IE911246A1

IE911246A1 - Lubricant for a ceramic surface and lubrication process

Info

Publication number: IE911246A1
Application number: IE124691A
Authority: IE
Original assignee: Rhone Poulenc Chimie
Priority date: 1990-04-13
Filing date: 1991-04-12
Publication date: 1991-10-23
Also published as: KR910018524A; CA2040356A1; JPH04227688A; PT97356A; FR2660930A1; EP0452189A1

Abstract

Material for lubricating the contact between a first surface 2 made of a ceramic and a second surface 1 (ceramic or metal). This material comprises a rare-earth fluoride and is deposited between the surfaces to be lubricated, advantageously by compacting.

Description

LUBRICATION PROCESS The present invention relates to a dry lubricant for a ceramic/ceramic and metal/ceramic friction pair and to a lubrication process .

Lubrication of moving components is generally ensured by oils or greases which may or may not be filled with particles. However, the use of these lubricants is limited by the temperature in use.

Thus, in high-temperature applications, lubrication of moving components is generally ensured by temperature-resistant inorganic materials such as graphite, calcium fluoride or molybdenum sulphide. This lubrication is a dry lubrication of the surfaces, in contrast to liquid lubrication employed at low temperature.

These solid lubricants are introduced in the form of deposits of greater or lesser thickness on the surfaces subjected to friction. They are deposited either directly in powder form or in the form of a composition with an organic or inorganic binder.

However, these solid lubricants which resist high temperatures and are introduced between the rubbing surfaces do not make it possible to obtain a proper lubrication of this surface. Thus, a layer of graphite deposited between two ceramic surfaces which are set in motion relative to each other will be removed very quickly. This phenomenon has been verified with many known solid lubricants. ' ιι I The objective of the invention is especially to overcome these disadvantages by proposing a solid lubricant for surfaces at least one of these being made of ceramic material, which, on the one hand, forms a stable layer between the two surfaces to be lubricated and, on the other hand, provides a very low coefficient of friction, especially under external conditions, in particular at very high temperature and under high load.

To this end the invention proposes a material for dry lubrication of the contact between a first surface made of a first material and a second surface made of ceramic material. This lubricant comprises at least one rare-earth fluoride as main component.

The rare earths mean the elements of the lanthanide group which have an atomic number ranging from 57 to 71, including yttrium of atomic number 39.

Thus, by way of example, cerium, lanthanum, neodymium and gadolinium fluorides may be mentioned.

According to a preferred characteristic of the invention, the lubricant of the invention is arranged in the form of a layer or film on one of the surfaces to be lubricated. The lubricant may advantageously be compacted.

According to another characteristic of the invention the lubricant of the invention also comprises an inorganic or organic compound forming a binder in which the rare-earth fluoride is dispersed.

By way of example, resins such as polyquinoxyline, polybenzimidazole, polyimide, acrylic, polyvinyl, acetate, phenolic, silicone, epoxy, polyamide, urethane, polyvinylbutyral or similar polymers may be mentioned as an organic binder.

Similarly, by way of example, compounds based on silicate or phosphate, such as sodium silicate and sodium and/or potassium and/or aluminium phosphate may be mentioned as a mineral or inorganic binder which is suitable for the invention.

The lubricant of the invention may also comprise various additives such as additives for improving corrosion resistance, for promoting the application of the lubricant, colorants, wetting agents, viscosity improvers or the like.

The binder and rare-earth fluoride concentrations are not critical. However, according to a preferred embodiment, the weight concentration of rare-earth fluoride in the lubricant is at least 50 %, preferably between 80 % and 95 %.

The abovementioned first surface may be made of any material, but this material will advantageously be resistant to high temperatures, such as a metallic material, of refractory type, for example a nickel- or cobalt-based alloy, or a ceramic such as nonoxide (SiC, Si3N4, BN) or oxide (mullite, zirconia, etc) ceramic.

In the preferred embodiment of the invention the lubricant of the invention is advantageously especially suitable for ensuring lubrication between two surfaces made of ceramic material.

The nature of the ceramics is not critical and, for example, ceramics based on SiC, BN, Si3N4, zirconia, mullite or the like may be mentioned.

Thus, the lubricant arranged between the surfaces made of ceramic material ensures an effective lubrication, especially at high temperatures and under high load temperature increase. In addition, the lubricant is not removed and therefore permits a proper lubrication for a very long time (tens of hours).

Furthermore, since rare-earth fluorides are stable at high temperature, a good level of lubrication is maintained even after a long period of use.

Another subject of the invention is a process for lubricating the contact between two surfaces at least one of which is made of ceramic material. This process consists in interposing between the two surfaces to be lubricated a layer or a film of a lubricating material comprising at least one rare-earth fluoride.

The rare earth has been defined above, as have the preferred elements of the invention.

According to a preferred embodiment of the invention the lubricating material comprises an organic or inorganic binder in which the rare-earth fluoride is dispersed.

These organic or inorganic binders have been defined above, as have the preferred binder and rareearth fluoride compositions.

The rare-earth fluorides employed are advantageously powders whose mean particle diameter is preferably smaller than or equal to 50 pm.

The layer or film of lubricating material is deposited onto one or both surfaces to be lubricated before they are placed in position.

The components may be subjected to a heat 10 treatment to evaporate off any solvents which the binder may contain.

A heat treatment may also be applied to the components before they are fitted, in order at least partially to pyrolyse the binder of the lubricating materials.

It may also be advantageous to compact the film or layer of lubricating material before the components are set in motion.

According to another embodiment of the 20 process-of the invention the lubricating material may be formed into a desired shape, for example a ring, washer and the like, by moulding the composition using any conventional process.

According to yet another embodiment of the 25 process of the invention the lubricating material is applied to the surface of one of the materials either using a plasma torch or using a flame blowtorch. Thus, in this case the binder is unnecessary.

Other objectives, advantages and details of the invention will appear more clearly in the light of the detailed description and of the examples which are given below solely by way of guidance and in the light of the attached figures, in which: - Figure 1 shows a diagrammatic sectional view of two ceramic components lubricated according to the process of the invention, - Figure 2 shows the variation in the 10 coefficient of friction (K) as a function of time between two SiC ceramic rings with graphite lubricant (Ex. 2), - Figure 3 shows the variation in the coefficient of friction (K) as a function of time between two SiC ceramic rings with CeF3 lubricant + binder (Ex. 3), Figures 4a and 4b show the variations in the applied load (F) and in the coefficient of friction (K) respectively as a function of time, between a ceramic (SiC) ring and a metal ring with a CeF3 lubricant + binder (Ex. 4), and Figures 5a and 5b show the variations in the applied load (F) and in the coefficient of friction (K) respectively as a function of time, between ceramic (SiC) rings and a metal ring with a CeF3 lubricant + binder (Ex. 5).

Lubrication tests on two ceramic components 1, 2, one of which is driven in a rotary Ί motion in the specified direction, were carried out bycovering the face 3 of the component 1 with a lubricating material, for example by spreading the material on this surface.

In the assembly which is illustrated, rings 4, 5 are arranged so that they bear on the surface of the ceramic component 1. They allow the powder filling and compacting volume to be defined. These rings can be withdrawn after the lubricating material is deposited, advantageously after this material has been compacted.

Thus, before the components are set in motion, a load of 100 to 300 kg is applied to compact the spread lubricating material.

The components are then set in motion, for example by making the component 2 rotate at a speed of 0.1 m/s.

To determine the effectiveness of the lubricating material the driving torque needed to drive the component 2 in rotation is measured at various temperatures (20°C to 1000eC). Measurement of this torque results in the determination of the coefficient of friction (K). These measurements are performed for different loads which are applied to the ceramic components 1 and 2.

The tests carried out with various lubricating materials are collated in Table I below.

EX T°C -, LUBRICANT Time (min) Coeffi- cient of friction 1 Graphite fabric 10 0.95 30 0.75 10 60 0.75 2 20 KS 75 (Lonza) 5 0.80 graphite 30 0.80 + binder 60 0.80 15 3 20 CeF3 + binder 5 0.50 30 0.30 60 0.32 4 1000 CeF3 + binder 5 0.18 20 30 0.12 60 0.06 Experimental conditions: sliding speed = 0.1 m/s normal load applied = 1000 N Tests 1 and 2 show clearly that the materials introduced into the contact are not trapped because the value of the coefficient of friction is high after a short period of operation. This phenomenon is revealed by the curve of Figure 2, where the rapid increase in the value of the coefficient of friction (K) is attributable to the departure of the lubricant (Examples 1 and 2).

On the contrary, with a lubricating material in accordance with the invention (Examples 3 and 4) the trapping is permanent and results in a stable operating situation (Fig. 3) even when the applied load increases (Fig. 4) or when the temperature rises (Fig. 5).

Trapping of the lubricant in the contact may be improved by increasing the self-adhesiveness of the particles among themselves and to the first bodies. In Examples 3 and 4 the CeF3 powder was treated with an organic binder (Monsanto B74 polyvinyl resin) in a proportion of 5 % on a mass basis.

Similar results were observed with binder concentrations of 10 % and 20 %, and with a polyvinyl resin of higher molecular weight.

Furthermore, a test was performed with deposition of a layer of CeF3 onto the surface of a metal component by spraying a 25-40 pm particle size powder using a plasma torch. The coefficients of friction between this metal component and an SiC ceramic component were determined at various temperatures and under various loads.

Thus, it was found that at room temperature the coefficient of friction is high but decreases rapidly when the temperature rises and becomes very low at temperatures above 500°C, even under high loads of, for example, between 200 daN and 1000 daN, as illustrated in Figure 6a, showing the variation in the coefficient of friction K as a function of time, and in Figure 6b, showing the variation in the applied load F in daN as a function of time, the temperature of the experiment being 800°C.

Claims

1. Solid material for dry lubrication of the contact between a first surface made of a first material and a second surface made of ceramic, 5 characterised in that it comprises at least one rare-earth fluoride.

2. Material according to Claim 1, characterised in that it comprises a cerium, lanthanum, neodymium or gadolinium fluoride. 10

3. Material according to Claim 1 or 2, characterised in that the rare-earth fluoride is compacted.

4. Material according to Claim 1 or 2, characterised in that the rare-earth fluoride is 15 applied to a surface using a plasma torch or a flame blowtorch.

5. Lubricant according to one of Claims 1 to 3, characterised in that it comprises an inorganic or organic compound forming a binder. 20

6. Material according to Claim 5, characterised in that the compound forming a binder is an organic resin chosen from the group comprising resins such as polyquinoxyline, polybenzimidazole, polyimide, acrylic, polyvinyl, acetate, phenolic, 25 silicone, epoxy, polyamide or urethane polymers.

7. Material according to Claim 5, characterised in that the compound forming a binder is an inorganic resin chosen from the group comprising silicate- or phosphate-based compounds.

8. Material according to one of the preceding claims, characterised in that the first surface is made of a material chosen from the group 5 comprising nickel- or cobalt-based metallic materials of refractory type and ceramic materials (chosen from nonoxide (SiC, Si 3 N 4 , BN) and oxide (mullite, zirconia) ceramics .

9. Material according to one of the 10 preceding claims, characterised in that the two surfaces are made of ceramic material.

10. Material according to one of the preceding claims, characterised in that the ceramic material is chosen from the group comprising ceramics 15 based on SiC, BN, Si 3 N 4 , zirconia and mullite.

11. Process for dry lubrication of the contact between two surfaces one of which is made of ceramic material, characterised in that it consists in interposing between the two surfaces to be lubricated a 20 layer of a lubricating material comprising at least one rare-earth fluoride.

12. Process according to Claim 11, characterised in that the lubricating material comprises an inorganic or organic binder in which at 25 least one rare-earth fluoride is dispersed.

13. Process according to Claim 12, characterised in that the rare-earth fluoride represents at least 50 %, preferably between 80 % and !E 911246 95 %, of the lubricating material, on a mass basis.

14. Process according to Claim 12 or 13, characterised in that the organic binder is chosen from the group comprising resins such as polyquinoxyline, 5 polybenzimidazole, polyimide, acrylic, polyvinyl, acetate, phenolic, silicone, epoxy, polyamide and urethane polymers .

15. Process according to Claim 12, characterised in that the inorganic binder is an 10 organic resin chosen from the group comprising silicate- or phosphate-based compounds.

16. Process according to Claim 11, characterised in that the lubricating material is deposited onto one of the surfaces to be lubricated 15 using a plasma torch or a flame blowtorch.

17. Process according to one of Claims 11 to 16, characterised in that the rare-earth fluoride is a cerium fluoride, lanthanum fluoride, neodymium fluoride or gadolinium fluoride. 20

18. Process according to one of Claims 11 to 15 and 17, characterised in that the layer of lubricating material is compacted between the two surfaces to be lubricated.

19. Process according to one of Claims H to 25 15 and 17 to 18, characterised in that the layer of lubricating material is compacted to a desired shape before it is arranged between the surfaces to be lubricated. 1 4

20. A solid material according to Claim 1, substantially as hereinbefore described and exemplified

21. A process according to Claim 11, substantially as hereinbefore described and exemplified Dated this the 12th day of April, 1991 F. R. KELLY & CO.