Galvanization or galvanizing is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method of galvanization is hot-dip galvanizing, in which the parts are submerged in a bath of molten hot zinc. We have a continuous hot-dip galvanization setup for producing galvanized iron (GI) wires. The molten zinc bath is maintained at 450oC, through which 40 galvanizing wire lines run parallelly. The steel wires pass through this molten zinc bath at line speeds of 40 to 130 m/min. The smaller diameter wires move at higher speeds and vice versa. Thus, the coating thickness is lower for thin wires and higher for thick wires owing to the varied residence time in the molten zinc bath. The wire diameters range from 1.4 - 5 mm and corresponding zinc coating range from 50 - 300 gsm.
Zinc is a major consumable for GI wire production. Often, it is observed that there is a variation of zinc coating across the length of wire. The actual coating thickness often becomes more than the desired coating thickness. This results in material loss due to increased zinc consumption as well as variation in final product quality delivered to the customer.
Currently, we undertake offline zinc coating tests (volumetric zinc coating as per IS 6745) wherein we need to cut a test sample after production of approx. 1 MT wire. This is a reactive mode of determining the coating thickness and does not give continuous feedback to the operators. Any necessary corrective action is thus significantly delayed. Hence, we are looking for a portable zinc coating measurement equipment which will help the operator to monitor zinc coating as and when required, without having the need to cut the test samples. This will enable frequent monitoring of the coating thickness, based on which corrective actions can be taken.
In case of concerns raised by customers regarding the coating, the provision of a portable thickness measuring device will eliminate the need of carrying back a cut sample from customer setup and testing at our laboratories by a volumetric testing method. Also, cutting a test sample is often not possible since wires are continuously formed into wire products and cutting a test sample in between (from the regions of concern) may lead to wastage of the entire bundle at the customer end. Thus, the need for a non-destructive test at the customer end is important and can be carried out if such a portable wire coating thickness measuring device is available. In this way, we will be able to reduce material losses resulting from excess zinc coated on the wires. This will also enable better coating consistency provided to the customer.