Lubricating linear guides: grease, intervals and relubrication in practice

Without a separating lubricant film, steel runs on steel in a profiled rail guide: the hardened balls or rollers damage the hardened raceway, and the carriage grows loud and inaccurate. The lubricant film separates the rolling elements from the raceway, displaces moisture and protects against corrosion.

The two most common causes of failure are self-inflicted: dry running from missing or late relubrication, and contamination from chips, dust or coolant getting into the carriage. Both destroy the lubricant film. That is why seals and wipers belong to the lubrication strategy just as much as the grease itself.

Most applications are lubricated with grease. Grease stays in the carriage, adds sealing against dirt and needs no feed line. Oil is used where high speeds, high temperatures or an existing central lubrication argue for it. Oil also carries away heat and wear debris, but it has to be fed continuously. For most maintenance teams, grease is the more robust choice.

Rolling bearing greases on a lithium soap base of medium consistency are common. What matters is not the brand, though, but the manufacturer approval: the guide maker defines which greases are compatible with its seals, raceways and plastic parts.

In its maintenance instructions, Bosch Rexroth names greases per DIN 51825 K2K, for example, and explicitly excludes greases with solid lubricant content such as graphite or MoS2. Such additives settle in the rolling contact and disturb the lubricant film. Stick to the approval list of your series instead of reaching for any universal grease.

New carriages are lubricated and preserved from the factory; the initial lubrication lasts until commissioning. After that, relubrication in service begins. A fixed interval in kilometres or hours cannot be stated in general: it depends on load, speed, stroke, mounting orientation and environment. Short strokes, contamination, vibration and high temperatures shorten the interval markedly.

The reliable base figure comes from the manufacturer catalog or the manufacturer calculation program. In its mounting instructions, Rexroth explicitly refers lubrication intervals to the product catalog and makes any interval extension dependent on the technical limits of the application. For individual series the manufacturer also offers a long-term lubrication that runs for several years without relubrication.

Lubrication is a spare-parts topic, not a one-off. PTS stocks the matching seals, wipers and lubrication adapters as catalog items, not just the rail. How strongly load and stroke drive the service life, and with it the lubrication interval, is shown in the life calculation; the correct initial lubrication already belongs to installation.