MODENGY adaptive solid-film coatings for petal gas-dynamic bearings. Selection on the service temperatures conditions

The important elements of the high-speed energy machines are petal gas-dynamic bearings (PGDBs). These are modern supports with gas lubrication. However, in the moments of starting, stopping, under transient and emergency modes their operability and service lifetime are provided by special solid-film coatings. They are applied onto the carrying surfaces of the petals. 

Such coatings operate under complex enough conditions, so they must have high thermo- and wear resistance, provide low friction coefficient, and good adhesion to the basis.

Service temperatures of the bearings can cover the range from -50 to +700 °С and above. None of the solid lubricating materials known for today that form the base of the coatings is able to operate effectively under these conditions.  

So, friction coefficient of molybdenum disulfide grows significantly at higher than +300…+350 °С because of oxidation accompanied by forming molybdenum trioxide. In order to realize lubrication mechanism, graphite requires moisture presence in it which evaporates at higher than +200…+250 °С. Oxides of some metals, and calcium fluoride, on the contrary, reveal their lubricating properties within a high-temperature spectrum only - above +400 °С. 

That’s why solution of the described problem is in the field of combining solid lubricating materials with various additives, and creating adaptive coatings. The adaptive mechanism means that new structures are formed in the coating while transiting through the certain temperature limits. This is the way how it gets adapted towards the new operational conditions in a reversible way. 

The Modengy company has designed a series of the adaptive coatings that have found an application for PGDBs. Some of their comparative features are presented in Table 1.

Table 1. Comparative features of MODENGY coatings for PGDBs

On Fig. 1, appearance of the elements of the thrust petal gas-dynamic bearing treated with MODENGY 1071 coating is presented as an illustration.

 Fig. 1. Elements of the petal gas-dynamic bearing treated with MODENGY 1071 coating

Fig. 2. Tests of coatings for foil bearings according to ASTM G99

At selecting the coatings, the operating medium (gas) kind, and a number of other factors should be taken into account. That is why we recommend you to address to the Modengy’s Engineering Center where you will be assisted in this point.