GEAR BOX CONTAMINATION - LUBRICATION SOLUTION

GEAR BOX CONTAMINATION:

•“Wear and tear” is a common expression used to describe the ageing of the mechanical systems.

•Wear commonly occurs as a result of the contamination and degradation of the lubricant.

•The contaminants can… not only cause a breakdown in the health of the lubricant, but will also interact with the moving surfaces to cause wear, leading to component failure.

•Adhesion, abrasion and corrosion of component surfaces will typically result from oil contamination as will poorly specified or unhealthy lubricants.

•The wear rate can be reduced as a result of some basic measures to protect the gear box from wear.

LUBRICATION:

•Proper Lubrication with timely addition / replacement plays vital role in maintaining the gear boxes with efficiency and increasing its working life.

•Oil level should be checked in all the gear boxes oil indicators / dip sticks.

•Oil level should be in between the minimum and maximum limits of the dip stick (or indicator).

•Testing of the lubricating oils used to be carried out periodically. The following tests are to be done…

1. Dirt contamination
2. Moisture
3. Volatile materials (Benzene, kerosene, spirit etc,)
4. Viscosity
5. Acidity
6. Alkalinity due to soda (Na2 Co3) etc.,

LUBRICATION MANAGEMENT:

1.Right Selection of the Lubricants.
2.Quality of the oil is to be maintained free from contaminants, should be stored properly before use.

•During recent developments, gear boxes designs changed… new surface hardening techniques & metallurgy has enabled the manufacture of smaller gear boxes for a given hp rating.

•These changes have resulted in much more aggressive surface loading, and the thickness of super-hard material is often razor-thin.

•These harder surfaces are more resistant to particle-induced sliding wear, but they are highly susceptible to particle-induced rolling wear, which occurs at the pitch line of the gear tooth where load is transferred.

•When a particle is squeezed in the load zone, it can fatigue the hardened material, resulting in small formation of dent, producing a proud area around the dent’s crater.

•The plastic deformation that occurs where the surface is dented can dramatically alter the material’s physical properties, making it more susceptible to wear and fatigue.

•Resulting that the gear boxes tent to run hot, increasing the risk to the lubricant.

IDENTIFYING THE SOURCES OF CONTAMINATION:

•Contaminants are hard particles, moisture, high temperature and aeration. The other examples are radiation, process chemical or physical matter from the environment.

•Ingression points of the gear box contamination are seals and the breathers. This will be during maintenance activities such as top –ups, drain and refill etc.,

•Wet conditions may ingress moisture into the gear box.

•Dust particles are ingresses in the gear boxes from the environment.

CONTROLLING THE SOURCES OF CONTAMINATION:

•SEALS: Standard lip seals are low-cost item, but require frequent replacement. Their ability to seal against oil leakage and dirt/water ingress is poor by comparison to labyrinth seals. These seals cannot be directly loaded or pressurised with external forces.

•BREATHERS: snorkel type, or vent plug type breathers can prevent large bodies to ingress into the gear box, but cannot stop a destructive 10 µm particle from entering into the gear box. (like a ball rolling into a open door).

•Upgrading the vent into a proper contaminant-exclusion breather should minimise the ingression of hard particles and moisture. (1 µm filters).

• For applications where volume changes are minimum and the dusty environment, the bladder type (also known as expansion chamber) of breather is recommended to use.

•The bladder allows for expansion and contraction of the air within the casing as a result of temperature changes.

FILTRATION OF GEAR BOX OILS:

PORTABLE OFF-LINE FILTRATION: Some gear boxes may incorporate a small pump with a filter.
Many gear boxes don’t have filtration facility. In such cases filter carts can usually adopted by replacing the fill and drain plugs with quick –connect fittings.

At least 5 to 7 times the volume of the oil in the system should be passed through the filter cart to ensure adequate clean up.

PERMANENT OFF-LINE FILTRATION: Larger units where large volumes of oil and high levels of cleanliness must be maintained, a permanent off-line circuit should be employed.