Rotary Clamp Research Articles

Study on anti-galloping efficiency of rotary clamp spacers for eight bundle conductor line

Rotary clamp spacer is a prospective anti-galloping device for bundle conductor lines. The rotation-free clamp of a rotatory clamp spacer allows the connected sub-conductor rotate freely around its axis, which makes ice shape along span uniform and weakens the aerodynamic loads on the iced sub-conductors to diminish or control the galloping. In this paper, the cross-section shapes of accreted ice along sub-conductors, which are connected with rotation-free clamps of a spacer, are numerically modeled, and the aerodynamic coefficients of the iced sub-conductors along span are then simulated by means of the software developed for aerodynamic characteristics of transmission conductors based on the computational fluid dynamics software Fluent. Considering the ice shape distribution along the sub-conductors, the galloping of iced eight bundle conductor lines with different installation schemes of rotary clamp spacers are numerically studied by means of the finite element software ABAQUS. The anti-galloping efficiencies of rotary clamp spacers with different installation schemes under different parameters, including initial wind attack angle, ice thickness, ice accretion angle, span length, conductor type and continuous spans, are evaluated by comparing with dynamic responses of line with fixed clamp spacer under wind loads. Based on the results, optimal schemes to diminish or control galloping of eight bundle conductor lines are proposed.

An aerodynamic anti-galloping technique of iced 8-bundled conductors in ultra-high-voltage transmission lines

Galloping of iced conductors is a kind of self-excited aeroelastic vibration with low frequency and large amplitude causing various damages on transmission tower-line systems. A newly designed galloping simulation device is employed in the wind tunnel for developing an aerodynamic anti-galloping technique of iced 8-bundled conductors in ultra-high-voltage (UHV) transmission lines. The anti-galloping technique is based on the proposed rotary clamp spacers, which allow the connected sub-conductors to rotate around its axis. Iced 8-bundled conductor models of UHV lines with and without twistable sub-conductors have been tested in the wind tunnel under various wind attack angles and five different ratios of vertical vibration frequency over the torsional. Aerodynamic damping ratios were identified from measured response data, and were used as indicators of galloping for iced 8-bundled conductor models with and without twistable sub-conductors. Equations of motion for iced 8-bundled conductors with and without twistable sub-conductors are respectively established, and the aerodynamic instability of the system can then be predicted by solving the eigenvalue problem associated with equations of motion. In order to further validate the anti-galloping effects of the rotary clamp spacers, finite element simulation has been conducted for a real UHV transmission line with a span of 500 m located in the galloping-prone area.

Problems of Clamping Rotary Tools

Abstract The basic function of all rotary tool clamps used is to clamp a tool firmly and with as small deviation of the tool axis from the axis of rotation of the machine tool spindle as possible throughout the service life of both the tool and the clamp. Another important function of a clamp is to bring the cutting lubricant to the cutting point. A lubricant pressure of 60 and more bars is currently used there. To ensure the proper operation and long service life of the machine spindle, it is necessary that, especially in the case of high-speed machines, the clamp with the tool clamped meets the specified condition of the overall unbalance.

Research on Combination Anti-Galloping Method between Interphase Spacer and Rotary Clamp Spacer for Transmission Lines

The efficacy of single anti-galloping equipments is limited due to shortage of relevant galloping mechanisms or more complex wind and ice conditions. In this paper, a combination anti-galloping method between interphase spacers and rotary clamp spacers is proposed to avoid or reduce the “whole galloping” and “subspan” galloping phenomenon which occur notwithstanding installing interphase spacers. The combination method is designed using multi-mechanisms anti-galloping design, controlling phase-to phase clearance, affecting structural whole properties, and changing iced shape. The galloping critical conditions of wind and ice to excite “whole galloping” and “subspan” galloping are increased by using rotary clamp spacers than by using only interphase spacers. The anti-galloping effect can be improved greatly by using the combination method.

Study on Anti-Galloping Mechanism and Experimental Effect of the Rotary Clamp Spacer

The rotary clamp spacer is a new type of anti-galloping equipment, and it has been already widely used to restrain the line galloping, but the profit and the effect of this spacer need to be studied. On the basis of extensive research this paper presents the mechanism and causation of line galloping, and analyses the configuration and the anti-galloping mechanism of the rotary clamp spacer, and investigates the overseas application and the effect of the rotary clamp. The investigations demonstrate that the rotary clamp spacer has better anti-galloping effect than bundle conductor spacer

A Study on the Manufacturing System of the Axes Linked Ultra-Precision Grinding of Aspheric Surface

The manufacturing system developed in this paper is mainly used for the ultra-precision grinding of the hard-cutting materials, such as high strength steel and carbonized tungsten, which are characteristics with axisymmetric aspheric surface. Under the priority of accuracy and grinding rigidity to design the key components of multi-axis linked parallel grinding system of aspheric surface, such as high speed grinding spindle, B axis grinding rotary table, clamps and center high adjusting system. Maximum speed of the grinding spindle is 90,000rpm, spindle rotating accuracy is 0.1μm, rotation-angle-accuracy of B axis is , center height adjusting accuracy is 0.1μm, using the system can realize parallel grinding of aspheric surface[1].

Transient non-uniform extensional flows realized in certain types of rheometers

The previous concept of non-uniform stagnant motions (NUSM) is applied to the analysis of steady and transient extensional flow realized in certain types of rheometers, including, in particular, the spin-line rheometer (SLR), the filament stretching rheometer (FSR) and the rotary clamp extensometer (RCE). It is shown that the corresponding approximate solutions depend on two material functions as well as on the specimen geometry. It also turns out that the transient extensional viscosity function and extensional modulus determined on the basis of quasi-elongational approximations may be overestimated or underestimated as compared with more realistic values resulting from the present considerations.

A new elongational rheometer for polymer melts and other highly viscoelastic liquids

In polymer melt elongational rheometry only by the rotary clamp technique large elongations can be obtained homogeneously. However, as described in this paper, there still remain disadvantages that led to the development of a new rheometer with the following main features: The dimensions of the required sample are small (60 × 7 × 2 nun3), the sample is supported by a cushion of inert gas and, after having reached the test temperature of up to well above 300°C, it can be extended by a new type of clamps that make use of metal conveyor belts. The resulting tensile force is measured with a resolution of better than 100 mgf (0.001 N). The strain rate range is 0.001-1 s−1, and the maximum Hencky strain is 7, corresponding to a maximum stretch ratio of 1100. Within the sample, the temperature variation in time and space is less than 0.1°C. For the evaluation and documentation of the test performance, a video camera records the top and side views of the sample that carries a marking powder to permit the evaluation of the true strain rate. The operation of the instrument is easy, and so is the sample preparation, but care must be taken concerning the necessary isotropy and ‘internal homogeneity’. Examples of test results are given for several polymer melts at various temperatures: (1) Polystyrene up to a total Hencky strain larger than 7 at 170°C, (2) several types of polyethylene (LDPE, LLDPE, HDPE) at 150°C, (3) poly(amide) at 250°C, and (4) poly(ethersulfone) at 350°C. The wide applicability of the new rheometer is demonstrated by adding results obtained from samples of bread dough. The surface tension has no influence on the results if an error of 3% can be tolerated. From the results it follows that by means of the newly developed rheometer many problems in polymer melt elongation have been solved.

Experimental methods in polymer melt rheology

AbstractExperimental developments in different areas of polymer melt rheology and recent results are reviewed: Shear oscillations were performed with mixtures of polyisobutylenes (PIB) of relatively small molecular mass distributions and with blends of polystyrene (PS) and polymethylmethacrylate (PMMA). For the latter, the interfacial tension between the melts of PS and PMMA can be derived from the results. ‐ In constant shear rate flow, the measurement of the first normal stress difference N1 in a commercial cone‐and‐plate rotational rheometer is simple if the test temperature is kept extremely constant. By a further modification a partial integral of the pressure distribution is measured from which the second normal stress difference N2 can be determined. ‐ The molecular orientation in shear flow results in a rheological anisotropy that can be studied in a parallel‐plate shear rheometer in which the polymer melt sample can arbitrarily be sheared in two perpendicular directions. ‐ For melt elongation by rotary clamps constant, arbitrary ratios of the strain rate components can be applied. Planar elongations of the PIB samples indicate an influence of the width of the molecular mass distribution. More general elongations with a change of the strain rate ratio during the test are of especial interest as is documented by the comparison of the resulting stresses with predictions from different network theories. ‐ In a rheometer for simple elongation at 170°C, recovery after melt extension of the PS/PMMA blends reveals a value of the interfacial tension equal to the one obtained from shear oscillations.

Transient elongational flow behavior of thermotropic liquid crystalline polymers

The transient elongational viscosity ▪ behavior of two thermotropic liquid crystalline polymers, LCPs (hydroxypropylcellulose, HPC, and a copolyester of 2-hydroxy-6-naphthoic acid and para-hydroxybenzoic acid, Vectra A900), has been found to be similar to that determined for isotropic melts of linear polyolefins such as high-density polyethylene (HDPE). Measurements were made on a newly constructed rotary clamp extensional rheometer designed to handle low-viscosity materials at high temperatures. The values of ▪ were observed to follow linear viscoelastic behavior at low strains and subsequently show mild strain hardening with increasing strain. The elongational flow behavior of HPC in the isotropic state was also determined and compared to that in the anisotropic state. Differences in the behavior appear to be related to differences in the structure of the melt and might indicate the influence of the melt state on the flow behavior of LCPs. However, the generality of these results to other LCP systems is uncertain because of the possible influence of residual crystallinity. The predictions of the Doi theory for elongational flow were also compared to the experimental behavior of the isotropic and anisotropic melts. It was found that the Doi theory could not predict quantitatively the elongational flow behavior of LCPs when the parameters in the model were determined from shear viscosity data. Additionally, while the Doi theory showed some qualitative agreement with the experimental behavior of both isotropic and anisotropic melts at low strains, it was unable to predict the strain-hardening behavior seen in those systems.

Melt elongation of a commercial poly(methyl methacrylate) product and a commercial polystyrene

AbstractMelts of a commercial poly(methyl methacrylate) product and a commercial polystyrene were elongated homogeneously up to Hencky strains of ε > 4 by means of the rotary clamp technique. For this purpose, certain modifications to the rheometer were necessary which are described in detail. Both polymer melts show strain hardening, i. e. the elongational viscosities are higher than the threefold of the linear viscoelastic limiting viscosity measured in shear. The degree of hardening is very different: For the poly(methyl methacrylate) product the hardening is only small, and so are the recoverable portions of the total strains, whereas for the polystyrene the opposite is true. This different behaviour is connected with a difference of the linear viscoelastic relaxation spectra at long relaxation times. The test results can be described efficiently by the Lodge‐Wagner rubberlike liquid constitutive equation.

A New Extensional Rheometer for Polymer Melts

A Meissner-type uniaxial extensional rheometer has been constructed. The characteristic features of this rheometer are the following :(1) The distance between two rotary clamps has been decreased to 12 cm, and the measurement can be done with a small amount of sample.(2) The rotary clamps and the motors are equipped on the top cover in order to make it very easy to install and remove samples.(3) The sample in extension can always be seen through the glass windows at both sides of the oil bath. The elongational flow behavior for various polymer melts (polystyrenes with narrow and broad molecular weight distributions, low-density polyethylene, high-density polyethylene, and polypropylene) was measured using this rheometer. It has been confirmed that this extensional rheometer can be used to obtain a homogeneous, uniaxial elongational deformation under a constant strain rate.

Polymer melt elongation—methods, results, and recent developments

AbstractFor film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}11 ⩾ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}22 ≥ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}33, the ratio m = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}22/\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}11 characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation‐induced anisotropy of the rheological behavior.

Multiaxial elongation of polyisobutylene with various and changing strain rate ratios

The multiaxial elongational rheometer equipped with rotary clamps is modified such that in addition to simple, equibiaxial and multiaxial elongations also tests with new modes of elongation can be performed. As an example, polyisobutylene is elongated with a ratio of the principal strain rates of\(m = \dot \varepsilon _{22} /\dot \varepsilon _{11} = 0.5\) and magnitudes of the maximum strain rate\(\dot \varepsilon _{11} = 0.008\), 0.04 and 0.08 s−1. As a test result, the first elongational viscosityµ1(t) is obtained which follows closely the linear viscoelastic shear viscosity\(\mathop \eta \limits^ \circ (t)\). In contrast, the second elongational viscosityµ2(t) remains below\(\mathop \eta \limits^ \circ (t)\). By means of a further modification of the rheometer, the test modes can be varied during the deformation period. This allows one to investigate the influence of a well-defined rheological pre-history on the following rheological behaviour. As an example a variation ofm = 0.5 → 2 was performed. The measured normal-stress differences superpose from the single steps of deformation similar to the linear viscoelastic prediction.

EXPERIMENTAL ASPECTS IN POLYMER MELT ELONGATIONAL RHEOMETRY

After describing the present state-of-the-art, the open experimental problems are listed that prevent a broader application of elongational rheometry to more types of polymer melts. Small samples are preferable for the investigation of structure-properties relationships. Hints are given for the preparation of such samples and for the reduction, in simple elongation, of the error due to inhomogeneous deformations near the sample ends. Large elongations can be performed homogeneously with rotary clamps. However, it is important to characterize the quality of each test, because small errors in the strain rate lead to drastic changes in the stress-strain diagrams obtained for large strains, e.g. e > 4 (HENCKY strain) for melts of LDPE (low density polyethylene). For HDPE the main difficulty is the preparation of homogeneous samples, which requires a special cooling procedure after extrusion. The maximum elongations obtained so far are ϵmax = 5.5 for HDPE and ϵmax = 7 for LDPE. With modified rotary clamps, different modes of multiaxial elongational flows can be realized with polyisobutylene at room temperature. Eight such clamps in circular and rectangular arrangements are used for equibiaxial and planar elongations, respectively. Planar elongation gives two independent material responses. In presenting the test results, new definitions of the elongational viscosities concisely elucidate deviations from linear viscoelastic behavior. For other multiaxial flows the rotary-clamp-technique can also be applied, e.g. for flows with arbitrary ratios of the strain rate components and even with a variation of these ratios with time during an experiment. For a broader application, miniaturization of the rheomeler and operation at higher temperatures require further modifications

Multiaxial elongational flows of polymer melts—classification and experimental realization

For the class of multiaxial elongational flows with constant strain rates, a new classification system is proposed. Ordering the main strain rates such that ∈ . 0  ∈ . 11 ⩾ ∈ . 22 ⩾ ∈ . 33, the constant ratio m  ∈ . 22/ ∈ . 11 characterizes the special type of flow, e.g. in simple elongation m = − 1/2, in equibiaxial elongation m = +1, and in planar elongation (“pure shear”) m=0. For the representation of the test results, three elongational viscosities μ i = A i σ i / ∈ . 0 are defined from the three normal stress differences σ i such that for the linear viscoelastic limit the time-dependent linear viscoelastic shear viscosity follows: μ i ( t)→ ▪ t. For the realization of such multiaxial elongational flows, rotary clamps are used. They are modified such that the force components along and normal to the direction of motion at the clamp can be measured separately. The investigation was performed with polyisobutylene in simple, equiviaxial, and planar elongations. The latter mode of testing is of special interest because two different elongational viscosities are determined simultaneously. The results show that for small deformations the material behaviour is linear viscoelastic. For larger deformations there are different deviations the character of which depends on m, i.e. the type of the elongational flow. From the general single-integral constitutive equation it follows that the predicted stress differences for the different m are very differently connected with the different parts of the equation, as in the case of the two normal stress differences in simple shear flow.

Addendum: Rotary Clamp in Uniaxial and Biaxial Extensional Rheometry of Polymer Melts [J. Rheol., 25 1 (1981)

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Rotary Clamp in Uniaxial and Biaxial Extensional Rheometry of Polymer Melts

The rotary clamp consisting of a pair of gears is a basic construction element for the design of various types of extensional rheometers for polymer melts. With the most recent model of the uniaxial extensional rheometer, built with rotary clamps, homogeneous deformations of Hencky strains up to e=7 have been performed with a low‐density polyethylene melt. For the evaluation and discussion of results from tests with large deformations, it is vital that parameters which characterize the quality of each test be defined and measured. Otherwise, the measured force and the rotational speed of the clamps might be of little relevance for the stress, strain, and strain rate within the sample. The biaxial extensional rheometer consists of eight rotary clamps in a circular arrangement. With this new instrument, extensional Hencky strains up to e11=e22=2.2 can be achieved for a polyisobutylene sample. Such a high deformation corresponds to a compression in the third direction of e33=−4.4. The material within the sam...