CN111139475A

CN111139475A - Preparation of self-lubricating coating suitable for middle-low temperature air bearing journal

Info

Publication number: CN111139475A
Application number: CN201910602877.0A
Authority: CN
Inventors: 丁春华; 李�浩; 付冬梅; 刘艳
Original assignee: Yancheng Baisheng Machinery Co ltd
Current assignee: Yancheng Baisheng Machinery Co ltd
Priority date: 2019-07-04
Filing date: 2019-07-04
Publication date: 2020-05-12

Abstract

The invention discloses a preparation method of a self-lubricating coating suitable for a middle-low temperature (room temperature-450 ℃) air bearing journal. Firstly, Cr is mixed according to the weight ratio₂O₃: 5% -20%, graphite powder: 15% -20%, CaF₂: 1% -5% of nano MoS₂: 1 to 3 percent of NiCr alloy powder (80/20) and the balance. And ball milling the mixture by adopting a ball milling process to obtain mixed powder with uniformly distributed components. The powder is prepared into slurry to be coated on the surface of a shaft neck, after the coating is dried, the density of the coating is improved by adopting a cold isostatic pressing method, induction sintering is carried out for 1-2 hours in vacuum or nitrogen protective atmosphere, and a high-temperature-resistant self-lubricating coating with fine and uniform microstructure is obtained after sintering. The friction and wear performance of the self-lubricating coating prepared by the invention at room temperature of 450 ℃ is obviously superior to that of the existing self-lubricating coating.

Description

Preparation of self-lubricating coating suitable for middle-low temperature air bearing journal

Technical Field

The invention belongs to the field of medium and low temperature friction and wear materials, and particularly relates to a preparation method of a medium and low temperature (room temperature-450 ℃) self-lubricating coating.

Background

At present, the elastic foil aerodynamic bearing has been successfully applied to high-speed rotating machines, such as air refrigerators, auxiliary energy units, various small turbo compressors and aviation machines, that is, the foil aerodynamic bearing has been well applied to both civil and military fields. One of the key technologies in foil aerodynamic bearing technology is start-stop lubrication. During normal high speed operation, the bearing is supported on a thin film of air generated by itself and therefore does not wear, but at start-up and shut-down of the shaft the foils rub against the journal, inevitably resulting in wear. The air bearing has failed when the foil wears more than 25% of its thickness and when the shaft wears more than 0.025 m. High-temperature oxidation resistance, high-temperature corrosion resistance and basic mechanical strength

Therefore, such bearings often require the use of self-lubricating coatings, such as those provided on the journal. In order to improve the frictional wear performance and the mechanical property of the coating, how to realize the coating with low porosity and greatly improved medium and low temperature lubricating property of the coating is the key of the problem.

Disclosure of Invention

In view of the above, the invention aims to provide a preparation method of a self-lubricating coating with high medium-low temperature lubricating performance.

In order to achieve the purpose, the preparation method adopted by the invention comprises the following steps: firstly, NiCr with the purity of more than 99.0 percent and the particle size of 30-200 mu m, graphite powder and Cr are mixed₂O₃、CaF₂、MoS₂Powder of Cr₂O₃: 5% -20%, graphite powder: 15% -20%, CaF₂: 1% -5% of nano MoS₂: 1% -3%, the rest is NiCr. Ball-milling the mixture for 3-5 hours by a high-energy ball mill under the conditions that the ball-material ratio is 8-10: 1 and the rotating speed is 800-1200rps and under the protection of nitrogen, so that the powder is uniformly mixed, and the composite powder with the particle size of less than 20 mu m is ball-milled. Adding polyvinyl alcohol (1.5-3.0 wt%) as binder into the above composite powder, and mixing with alcohol (75 wt% of alcohol and 25 wt% of water) at a weight ratio of 8-10: 1Slurry, coating the prepared slurry on the surface of the shaft neck to form a coating, and then drying the coating at the temperature of 100-120 ℃, wherein the drying time is 0.5-1.0 hour. Then, the coating of the shaft neck is processed for 5 to 10 minutes by a cold isostatic pressing method under the condition of 50 to 70 Mpa. Finally, sintering the coating subjected to cold isostatic pressing for 1-2 hours at the temperature of 900-1100 ℃ under the vacuum condition or the protection of nitrogen.

The invention adopts graphite powder as a lubricating phase, the graphite powder has good self-lubricating property at room temperature of 450 ℃ below zero and very low cost, the granularity of the powder after high-energy ball milling is less than 20 mu m, and the active energy of the surface of the powder is higher and the sintering property is better. Moreover, the self-lubricating alexandrite ink powder and CaF can be prepared under certain ball milling conditions₂Particle size of less than 5 μm, nano MoS₂The particle size is only 50-100nm, so that the lubricating phase of the coating prepared by sintering is fine and is uniformly distributed.

Detailed Description

Example 1: firstly, NiCr with the purity of more than 99.0 percent and the particle size of 30-200um, graphite powder and Cr are mixed₂O₃、CaF₂、MoS₂Powder of Cr₂O₃: 10%, graphite powder: 20% of CaF₂: 1% of nano MoS₂: 1.5 percent and the balance of NiCr. And (3) mixing the mixture by a high-energy ball mill at a ball-to-material ratio of 10: 1, ball milling for 3 hours under the conditions that the diameter of a GCr15 steel ball is 5mm and the rotating speed is 1200rpm and under the protection of nitrogen, uniformly mixing the powder, and carrying out ball milling on the powder to obtain composite powder with the particle size of less than 10 mu m, wherein Cr is₂O₃、CaF₂Has a particle size of less than 5 μm and a nano MoS₂The particle size is 50-100 nm. Adding polyvinyl alcohol with the total weight of 3 percent into the composite powder as a binder, mixing the mixture with alcohol (the components are 75 percent of alcohol content and 25 percent of water) according to the weight ratio of 8: 1, stirring the mixture to prepare slurry, coating the prepared slurry on the surface of a shaft neck to form a coating, and then drying the coating for 0.5 hour at the temperature of 100 ℃. Processing the shaft neck coating for 10 minutes under the condition of 50Mpa by adopting a cold isostatic pressing method; finally sintering the cold isostatic pressed coating at 900 ℃ for 3 hours under the vacuum condition or under the protection of nitrogenIt is just needed.

Example 2: firstly, NiCr with the purity of more than 99.0 percent and the particle size of 30-200um, graphite powder and Cr are mixed₂O₃、CaF₂、MoS₂Powder of Cr₂O₃: 15%, graphite powder: 15% of CaF₂: 3% of nano MoS₂: 2 percent, and the balance of NiCr. Ball-milling the mixture for 2 hours by using a high-energy ball mill under the conditions that the ball-material ratio is 9: 1, the diameter of a GCr15 steel ball is 5mm, the rotating speed is 900rpm and under the protection of inert gas, uniformly mixing the powder, and ball-milling the powder into composite powder with the particle size of less than 15 mu m, wherein Cr is contained in the composite powder₂O₃、CaF₂Has a particle size of less than 5 μm and a nano MoS₂The particle size is 50-100 nm. Adding polyvinyl alcohol accounting for 3 percent of the total weight into the composite powder as a binder, mixing the powder with alcohol (the components are 75 percent of alcohol content and 25 percent of water) according to the weight ratio of 10: 1, stirring the mixture to prepare slurry, coating the prepared slurry on the surface of a shaft neck to form a coating, and then drying the coating for 1.0 hour at the temperature of 120 ℃. Treating the shaft neck coating for 7 minutes under the condition of 60Mpa by adopting a cold isostatic pressing method; and finally sintering the cold isostatic pressed coating for 2 hours at 1000 ℃ under the vacuum condition or the protection of nitrogen.

Example 3: firstly, NiCr and Cr with the purity of more than 99.0 percent and the particle size of 30-200um are mixed₂O₃、CaF₂、Ag、MoS₂Powder of Cr₂O₃: 20%, graphite powder: 17% of CaF₂: 2% of nano MoS₂: 3 percent, and the balance of NiCr. Ball-milling the mixture for 3 hours by using a high-energy ball mill under the conditions that the ball-material ratio is 8: 1 and the rotating speed is 800rpm and protecting with inert gas to uniformly mix the powder, and ball-milling the powder into composite powder with the particle size of less than 10 mu m, wherein Cr is₂O₃、CaF₂Has a particle size of less than 5 μm and a nano MoS₂The particle size is 50-100 nm. Adding polyvinyl alcohol accounting for 3 percent of the weight of the composite powder into the composite powder as a binder, mixing the mixture with water or alcohol according to the weight ratio of 9: 1, stirring the mixture to prepare slurry, coating the prepared slurry on the surface of a shaft neck to form a coating, and then heating the coating at 110 DEG CThe coating was dried for 45 minutes under the conditions of (1). And (3) treating the journal coating for 5 minutes under the condition of 70Mpa by adopting a cold isostatic pressing method, and finally sintering the cold isostatic pressed coating for 1 hour at 1050 ℃ under the vacuum condition or under the protection of nitrogen.

The composite powder is sintered, and Cr in the coating₂O₃Graphite powder, CaF₂Nano MoS with particle less than 5 micron₂The particle size is 50-100nm and these components are uniformly distributed in the matrix NiCr alloy. Tests show that the coating of the invention is suitable for medium and low temperature, wherein the Cr is₂O₃(5% -20%), graphite powder (15% -20%), CaF₂(1% -5%) and nano MoS₂The weight ratio of (1-3%) and the balance of NiCr is proper, and the performance of the obtained lubricating coating in the formula range is superior to that of the existing PS304 coating. Test data show that the abrasion loss is reduced by 25 percent compared with the existing PS304 coating at room temperature of 450 ℃, the strength is improved by 30 percent, and the microhardness is improved by 40 percent, which has great significance for prolonging the service life of the foil bearing and reducing the maintenance cost.

Claims

1. A preparation method suitable for a medium-low temperature self-lubricating coating is characterized by comprising the following steps:

1) firstly, a mixture with a purity of more than 99.0% and a particle size of 30-200 μm: NiCr, Cr₂O₃Graphite powder, CaF₂And nano MoS with purity of more than 99.0 percent₂Powder, according to: cr (chromium) component₂O₃: 5% -20%, graphite powder: 15% -20%, CaF₂: 1% -5% of nano MoS₂: 1% -3%, the balance of NiCr by weight to form a mixture, wherein the nano MoS₂The particle size is 50-100 nm;

2) ball-milling the mixture for 3-5 hours by a high-energy ball mill under the conditions of ball-material ratio of 8-10: 1, rotation speed of 800-1200rps and nitrogen protection to uniformly mix the powder, and ball-milling the powder to form composite powder with the particle size of less than 20 mu m, wherein after ball-milling: graphite powder and Cr₂O₃、CaF₂Has a particle size of less than 5 μm;

3) adding water-soluble micron-sized powdery polyvinyl alcohol which is 1.5-3.0% of the total weight of the composite powder as a binder, mixing the mixture with alcohol with the concentration of 75% according to the weight ratio of the composite powder to the alcohol of 8-10: 1, stirring to prepare slurry, coating the prepared slurry on the surface of a shaft neck to form a coating, and drying the coating at the temperature of 100-120 ℃ for 0.5-1.0 hour; at the moment, the alcohol and the water in the coating are completely volatilized;

4) treating the journal coating for 5-10 minutes under the condition of 50-70Mpa by adopting a cold isostatic pressing method, and finally sintering the journal coating treated by the cold isostatic pressing method for 1-2 hours at the temperature of 900-1100 ℃ under the vacuum condition or the nitrogen protection atmosphere; wherein, in the sintering process, the melting point of the polyvinyl alcohol is only 230 ℃, and in the sintering process of 900-1100 ℃, the polyvinyl alcohol in the coating is completely volatilized.