Heat exchanger structure and method of manufacturing same

This invention relates to a heat exchanger structure in which a passage for the cooling or heating fluid is formed. The inner surface of the passage is roughened, and provided with a plurality of lengthwise-extending, inwardly-projecting, linear or spiral, continuous or intermittent fins. The cooling or heating fluid is passed through the passage to promote an increase in the heat exchange rate. In order to manufacture such a heat exchanger structure, a pipe provided on its inner surface with a plurality of lengthwise-extending, inwardly-projecting, continuous or intermittent fins is inserted between a plurality of complementary members to combine these parts in the shape of a mold. The exposed portions of the joint surfaces of these complementary members and such portions of the complementary members and pipe are then hermetically vacuum-sealed. The resultant complementary members and pipe are diffusion-welded unitarily by the hot isotropic pressure welding. A nickel plate or a nickel alloy plate or a stainless steel plate, which is laminated on the portion of the assembled parts which requires to have the wear resisting properties is also diffusion-welded at the same time.

FIELD OF THE INVENTION 
This invention relates to a heat exchanger structure, such as a mold for 
continuous casting, and a blade inlet, which must be cooled or heated, and 
which have in a heat exchanger structure body a completely-formed passage 
for a cooling or heating fluid; and a method of manufacturing such heat 
exchanger structures. 
BACKGROUND OF THE INVENTION 
A generally-used cooling system for, for example, a mold for a continuous 
casting is a system in which the cooling water is passed through a space 
formed between a recess, which is provided in the rear surface of a mold 
body, and a back frame. However, in this cooling system, a sufficiently 
high cooling efficiency cannot be obtained, and there is the possibility 
that the water may leak from a region between a back frame and a mold 
body. Moreover, it is difficult to provide this region with a seal for 
preventing the leakage of water therefrom. With a view to eliminating 
these inconveniences, a mold having a cooling water passage formed 
completely within a mold body has recently been proposed. 
However, it is very troublesome to form such a cooling water passage in a 
mold of this construction. Therefore, a smaller number of larger-diameter 
bores is more often the case than a larger number of smaller-diameter 
bores. The larger the diameter of a cooling water passage, the more easily 
the cooling water flowing therethrough separates into supernatant, 
intermediate and bottom layers. This causes a great decrease in the 
cooling efficiency. 
OBJECT OF THE INVENTION 
An object of the present invention is to provide a heat exchange structure, 
such as a mold for continuous casting, which is capable of solving these 
problems; and a method of manufacturing such heat exchanger structures.

DESCRIPTION OF THE EMBODIMENTS 
FIGS. 1 and 2 show a mode of embodiment of a mold, which constitutes a heat 
exchanger structure A, for continuous casting. In this embodiment, a 
cooling water passage 2 having at its both ends a cooling water feed port 
3 and a cooling water discharge port 4 is formed so as to zigzag back and 
forth through the interior of a mold body 1 which consists of a material 
having a high heat conductivity, such as copper or a copper alloy. 
The design of the cooling water passage 2 in this embodiment, in which the 
passage 2 extends so that a fluid can circulate over its whole length, can 
be modified in various ways. A mode in which a plurality of cooling water 
passages having cooling water feed ports and cooling water discharge ports 
at their respective lower and upper ends are formed independently of one 
another, and a mode in which a plurality of cooling water passages 
extending in a non-vertical direction and having their respective cooling 
water feed ports and cooling water discharge ports are formed can also be 
employed. 
The inner surface of the mold body 1, i.e. the surface, which a melt or a 
solidified shell contacts, is provided additionally with a wear resisting 
protective layer consisting of nickel or its alloy. Accordingly, this mold 
is not different at all from the generally-used mold for continuous 
casting. 
As shown in FIG. 2, which is an enlarged view of a principal portion the 
above embodiment, a plurality of lengthwise-extending fins 5, 5 . . . are 
formed on the inner surface of the passage 2 so that these fins project 
inward therein. 
These fins 5 increase the area of the inner surface, which the cooling 
water contacts, of the passage 2, and enable the cooling efficiency to be 
improved. Hence, it is desirable to form the largest possible number of 
fins 5, 5 . . . that enables a required level of flow rate of the cooling 
water to be maintained, in such a manner that the fins project inwardly 
into the passage 2. 
Each fin 5 may not necessarily be formed continuously over the whole length 
of the cooling water passage 2; it may be formed in a rack-like 
construction. 
The inner surface of the passage 2 may consist of a rough surface having 
small particles thereon, or rough surfaces composed of stripes of minute 
projections and recesses. These rough surfaces enable the efficiency of 
heat conduction of the inner surface of the passage 2 to be greatly 
improved. 
A method of manufacturing a mold for continuous casting, which is provided 
with these fins 5, will now be described with reference to FIGS. 3-6. 
First, two divisional members 1', l" provided in one surface thereof with 
grooves 2', 2", which are to form a cooling water passage 2, are prepared. 
The inner divisional member 1' out of these two divisional members 1', 1" 
can be formed of copper or a copper alloy, which has high thermal 
conductivity, and the outer divisional member 1" stainless steel, which 
has a high strength. 
A pipe 6 shown in FIG. 4 is prepared, which is to be fitted in a space 
formed by the grooves 2', 2" when the divisional members 1', 1" are 
engaged at their respective grooved surfaces with each other. 
This pipe 6 is provided on its inner surface with a plurality of continuous 
or intermittent fins 5, 5 . . . , which extend in the lengthwise direction 
of the pipe 6 and are spaced in the radial direction thereof, and which 
project inward so as to form a rack-like structure. 
These divisional members 1', 1" and pipe 6 are then assembled with the pipe 
6 fitted in the grooves 2', 2", as shown in FIG. 5. The peripheries of the 
portions of the joint surfaces 7 of the divisional members 1', 1" which 
are exposed to the outside, and the peripheries of the portions of the 
joint surfaces 7 of the divisional members 1', 1" and pipe 6 which are 
exposed to the outisde are then hermetically sealed. Sealing is effected 
by electron beam welding so that air is not left on the inner side of the 
seal. 
The resultant product is then formed into a unit by hot isotropic pressure 
welding, in which the pressure of a required gas, such as a 
high-temperature and high-pressure argon is applied to the whole surface 
of the product. 
Owing to this hot isotropic pressure welding, diffusion bonding occurs in 
the joint surfaces of the two divisional members 1', 1', and also between 
the pipe 6 and divisional members 1', 1" if the pipe 6 consists of a 
material which can be diffusion-bonded to the divisional members 1', 1". 
The pipe 6 is generally formed of the same kind of material, i.e. copper or 
a copper alloy as the divisional members 1', 1", and the heat exchanger 
structure A is used with the pipe 6 and divisional members 1', 1" joined 
to one another unitarily. However, the pipe 6 may consist of any material. 
The heat exchanger structure A may be formed in an arbitrary shape. For 
example, as shown in FIGS. 7 and 8, a heat exchanger structure may be 
formed by preparing double tube type cylindrical body consisting of inner 
and outer cylindrical members; and inserting a pipe 6 between the contact 
surfaces of these inner and outer cylindrical members so as to extend in 
the longitudinal direction thereof or spirally in the circumferential 
direction thereof, and thereby make a passage 2 for cooling water or 
steam. 
In this case, if the two divisional members 1', 1", which consist of 
different kinds of metals, are diffusion-welded to each other unitarily 
with a member of a metal, which is a different kind from those of the 
divisional members 1', 1", held therebetween, the members of different 
kinds of metals which cannot normally be welded to each other become 
weldable. Such an additional metal member increases the bond strength of 
the divisional members of different metals even when these metals can be 
welded to each other welding of the metal members can be performed easily, 
and the efficiency of the operation is improved. 
Some other methods of manufacturing molds for continuous casting, which is 
provided with fins, will now be described with reference to FIGS. 9-13. 
First, as shown in FIG. 9, in a metal box 8, which is opened at its upper 
side only, and which has an outer shape similar to that of a desired mold, 
a pipe 6 is inserted so that the pipe 6 extends along a space in which a 
cooling water passage is to be formed. 
This pipe 6 is provided on its inner surface in the same manner as in the 
previously-described embodiment with a plurality of continuous or 
intermittent fins 5, which extend in the lengthwise direction of the pipe 
6 and project inwardly into the pipe, and which are spaced in the 
circumferential direction thereof. 
The space between the outer surface of the pipe 6 and the inner surface of 
the metal box 8 is then filled with aggregate metals 9, such as metal 
powder, metal particles, metal wires and metal plates. The opening at the 
upper side of the metal box 8 is closed with an upper plate 8' thereof 
with the opened portions of the pipe 6 left as they are. The resultant 
product is diffusion-welded unitarily by the hot isotropic pressure 
welding with the joint portions 7 of the metal box 8 and upper plate 8' 
and the joint portions of the upper plate 8' and the circumferential 
surfaces of the end portions of the pipe 6 kept sealed airtight. 
During this hot isotropic pressure welding operation, the metal box 8 and 
upper plate 8' and the aggregate metals 9, and the aggregate metals 9 and 
pipe 6 are unitarily combined. 
The material of the pipe 6 in this embodiment is identical with that of the 
pipe in the previously-described embodiment. 
Of course, the outer shape of the metal box 8 may be determined arbitrarily 
as in the previously-described embodiment. Also, the mode of dividing the 
mold body, and the thickness of the walls thereof may be determined 
arbitrarily as shown in FIGS. 9-13. 
In a further embodiment, a principal portion of which is shown on an 
enlarged scale in FIG. 14 which corresponds to FIG. 2, the fins 5, 5 . . . 
on the inner surface of a passage 2 are formed so as to extend in a 
spirally-twisted state in the lengthwise direction of the passage 2. 
These fins 5 cause the area of the inner surface, which the cooling water 
contacts, of the passage 2 to be increased, and also the cooling 
efficiency to be improved, in the same manner as in the 
previously-described embodiment. The fins 5 also perform the function of 
swirling the cooling water which flows in the passage 2 along the 
spirally-twisted surfaces thereof. Therefore, it is desirable that the 
largest possible number of fins which enable a required flow rate of 
cooling water to be maintained be provided. The angle of twist of the fins 
may be arbitrarily determined but, if it is too large, the cooling water 
does not flow smoothly. Accordingly, a suitable angle of twist of the fins 
is 5.degree.-10.degree.. 
The fins may not necessarily be formed continuously over the whole length 
of the cooling water passage 2; they may be formed intermittently in the 
same manner as in the previously-described embodiment. 
The methods of manufacturing the molds for the continuous casting of these 
embodiments are not substantially different from those of the same 
embodiments. For example, the mold shown in FIG. 6 can be manufactured in 
the same way as the mold shown in FIGS. 3-5, and the manufacturing methods 
shown in FIGS. 7-13 can also be applied in the same way as described 
above. 
According to the present invention described above, a plurality of fins are 
formed on the inner surface of a passage for a fluid, such as cooling 
water, so as to extend in the lengthwise direction thereof and project 
inwardly from the same inner surface. This enables the area of the inner 
surface of the passage to be increased greatly, and the cooling or heating 
efficiency to be thereby improved to a great extent. 
Since the fins are formed so as to extend spirally in the lengthwise 
direction, the cooling or heating fluid flowing in the passage is also 
turned spirally. Accordingly, the portion of the water which is on the 
side of the inner surface of a mold body, i.e., on the high-temperature 
side thereof when the same portion of the water is in a certain part of 
the water passage is moved to a position which is far from the inner 
surface of the mold body as the water flows. While the water further flows 
a certain distance, the mentioned portion of the water is moved again to a 
position close to the inner surface of the mold body. Since the cooling 
water flows as it passes such positions alternately and repeatedly, the 
whole of the fluid, such as cooling water takes part in cooling the 
high-temperature portions of a mold body which are close to the inner 
surface thereof. This enables the cooling efficiency to be increased, and 
the cooling water to flow through the passage smoothly. 
If the inner surface of the cooling water passage is made rough, the area 
of the heat conductive surface increases, so that the heat-conducting 
effect becomes large. 
According to the present invention, complementary members having grooves in 
the opposite surfaces thereof and consisting of copper or a forged copper 
alloy, which generally has highly reliable mechanical strength, or a metal 
box and an aggregate metal, such as metal powder; and a pipe fittable in 
the above grooves or extending along a space which is to form a passage 
for the cooling water may be prepared. Therefore, a passage for the 
cooling water can be made simply and accurately even when it is long or is 
bent in a complicated manner. According to the present invention, a 
fin-carrying water passage which cannot possibly be made by a conventional 
method can be formed easily. Hence, the cooling or heating efficiency can 
be increased without causing a decrease in the strength of the mold. 
Moreover, since the forge-rolled copper or copper alloy can be used, the 
strength of the mold is high, and the reliability thereof can be 
increased. Also, a suitable wear-resistant material can be attached easily 
to a desired portion, such as the inner surface of the mold.