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Characteristics and Applications of Dry Film Lubricants

Dry film lubricants are also known as solid film lubricants, which are responsible for minimizing the friction present in between those surfaces which are thriving in extreme environments like temperature alterations, pressure alterations, and limitations of using liquid and oil. These lubricants are prepared through a series of steps that need constant attention as these delicate steps cannot go unnoticed. After the preparation phase, when dry film lubricants are formed, they possess excellent properties and characteristics, which are the key motive of their great performance in the industries.

Depending upon these properties, the applications that are performed by dry film lubricants are considered outstanding in their nature as they are providing the industries with outclass results.

Introduction

In many extreme environments like environments with low and high pressure, low and high temperature, and where one can’t use the oils and the liquids, solid film lubricants and dry film lubricants reduces friction between the surfaces. Another interesting alternative to fluid lubricants is this coating, as it can lessen friction and prevent galling and seizing, particularly in environments of low or high temperatures where the fluids may vaporize or freeze.

A broad range of options of lubricant coatings is provided by Metal Coatings Corp. that protects the items like the smallest fasteners and huge industrial components that need a coating for the reduction in friction.

 

What are the names of the most usually utilized dry film lubricants?

Even though they can be dipped, anoplate sprays them on like paint. Perhaps, Polytetrafluoroethylene (polymer material PTFE), MoS2 (molybdenum disulfide), and inorganic compounds graphite are the most usually utilized dry film lubricants. High lubricant characteristics are possessed by them, which allows them to have applications in which friction needs to be reduced, and oils or greases need to be removed. Dry lubricants are utilized as a replacement for oils and greases. Sometimes, the dry lubricants are utilized as the “back-up” lubricant under the grease. It is done so that less addition of grease won’t be able to lead to failure.

What is grease and oil’s function?

Grease and oil perform best when shaft speeds and surface areas allow an oil film for efficient formation. However, this can be the result as long as the functioning temperatures are within a specific range of between 212 F and -4 F typically). If the machines are functioning in extreme conditions, then the lubricant’s state can change, and it can stop the formation of the fluid film. When talking about extreme conditions, we are talking extreme from the perspective of a lubricant.

Your gears would be grinding if a protective film won’t be able to be formed. However, if you don’t get a protective film, then there will be no need for a protective lubricant as it is rendered useless.

Reasons

This is the reason that why once the fluid film goes away, the particular materials are utilized for aiding in the protection of the surfaces. Those particular materials are known as dry film or solid film lubricants. These particular materials can be utilized as an additive in greases and oils and can be utilized in pure form, too (free-flowing powder). During manufacturing, they can be alloyed or added to the surface of the component, too (for instance, a non-stick cooking pan).

Protective conditions

As compared to most of the oil-based lubricating fluids, the protection that is offered by them is far superior. Upper-temperature ranges are possessed by them, and they are way more than the surface-protecting ability of most synthetic and mineral base stocks. These agents are generally utilized in conditions like extreme environmental and chemical contamination and extreme pressure and temperature.

They are utilized as an additive or in their pure form that is a free-flowing powder. Solid lubricants form boundary films that are capable of working under extreme speed, temperatures, or loads and maintain steady viscosity (thickness). However, grease and oil fluid’s viscosity that is utilized for hydrodynamic lubrication can be affected by these functioning conditions.

What are the uses of these agents?

These agents are generally utilized in conditions like extreme environmental and chemical contamination and extreme pressures and temperatures. They can be used generally as an additive or in their pure form. When solid lubricants make the boundary films, they are capable of maintaining steady viscosity (thickness) even under heavy speed, temperatures, or loads. The viscosity of grease and oil fluid films that are utilized for hydrodynamic lubrication can be affected by these conditions of operation.

What is hydrodynamic lubrication?

When the lubricant is not enough for reaching hydrodynamic lubrication, then you use these, and they are as the micro ball bearings that can aid in the separation of the two mating surfaces. This is a common occurrence with sliding, slow-moving, and heavily loaded surfaces. Molybdenum disulfide (as an additive) stays in one place till the time of the next lubrication interval. The most typical dry lubricant is molybdenum disulfide, which is usually added to the heavy-duty greases that are utilized in the equipment of construction, they are also called moly-fortified greases, but they are not the only ones.

Diverse characteristics are possessed by each material. Following are the most usual materials

  • Tungsten disulfide
  • Cerium Fluoride
  • Calcium Fluoride
  • Talc
  • Boron Nitride
  • Graphite
  • Teflon (Polytetrafluoroethylene) PTFE
  • Molybdenum disulfide (MoS2), also known as moly

Other than graphene, Teflon and graphite are the most recognized and usually utilized dry lubricants in the industry.

What are the general characteristics of Dry Film Lubricants?

Different characteristics are possessed by each solid film coating substance.

  • WS2 and MoS2 function well in a vacuum and can bear high loads.
  • High oxidation and environmental temperatures are possessed by graphite.
  • WS2 and MoS2 can’t bear detergents, and they are oilioscopic.

What are the conditions for the application of dry film coatings?

As compared to other conventional lubricants, solid-film lubricants are the perfect additives or alternatives. Following conditions are usually needed for the application of the dry film coatings:

Typical Surfaces

One can utilize solid film lubricants on all kinds of surfaces. If one wants extended service life and long-term lubrication, the perfect choice will be the dry film lubricants as they have long-term lubrication and extended service life.

Extreme Environments

Most dry coatings can function in extreme environments and high speeds, pressures, and temperatures. Liquid lubricants can also fail in some cases when the conditions are these. For instance, typical organic greases and oils can be evaporated because of the high altitude/space applications or manufacturing of the semiconductor. Dust and dirt won’t be attracted by the dry film lubricants even in the dirty and dry applications, and that characteristic will form an abrasive and gummy mixture with grease and oil.

Reciprocating Motion

A reliable lubricant determines a typical application with the reciprocating motion for minimizing wear and tear. The capability of maintaining a proper lubricating film can be lost by the liquid lubricants in extreme conditions like high temperature or pressure. Although solid or dry lubricants aid in avoiding corrosion, fretting, seizing, and galling and they do not migrate too.

What is Polytetrafluoroethylene?

If one needs the sliding action of parts, then PTFE can be utilized; for instance, it is already utilized in slide plates, gears, and plain bearings. Colorless film capacity is offered by PTFE. It has good sliding friction reduction. It also possesses good chemical resistance, and at low loads, it provides a low coefficient of friction. PTFE possesses a low load-carrying capacity.

Dry film and solid lubricants can perform a significant role in the smooth running of the world, particularly in extreme conditions. One can find solid lubricant additives in high-performance greases.

What is molybdenum disulfide?

MoS2 can lubricate even in a vacuum, and it is also utilized in space vehicles and CV joints. Molybdenum disulfide prevents stick-slip, and with increasing loads, it provides decreased friction. MoS2 protects against fretting corrosion. Molybdenum disulfide also provides remarkable adhesion, a broad service range of temperature, and a high load carrying capacity.

 

What is graphite?

Various applications use graphene, for instance, applications like ball bearings, brass instrument valves, railway track joints, and air compressors, among various others. Particles can be stuck by the liquid lubricants, and graphite is used frequently in the lubrication of the locks. Sticking particles can worsen the problem. Under high loads, graphite offers a low coefficient of friction. Even in high humidity, graphite provides good lubrication. Graphite protects against fretting corrosion and also benefits from high-temperature stability.

What is proper lubrication’s role?

If you want to maintain equipment or machinery, one of the most significant aspects isproper lubrication. Always make sure to get a lubricant (either a solid or fluid) that your original equipment manufacturer specifies when you have to choose a lubricant.

Why and How to select a dry film lubricant with a pigment?

Forming dry film lubricants with the resin binders is the same as forming corrosion prevention coatings and paints. When needed, lubricant functions as a pigment and determines the color aesthetics in this case. Formation of the film is helped by the lubricant pigments as the lubricant pigments separate the mating surfaces that are in relative motion, therefore guaranteeing corrosion and wear resistance, a lower coefficient of friction, and wear and corrosion resistance.

Basis of selection

The basis of selection for the dry film (solid) lubricants is the required performance and the environment that is needed to be endured by them. Some of the typical dry film lubricants include boron nitride (BN), indium (In), antimony oxide (Sb2O3), tungsten disulfide (WS2), fluorinated ethylene propylene (FEP), graphite, MoS2, and PTFE.

Atmospheric moisture

Graphite doesn’t need atmospheric moisture for performing as a lubricant. However, MoS2’s desirable characteristics are significantly affected by the moisture’s presence. PTFE’s wear or corrosion resistance is not impacted at all by the moisture.

MoS2

If one needs material with the capability of carrying a load as high as up to 250,000 pounds per square inch, then the perfect material for the job is MoS2. Fifty thousand pounds per square inch of load-carrying capability is possessed by graphite, and 6,000 pounds per square inch of load-carrying capability is possessed by the PTFE.

Graphite

MoS2 and PTFE can function even in temperatures of 750 F and 500 F, respectively, whereas graphite excels in thermal capacity. Solid lubricants decompose and oxidize at higher temperatures. Graphite is currently being utilized in the firearms, railway track joints, bearings, and open-gear fasteners functioning at extremely high temperatures. But, graphite is electrically conductive, which is a disadvantage as it can be the reason for corrosion too.

Fluoropolymers, for instance, PTFE, has limited thermal capacity and load-carrying capability along with a low coefficient of friction.

Boron nitride (hexagonal) is used in space vehicles’ internal parts.

Tungsten disulfide is usually utilized in space vehicles for ball bearings, but it is costly. In comparison with MoS2, tungsten disulfide possesses better frictional characteristics at higher loads and higher temperatures.

What are the resin binders?

A bond is created between the dry film lubricant and the surface that needs protection by using various types of resins as bonding agents. Corrosion resistance isn’t provided by inorganic binders like silicates, and they are not much resistant against moisture too. Although, in 538°C (1000°F ), corrosion and wear protection is ensured by a Boric Oxide (B2O3) binder along with lead sulfide (PbS) as a lubricating pigment. Although at less than 1000 F (538 C) temperatures, it does not perform as a lubricant.

What are the common types of resin binders?

Generally, the classification of the common types of resin binders that are used with solid film lubricants is as either:

 

  • Thermoplastic binders, or
  • Thermosetting binders

A solvent evaporation process, for instance, ambient air curing, is used to cure the thermoplastic binders, whereas heat energy is needed by thermosetting binders for curing. Sometimes, the thermosetting resins are not suitable for military applications because of their demands of curing temperature.

 

What are thermosetting resin binders?

Silicone resins, epoxy resins, urethanes, and phenolic resins are the famous thermosetting resin binders that are usually considered for solid film lubricants. We can also consider a mixture of resins. Although, each of the resins has its particular advantages and drawbacks. One should keep the particular end-use in mind if choosing a mixture of resins. Epoxies generate wear debris that lessens the performance of the lubrication over the long term, making the service life short. Although, good adhesion to the metallic substrates is formed by epoxies. There should not be any kind of utilization of phenolic resins in alkaline environments.

What are phenolic resins?

Phenolic resins are appropriate for high vacuum applications, and they don’t produce dangerous wear debris. Although as compared to epoxy resins, the adhesion of phenolic resins to the metals is not as good. Even though the bonding strength of silicones with metals is good, it still produces harmful debris. The reasonable bonding strength is produced by a combination of phenolics with epoxy resins with metals for general applications. High-temperature curing is needed by the ceramic resins, and that can interfere with the substrate’s metallurgical characteristics. When a resin is being selected, the main things to consider are the baking duration and the curing temperature.

What are thermoplastic resin binders with solvents?

A solvent component will be needed by the air-drying type of thermoplastic resin binders, like acrylic resins. One can achieve curing by allowing the evaporation of the solvent so that a hard coating will be formed on the intended surface by the dry film lubricant that is dispersed in the resin.

How to Apply a Formulated Resin-based Product?

What is surface pretreatment?

If there is no systematic conduction of the application process and surface preparation, then even the best formulations can fail in service. If the pretreatment includes a phosphate treatment, grit blasting with aluminum oxide (Al2O3) of 220 mesh, and vapor degreasing, then the best results are obtained for the steel surfaces.

What is the application of a Formulated Resin-based Product?

Corrosion-resistant coating application methods are the same as resin-bonded dry film lubricant application methods. In many cases, the thickness of the film should be specifically controlled for good corrosion prevention as it should be in the range of .0002 to .0005 inches. Coating application methods like brush and roll coating, electrostatic spray, dipping, and conventional spray are all applicable for resin-bonded solid lubricants too. Dimension and complexity of the parts, number of parts to be coated, and total surface area determine the final selection of the method.

Graphite/Molybdenum disulfide (MoS2) in Silicone Resin, Polytetrafluoroethylene in Phenolic Resin, and Molybdenum disulfide (MoS2) dispersed in Phenolic Resin are the typical Final Products Results. Lubricating materials of three types are the main focus of our solid dry film lubricant coating operation:

What is molybdenum disulfide?

In high load-bearing applications, protection against friction is provided by moly dry film lubricant, which is commonly known as Molybdenum Disulfide. 250,000 psi or more of Lubricant quality can be maintained by the moly coated item’s surface. Additional high-performance resins are included in most of the MoS2 coatings for enhancing their bonding with the coated part’s base metal.

What is xylan?

In a matrix of stable and strong organic polymers, the mixture of the fluoropolymer compounds with low-friction is known as Xylan®. Resistance to chemicals, corrosion, cold, heat, and friction is provided by this fluoropolymer coating along with remarkable surface wear characteristics.

What are fluoropolymer coatings?

They form a slick, hard, and smooth finish and are the best solid/dry film lubricants. One coat system is used to apply these coatings as it can cause these coatings to fuse to the substrate for excellent adhesion.

What is air-assisted spray application and preparation of aqueous-based dry film lubricant formulations containing sucrose?

Sucrose was included in starch-oil composites aqueous dispersions for determining if the starch–oil composite dry film lubricant’s thin films lessened COF as efficiently as the previous coatings did that were previously applied with doctor blades. The starch–oil composite dry film lubricants thin films were air-sprayed onto the metal surfaces. In the earlier formulations, sucrose was needed for promoting flexibility and adhesion to the thicker composite coatings as these coatings peeled off and cracked the metal surfaces and were made without sucrose. The current study shows that in the formulation of aqueous dry film lubricant, the concentration of sucrose was within the ranges and maintained between 8.4 and 5.7 wt%.

Siphon feed spray gun

Starch-oil composite’s aqueous dispersions were applied by using a siphon feed spray gun. It was a high-pressure area’s low volume flow that applied the aqueous dispersion and shaped its pattern after it was discharged from the nozzle assembly.

What are the methods of application of the dry film coatings?

Following are the ways to apply dry film coatings.

  • Composites: Solid film lubricants can be generally alloyed into sintered materials and polymers to enhance particular characteristics.
  • Impingement Coatings: Impingement coatings are anti-friction coatings. They are tungsten disulfide (WS2) and molybdenum disulfide (MoS2) that don’t need a curing process and are capable of being applied at room temperature. These coatings are of less than 0.0001″, making them extremely thin, and they do not affect the tolerances of normal machinery. They are capable of functioning as the sole lubricant. They also perform well with hydrocarbon-based greases and oils.
  • Dipping/Spraying/ and Brushing: One can add solid film lubricants to specified binders and resins. The application of lubricants is made on the specified components that, after the assembly, are usually not accessible for lubrication. The component’s base material determines the availability of numerous thermal cure and air cure products.

Conclusion

Dry film lubricants have three main types in which they perform and excel marvelously. This is due to the excellent properties that these lubricants possess and ultimately are the cause of enhancing their productivity. However, the applications of dry film lubricants are quite interesting and effective for the massive growth of our industries in a lot of ways because they play a pivotal role in daily lives as well.

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