Influence of Hot-Dip Galvanizing on Mechanical Properties of Pressure-Locked Gratings

Abstract

Pressure-locked gratings are made by pressing cross bars into tapered slotted bearing bars under high pressure. The end result is a grate with rectangular meshes. Grating design process is based on the assumption that the load is carried by the bearing bars. Grating as a final product is protected against corrosion, usually using hot-dip galvanization. Comparative observation of non-galvanized and hot-dip galvanized gratings shows that zinc not only forms a thin coating on the whole surface of bearing and cross bars, but also fills the voids located in the joints of the bearing and cross bars. Steel changes its properties due to high temperature in the hot-dip galvanization process. Additionally, during the technological process the material of a bearing bar is subject to plastic deformations. Therefore it can be assumed that the above mentioned changes affect the mechanical properties of the grating, especially its stiffness and strength. However, grating design process includes only strength characteristics of non-galvanized bearing bars, determined by steel grade. The aim of the paper is to investigate effect of hot-dip galvanizing on the mechanical properties of gratings and make the recommendations for their production. The paper compares the results of tensile tests of samples of non-galvanized bearing bars without heat treatment, non-galvanized bearing bars subjected to hot-dip galvanizing temperature and hot-dip galvanized bearing bars. The assembled samples of hot-dip galvanized steel gratings and non-galvanized steel gratings were subjected to a bending test. There was a significant increase in the stiffness of the hot-dip galvanized grating. Calculation coefficient was proposed to be included in the design stage of production process to incorporate increase of stiffness of galvanized grating caused by hot-dip galvanization. Guidelines are presented how include results of the work in the production management of galvanized steel products manufacturing.