DE3345542C2 - Method for controlling the melting and casting process in investment casting technology, in particular in dental technology and device for carrying out the method - Google Patents

Abstract

In the melting and casting process, the temperature profile over time and, in particular, the gradient of the temperature curve are evaluated in order to automatically determine the optimal casting temperature or to be able to select between old and new crucibles. Due to the lower heating power during the melting interval, this is stretched, which means that the melting material is heated more evenly and enables the melting interval to be identified more clearly.

Description

The invention relates to a method according to the preamble of claim 1 and to a Device for performing the method according to the preamble of claim 10.

Method and device of the generic type are known from DE-OS 21 58 115. There will the temperature of the melt measured by means of a thermocouple or an IR radiation detector. As soon as the measured temperature has reached a preset value, a Time delay relay initiated the casting process.

From the company brochure "Prestomat Bl" of the company DEGUSSA is a similar device with resistance heating and a Heizstromreglcr known, in which a thermocouple continuously a target / actual comparison between the measured temperature performs a presettable value.

The disadvantage of these known methods and devices is that the casting temperature of the material to be melted must be known exactly, and that measurement errors occur aged sensors, different radiation properties of the crucibles etc. the entire casting result so far can falsify the fact that the melt or the casting is unusable. If the "casting temperature" If too low is selected, the melt has not yet completely melted, i.e. H. they are still primary crystals present, which leads to unsatisfactory casting results. If the casting temperature is reversed If set too high, voids will appear in the molding during casting.

From DE-OS 31 46 391 a control panel is known, which an operator in the simplest possible way Provides information about the point at which (in a predetermined period of time) the casting process takes place is currently located. This control panel likes to monitor the casting process for an operator make it easier, however, the actual commands, in particular the time of casting, still have to be made by are developed and given to the operator.

With the known techniques it is absolutely necessary to know the optimal casting temperature in advance. The casting temperature, in turn, depends on the type of metal alloy to be cast. The casting temperatures of various alloys must be determined empirically, whereby one must know the exact composition of the alloy in each case. Minor deviations from the mixing ratios resultic feil uci'ciiS in üfiVcfwcriüafcfi rOi'iniingcn. To achieve ϋίιϊ iiüfi fc- producible casting processes, US-PS 36 20 294 a proposed solution for how one can clearly understand a previously determined temperature profile when heating for each casting process. Here, too, it is assumed that the exact composition of the alloy is known and that laborious experiments to determine the optimal casting temperature or the optimal temperature profile have been carried out before the actual casting.

Proceeding from the above-mentioned prior art, it is an object of the present invention to process and to develop the device in such a way that even if the optimal casting temperature value is not exactly known of the material to be cast are still flawless casts achievable.

ίο This task is carried out by the in the identifying Part of claims 1 and 10 specified features solved. Advantageous refinements and developments the invention can be found in the subclaims.

The invention is based on the knowledge that the time course of the temperature or the radiation intensity of the material to be melted and in particular the change in temperature over time (differential quotient or difference quotient) provide excellent information about the condition of the melt material.

Particular attention should be paid to the melting interval. In the case of alloys, there is a difference one solidus temperature and liquidus temperature. When heating up, the first melting takes place at the solidus temperature. There are still primary crystals in the melt, which only occur when the Liquidus temperature are completely melted. The melt is then liquid. When it heats up, the Temperature of the melt continuously up to the solids temperature. Then the heat supplied is for the phase change is required The temperature of the melt does not rise (or only very slightly) until the phase transition is complete. The temperature rises only after it has completely melted then again.

An essential aspect of the invention is to automatically identify the melting interval by evaluating the temperature profile over time.
Another aspect of the invention is to extend the melting interval by controlling the heating power. Usually, a high heating power of an induction coil heats the melt inhomogeneously. The magnetic field creates induction currents in the heated melt, which increase the temperature. If the energy is too high or if the frequencies are too high, the outer layers of the melt are heated up more than the inside of the melt due to the skin effect. The melting interval is then not pronounced in such cases, in particular there is no clearly recognizable horizontal section of the temperature curve. For this reason and in order to achieve a homogeneous temperature in the melt, the heating power is reduced when approaching the solidus temperature or at least when it is reached, while it is higher when heating up to the solidus temperature and after passing through the melting interval. After leaving the melting interval, the melting material is further heated by a specified temperature value (temperature interval) until the

bo casting temperature is reached. Upon reaching the casting

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to a lower value, so that the temperature does not rise any further. In addition, a Target member started, which limits the casting time.

If you use carbon crucibles, especially when smelting dental gold, and you measure the temperature using infrared radiation sensors, the following problem occurs: On the one hand, in contrast to ceramic

The coal crucible itself through the induction coil warmed up. On the other hand, older, i. H. already repeatedly used coal crucibles compared to new ones Charcoal crucibles have a different temperature / radiation characteristic. With the invention it is possible from the Automatic detection of the steepness of the temperature increase, whether an old or a new crucible is present. Dependent on of this differentiation criterion, only an additive correction value is required in order to reduce the Make the temperature curves of old and new crucibles consistent, whereupon the evaluation the temperature profile can be identical. In the following, the invention is explained in more detail by means of exemplary embodiments in connection with the drawing explained. It shows

F i g. 1 shows the temperature profile of the molten material in the method according to the invention during casting on the The atmosphere;

2 shows a similar temperature profile during casting in a vacuum;

F i g. 3 two comparison curves of the temperature profile with normal and extended melting intervals;

F i g. 4 and 5 show two exemplary embodiments of casting devices in which the invention is used;

6 is a schematic view of a control panel for the device according to the invention;

F i g. 7 is a block diagram of the control unit of the device according to the invention; and

Fig. 8 the temperature profile for old and new Charcoal crucibles.

First, let us consider the method according to the invention with reference to FIG. 1 explained. Here the temperature ■ & is shown over time t. Before the heating is switched on, the melted material is at the temperature fo (time ίο, t'o). For preheating, known per se, the induction coil is operated with full heating power H 1. The temperature of the melt rises relatively quickly, ie steeply, which curve section 1 expresses. At the point in time t \ , the solids temperature ⁱ &'\ is reached, ie the first alloy components change from the solid phase to the liquid phase. Despite the full heating power H \ , the temperature no longer increases significantly at this point in time, rather the temperature curve runs over a flat section which even has oscillating temperature profiles with a slight drop in temperature despite the heating power H \ being switched on . This is explained by the energy consumption during the phase transition. This is shown by curve section 2.

The preheating is ended by a specified period of time after the solidus temperature ■ & ■ Ί has been reached, & h. the heating is switched off (heating output H Θ). It is then also possible to insert a casting muffle into the casting device. Due to the switched-off heating power, the temperature decreases again, so what is seen from the graph section 3. Then, the heating again fully switched on, ie the heat output H 1 in turn is followed by a relatively steep rise in temperature up to the point U flattens the temperature curve and the Solidus temperature i | is reached again. This is recognized by the fact that the increase over time or, more precisely, the differential quotient d <falls below a predetermined value. The beginning of the melting interval has now been reached

If heating is carried out without preheating, then from the point in time b5 to and the temperature · #> along the dashed line 4, until the solidus temperature ft \ is reached.

To stretch the melting interval, the heating power is now switched to a lower value H 2 at time ίι, so that the temperature practically does not change or, more precisely, changes only very slightly. This is shown by curve section 5. By extending the melting interval, a homogeneous temperature distribution is now possible and all alloy components can pass from the solid to the liquid phase. This is reached at time ti , whereupon the temperature rises again despite the still reduced heating power H 2. This increase is clearly identified at the point in time h , since the differential quotient of the temperature profile has again exceeded a certain threshold value. The temperature fi ₂ present at this point in time h represents the liquidus stone temperature as a first approximation, which indicates the end of the melting interval. This temperature lh is stored, whereupon the heating is switched back to full heating output H 1. The temperature continues to rise according to curve section 6. Has the temperature increased from the liquidus temperature lh by a predetermined fixed amount Δ & and has the temperature ih = ih + Δι at time U? reached, the desired casting temperature is ih. achieved. A signal indicating readiness for pouring is now generated (in FIG. 1 labeled "green") and at the same time the heating power is again switched to a lower value H 2 , which is selected so that the temperature does not rise any further (curve section 7) .

A "casting interval" is now set, ie the casting process must be completed within a set period of time (u - / 5) from the reaching of the casting temperature ih. In the specific circuit, a timer is started for this purpose, which generates a warning signal (marked "red" in the drawing) after a fixed predetermined period of time has elapsed, which indicates that the casting time has expired.

From Fig. 1 it can be seen that in the invention - In contrast to the prior art - no longer worked with a fixed casting temperature will; rather, this casting temperature is determined as a relative value from the temperature profile of the melted material. Regardless of the alloy to be melted, the optimum casting temperature is automatically achieved determined.

F i g. Figure 2 shows a similar temperature curve for casting in vacuum. Here, however, the effect can occur that, after further heating above the liquidus temperature i? 2, an oxide layer tears open. If infrared radiation sensors are used to measure the temperature, the tearing open of the oxide layer changes the radiation intensity despite a further increase in temperature. The radiation intensity measured by the infrared radiation sensor follows the dashed curve section 8. It could thus occur that, in terms of measurement technology, the temperature interval ΔΘ- of FIG. 1 is not detected.

For this purpose it is provided that a predetermined period of time (h - ί 3) after reaching the liquidus temperature ih. after the temperature has increased by a value Aih , the current temperature t'h present at this point in time t 'is saved. If the oxide layer does not tear, the process proceeds as in connection with FIG. 1, ie a further increase in temperature Δ & 2 occurs until the casting temperature is reached at a temperature > h. If, on the other hand, the oxide layer tears open, the temperature runs along the dashed line 8. To avoid these two curves

To be able to differentiate, it is now continuously monitored whether, after the stored temperature i% has been reached for the first time at time t ' _3, this temperature is (apparently) undershot again. If this is the case, the system waits until the apparent temperature, starting from the value i% , has decreased further by a fixed predetermined amount ΔΌ · νι and the temperature value y? 5 is reached at the point in time t \. At this point in time, the apparent casting temperature is detected, the heating power is switched to the reduced value H 2 and the casting signal is generated, whereupon a comparison with FIG. 1 shorter casting interval is specified.

The value Δ $ _2/2, i by which the temperature of the value? 4 to apparent casting temperature "? May drop s, corresponds to just half the temperature difference"? 2 about which with existing oxide layer, the temperature starting from "? 4 increased until the casting temperature ■ &■> is reached. Furthermore, the temperature difference Δϋ · corresponds to the F i g. 1 is just the sum of Δΰ \ + Δ & ι.

The remaining curve sections in FIG. 2 correspond to those of FIG. 1, so that a further explanation is not required.

F i g. 3 shows the stretching of the melting interval more clearly. If the temperature is increased with full heating power H 1 according to curve 9, no pronounced horizontal section of the temperature curve can be seen for some materials or alloys.

As curve 9 shows, the temperature runs between the solidus temperature & s and the liquidus temperature «? /. between the times fi and h with a clear gradient, the time interval for passing through this temperature difference being relatively short. As mentioned above, due to the inhomogeneous temperature distribution or non-uniform heating due to the skin effect, it may well happen that not all of the storage components, especially in the interior of the melting material, are already in the liquid phase, although the radiation sensor, which essentially measures the surface temperature, already has the Indicates liquidus temperature. This harmful effect can be switched off by switching the heating power. In connection with F i g. 1 and 2, the switch from full heating output H 1 (for example with 220 V) to reduced heating output (for example 160 V) was spoken of. In curve 10 of FIG. 3, three different heating outputs H \ (e.g. 220 V), H ₂ (e.g. 200 V) and H] (e.g. 160 V) are used. If the temperature curve at time fi at full heating output H \ has a slowing slope, i.e. if the differential quotient d & ldt falls below a predetermined positive threshold value at time fi, the heating output is first switched to the lower level H ₂ The temperature curve now runs flatter into the horizontal section , which begins at the time t \ at the solidus temperature #s. A switch is then made to an even lower heating power H3 , so that the favorable horizontal temperature curve section is passed through. The solidus temperature of & _s is recognized that the differential quotient d ldt a second smaller threshold value, for example zero Begins reached after passing through the horizontal portion at the time t _2, the temperature curve to rise again, the process is as g in connection with F i. 1 and 2, that is, at time t ₃ , there is a switch back to full heating power H 1

In the following, reference is made to FIG. 4 referred to. There is shown a casting device in which the present invention can be used. This casting device corresponds essentially to the casting device of the older ones Patent application P 33 05 418.5 except for the implementation of the method according to the present Invention necessary parts. F i g. 4 shows essentially a vertical section through a casting device A frame structure 11 is essentially box-shaped, on its front side for retraction and extension of push parts 12 and 13, however, open. The upper part of the framework 11 has a reinforced one Cross bar 34, which has a downwardly directed U-shaped profile. The horizontal abutment surfaces this profile are opposite the top of the upper thrust part 12, which is a substantially H-shaped Has cross-sectional profile. A recess is provided in the crossbeam of this H-shaped profile, in which a crucible 24 can be inserted. Ring around the lower half of the crucible 24 is an induction coil 31 arranged at a certain distance from the crucible 24 and provides in connection with a high-frequency generator (not shown) for heating the material to be melted in the crucible 24. The crucible 24 runs from top to bottom conically tapering and has a circumferential in the area of its upper end Shoulder or a collar that comes to rest on a retaining ring 44. The retaining ring 44 is at the top of the crossbar of the H-shaped cross-sectional profile. The upper thrust part 12 is in side guide rails 21 can be displaced with respect to the supporting structure 11. The storage takes place via ball bearings 29, these have a game that allows a vertical displacement of the thrust part 12. The game is here so large that the thrust part 12 can be moved as far in the direction of the upper cross bar 34 that the mutually associated abutment surfaces of the thrust part

12 and the cross bar 34 can be brought into firm contact with one another, the in a groove on the top of the thrust part 12 provided seal 35 for a seal that can be loaded with overpressure or underpressure Closure between the upper cross bar 34 and the upper push part 12 is provided in the wall of the push part 12, one or more coolant lines 38 can be provided through which coolant, for example Water is directed.

Below the push part 12 is a lower push part

13 arranged, also in ball-bearing guide rails 28 is displaceable Here, too, the ball bearing 29 has a game that allows vertical displacement

so the pushing part 13 is allowed. The pushing part 13 has a substantially U-shaped cross-sectional profile, which is shown in its interior allows the inclusion of a casting muffle 25 The top of the push part 13 forms a Abutment surface that can be brought into contact with the underside of the upper sliding part 12 is also here in one A seal 36 is embedded in the groove on the abutment surface of the lower thrust part 13. The lower thrust part 13 is by a piston-cylinder arrangement (cylinder 32 and piston 33) attached to a lower cross bar 58 the underside of the framework 10 is supported, vertically displaceable. If the lower thrust part 13 raised by the piston-cylinder arrangement 32, 33, it presses against the upper thrust part 12, whereby this is also raised until it comes to a stop on the upper crossbar. The upper crossbar 34, the upper push part 12 and the lower push part 13 together with the seals 35 and 36 form a Chamber 56, which can be evacuated or pressurized with

is beatable. This chamber 56 thus receives the crucible 24 and the casting muffle 25 and thus forms one Melting and casting room. In the upper cross bar openings 37 and 57 are provided through which the chamber 56 can be connected to a vacuum pump or a compressed gas source.

In addition to the lifting device formed from the piston-cylinder arrangement 32, 33, which is used for closing of the casting device is used, is a further lifting device formed from a piston-cylinder arrangement 39, 40 provided, which are used to raise and lower the casting muffle 25 and to open or close at the same time. Closing the crucible 24 is used. The piston-cylinder arrangement 39, 40 is in a recess 41 in the lower Area of the thrust part 13 is arranged. The piston rod 39 protrudes through the bottom wall of the Push part 13 through and is attached to a support plate 47 which carries the casting muffle. The casting muffle is thus displaceable between two limit positions, the upper limit position shown in dashed lines for the casting process is used. A funnel 27 then comes close to the casting muffle 25 below the pouring opening of the crucible 24 to lie. The support plate 47 is on one side (on the right in FIG. 4) to one Extended connecting arm to which a vertical lift ram 46 is attached. By lifting the casting muffle 25 the lift tappet 46 is thus also raised. This lift tappet 46 is aligned when the thrust parts are closed another lifting ram 45 ', which is in an opening in the transverse part of the H-shaped cross-sectional profile of the thrust part 12 is guided and opens into a horizontal lifting arm 45 which is in a bore of one of the crucible parts is attached. The mutually facing ends of the two lift tappets 45 'and 46 are in the lower limit position the piston-cylinder arrangement 39, 40 at a distance from one another. This makes a dead one Created passage that ensures that the casting muffle 25 the two lift tappets 45 'and 46 come into contact with each other and then in the last part of the upward movement the casting muffle 25 ensures that the crucible 24 is opened. Above the crucible 24 has the Cross bar 34 an opening which is closed by a sight glass 48. The sight glass 48 is by means of a retaining ring 42 attached. Above the sight glass is a temperature sensor in the form of an infrared radiation sensor 60 attached. The sensor 60 and its supply lines 62 are attached to the upper one by means of a holder 61 Cross bar 34 held. The supply lines 62 lead to a control unit 63, which is also for example The piston-cylinder arrangement 39, 40, which triggers the casting process, controls via solenoid valves. Is so reaches the optimum casting temperature according to the method described above, the casting process can here run automatically.

F i g. Figure 5 shows another casting apparatus in which the invention can be used. There are crucibles here 24 and heater 31 attached to a rotary arm 65 which has a counterweight 66 and around a vertical axis 67 is rotatable. This is a centrifugal casting device with a centrifugal arm 68, which is accessible from above, as its housing cover 70 can be opened via a hinge 69. 71 with a receptacle for a casting mold is designated. A control panel 72 is separated from the sling arm 68 by a partition 73

6 shows a section of the control panel of the device according to the invention. They are different Control function switch or button provided. By means of a switch 74, two operating modes can initially be selected to be selected. On the one hand, the operating mode in which the casting process when a preset Casting temperature is triggered as well as the operating mode in which the casting temperature according to the invention is automatic is determined. The process described in connection with FIG. 1 is carried out with a button 75 of preheating started. With a button 76 is the

ίο process described in connection with FIG started without preheating (curve section 4). The casting process can be triggered manually using the button 77 will. With a button 78 the heating can be switched off at any time, even during the automatic sequence will.

A switch 79 can be used to preselect different heating levels for the heating power when the casting temperature is reached. The temperature difference Δ & according to FIG. 3 can be selected. Furthermore, a display 81 is provided which shows the absolute value of the infrared emission.

Two temperature curves 82 and 83 are then provided along which light-emitting diodes 84 to 91 are arranged are. These light-emitting diodes show the operator in which section of the curve the temperature is each is located. If the first operating mode is selected via switch 74, the temperature runs lengthways the curve 82, whereupon the corresponding diode 84 lights up depending on the temperature reached, until the last diode lights up when the preset final temperature is reached.

If the second operating mode with automatic determination of the optimal casting temperature is selected, then the temperature moves along curve 83. When reached

The diode 85 lights up if you are still in the melting interval some time after this temperature has been reached, the diode 86 lights up. If the temperature begins to rise again at the end of the melting interval, the diode 87 lights up or when it is reached of temperature & 2 the diode 88. When the casting temperature lh is reached, the diode 89 lights up here with a green color. At time r ₅ , ie after the casting interval has elapsed, the red diode 90 lights up. As soon as the diode 89 lights up, the operator must therefore press the button 77. If, on the other hand, the diode 90 lights up, then he recognizes that he is no longer allowed to trigger the casting process.

If operational malfunctions occur during the automatic process, this increases especially after it has been run through of the melting interval does not clearly show the temperature, after a predetermined period of time has elapsed The lighting of the diode 91 indicates that the maximum time has been exceeded without the casting temperature being affected was achieved. The melting process must then be stopped.

F i g. 7 shows a block diagram of the control unit 63. The core of the control unit is a microprocessor 92, which is connected to a switchable mains voltage (see switch 79) via a transformer 93. Of the

The microprocessor has several inputs 94 which can be connected to the switches or buttons according to FIG. 6 connected are, as with the reference numerals 74 to 78, which relate to the switches or buttons of FIG. 6 refer, indicated

Furthermore, the microprocessor has several outputs 95 and 96, on the one hand the light-emitting diodes 84 to 91 and on the other hand switch over the different power levels for the heating output, the heating

Turn off power completely and / or control actuators to trigger automatic pouring.

An analog / digital converter 97 is provided as a further input for the microprocessor 92. Then a signal from a potentiometer 80 (cf. also FIG. 6), with which the temperature difference Δ & according to FIG. 1 is preset or, more precisely, a predetermined value W for the output signal of the sensor 60, this signal corresponding to the value Δ & in accordance with the radiation, current or voltage characteristics of the sensor. Finally, in the operating mode according to curve 82, FIG. 6 the absolute value of the casting temperature is set.

The micro processor 92 evaluates the analog / digital converted Part of the sensor 90 continuously forms the differential quotient or, more precisely, the differential quotient to determine the slope of the temperature curve, the comparison operations described in off, if necessary, calculates the correction values described and generates the various control signals its outputs. For this purpose, the microprocessor contains - as usual - arithmetic units, data memories, and program memories as well as the corresponding driver circuits for the blocks for the outputs 95 and 96. To the explanations given above, it is easily possible for a person skilled in the art to use the microprocessor to be programmed in such a way that it carries out the procedural steps described.

F i g. 8 shows temperature profiles of old and new crucibles, which are automatically differentiated according to the invention can be. Usually, alloys are melted in ceramic crucibles, while gold is in the Carbon crucible is melted, which is set in a ceramic crucible. Charcoal crucibles now show at the same Temperature different radiation intensities, with new, unused crucibles a lower radiation intensity (darker radiation) than older crucibles that have been used several times. When measuring temperature by means of an infrared radiation detector this would lead to a falsification of the measurement result.

To avoid this error, the slope of the curve is determined during the first heating phase, ie before the liquidus temperature is reached. In detail, a predetermined period of time after switching on the full heating power, ie in the example of FIG. 8 at time / 7 the slope of the curve was determined by forming the differential quotient dtf / dt (in digital technology, of course, the difference quotient). This value is compared with a predetermined threshold value. If the ascertained slope value is below the threshold value, a new crucible is present, while conversely an old crucible is recognized. Experimental measurements have now shown that in the temperature range of interest for the casting temperature (eg 1500 ⁰ C) of an infrared radiation sensor is different, the output signal to a relatively constant value ΔΤ at old and new crucibles. By adding or subtracting this value ΔΤ , the two curves of FIG. 8 can be transformed in such a way that a single, corrected curve can be used for both cases. If one chooses the curve for the old crucible as the relevant curve and accordingly sets the casting temperature to the value ft _g i, then when the presence of a new crucible - as described above - has been recognized, only the value for the output signal of the infrared sensor has to be added Add ΔΤ . If the output signal of the infrared radiation sensor reaches the value ## then the value & g 2 = & g 1 + // ^ is signaled to the micro processor by adding ΔΤ , which is then recognized as the preset value for the casting temperature.

Conversely, you could of course also use the curve for the new crucible as a reference curve. In this case, upon detection of an old crucible from the output signal of the sensor would have the value ΔΤ are subtracted, in which case of course the value _g \ would have to be stored as a threshold value for detecting the casting temperature.
The following values have proven to be favorable values for the individual variables described above: For the heating of an induction coil, 220 V is used with the greatest heating output H 1 For the heating output HI in FIG V proved to be favorable. For the heating power HZ during the melting interval as well as during the casting interval (heating power H 2 in FIG. 1) 160 V is recommended.

As a temperature difference Λ «? (Ίη F i g. 1) for overheating of the material to be melted above the liquidus temperature, 100 ° C is advisable.

The voltage values given above refer to a series transformer for control the induction coil 3t.

List of reference symbols

11th Framework 12th Push part 13th Push part 35 21 Guide rail 24 crucible 25th Casting muffle 27 Feed hopper 28 Guide rail 40 29 ball-bearing 31 Heating device (induction coil) 32 cylinder 33 Pistons 34 Crossbar 45 35 poetry 36 poetry 37 opening 38 Coolant line 39 Pistons 50 40 cylinder 41 Recess 42 Retaining ring 44 Retaining ring 45 Lift arm 55 45 ' Lift tappet 46 Lift tappet 47 Support plate 48 Sight glass 56 chamber 60 57 opening 58 Querriegei (lower) 60 Temperature sensor 61 bracket 62 Supply line 65 63 Control device 65 Swivel arm 66 Counterweight 67 vertical axis

13th

68 Schleuderann

69 hinge

70 housing cover

71 Recording

72 Control panel 5

73 partition

74 switches

75 buttons

76 buttons

77 ι ο button

78 buttons

79 switches

80 final control element (Potentiometer)

81 display 15

82 temperature curve

83 temperature curve

84 light emitting diode

85 light emitting diode

86 LED 20

87 light emitting diode

88 light emitting diode

89 light emitting diode

90 light emitting diode

91 LED 25

92 micro processor

93 transformer

94 entrance

95 exit

96 exit 30

97 Analog / digital converter

98 final control element (potentiometer)

99 amplifiers

In addition 8 sheets of drawings

35

40

45

50

55

65

Claims (15)

Patent claims: 1. A method for controlling the melting and casting process in investment casting technology, in particular in dental technology, in which the melt material is heated and the temperature of the melt material is measured, characterized in that the change over time (d & ldt) of the melt material temperature (t?) After Time (t) is determined and the time of pouring and / or the temperature suitable for pouring can be determined as a function of the determined value. 2. Vei drive according to claim 1, characterized in that that the time course of the temperature is measured in such a way that a first temperature value (i? i) is determined in which a predetermined Reduction of the temporal rise in the temperature of the melting material occurs with effective heating, that a further rise in temperature is determined after reaching the first temperature value, that from the detection of the further rise in temperature, heating continues until a predetermined one Temperature difference reached and a third temperature value (# 3) occurs and that then a ready-to-pour signal is generated or the casting process is initiated automatically. 3. The method according to claim 2, characterized in that the heating of the melting material from reaching the first temperature value ($ 1) with reduced heating power (H 2) takes place until the second temperature value (# 2) is measured and that from the second temperature value (# 2) is heated with greater heating power (H 1). 4. The method according to claim 3, characterized in that the heating of the melting material when the third temperature value (# 3) is reached with reduced heating power (H 2) , the reduced heating power is set so that no further temperature rise occurs. 5. The method according to claims 2 to 4, characterized in that the casting process is _{initiated when the third temperature value («? 3} ) is reached and is terminated after a predetermined time (U - I5). 6. The method according to claims 2 to 4, characterized in that a signal indicating the readiness for pouring is generated when the third temperature value («? ₃ ) is reached and that a signal for the end of the readiness for pouring is generated after a predetermined period of time since the start of the readiness for pouring will. 7. The method according to claim 1, characterized in that the determined change value with a The threshold value is compared and that as a function of whether it is exceeded or not reached Threshold value, a temperature value is set that indicates the availability for casting. 8. The method according to claim 7, characterized in that when the temperature values are below the threshold value, a constant correction value is added to the currently measured temperature values and that the sum of these values is compared with a predetermined temperature value which represents the casting temperature. 6 ^Λ > 9. The method according to any one of claims 1 to 6, characterized in that a predetermined period of time (ti - f 3) after reaching the second temperature value, a fourth temperature value (1%) is determined and stored that it is determined whether despite further switched on Meizung this fourth temperature value is again undershot and that the readiness for casting is indicated when the temperature has fallen by a predetermined value (A # _2/2 ) from the fourth temperature value (A) to a fifth temperature value (# 5). 10. Device for performing the method according to one of claims 1 to 9, with a crucible, an adjustable heating device, a temperature sensor for measuring the temperature of the melt and with a control device for triggering the casting process as a function of the temperature of the melt, characterized in that, that the control device (63) is designed and connected to the temperature sensor (60) and the heating device (31) in such a way that the output signal of the temperature sensor (60) is constantly monitored, its temporal change (d & ldt) is determined and the temporal change as a function of predetermined threshold values Change in temperature, the heating device (31) is reversed and / or a casting process is initiated. 11. The device according to claim 10, characterized in that the control device reverses the heating device (31) to lower heating power when a first threshold value of the temporal temperature change is reached, that the control device (63) the heating device (31) after a second threshold value of the temporal temperature change is exceeded reverses to higher heating power, that the control device (63) stores the temperature value (vFj) at the second control value and adds a predetermined temperature difference (di9) so that the control device (63) compares the output signal of the temperature sensor (60) with this sum value and if it is equal of both signals, the heating device (31) reverses to a lower heating power and at the same time generates a signal indicating that it is ready to be poured. 12. Apparatus according to claim 10 or 11, characterized in that the control device (63) contains a timing element that is controlled by the ready-to-pour signal and that according to the predetermined Period of time generated a signal for the termination of the readiness for casting. 13. The apparatus according to claim 10, characterized in that the control device as a function a correction value from a predetermined third threshold value of the temperature change over time (. ^ 77 on the output signal of the temperature sensor (60) is added and this sum value is reached with a predetermined value, where if these values are the same, the signal indicating readiness for casting is generated. 14. Device according to one of claims 10 to 12, characterized in that the control device (63) has a second Zcitglied with adjustable duration, which is started by exceeding the second SchweÜwert the temporal temperature change (temperature lh) , that the control device after the expiry the actual temperature value (1%) given by the second member stores that the control device (63) monitors whether this temperature value (i'h) is undershot when the heating power is switched on and that the control device at Falling below this temperature value (/ ?,) compares whether the temperature measured by the temperature sensor is lower than the stored temperature value (Λ) minus a constant temperature value [Δϋ ^ ι ^. 15. Device according to one of claims 10 to 14, characterized in that the temperature sensor is an infrared radiation sensor.