US2184535A - Treating lead alloys - Google Patents

Description

Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE mums man ALLOYS No Drawing., Application December 21, 1938, Serial No. 246,999

4 Claims.

This invention relates to the treatment of lead alloys, particularly =type metal compositions which ordinarily consist of lead, antimony and tin but which may comprise minor amounts of other elements.

Among other features the invention provides a process for refining-the metal to remove objectionable impurities therefrom and to enhance the recasting properties of the alloy.

As is well known, type metal is melted and cast into Monotype, Linotype, stereotype or similar forms which, after they have served their purpose, are remelted for reusing. In the process of remelting and recasting, there ordinarily forms on the metal a certain amount of dross which, if not removed, will interfere in the casting, not only by clogging up the machine but also by causing the metal to be sluggish thereby producing imperfect castings.

This dross or ash, which is often referred to as skim, consists of impurities such as oxides,

either inherent in the alloy, or formed in the melting and casting process from one or more of the elements of the alloy, or by contamination with other metals with which the alloy comes in contact. Obviously, there is a definite loss of metal in the dross itself which destroys the desirablecomposition of the alloy. This loss further is aggravated by occlusion of metal within the dross or oxide particles and the inclusion of metal prills held mechanically in the dross when same is removed from the metal.

To adjust the composition of the metal, it is ordinarily necessary to add new metal. Further, in order to recover the metal in the' dross the latter must be retreated, both of which operations add to the cost of metal.

In the present invention, as will be seen hereafter, not only is the dross formation greatly reduced but, also, the objectionable impurities inherent in the metal are minimized by special refining methods whereby a higher grade alloy of superior quality is produced. V

The practice of treating the rough or pig metal intendedfor the make up of the type metal orsimilar alloy usually consists of melting the stock metal in a pot or kettle for the removal of certain impurities such as copper, zinc, sulphur,

etc., by means of fluxes which allow the reac-.

tions to take place at certain temperatures. Some of these impurities however, when present in proportional ratios such as copper, iron, sulphur, arsenic, do'not react at these temperatures but form compounds between themselves and/or with the metals composing the alloy, the compounds being, in many instances, soluble in the alloy at operating temperatures. In order to break up these compounds, it is common practise to oxidize the harmful components at a temperature at which they are insoluble in the alloy. This method results in a loss of a portion of the metals which constitute the alloy.

An object of theinvention is to reduce the valuable elements of the type metal to their metallic state so that they readily alloy into the des red composition and thus overcome the objections previously mentioned. To bring this about,-an organic compound of the carbohydrate group, preferably in solid form, is added to the molten metal, said carbohydrate supplying at one and the same time reducing gases, steam and carbon in a nascent or active form which react selectively on the harmful compounds in the alloy.

Carbohydrates may be represented by the gen- 1 eral fbrmular Ca:( HO)y aind readily decompose upon heating, into steam and combustible gases such as hydrogen, carbon monoxide and hydrocarbons, which gases, except the steam, are strictly reducing in the action on the metal. The steam, which does not decompose at the prevailing temperature, eflectively agitates the metal bath to insure completeness of the reactions.

The addition of the carbohydrate comprises the first step of the improved process of which the second consists of treating the metal with a reducing gas, suchas hydrogen, in order to completely reduce residual metal oxides. The third and final step is the addition of a small amount of metallic deoxidizer. Indications are that the addition of a small amount of the deoxidizer inhibits intercrystalline oxidation on the grain boundaries .of the alloy thereby increasing the ductility of the solid metal which is readily evidenced, as will be seen later, by bend tests: The small amount of deoxidizing metal also slightly increases the 'viscosity of the alloy in the fluid creased ductility measured by the number of bends before breaking of Linotype rules.

Thus it has been found that the amount of dross from metal treated by this improved process is substantially reduced, amounting to only some .02% to .13% of the metal (depending on the amount of metal used per hour in the machine) as compared to the well known much higher drossing losses ordinarily encountered. Higher density of the alloys when treated by the improved process is evidenced by the lack of aforesaid porosity'in the cast metal. Likewise the increase in ductility is evident from the fact that two point hair-line rules can be rolled up fifty or more times before breaking which is impossible with rules made from the same type metal subjected to the usual caustic treatment. Such rules usually fall after only a few rollings.

In carrying out the process of the invention, the carbohydrate is preferably added by means of a tool designed to hold this reagent at the bottom of melting pot or kettle. The boiling action accompanying the decomposition of the carbohydrate effectively stirs the metal during the reaction period which -preferably is carried at a temperature of not higher than 600 to 650 F. The amount of carbohydrate necessary to complete the reaction is usually about two ounces per ton of metal.

As soon as the boiling action has somewhat subsided, the reducing gas, e. g., hydrogen, is introduced through a pipe submerged in the bath, care being taken to clear the pipe of air before submerging the tip thereof in the: molten metal. The reducing gas treatment is,preferably performed atthe sametemperature as the carbohydrate treatment.v

Immediately on completing the first two steps, that is, adding the carbohydrate and subjecting the metal to the reducing gas, the surface of the greases metal is smmmed for the removal of any skim that may have formed during these steps in the process. These skims can be re-treated for the recovery of any valuable constituents and as the amount of skim formed is small, its treatment adds little to the cost of manufacture.

The deoxidizer is next added either in elemental or alloy form, the latter being ordinarily preferred as more economical inasmuch as losses are minimized when such deoxidizers as the alkali or alkaline earth metals are used.

In order to expel any excess gases dissolved or occluded in the metal during the preceding steps, the metal is allowed to cool to approximately its freezing point and the surface skimmed clean. It is then reheated slightly to a temperature from 600 to 650 F. and cast into suitable molds.

What is claimed is:

l. The process for treating lead-base alloys which consists in establishing a bath of the metal and sequentially treating same with a carbohydrate, a reducing gas and a metallic deoxidizing agent thereby increasing the alloys resistance to drossing under repeated meltings and castings:

2. The process for enhancing the properties of type metal which comprises effecting decomposi tion of a carbohydrate within the body of a molten bath of such an alloy, subjecting the bath to the action of a reducing gas, and thereafter incorporating a small amount of a metallic deoxidizer therein.

3. The process for treating type metal which comprises establishing a molten bath thereof, decomposing a carbohydrate in the body of the bath, subsequently scrubbing the bath with hydrogen gas, incorporating a small amount of a metallic deoxidizer in the bath following the scrubbing treatment, lowering the temperature of the bath so treated to approximately its freezing temperature, skimming the cooled bath, and casting the purified type metal.

4'. In the treatment of type metal, the improvement which consists in subjecting the alloy to the scrubbing action of hydrogen gas, and thereafter incorporating a small amount of a metallic dioxidizing agent in the scrubbed metal.

HERMAN L. SMITH.