Lubricants are a means of controlling and reducing friction between sliding elements, but they are not a panacea from a technical or environmental point of view. Technically, the choice of a lubricant is not a trivial task and requires a deep knowledge of the application of use, the physical-chemical interactions and the chemical compatibility with the materials in contact.
On the other hand, the growing awareness about the need for environmental sustainability has greatly improved its developments towards biodegradable products , which cause less harmful effects on the environment by decomposing more easily in aquatic and terrestrial environments.
These features contributes to reducing their toxicity and polluting capacity. Low-friction polymers such as PTFE , PEEK , PPS , nylon, acetal or polyester , besides their high wear resistance, offer additional advantages that allow them to extend their useful life, such as good corrosion resistance , lower weight , lower noise and lower friction heat generation. However, their use is subject to certain specific applications under limited operating conditions.
Low-friction coatings, aka AFC — Anti-Friction Coatings, are dry lubricants which formulation is similar to that one of industrial varnishes, but with dispersed micro or nanometric particles , which make it possible to homogenise the roughness of the surface on which they are applied, smoothing it and making it slippery.
Although they are suitable for various lubrication regimes, they are particularly effective in limit lubrication states, where fluid lubrication cannot be ensured and therefore the surfaces contact each other, promoting undesired wear and tear. The effective lubricating film that is achieved with these coatings is very resistant, even at low friction speeds, oscillating movements, high loads and harsh environments.
Depending on the application, they can be used alone or combined with oils and greases. There exist coatings for different materials metals, plastics, elastomers, leather, and wood and their application is clean and can reapply by recovering their properties. Functional surface texturing is a process that allows changing the properties of the surfaces by the application of textures , at micro or nanometric scale.
This technology has been shown to be a useful tool for reducing friction, because it promotes micro-lubrication and decreases the effective contact area between surfaces.
Its main challenge is twofold: the development of manufacturing methods able to reproduce textures in a repetitive, economically and viable way and the design of the textures themselves. It is the job of the lubricant to keep these asperities apart and prevent them from contacting each other, thus lowering or eliminating metal-to-metal contact and friction.
Without an adequate oil film to separate the metal surfaces, metal-to-metal contact occurs, asperities from the two surfaces weld together and then are ripped apart from each other by the motion of the surfaces sliding against each other, causing adhesion smearing and abrasion cutting.
In severe cases, the two pieces of metal may weld and seize to each other. If the oil film is sufficient to keep the surfaces separated but is too high a viscosity for the speed of the moving surfaces, then some drag or internal resistance within the fluid fluid friction will occur. This can be thought of as friction caused by layers of oil being forced to slide past each other.
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Factors That Affect Friction A number of factors affect the frictional conditions at the interface between these two surfaces in relative motion. These factors are: Surface Finish — The number, roughness and even the directional contact points of the asperities on the surfaces can dramatically affect the frictional coefficient. Surface Interaction It is important to understand how two metal surfaces within a machine interact with each other. Related Articles. Ten Tips for Proper Bearing Maintenance.
Featured Videos. The Penn findings provide a better understanding of the nature of friction, which lacks a comprehensive model at the fundamental level. Industry has long been concerned with ways to reduce friction between objects, both to maintain the energy of the system as well as to reduce heat-generation and wear, which can weaken machinery and materials to the breaking point. The authors note that improved friction models can be used for the opposite effect; makers of some mechanical components such as automobile clutches may be interested in techniques to increase friction without changing the wear or adhesion of materials.
Even in the absence of rough edges or wear between sliding bodies, friction between the atoms at the surface causes vibrations which dissipate energy, but the exact mechanisms of this process remain unresolved. Scientists continue to explore the details of friction, and other open questions include the effects of environmental variables such as temperature and atmosphere.
Source: University of Pennsylvania Explore further. Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page. For general inquiries, please use our contact form. For general feedback, use the public comments section below please adhere to guidelines. Your feedback is important to us.
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