Die assembly for continuous vertical casting of tubular metallic products

A two-piece die assembly for use in continuous vertical casting of tubular metallic products from material such as bronze wherein one piece includes an outer sleeve and the other piece is an inner mandrel axially received in the sleeve, both pieces being made from graphite. In use, the sleeve is fixed to extend through the bottom wall of a crucible or furnace containing the molten metal to be cast, and for securement to the bottom of the crucible, an outwardly extending flange is provided intermediate the ends of the sleeve to underlie and engage the bottom of the crucible. The mandrel includes an upper section received in the upper end of the sleeve and a lower section having a transverse dimension less than that of the upper section to define with the sleeve a mold cavity surrounding the lower section. The upper section includes an enlarged head resting on the upper end of the sleeve and and alignment section snug fit within the upper end of the sleeve below the head so as to align the mandrel in the desired position in the sleeve. Molten metal is poured into the mold cavity through means of a plurality of passages provided through the upper section of the mandrel so as to extend from inlets in the upper surface of the head which is submerged in the molten metal in the crucible and to terminate in outlets communicating with the mold cavity.

BACKGROUND OF THE INVENTION 
In the vertical continuous casting of tubular metallic products or stock 
from molten metal such as bronze, it is known in the art to employ a die 
assembly composed of graphite parts. Because of the exceedingly high 
temperatures of the molten metal to be continuously cast such a die 
assembly has an exceedingly short life, usually limited to one casting 
operation. The cost of replacing such graphite die assemblies for each new 
continuous casting operation thus becomes quite significant. 
OBJECTS OF INVENTION 
The present invention relates to a die assembly of the aforementioned type 
as well as a method for pouring molten metal into the die cavity in a 
vertical continuous casting process utilized to cast tubular metallic 
products or stock. 
A primary object of the present invention is to provide improvements in 
such a die assembly such that it may be manufactured with a compact 
construction at lower cost than that heretofore obtainable and yet, at the 
same time, may be successfully employed in a commercial, vertical, 
continuous casting process. 
It is another object of the present invention to provide an improved die 
assembly for use in a vertical continuous casting process which die 
assembly enhances cooling of the die during operation. 
A further object of the present invention is to provide such a die assembly 
that may be manufactured from available graphite stock such as that 
designated ATJ made by Union Carbide Corporation and which may be employed 
in presently available continuous casting apparatus. Included herein is 
the provision of such a die assembly that may be manufactured in different 
shapes depending on the cross section of the tubular metallic product to 
be cast. 
A still further object of the present invention is to provide an improved 
method of introducing molten metal from a crucible into a die cavity in a 
vertical continuous casting process for casting tubular metallic products 
or stock.

DETAILED DESCRIPTION 
Referring to FIG. 1 of the drawings, there is illustrated apparatus 
including a die assembly embodying the present invention for continuous 
vertical casting of a metallic tubular product 10 having a longitudinally 
extending passage 11 from molten metal M received in a furnace or crucible 
having a bottom wall 12 and upstanding side walls 14 containing the molten 
metal M. One typical metal M to be cast is bronze, however, the die 
assembly of the present invention may also be used to cast tubular 
products or stock from aluminum, cast iron and alloys. 
The die assembly of the present invention is comprised of two pieces each 
made from graphite stock material such as that marketed under the 
designation ATJ by Union Carbide Corporation. The die assembly includes an 
outer sleeve generally designated 15 and an inner mandrel generally 
designated 16 received in the sleeve to form a mold cavity 17. In an 
installation, the outer sleeve is fixed against movement in the bottom 
wall 12 of the crucible to extend therethrough as shown in FIG. 1, and for 
this purpose the outer sleeve is typically provided with an intermediate, 
outwardly extending flange 18 underlying bottom wall 12 of the crucible. 
Sleeve 15 has opposite open top and bottom ends 19 and 20, respectively, 
and in the specific embodiment shown where cylindrical tubular products 
are to be cast, sleeve 15 has an internal surface 21 of cylindrical 
configuration. It will be understood that where other tubular 
configurations are to be cast such as hexagonal, rectangular or other 
polygonal configurations, the internal surface 21 of the sleeve will be 
configured accordingly. 
About the lower section of sleeve 15 is fixed a cooling manifold 22 which 
may be any conventional cooling manifold for purposes of cooling the 
sleeve and the cast product 10 during a casting operation. Cooling 
manifold 22 per se forms no part of the present invention and therefore 
need not be further described; except to point out that in the specific 
embodiment shown, the inner surface 23 of the cooling manifold is tapered 
for securement to the outer surface of sleeve 15, and this explains why 
the outer surface of sleeve 15 is tapered adjacent the cooling manifold 
22. 
In accordance with one of the features of the present invention which will 
be better understood from the description below, sleeve 15 is fixed in the 
bottom wall 12 of the crucible so that only a small portion approximately 
11/2 to 13/4 extends above bottom wall 12 in the crucible. In one specific 
embodiment, the overall longitudinal or axial dimension of sleeve 15 is 
approximately 7 inches. 
The other piece of the die assembly of the present invention includes an 
inner part termed "a mandrel" generally designated 16 to be received in 
outer sleeve 15 to define mold cavity 17. Mandrel 16 includes an upper 
section generally designated 30 and a lower section generally designated 
32. Upper mandrel section 30 includes an enlarged head 30a adapted to rest 
upon upper end 19 of the sleeve as shown in FIG. 1, and a reduced width 
section 30b below head 30a adapted to snugly fit within the open upper end 
of sleeve 15 for purposes of accurately aligning lower mandrel section 32 
in predetermined position within sleeve 15 in order to provide precision 
cross-sectional dimensions in the cast product 10. Since, as noted above, 
the internal surface 31 of sleeve 15 is cylindrical, the external surface 
of reduced width section 30b of the upper section 30 will have a 
cylindrical shape to correspond to that of inner sleeve surface 21. If 
other shapes are to be cast, these surfaces 21 and 30b will of course be 
correspondingly shaped. 
Lower mandrel section 24 includes at an intermediate portion thereof, a 
forming section 40 along which the molten metal M is formed as it falls by 
gravity through the mold cavity 17. In the specific embodiment where the 
product cast 10 is to have a cylindrical internal passage 11, the 
configuration of forming section 40 is that of a cylinder. In other 
situations where the tubular product to be formed is to have a polygonal 
or other shaped internal passage, it will be understood that the shape of 
forming section 40 will be configured accordingly. Also, since in the 
shown embodiment passage 11 of product 10 is to be centered or aligned 
with the longitudinal axis a--a of the product, forming section 40 will 
also be aligned with axis a--a. Mandrel 16 is formed such that when 
section 30b is received in the upper end of sleeve 15 with head 30a 
resting squarely on end 19 of sleeve 15, forming section 40 will be 
accurately aligned with axis a--a. 
Below mandrel forming section 40, is a lower section 42 which tapers 
downwardly and inwardly from forming section 40 as shown in FIG. 1, thus 
providing separation of the cast material M from the mandrel as 
illustrated in the drawing. In accordance with another feature of the 
present invention, lower section 42 of the mandrel is formed with an axial 
recess 44 extending into forming section 40 for purposes of admitting air 
into the mandrel for cooling. The dimensions of recess 44 which will be 
described below, are carefully selected so as to not unduly weaken the 
sections 40 and 42 of the mandrel but, at the same time, to provide 
enhanced cooling of the mandrel during operation. 
In accordance with the present invention, upper section 30 of the mandrel 
is provided with a novel configuration and dimension to permit sleeve 15 
as well as mandrel 16 to be formed with a more compact design requiring 
less graphite material. To this end, the upper section head 30a is 
dimensioned to abut and rest upon upper end 19 of sleeve 15; and the 
underlying securing and aligning section 30b is adapted to fit snugly 
within sleeve 15 so as to accurately align and position forming section 40 
of mandrel 16 within the sleeve to provide an accurate dimension and 
configuration to the product 10 to be cast. Section 30b therefore has a 
reduced diameter in comparison to head 30a; and since in the specific 
embodiment a cylindrical product is to be cast, section 30b has a 
cylindrical configuration conforming to the internal cylindrical surface 
21 of sleeve 15; and head 30 has a disc-like configuration coinciding with 
the upper end 19 of sleeve 15 as shown in the drawings. 
Further, in accordance with the present invention, the improved mandrel of 
the present invention also facilitates pouring or introduction of the 
molten metal M into the mold cavity 17. This is effected by means of a 
plurality of pouring passages 50 extending longitudinally through upper 
section 30 beginning at inlets at the upper surface of head 30a and 
terminating in outlets in the lower shoulder-like surface 30c of aligning 
section 30b which outlets communicate with mold cavity 17. In the specific 
embodiment, pouring passages 50 are provided in a circular array in upper 
section 30 of the mandrel as shown in FIG. 2 and to maximize efficiency, 
it has been determined that the total cross-sectional area of pouring 
passages 50 should approximately equal the transverse, cross-sectional 
area of mold cavity 17. Also in the preferred embodiment, passages 50 are 
oriented in parallel relation to each other. 
In contrast to die assemblies of the prior art, the present die assembly 
does away with the need of providing lateral pouring apertures through the 
sleeve 15. Instead, sleeve 15 of the present invention continuously 
encloses mold cavity 17 below upper mandrel section 30. Thus, the distance 
of projection of the die assembly above the bottom wall 12 of the crucible 
is minimized by the present invention as is the overall size of the die 
assembly. In addition, with the die assembly of the present invention, 
molten metal M flows by gravity directly vertically downwardly through 
upper section 30 of the mandrel in contrast to the prior art where pouring 
takes place laterally through the sleeve of the die assembly. 
While the abutment of mandrel head 30a against upper end 19 of sleeve 15 
prevents downward movement of the mandrel relative to the sleeve, it is 
preferred that a pin shown as 60 also be utilized to secure the mandrel in 
the sleeve against upward movement. Preferably, pin 60 should extend 
through the side wall of sleeve 15 and into upper section 30b of the 
mandrel below head 30a and in a path lying between adjacent pouring 
passages 50. For this purpose, pin passages are respectively laterally 
provided in the sleeve and mandrel to receive pin 60. 
With the present invention, the die assembly can be manufactured from less 
graphite stock at significant cost savings which becomes very significant 
when it is realized that a new die assembly must be replaced at each new 
casting operation since the high temperatures encountered during casting 
cause the surface of the mandrel to become marred or crusted. In one 
specific embodiment of the present invention, the sleeve and mandrel are 
made to each have an overall axial length of 7 inches. Further, the depth 
or axial distances of mandrel head 30a and aligning section 30b are both 1 
inch so that the total head section 30 depth is 2 inches. Also, the length 
of forming section is 1 inch and the length of lower section 42, 11/2 
inches. The diameter or cross dimension of the cooling recess is 13/4 
inches, while the thickness of the wall of lower section 42 is 
approximately 3/8 inches The axial distance of lower mandrel section 16 
between the forming section 40 and head section 30 is 21/2 inches. The 
diameter or cross dimension of the forming section 40 of the mandrel will 
of course vary depending upon the desired wall thickness to be imparted to 
the product 10.