US2179513A - Metal casting - Google Patents

Description

2 Sheets-Sheet l A. W. MORRIS METAL CASTING Nov. 14, 1939.

Filed April 12, 1955 NOV. 14, 1939. A W MORR|$ 2.179.513

METAL CASTING Filed April l2, 1935 2 Sheets-Sheet 2 Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE METAL CASTING of Rhode Island Application April 12, 1935, Serial No. 15,939 2 Claims. (Cl. 22-188) My present invention relates to the art of casting metals, and has particular reference to the production of better castings at lower cost.

The present practice in casting metals includes the use of sand or metal molds, and a furnace in which the metal to be cast is melted, the molten metal then being conveyed in ladies from the furnace to the molds and poured therein. The castings, when cooled, are sandblasted or tumbled, and then machined.

The problem of producing better castings comprises selection of the metal which is most suitable for the desired casting, casting of this metal 15 under the most suitable conditions, and use of a mold which does not change or effect the char--A acter of the casting or its surface whereby the completed casting has a smooth, unblemished surface, and requires little or no finishing or machining.

20 The principal object of my invention is to produce castings having ideal chemicalv and physical characteristics.

An additional object of my invention is to perform the casting operation under the conditions 25y most suitable for the metal being castl A further object of my invention is to utilize a mold that is inert or has a definite predetermined reaction to the cast metal.

Another object of my invention is to provide a 30 smooth cast surface that is unblemished and does not require finishing. l

A still further object is to obtain a nished casting of accurate,predetermlned size.

With the above and other objects and advanta- 35 geous features in view, my invention consists of novel arrangements of parts, and novel methods of casting, more fully disclosed in the detailed description following, in conjunction with the acconipanying drawings, and more specifically dei fined in the claims appended thereto.

In the drawings:

Fig. 1 ls a front elevationpartly in section, of `a novel casting furnace;

Fig. 2 is a central transverse section thereof;

45 and Fig. 3 is a perspective of a novel mold section. The casting of metals has heretofore been handled as follows: The metal has been melted within a furnace where the atmosphere in contact 50 with the mem bath has been suitame for the particular metal, as in an open-hearth, air, or electric furnace. The molten metal has then been tapped and taken from the furnace to the molds, and the desired pieces cast by pouring the metal into the molds.

In practice I have found the following objec- -tions to this common method. When the metal is taken from the furnace it cools rapidly before being poured for castings; to offset this the metal is superheated, which is costly and is bad metallurgically, whereby the metal isnot ordinarily maintained at the best casting temperature for 1 the desired metallurgical results in the casting, and the castings are not uniform. Moreover, lo the pouring temperature for different castings varies widely. But perhaps more important than the difficulty due to wide variation in temperatures between the furnace and the v molds is the common difficulty of varying atmosphericconditions. When the metal is taken from the furnace in a ladle it is soon exposed to and contaminated by the outside air both before `pouring and as the metal is poured into the molds; moreover, the molds are full of gases and air that also contaminate the metal poured into their cavities, as do also the cold surfaces of the molds. 'I'hese difficulties have not been entirely overlooked; I am aware that much work has been done to improve the methods of handling hot metals between the furnaces and the molds and to prepare the molds for receiving the metal. But so far as I know, .such improved methods are expensive and the results have not yet been satisfactory for metals melting at very high temperatures like steel, for in one way or another such metal is contaminated Amore or less during the transition time between furnace and mold or in the mold, and such metal is particularly sus-l ceptible to contamination by exposure to an atmosphere other than one specially prepared for the particular metal.

This is particularly .true of metals melting at very high temperature-2000 F. and above, which commonly need to be poured as the molds are being filled. I am aware of casting methods in which the molds are filled by suction action or by pressure causing mold filling movement of metal from a suitable reservoir. Withoutgoing into the distinctions in detail, one skilled in the art knows that these prior casting methods are not suitable for general application; they are expensive; and they have not and apparently cannot be used in a great many places where the Y casting molds must be filled by the metal pouring methods as distinguished from suction,r pumping, or immersion methods'. as in many instances the expense is tool great. But with metals at temperatures about 2000 F. substantially all casting is done by metal pouring methods to ll the l molds.

According to my invention I can pour the metal in the usual way to fill the mold, but I eliminate the time element in the present practice of transferring the metal from the furnace to position for pouring it into the molds. To do this I carry the mold to the melting furnace, insert it in the furnace, pour the metal to fill the mold while both mold and metal are in the furnace, and then either remove the mold with its casting from the furnace, or I may remove the casting from the mold while it is still in the furnace. In such operations there is a time element in the step of pouring the metal from the molten mass to fill the mold; with my mold filling method the pouring takes place while the mold is in the furnace and the operation is possible without using any time during which the molten metal is in transit between the furnace and any point outside of the furnace, and without exposing the metal while being poured to an` atmospheric condition different from that in the furnace. The metal is put in the mold before the mold leaves the furnace, and in its cast condition the metal is taken from the furnace either with or without the moldl as explained hereinafter. Thus, there is no chance for contamination of the molten metal by transporting it between the furnace and the mold, and yet the mold is filled by the desired and simple pouring step as from a ladle. Furthermore, by inserting the mold into the melting furnace prior to the ladle pouring operation, the interior mold surfaces and the cavities formed by them are prepared in an effective way for taking the hot metal under the best conditions. The extremely high temperature of the furnace will act instantly on said surfaces to dry them; and will also act instantly on all the gases carried in the mold cavities to expand these gases and drive them out of the mold. So before the mold can be filled these cavity gases (which cause so much trouble in the present casting practices) are driven out and dissipated in the much larger body of gases above the molten mass of metal whereby the cavity atmosphere before pouring will be substantially the same as the furnace atmosphere above the molten mass. That atmosphere is normally and suitably controlled according to the character of molten metal mass and is one that does not contaminate the metal; in other words, it is inert to the molten metal. It is an entirely different atymosphere than obtains in the mold cavities and against the surfaces of the metal as treated in thepresent casting practice where the metal is carried from the furnace and poured from a. ladle to the mold.

My method may be carried out in practice by labor saving apparatus of various kinds coordinated for the purpose, but it may be carried out by hand operations, and I want to emphasize that no expensive apparatus is needed.

Referring to the drawings, I may melt the metal, stainless steel for example, in an openhearth furnace represented in the drawings by the reference numeral I0. The melted metal rests on the hearth II and is at very high temperature when ready for casting, but need not be superheated. A characteristic of stainless steel is that given any opportunity it will absorb carbon with great avidity; it is an alloy and the less carbon it contains the less proportion of expensive elements is necessary in the alloy to give the stainless results. It is also susceptible to contamination in other respects. This is one reason that stainless steel castings made in the ordinary way are frequently defective.

I leave the molten body of stainless steel in the furnace and do my casting in the furnace. The open-hearth furnace has an atmosphere of hot gases passing over the surface of the melted bath; the gases are controlled so that the-composition of the alloy will remain as wanted in the casting. Furthermore, these furnace gases maintain the desired temperature in the liquid, such temperature of the metal being easy to regulate when it is in a large mass and kept in the furnace. I make use of this situation by holding the temperature and atmosphere above the furnace metal at the points best suited to casting. Ordinarily the furnace temperature needs to be kept far above the best casting point so as to compensate for the loss of heat when the metal is transported from the furnace to the molds, and when thus transported the metal is commonly poured in an atmosphere and at a temperature, both outside andginside the mold, that are not so good as the furnace atmosphere and temperature.

Referring to Figs. 1 and 2, I prefer to provide a ladle I2 inside the furnace, pivotally mounted on a bar I3 which may be rotated by a handle from outside the furnace. An endless chain con- -veyor I4 which may be stopped at any point, by

any suitable control mechanism, passes through the aligned doors I5, I6 of the furnace, and may pass below the furnace, but preferably extends over the top, thus affording a three point support by means of gears I1, I8, and I9 at the support points, one of the gears being motor driven. A plurality of book type molds 2U, see Fig. 3, each comprising a mold section 2I and a check section 22, are hingedly mounted in the conveyor and are adapted to be closed by a U-shaped plunger 23, and to be retained in closed position by a manually applied clamp 24; as the molds pass the ladle I2, they'are stopped, the ladle is tilted to ll the molds, and the molds move out to the agitator 25, where the clamp is removed, the agitation opening the molds to permit removal of the castings. A'second U shaped plunger arrangement 23 may be utilized to control the speed of opening of the molds. The ladle is hand lled by dipping into the molten metal, but may if desired be filled by means of an endless bucket arrangement. Any known type of releasable spring connection may be used for the conveyor and the molds to keep the molds open until closed as described.

The advantages in filling the mold by pouring the metal as described above are that its surfaces and cavities are nicely prepared by the heat of the furnace for receiving the casting, the

time for the molten metal to leave its furnace l body and get into the mold is brought to a minimum, and the exposure of the metal as it is being poured is in the atmosphere of the furnace gases and at the same temperature,with minimum risk of contamination. The pouring from ladle to mold can take place without any danger of pouring too much as' all excess drops immediately to the furnace bath, so that wastage or expense of remelting is avoided; the mold may if desired be made to take this into account as by having exit passages to cause a mold circulation of hot metal until its cavities are lled solidly. But the most important advantage resides in the ideal conditions surrounding the pouring operation for the transfer of metal rfrom the body in the furnace to the cavity in the mold, without contaminating exposure to atmospheric or cold body surfaces of the mold such as occur in the present mold pouring practice.

In using my method for making malleable castings there is a further advantage in that my molds may be moved directly from the furnace where they are filled to the annealing furnace in which the mold may be emptied and the casting annealed with a minimum heat loss; and the less handling between the melting furnace and the annealing furnace, the better their metallurgical character can be safeguarded. The method can be used with the air type of furnace as well as the open-hearth, and in the same way.

The operation of my method with regard to the electric furnace is essentially the same 'as in the case of the open-hearth furnace, with this and possibly additional advantages. A well known type of electric furnace is of the rocking type; as the furnace rocks in its normal operation for temperature transfer, the. molten mass can be ing the combined picked up by a pouring lip and the mold filled by the movement of the furnace as the mold is stopped within the furnace. One advantage in the use of an electric furnace resides in the better control of the atmosphere therein.

It will be of advantage in some instances to remove the castings while still in the furnace. This can be provided for by a shelf, not shown, at 'the side of the hearth where the casting can be left. And it will be advantageous in some instances to pass the castings as they are removed from the furnace through a furnace door directly into an annealing oven. One of the doorsv may bein a passage from the furnace to an annealing oven and opened to admit the casting from the furnace, the advantage residing in' the elimination of contaminating influences.

Stainless steel, malleable iron, grey iron, ordinary steel, and such very high melting point metals may readily be cast by pouring the metal -under this method. By stainless steel as used in this specification I mean to include all the steel and iron alloys which are important from their characteristic in resisting rust and acid. Alloy steels and irons of the class included are known by various names popularly called stainless steel but which include such metals as rustless iron, Silcrome, Invar, Durmet, and trade names now well known but which vary from time to time.

Malleable iron may be cast as described, with great increase in strength and quality, and at a great saving in cost. The production of malleable cast iron comprises, first, the production of white iron castings which are hard .and brittle, and second, the annealing of the white iron castings to obtain a ductile product, this annealing changcarbon in the casting to free carbon, technically known as temper carbon. The character of the casting depends on the composition and its uniformity, and the air furnace is used in the United States for high grade malleable, instead of the cupola, to increase the uniformity; the 'open hearth furnace'is used in Europe, for the same reason.

rllhe properties of malleable iron are largely controlled by the amount of carbon present, which may be as low as 2.00% or as high as 3.00%. High carbon in general makes the metal weak and less ductile, but produces sound machineable castings offgood surface; with high: carbon, the

silicon is ordinarily kept low to obtain best resuits in the neighborhood of .50% to .60% and conversely, is kept high, to as much as 1.20% to 1.30%v with low carbon iron. If` high carbon,

'high silicon are both used as with the present practice, the poured metal, using sand molds, will not be white as the carbon separates and becomes free as the temperature drops. The manganese and sulphur vary together, from .25% tol.49% for manganese, and from .05% to .14% for sulphur; phosphorous is preferably below .20% and may be less than .10%.

With the improved casting method, it is feasible to cast malleable iron having both high carbon and high silicon, thus obtaining greatly improved tensile and other physical characteristics, and quicker annealing, while retaining the desired white fracture, which shows that all the carbon is combined. Thus, when using a typical malleable iron havingv the following analysis:

Per cent C 2.75 Si .65 Mn .30 S .07 P .20 Fe Balance the tensile strength was determined to be 54,000 lbs. per sq. inch, the elongation in two inches, 18% and the reduction in area 18%.

When using a malleable iron as follows:

Per cent C 2.75 to 3.00 Si 1.20 to 1.50 Mn .30 to .70 P-; .05 to .l0 S .05 to .l0

the tensile strength became 70,000 lbs. per square inch, the elongation 24% and the reduction in area 25%.

The cost was also greatly reduced; casting time was cut 50%,

vas an example.

' Stainless steel as cast in the usual way cornes out of the mold with a rough surface where the sand has adhered, or a crustof blemished metal.`

When a smooth finish is needed, the rough surface or crust is cut or ground olf to expose the unblemished and permanent surface often desired for ornamental purposes and sometimes for machine parts that are wanted in finished forms and with finished surfaces. So far as I know, stainless steel shapes have not heretofore been cast without the crust that must be cut off to expose the ornamental character of the metal. According to one feature of my invention, I make stainless steel castings. that do not need to have their surfaces cut 0H to expose the ornamental character of the metal. V'

Stainless steel castings have heretofore been made in sand molds and not in permanent molds, the reason being that permanent molds have ingredients that react chemically on the stainless steel. The latter is peculiarly susceptible to diicult. It seems to be true from experience that when cast in sand molds, stainless steel will retain its chemical integrity except for the forming of the crust above mentioned.

According to my invention, I not only make stainless steel castings with their ornamental surface, but do this in a permanent mold.` The fact that I have discovered a way to make good stainless steel castings at a greatly lowered cost compared to known methods, has special significance.

Everyone knows that stainless steel would have a much wider use in making cast shapes if it were not so high in cost. One skilled in the art knows that the prohibitive cost is primarily due to the surface nishing operation, rather than the cost of the alloy metal itself, although the latter is expensive. Many shapes that are wanted in stainless steel form are not commercially available on account of the expense; for example, an ornamental door knob for an automobile can` be made of easily cast metal and chromium plated at a much less cost than the same piece can be made of stainless steel surface by prior art methods. So the plating method is used commercially because the stainless steel surface in that shape would be too expensive to obtain.

My invention is particularly aimed at increasing the uses of stainless steel shapes under these competitive conditions.

To practice my invention I proceed as follows:

I provide a permanent mold of metal lined with copper, the copper being alloyed with a hardener such as aluminum to toughen it and make it easier to cut the mold cavity, see Fig, 3, the mold sections 2l, 22 having the described lining 26. The mold may be entirely of copper and aluminum, and is made of sufficient bulk to absorb the heat of the cast metal and avoid fusing the mold surfaces. This will follow as a result of the high heat conductivity of the mold, which takes the heat from the molten steel so fast that the temperature at the molding surfaces is not high enoughover a sucient time to melt the mold. This characteristic of my mold enables me to use copper alloyed with aluminum even though such alloy will melt far below the melting point of any steel.

In making the mold for my purpose I select copper as its principal metal, which gives me the characteristic above mentioned. The addition of aluminum acts as a hardener to facilitate machiningthe mold and other handling.

In a general sense a copper mold used for casting steel will not contaminate the chemical characteristics of the steel. The metal of the mold is generally inert chemically to an ordinary steel metal being cast. By being generally inert, I mean that the body of one will not be affected by the body of the other in the wandering of chemical constituents from one to the other in the casting operation at the relative temperatures of contact. But in casting stainless vsteel I have discovered that this general inert condition is not all that is desirable to safeguard the casting againstsurface contamination. The surface of the casting in a stainless steel article is ,the thing my invention is particularly int-ended to make right and uniform in great numbers of castings from the same mold.

I have found that, although in extremely small quantities, there is enough migration of elements between ordinary copper and stainless steel at the casting temperature to contaminate the surappreciably.

face of the castings in repeated use of the mold. It is not ordinarily perceptible, so far as the bodies of .the metals are concerned, but is perceptible in the surface appearance of the stainless steel. And that is what I Want to safeguard.

I have discovered that this slight migration of elements may take place in either direction, from the stainless steel to the mold or vice versa, and either way it affects the surface. If the mold takes the elements from the hot metal, successive castings have a tendency to stick. If the hot metal takes elements from the mold, the mold surfaces are eaten away.

When I state that there is a migration of constituents between the metals in contact at cast ing temperature, it should be understood that I am speaking about such small quantities as would not ordinarily affect the body of either metal In that sense the bodies of the two metals may be chemically inert as they contact. But they are not chemically' inert with respect to such small migration as will mar the surface appearance of stainless steel if it absorbs material from the mold.

Thus, the stainless steel has an affinity for carbon, and will take carbon from the mold surface, if present. CopperA and aluminum have amnities for some of the metals of the stainless steel composition, and will draw these metals from the case metal surface. I have therefore added enough iron, nickel, silicon and chromium to the mold material to satisfy this affinity, whereby there is substantially no migration of metals from the stainless steel to the mold, and the surface of the cast stainless steel is smooth, clean and unblemished. Preferably, the amounts of the satisfying metals added are set so as to obtain a slight tendency to migration from the cast metal to the mold.

I have not thought it necessary to give exact constituents of my moldY invention as they may vary considerably in practice, and according to the character of stainless steely to be cast. The skilled metallurgist will know how to proceed from my disclosure. He will consider the subject of what metals will migrate between such casting metal and a copper mold. He will then alloy the copper from the mold so as to provide a definite but very small overbalance to direct the migration from stainless steel constituents to mold constituents. He need notl try to get an exact balance of chemical inertness (a dicult matter) because even if he should succeed in that way with respect to one mold and one melt of stainless steel, the next melt of stainless steel might throw out the balance and migration might be in the direction of the casting metal and mar the desired stainless surface. And when the constituents of the steel are changed (there being considerable variation possible in stainless steel) the mold work in the assumed case would be uncertain and not uniform. But by proceeding as I have disclosed herein, the alloyed copper mold can bring out the right surface in the stainlesssteel in a uniform casting manner with great economy in any desired shapes and in commercial quantities under a uniform practice. In this way many stainless steel shapes not heretofore commercially available are now made so. The extra cost of the stainless steel metal is small in comparison with the cost of the eliminated surface finishing operations.

For illustrative purpose I am disclosing the following example of mold and stainless steel constituents that may be used as disclosed or deliberately varied for the purposes ofpracticlng my invention:

\ Examples l. etal:

Per cent by weight Carbon .80- 16 l :i Il e alles@ .30- .50 ,Silicon .20- .40 Chromium 17.00-18.00 Nickel M10-10.00 Sulphur .025 Phosphorus .025 lron ance 2. Mold:

Copper 88.0 Aluminum 8.0 llrnn 1.0 Chromium 1.0 Silicon 1.0 Nickel 1.0

prise copper, a hardener such as aluminum, and a small fraction, in the neighborhood of 1%, of Fe, to saturate the aluminum in the mold, and thus eliminate migration. The addition of migration control ingredients depends on the particular cast metal and may be omitted for grey cast iron and malleable iron.

While I have described the casting of metals under furnace conditions, and the use of molds having inert characteristics with respect to the cast metals, whereby smooth, unblemshed castings of very high quality are obtained, it is obvious that changes in the apparatus and the methods described, to meet the requirements for casting different metals, may be made without departing from the spirit and the scope of the invention as dened inthe appended claims.

Il claim:

1. In the casting of malleable iron, the steps oi .pouring the metal into a mold consisting principally of copper and apprommately one per cent oi iron.

2. A metal mold forv the casting of malleable iron, consisting principally of copper and containing iron the amount of iron being less than two p er cent and more than one-half of one per cent.

ALBERT W. MORRIS.

Images