What are Friction Modifiers?

What are Friction Modifiers?

Friction modifiers are mild anti-wear additives used to minimize light surface contact, such as sliding and rolling. These can also be referred to as boundary lubrication additives. These additives are used in lubricants to modify the coefficient of friction (hence the name, Friction Modifiers). Friction modifiers are deployed to prevent wear on metal surfaces. Mostly used in transmission fluids and engine oils, these additives help slow down wear and increase fuel economy.

How do Friction Modifiers Work?

Source: Machinery Lubrication – Noria

A friction modifier molecule consists of two parts: a polar end (head) and an oil-soluble end (tail). The head attaches itself to the metal surface to create a cushion for the metal surface against another metal surface. The tails stand up like a carpet; vertically stacked besides each other in a Nano-sized sheet covering the metal surface. These molecules hold up when cushioned surfaces come in light contact with each other. This forms a thick boundary film that is softer than metal surfaces.

These additives have multiple functions beyond friction modification. They work as antioxidants and corrosion inhibitors as well. As the contact or load becomes heavier, the polar molecules are brushed off, thus rendering the additive useless in reducing friction.

Friction Modifier Applications

Friction Modifiers are typically used in engine oils and automatic transmission fluids. In engine oils, friction modifiers are deployed to improve fuel economy by reducing friction. In transmission fluids, friction modifiers are deployed to improve engagement on clutches. Some situations require some traction to operate properly.

Their use in engine lubricants increased in the 1970s due to the oil embargo. The lack of fuel led the automotive industry to improve fuel economy, thus reducing fuel usage. Continuous development has led to lower viscosity lubricants. Now, lubricants require robust friction modifiers to reduce wear and friction to offset the lower viscosity.

However, friction modifiers in these applications act differently based on shear conditions. This ensures equipment does not wear while also preventing too much slippage. This smooths the transition from a dynamic condition to static condition. For example, this is used in a gear change in a transmission.

Anti-Wear and Extreme Pressure (EP) Additives

As loads become heavier, engineers must adjust their lubricant to meet the tougher demands of heavier loads and higher temperatures. You should switch to a modifier that is classified as an anti-wear additive. A common and effective anti-wear agent is Zinc dialkyldithiophosphate (ZDDP). These additives react with metal surfaces once the environment reaches a high enough temperature.

As loads continue to increase, in addition to metal contact, the friction modifier must become more robust. In this instance, your lubricant must include extreme pressure (EP) additives. These additives are either temperature-dependent or not. Temperature-dependent EP additives activate as the metal surface temperature increases due to the extreme pressure. The reaction is driven by the heat produced from friction.

Final Thoughts

Lubricants with friction modifiers create more efficient operating environments. This leads to less wear, downtime, and carbon dioxide emissions. As friction modifier additives improve, lubricant manufacturers will aim to reduce to viscosity to reduce shear conditions. Conversely, this creates more components operating in thin boundary lubrication conditions. We will see continuous innovation of these additives to meet the performance and efficiency demands.

How Mineral Base Oils are Made

Oil-based liquid lubricants are composed of two (2) key ingredients: base oil and additive packages. Additive packages in a lubricant will tend to vary based on applications. This post will focus on the main ingredient, base oils. Base oils will comprise typically 80-99% of an oil-based lubricant. Before we look at the base oil in a finished lubricant, we have to understand how oil gets from a drilling site to a refinery and finally into your lubricant.

Extracting and Transporting Crude Oil

After crude oil is extracted from the ground at wellhead or platform drilling sites, it is transported via rail, ship, or pipeline. It is then stored at a terminal or hub. Oil & Gas Manufacturers then take the crude and refine it to meet product specifications. Some of these products include gasoline, heating oil, fuel oils, asphalt and road oil, and lubricants.

Separating the Crude Oil

The typical barrel of crude is 42 gallons. According to the American Petroleum Institute, only 0.5 gallons of crude oil in each barrel are used to make lubricants.

This is because lubricants require longer chain hydrocarbons. Most lubricants have hydrocarbon molecules with 26-40 carbon atoms. Crude oil is heated and vaporized then condensed; this process is known as distillation. The distilled oil is easily separated by hydrocarbon chain lengths. Shorter molecules rise to the top and longer molecules sink to the bottom. After the hydrocarbons with 26-40 carbon atoms are separated, they are sent to a refining process specific to lubricants.

Refining the Crude Oil

The distilled oil is refined using two different processes: extraction and conversion. Extraction involves four steps:

  1. Deasphalting: Takes residue at the bottom and separates into tar and compounds similar to lube distillates.
  2. Solvent Extraction: Remove most the aromatics and undesirable constituents of oil distillates. Results in neutral oil base stocks called reaffinates.
  3. Dewaxing: Reaffinates are dewaxed to produce a wax and dewaxed oil. The dewaxed oil becomes base stock for lubricants.
  4. Hydrofinishing: Changes polar compounds in oil by a chemical reaction. Oil becomes lighter in color and exhibits improved chemical stability.

The conversion process involves three steps and is becoming popular for refining. This process involves converting undesirable products into desirable products using hydrogen, heat, and pressure:

  1. Hydrocracking: Distillates are subjected to a chemical reaction at high temperatures and high pressure. The aromatic and naphthene rings are broken and joined using hydrogen to form an isoparaffin structure.
  2. Hydrodewaxing: A hydrogenation unit is used to deploy a catalyst that converts waxy normal paraffins to desirable isoparaffin structures.
  3. Hydrotreating: The first two processes broke chemical bonds, therefore it is necessary to saturate unsaturated molecules. By adding more hydrogen, the molecules saturate and become more stable and better able to resist oxidation

Classifying Refined Oil

This results in mineral oil base stocks that are classified into three different groups. API Groups I, II, and III are all mineral oil-based, but differ based the level of refining. The chart below gives a breakdown of each of the 3 mineral groups.

The key factors are: sulfur (%), saturates (%), and viscosity index. Some refer to Group III base stocks as “synthetic” due to the chemical processes they undergo. The natural chemical structure is altered from the natural structures found in mineral oil. However, the API classifies Group III oils as mineral because they originate from crude oil

The conversion process is more effective in reducing aromatic content, but the process is more expensive. Typically, the costs are passed along to end-users, but they get a higher quality base oil and better performance. Group II and Group III are becoming more prevalent as preferences shift towards conversion processes rather than extraction processes. Once refined, base stocks are blended with additives and additive packages to form a final product lubricant.