Rexroth Tightening System 350 System Documentation - Rhino ...

40/316 Bosch Rexroth AG | Tightening Technology 5 Construction Guidelines5.1 Layout of a bolted connectionSettling can be avoided or decreased using the following processes:– Constructive adjustment, i.e. bearing surfaces to prevent forces that exceed the yielding points (permissiblesurface pressing) of the materials– Selection of suitable (strong enough) materials– Suitable surface processing of the parts to be connected prevents settling near rough surfaces.– Tightening processes where settling (e.g. near rough surfaces) takes place during the tightening; thetightening result (tightening torque) is only determined after settling.5.1.2.3 Temperature influencesDue to fluctuations in temperature, the parts to be connected, as well as the bolt, can stretch or compress.Using materials with the same coefficient of expansion prevents the clamping force from changing whenthe temperature does.5.1.2.4 Securing bolted connectionsMechanical and chemical securing devices and compounds must be particularly taken into considerationdue to their settling characteristics. With elastic stop nuts, friction increases during tightening due to theplastic insert in the nut.5.1.2.5 Tightening factor a A (consideration of the uncertainty of the tightening)The clamping force of a bolted connection is influenced by numerous factors:– The large spread width of the friction actually occurring under the bolt head and at the thread; onlyan assumed typical value can be used for calculation– Differences depending on the selected tightening process, e.g. fast or slow tightening of the bolt,torque-controlled/angle-controlled process, yield point tightening– The precision of the tightening system usedWhen designing a bolted connection, the influencing factors must be taken into account so that in theworst case (minimum clamping force F Vmin reached), the function of the bolted connection is maintained,and that, if maximum clamping force F Vmax is reached, the bolt is not destroyed.The tightening factor describes the effect of the influencing factors on the clamping force of the tightening.The higher the tightening factor, the larger the bolted connection (bolt diameter) must be dimensioned.The definition for tightening factor a A is:F Vmax max. mounting clamp forcea A= ------------------- = -----------------------------------------------------------------------------------------------------F Vminmin. mounting clamp force requiredMore information on typical values for the tightening factor are described in VDI guideline 2230.5.1.2.6 Clamping force table according to VDI 2230The following table lists the guide values for mounting clamp forces (F M ) and tightening torques (T A ) dependenton a friction factor (μ G ) for headless bolts with metric coarse-pitch threads according toDIN ISO 262, head dimensions for hexagon bolts according to DIN EN ISO 4014 to 4018, fillister headbolts according to DIN EN ISO 4762, and “center” holes according to DIN EN 20 273.System 350 | 3 608 878 040/05.2008