US2387803A

US2387803A - Method of casting

Info

Publication number: US2387803A
Application number: US460259A
Authority: US
Inventors: Henry E Mcwane; Hugh K Mcgavock
Original assignee: Individual
Current assignee: Individual
Priority date: 1942-09-30
Filing date: 1942-09-30
Publication date: 1945-10-30
Anticipated expiration: 1962-10-30

Description

Oct. 30, 1945. HJE. M WANE ET AL METHOD OF CASTING Filed Sept. 30, 1942 swam Wow Patented Oct. 30, 1945 METHOD OF CASTING Henry E. McWane and Hugh K. McGavocln Lynchburg, Va.; said McGavock asslgnor to said McWane Application September 30, 1942 Serial No. 460,259

4 Claims. ((122-290) The present invention relates to casting introducing molten ferrous material into the casting cavities of chill molds by means of top gating. This method is particularly adaptable in casting chilled articles such as plow points by means of controlled apparatus such as is disclosed in my co-pending application Serial No. 460,566, filed Oct. 2, 1942. I

The use of top gating, especially in cooled metal molds, presents several distinct advantages. First, it permits pouring at a lower temperature than with bottom gating, allowing the casting to partially shrink as the mold is being filled, and thus minimizing the shrinkage strains in the casting. Next, the use of a cooler metal, by hastening the time of solidification, will reduce the fin size on the casting. Another important advantage resulting from the use of top gating is the reduction of sprue loss. We have been able by our casting methods to reduce the sprue loss to about 5% whereas the loss resulting from the use of conventional popring methods with bottom gating was approximately 50% of the weight,

of the casting.

While it is admitted that top gating of molds is not new, considerable difliculty has been encountered in the past in the production of satisfactory castings in permanent metal molds of liquid cooled type due primarily to conventional hand pouring from a foundry ladle with the necessary use of a relatively hot metal and lack of control of the size and velocity and direction of the pouring stream. The metal would contact the cold gate of the mold and freeze thereon, restricting and sometimes completely obstructing the gate. The use of gate liners of low heat conductivity and other means have been tried to overcome this factor but to date we know of no remedy that has been attempted which will produce completely satisfactory castings.

It is therefore one of the principal objects of our invention to overcome the difilculties heretofore encountered in casting chilled articles in top gated cooled molds.

Another important object of our invention is to provide a method of casting which so directs the stream of molten metal through the casting cavity of a cooled metal mold that the stream of molten metal itself will efiect the formation of gray iron in that portion of the casting desired gray while the wearing portions will be highly chilled.

Yet another object is to provide a method of casting ferrous articles in metal molds with to gating wherein the size of the stream of molten metal is controlled with respect to the gate size so that the molten metal is prevented from coming in contact with the gate.

Other objects and advantages will be apparent to those skilled in the art from the following description'and' by reference to the accompanyin drawing which forms a part thereof.

In the drawing, in which like characters of reference are employed to designate like parts:

Figure 1 is a face view of one half of a permanent metal mold illustrating the flow of molten metal into the casting cavit thereof from a bottom pour ladle, a fragment of which is shown in transverse section, and

Figure 2 is a transverse sectional view taken along the line 2-2 looking in the direction of the arrows and showing both halves of the mold 'in operative position.

In carrying out our improved method of casting chilled articles we contemplate the use of a liquid cooled mold having a top gate. The mold is positioned so that the gravity line of the metal being poured therein will coincide with the axis of the gate and correspond to that portion of the casting being produced which is desired to be gray. Preferably the mold is positioned so that the molcn metal will initially contact the lowest part of the casting cavity. A bottom pouring ladle, having a pouring orifice of smaller cross sectional area than that of the gate, is employed for introducing the molten metal into the mold.

In the drawing we have shown a two part metal mold I having a casting cavity 2 formed in mold blocks 3 and 4 which are provided with

water jackets

5 and 6, respectively. Through these jackets is circulated a cooling liquid 1 to which is transferred the heat of. the molten metal by means of the highly conductive blocks 3 and 4. A gate 8 is provided in the top of the mold to communicate with the casting cavity 2, and when the mold is in operative position will be preferably in a vertical line directly above the lowest part of the casting cavity. While other types of molds may be used, we have illustrated a mold for casting chilled plow points, our casting method being particularly adapted to the production of this article.

Directly above the mold l is positioned a pouring ladle 9 of refractory material and having a bowl Ill for the reception of a molten metal ll and a pouring orifice l2 communicating with the bottom of the bowl. This orifice i2 is generally of similar cross section to the gate 8 but is of smaller size and when the parts are in pouring position has its axi coinciding with the axis of the gate. A reciprocatingstopper or plug i3 is provided to open and close the orifice l2 and to regulate the velocity of the pouring stream ll by means of the extent of its opening movement.

In operation the parts are positioned as described above, molten metal is admitted to the bowl 10 of the pouring ladle 8 and the stopper I3 is raised to allow the metal to flow through the orifice l2 and into the gate 8. The metal passes through the gate 8 without contacting its cool metal walls, which would normally result in the metal freezing onto the gate, and then falls in a straight line to the lower portion l of the casting cavity 2. Because of the definite control 01' the metal stream and the fact that the metal may be poured at a lower temperature than with hand pouring, it almost immediately solidifies with a hard white structure upon coming in contact with this portion of the cool mold cavity.

With continued pouring the metal rises to fill the cavity 2 flowing in all directions away from the stream l4. Since the cavity 2 is comparatively thin, the stream of metal I4 will have the eilect of preheating the faces of the cavity which lie adjacent the path of the stream and this, together with the fact that heat of the pouring metal is conducted through a portion of the rising casting, the cool rate of this portion is sufliciently retarded to cause it to harden with a gray structure. This gray area we have indicated roughly as being within the dotted lines IS in Figure l. The portions of thecasting which will lie outside this area, specifically the working edges of the plow point, because they are not 1.-

affected by the heat of the stream, will solidify white. The amount of this gray area maybe varied by increasing or decreasing the rate of flow of the metal from the ladle 9, obviously the slower the pouring rate the greater the amount of heat radiated and conducted by the stream and the larger the gray portion of the casting. This pouring rate may be accurately controlled by the amount the stopper i3 is raised and the amount of opening of the orifice l2.

Thus it will be seen that by the combined use of controlled pouring and top gating we are able to produce castings and particularly such castings as chilled plow points which have optimum working characteristics. In addition, principally because of the low metal heat and slow pouring permitted by our methods, shrinkage has occurred in at least a part of the casting before the mold has been completely filled, thereby practically eliminating the large sprues necessary in rapid pouring. Also, because of the above-fins and cracked castings, which latter are caused priflcipally by shrinkage strains set up in the casting while within the mold, have been reduced to a minimum.

While only a preferred embodiment of our invention is herein shown and described, it is to be understood that changes which will be obvious to those skilled in the art may be made in the process, and the method may be applied to the production of other articles than herein disclosed without departing from the spirit of the invention or the scope of the appended claims.

We claim:

1. A method of regulating the chill in comparatively thin gray castings produced in a metallic mold having a top gate comprising positioning the mold so that the lowest portion of the mold cavity and the mold gate are aligned in the mean axis of that portion of the resulting casting desired to be gray, introducing a stream of molten iron through the gate into the mold cavity so that it initially contacts the lowest portion of the cavity, and controlling the rate of introduction of molten iron to control the degree of preheating of the walls of the mold cavity adjacent said stream to thereby regulate the depth of chill of the gray portion of the casting.

2. A method of regulating the chill in comparatively thin gray iron castings produced in a metallic mold having a top gate comprising positioning the mold so that the lowest portion of the mold cavity and the mold gate are aligned in the means axis of that portion of the resulting casting desired to be gray, restricting a stream of molten iron to a size less than the size of the gate, introducing the restricted stream into the mold cavity so that it initially contacts the lowest portion of the cavity, and controlling the rate of introduction of molten iron to control the degree of preheating of the walls of the molten cavity adjacent said stream to thereby regulate the depth of chill of the gray portion of the casting.

3. A method of regulating the chill in the casting of plow points in a metallic mold having a top gate comprising positioning the mold so that the lowest portion of the mold cavity which forms the tip of the plow point and the mold gate are aligned in the mean axis of the portion of the plow point desired to be gray, introducing a stream of molten iron into the mold cavity so that it initially contacts the lowest portion of the cavity, and controlling the rate of introduction oi molten iron to control the degree of preheating of the walls of the mold cavity adjacent said stream to thereby regulate the depth of chili of the gray portion.

4. A method of regulating the chill in the casting of plow points in a metallic mold having a top gate comprising positioning the mold so that the lowest portion of the mold cavity which forms the tip of the plow point and the mold gate are aligned in the mean axis of the portion of the plow point desired to be gray, restricting a stream mold cavity adjacent said stream to thereby regulate the depth of chill of the gray portion.

HENRY E. MCWANE. HUGH K. MoGAVOCK.