Galvanising evaluation

Introduction

An investigation was conducted into galvanised and painted sheeting of Chinese origin.

Investigation

Three sheets were supplied for inspection:

  1. Sheet supplied locally to be used for comparison as a control panel.
  2. Sheeting off of a 45mm thick panel of Chinese origin.
  3. Sheeting off of a 25mm thick panel of Chinese origin.

What We Found

Results

The control sample shows good bonding between the coating and the iron substrate (Figure 1). Compositional analysis shows that the coating consists of both aluminium and zinc, characteristic of an aluminium-zinc coating such as Galfan or Aluzinc/Galvalume, rather than a pure zinc galvanised layer.

1 (Custom)

Figure 1: Control Sample

 The sheeting from the 45mm panel has a very thin coating on comparison to the control sample (Figure 2). Results of compositional analysis confirm that this coating is also an aluminium-zinc coating.

2 (Custom)

Figure 2: Sample from 45mm panel

The coating on the 25mm panel is cracked and has therefore not bonded properly to the iron substrate (Figure 3). The compositional analysis does not detect any aluminium in the coating.

3 (Custom)

Figure 3: Sample from 25mm panel

Conclusion

On comparison with the locally manufactured sheet, neither of the sheets of Chinese origin is suitable for the application.

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