Energy losses through friction µ – 10 % = 1/2 E [AUS+BR+E+S] „Although rolling friction is already very low, manufacturers of roller bearings and lubricants work continuously on further improvements..“ SKF — one of the world´s biggest manufacturers of roller bearings made the following calculation: If it can be managed to drop the friction in all roller bearings installed on the globe only by further 10%, the combined total electricity consumption of the countries Australia, Brasil, Spain und Sweden could be cut to a half !
Roller Bearings are named after the Shape of their rolling Elements ball spherical roller symmetrical spherical roller asymmetrical cylindrical roller needle roller conical roller
Friction in Roller Bearings l small portion of rolling friction l but considerable share of sliding friction at: roller bearing rings cages and / or rolling elements against each other
Kinds of Lubrication of Roller Bearings 9,5% by oils 0,5% by solid lubricants only 90% by greases
The most important Parameters for selecting the suitable Lubricant revolution or DN - factor D = external bearing diameter [mm] d = internal bearing diameter [mm] n = revolution per minute [rpm] d m = medium bearing diameter [mm] = ——— D + d 2 DN = ——— n D + d 2 temperature range
Temperature Range of OKS Bearing Greases with MoS 2 with MoS 2 + Mo x - Active with MoS 2 with Mo x - Active with MoS 2 + Mo x - Active with PTFE with white solid lubricants with PTFE
Lubrication by greases Grease pump Contamination may cause bearing failures. Seals protect to a large extent from outside contaminations. Frequent relubrication is required when the hazard of grease contamination exists. Same applies if the grease should seal also against penetrating moisture. Contamination penetrating through labyrinth channels. Newly supplied grease pushes out both used up and contaminated grease through the labyrinth packing seals.
Relubrication Intervals for Grease lubricated Roller Bearings Small bearings with lateral seals or cover plates do not need any relubrication. They are already for - life lubricated. For all other roller bearings relubrication intervals become valid.
Guidelines for Relubrication Intervalls 10 000 6 000 4 000 3 000 2 000 1 500 1 000 500 300 200 150 100 50 20 000 15 000 10 000 7 500 5 000 2 500 1 500 1 000 750 500 250 20 000 15 000 10 000 5 000 3 000 2 000 1 500 1 000 500 1002005001 0002 0005 00010 000 n [U/min] t fa t fb t fc Lubrication interval, given by service hours t fa = radial ball bearing t fb = cylindrical roller bearing / needle bearing t fc = self aligning roller bearing / taper rolling bearing / axial roller bearing massive cylindrical roller bearing (0,2 t fc ), axial cylindrical roller bearing (0,5 t fc ) 500420 3602802402001601201008060 40 20 d=10 Example: A deep-groove ball bearing with an internal diameter d= 100mm running at a speed of n = 1000 rpm. The operating temperature lies between 60 and 70 °C. Which is the expected relubrication interval? The vertical in point n= 1000 rpm on the abscissa cuts the curve for d= 100mm. From there the horizontal leads to the outer left-hand scale (deep- groove ball bearings) indicating a relubrication interval of 10000 service hours
Correction of Relubrication Intervals The assessed intervals are valid only for: l bearings in stationary machines l normal load l ageing-proofed greases l temperature < + 70°C at the outer ring
Dependance of Relubrication Intervals on Tempearture 100 85 70 55 40 Lubrication interval °C Temperature at the outer ring l above 70°C the factor 0,5 applies for each temperature rise of 15°C i.e. with a temperature rise from e.g. 70°C up to 85°C the service life of the grease is cut by half. l below 70°C the factor 2 applies for each temperature drop of 15°C i.e. with a temperature drop from e.g. 70°C down to 55 °C the service life of the grease is doubled.
Lubrication by Oil is used at high speeds resp. at DN-factors exceeding 1.000.000 and in case heat conduction is necessary.
Oil bath lubrication Suitable only for bearings with low speeds. During stand-stills the oil level should not quite reach the middle of the rolling element at the bottom..
Oil injection lubrication At high speed it becomes necessary, that the air turbulence circulating with the bearing is penetrated by the oil. This is ensured by injecting oil under high pressure (min.15 m/s) from the side into the bearing.
Circulatory oil lubrication With increasing speed the service temperature rises and accelerates the ageing of the lubricating oil. By circulatory lubrication the oil can be cooled and consequently the service temperature be reduced. Cooling pump
Lubrication with Solid Lubricants Deep groove ball bearings with increased clearance required at: l high temperatures > + 200 °C l high temperature variations l low speed
Lubrication with Solid Lubricants - Exsample Lubrication by Solid Lubricants only at temperatures > + 200 °C OKS 230 MoS 2 -High Temperature Paste (for thin-film lubrication during assembly and maintenance) in connection with OKS 310 MoS 2 -High-Temperature Lubricant (for relubrication during operation) The carrying fluid evaporates residue-free above 200°C and dry MoS 2 films remain, which assure lubrication up to 450°C. Kiln-car bearings in the ceramics and brick industry
OKS Speciality Lubricants for Roller Bearings at: l High loads l Shock stress l Vibrations l Low or high speed l Stop-and-go operation l Very low or very high temperatures l Temperature variations l Humid conditions l Corrosive influences l Long-term lubricating needs l Use in the food industry