AU2011267433A1

AU2011267433A1 - Method for tightening screw connections

Info

Publication number: AU2011267433A1
Application number: AU2011267433A
Authority: AU
Inventors: Otto Widlroither
Original assignee: Robel Bahnbaumaschinen GmbH
Current assignee: Robel Bahnbaumaschinen GmbH
Priority date: 2010-06-15
Filing date: 2011-05-24
Publication date: 2013-01-31
Anticipated expiration: 2031-05-24
Also published as: DE102010023798A1; EP2582880B1; AU2011267433B2; ES2563077T3; CN102939418A; CN102939418B; WO2011157350A1; EP2582880A1

Abstract

In order to tighten screw connections, a screw-in torque (17) which is effective during the screwing in of a screw is sensed and a compensation value (18) which is dependent thereon is determined, and the setpoint torque (20) is increased as a function of the previously determined compensation value (18) for the complete tightening of the screw (7).

Description

1 US 1/7 A METHOD OF TIGHTENING SCREW CONNECTIONS [0001] The invention relates to a method of tightening screw connections by means of a power-driven wrench while achieving a defined target torque. [0002] Known from DE 1 708 657 is a device for tightening sleeper screws with a tightening torque which is independent of the screwing moment. A screwing operation of this type, however, results in the disadvantage that the actually effective pressing forces connecting the sleeper to the rail differ in dependence upon the friction values, even though the respective tightening moments are kept constant. The different friction values can be the result, for example, of unequal conditions of the thread surface. [0003] It is the object of the present invention to provide a method of the type mentioned at the beginning with which a constant pressing force is ensured for all screw connections. [0004] According to the invention, this object is achieved with a method of the specified kind in that a screwing-in torque effective during the operation of screwing-in a screw is detected and a compensation value dependent on the same is determined, and the target torque 2/7 for tightening the screw is increased in dependence upon the compensation value determined before. [0005] Detecting and taking into account the screwing-in torque makes it possible to adapt each screwing cycle exactly to each particular screw connection with regard to the tightening moment, resulting in a constant pressing force being effective at all times. Thus, the question of whether the screws or the screw bore holes are of different condition is of no importance for the connection of sleeper and rail. [0006] Additional advantages of the invention become apparent from the dependent claims and the drawing description. [0007] The invention will be described in more detail below with reference to an embodiment represented in the drawing in which [0008] Fig. I shows a simplified side view of a screwing machine, Fig. 2 shows an enlarged view of a servo screwdriver, Fig. 3 shows a screw connection for fixing a rail to a sleeper, and Figs. 4 and 5 each show a graphical representation of the torque in dependence upon the rotation angle. [0009] A screwing machine 1 visible in Fig. 1 is mobile on a track 4, formed of rails 2 and sleepers 3, and equipped with vertically adjustable servo screwdrivers 5. These serve for tightening a screw connection 6 which - according to an example shown in more detail in Fig. 3 - is 3/7 composed of a screw 7 with a screw head 8, and a screw bore hole 9 located in the sleeper 3. [0010] As can be seen in Fig. 2, each servo screwdriver 5 has a servomotor 10 and a wrench 12 rotatable about an axis 11. Additionally, a processor 13 equipped with a data memory is connected to a rotation angle gage 14 and a torque transducer 15. [0011] As visible in Fig. 3, a fastening means 19 in the shape of an elastic spring clip is provided between a base plate 16, resting on the sleeper 3, and the rail head 8. Said spring clip is in contact with both the base plate 16 and the rail 2. [0012] Beginning with the starting position shown in the left-hand half of the picture, the screw 7 is screwed into the sleeper 3 in a so-called no-load run, wherein the torque to be applied for that purpose may vary to a greater extent in dependence upon miscellaneous interference factors, such as rust, sand, grease, etc. [0013] Since the crucial factor regarding the connection of rail 2 and sleeper 3 is not the torque, but rather the pressing force effective via the screw connection 6, a screwing-in torque 17 registered during the screwing-in operation (no-load run) is stored. In this context, see Fig. 4, which shows the entire torque progression with respect to the rotation angle a (x-axis) of the screw 7. The screwing-in torque 17 which is increased due to an interference (here, for example, 40 Nm) 4/7 is ultimately added as a compensation value 18 to a selectable target torque 20 (for example 230 Nm) for tightly fastening the screw 7. With this, the torque which is actually effective via the screw connection 6 is finally increased to 270 Newton meter. [0014] In an advantageous variant of the screwing operation according to the invention, a head contact 21 of the screw head 8 on the fastening means 19 - which can be detected as a result of an erratic increase of the screwing-in torque 17 - is automatically registered during the screwing-in process parallel to the detection of a rotation angle a of the screw 7. Subsequently, as a compensation value 18, that screwing-in torque 17 is selected which was registered at a rotation angle a immediately prior to the head contact 21. Ultimately, the question of which value is actually chosen for said rotation angle a depends on the type of screw connection 6 and also on corresponding empirical values. [0015] According to a further variant of the invention as visible in Fig. 5, in a first screwing-in operation (al), the screw 7 - immediately after having been screwed completely into the sleeper 3 - is unscrewed by at least one rotation in an unscrewing operation (b). Subsequently, the screw 7 is screwed in again in a second screwing in operation (a2), wherein the compensation value 18 is only registered during said second screwing-in operation (a2). This is 5/7 added to the target torque 20 to finalize the screwing operation. [0016] This method compensates an effect which occurs frequently in practical operations. In this, the screwing-in torque 17 changes especially between the first and the second screwing operation of the same screw connection 6. The cause of this can be hydraulic effects (water, grease, oil in the thread blind hole) or dirt, contamination, burrs on the thread. [0017] The method according to the invention can naturally also be used in connection with other types of fastenings differing from the illustrated type of a rail fixation, such as the so-called K-type track.

Claims

1. A method of tightening screw connections (6) by means of a power driven wrench (12) while achieving a defined target torque (20), characterized in that a screwing-in torque (17) effective during the operation of screwing-in a screw (7) is detected and a compensation value (18) dependent on the same is determined, and the target torque (20) for tightening the screw (7) is increased in dependence upon the compensation value (18) determined before.

2. A method according to claim 1, characterized in that during the screwing-in operation a) a rotation angle a of the screw (7) is detected, b) the head contact of a screw head (8) on a fastening means (19) which can be detected as a result of an erratic increase of the screwing-in torque (17) - is registered, and c) as a compensation value (18), that screwing-in torque (17) is selected which was registered at a rotation angle a prior to the head contact.

3. A method according to claim 1, characterized in that in a first screwing-in operation, the screw (7) - immediately after having been screwed completely into a sleeper 3 - is unscrewed by at least one rotation 7/7 and subsequently, in a second screwing-in operation, is screwed in again, wherein the compensation value (18) is only registered during the second screwing-in operation.