Influence of work hardening ratio of parent tube on undershooting phenomenon in cold tube extrusion

Abstract

The influence of carbon steel work hardening ratio on the intensity of undershooting of outside diameter was investigated in the cold extrusion of carbon steel tube. Steel tubes with carbon contents ranging from ～0 to 1·0 wt-% were subjected to cold extrusion through a die and the intensity of undershooting of attaining the outside diameter was measured to evaluate the influence of the work hardening ratio. As an index of work hardening ratio, the so called n value was determined for each parent material using a stress–strain curve drawn by carrying out a tensile test. The n value decreases with increasing carbon content and the higher the n value, the higher is the intensity of undershooting. Elastic–plastic finite element analysis was carried out to simulate the experimental data and also, to design an appropriate die geometry for suppressing the undershooting phenomenon. The solution was the adoption of a double taper die for the suppression of the undershooting phenomenon due to the work hardening ratio.     

Short dies and thin walled inserts for room temperature or warm compaction - numerical determination of design features

Abstract

If a certain physical phenomenon is so complex that simplifying hypotheses are inadequate to represent it, the determination of design parameters through analytical procedures is unsuitable. In these cases, a numerical algorithm may be the alternative solution, to simulate the phenomenon in a manner that is more faithful to the actual physical situation. The design parameters of compaction dies have been determined by FEM. To evaluate the effects of higher temperatures, as in warm compaction, the available literature data have been used to include the variations of characteristic parameters of the involved materials. A wide range of die dimensions has been covered, focusing the interest on progressively shorter dies or thin inserts. A die can be coded as short when its axial extension is small in comparison to the radial size, which can vary significantly. Different insert materials have been considered, from HSS to PM steels and Co-WC. The deviations from classical Lame's formulae depend on the geometry of the die elements. The limitation on limit stresses requires a minimum wall thickness of the insert, which is higher than that considered dangerous for the instability of elastic equilibrium.     

Modelling of steel shrinkage and optimisation of mould taper for high speed continuous casting

Abstract

In high speed continuous casting, optimisation of mould taper is key for intensifying heat transfer and for improving the quality of the cast products. Mathematical modelling has been carried out by combining heat transfer, steel shrinkage and parabolic continuous taper model in order to optimise the mould taper profile. These models have been assembled to a set of software, the inputs of which include the steel grade, casting speed, casting temperature, length and the cross-section of mould tube, while the outputs consist of surface temperature of the strand, thickness of solidified shell, thermal linear expansion coefficient, steel shrinkage, distortion of the mould tube wall, the actual air gap, total taper and the continuous taper profile. Optimum mould taper has a parabolic profile which is tapered inwards that changes continuously along the length of the strand in order to achieve reduction in air gap while avoiding distortion of the mould tube.     

Effect of Mg on sintering phenomenon of aluminium alloy powder particle

Abstract

The effect of Mg on the sintering phenomenon of aluminium alloy powder particles has been examined using XPS analysis of the chemical reaction at the top most surface of the particle during heating. The relative density of the sintered material increases by 9% according to the increase of Mg content. The mechanical properties of the sintered material also increase remarkably as the Mg content in the particle increases. The ratio of the dimple patterns observed at the fractured surface after the tensile test also increases. It is considered that Mg acts to deoxidise the Al₂O₃ film that covers the particle surface as a barrier and helps sintering between the particles.     

Microstructure and yield phenomenon of an extruded Mg-Y-Cu alloy with LPSO phase

A yield phenomenon was firstly reported in an extruded Mg-6.8Y-2.5Cu alloy and the corresponding microstructure was also investigated in this work,The cast alloy is mainly composed of α-Mg,18R long period stacking order(LPSO) phase,eutectic phase(Mg₂₀Cu₄Y₁),and Mg₂Cu phase.The 18R LPSO phase at the dendritic grain boundary transforms into the 14H LPSO phase in the grain interior during homogenization.After extrusion,the grain size of the homogenized al...     

Effect of temperature on the behaviour of lubricants during powder compaction

Abstract

The study of the influence of temperature on the performance of admixed lubricants is important since higher densities are desired while keeping the ejection force at a reasonable level. Therefore, three lubricants admixed with iron powder were evaluated during compaction at 25, 65, and 110°C. An instrumented die permitting the measurement of the applied and transmitted pressures through the compact lead to the evaluation of the slide coefficient. This empirical parameter is related to the stress ratio and to the friction coefficient characterising the friction of the compact on the die wall. The evolution of the slide coefficient revealed a different behaviour at the beginning of compaction, where a higher shear resistance is desirable, compared with the end of compaction, which was more influenced by the amount of lubricant at the interface between the compact and the die wall. A too low shear resistance at that stage could however lead to stick–slip phenomenon.     

Experimental investigation of the phenomenon of centrifuging of liquids

The phenomenon of centrifuging of liquids inside a horizontal tubular device rotated about its axis of symmetry has been experimentally investigated. Extensive experiments were conducted using a transparent apparatus which enabled visualization and photographic recording of the centrifuging phenomenon. Several interesting and useful qualitative observations not reported hitherto have been recorded. The effects of liquid volume (υ _l ), density(ρ), viscosity (η), surface tension (γ), and the apparatus geometry,viz., diameter (d) and length (l), on the critical speed (n) required to centrifuge 100 pct of the liquid were systematically studied using several inorganic liquids, the physical properties of which were also experimentally determined. The generated data over a wide range of variables have been shown to fit the following dimensionless correlation derived from first principles: 1 $$\frac{n}{{60}}\left( {\frac{\gamma }{{\rho g^3 }}} \right)^{1/4} = KP^a \left\{ {\eta \left( {\frac{g}{{\rho \gamma ^3 }}} \right)^{1/4} } \right\}^c ;P = \frac{{4v_l }}{{\pi d^2 l}} \times 100$$ whereK,a, andc are constants specific to a prescribed value ofP.     

环形薄壁类粉末冶金零件压坯残余应力分析

针对环形薄壁类粉末冶金零件压坯的残余应力进行分析,采用修正的Drucker-Prager Cap弹塑性本构模型对金属粉末压坯压制、卸载和脱模过程进行数值模拟,同时考虑不同零件压坯几何参数(高径比和厚径比)以及压制工艺条件(摩擦条件和脱模角度)对压坯内残余应力的影响.研究结果表明,压坯脱模后的残余应力分布规律是压坯侧表面出现明显的压应力层,内部为拉应力区域,且越靠近压坯中心值越小.随着高径比和厚径比的增加,其残余应力逐渐减小;随着摩擦系数的增加,压坯表面的轴向残余压应力不断增大且压坯内部的拉应力也不断加大;适当增加脱模角度有利于压坯内应力释放而减小残余应力.通过正交模拟试验及方差分析可知,厚径比和脱模角度对金属粉末成形脱模后压坯残余应力影响更为显著.     

An Overview of the Studies about Heavy Metal Adsorption Process by Microorganisms on the Lab. Scale in Turkey

Abstract

Heavy metal ions, Cr(VI), Pb(II), Cu(II), Fe(III) and Ni(II) were removed from synthetic aqueous solutions by using Z. ramigem, an activated sludge bacterium, and R. arrhizus, a filamentous fungus. The adsorption isotherms were developed and it was seen that the adsorption equilibrium data fit both Freundlich and Langmuir isotherms. Heavy metal adsorption on free and immobilized cells was also investigated in various reactor types such as stirred tank reactors (single and multi-stage) and packed bed reactors.     

Constitutive data and friction measurements of powders using instrumented die

Abstract

An instrumented die has been developed to measure friction and constitutive data on powders during compaction. Such data is useful for quality assurance and as input data for computer models of die compaction. The measurement system consists of a die with radial stress sensors, punch force measurement, and a displacement transducer to measure punch displacement. The outputs of these sensors enable simultaneous measurement of density, die wall friction coefficient, and the triaxial stresses acting on the powder during the course of compaction.

The die system has been tested at three industrial sites on automated and manual presses measuring ferrous, ceramic, and tungsten carbide powders at applied stresses of up to 650 MPa and speeds of up to 26 mm s^-1. Sensor outputs were sufficiently noise free to permit the recording of useful data down to stresses less than 1 MPa. Typically the run to run reproducibility of friction coefficients was better than ± 0·005, depending on the type of powder and the applied stress. Variations in constitutive data were usually better than ± 4%, again depending on material and the stress. Die wall friction coefficients are found generally to decrease with increasing density and stress.

It has been possible to discriminate between different grades and batches of the same material using the frictional and constitutive data. Constitutive data for all types of powder can be accurately represented by an analytical relationship involving four adjustable parameters. This parametric form of data is suitable as input to finite element mathematical models.     

圆锥破碎机偏心套新型加工治具设计

圆锥破碎机是冶金设备中主要产品之一。过去偏心套的加工在3 m或5 m卧车上进行,由于偏心套太长并且内孔是1∶24锥度,想加工此产品就必须利用加长刀杆走复合锥度才能完成,走复合锥度并不是难度,难度在于刀杆过长且刚性相对不足,加工时产生让刀现象,无法使用;该偏心套新型加工治具以偏心套内锥面为基准,将镗杆设计与锥套相同的锥度,利用动力机构和支撑机构来增强镗杆的刚性,再利用动力机构的旋转,带动传动机构中的一齿差齿轮机构,使安装在丝杠上的行走机构实现锥套加工,解决了让刀现象,为超长锥套加工提供了宝贵经验。     

Modelling study of slag foaming phenomenon

A one‐dimensional model based on mass and momentum conservations has been developed to predict the heights of foams caused by gas injection. In the development of the model, a dimensionless number, N_foam = u_s.[(3C_d)/(4d_bg)]^1/2, has been deduced to characterise the foaming behaviour. According to the model, an increase in this dimensionless number results in an increase in foaming height. The validity of the model has been experimentally examined using silicon oils. The experiments have also shown that foamings can be classified into two types, namely one‐layer foaming and two‐layer foaming. The former type results in much larger height than the latter.     

APPLICATIONS OF SILICON NITRIDE

Abstract

The paper summarizes the known physical, mechanical, and chemical properties of silicon nitride. These are compared with the properties of several ceramics and other materials in common use, and it is shown how the combination of certain properties in silicon nitride make it an ideal material for six general types of application. For example, it is shown how the combination of thermal shock-resistance and electrical resistivity can be used to develop high-temperature electrical insulators.     

Increasing the life of molds for casting copper and its alloys

The work of the molds intended for casting copper and copper alloys in semicontinuous casters for producing flat billets is considered. It is shown that, to increase the resistance of mold plates, the inner space of the mold should have a taper shape toward the casting direction and take into account the shrinkage of the linear dimensions of the ingot during its motion in the mold. The taper shape increases the intensity and uniformity of heat removal due to close contact between the ingot and the mold inner surface. Testing of new design molds under industrial conditions demonstrates that their resistance increases by a factor of 4.0–4.5. The taper effect of the mold plates is much more pronounced in their narrow faces.     

Utilisation of silicon rubber to characterise tool surface quality during die compaction

Abstract

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.     

Machining Characteristics and Corrosion Behavior of Grain Refined AZ91 Mg Alloy Produced by Friction Stir Processing: Role of Tool Pin Profile

In the present study, influence of friction stir processing (FSP) tool pin profile on the microstructure evolution, corrosion and machining characteristics of the AZ91 magnesium alloy was investigated. Three different pin profiles namely simple taper, threaded taper and square taper were selected and FSP was carried out at 1400 rpm and 25 mm/min tool travel speed. Microstructural observations indicated grain refinement from a starting grain size of 166.5–7.9, 22.1 and 4.08 µm for FSPed samples processed by simple taper, threaded taper and square taper pins, respectively. In all the FSPed samples, decreased amount of secondary phase (Mg₁₇Al₁₂) was observed compared with that of the unprocessed sample. From the X-ray diffraction analysis, it was observed that the square taper pin tool had induced higher texture effect compared with the other two FSP tools. From the electrochemical studies, the corrosion resistance of the sample processed with square taper pin tool was observed to be more in comparison to that of the other samples; which could be attributed to the texture effect and decreased fraction of secondary phase. Machining behavior assessed by conducting drilling experiments showed a significant influence of grain refinement on the cutting forces.     

INFLUENCE OF IRON POWDER TYPE ON THE PROPERTIES OF SINTERED IRON AT VARIOUS DENSITY LEVELS

Abstract

The properties of various commercial and experimental iron powder types and of compacts made from them in the density range 6·8–7·87 kg/dm³ by single-pressing, double-pressing, and hot-forging techniques have been determined. It was shown that the ductility in all cases was more adversely affected than the tensile strength by the presence of porosity. However, it was also shown that at any particular density level or with a given processing schedule the mechanical properties varied widely, depending on the iron powder used. On the basis of the mechanical-property results, the powder types to be preferred at different density levels are indicated.     

Optimisation of baffles in six strand round bloom continuous casting tundish: a physical modelling study

Abstract

Physical modelling using water in a one-third scale model was carried out to ascertain the influence of various types of baffles with inclined holes on the liquid flow in a six strand round bloom continuous casting tundish. To characterise the flow in the tundish, residence time distribution (RTD) curves were measured for different types of baffles with inclined holes. Because there is no well known analysis model to characterise the melt flow in multistrand tundishes, a new model was presented to analyse RTD curves and its reasonability was discussed. Furthermore, a new approach for quantifying the similarity among the strands was proposed and the baffle was optimised to improve the inclusion floatation and strand similarity in the tundish.     

Relationship between physical structure and machinability of green compacts

Abstract

The dependence of green machinability on compact density and strength was investigated for room temperature and warm compacted steel powder compacts containing two different types of lubricant. Brazilian disc compression tests were employed to determine green strength, while machinability was assessed in terms of response to drilling.

For the room temperature compacted materials, it was found that high compact densities and strength were not, in most cases, associated with improvements in machinability. Furthermore, it was shown that lubrication (both type and quantity) and compaction pressure plays a critical role in determining the level of breakouts observed. In contrast, the use of warm compaction, in conjunction with specially designed lubricants, has been shown to be a suitable method of producing high density, high strength compacts while retaining good green machining characteristics. Mechanisms responsible for the observed behaviours of both the room temperature and warm compacted specimens have been forwarded in the present paper.