Contamination Control

Contamination is the scourge of hydraulic and lubricated mechanical systems. It enters from the atmosphere or is generated from within to rob lubricants and components of precious life. Contamination by definition, is anything in the oil that shouldn’t be there. The four most common lubricant contaminants are discussed below.

Particle Contamination
Abrasive particles are responsible for much of the wear that leads to mechanical failure. The amount of damage inflicted by particles depends largely upon their size, shape, hardness and chemistry. Abrasive particles must be controlled in any system deemed critical to operation or expensive to repair.

Where particles enter: Many particles enter the oil at those points where the machine interfaces with its environment while others are generated from within. Here is a summary of particle ingression sources:

• Vents and breathers: Open vents provide contaminants with free passage to the oil. Likewise, breathers that are made of very coarse material often fail to effectively control the clearance-sized particles that cause damage to the system.
• Ineffective or damaged shaft seals and wiper seals (hydraulics) allow particles to freely enter and permit leakage.
• New oil: Contrary to popular belief that “fresh” oil is clean, new oil is often very contaminated. It may ship dirty from the supplier, become contaminated in storage or become contaminated during transport to the machine.
• Filters: Filters that are full, damaged or defective can release stored particles (desorption) or fail to effectively remove particles.

How particles affect the oil: Particles, especially catalytic metal particles like copper, iron and lead increase the rate at which oxidation occurs. Particles also strip the oil of its polar additives, including anti-wear additives, extreme pressure additives, rust inhibitors and dispersants. Also, numerous, very small particles in stable suspension can cause the oil’s viscosity to increase.

How particles affect the machine: Abrasive particles are responsible for much of the wear leading to premature failure of mechanical components. Under sliding conditions, clearance-sized particles enter the oil film between surfaces and cut away material much like a lathe cuts metal. Under rolling contact conditions, particles transfer concentrated load between two surfaces in relative motion, resulting in surface fatigue, pitting and spalling .Particle-contaminated oil travelling at high velocity can also cause erosive wear.

Controlling particle contamination: Ideally, the entrance of particles is restricted at those points where it is ingested. However, to achieve modern contamination control objectives most machines require filtration. Numerous different filter media and separation mechanisms are available for removing particles. The performance of these devices is typically evaluated according to the following performance criteria:

Filter stability: How stable is the filter’s performance over time? Unstable filter performance equates to unreliable contamination control. Many factors influence filter stability including temperature variation, cold-starts, pressure surges and mechanical vibration. The filter’s size, design and construction influence its stability.

Filter capacity: This describes the amount of test contaminant a filter can remove, typically in grams.

Filter efficiency: How effectively does a filter remove particles of a given size? This is important information in assessing a filter's ability to meet the machine’s cleanliness