Twin roll casting

Details Twin roll casting Twin roll casting

1993-03-02

1995-01-24

Batten, Jr., J. Reed

Metal founding

Process

Shaping liquid metal against a forming surface

164428, B22D 1106

Patent

active

053835158

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the casting of light metal alloys by the twin roll casting process.
In this known process, molten light metal alloy is introduced into the bite between two cooled rotating rolls. Where the liquid metal comes into contact with the rolls, a skin is formed and this skin, which rapidly thickens, undergoes hot working before finally emerging from between the two rolls in the form of a strip. During the hot working of the material, the cast material initially is extruded towards the liquid metal feed because the strip is moving more slowly than the surface of the adjacent rolls. Where the strip is extruded from the roll bite, it leaves the machine at a greater velocity than the peripheral surface of the adjacent rolls and this is known as "forward extrusion". There is a neutral point between the entry side of the molten metal and the exit side of the strip where the movement of the strip is equal to the peripheral speed of the adjacent rolls. It is usual for both of the rolls, which are of the same diameter, to be driven from a common source and thus both roll surfaces have the same peripheral speed. In these circumstances the neutral point is in the same position for each of the two rolls.
One of the problems encountered in twin roll casting of light metal alloys is sticking of the casting to one or other of the rolls. In general, sticking becomes a greater problem as the thickness of the workpiece being cast is reduced. When casting workpieces of a thickness of, say, less than 2.5 mm, sticking of the casting to one or other of the rolls can become very critical.
It is an object of the present invention to provide a method of roll casting in which the problem of sticking of light metal alloy is at least reduced, if not entirely eliminated.
According to the present invention, in a method of casting a light metal alloy to form a strip, molten light metal alloy is introduced by way of a nozzle assembly into the gap between a pair of cooled rolls which are rotated to roll the solidfying metal into strip, characterised in that action is taken to prevent the strip from sticking to either of the rolls, said action comprising arranging the rolls to have their axes of rotation in parallel planes but inclined to each other thereby causing scrubbing forces to be applied to the opposite faces of the strip by the rolls, said scrubbing forces being sideways to the direction of movement of the strip out of the roll gap.
It is well established in the art of metal rolling that the profile of the material being rolled can be controlled by crossing the mill rolls. However, in the twin roll casting process, the profile of the cast strip is readily controlled by means other than by crossing the rolls.
In the method of the present invention, roll crossing is used to prevent sticking of the cast strip to either or both of the caster rolls.
By crossing the rolls of a twin roll caster, a scrubbing action is generated between the cast strip and the rolls independently of any forward extrusion and a slip force is applied to each surface of the cast strip. This additional force is perpendicular to the direction of movement of the strip in the plane of the strip and serves to generate a sideways scrubbing action between the surface of the strip and the rolls, thus preventing the strip material from sticking to the rolls. It has been found that-sticking can be avoided if the forward slip (or extrusion) is greater than typically 5%. This amount of relative movement can be achieved by crossing the caster rolls by approximately 6 degrees.
One or both of the rolls can be displaced by means of actuators which act between the chocks at the ends of the roll and the rigid housing of the caster. Although the position of the rolls can be altered once casting has commenced, it is more likely that the roll(s) will be displaced to the crossed position prior to the commencement of casting and held in that position during casting. The angle of crossing of the rolls is dependent on the casting condition, inter alia, the alloy bein

REFERENCES:
patent: 4501315 (1985-02-01), Bercovici
patent: 4979556 (1990-12-01), Braun et al.
English translation of Japanese patent publication 1-218745.

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