Note: Descriptions are shown in the official language in which they were submitted.
1 BACKGROUND OF THE INVENTION
FIELD OF T~E INVENTION
The present invention relates to a process for
producing a continuously cast bar which has a helical
groove and is substantially free from defects on the
inner and outer surfaces thereof, and to an apparatus
for the process.
DESCRIPTION OF THE PRIOR ART
For obtaining a long bar having a helical
groove, there are already known, or example, a method
which comprises first preparing a thick bar by casting
or the like, worklng it into a sguare-shaped bar or a
bar having a rectilineal groove by means of an extruder,
etc. and then giving a twist to the bar at its both
ends, and a method which comprises grooving a helix
continuously on the surface of a bar by means of rolling
or the like.
Although it is also possible by these
conventional methods to obtain a long bar having a
20 continuous helical groove by supplying a raw material
bar continuously during the extrusion, it is difficult
to avoid staining at the joint surface due to lubricant
used in the extrusion or to avoid structural change,
etc.
1 Although it is also possible to bond the
respective end faces by welding or the like after
completion of an extrusion, the inspection and the
detection of defects, if any, at the bond portlon
require much time and trouble, and further the
deformation of the helical groove at the bond portion
necessitates complicated and difficult work for
readjusting it.
SU~MARY OF THE INVENTION
According to the present invention, there are
provided a process for continuously casting a bar having
a helical groove which comprises casting a bar in a mold
for continuous casting which has a helical inner wall
surface or has a groove or protrusion helically cut on
its inner wall surface while rotating and drawing the
bar in conformity with the slope of the helix; a mold
for continuous casting having a monolithic structure or
combined structure, which has a molten metal-supplying
- part and a heating unit attached to the inside or
outside of the mold and in which the inner wall surface
on the side of the molten metal-supplying part or the
whole of the mold is heated above the solidification
temperature of a metal to be cast with the heating unit
and the side of the mold for taking off a continuously
cast bar is cooled below the solidification temperature;
a continuous casting process using the above mold, and
an apparatus for the continuous casting.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional side view of a casting
apparatus with combined heating and cooling units in a
situation at the beginning of a continuous casting.
Fig. 2 is a sectional side view of a casting
apparatus in casting operation and a sketch drawing of a
continuously cast bar formed.
PREFERRED EMBGDIMENTS OF THE INVENTION
The present invention will be described in
detail below.
Although the present invention can be applied
to all kinds of metals and their alloys, a body to be
cast immediately after solidification is required to
bear a shearing force caused by the rotation of the mold
or the rotation of the cast body itself, 90 that the
invention is more suitably applied to pure metals or
systems containing a small amount of an alloy.
A helical cast bar can be obtained by drawing
a body to be cast while rotating it in conformity with
the slope of the helix. When a longer bar is to be
cast, the cast body may be taken up around a jig such as
a spool or bobbin while being rotated together with the
jig. A cast bar having a helical groove can be also
obtained continuously by drawing the cast bar while
rotating the mold in conformity with the slop of the
helix, instead of rotating the cast bar itself.
1 In the present invention, a cast bar may be
rotated by, for example, rotating the moldr rotating a
jig for taking up the cast bar or rotating a molten
metal-holding part for supplying molten metal and the
5 mold part as one body as well as rotating the cast bar
itself.
When a long bar having a helical groove is of
a small diameter or when the pitch of the helix is
minute, the mold for continuous casting is desirably the
10 one which can ~chieve unidirectional solidification in
the opposite direction to the casting direction and
besides in which the shape of freezing interface is pre-
ferably such that solidification on the surface of t:he
cast bar is delayed behind solidification at the center
15 portion thereof-
For this purpose, it is effective that themold is constructed of a cooling part to be cooled at
temperatures lower than the freezing temperature of the
metal to be cast and a heating part to be heated at
temperatures higher than the freezing temperature. It
is also effective for the purpose of increasing a
temperature difference between the cooing and heating
parts to highten cooling effect by, for example, pouring
water directly onto the cast bar.
The larger the temperature difference between
the heating and cooling parts, the more the unidirec-
tional solidification is ensured. To attain this
object, it is necessary to provide a insulating layer
h l.~ 7 ~
1 between the two parts.
The heating part can be maintained above the
freezing temperature of the molten metal by heat
transferred from the molten metal-holding part, which,
however, is not always satisfactory for achieving
complete unidirectional solidification even when a heat
insulating layer is provided between the heating part
and the cooling part. Therefore, the heating unit is
preferably provided in the inside or outside of the
mold. Examples of heating units usable for such purpose
include one which makes use of resistance heating and
one which uses an induction heating.
By conducting the continuous casting with a
mold having a heating part~ insulating part and cooling
lS part as mentioned above while conducting the rotation in
conformity with the slope of helix, a continuously cast
bar having a helical groove can be easily produced
through a simple process step~
Although the shape of the cross-section of the
mold is basically a circle in the present invention, it
is not critical and may be also any one of polygons such
as triangles, etc. For example, when the cross-section
of the mold is rectangular and the inner wall surface of
the mold is helical, bars having helical appearance can
be obtained. When the cross-section is circular,
continuously cast bars having a helical groove can be
obtained by use of a mold having a groove or protrusion
hPlically cut on its inner wall surface.
~ t~ 3
1 The shape of the helical groove of the
continuously cast bar obtainable in the present
invention may be any desired one as long as it permits
drawing of the cast bar.
Example
Fig. 1 shows an example of a casting apparatus
for embodying the process of the present invention in a
situation at the beginning of casting. A molten metal-
holding furnace 1 is provided with a heating unit 2 and
a molten metal-holding crucible 3, and molten aluminum 4
is held therein. To the side wall of the molten-met:al
holding crucible is attached a combined mold provided
with a graphite-made heating part 5 having a built-in
mold heater 8, a copper-made mold-cooling part 6 whose
inside is cooled by water and an asbestos cloth insulat-
ing part 7 of 1 mm thickness which prevents heat trans-
fer between part 5 and part 6.
Although the mold is attached sideways in the
present invention, subsequent operations can be con-
ducted in completely the ~ame manner as above also whena similar mold is attached to the bottom part of the
crucible right downward. The mold has an inner diameter
of 30 mm, on the inner wall of which is cut one line of
helical protrusion 10 having a triangular cross-section
of 5 mm height and 10 mm base length in a pitch of
60 mm.
6 --
2~ $1
1 In starting the casting, the mold needs
to be plug~ed w~th ~ dummy block ~ so that mo'ten
aluminum may not leak out of the mold. Molten aluminum
with which the mold is filled freezes at the cooling
5 part and bonds itself firmly to the dummy block.
Although the solidification proceeds as far as the heat
insulating part, it does not proceed farther because the
heating part has been kept at a temperature higher by
several degrees centigrade than the free~ing temperature
10 of aluminum by means of a temperature controlling
apparatus. Owing to cooling due to heat transfer from
the reezed part, the free~ing interface assumes a ~3hape
somewhat convex toward the direction of progress of the
solidification.
After the solidification was confirmed in the
cooling part, the continuous casting was carried out at
a drawing rate of 50 mm/min while rotating the dummy
block and the continuously cast bar in conformity with
the helical shape of the inside wall surface of the
20 mold.
Fig. 2 shows the appearances of a pair of
rolls 11 for rotation and rotational drawing and a
continuously cast bar formed 12 having a helical groove
on its outer wall.
The continuously cast bar thus obtained had a
appearance of smooth, completely reproduced helix and
had no defects such as shrinkage cavity inside the bar.
