High Horsepower and High Torque Performance of EP Gear Lubricants

In recent months a series of premature gear failures in field operated vehicles produced indications of insufficient load carrying qualities in extreme pressure lubricants of the GL-4 specification conforming to the new Military L-2105A. This condition prompted dynamometer testing in an investigation of horsepower absorption and high torque absorption of these lubricants as compared with extreme pressure lubricants conforming to Military L-2105 specifications.

The results of the dynamometer testing showed that lubricants conforming to the new Military L-2105A were capable of withstanding continuous high horsepower applications where relatively low torque was required, but were not able to compare favorably with the extreme pressure lubricants of the Military L-2105A specification in regard to continuous high torque applications. The gear-tooth surfaces on such tests with lubricants conforming to the new Military L-2105A were severely scored, whereas the Military L-2105A lubricants produced a satisfactory tooth condition under identical testing conditions.     

Aluminium powder particles produced by SAMD technique: typical characteristics and correlations between processing conditions and powder size

Abstract

The present paper consists of two parts. In the first part the principles of a new method of metal powder production, termed 'solid assisted melt disintegration (SAMD)' are discussed and the typical characteristics of the produced powder are outlined. In the second part the effects of some processing parameters on the size distribution and mean diameter of the powder are reported. The SAMD method involves mixing solid particles (i.e. alumina) with the liquid aluminium alloy aided by mechanical agitation. The shear force induced by the impeller is transferred to the metal via the non-wetting solid medium and results in melt disintegration. The resulting mixture of aluminium droplets and alumina particles are subsequently cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminium powder particles. The SAMD technique has demonstrated the capability to produce a wide particle size distribution. The small sized particles (i.e. <53 μm) exhibited irregular shapes, but larger ones were mostly spherical. These powder particles were dense (pore free) without attached satellite particles and exhibited a relatively coarse microstructure. The processing parameters investigated include the size of Al₂O₃ particles, Al₂O₃/Al weight ratio, stirring speed and stirring time. It was concluded that there exists an optimum value for each of the aforementioned parameters corresponding to a minimum in the mean particle size.     

Interfacial reactions between AZ91D magnesium alloy and plaster mould material during investment casting

Abstract

Reactions at the mould/metal interface play an important role in determining the quality of investment castings. They are particularly critical in the case of magnesium alloys cast in industrial plaster moulds. In this work, reactions of molten magnesium alloy with plaster mould were studied. First the potential interactions with mould materials (including gases) were examined using thermodynamic considerations. Then thin sheets of AZ91D magnesium alloy were cast in industrial plaster moulds using vacuum assistance: the surface of sheets and plaster mould were characterised. The analysis of reaction products indicates that magnesium vapours diffuse through the plaster and reduce the silica present in the investment material according to the following reaction: 4Mg + SiO₂=2MgO + Mg₂Si. The extent of reactions is controlled by mould temperature and thickness of castings.     

Characteristics of TiC dendrites in as solidified Ti–Al–C alloys

Abstract

Results are reported on the dendrite secondary arm spacing of a series of as cast Ti–C and Ti–Al–C alloys in the composition range up to 10 at.-%C and 15 at.-%Al. The presence of Al leads to a significant decrease in the dendrite spacing, an effect of potential interest for improving mechanical properties. The structural refinement is attributed mainly to the slower diffusion of Al as compared with carbon, in the solute partitioning required for coarsening of dendrite arms.     

二甲醚作为中高温热泵工质的性能分析

对二甲醚（DME）作为中高温热泵工质的热工性能进行计算与分析,与传统热泵工质R22,R134a及自然工质R600a进行对比,并对变工况（冷凝温度75～95℃,固定循环温升45℃）进行理论计算。计算结果表明,DME制热性能参数与R134a接近,但COP值高于R134a,单位容积制热量在高温工况下具有更出色的性能。而且DME的GWP与ODP值均接近零,可作为绿色环保替代工质直接充注至R134a热泵系统,并可应用于中高温环境。     

J-CHART METHOD IN DESIGNING A PARTIALLY SOLAR HEATED DRYER

A new chart of simulation method, named J-chart, has been developed for predicting the long-term average performance of solar drying systems. The result of many simulations allows to develop a simple graphical method, represented by 3 charts and their polynomial correlations, to obtain a general design procedure for a partially solar heated dryer. The first one is the drying time, the second one is the fraction of heating load supplied by solar energy and the third one is the fraction of economized energy. These charts and the correlations are used in establishing relationships between the collector area and the weight of the produce to be dried or the dried produce. This method is developed by using the monthly average values for a moderate climate (Perpignan, Φ = 42.41^°) and with the assumption that the dryer is used daily over a year and the duration of drying operation is assumed to be less than 24 hours.     

Weld pool geometry during keyhole laser welding of thin steel sheets

Abstract

In industrial applications of laser welding it is often essential to obtain full penetration welds at high processing rates using minimal heat input. Keyhole welding meets these requirements when process parameters are kept close to the boundary where complete penetration switches to partial penetration welding. In the present work weld pool behaviour at the edge of the full penetration regime has been studied. Four types of keyhole penetration mode were observed. The first type is a completely developed keyhole through the material thickness and open in the root region, whereas the second type is closed at the root. The third mode is unstable and results in intermittent penetration involving periods of open and closed keyhole conditions interspersed with periods of lack of fusion. The fourth mode is a partial penetration mode. A possible explanation of the weld pool transient behaviour is presented based on three-dimensional reconstructions of the weld pools.     

Development of high quality thermal spraying process by shielding control

Abstract

The shielding controlled plasma spraying process was investigated to improve corrosion resistance of metal surfaces. In this process, a shielding nozzle that covered only spraying area was attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet was controlled by nitrogen flow. When the oxygen concentration in the shielding nozzle was maintained at 0·5%, the metal oxide contents in CoNiCrAlY coating and the porosity of the coating reduced to 0·2 and 0·3% at optimal spray particle size respectively. The corrosion potential in an acid solution including chloride ions was almost constant for 1000 h for CoNiCrAlY coating deposited by shielding controlled plasma spraying. On the other hand, those obtained by atmospheric plasma spraying process decreased in the corrosion potential largely after 10 h. Thus, it can be concluded that the shielding controlled plasma spraying process improves the corrosion resistance of the metal.     

基于USBKEY的安全认证网关的设计

在分析SSL等认证网关不足的基础上,提出一个基于USB KEY的安全认证网关的设计方案,然后给出其身份认证协议,并对其安全性进行分析。     

湖南某铁精矿中铁、锡、硫、砷的赋存状态研究

湖南某地产出的铁精矿铁品位难以提高,且含锡0.86%、硫0.77%、砷0.10%,严重影响了产品的质量。从工艺矿物学角度对产品中铁、锡、硫、砷的赋存状态及其载体矿物的共生嵌布关系、结晶粒度等方面进行分析,查明了产品中的锡主要是赋存于呈独立矿物形式产出的锡石内,铁赋存于磁铁矿内,砷赋存于毒砂内,硫赋存于磁黄铁矿、黄铁矿、闪锌矿、铁闪锌矿以及毒砂、黄铜矿、黝锡矿中,为选矿采用合理的选别工艺进行铁、锡、硫、砷分离,降低锡、硫、砷在产品中的含量,提高铁精矿的品位并为综合回收锡金属提供矿物学依据。