Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1873-11-18
1985-10-01
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164478, B22D 1104
Patent
active
045440174
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improved method of continuous casting, improved continuous casting apparatus and to material cast by the method or on the apparatus. In the continuous casting of metals, the molten metal passes from a container or tundish into a cooled mould in which the skin of the metal solidifies sufficiently to support the newly formed metal strand. Further solidification takes place as this strand is withdrawn from the bottom of the mould. The continuous casting apparatus may be of either vertical or horizontal type.
DISCUSSION OF PRIOR ART
In the case of steel the mould is usually made of copper and is water cooled. There is a strong tendency for the solidifying surface of the hot steel to stick to the cold surface of the mould. Such sticking is highly undesirable as it can tear the thin solidified skin and result in the uncontrolled loss of molten metal. Even if the skin does not rupture, this sticking can cause irregular cooling. This can initiate cracking and a poor surface that is expensive to rectify and in the worst excess can cause the cast metal to be scrapped. If there is an uncontrolled break out of molten metal this can also lead to the scrapping of the mould.
To reduce sticking and to permit the smooth passage of the steel strand through the mould various lubricants are used ranging from vegetable and mineral oils (especially rape seed oil) to various metal powders which are molten at the temperature of the surface of the steel, but solid at the cooled surface of the mould.
The mechanism by which mould powders lubricate has not been properly established. The geometry of the nozzle or mould is such that the mould lubricant used is unlikely to be subjected to any significant hydrodynamic pressure. The geometry is determined by factors other than the lubrication requirements, and it would be difficult, if not impossible, to modify the geometry in order to improve the lubrication using known lubricants.
It is known to divide a mould longitudinally into parts and to vibrate these parts one relative to the other(s) transversely of the direction of movement of the cast strand through the mould.
U.K. Pat. No. 967,699 discloses the use of lateral vibration of mould sections in conjunction with axial vibration, for the purpose of propagating the strand through the mould by means of the forward axial strokes, while eliminating or reducing contact and drag during the backward axial strokes. This prior disclosure specifies a frequency range of 5,000 to 50,000 cycles per minute (83 Hz to 833 Hz) and suggests that the higher the frequency, the better will be the result obtained.
U.K. Pat. No. 1,208,333 discloses the use of lateral oscillation of the walls of the mould in continuous casting, in synchronisation with axial oscillation, for the purpose of propagating the strand through the mould by means of the forward axial strokes while eliminating contact and drag during the reverse strokes. This prior proposal employs frequencies in the range 20 to 50 strokes per minute (0.3 to 0.8 Hz) and for the lateral oscillations, amplitudes preferably of the order of up to 10 millimeters.
U.K. Specification No. 570423 also proposed the use of a split mould with vibration means to move the mould parts towards and away from each other and relates to the use of a lubricant which will decompose to become soot-like solid particles at the casting temperature.
U.S. Pat. No. 3,626,510 discloses a hydraulic thrust bearing (e.g. for a gyroscope) in which a positive load supporting force is generated in an incompressible liquid layer filling a gap between relatively movable bearing surfaces, by oscillating one bearing surface normal to the gap so as to produce a beneficial increase in pressure in the lubricant film (the so-called squeeze film phenomenon).
It has now been found that the squeeze film phenomenon disclosed in U.S. Pat. No. 3,626,510 can be applied to the totally different art of continuous casting to improve the strength and stability of a lubricant film between a mould and a stra
Lin Kuang Y.
Striker Michael J.
The University College of Swansea
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