Optimisation of helical geometry of inspection probe for steam generator tubes of the PFBR

The steam generator (SG) tubes of the prototype fast breeder reactor (PFBR) located in Kalpakkam, India, need to be periodically inspected using the remote field eddy current (RFEC) technique. During the pre-service inspection of the SG tubes, it was found that the RFEC probes experienced frequent mechanical breakages. To avoid these failures, changes in the existing structural design of the RFEC probe were required. A helical groove design was proposed to obtain a smooth transition in the variation of stress across the probe during the inspection. It was difficult to calculate the flexural stiffness of the proposed helical geometry probe due to the varying cross-section along its length. In this paper, the smearing approach adopted to calculate the stiffness of the RFEC probe and the sensitivity analysis carried out to determine the optimal design of the probe are discussed. A probe was fabricated based on the helical groove design and tested to qualify its suitability for the SG inspection. The RFEC probe with helical grooves was employed for the pre-service inspection of the SG tubes of the PFBR. More than 200 tubes have been inspected using the proposed design and no mechanical failure of the probe has been observed.

Automated calculation of the profile of a disk cutter for the manufacture of helical grooves

The calculation of the profile of disk cutters, excluding undercutting for any complex profile of the helical groove, is proposed. The feature of the method is in the fact that the profile is specified by a small number of control points, which, using interpolation, is increased by tens or hundreds of times. The rational profile of the cutter is investigated depending on its three setting parameters. A numerical experiment was carried out for the profile of the cutter with the optimization of the setting parameters. Keywords: disk cutter, profile, helical groove, computer-aided design, calculation [email protected]

Static and Rotordynamic Characteristics for Two Types of Novel Mixed Liquid Damper Seals With Hole-Pattern/Pocket-Textured Stator and Helically Grooved Rotor

Noncontacting liquid annular seals, such as helical groove seals, are widely used at the impeller interstage and shaft end in the liquid turbomachinery to reduce the fluid leakage and stabilize the rotor-bearing system. However, previous literatures have expounded that the helical groove seal possesses the poor sealing property at low rotational speed condition and suffers the rotor instability problem inducing by negative stiffness and damping, which is undesirable for the liquid turbomachinery. In this paper, to obtain the high sealing performance and the reliable rotordynamic capability throughout full operational conditions of machines, two novel mixed liquid damper seals, which possess a hole-pattern/pocket-textured stator matching with a helically grooved rotor, were designed and assessed for the balance piston location in a multiple-stage high-pressure centrifugal liquid pump. To assess the static and rotordynamic characteristics of these two types of mixed liquid damper seals, a three-dimensional (3D) steady computational fluid dynamics (CFD)-based method with the multiple reference frame theory was used to predict the seal leakage and drag power loss. Moreover, a novel 3D transient CFD-based perturbation method, based on the multifrequency one-dimensional stator whirling model, the multiple reference frame theory, and the mesh deformation technique, was proposed for the predictions of liquid seal rotordynamic characteristics. The reliability and accuracy of the present numerical methods were demonstrated based on the published experiment data of leakage and rotordynamic force coefficients of a helical groove liquid annular seal and a hole-pattern liquid annular seal. The leakage and rotordynamic force coefficients of these two mixed liquid damper seals were presented at five rotational speeds (0.5 krpm, 2.0 krpm, 4.0 krpm, 6.0 krpm, and 8.0 kpm) with large pressure drop of 25 MPa, and compared with three types of conventional helical groove seals (helical grooves on rotor, stator or both), two typical damper seals (hole-pattern seal, pocket damper seal with smooth rotor), and a mixed helical groove seal. Numerical results show that two novel mixed liquid damper seals both possess generally better sealing capacity than the conventional helical groove seals, especially at lower rotational speeds. The circumferentially isolated cavities (hole/pocket types) on the stator can enhance the “pumping effect” of the helical grooves for mixed helical groove seals, by weakening the swirl flow in seal clearance (which results in the increase of the fluid velocity gradient near the helically grooved rotor). What is more, the helical grooves on rotor also strengthen the dissipation of fluid kinetic energy in the isolated cavities, so the mixed liquid damper seals offer less leakage. Although the mixed liquid damper seals possess a slightly larger (less than 40%) drag power loss, it is acceptable in consideration of the reduced (∼60%) leakage for the high-power turbomachinery, such as the multiple-stage high-pressure centrifugal liquid pump. The present novel mixed liquid damper seals have pronounced rotordynamic stability advantages over the conventional helical groove seals, due to the obviously larger positive stiffness and damping. The mixed liquid damper seal with the hole-pattern stator and the helically grooved rotor (HPS/GR) possesses the lowest leakage and the largest effective damping, especially for higher rotational speeds. From the viewpoint of sealing capacity and rotor stability, the present two novel mixed liquid damper seals have the potential to become the attractive alternative seal designs for the future liquid turbomachinery.

Definition of setting total error value at centerless ball grinding

There is defined a total basing error arising during centerless ball grinding using driving disk helical grooves with different forms. On the basis of computations there is offered a design of a driving disk with the trapezoidal helical groove. A design of a supporting knife which allows carrying out efficiently an automatic position correction of the measuring base of operation size during ball grinding is offered.

Numerical Investigation on the Static and Rotordynamic Characteristics for Two Types of Novel Mixed Helical Groove Seals

Non-contracting annular seals, such as helical groove seals, are widely used between the impeller stages in the liquid turbomachinery to reduce the fluid leakage and stabilize the rotor-bearing system. However, previous literature has expounded that the helical groove seals possess the poor sealing property at low rotational speed condition and face the rotor instability problem inducing by negative stiffness and damping, which is undesirable for liquid turbomachinery. In this paper, to obtain the high sealing performance and the reliable rotordynamic capability for full operational conditions of the machine, two novel mixed helical groove seals, which possess a hole-pattern/pocket-damper stator matching with a helically-grooved rotor, were designed and assessed for a multiple-stage high-pressure centrifugal liquid pump. In order to assess the static and rotordynamic characteristics of these two types of mixed helical groove seals, a three-dimensional (3D) steady CFD-based method with the multiple reference frame theory was used to predict the seal leakage and drag power loss. Moreover, a proposed 3D transient CFD-based perturbation method, based on the multi-frequency one-dimensional stator whirling model, the multiple reference frame theory and a mesh deformation technique, was utilized for the predictions of seal rotordynamic characteristics. The accuracy of the numerical methods was demonstrated based on the experiment data of leakage and rotordynamic forces coefficients of published helical groove seals and hole-pattern seal. The leakage and rotordynamic forces coefficients of these two mixed helical groove seals were presented at five rotational speeds (0.5 krpm, 2.0 krpm, 4.0 krpm, 6.0 krpm, 8.0 kpm) with large pressure drop of 25MPa, and compared with three types of conventional helical groove seal (helical grooves on rotor, stator or both), and two types of damper seals (hole-pattern seal, pocket damper seal with smooth rotor). Numerical results show that the mixed groove seals possess generally better sealing capacity than the conventional helical groove seals, especially at low rotational speed conditions. The circumferentially-isolated cavities (hole or pocket) on the stator enhance the “pumping effect” of the helical grooves for mixed helical groove seals, what is more, the helical grooves also strengthen the dissipation of kinetic energy in the isolated cavities, thus the mixed helical groove seal offers less leakage. Although the mixed helical groove seals possess a slightly larger drag power loss, it is acceptable in consideration of reduced leakage for the high-power turbomachinery. The present novel mixed helical groove seals have pronounced stability advantages over the conventional helical groove seal, due to the obvious large positive stiffness and increased damping. The mixed helical groove seal with the hole-pattern stator and the helically-grooved rotor (HPS/GR) possesses the lowest leakage and the largest effective damping, especially for the high rotational speeds. From the viewpoint of sealing capacity and rotor stability, the novel mixed groove seals are better seal concepts for liquid turbomachinery.

Machining and Characterization of Double-Helical Grooves on Cylindrical Copper Parts by Wire Electric Discharge Turning

In the work, the design and development of a novel Wire-EDM setup with double-wire guide discs is presented. It facilitates sparks to be generated between the workpiece and wire at two locations separated by the helical pitch distance. This sparking causes two helical grooves to be generated simultaneously on the surface of the workpiece when it is given suitable rotational speed and table feed. In this work, machining is carried out on rods of 1.5 mm diameter. Helical groves with helix angles ranging from 35 to 500 were generated and characterized. This method of machining the double helical grooves with a single pass reduces the machining time and eliminates the complexities involved in machining one groove at a time. It was observed that the proposed method is suitable for machining double helical grooves with helix angles in the range of 40 - 50°. The parts produced by the mentioned method can be used as EDM tools for generation of high aspect ratio holes in turbine blades and injection nozzles.

Assembly of MLT type permanent resistors

Considered technological processes of the assemblage of the constant resistors of MLT type for unattended installations, circular layout in two types: with the operation of welding the contact pins without welding (with pressure caps with leads); cutting helical grooves on the metallic base resistor on a special machine; varnishing and painting the raised resistors on the automated line. The equipment for straightening of axial contact terminals and laying of resistors from bulk in the pencil cassette is presented.

Developing of a Simscape Multibody Contact Library for Gothic Arc Ball Screws: A Three-Dimensional Model for Internal Sphere/Grooves Interactions

The Simscape Multibody software is a set of libraries and mechanical modeling and simulation tools for use with Simulink®. For what concerns the contact library, currently it contains only the models to describe impacts between simple geometries, such as spheres, cylinders and planes. When this environment is intended to be used to simulate the 3D dynamics of a system with a complex geometry, such as a ball screw, the built-in blocks are not sufficient. This paper presents a new contact library, containing blocks specifically designed to handle the contacts between a sphere and the two gothic arc helical grooves of a ball screw, as well as the interaction between adjacent spheres. The developed blocks are exploited to create a first case study dynamic model of a single nut not preloaded ball screw in presence of internal backlash. The results highlight the superiority of this multibody approach with respect to the quasi-static or lumped parameters models in terms of extracted information and understanding of the internal mechanics.