Skip to content
National Synthetics

National Synthetics

Independant Amsoil Dealer

Protect your Weekend with Amsoil Synthetics
Primary Menu
  • Login / Create Account
  • Vehicle Lookup
    • Auto & Light Truck
    • Motorcycles
    • ATV
    • UTV
    • Personal Watercraft (PWC)
    • Marine Outboard
    • Snowmobile
    • Heavy Duty
  • Shop Direct Now
  • Free Catalog
  • Amsoil Products
    • Signature Series
      • Motor Oil
    • Amsoil 2-stroke Powersports Lubricants
  • Blog
    • Amsoil Product Info
      • What are the benefits of using Amsoil Quickshot?
  • Contact us
Watch Videos
  • Home
  • Articles
  • Understanding Fluid Lubrication and Protection
  • Articles

Understanding Fluid Lubrication and Protection

Tisha Maguire April 19, 2023 4 min read

Different methods of lubrication protect machines from wear.

oil and gears

Original article based on April 11, 2023 Amsoil Blog by David Hilgendorf | Amsoil Technical Writer links added by National Synthetics staff

The primary function of fluid lubrication is to provide a durable film that protects moving parts by reducing friction and wear between surfaces; however, the level of protection provided is enabled by different methods of lubrication:

The reduction of friction by using a fluid can be divided into two basic types: full-film and thin-film. Full-film lubrication consists of four sub-types and thin-film lubrication consists of two sub-types.

Full-film lubrication

  • Hydrodynamic
  • Elastohydrodynamic
  • Hydrostatic-film
  • Squeeze-film

Thin-film lubrication

  • Boundary
  • Mixed-film

We’ll discuss the differences in that order:

Amsoil Banner What does oil viscosity mean

Hydrodynamic lubrication

Hydrodynamic, or full-film, lubrication exists when two surfaces are completely separated by an unbroken lubricant film so there is no metal-to-metal contact. The movement of the rolling or sliding action causes the film to become thicker and pressurized, which prevents the surfaces from touching.

When the two surfaces are moving in opposite directions, the fluid immediately next to each surface will travel at the same speed and direction as the surface. If two parts are moving in the same direction, a full hydrodynamic film can be formed by wedging a lubricant between the moving parts. Known as wedging film action, this principle allows large loads to be supported by the fluid. It works much like a car tire hydroplaning on a wet road surface. During reciprocating motion, where the speeds of the relative surfaces eventually reach zero as the direction changes, the wedging of the lubricant is necessary to maintain hydrodynamic lubrication.

The lubricant’s viscosity assumes responsibility for most of the wear protection and additives play a limited role. Although full-film lubrication prevents metal-to-metal contact, abrasive wear or scratching can still occur if dirt particles penetrate the lubricating film. Additional factors, such as load increases, can prevent hydrodynamic lubrication by decreasing the oil film thickness, allowing metal-to-metal contact to occur.

Engine components operating with full-film lubrication include the crankshaft, camshaft and connecting rod bearings, and piston pin bushings. Under normal loads, transmission and rear-axle bearings also operate under hydrodynamic lubrication.

Hydrodynamic Lubrication
Hydrodynamic Lubrication

Elastohydrodynamic lubrication

Elastohydrodynamic (EHD) lubrication is another form of full-film lubrication that exists when the lubricant reacts to pressure or load and resists compression, functioning as if it were harder than the metal surface it supports. As viscosity increases under pressure, the film becomes more rigid, creating a temporary elastic deformation of the surfaces. EHD occurs in the area where the most pressure or load affects the component. In roller bearings, for example, the metal surface deforms from the extreme pressure of the lubricant

The lubricant’s viscosity and additives work together to protect surfaces in an EHD system. Anti-wear additives are often used to protect engine bearings in high-load conditions, while both anti-wear and extreme-pressure additives work to protect gears in high-load conditions.

Elastohydrodynamic lubrication
Elastohydrodynamic lubrication

Hydrostatic-film lubrication

Hydrostatic-film lubrication is a full-film lubrication method common in heavily loaded applications that require a supply of high-pressure oil film. The high pressure in hydrostatic-film lubrication ensures that the required film thickness will be maintained to support a heavy load during extreme operation. Hydrostatic-film lubrication maintains a fluid film under high-load and low-speed conditions, such as those experienced at equipment startup.

Hydrostatic-film lubrication
Hydrostatic-film lubrication

Squeeze-film lubrication

Squeeze-film lubrication is a form of full-film lubrication that results from pressure that causes the top load plate to move toward the bottom load plate. As these surfaces move closer together, the oil moves away from the heavily loaded area.

As load is applied, the viscosity of the lubricant increases, enabling the oil to resist the pressure to flow out from between the plates. Eventually, the lubricant will move to either side, resulting in metal-to-metal contact. A piston pin bushing is a good example of squeeze-film lubrication.

Squeeze-film lubrication
Squeeze-film lubrication

Boundary lubrication

Boundary lubrication is a form of thin-film lubrication and occurs when a lubricant’s film becomes too thin and contact between the surface’s asperities occurs. Excessive loading, high speeds or a change in the fluid’s characteristics can result in boundary lubrication.

No surface is truly smooth, even when polished to a mirror finish. The irregularities, or asperities, on every surface may be so small that they are only visible under a microscope. When two highly polished surfaces meet, only some of these asperities on the surfaces touch, but when force is applied at right angles to the surfaces (called a normal load), the number of contact points increases.

Boundary lubrication often occurs during the start-up and shutdown of equipment. In these cases, chemical compounds enhance the properties of the lubricating fluid to reduce friction and provide wear protection. For instance, anti-wear additives protect the cam lobes, cylinder walls and piston rings in engine high-load conditions, while anti-wear and extreme-pressure additives protect ring and pinion gears in rear axles.

Boundary lubrication
Boundary lubrication

Other lubrication

Mixed-film lubrication is considered a form of thin-film lubrication, although it is a combination of hydrodynamic and boundary lubrication. In mixed-film lubrication, only occasional asperity contact occurs.

Solid-film lubrication is used in applications that are difficult to lubricate with oils and greases. To manage these difficult applications, solid- or dry-film lubrication is applied where the solid or dry material attaches to the surface to reduce roughness. Solid-film lubricants fill the valleys and peaks of a rough surface to prevent metal-to-metal contact. Common solid-film lubricants include graphite, molybdenum disulfide (MoS2, aka moly) and polytetrafluoroethylene (PTFE), also known as Teflon.*

AMSOIL synthetic lubricants are carefully formulated with the optimum blend of the highest quality base stocks and additives, ensuring lubricated components receive outstanding protection from contact wear.


Preferred Customer Banner

Synthetic vs Conventional Banner

Address:
National Synthetics – Independent AMSOIL Dealer
110 Northcutt Station
Acworth GA 30101
Phone:
+1 (678) 799-9062
Email:
sales@nationalsynthetics.com

Continue Reading

Previous: Synthetic vs. Conventional
Next: About Amsoil

Related Stories

The Difference Between Horsepower and Torque Torque HP Map
4 min read
  • Articles
  • Horsepower
  • Torque

The Difference Between Horsepower and Torque

April 29, 2023
Is an Engine Flush Good or Bad? Amsoil Engine and Transmission Flush
6 min read
  • Articles
  • General Purpose Cleaners & Protectants
  • Signature Series

Is an Engine Flush Good or Bad?

April 29, 2023
How Do I Switch from Conventional to Synthetic Oil? Amsoil Garage Mechanic
2 min read
  • Articles
  • FAQs

How Do I Switch from Conventional to Synthetic Oil?

April 27, 2023

Recent Posts

  • The Difference Between Horsepower and Torque
  • Is an Engine Flush Good or Bad?
  • How Do I Switch from Conventional to Synthetic Oil?
  • Amsoil Preferred Customer & Online/Catalog Promo
  • How to Perform Oil Analysis

Archives

  • April 2023
  • March 2023
  • February 2023

Categories

  • Articles
  • ATV/UTV
  • Biodegradable
  • Commercial
  • Diesel
  • Dirt Bike
  • Environment Friendly
  • European Motor Oil
  • ExclusivePromos
  • FAQs
  • Fuel Additives
  • Gasoline
  • Gear Oil
  • General Purpose Cleaners & Protectants
  • Grease
  • HistoricalPromos
  • History of Synthetic Motor Oil & Amsoil
  • Horsepower
  • Hydraulic Oil
  • Marine
  • Motor Oil
  • Motorcycle
  • Oil Analysis
  • Performance Improver P.i.
  • Race
  • Signature Series
  • Small Engine
  • Synthetic Water Resistant Grease
  • Torque
  • Transmission Fluid

You may have missed

The Difference Between Horsepower and Torque Torque HP Map
4 min read
  • Articles
  • Horsepower
  • Torque

The Difference Between Horsepower and Torque

April 29, 2023
Is an Engine Flush Good or Bad? Amsoil Engine and Transmission Flush
6 min read
  • Articles
  • General Purpose Cleaners & Protectants
  • Signature Series

Is an Engine Flush Good or Bad?

April 29, 2023
How Do I Switch from Conventional to Synthetic Oil? Amsoil Garage Mechanic
2 min read
  • Articles
  • FAQs

How Do I Switch from Conventional to Synthetic Oil?

April 27, 2023
Amsoil Preferred Customer & Online/Catalog Promo Four Free Can Coolers Promo
2 min read
  • ExclusivePromos

Amsoil Preferred Customer & Online/Catalog Promo

April 27, 2023

Contact Us:
National Synthetics

Leo & Tisha Maguire
110 Northcutt Station
Acworth, GA 30101
678-799-9062

  • Helpful Links:
    • Privacy Policy
    • Contact Us
    • Buy Direct
    • Free Catalog
  • Facebook
  • Twitter
  • Instagram
  • YouTube
Copyright © All rights reserved. | MoreNews by AF themes.