CENTRIFUGAL CASTING DEVICE AND CENTRIFUGAL CASTING METHOD

Abstract

A centrifugal casting device casts a cast product by pouring molten metal into a mold while rotating the mold, and includes: a control unit for controlling the rotational speed of the mold; and a determination unit for determining whether or not the head position of the molten metal flowing in the direction of a rotation axis of the mold has reached a predetermined position. The control unit rotates the mold at a first rotational speed, and rotates the mold at a second rotational speed in a case where the determination unit determines that the head position has reached the predetermined position.

Claims

1. A centrifugal casting device that casts a cast product by pouring molten metal into a mold while rotating the mold, the centrifugal casting device comprising: one or more processors that execute computer-executable instructions stored in a memory, wherein the one or more processors execute the computer-executable instructions to cause the centrifugal casting device to: control a rotational speed of the mold to rotate the mold at a first rotational speed; determine whether or not a head position of the molten metal flowing in a direction of a rotation axis of the mold has reached a predetermined position; and rotate the mold at a second rotational speed in a case where it is determined that the head position has reached the predetermined position.

2. The centrifugal casting device according to claim 1, wherein the second rotational speed is higher than the first rotational speed.

3. The centrifugal casting device according to claim 1, wherein the first rotational speed is set in accordance with a pouring speed that is a flow velocity of the molten metal at which the molten metal is poured into the mold.

4. The centrifugal casting device according to claim 1, wherein a plurality of recesses are formed in an inner circumferential surface of the mold.

5. A centrifugal casting method for casting a cast product by pouring molten metal into a mold while rotating the mold, the centrifugal casting method comprising: starting pouring of the molten metal into the mold in a state where the mold is rotated at a first rotational speed; determining whether or not a head position of the molten metal flowing in a direction of a rotation axis of the mold has reached a predetermined position; and rotating the mold at a second rotational speed in a case where it is determined that the head position has reached the predetermined position.

6. The centrifugal casting method according to claim 5, wherein the second rotational speed is higher than the first rotational speed.

7. The centrifugal casting method according to claim 5, wherein the first rotational speed is set in accordance with a pouring speed that is a flow velocity of the molten metal at which the molten metal is poured into the mold.

8. The centrifugal casting method according to claim 5, wherein a plurality of recesses are formed in an inner circumferential surface of the mold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a cross-sectional view of a centrifugal casting device according to an embodiment of the present disclosure;

[0011] FIG. 2 is a partial cross-sectional view of a cylindrical member;

[0012] FIG. 3 is a partial cross-sectional view of a mold;

[0013] FIG. 4 is a control block diagram of a control device;

[0014] FIG. 5 is a flowchart showing a rotation control process for the mold executed by the control device;

[0015] FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D are schematic diagrams explaining a mechanism of formation of an unsound layer in the cylindrical member; and

[0016] FIG. 7 is a graph showing a relationship between the switching timing from a first rotational speed to a second rotational speed, and the length of the unsound layer.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment

[Configuration of Centrifugal Casting Device]

[0017] FIG. 1 is a cross-sectional view of a centrifugal casting device 10 according to an embodiment of the present disclosure. The centrifugal casting device 10 of the embodiment casts, for example, a cylindrical member 12 as a cast product.

[0018] FIG. 2 is a partial cross-sectional view of the cylindrical member 12. The cylindrical member 12 is cut to a suitable length, and the cut cylindrical member 12 is used as a cylinder sleeve of an internal combustion engine. The cylinder sleeve is disposed in the bore of a cylinder block. A reciprocating piston is in sliding contact with the inner peripheral wall of the cylinder sleeve. For example, flake graphite cast iron is used as the material of the cylindrical member 12. The flake graphite cast iron is a material excellent in vibration absorbing performance, thermal shock resistance, and lubricating performance.

[0019] A number of spires (protrusions) 16 are formed on an outer circumferential surface 14 of the cylindrical member 12. The height of each spire 16 from the outer circumferential surface 14 is set according to the outer diameter of the cylindrical member 12. For example, in a case where the outer diameter of the cylindrical member 12 is 60 to 100 mm, the height of each spire 16 is set within a range of 0.5 to 1.2 mm.

[0020] The spires 16 can improve the adhesion between the cylinder sleeve and the cylinder block. Further, since the surface area of the cylinder sleeve is increased by providing the spires 16, heat generated in the cylinder sleeve by sliding of the piston or the like can be efficiently transmitted to the cylinder block. This improves the heat dissipation performance of the cylinder sleeve.

[0021] Returning to FIG. 1, the centrifugal casting device 10 includes a cylindrical mold 18. An annular groove 22 and an annular groove 24 are provided in an outer circumferential surface 20 of the mold 18 so as to cut out the outer circumferential surface 20 along the circumferential direction. A roller 26 is in contact with the annular groove 22, and a roller 28 is in contact with the annular groove 24. A motor 30 is connected to the roller 26, and the mold 18 is rotated about a rotation axis A by the driving force of the roller 26. A rotational speed sensor 32 is connected to the roller 28, and the rotational speed of the mold 18 is measured by the rotational speed sensor 32. The motor 30 is controlled by a control device 34.

[0022] An annular closing member 36 is attached to the distal end of the mold 18. The closing member 36 is provided with a window 38. Images of the inside of the mold 18 are captured through the window 38 by a camera 40 provided outside the mold 18. An annular frame 42 is attached to the proximal end of the mold 18. The frame 42 is provided with an opening 44. A pouring pipe 48 of a trough 46 is inserted into the mold 18 through the opening 44. Molten material (molten metal L) is supplied from a ladle 50 to the trough 46, and is poured into the mold 18 from the trough 46.

[0023] FIG. 3 is a partial cross-sectional view of the mold 18. When the cylindrical member 12 is manufactured, a mold wash 53 is applied to an inner circumferential surface 52 of the heated mold 18. The mold wash 53 contains a heat insulating material, a binder, a mold release agent, a surfactant, and water.

[0024] The water contained in the mold wash 53 applied to the mold 18 is evaporated by the heat of the mold 18 to form bubbles, and the surface of the mold wash 53 is spherically expanded to form protrusions 55. A large number of the protrusions 55 are formed on the surface of the mold wash 53, and recesses 57 are each formed between the protrusions 55. The recesses 57 are transferred to the outer circumferential surface 14 of the cylindrical member 12 to form the spires 16.

[0025] After the mold wash 53 is applied to the inner circumferential surface 52 of the mold 18, the pouring pipe 48 of the trough 46 is inserted into the mold 18 through the opening 44 of the frame 42. The motor 30 rotates the roller 26, whereby the mold 18 rotates. Thereafter, the molten metal L is supplied from the ladle 50 to the trough 46, and is poured into the mold 18 from the trough 46. The molten metal L contained in the mold 18 flows along the direction of the rotation axis A of the mold 18. Further, the molten metal L is supplied to the entire circumference along the inner circumferential surface 52 of the mold 18 by the action of the centrifugal force of the rotating mold 18.

[0026] As the rotational speed of the mold 18 increases and the centrifugal force increases, the contact pressure of the molten metal L against the inner circumferential surface 52 of the mold 18 increases, and the flow velocity of the molten metal L in the direction of the rotation axis A decreases. Therefore, the molten metal L solidifies before reaching a distal end P1 (FIG. 1) of the inner circumferential surface 52 of the mold 18, and there is a concern that the cylindrical member 12 having desired length and thickness cannot be obtained. On the other hand, in a case where the rotational speed of the mold 18 decreases and the centrifugal force decreases, the molten metal L does not enter the tips of the recesses 57 of the inner circumferential surface 52 of the mold 18, and the height of the spires 16 is reduced. The reduced height of the spires 16 reduces the adhesion between the cylinder sleeve and the cylinder block. Further, the reduced height of the spires 16 reduces the heat dissipation performance of the cylinder sleeve.

[Configuration of Control Device]

[0027] FIG. 4 is a control block diagram of the control device 34. The control device 34 includes a computation unit 54 and a storage unit 56. The computation unit 54 is, for example, a processor such as a central processing unit (CPU) or a graphics processing unit (GPU). The computation unit 54 includes a control unit 58 and a determination unit 60. The control unit 58 and the determination unit 60 are realized by the computation unit 54 executing a program stored in the storage unit 56. At least part of the control unit 58 and the determination unit 60 may be realized by an integrated circuit such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). At least part of the control unit 58 and the determination unit 60 may be realized by an electronic circuit including a discrete device.

[0028] The storage unit 56 is a computer-readable non-transitory tangible storage medium. The storage unit 56 is constituted by a volatile memory (not shown) and a non-volatile memory (not shown). The volatile memory is, for example, a random access memory (RAM) or the like. The non-volatile memory is, for example, a read only memory (ROM), a flash memory, or the like. Data and the like are stored in, for example, the volatile memory. Programs, tables, maps, and the like are stored in, for example, the non-volatile memory. At least part of the storage unit 56 may be included in the processor, the integrated circuit, or the like described above. At least part of the storage unit 56 may be mounted on a device connected to the centrifugal casting device 10 via a network.

[0029] The control unit 58 acquires the rotational speed of the mold 18 measured by the rotational speed sensor 32. The control unit 58 performs feedback-control of the motor 30 so that the rotational speed of the mold 18 becomes a predetermined rotational speed.

[0030] The determination unit 60 acquires the image of the inside of the mold 18 captured by the camera 40. The determination unit 60 analyzes the acquired image and determines whether or not the head position of the molten metal L flowing along the direction of the rotation axis A of the mold 18 has reached a predetermined position. The determination unit 60 may determine whether or not the head position of the molten metal L has reached the predetermined position, based on the elapsed time from the point in time when the molten metal L starts to be poured into the mold 18.

[Rotation Control Process for Mold]

[0031] FIG. 5 is a flowchart showing a rotation control process for the mold 18 executed by the control device 34. The rotation control process is executed when the molten metal L is poured into the mold 18.

[0032] In step S1, the control unit 58 controls the motor 30 to rotate the mold 18 at a first rotational speed. The first rotational speed is set to a rotational speed at which the relative centrifugal acceleration of the mold 18 is, for example, a value of 90 [G] to 100 [G]. The first rotational speed is set based on the flow velocity (pouring speed) of the molten metal L at which the molten metal L is poured from the trough 46 into the mold 18.

[0033] In step S2, the determination unit 60 determines whether or not the head position of the molten metal L flowing along the direction of the rotation axis A of the mold 18 has reached a predetermined position. The predetermined position is set, for example, to the distal end P1 (FIG. 1) of the inner circumferential surface 52 of the mold 18. The predetermined position is not limited to the distal end P1. In a case where it is determined that the head position of the molten metal L flowing along the direction of the rotation axis A of the mold 18 has reached the predetermined position (step S2: YES), the process proceeds to step S3. In a case where it is determined that the head position of the molten metal L has not reached the predetermined position (step S2: NO), the process of step S2 is repeated.

[0034] In step S3, the control unit 58 controls the motor 30 to rotate the mold 18 at a second rotational speed. The second rotational speed is set to a rotational speed at which the relative centrifugal acceleration of the mold 18 is, for example, a value of 100 [G] to 130 [G]. After the process of step S3 is performed for a predetermined period of time, the rotation control process is ended.

[Mechanism of Formation of Unsound Layer]

[0035] In a case where the cylindrical member 12 is cast by the centrifugal casting device 10, an unsound layer is formed at the distal end portion of the cylindrical member 12. Since the portion where the unsound layer is formed cannot be used as a cylinder sleeve, the distal end portion of the cylindrical member 12 is cut off and discarded. In order to reduce the amount of waste, it is required to reduce the length of the unsound layer in the cylindrical member 12.

[0036] FIGS. 6A to 6D are schematic diagrams explaining a mechanism of formation of the unsound layer in the cylindrical member 12.

[0037] The molten metal L initially poured into the mold 18 (hereinafter, referred to as a first group L1) flows in the direction of the rotation axis A along the inner circumferential surface 52 of the mold 18. At this time, since the mold 18 is rotating, the centrifugal force acts on the first group L1, and the flow velocity of the first group L1 in the direction of the rotation axis A decreases. The molten metal L contains impurities (slag). Since the impurities have a specific weight smaller than that of the flake graphite cast iron, which is the material of the cylindrical member 12, the impurities float on the inner circumferential side of the first group L1 (FIG. 6A).

[0038] The molten metal L (hereinafter, referred to as a second group L2) poured into the mold 18 after the first group L1 flows in the direction of the rotation axis A along the inner circumferential surface of the first group L1. Since the second group L2 is poured after the first group L1, the flow velocity of the second group L2 is higher than that of the first group L1 immediately after the second group L2 is poured. Therefore, the second group L2 overtakes the first group L1, and the second group L2 flows ahead of the first group L1. When the second group L2 overtakes the first group L1, the second group L2 sweeps away the impurities floating on the inner circumferential side of the first group L1 (FIG. 6B). Further, the second group L2 positioned at the head sweeps away the inclusions adhering to the inner circumferential surface 52 of the mold 18 (FIG. 6B). The inclusions are, for example, the peeled mold wash 53 or the like.

[0039] Since the centrifugal force caused by the rotation of the mold 18 also acts on the second group L2, the flow velocity of the second group L2 in the direction of the rotation axis A also decreases. The first group L1 and the second group L2 are pushed toward the distal end of the mold 18 by the molten metal L (hereinafter, referred to as a third group L3) poured into the mold 18 after the second group L2. As a result, the first group L1 and the second group L2 integrally flow in the direction of the rotation axis A (FIG. 6C). An oxide film is formed on the entire inner circumference of the molten metal L (FIG. 6C).

[0040] When the second group L2 reaches the distal end of the mold 18, a portion (hereinafter, referred to as a head portion LH) of the second group L2 that is located forward of the first group L1 is compressed, and the oxide film of the head portion LH of the second group L2 is folded. In the head portion LH of the second group L2, the proportion of the impurities, the inclusions, and the oxide film is relatively large, and thus an unsound layer is generated (FIG. 6D).

[0041] As the rotational speed of the mold 18 increases, the flow velocity of the first group L1 decreases, and therefore, the length of the head portion LH of the second group L2 increases, and the length of the unsound layer also increases. That is, in order to reduce the length of the unsound layer, the rotational speed of the mold 18 may be decreased to delay the decrease in the flow velocity of the first group L1. On the other hand, when the rotational speed of the mold 18 is decreased, the height of the spires 16 is decreased as described above. Therefore, in the embodiment, the rotational speed of the mold 18 is set to the first rotational speed at the point in time when the pouring of the molten metal L into the mold 18 is started, and the rotational speed of the mold 18 is set to the second rotational speed when the head position of the molten metal L reaches the predetermined position.

[Switching Timing between First Rotational Speed and Second Rotational Speed]

[0042] FIG. 7 is a graph showing a relationship between the switching timing from the first rotational speed to the second rotational speed, and the length of the unsound layer. The switching timing is indicated such that the point in time when the head position of the molten metal L reaches the distal end P1 (FIG. 1) of the inner circumferential surface 52 of the mold 18 is set as 0 [s].

[0043] As shown in FIG. 7, it is understood that the length of the unsound layer can be reduced by switching from the first rotational speed to the second rotational speed at the timing of 2 [S] to 3 [S].

[0044] As shown in FIG. 7, when the switching timing from the first rotational speed to the second rotational speed is too late, the length of the unsound layer increases. This is because the molten metal L that has collided with the closing member 36 returns toward the proximal end of the mold 18 together with impurities and inclusions.

[0045] According to the above-described embodiment, the length of the unsound layer can be reduced while the height of the spires 16 of the cylindrical member 12 is ensured. This in turn contributes to energy efficiency.

[0046] The following supplementary notes are further disclosed in relation to the above-described embodiment.

Supplementary Note 1

[0047] The centrifugal casting device (10) of the present disclosure is a centrifugal casting device that casts a cast product by pouring the molten metal (L) into the mold (18) while rotating the mold, the centrifugal casting device including: the control unit (58) configured to control the rotational speed of the mold; and the determination unit (60) configured to determine whether or not the head position of the molten metal flowing in the direction of the rotation axis (A) of the mold has reached a predetermined position, wherein the control unit rotates the mold at the first rotational speed, and rotates the mold at the second rotational speed in a case where the determination unit determines that the head position has reached the predetermined position. This makes it possible to reduce the length of the unsound layer while ensuring the height of the spires.

Supplementary Note 2

[0048] In the centrifugal casting device according to Supplementary Note 1, the second rotational speed may be higher than the first rotational speed. This makes it possible to reduce the length of the unsound layer while ensuring the height of the spires.

Supplementary Note 3

[0049] In the centrifugal casting device according to Supplementary Note 1, the first rotational speed may be set in accordance with the pouring speed that is a flow velocity of the molten metal at which the molten metal is poured into the mold. This can reduce the length of the unsound layer.

Supplementary Note 4

[0050] In the centrifugal casting device according to any one of Supplementary Notes 1 to 3, a plurality of recesses (57) may be formed in the inner circumferential surface (52) of the mold. This makes it possible to form the spires on the outer circumferential surface of the cast product.

Supplementary Note 5

[0051] The centrifugal casting method of the present disclosure is a centrifugal casting method for casting a cast product by pouring the molten metal into the mold while rotating the mold, the centrifugal casting method including: the first rotation step of starting pouring of the molten metal into the mold in a state where the mold is rotated at the first rotational speed; the determination step of determining whether or not the head position of the molten metal flowing in the direction of the rotation axis of the mold has reached a predetermined position; and the second rotation step of rotating the mold at the second rotational speed in a case where it is determined in the determination step that the head position has reached the predetermined position. This makes it possible to reduce the length of the unsound layer while ensuring the height of the spires.

Supplementary Note 6

[0052] In the centrifugal casting method according to Supplementary Note 5, the second rotational speed may be higher than the first rotational speed. This makes it possible to reduce the length of the unsound layer while ensuring the height of the spires.

Supplementary Note 7

[0053] In the centrifugal casting method according to Supplementary Note 5, the first rotational speed may be set in accordance with the pouring speed that is a flow velocity of the molten metal at which the molten metal is poured into the mold. This can reduce the length of the unsound layer.

Supplementary Note 8

[0054] In the centrifugal casting method according to any one of Supplementary Notes 5 to 7, a plurality of recesses may be formed in the inner circumferential surface of the mold. This makes it possible to form the spires on the outer circumferential surface of the cast product.

[0055] Although the present disclosure has been described in detail, the present disclosure is not limited to the above-described individual embodiments. Various additions, replacements, modifications, partial deletions, and the like can be made to these embodiments without departing from the gist of the present disclosure, or without departing from the essence of the present disclosure derived from the claims and equivalents thereof. Further, these embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of operations and the order of processes are shown as examples, and are not limited to these. Furthermore, the same applies to a case where numerical values or mathematical expressions are used in the description of the above-described embodiments.