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Boundary Lubrication Issues

Adhesion is the result of two parts that drag across one another without adequate lubrication-film separation. This is also called boundary wear or boundary lubrication. The particles can be scuffed with striations from the dragging. The particles may show signs of melting due to the localised over-heating. Spherical particles are common when compete melting occurs.

Microdelamination

Microdelamination is surface damage caused by steady state sliding and metal to metal contact at the microscopic asperity level. Damage occurs due to the plastic deformation at, or just below, the surface. The stress creates voids in the sub-surface belby layer initiating cracks. Cyclic motion causes the cracks to propagate resulting in particles which flake off.

Asperity Deformation

Asperity Deformation is caused by micro microscopic asperity contact that results in the asperities on the softer material plastically deforming, or smearing in the direction of movement. Repeated contact eventually leads to removal of the asperities at the weakest point.

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Types Of Wear

Abrasive wear particles are most commonly the result of dust or dirt in the oil. The dirt particles become wedged between two moving parts, embed in the softer surface, and cut into the harder one. The wear debris from this process appear to be miniture shavings from a machining operation.

Abrasive wear particles can be several hundred microns long. Hard metals tend to form smaller abrasive particles that may have a needle like appearance.

The primary corrective action for abrasion is to filter the oil to remove the contaminents. It is also important to minimise the ingress of contaminents, especially dust.

Fatigue

Fatigue wear is the result of repeated cyclic loading of surfaces with compression and sheer or compression and tension. This is most common in industrial bearings and gears.

The repeated loading of the same point on a gear or bearing causes micro-cracks to form and become interconnected. When the cracks intersect surfaces, spall occurs and flakes or chunks are released into the oil. These particles are commonly 10 to 30 microns at first and later grow to be 100 microns or more. Fatigue is often from one of the following root causes:

  • Improper assembly
  • Misalignment
  • Inbalance
  • Other conditions which concentrate loading in a non-uniform distribution.
 The corrective action for premature fatigue is typically to use another technology such as vibration analysis to find possible causes and minimise these. Fatigue will eventually require component replacement.

Corrosion and Lubrication Degradation

Corrosive problems are caused by water or other corrosive process media in oil, such as natural gas or sulphur.

Corrosion is especially a problem in refineries and crude oil processing facilities. Corrosive wear in industrial machinery is normally caused by contamination of the oil by water or other corrosive fluid.

Corrosive wear in engines can also be caused by degraded oil. Oxidation is a common way that oil gets degraded. Oxidation is caused when hydrocarbon oil molecules chemically react with oxygen from combustion gases, the atmosphere or moisture.

Long term high temperatures cause rapid oxidation. Measure the change in the dielectric constant, Total Acid Number or  Fourier Transform Infra-red (FT-IR) to give an indication of when to change the oil.

Also look at the colour of the oil. If it is degraded, then it will be very dark in colour (brown to black). Keep in mind that it may be dark and still be perfectly good, but if it is bad due to oxidation or other chemical deterioration it should also be very dark. Dielectric increase of 0.1 usually means its time to change the oil.

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Wear Particle Identification

No industrial oil analysis is complete without a comprehensive wear debris analysis. Wear debris analysis (WDA) is a non-intrusive way to see inside complex machinery without taking it apart. Accurate identification of wear debris fragments can tell you which machine elements are damaged, and the nature of the problem which generated the debris.

Most (80%) of abnormal machine wear comes from one of four mechanisms:

  • Abrasion
  • Fatigue
  • Adhesion
  • Corrosion

Wear debris analysis tells you both the mechanisms and the severity. Armed with this knowledge, you can go after the corresponding route causes such as dust contamination, vibration faults, lubricant starvation or water contamination.

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Oil Storage And Handling

Cleaning up your oil storage and using clean and correctly labelled storage containers is the first step in gaining control of your lubrication programme.

Care should be taken when handling lubricants. Incoming and used oils should be checked for contamination and to ensure that the correct oil is being used. Many problems may occur with wrong, mixed or contaminated oils throughout the plant.

At the least:

  • Label all your oils correctly with dielectric and viscosity.
  • Clean up.
  • Correctly label containers and equipment.
  • Accurately label sample bottles.
  • Store lubricants in a clean, dry location and use desiccating breathers.
  • Transfer lubricants using dedicated, tagged totes.

Contamination can best be controlled by learning what the contaminant is and identifying where it has come from. Contaminants may have many sources, including moisture acquired when sampling oil. Dirty or hazardous environments such as coal handling or chemical refineries have their own problems, as do cement plants and wet environments. Proper storage and handling of lubricants is a necessary first step, but this is often not enough. Exclusion technologies such as ensuring proper sealing of lubrication reservoirs on machinery is often the right solution. Filtration systems such as exclusion breather systems can greatly reduce contamination of particulates as well as moisture. Regardless of what solution is successful for your application, regular monitoring is necessary to maintain the integrity of your lubrication programme.

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Oil Analysis (Tribology)

Oil analysis, or oil analysis Tribology, is a non-intrusive means of determining whether the oil system is clean and dry, if the oil is fit for use, and if wear is occurring inside the machine.

A machine’s operating life is most often determined by the oil that lubricates its load-bearing surfaces. Good lubrication normally provides long life, even under harsh operating conditions, and poor lubrication results in short life, even under mild operating conditions. Industrial machines are generally supposed to have 40,000 hours (about 5 years) mean time between failure (MTBF). This can only happen if you have “good lubrication”. If you have “poor lubrication” or “no lubrication” you get a far shorter operating life.

There are 5 factors in maintaining good lubrication:

  • Clean oil
  • Dry oil
  • Oil with the right properties
  • Contamination Control
  • Wear debris monitoring

Particle counting is used to monitor the cleanliness level of the machinery. The cleaner the system, the longer it lasts.

Wear debris analysis is used to identify the root cause of abnormal conditions. This analysis of large particles provides the essential difference between conventional oil analysis and industrial oil analysis.

Viscosity is one of the most important properties of an oil. Without the correct viscosity a machine will not have the correct lubrication, resulting in severe damage. Viscosity is measured at 40°C and 100°C as it can differ significantly depending on the operating temperature.

Spectometric analysis is used to measure wear metals (partical size typically less than 5 microns), contaminants such as silica (dust) and additives levels (adding wrong lubricant, addaiive depletion)

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