Wind free
The decommissioning of a crane is called wind-free or “wind-free” or “after-work position” . The crane's slewing brake is permanently opened mechanically.
The point of the Windfrei is to keep the crane freely rotating in the wind . In this way, the crane boom can turn without a technical drive - i.e. independently - solely by the wind power from the wind. If the wind is blowing and blowing sufficiently strong and directionally stable, the boom will ultimately point very precisely into the lee . In this position, the wind force, which increases with the strength of the wind, acts as the mast tipping downwind, but the constant tilting moment of the counterweights acts in the opposite direction.
As a result of this measure, the crane is constantly aligned in such a way that the air resistance is lowest. This increases the stability of the construction considerably.
The emergency stop function of the brake is not impaired if used properly.
When it comes to cranes, there are two main ways of making a brake free of wind.
Mechanical wind clearance
The brake is released, the brake disc is held and locked in the open position manually by a threaded rod or lever.
- Advantage: simple and robust construction.
- Disadvantage: increased effort, as this is done with muscle power. In the event of improper use, there is a risk that the brake will remain open during operation.
Electric wind clearance
The brake is released, the brake disc is held in the open position and locked by an electrically operated bolt. After locking, no more energy is required to leave the brake open.
- Advantage: quick and easy wind-free, operating errors are almost impossible.
- Disadvantage: increased effort for the initial installation and adjustment work.
Bracing
If, for reasons of space, it is not possible to turn a crane freely in the wind , it can also be guyed to the jib. So that the direction of the boom is very stiff and thus also prevents swinging, two ropes are tensioned in a reverse V-shape from two attachment points on the ground by pulling the crane hook up as far as possible. The lower end points of the V should be on a line approximately across the desired direction of the boom and this line should be at a sufficient distance from the crane's axis of rotation in order to achieve a good lever length. When tensioning the ropes by pulling the hook, the boom direction and trolley position are free. The high wind forces that occur across the boom are absorbed by this bracing (in interaction with the counterweight), the tilting moment of the counterweights is roughly compensated by the resultant of the cable pulling forces, the drive of the cable drum is usually self-locking so that the cable tension is maintained remains.
Others
Especially at the beginning of a house construction site, when there is no lockable room, a tool box or a table saw (typically necessary for concrete formwork) is sometimes raised to about half the height for non-working and therefore unsupervised time. This means that valuable portable items are kept safe from theft when crane operation and / or power supply are blocked. On the other hand, the lifting rope is also loaded and excessive swinging of the hook is avoided.
Around 2000 it was common in Austria to set up cranes near autobahns with an advertising space - mostly as a three-sided prism on three ropes on a hook. The construction site at the crane did not actually have to be in operation. In times when there is no risk of strong winds, the construction company's advertising spaces are often raised outside of working hours.