JP6746683B2 - Mold for centrifugal casting - Google Patents

Description

The present invention relates to a centrifugal casting mold.

A centrifugal casting method is known in which a cylindrical mold is rotated at high speed around its axis and the injected molten metal is attached to the inner wall of the mold by centrifugal force to produce a tubular member which is a hollow casting.
In the centrifugal casting method, a method of applying a mold coating material in the mold may be adopted in order to easily pull out the molded cast product from the mold and to impart a shape to the outer surface of the hollow cast product. In this case, in order to facilitate the application of the mold coating material and to dry the applied mold coating material, it is desirable to cool the mold in advance to an appropriate temperature when applying the mold coating material.
For this reason, the outer surface of the mold is cooled after the cast product molded from the mold in the preceding casting cycle is pulled out and before the mold coating material is applied in the next casting cycle.

As described above, a technique has been proposed in which the inside of the casting mold is cooled between the casting of the cast product in the preceding casting cycle and the transition to the next casting cycle (for example, Patent Document 1).
Patent Document 1 discloses that when cooling or spraying or spraying a cooling liquid inside a high temperature casting mold, mist generated from the casting mold is recovered to prevent deterioration of peripheral equipment and improve the working environment. This technology is disclosed.

JP, 2004-160500, A

During cooling of the outer surface of the centrifugal casting mold, there was a difference in temperature drop between the parts on the outer surface of the mold, and the mold was deformed due to the temperature difference due to this. Due to this deformation, the mold release resistance when pulling out the cast product in the mold becomes large, a powerful and large device must be used for pulling out the cast product, and the equipment for the centrifugal casting process becomes large. Was having problems.
However, the technique disclosed in Patent Document 1 is mainly aimed at collecting mist generated when the casting mold is cooled, and is a technique such as deformation that occurs when the centrifugal casting mold is cooled from its outer surface. There is no particular perspective on the subject.

Therefore, it is an object of the present invention to provide a centrifugal casting mold that can uniformly cool the outer surface of the mold and can suppress deformation of the mold.

The inventors have found that, as a cause of the difference in temperature drop during cooling of the centrifugal casting mold from site to site, there is a difference in the degree of occurrence of the Leidenfrost phenomenon from site to site of the mold. .. That is, the outer surface of the mold has risen to about 300° C. due to the heat of the molten metal poured inside, and if cooling is attempted in that state, the cooling water will instantly evaporate on the outer surface of the mold, A layer of vaporized gas is generated between the outer surface of the mold and the liquid to cause a Leidenfrost phenomenon that hinders heat conduction, but the degree of occurrence of this phenomenon varies depending on the site of the mold surface.
The inventors of the present invention have focused on the above-mentioned points and, in order to suppress the occurrence of the Leidenfrost phenomenon and make the cooling effect of the mold uniform, provide a heat-insulating coating on the mold surface and lower the interface temperature. The above problem was solved by.
Here, the following technologies are proposed.

(1) A centrifugal casting mold (for example, a centrifugal casting mold 10 described later) having a coating (for example, a coating 10a described below) on an outer surface thereof, the coating serving as an iron oxide film or a main component. A centrifugal casting mold that is a film containing calcium.

In the centrifugal casting mold of the above (1), the coating made of the iron oxide film or the film containing calcium as the main component keeps the interfacial temperature of the mold within a range where the Leidenfrost phenomenon does not occur. Uniform cooling of the outer surface of the mold is not impeded by the Leidenfrost phenomenon. Therefore, the deformation due to the temperature difference in the centrifugal casting mold is suppressed.

(2) The centrifugal casting mold according to (1), wherein the coating is formed so as to cover substantially the entire outer surface.

In the centrifugal casting mold of (2) above, particularly in the centrifugal casting mold of (1) above, the coating is formed so as to cover substantially the entire outer surface. For this reason, the entire centrifugal casting mold is uniformly cooled, and deformation is surely suppressed.

(3) The mold for centrifugal casting according to (1) or (2) above, wherein the coating is a film containing triiron tetroxide among the iron oxide films.

According to the centrifugal casting mold of (3) above, the effect of suppressing the Leidenfrost phenomenon is particularly good. Therefore, cooling of the centrifugal casting mold becomes uniform, and deformation is surely suppressed.

(4) The centrifugal casting mold according to (1) or (2) above, wherein the coating is a film containing calcium as the main component and has a thickness of 0.4 mm or less.

According to the centrifugal casting mold of (4) above, the effect of suppressing the Leidenfrost phenomenon is particularly good. Therefore, cooling of the centrifugal casting mold becomes uniform, and deformation is surely suppressed.

(5) The centrifugal casting mold according to (1) or (4), wherein the coating is a film containing calcium carbonate as a main component among films containing calcium as the main component.

According to the centrifugal casting mold of (5) above, the effect of suppressing the Leidenfrost phenomenon is particularly good. Therefore, cooling of the centrifugal casting mold becomes uniform, and deformation is surely suppressed.

According to the present invention, it is possible to provide a mold for centrifugal casting that can uniformly cool the outer surface of the mold and can suppress deformation of the mold.

It is a process drawing of centrifugal casting performed using a metallic mold for centrifugal casting as one embodiment of the present invention. It is a figure showing the history of the temperature of the metal mold for centrifugal casting in the process of FIG. It is a figure showing the temperature dependence of the amount of bending at the time of cooling of a metallic mold for centrifugal casting. It is a conceptual diagram showing the coating given to the metal mold for centrifugal casting as one embodiment of the present invention.

First, the process of centrifugal casting performed using the centrifugal casting mold of the present invention will be described to clarify the cooling from the outer surface of the centrifugal casting mold, which is the subject of the present invention.

FIG. 1 is a process drawing of centrifugal casting performed using the centrifugal casting mold of the present invention. FIG. 1 shows a process of one cycle of centrifugal casting.
In FIG. 1, the steps of one cycle are performed in the order of (a)→(b)→(c)→(d)→(e)→(f), and this one cycle is cyclically repeated to make a casting product every time. Is made.
In the case of this example, the cast product is a tubular body, and one cast product that is a tubular body is cut into a plurality of pieces each having a predetermined length and processed into a cylinder sleeve of an engine.

In the above process, (a) is a mold cleaning process, (b) is a mold temperature adjusting process, (c) is a coating mold applying process, (d) is a pouring process, (e) is a curing process, and (f) is a process. Is a product drawing process.
In FIG. 1, a cylindrical centrifugal casting mold 10 is installed so that its axis is substantially horizontal. The centrifugal casting mold 10 is rotatably supported around the shaft by two sets of rollers. The two sets of rollers are a pair of rollers 21 on the left side and a pair of rollers 22 on the right side in FIG. These rollers 21 and 22 are rotationally driven by a power source such as a motor (not shown), and the centrifugal casting mold 10 rotates around its axis in accordance with this rotation. On one end side (left side in FIG. 1) of the centrifugal casting mold 10, an annular frame body 11 having an opening (not shown) in the center is fitted. Further, an end cap 12 is detachably fitted to the other end side (right side in FIG. 1) of the centrifugal casting mold 10.
The centrifugal casting mold 10 continues to rotate in steps other than the product drawing step (f).
The centrifugal casting mold 10 is characterized in that the outer surface thereof is coated with a specific coating, which will be described in detail later.

Next, the steps of one cycle from (a) to (f) will be sequentially described.
In the mold cleaning step of (a), the inner peripheral surface of the centrifugal casting mold 10 that is still hot because the work by the coating mold and the cast product is extracted in the immediately preceding cycle is partially shown by the rod 30 thereof. It is cleaned by the brush 31 attached to the tip side of the cleaning mechanism. The rod 30, and thus the brush 31, reciprocates in the axial direction of the centrifugal casting mold 10, at which time the centrifugal casting mold 10 continues to rotate at a low speed of about 180 rpm, for example. As a result, the entire mold, which is the inner peripheral surface of the centrifugal casting mold 10, is cleaned.

In the centrifugal casting mold 10 whose entire inner peripheral surface has been cleaned in the mold cleaning step of (a), a mold material is applied to the inner peripheral surface of the mold to form a mold. The coating mold is formed for the purpose of making it easier to pull out the molded cast product from the mold, but in the case of this example, also for the purpose of forming many fine protrusions or spines on the outer surface of the hollow cast product. is there. A cylinder sleeve processed from a hollow cast product cast by using the above-mentioned coating mold has a spiny transferred to the outer surface. When such cylinder sleeves are placed and cast into the engine block, the cylinder sleeves are firmly held in place by the outer surface spiny.

In order to facilitate the application of the mold coating material and to efficiently dry the coated mold coating material, it is necessary to cool the centrifugal casting mold 10 in advance to an appropriate temperature.
Therefore, in the mold temperature adjusting step (b) following the mold cleaning step (a) described above, cooling water is sprayed from the spray nozzle 41 onto the outer surface of the centrifugal casting mold 10 to cause centrifugal casting mold 10 to flow. Is cooling. That is, the centrifugal casting mold 10 is cooled by the heat of vaporization of the cooling water when the cooling water is sprayed on the outer surface of the high temperature centrifugal casting mold 10. The cooling water is sprayed while the centrifugal casting mold 10 is fitted in the centrifugal casting mold 10 while rotating the centrifugal casting mold 10 at a low speed of about 180 rpm, for example.

However, conventionally, when this cooling is performed, as described above, there is a difference in temperature decrease on the outer surface of the centrifugal casting mold 10, and the mold is deformed due to the temperature difference. It was If the centrifugal casting mold 10 is deformed, there is a technical problem that the mold release resistance at the time of pulling out a cast product becomes large, and it becomes necessary to use a powerful and large-sized device as a work extracting device.
The means for solving this technical problem is a specific coating applied to the outer surface of the centrifugal casting mold 10, which will be described in detail after explaining the steps of one cycle from (a) to (f). I will describe.

In the mold temperature adjusting step of (b), the centrifugal casting mold 10 cooled to an appropriate temperature by spraying cooling water from the spray nozzle 41 is applied to the inner peripheral surface in the following (c) coating type applying step. The mold coating material 60 is applied to the entire mold.
The coating of the coating material 60 in the coating material coating step (c) is performed by the nozzle 52 at the tip of the hollow shaft 51 extending from the coating material supplying device (not shown) into the centrifugal casting mold 10 through the opening of the end cap 12. The coating material 60 is sprayed onto the entire mold, which is the inner peripheral surface of the centrifugal casting mold 10. The hollow shaft 51 and the nozzle 52 spray the mold coating material 60 while moving in the longitudinal direction within the centrifugal casting mold 10.

On the other hand, the centrifugal casting mold 10 itself continues to rotate at a medium speed of, for example, about 1500 rpm, so that the mold material 60 is gradually applied to the entire mold, which is the inner peripheral surface, to form the mold 61.
Further, the temperature of the coating mold 61 at the time of applying the coating material 60 is, for example, about 150°C to 350°C.

When the coating die 61 is formed on the entire inner peripheral surface of the centrifugal casting mold 10 in the coating die coating step (c), next, the molten metal 70 is poured in the pouring step (d). The molten metal 70 is prepared in a melting furnace (not shown), a fixed amount is stored in a pot 71, and the molten metal 70 is poured from the pot 71 through a pouring pipe 73 of a trough 72 into the centrifugal casting mold 10, that is, the coating mold 61. During this time, since the centrifugal casting mold 10 continues to rotate at a high speed of, for example, about 2000 rpm, a centrifugal force acts on the molten metal 70, and for example, (e) after about 90 seconds have elapsed after pouring. In the curing process, a uniform cast product 74 is formed on the inner surface side of the coating mold 61.

Next, in the product drawing step (f), the rotation of the centrifugal casting mold 10 is stopped and the end cap 12 is removed. In this state, the work take-out device 80 is used to pull out the work in which the coating die 61 and the cast product 74 are integrated. The mold release resistance in this drawing is, for example, about 5.0 kN to 9.0 kN. When the coating mold 61 is removed from the drawn work, a cast product 74 having the spiny transferred to the outer surface is obtained. The weight of the cast product 74 in this case is, for example, about 10 kg to 35 kg.

When the product withdrawing process of (f) is completed and one cycle of the process is completed, the next one cycle starts again from the mold cleaning process of (a).

FIG. 2 is a diagram showing the temperature history of the centrifugal casting mold in the process of FIG.
In FIG. 2, the horizontal axis represents the transition of the steps (a)→(b)→(c)→(d)→(e)→(f) of one cycle described in FIG. 1 (that is, the transition of time). And the vertical axis represents the temperature (° C.).
The elapsed time (the approximate time zone in which observation was performed in this example) according to each step (a), (b), (c), (d), (e), and (f) in FIG. 2 and each step More specifically, an example of the temperature of the centrifugal casting mold is shown in the following table.

That is, the temperature of the centrifugal casting mold in the process of FIG. 1 changes as the process progresses as qualitatively represented in FIG. 2, and more specifically, the value as represented in the above table. Take
Therefore, in consideration of the temperature dependence of the bending amount during cooling of the centrifugal casting mold as described below, the temperature range in the above table is also considered.
FIG. 3 is a diagram showing the temperature dependence of the bending amount during cooling of the centrifugal casting mold.
The characteristics of FIG. 3 have been found by the inventors through experiments while conducting various studies.
In FIG. 3, Tk on the horizontal axis is the temperature [° C.] of the centrifugal casting mold 10, and Ti is the interface temperature [° C.]. Here, the interface is a boundary surface between the centrifugal casting mold 10 and the cooling water, and in the case of the present embodiment, the outer surface of the specific coating applied to the outer surface of the centrifugal casting mold 10 is the interface. Corresponds to.
Ti is written corresponding to each value of Tk, and as shown, Ti is lower than Tk, and a temperature gradient corresponding to the difference between Tk and Ti is generated in the thickness direction of the corresponding coating.
The vertical axis represents the bending amount [mm] of the centrifugal casting mold.

As can be understood from FIG. 3, the temperature Tk of the centrifugal casting mold 10 is 270 [° C.] and the corresponding interface temperature Ti is 245 [° C.], and in the region Z1 below this, the bending amount is 0. It stays in a range where there is not much problem such as .05 [mm] to 0.15 [mm]. On the other hand, in the area Z2 above the boundary, the bending amount increases discontinuously as 0.30 [mm] to 0.65 [mm]. Therefore, in the region Z2, the mold release resistance in the product drawing step (f) described above with reference to FIG. It causes problems in terms of quality. That is, when the centrifugal casting mold 10 is eccentric due to bending, a defect that the cast product becomes uneven in thickness occurs, and the spiny also varies.

As described above, the boundary value that the temperature Tk of the centrifugal casting mold 10 is 270 [° C.] and the temperature Ti of the corresponding interface is 245 [° C.] is the boundary value at this temperature, and the boundary value is higher than this. It is estimated that the phenomenon is active. That is, in this high temperature region, due to the Leidenfrost phenomenon, the cooling effect is different depending on the site on the outer surface of the centrifugal casting mold 10, resulting in uneven temperature distribution. It is estimated that the desired bend is occurring.

Therefore, in order to suppress the Leidenfrost phenomenon and efficiently cool the centrifugal casting mold 10, the temperature Tk of the centrifugal casting mold 10 is 270 [° C.], and the interface temperature Ti corresponding thereto is Tk. It can be seen that it is effective to suppress the occurrence of bending if the temperature Ti of the interface is kept so that the temperature becomes equal to or less than the boundary value of 245[° C.].

In order to suppress the occurrence of the Leidenfrost phenomenon and make the temperature Ti of the interface below the boundary value of 245[° C.] to make the cooling effect of the mold uniform, the inventors of the present invention have performed the cooling outside the mold 10 for centrifugal casting. The above-mentioned problems were solved by applying a heat-insulating coating on the surface and lowering the interface temperature.

FIG. 4 is a conceptual diagram showing a coating applied to a centrifugal casting mold as one embodiment of the present invention.
FIG. 4 particularly shows the centrifugal casting mold 10 already described with reference to FIG. 1 and the centrifugal casting mold 10 itself and the coating 10a applied to the outer surface thereof from the viewpoint of the cross-sectional view. ing. In the present embodiment, the coating 10a is a specific one as described below, and by applying such a coating 10a, the above-mentioned technical problem is solved.

Here, the temperature Ti of the interface is calculated by the following relational expression (1).

In this relational expression (1), Tk is the temperature of the centrifugal casting mold 10, Tw is the temperature of the cooling water, ρ is the specific gravity, Cp is the specific heat, and λ is the thermal conductivity. Further, (ρ·Cp·λ) is a physical property value, and in the above relational expression, (ρ·Cp·λ) _k is a physical property value of the coating 10a of the centrifugal casting mold 10 and (ρ·Cp·λ) _w is a cooling property. It is a physical property value of water.

As described above, if the interface temperature Ti is equal to or lower than the boundary value of 245 [°C], the Leidenfrost phenomenon is unlikely to occur. Therefore, physical properties satisfying the condition that the interface temperature Ti is 245 [°C] or less are satisfied. A substance exhibiting a value is suitable for the coating 10a on the outer surface of the centrifugal casting mold 10.

From the above relational expression, the coating 10a having a thermal conductivity λ of 2.0 W/m·K or less satisfies the condition that the interface temperature Ti is 245 [° C.] or less. Therefore, by applying such a coating 10a to the outer surface of the centrifugal casting mold 10, the occurrence of the Leidenfrost phenomenon is suppressed, and the centrifugal casting mold 10 is undesired due to uneven cooling in the cooling process. It turns out that a sharp bend is prevented.

Therefore, the inventors have conducted various experiments, and have specified the film suitable for the coating 10a applied to the outer surface of the centrifugal casting mold 10 by satisfying the above conditions. That is, black rust is commonly called "black oxide", i.e., triiron tetraoxide (Fe 3 _{O 4)} film is an example. In this case, iron hydroxide (FeO(OH)) is usually produced at the same time as triiron tetroxide (Fe ₃ O ₄ ), so it is considered that iron hydroxide is also suitable as a film forming the coating 10a. That is, the iron oxide film is suitable for coating the outer surface of the centrifugal casting mold. In addition, it was confirmed that a film containing calcim and calcium carbonate produced by the reaction of minerals (Ca) in water as a main component was suitable for the coating 10a. That is, a film containing calcium as a main component is suitable for coating the outer surface of a centrifugal casting mold.

In particular, when the coating 10a on the outer surface of the centrifugal casting mold 10 is formed of a film containing calcium carbonate (CaCO ₃ ) or calcium carbonate as a main component, the thickness of the coating 10a is 0.4 [mm] or less. The Leidenfrost phenomenon can be effectively suppressed, and the centrifugal casting mold 10 can be efficiently cooled.

The thickness L of the coating 10a as described above is calculated as a value satisfying the following relational expression (2) under the conditions shown in the following table.
That is, the following relational expression (2) was applied to the calculation:

In the relational expression (2), L is the thickness of the coating 10a, Q _J is the amount of heat that needs to be dissipated, and λ is the thermal conductivity (in the case of this example, calcium carbonate (CaCO ₃ ) or coating 10a containing calcium carbonate as the main component). Thermal conductivity), θ ₁ is the temperature of the coating 10 a on the side in contact with the centrifugal casting mold 10, θ ₂ is the temperature of the outer surface of the coating 10 a to which cooling water is applied, and A is the area of the outer surface of the coating 10. , T is the elapsed time.
In this case, if the elapsed time t is set too long, the casting cycle time will increase and the productivity will decrease, so 30 seconds was set as the upper limit.

The conditions set when the thickness L of the coating 10a is calculated by applying the relational expression (2) are as shown in the following table.

The operational effects of the centrifugal casting mold 10 of the present embodiment described above will be summarized.
(1) In the centrifugal casting mold 10, since the interface temperature of the mold remains within a range where the Leidenfrost phenomenon does not occur due to the coating made of the iron oxide film or the film containing calcium as the main component, the centrifugal casting mold 10 The uniform cooling of the outer surface of 10 is not hindered by the Leidenfrost phenomenon. Therefore, the deformation due to the temperature difference in the centrifugal casting mold 10 is suppressed.

(2) The coating 10a is formed so as to cover substantially the entire outer surface of the centrifugal casting mold 10. Therefore, the entire centrifugal casting mold 10 is uniformly cooled, and the deformation is surely suppressed.

(3) Since the coating 10a is a film containing triiron tetroxide (Fe ₃ O ₄ ) in the iron oxide film, the effect of suppressing the Leidenfrost phenomenon is good. Therefore, the centrifugal casting mold 10 is uniformly cooled, and the deformation is surely suppressed.

(4) The coating 10a is a film containing calcium as a main component and has a thickness of 0.4 mm or less. Therefore, the effect of suppressing the Leidenfrost phenomenon is good. Therefore, cooling of the centrifugal casting mold becomes uniform, and deformation is surely suppressed.
(5) The coating 10a is a film containing calcium carbonate (CaCO ₃ ) as a main component among films containing calcium as a main component. Therefore, the effect of suppressing the Leidenfrost phenomenon is good. Therefore, cooling of the centrifugal casting mold becomes uniform, and deformation is surely suppressed.

The present invention can be implemented with various modifications and changes in addition to the above-described aspects.
The above-mentioned example is the centrifugal casting mold applied to the manufacturing process of the cylinder sleeve (cylinder liner) of the engine.
However, the present invention is not limited to this mode, and is applicable to various molds for centrifugal casting, and when it is applied during the production of a relatively long tubular body or the like, since there is little bending during cooling, pulling out of the cast product Is easy, which is a great advantage in terms of production efficiency and quality control. Here, the quality control advantage is, specifically, the bending of the centrifugal casting mold during cooling is less likely to cause defects such as uneven thickness of the cast product, and variations in spiny formation are also less likely to occur. It becomes a point.

10... Mold for centrifugal casting 10a... Coating 41... Spray nozzle 60... Coating material 61... Coating mold 70... Molten metal 74... Casting product

Claims (1)

A centrifugal casting mold,
With a coating on the outer surface,
The coating is a film whose main component is calcium carbonate , which covers the entire outer surface of the mold and has a film thickness in the range of 0.2 mm to 0.4 mm.

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