Bearing lubrication

The selection of suitable lubricants relies primarily on the bearings’ maximum operating RPM.

Selecting Lubricants

In order to optimally use the performance of GMN high-precision ball bearings in machining operations, one must pay particular attention to suitable bearing lubrication.

The highest-possible RPM as well as maximum life expectancy are based on lubricant film formation that reduces friction between rolling and sliding bearing parts.


FURTHER LUBRICATION TASKS:

  • Attenuation of structural sound and vibrations
  • Heat removal
  • Sealing effect
  • Corrosion protection

The suitability for very high speeds of modern high-speed greases allows the increasing use of application-friendly and economical advantages of grease lubrication. Operating requirements which exceed the performance of lubricating greases provide oil-lubricated bearings with maximum service life in the highest speed and temperature ranges.

KL_Schmierung1_935x655

Criteria to choose lubrication types (+++++: very good · +: bad)

GREASE LUBRICATION

RPM SUITABILITY FOR GREASE LUBRICANTS

The selection of suitable grease lubricants relies primarily on the bearings’ maximum operating RPM.
The specific key RPM value n · dm considers the operating-related RPM of the bearing, and refers to the maximum speed capability of the required lubricant.
Consideration of key RPM values in selecting lubricants limits impacts on bearing performance due to lack of lubrication.
A speed-dependent separation of the lubrication film can lead to mis-friction, heating and increased bearing wear.

SPECIFIC KEY RPM VALUE: N · DM

n · dm bearing = n · (D + d)/2 [mm/min]

  • n: Bearing operating RPM
  • d: Bearing hole diameter [mm]
  • D: Outer diameter of the bearing [mm]

Many lubricant manufacturers offer a wide range of greases, which have been developed for use with fast-rotating or highly loaded ball bearings.
By means of a requirement-oriented combination or processing of base oil, thickener and additives during the production process, specific properties such as wear protection, low-noise resistance or temperature resistance are specifically offered.

You can find technical information about the topic of “Grease Lubrication of High-Precision Ball Bearings” in our download section.

 

KL_Schmierung2_935x650RGB

GREASE LUBRICANT DURATION

Consideration of the required lubricant duration is decisive for the long-term, reliable operation of grease lubricated bearings. The lubrication time can last more than five years under favorable operating conditions.

Calculation of the lubrication duration (tf) is done by considering the lubricant’s characteristics and the operating bearing loads.

  • Grease type, grease quantity, grease distribution
  • Design and type of bearing
  • Mounting conditions (cleanliness)
  • Operating conditions
    (Speed, speed characteristic, loads, temperature, etc.)

OPERATING CONDITIONS * FOR LUBRICANTS GUIDE TF

  • Standard grease based on lithium soap
  • Operating temperature up to 70 °C
  • Bearing load (P and C <0.1)
  • Favorable ambient conditions with regard to…
    dust,
    moisture
    … air flows through the bearing*

*(According to GfT Worksheet 3, rolling bearing lubrication, Sept. 2006)

Higher operating temperatures cause a reduction in the lubrication time. (From an operating temperature of 70°C, an increase of 15° Kelvin can halve the originally determined lubrication duration).

For higher bearing loads (P and C> 0.1), shock loads, and vibrations, appropriate corrections of the lubrication time guide values (tf) are necessary.

GMN recommends requirements-optimized special grease for extraordinary operating conditions.

 

KL_Schmierung3_935x935
Lubrication times for bearings with steel or ceramic balls 

GREASE-LUBRICATED GMN BALL BEARINGS

All GMN high-precision ball bearings can be delivered lubricated.

  • The standard fill level is 30 % (tolerance: ± 5 %) of the free space
  • 20-25 % fill level is recommended for easy bearing runs
  • 35 % grease provides high useful life
  • Bearings without grease are delivered with standard preservation.
  • Series KH bearings have a standard grease volume of 25 % (LUBCON TURMOGREASE Highspeed L 252).
  • Grooved ball bearings have a standard grease volume of 30 % (KLÜBER ASONIC GLY 32).Other greases are available upon request.

GREASE

Theoretically, a grease quantity of <10 % of the free volume of a bearing is sufficient for the lubrication.
For most applications, however, a grease volume of 25 to 30 % is recommended on the grounds of safety and consumption of lubricants.

A guideline value for greasing GMN high-precision ball bearings with group I grease can be found in the relevant technical information sheets, or in addition to further technical information in our download area.

Technical information sheet: “Greasing series 60 and 62”.

Technical information sheet: “Greasing series 618 and 619”.

GREASE LUBRICATION

GREASE LUBRICATION ON THE OUTER RING WITH AG BEARINGS

Systems for grease lubrication are used if the grease service life or RPM suitability for permanent grease lubrication are not sufficient.

Location of the lubricant feed at the
bearing pairs in an O arrangement.

 

KL_Schmierung4_935x635
B= bearing width (individual bearing), B0= axial distance to the closed side, ØB1 = hold diameter 
Location of the lubricant feed for
bearing pairs in a tandem arrangement.

 

KL_Schmierung5_935x635
B= bearing width (individual bearing), B0= axial distance to the closed side, ØB1 = hold diameter 

OVERVIEW

Location of lubricant supply for single bearings (+ AG)

You can find technical information on “grease relubrication” in our download area.

Further types and sizes upon request.

DRILL KEY DATA FOR INDIVIDUAL BEARINGS (+AG)

_KL_Engineering_Schmierung_Tabellen_ENG_1220x740px

OIL LUBRICATION

In comparison to grease-lubricated bearings, the use of lubricating oils provides long-term, reliable operation at maximum RPMs. In order to provide oil to fast-rotating bearings, various oil-air lubrication procedures (minimal volumes of lubricant), oil injection lubrication and oil fog lubrication are available.

OIL-AIR LUBRICATION

Oil-air lubrication offers targeted and quantity-adjustable lubricant supply to rolling and sliding surfaces in the bearing.

The lubricant is transported in an air stream in streaks along the inner wall of the see-through feed tube, and is fed in the required intervals evenly to the lubrication points.

Oil-air lubrication ensures the highest efficacy in regards to use and lubrication effects at maximum RPMs:

  • Reduced working
  • Minimal friction losses
  • Reduced heat generation
  • High operating safety
  • Targeted and quantity-adjustable lubricant supply
  • Low oil consumption
  • Low oil mist formation
  • Very good lubrication
  • Environmental friendliness and high profitability
  • Oil cooling and oil filtration not required (compared to oil injection lubrication)
KL_Schmierung6_550x435
Oil-air lubrication (diagram) 

PRELUB: THE LUBRICATION UNIT FOR GMN BALL BEARINGS

In order to ensure high quality from GMN high-precision ball bearings, we recommend our PRELUB electronically-controlled lubrication unit.

This is not only recommended for our spindles, but also provides precisely controllable feed of the lubricant for effective bearing lubrication as well as maximum operating safety.

OIL FEED THROUGH THE SPACER

In usual bearing lubrication systems, the oil injection nozzles are mounted in an in-between bushing or a spacer between 2 bearings.

KL_Schmierung10_935x435
Oil feed through a spacer 

OIL FEED THROUGH AN OIL NOZZLE

A nozzle position parallel to the spindle axis is sufficient for applications at high RPMs.
An angled nozzle position increases the RPM suitability for the bearing (more precise lubricant supplies in the roller area).

KL_Schmierung7_550x535
Parallel nozzle position 
KL_Schmierung8_550x535
Angled nozzle position 

DESIGN CHARACTERISTICS

  • Length and hole diameter for oil nozzles:
    Sufficient lubricant feed is ensured with a ratio between the nozzle length and nozzle hole diameter of more than 3 and less than 5 (pressure of the oil-air flow is greater than the counter-pressure caused by bearing turbulence).
  • Oil for high-precision spindles:
    Hydraulic oil with kinematic viscosity VG 32 or VG 46 mm2/second
  • Oil filtering:
    Cleanliness class 13/10 as per ISO 4406 (particle size <5 μm)
  • Oil volume per lubricant pulse:
    30 to 35 mm3 per connection for 1 or 2 bearings
  • Cycle time:
    VG32: 2 to 4 min., VG46: 4–10 min. (independent of the d-bearing)
  • Number of nozzles:
    1 per bearing
  • Nozzle diameter:
    1.2 mm (d-bearing <50mm) ….. 1.6 mm (d-bearing >70 mm)
  • Nozzle position:
    Between the cage and the IR edge (technical data tables, TA cage)
  • Oil feed, oil drain:
    Transparent hose di = 4 mm
  • Air pressure in front of the spindle:
    0,6 bis 1 bar
  • Air volume:
    3 bis 4 m3/h (50 bis 65 l/min) 3 to 4 m3/h (50 to 65 l/min)
  • Air quality:
    In compliance with ISO 8573: Particle size <5 μm,
    Particle concentration <5 mg and m3,
    Dew point <3 °C, oil concentration <1 mg and m3
  • Commissioning:
    Start-up of the spindle after ensuring oil supply

Technical information about the “Oil Lubrication” topic can be found in our download area.

DIRECT OIL LUBRICATION

OIL FEED THROUGH THE OUTSIDE BEARING RING

GMN special designs for direct oil lubrication provide compact bearing dimensions (through an oil feed hole in the outside ring (no space needed for oil feed), and also provide economical lubricant controls.

  • Saves space and costs
    (No axial injection nozzle and intermediate bushing required)
  • Reduced compressed air, oil consumption
    (Precise metering of lubricant quantities)
  • Separate lubricant quantity control per single bearing
  • Targeted lubricant supply to the rolling contact
  • Insensitive to axial airflow
    (Compared to conventional oil-air lubrication)
  • Oil supply by external ring, open side
  • Oil supply by external ring, closed side
  • O-rings in outer ring (sealing)
  • Widening of the groove to extend the oil supply possibility, tolerance compensation

GMN special designs for oil direct lubrication offer versatile and effective solutions for oil supply and sealing.

  • Oil supply by external ring, open side
  • Oil supply by external ring, closed side
  • O-rings in outer ring (sealing)
  • Widening of the groove to extend the oil supply possibility, tolerance compensation

You can find technical information on “Direct oil lubrication via AR” in our download area.

KL_Schmierung11_935x435

A AND AB SPECIAL DESIGNS

Seals: Seal in housing

  • Maximum bearing stability
KL_Schmierung12_550x550
Oil supply via open side - no overflow of the oil supply at high axial loads 
KL_Schmierung13_550x550
Oil supply via the closed side - oil supply directly to the rolling contact - Maximum rotational speed suitability 

L AND LB SPECIAL DESIGNS

Seals: Seal in outside bearing ring

  • No housing fitting needed
KL_Schmierung14_L_550x550
Oil supply via open side - no overflow of the oil supply at high axial loads 
KL_Schmierung15_LB_550x550
Oil supply via the closed side - oil supply directly to the rolling contact - Maximum rotational speed suitability 

R AND RB SPECIAL DESIGNS

Seal: without gasket

  • Low investment
  • Especially for axial attachment
    on the outer ring and tight
    Housing caps
  • Wide lubrication groove
KL_Schmierung16_R_550x550
Oil supply via open side - no overflow of the oil supply at high axial loads 
KL_Schmierung17_RB_550x550
Oil supply via the closed side - oil supply directly to the rolling contact - Maximum rotational speed suitability 

LUBRICATING OILS

Mineral lubricating oils provide sufficient bearing lubrication for machine tool spindles.

 

KL_Schmierung18_1220X15RGB

Frequently-used lubricating oils