axis and shows the operating correction parameters by software and the necessity of backlash adjustment between nut and ball screw, by using a performing linear laser for machine tools and research systems laboratory, that was acquired by the project RTT-5 Rotary-Tilting Tables for 5-axis Machining Center, where the authors participated. Compared with conventional methods of checking of table linearity deviations at the machining centers (checking with spirit leveling device, wire collimator, wire auto-collimator and yardstick ruler), the method by laser of unconventional determining brings the following advantages: linear resolution of 0.001 μm, method assisted by computer, in order to obtain the positioning accuracy ± 5 μm the repeatability of 5 μm/m. The measurements fall within the ISO 230-2, ASME B5-52, VDI 3441-DGQ, JIS and GB international standards, and permitting also the memorization of the measured data and the obtaining of the tabulated results, or in graphical form too, using XL 80 soft Laser, by forwarding the information to the computer.

Abstract: Microwave heating represents a modern technique to sintering the composites materials. The microwaves absorbance property of the materials is depending by the electrical permittivity of the materials. Researchers showed that the ceramic materials are suitable for sintering using microwave heating. The most important advantage of that sintering procedure is the reduced sintering time and temperatures. However, during the heating process these properties are changing and a pattern of the heating process cannot be established. The penetration depth of microwaves into materials depends on the electrical properties of them, and gives rise to a heat source. The electromagnetic wave absorption is responsible for the macro and micro structural changes in the materials morphology, and consequently for their electrical properties. Thermal runaway is one phenomenon which should be avoided during the microwave processing of the materials. The microwave heating consists in direct introduction of the energy in the volume of the material. If the absorbance properties of the material are increasing with temperature, than a critical phenomenon, called thermal runaway, appears during the heating process. This paper aims to study the thermal runaway of the BaCO₃ + Fe₂O₃ homogenous mixture and mechanical alloy in a mono-mode applicator, when the heat source is a microwave generator at 2,45 Ghz. A special mono-mode chamber has been designed with dimensions 140 x 140 x 70 mm and an active system for rotating the samples, in order to record the values of the temperature and to assure a uniform exposure of the samples to the high frequency electromagnetic field. The materials used in experiments were homogenous mixture of BaCO₃ + Fe₂O₃ which have been milled in a planetary ball mill for 5 and 20 hours. The experimental procedure consists in establishing the levels of the temperatures during the microwave heating process when the thermal runaway appears. These experiments have been done for fixed levels of microwave injected power from 0 1250 W. Numerical simulation for different heating conditions (microwave power, heating time, position of the samples inside the chamber) has been performed in order to elaborate a predictable mathematical model for continuous microwave heating and avoiding the thermal runaway of the homogenous mixture.

Abstract: Heated tool and electrofusion welding are the most used joining processes of higher than 2 mm thick polymer pipes. The two welding processes have different heating-cooling cycles and they produce different influences on the properties of the polymers. Exploitation of polymer pipes for water and gas distribution revealed ageing behaviour of the material in the welding area. The modification of the behaviour depends on the base material, on the applied welding process and on the used parameters. Thermal analysis can be used as tool to reveal and to evaluate the modification of the physical and mechanical properties. Such knowledge is important when prediction of the in use life is necessary to be predicted. Experimental programme was applied to HDPE 100 and HDPE 80, both welded using heated tool and electrofusion processes and different sets of parameters (factorial experiment principles were used to establish the welding parameters). Plasticity characteristics of the welds material, as elongation and relaxation modulus, were determined by using thermal analysis. Burst stress test, applied to the pipe, was considered. It has been observed important rate of the heating process of the surface in contact with the heater. The DSC analysis revealed a decreasing of the elongation with about 12% and decreasing of the relaxation modulus with amount up to 14%, for the material located at the interface between pipe and the heater. At 0.5 mm from the interface it was revealed an intensity of the modification up to half of the values recorded for the interface. That was explained on the poor thermal conductivity specific to the both materials. By using DSC thermal analysis it has been revealed that the polyethylene has high rate crystallization during welding cycle, after the heating to the viscous state. Such crystallization, together with potential non-uniformity of the heating provides modifications in the geometrical characteristics of the weld. For high energy input, the material experience large quantity of fluid material with important plastic distortion. That means high possibility to reject material during pressing step of the welding cycle. 10% increasing of the temperature, for the same heating pressure, involves 5-8% increasing of the dimensions of the fluid ring in the interface. About 10% difference between the relaxation modulus of the heated and non-heated HDPE and that means local ageing transformation of the HDPE. The material becomes more fragile than before the welding process.

Abstract: Abrasive water jet processing is one of the newest unconventional technologies. It can be used to cut different metallic materials (steel, titanium alloys, aluminium alloys, brass) or non-metallic materials (wood, plastics, glass, stone, granite etc.). Therefore, this technology can be successfully applied in different industries as: food industry, wood industry, aeronautic industry, automobile industry, mining industry. Between the advantageous of abrasive water jet processing technology it is worth noticing the following: it is rapid, very small processing forces are generated, it is silent, no thermal distortions occur. The aim of the current paper was to determine the influence of the feed rate on the quality of surfaces processed by AWJ at high pressure. The parameters that quantified the quality of the processed surface were those defined in the ISO/WD/TC 44 N 1770 standard: width of the processed surface at the jet inlet (Li), width of the processed surface at the jet outlet (Lo), deviation from perpendicularity (u), inclination angle (α) and roughness (Ra).

Abstract: Abrasive water jet (AWJ) is a nonconventional machining process in which abrasive grains in a high-speed water jet collide with the sample and erode it. This technology has been developed as an alternative to the conventional processes in order to facilitate the processing of hard materials as stainless steel, titanium alloys, composite materials, etc. However, it is not limited only to hard materials, since it has been successfully applied to process softer materials as aluminum, copper, plastics. Also, the abrasive water jet technology can be used both, to process thin metal sheets and plates since it offers many advantages such as: good surface quality, no thermal distortions, minimal burrs, low machining force, high flexibility. The aim of the current paper was to study the surfaces quality of samples made by aluminium, A1050, processed by AWJ in case of using different working regimes. The experimental tests have been performed on the Hydro-jet Eco 0615 water jet cutting machine. The parameters that have been varied were pressure, feed rate, abrasive quantity, distance between the cutting head and working sample while the diameter of focusing tube and diameter of water nozzle have been kept constant. The parameters taken into account to quantify the quality of the processed surface were those defined in the ISO/WD/TC 44 N 1770 standard (fig. 1): width of the processed surface at the jet inlet (Li), width of the processed surface at the jet outlet (Lo), deviation from perpendicularity (u), inclination angle (α) and roughness (Ra).

Abstract: In the pressing form made from calcined gypsum fixed in metal, wax can be cast with pressure. The device used to tide the pressing form should not bend. If the handling work is done carefully and correct one pressing form made from gypsum can be used for multiple wax models. To be used in construction the pressing forms, calcined gypsum must meet certain requirements regarding its constitution and functionality. To provide these requirements research work must be done to investigate characteristics such as: minimum compressive strength (wet and dry state), hardening time of calcined gypsum, gypsum dilatation after curing. To produce the pressing forms from calcined gypsum the following methods and operations have been used: operations concerning production of gypsum with the best physicochemical and mechanical properties in order to be used for construction of pressing forms (determining the quality of gypsum based on water and plaster ratio; establishing the influence of epoxy and curing solution on the mechanical resistance of the obtained gypsum; determining the influence of lime, boric acid, zinc chloride, sodium chloride on the hardening period of calcined gypsum); production of the models from wood and metal; fixing the model on the gypsum cushion; finding on the model the separation line and restrict the area used for gypsum moulding; applying grease on the model, on the plate under the model, on the walls and on all parts that come in contact with liquid gypsum to be poured; preparation of the gypsum solution.

Abstract: The dehydration of the products of vegetable origin is a complex technological process, involving heat and mass transfer, which is largely affected by the nature and characteristics of the fruits, but also by the technical performances of the equipment. Experimental laboratory tests must be performed in order to evaluate the effect and importance of these parameters, using equipments which are able to reproduce the technological dehydration process. In order to achieve these goals a specialized test rig was designed and built. The laboratory test rig allows different dehydration experiments to be carried out; all the parameters that affect the dehydration process - temperature, speed and humidity of the drying agent before and after the mass and heat transfer takes place, the weight and temperature of the dehydrated product, the direction of the drying agent etc. - are continuously monitored. The continuous monitoring of the working parameters is performed by the means of a specialized industrial computer, which allows the data aquision and transfer to a PC. The paper presents the details regarding the design and working process of the laboratory test rig, as well as the experimental results concerning the dehydration of plums and apricots. The results show that the dehydration process is affected by the temperature and speed of the drying agent, by the size of the particles and by the thickness of product layer.

Abstract: The paper presents an approach on the possibilities of using of standard tooling systems mostly designed for the applications in the field of cutting processes to the ultrasonic assisted cutting processes, which is an extension of the conventional cutting processes for the purpose of surface roughness improvement and cutting forces reducing. A brief description of the device for the ultrasonic assisting cutting processes is presented, than an overview of the process integration technique, as well as some consideration regarding specific design requirements. A few solutions for rapid adaptation of ultrasonic assisting devices on conventional machining centers are presented, with different levels of flexibility and precision. Finally some recommendations were made, based on specific advantages and drawbacks of each tooling system. The presentation suggests the possibility to realize more standardized devices for ultrasonic assisted cutting processes based on commercial tooling solutions.