FR2610855A1 - PROCESS FOR CASTING FERROUS ALLOYS - Google Patents

Abstract

TO OPTIMIZE THE SOLIDIFICATION TIME OF THE METAL IN A SHELL 10, 12 AND TO AUTOMATE THE PROCESS, A LASER PROBE 18, 20 IS PROVIDED TO MONITOR THE LEVEL OF THE METAL IN THE SHELL DURING THE FILLING AND THE TEMPERATURE SENSORS 22, 24 FOR THE JET OF METAL POURED AND FOR THE SHELL. PROBE AND SENSOR SIGNALS ARE ENTERED WITH OTHER PARAMETERS INTO A COMPUTER CONTROLLING ALL CASTING OPERATIONS. THE INVENTION IS APPLICABLE TO GRAVITY SHELL CASTING, CONTINUOUS CASTING AND CENTRIFUGAL CASTING FOR EXAMPLE.

Description

This invention relates to the casting of ferroalloys

  generous. It is well known that, after the pouring of molten metal into a mold, there is an optimum duration of solidification during which the molded or cast part must remain in the mold (this term generally refers here to a molding device and in particular a shell or an ingot mold). If this duration is greater or less than the optimal duration, the quality of the molded or cast part is decreased accordingly. Ferrous alloys can be cast in different ways, for example in continuous steelmaking machines, horizontal bar casting machines, centrifugal casting machines

  and shells for falling or gravity casting.

  Various attempts have been made in the past

  to provide casting equipment for deter-

  an optimal duration of solidification for different conditions

  For example, see U.S. Patents 4,200,139 and 4,304,288 which disclose a time reading station for recording solidification times in a system.

of memory.

  It has been discovered in the context of the invention that the quality of molded or cast parts can be improved if the solidification time is determined in a new way.

  and not obvious, using known or measurable parameters.

  According to the invention, in the production of castings made of substantially carbide-free cast iron in shells, the molten metal is allowed to solidify in the shell for a period of time and determined according to the following formula: K x Am x (t 2 - t1) x J x Mc Et = factor Q 1r the elements being indicated in o K = TC + 1/2 If percentages by weight; Cu + Mn T.C. = total carbon content, it being understood that all other elements are maintained in proportions

  to produce castings which are essential

  free from carbide and defects due to shrinkage; And = time of solidification until the ejection of the castings (in seconds); Am = maximum thickness of the shell wall; t2 = temperature of the liquid in the pouring vessel at the beginning of pouring (in F; C = (F-32) / 1,8); t1 = the temperature of the shell at the beginning of the pour (in F; C = (F-32) / 1,8); J = mass heat capacity of the liquid iron (in Btu / lb = 2.324 x 10 J / kg) (gray iron and ductile iron: 0.13 malleable iron: 0.11); Mc = shell conductivity (for a ferritic cast iron shell, use 0.12 x shell thickness measured from the inside of the cavity to the outer side of the back wall, use one side only); and

  Q factor = factor chosen on a curve according to the structure

  metallurgical strength and the required hardness.

  The formula according to the invention for casting in shells can be modified for application to other types of casting, such as those mentioned at the beginning. For example, for continuous casting machines, the formula would become: cadence of alternating movements K x Am x (t2 - t1) x J x M stroke of alternating movements factor Q o the stroke is expressed in millimeters and the rate of movement

in seconds.

  This form of the formula also applies to horizontal bar casting machines and the form of the formula

  indicated first is also applicable to centrifugal casting.

  In a particular application, whatever

  that is to say with a given equipment and with a ferroalloy

  Given all the variables, all the variables are known and constant except t2 and t1, ie the temperature of the molten metal.

  and the temperature of the shell (of the molding device in general)

  ral) at the beginning of the payment. These two temperatures can be detected

  using appropriate sensors.

  Therefore, all variables can be entered into a computer programmed with the formula according to

  the invention to allow the determination of the duration of

  specification for each casting operation. The present invention therefore makes it possible to automate the casting, the computer being also programmed to control the entire casting operation, including the positioning of the nozzle of a pouring vessel over a basket intermediate, the flow control of the poured metal (including the throttling of the flow at the end of the filling of the shell or mold), the adjustment of the exact weight of the metal poured, as well as the ejection of the workpiece (in the case of casting in shell for example) at the end of the determined solidification time. The computer can also provide production information and information

  for automatic process changes.

  Other features and advantages of the invention

  will become more clearly apparent from the following description

  an example of a non-limiting implementation, as well as the appended drawings, in which: FIG. 1 is a schematic representation,

  in perspective, a shell and the equipment used in

  pairing with it, including various sensors; and

  FIG. 2 is a graph illustrating the deter-

  The shell shown in FIG. I has two portions 10, 12 which are movable relative to each other, a fill port 14 and another port 16 for level measurement. More precisely, a laser probe 18 and a photoelectric cell receiver 20 are suitably aligned with the orifice 16 to enable detection of the level of liquid metal in the shell 10, 12. The probe 18 emits a beam of a width of about 3 mm, it has an air purge system

  to clean the optical system, as well as a cooling jacket.

  water, such as the receiver 20. The probe 18 and the receiver

  20 are used to monitor the payment and deliver corresponding signals to the computer, especially to obtain a

  Setpoint level, at which the pouring of metal is stopped.

  The large arrow on the part 10 of the shell indicates the opening for the ejection of the casting after the

duration of solidification.

  As schematically shown above the pouring orifice 14, the metal jet, designated by the large blackened arrow, is preferably surrounded by a cylindrical screen of inert gas directed downwards, as indicated by the two small arrows beside the jet. The metal is poured into the shell 10, 12 from a ladle or a temperature holding container, for example. A sensor 22 is provided for measuring the temperature of the molten metal during its fall from the pocket or container into the shell

  , 12, through the filling orifice 14. The sensor 22 parti-

  also determines the duration of solidification,

  therefore also to the determination of the instant of ejection of the piece.

  Like the laser probe 18, the temperature sensor 22 is also equipped with an air purge system and a cooling jacket

traveled by water.

  The arrows above the sensor 22 indicate

  the movements of the ladle or casting vessel.

  The positioning of the nozzle is carried out with great precision,

of the order of plus or minus 3 mm.

  Finally, a sensor 24 is provided for measuring the temperature of the shell 10, 12. This sensor also participates in the determination of the casting cycle and is also provided with a

  purge system and a cooling jacket.

  Figure 2 shows a graph for determining the Q-factor as a function of the desired hardness or microstructure. As already mentioned, the various parameters are introduced into a programmed computer that controls (in particular) the filling of the shell and also the duration of solidification, that is to say the time that elapses between the filling of the closed shell and opening the shell for ejection of the casting. It should be noted that the use of the Q factor is a numerical approach to control the rates of heat loss, both during the initial formation of the piece, in a

  shell with rapid dissipation of the heat, and during the cooling

  air deformation of the demolded part.

  Other embodiments of the invention are readily conceivable by those skilled in the art.

Claims (1)

R E V E N D I C A T I ON   Process for casting ferrous alloys in a shell for gravity casting in a casting machine   centrifuge, continuous casting machines or a casting machine   Horizontal strip of bars, characterized in that it comprises the setting of the duration And during which the molten alloy is allowed   to solidify in a shell (10,12) for gravity casting.   vity, or of the relation of cadence to the course of alter-   native in a continuous casting machine or a horizontal bar casting machine, according to the formula: Et = rate of reciprocating movements K xAmx (t2 -t1) x J x Mc stroke of reciprocating movements factor Q o | K1) the elements being indicated in o K = IT.C. + 1/2 If percentages by weight; Cu + Mn Et = time of solidification until ejection of the casting (in seconds); [Cadence and stroke of the reciprocating movements in seconds respectively millimeters]; T.C. = total carbon content, with the understanding that all   other elements are maintained in   making it possible to produce castings essentially free of carbides and defects due to shrinkage; Am = maximum thickness of the wall of the molding device (casting); t2 = temperature of the liquid in the pouring vessel at the beginning of pouring;   t1 = temperature of the molding device at the beginning of the pour-   is lying; J = specific heat capacity of the liquid iron; Mc = conductivity of the molding device; and   Q factor = factor chosen on a graph (Figure 2)   the metallurgical structure and the required hardness.