simpre takes place a mechanism is put in motion, because the conditions of speed, load, temperature (viscosity) or lubricant application methods are not favorable for the formation of a fluid film.
There are only a small amount of lubricant on metal surfaces, which allows this maximum interaction between the roughness of both surfaces, however, the anti-wear lubricant adtivo prevents this metal-metal friction allowing it to be of solid type. If the boundary lubrication prevails for a long time, you can break the solid film formed by the antiwear additive and presented a significant reduction in the life of the mechanism.
Under normal operating conditions, the film lubrication regime limit should disappear completely, otherwise, the lubricant has been improperly selected or is contaminated with a substance of lower viscosity.
Other circumstances that may give rise to this situation is when you vary the operating conditions of the machine, as in the case of subjecting the different mechanisms at pressures greater than the design, leading to hydrodynamic effects are totally null . Film boundary conditions are also presented immediately before the mechanism stops. Therefore, a team whose mechanical parts are subject to frequent stops and starts consuming more antiwear additive so the oil should be changed faster than those that run continuously, because these anti-wear additive only works when boot or when the mechanism stops.
adhesive wear under boundary film can be heard only during the time it takes to react with anti-wear additive metal superfiie, when the solid film formed by the antiwear additive is gone.
The lubricant film thickness (h) under a range boundary film lubrication between 0.001 and 0.05 um. In
codiciones boundary layer lubrication, the wear can be caused by corrosion, adhesion, fatigue, and plow (or abrasion), acting alone or in combination.
corrosion is initiated by the formation of a film when the surface boundary layer reacts chemically with their environment. These films may be formed by:
-metal oxides formed by oxygen or water in the air or lubricant.
-Sales resulting from reaction with a lubricant additive or oxidation products. Tine
corrosive wear occurs when the film boundary layer tends to be displaced to the edges of the surface rather than penetrate the true load bearing areas between the asperities.
adherence occurs when the surfaces are totally clean and has a rough microsoldadura between the two surfaces.
fatigue cycles is the result of high tension and compression acting on the two fences. These efforts produce plastic deformation alguan until part or all of the rough, they break or disappear from the surface. This mechanism of wear is evident, because of micropicaduras aparción on the surfaces of the elements in moviminto.
Plough (or abrasion) occurs directly when a roughness hard sharp or a third body (as a wear particle roughness strain or a film of dust) slots or scratch the surface.
All products used in lubrication contain anti-wear additives that control the conditions of boundary lubrication film, but there is market lubricants specially formulated to be used when these conditions prevail for long. The most used are:
* organic origin: are a mixture of paraffin type mineral oil and 5% to 7% of animal fat or a fatty acid. (Stearic, oleic, palmitic and lauric, etc). The acid radical has an affinity for metals, particularly iron and steel, the initial attraction being electrical in nature and the molecules orient themselves or bristle, as hair from a carpet. The effectiveness of fatty acids is due to the radical reaction between polar and metal surface, which results in a lubricating film of low shear, but adheres strongly to surfaces.
film lubricant compound or compound significantly reduces the risk of microsoldadura between the roughness of metal surfaces and therefore adhesive wear.
fatty acids are highly miscible with mineral oils, obtained lubricants and have an excellent power of boundary lubrication, and are known as oil of oiliness additives, compounds or Compound. Are effective for operating temperatures below 50 ° C.
* solid film: Most employees are grafitoy molybdenum disulfide (MoS2). Can be used in a colloidal base oil is added from 5% to 7% by volume, or powder to be added to the fat from 3% to 5% by weight. In the market get so much oil as fat, which already come with molybdenum disulfide. In the figure shows a mechanism that operates under constant lubrication conditions boundary film.
* With extreme pressure additives (EP): are made from paraffinic base and an additive package of metal type, such as phosphorus, sulfur and chlorine. Used for operating temperatures above 50 ° C.
