EP1645348A1 - Process and apparatus for manufacturing of a shell mould for investment casting - Google Patents

Abstract

Production of a shell mold comprises forming a shell by applying an aqueous layer to a model, drying above 25[deg] C using infrared radiation and removing the model from the mold. An independent claim is also included for a system for producing a shell mold.

Description

Field of the invention

The invention relates to the field of manufacturing molds. In particular, the invention relates to the manufacture of shell molds by applying one or more layers to a previously made model.

Background of the invention

In casting processes such as investment casting (often called investment casting) ceramic shell molds are often used. These shell shapes are created by applying one or more layers to a model of the later casting. The individual layers applied to the model contain a slip as well as a sand-based, usually granular, material applied to the slip. In the first applied to the model layer can be dispensed with the addition of the granular material. Following the application of a layer, it is dried before the next layer is applied or, after drying the last layer, the model can be removed. The successive application of the individual layers gradually creates a shell surrounding the model.

After the last layer has been applied, the model is removed from the shell and the shell is then fired. The removal of the model from the shell can be done in different ways. For example, if it is a wax model, it will be removed by smelting. On the other hand, if the model is made of a thermoplastic, the plastic must be burned out of the shell.

The drying of the individual layers applied to the model conventionally takes place at room temperature, care being taken that the water contained in a newly applied layer is removed rapidly but not spontaneously. Mostly, the drying is done at about 21 to 23 ° C and at a relative humidity of more than about 40%. To shorten the drying process It is recommended to expose the respective layer to be dried to an air flow. The air flow supports the removal of the evaporating moisture.

A disadvantage of the conventional drying methods is the comparatively long drying time of usually three to more than ten hours per shift. The reason for this is also the low diffusion gradient within the last applied layer. Even with a greatly extended drying time, the residual moisture in the applied layers can not be reduced arbitrarily. Especially in the deeper zones of the last applied layer, the remaining moisture tends to diffuse back into the adjacent, supposedly dried layer than to evaporate.

For these reasons, even after the last drying process, a certain residual moisture in the shell is always included. This residual moisture complicates and impairs the desired irreversible binding of the colloids contained in the slurry. In addition, with only reversible colloid bonds, moisture (e.g., from the ambient air) acting upon completion of the drying process can interfere with the bond of the shell structure by dissolving the reversible bonds.

In the case of insufficient irreversible colloid binding, melting or burning out of the model may cause the material of the model to burst beyond the shell due to its heat-induced expansion. This danger is the stronger, the less the irreversible colloid binding is completed. Although this danger can be reduced by subjecting the shell mold to a temperature shock (for example in a high-pressure steam autoclave). However, the water vapor used here again causes a moisture penetration of the shell shape with correspondingly negative effects on their strength.

In order to assist the drying process, it is proposed in GB 2 350 810 A to add water-insoluble organic fibers to the slurry. The incorporation of organic fibers has a positive effect on the drying time and also allows a reduction of the residual moisture. The cause of these positive effects is the capillary action of the mixed fibers, which promotes the removal and evaporation of moisture. In addition, the fiber composite causes a more uniform layer structure and allows an increase in the layer thickness.

Despite the beneficial effects of blending organic fibers, the drying time of a single layer is often too long. This leads, in particular in the case of multilayered shells, to the fact that it is almost impossible to produce a cast-ready shell mold in a single day. This may be acceptable in industrial applications where shell molds are produced continuously, but a variety of other applications, such as the production of prototypes, may make it desirable to reduce the manufacturing life of a single shell mold.

The invention has for its object to provide a method and a system for faster production of a shell mold.

Brief outline of the invention

According to the invention, there is provided a method of manufacturing a shell mold (in particular for investment casting) comprising the steps of providing a model, forming a shell surrounding the model by applying at least one aqueous layer to the model, and performing at least one drying operation in layers and layers the removal of the model from the shell, wherein the drying process above a temperature of 25 ° C and assisted by infrared light irradiation is performed.

The layer applied to the model may be a layer containing a refractory slip. The layer may further include a refractory granular material. According to a preferred variant of the invention, however, at least the first layer applied directly to the model does not contain any granular material. The slurry may contain a refractory, liquid binder such as an aqueous silica sol. Further, the slurry may comprise a refractory flour.

According to a first variant of the invention, in a multi-layered shell construction, each individual layer is subjected to a drying process according to the invention. According to a second variant of the invention, individual layers are either not (or at least not completely) dried or dried at a temperature of 25 ° C or below and / or without infrared light irradiation.

The drying process of a single layer may proceed at a substantially constant temperature or at a variable temperature. The drying process may be carried out at a temperature above 28 ° C or above 30 ° C and conveniently in a temperature range up to approximately 45 ° C. Preferred is a temperature range of about 36 ° C to about 42 ° C.

If several layers are applied to the model, the (maximum) drying temperature can change from layer to layer. Thus, the maximum drying temperature can increase substantially from layer to layer. Due to the cooling associated with the evaporation of the moisture, it is possible to choose the maximum drying temperature (ambient temperature) during the drying process above a temperature at which the model could lose its dimensional stability. Thus, the maximum drying temperature may be at least about 5 ° C (preferably at least about 8 ° C or 10 ° C) above the temperature at which a reduction in the stability of the model could begin.

During the drying process, a relative rotation between the coated model and at least one infrared light source can take place. This relative rotation occurs, for example, at a speed between 0.5 and 8 U / min, preferably between 1.5 and 4 U / min.

Furthermore, the drying process can be assisted by a flow of a gaseous medium such as air. The flow rate of the gaseous medium is, for example, about 0.5 to about 8 m / s, and preferably between about 1 and about 5 m / s. The drying process can be further assisted by the ambient humidity being less than 35% or less than 30%. According to a preferred variant of the invention, the room humidity is less than about 20% or less than about 10%.

The inventive method allows a shortening of the drying time. Thus, the drying process for a single layer may be less than one hour, preferably about 25 to 45 minutes. When three or more layers are applied to the model, the drying time for at least some of the layers applied after the first layer can be varied. Thus, the drying time of the second and / or the third layer and / or the fourth layer can be selected to be longer than the drying time of the other layers and in particular the subsequent layers.

The drying time can be adjusted depending on a desired degree of drying. According to a first variant, several layers are applied to the model and the individual drying process is carried out in each case until a complete drying of the last applied layer has been achieved. Complete drying can be assumed, for example, if the residual moisture of a layer is less than about 60% and preferably between about 55 and about 40%. According to a second variant, individual, several or all layers are only partially dried.

The model used to make the shell may be made of different materials (e.g., wax or a thermoplastic such as ABS). In a wax model, the melted out of the dried shell may be at a temperature greater than about 140 °, preferably about 150 °.

The inventive method is suitable for a variety of different applications. Thus, the method is particularly suitable for prototype production by means of investment casting (ie for the production of individual or fewer castings) due to the short drying time. However, the method is also suitable for industrial batch processes (e.g., using a conveyor constructed as a chain conveyor).

In addition to the method already described, the invention also includes a system for producing a shell mold. The system includes a desiltering device for applying a slurry layer to a model, and a drying device for drying the slurry layer applied to the model, the drying device comprising a drying chamber and at least one infrared light source disposed in the drying chamber, wherein the drying chamber is at a temperature greater than 25 ° C is adjustable. To set the drying temperature, a suitable regulating or control device can be present, which ensures compliance with the desired drying temperature or the desired drying temperature profile and the further drying temperature (for example program-controlled).

The heat energy required to achieve the drying temperature can be supplied by the infrared light source. In this case, the infrared light source as Heating device for the drying gas (eg air) act. To set the desired drying temperature, the energy consumption of the infrared light source can be controlled in a suitable manner. Additionally or alternatively, it is conceivable to provide a separate cooling device. By way of example, the cooling device can be designed such that it allows the supply of a cooling gas into the drying chamber. It would also be conceivable to provide an additional heating device separately from the infrared light source.

The system may include means for rotating the coated model with respect to the at least one infrared light source. Such a relative rotation between the coated model and the infrared light source ensures a more uniform surface heating and therefore improves the coating quality. Furthermore, a sanding device may be present for dressing the slip layer applied to the model. The sanding device is adapted to apply granular material (not necessarily sand) to the slurry layer in a manner known per se.

To automate the shell mold production, a transport device that moves the model between the desaturation device and the drying device (in the case of multi-layered construction back and forth) may be provided. The transport device can further ensure transport of the model to and from the sanding device. Appropriately, the transport direction is selected such that the desaturation device in front of the sanding device and the sanding device in front of the drying device.

Brief description of the drawings

Fig. 1

eine Seitenansicht eines erfindungsgemäßen Systems zum Herstellen einer Schalenform;

Fig. 2

eine Aufsicht auf dans System gemäß Fig.1;

Fig. 3

eine Seitenansicht der Trocknungsvorrichtung des in den Fign. 1 und 2 dargestellten Systems;

Fig. 4

eine Frontalansicht der Trocknungvorrichtung gemäß Fig. 3;

Fig. 5

eine Aufsicht auf die Trocknungsvorrichtung gemäß Fig. 3.;

Fig. 6

eine Protokoll eines Biegeversuchs bei einer auf erfindungsgemaßë Weise getrokneten Karamikplatte; und

Fig. 7

eine Protokoll eines Biegeversuchs bei einer auf konventionelle Weise getrockneten Keramikplatte.

Further advantages and details of the invention will become apparent from the following description of preferred embodiments and from the figures. It shows:

Fig. 1

a side view of a system according to the invention for producing a shell mold;

Fig. 2

a view of the system according to Figure 1;

Fig. 3

a side view of the drying device of the in Figs. 1 and 2 system shown;

Fig. 4

a front view of the drying apparatus of FIG. 3;

Fig. 5

a plan view of the drying apparatus of FIG. 3 .;

Fig. 6

a log of a bending test with a Karamikplatte according to the invention Dräkete; and

Fig. 7

a log of a bending test on a conventionally dried ceramic plate.

Description of preferred embodiments

Hereinafter, referring first to FIGS. 1 to 5 an inventive system 10 for producing shell molds explained. Following this, the method according to the invention will be explained by means of various examples and compared with a comparative example.

The Fign. Figures 1 and 2 show schematically the system 10 according to the invention for the automated production of shell molds. The system 10 allows the execution of the relevant process steps trickling, sanding and drying. For this purpose, a sanding device 12, a precipitating device 14 and a drying device 16 are provided. Furthermore, the system 10 comprises a transport device 18 for a model 20.

For the operation of the system 10, it does not matter if the model 20 is still uncoated or already provided with one or more layers. For purposes of illustration, the model 20 is shown in FIG. 1 simultaneously in four different process states, namely within the sanding device 20, within the desiltering device 14, within the drying device 16, and in a transport state. During normal operation of the system 10, the model 20 will only be in one of these four states shown in FIG. Namely, the system 10 is designed for rapid prototyping and not for industrial batch processes. However, the system 10 could be configured by multiple provision of the individual devices 12, 14 and 16 and corresponding redesign of the transport device 18 (eg as a chain conveyor) for batch processes.

In the exemplary embodiment illustrated in FIG. 1, the sanding device 12 is designed as a sand drum, in which sand or another granular material is scattered onto the rotating model 20 provided with a slip layer. In the case of the precipitation device 14, the exemplary embodiment is a slurry barrel which is filled with a suitable slip. The model 20 can be immersed in the slurry barrel 14 by means of the transport device 18 and rotated therein.

A model 20 received by the transport device 18 can optionally be supplied to the slurry drum 14, the sand drum 12 or the drying device 16. The transport device 18 itself comprises a take-up head 22 for the model 20 which is movable along an x-axis and y-axis. The take-up head 22 is rotatable about two mutually perpendicular axes, as indicated by the arrows 24, 26 in FIG.

When the system 10 is used as intended, the model 20 is first immersed in the slurry drum 14 and the sprayed model 20 is then either dried directly in the drying device 16 (in particular if it is the first slip layer) or first sanded in the sand drum 12 and only then then transferred to the drying device 16.

The drying device 16 is shown in FIGS. 3 to 5 shown in different views. As can be seen from these FIGS. the drying device 16 comprises a drying chamber 30. In the drying chamber 30 a plurality of arranged in a plurality of opposing rows of fans 32 and a plurality of infrared light sources 34 are arranged. The fans 32 cause an air circulation and lead to an air flow assisting the drying process. In Fig. 4 it can be clearly seen that the fans accelerate the air tangentially with respect to an imaginary, cylindrical body 36. The heat energy generated by the infrared light sources 34 leads to a heating of the air circulating in the drying chamber 30. The infrared light sources 34 therefore function as heaters. For uniform surface heating of the coated model 20 by the infrared light sources 34, the model 20 is continuously rotated within the drying chamber 30.

The drying device 16 further includes an air conditioner 38 for intake air cooling. The air conditioner 38 emits warm exhaust air and leads an air dryer 40 cooling air. This situation is illustrated by two arrows. The one on one Absorption drying principle based air dryer 40 introduces dry supply air into the drying chamber 30 and gives off moist exhaust air to the environment. This situation is also indicated by two arrows. As can be seen from FIG. 5, a main circuit 46 is formed within the drying chamber 30, which is essentially due to the constant air circulation caused by the fans 32. Furthermore, there is a secondary circuit 48, which includes the air dryer 40. In a mixing chamber 50 there is a thorough mixing of the main circuit 46 and the secondary circuit 48. This mixing ensures a reduction in moisture of the air in the main circuit 46, since moist air from the main circuit 46 enters the secondary circuit 48 and from there into the air dryer 40. Further, the mixing causes a cooling of the air in the main circuit 46, since the air dryer 40 from the air conditioner 38 continuously cooled air is supplied, which feeds the air dryer 40 in the secondary circuit 48.

The air conditioner 38 is controlled such that the desired drying temperature is set in the drying chamber 30. The air conditioner 38 therefore counteracts the return to the infrared light sources 34 heating the drying air. If necessary, in addition to the infrared light sources 34, a separate heater may be provided (eg, the air conditioner 38 could also be configured to supply warm air to the air dryer 40). Also, the air conditioner 38 different from the Fign. 3 to 5 (additionally or exclusively) communicate with the mixing chamber 50. The air conditioner 38 (and to some extent the air dryer 40) thus allows adjustment of a desired drying temperature. For this purpose, the air conditioner 38 and the air dryer 40 may be coupled to a suitable control or regulating device (not shown), which program-controlled influence on the prevailing in the drying chamber 30 drying parameters.

At this point it should be noted that the in Figs. 3-5 of the arrangements of fans 32 and infrared light sources 34 are merely exemplary. For example, it would be conceivable to arrange the infrared sources 34 serving additional surfaces of the model 20 in addition to the air heating and the surface heating. For example, the infrared light sources 34 may be arranged in (two or more) opposite rows with respect to the model 20 so as to emit the infrared radiation substantially perpendicular to the model 20.

By means of the with reference to Figs. 1-5 described, various samples of ceramic molds were made using wax models and tested. All samples were prepared using a slurry containing a binder suspension of WEXCOAT from Wex Chemicals, Greenford, London, England (with a SiO ₂ content of 24%), a proportion of 1 to 5% of organic fibers of 1 length mm and Molochite flour (-200 mesh). The viscosity of the slurry was initially 41 s (measured by the WEX-cup method). The models were immersed in the slurry cask 14 for about 10 seconds and then sanded in the sand drum 14 with Molochite grains (diameter 0.3 to 0.5 mm), apart from the first layer. Then, the coated models were layer-wise subjected to an infrared light irradiation assisted drying process in the drying apparatus 16.

The wax model used had a cubic shape in which a blind hole with a diameter of 20 mm and a depth of 20 mm was formed. Inside this blind hole, the surface temperature and humidity surface values listed in the tables below were measured during the drying process.

A first model grape was provided with a total of six layers (or - in a dried state - coatings), wherein the first layer was not sanded. Each individual layer was completely dried in a separate drying process. The individual drying operations were carried out at a flow rate of about 1.5 m / s under constant irradiation with infrared light. The maximum drying temperature has gradually increased from layer to layer. A drying process was considered complete when the measured residual moisture on the surface was less than about 55%. During the drying process, the sample was rotated at a rate of about 2.5 rpm with respect to the infrared light sources. The humidity in the drying chamber was gradually reduced. Care was taken that the humidity was always less than about 20% whenever possible and the temperature was always above about 30 ° C.

The total process time as well as the individual drying parameters and surface conditions per layer during one of the initial experiments (with still comparatively high humidity in the drying chamber) can be found in the following table. The drying parameters and surface conditions were measured two to five times per drying process.

Ceramic mold 1

Time [h: min] Drying time [h: min] coating drying conditions surface conditions Temperature [° C] Humidity [%] Temperature [° C] Humidity [%] 00:00 00:10 Without sand 29 19 00:10 00:00 2 layer 29 22 00:15 00:05 30 38 00:25 00:15 33 25 00:30 00:20 34.5 19 00:33 00:00 3 layer 34.1 17 00:38 00:05 33.6 22 00:43 00:10 33.5 22 0:58 00:25 33.8 21 1:03 00:30 34 20 24 53 1:07 00:00 4th shift 34 19 1:17 00:10 34.2 19 1:27 00:30 34.7 19 25 60 2:05 00:58 35.7 18 35 47 2:10 00:00 5th shift 36 18 2:55 00:45 38.1 16 3:05 00:00 6th shift 38 15 3:35 00:30 38.4 14

As can be seen from Table 1, the total processing time of all six layers was 3 hours and 35 minutes in total. The pure drying time was about 3 hours and 15 minutes. The first layer (without sand) was dried for 10 minutes, the second layer having reached a surface residual moisture of approximately less than 55% after approximately 20 minutes. The corresponding drying time for the third layer was about 30 minutes, about 58 minutes for the fourth layer, about 45 minutes for the fifth layer, and about 30 minutes for the sixth layer.

The thickness structure of the first ceramic mold sample is shown in the following table: Status dimension Dick growth wax model 35.0 mm 0 mm Cover without sand 35.5 mm 0.25 mm 2nd coating 37.0 mm 0.75 mm 3rd coating 39.0 mm 1.0 mm 4th coating 40.5 mm 0.75 mm 5. coating 42.0 mm 0.75 mm 6. coating 44.0 mm 1.0 mm

According to this table, the slip / sanding composition used had an average layer buildup of 0.8 mm per coating.

The table below shows the drying parameters and surface conditions for another seven-coating ceramic sample. The prevailing in the drying chamber flow rate was about 1.5 to 2.0 m / s.

Ceramic mold II

Time [h: min] Drying time [h: min] coating drying conditions surface conditions Temperature [° C] Humidity [%] Temperature [° C] Humidity [%] 00:00 00:08 Without sand 33.7 17 00:08 00:00 2 layer 34.3 17 00:18 00:10 34.7 17 00:28 00:00 3 layer 35.2 15 0:58 00:30 36.8 14 26.4 55 1:01 00:00 4th shift 36.9 14 1:31 00:30 37.2 12 29 64 1:36 00:35 37.4 11 27 52 1:41 00:00 5th shift 37 13 2:11 00:30 38.2 10 27.3 58 2:16 00:00 6th shift 38.4 10 2:46 00:30 38 10 27.6 48 2:51 00:00 7th shift 38 10 3:21 00:00 38.8 8th

The following two tables show corresponding measurements on two identical ceramic mold samples with eight layers each and drying at a flow rate between 2 and 4 m / s. The viscosity of the slurry used in these samples was about 38 seconds.

Ceramic mold III / 1

Time [h: min] Drying time [h: min] coating drying conditions surface condition Temperature [° C] Humidity [%] Temperature [° C] Humidity [%] 00:00 00:08 Without sand 35.9 17 00:10 00:00 2 layer 36.5 17 00:30 00:00 3 layer 38.6 14 1:20 00:50 29 70 1:25 00:55 60 1:30 1:00 28.6 45 1:30 00:00 4th shift 37.4 16 2:00 00:30 72 2:05 00:35 27.8 42 2:10 00:00 5th shift 39 15 2:40 00:30 27.9 45/52 2:43 00:00 6th shift 3:13 00:30 38,9 16 76 3:18 00:35 59 3:25 00:00 7th shift 3:55 00:30 65/70 4:00 00:35 48/52 4:05 00:00 8th shift 5:00 00:55 Finished

Ceramic mold III / 2

Time [h: min] Drying time [h: min] coating drying conditions surface conditions Temperature [° C] Humidity [%] Temperature [° C] Humidity [%] 00:00 00:12 Without sand 37.8 12 00:12 00:00 2 layer 37 10 00:32 00:20 39.1 15 27.5 45/59 00:37 00:25 42/58 00:42 00:00 3 layer 38,9 14 1:20 00:38 39.2 14 29 75 1:32 00:50 42/61 1:37 00:55 39.2 9 29.8 40/52 1:42 00:00 4th shift 38,9 11 2:32 00:00 5th shift 39.8 10 3:02 00:30 30.5 48/61 3:07 00:35 30.4 44/53 3:12 00:00 6th shift 39.5 16 3:42 00:30 44/50 3:42 00:00 7th shift 38.2 9 4:12 00:30 38 13 30 48/52 4:12 00:00 8th shift 4:42 00:30 29.8 47 Immediately melted out

Immediately after the application and drying of the last layer took place in the illustrated ceramic mold samples, the melting of the wax model. Melted in a preheated to 150 ° warming cabinet. After every 15 to 20 minutes, the wax was completely melted out. A visual inspection showed that the samples produced in the drying chamber could be melted out without any damage or cracks.

A ceramic mold sample prepared in parallel under conventional drying conditions (see following table) was completely destroyed by cracks under the selected melting conditions. The comparative sample was prepared in the same manner as the above ceramic molds by repeated precipitation, sanding and drying. However, drying was carried out under conventional drying conditions (no drying chamber was used) and without red-light irradiation but with accelerated ambient air (1.5 m / s).

comparison sample

Time [h: min] Drying time [h: min] coating drying conditions surface conditions Temperature [° C] Humidity [%] Temperature [° C] Humidity [%] 00:00 00:30 Without sand 22 54 00:30 00:30 2 layer 1:30 1:00 22.5 55 1:30 00:00 3 layer 2:30 1:00 25.4 43.7 23.6 67 4:00 2:30 25.0 63 4:15 00:00 4th shift 24.5 48 5:30 1:15 25.0 66 6:15 2:00 25.5 65 6:45 2:30 25.0 69 7:15 3:00 25.6 46 7:20 00:00 5th shift 24.0 51.5 1 day later 21:30 00:00 6th shift 21.0 46 23:00 1:30 23.1 43.2 22.8 66 23:30 2:00 24.0 40.7 23.3 70 24:30 3:00 23.0 58 24:30 00:00 7th shift 25:30 1:00 22.4 42.4 27:30 3:00 25.0 41 25.0 50 27:45 00:00 8th shift 30:45 3:00 26.0 62 Real time here: 17:15; Melt out 24 hours later

As can be seen from the above table, the drying times in the comparative sample are significantly longer than in the samples produced by the method according to the invention.

The strength of the samples according to the invention is also clearly superior to the strength of conventional samples. For the determination of the flexural strength of the ceramic test strips with the dimensions 50 mm x 20 mm x 5 mm were prepared. To prepare the test strips, a silicone mold with several cup-shaped depressions was used. The silicone mold was repeatedly beschlickert, sanded and dried to apply several coatings. Typically, six to eight coatings were made to achieve a stripe height of about 5 mm.

The test strips according to the invention were subjected (partly simultaneously with model screws) to a drying process in the drying chamber at a temperature of about 40 ° C., an air humidity of about 5 to 10% and a drying time of about 30 minutes. During the drying process the strips were irradiated with infrared light. The conventional test strips, on the other hand, were dried at room temperature and at a relative humidity of about 50%. Each layer was dried until the surface moisture was less than 60% (typically many hours to one day). Subsequently, all test strips were subjected to a bending test. Here the strength tester 7/18 of the company Feinmechanik Ralf Kögel was used.

Fig. 6 shows the experimental protocol of the test strips dried in accordance with the invention, and Fig. 7 shows the test protocol for conventional test strips (two green bodies and two fired samples were tested and the test strips were baked for one hour at 950 ° C). A comparison of the respective characteristics clearly shows that the load capacity of the samples according to the invention, at least in the fired state, exceeds the load capacity of the conventionally dried samples by almost 50%. The green compacts dried according to the invention also show a significantly higher load-bearing capacity than the green compacts dried in a conventional manner.

The advantages of the invention are probably due to the fact that at higher drying temperatures, the ion exchange is intensified on the surface of the binder colloids, which allows a strong irreversible binding of these colloids with each other. Furthermore, the intensive, surface-related drying by the infrared light irradiation leads to a stronger diffusion gradient within the applied slurry layer and thus to an accelerated drying. The effect of evaporative cooling can increase the drying temperature, even beyond the temperature at which the model used would lose its stability. This also allows accelerated drying.

Preferably, each coating layer undergoes complete drying to produce an irreversible colloid bond. Thus, the desired final strength of the entire shell is reached immediately after the end of drying of the last layer. In other words, it is no longer absolutely necessary to wait until the last layer has dried to allow the model to be melted / burned out and the ceramic mold to be fired. However, this finding does not preclude, in certain cases, a final, longer final drying.

To achieve particularly short drying times, it was expedient to reduce the humidity in the drying chamber. As part of ongoing testing, humidity has been reduced to below 10%, often to 2% to 8%.

In the experiments, it has been found that the first layer with sanding (usually the second layer applied to the model) dries relatively quickly (about 20 minutes), but the first or the second subsequent layer has an above-average length (to to 60 min) needed to dry completely. The subsequent layers have drying times of typically 30 to 35 minutes. The residual moisture in the dipped layer often increases to over 80% at the beginning of drying, then stays at 65 to about 70% for about 2 to 10 minutes (typically about 5 minutes), almost spontaneously below 50, before the end of drying to be detected % bend.

When using the method according to the invention for the prototype production, it makes sense to work with only one slip of the same viscosity for all coating layers (unit dresser) and only one grain size of the scattering material. The standard slurry results in improved wetting while reducing the flow time to 38 seconds (measured with the WEX cup). By inserting a dip layer without sanding at the beginning of the shell construction with brief drying (typically less than 15 minutes), a sufficient surface quality of the castings can be achieved.

The invention has been explained by way of example with reference to various embodiments. Modifications and additions may be made by those skilled in the art based on their expertise. In particular, the position, the positioning and the number of red light sources as well as the arrangement and the number of fans can be changed.

Claims (25)

Method for producing a shell mold, in particular for investment casting, comprising - Providing a model; - Forming a shell surrounding the model by applying at least one aqueous layer on the model and by performing at least one drying process in layers; and - removing the model from the shell, characterized,
that the drying process above a temperature of 25 ° C and supported by infrared light irradiation is performed. Method according to claim 1, characterized in that
that the drying operation is carried out in a temperature range of about 30 ° C to about 45 ° C, preferably from about 36 ° C to about 42 ° C. Method according to claim 1 or 2, characterized
that several layers are applied to the model and that the maximum drying temperature is substantially increased from layer to layer. Method according to one of the preceding claims, characterized
that the maximum drying temperature during the drying process at least about 5 ° C, preferably at least about 8 ° C, is chosen above a temperature at which a reduction in the stability of the model used. Method according to one of the preceding claims, characterized
that occurs relative rotation between the coated pattern and at least one infrared light source during the drying process. Method according to claim 5, characterized in that
that the relative rotation min, preferably between 1.5 and 4 rpm, takes place at a speed between 0.5 and 8 U / /. Method according to one of the preceding claims, characterized
that the drying process is assisted by a flow of a gaseous medium. Method according to claim 7, characterized in that
that the flow velocity of the gaseous medium between about 0.5 and about 8 m / s, preferably between 1 and 5 m / s, is. Method according to one of the preceding claims, characterized
that the drying process at a room humidity of less than 35%, preferably less than about 20%, is performed. Method according to one of the preceding claims, characterized
that the drying process is carried out for a duration of less than 1 h, preferably for about 25 to 45 min. Method according to one of the preceding claims, characterized
that are applied to the model, three or more layers and the drying period for at least some of the coated layers after the first layer is varied. A method according to claim 11, characterized in that the drying time of the second and / or the third and / or the fourth layer is selected to be longer than the drying time of the other layers. Method according to one of the preceding claims, characterized
that can be applied several layers on the model and the individual drying process is carried out until in each case, until a complete drying of the layer applied last is achieved. A method according to claim 13, characterized in that
is that then assumes a complete drying, the residual moisture of a layer is less than approximately 60%, preferably between about 55 and about 40% weight. Method according to one of the preceding claims, characterized
that the model consists of wax, which is removed at a temperature of more than about 140 ° C by melting from the dried shell. Method according to one of the preceding claims, characterized
is performed that the drying process in a drying chamber (30). Method according to one of the preceding claims, characterized
in that a heat energy required to achieve the drying temperature is supplied by at least one infrared light source (34). Method according to one of the preceding claims, characterized
that the method is used for prototype production. System (10) for producing a shell mold, in particular for investment casting, comprising a precipitator (14) for applying a slurry layer to a model (20); and a drying device (16) for drying the slip layer applied to the model (20), comprising a drying chamber (30) and at least one infrared light source (34) arranged in the drying chamber (30), wherein a temperature of more than 25 in the drying chamber ° C is adjustable. System (10) according to claim 19, characterized
that the infrared light source (34) as heating means for a Trocknungsgasfungiert. System according to claim 19 or 20, characterized
in that a cooling device (38, 40) for feeding a cooled drying gas into the drying chamber (30) is present. System according to one of claims 19 to 21, characterized
Heinz that a device is provided for the drying chamber (30) in addition to the infrared light source (34). System according to one of claims 19 to 22, characterized
in that there is a device (22) for rotating the coated model (20) with respect to the infrared light source (34). System according to claim 19 or 23, characterized
that a sanding device (12) is provided for sanding the coating applied to the model (20) slip. A system according to any one of claims 19 to 24, further comprising a transport device (18) for transporting the model at least between the precipitator (14) and the drying device (16).

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