Galvanizing

Manufacturing Processes
November 21st 2011

Galvanized & Galvannealing processes

Objective
The main goal of this report is to research and become versed about some of the other processes within the program of teaching in this course, that we didn’t have the time to learn about, in our case, processes like galvanized and galvannealed. Another goal is to learn the differences betweenthese two procedures, and in a given case, to be able to discern which of these would do a better job.

Introduction
In this paper we exhibit processes such as galvanized and galvannealed, their attributes, differences, and most of the details that characterize them in order to be completely knowledgeable in case we have to settle upon one of them.
The corrosion of steel is a global problem of majorproportions that needs to be controlled, that is why it is investigated in universities and research centers to try to quantify and minimize costs. Galvanizing is the electrochemical process by which a metal can be covered with another one. The function of this coating is to protect the surface of the metal on which the process is done.

Galvanizing

It’s called Galvanizing because thedevelopment of this process was based off the Works of Luigi Galvani, whom, when experimenting, was slowly skinning a frog at a table where he had been conducting experiments with static electricity by rubbing frog skin. Galvani's assistant touched an exposed sciatic nerve of the frog with a metal scalpel, which picked up a charge. At that moment, they saw sparks and the dead frog's leg kick as if inlife. He then discovered that different kinds of metal present a different degree of reaction in the frog’s leg, therefore every metal has a different charge.
The most common galvanizing process consists in depositing a coat of zinc (Zn) over iron (Fe). Zinc being the most oxidized, less noble than iron and generating a stable oxide protects the iron from rust when exposed to oxygen in the air.In general it is used in pipes for the conveyance of water whose temperature does not exceed 60 ° C because if it were to be over 60º C it would revers the polarity of the zinc on the steel pipe and this would corrode it instead of it being protected by the zinc.
To prevent corrosion in general is essential to avoid contact between dissimilar materials with different oxidation potential, whichmay cause galvanic corrosion problems because of their combination. One of the mistakes most often made is the use of copper tubing combined with galvanized steel pipes.
If copper tubing, which is a noble material, is located upstream of the plating, copper ions, which necessarily exist in the water or copper particles can be carried away by erosion or any other source, is cemented ontothe galvanized zinc downstream and it is oxidized to form a stack local bimetallic Cu / Zn in the points at which copper ions are deposited as metallic copper on the galvanized. From that time will accelerate the corrosion of the galvanized coating on all these points.
Missing the zinc coating, the stack will be Cu / Fe and will continue to corrode until the steel tube is perforated.The case however hasbeen the poor quality of design: the installation of copper tubing upstream, which is what caused the corrosion of galvanized downstream.
By contrast, in the case of copper pipes are not installed at the end of the network, ie, downstream of galvanized pipe, there won’t be a problem if it is ensured that no water returns after passing by the copper through the plating. If there is that risk ananti-return system must be placed.
Other widely used galvanizing processes are those that are coated for primarily decorative pieces like buckles, buttons, keychains, desk items, and a lot of products are plated in copper, nickel, silver, gold, bronze, chromium, tin, etc. .. In the case of jewelry, gold baths are used (usually 18 to 21 carats). Also lining scarce metal jewelry such as platinum and...