Dry lubrication processes and methods of lubricant film formation owe their great development during the development of the space program, where limiting the effects of linear and rotational friction in extreme conditions was of strategic importance. Dry lubrication is desirable wherever there are sliding movements between metal-to-metal contact and other methods of lubrication, and thus methods of reducing friction and wear of metal surfaces are difficult or even impossible.
Film solid lubricants can be categorized by the composition of the solid particles used, the media in which they are dispersed, and the type of binder used in the formulation. Some film lubricants are forced into metal structures mechanically, others air dry , and others require oven drying to achieve maximum thickness or adhesion .
Other molybdenizing methods are also widely used, in particular: molybdenum electroplating , molybdenum anodizing , molybdenum passivation , non-aqueous media , ionic fluids , vacuum deposition .
Molybdenum is a silvery metal that sits between chromium and tungsten in group 6 of the periodic table.
Coatings based on dry and solid lubricants are a desirable alternative to liquid lubricants to minimize friction and prevent galling and abrasion , especially in high or low temperature environments where liquid lubricants can freeze or evaporate .
In today's considerations, we will focus on one method of molybdenizing rubbing surfaces in the form of mechanically pressing micronized molybdenum disulfide MoS2 into the metal structure . We write extensively about molybdenum properties at: https://sklepsmary.pl/blogs/aktualnosci/molybden-wlasciwosci-ogolne
Let me just briefly remind you that, like graphite , molybdenum disulfide (MoS2) has a layered hexagonal crystallographic structure , which provides it with low shear strength and very high lubricating properties . Its temperature resistance is similar to graphite: +400°C and its very good mechanical properties make it suitable for permanent lubrication of small elements even under very heavy loads . In addition, MoS2 is an extremely efficient dry lubricant , thanks to its effective particle size range (1 to 100 µm) and its very low coefficient of friction (≤ 0.1).
The main goal that we want to achieve by mechanically molybdenizing a metal surface is to create a molybdenum coating on the treated surface and reduce friction by co-deposition of molybdenum particles in the nanocrystalline surface. .
This applies in particular to hard-to-reach lubrication points, such as pins in chains , or dangerous ones, such as molybdenum plating of bullets used in sniper weapons, or molybdenum plating of journals in power plants or engines in competitive sports. There, dry lubrication is recommended due to the difficulty in accessing the lubricant, and this method of emergency lubrication is recommended despite the time-consuming and costly lubrication method.
The exceptionally low coefficient of friction that we obtain after molybdenum plating avoids excessive friction and its consequences , such as the formation of high temperatures, seizing phenomena and premature wear of the machined parts. The applied micro-coating is permanently deposited on the surface of the treated parts and cannot be removed without simultaneously removing part of the substrate itself.
Parts and surfaces to be mechanically coated with molybdenum should be prepared in such a way as to ensure a good micron bond between the molybdenum structure and the metal particles.
The surface prepared for molybdenizing must be cleaned of grease, oil, dust, etc. by immersion in solvents or alkalis, by manual application (using materials such as brushes), ultrasonic cleaning or biological type cleaners that clean by "eating" dirt.
Surface roughness, which allows particles to anchor in surface irregularities, and thus give the interface good mechanical adhesion, is not required because we use mechanical force to connect and cooperate two surfaces (e.g. rubbing, impact with molybdenum as in sandblasting).
After impact or mechanical rubbing into the surface, the dry lubricant is forced onto the surface and fuses with it, creating a new structure on the surface with a very low coefficient of friction and new technological parameters that are not exposed to flaking of particles.
The frictional properties of the surface coating created in this way are controlled by their chemical composition and microstructure, such as crystallinity and grain size distribution, therefore it is important to use top-shelf molybdenum powders, especially those with very fine grains, to obtain the right effect. Coarse molybdenum can act as fine sandpaper and not bring the desired effect.
In addition to molybdenizing, dry lubrication processes by mechanical saturation of metal surfaces are used with other compounds, including: graphite , molybdenum disulfide (MOS2) or tungsten disulfide (WS2), boron nitride . All these treatments cause molecular bonding, and thus very strong adhesion of lubricant particles to the treated surfaces. Most often, these processes are based on air compression systems to achieve supersonic speeds and to bind the powders to the metal structure.
Other commonly known methods of applying molybdenum coatings are:
Molybdenum electroplating which consists of coating molybdenum in an aqueous solution on iron, nickel or carbon substrates, molybdenum anodizing which provides protective coatings for aluminum substrates, transforms the metallic surface into a ceramic state by oxidation.
Another widely used method is molybdenum passivation.
Passivation is a two-step post-production process: the first step is pickling, which cleans the surface by removing oils and other contaminants. This is followed by immersing the substrate in a passivating bath which deposits a thin protective layer that essentially restores the metal surface to its original condition.
An alternative to the molybdenum coating methods described above are water-based and molybdenum coatings
a Non-aqueous media: the primary method of deposition of a molybdenum coating using non-aqueous media is the electrolysis of fused salts
b Ionic fluids: Ionic fluids are formed by delocalization of the ionic charge, which results in a decrease in lattice energy
c • Vacuum deposition. Various vacuum deposition technologies are currently in use, including physical vapor deposition (PVD), PVD by vacuum evaporation, PVD by sputtering, ion plating, and several others.
We decide which method to use for our application based on working conditions, our financial resources and expectations we expect from the molybdenum layer.
Molybdenum products used for surface coating:
Lubrifiant Ambersil Dry Moly, Graisse MoS2 ITW, LOCTITE 8191, LUBRIFIANT SEC AU BISULFURE DE MOLYBDENE EN AEROSOL MOLYDAL, LUBRI MoS2 PS 2262 MOS2, Molybdenum Disulfide (MoS2) Aerosol Spray, DRY MOLY Spray ROCOL, Grasso Spray al Bisolfuro Molybdeno Ambro-So , Grease with molybdenum disulfide – TermoPasty, Molyslip Dry Moly Spray Aerosol , Molyfilm Kano, Molybdenum disulphide Cofan , MoS2 penetrating oil Molydal, Solent Maintenance EP Open Gear Aerosol with Molybdenum Lubricant, Petrelplus Molypet-Molybdenum MOS2 Spray, Moly (MoS2) Aerosol Spray IKV Lubricants , SealXpert Moly G-Rapid Spray, Phillips Molybdenum Gun Lubricant-100ml Aerosol, Dry Moly Lube Molybdenum CRC, Ambersil Dry Moly Lubricant Aerosol Spray, Fuchs Gleitmo 900, Suresta Moly Chain Oil Spray, Jet-Lube Marine Moly, BRUGAROLAS BESLUX MOLYSPRAY, CRC Molybdenum Disulfide Dry Film, Molybdenum LB 8017, Solent Maintenance SD1-500B, MO-DI Dry Film Moly Spray, Action Can Dm-90, SCHAEFFER"S 202 Moly 5th Wheel, MOLYKOTE D-321 R, Molykote Powder Spray, CPI DRY MOLY AEROSOL LUBRICANT, Universal Spray-On Grease with MoS2 Weicon, Lubricant Chain Liquid Gold Coast Chemical, 12014 MOLY-SPRAY Dry Film Lubricant, Orapi 700 Moly Spray, MOLI-GUARD - Dry Lubricant Spray.