Pitch Screw Research Articles

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.

Metrological atomic force microscope using a large range scanning dual stage

We developed a metrological atomic force microscope (MAFM) using a large range scanning dual stage and evaluated the performance in the measurement of lateral dimension. AFMs are widely used in nanotechnology for very high spatial resolution, but the limitation in measurement range should be overcome to expand its application in nanometrology. Therefore, we constructed new MAFM having a large measurement of 200 mm × 200 mm by using a dual stage and an AFM head module. The dual stage is composed of a coarse and a fine stage to obtain large scanning range and high resolution simultaneously. Precision surfaces and PTFE sliding pads guide the motion of coarse stage, drove by a fine pitch screw and DC motors. Flexure hinges and PZT actuators are utilized for the fine stage. Multi-axis interferometers measure the five degrees of freedom motion of the dual stage for the position control and the compensation of parasitic angular motions. The vertical displacement of AFM tip is measured by a built-in capacitive sensor in the AFM head module within the range of 38 µm. The performance of the dual stage was evaluated and the expanded uncertainty (k = 2) in the measurements of 1-D displacement L was estimated as \( U(L) = \sqrt {(2.8nm)^2 + (3.0 \times 10^{ - 7} \times L)^2 } \). The relative uncertainty in pitch measurement was less than 0.02 % and the improvement of accuracy was verified by comparing with other MAFM, which are mostly due to the expansion of scan range and the compensation of angular motion. To enhance the performance, we will reduce the vibration and examine the motion of stage in the vertical direction during a long range scan.

Holding power of variable pitch screws in osteoporotic, osteopenic and normal bone: Are all screws created equal?

Introduction Biomechanical properties of four different commercially available small fragment cannulated screws (Twin fix (Stryker, Freiburg, Germany), Herbert, (Zimmer, Warsaw, USA), Omnitech (Unimedical, Torino, Italy), Barouk (Depuy, Warsaw, USA)), with variable pitch, used for fracture fixation were compared. Materials and methods Polyurethane foam blocks of three different densities with mechanical properties similar to osteoporotic, osteopenic and normal bones were used to conduct the tests. Each screw was tested for pushout and pullout holding power after a primary insertion and for pullout after a repeated insertion into the respective foam blocks. Results The mean pullout and pushout strengths of all screws correlated to the foam density, and were significantly ( p < 0.001 and <0.001, respectively) better in foam with higher density. The mean pullout strength of each screw was consistently lower after reinsertion into the osteoporotic, osteopenic and normal bone densities by 4–30%, when compared to the index insertion (Fig. 4b). Yet, this difference was not found to be statistically significant ( p = 0.23). The Barouk screw performed significantly ( p < 0.0001) better than the other screws in all three different densities of foam for both for pushout and pullout after index insertion as well as for pullout tests after reinsertion. Conclusion The holding power of screws is directly correlated to bone density, thread design and number of threads engaging the bone. Reinsertion through the same hole could reduce the ultimate pullout strength. The surgeon should consider the advantages and disadvantages of each implant, depending on the clinical situation and choose accordingly.

Biomechanical Properties of New Mini Compression Screws

The aim of the current study was to compare the compression forces achieved by the new commercial mini compression screws in cortical and cancellous bone. The following screws were tested: AO partially threaded 4-mm cancellous screw, AO 3.5- and 2.7-mm cortical screws (Synthes - USA) , self-tapping cannulated 3-mm VisAntares (EOS - France), 3- and 2.3-mm Omnitech (Biotech - France), 3-mm Barouk (DePuy - France), and 3-mm Bold screws (Newdeal - France). The compression forces of screws in bone were tested using a load cell between pieces of longitudinally-split sheep tibias as a cortical and cancellous bone model. The AO 3.5-mm, 2.7-mm cortical and 4.0-mm partially threaded cancellous headed screws provided significantly (p < = 0.05) better compression forces than all the tested headless screws, both in cortical and cancellous bone. A loss of compression was noted when the headless screws were totally countersunk. The cortical and cancellous screws with heads provided superior compression than headless screws. Headed screws may be preferable to headless differential pitch screws in situations where compression is important ie, arthrodeses or fracture fixation. Care should be taken not to countersink the headless screws during insertion into cortical bone.

Geometrical method to determine the reciprocal screws and applications to parallel manipulators

SUMMARYScrew theory has demonstrated its wide applications in robot kinematics and statics. We aim to propose an intuitive geometrical approach to obtain the reciprocal screws for a given screw system. Compared with the traditional Plücker coordinate method, the new approach is free from algebraic manipulation and can be used to obtain the reciprocal screws just by inspecting the structure of manipulator. The approach is based on three observations that describe the geometrical relation for zero pitch screw and infinite pitch screw. Based on the observations, the reciprocal screw systems of several common kinematic elements are analyzed, including usual kinematic pairs and chains. We also demonstrate usefulness of the geometrical approach by a variety of applications in mobility analysis, Jacobian formulation, and singularity analysis for parallel manipulator. This new approach can facilitate the parallel manipulator design process and provide sufficient insights for existing manipulators.

Effect of tool geometry on tool wear characterization and weld formation in friction stir welding of 316L stainless steel

316L stainless steel plate was friction stir welded using PCBN tools. The effect of tool shoulder profile and tool probe profile on tool wear characterization and weld formation was investigated. Two different shoulder profiles (screw with different pitches) with four different tool probe profiles (two different probe end shapes and two different probe lengths) have been used to fabricate FSW zone. Experimental results show that the tools with narrow pitch screw shoulder profile produce deeper FSW zone compared to the tools with wide pitch. The tools with spiral probe profile produce deeper FSW zone compared to the tools with chamfer probe profile. The tools with wide pitch screw shoulder profile is apt to produce lower working loads. The wear resistant of tools with chamfer probe profile is significantly higher than that of tools with spiral probe profile. The relation between tool geometries and tool wear and weld formation is discussed.

Biomechanical Comparison of a Fully Threaded, Variable Pitch Screw and a Partially Threaded Lag Screw for Internal Fixation of Type II Dens Fractures

Stiffness and load to failure were studied in a human cadaver model of Type II odontoid fractures stabilized with either a single partially threaded lag screw and washer or a headless fully threaded variable pitch screw. To determine whether a headless fully threaded variable pitch screw provides biomechanically superior fixation of Type II odontoid fractures in comparison with a partially threaded, cannulated lag screw and washer. Surgical treatment of Anderson and D'Alonzo Type II odontoid fractures is often performed using a partially threaded cannulated screw and washer. Reported clinical failure rates of this construct are as high as 20%. This technique requires perforation of the cortex of the tip of the dens, placing the brainstem and vertebrobasilar circulation at risk. A headless fully threaded variable pitch screw has not been described for this application. A transverse osteotomy was created at the base of the dens in 16 human cadaver C2 specimens and stabilized using either a headless fully threaded variable pitch screw or a partially threaded cannulated lag screw and washer. Specimens were loaded to failure under a static, posteriorly directed force applied to the surface of the dens. Stiffness and load to failure were measured and the mode of failure for each specimen was determined. Stiffness and load to failure were greater for the headless, fully threaded variable pitch screw compared with the partially threaded lag screw and washer. The mode of failure for all specimens was via anterior screw cut-out at the C2 vertebral body. A headless, fully threaded variable pitch screw was biomechanically favorable in comparison with a partially threaded lag screw and washer in this cadaver model of Type II dens fractures. The mode of failure at the C2 vertebral body may have important implications for further improvements in construct strength.

Internal Fixation of Juvenile Osteochondritis Dissecans Lesions of the Knee

Background Operative techniques for the management of juvenile osteochondritis dissecans lesions of the knee include drilling, internal fixation, fragment removal, and chondral resurfacing. Purpose To evaluate the functional and radiographic outcome of internal fixation of juvenile osteochondritis dissecans lesions of the knee. Study Design Case series; Level of evidence, 4. Methods The study design was a retrospective case series. Twenty-six knees in 24 skeletally immature patients underwent internal fixation of osteochondritis dissecans lesions. Mean follow-up was 4.25 years (range, 2-14.75 years). Mean patient age was 14.7 years (range, 11-16 years). There were 13 boys and 11 girls. Lesions were graded per the Ewing and Voto classification, with 9 stage II lesions (fissured), 11 stage III lesions (partially attached), and 6 stage IV lesions (detached). Methods of internal fixation included variable pitch screws (n = 11), bioabsorbable tacks (n = 10), partially threaded cannulated screws (n = 3), and bioabsorbable pins (n = 3). Mean follow-up was 4.25 years (range, 2.0-14.75 years). Results Healing occurred in 22 of 26 lesions (healing rate, 84.6%). There was no significant difference in healing rate for lesion location, fixation method, or lesion grade. In fact, all 6 stage IV (detached) lesions healed. The mean postoperative Lysholm score was 85.8, mean postoperative International Knee Documentation Committee score was 82.6, and mean postoperative Tegner activity level was 7.4. Mean time to healing was 6 months. Eight patients underwent additional procedures: 4 for nonunion, 1 for hemarthrosis, and 3 for elective screw removal. Conclusion Given the relatively high healing rate, good functional outcome, and low complication rate, the authors advocate internal fixation of unstable juvenile osteochondritis dissecans lesions of the knee, even for detached lesions and in patients with a history of surgery for the osteochondritis dissecans lesion.

Bending Stiffness and Pull-Out Strength of Tapered, Variable Pitch Screws, and 6.5-mm Cancellous Screws in Acute Jones Fractures

Stabilization of fifth metatarsal Jones fractures with intramedullary screws is popular, particularly in athletes, because nonoperative treatment involves prolonged casting and a distinct risk of nonunion or delayed union. Conventional lag screws of various diameters are routinely used for Jones fracture fixation. More recently, tapered, headless, variable pitch screws have become available as an option. These screws have the advantage of not having a protruding screw head, but information regarding their performance in Jones fracture fixation is limited. To determine whether differences exist in the mechanical integrity of fifth metatarsals fixed with each type of screw, this study was designed to compare Jones fracture fixation with 6.5-mm partially-threaded lag screws and headless, tapered, variable pitch compression screws with a 4-mm leading-thread diameter and 5-mm trailing-thread diameter. Simulated Jones fractures were created in 20 matched pairs of fresh-frozen fifth metatarsals. One bone from each pair was stabilized with a tapered, variable pitch screw, and the contralateral with a 6.5-mm partially-threaded cancellous lag screw. The stiffness in lateral-to-medial bending of the resulting constructs and the resistance of the screws to pulling out of the distal fragment were quantified. There was no demonstrable difference in bending stiffness between metatarsals fixed with the two types of screws (p = 0.688). The 6.5-mm screw provided significantly higher resistance to pull-out (p = 0.001). Headless, tapered, variable pitch compression screws of the size tested are not entirely comparable to 6.5-mm lag screws in this application. They are effective in resisting bending but do not offer equivalent resistance to thread pull-out.

O.072 Bioabsorbable fixation devices in anterior skull base fractures

Most commonly seen in the knee, elbow and ankle, osteochondritis dissecans (OCD) represents an underlying bony fragment separation from the subchondral region with or without articular involvement. Osteochondral or chondral injuries are associated with trauma and can occur in any joint. Unstable OCD and traumatic osteochondral or chondral lesions demand operative treatment, particularly if displaced. Principles of treatment include anatomic reduction, rigid fixation, enhancement of blood supply, and restoration of articular congruity. Internal fixation can be achieved through open or arthroscopic approaches with one of many devices including cannulated screws, metal pins, and bioabsorbable pins. Cannulated screws can provide rigid fixation and compression across lesions. AO screws must eventually be removed to avoid articular damage and allow weightbearing. Headless, variable pitch screws, however, can be placed below the articular margin, do not need to be removed, and provide compression because of their differential pitch designs. Metal pins in the form of Kirschner wires (K-wire) can be placed antegrade through the lesion, or retrograde from behind the lesion. K-wires can potentially migrate, bend or break, and they must eventually be removed. Bioabsorbable pins have several advantages including bioresorbable properties obviating the need to remove them, low-profile designs, and a decrease in stress-shielding compared with metal implants. The most common reported complication with bioabsorbable pins is a reactive synovitis. Newer devices recently described for OCD lesions of the capitellum include pull-out wires and dynamic staples. The purpose of this article is to present different options for operative fixation of these lesions.

Effect of thread pitch on pull‐out strength of laparoscopic myoma screws

The purpose of this study was to evaluate the effect of thread-pitch on pull-out strength and bending strength of buttress-thread screws designed for laparoscopic myoma extraction. The ultimate failure load of four 5-mm diameter buttress-thread screws with 3-, 4-, 5-, and 6-mm thread pitch, 40 mm in thread-length were examined on fresh myoma specimens. The myoma tissue at each traction site was evaluated histologically to determine its density. The critical minimal pull-out strength based on moderate-density myoma group was estimated. The bending strength was also determined for each screw. A wide range of ultimate failure loads with a mean +/- SE of 129.3 +/- 5.5 N (range, 30.4-255.7 N) for all screws and tissue densities was recorded. In moderate-density myomas, the mean ultimate failure loads decreased linearly with increasing thread-pitch from 3 mm (148.0 +/- 9.5 N) to 6 mm (119.8 +/- 9.4 N) (test for trend: P < 0.05). Based on the criterion of a minimum pull-out strength of at least 50 N in not less than 95% of tractions in medium-density myomas, the 3-mm and 5-mm pitch screws were found to have acceptable properties. The 5-mm pitch screw had less thread-turn than the 3-mm pitch for the same thread-length and would need less application time. The bending strength also decreased with increasing thread pitch from 3 to 5 mm, then became stable at around 15 N. The pull-out strength of soft tissue buttress-thread screws decreased linearly with increasing thread-pitch. Thread-pitch should be considered when designing laparoscopic myoma-screws.

Effect of diameter of the drill hole on torque of screw insertion and pushout strength for headless tapered compression screws in simulated fractures of the lateral condyle of the equine third metacarpal bone

To compare variables for screw insertion, pushout strength, and failure modes for a headless tapered compression screw inserted in standard and oversize holes in a simulated lateral condylar fracture model. 6 pairs of third metacarpal bones from horse cadavers. Simulated lateral condylar fractures were created, reduced, and stabilized with a headless tapered compression screw by use of a standard or oversize hole. Torque, work, and time for drilling, tapping, and screw insertion were measured during site preparation and screw implantation. Axial load and displacement were measured during screw pushout. Effects of drill hole size on variables for screw insertion and screw pushout were assessed by use of Wilcoxon tests. Drill time was 59% greater for oversize holes than for standard holes. Variables for tapping (mean maximum torque, total work, positive work, and time) were 42%, 70%, 73%, and 58% less, respectively, for oversize holes, compared with standard holes. Variables for screw pushout testing (mean yield load, failure load, failure displacement, and failure energy) were 40%, 40%, 47%, and 71% less, respectively, for oversize holes, compared with standard holes. Screws could not be completely inserted in 1 standard and 2 oversize holes. Enlarging the diameter of the drill hole facilitated tapping but decreased overall holding strength of screws. Therefore, holes with a standard diameter are recommended for implantation of variable pitch screws whenever possible. During implantation, care should be taken to ensure that screw threads follow tapped bone threads.

Kinematic optimization of ball-screw transmission mechanisms

Abstract The paper proposes a method for the kinematic optimization of transmission mechanisms, where non-circular (NC) gears are used to perform a mechanical control on the output motion. The investigation presented here deals with the motion control of a ball-screw transmission mechanism. The objective is lowering the peak acceleration value of the screw, by designing a pair of variable radius gears as a driving mechanism. The kinematic characteristics of the ball-screw mechanism are analyzed by means of non-dimensional motion equations in order to formulate the optimization problem. A genetic algorithm (GA) is then implemented to optimize the objective function, and a penalty method is used to fulfil the design rules. The kinematic analysis of the optimal mechanism revealed a 37% reduction of the peak acceleration of the screw in comparison with a constant pitch screw, operated at a constant speed. A kinematic simulation is used to validate the method.

Oil extraction of oleic sunflower seeds by twin screw extruder: influence of screw configuration and operating conditions

The objective of this study was to investigate the effects of screw configuration, position of screw elements and spacing between them allowing to realize oil extraction of oleic sunflower seeds on a twin-screw extruder. Experiments were conducted using a co-rotating twin-screw extruder (Model Clextral BC 45, France). Twelve screw profiles were examined to define the best performance (oil extraction yield, oil quality, mean residence time, and thermo-mechanical energy input) by studying the influence of operating conditions temperature pressing, screw rotation speed and seed input flow rate. Generally, the position and spacing between two screw elements affected oil extraction yield. An increase of oil extraction yield was observed when the reversed screw elements were configured with increased spacing between elements or/and with smaller pitch screw. In addition, more oil extraction yield was produced as the temperature pressing, screw rotation speed and seed input flow rate were decreased. The higher oil extraction yield was obtained under operating conditions 80 °C, 60 rpm and 24 kg/h. Furthermore, the operating parameters influenced energy input and mean residence time of matter. Both energy input and mean residence time increased when the temperature pressing increased. However, increase of screw rotation speed and seed input flow rate decreased mean residence time. Effect of the operating parameters on oil quality was unimportant. In all experiments tested, the oil quality was very good. The acid value was below 2 mg KOH/g of oil and total phosphorus content was very poor, below 40 mg/kg.

Internal fixation devices for the treatment of unstable osteochondritis dissecans and chondral lesions

Most commonly seen in the knee, elbow and ankle, osteochondritis dissecans (OCD) represents an underlying bony fragment separation from the subchondral region with or without articular involvement. Osteochondral or chondral injuries are associated with trauma and can occur in any joint. Unstable OCD and traumatic osteochondral or chondral lesions demand operative treatment, particularly if displaced. Principles of treatment include anatomic reduction, rigid fixation, enhancement of blood supply, and restoration of articular congruity. Internal fixation can be achieved through open or arthroscopic approaches with one of many devices including cannulated screws, metal pins, and bioabsorbable pins. Cannulated screws can provide rigid fixation and compression across lesions. AO screws must eventually be removed to avoid articular damage and allow weightbearing. Headless, variable pitch screws, however, can be placed below the articular margin, do not need to be removed, and provide compression because of their differential pitch designs. Metal pins in the form of Kirschner wires (K-wire) can be placed antegrade through the lesion, or retrograde from behind the lesion. K-wires can potentially migrate, bend or break, and they must eventually be removed. Bioabsorbable pins have several advantages including bioresorbable properties obviating the need to remove them, low-profile designs, and a decrease in stress-shielding compared with metal implants. The most common reported complication with bioabsorbable pins is a reactive synovitis. Newer devices recently described for OCD lesions of the capitellum include pull-out wires and dynamic staples. The purpose of this article is to present different options for operative fixation of these lesions.

Screening of variables for extrusion of rice flour employing a Plackett–Burman design

A screening experiment with ten variables employing a Plackett–Burman experimental design was conducted on extrusion of rice flour. The variables include, hardware variables (mixing disk and reverse pitch screw elements), feed variables (moisture, sugar, salt and amylose contents, and particle size) and operating variables (barrel temperature, feed rate and screw speed). The response functions were extrusion characteristics (torque, specific mechanical energy and residence time), product attributes (water solubility index, water absorption index, and bulk density, peak viscosity, hot paste viscosity and cold paste viscosity). The response functions were highly affected by the hardware variables. A Plackett–Burman experimental design can serve as a useful tool for screening large numbers of variables and reducing the number of experiments.

On the design of rotating speed functions to improve the acceleration peak value of ball–screw transmission mechanism

The objective of this paper is to design a polynomial rotating speed function for the crank of a ball–screw transmission mechanism with the aim of lowering the peak acceleration value of the screw. For the purpose of analyzing the kinematic characteristics of the mechanism, the non-dimensional motion equations of the ball–screw transmission mechanism were derived. From the analysis, a set of design rules was devised and a polynomial rotating speed function of degree 6 was designed. It was revealed from computer analysis that as the rotating speed function was applied to the crank input, the peak acceleration value of the constant pitch screw, operated at a constant speed, was decreased by 20%. For comparison purpose, a computer-controlled test rig for characterizing the kinematics of a ball–screw transmission mechanism was also designed and manufactured. The results from the tests and the analytical model were comparable.

A biomechanical comparison of headless tapered variable pitch and AO cortical bone screws for fixation of a simulated lateral condylar fracture in equine third metacarpal bones.

To compare drilling, tapping, and screw-insertion torque, force, and time for the 4.5-mm AO and 6.5-mm Acutrak Plus (AP) bone screws, and to compare the mechanical shear strength and stiffness of a simulated complete lateral condylar fracture of the equine third metacarpal bone (MC3) stabilized with either an AO or AP screw. In vitro biomechanical assessment of screw-insertion variables, and shear failure tests of a bone-screw-stabilized simulated lateral condylar fracture. Eight pairs of cadaveric equine MC3s Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials-testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Standardized simulated lateral condylar fractures were stabilized by either an AO or AP screw and tested in shear until failure. A paired t test was used to assess differences between screws, with significance set at P < .05. Insertion and mechanical shear testing variables were comparable for AO and AP insertion equipment and screws. The 6.5-mm tapered AP screw can be inserted in equine third metacarpal condyles and is mechanically comparable with the 4.5-mm AO screw for fixation of a simulated lateral condylar fracture. Considering the comparable mechanical behavior, the potential for less-persistent soft-tissue irritation with the headless design, and the ability to achieve interfragmentary compression by inserting the screw in one hole drilled perpendicular to the fracture plane, the 6.5-mm tapered AP screw may be an attractive alternative for repair of incomplete lateral condylar fractures in horses.

Pumping performance analyses of a turbo booster pump by direct simulation Monte Carlo method

The pumping performance of a new type of turbo booster pump in the free molecular and transitional flow regimes is investigated using the direct simulation Monte Carlo (DSMC) method. The problem is modeled as a 3D channel with variable pitch and ditch depth screw grooves. A real 3D analysis in a rotating frame is proposed to simulate the flow field. Additional terms arising from the Coriolis and centripetal accelerations are formulated, and the variable soft sphere (VSS) model and no time counter (NTC) collision scheme are used. The intermolecular collisions are regarded as inelastic by applying the Larsen–Borgnakke model. Numerical results show good quantitative agreement compared with the experimental data.

Measurement of three‐dimensional velocity field in the translational region of a co‐rotating twin‐screw extruder

AbstractThe velocity field in the screw channels of a co‐rotating twin‐screw extruder was measured using laser Doppler anemometry. Velocity distributions were measured for two screw elements having pitches of 14 and 28 mm, respectively. The magnitude of radial velocity component for both elements was no more than 10% of the magnitude of total velocity. The radial and the axial velocity components were similar for both screw elements. Wider range of tangential velocity values and steeper gradients near the flights were observed for smaller pitch screw element.