Particle Contaminant Characteristics
Particles are not just defined by their composition, size, and amount. They have many significant physical and chemical characteristics. These characteristics determine how potentially destructive a particle can be as a contaminant in your equipment. The table below details these important characteristics.
| Characteristic | Definition | Significance |
|---|---|---|
| Size | Spherical diameter measured in microns. | Particles enter into critical clearances, causing wear. Bigger particles become smaller particles. |
| Surface Area | An object’s total exterior. | As particles become smaller their combined surface areas increase, causing more wear and reactions. |
| Density | Determines the buoyancy of an object. | Less-dense material will remain in the oil longer causing more wear and reactions. |
| Shape | A particle’s roundness or sharpness (angularity). | Dictates what type of wear the particle will cause, indentations or abrasions. The more angular, the more wear. |
| Hardness | A particle’s resistance to deformation or fragmentation. | The particle’s hardness compared to the machine surface’s hardness will dictate ability to cause wear. (See table below for hardness.) |
| Composition | The particle’s capacity to react with other surfaces. | A non-reactive particle may cause damage because the particles it creates by abrasion can be highly reactive, promoting oxidation and creating acids. |
| Polarity | Possessing an ionic charge which determines how likely the particle is to stick to other things. | Promotes the attraction of other ionic things, including scavenging performance additives. Can cling to surfaces, restricting flow. |
Common dirt particles consisting of silica and aluminum can be harder than a hacksaw blade. The table below illustrates various materials’ relative hardness. Mohs Scale of Hardness defines an object’s resistance to scratching by a standardized object.
| Particle Type | Mohs Hardness |
|---|---|
| Fingernail | 1 |
| Babbitt Particles | 1 |
| Aluminum | 1 – 3 |
| Road Dust (Silica) | 2 – 8 |
| Copper, Silver, Gold | 3 |
| Forged Steel | 4 – 5 |
| Knife/Hacksaw Blade | 5.5 |
| Rust | 5 – 6 |
| Quarry Dust | 5 – 9 |
| Glass | 6 – 7 |
| Aluminum Oxides | 9 |
| Diamond | 10 |
Particles can be very destructive. Their destructive capacity increases tremendously as the number of particles rises. Additionally, particles create more particles that cause wear, lubricant degradation, and surface fatigue to opposing surfaces. Controlling particles and their propagation is critical for equipment health and survival.