On suitability of novel fluidised bed technique for separation of metallic powders during commercial powder metallurgical processing

Abstract

Experiments have been performed to test the efficiency with which a novel fluidised bed technique could separate different metallic powders in terms of size and density. The overall aim was to assess the potential of this technique for the commercial separation of defective powder fractions from mechanically alloyed (MA), iron based powders. Separation in terms of size was readily achieved, with the largest powder particles sinking to the bottom of the fluidised bed. In a simulated commercial process, density separation of defective Fe₃Al powder could not be demonstrated as any differences in density were overshadowed by size and morphology differences. However, from a batch of iron based powder (ρ=8·02 g cm^?3), seeded with six other metallic powders, aluminium powder (ρ=2·70 g cm^?3) segregated strongly to the top of the bed from where samples containing 93 vol.-%Al were taken. The process is thought to be sensitive to differences in density of a factor of 1.1–3.     

12—THEORETICAL CONSIDERATIONS IN OPEN-END SPINNING

Two problems are discussed in this paper. In the first, the effect of the deposition of fibres in open-end-spinning systems on the yarn irregularity produced is considered.

The drafting operations are divided into two types, that is, System I and System II. System I is the type in which fibres are accelerated when the leading ends arrive at a point or a specified area, and System II is the type in which the trailing ends are accelerated in the same way as those of System I. System II is more profitable if the fibres have non-uniform length, and the leading-fibre-end-density function contains most of the irregularity. The rotating-drum spinning method is also considered from the viewpoint of yarn irregularity, and the range of wavelengths that should be decreased by this method is calculated. The conclusion is that the total draft must be smaller than 2πR/[lbar], where R is the inner radius of the drum and [lbar] is the mean fibre length.

The second problem concerns the separation draft. Open-end drafting systems require very high drafts for separating the fibres. The problem is to determine what value of draft is needed. The conclusion reached is that perfect separation is impossible because of the random arrangement of fibres. The probability of separation is presented and calculated theoretically.     

Wettability of glass fibers by reactive thermoplastic/polyester blends: comparison between compatible and incompatible blends

The evolution of morphology of reactive thermoplastic/unsaturated polyester blends at the surface of glass fibers is investigated during curing. The study focuses on two different types of thermoplastics, incompatible and compatible respectively with the polyester resin. Poly(dimethylsiloxane) and poly(methyl methacrylate) are chosen as incompatible thermoplastics, and poly(vinyl acetate) as a compatible thermoplastic. In the presence of incompatible thermoplastics, the blends form an emulsion during the entire course of curing. In that case, a correlation exists between the surface tensions of the components of the blend measured before curing and the final morphology at the surface of the fibers. For a compatible thermoplastic, on the other hand, a reaction-induced phase separation occurs during curing. In that case, the morphology at the surface of the fiber after phase separation cannot be fully determined by the surface tensions of the components.     

拉么锌矿采空区稳定性及地表陡崖岩移观测的研究

本文简要介绍了拉么锌矿采空区稳定性及地表陡崖岩移观测研究的方法及特点,文中根据井上井下的空间关系和考虑各种影响因素,分析了采矿结构的稳定性;阐述了地下开采引起山体失稳的有效防治措施及监测系统;并提出了空区的处理方案。     

Continuous separation of Fe–Al–Zn dross phase from hot dip galvanised melt using alternating magnetic field

Abstract

Experiments to continuously separate Fe–Al–Zn dross phase from hot dip galvanising zinc melt were conducted on a laboratory scale apparatus by using high frequency alternating magnetic field. Effects of processing time (t) on separation efficiency were investigated. The experimental results show that using the electromagnetic repulsive force resulting from the electrical conductivity difference between zinc melt and Fe–Al–Zn dross phase, the deleterious zinc dross particles causing surface defects of galvanising steel sheets can be continuously separated from the zinc bath under alternating magnetic field, and the separation efficiency increases with the increase in processing time. When the magnetic frequency is 17·5 kHz, the effective magnetic flux intensity is 0·1 T, the cross-section of the ceramic square pipe is 10 × 10 mm, and the processing time is 0·6–2·5 s, the separation efficiency of zinc dross varies from 43·76 to 85·71%, and the experimental results are in reasonable agreement with the theoretical results.     

Characterization of thermoplastic polyurethane adhesives with different hard/soft segment ratios containing rosin as an internal tackifier

Three thermoplastic polyurethanes (TPUs) containing different hard/soft (h/s) segment ratios (1.05-1.4) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′diisocyanate) and polyadipate of 1,4-butanediol (M _w = 2440) were allowed to react to produce the prepolymer. To provide the polyurethanes with high immediate adhesion to different substrates, a rosin + 1,4-butanediol mixture (1 : 1 equivalent%) was used as chain extender (TPU-Rs). These TPU-Rs had two types of hard segments: (i) Urethane hard segments, produced by reaction of the isocyanate and the 1,4-butanediol, and (ii) Urethan-amide hard segments, produced by reaction of the isocyanate and the carboxylic acid functionality of the rosin. The TPUs and TPU-Rs were characterized using FTIR spectroscopy, gel permeation chromatography, differential scanning calorimetry, stress-controlled plate-plate rheology, stress-strain measurements, and Brookfield viscosity. The TPUs and TPU-Rs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC joints. The addition of rosin as an internal tackifier increased the average molecular weight, more markedly in the TPU-Rs containing higher hard/soft segment ratios, but the elastic and viscous moduli decreased. An increase in the hard/soft segment ratio of the TPU-Rs retarded the kinetics of crystallization (which was determined by the soft segment content in the polyurethane), and increased the immediate T-peel strength in PVC/polyurethane adhesive/PVC joints (which was determined by the urethan-amide hard segments). Furthermore, addition of rosin to the polyurethanes decreased the final adhesion, although always reasonably high peel strength values were obtained.     

Attitude Stabilization of a Biologically Inspired Robotic Housefly via Dynamic Multimodal Attitude Estimation

In this paper, we study sensor fusion for the attitude stabilization of micro aerial vehicles, particularly mechanical flying insects. Following a geometric approach, a dynamic observer is proposed that estimates attitude based on kinematic data available from different and redundant bioinspired sensors such as halteres, ocelli, gravitometers, magnetic compass and light polarization compass. In particular, the traditional structure of complementary filters, suitable for multiple sensor fusion, is specialized to the Lie group of rigid-body rotations SO(3). The filter performance based on a three-axis accelerometer and a three-axis gyroscope is experimentally tested on a 2-d.o.f. support, showing its effectiveness. Finally, attitude stabilization is proposed based on a feedback scheme with dynamic estimation of the state, i.e., the orientation and the angular velocity. Almost-global stability of the proposed controller in the case of dynamic state estimation is demonstrated via the separation principle, and realistic numerical simulations with noisy sensors and external disturbances are provided to validate the proposed control scheme.     

Fast model of thermal camber evolution in metal rolling for online use

Abstract

Mill engineers aiming to improve the geometry of rolled strip require knowledge of the temperature distribution in the roll. Theoretical evidence shows that the core temperature evolves more slowly than surface temperatures and governs the thermal expansion of the work roll. For practical purposes then, a model that predicts core temperature will allow online prediction and tracking of roll cambers. The present paper builds on previous work in developing rapid models of roll core temperature. A previous model derived using Laplace transforms is improved using a matrix formulation and conversion from an explicit to an implicit time discretisation. The implicit solution is more stable and allows for larger time steps than the explicit formulation or iterative methods used previously. The model has been tested and found to make good qualitative predictions but to underestimate the camber in comparison with actual plant data and a two-dimensional finite difference model.     

The Static Failure of Adhesively Bonded Metal Laminate Structures: A Cohesive Zone Approach

Adhesively bonded metal laminates are used in aerospace applications to achieve low cost, light weight structures in the aerospace industry. Advanced structural adhesives are used to bond metal laminae to manufacture laminates, and to bond stringers to metal laminate skins. Understanding the failure behaviour of such bonded structures is important in order to provide optimal aircraft designs. In this paper, the static failure behaviour of adhesively bonded metal laminate joints is presented. A cohesive zone model was developed to predict their static failure behaviour. A traction–separation response was used for the adhesive material. Three joint configurations were considered: a doubler in bending, a doubler in tension and a laminated single lap. The backface strains and static failure loads obtained from experimental tests were used to validate the results from finite element modelling. The models were found to be in good agreement with experiments.     

22—STUDIES ON THE NOBLE COMB. PART I: THE INFLUENCE OF CIRCLE TEMPERATURES

The combing performance of the Noble comb is dependent on the withdrawal force of the ingoing slivers, the setting of the drawing-off rollers, the absolute temperatures of the small and large circles, and the quantity of ether-extractable matter present. The withdrawal force has the greatest effect on the production of minimum noil and is also a major factor in the selection of the optimum temperatures to be used at any given setting. A theory of fibre selection and fibre migration is presented in order to explain the experimental conditions characterizing minimum noil. It is shown that changes in mean fibre length sometimes conflicted with changes in percentage noil. Certain modifications to the comb were made in order that the combed slivers from the small and large circles could be separated.