Greases

Tips on greases include the following topics:
Grease Additives
Grease Characteristics
Grease Definitions

Grease Service Classification
Grease Compatibility
Grease Properties
Applying Grease

Grease Lubrication Schedule - Spherical Roller Bearings  

Introduction

Grease may be defined as a solid to semi-solid material produced by the dispersion of a thickening agent in a liquid lubricant. Other ingredients imparting special properties may be included.

Regular Grease

Thickener Lubricating Oil Additives
5 - 20% + 75 - 95%  + 0 - 15%

(Fatty acid, animal fat plus Metal Hydroxide - calcium,Lithium or aluminum)

   

Complex Grease

Complex grease is similar to a regular grease except that the thickener contains two dissimilar fatty acids, one of which is the complexing agent. This imparts good high temperature characteristics to the final product.

Lubricating Oil

The high percentage of oil by weight (75-95%) in a grease necessitates that it be of high quality and proper viscosity for the intended application. A light viscosity oil is normally used for low temperature, low load and high speed applications. Conversely a heavy viscosity oil is generally used for high temperature, high load and slow speed applications.

Additives

The most common additives found in grease are as follows:

  • Oxidation Inhibitors
  • prolong the life of a grease
  • EP Agents
  • guard against scoring and galling
  • Anti-Corrosion Agents
  • protect metal against attack from water, sulphides or corrosive elements
  • Anti-Wear Agents
  • prevent abrasion and metal to metal contact

    Grease Characteristics

    The most important factors affecting the properties and characteristics of a grease are:

    • Amount and type of thickener
    • Oil viscosity and physical characteristics
    • Additives

    A grease is expected to:

    • Reduce friction and wear
    • Provide corrosion protection
    • Seal bearings from water and contaminants
    • Resist leakage, dripping and throw-off
    • Resist change in structure or consistency during service
    • Maintain mobility under conditions of application
    • Be compatible with seals
    • Tolerate or repel moisture

    Grease Definitions

    Consistency - is the degree of hardness of a grease and may vary considerably with temperature. This has been classified by the National Lubricating Grease Institute (NLGI) into the following categories:

    NLGI GRADE PENETRATION @ 25C (1/10th mm)
    000 445 - 475
    00 400 - 430
    0 355 - 385
    1 310 - 340
    2 265 - 295
    3 220 - 250
    4 175 - 205
    5 130 - 160
    6 85 - 115

     

    Shear Stability - is the ability of a grease to resist a change in consistency during mechanical working. Under high rates of shear, grease structures tend to change in consistency (usually softer). Oil Separation - is the percentage of oil which separates from the grease under static (e.g. storage) conditions. It cannot predict separation tendencies in use under dynamic conditions. High Temperature Stability - is the ability of a grease to retain its consistency, structure and performance at temperatures in excess of 125C.

    Grease Service Classification

    The following five (5) categories for Automotive Service Greases have been developed by the NLGI. The scope of this classification (ASTM D 4950) covers greases designed for the lubrication of chassis components and wheel bearings of passenger cars, trucks and other vehicles. The NLGI classifies automotive service greases into two (2) main groups. Chassis greases, designed by the prefix L and Wheel Bearing greases designated by the prefix G. The following table outlines the five (5) categories:

    NLGI Automotive Service Grease Categories

    Category

    Service

    Performance

    LA
    chassis

    Frequent relubrication intervals (<3200 km). Mild duty (non-critical applications).

    Oxidation resistant, shear stable, and corrosion and wear protective.

    LB
    chassis

    Prolonged relubrication intervals (>3200km). Mild to severe duty (high loads, vibration, exposure to water).

    Oxidation resistant, shear stable, and corrosion and wear protective even under heavy loads and in presence of aqueous contamination. Temperature range -40C to 120C.

    GA
    wheel bearings

    Frequent relubrication intervals. Mild duty (non-critical applications).

    Temperature range -20C to 70C.

    GB
    wheel bearings

    Mild to moderate duty (cars, trucks in urban and highway service.)

    Oxidation and evaporation resistant, shear stable, and corrosion and wear protective. Temperature range -40C to 120C with occasional excursions to 160C.

    GC
    wheel bearings

    Mild to severe duty (vehicles in frequent stop and go service, trailer hauling, mountain driving, etc.)

    Oxidation and evaporation resistant, shear stable, and corrosion and wear protective. Temperature range -40C to 120C with frequent to 160C and occasional excursions to 200C.

    Grease Compatibility

    Occasionally, grease substitution in an application may be necessary to correct problems arising from the original product in service. If the thickeners are incompatible, the mixture will fall short of the properties of the individual greases. It is strongly advised that, in all cases, the old grease be purged or cleaned out from the system before a new one is introduced.

    However, compatibility between greases is temperature dependent. As the temperature rises, the problems associated with incompatibility also increase. The following chart indicates the compatibilities of major Petro-Canada greases. With competitors' products, it is strongly advised to treat them as incompatible unless strong evidence exists to the contrary.

     

        Aluminum Complex Lithium Polyurea Lithium Complex Barium Complex Silica Clay
        Supreme Multipurpose Chevron Precision Barimol Thermex Bentone
        EP 2 EP 2 SRI 2 EP 2 Heavy No RM 2
    Lithium Multipurpose Yes            
      EP 2 140            
    Polyurea Chevron Yes Yes          
      SRI 2 130 145          
    Lithium Precision Yes Yes Yes        
    Complex EP 2 150 170 158        
    Barium Barimol Yes Yes Yes Yes      
    Complex Heavy 168 153 173 160      
    Silica Thermex Yes No No No Yes    
        115 (*) 80 (*) 173    
    Clay Bentone No No No Yes Yes No  
      RM 2 58 95 (*) 183 173 75  
    Calcium Sulphonate Grease No Yes No Yes Yes No No
    Complex OG-2 98 125 95 125 140 (*) 95

    Notes:

    • 1. The number quoted indicates the temperature, in degrees Celsius, at which incompatibility sets in.

    • 2. (*) Indicates the mixture is incompatible at all temperatures.

    Grease Properties

    The following chart is designed to help you select a type of grease that will satisfy the intended application.

     

    REGULAR GREASES

    COMPLEX

    SYNTHETIC CLAY

    Properties

    Calcium

    Lithium

    Sodium

    Aluminum

    Calcium

    Barium

    Lithium

    Polyurea

    Bentone

    Dropping Point C

    80-100

    175-205

    170-200

    260+

    260+

    200+

    260+

    250+

    None

    *Max Temp C

    65

    125

    125

    150

    150

    150

    160

    150

    150

    High Temp Use

    V. Poor

    Good

    Good

    Exc

    Exc

    Good

    Exc

    Exc

    Exc

    Low Temp Mobility

    Fair

    Good

    Poor

    Good

    Fair

    Poor

    Good

    Good

    Good

    Mech. Stability

    Fair

    Good

    Fair

    Exc

    Good

    Fair

    Exc

    Good

    Fair

    Water Resist.

    Exc

    Good

    Poor

    Exc

    Exc

    Exc

    Exc

    Exc

    Fair

    Oxidation Stability

    Poor

    Good

    Good

    Exc

    Exc

    Poor

    Good

    Exc

    Good

    Texture

    Smooth

    Smooth

    Fibrous or Smooth

    Smooth

    Smooth

    Fibrous

    Smooth

    Smooth

    Smooth

    *These temperatures refer to continuous operation. They may be exceeded temporarily in the case of complex greases, and where rigorous lubrication practice is followed.

    Applying Grease

    The over-packing and over-greasing of bearings accounts for more failures than any other factor. Excess grease in a bearing cavity increases internal friction, which in turn raises the bearing temperature above the dropping point of the grease. This causes oil separation and eventually lack of lubrication. When packing a split housing pillow block bearing ensure that the grease cavity is only one-third full.

    Re-greasing intervals are determined from:

    • severity of service

    • environment

    • condition of seals

    • shock loading

    The following chart provides a guide to re-greasing intervals and the amount of grease to be applied.

    Grease Lubrication Schedule

    Spherical Roller Bearings

    Shaft Size

    Amount of grease

    Operating speed (rpm)

    500

    1000

    1500

    2000

    2200

    2700

    3000

    3500

    4000

    4500

    Inches

    MM

    IN 3

    CM 3

    Lubrication cycle (months)

    3/4-1

    25

    0.39

    6.4

    6

    6

    6

    4

    4

    4

    2

    2

    1

    1

    1 1/8-1/ 4

    30

    0.47

    7.7

    6

    6

    4

    4

    2

    2

    1

    1

    1

    1

    1 7/l6-1 1/2

    35

    0.56

    9.2

    6

    4

    4

    2

    2

    1

    1

    1

    1

    1/2

    1 5/8-1 3/4

    40

    0.80

    13.1

    6

    4

    2

    2

    1

    1

    1

    1

    1/2

     

    1 15/16-2

    45 - 50

    0.89

    14.6

    6

    4

    2

    1

    1

    1

    1

    1/2

     

     

    2 3/16-2 1/4

    55

    1.09

    17.9

    6

    4

    2

    1

    1

    1

    1/2

     

     

     

    2 7/16 -2 1/2

    60

    1.30

    21.3

    4

    2

    1

    1

    1

    1/2

     

     

     

     

    2 11/16-3

    65 - 75

    2.42

    39.7

    4

    2

    1

    1

    1/2

     

     

     

     

     

    3 3/16-3 1/2

    80 - 85

    3.92

    64.2

    4

    2

    1

    1/2

     

     

     

     

     

     

    3 11/16-4

    90 - 100

    5.71

    93.6

    4

    1

    1/2

     

     

     

     

     

     

     

    4 3/16-4 1/2

    110 - 115

    6.50

    106.5

    4

    1

    1/2

     

     

     

     

     

     

     

    4 15/16-5

    125

    10.00

    163.9

    2

    1

    1/2

     

     

     

     

     

     

     

    Temperature 90C (200F)

    Horizontal Shaft Equipment