Note: Descriptions are shown in the official language in which they were submitted.
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~ ~ gc~ ~ ~ KAB--7240
BACKGROUND OF THE INVENTION
3 The present invention relates to a metho~ of making
4 tubular, curved or straight molds for continuous casting,
under utilization of a copper alloy.
7 German printed patent application 25 33 528 discloses
8 a method of making such a mold by deforming a copper or copper
g alloy blank by means of explosives for forming the blank
in order to obtain the desired contour of the mold. This
11 method offers the advantage of a high-quality surface of the
12 resulting mold; also, the dimensions of the cavity attained
in this fashion are very accurate. Additionally, the surface
14 o~ the mold is actually harclened. Assumlng, for instance,
an original hardness of 40 Rockwell B, the explosive-orming
16 method above will result in a hardness of from 50 to 75 Rock-
17 well B.
~8
i9 The explosion deforming or forming as described is
disadvantaged by the fact that the resulting wall thickness
21 is too low to permit any significant subsequent reductionl
22 e.g., by means of cold-workingO Consequently, the overall
23 strength of the mold and, therefore, the stability as to
24 shape and in~egrity of the cross section is fairly poor.
Moreover, cold-working is usually employed in order to
26 strengthen the material; but as soon as the temperature
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KAB-7240
1 rises to 350C, that process reverses itself so that a
2 highly used mold wears out rather quickly. The mold's strength
3 can be increased to some extent throu~h appropriate selec-
4 tion of the copper alloy constituents. Unfortunately,
the heat conduction goes down; and such a mold may have the
6 tendency of cracking in the surface level of the molten
7 material.
9 DESCRIPTION OF THE INVENTION
11 It is an object of the present invention to provide
12 a new and improved method of making molds for continuous
13 casting without restrictions as to wall thickness, preferably
14 for making castings of a large diameter. More~ver, the mold
is to have (a) a very great strength over its entire wall
16 thickness, (b) a high softening temperature, and (c) a high
17 thermal strength. Moreover, it should be possible to select
18 alloying components so that magnetic stirring is made possible;
19 furthermore, electrical conduction and heat transfer charac-
teristics should be subject to control.
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22 It is, therefore, a specific ob~ect of the present
23 invention to provide a new and improved method for makiny
24 molds for continuous casting under utilization of the explosive
type forming technique.
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In accordance with the preferred embodiment of the present inven-
tion, the objects thereof are obtained by using a tubular blank of an age-
hardening copper alloy which blank is solution heat treated at a temperature
within a range that is appropriate for the particular alloy; alternatively,
the tubular blank is formed at such a temperature; subsequently, the tube is
age hardened for at least 15 minutes at a temperature of between ~00C and
600 C; finally, the tube is explosion-formed in order to obtain its final
dimensions. In the case of making a curved mold, a bending step is inter-
posed between the annealing and the age-hardening. The mold walls, part-
icularly of the cavity, can be straight or curved, round or rectangular,tapered or conical.
Molds made by the afore-described steps have strength values which
are considerably higher than the ones in conventionally made molds, the rea-
son being that an age-hardening copper alloy has been used. The strength in-
crease during age-hardening at 400 C to 600 C is attained by internal pre-
cipitation. The thws improved mold lasts longer, retains its shape better,
particularly under thermal load and tension, and wears out less, particularly
because of reduced abrasion.
The mechanical strength of the mold can be increased in further-
ance of the invention by mechanically cold-working the annealed and soft
tube. ~or instance, a mandrel is inserted into the tube prior to age-
hardening, the mandrel being curved or straight as desired; and together,
they are pulled through a drawing die. The degree of cold deformation may
be chosen to be between approximately 2% up to approximately 30%, depending
upon desired strength enhancement.
The subsequent age hardening results :in very high strength values;
there:Eorc, lt ls desirable to size the mol.d already after the initial anneal-
ing in orcler to obtain the desired geometry and dimensions o:E the mold, in
part:icular, o:E its c.avity. During age hardening, some distortion may occur,
but that will be compensated by the final explosion-:Eorming step; and one ob-
tains an optimum product, indeed.
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The copper alloy to be used depends upon the specific requirements
for the type o-f mold and its intended use. An age-hardening alloy for a
wide variety of uses will include 0.3 to 1.2 chromium and 0.05% to 0.2%
zirconium, the remainder being copper. These and all following percentages
are by weight. This particular copper alloy exhibits the requisite high
thermal conductivity for a mold for continuous casting. Conventional molds
are made from SF copper or a copper silver phosphorous alloy; but the pre-
sently proposed copper chromium zirconium alloy, worked in accordance with
the inven-tion~ has a much higher temperature s~rength and
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KAB-7240
1 persistence to wear and abrasion; such a mold is almost
2 completely free from contour deformation and distortion
3 and has a long life.
EXAMPLES
7 (1) In the followingl the making of a copper chromium zirconium
8 mold will be described w-ith reference to a specific example:
g
A copper alloy having 0.7~ chromium and 0.18% zirconium,
11 the remainder being copper and the usual impurities, was used
12 to cast a pin, i.e., a round, cylindrical blank or billet.
13 This blank or billet was extruded at 1,030C in order to
14 obtain a tube, which was then qllenched in water. This parti-
cular working and tube-forming step served also as the initial
16 solution heat treatment or annealing step for the material.
Certain tubular/
17 /lengths were cut from this tube and pre-bent in an appropriate
18 bending machinQ.
i9
A circular die member was introduced into such a cut
21 tube and explosive charges were uniformly distributed around
22 the periphery of that tube and fired. This particular step
23 served as a cold-working step to enhance the strength of
24 the material and to pre-siæe the tube. Thereafter, the
die member was removed from the tube, and the latter was
26 age-hardened at 475C for four-and-one-half hours. The shape
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~ KAs-7240
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1 of the thus treated tube was slightly distorted. Therefore,
2 after cooling a die was inserted, having a cross section
3 which did exactly correspond to the cross section of the
4 mold ca~ity to be made. This die was slightly curved and,
of course, the orientation of the curvatures have to match.
6 Thereafter, another explosion deformation step was performed,
7 just as described above, which constituted another cold-
8 working step hy means of which the mold attained the desired
9 dimensions.
11 The mold made :ln this manner did exhibit the following
12 properties:
13
14 Thermal conductivity87% (of pure copper)
So~tening temperature 525C
16 Hardness HB 2.5/62.5 145
17 Tensile strength442 Newtons/mm
18 Yield point (elongation at rupture) 26%
19 High temperature strength:
220C 380 N/mm2
21 350C 318 N/mm2
22 10% drop in strength at room temperature after
23 one hour of age-hardening.
2~
This mold has retained its dimensions even after
26 450 runs of casting charges, particularly in the level of
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K~B-7240
1 the surface of the molt~n material. Only the bottom of
2 the mold exhibited some wear.
4 (2) A straight mold with conical (tapered), rectangular
5 cross section was made from the same copper chromium zirconium
6 alloy, in accordance with the following example. This mold
7 was still stronger.
9 A round tube was made by extrusion at 950C, and the
rectangular (square) cross section resulted from a subsequent
solution heat treated /
11 drawing step. This square tube was / for 45 minutes
12 at 990C. Following cooling, suitable lengths were cut; and
}3 each length was sized and cold-worked by means of a mandrel
14 and a die under reduction of the wall thickness by 15% in
order to obtain the final ~;men~ion. Thereafter, the tubular
16 pieces were age-hardened for six hours at 450C. The final
17 sizing was obtained by the above-mentioned explosion deforma-
18 tion.
~.9
The molds made in the afore-described manner did have
21 the following properties.
22
23 Thermal condcutivity 84% (of pure copper~
24 Softening temperature 510C
Hardness HB 2.5/62.S 159
26 Tensi;le strength 521 Newtons/mm2
27 Elongation a-t rupture 21%
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KAB-7240
1 This particular mold exhibited decid~dly less wear
2 at the bottom.
4 (3~ In some cases, one needs a mold of a still higher
thermal conductivity; for instance, when the quality of
6 the cooling water is rather poor~ The alloy may consist
7 hexe o~ copper with just 0.05~ to 0.3% zirconium. The
8 working method is carried out as described. An interposed
9 cold-working step raises to a tensile strength of up to
350 N/mm2 at a thermal conductivity of above 93~ of pure copper.
11 This material softens at a tempera~ure of above 550~C.
12
13 (4) Magneti.c sti.rring is another special requirement, which
14 means that the electrical conductivi~y of the mold should be
quite low in order to make sure that the magnetic stirring
16 field is not signi.ficantly weakened. Unfortunately, the
17 thermal conductivity drops with the electrical conductivity
18 so that the mold wall temperatures will be quite high during
19 casting. Thus, in order to avoid thermal deformation of
the mold, its strength must retain high values, even at
21 high operating temperaturesO
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23 In accordance with the invention, it was found that,
24 for instance, an age-hardening copper-nickel-phosphorous
alloy is well suited for such a purpose; particularly,
26 a composition of 0.~% to 1.5% Ni and 0.1% to 0.3~ P (remainder
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KAB-7240
1 being copper plus impurities~. Alternatively, a copper -
2 cobalt-beryllium alloy or a ~opper-nickel-beryllium alloy
3 can be used with 1 to 2~5%-~o;or 1 to 2.5% Ni; or
4 0.5 to 1.5~ Ni plus 0.5 to 1.5~ Co, and 0.3 to 0.6% beryllium
in each instance (remainder Cu plus impurities). Another
6 alloy consists of copper nickel silicon with 0.2 to 1.1~ Si
7 and 1.2 to 3.5~ Ni (remainder Cu plus impurities).
9 A copper cobalt-berylliurn alloy with 2.2% Co and 0.54 Be
(remainder Cu and impurities) was used to make a rectangular,
11 tubular mold at interior dimensions of 200mm by 220mm;
12 wall thickness 14mm.
13
/treated
14 A near-square tube WdS made by extrusion and solution heat/
for 45 minutes at 935C. A bending machine provided the
16 desired curving~ After cutting, the lengths were explosion
17 deformed as described and sized over a mandrel. Each piece
18 was then age-hardened at 480C for five hours. Any distor-
19 tion that may have resulted was eliminated by another
explosion deforming over a mandrel, and the resulting molds
21 were sized again.
22
23 A mold made as per the last-mentiolled method did haYe the
24 following properties:
26 Therrnal conductivity 54~ (of pure copper)
27 Softening temperature 505C
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1 Hardness HB 2.5/62.5 235
2 Tensile strength 805 N/mm2
3 El.ongation at rupture 17%
4 ~igh temperature strength:
200C 735 N/mm2
6 350C 622 N~mm
8 Such a mo].d was then used in conjunction with magnetic
g stirring, and the low field attenuation resulted in a
significantly improved stirring effect. The mold retained
11 its size even after 100 casting runs.
12
13 The invention is not limited to the embodiments
14 described above; but all changes and modifications thereof,
not constltuting departues from the spirit and scope of
16 the invention, are intended to be included.
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