Effect Of Screw Geometry Research Articles

Effect of Screw Geometry on Fiber Length and Dispersion in FRTP During Injection Molding

Effect of Screw Geometry on Fiber Length and Dispersion in FRTP During Injection Molding

Development of Polymer Blend Morphology along an Extruder with Different Screw Geometries

Abstract The morphology development of an immiscible polymer blend along a single screw extruder was investigated, concentrating on the effect of screw geometry. Three different screw geometries were evaluated: one with conventional screw elements; the other two with a fluted and Pineapple mixing element, respectively. The experiments were conducted using a polypropylene/polyamide-6 (PP/PA 6) blend. The blend samples were collected from four different positions using specially designed sampling device along the extruder online during blending and were then examined using scanning electron microscopy. The experimentally observed morphology evolution was evaluated both qualitatively, in terms of spatial distribution of dispersed phase, as well as quantitatively, by analysis for the size of the dispersed phase. The morphology development was interpreted with the aid of the flow fields occurring along screw elements. The results showed that the screw with conventional screw elements produce the coarsest and most non-uniform morphology whereas the screw with a fluted mixing element appears to produce the finest and most uniform morphology at the end of the extruder. The Pineapple mixing element, with a characteristic of chaotic mixing, facilitates to form thinner laminar layers of dispersed phase. The experimentally observed morphology difference between the conventional and fluted mixing element was demonstrated by the simulation.

The effect of screw geometry on melt temperature profile in single screw extrusion

AbstractExperimental observations of melt temperature profiles and melting performance of extruder screws are reported. A novel temperature sensor consisting of a grid of thermocouple junctions was used to take multiple temperature readings in real time across melt flow in a single screw extruder. Melt pressure in the die and power consumption were also monitored. Three extruder screws at a range of screw speeds were examined for a commercial grade of low density polyethylene. Results showed melt temperature fields at low throughputs to be relatively independent of screw geometry with a flat‐shaped temperature profile dominated by conduction. At high throughputs, melting performance and measured temperature fields were highly dependent upon screw geometry. A barrier‐flighted screw with Maddock mixer achieved significantly better melting than single flighted screws. Low temperature “shoulder” regions were observed in the temperature profiles of single‐flighted screws at high throughput, due to late melting of the solid bed. Stability of the melt flow was also dependent upon screw geometry and the barrier‐flighted screw achieving flow with lower variation in melt pressure and temperature. Dimensionless numbers were used to analyze the relative importance of conduction, convection, and viscous shear to the state of the melt at a range of extrusion conditions. Polym. Eng. Sci. 46:1706–1714, 2006. © 2006 Society of Plastics Engineers

The Effects of Screw Geometry on the Pumping Efficiency of Micro‐Screw Pump

AbstractThe design of a novel micro‐screw pump for viscous fluid is described. The device consists of a rotating screw in the centre of the channel, connected with a shaft and micro motor. The objective of this research is to investigate the effect of using various screw geometries on the pump performance. Theoretical analysis by finite volume simulations is carried out to study the influence of pitch, diameter of the screw and the thread (flight depth) to evaluate the optimal dimensions for the pump and to obtain the maximum flow rate. When the screw rotates, a net force is transferred to the fluid due to the differential pressure on the depth of the thread and pressure gradient along the screw axis, thus causing the fluid to displace. The three‐dimensional simulations indicate a gradual increase of the average velocity with increasing the screw diameter. The maximum average velocity can be obtained when the ratio between the pitch and screw diameter (pi/d) is 0.6. Effective pumping is achieved by increasing the thread and pitch at maximum screw diameter. The numerical simulation has been validated experimentally.

Biomechanical Evaluation of the Pullout Strength of Cervical Screws

In the process of anterior cervical fusion, little is known about the biomechanics of anterior cervical screw pullout. In this study, three different aspects of cervical screw fixation were evaluated: self-tapping (ST) versus self-drilling (SD) screws, the effect of screw geometry (length, diameter, thread pitch), and the use of rescue screws. Nine screws consisting of different diameters, lengths, and thread pitch (cancellous and cortical) were tested in peak pullout force in an artificial bone model using an MTS 858 Mini Bionix test system. Rescue screws (4.5 mm) were then inserted in the failed holes of 4.0-mm screws and extracted to determine their holding strength. Length of screws and thread pitch both had a significant effect on the pullout force. Each 1 mm of increased screw length translates to 16 N of increased force to pullout in the foam bone model. Pullout strength did not vary significantly according to screw diameter or between SD and ST screws. However, the SD screw has an advantage because it can decrease the length of surgery. A decrease in pullout force of between 43% and 70% was found when using rescue screws. In situations in which the use of rescue/salvage screws is required, the surgeon should anticipate a significant decrease in the holding force compared with the original screw. Future directions for research include an evaluation of pullout force for screw and plate constructs.

The effect of screw taper on interference fit during load to failure at the soft tissue/bone interface

The effect of screw geometry on the pullout strength of an anterior cruciate ligament reconstruction is well documented. The effect of a truly tapered screw has not been previously investigated. Thirty bovine knees in right and left knee pairs were collected. Superficial digital flexors from the hind legs of sheep were harvested to form a quadruple tendon graft. For each knee pair, one tendon graft was fixed using a tapered screw ( n=15) and the other with a non-tapered screw ( n=15). Interference screws were manufactured from stainless steel, and apart from the tapered or non-tapered profile were identical. The screws were inserted into a tibial tunnel already containing the tendon graft. The interference fit was tested by extensile load to failure tests. The insertion torque of the screws and first sign of load to failure (by pullout) of the interference fit were recorded. Results were analysed using paired t-tests. The results indicated that tapered screws have significantly higher resistance to interference failure ( p=0.007) and insertion torque ( p<0.001) than non-tapered screws. The improved biomechanical performance of tapered screws demonstrated in this study may translate into superior clinical results, particularly at the tibial attachment of hamstring anterior cruciate ligament reconstruction, and also of hamstring fixation to the medial femoral condyle for patella instability.

Mixing effects of constituting elements of mixing screws in single and twin screw extruders

In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It is found that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for single and twin screw extruders, with particulate solids of different particle sizes like, maize grits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for single screw extruders like, pineapple-heads, and slotted flight sections for counter-rotating twin screw extruders are investigated. The effects of screw geometry on mixing has been measured using co-rotating twin screw extruder modular elements like: single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution (RTD) measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained.

Analysis and experimental evaluation of twin screw extruders

AbstractTwin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co‐ and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix.

A Study of Factors Affecting the Performance of Screw Conveyers and Feeders

A study of the literature on screw conveyers and feeders has been made. Most of the work is concerned with conveying material and in these cases the degree of fill in the trough is kept low to protect intermediate bearings and minimize power requirements. An equally important application for the screw, but one which has received less attention, is its use as a constant rate feeder and in this case the screw is run full. The object of the present work has been to find the effect of various parameters on screw performance at all degrees of fill. Experiments are described in which the effects of screw geometry, speed, filling, and the use of materials with different properties have been investigated.