US2692187A

US2692187A - Method of pickling and pickling compositions

Info

Publication number: US2692187A
Application number: US251981A
Authority: US
Inventors: Allan E Chester; Joseph T Irwin
Original assignee: Poor and Co
Current assignee: Brent Chemicals Corp; Poor and Co
Priority date: 1951-10-18
Filing date: 1951-10-18
Publication date: 1954-10-19
Anticipated expiration: 1971-10-19

Description

Patented Oct. 19, 1954 UNITED STATES PATET OFFICE METHOD OF PICKLIN G AND EICKLING COMPOSITIONS tion of Delaware No Drawing. Application October 18, 1951, Serial No. 251,981

14 Claims.

This invention relates to the acid pickling of metals, more particularly the acid pickling of steel, and to new and useful pickling compositions.

One of the objects of the invention is to provide a new and improved method of pickling ferrous metals in which the pickling process is greatly accelerated.

Another object of the invention is to provide a method of pickling steel sheets prior to galvanizing.

Still another object of the invention is to provide a method of pickling which results in a longer life for the pickle tank or vessel where the pickling operation is practiced.

Another object of the invention is to provide a pickling method which can operate satisfactorily at relatively high iron concentrations.

Still a further object of the invention is to provide a method of pickling ferrous metals to produce surface characteristics that bring about better adherence of other metals which are electrodeposited on said ferrous metals.

A further object of the invention is to provide new and useful pickling compositions which can be added to acid pickling baths in order to produce new and improved results. Other objects will appear hereinafter.

These objects are accomplished in accordance with this invention by providing a pickling bath containing a compound capable of liberating colloidal sulfur, preferably sodium thiosulfate, and a chromium aldonate, e. g., a reaction product of a water soluble chromic compound of an alkali metal with an aldonic acid in proportions such that the ratio of chromium atom to alkali metal atom is within the range of 1:1 to 1:3, the ratio of chromium atom to the aldonic acid molecule is within the range of 1:1 to 1:3, and the ratio of total alkali metal atom plus the aldonic acid molecule to chromium atom is at least 3:1.

The chromium aldonates preferably employed for the purpose of the invention are the chromium gluconates, but it will be understood that the chromium aldonates may be derived from other aldonic acids, as, for example, mannonic, arabonic, galactonic and xylonic. These acids are obtainedv by the oxidation of the corresponding aldoses and all of them, including gluconic acid, have alpha and beta lactone forms. The alkali metal ion may be either sodium, potassium or lithium. Chromium aldonates which are satisfactory for the purpose of the present invention are described in U. S. Patent No. 2,428,- 356.

The invention will be illustrated but is not limited by the following examples.

Example I A composition suitable for use as an addition agent to an acid pickling bath was prepared by mixing together the following ingredients:

2703 pounds of water 2'70 pounds 5 ounces dextrose 27 pounds /2 ounce caustic soda 1900 pounds sodium thiosulfate 3720 cc. chromium gluconate, derived by mixing together:

48 pounds of sodium hydroxide 48 pounds of chromic anhydride 444 pounds of 50% gluconic acid, and making up to gallons of water as described in Example I of U. S. Patent No. 2,428,356.

The aforementioned ingredients were mixed in the order given. Caustic soda and dextrose are optional ingredients, the dextrose being added as a reducing agent and the caustic soda to make it possible to ship the product in steel drums.

Example II A hydrochloric acid pickling bath was prepared containing 10 to 15% I-ICl. The composition described in Example I was added in proportions of 0.5 to 2.0 gallons per thousand gallons of the pickling bath at the start of the pickling operation. In the bath cold rolled carbon steel sheets were pickled. To replace the dragout of acid an additional 0.5 to 2 gallons of the composition of Example I were added per thousand pounds loss of HCl as the pickling process continued.

In comparative tests using 2 parts of the addition agent described in Example I per thousand parts of 15% H0; solution, compared with a 15% I-ICl solution containing no addition agent, it was found that the bath containing the addition agent produced uniform attack on the steel in 3 minutes, which could not be accomplished in 20 minutes without the addition agent.

Example III solution may be varied plus or minus 50% of the quantity given in Example I.

The employment of a substance such as sodium thiosulfate which liberates colloidal sulfur in the pickling solution is not claimed herein per se but is the subject of another application of one of the joint inventors, United States Serial No. 694,424, filed August 31, 1946. Itwill be understood that other substances capable of liberating colloidal sulfur as, for example, sodium polysulfide may be employed in the practice of the invention.

The chromium aldonate apparently acts as a cathode depolarizer of the couples formed on the surface of the metal which is being pickled. As a result, the pickling action is exceedingly rapid and at the same time a uniform attack of the acid on the metal is obtained.

The thiosulfate tends to prevent the formation of alpha and gamma iron oxide and the sulfur which is liberated to some extent also acts as a depolarizing agent. The resultant pickling bath therefore may be described as a depolarized pickle bath. The quantity of sodium thiosulfate or chemically equivalent amount of another sulfur liberating compound is subject to variation but is preferably within the range of l to 8 parts of sodium thiosulfate per 700 parts of 7% sulfuric acid or about 1 to 8 parts colloidal reactive sulfur in 5000 parts of sulfuric acid.

With the pickling composition described in Example I the optimum results are obtained by using 1 to 3 parts of said composition per thousand parts by weight of a pickling solution containing either sulfuric acid or hydrochloric acid in the concentrations previously described.

The pickling temperatures are preferably within the range of 120 F. to 200 F. in sulfuric acid pickling baths and within the range of 60 F. to 120 F. in hydrochloric acid pickling baths.

In the practice of this invention results have been produced which have not before been attained in the acid pickling of ferrous metals.

The invention is especially useful in pickling sheet steel which is to be galvanized. The pickling action provided by the invention appears to produce better wetting between the surface of the sheet and the metal which is applied in the galvanizing process. One of the principal advantages of the invention is the provision of a more uniform pinpoint etch with an acceleration of pickling speeds. The practice of the invention is particularly desirable in that it provides longer life of the pickle tank. It also has the advantage that the process may be operated with the same solution for a longer period of time because the operation proceeds satisfactorily at relatively high iron concentrations. The ferrous metals which are pickled in acid pickling baths in accordance with the practice of the invention have excellent surface characteristics and provide better adherence for electrodeposited metals than ferrous metals which have been acid pickled by ordinary methods.

The invention is hereby claimed as follows:

1. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in an acid pickling bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

2. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a sulfuric acid picking bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

3. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a hydrochloric acid pickling bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

4. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in an acid pickling bath containing a chromium gluconate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being enective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

5. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a sulfuric acid pickling bath containing a chromium gluconate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufiiciently small amount to remain dis persed in colloidal form.

6. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a hydrochloric acid pickling bath containing a chromium gluconate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being efiective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

7. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in an acid pickling bath containing chromium gluconate and sodium thiosulfate, the quantity of sodium thiosulfate being sufficient to liberate 1 to 8 parts of colloidal sulfur to 5000 parts of the acid contained in said bath.

8. An acid pickling bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate about 1 to 8 parts colloidal sulfur to 5000 parts of the acid content in said bath.

9. A sulfuric acid pickling bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate about 1 to 8 parts colloidal sulfur to 5000 parts of the acid content in said bath.

10. A hydrochloric acid pickling bath containing a chromium aldonate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate about 1 to 8 parts colloidal sulfur to 5000 parts of the acid content in said. bath.

11. An acid pickling bath containing a chromium gluconate and a .compound capable of libcrating elemental colloidal sulfur, the quantity of said last named compound being efiective to liberate about 1 to 8 parts colloidal sulfur to 5000 parts of the acid content in said bath.

12. A sulfuric acid pickling bath containing a chromium gluconate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate about 1 to 8 parts colloidal sulfur to 5000 parts of the acid content in said bath.

13. A hydrochloric acid pickling bath containing a chromium gluconate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate about 1 to 8 parts colloidal sull5 fur to 5000 parts of the acid content in said bath.

14. An acid pickling bath containing chromium gluconate and sodium thiosulfate, the quantity of sodium thiosulfate being sufficient to liberate 1 to 8 parts of colloidal sulfur to 5000 parts of 5 the acid contained in said bath.

References Cited in the file of this patent UNITED STATES PATENTS 10 Number Name Date 1,995,766 Chester Mar. 26, 1935 2,249,383 Hilty July 15, 1941 2,428,356 Chester et a1. Oct. 7, 1947 OTHER REFERENCES Modern Inorganic Chemistry, Mellor, pub. Longmans Green, p. 475.