US1781119A - Process of producing malleable-iron castings - Google Patents

Description

l.. H. MARSHALL Filled April l27, 1928 Nov. l1,` `1930.

' '..flPRoCEss on PRODUCING MALLEABLE IRON CASTINGS l Patented Nov. 11, 1930 UNITED STATES PATENT OFFICE A LESLIE H. MARSHALL, OF COLUMBUS, OHIO, ASSIGNOB OF GIVE-HALF TO ADIN A. GRUBB, 0F COLUMBUS, OHIO PROCESS OF PRODUCING MALLEABLE-IRON CASTINGS Application led April 27,

The invention relates to improved methods of producing malleable iron castings and the invention has to do especially With the annealing treatment employed in the production of the castings.

One object of the invention is to provide an improved process of producing rust-proof malleable iron castings by which the time, labor and cost of production are reduced while the standard of quality is amply maintained.

Another object of the invention is the production of malleable iron castings having uniformly good machining qualities.

Various other objects which-are more or less incidental or ancillary to those above noted will appear in the following description.

In the usual procedure for making malleable iron castings, the metal is first cast as white iron. In this condition the ironis hard and brittle and can be machined only by grinding. Such castings, with orl without sand blasting or other definite cleaning operations, are then packed in annealing pots, either with or Without a surrounding pac ing of gravel or other refractory material. If the castings are smally and the pots not large, the packing material is sometimes omitted, but Where the castings are large the packing material is usually employed to support the castings and prevent their distortion at the elevated temperatures of the annealing treatnient. The packing material also tends to lessen oxidation'of the castings during the heat treatment.

The annealing pots or boxes when packed with the castings in one or the other of the above described Ways, are carried into the annealing furnace, said furnace is closed and the tiring started. Commonly an open llame type of furnace is employed in which the flames and hot gases sweep from the combustion chamber through the annealing chamber over and around the aimealing boxes and thence out through suitable flues.

To properly anneal the castings a very definite treatment is required. Thus they must be held at an elevated temperature, (1400 to 1800 F.) for aperiod of from one six days. Thehigher the temperatures within 1928. Serial No. 273,208.

the stated range the shorter is the holding period. Then the temperature is allowed to fall not faster than 10 F. per hour until it has reached 1000o F. The doors of the fur-l nace can then be opened and the annealingv pots and their contents allowed to cool to room. temperature. In commercial practice v the total time of the annealing cycle may Vary in different plants, from six vto fourteen days.

It is evident from the above that the castings during the annealing treatment receive a severe and protractedexposure to oxidizing conditions. In spite of the protection afforded by the gravel packing, the castings have an oxidized surface as they come from the anneal and frequently as high as 1% or more of the castings are rendered Worthless by such oxidation.

A very considerable percentage ofthe malleable iron produced is subjected to some rust-proofing process soon after it is annealed. Usually this recess is that of hot dip galvanizing in w ich the castings are given a zinc coating by immersing them in a bath of molten zinc. The castings must be clean and free from oxide or scale in order to take satisfactory zinc coatings. Accrdl by gumming and clogging the cutting tool.

I believe that the formation of this tough outer layer on the annealed castings is due to decarbonization of the surface metal by reason of the oxidizing conditions that maintain during the prolonged heat treatment. The structure of American or 'black heart malleable cast iron, after the anneal, consists essentially of a matrix of soft-iron through which is interspersed nodules of graphite. The presence of the graphite lowers the strength of the metal somewhat but it adds greatly to the ease with which the metal can be machined. With oxidizing conditions prevailing during the anneal, the

the castings, such castings having what the be threaded on the surface.

trade terms a picture frame fracture. In this case, an appreciable percentage of combined carbon is present in the exterior layer While the interior, or by far major portion of the casting, is free from combined carbon. I believe this condition is due to the fact that a certain amount of silicon, as Well as some but not all of the carbon, is oxidized out of the surface layer during the anneal and that this diminution of silicon prevents the complete graphitization of the carbon. The ungraphitized carbon combined with the iron forms a very hard compound which, as previously stated, seriously interferes with the machining of the casting.

Both of the last two defects become especially noticeable when the castings have to In such a case the machining is conned largely to the section having the undesirable structure and While the major part of the casting may be normal, the machining is just as diilicult as it would be if the casting were unsatisfactory throughout. A striking example of such a case is to be found in malleable cast iron pi e fittin s, of which a large tonnage is pro uced, W ere a considerable percentage of the surface of each casting is threaded.

As all three ofthe above described objections to the prior practice are due to thel presence of oxidizing conditions during annealing of the castings, I have sought to devise a method of easily and effectively maintaining non-oxidizing and preferably slightly etching conditions through the prolonged annealing v treatment, or at least while the temperatures are high enough to cause a substantial amount of oxidation of the castings.

The non-oxidizing conditions should obtain certainly above 1000o F. and preferably above 700 F. To this end the process provides for the maintenance around the castings of an atmosphere of non-oxidizing and preferably slightly etching gas or vapor, during the heat treatment of thecastings, or at least during the existence of oxidizing temperatures. This can be done in various Ways. For example, some at least of the advantages of the process can be attained by conducting the non-oxidizing gas or vapor as such into closed pots or boxes which hold the castings during the annealing heat treatment. However, a method Which I prefer because of its marked simplicity and effectiveness is to introduce into the closed annealing pots containing the castings a substance adapted when heated to say 1000o F. or less to evolve a gas or4 vapor having the desired non-oxidizing properties. I prefer also to employ the atmosphere of a'gas or vapor that is heavier than air and to use tight-bottomed annealing boxes so that in the early stage of the heat treatment the relatively heavy gas or vapor displaces any air present and forces it from the container through leakage openings around the top thereof. Various substances can be employed to furnish the gaseous or vaporous atmos here, such, for example, as ferric chloride, ferrous sulphate, and bleaching powder. However, I have securedthe best results with halogen compounds that volatilize before temperatures are reached at which the substantial oxidation of the castings can occur. In order that my invention and the method of practicing it may be clearly understood, I shall now describe preferred methods of proceeding, reference being had to the accompanying dra-Wings in which suitable apparatus is diagrammatically shown.

In the drawings:

Fig. 1 is a vertical section through a stack of annealing pots or boxes filled with castings ready for the annealing heat treatment.

Fig. 2 shows diagrammatically a typical open flame furnace with a series of stacks of annealing pots arranged therein for the heat treatment.

Fig. 3 is a transverse section on 3, 3 of Fig. 2.

A preferred specific procedure employing the apparatus illustrated is as follows: White iron castings that are to be malleablized, having first been thoroughly cleaned bysand blasting, tumbling or other suitable method are packed as at 1, 1 in a tight-bottomed annealing pot or box 2 and all voids around and between the castings are lilled With a packing 3 consisting of 95% to 98% of sand and the balance (5% to 2%) of ferrie chloride, the percentages being by Weight. The chloride may be anhydrous or ycommercial ferric chloride crystals (FeCla-GHZO) may be used. I have made satisfactory use of a packing consisting of 98% silica sand of about 8 mesh size and 2% of commercial ferric chloride crystals crushed to one inch and smaller pieces. A substantial layer of this packmg material is preferably placed over the topmost castings to prevent oxidizing gases sweeping 1n and reaching the surfaces of the castings. If a single annealing pot or box is to be employed a metal cover should be used to close its top, but inthe present instance the pot 2 is closed by the bottom of 5 a second pot 2 placed upon the top of pot 2, the pots being provided at their upper edges with upwardly extending .fianges to facilitate such stacking. The second pot .2 is packed I with castings and packing material in the same manner as above described, and vsimilarly athird pot 2 may be stacked upon the second pot and similarly packed with castings. The top pot is then closed with a suitable metal plate 4. Tol reduce flow of gases through the joints betweenthe pots and between the top pot and its cover 4, said joints are sealed by lutings 5 of suitable material such as paste formed by mixing powdered iint and water. To facilitate handling, the 20 pots are stacked upon a suitable base 6.

Y The annealing pots having been packed and stacked in the manner described, are placed in an annealing furnace, designated in its entirety by 7, as indicated in Figs. 2

' 25 and 3. Then, the furnace charging door 8 having been closed', heating of the furnace is begun. In the furnace shown'heat is supplied by a powdered coal burner 9. The 'flames and hot combustion gases of the burner'are projected into -the urnace over and around the stack of annealing pots, the gases finally passing out of the furnace at points near the floor through ducts 10, 10 which lead to lues 11 which in turn communicate with a stack or other suitable draft means. The furnace, heated in this manner, has its annealing chamber gradually brought up to some suitable temperature between 1400" F. and 1800 F. and ythere held for one to six days, according to the temperature, aspreviously explained. For example, a satisfactory procedure is to consume 25 hours in heating the furnace to a temperature of 1650 F. after which the temperature is held between 1600 F. and 1650 F. for 60 hours, and after that the furnace is allowed adually to cool to a temperature of approximately 1000 F. over a period of 80 hours. The doors of the furnace are then opened and the pots and their contents allowed to cool to room temperature.

,The castings thus treated when removed from the annealing pots, because of the nonoxidizing and etching conditions maintained therein, are found to be bright and clean in appearance and in an especially good condition for the application of zinc or other rustproof coatings. Furthermore, because of the non-oxidizing conditions under which the castings have been annealed, the castings as they come from the auneal are not only bright and clean but .are substantially free from superficiall layers that are either tough or unduly hard, so that'the castings have uniformly good machining qualities.

If the castings annealed in accordance with my process are to be left exposed to air for any considerable length of time, a day or more, before receiving a rust-proof coating,

they should be washed in a caustic solution to remove or neutralize the traces of halide that remain on them. Otherwise they will tarnish. A suitable treatment consists in agitating the castings for five minutes in a hot (just below the boiling point) 10% aqueous solution of tri-sodium phosphate to which has been added one volume of soluble oil to 30 volumes of the aqueous solution. (The lterm soluble oil is used to denote an Oil vhas been indicated, the time and temperature of the annealing heat treatment can be considerably varied. Also, as has been stated,

use can be made of various other substances y inl place of the ferrie chloride. For example, the ferric chloride of the foregoing specific example can be replaced by a similar amount of ferrous sulphate. However, the latter substance does not give an atmosphere that is as'completely non-oxidizing as can be secured br the use of halogen compounds and I accor in ly. prefer to use the latter.

Some og these halogen compounds merely vaporize and thus displace any air resent in the container, the vapors being heavier than the air. The vapors also react to some extent with any scale that may form on the casting and this slight etchingjef'iect tends further to insure clean castings at the end of the annealing treatment. Examples of haloen compounds that merely vaporize, at least 1n part, below 7 00 F. are aluminum chloride, antimony chloride, arsenic chloride, mercurio chloride, phosphorus trichloride, carbon tetra chloride, sulphur monochloride and bismuth chloride. Others of the halogen comn pounds liberate halogen gases on heating and they are therefore particularly suitable as the halogen gas has a somewhat stronger etching effect than the halide vapors above noted, as well as serving to dis lace any air present and affording anon-oxi izing atmosphere. Examples of this latter class of halogen compounds are gold (auric) chloride, ferric chloride, cupric chloride, phosphorous pentachloride, sulphur dichloride, sulphur tetrachloride and bleaching powder. .Halogen compounds other than chlorides can be used. For example, anhydrous ferrie bromide is operable in the process, though some of the other halogen compounds are preferable because of their lower cost. While the ferric chloride the desired atmosphere and thisl can be done lby using the substancemore or less in excess.

. sodium chloride.

. It is to be observed further that the halogen compound employed need not be introJ duced 'as such into the treating container. Thus, in the packing materialthere can be substituted for the 2% of ferrie chloride, for example, 4% (by weight) of a mixture of equal amounts by Weight of powdered ferrous sulphate (calcined) and powdered On heating the packing, these two compounds react to give ferrie chloride and sodium sulphate. Any other known method of forming ferrie chloride, by reaction within .the packing, might be used. However, this method of introducing the faerric chloride usually contaminates the packing, as With the sodium sulphate in the' eX- ample just given, and this may be undesirable.

The packing material employed in the proc#I ess can to advantage be used over and-over again. It is desirable to have the vaporizable compound present in excess so as to insure non-oxidizing conditions. Some of the halide vapor. material recondenses on the inert material of the packing and thus would be lost if the packing were not repeatedly used. It can bereused successfully if enough of the vaporizable compound is added after each treatment to make up for the loss in the last preceding anneal. The amount -to'be added can best be determined by trial, that is by making a series of runs adding various amounts of the vaporizable compound tov the reused packing material and noting the minimum amount that prevents oxidation of the castings. I have found that where a packing containing 2% of commericial ferrie chloride crystals is used, an addition of 1% of said crystals is enough to adapt the packing for reuse.

In some instances offtrouble with castings having the picture frame type of fracture,

I find it desirable to supplement the nonoxidizing atmosphere during the heat'treatment by the addition of asmall amount; of finely divided ferro-silicon to the packing material. In my copending application Serial No. 242,838, filed December 27,192?, I have described .a method for form-ing silicon or silicon alloy coatings on iron or other articles. In that method a typical procedure is to surround the article to be c oated with a packing comprising inert materlal, such as gravel, and suitable percentages of a vaporizable halide, such for example as anhydrous ferro-silicon than is employed in the coat.- I

4ing process, While no appreciable coating of silicon or silicon alloy is formed on the casting, nevertheless the effect is to prevent loss of silicon from the casting and thus obviate the above described troubles which go with the picture frame fracture. To carry out this modification of the process it is ordinarily sufficient to add to the packing material containing the usual (above specified) amount of hahde, 0.25% by Weight of ferrosilicon (50% silicon), indeedI have found as little as 0.1% of 20 mesh ferro-silicon (50% silicon) to be sulicient for the purpose.

It is to be observed that if the packing material containing a halide is to be out of use for any extended `period of time, it should be kept in a closed container, as it tends to pick up moisture from the air and detericrate.

In'cases Where it may be feasible or expedient to provide they non-oxidizing atmosphere by introducing a non-oxidizing gas as such into the otherwise closed annealing pot or container, as mentioned in the earlier part of this specification, the halogens, viz., chlorine, bromine, iodine and uorine are the most suitable non-oxidizing gases for the purpose; and of these gases chlorinel is the cheapest and to be preferred. The pressure and rate at which t e gas is passed into the container will best be determined by trial, the object being, of course, to secure the desired result With a minimum amount of the g My improved method of annealing in a halogen atmosphere tends to loosen the adherent sand and scale found on the castings as they come from the mold. It is possible, therefore, to anneal castings just as they come from the foundry 4and dispense with the cleaning operation previous to packing` them for the anneal. It is then usually necessary .to give the annealed castings a slight amount of tumbling to remove the last traces of sand or scale.

It frequently happens that castings have sand burned into their surface in the casting process, making them dificlt or impossible to clean. Some are of such shape that ,parts of the surface cannot be readily reached by the ordinary methods of cleaning. Such castings after being annealed in a halogen atmosphere can be easily cleaned by the usual methods.

In characterizing herein the gas or vapor in the annealing pots as non-oxidizing, that term is of course used in its strict or limited sense indicating that the gas or vapor is of such a nature that it will not form a yfilm of metallic oxides on the castings during the annealing process.

It will now be apparent that my process, especially in its preferred forms, affords an exceedingly simple and easily practiced method of avoiding the previously explained ill effects of oxidizing conditions during the malleablizing treatment, and it Will also be apparent that satisfactory rust-proofed malleable castings and machined malleable castings can be produced at lower cost by my improved method than by the prior methods.

While I have set forth some of the variations as to materials and procedure which may be followed in the carrying out of my invention, it should be understood that I have not attempted to point out all such variations but that the invention comprehends all such modifications Within the scope of the appended claims. Since, as has been' explained, use can be made in my process of either halogen compounds that merely vaporize or those that evolve halogen gas at or below iron oxidizing temperatures, for the sake of simplicity and to avoid multiplication of claims, I shall in the appended claims use the term halogen gas in a broad sense coinprehending both halide vapor and halogen gas.

What I claim is l. The improvement in the art of producing malleable iron castings which consists in subjecting White iron castings to a heat treatment at temperatures and for a period of time adapted to eiect malleablization of said castings, and maintaining around said castings a non-oxidizing and etching gaseous atmosphere While the temperature of the heat treatment is above 1000 F.

2. The improvement in the art of producing malleable iron castings which consists in subjecting white iron castings to a heat treatment at temperatures and for a period ot time adapted to effect malleablization oi said castings, and maintaining around said castings a non-oxidizing and etching gaseous atmosphere while the temperature of the heat treatment is above 700 F.

3. The improvement in the art of producing malleable iron castings which" consists in subjecting white iron castings to a heat treatment at temperatures and for a period of time adapted to effect malleablizationof said castings, and maintaining around said castings a non-oxidizing atmosphere of halogen gas while the temperature of the heat treatment is above 1000 F.

4. The improvement in the art of producin malleable iron castings which consists in su jecting White iron castings to a heat treatment at temperatures and for a period of time adapted to effect malleablization of said castings, and maintaining around said castings a non-oxidizing atmosphere of halogen gas While the temperature of the heat treatment is above 7 00 F. e y

5. The improved process of roducingmalleable iron castings which inclu es enclosing White iron castings in a tight bottomed container together with a substance capable when heated to temperatures below 1000 F. of evolving a non-oxidizing and etchin .gas heavier than air, and subjecting the saidgcontainer and its contents to a heat ltreatment at temperatures and for a period of time adapted to effect malleablization of said castings, whereby a non-oxidizing and etching atmoshere is maintained around the castings durling the said heat treatment.

6. The improved process of producing malleable iron castings which includes enclosing white iron castings in a tight bottomed container together with a substance capable when heated to temperatures below 700 F. of evolvinga non-oxidizing and etching gas heavier than air, and subjecting the said container and its contents to a heat treatment at temperatures and for a period of time adapted to effect malleablization of said castings, whereby a non-oxidizing and etching atmosphere is maintained around the castings during the said heat treatment. i

7. The improved process of producin malleable iron castings which includes enclosi ing White iron castings in a tight bottomed container together with a substance capable when heated of evolving a non-oxidizing halogen gas heavier than air, and subjecting the container and its contents to a heat treatment at temperatures and for a period of time adapted to effect malleablization of said-castings, 'whereby a halogen gas atmosphere is maintained around said castingsduring said heat treatment. j

8. An improved process of producing malleable iron cast-ings which comprises enclosing White iron castings in a container together with a solid packing material composed in part of a refractory substance and in part of a substance capable when heated of evolving a non-oxidizing and etching gas, and subjecting the container and its contents to heat treatment at temperatures and for a period of time adapted to eliect 'malleablization of said castings, whereby a non-oxidizing and et ching atmosphere is maintained around the castings during the said heat treatment.

9. An improved process of producing malleable iron castings which comprises enclosing white iron castings in a container to gether with a packing material composed in part of a refractory substance and in part of a substance capable, when heated, of evolving a non-oxidizing halogen gas, and subjecting the container and its contents to heat treatment at temperatures and for a period of time adapted to effect malleablization of said castings, whereby a non-oxidizing atmosphere is maintained around the castings during the said heat treatment.

10. An improved process of producing malleable iron castings which comprises enclosing white iron castings in a container together With a packing material composed in part of a refractory substance and in part of ferrie chloride, and subjecting the container and it-scontents to heat treatment at temperatures and for a period of time adapted to ef fect malleablization of said castings, whereby a non-oxidizing atmosphere is maintained around the castings during the said heat treat-- ment.

11. An improved process of producing malleableiron castings which comprises enclosing White iron castings in a container together with a. packing material composed in part of a substance capable, when heated, of evolving halogen gas and in part of ferrosilicon, and subjecting the container and its contents to heat treatment at temperatures and for a period of time adapted to effect malleablization of `said castings, whereby a non-oxidizing atmosphere is maintained around the castings and loss of silicon from the castings is obviated during the said heat treatment.

In testimony whereof, hereunto aHix my LESLIE H. v MARSHALL.

signature.

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