Pre Galvanized (Conforms to BS 2989, Superseded by BS EN 10142:1991)
Also termed as Mill Galvanized, Hot Dip Mill Galvanized or Continuous Hot Dip Galvanized Pre-galvanized steel is produced by coating coils of sheet with zinc by continuously rolling the material through molten zinc at the mills. This is also known as mill galvanized or hot dip galvanized. These coils are slit to size and then fabricated by roll forming, shearing, punching or forming to produce pre-galvanized cable tray products.
This finish is usually used in normal atmosphere pollutants. In contradiction of what many people think, it can also be used in the presence of moisture as the cable ladder or tray is protected from corrosion by two ways. During fabrication, cut edges and welded areas are not normally zinc coated; however, the zinc near the uncoated metal becomes a sacrificial anode to protect the bare areas after a short period of time. This is how
The existing layer of zinc which isolates the steel from the effect of the external environment. The existing Zinc will also protect the bare exposed steel points, preventing corrosion to occur.
The protective lives of the exposed points depend upon three major factors:
The thickness of Zinc coating, where greater thickness results in better preservation.
The most exposed points will have a short life span compared to other points.
Major environment factors like harsh climatic conditions, exposure to chemicals, industrial plants and finally the coastal regions where the effect of salt and moisture will drastically reduce the protective life period.
Hot Dip Galvanized after Fabrication Conforms to BS 729 superseded by BS EN 1461
Also termed as Hot Dip Galvanized Or Batch Hot Dip Galvanized
In this process, cable tray are fabricated from steel and then completely immersed in a bath of molten zinc @ 450° C, where a metallic bond occurs resulting in a zinc coating that completely coats all surfaces, including edges and welds.
The zinc thickness is controlled by the amount of time each part is immersed in the molten zinc bath as well as the speed at which it is removed.
Hot dip galvanized finish can be used in tougher environment for pre-galvanized finishes due to the absence of cut edges or weld points. The layer of zinc which bonds to steel provides a dual protection against corrosion. It protects first as an overall barrier coating. If this coating happens to be scratched or gouged, zinc secondary defense is called upon to protect the steel by galvanic action. Hot dip galvanizing after steel fabrication is recommended for prolonged outdoor exposure and will protect steel for many years in most outdoor environments and in many aggressive industrial environments.