All steel sheet and tube products contain 2 basic elements - carbon and iron - and may have some compositional differences and various manufacturing processes. In the case of hot-dipped galvanized steel coils and cold rolled steel coils, they are similar steel products with unique properties and applications.
Often referred to as hot-dipped galvanised steel, galvanised steel is produced, as the name suggests, by immersing the steel product in molten zinc, the zinc layer then being rapidly oxidised in the open air. Compared to iron, zinc is less reactive in the redox process, which is why it is so popular as the zinc layer protects the steel in our lives.
Cold rolling and hot rolling processes are two methods of forming steel. Cold rolled products have a higher degree of product dimensional accuracy and are suitable for applications with high dimensional requirements. Cold rolling occurs below the crystallisation temperature and is controlled by different types of rolls. The basic product is cold rolled sheet and coil, which can also be formed into other shapes such as cylinders, I-beams and tubes.
Can cold rolled steel products be galvanised? The answer is yes, they are two different processes used for different purposes, one for forming and the other for corrosion protection. The only limitation of galvanised steel is that it cannot be used in high temperature conditions and if the surface is scratched, the zinc layer will lose its protection at the point of scratching.
Galvanised steel products can be produced from both cold-rolled and hot-rolled steel. Generally, hot-rolled steel has a better yield strength than cold-rolled steel because the cold-rolling process breaks down the grain structure of the steel, while hot-rolling improves it. Cold-rolled steel has better surface conditions than hot-rolled steel. The customer should choose the right steel for your different applications.
Yes, two types of fire protection can be successfully used on hot-dipped galvanised steel; cement-bonded concrete and fire protection coatings. Cement-bonded concrete can be either dense or lightweight. The dense version is most commonly used for outdoor structural elements that are likely to be impacted, such as vehicle bumpers. Lightweight cement-bonded concrete is most often used where weight is a consideration or in areas that are less likely to be impacted. Moisture penetrates lightweight fireproofing materials more readily than lightweight fireproofing materials, so it is important that the lightweight material completely covers the area of its application and is of the thickness recommended by the manufacturer.
Fire retardant coatings are reactive materials and begin to foam once a specific temperature threshold is exceeded. The foam reduces the heat transfer to the steel, which is further protected from excessive heat by the ceramic binder. Regardless of the type of fire protection used, there are a number of problems when fireproofing hot-dipped galvanised steel. The fireproofing material is a porous material and can break down, allowing water and other corrosive elements to enter the underlying steel. The fireproofing can then act as an insulator, preventing the corrosive elements and water from drying out, which can further increase the corrosion rate of the galvanised coating. In addition, fireproofing may be difficult to remove and to detect moisture and other corrosive elements beneath the material.