Manufacturing equipment for galvanized steel sheet, and manufacturing method of galvanized steel sheet

Patent metadata

Field	Value
Publication number	US-9487852-B2
Application number	US-201113818128-A
Country	US
Kind code	B2
Filing date	Aug 9, 2011
Priority date	Sep 2, 2010
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

A manufacturing equipment for galvanized steel sheet includes coating tub to coat steel sheet dipped in coating bath wherein the bath including molten zinc and Al is stored at bath temperature T 1 , separating tub to separate by a flotation top-dross by precipitating the top-dross in the bath wherein the bath transferred from the coating tub is stored at bath temperature T 2 lower than T 1 , adjusting tub to dissolve dross wherein the bath transferred from the separating tub is stored at bath temperature T 3 higher than T 2 and Fe of the bath is unsaturated, and circulator to circulate the bath in order of the coating tub, the separating tub, and the adjusting tub.

First claim

The invention claimed is:

1. A manufacturing method of a galvanized steel sheet, the manufacturing method comprising:
circulating a coating bath which is a molten metal including a molten zinc and a molten aluminum in order of a coating tub, a separating tub, and an adjusting tub;
coating a steel sheet which is dipped in the coating bath at the coating tub in which the coating bath transferred from the adjusting tub is stored at a predetermined bath temperature T 1 ;
separating by a flotation a top-dross which is precipitated at the separating tub in which the coating bath transferred from the coating tub to the separating tub is stored at a bath temperature T 2 which is lower than the bath temperature T 1 of the coating tub;
dissolving a residual dross at the adjusting tub in which the coating bath transferred from a lower part of the separating tub is stored at a bath temperature T 3 which is higher than the bath temperature T 2 of the separating tub; and
decreasing a temperature of the coating bath of the separating tub to a temperature lower than a temperature of the coating bath of the coating tub, thereby preventing a formation of bottom-dross, and removing top-dross separated by the flotation,
wherein an aluminum concentration in the coating bath of the separating tub is more than 0.14% by mass,
wherein an aluminum concentration in the coating bath of the coating tub is 0.15% to 0.25% by mass, and
wherein a first zinc-included-metal which includes an aluminum with a concentration higher than the aluminum concentration of the coating bath in the coating tub is supplied to the adjusting tub and is not supplied to the separating tub.

2. The manufacturing method for the galvanized steel sheet according to claim 1 ,
wherein the bath temperature T 2 of the separating tub is at least 5° C. lower than the bath temperature T 1 of the coating tub and is higher than a melting point of the molten metal.

3. The manufacturing method for the galvanized steel sheet according to claim 1 ,
wherein the bath temperature T 1 , the bath temperature T 2 , and the bath temperature T 3 satisfy a following formula (1) and a following formula (2) in degrees celsius, when a difference of a bath temperature decrease of the coating bath when transferred from the adjusting tub to the coating tub is ΔT fall in degrees celsius
T 1 +ΔT fall −10 ≦T 3 ≦T 1 +ΔT fall ±10  (1)

T 2+5 ≦T 3  (2).

4. The manufacturing method for the galvanized steel sheet according to claim 1 ,
wherein at least two of the coating tub, the separating tub, or the adjusting tub are made by dividing one tub with a weir, and
a bath temperature of each tub which is divided by the weir is controlled independently.

5. The manufacturing method for the galvanized steel sheet according to claim 1 ,
wherein a storage of the coating bath in the coating tub is five times or less of a circulating volume of the coating bath per one hour.

6. The manufacturing method for the galvanized steel sheet according to claim 1 ,
wherein a storage of the coating bath in the separating tub is two times or more of a circulating volume of the coating bath per one hour.

Assignees

• Okada Nobuyoshi
• Hoshino Masanori
• Sakatoku Atsushi
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Okada Nobuyoshi
• Hoshino Masanori
• Sakatoku Atsushi

Classifications

• C23C2/04

  characterised by the coating material · CPC title

• C23C2/06

  Zinc or cadmium or alloys based thereon · CPC title

• C23C2/12

  Aluminium or alloys based thereon · CPC title

• C23C2/003 Primary

  Apparatus · CPC title

• C23C2/28

  Thermal after-treatment, e.g. treatment in oil bath · CPC title