US2231120A - Process for producing malleable iron castings - Google Patents

Description

Patented Feb. 11, 1941 PATENT OFFICE PROCESS FOR- PRODUCING IRON CASTINGS Gerth Herrmann, Wnppertal-Barmen, Germany No Drawing. Application February 28, 1939, Se-

rial No. 259,027. In Germany January 18,

2 Claims. (Cl. 148-16) Thisinvention is concerned with a new method for producing malleable iron castings.

The usual method for obtaining white heart malleable iron castings consists in placing the raw castings together with comminuted iron ore in layers into annealing pots, so-called temper pots, and subjecting them in a suitable oven or furnace for a considerable time to a temperature of about 1000 C. The carbon which is chemically bound with iron is thereby partly liberated in the form of free carbon (temper carbon), depending on the annealing time and the temperature employed. Part of this liberated carbon is wholly withdrawn from the casting and escapes in gaseous form, being chemically bound as carbon monoxide and carbon dioxide by the oxygen liberated from the iron ore. One of the disadvantages of this method resides in th ne'- cessity of heating up to and maintaining at the annealing temperature not only the castings being treated but also the annealing pots and the iron ore, which constitute a multiple of the mass and weight of the castings, thereby occasioning a considerable and quite costly consumption of heat.

The present invention avoids the drawbacks of the usual method by accomplishing the annealing and decarbonizing of the material according to a new process which uses a uniform gaseousatmosphere and dispenses with the use of auxiliary means, such as annealing pots and iron ore and the like. The details pertaining to the new process are explained below.

The new process is based on the discovery, supported and tested by experiments and practical use, that satisfactory and unobjectionable results in effective decarbonization are obtained by heating or annealing the castings in a suitably heated retort in an atmosphere of illuminating gas, or gas of similar composition, for example, generator gas, water gas, Mond gas, or the like. The castings are for this purpose packed in lightweight iron loading baskets and are introduced preferably under a seal-protected hood into an annealing oven which may be heated electrically, by gas or by coal, or in any other.

either partially or wholly, in order to form carbon dioxide, which isthe active ingredient for oxidation of the carbon liberated from the castings. However, according to the preferred form of the invention, ordinary unburned gas is used, but 5 is mixed with a small amount of air before or as it is introduced into the annealing chamber. The oxygen of the air produces a partial combustion of the gas (without flame formation), reacting with carbon monoxide which is a constit- 10 uent of all the gases suggested for use to form carbon dioxide, and thereby obtain a gas suitable for the desired reaction.

' In order to avoid a cessation of the chemical reaction and to obtain sufficient decarbonization 15 of the casting material, the gas which absorbs thecarbon must be continuously removed and renewed by fresh gas, together with the requisite small quantity of air. The gas which is withdrawn from the oven still has a high heating 20 value and may be used for any desired and suitable heating purposes, thus rendering the method very economical.

Depending on the condition of the gas employed for the process, it maybe desirable to 25 withdraw its moisture content, which otherwise could cause spunk or scale formation on the'surface of the iron. A suflicient drying of the gas may be obtained, for example, by conducting it through'calcium chloride or through silica jel, or by subjecting it to cooling. Such separate removal of moisture is, however, usually unnecessary in practice, since small traces of moisture cannot act detrimentally.

An example of carrying out the new process is described below with respect to a raw casting having a low carbon content of about 2.8% to 3.1%, a silicon content of 0.9% to 1.1%, a manganese content of about 0.35%, and a sulphur content of about-0.2%., 40

The casting is placed in a retort, heated to 980 C., and annealed by substantially maintaining that temperature for about 24 hours. At the conclusion of this first annealing period, the closure, for example, the sealhrg hood, of the retort or oven, is removed in order to obtain a cooling of the casting in air down to about 760 C. This latter temperature is maintained for about 10 hours, with subsequent progressive slow cooling amounting to an hourly reduction of tem- -perature by about 5 C., down to 650 C., whereupon the casting is removed from the retort. A gas mixture comprising substantially equal parts of air and illuminating gas is introduced into the retort and continuously circulated through it during the pre-heating and also during the annealing period. For example, in the annealing of about 4 tons of raw castings a total amount of about 200 cubic meters of a mixture of gas and air in the ratio of 1:1 is conducted through the retort during the entire annealing operation. No appreciable gas supply is required during the latter part of the process, that is, during the cooling from substantially 760 C. to 650 C.

It is understood that the terms used here and also in the accompanying claims are to be interpreted with sensible latitude. Reference to a specific gas, wherever used, is intended to comprehend the use of an equivalent gas or gas mixture to the extent noted in the foregoing specification. Likewise, references to specific temperature conditions are meant to convey temperatures of or substantially in the neighborhood of those indicated.

Changes may be made within the scope and spirit of the appended claims, wherein is defined what is believed to be new and desired to have protected by Letters Patent of the United States.

What is claimed is:

1. The process of producing white heart malleable iron castings, which consists in placing the raw casting into a sealed retort, heating said retort to heat the casting contained therein to annealing temperaure, and maintaining in said retort during the entire process of heating and annealing oi said casting a gaseous atmosphere consisting of illuminating gas mixed with air in such proportion that only cracking thereof, that is, a chemical reaction without flame formation takes place to obtain effective decarbonization of said casting without oxidation and formation of scale thereon.

2. The process defined in claim 1, together with the step of continuously circulating through said retort a fresh gaseous mixture of the composition specified and maintaining the pressure of said gaseous mixture substantially uniform, 20