The effect of the feed section groove taper angle on the performance of a single‐screw extruder

A new mechanism is described that allows adjustment of the groove geometry in grooved feed extruders. This mechanism enables efficient, continuous and independent change of the groove geometry during the extrusion process. The patented solution of the activated grooved feed section enables one to change the number of grooves, taper angle and, connected with it, groove depth. The paper contains the graphical presentation of the selected results of experimental studies of autothermal extrusion of a medium density polyethylene in an extruder with the grooved feed section in which the groove taper angle, and thus groove depth, was changed during the extrusion process. The influence of changing the groove taper angle in the range from 0 to 5.236 × 10^?2 rad and screw speeds ranging from 177 to 279 rev/min on extruder output was studied. The energy efficiency of the extruder was studied as well.     

开槽机筒单螺杆挤出机的研究进展

分析了轴向直槽机筒单螺杆挤出机和螺旋开槽机筒单螺杆挤出机在基本结构、物料输送机理及工业应用领域等方面的不同。随着开槽机筒单螺杆挤出机产量的提高,常规的熔融方式无法实现高产量下物料的高效彻底熔融,因而开槽机筒单螺杆挤出机存在产量与熔融能力无法匹配的问题,通过分析现有解决途径,指明了其未来的发展趋势。     

Melting performance of single screw extruders with a grooved melting zone

A novel melting model for single screw extruders with a grooved melting zone 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 barrel grooves and the screw channel in the grooved melting zone. A new single screw extruder platform with hydraulic clamshell barrels was constructed to investigate the melting of solid polymer with different combinations of barrels and screws. The melting model was verified by experiments. The results showed that the melting started earlier and finished in a shorter length for single screw extruders with a grooved melting zone than that for conventional single screw extruders and the melting efficiency was improved by introducing a grooved melting zone to a single screw extruder. The theoretical values are consistent with experimental results. The novel single screw extruder with grooved melting zone can dramatically increase the plasticizing efficiency and the throughput.     

Movement of powders in a single-screw extruder at high counterpressure

Mathematical models for the conveying of powder resins in single-screw extruders with smooth barrels are well known. It is the aim of this paper to define the range of operating conditions where these models can be adapted to single-screw extruders with grooved barrels. In order to calculate throughput and torque characteristics the relevant friction parameters and powder properties have been determined. Furthermore it has been clarified to what extent the friction forces in grooved barrels can be described by a coefficient of effective friction. The influence of dynamic bridge formations in grooved areas is discussed.     

沟槽机筒单螺杆挤出机耦合双槽熔融理论研究

利用自制的液压剖分式沟槽机筒单螺杆挤出机实验平台,研究了沟槽机筒单螺杆挤出机的熔融长度和螺杆转速的关系,实验验证了单螺杆挤出机固体输送段和熔融段机筒均开设沟槽的耦合双槽熔融理论。结果表明,与传统光滑机筒单螺杆挤出机和IKV单螺杆挤出机相比,在熔融段机筒开设沟槽的单螺杆挤出机的熔融长度较短且熔融过程比较稳定,熔融效率得到较大提高。     

Grooved feed single screw extruders—improving productivity and reducing viscous heating effects

Owing to their high productivity, pressure invariance, and controlled throughput and melt temperature, groove feed systems are becoming widely accepted for the extrusion of pipes, blown films, and blow molded articles. Within the research presented in this paper, a fully instrumented 45 mm extruder equipped with a grooved fed bushing was used to measure pressure distributions, screw and die characteristics, and melt temperature profiles. The screw geometry included decompression and compression zones, and Saxton distributive and Maillefer dispersive mxing heads. The screw and die characteristic curves show the high system productivity where throughputs comparable to 60 and 90 mm conventional extruders were measured. The high throughput induced a dramatic reduction in melt temperature measured at the tip. To better understand and confirm our experimental findings, analytical models were used.     

单螺杆挤出机螺旋沟槽固体段产量的实验研究

在自制的测试仪上对单螺杆挤出机螺旋沟槽固体输送段的产量进行了实验研究,探讨了沟槽衬套、螺杆的结构参数,物料粒径大小及螺杆转速对单螺杆挤出机固体输送段产量的影响,同时将螺旋沟槽单螺杆挤出机与IKV挤出机固体输送段的产量进行了对比。实验研究表明：粒径越小,螺旋衬套沟槽越宽,固体输送段产量越高;螺杆螺距变化对挤出机固体输送段产量的影响很小;IKV直槽挤出机固体输送段的产量明显小于螺旋沟槽衬套挤出机的固体输送产量,而且随着转速的增加,趋势越明显。     

含气泡油滴撞击矩形沟槽壁面的数值分析

采用耦合水平集-体积分数（CLSVOF）方法对含气泡油滴撞击矩形沟槽壁面现象进行数值模拟研究,考察了油滴撞击壁面后的形态演化过程,分析了中心射流形成机理和气体夹带的分布规律,并探究了沟槽宽度、沟槽深度和撞击位置对油滴铺展特性的影响。研究表明：含气泡油滴在矩形沟槽壁面铺展时会形成中心射流,沟槽内部存在气体夹带现象。气泡底部的速度旋涡是形成中心射流的主要原因,沟槽内的气体夹带受油滴铺展速度影响呈现规律性分布。沟槽宽度对含气泡油滴在垂直沟槽方向和平行沟槽方向的铺展长度影响较大,但对铺展高度影响较小。当无量纲沟槽宽度为0.3时,油滴形成颈部射流并在运动后期使垂直沟槽方向的铺展长度迅速增加。此外,沟槽深度也对含气泡油滴在各方向的铺展有重要影响,沟槽深度越大,中心射流现象越难形成。撞击位置变化不改变油滴在沟槽壁面上的运动演化过程,但对沟槽内部的气体夹带规律有一定影响。     

Tailoring the grooved texture of electrospun polystyrene nanofibers by controlling the solvent system and relative humidity

In this study, we have successfully fabricated electrospun polystyrene (PS) nanofibers having a diameter of 326 ± 50 nm with a parallel grooved texture using a mixed solvent of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF). We discovered that solvent system, solution concentration, and relative humidity were the three key factors to the formation of grooved texture and the diameter of nanofibers. We demonstrated that grooved nanofibers with desired properties (e.g., different numbers of grooves, widths between two adjacent grooves, and depths of grooves) could be electrospun under certain conditions. When THF/DMF ratio was higher than 2:1, the formation mechanism of single grooved texture should be attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. When THF/DMF ratio was 1:1, the formation mechanism of grooved texture should be ascribed to the formation of wrinkled surface on the jet surface at the early stage of electrospinning and subsequent elongation into a grooved texture. Such findings can serve as guidelines for the preparation of grooved nanofibers with desired secondary morphology.     

The melting performance of single screw extruders. II

In the previous paper (1) the melting performance of a number of recent screw designs was analyzed, using a rather simple theory. A new screw design was proposed. Here the results of more elaborate calculations, are given in which the influence of the flight clearance and of a shear-thinning temperature dependent viscosity are investigated. The former conclusions are not altered in essence by these effects. Experimental results with a prototype screw are presented, showing that melting capacity is increased. Up to 100 percent increase in throughput is possible in the high RPM range (in comparison with a much longer traditional compression screw), provided that the feed capacity is sufficient. This usually requires the use of a grooved, well-cooled, feed section; the capacity of such a feed section depends, for a given screw geometry, on channel depth and granule dimensions. The melt leaves the melting section at a relatively low temperature. The melting section only melts the material and does not raise, its temperature unnecessarily. A further step towards separating distinct tasks of the extruder by functional screw design has been made.     

水平横槽纹管内氨沸腾换热及压降特性实验研究

对水平横槽纹管内氨沸腾换热及其压降特性进行了实验研究，获得了不同热流密度、不同质量流速和不同局部蒸汽干度下沸腾换热和压降的实验数据。实验结果表明，在本实验的参数范围内，与光滑管相比，横槽纹管在压降增加不大的情况下可使管内沸腾换热系数提高３０％～１５０％，横槽纹管的节距减小对传热强化的作用明显，而对槽深的影响不大。还给出了横槽纹管内氨局部沸腾换热和压降的无因次准则关系式。     

横纹管强化吸收器的传热传质实验研究

在吸收式热泵的吸收器中,利用LiBr水溶液为工质,对横纹管强化管外降膜吸收过程进行了研究。实验结果表明:影响横纹管传热强化的主要因素为LiBr水溶液喷淋密度、横纹管结构参数节距和槽深,各个因素对强化效果影响不同;与光管相比,横纹管的传热传质效果明显得到了增强,但是不同结构参数节距与槽深的横纹管,其强化传热传质的效果不同。在实验范围内,横纹管强化LiBr溶液吸收水蒸气的传热系数是光管的2.1—3.25倍,传质系数是光管的1.25—1.93倍。     

双螺杆挤出机传动系统分析及高扭矩设计探讨

介绍了双螺杆挤出机传动系统的发展情况,对双螺杆传动系统进行了归类与分析,并着重阐述了高扭矩型双螺杆挤出机传动系统的设计及技术关键。     

Fundamentals of plasticating extrusion. II. Experiments

Experiments were performed to develop quantitative information for designing plasticating extruders for low density polyethylene. Screw design variables explored included feed section length, compression section taper, and minimum channel depth. Operating variables included were screw speed, barrel temperature, and back pressure. A moving picture film illustrates temperature action and cross-channel temperature distribution for some typical experiments using a new type of extruder screw for 2.5 inch and 8 inch diameter extrusion. The information gathered was used to obtain relations between performance and screw dimensions and revealed an optimum combination of feed section length and compression taper.     

Processing of reinforced plastics using multi-screw compounders

Polymer modification by addition of reinforcing agents represents a popular means of increasing physical property values. The polymer matrix has been forced to accept up to 55 percent by weight of fibrous reinforcement and 80 percent by weight of powdered types in order to meet application requirements. These materials demand sophisticated mixing equipment which must provide extensive intake and conveying capabilities, polymer wetting of reinforcement, and dispersion of reinforcement. This process must also be conducted with controlled shear intensity and excellent temperature and residence time control in order to respect polymer thermal sensitivity and product requirements. The extrusion process is a proven economical method for incorporating reinforcements into polymer resins. Co-rotating intermeshing twin-screw extruders are particularly suited for these tasks. Positive conveying, self-wiping, and shear intensive mixing characteristics provided by the screw mechanism satisfy requirements of reinforcement compounding. This mechanism allows interruption of streamline flow which is needed to disperse both high and low aspect ratio reinforcing agents into a polymer matrix. Mathematical representation of the benefits of twin-screw extrusion (relative to single-screw) related to pumping and mixing capability have been developed based on the classical pressure flow continuity equation with proper selection of boundary conditions.     

The melting behavior of a low density polyethylene powder in a screw extruder

An experimental investigation into the performance in general and the melting behavior in particular of a single screw extruder running with a low density polyethylene power has been carried out and the results compared with those for a granular feedstock of low density polyethylene having similar melt properties. It was found that the tendency was for the output rate, pressure generated and specific power consumption to be lower for the powders, and that the removal of barrel heating near the feed hopper increased these parameters. Two melting mechanisms were observed in powder extrusion; one being the classic “Maddock” type, and the other such that the solid bed and melt pool were in reversed positions relative to the Maddock case. There was a trend for this latter mechanism to operate with low screw speeds, shallow channels and full heating. Melt initiation occurred nearer the feed end and melting was completed much more quickly with powders. An explanation of the mechanisms is proposed which is based on the observation of early melt initiation, and the industrial practices of feed zone cooling and increasing feed pressure generation to improve the performance of extruders running with powders are seen to be consistent with this proposition.     

Melting of thermoplastics in single screw extruders

Some experiments on the melting of thermoplastic polymeric materials in single screw extruders are described. Although these were of the now familiar screw extraction type, special care was taken to distinguish between material melted by screw rotation and that melted during the subsequent cooling operation. A barrel which could be split longitudinally was also used, thus avoiding some of the disadvantages of axial extraction. A theoretical model is proposed which, unlike previous models, allows the solid bed of material in the screw channel to accelerate naturally, and also allows for the presence of a film of molten material between the bed and the screw. This model gives satisfactory predictions of melting performance. Comparison with experimental results shows that break-up of the solid bed occurs when the model predicts rapid acceleration of the bed. Bed break-up and the resulting surging may be reduced or prevented by the use of screw cooling which has the effect of inhibiting the formation of a melt film at the screw surface.     

Scale-up of single screw extruders

Scale-up from small laboratory size extruders to large production size extruders is a procedure of great practical importance. Many scale-up rules and theories have been proposed in the past, however it is not always clear how the different scale-up methods will affect extruder performance. A basic analysis of scale-up in plasticating single screw extruders is developed from which the effect of a certain scale-up strategy on extrusion performance can be evaluated in terms of solids conveying, melting, melt conveying, mixing, residence time, heat transfer, power consumption, and specific energy consumption. Various existing scale-up theories are evaluated and compared using the basic analysis. A number of existing scale-up theories have some significant drawbacks, in particular with non-constant specific energy consumption and imbalance between melting rate and pumping rate. Conditions that are desirable to achieve in scale-up are enumerated and ranked in terms of importance. This leads to two new scale-up methods that result in constant mechanical specific energy consumption and high throughput rates. The first scale-up method keeps the specific surface area constant. This scale-up should work well for high values of the Brinkman number. However, at low values of the Brinkman number, the melting rate may be insufficient. The second scale-up method keeps the melting rate at low Brinkman number equal to the pumping rate and, thus, should be useful in cases where the first scale-up method cannot be used.     

Scale-up rules for mixing in a non-intermeshing twin-screw extruder

Various scale-up rules and theories have been presented for extrusion, including both single- and twin-screw extruders. Until now, however, most of these theories have concerned fully-filled channels, not only for twin screw extruders of the co-rotating fully intermeshing type (COTSE) or non-intermeshing counter-rotating type (NITSE), but single screw extruders as well. As the demand for distributive mixing and devolatilization devices increases, more and more nonintermeshing twin screw extruders with regions of partially-filled channels are being used. Therefore, developing scale-up rules for such screw extruders is imperative. In this paper, scale-up rules are developed, theoretically and experimentally, by examining the relationship between distributive mixing and important flow parameters. Two partially-filled NITSE's, with screw diameters of 0.8 and 2 inches, have been studied by using a flow visualization technique entailing a dye tracer to study the effects of distributive mixing by varying such parameters as: percentage of drag flow, screw stagger, and screw velocity. Qualitative evaluation of the spread of the dye with the number of screw revolutions was obtained from videotape of the experiments. Factorial experimental design method has been applied for evaluating these results. Finally, new scale-up rules were developed and compared with rules in the literature.