BEARING LUBRICATION INTRODUCTION

Speed, Load & Viscosity Relationships

Obviously friction and loading are the main concern and these issues can be easily resolved by Steel Shield ABF Technology through electrochemical ionization.

Lubricant Grease & Oil

Use Conditions Guidelines (refer to your equipment manual)
Use grease, when:	Use oil, when:
Shock loadings happen Cooling is not the main concern Low or moderate speed bearings are used Bearing running at intermittent condition Bearing starts or stops frequently Bearing changes rotation directions frequently Prevention of oil leakage is necessary so as to prevent safety, health and environmental risks Housing and seal designs simplification is necessary, and piping reduction or elimination	Need to eliminate heart from the bearing Bearing speed is high Need to remove contaminants, and flush the bearing Other mechanical components like gear boxes dictate that liquid lubricant is a must

ROLLING BEARINGS

These bearings are characterised by they types of roller, size, number of rows of elements and the groove type. They can be designed to support both radial and axial thrust loads. A ball bearing has a point contact while the roller bearing has a line contact which affect the method of lubrications.

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Fluid (Oil) Lubrication

Viscosity, base oil type and additive type are the three main criteria in lubricant selection. `ND_m` is the speed of rolling element bearings where it equals to rpm x (ID + OD) /2. Low speed bearings have `ND_m` vales below 50,000 while values between 100,000 and 300,000 are the average speeds. Values above 400,000 are high speed bearings. `ND_m` values above 700,000 (or up to 1,500,000 use mist lubrication) is the upper limit of oil lubrication. The minimum viscosity of 13cSt is the rule of thumb for many moderate speed bearings.

To find the "Minimum Required Lubricant Viscosity at Operating Temperature", please click here.

We can also consider the minimum viscosity at the operating temperature based on the speed and the type of bearing:

Minimum Oil Viscosity (cSt) at Operating Temperature
`ND_m`	Ball Bearing	Cylindrical, Tapered & Needle Bearing	Spherical Bearing
50,000	22-45	50	65-100
100,000	15-20	~28	30-45
200,000	10-20	~18	20-30
400,000	7-8
500,000	6

Plot the graph of viscosity-temperature after the minimum viscosity is selected. This ensures the selected ISO grade lubricant has a viscosity greater than the minimum at the operating temperature. Generally, the actual viscosity used at the operating temperature is between 1.5-2 times the minimum viscosity. The Kappa Ratio (K) is indicates the actual viscosity of the oil being used to the minimum viscosity required. Kappa ratio equals to 4 can maximize the bearing life where the ratio equals to 1 refers to the minimum condition to prevent boundary lubrication (metal-to-metal wears). However, if Kappa ratio is too high, it will lead to bearing failure due to fluid friction and excessive heat generation.

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Grease Lubrication

Base oil, additives and thickeners are the basic elements of greases. Greases are usually limited to rolling bearings with speeds up to `ND_m` values of 350,000 for ball bearing, and 150,000 for spherical bearings. The thickener type of the grease is based on the type of application, water resistance and operation temperature. When switching to other grease type, it is recommended to flush all the oil grease out of the bearing in order to prevent incompatibility of new and oil greases. If two incompatible grease are mixed together, softening may happen causing the grease to leak out of the bearing and damage the bearing.

The grease grade is classified by NLGI which is determined by the application method and bearing speed. NLGI No.1 grease have good low temperature dispensing ability while NLGI No.3 is suitable for higher speed or electric motor bearing to reduce churning and heat creation. NLGI No.2, 1, 0 or 00 grades are suitable for centralized grease system, and NLGI No.00 or 000 are being recommended for gearboxes which require semi-fluid greases.

The grease base oil viscosity is an important factor. 150-220 cSt@40℃ is suitable for shock loading applications. 75 to 120 cSt@40℃ greases are suitable for bearing speed between 200,000-300,000 `ND_m` without subject to shock loadings. Grease base oil with viscosities 25 to 75cSt@40℃ can be used for pumping operation at low temperature, or for high speed bearing (300,000 to 400,000 `ND_m`). Grease base oil with viscosities higher than 460 cSt@40℃ are good for high temperature, high loading conditions with water resistance ability. If the operation subjects to high centrifugal forces such as coupling, base oil viscosity of 800 cSt@40℃ or even higher should be applied.

Extreme Pressure (EP) additives such as Molybdenum (Moly) in greases is a solid additive. It is not recommended to use "Moly" greases in moderate or high speed rolling bearings because those solid additives can accumulate inside the bearing components. Also, if the operating speed of the bearing is over 1,600 rpm, "Moly" greases should be avoided because Moly can be centrifuged out of the lubricant and causes bearing failure. No matter the bearing speed is high or low, "Moly" greases can damage the surface of the bearing metals and greatly reduces the bearing life, and induces high replacement cost and downtime cost for the users.

Check here for more information about the serious problem associated with "Moly" and other solid additives.

Many lubricant manafacturers use Liquid extreme pressure additives to provide protections against shock loading and metal wears. However, the oxidiation stability can be reduced when these additives applied. This is not favour to life-long sealed bearings. Meanwhile, sulphur based extreme pressure additives can corrode yellow metals like copper, bass or bronze.

In order to solve and avoid the problem mentioned above associated with solid additives and extreme pressure additives, Steel Shield ABF Technology was invented. It is now replacing the old lubrication technologies. Click here for more.

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Quantity And Interval Of Relubrication

The quantity and grease type for relubrication must be follow strictly to the manufacturer manual. The following information provides a general rule-of-thumb.

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