HU210241B - Method for making large sized mould for precision casting - Google Patents

Abstract

The present invention relates to a method for making a mold for precision casting, whereby a sample of material to be destroyed is prepared on the basis of a master pattern, immersed in a coating sludge, the coating sludge is dried, and the coating of the coating sludge is thickened as necessary, then the resulting coating is bound and fired. The essence is that the master pattern is divided into several parts along at least one resolution plane, the sample being split into two planes (33) that can be inserted into two planes parallel to the resolution plane, is produced as a thin-walled wax sample. 14 pages (including 4 tabs)

Description

Scope of the description: 14 pages (including 4 pages)

HU 210 241 ák, in the wall of the wax samples several holes (12) are made in the wall of the parts, a passageway (16) inlet to the one of the parts is connected to a deflecting funnel, then immersed at least twice in the coating sludge and coated with a corundum mixture in the fluidized bed, then into the holes (12) in the holes (12). the outer and inner wall coverings are connected to each other by clamps (15), then immersed in at least one denser coating sludge used at the previous immersion and sprayed with a mixture of corundum with a larger particle size than before, and the wax sample is melted in a known manner and coupled with the clips (15). , the body comprising the inner core (18) and the shell-like outer shape (17) is burnt out, the fitting shapes (33) are released, the sealing remains closed, the now open surfaces of it are sealed, e.g. si along formations (33) are aligned and secured along projections formed on the resolution plane.

The present invention relates to a method for making a larger mold for precision casting, whereby a sample of material to be destroyed based on a master pattern is immersed in a coating slurry, the coating slurry is dried, a further layer of the coating sludge is thickened as required and the resulting coating is bonded and burned. . The method according to the invention makes it possible to produce a mold which makes it possible to produce a relatively thin finished product having a small inner wall and having a thin wall.

Lossy pattern precision casting technologies generally consider castings of at least 0.5 m in length, generally at least 2 to 5 kg, which are difficult or impossible to make on the basis of a single sample of lost material (such as a wax sample) using known precision casting techniques. because the pattern cannot be created in a self-supporting structure.

One variant of precision casting is the lost pattern (wax pattern) process, which is subsequently destroyed or melted in the casting process. This is very suitable for the production of complicated objects and parts with an outlined surface. The most important steps of known technologies are, for example, dr. Ferenc Varga's edited book “Foundry Handbook” (Technical Publisher, Budapest, 1985). The detailed description shows that the procedures developed so far require costly tooling, so precision casting is an economical solution for at least a few hundred more than a few thousand items. In addition, the book states that the precision casting technique is practically impractical or at very high cost for hollow products where the cavity exit is smaller than the typical size of the interior space. In order to achieve a precision casting process, the book recommends modifying the construction of such articles, which, however, is unacceptable for, for example, art and craft items.

In the embodiment of the precision casting described herein, a sample is first formed with a suitable tool, for example by means of injection molding, for destruction or melting, of which more are shriveled, i.e. they are also coupled with an element of destruction material, and the samples are coated with a coating containing a refractory binder by immersion or spraying. By burning it, the mold used to produce the final product is obtained. The wiping or melting material may be a wax mixture of known composition, generally 50% by weight of paraffin and 50% by weight of stearin.

The wax pattern precision casting technology is dr. Károly Bakó, József Sándor, dr. Zsolt Szabó and Zoltán Sziló's Paper on Casting Production Technology (Technical Publisher, Budapest, 1986) describes it. The essence of the process is that wax samples are formed by injection molding of a special wax or plastic blend for the manufacture of mainly small, complex shaped castings. In the course of its implementation, a wax pattern of solid material is first formed, from which a final product of solid material is finally produced, so the process can be used only in the manufacture of small massive solid or possibly holes. Additionally, filling larger volumes with molten metal poses a number of problems; in some cases, the quality characteristics of the final product (especially the strength indicators) are unacceptable.

In this process, the bouquets obtained by shrinking solid wax samples are immersed in a coating sludge, or the coating sludge is sprayed onto them to form a foamed coating comprising a refractory binder, mostly ethyl silicate or water glass and a finely divided filler such as quartz flour or silimanite. Optionally, an additional layer of quartz sand or coating layers of the same composition are applied to this coating. The coated bouquets are then embedded in sand, if necessary, after the drying and binding of the molding material, the wax is thawed from the molds. Depending on the composition of the molding material, relatively large molds can be made with a self-supporting structure. This process still does not allow the economical production of thin-walled shell-like castings, individual products with internal cavities, and is generally used for making solid castings.

The aforementioned books show several methods for using hollow precision

EN 210 241 Β castings can be made. They use a core of ceramics or urea, the preparation of which requires separate equipment, separate tooling, and is therefore very costly due to the material. Therefore, this manual suggests that internal hollow castings should not be made by precision casting or only by modifying the construction. This proposal also applies to larger castings, which are produced in parts, then assembled by welding or other suitable means, ensuring surface quality and continuity by surface treatment such as sanding.

The preparation of a mold for facilitating the casting production of shell-like structures is proposed in U.S. Pat. No. 3,775,708, in which the waste-like sample bearing the shell-like structure is externally and internally deposited into a slurry bearing the mold material, and the coating is dried after reaching the required thickness. a part of the coating is removed from the surface to release the pre-formed ribs on the surface of the sample and to separate the outer coating into two separated portions. Removal of the material to be destroyed, for example after defrosting the wax, burns the remainder of the inner part to form a very good surface-quality mold which is well suited for casting the shell structure. The process itself is not traceable to complicated products, above all for the production of cylindrical castings, but it is totally unsuitable for making larger castings using the precision casting method.

On this basis, it can be concluded that the precision casting technology needs to be further developed, especially with regard to mold formation. That is why our goal is to further develop molds for making molds.

The invention is based on the recognition that the mold must be made of several wax samples of a certain size, determined by the resolution of the master pattern corresponding to the casting to be produced, from which part of the mold is separately manufactured by immersing and waxing the wax sample into the sludge. and coating them from outside with a fluidization process and then assembling the parts to form a specially formed core core.

It is therefore an object of the present invention to provide a method by which the mold for precision casting can be produced simply and at a relatively low cost so that the precision casting becomes suitable and economically feasible for the production of larger individual casting products. It is also an object of the present invention to provide precision casting for the production of single or small series products of a shell-like larger size, possibly formed with a large inner cavity.

As a solution to this problem, a method for producing high-quality molds has been developed for precision casting, in which a sample of material to be destroyed is prepared on the basis of a master pattern, immersed in a coating slurry, the coating slurry is dried, the coating of the coating slurry is thickened as necessary and then the resulting coating is sealed. and firing, where according to the invention, the master pattern is divided into several portions along at least one resolution plane, each sample of material to be destroyed in a two-walled wax pattern, with a plurality of warp patterns in the wall of the wax samples, divided into two planes parallel to the resolution plane. , a funnel-like elevation defining an inlet passage is attached to one of the parts, filled with wax as needed, and then applied to the coating sludge v. After submersible immersion in a fluidized bed with corundum mixture and dried as necessary, re-immersed and fluidized bed coated or dried as necessary to increase the thickness of the blend coating, then the terminals connecting the outer and inner walls of the wax sample are attached to each other in the holes, then at least once before immersed in denser coating sludge used for immersion, and mixed with a mixture of corundum with a larger particle size than before, the wax or wax sample material is defrosted in a known manner and the body comprising the inner core and the shell-like outer shape joined with the clips is fired, the fitting shapes are released, sealed during casting the remaining, now open, surfaces of it are sealed, for example, with a shell sand and the parts are joined together along the fitting shapes and formed in the resolution plane they are fixed there along projections. The strength of the finished mold may be increased by a preferred embodiment of the method according to the invention in which the parts along the projections are held together by an elastic material fastening eye and clamped to the parts by tensioning the fastening eyes.

The efficiency of the assembly can be increased by creating a cone-like protrusion crossed by the plane of resolution for surfaces that remain closed during casting along the casting plane.

In the case of a wax sample formed with an internal cavity and in the same casting, it is particularly advantageous to implement the method according to the invention where, after fluid bed coating, a hook is inserted in the inlet passage in the inlet passage on the side of the wax sample facing the inner cavity and a flexible tube connected to the internal cavity is placed in the flexible cavity an air stream that flows through the inner cavity and through at least one bore along the tube to dry the coating or allow its material to be bonded, i.e. crosslinked.

Particularly preferred for the strength of the mold is the process of the present invention, wherein a mixture of an average particle size of 0.15 to 0.20 mm is used for fluidized bed coating, and about 1 mm of average particle size or a corundum blend, while fluidized bed coating is used. two layers, at least two, are applied to the outer surface by spraying.

EN 210 241

The basis for forming the mold is the wax pattern. Therefore, it is very advantageous to implement the method of the present invention by forming an elastic-shaped mold having an expansive opening on two or more separate parts carrying the negative impression of the surface based on the master pattern during the preparation of the wax sample. during the preparation of the mold, embedded in a substrate bearing a portion of the master pattern, preferably a patterning clay, an adapter element (s) adjacent to the master pattern on the surface of the substrate, and, if necessary, a passage corresponding to the filler opening, the remaining part of the surface of the master pattern and the rest applying at least two layers of silicone polymer to the surface of the carrier (s) and the surface of the passage on the substrate, after application of the first layer, but prior to application of the last layer, the coating is mixed; The first layer of cured coating is cured after the application of the last layer of the coating layer, and the surface of the cured first coating is cured with a hardening material, which is hardened to form the first carrier half body, separated from the carrier material, the master pattern is separated from it, the master pattern is removed from it and the master pattern is removed from it, the master pattern is removed and the master pattern is removed from it, the master pattern is removed and the master pattern is removed from it. the surface is cleaned and placed in a cured coating in the first carrier half, then a second coating comprising at least two silicone polymer layers and a layer of mesh-like flexible material on the free surface and the adapter element (s) is prepared, and the second coating is cured. , after the hardening of the cured second coating, the material is coated with a second carrier half-body material to form a solid support structure comprising at least two parts, After opening the silicone polymer layers, the master sample is removed, then the first and second carrier halves and optionally the expelling portion (s) are combined, the mold is retained and supported, and the mold cavity is partially filled with a molten wax mixture. and shaking the mold to form a wax layer from the wax mixture on the inner surface of the mold, before the wax layer has cooled to ambient temperature, the mold is partially filled with a wax mixture and a wax layer is formed from the wax mixture in the previous material, whereby the layers are paraffin and stearin wax in equal proportions, and from 1 to 4% by weight of pine resin and / or a wax blend containing 3 to 5% by weight of polyethylene.

The preparation of the wax layers is facilitated by a particularly preferred embodiment of the method according to the invention, in which the carrier material is preferably plastered with cooling elements, preferably cooling fins and / or cooling coils, while the carrier structure is cooled by the use of the cooling elements in the formation of the wax layers.

Cooling may be avoided if the process according to the invention is preferably carried out by preparing the first and further wax layers with a gradually decreasing, melted wax mixture of the same composition, and pouring the wax mixture into the mold in excess, then forming a wax layer of the desired thickness. after the excess of the wax mixture is poured out of the mold.

The effectiveness of creating the wax layers is improved by the appropriate measure when the cavity is filled with the wax mixture up to three-quarters of its height and then shaken and shaken by irregular movement.

The wax sample and the product to be manufactured from the mold made therefrom allow for a material-saving production if the process according to the invention is preferably carried out by making a wax sample having an average wall thickness equal to the cast thickness of the casting to be made from the master sample with the wax mixture.

A preferred embodiment of the method according to the invention which allows the particularly secure grip of the mold is swallowed by the insertion of reinforcing elements into the carrier material, suitably embedded in the clay.

In the case of complex castings, it is preferred to implement the method according to the invention whereby the mold is formed by dividing the surface of the master pattern into more than two parts and by producing the silicone polymer coating separately on the parts, whereby the expansive parts of the mold are ordered as required.

Practice shows that the silicone polymer coating in the process according to the invention is very useful if the polysiloxane with a relative molecular weight of 30,000 to 600,000 mole and the polysiloxane of relative molecular weight of 100,000 to 200,000 mole is 1: 1 to 2: 1 wt.

1 to 7% by weight of a known catalyst and accelerator, and 0.5 to 35% by weight of a filler, preferably containing 0.5 to 3% by weight of flocked silicate as filler or at least one component thereof.

The strength of the silicone polymer coating is enhanced by the use of a gauze or a plastic or metal flexible web in the process of the present invention as a mesh material.

The production of wax samples and, consequently, the production of molds, and thus the production of a large series of castings from the master pattern, is advantageously accomplished by the method according to which a wax sample formed from the silicone polymer form is formed into a metallic form in metal and further wax samples are formed. made of metal.

Good! It is also advantageous for the known method and the method of the invention to defatten the surface of the master pattern prior to embedding in the carrier material and to coat it with a material that facilitates the removal of the silicone polymer. The present invention will now be described in detail by way of example, with reference to the accompanying drawing. It is in the drawing

Fig. 1 is a top plan view of one embodiment of a silicone mold;

Figure 2 is a cross-sectional view of the arrangement of Figure 1;

EN 210 241

Figure 3 shows the arrangement of a wax pattern in the form, a

Figure 4 is a cross-sectional view of the arrangement of Figure 3;

Fig. 5 is a cross-sectional view of a wax sample having an open surface on a side with holes, a

Fig. 6 is a cross-sectional view of the hollow wax pattern of each side with holes, a

Figure 7 is a side view of the clamp forming the core support required in the mold, a

Figure 8 is a possible design of a hollow mold and inlet system, a

Figure 9 is an enlarged detail of IX of Figure 8;

Figure 10 is a block diagram of a device for venting a hollow shape, a

Figure 11 is a cross sectional view of a hollow form designated for ventilation in a ventilation (drying) position, a

Figure 12 resolution of a larger masterpiece, a

Figure 13 is a cross-sectional view of a wax sample corresponding to the lower half of the master pattern of Figure 12 and a top view of the silicone polymer form receiving it;

Figure 14 is a side view of a fastening eye for assembling the outer shell of the mold, while a

Fig. 15 is a cross-sectional view of a hollow mold in accordance with the invention with a fixing eye and gripper clip.

In carrying out the method according to the invention, the master pattern 4 (Fig. 12) representing the shape of the cast to be produced is first broken down into a portion bounded by the required number of resolution planes 31. The partitioning planes 31, which are generally at a distance of up to 50 cm, are designated at locations that are readily available for machining later. Thus, for example, the master pattern 4 of Figure 12 is divided into two halves, namely the lower part 36 and the upper part 37. In accordance with the resolution planes 31, later positive and negative joining shapes 33 (orientation pins and recesses) are formed later on both coated and uncoated portions of silicone.

In the next step, using a silicone, a multilayer mold is made of each part. For this purpose, in each of the portions designated by the resolution planes 31, in accordance with the principles known as the starting sample, it is generally designated as a longitudinal dividing plane along the longitudinal axis, the parts of the sample surface which are expired as necessary are designed and made, then the master sample 4 is cleaned, the surface is degreased and the soap is wet. as a solution to facilitate separation. The master pattern 4 is then placed in a carrier material, preferably a molding clay or similar mixture (FIGS. 1 and 2), up to the level designated by the dividing plane or the lines delimited by the resolution planes 31, in which elements defining 5 elevations and 6 aeration passages are arranged, or and assembling the wax sample to form an elevation element, such as a 9-piece truncated cone. The elevation 5 later provides a funnel-like space defining a relatively large inlet opening associated with the molded mold, which in the case of a casting having an open cavity at least one side in a plane corresponding to the open cavity, in the case of a cast with a closed cavity, is less demanding, less visible, optionally left open. part of the form to be prepared. On the surface of the substrate 7, the engaging elements (protrusions or recesses) are formed in the dividing plane 3 ', for example by inserting individual-shaped bodies. The carrier material 7 and the master sample 4 contained therein are then placed in a raised frame 1 (FIGS. 1 and 2).

A mixture of 4 master patterns included in the frame 1 and the carrier material 7 in the dividing plane and the associated surface of the substrate 31, for example, comprises a mixture of a silicone polymer as described in the patent specification HU-A 197 238. According to the description, the base mixture is from 30,000 to 600,000 mole relative polysiloxane and

100,000 to 200,000 mole of polysiloxane with a relative molecular weight of 1: 1 to 2: 1 by weight, 1 to 7% by weight of catalyst and accelerator to which 0.5 to 35% by weight of filler is added, and In accordance with the present invention, 0.5 to 3% by weight of the flocculated silicate, such as Aerosil 200 or Aerosil 2000, is applied. After the first layer has been applied and partially solidified, a second layer is applied directly from the same mixture. The latter is provided with a layer of flexible mesh material, such as a mesh, in which generally one or more additional layers of polymer are prepared from said mixture. For the sake of simplicity, the layered structure is not shown in our drawing. The flocked silicate has the function of preventing the silicone polymer from sliding off the heavily bent, vertical surfaces of the master pattern, while the mesh-like flexible layer contributes to making the layered silicone polymer relatively good shape and exhibit favorable strength values. The silicone polymer coating is also applied in the dividing plane, in the resolution plane 3l, to the entire free surface of the carrier material, or to part thereof, or to the 3 'inserting elements therein, and optionally to the portions defining the elevation. Similarly, the expiring parts are applied, on which the same number of polymeric layers are applied on the surface of the master sample 4 on the surface. After the silicone polymer is bonded, the master pattern 4 and the expanse parts together with the material covering them up to the splitting plane 31 and the plane of resolution 31 are cast in the frame 1 with gypsum or the like after the number and size of reinforcing elements, e.g. The protrusion 3 'of the silicone polymer extending from the dividing plane 3 has protrusions 3 and the protrusion planes 31 and 33

HU 210 241 Β adaptive elements have been formed, the negative shape of which also occurs in gypsum.

After the gypsum is bonded, the structure consisting of the bearing clay, the silicone polymeric material 2 of the gypsum-fixed shape 35 and the master sample 4 is reversed, the carrier material 7 is removed and the master sample 4 is removed from the finished half of the mold 2. Its contaminated surfaces are cleaned and returned to the silicone polymer form gripped with gypsum, all of which is incorporated into the frame. The free surfaces of the silicone polymer-shaped mold 2 and the master samples 4 are then coated with a separating composition, such as an aqueous solution of a wash soap, and the surfaces are coated with the same composition of silicone polymer-based mixture as described above, in the form of a screen-like material on the second layer. we also put it on. In this case, the silicone polymer layer of the required thickness is made on both the expansive parts and the free surfaces, and after bonding, the plaster is also applied here, whereby also reinforcing elements, metal wires are used. This provides a silicone mold 2 for defining two half bodies and, where appropriate, a plurality of surface elements designated with a plurality of matching expansions, wherein the interleaving elements in one of the half bodies of the mold 2 represent protrusions forming the recess in the other, and through which the half bodies can be joined to each other to substantially interleave each other. opening will not stay. After the gypsum is bonded, the two half bodies receiving the form 2 are opened, the silicone polymer 2 of the mold 2 and the master samples 4 are removed. The inner surface of the residual cavity follows every small detail of the outer surface of the master pattern 4 with great precision. An elevation is connected to this cavity. The two half bodies on the master samples 4 are formed at each of the parts defined by the resolution planes 31, e.g.

Subsequently, the sealing surfaces corresponding to the resolution plane 31 are formed on the plaster surface embedded in plaster casts made of plaster strips 31 and planar planes 31, and the plaster surface 33, which accommodates them, in a manner corresponding to the plane of resolution 31 (FIG. 13). that do not appear in the casting pattern. 25 In each closure, on the one hand, a free-standing indentation in the resolution plane 31, which is coated with a silicone layer, is formed in the resolution plane 31 against the closure surface 31 of the silicone half body. In this way, a silicone polymer bounded cavity is formed which defines the space required for the fitting of the parts selected on the basis of the master pattern 4, and in which the fitting shapes 33 required for precise assembly are present.

The two halves of the two molds formed with the elevation 5 and the body attached thereto (Fig. 13) can also be made of metal, for example by casting or by metal cutting processes (preferably by copying milling). Metal halves can be used primarily for large-scale production, which are expensive items. However, they make it possible to produce hollow parts of the same mass with high precision, and the mold itself can be automated. Preferably, the metal half bodies are formed from the master sample 4 by a molded silicone mold 2 as previously prepared, the surface of which can be suitably mapped in metal. This procedure is generally traceable to simpler products and is rewarding for large-scale production.

Using the two halves of the two halves including the 5 elevations, the wax pattern is then formed using the mold elements created as needed. Here, the elevation 5 is essentially a funnel-like inlet (FIGS. 3 and 4 and FIG. 15), through which casting mold can be introduced into the silicone mold 2. In accordance with the invention, the casting wax is not the usual composition, but in addition to the paraffin and stearin wax, which is equally present in the known manner, contains 1 to 4% by weight of pine resin and / or 3 to 5% by weight of polyethylene as the additive. This doped mixture is an important element of the precision casting process of the present invention. Accurate dosing of the additive will depend on the particular workshop conditions and is responsible for guiding a relatively fast stacking of the blended mixture along the walls of the mold 2, thereby providing an even thickness of the wax layer 8. In practice, it is heated to a temperature above the melting point of said composition of wax, by filling the inner space of the silicone polymeric material 2 with a melt and allowing a portion of it to solidify along the inner surface. Meanwhile, a plurality of gypsum and form 2 is preferably jogged, shaken by low amplitude movement, and any bubbles that may be present are removed. Thus, on the inner surface of the mold 2, a relatively thin coating layer of wax is formed. After the formation of the first layer, the liquid wax, which is the predominant part of the injected material, is poured out of the interior space after a certain period of time. After a short waiting time, the wax mixture of the same composition but lower temperature is poured into the mold, filling it up to three-quarters of its height, and then the molded material circulates the mold 2, the wax is slipped in it while the gypsum is jogged. This increases the thickness of the deposited wax layer. Here, after a period of time determined by experience, a substantial portion of the wax is poured, and similarly, preferably one or more additional waxes of lower temperature are poured into the mold, the wax layer 8 having the desired thickness is formed by rolling and moving in a circular manner. The thickness of the wax layer 8 is preferably the same as the desired thickness of the finished product. Thus, 11 wax samples (Figs. 5 and 6) are selected from each of the 4 selected specimens. It is advisable to cool the layers between layers if6

EN 210 241, but be careful not to cool to room temperature during the wax, because in this case, the layers of the resulting shell-like wax sample are not sufficiently bonded to each other. If the conditions so warrant, this is necessary due to the construction of the casting to be made, or if the casting work is too hot, the cooling rate may be increased if the gypsum elements of the expired parts have been previously cooled. Likewise, in the clamping plaster body, cooling fins may be provided, or a cooling coil may be used on which cooling water flows.

Generally, wax samples 11 formed in portions of the large masterpiece 4 (e.g., bottom 36 and upper portion 37) generally form a body surrounded by an open surface 13 or an inner cavity 19 (FIGS. 5 and 6). In this latter case, the aperture remaining at the point of elevation 5 is covered with a seal 14. According to the invention, the mold is formed from the wax samples 11, which is the basis for making the cast.

For the purpose of producing the mold, the wax sample 11 formed with the closed and the open inner cavity 19 is first placed in a position corresponding to the closure in the line of the inner opening of the associated part.

A hole of 10 to 10 mm in diameter or 15 openings is made. The wax sample 11 is then coupled with a support consisting of 28 waxes, known in accordance with known principles, which defines an inlet system for subsequent casting, which forms an element similar to the elevation 5. Prior to solidification in the wax 28, 25 hooks were placed (this is the supplemented wax pattern shown in Figure 8 but already coated as a semi-finished product). In the wax sample 11 with both the open and closed inner cavities 19 (5 and 5)

Fig. 6) In a plurality of experimental locations, several boreholes 12 are formed. The number and distribution of the holes 12 depend essentially on the size and complexity of the mold to be made.

In the next step of making the mold, it is immersed in a sludge covering the wax pattern. The composition of the coating sludge is the usual liquid phase of about 95% by weight of 2: 1 by weight of ethyl silicate and denatured alcohol, the residual water is as needed and 0.3 to 0.7% by weight of hydrochloric acid. The viscosity of the coating sludge is adjusted by adding quartz flour having an average particle size of 20 to 80 Nm, so that a dose of about 1 dm ^{3 of} the mixture is flushed out with a hole with a diameter of 4 mm in about 50 to 60 seconds. Preferably, the wax sample is coated to maintain a constant temperature during immersion, generally between 18 and 24 ° C.

The wet surface wax sample 11 taken from the coating sludge is coated with a corundum mixture on the inner and outer surfaces by immersing in the fluid bed according to the invention and then suspended by the hook 25. In the fluidized bed (not shown in the drawing), corundum with a particle size of 0.15 to 0.20 mm is kept in flow.

Generally, by immersing in the fluid bed, two layers are formed, whereby the first layer is allowed to dissipate to a lesser extent before the second layer is prepared, or dried in a wet environment. After the second or possibly additional layer of fluidized bed is prepared, the formed coating is dried.

The holes of the wax sample coated with the bed in the fluidized bed 11 are then shown in FIG. 7, or with similar terminals 15, which are bound to the material of the layers formed on the outer surface of the holes 12 on the edges of the holes 12 and on the surface of the inner cavity. The terminals 15 serve as core supports for the mold to be made. The wax sample 11 is then immersed in a coating sludge, but this time, more thick sludge is used to prepare the fluidized bed. An additional layer (s) of corundum on the so-moistened surface is prepared by spraying with a corundum having an average particle size of greater than, for example, 1 to 1.7 mm, preferably about 1.6 mm. If necessary, an additional 2 to 3 layers of this relatively large particle corundum are also provided, and generally the three layers are sufficient. Prior to applying the material of the fourth and further layers, the wax sample 11 is immersed in a coating slurry that is used or slightly denser than the third layer, and the layers are dried to a greater or lesser degree after application of their material.

As a result of the above steps, a semi-finished product (Fig. 8) having a shell structure covering the wax sample not shown in Fig. 8 is formed, and this shell structure comprises an outer shape 17 and an inner core 18 defining a mold cavity 20. The cavity 20 between the outer mold 17 and the inner core 18, which marks the outer and inner surfaces of the casting to be prepared, is provided with an inlet passage 16 filled with wax. The inner core 18 and the outer shell 17 are capped by the corundum mixture in the holes after the cross-linking of the inner and outer shells, respectively, and in the case of larger inner cores, the clamps of FIG. The clips 15 are externally and internally surrounded by the corundum mixture. A detail of this solution is illustrated in detail in Figure 9, where it can be seen that the outer mold 17 and inner core 18 formed by the coating sludge and the corundum mixture surround the terminals 15 partially or completely. At each of the portions designated at the resolution plane 31, there is a wax-filled cavity 28 between the closure and the part, one of the inner surfaces of which is provided with silicone-polymer or metal-shaped shapes 33 corresponding to the resolution plane 31. In the preparation of the layers, another important step of the process according to the invention, namely drying, is mentioned. This operation is indispensable for a product having a closed inner cavity 19, which must be carried out for as long as the solvent used for the preparation of the coating sludge does not substantially disappear, and the crosslinking of the ethyl silicate does not occur. For this purpose, it is advantageous to utilize the ventilation arrangement shown in FIG. Fig. 25 shows a hollow shape 26, in which the wax sample 11 is still present, is hooked to the hook 27 by the hook 25 and to the outlet 21 of the inner cavity 19 for venting.

A flexible tube 24 fed from a manifold 23 connected to a pressure regulator 22 connected to a pressure regulator 221 is attached. By switching on the fan 21, an air flow starts in the direction of arrow E and the air flowing from the manifold 23 passes through the flexible tube 24 to the inner cavity 19 bounded by the inner core 18, and then exits in the direction of the arrows A, B, C and D, optionally through the holes 12. . It flows along the surface of the coating layer during its flow, creating the conditions for intense evaporation and ventilation. In general, no separate drying of the outer form 17 is required; If not, the required airflow can be maintained along the outer form 17 using the fan 21

The wax sample 11, which is suitably dry and thus well covered by the coating sludge 17 and the inner core 18, optionally carrying the terminals 15 in the holes 12, is then immersed in hot water or other liquid, using or otherwise using elevated temperature. the wax 28 is defrosted from the cavity 20 and from the inlet passageway 5 as inlet 16. The wax 28 can be reused in a known manner for producing wax samples. This results in a self-supporting semi-finished product that is already resistant to minor mechanical stresses and is also burned in a known manner, at a typical temperature of about 900 ° C, to provide some parts of the desired mold. The parts 32 are joined by a hollow space receiving the hollow space. Within the hollow space, the fitting shapes 33 are formed and are disposed in the resolution planes 31, and there is a cone-like projection 25 crossed by the resolution plane 31 in the central region of the hollow space. After removal of the head sections 32, the resulting parts must be assembled and molten metal can be poured into one of them, i.e., the casting, by means of an overflow line 16 connected to one of them.

The wax sample is then immersed in a coating sludge. The composition of the coating sludge is conventional, comprising about 95% by weight of ethyl silicate and denatured alcohol in a 2: 1 weight ratio, the residual water content being between 0.3 and 0.7% by weight of hydrochloric acid. The viscosity of the coating sludge is adjusted by adding quartz flour with an average particle size of 20 to 80 Nm, so that the mixture flows out over a 50 mm to 60 mm hole with a 4 mm diameter hole. Preferably, the wax sample is coated to maintain a constant temperature during immersion, generally between 18 and 24 ° C.

The wet surface wax sample taken from the coating sludge is then coated in several layers with a corundum mixture by immersion in a fluid bed. In the fluidized bed, corundum with a particle size of 0.15 to 0.20 mm is kept in flow. After the first layer has been reduced to a lesser extent and possibly dried, a further layer is prepared by immersion in the fluid bed, and then the finished coating is dried. Subsequently, the above-mentioned preformed holes are provided with pivot-shaped core supports. The wax sample is then immersed in a coating sludge which is, however, denser than the sludge used to make the first two layers. On the wet surface, a layer of corundum is made, preferably by spraying with corundum larger than the above, for example, with an average particle size of about 1 mm. If necessary, we can make up to 4 ... 5 layers, usually 3 layers are enough. Prior to preparing the fourth and further layers, the wax sample is immersed in the coating layer used or slightly denser in the third layer, and the layers are dried.

With the help of the previous steps, a workpiece with a wax-filled inlet cavity is formed, which provides a space between the inner core receiving the wax sample and the outer form. The inner core and the outer shapes are retained by the core supports relative to each other as internal and external shells. Each part has a wax-filled cavity between the seal and the part, one of the inner surfaces of which is provided with silicone polymer or metallic material formed according to the adapter plane.

In the preparation of the layers, another important step of the process according to the invention, namely drying, is mentioned. This operation is indispensable for the inner cavity, which must be carried out for as long as the solvent used for the preparation of the coating sludge does not substantially disappear, the crosslinking of the ethyl silicate or the like is not accomplished. For this purpose, a ventilation arrangement based on the fan is preferably used, such that the product shown in Fig. 3 is hooked to the hook and a supply tube connected to the distributor tube connected to the fan outlet is inserted into its internal cavity. When the fan is switched on, the air flow starts and the air flowing from the distributor pipe into the space enclosed by the inner tube provides intensive ventilation. Separate drying of the outer shell is not usually required, the air in the room is usually suitable for this purpose.

After drying, the product obtained is immersed in hot water or a similar liquid, from which the wax is thawed. The wax can be reused. The burning of the self-supporting product having a lower mechanical stress, thus obtained, at a temperature of about 900 [deg.] C., yields a portion of the mold to be produced, to which a head defining a hollow space is attached. Within the hollow space there are fitting shapes in the respective plane corresponding to the matching planes, and there is a cone-like protrusion 38 passing through the centering plane in the middle portion. These parts must then be assembled.

In the process of assembly, the wall defining the hollow space is first cut, thereby making the connecting shapes 33 and the aforementioned conical protrusion 38 accessible. The latter is also cut off and the resulting opening, which is released under the resolution plane 31, is heated with sandpaper used in casting. The same is true for surfaces corresponding to the resolution planes 31 that are afraid that liquid metal will flow during casting.

EN 210 241

The mold parts are then assembled by aligning the respective surfaces of the lateral projections carrying the adapter shapes 33 and joining the lateral protrusions with the fixing eye 34, such as spring steel clamp 34, or the like, as shown in FIG. . Thus, the shape shown in Figure 15 is obtained.

If the desired product is relatively simple in shape, the inner core 18 may also be formed as a cylindrical or similar shaped grip, such as a solid material, held in place by the clips 15, which are fixed at the center position when assembling the parts. This solution may, if necessary, simplify the proposed procedure considerably, reducing the risk of scrapping.

The molded mold of FIG. 15 is embedded in a preheated aggregate which is compacted by vibration. If the mold according to the invention is properly formed, the outer surface of the cast will be smooth, possibly with a thin line that can be easily removed. In contrast, there is no need to combine the casting with multiple pieces by welding or other process.

The method of the invention provides a relatively large self-supporting mold suitable for the production of shell-like casting, in which a hollow, thin-shell hollow material is obtained in a material-saving manner, and only then requires a simple surface improvement machining.

Claims (20)

A process for making a larger mold for precision casting by preparing a sample to be destroyed on the basis of a master sample (4), immersing it in a coating sludge, drying the coating sludge, re-immersing and drying the coating sludge layer, and firing, characterized in that the master sample (4) is divided into several portions along at least one resolution plane (31), each of which has a destructive sample provided with two alignment shapes (33) parallel to the resolution plane (31). forming a thin-walled wax pattern (11), making a bore (12) at a plurality of locations in the wall of the wax patterns (11), connecting a funnel-shaped elevation (5) defining an inlet passage (16), which is filled with wax (28); fluid bed after immersion in coating sludge The cores are coated with corundum mixture and dried as needed, re-immersed and fluidized bed coated or dried as needed to increase the thickness of the mixture coating, and then the staples (15) joining the outer and inner walls of the wax sample (11) into the holes (12). , then immersed at least once in a coating slurry thicker than that used in the previous immersions and sprinkled with a mixture of corundum of a larger particle size, then melted the wax (28) and the material of the wax sample (11) in a known manner and 18) and a body having a shell-like outer shape (17) is fired, the joining shapes (33) are exposed, and the open surfaces that remain closed during casting are sealed, for example, by sandblasting, and the parts are joined together along the joining shapes and secured along projections formed in the plane (31). Method according to claim 1, characterized in that along the projections the parts are held together by an elastic fastening eye (34) and the fastening eyes (34) are clamped to the parts by a tensioning bandage (35). Method according to claim 1 or 2, characterized in that along the resolution plane (31), at the surfaces that remain closed at the time of casting, a tapered protrusion (38) is formed which is intersected by the resolution plane (31). 4. Method according to any one of claims 1 to 3, characterized in that in the case of a wax sample (11) formed with an inner cavity (19), after the fluidized bed coating, a hook (25) is provided in the inlet passage (16) inserting into the inner cavity (19) a flexible tube (24) coupled to a fan (21), creating an air stream moving along the flexible tube (24) through the inner cavity (19) and at least one bore (12) to dry the coating. 5. A method according to any one of claims 1 to 3, characterized in that during the preparation of the wax sample (11), a mold (2) with elastic material bearing two or more separate portions of the surface of the wax sample (4) is formed by embedding a part of the master sample (4) in a carrier material (7), preferably in a patterning clay, during the preparation of the mold (2), on the surface of the carrier material (7) which adjoins the master sample (4) ') and, if necessary, forming a passageway corresponding to the pouring aperture, extending at least on the other portion of the surface of the master sample (4) and on the surface of the carrier material (7) covering the surface of the passage (s) applying a coating composition comprising at least two layers of a silicone polymer after applying the first layer, but prior to applying the coating, the coating mixture layer is covered with a screen-like flexible material, after applying the final layer of the coating layer, the resulting first coating is cured and the surface of the cured first coating is cured to form a first carrier half body; extracting the master sample (4), cleaning its free surface and returning it to the cured coating in the first substrate half body, thereafter at least two layers of silicone polymer on its free surface and on the surface (3 ') of the formed adapter member (s), and comprising a layer of screen-like flexible material A second coating is prepared, then the second coating is cured, then, after solidification, the second coating is coated with a second carrier half body material to form a solid support structure of at least two parts which upon opening is formed by a silicone polymer layer ( 2) the inside of the master sample (4) is removed, the first and second carrier half bodies and optionally the end portion (s) are joined, the mold (2) is gripped and supported thereafter, and the cavity of the mold (2) partially melted filling and shaking the mold (2) to form a wax layer (8) on the inner surface of the mold (2), partially filling the mold (2) with the wax mixture at least once more before cooling the wax layer (8) to ambient temperature and associated wax layer (8), wherein the layers are formed from a mixture of paraffin and stearin wax in equal proportions and from 1 to 4% by weight of pine resin and 3 to 5% by weight of polyethylene. Method according to Claim 5, characterized in that the first and further wax layers (8) are formed with a gradually decreasing temperature, molten wax mixture of the same composition, and the wax mixture is poured into the mold (2) in excess to form each layer, After forming the wax layer (8), the excess wax mixture is poured out of the mold. Method according to claim 5 or 6, characterized in that the cavity is filled with the wax mixture up to three quarters of its height. 8. Figures 5-7. A method according to any one of claims 1 to 3, characterized in that the wax mixture produces a sample of wax of average wall thickness equal to the wall thickness of the casting to be made from the master sample (4). 9. Method according to any one of claims 1 to 3, characterized in that stiffening elements are preferably incorporated in the support material (7). 10, 5-9. A method according to any one of claims 1 to 4, characterized in that cooling elements, preferably cooling irons and / or cooling coils, are incorporated into the carrier material (7), while cooling the support structure during the formation of the wax layers (8). 11. A method according to any one of claims 1 to 3, characterized in that the mold (2) is formed by dividing the surface of the master sample (4) into more than two parts and by separately producing the silicone polymeric coating on the parts. 12. The process according to any one of claims 1 to 3, characterized in that the silicone polymer coating is a mixture of polysiloxane having a relative molecular weight of 30,000 to 600,000 mole and polysiloxane having a relative molecular weight of 100,000 to 200,000 mole, It is prepared from a composition containing from 1 to 7% by weight of a known catalyst and accelerator and from 0.5 to 35% by weight of a filler. 13. A12. The process according to claim 1, wherein the filler or at least one component thereof in the silicone polymer coating composition is 0.5 to 3% by weight of fluffed silicate. 14. Figures 5-13. A process according to any one of claims 1 to 3, characterized in that the silicone polymer coating is used as a screening material in the form of a binding gauze or a flexible mesh made of plastic or metal. 15. A process according to any one of claims 1 to 3, characterized in that the wax sample formed from the silicone polymer form is formed into a metal form and further wax samples are prepared from the metal form. 16. A method according to any one of claims 1 to 4, characterized in that the surface of the master sample (4) is degreased and coated with a material to facilitate the removal of the silicone polymer before being embedded in the support material (7). 17. A process according to any one of claims 1 to 4, characterized in that corundum having an average particle size of 0.15 to 0.20 mm or a mixture of such corundum is used for the fluidized bed coating. 18. A process according to any one of claims 1 to 3, characterized in that the mixture is sprayed with a mixture having an average particle size of 1 to 1.7 mm or made with such corundum. 19. A process according to any one of claims 1 to 3, characterized in that two layers are produced by fluid bed coating, by at least two layers by spraying on the outer surface and generally by one on the inner surface. 20. A method according to any one of claims 1 to 4, characterized in that the inner core (18) is formed as a cylindrical body which is displaceable on the smallest part of the inner surface of the outer mold (17) or is symmetrical to the inner surface. ) in the center position.