Method of descaling ferrous metals

Patented Mar. 24, 1953

2,632,718

UNITED STATES PATENT OFFICE

2,632,718

METHOD OF DESCALING FERROUS METALS

Nathan H. Brodell, Canton, Ohio, assignor, by mesne assignments, to William Isler, Cleveland Heights, Ohio

No Drawing. Application August 21, 1946, Serial No. 692,142 (CI. 134—4) or other solutions of ferric chloride, may however, be employed with desirable results. If the articles, when immersed, are at a temperature above the boiling point of the solution, undesirable chemical changes occur in the solution.

After the coating has been thus formed on the articles, they are removed from the solution, and are permitted to dry. In some cases, however, the articles may be subjected to the next step in the treatment before the coating has dried. This next step consists in subjecting the coated articles to a conventional anneal in an annealing furnace, or to a conventional heat treatment which is a part of a hardening of the article. Such anneal or other heat treatment usually involves heating the articles to a temperature above 1200° F. and maintaining the articles at such temperature for a predetermined period of time.

This anneal or other heat treatment causes the ferric chloride to break down to form ferrous chloride, free iron, or iron oxide, or a combination of two or more of these, with a liberation or evolution of chlorine. The chlorine, thus liberated or evolved, has an oxidizing effect on the scale, which tends to loosen the scale.

Following this treatment, the articles are removed from the heat treating furnace, and quenched in a solution of caustic soda (NaOH), which is preferably a 10% aqueous solution of caustic soda. The articles are preferably quenched before they have cooled to a temperature below about 1100° F., but good results have been obtained when the articles are quenched from a temperature as low as about 800° F. The solution of caustic soda, prior to such quenching treatment, may be at any temperature from room temperature to the boiling point of the solution. This quenching treatment causes the loosened scale to fall away from the articles, and leaves them with a smooth, clean, mottled appearance.

In order to avoid injury to the hands of the operator when handling the articles after they have been removed from the quenching bath, any slight traces of caustic Soda which adhere to the articles are preferably removed by rinsing them in hot or cold water.

The method, as thus described, removes scale from the articles in an inexpensive and highly efficient manner, and is particularly advantageous in that it removes scale from recesses and

Claims.

This invention relates, as indicated, to a method of descaling ferrous metals, but has reference more particularly to the descaling of ferrous metal articles, such as castings, forgings, bar stock, tubing, etc.

A primary object of the invention is to provide a method of the character described, which is effective to remove scale from such articles in an inexpensive but highly efficient manner, and the use of which is free from objections which are in- ¹⁰herent in conventional descaling methods, such as pickling, sand blasting, shot blasting, and the like.

Another object of the invention is to provide a method of the character described, which uti- 15 lizes readily available and inexpensive chemical compounds.

A further object of the invention is to provide a method of the character described, which makes use of steps employed in the conventional heat 20 treatment methods, such as annealing and hardening.

A still further object of the invention is to provide a method of the character described, which is effective to remove scale from portions 25 of ferrous metal articles which are usually inaccessible by sand and shot blasting methods, such aS recesses and corners in intricate castings and forgings.

Other objects and advantages of the invention ₃θ will be apparent during the course of the following description.

In accordance with the invention, the sCalebearing articles, as for example, steel forgings, are first immersed in a saturated aqueous or other solution of ferric chloride (FeCh). The solution of ferric chloride is preferably at room temperature, but may be at any temperature below the boiling point of the solution. The scale-bearing articles are also preferably at room temperature, _4Qbut may also be at any temperature below the ⁴boiling point of the solution. In practice, however, the articles, prior to immersion, should be at a temperature not in excess of about 150° F.

The articles, as stated, are immersed in the ₄₅solution of ferric chloride which forms a glossy crystalline coating when dried. By using a saturated solution of ferric chloride, a maximum number of ferric chloride crystals are deposited upon the surface qf the articles. Weaker aqueous 50

2,632,718 corners in intricate castings and forgings which are usually inaccessible by sand blasting methods. Moreover, the chemicals which are employed are available in commercially desirable quantities at relatively low cost. A further advantage lies in the fact that the heat treatment which is a part of the method serves the double purpose of annealing or hardening the article and breaking down the coating to loosen the scale on the article.

The ferric chloride may, if desired, be added directly to the furnace either in crystalline form, or as a vapor, gas, or liquid, the ferric chloride in this form reacting with the scale to loosen the scale.

Instead of using ferric chloride as the oxidizing agent, other chlorides of polyvalent metals may be used with satisfactory results, such, for example, as stannic chloride, cupric chloride and mercuric chloride. As a matter of fact, any completely oxidized polyvalent metallic halide is effective to produce satisfactory results. Organic compounds having physical properties similar to such metallic halides may also be used, such organic compounds being those included under the generic name of “aliphatic and aromatic polyhalides.” Carbon tetrachloride has also been used, with good results.

Instead of using caustic soda as the solution in which the articles are quenched, other compounds, such as sodium carbonate (NaCOs), ma? be used with fairly good results. Other quench ing media, such as a 10% aqueous solution of sodium chloride, or water alone, may be used, a..> these furnish a sufficiently drastic quench. In some cases, particularly where it is desired to harden the articles, oil may be used as a quenching medium.

Instead of immersing the articles in the quenching media, the quenching medium can be sprayed onto the articles.

It will be understood that the various changes in temperatures, strengths of solutions, and other details of the method may be resorted to, without departing from the scope of the subjoined claims.