A novel design on smooth rotor profile with meshing clearance for screw vacuum pump

Cross-section profile of rotor takes a great effect on the performance of dry-screw vacuum pump. A novel smooth rotor profile consisting of eight segments of curves, including arcs and conjugate correction curves is proposed. Advantages are that it can be used to solve the unsmooth connection and no meshing clearance in traditional profile. The meshing model for new profile can directly generate stable addendum clearance, tooth clearance, tooth side clearance, and radial clearance. The influences of the epicycloid rotation angle, arc radius and involute offset distance of the conjugate correction curve on the clearances are studied according to established theoretical model. And transient flow field of vacuum pump is analyzed by using the commercial software Ansys-Fluent®. Compared to traditional screw vacuum pump, the results shows that pressure in inlet and pump cavity is lower, and maximum pumping speed is higher, indicating that the proposed design is superior.

A shear center demonstration model using 3D-printing

Locating the shear, or flexural, center of non-symmetric cross-sectional beams is a key element in the teaching of structural mechanics. That is, establishing the point on the plane of the cross-section where an applied load, generating a bending moment about a principal axis, results in uni-directional deflection, and no twisting. For example, in aerospace structures it is particularly important to assess the propensity of an airfoil section profile to resist bending and torsion under the action of aerodynamic forces. Cross-sections made of thin-walls, whether of open or closed form are of special practical importance and form the basis of the material in this paper. The advent of 3D-printing allows the development of tactile demonstration models based on non-trivial geometry and direct observation.

The supply of the public lacus of Pompeii, estimated from the discharge of their overflow channels

The term lacus generally identified the public fountains in the main streets of ancient Roman towns, providing for the population daily water demand. The simplest lacus consisted of a stone basin and a spout stone, concealing one or two supply pipes. 35 street fountains of this type have been surveyed in Pompeii, to gather information on their supply and its variation in time. A new method was devised for calculating the discharge through the overflow channel of each lacus, and this value was taken as an estimate of the water supplied to each fountain. The overflow channel internal cross-section width was measured at four elevations, and the cross-section profile was reconstructed based on these data. Three water levels of 1 cm, half of the cross-section height and entire cross section height, were considered at each channel’s inlet, obtaining a corresponding channel discharge. The values obtained, ranging from 0.03 to 2.9 l/s, were checked against the trajectory of the fountain water jet, making sure that it remained within the basin length. For 28 fountains the average discharge was found to be 0.08 l/s when the water was at the lowest level, 0.43 l/s for the intermediate level and 1.18 l/s for a full inlet. The average time of residence of the water, in the lacus draw basin, was estimated between 11 min and 3 h. An estimate of the demand of all the town lacus was compared with the capacity of the aqueduct channel entering at Porta Vesuvio: the town lacus could have been supplied contemporaneously at the minimum and intermediate discharges.

On adequacy of parameters of strip cross-section profile. Part 2. Local thickenings and thinnings

At present, the cross-section profile of the rolled strip is characterized by geometrical parameters such as wedge, convex, difference of thickness, displacement of convex, and edge wedge. Some of these parameters are redundant. Techniques for calculating the values of these parameters are known and generally accepted. However, there are features of the cross-section profile of rolled strips, such as local thickenings/thinnings, the methods of calculating values of which are not common: practically every scientific school of rolling scientists or specialists of rolling production use their own techniques, which often produce different results for the same cross-section profiles. The problem of identifying and calculating the local thickenings/ thinnings parameters of the rolled strips cross-section profile is to define a so-called “zero level”, the excess/understatement of which is a sign of local thickenings/thinnings. The paper continues to analyze the accuracy and adequacy of the calculation of the cross-section profile parameters of rolled strips for local thickenings/thinnings. A new method based on statistical methods is proposed. The target function that the thickness distribution across the width of the rolled strip must correspond to is a symmetrical quadratic parabola. However, the actual distribution is always different from the target one for a number of reasons, such as ring wear of the work rolls. In the first step, in the proposed technique, the Walter-Shuhart procedure (control cards) eliminates as emissions of strip thickness values that are dramatically different from the target distribution. But since without excluding the nonlinear (parabolic) component of the measured cross-section profile this procedure cannot be applied, it applies to the first derivative of the cross- section profile thickness distribution function. To determine the “zero level,” after calculating the upper and lower limits of the allowed values of the first derivative, all thicknesses associated with these emissions were eliminated. The result of the repetitive process is a “zero level” according to which the local thickening/thinning parameters are calculated.

On adequacy of parameters of strip cross-section profile. Part 1. Predictive interval

Increasing the level of automation of metallurgical units and the development of industrial information systems increases the number of p ters of production and technological processes available for analysis. The consequence is an increase in the complexity and duration of preliminary data preparation for subsequent mathematical and statistical analysis. It is therefore important to develop new and improve existing techniques for the automated process of primary data production. When developing methods of primary data preparation, it should be taken into account that accuracy and adequacy of results of subsequent mathematical analysis are determined by accuracy and adequacy of used initial data. The cross-sectional profile parameters of hot-rolled strips, such as wedge, convexity, thickness variation, displacement, wedge in near-rim zones, local thickenings and thinning of the strip are calculated parameters, i.e. secondary to actual strip thickness measurements over the length and width of hot-rolled strips. As technology is improved in cold rolling shops, the number of grade groups is increasing, for which technological modes of units and processing routes are selected. They are based on actual values of parameters of cross-section profile in order to further reduce the probability of formation of inappropriate products and increased metal consumption. The presented article provides an overview of conventional calculation methods for parameters of cross-section profile of hot-rolled strip and gives an assessment of accuracy and adequacy of application of the parameters averaged along strip length to the whole strip.

Study on a straightening process by reciprocating bending for metal profiles

The straightness is a critical quality parameter of metal profiles, and straightening is a necessary process in metal profile production. Due to the limitations of the existing straightening methods, the straightening process by reciprocating bending for metal profiles is proposed. The curvature is unified by multiple reciprocating bending, and then the straightening is completed by reverse bending. The process has the advantages of high straightening efficiency, flexibility, and wide straightening range. In order to verify the feasibility of the process, numerical simulation and physical experiment are carried out with the rectangular section profile with “C” shape and “S” shape. The results show the profiles of different shapes are unified into arcs of the same size after multiple reciprocating bending. In addition, the smaller the elastic area ratio (ratio of elastic deformation to overall deformation) is, the better the effect of unification curvature is. The residual deflection is basically the same after straightening, and straightness is within 0.1%.

Quantitative study on the relationship between the transverse thickness difference of cold-rolled silicon strip and incoming section profile based on the mechanism-intelligent model

Cold-rolled non-oriented silicon strip is widely used, and users have strict requirements for its transverse thickness difference. It is of great significance to study the quantitative relationship between the transverse thickness difference and incoming section profile of cold-rolled silicon strip and to formulate appropriate control indexes of the hot-rolled profile. To achieve the above purpose, this paper first proposes a method to describe the section profile of hot-rolled strip. A mechanism model for predicting the transverse thickness difference of cold-rolled silicon strip is established. Based on the characteristics of neural network transfer learning, the calculated results of the mechanism model are combined with actual production data, and the PSO-LM-BP neural network is trained by using the strategy of pre-training + retraining to obtain the mechanism-intelligence model for the prediction of the transverse thickness difference of cold-rolled silicon strip. The innovation of this paper is the combination of physical model and neural network. The prediction accuracy of the model is improved by two orders of magnitude on average, and the operation time is reduced. The relationship between the hot-rolled strip section crown, wedge and cold-rolled strip transverse thickness difference is quantitatively analysed, and the control strategy diagram of the key parameters of the hot-rolled section is finally obtained. The production of cold-rolled silicon strip with 1420 mm UCM shows that this strategy has a beneficial effect on the transverse thickness difference control of a cold-rolled strip.