Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/12—Accessories for subsequent treating or working cast stock in situ
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0637—Accessories therefor
  • B22D11/0648—Casting surfaces
  • B22D11/0651—Casting wheels

Definitions

• the invention relates to hoops and rolls of continuous casting of aluminum alloy, these hoops having an improved lifespan, compared to the freight made from traditional steels, and retaining good productivity with the casting.
• the molten metal is directly cast at a temperature of approximately 680 ° C. between a pair of cooled rollers rotating in opposite directions, which fulfill the double function of solidifying the metal by strip and hot rolling of this metal.
• rollers To obtain the maximum productivity of the installation, the rollers must be effectively cooled and have good thermal conductivity in order to promote the evacuation of calories.
• These rollers are produced in two parts: a central core comprising cooling means and a hoop which is mounted on this core and comes directly into contact with the cast aluminum.
• This hoop constitutes the part of the roller receiving the most intense stresses and, after a certain number of hours of operation, must be revised due to the cracks of thermal origin which have developed.
• the first characteristic that is required of a material, to produce frets of a continuous casting machine, is good thermal conductivity.
• these .frettes are subjected, in operation to a certain number of constraints, of mechanical origin, namely: hooping, bending, torsion. These constraints impose a minimum of mechanical strength and toughness.
• the main stress is thermal cycling which causes plastic fatigue of the surface, the initiation and propagation of a network of micro-cracks. This deterioration requires periodic reconditioning of the hoop, an operation which consists in eliminating, by machining, the thickness of deteriorated metal.
• the object of the present invention is to provide new aluminum continuous casting hoops which, while preserving a high productivity of the installation linked to good thermal conductivity, provide a service life at least comparable to the best products currently available. used, this thanks to the use of an alloy steel having a high resistance to fatigue of thermal origin.
• the subject of the invention is therefore a hoop of a continuous casting roll of aluminum, characterized in that it is in the form of a forged cylindrical casing, having undergone a heat treatment and machined, of an alloy steel having the co following position, as a percentage by weight:
• the composition is as follows: C; 0.31 to 0.35; Mn: 0.30 to 0.50; If: 0.15 to 0.35; i less than 0.25; Mo: 0.90 to 1.10; V: 0.13 to 0.20; S - ⁇ i 0.020; P ⁇ 0.020; Cu 0.30; the remainder being essentially iron and residual impurities.
• Fig.1 is a schematic view of a horizontal continuous casting installation
• - Fig.2 is a schematic side ITAva ⁇ tion and partial section of a portion of the ins ⁇ tallation of Fig.1;
• - Fig.3 is a diagram illustrating the stress cycle as a function of the elongation undergone by the metal of the hoop;
• - Fig.4 shows histograms illustrating the number and depth of cracks for four grades of steel, them according to the prior art and two according to the invention.
• the principle of continuous casting of light alloy shown in Fig. 1 and 2 relates to so-called horizontal casting.
• Aluminum, melted in an oven which is not shown, is kept at constant level in a cana '' 1 and introduced, by means of a nozzle 2, between two rollers 3, at a temperature of around 680 ° C.
• the rollers (or cylinders) 3 are rotated in opposite directions with a spacing which determines the thickness of the solidified sheet 4.
• the rolling grip constitutes a continuous ingot mold in which, in contact with the cold cylinders, the cast aluminum solidifies, while it is driven by the rotation of the cylinders.
• Each roller has a cooling circuit traversed by a fluid, generally by water.
• Each roll is produced in two parts, namely:
• a core 5 which is a steel cylinder in which are formed longitudinal channels 6, supply and outlet of water by the pins 7. These channels are fed, by radial channels 8, peripheral channels 9 and a hoop 10 which is mounted on the core, so that it is in direct contact with the cooling fluid which circulates in the channels 9.
• This hoop constitutes the consumable part of the roller. mier is to extract the calories from the solidifying alloy. It is understood that the productivity of the casting machine is directly linked to the transfer of calories through the hoop.
• this hoop must have good thermal conductivity, but also appropriate mechanical properties in relation to the stresses to which it is subjected.
• the stress regime, at each point of the frets, is defined by the cumulation of the stresses of mechanical origin and the stresses of thermal origin due to the cycling of the thermal gradient.
• the mechanical stresses originate from:
• the temperature is not homogeneous: the fibers would like to expand differently, but they are embedded in the neighboring fibers, hence a state of constraints, depending on the thermal gradient.
• frets the inside can be seen, at constant temperature, close to that 'of the cooling water. The external face comes, at each rotation, into contact with the liquid aluminum, then when the sheet comes out of the grip, the hoop cools down by the ambient air, and by the thermal transfer towards the fluid cooling.
• the first heating is represented by the line 0A, then by the curve AB, which corresponds to the plastic deformation on the stress-deformation diagram in FIG. 3.
• the predominant stresses are those induced by the thermal cycle (which are superimposed, of course, the stresses, even modest, of mechanical origin).
• the fatigue resistance of thermal origin appears to be directly linked to the mechanical characteristics of the steel at the stress temperatures, and in particular, directly linked to the limit of elasticity of the material.
• Manganese or Silicon to provide the steel with a homogeneous and stable structure, of good toughness.
• hot tool steels used, in particular, for the forging and forging of steels, which have a high elastic yield strength, good resistance to thermal fatigue and which would seem to be able to be used to constitute frets. continuous casting of aluminum.
• these steels have a too low thermal conductivity, which causes a more or less significant loss, or even incidents, or an impossibility of operation of the machine.
• the search for a steel composition optimized for continuous casting hoops consists in using, at best, the alloying elements in order to obtain the best resistance with a thermal conductivity little modified compared to standard steels.
• the selection criteria are, of course, the mechanical characteristics of the steel.
• thermal fatigue is a complex mechanism. In addition to the effect of the stresses generated by the cycling of the thermal gradient, it integrates the effects of external aggressions, and those of internal modifications of the material, which influence the formation and development of the crack network.
• the frets for the casting roller according to the present invention are produced from a steel grade produced in an electric oven, poured into a pocket where it is refined and degassed, then finally molded in an ingot mold.
• the ingots are heated to about 1200 ° C, drilled to obtain blanks which are themselves forged into tubes of 500 to 1000 mm in diameter. These blanks are then austenitized at around 970 ° C, then quenched and subjected to tempering to give them the required metallurgical quality.
• the grades according to the present invention are characterized by a simplicity of implementation during the hot transformation and subsidiary treatments for refining the structure in order to obtain the best ductility properties. which is difficult to obtain for carbon grades higher or co 'n taking more alloying elements.
• Table I below indicates the weight compositions of the various steels tested, for comparison purposes.
• This device comprises a finely rectified cylindrical test piece, which is intermittently heated at the surface by high frequency induction and which is permanently cooled internally by a circulation of water.
• test piece of the generator power, of the self-test piece coupling, of the cooling, made it possible to define a thermal cycle inspired by the temperature measurements recorded on real frets in operation.
• the test results are plotted on a histogram represented in Fig. 4, where the numbers and the depths of the cracks are represented.
• the cracking mechanism is always similar: the cracks which were created first, from the micro - surface accidents, are those which develop the most in depth. Then forms, a network of secondary cracks of less importance.
• the criterion retained is the maximum depth of the main cracks: these are the cracks which determine, on a hoop, the amount of metal to be removed to renovate its working surface.
• the improvement in the resistance to fatigue of thermal origin consists in an unexpected reduction in the mesh of the network of main cracks and in a reduction in the maximum depths of the cracks, all other things being equal.
• the frequency of the first initiated cracks is approximately one to two cracks per linear centimeter.
• the frequency of cracks initiating approximately simultaneously is much higher.
• the distribution of the deformations and stresses due to thermal cycling is thereby distributed, which contributes to the least penetration of degradation by thermal fatigue.
• a continuous aluminum casting machine equipped with rollers with a diameter of 630 mm made it possible to cast 9,960 tonnes in approximately 4,800 hours.
• 3,200 tonnes were poured in 1,000 hours.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Metal Rolling (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)
• Forging (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
• Braking Arrangements (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Nonmetallic Welding Materials (AREA)

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Publications (2)

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• 1985
  • 1985-03-15 FR FR8503867A patent/FR2578768B1/fr not_active Expired
• 1986
  • 1986-03-14 US US07/191,820 patent/US4802528A/en not_active Expired - Lifetime
  • 1986-03-14 JP JP61501736A patent/JP2650679B2/ja not_active Expired - Lifetime
  • 1986-03-14 EP EP86901895A patent/EP0215874B1/de not_active Expired
  • 1986-03-14 WO PCT/FR1986/000086 patent/WO1986005423A1/fr not_active Ceased
  • 1986-03-14 ES ES553346A patent/ES8707878A1/es not_active Expired
  • 1986-03-14 DE DE8686901895T patent/DE3660610D1/de not_active Expired
  • 1986-03-14 AT AT86901895T patent/ATE36820T1/de not_active IP Right Cessation
  • 1986-03-14 KR KR1019860700737A patent/KR960015337B1/ko not_active Expired - Lifetime

Non-Patent Citations (1)

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