US3414045A - Method for centrifugal casting - Google Patents

Description

Dec. 3, 1968 D. J. HARVEY 3,414,045

METHOD FOR CENTRIFUGAL CASTING Filed Dec; 20, 1965 //V VE N TOR United States Patent 3,414,045 METHOD FOR CENTRIFUGAL CASTING Douglas J. Harvey, Utica, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Dec. 20, 1965, Ser. No. 514,894 3 Claims. (Cl. 164-116) ABSTRACT OF THE DISCLOSURE The method of centrifugal casting wherein a mold is filled with molten material and then rotated at a continuously varying speed so as to generate shearing forces for grain refining purposes.

This invention relates to improvements in method for centrifugally casting both metallic and nonmetallic parts.

It is well known that the translation of a molten ma terial, such as liquid metal across the solid material of a solidifying system, will produce grain refinement. This translation can be done in many ways; e.g., by stirring or by other mechanical actions. A casting formed with grain refined in this way will have considerably improved physical properties. For instance, the finer grain produces a casting that is more ductile, i.e., it is not as sensitive to impact failure wherever notches or scratches occur. Also, a grain refined casting is more resistant to corrosion and has a higher strength. For example, a tube or pipe with a refined grain structure is able to withstand higher internal pressures.

With the foregoing in mind, a novel centrifugal casting method is proposed for producing greater grain refinement than heretofore has been possible. In fact, accurate grain refinement control is possible. By the novel method continuously changing tangential forces are imposed on a casting mold so as to generate a shearing flow that contributes to this greater grain refinement.

Also contemplated by the proposed method is the imposition of tangential forces that continuously and cyclically accelerate and decelerate a casting mold so as to achieve the desired greater grain refinement.

The foregoing and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings, in which:

FIGURE 1 illustrates schematically apparatus incorporating the principles of the invention;

FIGURE 2 is a cross-sectional view of a zinc=0.l% aluminum alloy casting made by conventional centrifugal casting apparatus; and

FIGURE 3 is a cross-section of a zinc=0.l% aluminum alloy casting made within the FIGURE 1 apparatus.

Referring now to the drawings in detail and initially to FIGURE 1, the numeral denotes generally a mold of annular configuration appropriate for molding ringlike castings of metallic or nonmetallic material. A suitable opening 11 is provided for pouring the molten material into the mold 10 while rotating, after which the opening 11 may be closed, if necessary, in a known way. The closed and filled mold 10 is then rotated at the proper speed to achieve the centrifugal casting by a drive train, designated generally by the numeral 12. As will become apparent, the drive train 12 imposes a continuously changing tangential force on the mold 10 so that a shearing action occurs between the molten material and the solidifying material of the casting. This shear flow produces the desirable effect of substantially greater grain refinement.

The drive train 12 employs a constant speed drive motor 14 of any conventional type and a drive shaft 16, which is connected to the drive motor 14, and a driven shaft 18,

Patented Dec. 3, 1968 ice which is connected to the mold 10. In this FIGURE 1 embodiment the axis of the mold 10 is aligned with the axis of the driven shaft 18. The driving and driven shafts 16 and 18 are appropriately journaled on a support platform 20 at an angle a and joined together by a nonconstant velocity universal joint 22 of the well known Hooke type. The angular relationship of the driving and driven shafts 16 and 18 and the universal joint 22 contribute, as will become apparent, to the generation of the mentioned continuously changing tangential force that is imposed upon the mold 10.

The universal joint 22, when driven at a constant speed by the drive motor 14, will cause the angular velocity of the driven shaft 18 to continuously and cyclically change. The minimum and maximum speeds of the driven shaft 18 can be obtained with this type of universal joint 22 by multiplying the speed of the driving shaft 16 respectively by the cosine and secant of the angle a. Thus, if the speed of the driving shaft 16 is r.p.m. and the angle a is 25, the speed of the driven. shaft 18 will vary from 90.6 to 110.3 revolutions per minute. Therefore, during each revolution the mold 10 is both accelerated and decelerated by the imposition of the appropriate tangential driving forces thereto. By these accelerations and decelerations of the mold 10, the mentioned shearing action is produced by the flow of the molten material across the solidifying material thus producing more nuclei.

The alloy of the FIGURE 2 cross-section was made from a conventional centrifugal mold that was not accelerated and decelerated. This can be done by transferring drive from the constant speed motor 14 to the mold 10 through a straight shaft (not shown). The mold 10, therefore, would revolve at the constant speed of the motor 14. Note that the FIGURE 2 cross-section shows a rather large columnar grain structure. The same alloy, when cast by the FIGURE 1 apparatus; i.e., cast the mold 10 while being cyclically accelerated and decelerated, is shown in FIGURE 3 and has the substantially greater grain refinement with the aforementioned inherent advantages. Obviously, the grain refinement can be controlled so as to be somewhere between the FIGURES 2 and 3 examples, or even made greater and less than these FIGURES 2 and 3 examples, as will be now well understood by those versed in the art.

A flywheel 24, if needed, can be fixedly installed upon the driving shaft 16 in some known way. Such need would arise when the mass of the mold 10 was substantially greater than the mass of the drive motor 14 so that the mold 10 attempted to drive the motor 14. This reverse drive would introduce undesired velocity fluctuations into the drive train 12.

Briefly reviewing the method and operation of the FIG- URE 1 apparatus, the mold 10 is initially filled through the opening 11 with the molten material from which the part is to be formed by centrifugal casting. With the drive motor 14 revolving the driving shaft 16 at 100 r.p.m. and the angle a equal to 25, the speed of the driven shaft 18 will vary, as explained before, to produce the desired accelerations and decelerations of the mold 10 during each revolution of the driving shaft 16. These cyclic accelerations and decelerations generate the shearing flow, which results in the substantially greater grain refinement illustrated in FIGURE 3.

From the foregoing it will be appreciated that by the novel method significantly greater grain refinement of centrifugal castings can be achieved without any substantial increase in the cost of the apparatus and without resort to complex mold motions. A further benefit is that these castings formed by the novel method and apparatus have substantially improved physical characteristics without any significant increase in the cost of their production.

Moreover, there is the ability to control grain refinement to an extent not before possible.

The invention is to be limited only by the following claims.

What is claimed is:

1. The method of centrifugal casting comprising the steps of filling a mold with a molten material, rotating the mold at a continuously varying rate of speed so as to impose thereon tangential forces that also continuously and cyclically change for generating a shearing flow of the molten material within the mold.

2. The method as described in claim 1 wherein the mold is rotated so that the tangential forces continuously and cyclically accelerate and decelerate the mold.

References Cited UNITED STATES PATENTS 1,501,338 7/1924 Henry 1641l6 X 1,620,830 3/1927 Moore et al. 164-115 1,943,720 1/1934 Campbell 164-115 X 2,556,490 6/1951 Chamberlain 6824 X 2,778,162 1/1957 Gil'fen 164-114 X J. SPENCER OVERHOLSER, Primary Examiner.

3. The method described in claim 1 including the step 15 MAR, Assistant Examine"-

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