Does it matter whether wet or dry glass panes are moved with a vacuum lifting device? And if so, what changes do you have to expect? Does it make sense to dry glass panes before transporting them?
We would like to clarify these and similar questions today. A load test for suction cups is a good way of clarifying technical issues. You can see how this manifests itself in the load test in the following videos. Simply click on the link and the video will open on an internet-enabled PC.
Is there any difference at all between dry and wet glass panes?
To do this, a Pannkoke 388 suction cup is simply subjected to a load test once in a dry state. The glass pane is then sprayed with water and the test is repeated. Will there be a change? And if so, how will it turn out?
The experimental set-up is quite simple: a fixed glass pane on which a vacuum cup is sucked in. The lower operating point is selected as the vacuum value. For our vacuum lifting devices, this is -0.6 bar. The suction cup is attached to a crane scale and then to a spindle. Tensile stress can now be built up via the spindle when it is shortened. The crane scale provides the tension in kg. When the maximum tension is reached, maintenance is carried out. According to EU standard EN 13155, a vacuum lifter should be able to hold the nominal load for at least five minutes in the event of a power failure. We therefore generally use this time period. The suction cup should not slip. To move glass panes and the like, we therefore need the static holding force and not a dynamic holding force, which is always higher. At least that's what our tests have shown.
Find it on YouTube:
Suction cup 388 - Load test dry & wet
In principle, the result should come as no surprise. The friction is minimised by the water film between the suction cup surface and the glass pane. However, as the friction between the suction cup surface and the glass pane is the only thing holding the glass pane up when the suction cup is used vertically, the load-bearing capacity must decrease.
What is perhaps a little shocking is the extent of the loss in load-bearing capacity. When dry, it was still a good 200 kg and with the sprayed glass pane? Do you remember it from the video? No? Look at it again or believe me, it was about 36 kg. As you can see, that's a very big change. The lesson learnt from this is never vacuum wet surfaces and try to transport them vertically or simply increase the number of suction cups on our 388 suction cups by a factor of approx. 6.
Only transport dry glass panes with a vacuum lifter, as the load-bearing capacity decreases considerably depending on the type of suction cup. Always remember this, because Your and your colleagues' safetypeople, only move dry glass panes vertically. Wet glass panes have friction factors that are much lower.
If the glass pane is wet, try to wipe it as dry as possible. The use of rubber lips like those used by window cleaners also helps a lot. It is better to rub with a dry cloth afterwards.