US 2205327 A
Description (OCR text may contain errors)
June 18, 1940. LL'AM 2,205,327
IEANS FOR CASTING METALS Filed June 29, 1939 2 Sheets-Sheet 1 wmm June 18, 19-40. J.wn |AMs 5, 2
IEANS FOR CASTING nuns Filed June 29, 1939 2 Sheets-Shed 2 Patent ed June 18,1940
UNITED STATES PATENT OFFICE MEANS FOR, CASTING METALS John Williams, Palmyra, N. J.
Application June 29, 1939, Serial No. 281,94!
'1 Claims. (o1. 22-'129) This invention is a continuation in part of my application for patent filed December 6, 1938, Serial Number 244,151.
This invention relates to an improved means for casting metals.
It is well understood that for the production of sound castings, adequate provision must be made for feeding the volumetric shrinkage which occurs when the molten metal solidifies in the mold. The conventional method of supplying the deficiency resulting from this shrinkage is to provide one or more relatively large reservoirs or heads of molten metal connected withthe mold cavity, the metal in these reservoirs remaining liquid longer than the metal of the casting proper and flowing into the mold cavity under the influence of gravity and atmospheric pressure to fill the voids created by the shrinkage. When the casting is small and is of a form to afford a suitable directional solidification, a single head may suffice, but when the casting is large or of complicated form, it may be necessary to employ a number of separate heads in order to adequately feed the shrinkages in different parts of the casting. Usually, the aforedescribed reservoirs or heads extend to the top of the mold, and are, therefore, open at the top to atmosphere; but when a portion of the casting requiring feed metal is located low in the mold, it is sometimes expedient to confine the reservoir entirely to theinterior of the mold. Such enclosed reservoirs are known as blind heads.
Blind heads have several potential advantages over the open head or riser. 'I'hey frequently permit of bottom gating into a head, which is productive of a cleaner and sounder casting; frequently they can be more readily located in the ,moid with respect to the area of the casting which they are required to feed; they can generally be designed and applied for easier removal, which results in a reduced cleaning cost; and they afford a substantially increased yield, as compared with the open reservoir, by conserving the total amount of molten metal required to produce the casting. The blind head as heretofore used is not as eflicient as the open riser, however, in the function of supplying molten metal to the shrinking casting. This is due in part to the reduced hydrostatic head inherent in the relatively low location of the reservoir with respect to the mold cavity; but more particularly, the reduced efilciency arises from loss of atmospheric-pressure resulting from the fact that the molten metal in the head as well as in the casting tends to solidify rapidly where itcontacts with the mold to form source.
an air-tight skin or shell of solidified metal around the bulk of the still molten metal in the interior of the head and casting. With atmospheric pressure thus excluded, the normal fiow of molten metal from the head into the voids formed in the casting as previously described is materially lessened, stopped, or even reversed, as the flow of molten metal is then affected only by gravity. Under these conditions the pressure of the molten metal is considerably lower than the pressure of the atmosphere, and this difference of pressure is, at times, suflicient to distort the still plastic air-tight skin or shell of the casting and head, pushing it inward. In some cases this difference of pressure causes a rupture of the skin of the casting, admitting air or mold gases to the interior of the casting. By reason of this inefiiciency and in spite of the inherent advantages mentioned above, blind heads heretofore have been used sparingly; and when used, there has been a tendency to form such heads substantially larger. than theoretically necessary, in an attempt to correct the fault by providing a. relatively large volume of molten metal at the feeding The relative effects of gravity and of atmospheric pressure upon the feeding ability of a reservoir of molten metal may be compared from the generally known physical laws and values. To obtain, by gravity alone, a pressure equal to the usual, pressure of the atmosphere would require a column of molten metal approximately 52 inches high for iron base metals, approximately 45 inches high for copperbase metals, and approximately 151 inches high for aluminum base metals. From this data it is apparent that a reservoir, upon which atmospheric pressure is permitted to act, is competent to feed the interior is excluded, to' a height considerably above the level of molten metal in the reservoir.
A principal object of the present invention is to provide an inexpensive and practical means for overcoming the aforedescribed fault of the blind head, to thereby afford assurance of a proper functioning of heads of this type, and to make this type of head, with its several substantial advantages, generally available for the more economical production of sound castings.
More specifically, an object ofthe invention is to provide means for preventing segregation, as described, of the mass of molten metal in the head from the atmospheric or other pressure that is relied upon to effect the' fiow of said metal to the casting for feeding shrinkage in the latter.
Another object is to provide means for obtaining the aforesaid result which will permit reduction in the size of the head with assurance of a proper functioning of the head to the desired end.
While the invention has a particular application to blind heads, as described above, it will be apparent that in principle it may be used to substantial advantage with heads of other types, and also in various types of mold.
In the attached drawings:
'Fig. 1 is a plan view of the lower portion or drag of a conventional sand mold with the pattern in place, said pattern providing for a blind head of the character described above;
Fig. 2 is a vertical sectional view taken on the line 2-2, Fig. 1, the pattern being replaced in this view by the actual casting;
Fig. 3 is a view in perspective of the air-permeable element which, in accordance with the invention and as shown in Fig. 2, is established in the wall of the blind head;
Fig. 3a is a view in perspective of a modified form of element;
Fig. 4 is a view in perspective of the pattern;
Fig. 5 is a view in perspective of the finished casting, and
Fig. 6 is a view in perspective of a more complicated form of casting illustrating the use of multiple blind heads, together with an open riser. The pattern and mold shown in Figs. 1, 2 and 4 of the drawings are, with a single exception hereinafter described, entirely conventional for production of the casting illustrated in Fig. 5.-
The distribution of the metal in this casting is such that a single head or reservoir may be used to feed the shrinkage, and the pattern has been formed to provide this head. The head, indicated in Fig.2 by the reference numeral I, 18 of the blind type, and is entirely encased within the sand of the mold. The head connects with the lower part of the casting cavity 2 at the end thereof which forms the flanged end 3 of the casting, and the pouring gate 8, which extends to the top of the mold and through which the molten metal is introduced into the mold cavity and into the head, joins the lower part of the latter, as illustrated. It will be noted th at the greater mass of metal in the casting is in the flanged end 3, and that the mass decreases progressively toward the opposite end through the tubular portion 5. solidification of the molten metal in the mold takes place progressively, therefore, from the outer extremity of the tubular end 5 of the casting through the flange portion 3 to the. head I, and the head is proportioned volumetrically with respect to the casting cavity so as to insure that at least a part of the molten metal therein shall remain in the fiuid state until the metal in the casting cavity has completely solidified and shrinkage has terminated.
Referring now to Fig. 2, .it will be noted that the mold departs from the conventional in the provision of an insert 6 which is set .into the sand of the mold and projects to a substantial extent into the upper part of the head I. This insert, see Fig. 3, takes the form in the present instance of a cylinder or rod of air-permeable composition, and may be molded, for example, from sand of sufiiciently coarse grain to insure the essential property of air-permeability, and subsequently hardened by baking or by other suitable means to confer the necessary physical strength. When established in the mold as illustrated, an insert of this character forms 9.
passage for air between the mass of sand in the mold, which is itself permeable to air, and a point in the interior of the head remote to the wall of the head chamber. It is apparent that with this device, assuming that the sand which forms the body of the mold is exposed to the atmosphere,.the entire wall surface of the head chamber mightbe sealed against passage of air without excluding atmospheric pressure from the chamber or from the molten metal contained therein.
As explained above, the fault of the blind head arises primarily from the early solidification of the molten metal in the areas immediately adjoining the wall surfaces of the head chamber, with resultant exclusion of atmospheric pressure from the still molten metal in the interior of the head. By providing a passage for atmospheric air through this otherwise impermeable shell of solidified metal to the molten and still fluid metal in the interior of the head, so that the fluid metal remains subject to atmospheric pressure, the aforedescribed device acts to entirely correct this fault.
Fig. 2 of the drawings illustrates the manner in which the device so functions. This drawing shows the metal in the mold after complete solidification. The heavily cross-hatched portion immediately adjoining the wall of the head indicates the area of the head in which initial solidification of the metal is apt to occur prior to the time when shrinkage of the metal in the casting proper has been completed. The projecting part of the insert'6, being of relatively small cross-sectional area and having a negligible capacity for conduction of heat, is incapable of chilling the molten metal by which it is substantially surrounded to the-point of solidification, and accordingly the insert is effective to establish a path for atmospheric pressure through the shell of solidified metal to. the fluid metal in the head. The head thereby remains functionally effective, as hereinbefore described, to
, supply the deficiency of ,metal in the casting created by shrinkage.- This transfer of metal from the head to the casting under the effect of atmospheric pressure is indicated by the presence of the cavity 1 in the head, and it will bev noted that at the conclusion of the operation, the cavity still remains in communication through the insert with the atmosphere.
It will be apparent that the use of an open riser instead of the blindhead would require for production of the casting a considerably increased volume of molten metal. This advantage of the blind head over the open riser in the factor of yield will be made more apparent by reference to Fig. 6, wherein is shown a .casting of a character requiring the use of multiple feeding heads, several of which are employed to feed parts of the casting which are set low in the mold. By use of my invention, blind heads may be used with assurance that they shall function efliciently .to afford sound castings of this character, and with the advantage of a yield materially greater than that obtainable by theuse-pf open risers. In the blind head itself, the invention works a still further economy in yield by permitting the use of a smaller head than heretofore has been considered practical to adequately feed a given shrinkage.
It is apparent that the insert 6 may take other forms than that described above without departure from the invention. It may be composed,
for example, and as shown in Fig 3a of any,- 75
suitable refractory material either permeable or impermeable, and if the material is not inherently permeable the rod may be made so by providing one'or more longitudinal passages B of small diameter to admit air while excluding metal from the inner end. The device might theoretically consist of a suitably shaped projection formed integrally with the ,mold itself and of a character to provide a passage for atmospheric air into the head, this applying more particularly to permanent molds; and in such molds, composed of inherently impermeable material, it is obvious that the passage must extend to the outer surface of the mold body. The principle may be used'also in obvious manner to impress upon the feed metal in the head pressures in excess of atmospheric to effect an even more positive feeding of the metal to the shrinking parts. The invention may also be used to advantage in connection with other than blind heads, and in open heads, for example, where conditions or the form of the head are such that the efficiency of the shrinkage-feeding function may be improved by providing access for atmospheric or other pressure to a point in the interior of the head remote to the wall surface.
1. In means for supplying molten metal to feed" shrinkage in a solidifying casting, the combination with a mold having a casting cavity and a communicating blind reservoir for molten feed metal, of gas-penetrable means accessible to atmospheric air and projecting into the interior of said reservoir for immersion in the mass of feed metal, said projecting means providing for application of atmospheric piessure at a point in the interior of said mass.
2. In means for supplying molten metal to feed" shrinkage in a solidifying casting, the combination with a mold having a casting cavity and a communicating blind reservoir for molten feed metal, of means for delivery of gas from external source at a point in the interior of the mass of said feed metal.
3. A metal casting mold comprising a casting cavity, a head communicating with said cavity, and means for providing a passage for atmospheric or other pressure to a point in the interior of the head remote to the wall of the latter, said means comprising a gas-permeable rod-like element of refractory material substantially chemically inert to the molten metal, said rod projecting into the interior of the head to an extent greater than the ultimate thickness of the shell of solidified metal forming around the mass of still molten metal in the head during solidification of the casting proper and affording a path for uninterrupted application of said pressure to the liquid metal encased by said shell untilshrinkage of the said casting is completed.
4. A metal casing mold comprising a casting cavity, a head communicating with said cavity,
said head being of a character to supply molten metal to the cavity to "feed shrinkage occurring in the casting proper as the latter solidifies, and a gas-permeable rod-like element of refractory material substantially chemically ine'rt to the molten metal projecting into the head and extending to the central portion of the latter so as to provide a passage for atmospheric or other pressure to the area of the head from which the molten metal is supplied in feeding said shrinkage, saidelement being relatively small in the transverse dimensions so as to exert no sub.- stantial chilling effect upon the molten metal in which it .is immersed.
5. A metal casting mold comprising a casting cavity, a head communicating with said cavity, said head being of a character to supply molten metal to the cavity to feed shrinkage occurring in thecasting proper as the latter solidifies, and
a gas-permeable rod-like element of refractory material substantially chemically inert to the molten metal projecting into the head and extending to the inner area of the latter from which the molten metal is supplied in feeding said shrinkage so as to afford a passage for uninterrupted application of atmospheric or other pressure to the shrink cavity within the head, said element being structurally strong but relatively small in the transverse dimensions so as to exert no substantial chilling effect upon the molten metal in which it is immersed.
6. A metal casting mold comprising a casting cavity, a blind" head communicating with said cavity, and means for providing a passage for atmospheric or other pressure to a point in the interior of the head remote to the wall of the of said pressure to the liquid metal in the inner area of the head until shrinkage of the said casting is completed.
7. A metal casting mold comprising a casting cavity, a blind" head communicating with said cavity, said head being of a character to feed shrinkage occurring in the casting proper as the latter solidifies, and a structurally-strong gaspermeable rod-like-element of refractory material substantially chemically inert to the molten metal projecting into the head and extending to the inner area of the latter from which the molten metal is supplied to feed said shrinkage, thereby to afford a passage for uninterrupted application of atmospheric or other pressure to the shrink cavity within the head, said element being relatively small in the transverse dimensions so as to exert no substantial chilling effect upon the molten metal in which it is immersed.