Improve the effect of Galvanizing on Steel Products
In the past, the most common form of corrosion protection for metallic surfaces has been through the hot dip galvanizing process whereby a zinc layer is firmly alloyed with the steel surface. This method has been improved on by the inclusion of aluminium as an alloy with the zinc in a redesigned coating process. The International Lead Zinc Research Organisation has already obtained worldwide patents upon this news form of coating in 1981. Galfan (from “Galvanization Fantastique”), is however still a fairly unknown product in the South African market as very few steel manufacturers are aware of this improvement. Combining Zinc & Aluminium
Galfan, in the form of 95% zinc and 5% aluminium coating is superior to pure zinc in that the rate of corrosion with time has a parabolic rather than linear form. This is due to the fact that zinc corrodes at a faster rate than the aluminium. Hence, as the zinc element corrodes, an aluminium rich surface is developed with a greater resistance to corrosion, resulting in an extended life of the protection.
This eutectic Zn-Al misch metal also contains small additions of cerium lanthanum rare earths to improve the reliability of the coating process. This combination results in a physical structure which has a more crystalline from and improved mechanical characteristics.
A further advantage of the zinc aluminium coating is that it has a finer microstructure and provides better cathodic protection. Consequently, in the event that the surface becomes scratched the coating has the ability to restore itself more effectively than when zinc on its own is present, and continue the corrosion protection.
 |
| Full-side corrosion resistance during an automotive cyclical corrosion test |
 |
| Example of resistance to salt spray: 5% NaCl |
 |
| Comparison of electrode life |
Aluminium is more electropositive than zinc, and corrodes at a lower rate. A “passive barrier” is created when the coating produces an oxidising film blocking the wire from oxidisation and corrosion. The aluminium oxide crystals are more uniform and less porous therefor the passivating performance is more effective.
Other reasons for using a zinc-aluminium alloy
Zinc has a cathodic feature which promotes its sacrificial protection. When zinc is scratched, damaged or abraded away, zinc oxides cover the exposed steel surface. The steel-zinc alloy is therefore important for the internal protection and adhesion of the coating to the steel.
The aluminium oxides on the other hand are externally more stable and hence provide the initial barrier required at the surface to withstand the effects of the environment and the potential for damage. The aluminium is more ductile than the zinc thus improving the formability of the surface by withstanding flaking and cracking when the wire is bent or twisted.
Research on the properties of Galfan
Various studies have been done with the following results:
- At short intervals up to two years and eventually after a full 8 years, specimens were removed and tested to determine the loss in their coating content.
- The Galfan coated specimens were less corroded than those that were galvanised. Loss in Galfan coating after 8 years was approximately 15% whilst the Zinc-coated specimens lost up to 65% of the coating. (Corrosion Testing Laboratories February 2001)
Conclusions
In conditions of extreme exposure it is necessary to ensure that the coating type is appropriate. In the past zinc only coated wire would have had to be carefully maintained and at times replaced when conditions were extremely severe.
Now with the availability of Galfan, new opportunities have been opened and the service life of hydraulic structures especially, using gabions and mattresses has been improved considerably.
Users of Galfan in certain parts of the world have stated that Galfan is capable of providing 4 to 5 times greater protection than zinc coating of the same thickness.
In addition to this, it has been found that Galfan wire is easy to weave and its finish allows the cut ends of the selvedge to “heal over” thus providing resistance to corrosion. Galfan also maintains a “like-new” appearance until the end of its life span.
Finally, Galfan allows the end-user to achieve two important goals at the same time: First the provision of a longer corrosion life and second considerably lower cost per year of service life.
Chemvet by Nampo
Chemvet @ NampoNampo 2011 was weer gekenmerk deur boere met hulle families en vriende wat van heinde en verre na Bothaville gestroom het om een van die wêreld se grootste Landbouskoue by te woon. Die weer was puik en aangesien Woensdag, 18 Mei ‘n vakansiedag was, het Nampo ‘n rekord aantal besoekers gehad op die dag. Skougangers het by hul duisende gearriveer. Parkering, kos en koeldrank was amper te min, maar die positiewe belangstelling en vooruit visie van boere was aan die orde van die dag.
Die Chemvet uitstalling was weer oorlaai met omheining navrae van boere wat opnuut met met beeste, skape, wild en veral eksotiese wildspesies wil boer. Daar is verseker ‘n verskuiwing van fokuspunt. Twee jaar gelede was ons oorheersende navrae oor sekuriteitsheinings. Verlede jaar slegs inligting oor wildheinings en nou is daar verseker ‘n groot aantal boere wat weer beplan om met vee te boer.
By Chemvet is ons oortuig dat lae staalpryse verseker nou verby is en ‘n versekerde prysverhoging vanaf 1 Julie in die mark gesien gaan word.
Baie dankie aan alle lojale Chemvet klante wat weereens oë kom wys het op ons stalletjie. Aan almal wat vir die eerste keer ‘n navraag na ons verwys het, baie dankie en baie welkom. Chemvet bou vanaf 1979 ‘n tevrede klantebasis op en streef daarna om u met net die beste diens te bedien.
Chemvet @ AVI Africa
Chemvet once again exhibited at this year’s AVI Africa, held at Emperor’s Palace from 31 May to 2 June, where the cream of the poultry sector, locally and abroad, attended the show. This gave us the opportunity to meet up with all our loyal clients, while giving us the chance to impress the new faces who could not believe the state of the art poultry housing that we are able to provide.
Mr. Nick du Plessis is currently involved in a number of large deals in the United Kingdom, which is indeed a feather in our cap. Locally, things are also going very well and with every new order, we are able to increase our expertise even further.
Thank you to everyone who took the time to come and visit us at AVI Africa. To those who missed us, please give us a call on 011-437-9000.
Remember: At Chemvet we engineer relationships.
