RU2306194C2 - Method for casting, namely head of engine cylinder unit - Google Patents

Abstract

FIELD: processes and apparatuses for casting parts having inner openings or cavities.

SUBSTANCE: method comprises steps of forming openings and (or) cavities by placing into casting mold one or more casting cores made, for example of sand; making main casting core in core box together with one or more additional casting cores designed for combining with main casting core; applying at least on one additional casting core in its predetermined zones standard-thickness coating made of material destructed at contact with melt metal; forming two coaxial openings in casting core and in layer of coating material; placing in said openings guide for valves of inlet and outlet ducts of head of cylinder unit; placing monolithic group of cores with coating into casting mold for pouring metal. It is possible to make cores onto which coating is to be applied in the form of hollow inserts made of heat resistant material and filled with sand and polymerized resin.

EFFECT: improved quality of cast parts.

13 cl, 10 dwg

Description

FIELD OF THE INVENTION

The present invention relates mainly to technology for the production of foundry parts, in particular it relates to processes for free casting in a chill mold and processes carried out at low pressures, which use casting cores to obtain internal cavities in the casting. A typical example of such a casting process is the process used to make engine cylinder heads, where internal casting rods are needed to create a cooling jacket for cooling water for the engine, intake and exhaust channels, and any other auxiliary cavity.

State of the art

Usually, for medium and large-scale production, the molding of the cylinder head of the engine is carried out by using a stationary external mold called a chill mold, where inside and also sometimes outside, casting cores are required that are inserted (assembled) into the chill mold to create a single body ready for casting.

In the casting process using a chill mold using casting rods made of sand and polymerized resin, the main difficulty is to completely collimate the inner part of the part to be molded to the part that the casting rods form with the outer side that the chill molds, in order to obtain required size accuracy. The cores are created in appropriate molds, called core boxes, and then they are usually pre-assembled in close proximity to the chill mold.

A group of pre-assembled foundry cores is assembled using automatic devices (gripping and clamping devices) and stacked (assembled) in a chill mold. At this stage, it is possible to pour molten metal, which will fill the space formed between the sand casting cores and the chill mold.

Sand ridges, called signs, are created on the foundry cores to hold the group of composable foundry cores in the desired position. Such signs are installed in the chill mold, and they do not represent a part of the product obtained by casting. In the specific case of casting cores for inlet and outlet channels of the cylinder head of the engine, whose surfaces form the final shape of the casting, such casting cores are introduced into the core of the cooling jacket and, during the stage of moving the group of cores into the chill mold, if the assembly is done manually, they are in loose condition due to the presence of gaps that will be filled with a mass of metal. Then they are installed due to gravity to the lower zone of the corresponding passages provided in the casting core of the cooling jacket. When the casting rods for the channels are in contact with the lower part (lower base) of the chill mold, they take their final position.

When the assembly of the casting cores is carried out by automatic devices, the casting cores for the channels are held in appropriate positions relative to the cooling jacket using a special automatic device, but usually only from the flange connection with the inlet and outlet pipelines. The operation fully requires the application of a method that should be carried out carefully.

Since traditional technology requires that the casting cores of the cooling jacket are molded separately from each other, as separate cores, the inside of the core box of the cooling jacket must also be provided with all other elements whose geometric characteristics depend on the external thickness of the parts inside the casting (channels, etc.). n.) and which are intended in the process of subsequent assembly of foundry cores for placement of other cores. However, since the outer portions of the channels are not subject to movement, since they are usually half the height in the cooling jacket, they currently use moving parts controlled by gears, cam shafts or, in the best case, by pneumatic cylinders, almost always moving along inclined axes.

In the case of the cylinder head of the engine, in order to facilitate the extraction of these moving parts, it is necessary to give a greater slope (angle of movement) and deform the channels along the outer thickness, providing excess material to obtain the minimum thickness required by the casting operation. This implies a reduction in the core of the cooling jacket, leading to increased fragility of the core and lower efficiency of the cooling system.

In other cases, the problem of creating a passage for casting cores for channels through the openings provided in the cores for the cooling jacket is solved by dividing the latter horizontally into two halves, which are then attached to each other with adhesive after the introduction of the channels.

However, this implies higher production costs and lower quality of products, primarily due to burrs in the casting, which may occur in the chamber for water circulation, and due to gas bubbles in the casting, which may occur due to the possible contact of the molten metal with adhesive, fastening halves of foundry cores.

Another foundry process, called Lost Foam (gasification casting), consists of creating multiple sectors of polystyrene by using special molds. As soon as these sectors are attached to each other, they become consistent with the part that will be cast. The polystyrene model thus obtained is coated and then placed in a container, which is then filled with vibration with ordinary sand or similar material. Using a special channel for pouring, also made of polystyrene, molten metal is poured into a container. As soon as the polystyrene burns out, it is replaced by a metal, thus forming the desired casting.

This process eliminates the creation and installation of sand casting cores coated with polymer material. On the other hand, however, in addition to various technological problems, it also has the disadvantage in the case of casting the cylinder head of the engine that the shapes of the channels, even having a coating, are not optimal, since their surfaces are molded and, therefore, are directly completed with polystyrene surfaces . Joints may also be present in them, resulting from the joining of polystyrene sectors. In addition, the need to use glue is the main cause of gas bubbles. In fact, this method is almost never applied.

Objectives and advantages of the invention

The aim of the present invention is to eliminate the disadvantages of the prior art mentioned above, by proposing a new casting method that allows you to get products of higher quality castings, thereby reducing the amount of production waste due to defects in size, and additionally introduce new design capabilities.

Another objective of the invention is to provide a casting method that makes it possible to perfectly position each casting rod and easily install the casting cores in a mold or in another bar, regardless of their shape.

Another objective of the invention is to provide a casting method that makes it possible to significantly simplify core boxes, that is, so that they do not have any complex shapes, cutouts and connected movable elements, and which, therefore, will be cheaper, more reliable and easier to maintain .

Another objective of the invention is to provide a method of chill casting for the manufacture of engine cylinder heads, which makes it possible to produce casting cores for the intake and exhaust channels of the engines without any deformation in the outer thickness and having the most variable and complex shapes, as a result of which it is possible to improve the technical engine performance, and engines will be more environmentally friendly in terms of exhaust emissions in accordance with new casting technology.

Another objective of the invention is to provide a method for casting engine cylinder heads. The method makes it possible to introduce channel inserts into castings made of a material capable of withstanding the heat generated by molten metal in order to obtain perfectly smooth channels, which should help increase engine efficiency.

These and other objectives of the invention are achieved through the casting process according to the following claims.

Brief Description of the Drawings

Additional features of the invention will be shown more clearly with reference to the accompanying illustrative and non-limiting drawings. In such drawings:

figure 1 shows the casting cores of sand and polymerized resin to create inlet and outlet channels of the cylinder head of the engine;

FIG. 2 shows a cross-sectional view of a core box for molding casting cores shown in FIG. 1, as an embodiment of the invention using inserts around the inlet and outlet channels.

figure 3 shows the casting cores for channels with inserts used when using the core box shown in figure 2;

figure 4 shows a cross section of the casting cores for channels introduced into the mold for coating them with foam material;

figure 5 shows a group of valve seats and casting rods for channels covered with foam material;

figure 6 shows the core box for the cooling jacket, not yet filled;

Fig.7 shows a core box (Fig.6) with a group of casting cores for the channels shown in Fig.5, which are installed in it;

on Fig shows a group of casting cores, valve seats and a foam coating obtained by molding the casting core for the cooling jacket in the core box shown in the previous drawing, and the valve guides are inserted into the coating;

figure 9 shows a diagram of the completed layout of the casting cores of the chill mold, consisting of a group of casting cores shown in the previous drawing;

Figures 9a and 9b show two enlarged scale details of the layout of the foundry cores, where the black sections indicate the differences in shape and differences in the size of the volume of the cooling jacket, which can be obtained using the thoroughly discussed casting method, compared to the currently existing method. ;

10 shows a layout diagram of casting cores according to an embodiment of the invention using inserts.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention relates to a casting method for producing castings having internal cavities. As you know, such cavities are obtained by installation in a mold, such as a chill mold, designed to receive molten metal, one or more casting cores made of sand and polymerized resin or other material. Such rods, in turn, are made in advance in special casting molds called core boxes. In the case of a larger number of cores, they are manufactured separately, each in the corresponding core box, and then they are assembled with each other before being installed (assembled) in a mold or chill mold. To this end, casting cores are usually provided with additional protrusions and cavities, called positive and negative signs, so that they support each other, and other protrusions of sand, intended for laying in the corresponding areas in the chill mold that do not form casting elements.

The method according to the present invention provides for coating one or more casting cores made of sand or other material with a layer of foam material, such as polystyrene, only in the shaped zones using a special casting mold, and then laying them in a chill mold.

It is assumed that the material for coating the casting cores will be destroyed upon contact with the casting metal, which replaces it, thereby setting the desired thickness of the casting, so that the final surface of the casting will be determined by the surface quality of the casting core.

In particular, the method discussed in detail has been tested and proved to be particularly advantageous in foundry processes that require the creation of a main casting core and one or more auxiliary casting cores. According to the study, after they were created in the usual way in the corresponding core boxes, such auxiliary casting rods are placed in the mold and covered with foam material only in the shaped zone with the thickness required for casting, and then they are laid (pre-assembled) in the main core box, which will still be molded, that is, into an empty one.

In order to receive auxiliary rods already covered with foam, the box with the main casting rod may be empty by the amount of volume corresponding to the volume of the shapes of these auxiliary casting rods, since the shapes and thickness are replaced by the rods and the coating layer. As a result, the box with the main casting core is much easier and cheaper to use, since it makes it possible to exclude any internal cut-out and any movable elements that are required to ensure the placement of auxiliary casting cores. In addition, only the box with the main casting core has external signs of auxiliary cores, which will be pre-arranged in it. After molding the box with the main casting core with sand and polymerized resin, a single monolithic body is obtained, which is already arranged and possesses to a large extent geometric accuracy, consisting of the main foundry core and auxiliary foundry cores, which are integral with the main foundry core due to the coating, which forms the thickness of the casting.

Such a monolithic body can then be easily transported and placed in a mold or chill mold.

In addition to foundry cores made of sand or other material, the casting method discussed in detail can be applied using thin hollow inserts consisting of a heat-resistant material, such as metal or composite material, and intended to be embedded in the molding in order to create perfectly smooth internal surfaces of the cavities. In terms of size, a box with a main casting core is capable of accepting both casting cores of sand and inserts coated with foam.

If inserts of metal or other material are to be introduced into the casting and these inserts have an internal cavity where such a cavity corresponds to the design of the casting rod, these inserts should be installed in a special core box, in which the thickness of the insert is additionally taken into account, after which the box is subjected to molding . The resulting casting core will be provided with signs and embedded inserts only in the contoured area and, in addition to the service function as a support for the inserts, such a casting core will also prevent molten material from entering the hollow part of the embedded insert.

A distinctive feature that allows preliminary layout of already coated foundry cores in a core box that has yet to be molded (empty) makes it possible to give such auxiliary foundry cores any geometrical shape that would otherwise be impossible. Therefore, it is possible to create even several passages, labyrinths and such a shape that was not possible before, and there is no need to perform a sequential layout, but only after molding all the rods.

Therefore, the described process proceeds in the outer thickness of all auxiliary casting cores, which do not have any deformation and are ideal in shape, like drawings, a process that was never possible by traditional technology, as often it was required to create internal forms of a box for the main foundry core movable elements for movement, which could only be created using special deformation.

In any case, the designer in the field of foundry is provided with new technology, which makes it possible to create castings in which even other related parts can be embedded, which are currently cast separately, according to the restrictions that exist in modern traditional casting technology.

This new technology can also be used to stiffen by pre-coating brittle foundry cores with foam to facilitate processing, or to better protect against damage after being pre-assembled in the mold, or to limit exposure to metallostatic pressure.

The aforementioned is achieved as a preliminary arrangement directly in the mold, in this case, the coating thickness can be equal to or less than the thickness of the casting, or by laying the pre-coated foundry cores in another core box that will still be molded, in which case the coating should be equal to the thickness of the casting.

In order to cover both casting cores and inserts with polystyrene or other equivalent material, it is necessary to have a special casting mold consisting of one lower concave half and the other upper concave half, while convex elements consist of casting cores or inserts, on which should be coated.

A mold is created with supporting surfaces for all the core marks corresponding in volume to the core boxes, casting molds or chill molds, taking into account the specific permissible deviations and thermal expansion.

Detailed description of an embodiment of the invention

The described casting method is particularly, but not exclusively, suitable for use in the process of chill casting of the engine cylinder head. In this case, with reference to the accompanying drawings, the main casting rod 11 is a cooling jacket rod, which is a rod designed to create passages for circulating coolant, while the auxiliary casting rods are mainly rods associated with the inlet 12 and exhaust channel 13.

The latter plus other auxiliary casting cores, such as, for example, cores designed to create an exhaust gas circulation chamber and which partly include a cooling casing casting core, are formed in conventional core boxes in a conventional manner. Immediately after molding, such casting cores are installed in a single casting mold 19 (FIG. 4) for coating with foam material 18, such as polystyrene. The valve seats 14, 15 for the intake and exhaust valves can be pre-installed in the specified mold on specific starting points. In addition, the mold can be provided with movable cylindrical pins 16, 17 designed to create seats 16 ′, 17 ′ (FIG. 5) into which the guides 16 ", 17" for the valves will be inserted.

Polystyrene 18 or an equivalent material injected into the mold covers only the shaped zones of the rods inserted into it with the thickness required for casting, thereby excluding the core marks 12 ′, 13 ′ from the coating. Also, valve seats are mounted on the outer diameter, while in the inner part they will be aligned with the conical edges of the casting rods for the channels. For this particular application, valve seats 14, 15 must have a corresponding machining allowance in the inner diameter. The outer diameter of the valve seats is created by a cone corresponding to its inner part, and such a cone is required for the coating material in order to maintain and hold the valve seats in a certain position during further processing, up to the layout in a chill mold or mold. The metal will then block the valve seats on the cast.

The group consisting of channels 12, 13 and valve seats 14, 15 is covered with foam 18 (represents a single body (Figure 5)), then installed (pre-assembled) in the core box 20 for the cooling jacket (Figure 6, 7 ) As can be seen from the above, the core box 20 for the cooling jacket has a very simple design, since it does not contain shapes corresponding to the external thickness of the pre-arranged auxiliary casting cores.

In fact, instead of such forms, there are places of starting points 20 ′ and negative pivot marks 20 ″ (FIG. 6), intended for receiving auxiliary foundry cores with corresponding signs and valve seats covered with foam material. The core box therefore does not contain any cutouts and movable elements.

At this stage, the core box for the cooling jacket is filled with sand and polymerized resin, thereby creating a very accurate monolithic group, where the foundry core 11 for the cooling jacket covers and preserves the outer layer of the casting core for the channels, consisting of foam material on the shaped zones (Fig. 8 ) Therefore, ideal relative positioning is also created between each of the rods.

When the entire group of auxiliary casting cores, valve seats and foam material is molded into a single body with a cooling jacket shaft, the 16 ", 17" valve guides can be automatically inserted into the corresponding seats 16 ′, 17 ′ created in the foam material . Special sealing elements are used at the joints between the foam material and the upper half of the core box for the cooling jacket in order to prevent sand from entering the saddles of the guides during molding.

Valve guides can be solid (without central holes), since machining for introducing valve stems is performed using valve guides embedded in the molding. Among other things, this helps prevent the use of traditional stiffening spacers around the valve guide in the channel casting rods.

The valve guides may be provided with a concave rounded groove in the areas embedded in the foam material, which can hold the valve guides in the cast metal in a certain position when the latter replaces the foam material.

In the upper part of the valve guide, there is often another rod 21 for the longitudinal oil channel, as in the case shown in FIG. 10, or a rod for the valve pusher chamber, which creates the sprues (cast metal supplied during the casting shrink during cooling).

As a result, the upper end of the valve guides will always be guided into the corresponding seat created in the specified upper shaft 21 or in the shaft for the valve follower chamber, and therefore will be locked in the correct position even when the cast metal has destroyed or destroys the foam material around the guides for valves without producing the same destruction of valve guides. In the lower part, the valve guides are introduced and stopped in the corresponding seats 22 created in the casting rods for the channels (Figure 3).

From this moment, a monolithic group consisting of a rod 11 for a cooling jacket, auxiliary casting rods, valve seats, valve guides, foam material together with other casting rods, such as rod 21, can be installed in a chilled form (Figures 9 , 10). During casting, molten metal will destroy and replace the foam, setting the required thickness and introducing valve seats and valve guides.

Figure 10 shows the same arrangement as described above, but where the channel rods consist of hollow metal inserts 23 (or made of another material capable of withstanding the heat generated by the cast metal), filled with sand and a polymerized resin having a support function as well as serving to prevent any penetration of molten metal into the inserts. The inner part of such inserts has the same characteristics with sand rods in terms of size. Sand casting cores and inserts 23 coated with polymerized resin are formed in a special core box 10, for which the thickness of these inserts should be taken into account (Figure 2).

At one end, inserts end opposite the valve seats, while at the opposite end they end flush with the edge of the starting material to create a cast. Since the rods 12, 13 for the inlet and outlet channels or any other auxiliary casting rods are installed (pre-assembled) after they are covered with foam material 18 in the core box 11 for the cooling jacket, there is no structural restriction for the casting rods, intended for channels, and for other auxiliary rods. For example, the inlets can be connected to each other using a single chamber without any horizontal interruption towards the top of the valve seats. Such a chamber can even reach the connecting flange of the inlet pipe and form a single chamber combined with the same pipe without creating any problems with the layout of the cooling jacket. This approach can also be extended to inserts made of another material and embedded in castings.

As a result, the chief designer will have complete freedom in design, since the restrictions associated with today's designs, such as forced passage of pipes through the cooling jacket, are eliminated. For example, as shown in Figures 9a and 9b, the camera water jacket can be created in the form of a more rounded design (black areas) instead of modern inclined surfaces and sharp edges, making it possible to move. Rods for channels along the external thickness also have no deformation, with a constant and ideal thickness, exactly as in the specification to the drawing.

In short, the method of chill casting, proposed and used to create the head of the engine block, allows you to get the following advantages:

- inlet and outlet channels without any internal structural limitations and without deformation in the outer layer and, as a result, with a constant casting thickness;

- inlet and outlet channels, consisting of heat-resistant inserts embedded in the casting process;

- higher geometric accuracy in the position of the inlet and outlet channels and the cooling jacket relative to the combustion chambers;

- a cooling jacket with a large volume for the passage of water in more critical areas;

- valve seats introduced during the casting process;

- valve guides introduced during the casting process;

- the possibility of eliminating the holes created by rod signs designed to support the casting rod for the cooling jacket at the pouring stage, thereby eliminating the machining required for plugging such holes.

Claims (13)

1. A casting method for the manufacture of parts having internal cavities or openings, wherein said openings and / or cavities are created by installing in the mold or chill mold intended for receiving molten metal one or more casting cores made of sand or other material wherein each casting core is made separately in a corresponding core box and, before being installed in the mold or chill mold, a step of coating at least one casting core is provided a layer of material capable of collapsing upon contact with the cast metal, characterized in that the method includes the step of forming two coaxial holes (22, 16 ′, 17 ′), at least in the casting core and in the layer of material covering said casting core, respectively wherein the valve guide (16 ", 17") is installed in said coaxial holes before installing the coated casting cores in the mold or chill mold. 2. The casting method according to claim 1, characterized in that the casting cores are installed in the mold (19) for coating with a layer of material by injection, while the holes (16 ′, 17 ′) in this layer of coating material are obtained using movable cylindrical pins (16, 17), which is supplied with the specified mold. 3. The casting method according to claim 2, characterized in that the guides for the valves (16 ", 17") are continuous, without central holes, and the machining for introducing the valve stems is performed using valve guides embedded in the casting. 4. The casting method according to any one of claims 1 to 3, characterized in that each of the valve guides is performed with a concave rounded groove in the area introduced into the coating material layer to hold the valve guides in the cast metal in a certain position when replaced by metal layer of coating material. 5. The casting method according to claim 1, characterized in that the main casting core (11) is designed to create a cooling jacket in order to circulate the coolant of the engine cylinder head and auxiliary casting rods, which are mainly foundry valve stems (12, 13) for inlet and outlet channels. 6. The casting method according to claim 5, characterized in that the upper part of each valve guide is guided and locked in the correct position during casting into the corresponding seat created in the upper rod (21) for the longitudinal oil channel or for the valve follower chamber. 7. The casting method according to claim 1, characterized in that the casting cores on which the coating is applied are made in the form of hollow inserts (23) made of heat-resistant material. 8. The casting method according to claim 1, characterized in that the casting cores, which are coated, are made in the form of hollow inserts made of heat-resistant material, only on the template zones filled with sand and polymerized resin to create core marks and prevent the penetration of molten metal. 9. The casting method according to claim 1, characterized in that the coating material of the casting cores made of sand and polymerized resin or inserts is a foam material, such as polystyrene. 10. The casting method according to claim 1, characterized in that it further includes the step of layering at least the valve seats (14, 15) for the inlet and / or outlet channels in the mold (19) for coating at least one the casting core with a layer of material capable of collapsing upon contact with the casting metal embedded in said valve seat. 11. The casting method according to claim 10, characterized in that the valve seats in outer diameter are coated with a layer of material. 12. A mold for coating casting cores for inlet and outlet channels in a casting method according to any one of claims 1 to 11, characterized in that it is provided with cylindrical movable pins (16, 17) designed to create at least holes ( 16 ′, 17 ′) in the coating material into which the valve guides (16 ", 17") for the intake and / or exhaust valves will be installed. 13. The mold according to claim 12, characterized in that it is configured to receive at least the valve seats (14, 15) for the intake and / or exhaust valves.

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