FR2720213A1 - Method and devices for heating metallic bodies. - Google Patents

Abstract

The invention relates to a method and a device for heating a metallic body to a temperature situated between the solidus temperature and that of the liquidus, the heating being carried out over time with energy inputs of different values. The metal body is heated by means of a specially designed induction coil device.

Description

Method and devices for heating metallic bodies The invention

  relates to a method of heating a metal body to a temperature between the temperature of

solidus and that of liauidus.

  To heat and, in particular, to heat inductively, metallic bodies, one proceeds in general so that to the metallic body is brought a quantity of heat, predetermined as a function of time. Examples of such a state of the art can be found in US-A-3,663,730 or E? -A-0,147,243. The question of the quantity of energy as a function of time is therefore of a secondary importance, so that in general we work

  with regular energy intake.

  This procedure was also used when it was a question of manufacturing a metal and thixotropic objects starting from the process, as it is indicated for example in the US-A-3 954 455 and 4 434 839. Such metals Thixotropics can be treated in the most different ways, such as for example in a pressure foundry (see AFS International Cast Metals J., September 1976, pages 11 to 22). There is then heating of a metal part of predetermined length and brought to the casting chamber of a pressure molding machine. The heating is generally carried out inductively by means of an induction coil surrounding the metal part and introducing thermal energy practically only in the

  direction from outside to inside.

  As technicians know, the temperature ranges for a thixotropic material are relatively narrow. It is therefore easily possible that the outside temperature of such a metal part is different from the inside temperature, so that the optimum temperature is not reached for the entire cross section. Also, in practice, the most different factors can make it more difficult

  compliance with these narrow limits.

  This is why the purpose of the invention is to better control compliance with the predetermined temperature range and the solution is given according to the invention by the fact that the heating is carried out over time with an energy supply of different value. It turned out that having a predetermined energy profile, for example by the fact that one begins first with a high energy intake, then one decreases the energy intake, that preferably the decrease in the energy as a function of time is effected by degrees, and that in particular, for each different degree of energy, a special heat source is used and the metallic body being transported from a heat source to the source of next heat, could in this way achieve the result successfully, because the heat propagation process is relatively slow. If, however, it is heated at the end faster than at the start, the heat will no longer have sufficient time to propagate over the entire cross-section in a homogeneous manner, so that differences in temperature and structures over the extent of the cross section. On the other hand, in the method according to the invention, preferably first a rapid heating is carried out (even if at first it is irregular). This quantity of energy introduced at the start will then give time to allow a regular distribution over the value of the cross section, a cautious thermal contribution (because reduced) then taking place simultaneously, this energy brought slowly can also be better repaired . It is then obvious that the method according to the invention is in no way limited to pressure molding although the application of this method is preferably carried out in this field. The invention can also be applied to other molding processes, with practically similar advantages, processes for which heating of the metal body is necessary,

  as for example this is done for forging.

  Naturally there is also the problem of monitoring the optimal thixotrcpe state of a metal thus treated. Especially concerning the pressure molding process, as for example forging, but also concerning pressure molding, such monitoring and such regulation. this is done by the fact that the forming pressure over time is measured, that the pressure variation is determined as a function of time, and that, correspondingly to the pressure variation, the heat allowing to reach a pressure variation CE C NSIGNE predetermined is regulated, because the pressure of mage, respectively the pressure of forming-shaping will vary with the states taken by the metal as one could observe it. It is obvious that such regulation is most advantageously linked to the process of the present invention, but without this being of automatic inventive significance. This also applies analogously in the case where the pressure cycle cycle is measured, the heating time is measured and the thermal energy to be supplied is modified ... obtain an adaptation of the two measured time values . It is a question here of the fact that the temperature of the metal and the cycle time must be made to agree in order to avoid having too long cooling times for the metal making the cycle last too long or else not waste precious production time. These processes are. implemented, in practice, according to the invention in the advantageous way -us by means of devices characterized by the fact U ': - a device intended to reduce the energy supplied to the metal body in time - the output signal of the pressure differentiation device can be re: brought to a device for adjusting the supply of energy to a: sccs .: induction for - heating of u. crcs méallque - a temperature between the temperature of solidus and that of liquidus, in order to adjust at least arproximatively the difference in pressure of introductionr. as a function of time for

  reach a predetermined measurement value.

  - the time transducer is made to apprehend the cycle time of the machine and in that its output signal can be brought to an evaluation device intended to modify the energy supply to an induction device intended for body heating metal at a temperature between the solidus temperature and the

liquidus temperature.

  Other details of the invention result from the

  description below of an exemplary embodiment shown

  schematically in the single figure of the drawing.

  In the drawing, a die-casting machine 1 is shown with a casting mold 2 which can be filled with metal by an opening 35, a chamber in which a molding piston 3 is displaceable by means of a drive of a piston. drive 5 movable in a drive cylinder 4 and connected to the molding piston 3 by a piston rod 6. Along the guide columns 9 is mounted so as to be able to move a movable mold holder 10, using of a drive known per se, not shown, to be placed on a stationary mold holder 11. To these mold holders 10, 11 are attached in a known manner half-molds 38, 39 which in the attached states shown delimit a hollow molding space 37 connected to the interior space of the molding chamber 2 by

  through a casting section 36.

  The parts described so far are of a conventional nature and can be carried out in different ways. It should also be noted that the invention is in no way limited to die casting machines, which is why the machine 1 shown should only be understood as

for example.

  With the molding machine 1, preferably produced in the form of a pressure molding machine, there is associated a heating device 20 intended to heat metal bodies 19 which are introduced, after reaching a thixotropic state, by means of devices known in itself, for example using a positioner robot (not shown), or a corresponding transport device, the introduction being made at each casting cycle of the machine 1, into the filling opening 35 of the molding chamber 2. The heating device 20 is, with the exception of the characteristics according to the invention which will be described below, also of a nature known per se and therefore these details do not need to be modified,

  this corresponds to the knowledge of a man of average art.

  In the embodiment shown, the heating device 20 is made for vertical metal bodies 19, of roughly cylindrical shape, one of which is located each time on a platform 18, on a turntable 17 shown only up to its axis of rotation A. The turntable 17 has a lifting and lowering shaft 16 (see arrow 15) and can be driven by means of a toothed wheel 14 keyed onto this shaft 16. Is used for the drive an electric motor M shown alongside and whose pinion 13 meshes with the toothed wheel 14. In this way the turntable can be controlled, to perform, in addition to the up and down movement controlled by a non-fluidic group shown (for example a hydraulic unit) placed at the lower end of the shaft 16, to also perform a step-by-step rotation movement, which takes place in a known manner and is coordinated with c the vertical movement, so that the metal bodies 19 first immerse in a first induction coil 21, that after a corresponding initial heating they are again pulled out by lowering the turntable 17 following which the turntable 17 is rotated an additional step and the specific metal body then arrives under the induction coil 22 then comes where it is heated again, after which the process is repeated until reaching the coil 23 the next. The number of induction coils required depends on the time required for heating, respectively the size of the metal body 19, the product to be produced and the type of molding machine 1 as well as its cycle time. At the end of the heating, the metal body 19, the heating of which is finished, is then taken from its platform 18 and brought to the

  machine 1, respectively at the opening 25.

  All the parts described so far are, in the

  measure o it is a description, of a classical nature.

  According to the invention, there is now provided a programmed heating of the metal bodies 19, for which at least one of the arrangements described below can be taken. he

  It is obvious from reading the description below that this

  is not necessarily a turntable 17 which must be provided, but that the metal bodies 19 can also be moved linearly on a path, since also in some cases it may be enough to have a

single coil 21, 22 or 23.

  First it is visible in the drawing without any problem that the induction coils 21 to 23 are not of identical construction. Much more on the coil 21 shown in section, it is visible that it has about 6 turns, while on the other hand the coil 22 coming next already contains 8 turns, the third coil 23 containing even more. In this way, the energy supplied to the metal bodies 19 is reduced at each step from one coil to another, the ratio between the numbers of turns cited or between the mutual numbers constituting only one

  example and not being absolutely applied in practice.

  Indeed the value and the lowering of the energy brought to the metallic bodies will depend on some factors which

  will be discussed below.

  Each of the coils 21 to 23 is connected to a power supply unit 24. For this, each time -7 is shown only one line 21a, 22a, respectively 23a, although these are naturally pairs of lines . The unit 24 can be connected to the network because a main switch S. The value, respectively the basic level of the energy supplied to the coils 21 to 23 can be adjusted using an adjustment device 25 produced in itself in any way (shown here as a rotary button). In addition, a programming unit 26 may preferably be provided by means of which the energy supplied to the coils 21 to 23

  can be adjusted as a function of time.

  The unit 26 can be connected at will via an Si switch. It can contain a program by means of which the electrical energy supplied to the coils 21 to 23 (or at least to one of they, for example only at the first coil 21) evolves as a function of

  predetermined curve, here in general undergoes a decrease.

  This curve (the one shown in 26) is not linear in appearance. In general it will be an exponential curve, however different types of non-linearity of the applied device will lead to a superposition of other curves, passing through the exponential curves mentioned and give this somewhat modified curve, for example another exponential curve, such as a

quadratic function.

  It is clear that, if the programming unit is used, it would be sufficient to have a single induction coil thus controlled to ensure the heating of the metal bodies 19, although in practice for various reasons it is prefers heating by degrees with several coils. It is obvious, due to this heating by degrees, also that the exponential curve indicated at 26 can be obtained by approach by iteration steps, in the case where this is desired. For this one can use analogous circuits those which are conventional for

  get a slow start of electric ocoot m ves.

  Precisely in the case of an installation intended for die-casting and in particular a die-casting installation, as shown in the drawing, there are also still other factors which can be applied individually per se, suitably however. combination. First, it was observed that the state of heating of the metal bodies 19 clearly influences the energy cost of group 4, 5. The increasing pressure, already when liquid metal is used, varies its angle of climb in the case of a thixotropic material, in a completely clear manner as a function of the states through which the metal has passed and as a function of its temperature. This clarity of the phenomenon comes from the fact that a thixotropic material partly contains a solid material and that the share of solid metal in this temperature limit range (close to what is called "the temperature of the solid phase lines") ) can visibly move very quickly

  which leads to large pressure fluctuations.

  This is why a folder to optimize the temperature consists in that this increase in pressure, that is to say the modification of the pressure as a function of time is measured, then that the heating of the metal is subjected to a command. . Which pressure to use concretely in the case of a die casting machine can be decided according to the particular case; because it is known that, for example, the pressure at the level of the drive piston 5 is certainly correlated to that prevailing on the molding piston 3 and this again is correlated with the pressure prevailing in the hollow molding space 37 or in the molded mass 36, but that however there will be

differences.

  In the illustrated embodiment, three pressure sensors 7, 8 and 40 are provided, the first two of which are each arranged on the front face and on the rear face of the drive piston 5, the last sensors 40 however being placed ians the mold. Within the meaning of the explanation given above, however, any other type of measurement can be used as in the molded product 36 or directly on the molding piston 3 (or else a combination of this with a corresponding weighted mixture or

unweighted between signals).

  Each of the pressure sensors 7, 8, 40 used for this purpose is connected by its outputs to an associated differentiating stage 27, thereby obtaining a value of the ACTUAL increase in pressure as a function of time. This differentiating stage 27 suitably includes not only the differentiation capacitor indicated on it, but if necessary also also a signal forming stage, which converts the difference signal obtained into another signal preferably a rectangular signal of amplitude and / or of corresponding duration (of predetermined amplitude but with a duration varying correspondingly to the increase in pressure). Depending on the circuit design, however, it is also possible to convert into a signal at a frequency corresponding to the pressure increase (for example by means of a frequency generator controlled by the signal

of difference).

  Inside the layout of electrical lines is provided, at any point suitably, a switch S2, s * respectively S4, so that the circuit can then operate with a pressure sensor or the other or a combination of these pressure sensors. This evaluation of the pressure increase signal obtained from stage 27 can then be carried out each time in a stage 28. Depending on the type of pressure increase signal sent by stage 27, stage 28 will therefore be of corresponding design. If the signal amplitude corresponds to the pressure increase, then a direct comparison can be made, that is to say a set threshold value of stage 28, that is to say stage 20 can be realized as a threshold value switch, a crossing in the downward direction of the threshold value signifying that the applied pressure is within the limits of the admissible treatment range, whereas by O10 against a crossing in ascent leads to a signal output from stage 28 aimed at increasing the value of the programming stage 26 by a predetermined degree (ie increasing the heating energy by a predetermined value). The programming stage 26 can also work without the exponential curve function explained above and the heating energy can simply be adjusted according to the signals obtained, including the output signal from stage 28

is just the first example.

  In the drawing is in any case shown a preferred embodiment for which the magnitude of the pressure increase, resulting from the pressure increase signal from stage 27, is compared with a SET value provided by a sensor of value of SETPOINT 29, and which is preferably adjustable, to thus obtain a finer regulation of the heating of the bodies

metallic 19.

  In the case where the pressure increase signal of stage 27 is a signal of predetermined duration or a frequency signal, there would be a possibility for exploiting it, if stage 28 contains an integrator (or if a such a device is mounted upstream of it) so as to again obtain an amplitude signal. It is however obvious that the skilled person has many other possibilities of exploitation, so that it is useless to return more

in detail here on this subject.

  Another factor to take into consideration in forming machines, such as in particular a die-casting machine, is the cycle time. Because, as mentioned above, respecting a relatively narrow temperature range plays a large role in ensuring the quality of the blanks to be produced, it is important that the cycle times of the machine 1 and of the processing device heater 20 are designed to suit each other to prevent temperature fluctuation

  metallic bodies 19 brought to the machine 1.

  According to the invention, the adaptation is carried out for a molding machine, such as for example a pressure molding machine 1, by the fact that first the cycle time of the machine is determined insofar as this time cycle is not predetermined and therefore considered to be a fixed value. To determine the cycle time, it is possible to provide a switch S5 which is actuated by the movable mold holder 10 at the start and at the end of the cycle, here with switching on at the start and switching off at the end, when moving the mold holder

  , to the left (if we refer to the drawing).

  The actuation of the switch S5 triggers an on-off oscillator 30 which acts here as a timer. It is obvious that by means of the switch S5 it is also a logic gate circuit which can be opened to let

  run a clock generator running continuously.

  As a variant, it is also possible to use other timers such as a bi-stable rocker circuit (flip-flop) actuated by the switch S5 or else a capacitor belonging to an RC component and which is charged by switching the switch S5. . It is also obvious that the operation of the switch S5 can be reversed if desired by opening in the event of a displacement of the support 10 to the right and by opening, after return of the support, to the left from the position shown. In this case, there is neither an inverter nor a timer at the output for which an inversion behavior is automatically obtained (for example, the time of discharge of a capacitor having a function is measured.

  time determination instead of measuring on the load).

  In the case where the cycle time of the heating device 20 is invariable, then it would suffice (in a manner analogous to what we have in the case of stage 28) to compare it with a fixed value ("value of threshold"). It is however preferred to also provide for the heating device 20 a timer 30a (or else another timer) controlled by the energy supply device 24, the! 2 if necessary by a control stage 31 intended for the motor M, and to compare the two: cycle times between them in a comparator stage n. In the case of the timer 30, 30a this can be done simply by means of a counting and counting counter n which is supplied by the signal of the timer, for example in the direction of an accumulation counting, by the signal of the timer 30a in the direction of a decrease count, so that in the event of coincidence of the cycle times at the output of the counter n, zero is obtained each time. Then in case of deviation in one or the other direction we obtain at the output of the counter n a positive or negative signal which is brought to stage 26 to obtain more speed or less speed of heating of the bodies

metallic 19.

  This signal must also be brought either to the device determining the cycle time of the heating device 20, such as stage 31 of the engine M, respectively to the group (not shown) intended for lifting and lowering the turntable 17 to obtain a corresponding adaptation of the cycle time or this is done, as is preferred according to the invention, by means of a more precise method. It has indeed turned out that the consumption behavior or current capture of the coils 21, 23 was not regular. Much more, a clear jump in current consumption is obtained when, on heating the metal bodies 19, at a temperature between the temperature of solidus and that of liquidus, a determined stage of this range is obtained. An essential aspect of the present invention is that this phenomenon, for which no sufficient reason has yet been given at present, is used for adjustment purposes, this adjustment being able to also be carried out independently of an adjustment of the heating, ie is to say that this aspect of this

  invention is of particular and automatic importance.

  Thus on at least one coil, here - as preferred - the first coil 21, a measurement circuit 32 can be connected to measure the energy consumption of this coil 21. It is obvious that such measurement circuits are always located at two conductors of a load as already noted, causing the line which is only represented by a drawing line to include two conductors. This arrangement 32, suitably constructed in the form of an intensity measurement circuit, provides a corresponding output signal when the jump cited on the control circuit 31 occurs which also has an output F intended for the fluid group intended for raise and lower the turntable 17. The circuit 31 is preferably constructed so that when the jump signal mentioned appears, the cycle time can be reduced by a value so that one can continue working with the new cycle time without receiving a jump signal. If necessary, stage 32 can also be connected to energy control stage 26 and, in the event of the appearance of a jump signal, can trigger a

  (slight) decrease in heating energy.

? EVELNDICATIONS

  1. A method of heating a metal body at a temperature between the temperature of solidus and that of liquidus, characterized in that the heating is carried out over time with an energy supply of different value. 2. Method according to claim 1, characterized in that first begins with a high energy intake, then decreases the energy apporz, in that preferably the decrease in energy as a function of time s 'effect by degrees, and in particular that for each different degree of energy, a special heat source is used and the metallic body being transported

  from one heat source to the next heat source.

  3. Method according to any one of the claims

  previous, characterized in that the decrease in energy, at least approximately, follows an exponential curve and / or in that the energy input from an inductive heat source is measured and, in case of variation of the value of energy consumption, energy is subject to a predetermined decrease in value.

  4. Method according to any one of the claims

  above, characterized in that the forming pressure over time is measured, that the pressure variation is determined as a function of time, and that, correspondingly to the pressure variation, the heat energy allowing d '' reach a pressure variation DE

  PRESET SETPOINT is set.

  5. Method according to any one of the claims

  above, characterized in that the pressure forming cycle time is measured, in that the heating time is measured and in that the thermal energy to be supplied is modified to obtain an adaptation of the two measured time values.

  6. Device for implementing the method according to

  any one of the preceding claims, with at

  at least one device with induction coil, produced to heat metallic bodies and connected to a current source, characterized in that a device intended to reduce the energy leads to the metallic body according to the

time is scheduled.

  7. Device according to claim 6, characterized in that the energy reduction device has a transport device for the metal body, as well as a series of induction coils, placed on this transport device and having densities d increasing windings, to which the metal body can be brought, one after the other, using the transport device and / or in that a measuring device intended to apprehend the caz: ée thermal energy, for example a current measuring device, es: orevu on at least one induction coil and in that the output signal of this measuring device can be brought to a control device

  intended to regulate the energy supply to the metallic body.