The impact of temperature on coefficient of friction in self lubricated sliding bearing for Valves application.

Since a couple of years, SLIB ITALY, has developed a specific test bench for sliding bearing, and after tons of collected data, we have available specific information on various aspect of the bearing performances.

In this short article I would like to focus on the consequential variation of coefficient of friction with temperature changes. The tests carried out on our TX make clear a strong connection between the two factor.

TX is a composite self lubricated bearing made by two parts, the metal shell that can come in several different alloys (316, carbon steel, 625, F51, Titanium and others) and the reinforced textile internal layer, (see images below).

Tx is used primarily in trunnion mounted ball valves for high pressure application, where the dynamic load performance and the low coefficient of friction are crucial to the functionality of the valve.

The temperature range where those valve operate is usually between -50°C + 200°C even if TX can cover a wider temperature range.

The test bench we use is designed to cover the requirement of SHELL PR2 TAT SHELL with the following characteristics:

We tested TX with the following parameters:

• 100 cycles at 10°C step from -50°C to +200°C
• Shaft rotation at 90° with load applied from 0° to 30° and backwards from 30° to 0°
• Rotation speed: 0.083 m/s
• Shaft roughness of the Test Bench: 0.5 - 0.8 Ra
• Shaft hardness of the Test Bench : 1100 Vickers 

As you are able to see from the graph below the coefficient of friction change with the increasing of temperature, it goes from above 0.1 at -50°C to below 0.02 at 200°C.

In conclusion, it's important to consider the temperature range of the Valve before designing the dimension of the bearing: remember that a lower coefficient of friction means a lower torque on the Valve system.

If you want to have more detailed information about TX sliding bearing go to the download page of in our website.