EP2407567A2

EP2407567A2 - Alloy cast iron for producing a seal, seal, and method for producing such a seal

Info

Publication number: EP2407567A2
Application number: EP10751013A
Authority: EP
Inventors: Young Jin Ma
Original assignee: Caterpillar Precision Seals Korea
Current assignee: Caterpillar Precision Seals Korea
Priority date: 2009-03-10
Filing date: 2010-03-10
Publication date: 2012-01-18
Also published as: US20120058710A1; WO2010104322A2; JP2012520395A; EP2407567A4; WO2010104322A3; KR101091839B1; CN102348820A; KR20100101962A; JP5462291B2

Abstract

Alloy cast iron for a seal, a seal, and a method of manufacturing the seal are provided. The alloy cast iron for a seal includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron. Therefore, a seal can be produced using a centrifugal casting method and thus productivity of the seal is improved and the seal having excellent abrasion resistance is produced.

Description

[Technical Field]

The present invention relates to alloy cast iron for a seal, a seal, and a method of manufacturing the seal, and more particularly, to alloy cast iron for a seal, a seal, and a method of manufacturing the seal that can apply a centrifugal casting method having excellent productivity.

[Background Art]

In generally, an endless track is used for vehicles for agriculture and engineering works such as an excavator or a bulldozer and is used for a tank and an armored car for a military purpose.
A track roller for supporting to rotate a chain belt for functioning as a wheel is provided in an endless track vehicle. In order to reduce abrasion by reducing a rotation friction, a lubricant is filled within the track roller, and in order to prevent the lubricant from being leaked to the outside or to prevent a foreign substance from being injected into the lubricant from the outside, a floating seal is mounted in the track roller.
The seal is formed with special alloy cast iron having both a sealing function of preventing leakage of a lubricant within the roller and a bearing function of rotating the roller.
Conventionally, a seal was manufactured using a shell mold casting method. However, in the shell mold casting method, the seal is manufactured through a molding step, an injection step, a shorting step, a finishing step, a heat treatment step, a grinding step, a lapping step, a cleaning step, a buffing step, and an inspection step, and the shell mold casting method has a complicated production process.
Accordingly, it is preferable to manufacture a seal using an environment-friendly centrifugal casting method with a simple manufacturing process, but the centrifugal casting method is different from a shell mold casting method and thus even if the same alloy cast iron is used, a formed seal has a structure different from an existing structure. Therefore, when a seal is manufactured with conventional alloy cast iron using a centrifugal casting method, the seal has large brittleness and small airtightness and abrasion resistance.

[Disclosure]

[Technical Problem]

The present invention has been made in an effort to solve the above problems, and the present invention provides alloy cast iron for a seal that can apply a centrifugal casting method.

[Technical Solution]

According to an aspect of the present invention, there is provided a seal including 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.
According to another aspect of the present invention, there is provided a method of manufacturing a seal, the method including: melting alloy cast iron for the seal; injecting the melted alloy cast iron into a rotation mold; forming the seal by a rotation of the rotation mold; and separating the seal from the rotation mold and performing heat treatment of the seal, wherein the alloy cast iron includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.
According to another aspect of the present invention, there is provided alloy cast iron for a seal including 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.

[Advantageous Effects]

According to the present invention, a seal can be produced using a centrifugal casting method and thus productivity is improved, and the produced seal has excellent abrasion resistance.

[Description of Drawings]

FIG. 1 is a partially cut-away perspective view illustrating a track roller and a seal mounted thereto;
FIG. 2 is a phase equilibrium diagram illustrating a eutectic reaction and a hypereutectic reaction according to a carbon content;
FIG. 3 is a picture illustrating a structure of a seal formed with alloy cast iron for a seal according to an exemplary embodiment of the present invention;
FIGS. 4 and 5 are pictures illustrating a structure of an existing seal;
FIG. 6 is a diagram illustrating an X-ray diffraction result of the seal shown in FIG. 3; and
FIG. 7 is a view illustrating a method of manufacturing a seal according to another exemplary embodiment of the present invention.

[Best Mode]

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a partially cut-away perspective view illustrating a track roller and a seal mounted thereto.
A seal 100 is formed with special alloy cast iron having both a sealing function of preventing leakage of a lubricant within a track roller 120 and a bearing function of rotating the track roller 120.
In order to reduce abrasion by reducing a rotation friction, a lubricant is filled within the track roller 120, and the seal 100 is mounted to prevent the lubricant from being leaked to the outside or to prevent a foreign substance from being injected into the lubricant from the outside.
According to an exemplary embodiment of the present invention, the seal 100 can be manufactured using a centrifugal casting method.
The centrifugal casting method is a casting method of flowing a melting metal while rotating a mold and forming a casting using a centrifugal force.
In a casting having a complicated form or a microstructure, a flow path of a melting metal is formed in a radius direction by radially disposing a mold along a circumference, and a casting flows to the center of a circular plate and a casting is cast while being pressurized by a centrifugal force by rotating the circular plate.
Such a centrifugal casting method will be described in detail later in FIG. 5, and a seal can be manufactured through an injection step, a finishing step, a grinding step, and a lapping step, and thus the centrifugal casting method has a simpler process than that of a shell mold casting method, thereby improving productivity.
The seal is formed with special alloy cast iron. A main component of the seal is iron (Fe), and hereinafter a main component of the present invention will be described.
Alloy cast iron for a seal according to an exemplary embodiment of the present invention includes 3.8 to 4.2wt% of carbon, 3.3 to 4.7wt% of nickel, 2 to 5wt% of molybdenum, 1.2 to 2.0wt% of silicon, 16 to 18wt% of chrome, and 0.8 to 1.5wt% of manganese.
The seal performs both a sealing function and a bearing function within the roller, and thus abrasion resistance is one of the most important characteristics of the seal. Accordingly, carbon is provided in the seal to provide enough hardness to the seal and the remaining austenite, and carbon preferably has a content of 3.8 to 4.2wt%.
FIG. 2 is a phase equilibrium diagram illustrating a eutectic reaction and a hypereutectic reaction according to a carbon content.
Referring to FIG. 2, in alloy cast iron for an existing seal, a content of carbon (C) is about 3.0 to 3.7wt%, and the existing alloy cast iron induces generation of austenite rather than generating carbide by performing a eutectic reaction or a hypoeutectic reaction, as in a portion A of FIG. 2.
However, in a seal manufactured by alloy cast iron for a seal according to an exemplary embodiment of the present invention, a content of carbon (C) is 3.8wt% to 4.2wt%, as in a portion B of FIG. 2, and thus an amount of carbide increases by inducing a hypereutectic reaction at a segment having no brittleness.
That is, the seal manufactured by alloy cast iron for a seal according to the present exemplary embodiment performs a hypereutectic reaction, and thus the seal has a large amount of carbide. This means that the seal has abrasion resistance much greater than that of an existing seal. Therefore, it is preferable that carbon has a content of 3.8wt% to 4.2wt%.
However, in such a case, brittleness and hardness increase together with increase of abrasion resistance, but alloy cast iron for a seal according to the present exemplary embodiment can suppress excessive increase of hardness by addition charging of nickel (Ni) for stabilizing austenite and molybdenum (Mo) for suppressing excess generation of martensite and carbide, thereby preventing from being broken.
It is most preferable that nickel has a content of 3.3wt% to 4.7wt%, and it is preferable that molybdenum has a content of 2wt% to 5wt%.
Further, as silicon has a content of 1.2wt% or more, stability of austenite can be improved. However, when silicon has a content exceeding 2.0wt%, the seal may be broken and thus it is preferable that silicon has a content of 1.2wt% to 2.0wt%.
As alloy cast iron for a seal according to the present exemplary embodiment includes chrome of 16wt% to 18wt%, in a structure of the generated seal, carbide has a uniform distribution, and the alloy cast iron includes 0.8wt% to 1.5wt% of manganese and thus has excellent castability.
Hereinafter, the present invention is described in detail through the exemplary embodiment, but the present invention is not limited thereto.
Table 1 represents a composition of alloy cast iron for various seals, and Table 2 represents a result in which a seal is formed with a seal composition having a component of Table 1 using a centrifugal casting method and in which the formed seal performs a spinning test with mounted in a roller, as shown in FIG. 1.
Here, in the spinning test, a rotation speed uniformly increases in units of 100 rpm from 100 rpm to 900 rpm, and whenever rpm increases, weeping and leakage were checked.
After the spinning test is complete, tearing of a contact surface of the seal was checked by naked eyes, and when tearing of a contact surface of the seal is not checked by naked eyes, tearing of a contact surface of the seal was observed by a microscope.

Hereinafter, when there is no specific description, a unit of wt% is used.

[Table 1]

	No.	C	Ni	Mo	Si	Cr	Mn	Fe
	1	3.8	3.81	2.14	1.2	15.54	0.1	73.4
	2	3.64	3.77	3.9	1.5	15.94	0.2	71
	3	3.63	3.95	4,11	1.56	16.95	0.51	69.27
	4	3.65	4.5	4.07	1.53	17.08	0.86	69.29
	5	3.83	4.66	4	1.48	17.01	0.5	68.5
	6	3.7	4.56	3.85	1.5	17.14	0.87	68.34
	7	3.7	3.6	2.1	1.8	16.4	1.25	71.1
Comparative Example	8	4.3	4.7	4.5	1.9	16.2	1.2	67,17
	9	4.27	4.7	5	1.75	16.18	1.5	66.57
	10	4.05	3.2	3.9	1.72	16.3	1.25	69.55
	11	3.9	4.7	5.0	2.2	18.8	1.2	64.18
	12	3.95	4.8	4.5	1.75	16.18	1.25	67.55
	13	3.87	4.79	5	1.7	16.1	1.25	67.26
	14	3.87	4.6	1.3	1.72	17.3	1.25	69.94
	15	3.87	4.7	1.2	1.9	16.5	1.3	70.5
	16	4.1	3.3	5.6	1.9	16.5	1.3	67.25
	17	3.9	3.9	5.9	1.87	16.42	1.25	66.73
	1	3.8	3.77	3.9	1.2	18.1	1.25	67.92
	2	4.05	3.95	4.11	1.72	18.0	1.25	66.9
	3	3.8	4.5	4.07	1.9	16.5	1.3	67.9
	4	4.1	4.66	5	1.87	16.42	1.25	66.64
	5	3.8	3.3	2.1	1.7	17.1	1.25	70.72
Exemplary Embodiment	6	4.2	3.5	4.11	2.0	16.5	1.3	68.37
	7	4.2	4.06	4.07	1.87	16.42	1.25	68.1
	8	4.1	3.95	2.1	1.32	16.42	1.25	70.82
	9	3.9	4.5	3.85	1.8	16.2	1.2	68.51
	10	4.1	3.77	4.07	1.75	18.0	1.5	66.79
	11	4.07	3.6	3.9	1.72	16.3	1.25	69.13

Referring to Table 2, when alloy cast iron for a seal according to the present exemplary embodiment includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2wt% of silicon, 16wt% to 18wt% of chrome, and 0.8wt% to 1.5wt% of manganese, in the alloy cast iron, weeping and leakage are not generated up to a rotation speed of 900 rpm, and tearing of a contact surface of the seal was not found.
Therefore, because a centrifugal casting method having a simple manufacturing process can be applied to the alloy cast iron for a seal according to the present exemplary embodiment, production efficiency of the seal can be improved and the formed seal has excellent durability.
Further, when a drop test of the formed seal is performed at a height of 5m, the formed seal was not broken. This is because alloy cast iron for a seal according to the present exemplary embodiment includes nickel (Ni) and molybdenum (Mo) and thus excessive increase of hardness is suppressed.
FIG. 3 is a picture illustrating a structure of a seal formed with alloy cast iron for a seal according to an exemplary embodiment of the present invention, FIGS. 4 and 5 are pictures illustrating a structure of an existing seal, and FIG. 6 is a diagram illustrating an X-ray diffraction result of the seal shown in FIG. 3.
A seal formed with alloy cast iron for the seal using a centrifugal casting method includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron. Further, the seal may include inevitable impurities generated while performing other processes, and the impurities include cobalt (Co), tungsten (W), phosphorus (P), and vanadium (V).
Referring to FIGS. 3 to 5, FIG. 3 illustrates a structure of a seal formed with alloy cast iron for a seal according to the present exemplary embodiment using a centrifugal casting method, and FIGS. 4 and 5 illustrate a structure of a seal formed with existing alloy cast iron using a shell mold method, and in FIG. 3, an amount of pro-eutectic carbide A of a hexagonal shape is larger, and an amount of austenite and martensite B is less than those of FIGS. 4 and 5.
In a centrifugal casting method, when casting is performed, carbide may not be fully generated due to a fast cooling speed, but after casting, second carbide is generated through a heat treatment step, and most of the second carbide is transformed into martensite and carbide.
That is, a microstructure of a seal formed with alloy cast iron for a seal of the present exemplary embodiment using a centrifugal casting method includes 10 to 20% of austenite, 25 to 35% of martensite, and 50 to 60% of carbide. This can be seen through an X-ray diffraction result of FIG. 6.
This is because a seal manufactured according to the present exemplary embodiment performs a hypereutectic reaction at a segment having no brittleness and thus an amount of carbide increases, as described in FIG. 2.
Therefore, when a seal composition has the above range, the seal can be produced using a centrifugal casting method and thus productivity can be improved, and the produced seal has excellent abrasion resistance.
FIG. 7 is a view illustrating a method of manufacturing a seal according to another exemplary embodiment of the present invention.
As described above, a centrifugal casting method can be applied to alloy cast iron for a seal according to another exemplary embodiment of the present invention, and a method of manufacturing a seal according to the present exemplary embodiment includes a step of melting alloy cast iron for the seal; a step of injecting the melted alloy cast iron into a rotation mold; a step of forming a seal by a rotation of the rotation mold; performing heat treatment of the formed seal, and a step of finishing, grinding, and lapping a surface of the seal.
Referring to FIG. 7, a molten metal 510 in which alloy cast iron for a seal according to an exemplary embodiment of the present invention is melted is injected into a rotation mold 520. The rotation mold 520 is formed with copper and two mold frames of the rotation mold 520 are laterally coupled.
The alloy cast iron includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.
A spindle 550 is attached to a lower part of the rotation mold 520 and rotates with a speed of 300 to 2,000rpm by driving of a motor 530 connected to a gear 540. Thereby, the molten metal 510 injected into the rotation mold 520 is compressed to and solidified in an engraving mold 560 of the inside thereof according to a shape of a seal to cast, formed within the rotation mold 520 by a centrifugal force, thereby manufacturing a dense seal.
The manufactured seal is separated from the rotation mold 520 and heat treatment of the seal is performed. The rotation mold 520 is formed with copper and so on and thus has high heat conductivity, thereby increasing a cooling speed of the seal. Therefore, the formed seal does not generate enough carbide and thus second carbide is generated through a heat treatment step.
The formed seal includes iron includes 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron, and a microstructure of the seal includes 10 to 20% of austenite, 25 to 35% of martensite, and 50 to 60% of carbide.
The seal separated from the rotation mold 520 has a non-uniform surface, and unevenness may be formed in a coupling portion of the rotation mold 520, and in order to make uniform a surface roughness, the seal can be manufactured through a grinding step and lapping step of grinding a surface of the seal.
Because the centrifugal casting method can manufacture a seal having no irregular thickness due to a centrifugal force and does not disturb solidification contraction, a seal to be manufactured has a low casting stress, and the centrifugal casting method has a simple manufacturing process and increases production efficiency.
The embodiment of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

A seal comprising 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.
The seal of claim 1, wherein a microstructure of the seal comprises 10 to 20% of austenite, 25 to 35% of martensite, and 50 to 60% of carbide.
A method of manufacturing a seal, the method comprising:
melting alloy cast iron for the seal;

injecting the melted alloy cast iron into a rotation mold;

forming the seal by a rotation of the rotation mold; and

separating the seal from the rotation mold and performing heat treatment of the seal,

wherein the alloy cast iron comprises 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, the remaining of iron, and impurities generated upon melting.
The method of claim 3, further comprising grinding and lapping of making uniform a surface roughness of the seal in which heat treatment is performed.
Alloy cast iron for a seal comprising 3.8wt% to 4.2wt% of carbon, 3.3wt% to 4.7wt% of nickel, 2wt% to 5wt% of molybdenum, 1.2wt% to 2.0wt% of silicon, 16wt% to 18wt% of chrome, 0.8wt% to 1.5wt% of manganese, and the remaining of iron.