Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1986-03-24
1987-08-04
Tufariello, T. M.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
C25F 100
Patent
active
046844511
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process and a device for bringing a strip traveling at a high speed in a liquid into contact with a diverting roll, which make it possible to avoid the formation of a liquid layer interposed between the strip and the roll.
In electrolytic degreasing of a metal sheet or a metal band, for example, an attempt is made to pass this strip at a very high speed between electrodes immersed in a reactive liquid used as an electrolyte. This electrolyte may be, for example, an alkaline solution and, in this case, the electrodes produce a release of hydrogen or oxygen gas on the faces of the metal sheet as it passes between the electrodes, this metal sheet itself forming an electrode of opposite sign to the fixed electrodes between which it travels. The gas release considerably accelerates the degreasing in the reactive liquid, with the result that it is possible, when the operating conditions have been suitably chosen, to pass the strip of metal sheet or of metal band at a very high speed through the electrolyte, between the electrodes.
The electrolyte is generally held in a tank in which the electrodes are immersed and in which means are provided for guiding the metal sheet as it travels through the electrolyte. Such means consist, in particular, of diverting rolls which make it possible to change the direction of travel of the metal strip. This metal strip is driven at a high speed and is subjected to a degree of lengthwise traction which enables the diverting rolls to be partly enclosed by exerting a certain radial force on these rolls and to control its position between the electrodes accurately during its passage.
Now, it has been observed that above a certain speed of the strip, in the region of 500 m/min, an actual and efficient contact between the strip and the diverting roll no longer takes place, and this is reflected in poor guiding of the strip, which "floats" over the surface of the roll, and an inadequate coupling between the roll and the strip, especially when the former is responsible for applying traction to the strip and/or driving it.
This loss of contact between the strip and the roll is due to the fact that some of the liquid is entrained into the contact zone between the strip and the surface of the roll and forms a layer of liquid which reduces adhesion. This phenomenon, known as "aquaplaning" is all the more noticeable the higher the speed of the strip. In practice, this phenomenon prohibits the use of speeds of travel of the metal strip which are greater than 500 m/min in electrolytic degreasing tanks.
To overcome this phenomenon, it has been proposed to machine circumferential grooves on the side surface of the diverting rolls, a result of this being to reduce the aquaplaning between the strip and the roll owing to a phenomenon which is somewhat similar to that underlying the improved adhesion of rain tires with special patterns on automobile vehicles. Using grooved diverting rolls it has been possible to raise the limiting speed of the metal strips in electrolytic degreasing plants to a value of between 600 and 700 m/min.
However, the aquaplaning reappears above this speed, and this correspondingly limits the potential of electrolytic degreasing plants.
The purpose of the invention is consequently to provide a process and a device which make it possible to keep the strip perfectly applied to the roll, even at very high travel speeds, for example above 700 m/min.
To this end, a certain quantity of a gas which is insoluble in the liquid and capable of mixing with the entrained part of the liquid is introduced in the vicinity of the roll surface, and at least upstream of the contact zone between the strip and the roll, to form a fluid which is compressible in the contact zone between the strip and the roll.
The quantity of gas which is introduced must merely be sufficient to make the fluid entrained into the contact zone sufficiently compressible to maintain perfect contact between the strip and the roll.
The gas may be introduced by direct injection in the vicinity o
REFERENCES:
patent: 3097971 (1963-07-01), Skipton
patent: 4441975 (1984-04-01), Carter
Journal of the Iron and Steel Institute, vol. 201; No. 5, May 1963, W. G. Jaffrey et al.: "The Support of Thin Steel Strip on Air Cushions", see pp. 401-407.
Damiron Pierre M.
Legoupil Jean-Luc
Clecim
Tufariello T. M.
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