We describe the ITH hydraulic bolt-tensioning cylinders as stretching tools because they stretch the bolts in a way that is completely free of friction and torsion. The principle of the bolt-tensioning cylinder, the ITH Stretch Method, is explained briefly below, as well as its advantages in relation to the torque process. The navigation system takes you to examples and gives a general overview of the different products.
The Stretch Method:
Bolt connections, which are pre-tensioned using the ITH Stretch Method, achieve a reproducible pre-tensioning force with a close tolerance of ±2.5%.
A bolt-tensioning cylinder is threaded onto the projecting thread of the bolt. Hydraulic pressure is then applied by means of a hydraulic unit, thereby extending the bolt without any twist or friction. The hydraulic pressure of the bolt-tensioning cylinder has a linear relationship to the pre-tensioning force of the bolt-tensioning cylinder, thereby assuring a high degree of reproducibility. Once the required hydraulic pressure is achieved, the nut is threaded down free friction using a manual torque wrench with a defined torque.
All ITH bolt-tensioning cylinders are designed for the required tension of the bolt. Thanks to this principle and the absence of torsion and friction, it is possible to pre-tension the bolt to 98% of the yield strength.
|
|
|
| |
| Threading the bolt-tensioning cylinder on using a hand ratchet or power wrench | The pre-determined hydraulic pressure is applied and the bolt is stretched without friction or twist. | Threading the nut down with torque control using a manual torque wrench. The connection is now pre-tensioned. | |
Advantages of the ITH stretch method:
The ITH Stretch Method has a number of advantages over the conventional torque process. For tensioning, the standard torque process first has to overcome the moment of the thread pitch as well as the frictional resistances in the thread and on the contact surface. Due to the widely varying resistances, the pre-tensioning of the bolt may vary by up to 100% (friction class B μges 0.08 to 0.16).
Advantages at a glance:
- High pre-tensioning forces with small tool dimensions (e.g. thread W 510 or M340; 45,000 kN)
- No bending stress in the bolt
- Only tensile stress in bolt
- Simultaneous parallel pre-tensioning of several bolts (multi-tensioning system)
- One bolt-tensioning cylinder can be used on bolts of several dimensions
- Perfect for use with stainless steels as there is no risk of cold soldering (seizing) of the thread.
- Bolted joints subject to high temperatures (e.g. in gas turbines) can be released even after long periods of time.
- Linear relation between the pre-tensioning force of the bolt and the hydraulic pressure of the bolt-tensioning cylinder guarantees high reproducibility.
- Low αA value for certain grip lengths.
- Well suited for on-site assembly.
