US 2670284 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Patented Feb. 23, 1954 iriioiinoir'ion or summons ALLOY Carl M.- Zvanut, Alton, Ill., assig'iio'r to" Olin Industries, 1110., East Alton, 111;, a corporation of Delaware its mettle. Application Jnnei28,1950',
Serial No. 170,963
This invention relates to the production of nonierrous metals and, particular, to the pro-- duction of tin-bronze.
. Cast tin-bronze is subject to certain defects which have long been observed and: for which remedies have been sought. Among the chief of these defects are porosity, and segregation of the tin. Segregation of the tin in a cast tinbronze. bar may occur in the interior of the bar, called normal segregation, or at the surface of the bar, called inverse" Segregation or sweat. Porosity may occur within the bar or at the surface'of the bar, or both.
Porosity in a cast bar is particularly undesirable when the bar to be cold rolled. A strip rolled from a badly porous casting will contain internal gas holes even to thin gauges.
Severe normal segregation of tin leads to banding of tin-rich areas when abar in which the segregation occurs is rolled. This banding results in a low fatigue life for the strip. Inverse segregation of tin in a cast bar results in fragmentation of the tin layer on the surface of the casting and the development of fissures and surface roughness during the rolling. f
It has been discovered that, in commercial practice, one source of porosity is the occlusion in the cast bar of gases" generated during the melting process by the hydrocarbons with which much of the scrap, used commercially as a source of metal, is coated. However, it is not commercially feasible to render the scrap oil-free before melting.
Inverse segregation has been attributed by the literature of the prior art to the presence of reducing materials or conditions in the melting process, and accordingly oxidizing fluxes or oxidizing conditions have heretofore been thought desirable.
The object of the invention is to provide an economical, efiicient, and expeditious process of degassing non-ferrous alloy melts.
Further objects will become apparent to those skilled in the art in the light of the following description:
In accordance with this invention, generally stated, a process is provided by which tin-bronze bars are produced, which are non-porous and in which the tin is uniformly distributed. This process can be used to produce such bars even from scrap metal contaminated with oil and grease. The process is characterized by the feature that, after the slag or dross has formed in the usual way upon the surface of the melt, graphite is applied thereto.
In carrying out the process, a furnace is charged with metal toproduce the desired alloy.
The melting may be carried out in any suitable furnace, such as an electric furnace of the character shown in United States Patent No. 1201, 6'71, but preferably one which does not substantially aggravate the reducing conditions inherent in the presence of hydrocarbons on the charge (1. e., oily scrap). During the melting no fluxes of special composition need be added, but the melt is permitted to become covered with slag uor dross in the normal way. After the surface of the melt is covered with slag, powdered graphite is dusted on the surface of the slag cover. The graphite is distributed over the surface with reasonable uniformity and in an amount suffi cient to create fissures or cleavages in'the slag layer so that the latter becomes discontinuous. The specificamount of graphite required in any given case cannot be forecast with certainty, the best measure being to-continue the dusting of graphite until the continuity of the slag-cover begins to break. Continued addition of the graphite accentuatesthe discontinuity of the slag layer to the point that the slag becomes lumpy; About five or ten minutes after the slag coating has been disintegrated; the molten metal is sufll= ciently degassed for practical purposes. '7-
Alternativelm-a layer-of graphite may be ap plied to the surface of the melt as soon as a substantial liquid phase is produced, but before it is heavily slagged. In this instance a layer of graphite from A1 inch to 1 inch thick may be dusted on the surface so that, as the slag is formed, it agglomerates rather than forming a continuous layer. Thus, in this case, the charge is degassed as melting continues.
In order to assure the production of castings which are free of porosity and segregation, it is of course necessary to observe the usual precautions in pouring the molten metal, dressing the molds, etc.
A specific example of the procedure employed in accordance with this invention is illustrated by the making of a pair of small lS-pound castings of an alloy consisting of 4.67% tin, 0.23% phosphorus, and the balance copper, in the form of an ingot 3 inches by 1 inches by 12 inches. Oily scrap having the above-noted composition was charged into a high frequency electric .melting furnace where the metal was brought to a temperature of 1200 C. During the melting, the surface of the melt became covered with a continuous layer of slag. During the melting, the molten metal became heavily gassed with vapors arising from the oil on the scrap. About eight minutes before the metal was ready to be poured, powdered graphite was sprinkled upon the surface of the slag to an extent such as to make a layer of slag and graphite about 1 inch thick on the surface of the molten metal. The metal was poured at a temperature of -1230 C. into a water-cooled mold dressed with lampblack. The castings produced had a density of 8.83 grams per cubic centimeter, and 8.82 grams per cubic centimeter, respectively, as compared to an optimum value of 8.87 grams per cubic centimeter, and both were free from inverse segregation. A similar set of castings made without the graphite treatment of the surface of the melt were bars unfit for rolling.
In instances where it is desirable to introduce v the phosphorus after the charge has become molten, the phosphorus is preferably introduced before the graphite is applied to the surface of the melt.
The graphite employed in accordance with the presentinvention may be any commercial graphite, but preferably is in powder form, having a fineness, of at least 97% through a No. 200 U. S. Standard sieve.
The action of the graphite in rendering the slag layer discontinuous thereby vents the slag layer so that the occluded gases may readily escape from the melt, through the slag layer, or the fissures created therein.
From the foregoing description, those skilled in' the art should realize that the invention accomplishes its object and provides a simple and inexpensive method of degassing non-fer.- rous alloy melts. While one specific example of the procedure has been disclosed in detail, it is not to be understood that the invention is limited to that embodiment, but that it is applicable at large to non-ferrous alloy melts wherein segregation and porosity problems are encountered. Moreover, while the disclosure has emphasized the use of scrap which is contaminated with oil orgrease, it is to be understood that, even in cases where the scrap is clean, the tendency to gas may exist and the operation of the graphite V or equivalent, in rendering the slag layer discon- 4 tinuous and thus venting the gases from the molten metal, is within the purview of this in vention. Furthermore, while graphite has been disclosed as an example of the agent for rendering the slag layer discontinuous, and is the only agent presently proved to be effective, it is envisioned that other materials having a specific gravity comparable to that of graphite, and which are not readily wetted by the molten slag, may function similarly, and consequently such equivalents are contemplated by and within the scope of the present invention.
Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:
. 1. In the art of producing non-ferrous alloys.
in which a charge of metal contaminated with gas-forming material is melted in a furnace, and a slag cover is allowed to form on the melt, the process of degassing the melt which comprises introducing graphite into the slag cover in an amount suflicient to render the slag cover discontinuous, and maintaining the slag cover discontinuous and the melt quiescent for a time sufficient to permit gases to escape from the melt. .42. In the art of producing non-ferrous alloys, in which a charge of metal contaminated with gas-forming material is melted in a furnace, and a slag cover is allowed to form on the melt, the process of degassing the melt which comprises dusting powdered graphite on the surface of the slag cover until the slag cover becomes discontinuous, and maintaining the slag cover discontinuous and the melt quiescent for a time sufficient to permit gases to escape from the melt.
. a CARL M. ZVANUT.
. References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 130, 63? Hersey Aug. 20, 1872 1,730,775 Lukens Oct. 8,1929 1,775,159 Donaldson et a1. Sept. 9, 1930 2,181,094 Ness' Nov. 21, 1939 2,221,626 Anderson Nov. 12, 1940 22,302,999 OBrien Nov. 24, 1942 2,479,211 Christensen Augglfi, 1949