Variable speed refrigeration system with HPF input rectifier stage

This paper is based on the analysis and implementation of a new drive system applied to refrigeration systems, complying with the restrictions imposed by the IEC standards (Harmonic/Flicker/EMI-Electromagnetic Interference restrictions), in order to obtain high efficiency, high power factor, reduced harmonic distortion in the input current and reduced electromagnetic interference, with excellent performance in temperature control of a refrigeration prototype system (automatic control, precision and high dynamic response). The proposal is replace the single-phase motor by a three-phase motor, in the conventional refrigeration system. In this way, a proper control technique can be applied, using a closed-loop (feedback control), that will allow an accurate adjustment of the desirable temperature. The proposed refrigeration prototype uses a 0.5Hp three-phase motor and an open (Belt-Drive) Bitzer IY type compressor. The input rectifier stage's features include the reduction in the input current ripple, the reduction in the output voltage ripple, the use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) in the input current, in compliance with the IEC61000-3-2 standards. The digital controller for the output three-phase inverter stage has been developed using a conventional voltage-frequency control (scalar V/f control), and a simplified stator oriented Vector control, in order to verify the feasibility and performance of the proposed digital controls for continuous temperature control applied at the refrigerator prototype. ©2008 IEEE.

Estimation of electrical machine speed using sensorless technology and neural networks

The use of sensorless technologies is an increasing tendency on industrial drivers for electrical machines. The estimation of electrical and mechanical parameters involved with the electrical machine control is used very frequently in order to avoid measurement of all variables related to this process. The cost reduction may also be considered in industrial drivers, besides the increasing robustness of the system, as an advantage of the use of sensorless technologies. This work proposes the use of a recurrent artificial neural network to estimate the speed of induction motor for sensorless control schemes using one single current sensor. Simulation and experimental results are presented to validate the proposed approach. ©2008 IEEE.

α-SiAION: Development and machining test on gray cast iron

The α-SiAlON ceramic cutting tool insert is developed. Silicon nitride and additives powders are pressed and sintered in the form of cutting tool inserts at temperature of 1900 °C. The physics and mechanical properties of the inserts like green density, weight loss, relative density, hardness and fracture toughness are evaluated. Machining studies are conducted on grey cast iron workpiece to evaluate the performance of α-SiAlON ceramic cutting tool. In the paper the cutting tool used in higher speed showed an improvement in the tribological interaction between the cutting tools and the grey cast iron workpiece resulted in a significant reduction of flank wear and roughness, because of better accommodation and the presence of the graphite in gray cast iron. The above results are discussed in terms of their affect at machining parameters on gray cast iron.

Mexico: export promotion policies on the cutting edge

Includes bibliography

Estudio digital radiográfico y densitométrico en mandíbulas de cerdos sometidos a osteotomía con alta y baja velocidad, con refrigeración líquida

The influence of the type of rotary cutting instrument on bone repair after osteotomy in swine jaw, was evaluated using digital and densitometric radiographic examinations, at controlled times. Two cross-sectional dissections were made through the base of the right jaw, one using a high speed rotary instrument and the other using low speed, both with liquid cooling. After established periods the animals were sacrificed and their jaws removed for direct and indirect digital radiographic and densitometric studies using the CROMOX, DIGORA and ODR systems. In the initial periods (7 and 28 days) the bone density was higher in osteotomy areas performed with high rotation speeds, and in the final periods (60 and 90 days) the bone density was higher in the osteotomies performed with low rotation, indicating a better final bone repair with the use of low rotation. The qualitative analysis of the repair process was made by the ODR system which obtained three-dimensional and coloured digital images, which enable the bone thickness to be measured using an aluminium wedge. This showed that by twenty-eight days the bone repair was already apparently complete. © 2010 SECOM.

Qualidade fisiológica de sementes de Brachiaria e avaliação da produtividade de massa seca em diferentes sistemas de integração lavoura-pecuária sob irrigação

The speed and magnitude of tropical pastures expansion in Brazil are related to the availability of quality seeds. This research aimed to evaluate the physiological quality of seeds of two Brachiaria species submitted to germination and viability tests and also estimate, for both species, the fresh and dry mass yield, under different irrigated crop-livestock integration systems. For field analysis, the experimental design was a randomized complete block, in subplots, with four intercrops in the plot (Brachiaria brizantha cv. Marandu and Brachiaria ruziziensis simultaneously established with corn and nitrogen fertilization coverage), and four forage cutting times, in the winter/spring season, in subplots, with four replications. In the laboratory, the experimental design was completely randomized, with four replications per treatment/test. The germination and viability tests indicated that B. brizantha seeds showed higher physiological quality, when compared with B. ruziziensis, while the tetrazolium test and germinated seedlings characteristics were similar. The B. ruziziensis, simultaneously intercropped with corn, was the less viable intercrop, due to the lower fresh and dry mass yield and litter deposition on the soil surface. In general, the pasture formation for the second season cultivation, intercropped with corn, was an excellent alternative for crop-livestock integration under a no-tillage system.

Cutting performance of diamond coated Si3N4 tool during turning

Silicon nitride cutting tools have been used successfully for machining hard materials, like: cast irons, nickel based alloys, etc. However these cutting tools with diamond coating present little information on dry turning operations of gray cast iron. In the present work, Si3N4 square inserts was developed, characterized and subsequently coated with diamond for dry machining operations on gray cast iron. All experiments were conducted with replica. It was used a 1500, 3000, 4500 m cutting length, feed rate of 0.33 mm/rev and keeping the depth of cut constant and equal to 1 mm. The results show that wear in the tool tips of the Si3N4 inserts, in all cutting conditions, was caused by both mechanical and chemical processes. To understand the tool wear mechanisms, a morphological analysis of the inserts, after experiments, has been performed by SEM and optical microscopy. Diamond coated PVD inserts showed to be capable to reach large cutting lengths when machining gray cast iron. © (2010) Trans Tech Publications.

Development of ceramic cutting tools for future application on dry machining

Advanced ceramic materials constitute a mature technology with a very broad base of current and potential applications and a growing list of material compositions. Within the advanced ceramics category, silicon nitride based ceramics are wear-resistant, corrosion-resistant and lightweight materials, and are superior to many materials with regard to stability in high-temperature environments. Because of this combination the silicon nitride ceramics have an especially high potential to resolve a wide number of machining problems in the industries. Presently the Si3N4 ceramic cutting tool inserts are developed using additives powders that are pressed and sintered in the form of a cutting tool insert at a temperature of 1850 °C using pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and the mechanical response of this array microstructure was characterized for hardness Vickers and fracture toughness. The results show that Si3N4/20 wt.% (AlN and Y 2O3) gives the best balance between hardness Vickers and fracture toughness. The Si3N4/15 wt.% (AlN and Y 2O3) composition allows the production of a very fine-grained microstructure with low decreasing of the fracture toughness and increased hardness Vickers. These ceramic cutting tools present adequate characteristics for future application on dry machining. © (2010) Trans Tech Publications.

Evaluation of the dentin-pulp complex after cavity preparation with ultrasonic diamond tip

The aim of this paper was to compare the dentin-pulp complex response to cavity preparation in human teeth using ultrasonic chemical vapor deposition (CVD) diamond tip and high-speed diamond bur. Class V buccal cavities were randomly prepared in 40 premolars from 14 patients aged 11 to 15 years. The cutting time was recorded and the cavities had the axial walls protected with gutta-percha and were filled with glass ionomer cement. The teeth were extracted at intervals of 0, 5, 10 and 20 days, and were decalcified, sectioned and stained by Hematoxylin & Eosin, Masson's Trichrome and Brown & Brenn techniques. The inflammatory response and cell disorganization were blindly evaluated by two examiners. The remaining dentin thickness (RDT) was measured by a linear scale using computer software. Statistical analysis by one-way ANOVA showed no statistically significant difference (P≤0.05) among the cavities prepared with either type of instrument, with mean RDT of 1132.50 mm. Cutting time and the pulp-dentin complex responses were analyzed statistically by Kruskal-Wallis and Dunn tests (P≤0.05). The ultrasonic CVD diamond tip took 5 times longer to prepare the cavities and there were no typical inflammatory pulp responses in cavities prepared with either type of cutting instrument, only mild to moderate cell disorganization was present. Even taking longer to cut the dental substrate, the ultrasonic CVD diamond tip produced similar pulp response compared to the conventional high-speed diamond bur.

Improving accuracy and speed of optimum-path forest classifier using combination of disjoint training subsets

The Optimum-Path Forest (OPF) classifier is a recent and promising method for pattern recognition, with a fast training algorithm and good accuracy results. Therefore, the investigation of a combining method for this kind of classifier can be important for many applications. In this paper we report a fast method to combine OPF-based classifiers trained with disjoint training subsets. Given a fixed number of subsets, the algorithm chooses random samples, without replacement, from the original training set. Each subset accuracy is improved by a learning procedure. The final decision is given by majority vote. Experiments with simulated and real data sets showed that the proposed combining method is more efficient and effective than naive approach provided some conditions. It was also showed that OPF training step runs faster for a series of small subsets than for the whole training set. The combining scheme was also designed to support parallel or distributed processing, speeding up the procedure even more. © 2011 Springer-Verlag.

Influence of optimized lubrication-cooling and minimum quantity lubrication on the cutting forces, on the geometric quality of the surfaces and on the micro-structural integrity of hardened steel parts

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Laser ultrasonics system for measurement of speed of sound in gases

In this work we developed a setup to measure the speed of sound in gases using a laser ultrasonics system. The mentioned setup is an all optical system composed by a Q-switched Nd:YAG laser to generate the sound waves, and a fiber optical microphone to detect them. The Nd:YAG provided a laser pulse of approximately 420 mJ energy and 9 ns of pulse width, at the wavelength of 1064 nm. The pulsed laser beam, focused by a positive lens, was used to generate an electrical breakdown (in the gas) which, in turn, generates an sound wave that traveled through a determined distance and reached the fiber optical microphone. The resulting signal was acquired in an oscilloscope and the time difference between the optical pulse and the arrival of the sound waves was used to calculate the speed of sound, since the distance was known. The system was initially tested to measure the speed of sound in air, at room pressure and temperature and it presented results in agreement with the theory, showing to be suitable to measure the speed of sound in gases. © 2012 American Institute of Physics.

A new design methodology for multipulse rectifiers with Delta auto-connected transformers and a retrofit application in Adjustable Speed Drives (ASDs)

Multipulse rectifiers can replace a conventional six pulse three-phase rectifier (diode bridge) providing a DC voltage with low ripple, low Total Harmonic Distortion of current (THDi) and a high Power Factor (PF). In this context is presented a multipulse rectifier with generalized Delta-differential autotransformer topology, which can provide any level of DC output voltage for any level of three-phase AC input voltage. This paper presents all the possible configurations for Delta topology in order to choose, through graphics, one configuration that presents reduced weight and volume. The average voltage on the DC bus must be compatible with the DC voltage in the six pulse rectifier used in commercial ASDs. Therefore, it is possible to apply the retrofit technique to replace the conventional bridge rectifier by the proposed multipulse rectifier. Based on mathematic models and simulation results, an 18-pulse rectifier with Delta topology, 220 V of line voltage, 315 V of DC output, and rating 2.5 kW of power was designed, implemented and applied for three different commercial ASDs. Experimental results as voltage and current waveforms and results about PF and THDi will be presented. © 2012 IEEE.

Rough turning of titanium alloy (6Al-4V)

Metal machining is the complex process due the used cutting parameters. In metal cutting process, materials of workpiece differ widely in their ability to deform plastically, to fracture and to sustain tensile stresses. Moreover, the material involved in the process has a great influence in these operations. The Ti-6Al-4V alloy is very used in the aeronautical industry, mainly in the manufacture of engines, has very important properties such the mechanical and corrosion resistance in high te mperatures. The turning of the Ti-Al-4V alloy is very difficult due the rapid tool wear. Such behavior result of the its low thermal conductivity in addition the high reactivity with the cutting tool. The formed chip is segmented and regions of the large deformation named shear bands plows formed. The machinability of the cutting process can be evaluated by several measures including power consume, machined surface quality, tool wear, tool life, microstructure and morphology of the obtained chip. This paper studies the effect of cutting parameters, speed and feed rates, in the tool wear and chip properties using uncoating cemented carbide tool. Microe-structural characterization of the chip and tool wear was performed using scanning electron microscopy (SEM) and Light Optical Mcroscopy (LOM).

Queen lipid content and nest growth in the leaf cutting ant (Atta sexdens rubropilosa) (Hymenoptera: Formicidae)

The relationship between the queens' lipid content and nest growth (population size, biomass and nest architecture) was studied from founding up to 1 year. Nests aged 3, 4, 5, 6, 9 and 12 months were dug in the field, and their dimensions were measured. The ant nest population and fungus garden was also collected. The sample was taken to the laboratory where we counted the worker population and weighed the biomass (fungus plus offspring) and queens. Queens were separated for the determination of lipids. The lipid content in the bodies of queens decreased in the first months, then stabilized (at 4-6 months) before increasing in months 9 and 12. Nest biomass (symbiotic fungus and offspring) and worker population increased over time. The structural growth of the nests was observed by excavating around them. Initially nests (3 months old) had one chamber at an average depth of 15 cm. By 1 year, the nests had three or four deep chambers, and were about 3-4 m deep. Our study contributes to knowledge of the dynamics of the energy-reserve expenditure by queens during colony founding and colony development for up to 1 year. © 2013 Copyright Taylor and Francis Group, LLC.