RU2231414C2 - Method for producing large-size castings having complex-shape inner cavities with use of investment patterns - Google Patents

Abstract

FIELD: manufacture of complex-shape castings with use of investment patterns.

SUBSTANCE: method comprises steps of placing core of water soluble salt into press-mold; fixing core by means of marks and supporting insertion piece in order to prevent its damage; in order to eliminate cracking and shrinkage of pattern, fastening metallic inserts in press-mold for forming voids in thickened zones of pattern; pressing-in to press-mold pattern composition; extracting pattern out of press-mold together with insert and supporting insertion piece; then removing insert and insertion piece from pattern; closing holes after insert with pattern composition; closing void formed in pattern after removal of insert by means of plug; assembling patterns to unit; washing pattern unit and applying ceramic coating; forming openings in envelope in zones spaced from pouring basin for discharging pattern mass at melting it.

EFFECT: improved quality of castings, lowered labor consumption of process.

4 cl, 13 dwg, 1 ex

Description

The invention relates to foundry, in particular to the manufacture of large-sized castings of variable cross-section with developed internal cavities of complex configuration, according to investment casting.

A known method for producing large castings according to investment casting (SU 1567316, 22 C 9/04, 03.03.08.87, 05/30/90), including the manufacture of models of castings by pressing the model mass into a mold with a form-preserving core of water-soluble salt, dissolving the core in water, assembly of the model block and the gating system on a metal frame, the manufacture of the ceramic shell, removal of the model composition from it, calcination of the ceramic shell, pouring it with metal. A water-soluble form-preserving rod for strength and fixation is mounted on the rod support element, which is a metal frame. The specified core dissolves after the assembly of the model block, the frame falls off.

This method is used for the manufacture of thin-walled parts having an extended surface. If it is necessary to manufacture large-sized castings containing thin-walled and thick-walled elements, this method does not provide the required quality of the model.

A known method of producing large-sized castings of variable cross-section on investment casting (Ya. I. Shklennik and others. Lost wax casting, M., 1984, pp. 166-167, 217-228, 228-239, 278-279), including making models of castings by pressing the model mass into a mold with a rod of water-soluble salt, fixed with signs, dissolving the rod in water, assembling the model block and the sprue system from model links of small castings on a metal frame, manufacturing a ceramic shell, removing it model composition , Zaformovyvanie filler, calcining the ceramic shell, filling it with metal.

To obtain thickened parts of the model, the method uses inserts from the model composition. The inserts are made in advance and put in the mold before pressing the model. Then they are removed during the flooding together with the model.

Inserts from the model mass can reduce the temperature deformations of the model and, as a consequence, reduce the model tightening and cracks.

The manufacture of a ceramic shell in the known method is carried out in layers. When applying each layer, the surface of the model block is wetted with a refractory suspension, sprinkled with granular refractory and dried.

Removal of the model composition is carried out by smelting. The ceramic shell is molded with a dry filler, the filling of which is carried out on a vibrator table. In this case, the entire ceramic shell is molded in one step. The flask is mounted on a vibration table, the ceramic shell is placed in the flask on a pre-prepared pillow of dry filler, the filler is poured into the flask, and vibration is turned on.

Annealing a ceramic shell and pouring it with metal is carried out by known methods.

The disadvantages of the method include the following. The thick-walled assembly of the model is retained until the model is heated and, when the model mass is heated, when the model is heated, it can deform the ceramic shell due to thermal expansion.

For large volume castings, the consumption of model mass increases, in addition, a special mold is required, which is manufactured separately.

The inserts used in the known method are not always applicable, but only on the details of a simple configuration.

When performing the indicated cavities in the models by the rod, when pressing the model mass, breakage of the rod is possible due to the large load on it. It is impossible to make extended complex cavities in models.

In the known method, it is impossible to assemble a heavy model block for large castings on a metal frame-riser due to the lack of strength of the model mass.

In the process of model flooding, parts of the ceramic shell that are massive and remote from the sprue bowl may undergo deformation. In addition, it is difficult to remove blockages from the removed parts of the ceramic shell.

For castings with complex extended cavities in the voids of the ceramic shell when filling with filler, leaks can remain, which leads to breakdowns of the ceramic shell by metal during the pouring process.

The task to which this technical solution is directed is to improve the quality of castings and reduce the complexity, due to

- exclusion of defective models for defects in shrinkage tightening, cracks, rod breakage,

- exclusion of cracking of the ceramic shell during the smelting of the model composition,

- creating the strength of the model block and the convenience in working with it,

- simplifying the removal of the ceramic shell from the internal cavities of the casting,

- exclusion of penetration of the shell in places of internal cavities during pouring of metal.

To do this, in the method for producing a large casting with internal cavities of a complex configuration according to investment casting, including the manufacture of model block elements by pressing the model mass into molds with soluble salt rods installed in them to perform internal casting cavities, removing rods in water, assembly of the model block on a metal frame of model elements, the manufacture of a ceramic shell, removal of the model composition from it, molding of the ceramic shell with molder, calcining the ceramic shell, pouring it with metal, according to the invention, for supporting the rods in the mold, support liners are installed that are removed from the model after removing it from the mold, the holes from the support liners are sealed with a model mass until the rods are removed, to form voids in In thickened areas of the model, metal inserts are installed in the mold, which are removed from the model before the assembly of the model block, the voids inserted by the inserts are covered with plugs from the model mass.

To create strength for the volume model block and the convenience of working with it, the assembly of the model block elements is carried out on a prefabricated prefabricated metal frame with handles along the axis of gravity of the model block, on which the elements of the casting model and the gate-feeding system are mounted.

The prefabricated metal frame is removed from the ceramic shell after the model mass is refluxed.

In order to prevent cracking of the ceramic shell, additional holes are made in it in places remote from the sprue bowl, which are blocked after the model mass has been fused with ceramic plugs.

The molding of the ceramic shell with the filler is carried out sequentially in two stages, at the first stage, the voids in the ceramic shell are filled in the places where the casting cavities are formed, at the second stage, the ceramic shell is completely filled with the filler.

The use of metal support liners installed in the mold in critical places and removed from the model after it is pressed in allows the rod to withstand a higher load when pressing the model mass into the mold at high pressure by reducing the length of the shoulder of the application of force. High pressure is required by technology. In sandy-clay forms, rods are supported by metal foals. In investment casting, rod support did not exist. The draws are not suitable for this purpose for several reasons. Firstly, they can move when the model mass is pressed in, because it is impossible to fix them in the mold. Secondly, there is a danger of unsupervised, especially in the thin-walled parts of the casting. In addition, the foals are oxidized during calcination and scaling is formed. When the rod is soaked in water, the foals are oxidized, etc.

In castings of complex configuration (variable cross-section), to exclude temperature defects of the model (tightening, cracks, shrinkage, etc.), the model mass is pressed into a thick paste at high pressure. The minimum insertion temperature and pressure depend on the content of the components and the complexity of the configuration of the part.

In the prototype, the insert eliminates model defects. In the proposed solution, the insert eliminates defects in both the model and the ceramic shell when the model is refluxed, it is more convenient to use, because is part of the mold of the model. The void formed by the insert is blocked by plugs from the model mass.

The metal frame is made in the form of a three-dimensional spatial structure for models widely located in space, of large weight.

Prefabricated metal frame manufacturing allows:

- to obtain volumetric model blocks, and due to this, complex large-sized castings, while it can be removed in whole and in part, depending on the design of the casting,

- increase the strength of the assembled model block,

- the handles allow you to hold the model unit during technological operations, which increases the convenience in work,

- Often, the remaining holes from the metal frame are fenders.

The implementation of additional holes remote from the sprue bowl of the ceramic shell, subsequently blocked by plugs, simplifies and reduces the time it takes for the model mass to exit the ceramic shell during flooding, and prevents cracking of the ceramic shell. Holes are used to purge the ceramic shell to remove blockages.

Sequential backfill in two stages during the molding of the ceramic shell allows the creation of conditions for the necessary sufficiently dense filling of the internal voids of the ceramic shell to prevent penetration by metal during pouring.

Figure 1 presents a sketch of the finished part, a General view (shown conditionally, in fact, the blade from the entrance to the output is rotated 90 °);

Figure 2 - model, General view.

Figure 3 - model, view A.

Figure 4 - mold assembly, General view.

Figure 5 is a complete mold, view B.

6 is a profit model.

7 is a model of the sprue bowl.

On Fig - a metal frame for assembling a model block.

In Fig.9 - model unit assembly.

Figure 10 - model block Assembly, section, deployed 90 °.

In Fig.11 - the warming of the model mass from the mold.

On Fig - a device for forming the inner cavity of the casting.

On Fig - molded into the flask ceramic form, after filling the internal cavities with filler, ready for filling.

The method is as follows.

Water-soluble rods are installed in the iconic parts of the mold, consisting of two half-forms, on additional support liners. All elements of the model block are pressed into molds in which detachable metal inserts are made in thickened places.

Models are pressed with a model mass based on paraffin and ceresin, the required strength characteristics and physical properties of the model mass are regulated by the rosin and VD polyethylene content, and the model quality by pressing parameters: temperature and pressure.

After pressing and removing the model, the inserts and support liners are removed. The voids from the liners are blocked by prefabricated plugs from the model mass, the holes from the supporting inserts are sealed with the model mass.

To assemble the model block, a prefabricated metal frame is prepared, the design and fastening of which depend on the model block being assembled. The metal frame is equipped with handles that are located on the axis of the center of gravity of the model block. A thin layer of 1-2 mm of model mass is applied to the frame by dipping.

When assembling a model block, all elements are soldered together and at the same time firmly attached to the frame. In the areas of the model block remote from the sprue bowl, cone-shaped models are soldered in the form of round or oval plugs 10-12 mm thick.

On a model block in a known manner, similar to the prototype, 5-6 layers of ceramics are applied using air drying in layers.

When using vacuum drying, the voids are punctured with a thin needle. Before applying another layer of ceramic, the needle is inserted into the hole, and before drying, the hole opens. When applying each layer from the ends of the sprue bowl and “breakdown”, the ceramic is cleaned.

In a known manner, from the ceramic mold, the model mass is refluxed in its melt at a temperature of 18 ± 10 ° C or by other known methods (autoclave, etc.)

For refluxing, ceramic molds are set so that when released from the model mass, the mold and frame remain in a stable state. The frame is removed from the hot mold after the model mass is fired.

After draining the model mass, the hot ceramic mold is immersed for 5-10 minutes in a bath of water with a temperature of ≥ 90 ° C with a sprue bowl up. The washed ceramic mold is dried in a known manner. After drying, the sprue bowl and the holes from the frame are sealed with thick paper, and ceramic plugs pre-manufactured using serial technology are inserted into the cone-shaped holes and the places of their installation are covered with putty, for example, from fireclay flour on liquid glass. Then the ceramic shell is molded into a flask, for example, with a dry filler. Forming is carried out in two stages. At the first stage, internal forming cavities are filled, after which the ceramic shell is completely filled with the filler.

Calcination of ceramic molds, metal smelting, mold casting, knocking out castings from the flask are carried out according to well-known technology.

The removal of ceramic shell waste and backfill from the inner cavity of the casting is carried out simultaneously with the beating of the ceramic shell from the outside of the casting in a known manner.

An example of a specific implementation of the method is considered on the example of casting the impeller of a high-pressure pump of the type TsNS-180, in which the wall thickness of the hub is up to 20 mm, the thickness of the blades is up to 6-7 mm, and the diameter of the wheel is 310 mm. The inter-disc distance is variable and is divided by seven thin blades, the plane of which is 90 ° turned along its length. At the entrance, the end of the scapula is in the horizontal plane, at the exit - in the vertical. In all the drawings, for illustrative purposes of the protected elements of the technology, the blade is shown in one (vertical) plane. The weight of the cast billet is 14 kg, the draft weight is 24 kg.

The rods 1 made of water-soluble salt made according to the well-known technology are installed in a mold consisting of two half-molds 2 and 3, for fitting the model. The water-soluble rod 1 is fixed with signs 4 and rests on the support liner 5. In the upper half-mold 2, the insert 6 is attached. In the lower half-mold 3 is attached the insert 7. The inserts 6 and 7 are fixed by means of a fastening (not shown in the drawing), which passes through the walls of the half-mold 2 and 3, for example, in the form of a bolt or screw, which is screwed into the threaded hole of the insert 6.7. The fastening of the insert 7 after pressing is removed from the outside of the mold 3. The insert 6 is removed along with the upper half of the mold. Inserts 6.7 form voids in the thickened areas of the model. The half-molds 2,3 are fastened with coupling bolts 8. Through the press-in hole 9, the model mass is pressed in a known manner.

All elements of the model block are pressed with the same model weight into separate molds. The model mass with the content of components: ceresin 23%, paraffin 67%, polyethylene 4.2%, rosin 5.8% is pressed into a thick paste with a temperature of 58-65 ° C.

The model is kept in the mold under pressure for 10 minutes, after which the pressure is removed, the insert 7 is fastened, the ties 8 are removed. The mold is held for 20 minutes. After that, plugs 10, prefabricated from the model mass, are also dismantled. The profit models 11 and the sprue bowl 12 are pressed in with inserts and, after their extraction, the voids are closed with plugs.

On Fig shows a view of how to remove the model together with the insert 7 and the supporting liner 5. From the removed model remove the supporting liner 5, and the hole from it is closed with a model mass. Then insert 7 is removed, and immediately a metal frame 13 of three rods connected to the upper part by two couplers 14, 15 is inserted into the voids formed. Grooves 16 are made at the ends of the extreme rods for fastening the rods in the model. The model mass is applied to the frame. The protruding parts of the middle link 13 are handles for working with the unit.

Figure 10 shows the assembled model block, where the voids formed by the inserts in the casting model, profits, and the sprue bowl are blocked by plugs 10. When assembling the model block, the frame extreme thrusts are installed in sockets 17 on the casting model, which were made when the model was pressed into the press form, and filled with model mass. After the model mass poured into the nests 17 hardens, the model 11 arrived and the model 12 of the sprue bowl are successively soldered to the casting model and the frame. In the lower part of the model block, cone-shaped models of 19 “plugs” from the model mass are soldered onto the hub of the impeller model 18 to form holes 20 in the forming ceramic shell 21. The finished model block is transferred for applying ceramic.

When applying ceramic, the average thrust and cross ties of 14.15 metal frames are used to hold and suspend the block.

The washing of the model block and the application of ceramic coating is carried out according to known technology on a suspension of distensilimanite in a hydrolyzed solution of ethyl silicate, followed by sprinkling with granular electrocorundum. Before drying each layer, the deposited ceramics are cleaned from the end of the bowl 12 and the end of the “plugs” 19. In total, six layers are applied to the model block. After each layer, the block is suspended by a tie 14.15 in a ventilated chamber for 3 hours.

Removing the model mass from the ceramic mold is carried out according to known technology. The block is placed in the basket 22 on special supports 23 (Fig. 11) so that when freed from the model mass, the frame and ceramic form remain in a stable state. The basket is lowered into a bath 24 with a model mass heated to a temperature of 180 ± 10 ° C. After 20 minutes, the basket 22 is lifted, the mass drains, the freed frame is removed, the remaining model mass is drained from the ceramic shell 21.

Hot ceramic mold 21 is installed in the sprue bowl up into the basket and immersed in hot water at a temperature of ≥ 90 ° C for 5-10 minutes.

The washed ceramic shell 21 is dried at a temperature of 100-200 ° C according to known technology. The dried ceramic shell 21 is tested and blown with compressed air through a gate 12 and openings 20 in the lower part of the ceramic shell. Then in the holes 20 are installed ceramic plugs 25, made in advance according to the known technology, and putty putty with finely ground ceramics on liquid glass.

The sprue bowl and holes from the frame are sealed with thick paper. The hole 26 on the outer diameter of the disk is sealed with adhesive tape or paper.

The ceramic shell 21 is installed, for example, in the device (Fig. 12) for filling the internal cavity of the ceramic shell with a dry filler prepared from crushed waste ceramic shell formed after the ceramic is beaten. The device is equipped with a vibrator. The device consists of an inclined rotary table 27 having an angle of inclination of 3-5 °, on which a removable plate 28 with a fixed stand 29 is mounted. A ceramic shape is inserted into the stand hole of the gating cup down. The form is placed by a disk on a stand, sheathed with soft rubber 30. A gap of 5-10 mm should remain between the sprue bowl and the removable plate. A felt (or felt) ring 31 is mounted on top of the ceramic mold. A soft plug 32 is inserted into the central hole of the ceramic shell. The filler is poured into the central hole of the ceramic shell to the top of the felt ring 31. The vibrator is turned on. As it settles, the filler is refilled so that its level is slightly higher than the upper edges of the felt ring. During vibration, the table is rotated about an axis two to three times. Compaction lasts 40-50 s. After the vibrator stops, the felt ring is removed. A flask 33 is mounted on the ceramic mold, which is attached to the removable plate 28. The fixed flask is removed and canted. The removable plate with stand are removed, the soft cork is removed. The flask is filled up with filler and compacted by vibration.

The implementation of the invention will improve the quality of castings while reducing the complexity of the process.

Claims (4)

1. A method of producing a large casting with internal cavities of a complex configuration for investment casting, including the manufacture of model block elements by pressing the model mass into molds with soluble salt rods installed in them to perform internal casting cavities, removing rods in water, assembling the model block on a metal frame made of model elements, the manufacture of a ceramic shell, removal of the model composition from it, molding the ceramic shell with filler, roasting the ceramic shell, pouring it with metal, characterized in that for supporting the rods in the mold, support liners are installed that are removed from the model after removing it from the mold, the holes from the support liners are sealed with a model mass until the rods are removed, to form voids in thickened at the places of the model, metal inserts are installed in the mold, which are removed from the model before the assembly of the model block, the voids inserted by the inserts are covered with plugs from the model mass. 2. The method according to claim 1, characterized in that the assembly of the elements of the model unit is carried out on a prefabricated prefabricated metal frame with handles along the axis of the center of gravity of the model unit, on which the casting models with the gate-feeding system are mounted, and the prefabricated metal frame is removed from the ceramic shells after refluxing the model mass. 3. The method according to claim 1, characterized in that in the ceramic shell in places remote from the sprue bowl, additional holes are made that are blocked after the model mass has been fired with ceramic plugs. 4. The method according to claim 1, characterized in that the molding of the ceramic shell with the filler is carried out sequentially in two stages, at the first stage, the voids in the ceramic shell are filled in the places where the casting cavities are formed, at the second stage, the ceramic shell is completely filled with the filler.

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