Study on the melting performance of single screw extruder with grooved melting zone and barr screw

A novel melting mechanism for single screw extruder with grooved melting zone and barr screw was established. The whole solid-plug, which came from the grooved feed zone, was ruptured and melted mainly by continuously changing the volume of the screw channels and the barrel grooves in the grooved melting zone. A new single screw extruder platform with hydraulic-clamshell type barrels was constructed to investigate the melting performance of different combinations of barrels and screws. The melting model was verified by experiments. Compared with conventional single screw extruder, the melting started earlier and the melting length was shorter in the single screw extruder with grooved melting zone. The melting efficiency was improved by the grooved melting zone and the melting stability was improved by the barr screw. The dimensionless analysis of energy indicates that the heat convection and viscous dissipation are the main melting heat sources for the single screw extruder with grooved melting zone.     

Using contrast material techniques to determine metal flow in screw extrusion of aluminium

Screw extrusion is a new continuous solid state processing method for aluminium. In this process, small pieces of aluminium are continuously inserted into a container wherein a rotating screw pushes the material forward. The material is heated, consolidated and extruded through a die in front of the end of the screw in one single continuous process. Understanding the material flow and the pressure generating mechanism is vital for optimizing screw, container and die designs, thereby increasing capacity, material quality and process stability. Full scale experiments using a prototype extruder were chosen as the means of investigation. In this paper, it is reported on the development of a novel contrast material technique to visualize material flow in the screw channels and the extrusion chamber. Extrusion of Ø 10 mm aluminium profiles was performed using both single and double flight screws. The experimental technique provided a means for evaluating the frictional conditions between the aluminium and the surface of the extruder. Different feeding schemes were used to identify regions of high material flow rate together with dead metal zones in the screw channels and in the extrusion chamber. It is demonstrated how newly fed material interacts with and displaces material already present and how the screw pushes material into the extrusion chamber. The instantaneous extrusion velocity was measured and significant variations were detected for all feed rates. An explanatory model of the extrusion pressure generating mechanism in the extrusion chamber and the screw channel is presented linking the material flow and the consolidation process to the extrusion velocity variations.     

金属粉末3D打印机的机械结构设计

为了降低工业成本和提高零件机械性能,将金属粉末注射成型技术和快速成型技术相结合,提出了金属粉末挤出堆积快速成型工艺,工艺装备的机械结构由三维快速成型平台和单螺杆挤出装置两部分组成。三维快速成型平台采用伺服电机驱动高精度威远滚珠丝杆副、HIWIN直线导轨副结构,单螺杆挤出装置由大功率伺服电机驱动螺杆转动,采用ABLE减速机增大螺杆转动所需扭矩。     

Effects of processing parameters on microstructure of semi-solid magnesium alloy

In this paper, the effects of pouring temperature of magnesium melt, preheating temperature of the barrel of the screw mixer, and shear rate on the solidified microstructures of semi-solid slurry were investigated by a mechanical stirring semi-solid process. The appropriate processing parameters of slurry preparation were obtained, and the mold filling ability of semi-solid slurry for thin-walled casting was examined. Results indicate that the solid volume fraction of non-dendritic microstructure increases with a decrease in pouring temperature of magnesium melt and the barrel preheating temperature of the screw mixer. Also the grain size of primary α-phase is reduced. Furthermore, the solid volume fraction of semi-solid nondendritic structure decreases with an increase of shear rate. The fine and round granular microstructure with 30～50 μm in size of semi-solid AZ91D magnesium alloy was presented. Finally, a 1.0 mm thin-walled casting with a clear contour and good soundness was successfully made by semi-solid rheo-diecasting.     

2A12合金的无润滑管材挤压工艺实验研究

为了在国产35 MN挤压机上实现2A12合金管材的无润滑挤压,减少废品的产生,通过分析2A12合金的材料性能及国产35 MN挤压机的结构特点,对挤压机的穿孔针系统结构进行改造,并在该挤压机上进行了2A12合金的无润滑管材挤压实验.实验结果表明,在合理控制挤压速度、挤压温度、铸锭加热温度等工艺参数的条件下,可以实现2A12合金的无润滑管材挤压;挤压产品的内表面质量好,偏心度得到很大改善.     

基于Smith-模糊控制算法的橡胶挤出机料筒温度控制系统研究北大核心

为提高橡胶挤出机料筒温度控制系统输出响应的动态与稳态性能,并在干扰作用下使系统输出稳定在目标值,采用智能算法结合PID控制原理,设计一种Smith预估算法结合模糊控制算法与PID控制的控制器,用于橡胶挤出机料筒温度控制。利用MATLAB软件建立控制器仿真模型,与增量式PID和模糊PID控制器的控制效果进行对比。结果表明:在干扰作用下,Smith-模糊PID控制使得料筒温度控制系统输出稳定在目标值;采用Smith-模糊PID控制器的料筒温度控制系统鲁棒性强,将该控制器应用于橡胶挤出机料筒温度控制,可以在一定程度上提升挤出半成品质量和挤出机械的智能化水平。     

Experimental and CFD investigation on the solidification process in a co-rotating twin screw melt conditioner

Twin screw melt conditioners are used for mixing purposes and are mainly used for polymer processing. These conditioners (extruders) can be used for liquid metal processing in which liquid metal/slurry is subjected to high shear stress. This process results in grain refinement of structure. In this article, in a co-rotating twin screw melt conditioner, the solidification process of a liquid along with temperature variations of the melt with regard to the complexity of the flow has been examined. With the aid of dynamic mesh scheme, a Computational Fluid Dynamic (CFD) simulation was performed. The achieved results were in good agreement with values based on the experimental measurements. It was concluded that shearing and pouring temperatures play important roles in solidification progression and the main reason of surviving nuclei is heat dissipation from the barrel. Also, the main factor affecting the grain size is the temperature differences between the pouring and the setting temperature. It was observed that, the twin screw melt conditioner can decrease the temperature gradient and with the help of turbulence, providing appropriate conditions for formation of fine and equiaxed grains.     

Taper barrel rheomoulding process for semi-solid slurry preparation and microstructure evolution of A356 aluminum alloy

The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced. The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the cause of solidification, which was further caused by the relative rotation of the internal and external taper barrel whose surface contained wale and groove. The heat transmission model of TBR process, the flow rules and the shearing model of the alloy melt were deduced. Taking A365 as experimental material, the microstructure evolution rules under different slurry preparation processes were analyzed. The results show that decreasing the pouring temperature of A365 alloy melt properly or increasing the shearing rate helps to obtain ideal semi-solid microstructure with the primary particle size of about 70 μm and the shape factor of above 0.8.     

发射药螺杆挤压机叶片强度分析及结构参数优化

对于发射药挤出成型用的螺杆挤压机的双锥度螺杆,在采用某种工艺的时候,药料的相互剪切和挤压作用大大提高。利用ANSYS有限元分析软件,通过模拟药料在挤压过程中的流动和应力分布情况以及流固耦合,对现有的螺杆进行强度分析,校核其是否适应新的工艺。以降低流道内最大压力差为优化目标,螺杆强度为约束条件,通过改变螺杆的结构参数,提高螺杆挤压机的挤出效率。结果表明：楔形角对流道最大压力差影响显著大于螺棱宽度;通过正交试验得到最佳参数组合为楔形角均为24°,螺棱宽度为1.5 mm,此挤出流道内压力差达到最小。     

Solid-state recycling of aluminium alloy swarf through cold profile extrusion and cold rolling

In this study, the possibility of solid-state recycling of aluminium alloy machining swarf using cold extrusion and a subsequent cold rolling process is investigated. Cast Al-Si alloy swarf was cold compacted into billets and successfully profile-extruded into square bars with a rectangular cross-sectional aspect ratio of 1:1.8 under an extrusion ratio of 4 or more. After annealing, the extruded bars underwent multi-pass cold rolling into 1-mm thick strips with a total rolling reduction of 85%. Optical microscopy demonstrated that in material recycled using only an extrusion process, coarse residual voids existed in regions where insufficient plastic strain was introduced, causing a visible expansion of the material during heat treatment. However, uniaxial tensile tests showed that extrusion-recycled material had a higher mechanical strength than the original aluminium alloy, implying sufficient bonding among the individual pieces of machining swarf. It was also found that the strength and density of material recycled through extrusion and an additional rolling process were superior to material recycled using extrusion only. Moreover, it was observed that the ductility of the recycled materials was inferior to that of the original aluminium alloy.     

Etch pit formation on metal films by wet chemicals

It is well known that the voids formed on metal interconnects shorten their lifetimes substantially in VLSI by inducing electromigration. Voids are often found on metal films after stripping photoresist films on metal films. These voids turn out to be etch pits formed by wet chemicals attacking the necks of the hillocks of CuA1₂ and Si precipitates. Etch pits are formed most easily by phenol-based strippers, while very few etch pits are formed by the ashing treatment (photoresist stripping employing a barrel type-plasma etching system). Also, it was found that etch pits tend to form more often on the metal films of Al-l%Si-0.5%Cu than on these of Ai-I%Si. Therefore, the remedy for void formation after photoresist stripping may be as follows: 1) Minimization of hillock formation by lowering residual gas contamination during the metal deposition process, 2) using phenol-free organic strippers or a plasma etching technique for photoresist stripping, and 3) using AI-I%Si alloy instead of AI-I%Si-0.5Cu alloy for the metal interconnect.     

退火工艺对锆合金成形性能的影响（英文）

研究退火工艺(ATs)对Zr-Sn-Nb合金带材显微组织的影响。基于核燃料组件用条带特征,进行冲制实验,并定量表征锆合金带材的成形性能。结果表明,580℃退火(AT I)样品、620℃退火样品(AT II)和原材的小角度晶界占比分别为14.3%、23.2%和12.4%。AT I带材的成形极限裕度为0.43%,而原材和AT II带材的成形裕度分别仅为-0.35%和-2.8%。退火工艺影响带材再结晶织构的演化过程和改变晶粒尺寸。由于织构总量和极密度变化与带材各向异性程度密切相关,小角度晶界影响带材冲制过程中颈缩单元的应变路径与裂纹扩展,而晶粒尺寸影响带材硬化指数。     

Investigation on Temperature Change of Cold Magnesium Alloy Strips Rolling Process with Heated Roll

Magnesium alloy strips are widely used in aerospace, automotive industry, etc., which are difficult to produce through cold forming process due to their poor deformation ability. In this article, we studied whether the rolling process with heated roll could be used to roll cold magnesium alloy strips. Thermal-mechanical finite element simulation of the rolling process, using heated roll and cold strips to produce the magnesium alloy strips, was carried out. Influences of roll temperature, rolling velocity, rolling reduction ratio, and initial strip thickness on the thermal field and the mean temperature of magnesium alloy strips were analyzed. Both the heated area in strips in rolling deformation zone and the mean temperature of strips at exit of rolling deformation zone increase with increasing the roll temperature and/or rolling reduction ratio, and/or with decreasing the rolling velocity and/or initial strip thickness. Finally, a formula was developed to predict the mean temperature of strips under different rolling conditions, which also could be used to calculate the critical value of parameters in rolling process.     

Mechanical properties of thixomolded AZ91D magnesium alloy

Tensile properties of thixomolded AZ91D alloy were studied to investigate the fracture mechanism by the microstructure and decohesion surfaces of tensile specimens which were manufactured at different processing conditions including barrel temperature, shot velocity, mold temperature and screw rotation speed. The results revealed that mechanical properties of thixomolded AZ91D mainly depended on porosity level, the size and volume fraction of primary solid phase and the size of α-Mg and β-Mg₁₇Al₁₂ in liquid phase. The increase in barrel temperature and shot velocity would cause the increase of both strength and ductility, while increasing mold temperature or improving screw rotation speed was coupled by the reduction of tensile properties. The tensile behaviors for different processing parameters were reasonably interpreted through the dependant factors during the deformation.     

The Plating of Screw Threads

The peculiar problems associated with the plating, and more especially barrel plating, of threaded components are considered from first principles. An experimental investigation into the barrel plating of cadmium has shown that the scatter of thickness on individual items in a barrel load depends more on the average thickness of metal deposited than on any other single factor. The scatter of individual thicknesses increases as the average thickness of metal deposited on the load increases, and a graph has been derived showing the batch average to be aimed for in order to achieve any specified minimum individual thickness. The bearing of these results on manufacturing, plating and inspection practice is discussed, and recommendations are put forward to eliminate some of the troubles at present encountered and to rationalise methods of specifying screw dimensions and plating thicknesses.     

Influence of Hot Deformation on Mechanical Properties and Microstructure of a Twin-Roll Cast Aluminium Alloy EN AW-6082

Thin strips of medium- and high-strength age-hardening aluminium alloys are widely used in the automotive industry. Reducing their production costs caused by high energy consumption is an actual challenge. The implementation of the twin-roll casting technology is promising. However, mechanical properties of directly cast high-alloyed thin aluminium strips are oftentimes inadequate to standard specifications. In this work, the influence of a hot deformation following a twin-roll cast strip process on the mechanical properties and microstructure is investigated. For this study strips of age-hardening aluminium alloy EN AW-6082—manufactured at a laboratory scaled twin-roll caster—were single-pass rolled at temperatures of 420 °C and true strains of up to 0.5. The mechanical properties of the as-cast and by different strains hot deformed material in the soft-annealed and age-hardened states were characterized by tensile tests. The results reveal that the twin-roll cast material features the necessary strength properties, though it does not meet the standard requirements for ductility. Furthermore, the required minimum strain during hot rolling that is necessary to ascertain the standard specifications has been determined. Based on micrographs, the uniformity of the mechanical properties and of the microstructure as a result of recrystallization due to hot metal forming and heat treatment were determined. A fine-grain microstructure and satisfactory material ductility after prior rolling with a true strain above 0.41 for the age-hardened state T6 and above 0.1 for the soft-annealed state O have been established.     

铂银合金超细丝材制备及研究

铂银(Pt-Ag)合金是优良的贵金属力学材料,具有高的抗拉强度、低电阻率、高弹性以及良好的耐腐蚀性,铂银丝材、带材在航空航天等领域起到重要作用。由于铂银合金熔炼及后续加工困难,影响了材料组织及产品性能。通过非自耗真空电弧炉熔炼制备的铂银合金铸锭,有效改善铂银合金铸锭的组织及加工性能,可以避免成分偏析、比重偏析、气孔、银的严重挥发等问题。通过对铂银铸锭轧制工艺、拉丝工艺、退火工艺的研究分析,简化生产工艺,提高了丝材性能,可稳定、高效生产超细铂银丝材的制备工艺,丝材的最小直径可至0.02 mm。     

关于锥形辊穿孔机轧辊转速对毛管分层缺陷影响的讨论

指出了锥形辊穿孔机也要和桶形辊穿孔机一样,要重视对穿孔机轧辊转速的控制。难变形钢和合金管坯在锥形辊穿孔机上穿孔,毛管的主要质量问题也是分层缺陷;降低轧辊转速是消除毛管分层缺陷的关键;只依靠大辗轧角,不能消除某些合金毛管分层缺陷;通常所说的斜轧穿孔金属扭转变形这种“连续”的不均匀变形,不是毛管分层缺陷产生的原因。     

反应挤出法碱分解黑钨矿

针对目前黑钨矿碱法分解工艺中存在的反应温度高、生产效率低等问题,开发了一种黑钨矿碱分解新工艺,以双螺杆挤出机为反应器,采用反应挤出法对高黏度黑钨矿的碱分解过程进行了研究,系统考察浸出时间、温度、螺杆转速和碱用量对钨矿浸出效果的影响。在矿水质量比为2.67:1、碱用量为理论量的1.5倍、温度为120℃,螺杆转速为180 r/min和反应时间为2.5 h的条件下,浸出渣中WO3的含量为2.54%,钨矿的浸出率达99.13%。     

A simple model of throughput and pressure development for single screw

To be able to predict the throughput of a single-screw extruder or the metering time of an injection moulding machine for a given screw geometry, set of processing conditions and polymeric material is important both for practical and designing purposes. The model is based on viewing the entire screw simply as a pump, conveying a solid and a molten fraction. The evolution of the solid fraction is the essence of the plastication process, but under a particular hypothesis on solid bed acceleration, its influence on the throughput is nil. This allows getting a good estimate on the throughput and pressure development along the screw. Calculations are compared to a large set of experiments available from the literature. Consistent agreement with these published results is obtained, both for throughput and pressure along the screw. The effect of the plasticating process on the throughput is non-existent if the plastication length is short, and more visible if the plastication length takes a good part of the screw length (for instance, at higher screw rotation frequency). This diminishes the throughput value and widens the pressure peak. The model also shows that the screw geometry is the most important parameter, followed by polymer rheology and processing conditions. Melting properties and length seem to intervene to a lesser extent. Finally, the model is used for screw design, highlighting the influence of the compression zone on throughput.