Greases for Machine Tools
In general, the most important lubrication points for grease applications in machine tools can be divided into the following areas:
- Spindle bearings,
- Chucks and
Grease lubrication for spindle bearings
For grease lubrication in spindle bearings, the lower outlay for sealing, in contrast to oil lubrication, and the omission of a lubricant circuit speak for themselves.
Grease lubrication systems can be designed both as lifetime lubrication and as a relubrication system.
Further requirements for the greases used here are:
- effective corrosion protection for long component life
- high wear protection
- high resistance to coolants (especially with open bearings).
Due to the high demands, especially with regard to lifetime lubrication in combination with high speeds, FUCHS recommends RENOLIT HI-SPEEED 2 to use a grease based on a synthetic base oil with low viscosity.
Grease lubrication chuck
Greases for chucks are subject to special requirements. You must ensure a secure separation of the friction partners to prevent fretting corrosion, but also ensure a constant clamping force.
Furthermore, they must have a good resistance to the metalworking media used, so as not to be washed out after a short time. Here are paste-like greases like
Greases for gearboxes
Gearbox lubrication uses two different principles.
- Sump lubrication: In this case, one or more gears dip into a sump comparable to the oil sump. Entrained excess grease is thrown off again and flows back to the housing wall in the sump, where it is available for lubrication again.
- Stick Lube: With this principle, the grease used is much more consistent and adheres to the gears. Excess grease is not thrown off, but only pushed out of the lubrication point and remains in the immediate vicinity of this. In this case, constructive measures should be taken so that the grease can be returned to the lubrication point during standstills or shocks and these are not depleted in the long run.
- Relubrication via central lubrication system: Here, the grease required for lubrication is transported from a central reservoir to the individual lubrication points. Excess grease is thrown off, as in sump lubrication, but is lost here and is no longer available for lubrication.
The gear oils are to be selected according to the respective requirements regarding the speed and load of the gearbox. At higher speeds greases with low base oil viscosities are used. With decreasing speed or increasing load, grease with correspondingly higher base oil viscosity is used.
The use of greases with an unmatched, too high base oil viscosity can lead to excessive self-heating. If the viscosity of the base oil is too high, the internal resistance that the grease opposes to the movement is too high, and the resulting losses lead to excessive heating of the system.
If the viscosity is too low, the separating effect of the lubricating film is too low and metallic friction also causes heat and wear.