How to make a choice between rolling element bearing and journal (plain) bearing?

Question

I wonder if there exist a formal guideline to help engineers choosing the right type of bearing.

Except in some few cases, this is not very evident to me. As far as i know, the plain bearing systems are really simple, so why bothering to design the rolling element bearings? I guess there is a reason, but i don't see it.

I've done some research on the web, besides the economic factors and some other vague statements i couldn't find anything useful.

Answer 1

rolling element bearings produce less friction, last longer, can position a rotating shaft with greater accuracy, and do not require pressurized lubrication in order to carry large loads.

sliding contact bearings are cheap, easy to install, and are adequate for light loads without pressure lubrication, and are fine for cost-sensitive applications.

Answer 2

To add to the list of criteria in other answers:

• Cooling. If a bearing supporting a rotor transmitting say 10MW of power dissipates only 0.01% of that power in friction, that is still 1kW of heat being generated in the bearing. Rolling element bearings are relatively easy to cool via the lubricating oil since there an unobstructed flow path between the rolling elements. Sliding bearings are not.

At the other end of the design spectrum:

• Size. Manufacturing a 2mm diameter journal bearing can be as trivial as drilling a 2mm diameter hole in something. Manufacturing a 2mm diameter rolling element bearing is slightly more difficult - though it has been done: https://www.nskmicro.co.jp/english/products/products04.html

Answer 3

It’s difficult to say when we should select the rolling element bearing or the other one, sometimes we have to consider the upsides and downsides of each to decide. Also the working condition and the load tell us which is the best option. Here I’m going to mention the most important advantages and disadvantages of both.

The advantages of plain bearing

1- This type usually have a large bearing surface which reduces the sensitivity to impact forces

2- Noiseless

3- Suitable for high and rough rpm

4- Easy to assemble and disassemble thanks to split joints

5- Very long lifespan

The disadvantages

1- High starting torque

2- High consumption of oil

3- Continue control

4- Low rendement thanks to friction

The advantages of rolling element bearings

1- Low friction

2- The starting torque is not larger than the service torque

3- Slight consumption of lubricant

4- These types don’t need continue inspection and maintenance

5- Low response time

6- Thanks to normalisation the interchangeability is often possible

The disadvantages

1- Vibrations and impacts lead to pitting and fretting so eventually the failure of rings and rolling elements

2- Limited lifespan (usually measured in hours)

3- Thanks to centrifugal force and its impact on the rolling elements these types aren’t suitable for high rpm

4- Excessive sealing

So according to upsides and downsides we can conclude the combination of high rpm, long lifespan and large loads push us toward journal bearings, for instance gas turbines, or hydraulic turbines, generators, huge ships

To damp the strong impact in low rpm we can also use plain bearings, hamers, press machines

Some industries require low maintenance, like oil and gas, here the rolling element bearing is a good option.