No description available.

No description available.

Many orthopedic conditions in dogs require the placement of bone screws in the proximal tibial metaphysis. Currently, both cortical and cancellous screws are used clinically depending on the surgeon’s preference; however, the ideal screw for use in the proximal tibia has not been determined. Currently, both the manual and power tapping techniques are used during surgical procedures of the proximal tibia in dogs. However, it is unknown if the use of power tapping when placing screws in the canine proximal tibial metaphysis affects screw purchase. Measurement of axial pull-out strength is traditionally used to evaluate and compare the holding power of screws inserted in bone. This study compares the axial pull-out strengths of 3.5 mm cortical and 4.0 mm cancellous screws inserted using manual and power tapping techniques in the proximal tibial metaphysis

Effective heat transfer through a bed of particulate solid largely affects the production rate and the process stability in an extrusion process. Most classical models in single screw extrusion treat the solids bed as a continuum behaving as an elastic plug or fluid while neglecting the discrete nature of the particles and the presences of the fluid. The heat transfer within the solids bed in these models is calculated based on thermophysical properties of the bulk system without consideration for the presence of the interstitial fluid. From a practical point of view, experimental measurements of solids bed heat transfer within a rotating screw, particularly cross channel, as the bed moves down the length of the solids conveying zone are impossible to perform. A new device was designed to model the radial compressive stresses and shear stresses on a solids bed of plastics, similar to the environment within the screw channel of a single screw extruder. This device enables the user to visualize the nature of the solids bed under different experimental conditions through a transparent wall. Also, the device provides ways to explore the heat transfer in a solids bed under different conditions by embedded thermocouples on the top or through the front wall of the containing chamber. The results reported in this study have shown that the discrete nature of the solid bed has a strong affect on the heat transfer within the bed. The rate of heat transfer within the different beds of polymer did not appear dominated by the thermophysical properties of the materials. Rather, the evidence supports that conduction through the pseudo-static interstitial fluid (i.e. air) dominated the rate at which a polymer bed heats up; a finding similarly found for the sintering of powdered metals and ceramics in the literature. This finding would imply that differences in melting rates found in extruders are not related to the heat transfer in the solids bed; however, this statement only holds true so long as the granules making up the bed remain static (i.e. plug-like) and do not circulate within the screw channel. Quite interestingly, pellet circulation within the solid bed was observed in LLDPE over a range of test conditions. This pellet circulation resulted in enhanced heat transfer within the bed of LLDPE (a raise of 10°C) compared to PS and PP. PP exhibited pellet circulation but only over a small window of operation. Different ways to improve heat transfer within solid bed were subsequently tested in this project, such as starve feed, forced convection and spherical particle. From this work, improved understanding of heat transfer in the solids conveying zone of a single screw extruder was gained. / Thesis / Master of Applied Science (MASc)

The linear actuator is widely used in the industrial and aerospace arenas. The application of the linear actuator varies. The ball screw type linear actuator or ball screw system is one design. The ball screw is a mechanical system that converts rotation motion into a linear motion. The ball screw linear actuator, compared with other linear actuators, has better efficiency, higher speed, less noise, and higher load capacity. Ball screw linear actuators are used in a number of areas, such as coordinated measuring machines, 3D printers, and aerospace actuators. In this research, the industrial sponsor provided a ball screw linear actuator, and they required its accuracy to be improved. The linear actuator suffers from an accuracy problem due to various reasons. One of the major problems is nonlinear friction, which makes it difficult to estimate using the simple friction model. In this thesis, a LuGre friction model is introduced and applied to the ball screw system. The sponsor’s ball screw system includes the ball screw sliding table, AC servo drive, AC servo motor, and a linear encoder sensor. The hardware control system for the ball screw system needs to be built. Therefore, this thesis describes how a custom ball screw control system was built. The control hardware ball screw system includes a microcontroller and a custom-made digital-to-analog converter. The linear encoder position sensor’s reading methods were tested and implemented in the microcontroller. A custom digital-to-analog converter was made and tested. The control algorithms based on the LuGre friction compensator are discussed and were simulated in the Matlab Simulink environment. Then, the physical implementation of the control algorithms on ball screw system hardware were made. Finally, a new proposed control method based on the LuGre friction model performed best in terms of accuracy consistence and tracking compare to the other mentioned controllers. / Thesis / Master of Applied Science (MASc)

The deflections of screw rotors under machining forces cause mismatch between the male and female rotors and, consequently, accelerated wear and suboptimal efficiency in their performance. Optimizing the machining process to minimize the generated forces and accounting for the resulting mismatch in the design of the rotor profile requires accurately computing the machining forces in computer simulations. Virtual machining systems combine graphics-based computation of the Cutter-Workpiece Engagement (CWE) with the physics-based models of machining mechanics to simulate the forces during complex machining processes. However, because of the high computational load of graphical simulations, virtual machining is not suitable for the repetitive force simulations that are required for optimizing the design and manufacturing of rotors. In this work, we present a new method that simulates screw milling forces based on the process kinematics instead of graphical simulations. Utilizing mathematical equations that describe the process kinematics, the theoretical rotor profile is determined for feasible combinations of cutting tool profile, setup angle, and centre distance. Subsequently, to find the milling forces, the cutting edge is discretized into multiple small edge segments and a mechanistic cutting force model is used to determine the local cutting forces at each segment. After geometric and kinematic transformations of these local forces, the screw milling forces are obtained for each roughing and finishing pass. Instead of graphics-based methods, the engagement conditions between the cutter and workpiece are determined by the ensemble of 2D rotor and tool profiles; as a result, the computational efficiency is increased substantially. The semi-analytical nature of the presented method allows for computing the forces with arbitrary resolution within a reasonable time. The accuracy and efficiency of the presented method is verified by comparing the simulated forces against a dexel-based virtual machining system. / Graduate

Yes / When compounding polymers with additives to develop materials at specifications (colouring plastics is the simplest example), the difficulties is in getting the formulation right the first time. Also, when developing completely new materials such as in nanotechnology applications, there is a need to do the initial trials safely and with as small quantities as possible to enable a wide range of experimentation. Wiith traditional applications, often the initial compounding formulation is done using small single or twin screw extruders but with machines that have a fair output to instruct the large scale operation. This step is costly in material wastage and time but more importantly it often does not provide the right formulation which in turn results in bigger wastage cost at the industrial scale before the right formulation is eventually obtained. With the very new material formulations, any reduction in cost of development is always essential. With these aims in mind, we have developed a new minimixer capable of handling tiny quantities of order 10-100g but the minimixer is capable of reproducing the very high mixing conditions experienced in large machines. This invention provides a new opportunity to develop new products quickly, safely and cheaply. The application is not restricted to polymers and can be extended to other soft materials. It has also other spin-offs as a research tool for studying mixing and developing new, more efficient, mixing flows. In this paper we explain the principle of operation we have engineered to produce such intense mixing. Basically, the device is based on combining two opposing flows: a single screw extruder circulation flow with a twin screw extruder mixing flow. The mixing is carried out as a batch but on its completion, the single screw extruder flow is reversed and becomes co-current with the twin extruder flow to enable the discharging of the batch through a die. In the paper we present mixing data obtained with various polymer-additive combinations tested in the minimixer under various conditions of screw speeds, mixing times and temperatures and at the larger scale to underpin the operation of this novel mixer. The quality of mixing of the extrudate was measured using a variety of methods depending on applications: using image analysis of microtome sections of the extrudate or of blown film samples produced from the formulations or measuring electrical properties.

No / An infrared temperature sensor has been used to provide real time quantification of the thermal homogeneity of polymer extrusion. The non-intrusive sensor was located in the barrel of a single screw extruder, positioned such that it provided a measurement of melt temperature in the channel of the metering section of the extruder screw. The rapid response of the technique enabled melt temperature within the extruder screw channel to be monitored in real time, allowing quantification of the thermal stability of the extrusion process. Two polyethylenes were used in experiments with three extruder screw geometries at a range of screw speeds. Data generated by the infrared sensor was found to be highly sensitive to thermal fluctuations relating to the melting performance of the extruder screw. Comparisons made with an intrusive thermocouple grid sensor located in the extruder die suggested that the infrared technique was able to provide a similar level of information without disturbing the process flow. This application on infrared thermometry could prove highly useful for industrial extrusion process monitoring and optimization.

Com disseminação dos implantes osseointegrados na pratica clinica a ocorrência de complicações mecânicas tornam-se comuns, causando problemas para pacientes e profissionais. O objetivo deste estudo foi comparar o grau de rotação de parafusos de titânio (grau 5), durante testes de torque, re-torque e os valores de destorque (Ncm), sobre infra-estruturas fundidas em monobloco, soldadas com solda TIG e solda Convencional, a partir de abutments tipo UCLA com cinta usinada em Co-Cr. Um dispositivo leitor da quantidade de graus foi especialmente desenvolvido para este estudo, juntamente com um software. Seis implantes Titaniun Fix de 3,75 mm de diâmetro e 13 mm de comprimento e hexágono externo foram montados na base de um dispositivo e diretamente sobre eles foram obtidos os padrões para fundição dos corpos de prova. Para os grupos que foram submetidos a soldagem os corpos foram montados à análogos de implantes Titaniun Fix, e vazados blocos de gesso especial tipo IV (Durone) para serem seccionados e fundidos. Cada corpo de prova foi formado por dois abutments tipo UCLA com cinta em Co-Cr, interligados por uma barra acrílica. Foram obtidos 10 corpos de prova para cada grupo e 60 parafusos de titânio (Grau 5- Titaniun Fix) foram usados para os testes. Obteve-se então a medição do ângulo criado durante o aperto e re-aperto dos parafusos, sendo o re-aperto realizado após 10 minutos do aperto inicial, ambos sob torque de 30Ncm. Após o procedimento de re-aperto, o valor de destoque era imediatamente aferido e anotado em Ncm, possibilitando avaliar a quantidade de torque retido pelo parafuso após o procedimento, sendo esta seqüência realizada 3 vezes para cada corpo de prova. Sendo a análise estatística realizada para essa comparação (ANOVA) Análise de Variância a um critério de classificação, o teste Tukey, para verificar se havia diferença estatística entre os grupos. Os resultados revelaram que durante os procedimentos de torque (aperto), os parafusos empregados em infra-estruturas fundidas em monobloco apresentaram um maior grau de rotação (56,12°), quando comparados aos parafusos empregados em infra-estruturas segmentadas e fundidas separadamente soldadas com solda TIG valor médio de (43,2°) e solda Convencional com valor médio (35,7°), sendo a diferença entre os grupos estatisticamente significante em todos os grupos para o momento torque; p<0,05. Durante o momento re-torque, o ângulo formado na cabeça dos parafusos também foi sempre maior para o grupo monobloco (15,55°) , comparado aos grupos solda TIG (10,15º) e solda Convencional (9,85°) , sendo que diferença estatisticamente significante foi encontrada entre os grupos monobloco em relação aos grupos soldados, e não havendo diferença estatística entre os grupos soldados, p<0,05. Os valores médios de destorque (quantidade de torque retido durante o aperto dos parafusos) foram maiores para o grupo solda TIG (26,77Ncm) em relação aos grupos monobloco (26,55Ncm) e grupo solda Convencional (25,10Ncm) respectivamente, porém sem diferença estatisticamente significante entre os grupos. Tanto para o momento de torque quanto para o momento de re-torque, infra-estruturas do grupo Monobloco permitiram maior rotação dos parafusos dos abutments, quando comparados com os grupos Soldados. Na análise dos valores de destorque, estatisticamente os grupos foram considerados semelhantes. / With the spread of osseointegrated implants in clinical practice the incidence of mechanical complications have become common, causing problems for patients and professionals. The aim of this study was to compare the degree of rotation of titanium screws, during testing of torque, re-torque and destorque values (Ncm) in one-piece casting infrastructures, welded with TIG and Conventional welding, from UCLA strap machined Cr-Co abutments. A reader device for the number of degrees has been specially developed for this study, together with a software. Titaniun Fix implants (n=6) of 3.75mm in diameter and 13mm in length and external hexagon were mounted at the base of a device and they were obtained directly from the casting patterns of the specimens. Groups that were subjected to welding were mounted to the implant analogues, submitted to special plaster type IV (Durone) blocks. Each sample was formed by two UCLA type abutments with strap on Co-Cr, connected by an acrylic bar. It were obtained 10 specimens for each group and 60 titanium screws (Grade 5 - Titaniun Fix) were used for testing. The measurement of the angle created during tightening and re-tightening the screws, and re-grip performed 10 minutes after the initial torque, both under torque 30Ncm were obtained. After re-tightening procedure, the value of destoque was immediately measured and recorded in Ncm, to evaluate the amount of torque by the screw retained after the procedure, being this sequence performed three times for each specimen. The statistical analysis used were, analysis of variance (1 way - ANOVA) and the Tukey test to see whether there were differences between the groups. The results revealed that during the procedures of torque (tightening), the screws used in the one-piece infrastructure castings showed a higher degree of rotation (56,12°) compared to the screws used on targeted infrastructure and rendered separately welded with TIG (43,2°) and Conventional welding with a mean value (35,7°), bei ng the difference between the groups statistically significant in all groups for the torque moment (p<0.05). During the re-torque, the angle formed at the head of the screws was also always greater for the one-piece casting group (15,55°) compared to TI G welding groups (10,15°) and Conventional welding (9,85°), and significant diffe rences were found between the groups (p<0.05). The average values of destorque (retained amount of torque when tightening the screws) were higher for the TIG welding group (26,77Ncm) compared to one-piece casting groups (26,55Ncm) and Conventional welding group (25,10Ncm), respectively, however no statistically significant difference between groups were found. For both the torque and re-torque moments, one-piece infrastructure group allowed more rotation of the abutment screws when compared with the welded groups. In the analysis of destorque values, the groups were statistically similar.

<p>Loosening of implants is a frequent complication in orthopaedic surgery. The aim of this thesis was to evaluate hydroxyapatite coating of pedicle screws with mechanical and histological methods and to correlate the results with the radiological findings.</p><p>Hydroxyapatite (HA) coating of pedicle screws was investigated in experimental studies in sheep. Nine sheep were operated on with destabilising laminectomies at L2-L3 and L4-L5 and stabilised with pedicle screw instrumentations, where HA coated and uncoated screws were used in a randomised fashion. After both 6 and 12 weeks of implantation, the HA coated screws demonstrated a higher bone-to-implant contact and a higher amount of bone in the area close to the screw. The pull-out resistance, stiffness and total energy to failure was higher for the HA coated screws after 12 weeks of implantation.</p><p>HA coating of pedicle screws was examined in two clinical studies. In the first series, the patients were stabilised with pedicle screw instrumentations, where HA coated screws were used in either the upper or lower instrumented level in a randomised fashion. After 10-22 months of implantation, the extraction torque was markedly higher for the HA coated screws. In the second series, instrumentations with uncoated, partly HA coated or fully HA coated screws were used. After 11-16 months implantation, the extraction torques were recorded. There were significant differences between all three groups, with the lowest extraction torques for the uncoated screws and the highest torques for the fully HA coated screws. The frequency of radiolucent zones surrounding the screws was higher for the uncoated screws than for the HA coated screws.</p><p>Radiographs from both experimental and clinical studies were examined. Screws demonstrating radiolucent zones were compared to screws without zones with respect to pull-out resistance, extraction torque, bone-to-implant contact and amount of bone surrounding the screws. All these variables demonstrated higher values for the screws without radiolucent zones. The frequency of radiolucent zones surrounding uncoated screws in the clinical study was 53%.</p><p>Conclusions: Radiolucent zones are good predictors of screw loosening. The frequency of radiolucent zones is higher than previously described. Hydroxyapatite coating improves the purchase of pedicle screws and reduces the frequency of screw loosening.</p>