Grease is a semisolid lubricant used in applications where liquid oil would leak away or where frequent lubrication is impractical. Selecting the right grease requires understanding three key factors: consistency (NLGI grade), thickener type, and base oil viscosity. This guide walks you through each factor.
1. What is Grease?
Grease consists of three main components:
- Base Oil (75-90%): Mineral or synthetic oil that provides lubrication
- Thickener (5-20%): Soap or non-soap material that holds the oil in a semisolid matrix
- Additives (1-5%): Anti-wear, extreme pressure, anti-oxidant, rust inhibitors
The thickener acts like a sponge, releasing oil under pressure and reabsorbing it when pressure is removed. This makes grease ideal for sealed-for-life bearings and applications where oil would leak.
2. NLGI Consistency Grades
The NLGI (National Lubricating Grease Institute) grade measures the hardness/consistency of grease. It ranges from 000 (very soft) to 6 (very hard).
| NLGI Grade | Consistency | Appearance | Typical Applications |
|---|---|---|---|
| 000 | Very soft | Almost liquid | Centralized lubrication systems, gearboxes |
| 00 | Soft | Semi-fluid | Enclosed gear drives, open gears |
| 0 | Very soft | Pourable | Centralized systems, cold climates |
| 1 | Soft | Very buttery | Centralized systems, low-speed bearings |
| 2 | Medium | Buttery | Most common; wheel bearings, general purpose |
| 3 | Firm | Buttery (stiffer) | High-speed bearings, hot climates |
| 4 | Very firm | Putty-like | Heavy loads, slow speeds |
| 5 | Hard | Very stiff | Open gears, bridge bearings |
| 6 | Very hard | Block-like | Specialty applications |
NLGI #2 is the most widely used grade for general-purpose applications, including automotive wheel bearings, electric motors, and most industrial bearings. NLGI #1 is preferred for centralized lubrication systems and cold climates.
3. Thickener Types
The thickener determines grease properties like water resistance, temperature range, and mechanical stability. Here are the most common types:
Lithium Soap (Simple Lithium)
- Temperature range: -20°C to 120°C
- Water resistance: Good
- Mechanical stability: Good
- Cost: Moderate
- Applications: General-purpose, automotive, industrial bearings
- Most common type — accounts for ~70% of all grease produced
Lithium Complex Soap
- Temperature range: -30°C to 180°C
- Water resistance: Excellent
- Mechanical stability: Excellent
- Cost: Higher
- Applications: High-temperature, heavy loads, wet environments, steel mills
- Premium multi-purpose grease — superior to simple lithium
Calcium Soap
- Temperature range: -10°C to 80°C
- Water resistance: Excellent
- Mechanical stability: Fair
- Cost: Low
- Applications: Water pumps, marine equipment, low-temperature wet environments
- Limited by low dropping point (~100°C)
Calcium Sulfonate Complex
- Temperature range: -20°C to 180°C
- Water resistance: Exceptional
- Mechanical stability: Excellent
- Rust protection: Outstanding
- Cost: High
- Applications: Marine, mining, steel, food processing (if NSF registered)
Aluminum Complex Soap
- Temperature range: -20°C to 150°C
- Water resistance: Excellent
- Mechanical stability: Good
- Cost: High
- Applications: Food processing (NSF H1), paper mills, canning
Polyurea (Non-Soap)
- Temperature range: -30°C to 180°C
- Water resistance: Fair
- Oxidation resistance: Excellent
- Cost: High
- Applications: Electric motor bearings, sealed-for-life bearings, high-temperature
- Not compatible with soap-thickened greases
4. Thickener Compatibility
Not all greases are compatible with each other. Mixing incompatible thickeners can cause the grease to soften or harden, leading to lubrication failure.
| Lithium | Li Complex | Calcium | Ca Sulfonate | Al Complex | Polyurea | |
|---|---|---|---|---|---|---|
| Lithium | ✓ | ✓ | △ | △ | △ | ✗ |
| Li Complex | ✓ | ✓ | △ | △ | △ | ✗ |
| Calcium | △ | △ | ✓ | △ | △ | ✗ |
| Ca Sulfonate | △ | △ | △ | ✓ | △ | ✗ |
| Al Complex | △ | △ | △ | △ | ✓ | ✗ |
| Polyurea | ✗ | ✗ | ✗ | ✗ | ✗ | ✓ |
✓ = Compatible, △ = Conditionally compatible (test first), ✗ = Incompatible
5. Base Oil Viscosity
The base oil viscosity affects the lubricating film thickness. Greases use the same ISO VG grading system as oils:
- ISO VG 100-150: High-speed bearings, electric motors
- ISO VG 220: General-purpose, most common
- ISO VG 320-460: Heavy loads, slow speeds, high temperatures
- ISO VG 680+: Extreme loads, open gears
6. Additive Packages
Extreme Pressure (EP) Greases
EP greases contain sulfur-phosphorus or other additives that protect metal surfaces under high pressure and shock loads. Look for Timken OK Load ratings of 35 lbs or higher, or 4-ball weld load of 300 kg+.
Anti-Wear (AW) Greases
AW greases provide wear protection under moderate loads. Suitable for most general-purpose applications.
Solid Lubricant Additives
- Molybdenum Disulfide (MoS2): For extreme pressure and boundary lubrication
- Graphite: For high-temperature and dry environments
- PTFE: For low-friction, chemical resistance
7. Application-Specific Recommendations
Automotive Wheel Bearings
- NLGI #2 Lithium or Lithium Complex
- EP additives recommended
- Base oil ISO VG 100-220
- Temperature range: -30°C to 150°C
Industrial Electric Motors
- NLGI #2 Polyurea or Lithium Complex
- Low oil separation, low noise
- Base oil ISO VG 100
- Avoid EP additives (can cause bearing noise)
Construction & Mining Equipment
- NLGI #1-2 Lithium Complex with EP
- Excellent water resistance
- High mechanical stability
- Base oil ISO VG 220-460
Food Processing Equipment
- NSF H1 registered (incidental food contact)
- Aluminum Complex or Calcium Sulfonate
- NLGI #2
- White/translucent color
High-Temperature Applications
- Lithium Complex, Polyurea, or Clay-thickened
- Synthetic base oil (PAO or ester)
- NLGI #2
- Temperature range up to 200°C+
8. Grease Maintenance Best Practices
- Follow manufacturer recommendations: Always check equipment manuals for specified grease type and interval
- Don't over-grease: Over-greasing causes overheating. Fill bearings 30-50% full
- Clean fittings: Clean grease fittings before lubricating to avoid contamination
- Store properly: Keep grease containers sealed, away from moisture and dust
- Don't mix greases: If changing type, clean out old grease completely
- Monitor condition: Check for color change, hardening, or oil separation
Quality Greases for Every Application
We manufacture lithium, lithium complex, calcium, and polyurea greases in NLGI #0-#3 with EP and solid additives. OEM/ODM available.
Request Grease SamplesConclusion
Selecting the right grease involves matching NLGI grade, thickener type, base oil viscosity, and additives to your specific application. When in doubt, consult the equipment manufacturer's recommendation or a lubrication engineer. Remember that using the wrong grease can cause premature bearing failure and costly downtime.
At KLAClube, we offer a complete range of industrial and automotive greases including general-purpose lithium, high-temperature lithium complex, EP greases with MoS2, and specialty formulations. Contact us for technical support and OEM/ODM services.