De-dross System for Float Tin Bath

Using Linear Motor

Oxygen can enter the float tin bath through air leaks in the bath structure, in a contaminated nitrogen supply, or via extraction from the bottom surface of the glass. 

The Solubility of oxygen in molten tin as below:

The solubility is quite temperature dependent. At temperatures typical of the hot end of the bath, the oxygen solubility is 900 ppm, while at the exit end, it is on the order of 10 ppm.

Thus air ingress at the hot end of the bath has the potential to produce substantial amounts of dissolved oxygen. This tin then flows to the cold end, where exsolution occurs, resulting in the formation of tin oxide precipitate or " dross" on the surface of the tin. When this dross is trapped under the ribbon, it can attach itself to the ribbon forming a defect known as tin pickup.

Removal of dross is generally achieved using de-dross pockets, and using roll de-dross machine.  However, the roll machine can not clean molten under the glass ribbon. 

Using linear motors to drive tin into these pockets can significantly increase de-dross effectiveness. Two linear induction motors are installed on de-dross pockets situated at each side of the bath. They propel polluted tin into the de - dross pockets, forcing clear molten tin out of the submerged outlets of the pockets back into the bath. The dross accumulates in the pockets and can be raked out periodically. Using linear motors to force tin into the pockets means they work more effectively 24hrs a day, providing a cleaner tin surface.

A linear motor installed on a de-dross pocket