EP1375695B1

EP1375695B1 - Wear-resistant sliding member

Info

Publication number: EP1375695B1
Application number: EP02703886A
Authority: EP
Inventors: Hiroyuki Nippon Piston Ring Co. Ltd TAKAMURA
Original assignee: MAN B&W Diesel AS; Nippon Piston Ring Co Ltd
Current assignee: MAN B&W Diesel AS; Nippon Piston Ring Co Ltd
Priority date: 2001-02-28
Filing date: 2002-02-22
Publication date: 2008-11-12
Anticipated expiration: 2022-02-22
Also published as: CN1501986A; JP4790135B2; CN1209483C; EP1375695A4; KR100531995B1; RU2245472C1; JPWO2002068706A1; SE0302260L; WO2002068706A1; KR20030091994A; SE526621C2; EP1375695A1; JP2004107678A; SE0302260D0

Description

The invention relates to a sliding member having a base metal and a sprayed coating formed on an external sliding surface of said base metal by spraying of a powder mixture.
Recently, internal combustion engines are strongly demanded to have higher power and performance. Sliding members, such as piston rings and cylinder liners employed in the internal combustion engines are burdened with ever increasing severe conditions, whereby every sliding member is required to have higher abrasion resistance and scuffing resistance.
Conventionally, chrome-plating treatment is applied to enhance the abrasion resistance of the sliding member. However, the chrome-plating treatment is insufficient to improve the scuffing resistance of the sliding member, so that it tends to be replaced by spraying treatments.
A sliding member as mentioned above in the form of a piston ring is known from JP 6 221 438 A , where the sprayed coating on the sliding surface of the piston ring comprises molybdenum, nickel-chrome alloy and fine powders of chrome carbide. The piston ring as proposed above has a sliding resistance increased due to the ceramics powders contained in the sprayed coating.
The DE 197 00 835 discloses a method of coating a metallic part by HVOF coating with a self-lubrication powder mixture consisting of in vol.% 25-75% of a carbide containing ceramic powder, 5-50% of a metal powder (Ni or Cr or a mixture of them) and 2-25% of a solid lubricant selected from the group of molybdenum disulfide, lead oxide, graphite, silver and titanium oxide. Hereby an upper limit of 25 % for the solid lubricant is permitted.
The JP 2000 - 017419A shows a sliding member having a coated sliding layer consisting of in % by weight 30-80%, molybdenum, 10-50% NiCr, 2-35% Cr₂O₃ with an additive of 1-7% SiO₂.
Starting from the prior art mentioned above it is the aim of the invention to provide an abrasion resistant sliding member formed with a sprayed coating that is prevented from increasing the sliding resistance and attacking the counterpart.
This aim is solved in that said mixture is consisting of by mass, 30 - 70% of molybdenum powder, 10 - 40% of nickel-chrome alloy powder, 3-40% chrome oxide and 2-15% of solid lubrication powder.
According a useful embodiment the solid lubricant powder is consisting of one selected from the group consisting of calcium fluoride, manganese sulfide and molybdenum disulfide.
The reason for an content range of 30 to 70% by mass of molybdenum powder is that, when the content of molybdenum powder below 30%, the coating deteriorates the scuffing resistance. When the content of molybdenum powder exceeds 70%, the coating is difficult to have a sufficient hardness.
The reason for an content range of 10 to 40% by mass of nickel-chrome alloy powder is that, when the content of nickel-chrome alloy powder is below 10%, the coating is difficult to have a sufficient tenacity. When the content of nickel-chrome alloy powder exceeds 40%, the coating deteriorates the scuffing resistance.
The reason for a content range of 3 to 40% by mass of ceramics powder in the form of chrome oxide is that, when the content of this constituent is below 3%, the coating is difficult to have a sufficient hardness. When the content of this constituent exceeds 40%, the coating becomes hard to attack the counterpart.
The reason for a content range of 2 to 15% by mass of solid lubricant powder is that, when the content of solid lubricant powder is below 2%, the lubrication effect is too insufficient to prevent the coating from increasing the sliding resistance and attacking the counterpart material. When the content of solid lubricant powder exceeds 15%, the coating becomes brittle.
The wear-resistant sliding member of the present invention is superior both in abrasion resistance and in scuffing resistance and is less attackable to the counterpart material due to the solid lubricant powder contained in the coating than the sprayed sliding member as known by the aforementioned references. Accordingly, it is advantageously employable as a piston ring or the like in highperformance, large-sized marine diesel engine. A special advantage is that it enables to lengthen life of engine.
Further advantageous embodiments and practical further developments of the higher-order steps are possible and ensue from the following description of an example by means of the drawings described below.

Brief Description of the Drawings:

Fig. 1: is a partial, cross-sectional view of a sliding member according to the present invention; embodies as a piston ring,
Fig. 2: is a schematic drawing of a rotary-type plane sliding friction tester,
Fig. 3: is a graph showing a result of scuffing resistance tests; and
Fig. 4: is a graph showing abrasion amounts measured in the abrasion resistance tests.

Description of an Embodiment of the Invention.
Referring to Fig. 1 showing a partial, cross-sectional view of a piston ring 10, according to an embodiment of the present invention, a sprayed coating C is formed on the external circumferential surface of the base metal M of the piston ring 10. The sprayed coating C is made by spraying a mixture containing, by mass, 30 to 70% of molybdenum powder, 10 to 40% of nickel-chrome alloy powder, 3 to 40% of ceramics powder in the form of chrome oxide and 2 to 15 % of solid lubricant powder.
The sprayed coating C is superior both in abrasion resistance and scuffing resistance while it is prevented from increasing the sliding resistance and attacking the counterpart material because of containing solid lubricant powder.

Examples:

Now, embodiments of the sliding member, according to the present invention, are further described referring to various tests conducted in comparison with other sliding members.
Eight types of test samples were prepared by forming eight types of coating of 300µm thickness on pieces of the same cast iron for piston rings, as a base material, of which the two samples Nos. 1 and 2 are comparative or corresponding to the other sliding members as known by the aforementioned reference. The six samples Nos. 3,4,5,6,7 and 8 are inventive. The coatings were made by plasma-spraying of the respective powdery mixtures, of which the composition is shown in Table 1.

Table 1

Sample	Remarks	Composition of Powdery Mixtures (mass %)
		Mo	Ni-Cr alloy	Ceramics	Solid Lubricant
No. 1	Comparative	45	20	35 (CrC)
No. 2	Comparative	65	30	5 (CrC)
No. 3	Inventive	40	15	30 (Cr₂O₃)	15 (CaF₂)
No. 4	Inventive	60	30	5 (Cr₂O₃)	5 (CaF₂)
No. 5	Inventive	40	15	30 (Cr₂O₃)	15 (MnS)
No. 6	Inventive	60	30	5 (Cr₂O₃)	5 (MnS)
No. 7	Inventive	40	15	30 (Cr₂O₃)	15 (MoS₂)
No. 8	Inventive	60	30	5 (Cr₂O₃)	5 (MoS₂)

Plasma-spraying conditions are as follows:
Gun: Sulzer Metco 7MB plasma spraying gun (product name)
Electric Voltage: 60 ∼ 70V
Electric Current: 500 A

Scuffing resistance and abrasion resistance tests were conducted for each specimens, as follows:

Scuffing resistance tests

Scuffing resistance for each sample was measured using a rotary-type plane sliding friction tester, as schematically shown in Fig. 2. The friction tester has a mechanism where a sample 11 is brought in contact with, and held pressed against, a rotary plane surface or counterpart material 12 rotating at a constant speed with a specified face pressure P for a specified period of time, and a face pressure at with scuffing occurs is measured as a critical scuffing face pressure. Face pressure was applied in a manner that initial face pressure of 2.45MPa was kept for 30 minutes, then, the face pressure was increased by 0.98MPa in each successive 5 minutes.
Measuring conditions were as follows:

Sliding speed: 5m/sec
Lubricating oil : SAE30 + white kerosene (1:1)
Oil amount: no oil applied, except initial application
Counterpart material: Tarkalloy (known as a product name owned by Nippon Piston Ring Co., Ltd. for a boron cast iron)

A result for the tests is shown in Fig. 3. As seen from Fig. 3 all the inventive samples Nos. 3 to 8 have their critical scuffing face pressure in a range of 7.8 Mpa while the comparative samples Nos. 1 and 2 have the critical scuffing face pressure in a range of 6.9 to 7.8 MPa. Accordingly, the inventive sliding member is similar or superior to the comparative one.

Abrasion resistance tests

Abrasion amounts for each samples and its counterpart material were measured using the aforementioned rotary-type plane sliding friction tester, as schematically shown in Fig. 2. The friction tester has a mechanism where a sample 11 is brought in contact with, and held pressed against, a rotary plane surface of counterpart material 12 rotating at a constant speed with a specified face pressure P for a specified test running time. Lubricating oil is applied to the counter material 12.
Measuring conditions were as follows:

Sliding speed: 6m/sec
Face pressure: 6MPa
Lubricating oil: Spinox S-2 (known as a product name owned by Nippon Oil Co., Ltd. for bearing oil)
Oil temperature: 60±10ºC
Oil amount: 10^-4m³/min
Test running time:100hr
Counterpart material: Tarkalloy (known as a product name owned by Nippon Piston Ring Co., Ltd. for a boron cast iron)

A result for the abrasion test is shown in Fig. 4. As seen from Fig. 4, all the inventive samples Nos. 3 to 8 have their abrasion amounts in a range of 14.1 to 17.1 µm while the comparative samples Nos. 1 and 2 have their abrasion amounts in a range of 17.5 to 22.3 µm. Accordingly, the inventive sliding member is better in abrasion resistance than the comparative one. All the inventive samples Nos. 3 to 8 have their counterpart abrasion amounts in a range of 1.1 to 1.8 µm while the comparative samples Nos. 1 and 2 have their counterpart abrasion amounts in a range of 2.8 to 4.3 µm. Accordingly, the inventive sliding member is much better in avoidance of attack on a counterpart than the comparative one.

Claims

A sliding member (10) having a base metal (M) and a sprayed coating (C) formed on an external sliding surface of said base metal by spraying of a powder mixture, characterized in that said mixture is consisting of by mass, 30 to 70% of molybdenum powder, 10 to 40% of nickel-chrome alloy powder, 3 to 40% chrome oxide and 2 to 15 % of solid lubricant powder.
The sliding member as claimed in claim 1, wherein said solid lubricant powder is consisting of one selected from the group consisting of calcium fluoride, manganese sulfide and molybdenum disulfide.