Method of controlling solution concentration in strip cleaning line

• US 6,494,961 B2
• Filed: 03/30/2001
• Issued: 12/17/2002
• Est. Priority Date: 03/30/2001
• Status: Expired due to Fees

• Current Assignee: Novelis Incorporated (Hindalco Industries Limited)
• Original Assignee: Alcan Incorporated (Alcan)
• Inventors: Simpson, Stephen D.
• Primary Examiner(s): EL ARINI, ZEINAB
• Application Number:
  US09/823,672
• Publication Number:
  US 20020139397A1
• Time in Patent Office: 627 Days
• Field of Search: 134/3, 134/15, 134/18, 134/28, 134/29, 134/32, 134/36, 134/41
• US Class Current: 134/3
• CPC Class Codes: C23G 3/023 by spraying
• CPC Class Codes: G01N 27/06 of a liquid involving electrolysis G01N27/26
• CPC Class Codes: G01N 31/16 using titration
• CPC Class Codes: G05D 11/138 by sensing the concentration of the mixture, e.g. measuring pH value

Abstract

An automatic control system is provided for acid concentration in an aluminum strip cleaning line wherein an aluminum strip is contacted with an acid solution while passing through an acid cleaning bath and the concentration of the acid in the bath is adjusted by adding either concentrated acid or water to the bath. A conductivity probe is provided in the acid bath and generates a first signal approximately proportional to the free acid concentration of the bath. An on-line process titrator periodically samples the acid bath and by a dual endpoint titration obtains the free acid concentration and total acid concentration of the bath and thereby generates a second signal indicative of the actual free acid concentration and the total acid concentration. These first and second signals are fed to a programmable logic controller, which based on the signal from the titrator calculates a correction factor for the signal from the conductivity probe to thereby obtain a corrected value for free acid concentration. The bath acid concentration is then adjusted as required based on the corrected specific conductivity value. The above procedure may also be used in the cleaning of an aluminum strip with an alkali solution.

Claims

1. A method for automatically controlling a cleaning solution concentration in an aluminum strip cleaning line wherein an aluminum strip is contacted with a chemical cleaning solution while passing through a cleaning bath and the concentration of the chemical in the bath is adjusted by adding either concentrated chemical or water to the bath wherein said chemical is selected from an acid and an alkali and wherein the bath has a free chemical concentration and a total chemical concentration,

which method comprises providing a conductivity probe in said cleaning bath and thereby generating a first signal approximately proportional to the free chemical concentration of the bath;

providing an on-line process titrator to periodically sample the cleaning bath and by a dual endpoint titrations obtain the free chemical concentration and total chemical concentration of the bath and thereby generate a second signal indicative of an actual free chemical concentration and the total chemical concentration;

feeding said first and second signals to a programmable logic controller;

based on the signal from the titrator calculating a correction factor for the signal from the conductivity probe to thereby obtain a corrected specific conductivity value for free chemical concentration and adjusting the cleaning bath concentration as required based on the corrected specific conductivity value.

2. A method according to claim 1, wherein the cleaning chemical used is an acid.

3. A method according to claim 2, wherein the bath temperature is measured and a correction factor is applied to the specific conductivity measurement based on the temperature.

4. A method according to claim 2, wherein the specific conductivity is continuously measured.

5. A method according to claim 4, wherein the titrations are conducted at predetermined timed intervals.

6. A method according to claim 2, wherein the acid cleaning solution is sprayed onto top and bottom faces of the aluminum strip by means of spray nozzles arranged above and below the strip.

7. A method according to claim 6, wherein the acid cleaning is followed by at least one water rinse wherein rinse water is sprayed onto the top and bottom faces of the strip.