Journal bearing design criteria - VII Measuring oil film thickness

Journal bearing design criteria - VII Measuring oil film thickness

As stated in the previous articles, radial journal bearings have operating parameters sufficient to carry the bearing load between the journal (shaft) and the bearing surface. These parameters include speed, load, oil flow, oil viscosity, bearing width, bearing diameter, bearing and oil temperatures, surface texture, etc. One of the main objectives in bearing design is to separate the bearing surface from the journal surface by means of an easily transformable elastic oil film with a suitable thickness. This oil film layer acts as a suspension. However, its easily transformable nature, the intensity and direction of the load, the size and direction of the shaft speeds and changeable nature of the thickness of this oil film at any time pose a risk in terms of the life of the bearing - shaft.

In terms of bearing design, it is a phenomenon that there should be an eccentricity (amount of offset of the centers) between shaft and bearing centers. This misalignment allows easier assembly, creates a place for oil volume and a dynamic operation and pressure-generation mechanism. As a result of this eccentricity, an oil layer that narrows and expands between the two surfaces is formed. In the lubrication literature, this oil layer is called oil wedge. An inclined wedge touches the shell (hub) and shaft surfaces and connects the surfaces to each other, and with this compression of the wedge the surfaces can move together. Again, the transverse wedges serve to adjust the position between the connected elements, the oil wedge moves the shaft away from the bearing surface and almost floats the shaft in the body of the oil, keeping the shaft suspended in the oil. Therefore, the shaft surface transfers the load to the bearing surfaces while rotating via this suspension. Thus, the bearings serve as the shaft supporting element. With the variable thickness of the oil layer, direct contact of the shaft and bearing surface is cut, ensuring a longer life of the system.

The nominal minimum film thickness in radial journal bearing, which carry variable loads such as the engine bearings in vehicles, is defined according to the surface roughness. Depending on the operation environment, the roughness of the shaft and the bearing surfaces must be greater than the sum. Here, in general, the average roughness (Ra) as well as the maximum surface roughness (Rt, Rz, etc.) should be taken into account. In the lubrication literature, there are tables and charts that recommend minimum oil film thicknesses at micrometer level for operation areas (engine bearings, electric motors, general purpose machine applications, slides, etc.). These charts should be used in bearing design. In addition, oil filtration and compliance in the system is another important factor that affects the minimum oil film. (To be continued)

25.11.2020 12:28:00
Prof. Dr. Ertuğrul Durak    

Corner Posts - Last Added

Sustainable engineering: Can lubricants reduce CO2 emissions?

Sustainable engineering: Can lubricants reduce CO2 emissions?

Today, our planet comes up against global problems such as climate change, limited natural resources and environmental pollution. Based on these problems, negotiations regarding ...

25.02.2023 11:35:00
Dr. Volkan Pelitli    
The story of lubricants modern era’s black gold

The story of lubricants modern era’s black gold

Lubricants are an important part of our industry and our daily life. Therefore, it has great importance in terms of sustainability that oils are managed environmentally friendly ...

25.02.2023 11:30:00
Dr. Hansu Jülide Köroğlu    
Climate resilient lubricating oil production

Climate resilient lubricating oil production

In September 2015, the United Nations (UN) General Assembly by making promises to end extreme poverty, to fight inequality and injustice and to combat climate change, set out to ...

25.02.2023 11:00:00
Prof. Dr. Filiz Karaosmanoğlu    
The importance of DGA test in transformer condition

The importance of DGA test in transformer condition

Many factors, such as global economic developments and the climate crisis, have had a significant impact on energy generation costs. This situation gives us serious responsibility ...

8.01.2023 11:30:00
Umut Arslan    
Sustainable lubricants and recycled base oil

Sustainable lubricants and recycled base oil

The independent Union of the European Lubricants Industry (UEIL), whose activities and online events I closely follow, continues to guide its members toward sustainability. Aiming ...

27.10.2022 12:30:00
Prof. Dr. Filiz Karaosmanoğlu    
The hidden hazard in transformers: PCB

The hidden hazard in transformers: PCB

PCBs (Polychlorinated Biphenyls) are an organochlorine class of synthetic oil-like compounds. They were described in the technical literature for the first time in 1881, and ...

22.08.2022 10:30:00
Umut Arslan    
Our planet and the year 2022

Our planet and the year 2022

Lubricants, which are essential for our industry and vehicles, should have the least possible negative impact on biodiversity loss, pollution, and climate change throughout their ...

15.08.2022 11:00:00
Prof. Dr. Filiz Karaosmanoğlu    
Planet Friendly

Planet Friendly

By processing hydrocarbons in coal, oil, natural gas, plant and animal resources and their waste, the chemical industry supplies chemicals, fuels, materials, lubricating oils and ...

17.06.2022 11:50:00
Prof. Dr. Filiz Karaosmanoğlu    
The lifeline of the maritime sector: marine oil analysis

The lifeline of the maritime sector: marine oil analysis

The oil analysis, which we may call an oil blood test, is defined and evaluated according to the environmental conditions and the level of criticalityof the equipment. The ...

12.06.2022 14:00:00
Umut Arslan    
Importance of oil analysis in transformers

Importance of oil analysis in transformers

We witness that significant increase in global energy costs make companies increase their investments in predictive maintenance in order to achieve their sustainability goals. I ...

1.03.2022 15:27:00
Umut Arslan