The invention relates to a hydraulic threaded bolt tightening device for tightening and loosening large bolts and to a method for tightening such bolts by means of the threaded bolt tightening device. The device comprises a cylinder supported on a machine part to be tightened by means of a threaded bolt and a nut. At least one piston is guided in the cylinder in a sealed manner. The cylinder is supported on a threaded bush screwed on to one end of the threaded bolt. The cylinder can be pressurized periodically. There are a pressure medium supply to the threaded bolt tightening device and a pressure medium connection on the threaded bolt tightening device. An adjusting ring is arranged in the cylinder and is connected to the nut by a form fit. A rotary drive for the adjusting ring has a drive connection to the adjusting ring.
A hydraulic threaded bolt tightening device of this type is described in DE 28 46 668 A1. In detail, the device comprises an extension measuring device having a measuring rod arranged within a central bore in the bolt to be measured. The extension measuring device has a housing and a sensing pin which can be displaced relative to the housing and is connected with housing and sensing pin between reference surfaces of the bolt, on the one hand, and the measuring rod, on the other hand. The relative displacement of the bolt reference surface in relation to the measuring rod reference surface provides a measure of the axial extension of the shank of the bolt. The sensing pin is a constituent part of a measuring sensor designed as an inductive transducer. The supply and measuring lines connected to the measuring sensor are led to a control cabinet which is arranged at a distance from the pressure container and is used for power supply and measured value processing. It is possible for a displacement tube, which is used to guide out the measuring rod reference surface and to connect the measuring sensor housings to be brought into engagement with the measuring rod by a quick-action coupling.
Although this known device enables remotely controlled tightening and loosening of bolted connections, the monitoring of the tightening and loosening is carried out purely based on a length measurement, which requires a measuring rod arranged within a central bore in the bolt to be measured. This necessitates increased expenditure in the production of the bolt and requires an additional extension measuring device in conjunction with the bolt tightening device.
The device described in DE 32 46 840 C2 for the automatic control of a plurality of stud tightening devices permits the tightening of numerous stud tightening devices simultaneously under the control of a central control unit, which supplies the signals designating the individual operations. When a specific operation has been completed, each tightening device supplies an output signal, which is picked up by the control unit, which then generates the signals designating the next operation. The control unit contains a follower processing unit for generating a common command signal for the various tightening devices, so that the latter can be driven simultaneously, and also a number of adjusters, which in each case pick up the command signal from the follower processor unit and transmit it only to the relevant associated tightening device. The triggering time of the adjuster corresponds to the time of the completion of the operation of the associated tightening device; it is independent of the other tightening devices and the follower processor unit. If one of the tightening devices does not operate, it does not supply any output signal. The other tightening devices are then deactivated and the device that does not operate unless it is either actuated or started up by hand. No statements relating to measuring the bolt extension can be gathered from DE 32 46 840 C2.
EP 0 928 660 A1 describes a threaded bolt tightening device for tightening and loosening bolts by heating the bolt by means of a bolt heating device inserted into a central bore in the bolt. It comprises a nut rotating device for rotating a nut screwed onto the bolt. An extension indicator measures the thermal extension of the bolt. A control unit controls the drive of the nut rotating device. There is also a power supply to the bolt heating device. The control unit comprises at least one device for actuating the nut rotating device for tightening and loosening the nut and also for interrupting the power supply to the bolt heating device when the measured value from the extension indicator reaches a predefined extension. When the nut is tightened, yet another device exerts a torque on the nut, stops the nut rotating device and interrupts the power supply to the bolt heating device when the nut has been rotated by a predefined angle. When the nut is to be loosened, a device rotates the nut with a predefined number of rotations if the nut is loosened such that it can be rotated, and then both stops the nut rotating device and interrupts the power supply to the bolt heating device.
U.S. Pat. No. 5,257,207 A describes a hydraulic threaded bolt tightening device for tightening and loosening bolts, in which a distance measurement between the flanges to be clamped is carried out. The distance measurement is carried out continuously with reference to the applied prestressing force. From this, the slope of the distance-prestressing force curve is determined in a control device, in order, by using a point of inflection that occurs when the settling point is reached, to determine whether full compression of a seal has been reached. This is followed only by elastic deformation, in particular extension of the bolt up to a predefined prestress. The feed rotation of the nut is carried out by hand without rotation angle measurement. In addition to the distance measurement to be carried out continuously, it is also necessary for the applied prestressing force to be measured continually via the pressure in the hydraulic threaded bolt tightening device.
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