U.S. patent number 3,552,478 [Application Number 04/758,270] was granted by the patent office on 1971-01-05 for method for starting and maintaining the supply of metal to a downward operating continuous casting mold.
This patent grant is currently assigned to Prolizenz A. G.. Invention is credited to Wilhelm Friedrich Lauener.
United States Patent |
3,552,478 |
Lauener |
January 5, 1971 |
METHOD FOR STARTING AND MAINTAINING THE SUPPLY OF METAL TO A
DOWNWARD OPERATING CONTINUOUS CASTING MOLD
Abstract
A method for starting and maintaining the supply of metal to a
downward operating continuous casting mold has the steps of sucking
metal from a reservoir up through a riser into a launder above the
reservoir, then closing the riser and keeping closed the downcomer
to the mold, thereafter letting the pressure rise in the launder
and subsequently opening the downcomer; then letting the metal flow
and starting the casting, thereafter rarefying the air pressure in
the launder, and then opening the riser again.
Inventors: |
Lauener; Wilhelm Friedrich
(Langenhard, CH) |
Assignee: |
Prolizenz A. G. (Chur,
CH)
|
Family
ID: |
4383649 |
Appl.
No.: |
04/758,270 |
Filed: |
September 9, 1968 |
Foreign Application Priority Data
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Sep 7, 1967 [CH] |
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12507/67 |
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Current U.S.
Class: |
164/474; 137/142;
164/257; 164/483; 137/1; 164/133; 164/481 |
Current CPC
Class: |
B22D
11/064 (20130101); B22D 11/18 (20130101); B22D
11/181 (20130101); Y10T 137/0318 (20150401); Y10T
137/2842 (20150401) |
Current International
Class: |
B22D
11/06 (20060101); B22D 11/18 (20060101); B22d
011/10 (); B22d 011/06 () |
Field of
Search: |
;164/82,87,281,61,64,254,256,257,258 ;137/1,142,147 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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879,153 |
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Jun 1953 |
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DT |
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105,587 |
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Sep 1942 |
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SW |
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Primary Examiner: Overholser; J. Spencer
Assistant Examiner: Roethel; John E.
Claims
I claim:
1. A method for starting and maintaining the supply of metal to a
downward operating continuous casting mold, provided with a dummy
bar, comprising sucking molten metal through a suction pipe from a
reservoir into a closed launder disposed above and connected to an
air suction device, the outlet means through which the melt enters
at least one supply duct to deliver melt to the mold being closed;
then interrupting the sucking of melt by closing the suction pipe,
thereafter letting the pressure rise in the launder, and then
letting molten metal flow through said outlet means and supply duct
into the mold; thereafter, as soon as a molten metal head has been
formed in the mold, beginning to lower the dummy bar, the metal
supply being continued through said supply duct, producing again a
rarefied air pressure in the launder, and finally opening again the
suction pipe.
2. A method according to claim 1 applied to the casting in
caterpillar mold, comprising putting the chains of articulated mold
blocks into motion simultaneously with the beginning of the
lowering of the dummy bar.
Description
The present invention relates to a method of starting and
maintaining the metal supply to a downward operating continuous
casting mold, for instance to a casting machine with caterpillar
mold, especially for casting strips of nonferrous metals, chiefly
of aluminum and aluminum alloys.
Several machines have been developed for the continuous casting of
strips. In one machine the mold cavity is defined by a cooperating
pair of endless chains of articulated mold blocks, and means are
provided for revolving each of said chains about its own center.
The chains are mounted so that over a part of their own length they
engage with each other and define between them a mold cavity having
walls which move continuously as the respective chains are revolved
together at the same linear speed. Machines of this kind have been
named "machines with caterpillar mold." In one of the said machines
the mold blocks of one row are not connected but are moved
separately in a guide system and maintained in circuit in such a
way that they meet again at the pouring end of the mold cavity to
form a closed mold with the blocks of the other row.
In the book "Handbuch des Stranggiessens" by E. Herrmann published
in 1958 by the Aluminium-Verlag GmbH in Duesseldorf (Western
Germany), the casting in caterpillar molds is described on pages 51
to 63.
When casting downward in caterpillar molds the metal supply
presents especially difficult problems as the ducts for the metal
supply must project into the closed part of the mold and must be
relatively long because of the special path followed by the mold
blocks; it follows that the column of molten metal in the supplying
ducts must be high and therefore it exerts a high metallostatic
pressure. It is therefore difficult to obtain the necessary
tightness between the supply ducts and the walls of the mold and to
prevent leakage of molten metal at the untight spots.
During casting the molten metal, a head must be maintained under
the upper end of the closed mold, as otherwise molten metal would
infiltrate into the gaps where the mold blocks are nearly in
contact one with the other, and would stop and possibly damage the
machine. Pouring the molten metal in a free fall into the mold,
which should be possible when casting thick sections, does not come
practically into question because of splashing and turbulence in
the head. One must use special devices, for instance several tubes
disposed side by side discharging into a slit nozzle fitted on the
cross section of the mold.
In any case one has to take care during casting that the head of
molten metal in the mold be maintained at a level as constant as
possible. The float valves in the mold, that are usually used with
direct casting, can practically not be utilized in the present case
for reason of restricted space. A control by changing the flow-in
or flow-out section of the supply tubes with simultaneous measure
of the level of the molten metal head in the mold (that is to say,
the level at which the molten metal makes contact for the first
time with the walls of the mold) is excessively difficult, the
difficulties increasing with the decrease of the thickness of the
casting; moreover, the level of the molten metal head in the mold
and as a consequence the quality of the casting would be subjected
to disturbing variations.
It is accordingly among the principal objects of the invention to
provide methods and means for such casting that avoid the pitfalls
of the prior art.
Further objects and advantages of the invention will be set forth
in part in the following specification and in part will be obvious
therefrom without being specifically referred to, the same being
realized and attained as pointed out in the claims hereof.
The mentioned difficulties of the prior art are avoided by the
method of the present invention, which method enables to maintain
constant the level of the molten metal head in the mold.
According to the invention a siphon is used. The molten metal is
sucked from a reservoir into a closed launder disposed above and
connected to an air suction device, the outlets through which the
melt enters the supply duct or ducts to the mold being closed; one
allows more melt to rise in the launder than necessary for forming
a molten metal head on the dummy bar of the mold. As soon as there
is enough metal in the launder, one interrupts the sucking of melt,
lets the pressure rise in the launder, for instance up to
atmospheric (which is the simplest method), and opens the
metal-supply ducts. As soon as melt has flowed through the ducts
and the molten metal head has been formed in the mold, one starts
the lowering of the dummy bar and therefore of the casting, the
metal supply being continued, possibly puts into motion the chains
of articulated mold blocks, and produces again rarefied pressure in
the launder. Once the desired rarification has been attained, one
opens the suction pipe and the siphoning begins. From that time
onward the control of the level of the molten metal head in the
mold takes place automatically by controlling the level of the
metal in the reservoir from which the melt is being siphoned for
the supply of the mold.
As a result of the friction of the flowing metal in the siphon, the
level of the molten metal in the reservoir is somewhat higher than
in the mold; for instance, with a casting speed of 3 meters per
minute during operation the level difference may be 30 to 50 mm.
However, when starting it is recommendable to choose for safety a
greater level difference, of 200 mm. for instance, the said
difference being afterwards diminished to about 30 to 50 mm.
In the accompanying drawing, the single FIG. is a schematic
fragmentary vertical sectional view and shows schematically the
principle of a device for carrying out the method according to the
invention in a machine with a caterpillar mold.
The siphon comprises a suction pipe 11, a launder 12 and a supply
tube 13 (of course, one may use several supply tubes, with or
without slit nozzle). A reservoir 14 for the molten casting metal
is provided, and the upper part 15 of a caterpillar mold. Valves 16
and 17 are provided, and a suction socket 18. When starting the
metal supply, one closes the supply tube 13 by means of the valve
17, opens the valve 16 and sucks air out of the launder 12, by
means of a suction device that is connected to the socket 18. The
molten metal 19 rises through the pipe 11 into the launder 12 and
fills the same up to the level 20. Then one shuts the valve 16,
lets the air pressure rise in the launder 12 (suitably up to
atmospheric pressure) and opens the valve 17. The result is that
molten metal flows from the launder 12 through the supply tube 13
into the closed part of the mold 15 and forms a head 22 on the
dummy bar 21. The molten metal level in the launder lowers to the
height 24 according to the amount of melt fown out. At that moment,
without shutting the valve 17, one puts into motion the mold
blocks, lowers the dummy bar according to the casting speed,
produces again an underpressure in the launder 12 by sucking air
through the socket 18 and opens thereafter the valve 16, thereby
putting the siphon 10 into operation. In the launder 12, a rarefied
pressure of 110 mm. for instance (760 mm. Hg - 110 mm. Hg = 650 mm.
Hg) may be sufficient. After reaching the underpressure necessary
to prevent melt from running out of the launder 12 through the
suction pipe 11 into the reservoir 14, the valve 16 may be opened
immediately, for instance one second thereafter.
By controlling the level 25 of the molten metal in the reservoir
14, the level 23 of the molten metal head in the caterpillar mold
is controlled at the same time. It is therefore not necessary to
dispose regulating devices in the molten metal head 22. The metal
level 25 in the reservoir 14, which reservoir may be fed from a
melting or a holding furnace, may be controlled for instance by
means of a floating valve.
Besides the advantages mentioned in the foregoing description, the
method according to the invention offers the further advantage that
it is in a great measure independent of the casting speed. One may
for instance change considerably the casting speed without changing
the flow cross section. The regulation takes place
automatically.
The method is especially advantageous with continuous casting in a
caterpillar mold. However, it may also be used suitably with other
downward continuous casting methods, for instance with the casting
between rolls, the strip casting between spaced parallel portions
of a pair of flexible metal belts which are moved along with
opposite surfaces of the strip being cast (Hazelett), the casting
in rotary strip casting machines as well as with the DC casting,
and that not only for casting thin plates, but also for casting
thick sections, for instance slabs and billets.
Siphonlike tubes used in continuous casting are known; however, as
distinguished from the method according to the invention, they
necessitate a pressure vessel as molten metal reservoir, which
makes the device much more expensive and its operation difficult;
moreover, they do not render possible the automatic control of the
level of the molten metal head in the mold during the whole
duration of the casting operation. To this must be added that the
use of pressure gas in the known devices increases the gas content
of the melt, whereas with the method according to the invention a
degassing takes place.
I wish it to be understood that I do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
* * * * *