US2046505A - Method of centrifugal casting - Google Patents

Description

July 7, 1936. c. A. DOWN 2,046,505

METHOD OF CENTRIFUGAL CASTING Filed Feb. 27, 1933 INVENTOR Quay-w CLFW ATTORNEYS Patented July 7, 1936 TT DFFICE METHOD OF CENTRIFUGAL CASTING Application February 27, 1933, Serial No. 658,840

5 Claims.

This invention relates to centrifugal casting and more specifically to a method of successively casting with a rotating mold and the product derived therefrom.

In general it is an object of the invention to provide a method of the character described which is not only simple but eificient, which may be carried out without elaborate apparatus or highly skilled labor, and which does not require more than a minimum of time for its operation.

Another object of the invention is to provide a method of casting whereby steep temperature gradients in the mold and sudden changes in gradient or temperature are avoided.

Another object is to provide a method which will prepare an uncbilled casting.

Another object is to provide a method whereby a series of castings of desired properties may be produced rapidly and without substantial apparatus depreciation.

Another object is to provide a method of casting whereby the surface of the mold does not rapidly deteriorate.

Another object is to provide a centrifugal casting having a combined and free carbon ratio of about one to two.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties, and the relation of constituents, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a sectional view in elevation of a device adapted to be used in connection with the invention; and

Fig. 2 is an enlarged detail of a portion of the device shown in Fig. 1.

In the art of casting in rotatable molds heretofore great diiliculties have been experienced in attempting to obtain a high rate of production. If the process were hastened by too rapid cooling of the molten material it became chilled and the product could not be machined. Moreover, the interior surface of the mold being subject to extremes'in temperature tended to disintegrate rapidly and become unfit for use. This was au mented by steep temperature gradients between the inner surface against which molten metal was dropped or thrown and the effective outer surface but a short distance therefrom which was kept at temperature often below that of the foundry. Attempts to cure one evil have increased others. For example, if the entire mold were continuously kept at a high temperature, comparatively few units could be delivered before the mold would have to be replaced at a cost practically prohibitive. As a result in many sizes and shapes centrifugal casting with an unlined mold has not gone into commercial production to the degree which the demand for the product warranted.

The present invention contemplates maintaining the mold at a temperature sufiiciently high at all times to prevent crystalline shock in the mold itself when the molten metal is added and yet not so high as to delay the cooling of the metal. This temperature again is not so low as to cause a chill in the molten metal as it freezes. The temperature is not so rigidly. preserved that a severe restoring temperature gradient has to be resorted to but it is from time to time carefully and not too rapidly restored to a general, predetermined temperature range. It has been found that for a casting of given weight and dimensions that a certain mold weight range is preferable in maintaining the fairly low constant temperature desired. Various other controls are referred to in the method hereinafter described.

The following is a description of one way of carrying out the method contemplated by this invention. Molten metal l0 such as iron is poured into a rotating iron mold I I which may if desired have a parting on its inner surface. The nearer the temperature of the molten iron is to its melting point the less is the heat required to be absorbed by the mold and the less it is subject to high temperatures with attendant chemical and physical changes.

The mold is rotated at a speed sufficient to prevent the collapse of the molten metal. Any greater speed tends to entrain air against the inner surface of the casting in such amounts as to "chill that surface. A mold speed giving an inner surface velocity of from 1500 to 1800 feet per minute has been found advantageous in connection with the illustrative data given below. If the speed is too high, checks or cracks may show in the casting and at extremely high speeds mold splash may occur, resulting in an undesirable lamination on or near the outer surface.

fast enough to give it a chill and yet the ratioshould be small enough to cool the former with as little delay as possible without chilling". The surface area across which the heat conducttion takes place, i. e., the inner mold surface, is another factor. The larger said area is for a given casting weight and mold weight, the greater and more rapid is the heat conduction. To a certain extent the mold mass and the inner surface may be considered complementary. For a linear axial foot, the product of the mold weight times the inner mold surface in square feet per unit weight of casting, may be about 68 to within a factor of one-tenth. This guide is particularly valuable for four-foot castings. An iron mold having an inner diameter of 1.44 feet and an external diameter of 2.29 feet and weighing 1204 pounds per linear foot is found efficiently to cast onehalf-inch pipe weighing 80 pounds per foot of length. It will be seen that this mold and casting fall within therule given above:

(casting weight per axial foot) Another example is a mold of 1.26 feet inner diameter and 2.29 feet external diameter weighing 1140 pounds per linear axial foot and used for casting pipe weighing pounds per linear foot.

The temperature of the mold is maintained at a medium level of from 500 to 800 F. Once the apparatus is in continuous production that temperature need not vary more than 100 above or below the medium which is roughly midway between room temperature and the temperature at which the casting is removed, which may be from 1100 to 1250 F. The mold temperature is prevented from becoming too high by the application of a cooling material thereto in any suitable fashion as through the conduit l2 when the temperature begins to rise at a time in the operation cycle after the molten metal has been introduced into the mold. For normal pipe sizes say from 1 to 2 feet in diameter, about 12 gallons of water per pipe per linear foot at a temperature of about 50 F. is satisfactory.

A mold coating may be used which will tend to aid in controlling the fluctuation in heat flow. For example, a dry mold coating I3 comprising powder-fine silica sand and lamp black may be applied to the mold interior prior to the pouring of the metal. The period of time while the casting is removed, mold coating applied and the trough inserted, permits the mold to lose some of its heat and return to a lower temperature.

On account of the lack of chill in castings cast by the above described method the usual annealing may be dispensed with. While the temperature of the casting is being lowered at a moderate rate any cementite present tends to decompose producing a grey iron as cast instead of a white chilled casing. The relatively slow cooling rate has a tendency to assist in crystal growth which produces a certain amount of flake graphite. The iron matrix appears to be largely the iron carbon compound pearlite with small areas of cementite. the ratio of combined carbon to graphitic carbon being about one to two.

Since certain changes in carrying out the above process, and certain modifications in the composition which embody the invention may be made 5 without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. i

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might 15 be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A method of centrifugally casting, comprising casting, in a mold, material in an amount in 20 pounds, for each foot of length of said mold, substantially equal to one seventieth of the product of the mass of said mold, per foot of length thereof, times the inner mold surface in square feet for each foot of length of said mold. 25

2. A method of centrifugally casting, comprising pouring molten material which is at a temperature near its melting point into a rotatingmold, maintaining said mold through a succession of castings'at a fairly uniform temperature roughly midway between the temperature of said material when it is removed from the mold and room temperature, preventing the inner surface of said mold from attaining a temperature substantially higher than the rest of 35 said mold by introducing while said mold rotates and before recharging a dry mold-coating against said surface, and recharging said mold, said uniform temperature being approximately between 500 F. and 800 F. and the deviations from said uniform temperature being approximately less than F.

3. A method of centrifugally casting, comprising pouring molten material which is at a temperature near its melting point into a rotating mold, maintaining said mold through a succession of castings at a fairly uniform temperature roughly midway between the temperature of said material when it is removed from the mold and room temperature, preventing the inner surface of said mold from attaining a temperature substantially higher than the rest of said mold by introducing while said mold rotates and before recharging a dry mold-coating against said surface, and recharging said mold, said mold-coating comprising as a mixture an insulating constituent and a lighter lubricating constituent, said uniform temperature being approximately between 500 F. and 800 F. and the deviations from said uniform temperature being approximately less 60 than 100 F.

4. A method of centrifugally casting,

prising pouring molten material which is at a temperature near its melting point into a rotating mold, maintaining said mold through a suc- 65 cession of castings at a fairly uniform medium temperature roughly midway between the temperature of said material when it is removed from the mold and room temperature, preventing the inner surface of said mold from attaining a 70 temperature substantially higher than the rest of said mold by introducing while said mold rotates and before recharging a-dry mold coating against said surface, and recharging said mold after it has cooled to a temperature not morei'lo rial as it congeals, removing said material when p it has solidified and at a temperature low enough to prevent said removed material from chilling by contact with air and high enough to prevent said mold from being. heated to substantially more than a medium temperature, preventing the inner surface of said mold from attaining a temperature substantially higher than the rest of said mold by introducing while said mold rotates and before recharging a dry mold-coating against said surface, and recharging said mold, said. medium temperature being approximately between 500 F. and 800 F. and the deviations from 1 said medium temperature being approximately less than 100 F.

1 CARLTON A. DOWN.

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