ASSEMBLY HAVING TWO MEMBERS MOVABLE IN CONTACT

Abstract: An assembly having two members arranged for relative movement in contact during or before or after the movement, wherein one member is of ceramics and the other is metal member whose contact surface is coated with a composition of Cu and LiF. Such a combination has small weight loss and max wear depth in a friction and wear test. It is useful for combinations such as tappet/cam, rocker arm/cam, valve/valve seat and liner/piston ring.

Description: This invention relates to an assembly having two members arranged for relative movement with respective surfaces in contact during or before or after the movement. The invention is applicable to relatively sliding members and also to contacting (abutting) members such as a valve member and a valve seat and rolling members such as in a roller bearing. For convenience the term "sliding member" is used, but herein carries a reference to such contacting members and rolling members. Also, the term "coating" includes a partial coating and especially includes a coating with a composition of Cu and LiF for only depressions formed on a surface of a metal member. Hitherto as sliding members for use in engines, use has been made of metal materials, such as heat-­ resistant alloys, with a lubricant such as oil, because many engine members have to be exposed to high temperature and to wear due to high speed. However, since the required conditions of use of such sliding members become more severe year by year and further there is a desire for avoiding the use of lubricant, there arises the drawback that such requirements for temperature and wear cannot be met by metal materials or that the metal member must be replaced after a short period. In order to eliminate or reduce this draw­ back, a ceramic material may be used for a sliding member. Suitable ceramic materials can endure high temperature and have high wear resistivity and high heat efficiency, but tend to be very hard and brittle. Therefore, not all ceramic materials can be used for a sliding member for this purpose. Hitherto, there has been no investigation as to what ceramic material is most suitable as a sliding member especially for an engine member which is to endure high temperature and requires high wear resistance nor as to what other sliding member is most suitable to be brought into contact with such a ceramic material. The present invention is able to eliminate or reduce the drawback mentioned above and to provide as assembly including a ceramic member, e.g. an assembly for use in an engine, in which there is a good combination between the ceramic member and another member to be brought into contact with the ceramic member, without use of lubricant. According to the invention, there is provided an assembly having two members arranged for relative movement with respective contact surfaces in contact during or before or after the movement, characterized in that one said contact surface is a surface of a ceramics member and the other is a surface of a metal member coated with a composition of Cu and LiF. The contact surfaces may be planar, cylindrical, frusto-conical or of any other shape. This invention is based on the finding that a ceramic material such as silicon nitride, sialon, partially stabilized zirconia or silicon carbide sliding, abutting or rolling against a metal member especially against metal member whose contact surface is coated with a composition of Cu and LiF by means of a plasma spray can provide high wear resistivity at any temperatures from room temperature to high temperature. Moreover, this is in contrast with sliding of ceramic material against ceramic material which at best cannot achieve high wear resistivity. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a schematic view showing a test apparatus for measuring a sliding characteristic; and Figs. 2 to 5 are diagrams illustrating the testing results of specimens. Fig. 1 is a schematic view showing a test apparatus for measuring sliding characteristics such as friction and wear. One specimen made of ceramic material is arranged in the test apparatus as a counter­ face roller 1 having a diameter of 50 mm. The ceramic counter roller 1 is rotated at 1,000 rpm by means of a driving device not shown. As the other specimen, a test specimen 2 made of for example metal material coated with Cu+LiF and having dimensions of 40 mm x 6.33 mm x 3 mm is arranged in the test apparatus in such a manner that it is brought into contact with the counter roller 1 by means of a loading arm 3 as shown in Fig. 1. One end of the loading arm 3 is secured to a supporting member 4 through a linear/rotary bearing 5 and a spring 6, and the support member 4 is moved pivotally by means of a pivot bracket 7. Moreover, on the support member 4, a tip portion of the loading arm 3 is brought into contact with a cam 9 connected to a motor 8 rotating at 3 rpm, and thus the loading arm 3 is moved forward and backward with a stroke of 12 mm three times per minute. A force of 20N is loaded at the other end of the loading arm 3 downwardly, and thus the ceramic counter roller 1 is brought into contact with the test specimen 2 at a constant pressure. The ceramic counter roller 1 and the test specimen 2 are surrounded by an insulated oven 10 so as to enable a test to be performed at high temperature. Using the test apparatus described above, weight loss and maximum wear depth between various ceramic materials and metals or ceramic materials are measured. The materials used for the specimens are shown in Table 1 together with their forming process. In Table 1, each coating layer is formed by a plasma spray. Moreover, in the high-speed tool steel coated with Cu+LiF, spherical depressions each having a diameter of 390 µm and a depth of 100 µm are formed at an interval of 460µm in the surface to be coated by means of an etching before a coating operation with Cu+LiF. Using the materials described in Table 1, friction and wear tests were performed at room temperature (R.T.) and at 538°C without lubricant to measure the weight loss and maximum wear depth. The test at 538°C is performed to demonstrate the useful­ ness of the specimen for a piston in a cylinder. The results are shown in the following Table 2. Further, to aid understanding, the results described in Table 2 are summarized in Figs. 2 to 5, where the numerals correspond to the Test Nos. of Table 2. These test results show that the weight loss and the max wear depth values are always smallest for contact between the specimen of high-speed tool steel (M2) whose surface is coated with Cu+LiF and various ceramics materials, regardless of the test temperature. Thus, combinations of metal, especially high-speed tool steel, coated with Cu+LiF and various ceramics materials are best for an assembly of sliding members. In contrast, a combination of 316 stainless steel whose surface is coated with Cr₂O₃ or Cr₃C₂ and various ceramics materials shows generally a large weight loss, and thus it is not preferable for such an assembly. Likewise the combination of a ceramics material and a ceramics material shows also a large weight loss, and thus it is not suitable for an assembly of sliding members. Combinations of metal materials whose surfaces are coated with Cu+LiF and various ceramics materials are thus preferable because weight loss and max wear depth are small regardless of the test temperature.

Claims: 1. An assembly having two members arranged for relative movement with respective contact surfaces in contact during or before or after the movement, characterized in that one said contact surface is a surface of a ceramics member and the other is a surface of a metal member coated with a composition of Cu and LiF. 2. An assembly according to claim 1 wherein said ceramics member is made of silicon nitride, sialon, partially stabilized zirconia and/or silicon carbide. 3. An assembly according to claim 1 or claim 2, wherein said metal member is made of a high-speed tool steel. 4. An assembly according to any one of claims 1 to 3 which is used in an engine. 5. An assembly according to any one of claims 1 to 4, wherein said two members are a tappet and a cam or a rocker arm and a cam. 6. An assembly according to any one of claims 1 to 4 wherein said two members are a valve and a valve seat. 7. An assembly according to any one of claims 1 to 4, wherein said two members are a liner and a piston ring.

Inventors: ODA, ISAO
Applicants: NGK INSULATORS, LTD.
Application year: 1986
Main classification: F16C33
IPC codes: F01L3, F16H53, F02F1, F01L1, F16J10, F16C33, C23C30, F02F5, F16J15, F16J9, C23C4