Solid Lubricants and Wettability

2023. 10. 18.

Solid lubricants play a vital role in establishing oil-free working environments by forming a lubricating film on the sliding surfaces during frictional motion. SGO has manufactured solid lubricants and conducted extensive research and development to enhance their performance.

Today's letter is about the findings of an internal experiment conducted on solid lubricants and their interaction with the wetting phenomenon.

Graphite Solid Lubricant Plugs

Solid lubricants are manufactured through a pressurization and molding process by mixing lubricating ingredients such as graphite, sulfide, and phosphide with resins to form internal pores. The key factor in enhancing the structure is the molding technology, ensuring well-formed internal pores. These internal pores retain lubricating oil and release it during usage, thus creating a stable lubricating film when combined with the fine particles of the solid lubricant.

To demonstrate this effect, we produced two samples with identical specifications: one was impregnated with lubricating oil, and the other was left unimpregnated. To ensure accurate performance comparison, we machined both samples on a general-purpose lathe, eliminating the influence of cutting oil typically used during CNC machining, and subsequently measured their weight.

As evident in the photo above, there was a mere 2g difference in weight between the lubricating oil-impregnated sample (No. 1) and the unlubricated sample (No. 2). In other words, the amount of lubricating oil impregnated in the solid lubricant is only 2g.

Now, let's check out the results of the comparative durability test conducted at the SGO Research Institute. Witness the remarkable impact that a mere 2g can have!

1) Durability Test Equipment and Conditions

Friction Wear Tester and Durability Test Conditions

2) Durability Test Results

Impregnated No.1 Test Results

Unimpregnated Sample No.2 Test Results

As a result of the durability test, it was confirmed that sample No. 1 exhibited a smoother friction surface and had less wear on both the friction surface and the shaft in comparison to sample No. 2.

Conversely, the friction surface of sample No. 2 appeared visibly rougher with irregularities when examined with the naked eye, as opposed to sample No. 1. Upon measuring the wear of both samples, it was evident that both sample No. 2 and the shaft had more wear than sample No. 1. This indicated a significant reduction in lubrication performance when using only non-impregnated solid lubricant.

Furthermore, during the test, the friction coefficient of sample No. 2 exceeded 0.25 (the test was halted when it exceeded 0.25), resulting in the test concluding prematurely at around 40 hours instead of the intended 72-hour duration.

3) Conclusion

Why is there such a big difference when only 2g of lubricant is impregnated into the solid lubricant?

These differences are related to the wettability, which comes from the shape of the internal pores and the structure of the solid lubricant. Wetting is the ability of a liquid such as lubricant to maintain contact with the surface of a solid lubricant, and is a phenomenon caused by interactions between molecules. When the adhesion and cohesion between the lubricant and the lubricant are balanced, the lubricant stably retains the lubricant.

In fact, when graphite plugs are immersed in lubricating oil, you can observe the *capillary phenomenon in which air bubbles escape from the internal pores in the lubricating oil.

Although the weight of the impregnated lubricant was only 2g, this test determined how much solid lubricant and lubricant play a role in the lifespan of the bearing and the safety of the machinery.

※ Capillarity: A liquid climbs a narrow pipe without external help such as gravity.

Thank you for your great interest!

Metalex Viernam 2023

M-Tech Osaka 2023

SGO attended Metalex Vietnam and M-TECH Osaka from October 4th to October 6th and received great attention from our visitors. We are thankful for their interest and support.

During these events, we gained valuable insights into our customers' requirements and demands, and we are committed to doing our best to meet them.

We always appreciate your support.

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