Zn-5%Al Hot Dip Galvanized PK Traditional Hot Dip Galvanized

There is a stack of galfan welded wire meshes.
Zn-5%Al welded wire mesh is brighter than galvanized wire mesh and wouldn't craze under pressure.

For many years, the traditional hot-dip galvanizing way is the only choice to produce welded wire mesh for manufacturers. However it can’t meet all the needs for high corrosion resistance, long service life and extensive application ranges. Until 1981 the United States finished the industry experiment about galfan hot dip galvanized, the galfan hot dip galvanized is extensively generalized to the world. The galfan is made from Zn-5%Al alloys and owns high corrosion resistance. The galfan hot dip galvanized is stronger than the traditional hot-dip galvanizing so it can sever a long life. With high corrosion resistance, the galfan coating welded wire can be used for many fields—steel panels, steel wire, steel pipe and even metal parts. The thickness of galvanized coating is thinner than before thus can reduce the use and cost of zinc.

The process of producing the hot dip galvanizing technology

The hot dip galvanized machines are about the pickling trough, plating auxiliary trough, RDL-916 hot dip galvanized equipment and double layer roll traction winding machine. The hot dip galvanizing alloy is made from the mixture of 95% zinc and 5% aluminum. In hot dip galvanizing technology, which use double solvents of ZnCl2 and NH4Cl as the plating auxiliary, the temperature should be under 450 °C.

Getting rid of the rust of welded wire mesh with diluting hydrochloric acid is the first step and removing the residual hydrochloric acid with water. Then galvanizing the welded wire mesh in the trough that filled with plating auxiliary. Scraping the extra zinc alloy with exquisite pearl after drying the welded wire mesh. Finally we use the double layer roll traction winding machine get the welded wire mesh.

Welded wire mesh is different from steel wire and steel panel for its opening mesh and the welding points. So here are strict demands for hot dip galvanized technology. Compared with the traditional hot dip galvanized, the chemical change between galfan alloy and iron ion is slower and the flow speed is faster. Because of these features, the galvanized coating thickness is reduced, the coating for welded wire mesh is evenly and even the appearance becomes nice. However the plating auxiliary 10% NH4Cl could create AlCl3·NH3, for its boiling point is under 400 °C, it would become evaporated gas under the hot dip galvanized temperature and the coating would seep iron badly. So as the new plating auxiliary the mixtures of chloride and fluoride take the place of NH4Cl.

The experimental results

We made the salt spray erosion test in the salt spray test chamber. With the sample paralleling with the flow at 30 degree oblique, we spray continuously in the condition that the pH of 2.5% NaCl is 6.5–7.2, the humidity is more than 95% and the salt fog settling volume is 1.2±0.2 ml/h per 80 cm2. The test period is 24 h and we get the following result.

The result of the salt spray erosion test
Erosion period Galfan welded wire mesh Traditional galvanized welded wire mesh
One day nothing on panels white rust on welded points
Two days nothing on panels white rust on welded points
Three days white rust on panels more white rust on panels
Four days more white rust on panels ten red rust points on panels
Six days Tow red rust points on panels more red rust on panels

According to the table, after 280 hours’ soak in 5%NaCl the corrosion of galfan welded wire mesh is slight while the traditional galvanized wire mesh lose 1‰ weight.

Compared with the galvanized welded wire mesh with some white rust, the galfan welded wire mesh looks nice after soaking for two weeks in the seawater. And the brightness of the galfan wire mesh is much higher than the traditional one. T whiteness meter shows that the galfan wire is twice as bright as the galvanized wire. We cut a part of the welded wire mesh and twine it on a 4 mm diameter round iron bar. The galfan welded wire mesh wouldn’t craze with forty times while the traditional galvanized wire mesh would craze after twenty times.

Conclusion

The Zn-5%Al alloys can improve production efficiency and the traditional manufacture technique suits the galfan hot dip galvanized technology.

Compared with the traditional hot dip galvanized the content of zinc could decrease 10–20% with galfan hot dip galvanized technology. The 11.6% of the cost decreases, the quality increases and the service life is long. The galfan welded wire mesh could not only be used for highway partition network, safety ceiling and chicken wire but also be used for construction and aquaculture industry.

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