Metal finishing Q&As since 1989

-----

Color coated galvanized sheet

Paint peel-off problem is coming because of rough surface developing during galvanising. Please suggest the route cause. We can arrange the sample to you after GP skin pass and colour coated.

Abhishek Pande
- Pune, India
2005

---

2006

Hi,
Gone through your query. Rough zinc coating is not the only cause of peeling off paints fromHDG sheet. Pretreatment plays an important role, make sure that good chromating done before painting, Phosphating of the sheets have to be done by ensuring proper dipping time in phosphating tanks, If necessary build up fresh solutions of phosphating chemicals in the tank. Too much DFT is one of the cause, oven temperature too high helps to develop pin hole on painted surface. Oven temperature too high at the entry of the oven etc
Hope above will be of some sorts of guideline to overcome the problem.
Best regards,

Mahbub Hossain
- Dhaka, Bangladesh

---

2007

For GI sheets it is not advisable to do the seven tank process of phosphating. We are using GI sheets in tons. For the spray painting on GI sheets you must apply the etch primer [[on eBay or Amazon] ]. This creates certain roughness on the surface of the sheet & acts as a binder between the sheet & the paint.

It has been very much successful. Please try this.

Jagjit Singh
heat transfers- New Delhi, India