China
Africa
Explore chapters and articles related to this topic
Design of Substructure
Published in Dongzhou Huang, Bo Hu, Concrete Segmental Bridges, 2020
The basic function of bridge bearings is to transfer loadings from the super-structure to the substructure. A bearing may be required to resist up to three types of axial loadings and to accommodate anticipated super-structure deformations. Though the cost of bridge bearings is small in comparison with the total cost of bridge construction, it is essential to choose a proper type of bearing as its failure may damage the bridge or cause long-term deterioration. Bearings are typically classified as fixed or movable/expansion. Fixed bearings will transmit longitudinal and transverse lateral loads, while expansion bearings generally only resist small friction forces from deformation of the bearing during longitudinal expansion and contraction. Movable bearings may include guides to control the direction of translation. Fixed and guided bearings should be designed to resist and restrain all unwanted translations. There are numerous types of bearings, such as elastomeric bearings, plain sliding bearings, spherical bearings, disc bearings, pot bearings, and rocker bearings. Three types commonly used in segmental bridge construction are neoprene bearings, disk bearings, and pot bearings. These will be discussed in this section. The resistance factor for bearings is generally taken as ϕb=1.0
Bearings, Slides, Guides, Ways, Gears, Cylinders, Couplings, Chains, Wire Ropes
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
Plain bearing materials most often encountered in industrial machines are bronzes and babbitts. Suitable bronzes and babbitts are available for practically all conditions of speed, load, and operating temperature encountered in general practice. Steel and cast iron are used for a limited number of purposes, usually involving low speeds or shock loads. There has been considerable growth in the use of plastic and elastomeric materials such as nylon, thermoplastic polyesters, laminated phenolics, PTFE, and rubber for bearings, particularly in applications where contamination of, or leakage from, oil-lubricated bearings might result in high maintenance costs or short bearing life. Some of these materials can be lubricated with water or soluble oil emulsions in certain applications. Allowable unit loads for these bearing materials usually are lower, although in a number of cases, nylon-filled bearings have been used as direct replacements for bronze bearings.
Applications of mechanical systems and technology
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Rotating shafts need to be supported. Depending on the application, the support is provided by plain bearings, ball bearings or roller bearings. In addition to providing radial support, the bearings sometimes also need to accommodate axial forces or end thrust along a shaft. The plain bearings for steel shafts are very often made from phosphor-bronze. This has good load carrying properties which can be enhanced by impregnating it with graphite, as will be described in Chapter 5. Nylon is sometimes used for light-duty low-speed applications. Figure 4.6 shows a plain bearing which is designed to give both radial and axial support.
Numerical Investigations of Molten Salt Pump Journal Bearings Under Hydrodynamic Lubrication Conditions for FHRs
Published in Nuclear Science and Engineering, 2023
Yuqi Liu, Shuai Che, Adam Burak, Daniel L. Barth, Nicolas Zweibaum, Minghui Chen
Figure 15 shows the applied static loads of the three bearings for different Sommerfeld numbers. The applied static load decreases as the Sommerfeld number increases. The plain journal bearing yields the maximum applied static load while the bearing with helical grooves has the smallest static load. Figure 16 shows the power loss profiles of the three different bearings with different Sommerfeld numbers. Because of the lack of lubricant without the grooves, the plain bearing has the largest power loss. On the contrary, the bearing with helical grooves has the smallest power loss, which shows a good capability in reducing the friction between the film and the bearing surface. Overall, in terms of the applied static load and power loss, the bearing with helical grooves shows the best performance because using grooves can increase the lubricated surface area and lead to adequate lubrication and reduced power loss.
A High Order Nonlinear Study to Evaluate the Seismic Response of Rotating Machines–Structure–Soil Foundation Systems
Published in Journal of Earthquake Engineering, 2021
Felipe Vicencio, Ernesto F. Cruz
For large rotating machines, journal fluid bearings are typically used. These elements play an important role in the seismic response and dynamic behaviour of the rotor. There are different types of bearings, which differ in their geometries and configurations; e.g. plain cylindrical, four axial grooved, elliptical, multilobe, and tilting pad. In this research, the plain cylindrical types journal bearings were considered because these are the most used on large gas/steam turbines and generators. To define the dynamic properties of the bearings, the internal forces generated in the fluid should be estimated. These properties can be expressed in terms of the hydrodynamic coefficients. These coefficients are proportional to the equivalent stiffness and damping values. Rao [1983, 2004] and Sawicki and Rao [2004] provides a good summary of how to analytically obtain these linearized coefficients for the approximation of long and short bearing type, by a perturbation from the equilibrium position of these bearings.
Investigation of Dry Sliding Friction Wear Behavior of CuSn11 Bronze Plain Bearing Applying Impregnated Graphite-Filled PTFE
Published in Tribology Transactions, 2022
Plain bearings are one of the machine elements that support the shafts. They operate at a certain speed and under a certain load. It is desirable that the produced bushings have good lubrication so that they can be used for a longer period of time. This reduces wear and increases the life of the bushing. In order to be used as an additive to PTFE, the additive ratio of graphite with higher lubricating properties was determined. Also, dry friction and wear behavior of the produced composite bushing was examined under different sliding speeds and loads. The study presented here aims to develop a self-lubricating metal–PTFE composite structure, with easy production applicability and long life, by using the porous structure of bronze and the excellent tribological properties of PTFE and graphite. The originality of this work is due to the method of application and the porous structure of bronze, unlike traditional methods. The bronze bushing used in this study has a porous structure and was obtained by powder metallurgy (TM). A self-lubricating structure is used with application of a spray coating method, which differs from other production methods (such as oil soaking or solid lubricant embedding etc.). The study is to find out how much of (and in what proportions) the PTFE + graphite composite with high lubricating properties should be impregnated into the bushing pores. The friction coefficients are determined at the end of different sliding speeds and different load variables that have effects on the friction coefficient. The effect on friction and wear of using a high rate (20% GF) of graphite was also investigated. It is believed that this study contributes to studies examining the dry friction and wear behaviors against steel materials among PTFE composite materials.