Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Patent
1988-05-09
1989-02-07
Lin, Kuang Y.
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
164429, 164448, 29132, B22D 1106, B22D 11128
Patent
active
048025283
DESCRIPTION:
BRIEF SUMMARY
The invention relates to hoops for rollers for the continuous casting of aluminium alloys, these hoops having improved life in comparison with hoops made of traditional steels and maintaining good productivity of the casting machine.
In the continuous production of cast aluminium the molten metal is directly cast at a temperature of about 680.degree. between a pair of cooled contrarotating rollers, which serve the dual purpose of solidifying the metal as a strip and hot rolling this metal.
It will be understood that the cylinders could not turn at a very high speed, because the alloy must be given the time to solidify in contact with the roller and must be enabled to undergo a certain rolling action.
In order to obtain maximum productivity of the installation, the rollers must be effectively cooled and have good thermal conductivity in order to assist the dissipation of calories. These rollers consist of two parts: a central core provided with cooling means and a hoop which is mounted on said core and comes into direct contact with the cast aluminium.
This hoop constitutes the part of the roller which takes the heaviest stressing, and after operating for a certain number of hours it must be overhauled because of the development of cracks caused by heat.
The first characteristic required of a material for making continuous casting machine hoops is good thermal conductivity. However, during operation these hoops are subjected to a certain types of stress of mechanical origin, namely hooping, flexion, torsion. These stresses dictate minimum mechanical strength and tenacity.
The main stress is thermal cycling, which results in plastic fatigue of the surface, and the initiation and propagation of a network of microcracks. This deterioration necessitates periodic reconditioning of the hoop, an operation which consists in machining off the layer of damaged metal.
Alloy steels normally used up to the present time for the production of these hoops corresponded to the following composition by weight in %: 0.90 to 1.30; Mo: 0.40 to 0.60; V: 0.10 to 0.20 with a content of S.ltoreq.0.020 and a content of P.ltoreq.0.020.
These steels are advantageous in respect of thermal conductivity properties and therefore the productivity of the installation, but on the other hand have limited resistance to cracks of thermal origin, with the consequence that their operating life is shorter and remachining is required more frequently, so that the consumption of hoops is increased.
Steels for hoops for the continuous casting of aluminium are also known which have the following composition by weight in %: to 3.0; Mo: 0.8 to 1.2; V: 0.3 to 0.5, with S.ltoreq.0.020 and P.ltoreq.0.020.
These steels have good mechanical strength and operating life properties, but they do not enable productivity results comparable with those obtained with the steels previously described to be achieved.
The present invention seeks to provide new hoops for the continuous casting of aluminium which, while retaining high productivity of the installation together with good thermal conductivity, ensure an operating life at least comparable to the best products in use at present, this being achieved by the use of an alloy steel having high resistance to fatigue of thermal origin.
The invention thus has as its object a hoop for rollers for continuous casting of aluminium, characterized in that it is in the form of a forged cylindrical jacket which has undergone heat treatment and been machined, and which is composed of an alloy steel having the following composition in percentages by weight: 2.80 to 3.40; Mo: 0.85 to 1.25; V: 0.10 to 0.30; S.ltoreq.0.020; P: .ltoreq.0.020; Cu: .ltoreq.0.030, the remainder being substantially iron and residual impurities.
In a preferred embodiment the composition is as follows: 0.90 to 1.10; V: 0.13 to 0.20; S.ltoreq.0.020; P.ltoreq.0.020; Cu: .ltoreq.0.30, the remainder being substantially iron and residual impurities.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained below in detail with reference to the accompanying
REFERENCES:
patent: 3587708 (1971-06-01), Khimich et al.
patent: 4232096 (1980-11-01), Franzen
patent: 4538668 (1985-09-01), Nishihara et al.
Boucher Andre
Seux Michel
Terrasse Joseph J.
Chavanne - Ketin
Lin Kuang Y.
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