Papers by Keyword: Absorptivity

Abstract: The heat input during conventional arc welding processes can be readily calculated knowing the power taken from the power source. The efficiency coefficient can be taken from the appropriate literature standards. Here, the intention of the performed research work was to develop a procedure for determination of heat input in arc and laser welding processes implementing Adams equation - modified Rykalin equation for two dimensional heat distributions (2-D). To realize this idea, it is necessary to determine two characteristic temperatures points in the HAZ with known peak temperature, and to determine distance between them. Implementing measured values for distance in Adams’ equation, heat input in arc welding can be directly determined in arc welded joints.In laser beam welding, the absorption of the beam in the metal is not known, so that the welding heat input cannot be calculated directly, and direct implementation of Adam’s equation is not possible i.e. absorption coefficient has to be determined first, and after that calculation of heat input is possible.The peak temperatures corresponding to specific microstructures can be obtained by performing welding simulation, by the Gleeble 1500 simulator in our case. As one of the peak temperatures, the melting temperature can be used corresponding to the fusion line, so that at least one characteristic peak temperature such as coarse grain zone, fine grin zone, intercritical zone, recrystallization, has to be determined by the simulation.Performed research showed that obtained values for heat input using Adam’s equation correspond pretty well with standard equation for heat input in arc welding.

Abstract: The absorptivity of La in pure copper and the effects of La microalloying on microstructure evolution of pure copper were studied by adding different La contents to pure copper under vacuum condition. The microstructure of copper ingots with different La contents were synthetically analyzed by means of optical microscope (OM) and scanning electron microscope (SEM), and the content of La in ingots was tested using inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results showws that the absorptivity of La in pure copper was more than 90% under vacuum condition and the burning rate was mainly determinated by autoxidation of La and the reaction with impurity elements in copper. The microstructure of copper ingot was refined with La addition. The columnar to equiaxed transition (CET) occured with 0.14% La addition and the microstructure of copper ingot was full equiaxed grains when La content was 0.16%. The CET mechanism was that the constitutional supercooling in copper melt was increased with La addition. The tensile strength of copper alloys could be improved slightly, while the elongation was decreased a little after La alloying.

Abstract: The aim of this paper is to highlight a method for improving laser beam efficiency. The laser weld bead profile depends on various parameters such as beam power, welding speed, wavelength of the laser radiation or the initial temperature of the material. Taking into account that laser beam welding efficiency is usually limited by synchronization of the laser source parameters, new methods were developed. In this paper is analyzed the influence of preheating the material and of the wavelength of laser radiation on the laser weld bead profile. Improvement in penetration depth was noted for preheating the material to around 140°C.

Abstract: During the process of monitoring of pulp fibres swelling, which is directly related to absorptivity, it was found that with the growing number of recycling cycles this characteristics significantly decreases. This phenomenon, which is considered as negative from the point of view of pulp fibres utilizing for paper manufacturing, could potentially find its positive application in other areas, eg. in the civil engineering for production of lightweight composites, where the reduction of water absorption of natural fibre materials is desirable.

Abstract: Quantitative measured values for absorption of copper and its alloys are jet unknown in the temperature range between 30 °C and 500 °C which has to be passed before material melts in the initial phase of laser beam welding. Thus this paper investigates temperature and wavelength dependent absorption for VIS and IR wavelengths. For this purpose specimens of copper and copper alloys are heated up and reflected laser light from the surface is measured by using an Ulbricht sphere in combination with a photodiode. During welding processes inert gases are in use to reduce oxidation. Hence the influence of shielding gases on the absorption will also be taken into account during the heating process of the specimens. Consequently this paper provides results for the temperature dependent absorption of copper and copper alloys for different wavelengths at atmospheric conditions and argon shielding.

Abstract: Based on CO₂-NaOH system, the absorption performances and the mass transfer of the rotating packed bed with the three different types of the gas-liquid distribution inducer were investigated. The experimental results showed that the structure of the gas-liquid distribution inducer have an important effect on the volumetric mass transfer coefficient and the absorptivity of CO₂. Due to the enhancement of the countercurrent contact between the liquid phase and the gas phase from the installation of the distribution inducer, an increasement of the volumetric mass transfer coefficient and a higher absorptivity of CO₂ could be obtained than those of the experiment in PRB without any inducers. Among the distribution inducers, the combination of the liquid distribution inducer of Type-B and the gas distribution inducer of Type-A could give a better volumetric mass transfer coefficient and a higher absorptivity of CO₂, which were 27.84×10^-3 s^-1 and 80.00%, respectively.

Abstract: Poly acrylic acid (PAA) was synthesized by solution polymerization. We analysed that MBA dosage, acrylic acid percentage, neutralization degree and surface crosslink have affections on PAA, mainly about three properties (including 0.9%NaCl solution's absorptivity, absorptivity under 2068Pa, and holding ability of moisture). The experimental evidence obtained that lower acrylic acid percentage is helpful to these three properties. Indexes increase at first and then decrease with neutralization degree raise. MBA dosage is against to absorptivity and retention capability, but useful to absorptivity under pressure. Scanning electron microscopy (SEM) was used to observe the surface of the PAA powder, and prove that surface crosslink promote form a kind of honeycomb structure. Under the optimum synthetic conditions, the absorptivity of 0.9%NaCl solution is 58.8 times, retention capability is 38.4 times, and absorptivity under 2068Pa is 33.6 times.

Abstract: Since CuInSe₂ (commonly called as CIS) materials has become one of most important photovoltaic materials, they are investigated with optical spectroscopies in this paper. The crystal structure, surface microstructure morphology and composition of the samples are analyzed in XRD and SEM with EDX, and the surface electronic state and optical properties of the samples are characterized in X-ray photoelectron spectroscopy (XPS) and Ultraviolet-visible Spectrum instruments. The results show that CIS phase is very uniform, some impurity phases appear in the samples， the atomic distributing percentages of the surfaces of bulk samples are very consistent in the composition ratio forming the crystal phases of the samples, and the atomic electrons are more active than ones in the relevant elements. Furthermore, the thin film of the sample has high solar energy absorptivity, and is suitable for to be manufactured as solar cell.

Abstract: Selective laser sintering (SLS) / melting (SLM) is a manufacturing technique which holds a very special place in the layer manufacturing process due to its widest range of material processing capability which no other technique can offer. It can process metals, rubber, composites, polymers and ceramics etc. As laser sintering technique is emerging as an advanced manufacturing technique, it is importance to study the phenomenon which affect the fabrication process, hence a study is undertaken to simulate the physical phenomenon such as laser absorption and Marangoni effect. By studying these phenomena, a much better control of the physical processes is possible during the laser sintering process of commercially pure titanium grade 2.

Abstract: The surface absorption coefficient of S304L stainless steel during Nd:YAG pulse laser welding process was derived by using the inverse engineering technique. The thermal-elastic-plastic finite element method is employed to calculate the temperature distribution, melting pool depth and shape with specific heat source. The derived melting pool depths and diameters with different values of absorption coefficient were compared with experimental results. In this study, the least square error method is used to obtain the equivalent absorption coefficient. The results show that the equivalent absorption coefficient of S304L stainless steel is in the range of 0.1~0.25 for low power intensity Nd:YAG impulse laser welding.