Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-01-13
2001-07-24
Dunn, Tom (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S415000, C164S079000
Reexamination Certificate
active
06263953
ABSTRACT:
The invention relates to a continuous casting method for producing material profiles which have cavities, and to a continuous casting apparatus for carrying out such a method.
According to the prior art, various methods of producing porous foamed metal bodies, honeycomb structures comprising steel parts and methods of continuously casting metal strands based on the principle of communicating tubes, including with gas being supplied, are known from the following patent specifications and laid-open patent applications:
German laid-open patent application 38 14 030 A1concerns a foam steel as a structural bracing material. This is produced by adhesively attaching sheets in metal-spheroidal form or provided with depressions on top of one another, which then form a honeycomb structure.
German laid-open patent application 44 16 371 A1discloses a method of producing long, porous foamed metal bodies on an aluminum basis. These foamed metal bodies, inserted in aluminum hollow profiles, increase the section modulus of the latter with respect to bending and twisting. The foamed metal bodies are foamed from metal powder and blowing agent, this mixture being heated to at least the melting temperature of the metal to form a porous metal body.
The disadvantage of the prior art from DE 38 14 030 A1 and DE 44 16 371 A1 is that, although the methods described there allows [sic] the production of components from a plurality of prepared parts with cavities formed as pores, production of material profiles with cavities in a single cast is not possible.
In WO 86/06431 and WO 88/04586 there are described methods which, although they allow good shaping for obtaining cavities in material profiles, are not particularly suitable for a lightweight construction of load-bearing components. In WO 88/04586 there are described a method and an apparatus for continuously casting metal strands from high-melting metals with cross sections close to the final dimensions, based on the principle of communicating tubes.
German laid-open patent application 35 16 737 A1 discloses a method and an apparatus for producing metallic materials interspersed with gas bubbles as cavities in the form of profiles, which have in relation to their own weight a higher section modulus with respect to bending, buckling and twisting stresses.
The method described there has the disadvantage that the gas bubbles introduced cannot be positioned, since they are introduced into an upwardly directed material strand in the still liquid state and consequently, owing to their buoyancy, initially move in the melt until the latter solidifies. Furthermore, in this method only a relatively small reduction in the relative density of the starting material is possible.
The invention is based on the object of providing a continuous casting method for producing material profiles, in particular steel profiles, which have cavities, and a continuous casting apparatus for carrying out such a method, the material weight of the profiles being reduced by introducing gas bubbles, which can preferably be arranged flexibly in their position and extent and which form cavities.
This object is achieved by a continuous casting method for producing material profiles which have cavities, comprising the steps of:
a) melting the material and forming a strand from the material;
b) cooling or leaving to cool the material strand, so that at least part of the material strand is at a temperature at which there is a pasty structure;
c) introducing gas into that part of the material strand which has a pasty structure so as to form cavities, the material strand being directed downwards from above; and
d) leaving the material to solidify.
With this method, cavities can be positioned as desired in material profiles, since the gas bubbles are introduced into such regions of the material strand where there is a pasty structure of the material. A pasty structure is understood to mean a state of the material between liquid melt and solidification in which gas bubbles—if appropriate under high pressure—can still be introduced into the material by means of nozzles or the like. Therefore, independent motion of the gas bubbles in the material strand is possible only to an extremely restricted extent—if at all—and should be eliminated entirely if a specific position and structure of the cavities are desired.
Moreover, directing the material strand downwards from above, counter to the direction of uplift of the gas bubbles in the material strand, achieves the effect that the gas bubbles are to the greatest extent unable to leave the pasty region of the material strand in the direction of the liquid region, but instead form a cavity filled with the gas, as intended.
Metallic materials are preferably used as the material.
In step c), the gas is preferably introduced at a plurality of points lying on an isothermal surface within the material strand. In this way, a plurality of cavities can be produced simultaneously by inclusion of gas bubbles.
In step c), an inert gas, for example argon, is preferably used, to avoid undesired chemical reactions taking place between the material and the gas, which can result in an alteration in the material structure in the solidified state.
In step c), the gas may be supplied continuously or in a pulsed manner. Consequently, with continuous movement of the material strand along the mould, both elongated, continuous cavities and cavities arranged one behind the other in the longitudinal direction of the material strand can form.
The structure of the cavities produced can be monitored by at least one ultrasonic measuring device, which is arranged in the region of the running-off material strand.
The outer skin of the material strand is preferably reinforced by fibers.
In step c), the speed of the material strand is preferably greater than the rate of uplift of bubbles formed from the gas. In this case, the gas bubbles introduced cannot escape upwards, in the direction of the liquid material region. On account of the pasty structure of that part of the material into which the gas bubbles are introduced, the rate of uplift is, however, negligible under normal circumstances. On account of its dependence on the size of the cavities, it may, however, be of a certain significance in individual cases when there are very large cavities.
The invention also relates to a continuous casting apparatus for producing material profiles which have cavities, with
a reservoir for liquid material which has a closable outlet opening at the bottom; and
a chilled mould for cooling liquid material leaving the outlet opening as a strand,
the mould being arranged beneath the outlet opening and essentially vertically;
at least one gas tube being provided for introducing gas, and
the gas tube having an outlet opening which, dependent on the material used, is arranged in the interior of the mould in a region in which the material strand has a pasty structure on account of the cooling by the mould.
This apparatus ensures both that the material strand is directed downwards from above and that the gas bubbles are introduced in that region in the interior of the mould in which there is material with the suitable, pasty structure.
A control device, for example a controllable valve block, is preferably provided, with which the introduction of gas into the material strand can be controlled in its amount, which depends on the gas pressure used, and/or its form, continuously or in a pulsed manner.
The supply of gas can take place via nozzles which are arranged at the outlet end of the gas tubes and the openings of which may have, for example, a round, slit-shaped or rectangular cross section, depending on the desired cross-sectional shape for the cavities. In particular in the case of a rectangular cross section, bridges may be provided in the nozzle openings to secure the core of the material strand.
At least one ultrasonic measuring device is preferably provided for monitoring the structure of the cavities of the material strand running off.
Electric signals of the ultrasonic measuring d
Banner & Witcoff , Ltd.
Dunn Tom
McHenry Kevin
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