The Shear Stability Index Are The Need Of The Time

The shear stability index (SSI) is a very important way to measure how resistant a fluid is to changes in viscosity caused by shear or mechanical stress. It is found by comparing the viscosity of the fluid before and after a shear test. A lower SSI number means that the fluid is less likely to change viscosity when it is sheared.

Importance in Lubricant Quality Control

The SSI is very important for checking the quality of lubricants, especially those that are multi-grade and thickened with polymers. These lubricants depend on polymer additives to work the way they're supposed to at a variety of temperatures. However these polymers can break down under shear stress, which can cause the lube to lose its viscosity and stop working as well.

Manufacturers of lubricant additives can make sure that their goods can handle the mechanical stresses that come up during use by measuring the SSI. These stresses can be found in engines and other machinery. This helps keep engine parts from wearing out too quickly, which keeps the equipment from breaking down too soon and makes it last longer.

Additional Benefits and Applications

In addition to checking the quality of lubricants, the SSI can also give information about other parts of how fluids behave and work. It can be used to do things like

Figure out how lubricants will work in high-shear situations: This knowledge is useful for gearboxes, high-performance engines, and hydraulic systems.

Improve the way lubricants are made: Lubricant makers can make goods with better shear stability if they know how the SSI is related to the type of polymer, its concentration, and the SSI.

Check to see if oils can be used with different materials: The SSI can help find problems that might happen when oils are used with seals, gaskets, and other parts.

Shear Stability Testing Methods

Standardized ways to test for the shear stability index (SSI)

There are a number of common tests that can be used to measure the SSI. The type of lube being tested and how it will be used affect the choice of test method.

DISST stands for the Diesel Injector Shear Stability Test.

The DISST makes conditions similar to the high shear that diesel fuel pumps go through.

The KOST (Kurt Orbahn Shear Stability Test)

A rotating disc in the KOST puts shear force on the lubricant.

Test for Sonic Shear Stability (SST)

The SST uses high-frequency sound waves to make the grease go through shear stress.

Understanding Shear Stability

Shear stability is a fluid's ability to keep its thickness even when it is under a lot of shear stress. Shear stress happens when different layers of fluid move past each other at different speeds, causing friction that could change the viscosity of the fluid.

Viscosity Modifiers and Shear Thinning

Viscosity Modifiers (VMs)

Additives made of polymers that make a stream thicker are called viscosity modifiers. They are often found in lubricants to keep the stickiness at the right level at different temperatures.

Shear Thinning

Shear thinning can happen to the plastics used in VMs when a fluid is put under shear stress; its viscosity drops. This is called shear thinning. When the layers of the fluid move past each other at different speeds, friction happens. Lubricants and other fluids that need to have a steady viscosity can't work as well when shear thinning happens.

Types of Viscosity Loss

Types of Loss of ViscosityViscosity Loss for a Short Time

When a fluid's viscosity drops under shear stress, this is called temporary viscosity loss. However, this change can be undone. The viscosity of the stream goes back to what it was before the shear stress was taken away.

Loss of viscosity permanently

On the other hand, permanent fluid loss can't be fixed. It happens when the shear stress in the fluid breaks the polymer chains inside it. The fluid's viscosity will always be lower because of this breaking.

Shear Stability in Lubricants

Good lubricants and things that raise the viscosity index (VI)

Viscosity index (VI) improvers , which use a low shear stability index (SSI),are often found in high-quality lubricants such as hydraulic fluids, multigrade engine oils, and some gear oils.

Resistance to Shear Thinning

Shear thinning is when the viscosity of a fluid drops under stress. Polymers with low SSI are made to prevent this. This resistance helps the oil keep its thickness and ability to protect even when it is under a lot of stress. By keeping its viscosity stable, the lubricant can successfully cut down on friction and wear, making sure that the machinery works well and lasts a long time.

Performance Implications

What Effects Does SSI Have on Fluid Performance

Small changes in the Shear Stability Index (SSI) can make a big difference in how well a fluid works. This shows how important it is to measure SSI correctly and use fluids that are stable in shear.

Consequences of Poor Shear Stability 

Fluids that aren't stable under pressure can have a number of problems. First, the film's strength can go down. Film strength is the fluid's ability to form a barrier between objects. This could cause more damage to the parts of the machine. The fluid may also be less able to keep its density when it is under stress, which could make the system less effective overall.

Additional Considerations

Factors Influencing Shear Stability

A fluid's shear stability is sometimes different; it can be changed by a number of things. Temperature and pressure can have a big effect on how well a fluid keeps its viscosity when it is under shear stress. Not only does the amount of shear stress matter, but also the type of stress that is used.

The shear stability index is a useful way to check the quality and performance of lubricants, especially those that are made to work in tough situations. The SSI helps keep equipment from breaking down or wearing out by making sure that lubricants can keep their viscosity under shear stress. This increases efficiency and lowers the cost of upkeep.