Oil and grease wear off over time by a process called oxidation. What once was a stable and effective lubricant is now just slush, varnish, and a thick substance that causes mayhem in your industry by ruining your equipment and machines. How does this degradation of oil happen, and why is it important to monitor your lubricant's oxidation rate?
Oxidation is the reaction of lubricant base oil with oxygen present in the surrounding air and moisture. The bad environment in which the lubricant is operating can have a damaging impact on its life, effectiveness, and performance. It also impacts the machine's oil change interval, downtime, and lubrication program.
How Oxidation Of Lubricant Occurs
Lubricants are vulnerable to attacks. Most non-synthetic lubricants have two components; mineral oil and additives. The oil part contains long chains of carbon, hydrogen, and oxygen atoms. These atoms have a strong bond between them, and if the right amount of hydrogen and carbon is present, then the molecule is said to be saturated, stable, and non-reactive to other atoms.
The problem arises when some hydrogen atoms break apart due to factors in the environment, leaving behind highly reactive and unstable molecules that start to take part in an oxidation chain reaction. From here begins the end of your lubricant's life. Let's see what causes hydrogen atoms to break apart from oil molecules.
Heat Accelerates Oxidation
An unfavorable condition or environment around the lubricant can cause the oxidation of oil molecules to occur. For example, when subjected to heat from the mechanical processes, the oxygen atoms present in the air become separated. These separate atoms then go looking for another element to bond with and produce a reaction. If these atoms encounter unsaturated hydrocarbons, they bond with them and form acids. These acids then attack the oil, resulting in its oxidation.
The energy required by oxygen molecules to separate is around 495 KJ. This energy comes from the heat that originates from sources such as mechanical processes, friction, the external environment, and more.
Oil molecules containing hydrocarbons require less energy to become unstable. So, any slight increase in heat can create a volatile environment for them, adding to the potential of oxidation and varnish formation.
Micro-dieseling is a pressure-induced thermal breakdown of oil particles. This occurs when an air bubble transitions from a low-pressure area to a high-pressure area in a system and results in an adiabatic compression of the air bubble within the oil. This rapid compression generates an enormous amount of heat and causes a thermal breakdown of oil surrounding the bubble.
Micro-dieseling is very common in hydraulic systems and causes the instant oxidation of lubricants.
Contaminants such as dirt, water, air, process fluids, acids, and more, can greatly impact the rate of lubricant oxidation. Dirt and grime, present inside machine components, contain fine metal particles that act as catalysts that spark and speed up a lubricant's degradation.
Similarly, air present in a lubricant's surroundings provides a source of oxygen that can react with oil, leading to its oxidation. Water can easily decrease a lubricant’s life. However, this is typically achieved by spoiling additives that attempt to prevent oxidation.
We can prevent lubrication oxidation by minimizing the air's availability and controlling the amount of heat near the lubricant. It is essential to remember that heat independently will not lead to oxidation. It will only aid and expedite the reaction process between two unstable elements. Since heat reduction is secondary and its control is also difficult, it is best to control your air’s availability.
To control heat, you need to choose the right viscosity grade lubricant for your application. Equipment optimization, having the proper lubricant plan, and machine maintenance are other ways to decrease your lubricant oxidation rate.