What are the ideal Properties for bearings lubricant?

Ideal properties of a good bearings lubricant are:

It should have moderate bearing loads. 

It should improved heat transfer behavior. 

It should have good corrosion protection properties.

It should give rise to low friction.

Soluble for high speed fluid film hydrodynamic lubrication, hence, low viscosity with reduced oil film friction. 

It should carry away as much heat from the surface as possible.

It should have antifoaming ability.

It should adhere to the surface and reduce the wear.

It should have good high temperature viscosity.

It should have thermal and oxidative stability.

It should have good thermal durability.

It should have good low temperature viscosity. 

It should have good cleaning effect on the surface.

What are the capabilities expected from an engine lubricant?

Anti-rust properties

Anti-corrosive properties

Anti-foam properties

Capacity to withstand the action of water which can affect additives or Resistance to hydrolysis

Anti-wear or capacity to contain wear 

Capacity to reduce surface friction of the lubricated parts or friction modifier

Thermal strength or capacity to withstand temperature changes

Capacity to the cold parts of an engine clean or Dispersivity 

Capacity to preserve oil film even in the presence of high pressures or Anti-scuffing

Capacity to resist the action of oxygen or Anti-oxidant

Capacity to separate contaminants or Demulsibility

Capacity to keep hot parts of an engine clean or Detergency

Capacity to stabilize the optimum viscosity or high viscosity index 

Capacity to neutralize acids formed during combustion or other sources thereby preventing corrosive wear or Alkalinity reserve

Capacity to separate insoluble elements or Centrifugibility and filterability

Where greases are applied as a lubricant?

Greases are applied where oils cannot be used as a lubricant. For example, in places where sealing does not exist or is inadequate, dirty environments, in inaccessible locations, in places where oil dripping or splashing cannot be tolerated.

Greases are classified based on the basis of soap type, soap content, base oil viscosity, dropping point and consistency. Consistency mainly is a measure of grease sealing properties, texture and dispensability. 

Lithium soap greases- it is generally are water resistant and corrosion inhibitor and have good mechanical and oxidation stability.

Sodium soap greases- it is generally are low torque resistance, excellent high temperature performance and ability to absorb moisture.

Calcium soap greases- It is generally are multi purpose grease, resist water wash out, non corrosive to most metals, work well in both grease cups and centralized lubrication systems. 

Greases are fine dispersion's of oil-insoluble thickening agents usually soap in a fluid lubricant such as mineral oil. When a bearing lubricated with grease and start to move, the grease structure is affected by the shearing action, and lubrication is provided by the oil component of the grease.

How to avoid failure of lubrication?

Lubrication is the most important PM work for rotating equipment. To ensure that lubrication is done correctly it is very important to have a dedicated database of all equipment needing lubrication comprising part to be lubricated, lubricant recommended by OEMs, interval for makeup & replacement etc and issue periodical lubrication schedule for implementation. It is very important to assign skilled technician for lubrication work. Also important is to monitor the lube oil level of the major equipment during daily walk down. It is also a good practice to check the viscosity of oil at regular intervals for major equipment.

It is very important to know that you are using the right lubricant for the application you are lubricating. Lubricants are designed to work in different environments and the operating temperature of the equipment that you are lubricating must be evaluated. Check what the temperature range the lubricant is able to work in and its viscosity are all so important. 

To avoid failure of lubrication you need to: 

Keep it clean 

Keep it dry 

Keep it cool 

The critical matter in lubrication is control the analyzing lubricant properties and suspended contaminants for the purpose of monitoring and reporting timely, meaningful and accurate information on lubricant and machine condition. An antioxidant is an example of an additive that will be expended over its useful life until it becomes empty without warning. Without antioxidants, oxidation byproducts are allowed to corrode equipment parts, thickening the oil and reducing the base oil’s lubricating properties. The rate of lubricant failure, and consequently machine failure, increases rapidly. 

As well as Contamination rates can also be a silent danger. The problem arises when too many contaminants are allowed to exist in the workings of a machine. These contaminants can generate more contaminants through three-body abrasion.

What are the possible causes for overheating oil in hydraulic system?

There are two ways to solve overheating problems in hydraulic systems: decrease heat load or increase heat dissipation. 

Hydraulic systems dissipate heat through the reservoir. Therefore, check the reservoir fluid level and if low, fill to the correct level

There are two main sources for unusual heat 

1. Leakage 

2. Problem in pump and oil flow. Check that there are no obstructions to airflow around the reservoir, such as a buildup of dirt or debris.

Heating of hydraulic fluid in operation is caused by inefficiencies. Inefficiencies result in losses of input power, which are converted to heat. A hydraulic system’s heat load is equal to the total power lost (PL) through inefficiencies and can be expressed as: 

PLtotal = PLpump + PLvalves + PLplumbing + PLactuators 

If the total input power lost to heat is greater than the heat dissipated, the hydraulic system will eventually overheat. Installed cooling capacity typically ranges between 25 and 40 percent of input power, depending on the type of hydraulic system.

Properties of lubricants

Whenever an object moves against another object, friction will be present, turning kinetic energy into heat and causing equipment to wear. Using lubricants helps to reduce this friction, allowing more work to be done for the same amount of energy input, lowering the temperatures of the materials in contact, and greatly extending the lifespan of the moving equipment.

Kinematic viscosity
Test Number & Name: ASTM D-445 Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids.

• Measure of internal resistance to flow.
• It is measured in Centi Stokes (CSt).
• Kinematic viscosity decreases with increase in temperature.
• Kinematic viscosity also Important in lubricant selection.
• Increase in used oil indicates oxidation.
• Specified at 40 degree C and 100 degree C.

Lubricity 

Some lubricants are said to have high lubricity, or oiliness. This property comes from the chemical compositions of the oils, which reduce wear and friction even in extreme conditions.

Pour Point

• Test Number & Name: ASTM D-97 Standard Test Method for Pour Point of Petroleum Oils.
• Lowest temperature at which the fluid will flow is known as pour point.
• It indicates lowest operating temperature.
• It measured in Degree C.

Cloud Point  

Petroleum-based lube oils contain dissolved wax. At a low enough temperature, referred to as the cloud point, this wax will separate from the oil and form wax crystals. These crystals can clog filters and small openings, deposit on surfaces such as heat exchangers, and increase the viscosity of the oil.

Viscosity index
Test Number & Name: ASTM D-2270 Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40°C and 100°C.

• It measure of fluids change of viscosity with temperature.
• Higher the Viscosity index lower will be the change of viscosity with temperature.
• Viscosity index Indicator of temperature range of operations.

Oxidation and Corrosion  

When lubricants are exposed to oxygen and certain metals or compounds at temperatures above 160 degrees Fahrenheit, they can be prone to oxidation. Oxidation of lubricants can lead to several undesirable consequences, such as increased oil viscosity, formation of corrosive acids, and sludge buildup. Preferred lubricants are those that have a high resistance to oxidation and inhibit corrosion by protecting components from water, oxygen, and chemical attacks.

Aniline Point

Aniline point of the lubricant oil is defined as the minimum equilibrium solution temperature for equal volumes of aniline and lubricant oil samples. It gives an indication of the possible deterioration of the lubricant oil in contact with rubber sealing; packing, etc.

Aromatic hydrocarbons have a tendency to dissolve natural rubber and certain types of synthetic rubbers. Consequently, low aromatic content in the lubricant oil is desirable. A higher aniline point means a higher percentage of paraffinic hydrocarbons and hence, a lower percentage of aromatic hydrocarbons.

Total Base Number (TBN)

• Test Number & Name: ASTM D 664
• Total Base Number measured the acid neutralizing reserve in oil.
• Total Base Number measured in Mg KOH/gm of oil.
• TBN is Important for deciding discard of oil.
• TBN is decreases due to Oxidation of oil, Water contamination and Fuel contamination.

Flash Point and Fire point

• Test Number & Name: ASTM D-92 Standard Test Method for Flash and Fire Points by Cleveland Open Cup.
• Lowest temperature at which the vapor above the liquid will ignite under flame is known as Flash point.
• Fire point is the lowest temperature at which a specimen sustains burning for five seconds.

Types of Lubricant

Types of Lubricant

•       Liquid

•       Solid

•       Semi solid

•       Gases

Liquid

lubricants are liquid/fluids

synthetic oils or Mineral oil 

Solid

MoS2, Graphite 

Semi solid

Greases

Atomized 2 stroke oils

Gases