Variable Screw Research Articles

0085 - Lumbar-Sacral Destruction Fixation Biomechanics: A Finite Element Study

ABSTRACT: The lumbosacral deficiency can occur with destruction following tumors or from the birth. Stabilization of the spinal column with lumbo-sacral deficiency is a challenge, therefore, developing a customized/innovative implant for a secure and rigid fixation is necessary. Previous fixation devices had some disadvantageous due to fracture and loosening. So, we came up with a new concept which is tuning fork plate for fixation of lumbo-sacral deficient models. This idea was started with a variable screw placement (VSP) system and provides a strong distal fix with screws and is fixed in the lumbar spine proximally. The purpose of this study is to evaluate the mechanical effectiveness of tuning fork plate by comparing with dual iliac screw fixation under different spinal motion through finite element analysis (FEA).

The effect of screw rotating speed on mass flow rate, temperature, viscosity, mooney scorch time anddie swell of cold feed rubber blending prepared by qsm 200 extruder machine

The effect of screw rotating speed on cold feed rubber blending production were evaluated. The specimens were prepared by using QSM 200 extruding machine with variable screw rotating speed 4, 6, 8, 10, 12, 16 and 20 RPM. The temperature set in the screw and head of the barrel was around 80 °C by using Temperature Controll Unit (TCU), and was set around 70°C in zone 1 and 2. Mooney Viscometer was used to evaluate the viscosity and Mooney Scorch Time of cold rubber blending before and after extruding process. In addition, the dynamic rubber process analyzer was used to evaluate the Die Swell of rubber blending after extruding process. The result indicated that the increase of screw rotating speed has a significant effect to increase the flow rate, temperature and the viscosity of the rubber blending. Otherwise, the Mooney Scorch Time (MST) increases due to the decrease of the screw rotating speed. It does not have a significant effect to the die swell of rubber blending.

Anterior retropharyngeal plate screw fixation with bilateral anterior transarticular screws for odontoid fractures ... a new comprehensive technique

Introduction: A certain group of odontoid fractures (Anderson and D’ Alonzo Type-2) are usually offered surgical treatment. Common surgical option is an anterior odontoid screw. Some of the fractures are not suitable for anterior odontoid screw (anterior oblique, displaced distal fragments and those with atlantoaxial instability) and these are usually offered posterior transarticular screws (Magerl’s) or posterior atlantoaxial screw rod/plate fixation (Goel-Harms technique). Posterior surgery involves atlantoaxial fixation with an indirect attempt to reduce and fuse the fracture . Posterior surgery has a risk of injury to the vertebral arteries, hemorrhage from the paravertebral venous plexus and the C2 root ganglion.Methods: A direct anterior submandibular retropharyangeal approach with open reduction and fixation (ORIF) using a customized variable screw placement (VSP) plate was used to realign and fix the fracture fragments in compression mode under direct vision. Twenty patients of type-II odontoid fractures (unsuitable for anterior odontoid screw) underwent an anterior retropharyngeal approach with anterior variable screw position (VSP) plate and screw fixation and eight amongst them, who had associated atlantoaxial instability underwent additional bilateral anterior transarticular screws.Results: All patients treated by this technique had 100% fracture site bone union without any implant failure. Longest follow-up has been for 3 years.Conclusion: Anterior retropharyangeal approach allows direct fracture fragment realignment under vision with an opportunity to fix in compression mode using the VSP plate, which ensures early fusion across the type-II odontoid fracture. Any associated instability can be treated by additional bilateral anterior transarticular screws. The approach is simple and safe without any risk to the vertebral arteries and biomechanically appealing.

Distributed parameter bi-zone model with moving interface of an extrusion process and experimental validation

ABSTRACTIn this work, a distributed parameter bi-zone dynamic model with moving interface of an extrusion process is presented. In this case, a variable viscosity is assumed along the extruder. A finite volume method is proposed for discretizing the dynamic model. The steady-state values of the variables were calculated by using an efficient optimization algorithm. Experimental tests performed with an industrial type twin screw extruder are compared against simulations for the case of variable screw speed and constant feed rate. The comparison shows good qualitative agreement between experimental and simulation results. This model can be used to design observers for estimating non-measurable variables as well as advanced control strategies.

Comparing Dorsal Tangential and Lateral Views of the Wrist for Detecting Dorsal Screw Penetration after Volar Plating of Distal Radius Fractures.

Background The dorsal tangential (DT) view has been shown to improve the detection of dorsal screw perforation during volar distal radius fracture fixation. Here we performed a cadaveric imaging survey study to evaluate if the DT view was uniformly beneficial for all screws. Methods Standardized placement of fixed-angle volar distal radius plates was performed on two cadavers. Fluoroscopic images depicting variable screw perforation of each of the four screw holes on the plate were generated. A 46-image survey was distributed at a large academic medical center. Respondents were asked to answer if the screw was perforating through the dorsal cortex in each image. Statistical analysis was performed using Fisher's exact test. A p value < .05 was considered significant. Results The DT view offered a significantly more reliable determination of dorsal screw penetration than traditional lateral imaging for the radial-most screw at all degrees of perforation and the middle two screws at 2 mm of perforation. Residents and attendings had more accurate screw readings overall using the DT view. Conclusions The DT view is superior to traditional lateral imaging in the detection of small amounts of dorsal perforation of the radial-most three screws of a fixed-angle volar plate.

Substantiation of rational design parameters of variable pitch screw of an extruder

The analysis of effectiveness of methods of feed material (extrudate) preparation for feeding showed that the thermal method of its processing with the use of the KMZ-2 extruder is of most practical and academic interest. The studies carried out by V.V. Novikov showed that in the process of its formation the extrudate moves throughout the length of working chamber in the space between the screw flights and the inner surface of body, due to this the obtained mixture is heated and compacted. Based on the theoretical researches carried out by V.Yu. Frolov, it was found that the screw should have a variable pitch gradually decreasing with the movement of the processed feed material along its axis. During its movement the processed feed material is compacted and reaches the condition that allows to take the required shape in accordance with process requirements. Determination of rational parameters of variable pitch screw of extruder in areas for loading and pressing is a very important task on both practical and theoretical grounds. The aim of the article is to determine the rational design parameters of variable pitch screw of extruder in areas for loading and pressing of processed feed material on the basis of sunflower cake. At the initial stage, the design parameters of variable pitch screw of extruder in the area for loading of processed feed material were considered. At the next stage, the process of its compaction and compressing by means of screw was considered. As a result of theoretical researches of variable pitch screw of the KMZ-2 extruder, it was found that the density increasing of the processed feed material on the basis of sunflower cake is proportional to the decreasing of pitch of screw flight. The density of processed feed material depends on its physical and mechanical properties.

Biomechanical Study Examining the S2 Alar Iliac Screw Insertional Torque

Introduction Prior biomechanical studies have examined the role of the iliac screw in lumbosacral fixation [Lebwohl, 2002; Cunningham, 2010] and while found to be significant, the ideal screw device and fixation technique have yet to be identified. An initial effort to define this biomechanical fixation includes measurements of current screw insertion torque across screw length was developed. The objective of this study was to measure the intraoperative torque required to place an S2-Alar iliac screw for spino-pelvic fixation. This fixation method often results in variable screw fixation strength and an improved understanding of the local torques required along the length of the screw will aid in improving this surgical fixation. Materials and Methods This IRB approved study involves obtaining informed consent of patients receiving long spinal fusions either for adult deformity. The surgical trajectory for the S2-Iliac screw will be identified as is currently practiced using O-arm Stealth Navigation. Next, the insertion torque of the iliac screw will be measured using the standard driver handle fitted with a torque cell sensor by the surgeon under 3D navigation (Stealth). Results There were 6 patients who underwent spino-pelvic fixation. 12 S2-Iliac screws were placed however Insertional torque was recorded in only 6 screws. Screw maps show that peak torques range from 0.71 to 9.73 Nm. Highest torques recorded were when the head of the screw approached the bone during insertion. These peak torques recorded are 1.91 times higher than Iliac screw insertional torques reported in a previous study. Conclusion Peak insertional torques range from 0.71 to 9.73 Nm and occurred as head of the screw approached the bone during insertion. However higher insertional torques were not recorded because it went beyond the capacity of the driver.

Design of variable screw pitch rib snapping roller and residue cutter for corn harvesters

The blocking between two snapping rollers will seriously constrict the harvesting efficiency for corn harvester. A variable screw pitch rib snapping roller was developed to solve this problem. The comparative experiment between fixed screw pitch rib snapping rollers and variable screw pitch rib snapping rollers illustrated that variable screw pitch ribs can avoid corn-stalk blocking effectively, and it can improve working efficiency by 56.7%. Conservation tillage with standing corn residue was testified that it had a strong control of soil wind erosion. In order to implement this mode of conservation tillage at a production scale, a cutter was developed in this study. Subsequently, two experiments were conducted, one was to test the cutting ratio (defined as the totally cut off stalk population divided by total stalk population), and the other one was to test standing-residue height. The experiment results showed that the mean cutting ratio increased significantly (p<0.05) along with increasing height of cutter-head above the ground (cutting height); the cutting ratio's mean value increased significantly (p<0.05) along with the decreasing angle between the cutter-head and the ground (cutting angle). The average standing-residue height increased along with the increase of cutting height from 300 mm to 500 mm. The average standing-residue height increased significantly (p<0.05) along with the decrease of cutting angle from 15° to 0° . Therefore, the newly designed snapping roller can improve the harvesting efficiency and prolong the working life of the cutting table; and the cutter can promote the popularization of the conservation tillage with standing corn residue in Northeast China.

New Manufacturing Technology for Variable Pitch and Variable Screw Profile Worms

One relatively new variant in gear transmissions is the rolling gear boxes. The rolling transmission wheels have variable pitch and variable screw profile surface section. In this paper it is presented the geometry of used helically surfaces and one new machining technology developed by our team. It is used the method of high machining, with high precision turning, which is a promising solution. The profile manufacturing can only be made on high precisions turning. The experimental researches were realized at the Direct-Line Ltd. in Budapest.

The Experimental Study on the Carbon Black Weighing and Discharging Process

In this paper the development trend of mixer feeding system is discussed first. Then against the problem of inaccuracy in automatic weighing and feeding of carbon black and powders which occurs frequently, we suggest that converter motor be used in screw feeder, and that electric heating and variable screw pitch be adopted. We did a series of experiments with the weighing system, and give some recommendations. Discharging is also described in detail. Finally, we provide further suggestions to avoid weighing inaccuracy of discharging system or fluctuations in feeding time and accuracy caused by material adhesion and so on, so that mixing quality can be improved and mixing cycle can be shortened.

Bi-Zone Modelling and Simulation of an Extrusion Process with Variable Screw Speed

This paper presents a non-linear infinite dimensional bi-zone model of an extrusion process through the representation of two systems of conservation laws coupled by a moving interface. The interconnection is performed under the assumption of constant viscosity along the extruder. In order to illustrate the behaviour of the model, the finite volume method is extended by using a color function to deal with a moving interface. Some simulations with variable screw speed are presented in order to illustrate the behaviour of the proposed model.

Effect of Selected Parameters on Process Efficiency and Energy Consumption During the Extrusion-cooking of Corn-rice Instant Grits

Abstract More and more people begin to pay attention to how foodstuffs are produced. Due to the changing lifestyle, consumers seek products that do not require long preparation. The extrusion-cooking process responds to this type of applications with an easy management of processing promising product stability and quality. Extrusion-cooking involves the extruding of granular material under high pressure and high temperature. Such a method of treatment of raw materials makes extrudates produced from natural ingredients, i.e. corn or rice, suitable for direct consumption and guarantees their prolonged shelf-life. In our study, mixtures for instant grits were prepared from corn with a rice additive of 25% and 50%. Extrudates were prepared using a single-screw extruder TS-45 (L/D=12:1). The range of the temperatures of the extrusion process was 125/130/135 °C. The process was carried out with the variable screw rotation speed of 80, 100 and 120 rpm. This paper presents the results of process efficiency and energy consumption during the extrusion-cooking of instant corn-rice grits. Based on a bidirectional analysis of variance, the process efficiency, regression equation and correlation coefficients were determined for evaluating the impact of the processing conditions on selected properties.

Posterior instrumentation improves the stabilities of Brantigan and Bagby and Kuslich (BAK) methods of posterior lumbar interbody fusion across the L4–L5 segments in a cadaveric model

BackgroundThe Brantigan and Bagby and Kuslich (BAK) cages for posterior lumbar interbody fusion have different geometric characteristics. However, both cage designs have been demonstrated to be helpful in restoring disc space across spinal motion segments in clinical observations. This study was designed to compare the biomechanical performance of these devices at one-motion segments and to determine the effects of posterior instrumentation on their stabilities. MethodsEight intact fresh human cadaver spines (L2-S1) were affixed within a testing frame for in vitro biomechanical testing: four randomly assigned spines for the BAK cage group and four for the Brantigan cage group. For each spine, the three-dimensional load-displacement behavior of each vertebra was quantified using the Selspot II Motion measurement system during the following steps: (1) intact state; (2) destabilization after laminectomy and discectomy across L4-L5; (3) stabilization using a pair of BAK cages or Brantigan cages; and (4) additional stabilization using variable screw plates (VSP) across L4-L5. ResultsThe Brantigan cage alone did not show satisfactory results in improving the stability of one-motion segment destabilized spines in left and right axial rotation. However, the BAK cages appeared to provide significant stability in extension, flexion, left and right lateral bending, and left axial rotation. After implanting the additional posterior instrumentation, both cages provided similar and significantly improved stabilities. ConclusionAlthough the results indicate that the Brantigan cage did not provide satisfactory improvement in the stabilities as the BAK cage in the one-motion segment model, implantation with additional posterior instrumentation may significantly improve the stabilities and reduce the differences between the two cage designs.

Radiologic changes of anterior cervical discectomy and fusion using allograft and plate augmentation: comparison of using fixed and variable type screw.

ObjectiveTo evaluate radiologic result of anterior cervical discectomy and fusion with allobone graft and plate augmentation, and the change of radiologic outcome between screw type and insertion angle.MethodsRetrospective review of clinical and radiological data of 29 patients. Segmental angle, height and screw angles were measured and followed. The fusion rate was assessed by plain radiography and CT scans. We divided the patients into two groups according to screw type and angles. Group A: fixed screw, Group B: variable screw. Interscrew angle was measured between most upper and lower screws with Cobb's methods.ResultsOverall fusion rate was 86.2% on plain radiography. Fusion was also assessed by CT scan and Bridwell's grading system. There was no difference in fusion and subsidence rates between two groups. Subsidence was found in 5 patients (17.2%). Segmental lordotic angle was increased from preoperative status and maximized at the immediate postoperative period and then reduced at 1 year follow up. Segmental height showed similar increase and decrease values.ConclusionACDF with allograft and plate showed favorable fusion rates, and the screw type and angle did not affect results of surgery.

Badania efektywnosci dzialania wytlaczarki nowej generacji. Cz. III. WSPOLDZIALANIE TULEI OBROTOWEJ ZE STREFA ROWKOWANA CYLINDRA

The effect of application of the rotational sleeve of the barrel cooperating with grooved barrel zone in the single screw plasticizing system on the course of low density polyethylene (PE-LD) extrusion process was determined. Research was conducted on a special test stand with an extruder equipped with plasticizing system of modular structure, containing a segment with a rotating sleeve of the barrel and a grooved cylinder zone, interchangeably, with six and eight rectilinear grooves. Selected parameters characterizing the extrusion process were determined during the extrusion of PE-LD with a variable screw speed and barrel sleeve rotation speed. It was found that the use of a grooved cylinder zone cooperating with a rotating sleeve of the barrel in the plasticizing system has a significant impact on the effectiveness of sleeve and the course of the extrusion process. Increasing the polymer mass flow rate with rotation speed of the sleeve is in the whole range screw speed test, which was not observed in the case of a uniform zone geometry, cylindrical without grooves.

Some functional properties of extruded acha/soybean blends using response surface analysis

The feed, comprising of acha flour and raw full fat soybean flour were mixed in ratios of 0:100, 12.5:87.5, 25:75, 37.5:62.5 and 50:50 of soybean flour to acha flour. The feed moisture content was adjusted to 15, 20, 25, 30 and 35% levels. Extrusion was carried out in a laboratory single screw extruder with variable screws and heaters following a 4K central composite (CCD) rotatable and nearly orthogonal design that required 36 extrusion runs. The extruder screw speed was varied at 90, 120, 150, 180 and 210 rpm while the extruder barrel temperature was adjusted to 100, 125, 150, 175 and 200°C. Effects of feed composition (FC), feed moisture content (FMC), extruder screw speed (SS) and extruder barrel temperature (TP) on extrudate bulk density (BD), browning index (BI) and expansion ratio (ER), were evaluated. Results showed that the BD ranged from 1.39 to 9.48 g/m3 while the BI ranged from 0.60 to 5.72. Extrudate expansion ratio ranged from 2.75 to 6.80. The 2nd order polynomial was adequate in modeling the dependence of BD, ER and BI on the extrusion variables. The cross product effects of the process variables had significant (P ≤ 0.05) effects on BD and BI, while the quadratic effect of feed composition had the greatest (P ≤ 0.00) effect on the expansion ratio. Predicted values were very close to the experimental values, making the model ideal for prediction of the dependence of the extrudate functional properties on the extrusion variables. Key words: Blends, acha, soybeans, response surface, extrusion.

Effect of screw design on hopper drawdown of spherical particles in a horizontal screw feeder

Screw feeders are used to remove material from hoppers and bins at a controlled rate. The evenness of the flow in the bin depends on the drawdown pattern, which in turn depends on the screw and hopper design, shape of the particles and wall friction effects. A key design requirement is to ensure that a progressive increase in the screws volumetric capacity is achieved along the entire length of the hopper's opening so as to produce even drawdown. If this is not achieved then compositional variations in the outgoing stream and other operational problems (such as caking) can be created. Screw designs to date have been generally based on analytical models and at times the predicted flow pattern is not achieved. In this study, the Discrete Element Method (DEM) is used to predict particle transport in a horizontal screw feeder system for a range of conventional screw designs including a variable screw pitch, variable screw flight outside diameters and variable core diameters. The influence of screw choice on the particle mass flow rate, the evenness of particle drawdown from the hopper, power consumption, screw wear and wall friction variations are all investigated. Important features captured by DEM that are not accounted for by the analytic model and which vary strongly between competing screw designs, include the particle circulation in the hopper, shearing of the particle bed in the trough just outside the screw and the spatially varying particle force along the hopper which leads to non-uniform drawdown and to the existence of large stagnant or slow moving zones. The screw design and consequent flow patterns also strongly affect the power draw with variations up to a factor of three and screw wear with large changes in their distribution and magnitude. Finally, the surface frictional properties of the screw are shown to strongly influence the rate of bed compaction within and along the screw leading to strong variation in mass flow rate, uniformity of drawdown and power draw.

Study on the Computer Numerical Control Process of Variable Pitch, Groove Depth and Groove Width Screw

The article introduces three design techniques of variable pitch &amp; groove depth &amp; groove width screw. We found parameterized mathematical model of the type of heterotypic screw by analyzing and computing. Then it can realize to CNC machining of variable pitch &amp; groove depth &amp; groove width screw on lathe.

The Effect of Interference Screw Diameter on Fixation of Soft-Tissue Grafts in Anterior Cruciate Ligament Reconstruction

The purpose of this study was to evaluate the effect that interference screw diameter has on fixation strength of a soft-tissue anterior cruciate ligament (ACL) graft. We prepared 32 fresh-frozen bovine tibiae with 9-mm ACL tibial tunnels. Accompanying 9-mm soft-tissue bovine Achilles grafts were also prepared. Bioabsorbable interference screws of increasing diameters were used for tibial fixation. There were 4 groups, consisting of 8-, 9-, 10-, and 11-mm screws for fixation of the 9-mm graft in the 9-mm tunnel. Tensile testing and cyclic loading from 50 to 250 N at 2 Hz for a total of 1,500 cycles were performed with a hydraulic biaxial materials testing machine. Graft slippage was measured with a video analysis technique with photo-reflective markers. At the end of cyclic testing, the grafts were loaded to failure, and the ultimate strength was recorded. All grafts failed at the tendon-bone-screw interface. The ultimate strength (+/- SD) was greatest for the 11-mm screw (624 +/- 133 N), with slightly decreased strength for the 10-mm (601 +/- 54 N), 9-mm (576 +/- 85 N), and 8-mm (532 +/- 185 N) screws. Graft slippage (+/- SD) was least for the 9-mm screw (2.65 +/- 2.38 mm). There were no statistically significant differences in ultimate strength and graft slippage between screws (P = .45 and P = .34, respectively). All interference screws tested provided adequate fixation strength. The results of this study show no statistical significance for ultimate strength or graft slippage with variable screw diameter. Aperture fixation with the interference screw technique provides adequate stability for soft-tissue grafts in ACL reconstruction. Although no statistical significance was found, there was a trend toward less graft-site motion when we used a screw diameter equal to tunnel size.

NC Milling of Profiled Screw

Machining of the variable pitch screw is difficult in mechanical manufacturing and that of variable pitch and depth screw is more difficult.This paper argues about applying macro program to machine profiled screw in NC milling machine tool and the result is of satisfaction.This provides another method for the machining of profiled screws.