Slide bearings - Wolf Kunststoff-Gleitlager GmbH

CCCCCCMathematical example13.5.9. Check of the minimum operating bearing clearance:13.5.9.1.Calculating the change of the operating bearing clearance due to temperaturefluctuationsPrefaceThis mathematical example bases on an operation with a non-slitted bushing, therefore we must first calculatethe necessary mold bearing clearance (change of the inside diameter of the stuffed bushing due to an increaseof temperature) by means of formula (6):Contents∆Sϑ Z= ∆ϑ •( d • ( α − α ) − d • α )2GehBu1Win which :∆ϑ : change in temperature measured from the installation temperature to the slide bearing temperature.With an assumed installation temperature of 20 °C follows for ∆ϑ : 75°C - 20°C = 55°Cd 2: outside diameter of the bushing = 36mmα Bu: coefficient of expansion of the bushing taken from table 6 for ZX-324V2T = 6,5*10 -5α Geh: coefficient of expansion of the casing taken from table 6 for steel = 1,2*10 -5d 1: outside diameter of the screw = 30 mmα W: coefficient of expansion of the screw taken from table 6 for steel = 1,2*10 -5MaterialoverviewDesignguidelinesyields to a change of the inside diameter of the stuffed bushing:∆SϑZ= 55 ° C •−5−5−5( 36 • ( 1,2 • 10 − 6,5 • 10 ) + 30 mm • 1,2 • 10 ) = − 0,0851 mmThis change of the inside diameter must be existing as minimum mold bearing clearance, inorder to avoid a clamping/grip of the bearing on operation.Mathematicalexample13.5.9.2 Calculating the minimum operating bearing clearanceThe minimum operating bearing clearance can be calculated by means of formula (4):Semin = ød1min− A oscrewin which :ød1 min:after pressing the bushing into a casing of an ISO-tolerance H5 follows for the “standard”class of bearing clearances according to table 1 an inside diameter of an ISO-tolerance D8.Consequently follows a lower dimensional deviation of 30,065 mm according to ISO.A oscrewfollows:S min: for the screw – handicap ø30d9 – follows an upper dimensional deviation of 29,935 mmaccording to ISO.e= 30 ,065 mm − 29 ,935 mm = 0,13 mmThe check of the minimum mold bearing clearance is effected on the following condition:TribologyConditions ofinstallationSlide bearings(cylindrical)Slide bearings(with collar)∆Sϑ z≤ Semin⇒− 0,0851mm≤0,13 mmAs this condition is fulfilled, a secure operation is possible for the required ambienttemperature of 65 °C.IndexWolf Kunststoff-Gleitlager GmbH • Heisenbergstr. 63 - 65 • 50169 Kerpen-Türnich • Tel. 02237/9749-0 • Fax. 02237/9749-2048