Grease is the "blood" of bearings. Especially in sealed bearings and medium and low-speed equipment, the selection of grease directly determines the lubrication effect, temperature rise and service life of bearings. Different from the fluidity of lubricating oil, grease focuses on long-acting protection and not easy to leak. The core of selection revolves around three working condition parameters: temperature, load and speed, combined with environmental characteristics. This article provides a standardized matching scheme to avoid blind grease selection.
Three Core Factors for Grease Selection: Temperature, Load and Speed
Selection by Working Temperature (The Most Critical Indicator)
Temperature directly determines the base oil type and dropping point of grease. Improper grease selection will cause high-temperature loss and low-temperature solidification, leading to lubrication failure.
- Normal temperature working condition (-20℃~120℃): Select lithium-based grease, which is universal with high cost performance, has good water resistance, rust resistance and lubrication performance, and is suitable for most conventional equipment;
- High temperature working condition (120℃~200℃): Select complex lithium-based grease and polyurea grease, with high dropping point, no loss at high temperature, strong oxidation resistance, suitable for high-temperature motors, oven fans and thermal equipment;
- Low temperature working condition (-40℃~0℃): Select low-temperature lithium-based grease and synthetic hydrocarbon grease, with good low-temperature fluidity, no solidification, suitable for outdoor severe cold equipment and refrigeration units;
- Ultra-high temperature working condition (＞200℃): Select high-temperature fully synthetic grease and bentonite grease with non-dropping point design, suitable for ultra-high temperature scenarios such as kilns and metallurgy.
Selection by Load Magnitude
Load determines the content of extreme pressure additives in grease. Heavy-load scenarios need to strengthen the oil film strength to prevent oil film rupture.
- Light load and uniform speed working condition: Select ordinary lithium-based grease without additional extreme pressure additives to meet basic lubrication;
- Heavy load, impact and alternating load: Select extreme pressure lithium-based grease and extreme pressure complex lithium-based grease with extreme pressure anti-wear additives, high oil film strength, preventing direct metal contact wear, suitable for heavy machinery, rolling mills and crushers;
Selection by Rotational Speed (Refer to dn Value)
dn value = shaft diameter (mm) × rotational speed (r/min), reflecting the bearing operation speed. The higher the speed, the thinner the grease needs to be and the smaller the friction.
- Low speed working condition (dn value ＜5×10⁵): Select grease with high consistency (NLGI 2#), not easy to lose, for long-acting lubrication;
- Medium and high speed working condition (dn value 5×10⁵~1×10⁶): Select grease with medium and low consistency (NLGI 1#, 0#), small friction and fast heat dissipation, suitable for high-speed motors and fans;
- Ultra-high speed working condition: Lubricating oil is preferred for replacement, grease is only suitable for sealed high-speed bearings, select low-viscosity synthetic grease.
Supplementary Grease Selection for Special Environments
- Humid and water shower environment: Select water-resistant lithium-based grease and waterproof complex lithium-based grease to avoid emulsification and failure when exposed to water;
- Dusty and high-impurity environment: Select long-acting sealed grease to enhance adhesion and reduce impurity adsorption;
- Corrosive environment: Select rust and corrosion preventive grease with corrosion inhibitors to protect the bearing surface.
Grease Usage Taboos
Greases of different brands and types are strictly prohibited to be mixed; the filling amount is controlled at 1/3~1/2 of the bearing internal space, excessive filling is easy to cause heating; regularly check the grease status, and replace it in time when it ages, turns black and agglomerates.
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