Single Screw Research Articles

Influence of Fused Deposition Modelling Nozzle Temperature on the Rheology and Mechanical Properties of 3D Printed β-Tricalcium Phosphate (TCP)/Polylactic Acid (PLA) Composite.

The primary goal of this study is to develop and analyze 3D printed structures based on a well-known composite known as β-Tricalcium Phosphate (TCP)– polylactic acid (PLA). There are some interesting aspects of this study. First, we developed 3D printable TCP–PLA composite filaments in-house, with high reproducibility, by a one-step process method using a single screw extruder. Second, we explored the physicochemical properties of the developed TCP–PLA composite filaments. Third, we investigated the effect of an FDM-based nozzle temperature of 190 °C, 200 °C, 210 °C, and 220 °C on the composite’s crystallinity and rheological and mechanical properties. Results confirmed the successful development of constant-diameter TCP–PLA composite filaments with a homogeneous distribution of TCP particles in the PLA matrix. We observed that a higher nozzle temperature in the FDM process increased the crystallinity of the printed PLA and TCP–PLA structures. As a result, it also helped to enhance the mechanical properties of the printed structures. The rheological studies were performed in the same temperature range used in the actual FDM process, and results showed an improvement in rheological properties at higher nozzle temperatures. The bare polymer and the composite polymer-ceramic melts exhibited lower viscosity and less rigidity at higher nozzle temperatures, which resulted in enhancing the polymer melt flowability and interlayer bonding between the printed layers. Overall, our results confirmed that 3D printable TCP–PLA filaments could be made in-house, and optimization of the nozzle temperature is essential to developing 3D printed composite parts with favorable mechanical properties.

Influence of Power Law and Isothermal Simplification on the Accuracy in Single Screw Extrusion

Abstract For the mathematical modeling of single screw extruders crucial simplifications are frequently made. In order to estimate the quality of these models it is necessary to evaluate the differences resulting from these simplifying presumptions. This study refers to the influence of two frequently used simplifications, the power-law model and the assumption of an isothermal flow. The differences due to the application of the power-law show an evident dependency on the descriptive material parameters. Depending on the Nahme-number the isothermal simplification proves partly clear differences from non-isothermal flows. These differences however are considerably reduced in the range of high Péclet-numbers.

Melt Intercalation in Montmorillonite/Polystyrene Nanocomposites

AbstractAtactic polystyrene (PS) was used to study the effect of flow field (shear and/or elongational) on the intercalation of polymer/clay nanocomposites (PNC). Three grades of (PS), with different molecular weights, were compounded with an ammonium-modified montmorillonite (Cloisite 10A) in a twin-screw extruder (TSE). The compounds were subsequently fed to a single screw extruder, fitted with one of three specially designed torpedo-attachments. The attachments were designed to provide combinations of different levels of shear and elongational deformations. The resins, TSE compounds, and final PNC’s were characterized for the degree of intercalation, degradation, rheological behavior, and mechanical properties. The data showed that the thermal decomposition of the quaternary ammonium intercalant caused severe damage to both PNC components: a collapse of the organoclay interlayer spacing, and the thermo-oxidative degradation of PS. In spite of these detrimental effects, the attachment employing combined elongational and shear flow resulted in generally larger gallery spacing and more improvement of the mechanical properties than the other two attachments.

A New Plasticating Model for Amorphous and Semi-crystalline Polymers in Single Screw Extruders

Abstract Polymeric thermoplastic materials can be subdivided in amorphous and semi-crystalline ones. In contrast to semi-crystalline polymers amorphous thermoplastic materials have no defined phase transition and hence no melt enthalpy. The glass transition region describes the change of the material behaviour from the state of a rubber like to an under-cooled fluid (glassy state). Setting the melt enthalpy in the Stefan-Neumann problem zero gives no valid results for the solid bed profile. Thus this condition is unsuitable for describing the plasticating process of amorphous polymers. In this paper a new model for the plastication of amorphous and semi-crystalline polymers in single screw extruders is presented. Therefore a new calculation method for the determination of the moving velocity between the glassy solid bed and the softened film region on the barrel surface is developed. The whole enthalpy to heat up the polymer on a critical flow temperature in the screw channel is considered.

Physical and Paste Properties Comparison of Four Snacks Produced by High Protein Quinoa Flour Extrusion Cooking

Extrusion cooking is used to produce puffed snacks based on cereals and feed ingredients. Because of its nutritional properties, quinoa flour has been employed to prepare various types of foods. This study evaluates the effects of including hyper-protein quinoa flour obtained through abrasive milling in four formulations cooked at 27% moisture content and processed in a laboratory level single screw extruder to determine their physical, textural, and pasting properties. The results indicated that additional hyper-protein quinoa flour in the cereal mixture reduced 47% the expansion index (EI), while the extrudate density (ED) and hardness increased 54 and 130%, respectively. After the extrusion process, the water absorption index (WAI), water solubility index (WSI) increased by more than 100%. The addition of hyper-protein quinoa flour (25–37%) did not affect the WAI, but an increase in the WSI was observed. The quinoa flour extrusion process generated changes on the color mainly in the L parameter, which decreased in the extruded snacks with quinoa flour inclusion (51.49), compared to the snack without inclusion (62.68). Changing the integrity of the starch granules and associated proteins, causing a decrease in the viscosity peaks during heating and subsequent cooling. The extruded samples revealed stability in the retrogradation process. Extruded snacks from quinoa could be an alternative approach to produce feed ingredients with high protein contents.

3D-Printed Bionic Titanium Alloy Artificial Lamina Prevents Epidural Adhesion and Restores the Stability After Laminectomy in Pigs.

Laminectomy can cause the dura mater to adhere to the surrounding scar tissue, leading to soft spinal stenosis after surgery. Although artificial laminae are considered ideal substitutes, they present challenges such as insecure fixation and insufficient bionics. In this study, we fabricated a bionic titanium alloy artificial lamina using three-dimensional (3D)-printing technology and evaluated its adhesion prevention and stability after laminectomy in pigs. An in vitro biomechanical pull-out resistance test indicated that the pull-out strength of the artificial lamina was close to that of a single pedicle screw and was significantly higher than that of a cortical screw. In vivo animal implantation results indicated precise laminectomy and artificial lamina implantation, as well as a safe operation process with the assistance of guide plates. X-ray and computed tomography results indicated the well fixation of bionic titanium alloy artificial lamina and screws 10 weeks after laminectomy. The artificial lamina was not loosened after being removed from pigs (postoperative week 12), exhibiting good stability. Additionally, no adhesion was observed in the artificial lamina group, whereas a large amount of scar tissue in the spinal canal covered the dural surface in the control group. Thus, 3D-printed bionic titanium alloy artificial lamina can prevent epidural adhesion after laminectomy, while restoring the structural stability of the posterior complex, suggesting the potential of lamina substitutes for adhesion prevention after laminectomy.

Characterization of Distributive Mixing in Polymer Processing Equipment using Renyi Entropies

Abstract A new method for characterization of distributive mixing in processing equipment, based on Renyi entropies, was developed. This method was applied to a twin-flight single screw extruder, in which tracer positions were determined through computer simulations of the flow field. The various entropies were calculated using particle concentrations in equal area domains of the mixer. Renyi entropies, which are function of a parameter β, were calculated for extruders of different lengths. We discuss the merit of using Renyi entropies for different values of β by pointing to the different mixing characteristics they probe. The relative Renyi entropy varies between 0 and 1 and represents a measure of distributive mixing quality, with 1 corresponding to perfect mixing and 0 corresponding to poorest mixing. We compare this new method of distributive mixing characterization to traditional ones based on the concepts of Scale and Intensity of Segregation, and the calculations based on Pairwise Correlations and Correlation Sums. The results show good agreement between the relative Renyi entropy and the traditional methods. Other advantages of the Renyi entropy such as reduced calculation time and geometric independence are discussed. For the case of a twin-flight single screw extruder, it is shown that a longer extruder is not necessarily more beneficial to distributive mixing.

Investigation of Flow Rate and Viscous Dissipation in a Single Screw Pump-Extruder

Abstract The focus of this investigation was to determine the effect of barrel rotation and screw rotation on the flow rate and viscous dissipation inside the screw pump-extruder. The screw pump-extruder was built to allow for barrel rotation and screw rotation independently. A Newtonian fluid, Polypropylene glycol, was chosen as the working fluid. The experimental results can be summarized by noting that the pumping capacity of the device was independent of which element was rotated at constant angular velocity and that barrel rotation generated higher temperature rise than screw rotation for the two screws evaluated. Also this analysis suggested that a large amount of viscous dissipation inside this extruder arises from the clearance flow. A new analytical model was proposed to evaluate the viscous dissipation for screw rotation. Calculations using this new mathematical model provided good agreement with the experimental data for both barrel and screw rotation.

Study on the internal irreversible losses and process exponent of single screw expanders

Study on the internal irreversible losses and process exponent of single screw expanders

Single Screw Transphyseal Bridging for Correction of Unilateral Carpal Valgus in a 5-Week Old Thoroughbred Foal

Single Screw Transphyseal Bridging for Correction of Unilateral Carpal Valgus in a 5-Week Old Thoroughbred Foal

29 Ankle Syndesmotic Injury: Tightrope vs Screw Fixation, a Clinical Academic Survey

Abstract Aim Unstable syndesmotic ankle injury requires surgical management in the form of screw or tightrope fixation. However, the superiority of one technique over the other remains debatable. Our Study aims to identify the fixation of choice in unstable ankle syndesmotic injury based on the surgeon’s level of experience. Methods A survey was undertaken to analyse the management of ankle syndesmotic injuries AO 44c in a 35-year-old patient. Surgeons attending an orthopaedic course were invited to participate in a survey categorised into groups: junior surgeons, middle grades and experienced. X-ray was shown to the 100 participants and treatment options were asked. Results 100 surgeons from 20 nations took part in the event. Juniors made up 39%, registrars 38% and experienced surgeons were 29%. 93% chose screw fixation, out of which 66% favoured a single screw over two screws. 3–4 cortices were virtually evenly divided in choice, with 54 % preferring three and 46% preferring four cortices. Only 22% of the time did they utilise a washer with screws. 52% of the surgeons allowed weight-bearing 4 to 6 weeks after surgery. 34% preferred to remove the screw at 1–2 months and 29% at 2–3 months post-operatively. Conclusions Data show that majority of junior level doctors manage their patients according to AO principles. The majority prefer one 3.5mm screw positioned between 2–4 cm above the ankle joint, with three cortices being somewhat preferred. Despite the lack of data to support one procedure, the majority of people remove their screws within 1 to 3 months.

Factors Affecting Slip Progression After In Situ Screw Fixation of Stable Slipped Capital Femoral Epiphysis.

Slip progression after in situ fixation of slipped capital femoral epiphysis (SCFE) has been reported as occurring in up to 20% of patients. We review SCFE treated with in situ single screw fixation performed at 2 hospitals over a 15-year period to determine the factors associated with slip progression. This case-control study reviews SCFE treated with in situ single cannulated screw fixation with minimum follow up of 1 year and full closure of the affected physis. Slip progression (failure) was defined as worsening of the Southwick slip angle of 10 or more degrees or revision surgery for symptomatic slip progression. Univariate and multivariate analyses were performed comparing success and failure groups for patient characteristics, screw type and position, and radiographic measurements. Ninety three patients with 108 slips met all criteria, with 15 hips (14%) classified as having slip progression (failure). All failures had 3 threads or fewer across the physis. Five hips had 2 threads across the physis, and 4 of the 5 were classified as failures. Lower modified Oxford bone scores were found in the failure group, though the difference was small (0.9, P=0.013). Failure was also associated with partially threaded screws (P=0.001). Failed hips were associated with lower initial Southwick angles (32.8 degrees) than successful hips (40.4 degrees) (P=0.047). In the stepwise model for multivariate regression, 4 factors were identified as significant, with lower initial number of threads (P<0.0001), mild initial Southwick category (P=0.0050), male sex (P=0.0061), and partially threaded screw type (P=0.0116) predicting failure. This study is the largest to date evaluating risk factors for slip progression after SCFE fixation, and the first to consider revision surgery for symptomatic slip progression. For stable SCFE, we demonstrate that 4 threads across the physis with a fully threaded screw of 6.5 mm diameter or greater was sufficient to avoid slip progression. We provide a risk stratification for progression of slip showing that in some cases 3 threads across the physis may be sufficient. Level III-case-control study.

Melt Conveying in Co-rotating Twin Screw Extruders

Abstract Computational fluid dynamics (CFD) based on a finite-volume method was used to simulate three-dimensional pressure and velocity fields for non-Newtonian fluids in fully filled screw elements in a co-rotating twin screw extruder. The employed method also allows the calculation of temperature fields for non-isothermal flow which requires a non-steady state calculation. The CFD code was first evaluated on simple flow cases such as flow of a Newtonian or non-Newtonian fluid through a cylindrical die or flow in single screw extruders equipped with different screws. The results agreed very well with analytical calculations (die flow) and experimental results (single screw extruder). In a next step, we wanted to establish the reliability of the numerical results for twin screw extruders by performing experiments on a 40 mm and a 58 mm screw diameter machine. Temperature and pressure distribution along the screw in the fully filled section in front of the die were measured. Melt conveying in several screw elements (different pitches) was studied for different materials (amorphous polystyrene and partially crystalline polypropylene) at various flow rates and screw speeds. It was attempted to measure axial pressure build-up for flow rates from nearly zero to beyond the drag capacity of the specific element. The measured bulk values of pressure were then compared to the corresponding values extracted from the CFD simulation results. So far, only isothermal calculations (at different temperatures) have been performed. The temperature profile along the screw was determined by calculating the energy dissipation in isothermal slices and converting the dissipated energy into internal energy (temperature increase, neglecting heat losses at the wall). General agreement between experimental and numerical results is good.

캐비테이션 소음의 위치 규명을 위한 추진기 상부 선체 표면 수중 음향센서 배치에 대한 실험적 연구

To localize cavitation noise using the beam forming method, sensors are mounted above the propeller on the hull surface of a model-scale ship. Beam forming results are highly dependent on the number and arrangement of sensors; thus, an array with a large number of sensors for a wide range will have good performance. However, it is difficult for such a system to be applied to a model scale, or to a full-scale ship in practical applications. A model-scale experiment was thus conducted at the cavitation tunnel of KRISO using various on-board sensor arrangements. The performance of each arrangement was verified from the experiment using the reference noise source, and it was confirmed that the location of the noise source could be estimated. Additionally, a feasibility study was carried out for a model ship with a single screw propeller, and it was confirmed that the location of the cavitation noise at the 12 o’clock position of the propeller was well represented.

Development of Thermoplastic Composite Tube from HDPE/Barley Straw Fibers Using Extrusion Method

This paper was devoted to the technological process of manufacturing a biocomposites tube made of low-density polyethylene and barley straw fibers. 50% of HDPE, 42% barley straw, 5% of shungite (mineral filler), 2% Maleid F (N, N-metaphenylenediamine) as coupling agent, and 1% Hexol CLA as lubricant were pre-mixed before compounding. The compounding of the raw materials was carried out on a co-rotating twin-screw extruder. The resulting granules were fed into the single screw extruder to obtain thermoplastic composite tubes. The temperature regime for the HDPE/barley straw composite processing was in the range of 145-160 °C and the screw rotation speed was 50 rpm. The tensile strength and modulus were found to be 27.7 MPa and 1687 MPa, respectively. The water absorption (24-h) and density of the specimens were 1.43% and 1.158 g/cm3, respectively. Based on the findings obtained from the present study, it can be said that the barley straw can be efficiently used in the production of tube formed HDPE composites.

Surgical interventions for treating intracapsular hip fractures in older adults: a network meta-analysis.

Surgical interventions for treating intracapsular hip fractures in older adults: a network meta-analysis.

A retrospective comparative study of postoperative sagittal balance in isthmic L5\u2013S1 spondylolisthesis using single segment or two-segment pedicle screw fixation

ObjectiveTo compare the radiographic parameters and clinical outcomes of isthmic L5–S1 spondylolisthesis with single segment or two-segment pedicle screw fixation.MethodsBetween January 2018 and January 2019, a total of 76 patients with isthmic L5–S1 spondylolisthesis were included in this study. All patients were treated with varying numbers of pedicle screw fixation with single-segment fusion during posterior lumbar interbody fusion (PLIF). Patients were divided into two groups, based on the number of pedicle screws placed during fixation, namely, 4 screws (4S) group and 6 screws (6S) group. Subsequently, the sagittal balance parameters were measured, which included slippage degree (SD), lumbar lordosis (LL), segmental lordosis (SL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and sagittal vertical axis (SVA). Clinical functional outcomes were assessed using the visual analog scale (VAS) for back pain and the oswestry disability index (ODI) scores.ResultsThe 4S group comprised of 10 males and 27 females, with a median age of 55.2 ± 10.8 years old and a mean follow-up of 16.95 ± 4.16 months. The 6S group comprised of 14 males and 25 females, with a median age of 58.1 ± 7.5 years old and a median follow-up of 17.33 ± 3.81 months. No significant differences were evident in all preoperative parameters between both groups. In contrast, the postoperative LL, SL, PT, SS, and SD values increased significantly, compared to the preoperative values in both groups (all P < 0.05). At the last follow-up, the 6S group exhibited better correction in LL, SL, and PT, relative to the 4S group (all P < 0.05). A significant SD difference was observed between both groups at all points post surgery (P < 0.05). The postoperative slip correction rate was significantly larger in the 6S group, compared to the 4S group (P < 0.05). The postoperative VAS and ODI scores of both groups improved significantly, when compared to the preoperative scores (both P < 0.05). However, there were no significant differences in the ODI and VAS scores between the two groups at all time points.ConclusionsThe clinical outcomes of both approaches appeared to be satisfactory. In terms of short-term outcomes, the 6S group exhibited better spinal sagittal restoration and stability than the 4S group.

Investigating the Effects of Tobacco Lignin on Polypropylene.

The utilization of eco-friendly materials, such as lignin, for higher value product applications became increasingly important as environmental concerns due to global warming increased. Melt blending is one of the easy ways to increase the usage of lignin in commercial applications. However, the degradation of the final product performance and increase in the production time and costs are of major concern. In the current work, the effects of blending lignin, extracted from tobacco plants, with polypropylene (PP) on the injection molding parameters, physical, thermal and mechanical properties are investigated. Blends of lignin (5, 15 and 30% by wt.) with PP were prepared using a Filabot single screw extruder. Results show that tensile strength decreases by 3.2%, 9.9% and 5.4% at 5 wt. %, 15 wt. %, and 30 wt. % of lignin addition, respectively. The tensile stiffness was almost unaffected by the addition of up to 15% lignin, but a 23% increase was observed at 30 wt. % loading. When compared to lignin processed via expensive processes, such as acetylation, tobacco lignin showed superior performance. The DSC results show unaffected crystallization and melting temperatures but a decrease in enthalpies and percentage of crystallinity. The SEM and optical micrographs of the coupon cross-sections show that the extrusion process has achieved a uniform distribution of lignin particles in the PP. Thermogravimetric analysis results show that tobacco lignin accelerates the onset decomposition temperature but does not influence the decomposition peak temperature. The increase in lignin content did not have a significant influence on the injection molding parameters, implying no additional processing costs for adding lignin to the PP. Overall, the performance of the tobacco lignin is comparable, if not better, than that of processed lignin reported in the literature.

Starr frame-assisted minimally invasive internal fixation for pelvic fractures: Simultaneous anterior and posterior ring stability

ObjectiveWe aimed to investigate the surgical techniques, efficacy, and safety of Starr frame-assisted minimally invasive internal fixation for simultaneous anterior and posterior ring stability in pelvic fractures. MethodsThe clinical data of 22 patients with anterior and posterior pelvic ring injuries who underwent Starr frame-assisted minimally invasive internal fixation were retrospectively collected. The anterior pelvic ring was fixed with an anterior subcutaneous internal fixator (INFIX), and the posterior pelvic ring was fixed with sacroiliac screws. The operative time, intraoperative blood loss, fluoroscopy times, number of assistants, complications, and weight-bearing time were analyzed. The Matta score was used to evaluate the fracture reduction. The Majeed score was used to evaluate clinical efficacy, and Gibbon's classification was used to estimate the occurrence of sacral nerve injury. ResultsAll 22 patients were treated with sacroiliac screws for posterior ring injuries, including 12 cases with single sacroiliac screws, nine with two sacroiliac screws, and one with three sacroiliac screws. INFIX was used for all anterior ring fixation, including two screws in seven cases, three screws in 13 cases, and four screws in two cases. The fracture reduction quality was excellent in 15 cases, good in four cases, and moderate in three cases by Matta scores. All patients were followed up for 6–20 (12.5 ± 5.7) months. Callus-formation time based on postoperative X-ray was 3–8 (4.3 ± 1.2) weeks. Weight-bearing time was 3–12 (6.3 ± 2.8) weeks after surgery. At the last follow-up, 15 patients were evaluated as excellent, five as good, and two as fair according to the Majeed score. Gibbons’ classification showed that one of the three patients with sacral nerve injury recovered completely and two did not recover. Complications occurred in six patients, including one with internal fixation loosening, two with anterolateral thigh paresthesia, one with malunion, one with nonunion, and one with heterotopic ossification. ConclusionsStarr frame-assisted minimally invasive internal fixation could stabilize the anterior and posterior pelvic rings simultaneously, overcoming the difficulty of fracture reduction. This technique can help patients with early postoperative weight-bearing and improved functional outcomes, providing a novel modality for the minimally invasive treatment of pelvic ring injuries.

Provisional fixation of unstable femoral neck basicervical fractures: A web-based survey and biomechanical assessment using a sliding hip screw construct

Objectives:Many hip fractures are considered rotationally unstable, especially during lag screw insertion. To counteract this instability, multiple provisional fixation constructs have been used to maintain the fracture reduction. This study aimed to compare the methods of provisional fixation biomechanically in ba sicervical femoral neck fractures.Methods:A web-based survey was sent by e-mail to members of three orthopedic assocations with questions concerning used techniques for provisional fixation of unstable basicervical femoral neck fractures and these results were used to guide our biomechanical assessment. Twenty, fourth-generation composite proximal femurs were osteotomized in the basicervical region to simulate a basicervical fracture. These fractures were anatomically reduced and one of the four provisional fixation constructs was applied. A sliding hip screw was then inserted with a torque limiter to the appropriate depth. The amount of fracture displacement during screw insertion was collected and analyzed.Results:Of the 142 respondents, 79.6% apply some form of provisional fixation. Derotational screw was the most commonly used provisional fixation (43.4%), followed by one superior Kirschner wire (K-wire) (39.8%). Biomechanically, the single derotation screw construct showed significantly less displacement (0.92 mm) than the one superior K-wire construct (3.09 mm). No other significant differences in fracture displacement were found between the groups.Conclusion:This study highlights that the majority of surgeons apply a form of provisional fixation during the surgical management of unstable basicervical femoral neck fractures. We have shown biomechanically that the single derotation screw had superior rotational stability when compared to the one superior K-wire.