What is a solid lubricant?
Solid lubricant is a kind of material that reduces the friction coefficient and put on with the aid of stopping direct contact of friction elements under normal use or excessive load. In super cases where liquid lubricants, together with oil and grease, can not be used, solid lubricants have an exceptional software marketplace. Besides, the solid lubricant is also an additive material for excessive-overall performance anti-chunk and anti-put on coatings. It is frequently blended with grease and lubricating oil within the shape of powder debris to play a sliding position. This kind of unique solid lubricant will slip whilst the friction pair slides quite Fill out difficult surfaces. Therefore, under excessive working situations, strong lubricant provides sufficient boundary lubrication situations, thereby decreasing the friction coefficient and reducing wear. Generally, speakme, stable lubricants have a better advantage than liquid oils beneath excessive vacuum conditions under 10-2 Pa and close to atmospheric stress above 104 Pa, and coffee temperatures under zero℃and high temperatures above 177℃.
There are five principal kinds of solid lubricants: carbon-primarily based substances, transition steel disulfides (which include mos2 and ws2), polymers (which include PTFE lubricant), soft steel, and ceramic excessive-temperature lubricating materials. Amongst them, total carbon-based substances and transition steel disulfides belong to the typical layered structure stable lubricant.
(1) The carbon-based totally lubricating material
Graphite is an ordinary carbon-based, totally lubricating fabric with high-temperature resistance and corrosion resistance and is thought for its reliable lubrication traits. Graphite has a layered stable with a hexagonal lattice. The atoms within the carbon base plane are bonded together with the aid of robust covalent bonds, even as the bottom planes are blended through vulnerable Van der Waals forces, resulting in a damaged mechanical dating among the plane. The presence of water vapor and oxygen inside the surroundings can sell the shear movement between graphite crystal layers. Whilst the base surface is worn; these active edges are neutralized (passivated) with the aid of adsorbing water or other vapors. Graphite can also preserve low friction. That is true for other carbon-based stable lubricants. Carbon-primarily based lubricants additionally include various types of DLC coatings and occasional-friction carbon coatings (NFC).
(2) Transition metal institution disulfide (TMD) lubricating substances
Within the TMD family, MoS2 and WS2 have widely used for their reliable lubrication overall performance. The number one mechanism for reaching low shear resistance on the interface is a base floor-oriented parallel to the sliding path and a switch film fashioned at the friction couple. MoS2 and WS2 coatings do not oxidize or react with water vapor in dry gasoline or ultra-excessive vacuum, thereby maintaining their reliable internal lubrication. However, in humid air, friction oxides together with MoO3 and WO3 can be shaped due to the dangling or unsaturated bonds on the brink of the base floor reacting with water vapor or oxygen in the environment. Right now, the sliding friction coefficient is particularly high (0.15 ~ zero.2), and the damage lifestyles are likewise concise.
(3) PTFE lubricant:
Polymer stable lubricant is usually deposited inside the form of a coating (film) at the floor of a substrate (inclusive of polymer-primarily based engine bearing cover). The molecular shape of those materials includes lengthy chains parallel to every other, and the bond energy between molecules susceptible may additionally slip underneath low shear strain. PTFE is common for such strong lubricants. Not like a different strong lubricants, PTFE does no longer have a layered structure, however PTFE macromolecules without difficulty slide, much like a layered shape. The minimal static and dynamic coefficient of friction of PTFE can be reduced to zero.04. The PTFE-coated metal can be used underneath harsh temperature, pressure, and medium, and may gain a prolonged protection period. Polymer-primarily based nanocomposites, along with PTFE / nano Al2O3, also show wonderful friction overall performance underneath specific check situations.
(4) soft metallic lubricating substances
Because of low shear energy and high plasticity, a few smooth metals additionally have lubricating properties, which include lead, tin, bismuth, indium, zinc, cadmium, and valuable metals consisting of gold and silver. As an instance, Zn and Sn have been used in sliding bearings, whilst treasured metals together with gold and silver have begun in the aerospace industry. In everyday lifestyles, tender metals are extensively used as strong lubricants in engine bearing materials.
Smooth metals used as solid lubricant substances typically have a face-centered cubic lattice, so their crystals are all isotropic. Consequently, those soft metals do no longer have a high bearing capacity, and the external load can simplest be borne by means of the substrate. Any other advantage of face-centered cubic crystals is that there’s no low-temperature brittleness, and the lubricating residences will no longer be lost in low-temperature environments.
(five) high temperature resistant lubricating substances
Positive oxides, together with B2O3, MoO2, MoO3, ZnO, Re2O7, TiO2, V2O5, and PbO, and so forth., have decrease melting factors, melt at high temperatures, and have better residences.