The Design of Rolling Bearing Mountings

3 Three-phase current standard motorOperating dataBelt drive: Power 3 kW; rotor mass 8 kg; nominalspeed 2,800 min –1 ; size 100 L; totally enclosed fancooledaccording to DIN 42673, sheet 1 – design B3,type of protection IP44, insulation class F.Bearing selectionLow-noise bearings in a simple, maintenance-freearrangement should be provided. These requirementsare best met by deep groove ball bearings.In DIN 42673, the shaft-end diameter specified forsize 100 L is 28 mm. Consequently, a bore diameter of30 mm is required. In this case a bearing of series 62was selected for both bearing locations, i.e. an FAG6206.2ZR.C3.L207. They guide the rotor shaft bothat the drive side and at the ventilating side. The springat the drive side provides clearance-free adjustment ofthe bearings and accommodates opposing axial loadson the rotor shaft.By adjusting the deep groove ball bearings to zeroclearance the adverse influence of bearing clearance onnoise behaviour is eliminated.Bearing dimensioningThe calculation of the bearings for this motor differssomewhat from the usual approach. As not even themotor manufacturer knows the amount of load at theshaft end, the permissible radial loading is indicated inthe motor catalogues.To determine the radial load carrying capacity, thedrive-side deep groove ball bearing is calculated.The calculation is based on an attainable life L hna of20,000 h and a basic a 23II value of 1.5. In addition, therotor weight, the unilateral magnetic pull and theunbalanced load have to be taken into account. As theDrive endlatter two criteria are not known the rotor weight issimply multiplied by a supplementary factor off z = 1.5.With these values a permissible radial loading of 1 kNis calculated for the shaft-end middle.Since the operating load in most applications is lowerthan the admissible load, an attainable life L hna of morethan 20,000 hours is obtained. The life of electric motorbearings, therefore, is usually defined not by materialfatigue but by the grease service life.Suffixes.2ZRC3L207Bearing with two shieldsRadial clearance larger than PN (normal)Grease filling with Arcanol L207Machining tolerancesShaft to j5; end cap bore to H6.The bore tolerance H6 ensures the slide fit required forfree axial adjustment of both bearings.Lubrication, sealingThe .2ZR design with shields on both bearing sideshas been successful in small and medium-sized electricmotors. The grease filling in these bearings is sufficientfor their entire service life. Increased operating temperaturesmust be taken into consideration in the case inquestion due to the insulation class F provided. Forthis reason the FAG high-temperature grease ArcanolL207 is used. The shields prevent the grease from escapingand protect the bearings from contaminationfrom the motor. Gap type seals protect the shaft openingat the drive side against dust and moisture. The requirementson insulation type IP44 are, therefore,met.Ventilation end3: Three-phase current standard motorFAG 10