JP2002178134A - Method for micronizing cast structure and micronizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for micronizing a cast structure and a micronizing device with which wear resistance, seizure resistance, strength and toughness in a cast product are good and a production cost is low. SOLUTION: The method for micronizing the cast structure, is performed by arranging a mold 2 on a turn table 11 and pouring molten metal 22 into the mold 2 and casting the metal 22 while rotating the turn table 11 at low speed and stopping the table 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for refining a cast structure, and more particularly to a method and an apparatus for refining a cast structure of a cylinder liner formed by casting. Things.

[0002]

2. Description of the Related Art Flaky graphite cast iron has good castability and is relatively inexpensive. In addition to having a self-lubricating effect of graphite, depending on the alloy components (for example, boron cast iron), hard flake graphite cast iron is hard. A cast structure in which a hard phase (eg, carbide) dispersed in a so-called “hard phase (mixed phase of cementite and steadite (Fe ₃ P)”) is required. ) Has been awarded.

In recent years, there has been an increasing demand for higher output of engines, especially diesel engines. Increasing the output of a diesel engine causes an increase in the explosive gas pressure applied to the cylinder liner. Therefore, various tribological (friction,
Wear) measures need to be taken. The forces acting on the cylinder liner are usually tensile stress in the circumferential direction of the liner due to the explosive gas pressure, bending stress of the liner mounting flange, side pressure acting on the piston, and thermal stress. The dimensions (particularly the wall thickness) of the cylinder liner are determined in consideration of such factors.

[0004] Here, the graphite shape of flaky graphite cast iron has a notch effect, and it is difficult to match a graphite shape exhibiting a good self-lubricating effect with a graphite shape which does not impair toughness. With the increase in output, insufficient strength of the cylinder liner has become a problem. As a solution, there has been proposed a composite cylinder having a cast iron material having excellent wear resistance and seizure resistance as an inner layer and a cast steel having excellent toughness as an outer layer (see Japanese Patent Application Laid-Open No. 60-169654).

The composite cylinder liner is cast by a centrifugal casting method. First, an outer layer is formed from a cast steel material, and after the outer layer is solidified, an inner layer is formed from a cast iron material on the inner surface of the outer layer. At this time, in order to prevent problems such as poor integration of the inner layer and the outer layer by welding and interposition and entanglement of slag and dross on the inner surface of the outer layer, an improvement measure such as adjusting a cooling rate of the molten metal has been proposed (Japanese Patent Laid-Open No. Hei 5 (1994)). -28559
No. 9).

[0006]

However, the centrifugal casting method has a problem in that the manufacturing cost is high because the apparatus configuration and the manufacturing process are complicated as compared with the pouring method.

Further, in the centrifugal casting method, it is difficult to control the solidification rate of the inner layer and to apply a centrifugal force during casting, so that it is difficult to obtain an A-type graphite structure having a good balance between strength and self-lubricating property. There was a problem.

Further, since cylinder liners of large diesel engines such as ships and trucks are thick cast products, it takes a long time to complete solidification (slow solidification speed). As a result, coarse flaky graphite and hard phase crystallization are caused. Flake graphite and hard phase cannot be refined once they are coarsely crystallized. As a result, the resulting cast product has high strength, but elongation according to the material specifications, that is, good toughness. There was a problem that can not be obtained.

An object of the present invention, which has been made in view of the above circumstances, is to provide a cast product having good wear resistance, seizure resistance, strength, and toughness, and a fine cast structure which is inexpensive to manufacture. An object of the present invention is to provide a method and a miniaturization device.

[0010]

In order to achieve the above object, a method for refining a cast structure according to the present invention is to provide a mold on a turntable, pour molten metal into the mold, and slightly apply a molten metal to the mold surface. After the solidified shell is formed, the turntable is cast while rotating and stopping at a low speed.

According to the above method, after pouring the molten metal into the mold, a flow can be generated in the molten metal solidified in the mold.

It is preferable that the turntable is sequentially rotated forward, stop, reverse, and stop so as to cause the molten metal in the mold to flow forward and reverse around the rotation center to solidify the molten metal.

Preferably, the rotation speed is 6 to 10 rpm, the rotation angle is 90 ° or more, or the rotation time is 3 seconds or more.

The stop time between the forward rotation and the reverse rotation or between the reverse rotation and the forward rotation is preferably 0.8 to 5 seconds.

It is preferable that after the molten metal is poured into the mold, after the solidified shell is formed on the inner wall of the mold, the turntable is rotated and stopped at a low speed.

It is preferable that the turntable is rotated at a low speed and stopped at intervals of 20 to 120 minutes after pouring.

Further, the mold may be a cylinder liner mold and the molten metal may be cast iron.

On the other hand, the apparatus for refining a cast structure according to the present invention comprises a mold for casting a molten metal, rotating means on which the mold is placed, and control means for controlling rotation and stop of the rotating means. It is a thing.

According to the above arrangement, the mold placed on the rotating means can be rotated while being controlled to rotate and stop by the control means.

Preferably, the rotating means includes a turntable on which the mold is placed, and a drive device for rotating and stopping the turntable in forward and reverse directions.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view of an apparatus for refining a cast structure according to the present invention, and FIG. 2 is a partially enlarged view of the rotating means of FIG.

As shown in FIGS. 1 and 2, a casting structure refining apparatus 1 according to the present invention includes a casting mold (a sand mold for a cylinder liner in FIG. 1) 2 for casting a molten metal. The control means 4 is connected to a motor (described later) 13 of the rotating means 3. Here, the casting mold 2 includes casting frames 5a, 5b, 5c and a core 6, and the casting mold 2 and the rotating means 3 are fixed by a fixing jig 7.

The rotating means 3 includes a turntable 11 on which the mold 2 is placed, a support portion 12 for supporting the turntable 11, and a motor (drive device) 13 for rotating and stopping the turntable 11 in forward and reverse directions. It consists of. The motor 13 is provided with a speed reducer 14 having a brake.
Meshes with the gear portion 16 on the lower surface of.

The control means 4 is not particularly limited as long as it can rotate the motor 13 intermittently and in the forward and reverse directions, but the intermittent interval, rotation speed, and rotation angle ( Or the rotation time) can be freely adjusted.

Next, a method for refining a cast structure according to the present invention will be described with reference to FIGS.

A mold (for example, an inner diameter of 580 to 620 mm and an outer diameter of 890 to 9
After placing and fixing a 30 mm cylinder liner mold 2, the metal melt (for example, cast iron melt) 2 is dropped into the mold 2 by using a suspension weir (tundish) 21.
Pour 2 Then, heat is generated in the feeder portion 23 of the mold 2.
A heat insulation treatment is performed, and a casting (for example, a cylinder liner) is cast.

After the pouring, the mold 2 and the rotating means 3 are allowed to stand for 20 to 120 minutes as they are to form a solidified shell layer having a thickness of 5 to 15 mm on the inner wall of the mold 2. The solidified shell layer has a structure in which a hard phase is dispersed and crystallized in an A-type graphite structure, and has abrasion resistance and seizure resistance.

Thereafter, when the mold 2 and the rotating means 3 are allowed to stand still, dendrites (dendrites) grow on the surface of the solidified shell layer, and flaky graphite continues to crystallize in the molten cast iron 22. Here, since the cylinder liners for ships and trucks are very large members, it takes a long time to complete the solidification (solidification speed is low). For this reason, coarse dendrites and flaky graphite tend to grow and crystallize.
As a result, a coarse hard phase and flaky graphite are crystallized in the A-type graphite structure, and the elongation according to the material specifications cannot be obtained.

Therefore, in the method for refining the casting structure according to the present invention, after forming a solidified shell layer on the inner wall of the mold 2, the motor 13 is driven to rotate the turntable 11 at a low speed and stop while the molten cast iron melts. 23 is coagulated. At this time, the low-speed rotation of the turntable 11 is sequentially repeated in the order of forward rotation, stop, reverse rotation, stop,. Further, the turntable 11 is instantaneously changed from the forward rotation state to the stop state or from the reverse rotation state to the stop state by the braking function of the speed reducer 14 of the motor 13. Thus, the turntable 11 does not rotate due to inertia.

When the mold 2 is rotated by starting the rotation of the turntable 11, only the mold 2 and the solidified shell layer are initially rotated. Therefore, the interface between the solidified shell layer in the mold 2 and the unsolidified molten cast iron 22 ( Hereinafter, this will be referred to as a solidification interface). However, immediately due to the viscosity of the molten cast iron 22,
The molten cast iron 22 itself starts to flow following the rotation of the mold 2 and the solidified shell layer. By sequentially repeating the rotation of the turntable 11 in the normal rotation, stop, reverse rotation, stop,..., A forward and reverse flow around the rotation center occurs in the molten cast iron 22 in the mold 2.

After that, the normal rotation of the turntable 11
The operations of stopping, reversing, stopping,... Are continuously performed until the solidification of the cast iron melt 23 is completed (for example, about 6 hours with the above-described cylinder liner mold). Completion of solidification is determined by the state of the inner peripheral portion of the feeder portion 23 because solidification of the molten cast iron 22 proceeds from the outer peripheral portion of the bottom of the mold 2 toward the inner peripheral portion of the feeder portion 23. I do.

Here, the method of pouring the molten metal 22 into the mold 2 is not limited to dropping, but any conventional pouring method can be applied. Is mentioned.

Next, the operation of the method for refining a cast structure according to the present invention will be described.

The molten cast iron 22 flowing following the rotation of the mold 2 and the solidified shell layer continues to flow by inertia for a while after the rotation of the turntable 11 (the rotation of the mold 2) is stopped.

At this time, if the rotation angle of the turntable 11 is small and the stop time of the turntable 11 is very short, during the flow due to inertia, the turntable 11 finishes reverse rotation and starts to rotate forward again. Become. In this case, the molten cast iron 22 does not flow in the opposite direction but continues to flow only in one direction. Also, turntable 1
If the stop time of 1 is long, the flow due to inertia stops during that time, but solidification proceeds during the stop time.

Here, the flow of the molten cast iron 22 following the rotation of the mold 2 and the solidified shell layer, and the separation and crushing of the growing dendrites and the flake graphite during the crystallization are caused by the acceleration (rotational speed) of the turntable 11. ), The displacement distance at the solidification interface in the mold 2 (the rotation angle of the turntable 11),
And the stoppage time of the turntable 11.

The effect of dividing and crushing the growing dendrite and the flake graphite during the crystallization is as follows.
2 is obtained when the mold 2 is caused to flow, and is hardly obtained when the rotational direction of the mold 2 and the flow direction of the molten cast iron 22 are the same.

The rotation speed and rotation angle of the turntable 11 are appropriately adjusted according to the time until the flow of the cast iron melt 22 starts flowing, the flow speed, the stability of the mold 2 and the viscosity of the melt. For large cylinder liners such as ships, trucks, etc., the rotation speed is 6-10 rpm
m, preferably 7 to 9 rpm, and the rotation angle is 90 to 240.
(Rotation time is 4 to 7 seconds, preferably 5 to 6 seconds).

In the case of a large cylinder liner such as a ship or a truck, the flow time of the molten cast iron 22 due to inertia is 0.8 to 1.5 seconds, so that the stop time of the turntable 11 is at least 0.8 seconds. This is necessary. further,
If the stop time of the turntable 11 is longer than 5 seconds, coarse dendrite growth and flake graphite agglomeration occur during the stop time, which greatly hinders the refinement of the cast structure of the cylinder liner. For this reason, turntable 1
The stop time of 1 is 0.8 to 5 seconds, preferably 0.8 to 2 seconds.
Seconds.

Further, in order to effectively reduce the size of the cast structure, it is preferable to alternately rotate the turntable 11 in the forward and reverse directions with a stop time interposed therebetween. However, the turntable 11 is rotated only in one direction. It may be. Also in this case, if the stop time of the turntable 11 is very short, the mold 2 starts rotating again while the molten cast iron 22 is flowing by inertia, and the molten cast iron 22 continues to flow in only one direction. As a result, the effect of cutting and crushing dendrites during growth and flake graphite during crystallization cannot be obtained.

As described above, according to the method for refining the cast structure according to the present invention, after the solidified shell layer is formed on the inner wall of the mold 2, the molten cast iron 23 is solidified while the turntable 11 is rotated and stopped at a low speed. ing. By rotating and stopping the turntable 11 at a low speed after the solidified shell layer is formed, the molten cast iron 22 flowing in the mold 2 does not directly contact the inner wall (sand wall) of the mold 2 during solidification.
Sand can be prevented from being caught in the molten cast iron 22. This solidified shell layer has the same A-type graphite structure as the solidified shell layer formed by the ordinary pouring method,
Has good abrasion and seizure resistance.

Further, when the molten cast iron 22 is solidified, the turntable 11 is repeatedly rotated at a low speed in the order of normal rotation, stop, reverse rotation, stop, and so on, so that the molten cast iron 22 being solidified in the mold 2 rotates. It flows around the center in the opposite direction, and the flow of the molten cast iron 22 causes the dendrite during growth and the flake graphite during crystallization to be divided and crushed.

Further, the solidification rate of the molten cast iron 22 is kept low by the cutting and crushing, but coarse dendrites and flake graphite do not grow and crystallize. As a result, a coarse hard phase is formed. And a fine cast structure without crystallization of flake graphite. As a result, even a thick cast product having a coarse cast structure due to a low solidification rate or the like can be a tough cast product having elongation according to the material specifications. Therefore, as described above,
It is possible to cope with an increase in engine output without using a two-layer composite cylinder having an outer layer made of cast steel and an inner layer made of cast iron.

Further, the method for refining the cast structure according to the present invention is more effective than the centrifugal casting method which is a method for producing a composite cylinder or a conventional large hollow cylindrical casting (for example, cast iron pipe, roll, etc.). Is simple and easy, and the manufacturing cost is low.

[0046]

(Embodiment 1) An outer diameter 93 is placed on a turntable.
After placing and fixing a mold having a size of 0 mm, an inner diameter of 620 mm, and a height of 500 mm, a chemical composition of 3.3 C-1.2 was set in the mold.
Pour molten cast iron of Si-0.8Mn-0.3P-0.03B-1.2Cu-Fe.
After that, the mold is heated and kept warm for the riser part, and is left still for 60 minutes.
m of a solidified shell layer is formed.

After the formation of the solidified shell layer, the motor is driven to rotate the turntable at low speed, such as forward rotation, stop, reverse rotation, stop,.
To solidify the molten cast iron. At this time, the rotation speed of the turntable is 8 rpm, the rotation angle is 180 °,
The stop time of the turntable was 1 second. Thereafter, operations such as forward rotation, stop, reverse rotation, and stop of the turntable are continuously performed until solidification of the molten cast iron is completed, thereby producing a cast test piece. (Example 2) A cast test piece is prepared in the same manner as in Example 1 except that the stop time of the turntable is set to 5 seconds. (Comparative Example 1) A mold having an outer diameter of 930 mm, an inner diameter of 620 mm, and a height of 500 mm was placed and fixed on a turntable, and the chemical composition was 3.3C-1.2Si-0.8Mn- in this mold.
Pour molten cast iron of 0.3P-0.03B-1.2Cu-Fe. afterwards,
Heating and heat retaining treatment is performed on the riser part of the mold, and the mold is allowed to stand still for 2400 minutes to produce a cast test piece.

Each of the cast test pieces of Examples 1 and 2 and Comparative Example 1 was subjected to a tensile test and an elongation test, and the tensile strength (MPa) and the tensile elongation (%) were measured. As shown in FIGS. Further, the cast structures of the cast test pieces of Examples 1 and 2 and Comparative Example 1 were observed, and the observation diagrams are shown in FIGS.

As shown in FIGS. 3 and 4, the cast test pieces of Examples 1 and 2 in which the molten cast iron was solidified while the turntable was rotated / stopped at a low speed had a tensile strength of 200%.
MPa, 180 MPa, tensile elongation 0.38%,
0.17%. Further, as shown in FIGS. 5 and 6, in the casting structure of the cast test pieces of Examples 1 and 2, a fine hard phase h, a short and flaky graphite G exhibiting a "worm-like" shape were obtained. Had crystallized. As shown in FIG. 6, in the cast test piece of Example 2, the flaky graphite G was slightly aggregated.

On the other hand, the cast test piece of Comparative Example 1 in which the operation of turning and stopping the turntable was not performed was as follows:
Tensile strength is 120 MPa, tensile elongation is 0.28%
Met. Further, as shown in FIG. 7, in the casting structure of the casting test piece of Comparative Example 1, the coarse hard phase h
, Long flaky graphite G was crystallized.

From the above results, the cast test piece of Example 1 has a tensile strength of 6 as compared with the cast test piece of Comparative Example 1.
7% and tensile elongation were improved by 36%. Example 2
Of the cast test piece of Comparative Example 1
Although the tensile elongation was slightly inferior, the tensile strength was improved by 50%.

Thus, by solidifying the molten cast iron while rotating and stopping the turntable at a low speed, a coarse hard phase and a fine cast structure without flake graphite crystallization can be obtained, and the tensile strength and tensile elongation can be reduced. It was confirmed that a high casting was obtained.

As described above, the embodiments of the present invention are not limited to the above-described embodiments, and it is needless to say that various other embodiments are also conceivable.

[0054]

In summary, according to the present invention, after casting a molten metal in a mold, a flow is caused in the molten metal being solidified in the mold to obtain a cast product having a fine casting structure. The effect is excellent.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an apparatus for refining a cast structure according to the present invention.

FIG. 2 is a partially enlarged view of the rotating means of FIG.

FIG. 3 is a view showing the tensile strength of the cast products of Examples 1 and 2 and Comparative Example 1.

FIG. 4 is a view showing tensile elongation of cast products of Examples 1 and 2 and Comparative Example 1.

FIG. 5 is a structure observation diagram of a cast product of Example 1 cast by a method for refining a cast structure according to the present invention.

FIG. 6 is a structural observation view of a cast product of Example 2 cast by a method for refining a cast structure according to the present invention.

FIG. 7 is a structural observation view of a cast product of Comparative Example 1 cast by a conventional casting method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refining apparatus 2 Mold 3 Rotation means 4 Control means 11 Turntable 13 Drive device 22 Cast iron molten metal (metal molten metal)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuhiko Inoue 5292 Aioi, Aioi-shi, Hyogo Pref.

Claims (9)

[Claims] 1. A method for refining a cast structure, comprising: providing a mold on a turntable, pouring a molten metal into the mold, and performing casting while rotating and stopping the turntable at a low speed. 2. The casting structure according to claim 1, wherein the turntable is sequentially rotated in a normal rotation, a stop, a reverse rotation, and a stop, and a forward and reverse flow around the rotation center is generated in the molten metal in the mold to solidify the molten metal. Method of miniaturization. 3. The rotation speed is 6 to 10 rpm, the rotation angle is 90 ° or more, or the rotation time is 3 seconds or more.
Or the method for refining a cast structure according to item 2. 4. The method for refining a cast structure according to claim 1, wherein a stop time between normal rotation and reverse rotation or between reverse rotation and normal rotation is 0.8 to 5 seconds. 5. The method according to claim 1, wherein the molten metal is poured into the mold, and after the solidified shell is formed on the inner wall of the mold, the turntable is rotated and stopped at a low speed. . 6. The method for refining a cast structure according to claim 1, wherein the turntable is rotated at a low speed and stopped at intervals of 20 to 120 minutes after pouring. 7. The method for refining a cast structure according to claim 1, wherein the mold is a cylinder liner mold and the molten metal is a cast iron melt. 8. An apparatus for refining a casting structure, comprising: a mold for casting a molten metal; rotating means on which the mold is placed; and control means for controlling rotation and stop of the rotating means. . 9. The apparatus for refining a cast structure according to claim 8, wherein the rotating means includes a turntable on which the mold is placed, and a drive device for rotating and stopping the turntable in forward and reverse directions.