Effect of power source characteristic on CO2 short circuiting arc welding

Abstract

Some problems are reported concerning the observation of the weld pool and effects of the power source characteristic on arc stability in CO₂ short circuiting arc welding. First, the effect of a power source with a constant voltage characteristic on CO₂ short circuiting arc welding is investigated by analysing the behaviour of the voltage and the current. From the results of this analysis, the cause of spatter generation is identified. A new power source characteristic is then proposed to improve the stability and the self-regulation of the arc. By adjusting the power source characteristic, the metal transfer can be stabilised in the CO₂ short circuiting arc welding process, i.e. the present authors have developed a power source having a non-linear characteristic. Its performance is verified by carrying out experiments.     

High chromium steel forgings for steam turbines at elevated temperatures

Abstract

The European COST programme has a long standing interest in the development of creep resistant 10%Cr steels for rotor forgings designed to operate at ≥600°C. The steel COST E is now widely used for steam turbine shafts, seeing a strongly rising market share, in addition to its applications in gas turbines. The fail–safe manufacturing procedure developed for COST E rotors at Saarschmiede is described; this procedure is backed up with an increasing amount of mechanical properties and long term data. More recently, the production of COST F steel rotor forgings for high/intermediate pressure turbines has commenced, with delivered weights up to 44 t. In an attempt to increase the permitted service temperature, the effect of boron additions has been investigated in a COST activity. Saarschmiede has produced full size trial rotors to develop a production procedure. These prototype components are now under testing and the production of boron containing 10%Cr steels has begun.     

Proposal of a SkilMate Hand and its component technologies for extravehicular activity gloves

In this study, we propose a SkilMate Hand for space extravehicular activity gloves which is equipped with devices of both a power assist and a tactile media. The paper focuses on development of component technologies for constructing a SkilMate Hand, which is proposed for recovering deteriorated haptic sensation in human hands. First, we manufacture a power assist device which compensates the bending moment exerted at a human finger joint utilizing a standing-wave-type ultrasonic motor. We plot the examined characteristics, propose a control policy of the actuators and show some control perforce in Bode plots. Second, we produce a tactile media device which is composed of a vibrotactile sensor element on the outer side and a vibrotactile display element on the inner side at the fingertips of the SkilMate Hand. Piezo-rubber is chosen to be used as a vibrotactile sensing transducer whose sensing performance is examined in the extremely high/low-temperature regions. We locate SkilMate in a wider framework of wearable intelligent machines which assist in affording such working surroundings that they can exhibit their skills in spite of their necessity for wearing special suits typical in hazardous environments. A proposal of a wearable intelligent machine such as that of a SkilMate with its concept has not been made before.     

高功率微波脉冲功率驱动源研究进展

通过文献调研 ,阐述了高功率微波脉冲驱动源的研究现状、发展趋势及其所涉及的一些如开关、绝缘和材料击穿、脉冲形成和二极管等相关关键技术的发展状况 ,简要评估后得出一些相关结论 ,力图为应用于高功率微波的脉冲功率驱动源系统找出以后的发展方向     

POWER MATE i-H的多通道功能在多工位数控组合机床中的应用

文章针对以往在多工位数控组合机床中使用通用交流伺服系统时设计和调试麻烦的问题，阐述了在实际应用中使用FANUC公司的POWER MATE i-H系统时，利用它的多通道功能可以使通道的分配和更改便捷、灵活，PLC程序的编制简便，同时通过它的LCD／MDI单元又便于调试机床，表明POWER MATE i-H的多通道功能十分适合在多工位数控组合机床和自动线中应用。     

纳秒级高压脉冲下绝缘击穿特性的研究

研究了液体和固体绝缘材料的击穿特性 ,通过蓖麻油、变压器油、聚酯薄膜、聚酰亚胺薄膜的击穿实验的波形处理和分析 ,说明了击穿电压与脉冲陡度、脉冲宽度和作用时间的相互关系 ,相对于直流、慢过程条件下绝缘击穿特性 ,纳秒级快脉冲下绝缘材料的击穿场强会大幅提高 ,其击穿场强随脉冲缩短而提高 ,但作用减小。给出了一些具体的绝缘材料击穿值     

Phenotypic analysis of heat stress in Holsteins using test-day production records and NASA POWER meteorological data

Weather station data and test-day production records can be combined to quantify the effects of heat stress on production traits in dairy cattle. However, meteorological data sets that are retrieved from ground-based weather stations can be limited by spatial and temporal data gaps. The National Aeronautics and Space Administration Prediction of Worldwide Energy Resources (NASA POWER) database provides meteorological data over regions where surface measurements are sparse or nonexistent. The first aim of this study was to determine whether NASA POWER data are a viable alternative resource of weather data for studying heat stress in Canadian Holsteins. The results showed that average, minima, and maxima ambient temperature and dewpoint temperature as well as 4 different types of temperature-humidity index (THI) values from NASA POWER were highly correlated to the corresponding values from weather stations (regression R² > 0.80). However, the NASA POWER values for the daily average, minima, and maxima wind speed and relative humidity were poorly correlated to the corresponding weather station values (regression R² = 0.10 to 0.49). The second aim of this study was to quantify the influence of heat stress on Canadian dairy cattle. This was achieved by determining the THI values at which milk, protein, and fat yield started to decline due to heat stress as well as the rates of decline in these traits after the respective thresholds, using segmented polynomial regression models. This was completed for both primiparous and multiparous cows from 5 regions in Canada (Ontario, Quebec, British Columbia, the Prairies, and the Atlantic Maritime). The results showed that all production traits were negatively affected by heat stress and that the patterns of responses for milk, fat, and protein yields to increasing THI differed from each other. We found 3 THI thresholds for milk yield, 1 for fat yield, and 2 for protein yield. All thresholds marked a change in rate of decrease in production yield per unit THI, except for the first milk yield threshold, which marked a greater rate of increase. The first thresholds for milk yield ranged between 47 and 50, the second thresholds ranged between 61 and 69, and the third thresholds ranged between 72 and 76 THI units. The single THI threshold for fat yield ranged between 48 and 55 THI units. Finally, the first and second thresholds ranged between 58 and 62 THI units and 72 and 73 THI units for protein yield, respectively.