Tribology Testing

The lubricating abilities, or tribology, of topical products, cosmetics and foods is increasingly being studied by formulators looking to deliver outstanding sensory experiences for the consumers of their products. We have a range of tribological testing capabilities to provide you with insights into your products and those of your competitors.

Tribology is the study of the friction, lubrication and wear of interacting surfaces. Biotribology, or soft tribology, is woman-applying-lip-balmthe specific study of compliant, biological surfaces such as the eyelid and cornea, tongue and palate, lips, mucous membranes or skin surfaces. The film forming and lubricating ability of layers of liquids and viscoelastic materials applied to these surfaces provides a fascinating and powerful data set for formulators of:

  • Eye drops for dry eye conditions
  • Generic pharmaceutical ointments, creams and lotions
  • Fat-reduced foods
  • Colour cosmetics, such as lipsticks, eyeshadow and eye-liner
  • Moisturisers, lip balms and sun-care products
  • Personal and intimate lubricants

Unlike rheology testing, where the sample under test is held in a defined gap between surfaces moving relative to each other, tribology testing entails bringing those surfaces into contact under a defined pressure and sliding one against the other, measuring the frictional drag over a range of sliding speeds. The surfaces and/or any applied lubricating liquid form the test sample.

tribology load and sliding speed
Contacting lubricated surfaces under a defined load are slid across a range of speeds.

 

tribology accessories
A range of typical tribological testing surfaces. Additionally custom-developed soft and elastomeric surfaces can be employed.

Stribeck Curves

Tribology test results are often displayed in the form of a Stribeck curve such as that shown below:

Stribeck Curve

The Stribeck curve anatomy is typically composed of three regions. At low speeds the surfaces are in close contact with asperities (surface roughness features) interlocking. Under these conditions lubrication is low, so friction is high. As sliding speed is increased the lubricant entrained between the upper and lower surfaces creates hydrodynamic lift, resulting in increasing separation of the surfaces and subsequent decreasing frictional drag. Lubrication at this stage is known as mixed boundary-hydrodynamic lubrication. Eventually, as sliding speed is increased, a complete separation of the surfaces ensues. Friction reaches a minima at this stage and the final part of the Stribeck curve anatomy is reached: hydrodynamic lubrication. From the key features of the Stribeck curve we can derive metrics that clearly differentiate between materials of differing lubricating qualities.

We have a variety of standard and custom built attachments and test methods that enable accurate, repeatable tribology testing for a wealth of material types. If you have a question regarding the tribological testing of your products please get in touch.

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