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Title:
CAST BAR DRAFT ANGLE
United States Patent 3818972
Abstract:
This disclosure relates to improvements in the casting groove on the periphery of an open casting wheel. The groove is formed with a draft angle in the range of 11-1/2° to 14-1/2° which results in an average increase in casting wheel life of more than 50 percent over prior art casting wheels.


Application Number:
05/295360
Publication Date:
06/25/1974
Filing Date:
10/05/1972
Assignee:
Southwire Company (Carrollton, GA)
Primary Class:
Other Classes:
164/433
International Classes:
B22D11/06; (IPC1-7): B22D11/06
Field of Search:
164/87,278,283MT
View Patent Images:
Primary Examiner:
Annear, Spencer R.
Attorney, Agent or Firm:
Hanegan, Herbert Wilks Van M. C.
Claims:
It is claimed

1. In a casting wheel having an open casting groove formed in the periphery thereof, said casting groove being defined by two side walls and a floor extending therebetween and wherein each of said side walls subtends a draft angle with the radial axis of said wheel; the improvement comprising providing said draft angle in the range of from about 111/2° to about 141/2° .

2. A casting wheel as defined in claim 1 wherein said draft angle is about 12° .

3. A casting wheel as defined in claim 1 wherein each of said side walls includes an upper section and a lower section, and wherein each of said sections subtends a different draft angle with the radial axis of said wheel.

4. A casting wheel as defined in claim 3 wherein the draft angle subtended by said upper section is greater than the draft angle subtended by said lower section.

5. In a casting wheel having an open casting groove formed in the periphery thereof, said casting groove being defined by two side walls and a floor extending therebetween and wherein each of said side walls subtends a draft angle with the radial axis of said wheel; said side walls including an upper section and a lower section, said lower section subtending a draft angle of about 91/2° and said upper section subtending a draft angle of from about 111/2° to about 141/2° .

6. A casting wheel as defined in claim 5 wherein the draft angle subtended by said upper section is about 141/2° .

7. In a casting wheel for solidifying a molten metal in a peripheral groove defined by a bottom surface and by two side walls extending radially beyond said bottom surface, a side wall having an inner surface with at least a portion thereof in a first plane of reference which forms an angle with a second plane of reference that includes said bottom surface, said side wall being of a thickness and of a casting wheel metal that are such that said side wall is distorted in shape in response to the heat of a molten metal in said peripheral groove to cause said angle to decrease by an amount less than a predetermined maximum, and being shaped so that in the absence of said heat, said angle is greater than a predetermined minimum by said predetermined maximum.

8. The casting wheel of claim 7 in which said casting wheel metal is steel, said molten metal is copper, and said predetermined minimum is 991/2° .

9. In a casting machine for solidifying a molten metal in a casting cavity defined by a casting wheel having a bottom surface and two side walls extending radially beyond said bottom surface and by a band urged against the outermost edges of said side walls with a predetermined force, a casting wheel with a bottom surface and side wall having an inner surface with at least a portion thereof in a first plane of reference which forms an angle with a second plane of reference that includes said bottom surface, said side wall being of a thickness and of a casting wheel metal that are such that said side wall is distorted in shape by said band and by the heat of a molten metal in said peripheral groove to cause said angle to decrease by an amount less than a predetermined maximum, and being shaped so that in the absence of said heat and said band, said angle is greater than a predetermined minimum by said predetermined maximum.

10. The casting machine of claim 9 in which said casting wheel metal is steel, said molten metal is copper, and said predetermined minimum is 991/2° .

11. In apparatus for continuously casting a bar from a molten metal comprising a casting wheel having a peripheral groove defined by two side walls and a bottom surface extending therebetween and constructed of a given metal, each of said side walls subtending a draft angle with the radial axis of said wheel, said peripheral groove being constructed according to the formula:

12. The apparatus of claim 11 wherein said given metal from which said peripheral groove is constructed is steel, and wherein said draft angle is in the range of from about 111/2° to about 141/2° when the molten metal intended to be cast is copper.

13. In a method of continuously casting molten copper in a casting wheel having a peripheral groove formed from steel and defined by two side walls and a bottom surface extending therebetween and wherein each of the side walls subtends a draft angle with the radial axis of the wheel, pouring the molten copper into the groove thereby causing thermal expansion of the groove and an increase in the initial draft angle, cooling and solidifying the molten copper in the groove causing a decrease in the draft angle to a value less than the value of the draft angle existing prior to the pouring of the molten copper, and extracting the solidified copper from the groove; the improvement comprising:

14. The method of claim 13 wherein said predetermined minimum value is 91/2° and said predetermined amount by which the draft angle existing prior to the pouring exceeds the draft angle existing after the cooling and solidifying is from about 2° to about 5° .

Description:
This invention relates to the metal forming arts, and more particularly to the continuous casting of molten copper and other metals by means of a casting wheel having a casting groove formed in the periphery thereof.

In the preparation of a metal rod or wire product by means of a continuous casting and rolling operation, molten metal is continuously cast into a continuous bar by a continuous casting machine and then, substantially immediately thereafter, hot-worked in a rolling mill to yield a continuous rod. The rod may then be cold drawn through a series of dies to form wire.

A typical continuous casting machine includes a conventional casting wheel having a casting groove in its periphery which is partially closed by an endless belt supported by the casting wheel and at least one idler pulley. The casting wheel and the endless belt cooperate to provide a mold into one end of which molten metal is poured to solidify and from the other end of which the cast bar is emitted in substantially that condition in which it solidified. Examples of such continuous casting machines are disclosed in U.S. Pat. Nos. 3,279,000 and 3,336,972, issued to D. B. Cofer et al. and assigned to the assignee of this invention.

The peripherally circumferential casting groove formed in conventional casting wheels has two side walls and a bottom surface or floor extending therebetween. In radial cross-section, the side walls inwardly converge toward the radial axis of the wheel. The slightly obtuse angle defined between each of the side walls and the bottom surface facilitates paying out of the cast bar from the groove. The amount that this angle exceeds 90°, or the angle subtended by each of the side walls and the radial axis of the wheel, is termed the "draft angle" of the wheel. Heretofore, the draft angle of conventional casting wheels has been approximately 91/2° .

During the normal casting operation, molten metal will tend to deposit and accumulate on the interior forming walls of the casting groove. Moreover, particularly during the casting of copper in a steel wheel, the thermal loading of the wheel resulting from the depositing of molten metal thereon and the simultaneous operation of cooling it into a cast solid bar causes the side walls of the casting groove to "close in," thereby reducing the draft angle of the casting groove and causing the cast bar to stick in the wheel. This condition obviously hinders the normal pay-out operation necessary to the continuous casting process, as well as causes severe mechanical stresses on the casting groove which results in surface cracking that seriously shortens the useful life of the casting wheel. This condition may be further aggravated by the tension of the endless belt on the mold walls.

Qualitatively, the situation can be described step-by-step, as follows:

1. Molten metal is poured into a relatively cold mold. The mold deflects due to thermal stresses caused by the molten metal. Simultaneously, a thin, weak shell is formed around the cast metal section. The mold cavity is then larger than it was prior to pouring.

2. The shell then becomes thicker and shrinks away from the mold some amount creating a gap which decreases heat flow away from the mold and allows the mold to shrink, reversing the deflection and heat flow process.

3. Towards the end of the cycle, heat transfer gradually decreases with accompanying decrease in mold temperature and mold temperature gradients. This causes the mold to "close in" with dimensions smaller than at the beginning of the cycle, with consequent contact and sometimes sticking between the sides of the mold and the cast bar.

4. As the bar is then continuously extracted from the mold, the mold temperature gradually reaches some steady value approximately equal to the initial temperature when the pour was made.

It has been determined that with a casting wheel having a standard draft angle of 91/2° as used in the industry, the "close in" described in steps 2 and 3 above will result in the draft angle being reduced to approximately 81/2° at that point in time, thereby seriously hindering the pay-out of the cast bar and setting up severe mechanical stresses in the casting wheel.

It is, therefore, a primary object of this invention to provide a casting wheel having an increased useful life.

Another object of this invention is to provide a casting wheel which facilitates extraction of the cast bar therefrom.

A further object of this invention is to provide a casting wheel having a casting groove that inhibits the tendencies of "close in" and surface cracking.

More particularly, it is an object of this invention to provide a casting wheel for use in a continuous casting operation wherein the peripheral casting groove has a draft angle that will not decrease below approximately 91/2° throughout the entire thermal cycle in a normal casting operation.

In accordance with this invention, the foregoing objects and others that may hereinafter become apparent are accomplished by providing a casting wheel having a casting groove with a draft angle in the range of from approximately 111/2° to approximately 141/2°, preferably approximately 12°. It has been determined in accordance with this invention that a casting groove having a draft angle in the range of 111/2° to 141/2° will not decrease below approximately 91/2° throughout any portion of the thermal cycle in a normal casting operation. Consequently, the tendency of the cast bar to stick in the casting groove is significantly reduced thereby facilitating easier pay-out and a corresponding increase in the life of the wheel. It has been found that casting wheels constructed in accordance with this invention have exhibited an average increase in useful life of more than fifty percent over the life of prior art casting wheels having draft angles of 91/2° .

While the lower limit of 111/2° is considered critical for the foregoing reasons, the upper limit of 141/2° is also considered significant and critical. To begin with, for structural reasons that will become hereinafter apparent, any increase in the draft angle necessitates an increase in the wall thickness of the mold where the outside surface of the mold remains perpendicular to the axis of rotation of the mold with a corresponding decrease in the heat transfer rate out of the mold and thus a decrease in the production rate. Therefore, it has been found to be advantageous to fabricate the casting mold so that mold side wall thickness is essentially uniform. It has been found that the decrease in the heat transfer rate is acceptable with draft angles up to 141/2°. Moreover, as the draft angle increases, the cross-sectional shape of the cast bar deviates to a greater extent from a rectangular shape which is less desirable for the rolling operation. Accordingly, the 141/2° limit has been determined to yield a bar having a cross-sectional shape that is still acceptable for the rolling operation. The preferable draft angle of 12° has been found to be an optimum in that it facilitates extraction of the bar from the groove while not unduly increasing the heat transfer rate nor yielding a shape that is undesirable for the rolling operation.

With the above and other objects in view that may hereinafter become apparent, the nature of the invention may be more clearly understood by reference to the several views illustrated in the accompanying drawing, the following detailed description thereof, and the appended claimed subject matter:

IN THE DRAWINGS

FIG. 1 is a highly-schematic elevation view of apparatus suitable to continuously manufacture rod, including a continuous casting machine and a rolling mill having a plurality of roll stands;

FIG. 2 is an enlarged radial sectional view taken along line 2--2 of FIG. 1, and illustrates a prior art casting groove having a draft angle of 91/2° which has cracks, ripping and metal build-up formed on the walls thereof;

FIG. 3 is a radial sectional view of one embodiment of a casting groove formed in accordance with this invention, and illustrates the walls of the groove being broken, the lower portion having a draft angle of 91/2° and the upper portion having a draft angle of 141/2° ;

FIG. 4 is a radial sectional view of the preferred embodiment of a casting groove formed in accordance with this invention, and depicts the groove having a draft angle of 12° ;

FIG. 5 illustrates the geometric relationship between a wedge and two inclined planes wherein the friction therebetween can be compared to the friction between a cast bar and a casting groove; and

FIG. 6 illustrates the normal forces and friction forces acting on a cast bar in a casting groove mold.

Referring now to the drawings in detail, there is illustrated apparatus for continuously manufacturing rod from molten copper and other metals. The apparatus includes a continuous casting machine generally designated by the numeral 10, and a rolling mill generally designated by the numeral 11.

The continuous casting machine 10 serves as a casting means for solidifying molten metal M to provide a cast metal such as a cast bar 12 that is conveyed in substantially that condition in which it solidified from the continuous casting machine 10 to the rolling mill 11 which serves as a hot-forming means for hot-forming the cast bar 12 into rod 16 or another hot-formed product.

The continuous casting machine 10 is of conventional casting wheel type similar to that shown in U.S. Pat. No. 3,336,972 and has a casting wheel 13 with a casting groove partially closed by an endless band 14 which is supported against the casting wheel 13 by a plurality of idler wheels 15. The casting wheel 13 and endless band 14 cooperate to provide a mold into one end of which molten metal M is poured to solidify and from the other end of which the cast bar 12 passes in substantially that condition in which it solidified.

The rolling mill 11 is of conventional type having a plurality of roll stands 17 arranged to hot-form the cast metal by a series of successive deformations. The continuous casting machine 10 and the rolling mill 11 are positioned relative to each other so that the cast bar 12 enters the rolling mill 11 substantially immediately after solidification so as to be in substantially that condition in which it solidified and at a hot-forming temperature within the range of temperatures for hot-forming the cast bar 12. No heating of the cast bar 12 is required between the casting machine 10 and the rolling mill 11 but in the event that it is desired to closely control the hot-forming temperature of the cast bar 12, means for adjusting the temperature of the cast bar 12 may be placed between the continuous casting machine 10 and the rolling mill 11 without departing from the inventive concept disclosed herein.

It will be understood that with the apparatus of FIG. 1, the cast bar 12 may be of any one of a plurality of lengths determined only by the amount of molten metal M solidified and may extend between the continuous casting machine 10 and the rolling mill 11. Thus, the steps of solidifying molten metal to obtain cast metal and of hot-forming the cast metal are generally being performed simultaneously once the apparatus of FIG. 1 is in operation.

Referring to FIG. 2, there is illustrated in radial cross-section a prior art mold 20 heretofore formed in the periphery of conventional casting wheels. The mold 20 includes a casting groove 21 defined by side walls 22, 23 and a bottom surface or floor 24 extending therebetween. Each of the side walls 22, 23 defines a slightly obtuse angle with the floor 24. The amount that this angle exceeds 90° is termed the draft angle α of the mold. The draft angle α can also be defined as the angle subtended by each of the side walls 22, 23 with the radial axis of the casting wheel 13. As was heretofore standard in the industry, the draft angle α of the prior art mold 20 is 91/2° .

As seen in FIG. 2, a build-up of metal 25 has formed on the side wall 22 which will tend to make the cast bar 12 stick in the mold 20 and thus hinder the normal pay-out or extraction process. The build-up or swelling caused by the metal 25 will further add to the "close in" effect that is evident during the thermal cycle in the casting operation. Also present in the prior art mold 20 are cracks and ripping formations 26 formed in the floor 24 and side wall 23. The cracks and ripping formations 26 represent, of course, failures in the mold 20 caused by the stresses set up therein as a result of the cast bar 12 sticking in the mold 20 and the friction forces developed as the cast bar 12 is extracted therefrom.

The relationship between the draft angle α and the friction force f between a casting and the sides of a casting wheel is analogous to a wedge contained between inclined planes and having friction on the contacting surfaces as illustrated in FIG. 5. Analyzing the trigonometric relationships wherein F = normal force and μ = coeffient of friction:

From statics

Σ F = O = μ F + μ F cos 2 α - F sin 2 α

μ (1 + cos 2 α) - sin 2 α = O

μ = sin 2 α/1 + cos 2 α

Then, for free motion between planes and wedge

μ < sin 2 α/1 + cos 2 α

Using trigonometric identities

sin 2 α = 2 sin α cos α

cos 2 α = cos2 α - sin2 α

sin2 α + cos2 α = 1

And for α ≠ π/2

μ < tan α

or

α > tan -1 μ

Completing the analogy with respect to a casting in a mold as seen in FIG. 6:

From statics

Σ F = O = 2 N sin α - 2 μ N cos α

Then, for free motion between the casting and mold

μ < tan α

or

α > tan -1 μ

It should be apparent, therefore, both in view of the foregoing analysis and from empirical evidence that there is a direct physical relationship between the draft angle and the friction force between the cast bar and the sides of the casting wheel. It has been determined in accordance with the invention that increasing the draft angle α to at least 111/2° will reduce the friction force sufficiently to permit extraction of the cast bar from the casting wheel throughout the entire casting operation without significant sticking and consequent stress and failure of the casting wheel.

A preferred embodiment of the invention is illustrated in FIG. 4 wherein there is depicted a mold 30 having a draft angle α of 12°. Not only will the increased draft angle α of 12° reduce friction and stress, but the "close in" effect during thermal loading will not reduce the draft angle below 91/2°, thereby preventing further sticking of the cast bar in the mold.

It should be apparent, however, that while the draft angle α of the mold 30 has been increased, the wall thickness of the mold 30 has been concomitantly increased to accommodate the increased draft angle. Consequently, the heat transfer rate out of the mold, and thus the production rate of the casting wheel, will be reduced. It has been determined that while a draft angle of 12° is an optimum, draft angles up to 141/2° can be tolerated without undue reduction in the heat transfer rate.

Referring now to FIG. 3, there is illustrated a mold 40 which represents another embodiment of the invention. The mold 40 includes a casting groove 41 having a floor 42 and "broken" side walls having angularly disposed sections 43, 44 and 45, 46, respectively. While the lower side wall sections 44 and 46 define a conventional draft angle α of 91/2°, the upper wall sections 43 and 45 define a draft angle α, of 141/2°. In this manner, improved extraction of the cast bar is facilitated while the heat transfer rate, and thus the production rate, is not diminished.

It should be understood that while the draft angle α of the mold 30 and the draft angle α, of the mold 40 have been specifically described herein as 12° and 141/2°, respectively, it is contemplated that the range of either angle may vary from about 111/2° to about 141/2° within the scope of this invention.

It should be apparent, therefore, that there is provided in accordance with this invention an improved casting wheel for use in a continuous casting operation wherein provided a draft angle in the range of 111/2° to 141/2° will facilitate extraction of the cast bar from the mold thereby reducing stresses and increasing the useful life of the casting wheel.

While the invention has been specifically illustrated and described herein with reference to preferred embodiments thereof, it is contemplated that minor modifications could be made without departing from the spirit of the invention.