Main bearings are an important part of a marine engine, responsible for converting sliding friction into rolling friction (the latter’s value being much lesser than its counterpart), thus helping the crankshaft to rotate freely and power a ship’s propeller adequately.
In the context of the high significance that main bearings hold, it’s important for marine engineers and on-board technicians to at least have basic knowledge and understanding of the marine diesel engine component, so that they would know what they deal with on day-to-day basis.
Today, we look at what supportive properties main bearings possess which allow them to perform function they are intended to, and the different types of main bearings used in marine engines.
Properties of Main Bearings – That Which Help Them in Their Function
Main bearings are required to have certain properties that can support them in their function. These properties can be attributed to the inherent properties of the material used in the construction of these bearings.
- They possess good load carrying capacity.
- They are anti-corrosive in nature.
- They possess high compressive and tensile strength.
- They have low value coefficient of thermal expansion.
- They can support the oil film, while at the same time being inert to reaction with lube oil.
- They are anti friction resistant.
Having looked at the set of unique properties main bearings must possess in order to be able to perform the desired function adequately, next, we take a look at the different types of main bearings used in the marine engines.
The Different Types of Main Bearings
In shipping industry, the deployed propulsion engines mainly use three types of main bearings. These are as follows:
1) Lead Bronze Bearing
A lead bronze main bearing consists of four layers.
Flash layers is the top-most layer, used to protect the main bearing from dust and corrosion.
It is followed by nickel barrier layer, primarily serving to prevent the diffusion of tin into the bearing’s metal.
Then we have the third layer, the lead bronze layer which confers anti-seizing property to the main bearing.
Finally, we have steel back layer. This layer provides structural support to all other layers of the main bearing.
2) Bi-metal Bearing
It is the second, most popular type of main bearing used in marine engines.
Bi-metal main bearing consists of three layers. First, we have the aluminum tin layer. Then we have the bonding layer which offers adherence support between the top layer and the shell of the bearing. The third layer is the steel back layer that provides shape and support to the main bearing.
3) Tri-metal Bearing
Lastly, we have the tri-metal bearing. A tri-metal bearing is commonly found in 2-stroke propulsion engine.
This type of main bearing comprises of five constructional layers.
At the top, we have a flash layer made from tin and lead. The second layer is called overlay layer. Interlay layer is the third layer and it serves to act as the anti-corrosive layer for overlay. Lining is the layer sandwiched between interlay and steel back – made from bronze and lead. Steel back is the layer that provides shape and structure support.
On that note, we come to the end of this blog post. Did you find the information helpful? If so, share it with others to help educate them. Do you have any questions about main bearings? Feel free to reach out.
And, while we are at the subject of main bearings and marine engines, check out this helpful post to learn about the maintenance tips to ensure your marine engine keeps performing at optimum level.