Rexroth Tightening System 350 System Documentation - Rhino ...

9 Tightening Processes Tightening Technology | Bosch Rexroth AG 239/3169.4 Example parameterizationsThe torque increases from positioning of the screw head until it reaches the torque threshold Ts (torquecontrolled).Ts should be at the beginning of the linear increase of the tightening graph (as the joiningprocesses of the tightening parts are almost complete here). From the torque threshold Ts, the incline(gradient) of the graph T = f (A) is continually measured throughout the entire tightening process until theyield point range of the bolt has reached approx. 50% of the maximum value of the gradient (Yp ≈ G max /2). It is slightly stretched by this (approx. 0.2%). Thanks to this minimum bolt cross-section constriction,it loses almost none of its strength and can be reused. The target parameter is thus reached in the transitionarea between elastic and plastic deformation.The maximum measured gradient value is written to a max. value memory starting from the torque thresholdset in the tightening step (setting under Gradient active from, on page 214), i.e. each higher valueis stored. This maximum value is the basis for calculating the gradient decrease. The yield point is reachedwhen the set gradient reduction is reached (in % of the measured maximum value of the gradient). In orderto ensure that this gradient reduction was not a one-time occurrence and that e.g. it was caused by irregularitiesin the tightening process, the tightening continues at a defined angle (setting under Control angle,on page 214). The tightening is ended and evaluated if the target function is still fulfilled once thecontrol angle has been reached. If the target function is no longer fulfilled, i.e. the yield point is smallerthan the defined value, the tightening will be continued until the set yield point is reached again. Then, itwill be tightened again with the defined control angle, etc.Torque monitoring (T–, T+) 1) and angle of turn monitoring (A–, A+) 1)) are used for error recognition. Theiradvantages include recognition of:– Lot jumps in bolts and components– Incorrectly used bolts (bolt quality)– Incompletely cut threads– Angle of turn increase from over-twisted threadsUseThe yield point-controlled tightening process is mainly used for:– Ring gear assembly– Wheel hub assembly– Flywheel assembly– Cylinder head assembly9.4 Example parameterizationsThe tightening steps available in the BS350 can be used to implement standard tightening processes, aswell as special tightening processes. Selected example parameterizations for this are listed in this section.Only entered parameters are described in the following tightening programs and control signal assignmenttables (PLC assignment tables). All other parameters are standard values or not used. Entry of stepnames is not described here.After tightening programs and control signal assignment tables have been generated, they must be sentto the appropriate controller before they become effective.Detailed information on sending data can be found in chapter 8, “Basic Commissioning” on page 171!9.4.1 Yield point-controlled tightening process with extended tightening stepThe extended tightening step is used to implement a yield point-controlled tightening of bolts.The tightening program Prg_YieldPoint with extended tightening step for implementing a yield point tighteningis described in table 9–2.1) Limit value definition (T–, T+) and (A–, A+) should be done via a statistical evaluation (≥ 50 tightenings).Too-small tolerance limits result in a high number of NOK tightening cases; too-large tolerancelimits impair fault recognition.System 350 | 3 608 878 040/05.2008