US2439443A - Casting apparatus for vibrating molds - Google Patents

Description

April 13, 1948. E. ASKE Y CASTING APPARATUS FOR VIBRATING MOLDS Filed March a, 1944 INVENTOR. I ZPVM fEAJ/Q B WM/MM A TTOFNYJ'.

Patented Apr. 13, 1948 OFFICE 2,439,443 CASTING APPARATUS FOR. VIBRATING MOLDS Irving E. Aske, Muskegon, Mich. Application March 3, 1944, Serial No. 524,852

2 Claims. (Cl. 22-57) This invention relates to improvements in casting apparatus for vibrating molds.

The main objects of this invention are:

First, to provide an apparatus for making castings which results in a product of substantially increasing tensile strength as compared; to castings manufactured by the common method.

Second, to provide an apparatus for use in making castings of irregular form--for example, such" use of liberal sprues, runners, gates, risers and chills quite commonly used in producing castings.

Fifth, to provide an apparatus for making castings which is desirable for use in conditions where alloys are added to the ladle after tapping the cupola for the producing of special alloyed castings of iron and steel. When this is done considerable gases are formed in the molten metal that become trapped in minute quantities and this condition is eliminated or minimized.

Objects relating to details and economies of the invention will appear from the description to follow. The invention is defined in the claims.

A preferred embodiment of the inventionis illustrated in the accompanying drawing, in which:

Fig. 1 is a fragmentary side elevation of a molding machine or apparatus embodying the features of my invention, a flask or mold being shown in position thereon.

Fig. 2 is a fragmentary end view partially in section looking from the right of Fig. l.

Fig. 3 is an enlarged fragmentary view partially in section on line 33 of Fig. 1.

Fig. 4 is a diagrammatic view illustrating the components of motion imparted to the casting bed or table.

In foundry work, it is a matter of common knowledge that shrink cavities,' gas pockets,

porosityand variable physical grain structure constitute the unpredictable factors in making metal castings. The principal technique which is pursued by foundries making these castings from sand molds involves a liberal use of large sprues, runners, gates, risers and chills and other devices for liberating trapped gases which greatly affect the tensile strength of the casting and sometimes causes complete rejection of the castings and in other instances welding operations and the like to repair the castings.

When the molds are poured, such as crankshafts for example, the first layers of metal to solidify are those which enclose the thin sections, and the surfaces of large sections that are in contact with the cool walls of the mold sand and this condition arises in all castings which are quite irregular. The solidified boundary layer of metal which encloses the liquid metal within the casting traps and difiuses the gases throughout the metalstructure and the amount which exceeds the gas absorption characteristlcof the metal will manifest itself in voids and porosity in the casting. Also, the solidifying metal will shrink in section and draw metal away from the molten section thereby causing a shrink cavity unless it happens that a riser is placed at that location to supply the shrink cavity with metal.

The use of the applicants apparatus results in the cooling and solidifying of the metal quite uniformly throughout its volume with a result that shrinks and gas pockets which would otherwise occur are eliminated or minimized and the grain structure is greatly improved.

I am aware that various methods and apparatus have been tried out to lessen these difficulties-for example, the jarring or jolting of the ingot molds which, however, cannot be used in the making of castings in sand molds for the rea son that the sand of the mold and the cores contained therein would be ruptured or torn loose and the casting rendered unfit for use.

My apparatus minimizes and substantially eliminates these various objectionable conditions in that I have produced an apparatus in which the vibratory motion imparted to the mold is of a character that it does not disturb th sand in the mold orthe cores placed therein. Further, the vibratory motion is of such intensity and of such a nature that the molten metal will completely fill out the smallest sections of the mold. Another advantage is that the forces produced. in the molten metal are directed so as to cause the metal to flow from the hottest sections to the cooler effect to produce an improved physical structure of the solidified metal.

The embodiment of my invention illustrated in the accompanying drawing is highly satisfactory in the accomplishment of these ends. In this embodiment, the base I is of suitable character to support the rocker shafts 2, the base being provided with pedestals 3 for this rocker shaft. The table 4 is provided with downwardly projecting brackets 5 pivotally engaging the rocker shafts 2.

These brackets are disposed centrally of the table provided with bushings H, see Fig. 3. The connecting rods. I! are provided with ball bearings l3 conventionally indicated in Fig. 3 which coact with the eccentrics M on the shaft 6. With this arrangement, the rotation of the shaft 8 imparts an oscillating movement to the table on its pivots or rocker shaft 2.

The table 4 is provided with a rim 15 adapted to retain the bed of sand or like granular material l6. This bed of sand l6 serves as a support for the flask ll of the mold l8 conventionally illustrated, the mold being a sand mold and being designed for the casting of a crank shaft. I have not illustrated the full details of the mold cavity as that seems unnecessary. It will of course be understood that where an integral casting is to be formed the various portions of the mold are in communication.

I have not attempted to illustrate the sprue holes but it is preferred that the mold be placed upon the table-that is, upon the supporting bed of sand on the table prior to the pouring operation. With the mold arranged as illustrated and the machine in operation, an oscillating movement is imparted to the table and to the mold thereon. There is of course a tendency to produce shock in the reversal of direction of oscillation and the sand bed efi'ectively absorbs that shock.

By referring to the drawing, it will be noted that a combined horizontal and vertical movement is imparted to the table, these movements being substantially at right angles to each other. The eifect of these combined forces is to produce a small rotary or orbital motion within the molten metal. The amplitude of the vertical motion varies from the maximum at the outer boundaries of the casting to zero at the axis center While the horizontal motion remains practically constant in amplitude throughout the casting. The bed of cushioning sand effectively eliminates the breaking down or destroying of the sand mold and the shifting of the cores. The speed of the shaft 6 should be such as to secure the desired action on the molten metal without disturbing or rupturing the sand of the mold or displacement of the cores. I-ligh frequency is important and I have found a "frequency of 1750 cycles per minute to produce satisfactory results with a wide range of castings in the matter of shapes and sizes and with different metals and alloys. Since the flask is resting upon the bed of sand the maximum acceleration of both vertical and horizontal movements of the outer edges of the flask may be approximately that of gravity without disturbing the mold and without imparting undesired raps or jolts to the mold. The bed of sand or granular material effectively dampens or eliminates undesirable jolts or jars. The flask is positioned so that it is entirely supported by the sand-that is, it isout of contact with the rim and may skid slightly sidewise in encountering a metal impact of the flask. The motion also tends to keep the sand in 'a uniformly distributed bed. The mold being displaceable both horizontally and vertically relative to the plane of the table and being loosely supported on the sand, facilitates during oscillation of the table displacement of the mold both horizontally and vertically relative to the plane of table and movement of the mold in an orbital path and a downward acceleration to the mold not substantially greater than that of gravity, all of which tends to improve the structural characteristics of the metal and to prevent undesired jolts or jars to the sand mold. The sand also provides a secure bed for the uneven surface of the flask to rest upon since the void spots between the flask and the sand quickly fill up with sand when the table is set in motion. When the flask is placed upon the rocker table and the motor is started, one side of the flask goes down the eccentric distance and the other side moves upward an equal amount. Since the table and the flask parting line are well above the rocker shaft or pivot center line, the flask parting line Will move horizontally the eccentric amount times the ratio of B/A, where as shown in Fig. 4 A is the distance between the rocker pin center line and the center line of the connecting rod pin l0 and B is the distance between the rocker pin center line and the parting line of the flask.

Another advantage of this arrangement of the mounting of the table is that the structure is balanced and there are no unbalanced forces set up to create a vibration other than that imparted by the intended vibratory motion which is practically confined to the table-that is, there are no vibratory motions setup at the base of the machine. While sand or like granular material is highly desirable and preferably used as a cushioning means, other cushioning means or materials might be substituted with desirable results.

It will be noted that the horizontal motion of the flask is simultaneous with the vertical motion. Thisresults in the molten metal in the mold-in molding a crankshaft for example-to flow from theoutside of the shaft towards the center and this causes a more uniform cooling of the entire mass of the metal and fills any voids that might have a tendency to form near the center of the shaft.

It should be noted that the rapidly rocking table produces vibratory forces in the molten metal having a varying vertical amplitude of zero from the rocker center line to a maximum at the outer edge of the mold. When the machine is designed to produce an acceleration equal to that of gravity at the outer edge of the casting the pressure created on the molten metal will be twice that of gravity on its upward motion and no internal pressure on the side going down since the maximum acceleration downward equals that of gravity. The result is that the metal circulates in the mold and the cooling rate is effectively equalized throughout the casting. The gases are enabled to rise and escape; also shrinks that would normally occur fill up with metal and very sound castings are produced. For example, in making crankshafts, several risers to feed metal into shrink cavities can be dispensed with and in some cases no risers are necessary.

The resulting castings have very substantially increased tensile strength without material increase in Brinell hardness.

A satisfactory manner of using my apparatus is to place the flask with its mold upon the bed of sand, and immediately after pouring the mold,

the machine is started and allowed to run for some minutes after the metal in the sprue has solidified. In small castings, it is preferable to run the machine during the pouring because of the quick solidification of the metal when it strikes the mold sand.

Another advantage is that a considerable saving may be made in relatively expensive alloy materials commonly used to-produce a given tensile strength as the tensile strength may be secured. Another important advantage is that a, much higher percentage of good castings saves substantial expense over the present practice of salvaging by means of welds, and loss of time and output resulting from scrapping castings that cannot be salvaged.

Another advantage of importance is that the supporting of the flask and mold therein upon the bed of granular material such as sand permits the gases to escape from the bottom as well as vantage where the metal is circulated as that 7 further facilitates the escape of the gases and it results in a verysuperiorquality of casting.

I have illustrated and described a highly emcient apparatus. I have not attempted to illustrate other adaptations of my-invention as it is believed that this disclosure will enable those skilled in the art to embody or adapt my invention as may be desired.

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

1. In a casting apparatus, a mold, a rockingly mounted table provided with a bed of granular material upon which said moldis supported, and means for rocking said table, said table having a peripheral rim for retaining the granular material thereon, said mold being supported by the granular material within and in spaced relation from said rim and being displaceable both hori- ,zontally and vertically relativeto the plane of the table and being loosely supported on said supporting pivots for said brackets whereby the table is supported for oscillating movement on an axis substantially below the plane of thetable, means for oscillating said table on its said axis at a frequency of approximately 1750 cycles per minute, granular material on-said table and withthe top of the mold. Thi is of particular adin said rim, and a mold supported on said granular material within and in spaced relation from said rim and being displaceable both horizontally and vertically relative to said table and being loosely supported on said granular material to facilitate during oscillation of the table-at said frequency displacement oi. the mold both horizontaliy and vertically relative to the table, and

granular material to facilitate during oscillation Y of the table displacement oi the mold both horimovement of the mold in an orbital path, and a downward acceleration of the mold not substantially greater than that of gravity.

. IRVING E. ASKE.

REFERENCES CITED 7 The following references are of record. in the tile of this patentt UNITED STATES PATENTS:

Number 'Name Date 1,561,953 .Sweetland Nov. 1'7, 1925 1,785,757 Young Dec. 23, 1930 1,008,104 Bell May a, 1933 j 2,109,528 Fine -..-Mar. 1, 193a 2,353,492 O'Connor July 11, 1944 FOREIGN PATENTS Number Country 7 a 7 Date 670,353 France Aug. '17, 1929 290.883 Germany Mar. 20, 1916 607,088 Germany Dec. 17, 1934 c

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