Start with the bearing and its operating conditions
The same grease is not necessarily suitable for two points that look similar. Bearing type and size, sealing and mounting all matter. The bearing or machine manufacturer may also specify requirements that cannot be inferred from a general lubricant name.
Record the following before making a choice:
- bearing type, designation, dimensions and mounting arrangement;
- rotational speed or another motion parameter, and the direction of the load;
- continuous temperature and possible short temperature peaks;
- contact with water, steam, dust, chemicals or process material;
- bearing position, vibration, access to the lubrication point and the product currently in use.
Temperature data should come from a measurement or documentation, not from the machine name. For a bearing near a dryer or steamer, measure the actual grease temperature and check how long the bearing runs at that temperature and how heat is dissipated from the bearing housing.
What does a grease data sheet actually tell you?
NLGI consistency is not a full specification
The NLGI grade describes consistency: how firm the grease is, measured as worked penetration to ASTM D217. On its own, it does not describe the base oil, thickener, temperature range, speed or water resistance. “The bearing needs NLGI 2” is therefore only one filter. The other properties still have to match the application.
Do not automatically equate NLGI 2 with EP2. EP (extreme pressure) means the grease contains additives that increase its load-carrying capacity, while the 2 in such a name refers to consistency. NLGI 2 alone does not tell you whether a grease has EP additives: in the SKF chart, both the general-purpose LGMT 2 and the EP grease LGEP 2 are NLGI 2. If the information conflicts, follow the bearing instructions and the data sheet for the specific product.
Base oil and thickener affect behaviour
Grease consists of a base oil, a thickener and additives. The base oil forms the lubricating film, so its viscosity at operating temperature must be high enough to support the load. The thickener gives the grease its semi-solid consistency and helps keep it at the lubrication point; the type and amount of thickener determine consistency. The base oil can also soften, harden, shrink or swell elastomer seals, so check that the grease is compatible with the seal material.
Do not transfer the properties of one thickener to an entire grease category. Before changing product, check the manufacturer’s documentation for compatibility with the grease already in the bearing: the thickeners, base oils and additives of different greases may be incompatible. If compatibility is not confirmed, purge the old grease with the new product in line with the plant procedure and monitor the bearing after start-up. Excessive softening of the grease or a bearing running hotter than usual can indicate incompatibility.
Match additives and special properties to the problem
Water resistance, EP performance, corrosion protection, high-temperature operation or a solid lubricant are not universal advantages. Each property has to be related to the bearing and its operating conditions. Schaeffler, for example, recommends EP greases with high base oil viscosity for high loads and greases with solid lubricants for mixed or boundary friction.
Check the product in its application context
The bearing grease range lists products by application and the composition information provided in the catalogue. For example, AERO 300 is described as a grease for heavily loaded roller bearings at high temperature, with a lithium-complex thickener in the catalogue data. GS ROLLER DR is described as a grease for bearings in dryers, steamers, stenters and rolling mills; the catalogue gives its thickener as calcium sulphate.
These examples show how to read documentation; they are not automatic recommendations for every bearing. Before ordering, compare the product data with the bearing designation, temperature, speed, load, sealing and existing lubrication procedure.
How to move from data to a grease choice
- Identify the lubrication point. Photograph the nameplate or bearing marking and record the machine manufacturer and component number.
- Collect operating conditions. Record speed, load, temperature, moisture, dust, chemicals, vibration and shaft position.
- Compare the data sheet. Check the base oil, thickener, NLGI grade, temperature range, permissible speed, load performance, water resistance and corrosion protection.
- Plan the product change. Do not mix greases just because they have the same NLGI number. Confirm compatibility or plan purging of the old product and a bearing check after the change.
- Set quantity and interval. Take the amount and frequency from the bearing, machine or dispensing-system documentation. The quantity depends on operating conditions, bearing type and size, mounting and the way grease is fed, so do not copy it from another point.
- Record the result. Keep the product, batch, date, quantity, person performing the work and temperature or vibration observations in the lubrication-point record.
A practical way to read the criteria
If the point is a roller bearing near a dryer, searching for “high-temperature grease” is not enough. Confirm the bearing temperature, roller speed, load, sealing, moisture exposure and manufacturer requirements. Only then can you assess whether a product described for dryer bearings suits this particular configuration.
How to prepare a product enquiry
In an enquiry about a product from the bearing grease range, include the machine name and model, bearing designation, speed, load, temperature, environment, grease currently in use and dispensing method. This makes it possible to check the right product group instead of choosing grease by name or NLGI grade alone.
