Minimum Quantity Lubrication and Its Importance

Lubrication of rolling bearings is one of the main tasks that deserve our attention. By maintaining proper lubrication procedures & the right quantity of lubricants, Reliability, Longevity & Energy Optimization goals can be achieved. But in practice, lubrication of rolling bearings is misunderstood normally & is a huge task. It’s very hard to believe that 40% of all the bearings used in different industries never live to their engineered life time, and selecting bad lubrication processes & the wrong amount of lubricants resulted in premature bearing failures in different industrial applications.

What is Minimum Quantity Lubrication?

There are ways of reducing lubricant or coolant consumption in various metal machining and forming processes. These methods are usually grouped under the terms “near dry machining” or, more inclusively, “minimum quantity lubrication”. MQL comprises technologies and practices for applying machining fluids or lubricants only at the location and amount needed for the part and process, and MQL can be applied to multiple manufacturing operations or in bearings.

MQL is a little bit bigger of an umbrella than near dry machining. MQL can also apply to the lubrication needed for sheet metal forming operations, blanking, forming, cutting, etc. Near dry machining is more specific to machining operations such as mills, drills, turning operations, and tapping.

Benefits of MQL or Near Dry Machining:

Efficient environmentally friendly practices of near dry machining can create several kinds of cost savings and improvements for a manufacturing shop.

1) Significantly reduced fluid/lubricant use

2) Safer cutting fluids and lubricants

3) Fewer employee health hazards

4) Faster machining speeds and feeds

5) Longer tool life

6) Lower fluid disposal cost

7) And a cleaner shop with reduced maintenance.

Large and small companies can reap the advantages of near dry machining even though their traditional cooling methods may still be effective.

Minimum Quantity Lubrication is increasingly important to provide a productive, affordable, and environmentally friendly machining process. Research shows that SKF MQL system could reduce the total cost of ownership by half compared to the internal weight machining process. To know more about how SKF has recorded significant benefits from its introduction of MQL, you can go through the article Minimum Quantity Lubrication Reduces Total Costs of Operation.

Nowadays, in our advanced technological era, there are multiple tools available to understand health of the rolling elements of the bearing. By using ultrasound tools, you can detect failures and control energy costs that contribute to the machine’s overall uptime with lower energy consumption.

To ensure your rolling machine elements functions properly, avoid these common lubrication mistakes:

Over- and Under-lubrication

When a machine element lacks grease, it will quickly cause the problem, usually failing. But over greasing may have a similar effect. This is why it is important to remember that lubricants have a volume of their own.

Excessive grease can be a resource jam, requiring extra maintenance and downtime hours. Similarly, excess greasing can lead to seal failure. Grease guns can create extraordinary levels of pressure, and excessive amounts of pressure can damage bearings. Similarly, excess lubricant pressure can break when the grease dries and cracks, further damaging the bearings. An ultrasound reading can help technicians know when enough is enough.

On the other hand, a lack of lubricant is likely one of the easiest problems to spot. Typically, excess heat and sound will radiate from the asset until failure.

Calculating a proper quantity for a roller bearing

The right amount of the grease needed to lubricate a bearings depends on the size of the bearing, application conditions, such as speed, presence of housing or seals/shields.

SKF recommends to use a following equation to calculate the amount of grease needed for a bearing in a housing, in case if grease filled from the side of the bearing (Grease Lubrication in Rolling Bearings):

(1)  

Where is the grease amount in grams, is the bearing outer diameter in mm and is the bearings width in mm. Note that if you have the dimension of the bearings in inches, then the same equation applies, however the pre-factor changes to 0.114 and the grease amount is in ounces.

For sealed/shielded bearings, 30%-50% of the free volume of the bearing should be filled with grease. In case of the low speeds, 100% of the free volume can be filled with grease.

Conclusions

We have tried to understand that, except for the proper lubricant selection, following the proper lubrication procedure & maintaining the proper quantity of lubricants & lubrication interval is also very important to achieve the maximum life of the rolling element. As tribologists or lubrication engineers, we should always understand these things to eliminate premature application failure & to do the proper lubrication cost optimization.