General description.
Supercaster rolling train is designed to produce cast billets from aluminum melt. A uniform liquid aluminum flow,passing through the ceramic distribution nozzle,falls into the channel between the water-cooled mould rolls,where three processes take place: metal cooling to crystallization temperature, crystallization and deformation.
The strip temperature at the outlet of the mould rolls is 270-350 ºC, depending on the strip thickness and alloy.
Parameters of the,cast roll billet:
Width-max 1,745 mm;
min 1,000 mm.
Thickness- max 10 mm;
min 5.0 mm.
Rolling reduction(draft)in deformation zone -max50%;
min 15%.
A mould roll consists of two parts:
Steel cylindrical core with channels for cooling water supply and circulation.Two-layered core: the outer layer is produced by the welding of a solid alloy on a softer core body.
Shell is a hollow cylinder from heat-resistant copper alloy made by centrifugal casting method.The roll shell is heated to a certain temperature(- 360"ºC)before landing on the roll core.Taking into account the contact between the core and the shell in the ribs area and considering that the contact area is two times smaller than the shell area,it is required to choose an exact interference or "tension"in order to provide a stable grip between the shell and the core.At the same time,it shall not cause any mechanical damage to the shell.
The service life of the mould roll core is practically unlimited(more than 10 years).Periodic repairs are required to restore the destroyed ribs and to clean the channels.Hard alloy surfacing is carried out with subsequent channel grooving.
The service life of the steel shells of the mould rolls - 6,570 machine-hours.
The continuous operation cycle -700-720 machine-hours.
The service life of the copper shells of the mould rolls -1,333 machine-hours.
The continuous operation cycle-240-250 machine-hours.
In the process of contact with liquid metal,the shell is subjected to temperature impacts(melt temperature ~700ºC),compressive force and tensile stress,mechanical influence of foundry equipment.All these impacts cause the thermal fractures (net shaped roll marks),shell surface aluminizing, mechanical burrs.The quality of the cast strip is reducing.Turning treatment and regrinding of the roll is required.The damaged layer is removed and the roll is ground during the turning treatment (machining). Depending on the depth of the net shaped roll marks,the turning removal is from 1.5 to 3 mm per shell radius.The shell worn to 50%(27 mm per the radius)shall be replaced.
The mould roll shell is the main working part of the technological equipment.Taking into account the contact of the shell with the melt and considering that the shell is subjected to temperature impacts and significant stress,caused by metal pressure,there are special requirements for the shell material and quality:
Long-term resistance to thermal cracking:
High tensile strength;
High yield strength;
Absence of hidden defects (blown holes,microcracks,foreign inclusions,etc.).
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