Screw Profile Research Articles

A Novel Optimization Design Method of Form Grinding Wheel for Screw Rotor

The profile accuracy of screw rotors plays a vital role in stabilizing the meshing operation between mated rotors. Such stability can minimize the vibration and noise, as well as improve the sealing performance and wear resistance. This is the main reason why form grinding is extensively applied as a finishing process to maintain high screw rotor profile accuracy. Since the installation parameters for form grinding wheels affect both the grinding wheel profile accuracy and grinding performance, it is essential to obtain reasonable installation parameters to guarantee the high precision and good grinding performance of form grinding wheels. In this paper, a novel optimization design method for form grinding wheels for screw rotors has been proposed. For the first time, the relationship between the grinding wheel installation parameters and profile accuracy is established to evaluate the grinding performance. A parameterized program has been designed based on space engagement theory. The characteristics of the contact line and profile features of form grinding wheels under different installation parameters have been investigated. Then, the proposed method was employed to select the correct range of installation parameters. To validate the proposed method, a set of experiments, including the manufacture and measurement of several screw rotors, was carried out. The results reveal that the precision of the screw profile is significantly improved compared with the empirical method, thus showing the effectiveness of the proposed method.

Influence of Processing Conditions on the Preparation of Clay-Based Nanocomposites by Twin-Screw Extrusion

AbstractThis review paper is devoted to the preparation of clay-based thermoplastic nanocomposites by melt blending in a twin-screw extruder. The influence of the main processing parameters (screw speed, feed rate, barrel temperature, screw profile) on the state of the clay dispersion at the micro- and nanoscale is characterized. The change of dispersion state along the screws and the corresponding mechanisms are presented. The interest of process modelling to predict the state of dispersion is evaluated and, finally, the main modifications of the twin-screw extrusion process to improve the clay dispersion are reviewed.

Nanocellulose Production by Twin-Screw Extrusion: Simulation of the Screw Profile To Increase the Productivity

Cellulose nanofibrils (CNFs) have gained increased attention since the last 15 years and can now be produced at high solid content in an energy-efficient way using twin-screw extrusion. In this stu...

Effect of screw profile and processing conditions on physical transformation and chemical degradation of gabapentin during twin-screw melt granulation

Twin-screw melt granulation (TSMG) was applied to process a powder blend consisting of 80% gabapentin (GABA) and 20% hydroxypropyl cellulose. The effect of screw profile and processing conditions on the process-induced transformation and chemical degradation of gabapentin was studied. When a neutral kneading block was used, gabapentin underwent polymorphic transformation. A forward kneading block in combination with processing under torque conditions was required to minimize chemical degradation and to inhibit polymorphic transformation of gabapentin. Both the size of the extruded granules and gabapentin degradant level correlated positively with the specific rate, the ratio between feed rate and screw speed. At higher specific rate, the barrel was filled to a greater extent. The material packing and compressive forces were enhanced, as proven by the increased rupturing of CAMES® sensor beads and GABA crystal size reduction. This resulted in more interaction between the powder particles and facilitated granule growth. Simultaneously, this also resulted in higher degradant level. To attain adequate tabletability, the specific rate must reach a threshold value. The development of an optimum TSMG process requires balancing processing parameters based on the physical and chemical stability of GABA as well as its tabletability.

Thermo-mechanical devulcanization and recycling of rubber industry waste

This work is focused on the recycling of natural rubber industry waste by means of thermo-mechanical devulcanization. With that aim, tests were carried out in an industrial twin-screw extruder, at different barrel temperatures, ranging from 80 to 220 °C. The extrusion was done with a screw profile specifically designed for the devulcanization process. The extent and quality of devulcanization were evaluated through the measurements of crosslink density, soluble fraction and Mooney viscosity, and by using the Horikx diagram. Results showed that a high degree of reclaiming (˜90%) was obtained, independently of the barrel temperature. The samples with the best devulcanization quality, i.e. the samples with a more selective sulfur bond scission, were found to be those treated at a lower input temperature. This was explained by the effect of the rubber homogenous self-heating which contributes to the local increase of the material temperature, during the devulcanization process. Moreover, it was found that the properties of the devulcanized rubber/virgin rubber blends were not significantly affected by the addition of the treated rubber. Results suggest that the entire natural rubber industry waste could be recycled into new competitive products, with low energy consumption. This would present a real contribution to the industrial recycling and thus a noticeable improvement of the environment.

Rheological Behaviour of PP Nanocomposites by Extrusion Process

The effect of organophilic clay (C15A) in PP compatibilized polymer (PP/PP-g-MA) through rheological experimental results is presented. This study focusses on the description of the rheological behaviour of the organophilic layers along the screws of a twin screw extruder by melting process, varying the screw profile as well as the processing conditions, namely screw speed, temperature and feed rate. Different levels of dispersion were found along the screws for all conditions and positions analyzed by rheology. The qualitative analysis of the images obtained by transmission electron microscopy, reinforced the results. Furthermore, the effects of the processing conditions on dispersion of C15A layers along the screw profile are analyzed using multiple linear regression techniques. The results show statistically significant differences of all rheology measures for all the processing conditions and positions along the extruder.

Monitoring the Diameter Changes of Flax Fibre Elements during Twin Screw Extrusion Using X-Ray Computed Micro-Tomography

ABSTRACT Fiber size aspect ratio is known to impact the mechanical and reinforcement properties of natural fiber-based composites. However, the representation of fiber diameter change occurring during the extrusion process is controversial compared to the length. Fiber elements undergo multidirectional stresses and complex interactions within the extruder, leading to their breakage, which consequently may modulate their reinforcing properties. To better understand these mechanisms, short fiber reinforced polymer composites were prepared from flax fibers and polypropylene matrix (PP) by melt mixing. Five sampling zones were selected along the screws, both in screw conveying elements and inside blocks of kneading discs. X-ray computed micro-tomography, and 3D images analysis were then used for monitoring sample diameter distributions along the screw profile, according to specific twin-screw compounding conditions. The effects of the considered processing condition on fiber bundle diameters decrease along the screw profile are quantified.

Investigation of the influence of coating and the tapered entry in the internal forming tapping process

This work investigated the effect of forming speed, tap coating and the tapered region of the tap in the tapping forming process. Robust statistical analysis was employed to identify the influence of the main effects on the thrust force, torque and its correlation with the microhardness and the quality of the thread profiles. The experiments were carried out with two levels for each factor. The material used was the 7075-T6 aluminium alloy, which has a low density and good formability, which is used in moulds for injection of plastic, aeronautical and automotive components. The results showed that the factors forming speed, tap coating and the tapered region influenced the thrust force and torque. The forming speed of 50 m/min generated a reduction of 61.3% in thrust force, 8.2% of microhardness in the crest and an increase of 98.5% in torque, 5.8% of microhardness in the middle. Taps with TiN-T1 coated increased the thrust force in 12.3%, the torque in 15.2%, the microhardness in the crest of 10.3% and in the root 6.9%. The tapered region with profile type E increased the thrust force in 13.7% and microhardness in the crest of 15.0%. On the other hand, there occurred a reduction in the torque of 7.0%. The thread profile produced with the TiN-coated, taper tool type C, and forming speed of 10 m/min produced the best topography in the screw profile. The microhardness at the base was not influenced by the forming tapping process and showed the same value in all tests.

Study and Analysis of Torque Handling Capacity of Slot Headed Grub Screw

A Grub screw is a type of screw generally used to lock an object within or against another object. These screws are headless and mainly used in all types of gears and shaft. The following work is based on optimization of the strength of flat slotted screw head with different slot shapes. In the paper, we have considered samples of 3 different slotted flat headed grub screw profile with their corresponding screwdriver profile. The aim was to obtain the maximum torque handling capacity among the identified slot shapes. An iterative process involving design upgradation and finite element analysis was carried out. For this purpose validation of the FEA was performed by torsion testing of the specimen in the torsion testing machine.The results showed that 17° slotted angle grub screw gives better torque handling capacity than 0° slot angle. The study shows that a variation in the slot shape of a grub screw can influence the torque handling capacity.

Extreme shear processing for exfoliating organoclay in nanocomposites with incompatible polymers

Twin screw extrusion at speeds exceeding several thousand rotations per minute (RPM) has the potential to provide extreme shear typically required to break up aggregates and provide good dispersion in polymer nanocomposites. In this work, a novel twin screw extruder with ultra-high screw speed capability has been used to compound the polystyrene (PS) with organically modified nanoclay without using any compatibilizer. The rheological properties and the morphology of the nanocomposites were investigated and compared with simulation after compounding. Screw profiles imparting more and less aggressive mixing were compared over a range of screw speeds from 400 to 4000 RPM. Morphological characterization revealed the necessity of intense shear stress for achieving intercalation and exfoliation when chemical interactions between filler and matrix are unfavorable. The nanocomposites exhibited greater elasticity indicating reinforcement up to a critical screw speed for each screw profile, but further increasing the screw speed resulted in significant polymer degradation, and thus lower viscosity and storage modulus. Moreover, based on calculations of the theoretical adhesion force between the organoclay layers and the shear stress imparted through mixing, the optimized screw speed for a specific screw profile was determined that would overcome lamellar adhesion to form exfoliated nanocomposites, while minimizing the effect of degradation. The resulting model could be extended to any well-defined extruder system as well as other agglomerated nanofillers.

Effect of extrusion temperature and screw speed on properties of oat and rice flour extrudates.

Whole oat and rice flours were mixed to develop instant flours by a high pressure and low mechanical shear extrusion process. The screw profile was designed aiming to obtain an infant food with gelatinized starch and high hydration ability. Response surface methodology was selected to study the impact of operating parameters such as temperature and screw speed (73-186 °C; 109-391 rpm) on physicochemical and pasting properties of the final extruded product. The main challenge of this study was to process high oats content, since they are characterized by high lipid and fiber content, which impact on material processing. The optimal response was achieved at 170 °C and 350 rpm. The optimal expansion ratio, bulk density, water absorption index, and water solubility index were 2.24, 289.65 kg m-3 , 6.42 g g-1 , and 4.75 g g-1 respectively. Overall, both temperature and screw speed affected the responses studied, except for water absorption index (only screw speed affected this response). Although lipids from oats reduce the expansion ratio of extrudates compared with samples containing higher starch proportions, their lipids protect the starch granules from mechanical degradation when higher screw speed values are used. As a result, both ungelatinized and gelatinized starches may be found in extrudates, which was confirmed by pasting property analyses. High oat content may be efficiently processed by optimizing the extruder conditions (temperature, screw speed, and profile), improving the nutritional properties of the final product. © 2017 Society of Chemical Industry.

A novel non-contact measuring system for the thread profile of a ball screw

Abstract. In order to meet the demand of high position accuracy, many methods have been developed for measuring the thread profile features of ball screws. However, most of these efforts are limited to measuring a small number of ball screw features and therefore less efficient. In this study, an automatic, non-contact measuring system for the thread profile of a ball screw was developed. It is capable of measuring most common features of the ball screw thread profile and can measure ball screws of different sizes and lengths. The main part of the system is the light curtain which has a high-resolution line-scan CCD camera to measure the projected outer contour of the target. Data points from the thread profile of a ball screw were collected by the measuring system and data pre-processing was performed. Then, the proposed method was used to calculate the most important geometric parameters and errors of the thread profile. The accuracy of the measuring system was verified by testing and evaluating four sets of ball screws from different manufacturers.

Study of powerful parameters of formation of gulf elements of different profile

When forming screw profile elements, bending radii of blanks are variable during one turn of the mandrel of a complex profile. The equation of the curvature radius of the mandrel profile and the analytical dependences for determining the torque and stress values in different zones are derived, as well as the dependencies of the curvature radii and the force of the winding, depending on the structural and technological parameters of the working bodies and agricultural machines. The method of determining the influence of the radius of curvature of the mandrel, and the influence of design and technological parameters on the torque value, is developed. The analytical dependences of the curvature radius of the complex profile of the mandrel on the magnitude of the torque and the angle of the mandrel rotation are deduced. The design of the device for guiding screw blanks of various profiles, which is protected by the patent of Ukraine on the utility model, is developed.

Mathematical model of forming screw profiles of compressor machines and pumps

The article presents the results of mathematical modeling of screw surfaces shaping for compressor machines and pumps. The study is based on a method of curve movable trihedron. A mathematical model of a flat gearing - the basis for a screw formation - is proposed. The model is based on geometric interpretation of plane curve trihedron motions and known in a geometric theory of plane mechanisms of the Bobillier construction. A geometric scheme of this construction was expanded due to introduction of evolutes simulating instantaneous motions of curves trihedra in a construction scheme. As a result, the mathematical model was obtained, which is more complete in comparison with the known models of flat gearing, which makes it possible to perform synthesis and analysis of profiled screws geometry. It realizes both direct and inverse problems of screws profiling with simultaneous obtaining the curvature of the desired profiles in absent ones. The proposed model can be used as a basis of automated system development for mutually enveloping surfaces screws shaping for compressor machines and pumps.

Pressing prismatic and screw profiles from copper M4

Pressing methods of prismatic and screw metallic profiles are considered. An example of cold pressing of a billet from copper M4 with the formation of a solid square-cross-section profile is presented. Conventional pressing (extrusion) and extrusion followed by torsion pressing (extrusion and screw pressing (ESP)) are compared by mechanical characteristics, energy intensity, and the destruction character of copper samples. Herewith, the ESP of the billet was performed in one facility during the united production process. Pressing prismatic and screw profiles for one pass at room temperature was performed for copper billets O11.7 × 60 mm. The billet was loaded with a puncheon with the help of a hydraulic press. After the deformation treatment, solid prismatic and screw copper profiles with a square cross section of 8 × 8 mm were formed. The results on mechanical properties, deformation regularities, and destruction mechanism during the uniaxial tension of the samples made of technical copper M4 in the delivery state and after hardening are presented. Mechanical tests for uniaxial tension of the samples with a working size of O3 × 15 mm were performed using an UTS-20k testing machine at a constant loading speed of 3.33 × 10–5 m s–1. A certain increase in the strength of copper subjected to extrusion for one pass at room temperature is established. Screw pressing after extrusion provides higher plasticity compared with the initial state and extrusion. A fractographic research of sample ruptures is performed using a Hitachi TM 3030 scanning electron microscope in the secondary electron mode. It is shown that the destruction mechanism of copper samples in the delivery state, as well as after extrusion and ESP, is qualitatively identical. The destruction of the samples of copper M4 both in the initial state and after the deformation treatment according to the specified modes occurred according to the viscous fracture mechanism. It is revealed that ESP-subjected copper possesses larger energy intensity in connection with an increase in plasticity. The rupture in a fibrous zone for the ESP-subjected sample differs by the tier arrangement of pit blocks. Large pits and micropits in all states of copper are present both in the fibrous zone and in the peripheral cut zone.

Waxy flour degradation – Impact of screw geometry and specific mechanical energy in a co-rotating twin screw extruder

Dextrinization of starch using extrusion processing is crucial to the quality of direct expanded products. To determine the extent of dextrinization, flour samples were extracted from a twin-screw extruder that had been brought to a sudden stop and molecular weights were determined by intrinsic viscosity. The screw profile and moisture feed content had the most significant impact on molecular weight reduction, reducing intrinsic viscosity from 1.75 to 0.70dL/g at the most. The breakdown, as shown by a reduction in intrinsic viscosity, had a strong negative correlation (r=−0.96) with specific mechanical energy. However, the extruder die did not have a measurable impact on the molecular weight reduction of waxy flour. Size exclusion chromatography confirmed intrinsic viscosity measurements were associated with reduction of the size of amylopectin molecules to approximately 1/10 the original molecular weight while native gliadin was nearly eliminated from the waxy flour following the extrusion treatments.

Processing and properties of pineapple leaf fibers‐polypropylene composites prepared by twin‐screw extrusion

Pineapple leaf fiber (PALF) is an agricultural waste, very abundant in some countries of East Asia (India, Thailand, and Philippines). Owing to its intrinsic mechanical properties, it could be used as a reinforcing fiber for thermoplastic polymers. In this article, PALF was used to prepare polypropylene‐based composites by twin‐screw extrusion. The variation of the fiber dimensions (length, diameter, and aspect ratio) induced by the compounding process was analyzed. PALF suffer from a significant reduction in length, but the bundles are very difficult to separate and their diameter remains almost constant. The change in fiber length and aspect ratio along the screw profile showed an exponential decrease, as already observed for other lignocellulosic fibers. The mechanical properties of composites prepared with 20 wt% PALF fibers show an increase in Young's modulus (+46%) and stress at break (+12%), but a strong decrease in elongation at break (−98%). These results confirm the potential value of this agricultural waste as effective reinforcing fiber for polymer composites. POLYM. COMPOS., 39:4115–4122, 2018. © 2017 Society of Plastics Engineers

Metamaterial-based manipulation of orbital angular momentum for sound

The existing wave-steering devices generally control acoustic beams carrying only linear momentum. But acoustic vortices imprinted with orbital angular momentum (OAM) obviously opens new degree of freedom to control wavefront, with wide applications such as in the design of acoustic “screwdrivers” capable to generate a rotation torque to rotate objects contactlessly. To overcome the drawbacks of the traditional methods for producing acoustic OAM, we have designed and fabricated an acoustic vortex emitter with multi-arm coiling slits that utilize diffraction effect to generate vortex beam, with broadband functionality and stable topological charge. Based on this, we further propose a new mechanism for producing acoustic OAM by converting acoustic resonances to OAM. As an implementation, we have designed and fabricated a thin planar device with high efficiency to verify our scheme. Compared with existing ways for OAM production by phased spiral sources that need sophisticated electronic control and by physically spiral sources that need screw profiles and may also have a bulky size, our acoustic resonance-based OAM production bears the advantages of high efficiency, planar profile, compact size, no spiral structure, and can be freely tuned to produce different orders of OAM. I will also discuss some potential applications of our proposed scheme for OAM manipulation by metamaterials.

Kinetic and process modeling of thermal and mechanical degradation in ultrahigh speed twin screw extrusion

In this article, a kinetic model is introduced in conjunction with experimental extrusion results to predict the evolution of depolymerization reaction at various operating conditions during ultra-high speed twin screw extrusion (TSE). A commercially available flow simulation software (LUDOVIC®) was used to calculate thermomechanical flow parameters for various screw profiles. The simulated local material temperature and mechanical shear rate were used as inputs to develop a kinetic model that separately describes the effects of temperature and shear on the extent of degradation reaction due to extruding at very high speeds. The model is validated through comparison with experimental gel permeation chromatography (GPC) results on extruded samples. A good agreement was found between theoretical and experimental results. This validation makes the model practically useful for processing optimization, which is a considerable challenge for realizing compounding benefits in ultra-high speed TSE.

Attempts to Optimize the Dispersion State during Twin-Screw Extrusion of Polypropylene/Clay Nanocomposites

Abstract Polypropylene/organoclay nanocomposites were prepared by melt-mixing in a twin-screw extruder. Polypropylene grafted with maleic anhydride was used as compatibilizer. The evolution of the microstructure along the screw profile was characterized through dead-stop experiments. In order to quantify the multi-scale dispersion state of the nanocomposites, different techniques have been used: scanning electronic microscopy (SEM) to observe the large remaining aggregates, X-Ray diffraction measurements to characterize the intercalation state by measuring the interlamellar distance, and finally rheological characterizations in the molten state to assess the dispersion state at the nanoscale. The effects of low barrel temperatures and high matrix viscosity were tested, in order to improve exfoliation by an increase in shear stresses.