JP2020006383A - Casting production method and casting device - Google Patents

Abstract

To provide a casting production method and a casting device capable of securely reducing the residual stains of a casting with a thickness difference, and further, realizing the reduction of production lead time and the reduction of production cost.SOLUTION: A cooling step S2 comprises: an inner-frame cooling stage S21 of cooling a molten metal in a mold 1; and a temperature difference dissolution stage S22. In the inner-frame cooling stage S21, the molten metal is cooled to above a behavior change temperature in the mold 1. In the temperature difference dissolution stage S22a, after the inner-frame cooling stage S21, at least a part of the mold 1 is opened, and further, a temperature difference between the temperature of a first thickness part T1 and the temperature of a second thickness part T2 is reduced till it reaches the behavior change temperature or lower.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a casting and a casting apparatus.

  Patent Literature 1 and Non-Patent Literature 1 disclose a conventional method for manufacturing a cast product. This manufacturing method is employed when manufacturing a large cast product such as an engine cylinder block. This manufacturing method includes a casting step and a cooling step.

  In the casting step, a molten metal such as cast iron is cast into a cavity of a mold made of a sand mold or the like. In the manufacturing methods disclosed in Patent Literature 1 and Non-Patent Literature 1, an outer mold and a core, which are sand molds, are used as molds, and especially, a core is provided with a pipe for realizing water cooling. In the cooling step, the molten metal in the cavity is cooled into a cast product. At this time, in the manufacturing methods disclosed in Patent Literature 1 and Non-Patent Literature 1, water is circulated in the core pipe to rapidly cool the core. When the temperature of the core reaches 550 ° C., the amount of water supplied to the pipes in the core is reduced.

  According to this manufacturing method, the core can be rapidly cooled by the water in the pipe. At the time when the temperature of the core becomes 550 ° C., the amount of water supplied to the pipe in the core can be reduced to reduce the temperature difference between the temperature of the outer mold and the temperature of the core. The residual distortion of the product can be reduced. For this reason, it is said that the annealing process that is usually performed on the cast product removed from the mold is unnecessary, and it is possible to shorten the production lead time, reduce energy consumption, reduce carbon dioxide emissions, and the like. .

JP 2011-56559 A

"Development of an Annealing-less Casting Technology for Large Cylinder Blocks Using Inner Core Water Cooling" (Monthly Magazine "Materials" Vol. 55 (2014) No / 12 pages 22 to 27)

  However, in the above-mentioned conventional manufacturing method, the residual distortion of a cast product having a difference in wall thickness cannot always be reduced.

  In addition, in this manufacturing method, the core having the pipe must be formed, and the manufacture of the mold requires time and effort. Therefore, it is difficult to reduce the production lead time and the production cost.

  The present invention has been made in view of the above-mentioned conventional circumstances, and it is possible to more reliably reduce the residual distortion of a cast product having a difference in wall thickness, to shorten a production lead time and to reduce a production cost. An object of the present invention is to provide a method and apparatus for manufacturing a cast product that can be effectively obtained.

The method of manufacturing a casting according to the present invention includes a casting step of casting molten metal in a cavity of a mold,
Cooling the molten metal in the cavity to a cast product,
The casting has a first thick portion having a first thickness and a second thick portion having a second thickness greater than the first thickness. ,
The cooling step is a cooling step in a frame that cools the molten metal in the mold until the casting exceeds a behavior change temperature at which the cast product switches from a state showing plastic behavior to a state showing elastic behavior.
After the in-frame cooling step, at least a part of the mold is opened, and the temperature difference between the temperature of the first thick portion and the temperature of the second thick portion is reduced until the temperature becomes equal to or lower than the behavior change temperature. And a temperature difference eliminating step.

  According to the confirmation by the inventor, when the temperature difference between the temperature of the first thick portion and the temperature of the second thick portion at the behavior change temperature is large, the residual strain increases. Further, for example, when cast iron is a molten metal, when the temperature difference at the behavior change temperature becomes 81.6 ° C. or more, residual strain becomes a problem. In order to reduce the residual strain, the casting is gradually cooled in a mold to a temperature lower than the behavior change temperature, or, in the case of cast iron, after reheating the casting to about 600 ° C. Annealing treatment to gradually cool down to the temperature is required. In this case, the production lead time is long, and problems such as securing of energy consumption and increase of carbon dioxide emission arise.

  In this regard, according to the manufacturing method of the present invention, in the temperature difference eliminating step of the cooling step, the temperature of the first thick portion and the temperature of the second thick portion are maintained until the temperature of the cast product becomes equal to or lower than the behavior change temperature. Reduce the difference. Thus, in this manufacturing method, the residual distortion of a casting having a difference in wall thickness can be reduced.

  The behavior change temperature is a temperature at which the cast product switches from a state showing plastic behavior to a state showing elastic behavior. In general, in metals, viscous and plastic deformation occurs quickly at 2/3 or more of the melting point, but viscous deformation hardly occurs at 1/2 or less of the melting point, and under small stress, it is difficult to be plastically deformed and the elastic behavior is low. Show. For cast iron, 550 ° C. is the behavior change temperature.

  Further, in this manufacturing method, it is not always necessary to provide the core with the pipe, and the manufacture of the mold does not always require labor. Further, after the in-frame cooling step, at least a part of the mold is opened, so that a part of the casting can be rapidly cooled.

  Therefore, according to this manufacturing method, it is possible to more reliably reduce the residual distortion of a cast product having a difference in wall thickness, and to effectively reduce the production lead time and the production cost.

  The temperature difference elimination step may include a local cooling step of cooling the second thick part more than the first thick part such that the temperature of the second thick part approaches the temperature of the first thick part. For example, a cooling device that cools the second thick part more than the first thick part can be adopted. In this case, it is possible to more effectively reduce the production lead time and the production cost.

  The temperature difference eliminating step may include a partial mold opening step of leaving a part of the mold around the first thick part so that the temperature of the first thick part approaches the temperature of the second thick part. In this case, the first thick portion is less likely to be cooled by the atmosphere due to the remaining mold portion, and the temperature difference between the temperature of the first thick portion and the temperature of the second thick portion is reduced.

  In the temperature difference eliminating step, it is preferable that the temperature of the first thick portion and the temperature of the second thick portion are equal at the behavior change temperature. In this case, the residual distortion of the casting can be minimized.

  The casting may be a cylinder block made of cast iron and constituting an engine. This cylinder block forms a cylinder bore in which three or more cylinders are arranged in series, and is formed integrally with one end of each of the cylinder portions, each of which has a second thick wall, and the first wall has a first wall. And a crankcase portion that is a thick portion. In this case, the effects of the present invention can be achieved in the cylinder block. In particular, the cylinder portion of the cylinder not located on the outside is less likely to be naturally cooled than the cylinder portion of the cylinder located on the outside, so that the effects of the present invention can be obtained.

The casting apparatus of the present invention is a casting apparatus having a mold in which a molten metal is cast, and a cavity in which the molten metal is cooled to form a casting is formed.
The casting has a first thick portion formed with a first thickness and a second thick portion formed with a second thickness larger than the first thickness,
It is further characterized by further comprising a cooling device that cools the second thick portion more than the first thick portion so that the temperature of the second thick portion approaches the temperature of the first thick portion.

  In this casting device, the cooling device cools the second thick portion more than the first thick portion, and reduces the temperature difference between the temperature of the first thick portion and the temperature of the second thick portion. Thus, in this casting apparatus, the residual distortion of a casting having a difference in wall thickness can be reduced.

  Further, in this casting apparatus, a core is not necessarily provided with a pipe, and a mold is easily manufactured.

  Therefore, according to the casting apparatus, it is possible to more reliably reduce the residual distortion of a cast product having a difference in wall thickness, and to shorten the production lead time and reduce the production cost.

  ADVANTAGE OF THE INVENTION According to the manufacturing method and casting apparatus of this invention, while reducing the residual distortion of the casting with a difference in wall thickness more reliably, shortening of production lead time and reduction of production cost can be effectively demonstrated. .

FIG. 1 is a process chart showing the manufacturing method of the first embodiment. FIG. 2 is a schematic cross-sectional view of a casting mold in a casting step in the manufacturing method according to the first embodiment. FIG. 3 is a schematic cross-sectional view of the cylinder block, the cooling device, and the like according to the first embodiment. The cylinder block in FIG. 3 corresponds to a sectional view taken along the line III-III in FIG. FIG. 4 is a schematic plan view of the cylinder block manufactured in the first embodiment. FIG. 5 is a graph illustrating a relationship between time and temperature according to the first embodiment. FIG. 6 is a graph showing a relationship between the position of the cylinder block and the residual strain according to the first embodiment. FIG. 7 is a process chart illustrating the manufacturing method of the second embodiment. FIG. 8 is a schematic sectional view of a cylinder block, a cooling device, and the like according to the second embodiment. FIG. 9 is a schematic sectional view of a cylinder block, a cooling device, and the like according to the third embodiment. FIG. 10 is a schematic plan view of a cylinder block according to the fourth embodiment.

  Hereinafter, Examples 1 to 4 that embody the present invention will be described with reference to the drawings.

(Example 1)
In the manufacturing method and the casting apparatus according to the first embodiment, a cylinder block W (see FIG. 4) of a vehicle engine is manufactured as a cast product, which is made of cast iron.

  As shown in FIG. 1, this manufacturing method includes a casting step S1 and a cooling step S2. The cooling step S2 includes an in-frame cooling step S21, a temperature difference eliminating step S22, and a natural cooling step S23. In the first embodiment, the local cooling step S22a is a temperature difference eliminating step S22.

  In the pouring step S1, first, the mold 1 shown in FIG. 2 is prepared. The mold 1 has one outer mold 1a, a plurality of first cores 1b, a plurality of second cores 1c, a plurality of third cores 1d, and a plurality of fourth cores 1e. I have. The outer mold 1a and the first to fourth cores 1b to 1e are sand molds formed by molding sand. A cavity 3 is formed in the mold 1. The cavity 3 communicates with a runner and a gate (not shown). The molten metal 5 of cast iron at 1400 ° C. is poured from the port of the gate to perform casting.

  In the in-frame cooling step S21 shown in FIG. 1, the molten metal 5 is cooled in the mold 1 for 70 minutes from the casting step S1. At this time, the outer mold 1a forms the outer shape of the cylinder block W, each first core 1b forms four first to fourth cylinder bores W1 to W4 arranged in series, and each second core 1c A case portion W5 (see FIGS. 2 and 3) is formed, and each third core 1d and each fourth core 1e form a water jacket W6. The first to fourth cylinder bores W1 to W4 are formed in the cylinder portions W7 that are the respective peripheral walls. Thus, the molten metal 5 in the cavity 3 is formed on the cylinder block W. Thereby, the cylinder block W is cooled to about 800 ° C. In this state, the cylinder block W has not switched from the state showing plastic behavior to the state showing elastic behavior.

  Thereafter, a temperature difference eliminating step S22 shown in FIG. 1 is performed. At this time, as shown in FIG. 3, the entire mold 1 is crushed, the molding sand adhered by sand shot is removed, and the cylinder block W is taken out. Then, the cylinder block W is placed on the work table 9 in the plan can so that each cylinder portion W7 faces downward. The worktable 9 is formed with four exhaust holes 9a communicating with the first to fourth cylinder bores W1 to W4.

  The local cooling step S22a is quickly performed on the cylinder block W. Here, the thinnest portion of the peripheral wall of the crankcase portion W5 is defined as a first thick portion T1, and the thickest portion of each of the cylinder portions W7 forming the second and third cylinder bores W2 and W3 is defined as a second thick portion. The section is referred to as T2. Then, the cooling device 7 is mounted on the cylinder block W.

  The cooling device 7 has two cooling rods 7a formed of straight pipes, and an air compressor 7b connected to the rear side of each cooling rod 7a. A plurality of exhaust ports 7c are formed at the tip of each cooling rod 7a by the length of the second and third cylinder bores W2 and W3. Each cooling rod 7a has a positioning pin 7c protruding radially above the exhaust port 7c. The mold 1 and the cooling device 7 are the casting device of the first embodiment.

  In the local cooling step S22a, each cooling rod 7a is inserted from the crankcase part W5 side, and the positioning pin 7c is brought into contact with the upper end of the cylinder part W7 forming the second and third cylinder bores W2, W3. In this state, the air compressor 7b is operated.

  The air compressor 7b blows out normal-temperature air from each exhaust port 7c of each cooling rod 7a. For this reason, the crankcase portion W5 is exposed to the atmosphere and is naturally cooled by air at room temperature, whereas the cylinder portions W7 forming the second and third cylinder bores W2 and W3 are forcibly cooled by air at room temperature. You. The air jetted into the second and third cylinder bores W2 and W3 is exhausted from the exhaust holes of the work table 9 to the outside without staying there. During this time, in the cylinder block W, the first thick portion T1 becomes lower than the behavior change temperature of 550 ° C.

  After performing the local cooling step S22a as the temperature difference eliminating step S22 for 10 minutes, the operation of the air compressor 7b is stopped. Next, as a natural cooling step S23 shown in FIG. 1, the cylinder block W is left in the atmosphere and cooled to room temperature. Thus, the cylinder block W before cutting is obtained.

  For the first thick portion T1 of the manufactured cylinder block W, the second thick portion T2 of the second cylinder bore W2, and the second thick portion T2 of the third cylinder bore W3, the relationship between time and temperature (° C.) is obtained. Was. FIG. 5 shows the results.

  As shown in FIG. 5, in the first embodiment, since the second thick portion T2 of the second cylinder bore W2 and the third cylinder bore W3 is cooled more than the first thick portion T1, the first thick portion T1 is formed. Is 550 ° C., the temperature of the second thick portion T2 of the second cylinder bore W2 and the third cylinder bore W3 is approaching the temperature of the first thick portion T1. Specifically, the temperature difference between the temperature of the first thick portion T1 and the temperature of the second thick portion T2 of the second cylinder bore W2 and the third cylinder bore W3 is 550 ° C., which is lower than 81.6 ° C. It was small.

  As Comparative Example 1, without performing the temperature difference eliminating step S22, immediately after the in-frame cooling step S21, the natural cooling step S23 was immediately performed to manufacture a cylinder block. This cylinder block has not been annealed.

  Further, as Comparative Example 2, the cylinder block of Comparative Example 1 was subjected to an annealing treatment.

  With respect to the cylinder blocks obtained in Example 1 and Comparative Examples 1 and 2, the residual strains of the second cylinder bore W2 and the third cylinder bore W3 were measured at two upper and lower portions in FIG. FIG. 6 shows the results.

  As shown in FIG. 6, the cylinder block obtained in Comparative Example 1 has a large residual strain. This is because the temperature difference between the temperature of the first thick portion T1 and the temperature of the second thick portion T2 is large at 550 ° C. in this cylinder block.

  Further, since the cylinder block obtained in Comparative Example 2 has been subjected to the annealing treatment, the residual strain is small. It is practical if the residual strain is 1000 μ or less. However, it is clear that there are problems such as a long production lead time, an increase in energy consumption and an increase in carbon dioxide emissions.

  On the other hand, in the cylinder block W obtained in Example 1, the residual strain is smaller than that in the cylinder block of Comparative Example 2. This is because, in the cylinder block W, the temperature of the first thick portion T1 and the second thickness are kept until the cylinder block W becomes 550 ° C. or less in the local cooling step S22a as the temperature difference eliminating step S22 of the cooling step S2. This is because the temperature difference from the temperature of the thick portion T2 is reduced. For this reason, it is understood that the residual strain of the cylinder block W can be minimized if the temperature of the first thick portion T1 is equal to the temperature of the second thick portion T2 at 550 ° C.

  In the first embodiment, since there is no need to perform an annealing process, it is possible to shorten the production lead time, reduce energy consumption, reduce carbon dioxide emissions, and the like.

  Further, in the first embodiment, it is not always necessary to provide the pipes in the first to fourth cores 1b to 1e, and the manufacture of the mold 1 does not always require labor. Further, after the in-frame cooling step S21, since the entire mold 1 is crushed, the cylinder block W can be rapidly cooled.

  Therefore, according to the first embodiment, it is possible to more reliably reduce the residual strain of the cylinder block W having a difference in wall thickness, and to shorten the production lead time and reduce the production cost.

(Example 2)
In the manufacturing method of the second embodiment, as shown in FIG. 7, the temperature difference eliminating step S22 of the cooling step S2 includes a partial disintegration and crushing step S22b as a partial mold opening step and a local cooling step S22a.

  In the partial disintegration and crushing step S22b, as shown in FIG. 8, a part of the mold 1 is left around the crankcase portion W5.

  Then, in the local cooling step S22a, the cooling device 7 is mounted on the cylinder block W with the cylinder block W lying down in the plan can, and the air compressor 7b is operated. Thus, when the first thick portion T1 of the cylinder block W becomes 550 ° C. or less, the operation of the air compressor 7b is stopped.

  Next, the natural cooling step S23 shown in FIG. 7 is performed to obtain the cylinder block W before cutting. Other configurations are the same as those of the first embodiment.

  In the second embodiment, the first thick portion T1 is hardly cooled by the air due to the remaining molding sand, and the temperature difference between the temperature of the first thick portion T1 and the temperature of the second thick portion T2 is easily reduced. . Other functions and effects are the same as those of the first embodiment.

(Example 3)
In the manufacturing method according to the third embodiment, in the temperature difference elimination step S22, the cylinder block W is placed on the smooth work table 11 in the plan can so that the crankcase portion W5 faces downward. The worktable 11 is not formed with the exhaust holes 9a as in the worktable 9 of the first embodiment.

  In the cylinder block W, as a local cooling step S22a, the respective cooling rods 7a are inserted from the second and third cylinder bores W2 and W3, and the positioning pins 7c of the cylinder part W7 forming the second and third cylinder bores W2 and W3. Make contact with the upper end. In this state, the air compressor 7b is operated. When the first thick portion T1 of the cylinder block W becomes 550 ° C. or less, the operation of the air compressor 7b is stopped. Other configurations are the same as those of the first embodiment.

  In the third embodiment, the air heated by cooling the second and third cylinder bores W2 and W3 is trapped in the crankcase portion W5, and the crankcase portion W5 is less likely to be cooled than is open to the atmosphere. For this reason, the temperature difference between the temperature of the first thick portion T1 and the temperature of the second thick portion T2 is easily reduced. Other functions and effects are the same as those of the first embodiment.

(Example 4)
In the manufacturing method according to the fourth embodiment, as shown in FIG. 10, the axial fan 13 blows air into the second and third cylinder bores W <b> 2 and W <b> 3 with the cylinder block W lying down in the plan can. The diameter D of the wind sent by the axial fan 13 is smaller than the width L of the cylinder block W and larger than the inscribed circle of the second and third cylinder bores W2 and W3. The axial fan 13 corresponds to a cooling device. Then, when the first thick portion T1 of the cylinder block W becomes 550 ° C. or less, the blowing of the axial fan 13 is stopped. Other configurations are the same as in the first embodiment.

  In the fourth embodiment, the same operation and effect as those of the first embodiment can be obtained.

  In the above, the present invention has been described with reference to the first to fourth embodiments. However, the present invention is not limited to the first to fourth embodiments, and can be appropriately modified and applied without departing from the spirit thereof. Needless to say.

  For example, in the first to fourth embodiments, the casting is a cylinder block of a vehicle engine. However, the present invention can be applied to a case where another large casting is manufactured.

  In the first to fourth embodiments, in the cylinder block W, the crankcase portion W5 is a first thick portion and the cylinder portion W7 is a second thick portion. It may be a unit. If the casting has three or more thick portions, the n-th thick portion is defined as the first thick portion, and the (n + 1) -th thick portion is defined as the second thick portion. Good. According to the consideration of the inventor, when a molten metal of cast iron is used, if the difference in thickness between the first thick portion and the second thick portion is 5 mm or more, the function and effect of the present invention become remarkable.

  INDUSTRIAL APPLICATION This invention can be utilized when manufacturing a large casting.

DESCRIPTION OF SYMBOLS 1 ... Mold 3 ... Cavity 5 ... Molten metal S1 ... Casting process W ... Casting and cylinder block S2 ... Cooling process T1 ... 1st thick part T2 ... 2nd thick part S21 ... Cooling process in a frame S22 ... Eliminate temperature difference Step S22a: Local cooling step S22b: Partial mold opening step (partial disintegration and crushing step)
W1 to W4: Cylinder bore W7: Cylinder part W5: Crankcase part 7, 13: Cooling device (13: axial fan)

Claims (6)

A pouring step of pouring the molten metal into the cavity of the mold,
Cooling the molten metal in the cavity to a cast product,
The casting has a first thick portion having a first thickness and a second thick portion having a second thickness greater than the first thickness. ,
The cooling step is a cooling step in a frame that cools the molten metal in the mold until the casting exceeds a behavior change temperature at which the cast product switches from a state showing plastic behavior to a state showing elastic behavior.
After the in-frame cooling step, at least a part of the mold is opened, and the temperature difference between the temperature of the first thick portion and the temperature of the second thick portion is reduced until the temperature becomes equal to or lower than the behavior change temperature. And a method for eliminating a temperature difference.   The temperature difference eliminating step includes a local cooling step of cooling the second thick part from the first thick part so that the temperature of the second thick part approaches the temperature of the first thick part. The method for producing a cast product according to claim 1, comprising:   The temperature difference eliminating step includes a partial mold opening step of leaving a part of the mold around the first thick portion so that the temperature of the first thick portion approaches the temperature of the second thick portion. The method for producing a cast product according to claim 1 or 2, further comprising:   4. The method of manufacturing a cast product according to claim 2, wherein in the temperature difference eliminating step, the temperature of the first thick portion and the temperature of the second thick portion are equal at the behavior change temperature. 5. The casting is made of cast iron, is a cylinder block constituting an engine,
The cylinder block forms a cylinder bore in which three or more cylinders are arranged in series, and each peripheral wall is integrally formed with one end of each of the cylinder portions and the cylinder portion having the second thick portion. The method for manufacturing a cast product according to any one of claims 1 to 4, further comprising a crankcase portion serving as a first thick portion. In a casting apparatus having a mold in which a molten metal is cast and a cavity in which the molten metal is cooled and formed as a casting,
The casting has a first thick portion having a first thickness and a second thick portion having a second thickness greater than the first thickness. ,
A cooling device that cools the second thick portion more than the first thick portion so that the temperature of the second thick portion approaches the temperature of the first thick portion. Casting equipment.

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