Numerical study on mixing performance of screw elements in intermeshing counter-rotating and co-rotating twin-screw extrudes

The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element method. Three dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated. The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method. The dispersive mixing performance was characterized by the mixing index, the logarithm of stretching, and the segregation scale. The distributive mixing per forulance was characterized by the resident time distribution. The results indicate that the counter rotating TSE can build higher pressure and generate higher axial velocity and shear rate, whereas the co rotating TSE has better performance in dispersive and distributive mixing.

GPU-enhanced DEM analysis of flow behaviour of irregularly shaped particles in a full-scale twin screw granulator

During twin screw granulation(TSG),small particles,which generally have irregular shapes,agglomerate together to form larger granules with improved properties.However,how particle shape impacts the conveying characteristics during TSG is not explored nor well understood.In this study,a graphic processor units(GPUs)enhanced discrete element method(DEM)is adopted to examine the effect of particle shape on the conveying characteristics in a full scale twin screw granulator for the first time.It is found that TSG with spherical particles has the smallest particle retention number,mean residence time,and power consumption;while for TSG with hexagonal prism(Hexp)shaped particles the largest particle retention number is obtained,and TSG with cubic particles requires the highest power consumption.Furthermore,spherical particles exhibit a flow pattern closer to an ideal plug flow,while cubic particles present a flow pattern approaching a perfect mixing.It is demonstrated that the GPU-enhanced DEM is capable of simulating the complex TSG process in a full-scale twin screw granulator with non-spherical particles.

Three-dimensional Modeling for Predicting the Vibration Modes of Twin Ball Screw Driving Table

As a redundant drive mechanism, twin ball screw feed system has the advantage of high stiffness and little yaw vibration in the feeding process, while leads to increased difficulty with vibration characteristics analysis and structure optimization. Only low-dimensional structure and dynamics parameters are considered in the existing research, the complete and effective model for predicting the table＇s vibrations is lacked. A three-dimensional（3D） mechanical model of twin ball screw driving table is proposed. In order to predict the vibration modes of the table quantitatively, an analytical formulation following a comprehensive approach is developed, where the drive system is modeled as a lumped mass-spring system, and the Lagrangian method is used to obtain the table＇s independent and coupled axial, yaw, and pitch vibration modes. The frequency variation of each mode is studied for different heights of the center of gravity, nut positions and table masses by numerical simulations. Modal experiment is carried out on the Z-axis feed table of the horizontal machining center MCH63. The results show that for each mode, the error between the estimated and the measured frequencies is less than 13%. The independent and coupled vibration modes are in accordance with the experimental results, respectively The proposed work can serve a better understanding of the table＇s dynamics and be beneficial for optimizing the structure parameters of twin ball screw drive system in the design stage.

Temperature and thermodynamic deformation analysis of the rotors on a twin screw multiphase pump with high gas volume fractions

The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor deformations heavily influence the backflow of the multiphase fluid through clearances within the twin screw multiphase pump and these deformations may even lead to pump failures. An accurate temperature and pressure distribution on the screw rotors need be obtained before the deformation analysis can be carried out. By means of small temperature and pressure sensors embedded into the groove at the root of the rotors, the temperatures of 12 points on the rotors and the pressure distributions of a twin screw multiphase pump under high GVFs conditions were recorded. Temperature test results were adopted to perform a heat transfer analysis for determining the temperature distribution on the screw rotors. Then deformation analyses, including thermal deformation, force deformation, and total deformation, were conducted according to the pressure and temperature distributions. Deformation analysis for different materials was also conducted under the same boundary conditions. A material was suggested for the manufacturing of rotors in a twin screw multiphase pump under the condition of high gas volume fractions.

Performance of Semi-solid Slurry Produced by Twin-screw Stirring Mixer and Rheo-diecasting Process of AZ91D Alloy

The microstructure of semi-solid slurry of AZ91D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated.Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-dendritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.

Numerical Simulation of Twin-Screw Extrusion with Wall Slip

Wall slip boundary condition is first introduced into twin-screw extrusion with the Navier slip law. Three-dimensional isothermal flow in the twin-screw extruder is simulated by using the finite element package POLYFLOW. Profiles of velocity contours in the screw channel and shear rate distributions in the intermeshing region are presented for different slip coefficients. Curves of axial pressure difference, average shear rate and dispersive mixing index vs. the slip coefficient are plotted and discussed. Comparisons are also made between the wall slip conditions and the non-slip condition. The simulation results indicate that, as the level of wall slip decreases, the axial pressure difference rises, the shear effect is intensified and the axial mixing is also enhanced. All these flow characteristics seem to level off with the increase of the slip coefficient. However, because of the inherent limitation of the Navier slip law, use of an overestimated slip coefficient would predict an over-sticky state between the screw surface and the polymer melt.

Study on Hardware-in-loop Simulation of Twin-screw Extruder Experiment System

In order to facilitate the teaching of industrial processes and experiments on the twin-screw extruder control debugging,and be closer to the actual testing,to reduce the debugging costs and the risk of debugging process,the paper designs a hardware-in-loop simulation of twin-screw extruder experiment system which is closer to scene,low cost and high safety.The system through the establishment of twin-screw extruder’s mathematical model on computer to simulate the realistic system and there is hardware practicality in the computer simulation loop.The hardware based on C8051F020 can operate in the simulation loop in real time.In computer software design, we desigh man-machine interface that is intuitive and easy to operate,can reflect twin-screw extruder main operation information vividly.Finally,twin-screw extruder’s 3 heater temperature mathematical model and PID incremental control algorithm are presented.

HA/UHMWPE Nanocomposite Produced by Twin-screw Extrusion

The HA/UHMWPE nanocomposite is compounded by twin-screw extrusion of the HA and UHMWPE powder mixture in paraffin oil and then compression molded to a sheet form. TGA measurement shows the HA weight loss after processing is about 1%-2% . FTIR spectra indicate the paraaffin oil residue is trivial and UHMWPE is not oxidized. SEM reveals the HA nano particles are homogeneously dispersed by twin-screw extrusion and the inter-particle spaces are penetrated with UHMWPE fibrils by swelling treatment. HRTEM image indicates the HA particles and UHMWPE are intimately contacted by mechanical interlocking. Compared with the unfilled UHMWPE, stiffness of the composite with the HA volume fraction 0. 23 was significantly enhanced to 9 times without detriment of the yield strength and the ductility.

藜麦挤压面条加工工艺优化

以藜麦为原料,采用双螺杆挤压技术制备藜麦面条。以蒸煮特性和质构特性为考察指标,在单因素试验的基础上,应用响应面法优化挤压藜麦面条的挤压工艺参数,探究挤压温度、物料水分含量和螺杆转速对面条品质的影响。结果表明,挤压藜麦面条的最佳工艺条件为挤压温度113℃、物料水分含量45%、螺杆转速80r/min,此时面条的蒸煮损失较低,硬度较高。

工况对双螺杆混输泵振动特性影响实验

为研究工况对双螺杆混输泵振动特性的影响,搭建双螺杆混输泵多通道振动测试系统,测试并分析不同含气率、转速及出口压力下混输泵振动参数。结果表明:排液开始时排液腔瞬时打开诱发射流,射流向竖直向的泵出口偏转从而产生压力脉动并诱发振动,导致泵竖直方向振动加速度有效值高于水平方向和轴向;含气率为7.5%时振动加速度有效值为纯液工况时的1.88倍,随着含气率进一步升高测量值降低;而含气率大于20%时,振动有效值继续升高。在转速为1450r/min时y方向振动加速度有效值是850r/min时的2.95倍;振动加速度有效值随出口压力变化较小。当转速由850r/min升高至1450r/min时,径向垂直方向振动加速度主频由75fn移动至50fn。研究可为提高双螺杆混输泵运行稳定性提供指导。

阻燃永久抗静电型TPAE复合材料的制备

研究将聚酰胺弹性体(TPAE)、氮磷系阻燃剂和聚季铵盐永久抗静电剂,通过双螺杆挤出机进行共混、熔融、挤出,制备得到阻燃抗静电的TPAE复合材料,考察其导电、阻燃和力学性能。结果表明:随着抗静电剂的增加,TPAE材料的表面电阻率呈降低趋势;氮磷系阻燃剂可使TPAE材料的阻燃等级达到UL94-V0级。

双螺杆挤压双菇复合膨化食品的配方研究

以大米粉为主要原料,辅以杏鲍菇和香菇等辅料,采用双螺杆挤压技术,经过拌料、挤压膨化、切割、烘烤、调味等工艺研制双菇(香菇、杏鲍菇)复合膨化食品。在单因素的基础上,以感官评分和膨化度为综合考察指标,利用Box-Beheken响应面优化双菇复合膨化食品的配方。实验结果表明,双螺杆挤压工艺参数为:挤压温度Ⅰ区50℃、Ⅱ区130℃和Ⅲ区150℃,调整转速为230.00 r/min,在此工艺条件下制备双菇复合膨化食品的最优配方为:以大米粉为基础配方,香菇添加量为10%,杏鲍菇添加量为9%、罗汉果甜苷添加量为0.03%,此时综合评分最高,为94.16。在此条件下制备的双菇膨化食品,膨化效果最好,具有较好的色泽和香菇杏鲍菇特有的香气。

大豆分离蛋白、豌豆分离蛋白和小麦面筋蛋白相互作用对高水分植物蛋白肉品质特性的影响

混合多种蛋白原料以创造具有所有原料特征的人造肉产品已经在食品领域得到研究。然而,在高水分植物蛋白肉生产领域暂未得到研究,目前也没有对使用大豆分离蛋白(SPI)、豌豆分离蛋白(PPI)和小麦面筋蛋白(WGP)的混合原料开发植物蛋白肉的研究。该研究的目的是减少植物蛋白肉生产的经济成本,考察由SPI、PPI和WGP共混制备的植物蛋白肉是否比仅用SPI和PPI、SPI和WGP制备的植物蛋白肉具有更好的品质特性以及考察SPI、PPI和WGP以不同比例混合时蛋白之间的相互作用对高水分植物蛋白肉品质特性的影响。研究结果表明,WGP占比的增加增大了产品的硬度和咀嚼性,所有的混合原料基样品均呈现很好的组织化结构,当样品配比为P20W30时达到了最高的组织化度(2.14±0.07),混合蛋白原料也使产品的持水率增加,表观观察和SEM也显示3种混合蛋白原料产品有着更好的拉丝效果和纤维化结构,此外,傅里叶变换红外光谱表明混合蛋白原料产品主要以稳定的β结构存在,WGP占比的增加降低了产品的流变性能。总的来说,该研究表明混合3种蛋白制备的植物蛋白肉有着更好的品质特性。

锥形双螺杆加工含能材料熔融过程数值模拟

螺杆挤出机是连续加工含能材料的一种重要设备,药料经过挤出机的加热和剪切作用能顺利熔融并进一步塑化。通过网格无关分析得出网格数量大于126万后,GCI(网格收敛指数)小于3%且最大压力变化幅度较小,确定采用网格数为1261205的网格进行模拟。首次使用FLUENT中的Solidification&Melting模型对锥形双螺杆挤出机加工含能材料的熔融过程进行模拟,得到熔融段熔体分数、流动速度和温度等参数;基于质量守恒定律模拟分析锥形双螺杆挤出机中药料熔融过程的压力变化。在此基础上,通过改变螺杆转速、机筒温度和螺杆温度,分析了工艺参数对熔融过程的影响;通过改变螺杆的槽深、导程和法向螺棱宽度,分析螺杆结构对熔融过程的影响。

10t/d双螺杆榨油机压榨油茶籽的工艺研究

为提高油茶籽油的品质,减少传统油茶籽制油工艺对油茶籽油的营养成分损失,对日处理10t双螺杆榨油机压榨油茶籽的工艺进行了研究。结果表明,最佳工艺条件为:油茶籽经过分级处理后入榨油茶仁水分控制在9%、油茶仁中含壳控制在8%时,压榨饼中残油率为2.49%,且产品符合一级油的国家标准。与市场上销售的油茶籽油相比,通过本工艺获得的油茶籽油中α-生育酚的保留率更高,从而进一步提高油茶籽油的营养价值,可为我国油茶籽油的高值化加工提供了技术参考。

双螺杆挤出机胶粉脱硫工艺条件的研究

研究同向双螺杆挤出机的螺杆结构、脱硫温度和螺杆转速对胶粉脱硫的影响。结果表明:螺杆结构越有利于提高螺杆的混合和剪切能力,胶粉的溶胶含量越大,交联密度越小;当脱硫温度从170℃升高至190℃时,胶粉的脱硫效果有一定改善;当螺杆转速从50 r·min^(-1)增至90 r·min^(-1)时,胶粉的脱硫效果明显改善;当脱硫温度为180~190℃、螺杆转速为50~70 r·min^(-1)时,中等混合和剪切能力螺杆脱硫的胶粉的脱硫效果较好,脱硫胶粉胶料的拉伸性能较优。

同向平双齿轮传动系统设计分析软件开发

同向平双齿轮传动系统设计过程复杂、参数众多,型号更迭导致结构参数匹配困难、工作量大,亟待开发专用设计分析软件以提高设计效果和效率。建立了同向平双齿轮传动系统优化模型,基于C++语言与Qt应用程序框架开发了同向平双齿轮传动系统专用设计分析软件;结合工程案例对软件的可运行性、优化效果、信效度进行了对比分析,验证了软件的有效性和可靠性。结果表明,所开发的软件实现了某同向平双齿轮传动系统比现有水平减重7.98%,优化结果稳定收敛且收敛精度达99.02%,齿轮安全系数偏差率控制在8%以内,实现了良好的高功率密度设计,有望推动行业设计方法转型升级。

双螺杆挤出机塑化系统电磁加热过程的数值模拟与实验研究及应用

探究电磁加热相比于铸铜加热对双螺杆挤出机塑化系统的影响,首先针对现有双螺杆机筒和线圈分布建立几何模型,使用comsol有限元软件研究了电磁加热过程机筒磁通量变化以及温度均匀性;另外,在数值模拟的指导下开展具体试验验证,对比了电磁加热和铸铜加热的机筒内壁及法兰温度均匀性、用电量及电磁辐射安全性。结果表明,电磁加热具有更高的控温精度,保证温度均匀性在±1℃以内,与模拟结果相吻合;在相同的加热时间内,电磁加热可以实现机筒和法兰同步加热,预热时间节约40%,生产过程节能50%;另外电磁辐射符合国家安全标准(GB 8702—2014),保证车间工人的人身安全。

双螺杆挤压温度对玉米淀粉结构和理化性质的影响

淀粉在挤压机内的熔融行为变化影响着挤出物的物理性质,探究淀粉挤压过程中熔融行为对于生产理想的热塑性淀粉基材料具有重要意义。本文探究不同挤压温度(60、70、80、90和100℃)对玉米淀粉结构和理化性质的影响。结果表明,在高温和机械剪切作用下,淀粉颗粒发生破碎,颗粒尺寸减小。淀粉分子内氢键被破坏,使淀粉更易与水分子结合,从而提高了热塑性淀粉(TPS)的水合特性。随着温度升高,直链淀粉含量增加,相对结晶度(RC)和双螺旋有序度(DO)减小,表明玉米淀粉在受热过程中长程和短程有序结构被破坏。挤压机的高温处理降低了TPS的焓值,破坏了淀粉糊形成凝胶网络的能力,样品存在弱凝胶行为,但刚性和弹性减弱。综上所述,双螺杆挤压温度使淀粉颗粒结构、晶体结构、水合特性和流变特性发生了不同程度的变化,为挤压优质热塑性淀粉材料提供新思路。

双螺杆制冷压缩机排气压力脉动特性的实验研究

为研究一台冷水机组用双螺杆制冷压缩机的压力脉动特性,本文测录了压缩机压缩及排气过程的瞬态压力变化,解析其压力脉动频域特性,研究了运行转速和冷凝温度对压力脉动特性的影响,对比了压缩机采用变频与变滑阀两种容量调节方式在相同制冷量下的压力脉动、噪声和热力性能。研究结果表明:压缩腔压力脉动来源于转子工作容积内压力周期性升高,并受齿间多通道泄漏过程的影响;排气腔压力脉动来源于工作容积与排气腔的周期性连通与脱开,受排气压力及气体质量流量等因素影响。随着转速的升高,排气腔压力脉动从转速为1380 r/min时的58.6 kPa升至4200 r/min时的141.0 kPa。随着冷凝温度的升高,压力脉动幅值从34℃时的132.0 kPa升至57℃时的314.0 kPa。在相同制冷量下与容调滑阀相比,双螺杆制冷压缩机采用变频的容量调节方式在压力脉动、噪声和热力性能方面均具有显著优势,压力脉动降低54.6%以上,噪声值下降2.9 dB(A)以上,COP提升5.5%以上。