Expansion Spring Research Articles

Determination of transient resistance low-current elektric contacts in dusty conditions the contact surfaces

Introduction. Now on transport, in automotive, aviation, space, household and other vehicles the tiny mechanically managed switches are widely used. The small weight and small dimensions belong to their benefits. However bad contact connection can lead to failure of devices on which work of all difficult technique depends. In household appliances it will not lead to serious problems, but for transport failure of contact system can lead to catastrophic consequences. The most important indicator of reliability of microswitches is non-failure operation of work. Failures of microswitches arise because of the thermal, electric, mechanical and chemical phenomena in a transitional zone of electric contacts. Now big distribution was gained by low-current contacts. Refusals and failures in such contacts appear generally because of hit in intercontact space of dust and other pollution, formation of the films which are not collapsing in case of short circuit of contacts, sudden change of force of pressing of contacts because of breakdown of an elastic element or an expansion spring. In article the mathematical model of contact systems in case of failure on the example of modern electronic microswitches of rod type is provided. Purpose. Creation of mathematical model of contact systems at failure on the example of modern electronic microswitches of rod type, research of operation of microswitches in actual practice operation. Methodology. Theoretical methods of research with use of personal electronic computer were applied to achievement of an effective objective. The theory of contact interaction of rough surfaces, the theory of electric contacts, methods of linear algebra, etc. have been used. The program complexes Mathcad, ANSYS were used. In case of pilot studies methods of mathematical statistics were applied. Results. In article the technique of determination of transitional resistance of low-current electric contacts considering possible dust content of contact surfaces, formation of films on surfaces of contacts and change of parameters of a roughness of contact surfaces as a result of plastic deformations is offered. For the studied contacts dependence of probability of failure on concentration of particles of dust is received. Practical importance. The technique described in article allows to determine the transitional resistance of electric contacts both during the normal work, and at failure. Conclusion. Development of mathematical models of contacts at failure gives the chance to estimate reliability of connections in actual practice of work, to choose key parameters of switching elements taking into account possible pollution, and also to develop new and to specify the available techniques of detection of failures.

In situ synthesis of hydroxyapatite for the production of natural rubber/poly(lactide-co-glicolide)/hydroxyapatite composites

Event Abstract Back to Event In situ synthesis of hydroxyapatite for the production of natural rubber/poly(lactide-co-glicolide)/hydroxyapatite composites Teo A. Dick1*, Andrés F. Vasquez1 and Luis Alberto Dos Santos1* 1 Federal University of Rio Grande do Sul, Materials Science and Technology, Brazil Introduction: Previously we have reported studies in a polymer blend consisting of 60 wt.% of Poly(lactide-co-glicolide) (PLGA) and 40 wt.% of natural rubber (NR) obtained from hevea brasiliensis’ latex[1],[2]. A cranial expansion spring was produced and tested in vivo with this material, with successful results[3]. PLGA is a well-recognized resorbable polymer, while NR is little researched for biomedical applications, even being described as improving angiogenesis and wound healing, which has been reported as being consequence of hevea brasiliensis’ serum content[4]. In this work the synthesis method and preliminary characterization of a tri-component material composed of the already described polymer blend and dispersed hydroxyapatite (Hap) are presented. The developed route utilizes the NR in solution in a wet chemical in situ process for Hap synthesis. In a bone repair application the angiogenic characteristics of the natural rubber would provide improved vascularization while the gradual resorption of PLGA would ensure an increasing degree of porosity while continuously provide access to the hydroxyapatite particles. Materials and Method: Composites consisting of PLGA, NR and Hap were produced in situ with the percentages of Hap of 0 wt.%, 10 wt.%, 20 wt.% and 30 wt.%. Highly concentrated solutions of NR in THF were prepared, followed by addition of 0.5 M solutions of Ca(NO3).4H2O and 0.3 M solutions of H3PO4, both in tetrahidrofuran (THF). During the entire process NH4OH was used to maintain a pH higher than 8 in the solution to ensure formation of hydroxyapatite as the only calcium phosphate phase. After aging under agitation for 24 hours, a PLGA solution in THF was added and the mixture was dried. The produced composite was washed in deionized water overnight. The same process of synthesis was performed in absence of NR for comparison, leading to a highly agglomerated product and impossibility of production of the composites. Results and Discussion: Phase analysis by x-ray diffraction and fourier transform infrared confirmed hydroxyapatite as the only calcium phosphate phase present. Differential scanning calorimetry has shown incomplete miscibility between NRL and PLGA and no influence of Hap in thermal properties. Scanning electron microscopy was used to evaluate the degree of agglomeration of Hap particles in the polymer matrix, showing dispersed aggregates with different sizes. Conclusions: The developed route successfully produces PLGA/NR/Hap composites in an in situ process. NR was crucial for particle dispersion, since the process performed in absence of polymer led to agglomeration of particles. The dispersion effect over Hap could be attributed to interaction with polymer chains, or latex biomolecules, or both, but further research is needed for confirmation. CNPq - Brasil. CAPES - Brasil.

Early Effect of Simvastatin Gel on Bone Formation of Orthopaedically Expanded Sagittal Suture of Rabbits

OBJECTIVES: To evaluate early bone-healing effects of local simvastatin application to orthopaedically expanded sagittal suture of rabbits. MATERIALS AND METHODS: A total of 30 male Rabbits of an average weight of 0 .75-1.0 kg and aged 2-3 months were used in this study. The animals were divided into three groups of ten animals each: simvastatin (group I), active control (group II), and passive control (group III). The sagittal suture was expanded with an expansion spring for one week, after that, the expander was removed and replaced with wire retainer for two weeks .At the time of wire retainer placement: Group I received an injection of 0.5mg simvastatin /0.5ml methylcellulose gel over the suture; group II received 0.5 ml of methylcellulose gel subcutaneously over the expanded suture; group III received no treatment. Half of the animals (five animals in each group) were sacrificed after two weeks of retention, and the sutures were prepared for radiological and histological assessment of regenerated bone. In the other half, the wire retainer was removed after two weeks of retention and the relapsed ratio of the expanded suture was calculated one week later. RESULTS: Local application of simvastatin has been found to have a positive influence on bone regeneration of orthopaedically expanded sagittal suture in comparison to control group. The density of the suture in the simvastatin group was significantly higher than control group. The relapse ratio in simvastatin gel treated group was nearly half that of methyl cellulose carrier gel and control groups, the difference was highly significant. CONCLUSION: 0.5 mg simvastatin greatly promote early bone formation of orthopaedically expanded sagittal suture.

The fabrication and clinical application of semi-fixed mandibular lingual arch expansion appliance

Semi-fixed mandibular lingual arch expansion appliance is composed of a mandibular molar band, a keyway and arch expansion spring. The arch expansion spring are used to expand maxillary arch symmetrically or asymmetrically when bolts of the two ends are inset into keyways. Dental arch expansion appliance for 25 patients with mandibular arch stenosis showed that semi-fixed mandibular lingual arch expansion had good effect and could be used to expand mandibular arch.

Axial compression test on ITER-TFMC conductors at room temperature

The superconductor used for the ITER TF Model Coil (TFMC) consists of 720 twisted Nb 3Sn-strands and 360 copper strands, which are cabled around a central spiral and are surrounded by a stainless steel jacket. The conductor is heat-treated at 650 °C in a stainless steel mould. After cool down to room temperature the conductor is found to be elongated by 0.45 mm/m, which can be attributed to the lower shrinkage of Nb 3Sn. This means that the jacket is under tensile stress and the cable under longitudinal compression after cool down. This effect aggravates upon cooling further to the operating temperature. The cable and the jacket can be interpreted as a double spring system, the jacket being the expansion spring and the cable being the compression spring. In order to evaluate and possibly predict such elongations, it is necessary to know the Young's modulus of the cable. Therefore, we investigated samples cut from a dummy conductor, a not heat-treated and a heat-treated TFMC conductor by mechanically compressing them. From the stress–strain diagram the elastic modulus of the cables was determined and found to be about one-tenth of that calculated assuming all components of the cable being fully bonded. The stiffness of the cables turned out to be fairly independent of the state of the cable as all three cables show almost the same modulus. The mechanical compression of the cable is about 8.5 times larger than the measured elongation of the jacket.

Effects of estrogen deficiency on tooth movement after force application: an experimental study in ovariectomized rats

Objective. The aim of this study was to investigate the effects of estrogen deficiency on tooth movement in ovariectomized rats. Material and methods. Forty-two adult female Sprague-Dawley rats were assigned at random to one of the following groups: test group (n=20), ovariectomized rats (or estrogen-deficient rats); control group (n=22), non-ovariectomized rats. Two months after ovariectomy, expansion springs exerting 10 g of force were inserted between the upper central incisors in both groups. The amount of movement was measured daily until tooth movement began and then at intervals of 3 days. The rats were sacrificed 18 days after applying the expansion spring and histomorphometric analysis was performed along the left upper central incisor root towards the apex of the alveolar bone. Results. The amount and speed of movement was observed to be greater in ovariectomized rats. On histomorphometric analysis, osteoblast and osteocyte counts on the pressure side were higher in the non-ovariectomized group than in the ovariectomized group (p<0.001). In contrast, the osteoclast count was significantly higher (p <0.01) in the ovariectomized group than in the non-ovariectomized group. The osteoblast and osteocyte counts were significantly higher (p <0.001) on tension side in the non-ovariectomized group than in the ovariectomized group. Conclusion. Estrogen deficiency increased orthodontic tooth movements but counts of osteoblasts, which are responsible for new bone formation, were lower in regions of tension and of pressure.

Orthodontic Buccal Tooth Movement by Nickel-Free Titanium-Based Shape Memory and Superelastic Alloy Wire

To examine the mechanical properties and the usefulness of titanium-niobium-aluminum (Ti-Nb-Al) wire in orthodontic tooth movement as compared with nickel-titanium (Ni-Ti) wire. The load deflection of expansion springs was gauged with an original jig. The gradient of the superelastic region was measured during the unloading process. Expansion springs comprising the two types of alloy wires were applied to upper first molars of rats. The distance between the first molars was measured with micrometer calipers. The force magnitude of the Ti-Nb-Al expansion spring was lower than that of the Ni-Ti expansion spring over the entire deflection range. The initial force magnitude and the gradient in the superelastic region of the Ti-Nb-Al expansion springs were half those of the Ni-Ti expansion springs. Thus, Ti-Nb-Al expansion springs generated lighter and more continuous force. Tooth movement in the Ni-Ti group proceeded in a stepwise fashion. On the other hand, tooth movement in the Ti-Nb-Al group showed relatively smooth and continuous progression. At 17 days after insertion of expansion springs, there were no significant differences between the Ti-Nb-Al and Ni-Ti groups in the amount of tooth movement. These results indicate that Ti-Nb-Al wire has excellent mechanical properties for smooth, continuous tooth movement and suggest that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti wire.

Response surface optimization of the feed compositions of biodegradable packaging foams

AbstractResponse surface methodology (RSM) was used to analyse the effects of polyvinyl alcohol (PVOH) and calcium carbonate (CaCO3) on the physical and mechanical properties (radial expansion ratio, bulk density, compressibility and spring index) of a biodegradable cushioning extrudate. A rotatable central‐composite design (CCD) was used to develop models for the objective responses. The experiments were run at 125°C with a feed rate of 27.8 l/h, screw speed of 215 r.p.m. and die diameter of 3.92 mm. Responses were most affected by changes in PVOH levels and to a lesser extent by CaCO3 levels. Individual contour plots of the different responses were overlaid. An optimum radial expansion ratio of 3.39, bulk density of 0.065 (g/cm3), compressibility of 32.27(N), and spring index of 0.906 were identified at 36% PVOH and 5% CaCO3. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Study on the Optimum Feed Compositions of Biodegradable Cellular Foams Blend with Talc Powder (Talc)

Response surface methodology (RSM) is used to analyze the effect of polyvinyl alcohol (PVA) and talc powder (talc) on the objective (radial expansion ratio, bulk density, compressibility, and spring index) attributes of a biodegradable cushioning extrudate. A rotatable central composite design (CCD) is used to develop models for the objective responses. The experiments are run at 125 C with a feed rate of 27.8 L/h, a screw speed of 215 rpm, and a die diameter of 3.92 mm. Responses are most affected by changes in PVA levels and to a lesser extent by talc levels. Individual contour plots of the different responses are overlaid, and regions meeting the optimum radial expansion ratio of 3.14, the bulk density of 0.106 g/cm3, the compressibility of 56.12 N, and the spring index of 0.892 are identified at the PVA level of 32% and the talc level of 4%, respectively.

Effects of local administration of clodronate on orthodontic tooth movement and root resorption in rats

Clodronate, a non-N-containing bisphosphonate, strongly inhibits bone resorption and also has anti-inflammatory properties. The purpose of this study was to examine the effect of the local administration of clodronate on orthodontic tooth movement. Both the right and left upper first molars of 26 7-week-old male Wistar rats were moved buccally with a standardized expansion spring. Clodronate solution was injected into the sub-periosteum area adjacent to the left upper molar every third day during the experimental period. The right first molar served as the control. Local injection of clodronate caused a significant (P < 0.001) and dose-dependent reduction in tooth movement in the rats. The number of osteoclasts on the clodronate-injected side was significantly less (P < 0.01) than on the control side. Local clodronate also inhibited root resorption incident to tooth movement. These results suggest that localized use of clodronate could be a useful therapeutic adjunct in orthodontic treatment.

Effects of tensile forces on the expression of type III collagen in rat interparietal suture

The aim was to investigate the direct contribution of mechanically induced stress to synthesized type III collagen in the interparietal suture. Twenty 4-week-old male rats were used as experimental animals. An activated expansion spring was placed across the interparietal suture. After expansion, the parietal bones including the suture were dissected and immunostained for type I and III collagens. Also, a three-dimensional model of the interparietal suture was developed to analyze stress during expansion. The localization of type III collagen in the suture was dependent upon the duration of expansion. Although the control suture exhibited no or little reactivity for type III collagen, it was observed as early as 15 h of expansion in the cambial layers, and was distributed throughout the suture at 50 h of expansion. The time-dependent distribution of type III collagen was fully consistent with that of tensile stresses calculated by the use of a three-dimensional finite-element model. It was concluded that the increases in tensile stress are associated with the synthesis of type III collagen in the suture.

Anchorage and retentive effects of a bisphosphonate (AHBuBP) on tooth movements in rats

The purpose of this study was to examine the effect of 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), a potent blocker of bone resorption, on orthodontic tooth movements in rats. In the first experiment, the right and left upper first molars were moved buccally for 3 weeks with a uniform standardized expansion spring under systemic administration of AHBuBP every other day. The total tooth movement during the 3-week experimental period was 40% of that in the control at a dose of 0.5 mg P/kg. In the second experiment, the right and left upper first molars were first moved buccally for 3 weeks without AHBuBP. The spring was then removed and administration of AHBuBP was initiated. The total relapse movement during the 3-week experimental period was 50% of that in the control at a dose of 0.5 mg P/kg. Results of the first and second experiments were both dose dependent. Histologic examination showed that in the experimental animals fewer osteoclasts appeared on the alveolar bone surface, and both bone resorption and root resorption were inhibited. Inhibition of tooth movement was also observed when AHBuBP was applied topically. These results suggest that AHBuBP could be useful in enhancing anchorage or retaining teeth in orthodontic treatment.

Effects of topical administration of a bisphosphonate (risedronate) on orthodontic tooth movements in rats.

In orthodontics, undesirable movement of anchor teeth during tooth movement and relapse of moved teeth after treatment are the main causes of unsuccessful results. If these tooth movements could be prevented with pharmacological agents, a less complex orthodontic force system and less extensive retention would be required. The purpose of this study was to examine the effect of topical administration of a bisphosphonate (risedronate), a potent blocker of bone resorption, on orthodontic tooth movements in rats. In the first experiment, both the right and left upper first molars were moved buccally with a standardized expansion spring under administration of risedronate. Risedronate solution was injected into the subperiosteum area adjacent to the left upper first molar. The right first molar served as a control with an injection of 0.9% NaCl solution. The topical administration of risedronate caused a significant and dose-dependent reduction of tooth movement after the orthodontic force was applied. In the second experiment, the right and left upper molars were first moved buccally for three weeks. The spring was then removed, and administration of risedronate was begun. The topical administration of risedronate inhibited relapse of the tooth in a dose-dependent manner. The administration of risedronate did not affect either overall growth of the animals or longitudinal growth of tibiae. These results suggest that topical application of risedronate may be helpful in anchoring and retaining teeth under orthodontic treatment.

Electronically controllable vibration damping device

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Shielded Electrohydraulic Lithotripsy of Urinary and Biliary Calculi: A New Possibility

A new transurethral lithotripsy concept, using an electrohydraulically generated shock wave to drive in a jackhammer manner a hollow spring with a metal end cap, was tested in vitro and shown to fragment urinary and biliary calculi effectively. The prototype device was fabricated from a hollow stainless steel expansion spring (1.6-mm outer diameter, 12-mm long). The primary electrohydraulic lithotripter used was the Wolf model 2137.50 (Richard Wolf Medical Instruments Corp.) with a 3.3F probe placed inside the prototype device and securely attached using a short piece of hypodermic tubing. The mechanism worked by confined electrohydraulic discharge, driving the spring and the cap to impact the stone. The results show that shielded electrohydraulic lithotripsy is effective in fragmenting both urinary and biliary calculi and is only 23% less efficient than an unshielded electrohydraulic discharge. However, the advantages to a shielded instrument may be substantial. When the shielded electrohydraulic device was discharged against the experimenter's finger, no pain was felt. Shielded electrohydraulic lithotripsy in the future may be used for ureterolithotripsy without the need for anesthesia or a ureteroscope.