What could possibly happen?
„The vacuum lifter carries the load. Why should I clean the suction cups?“
Always bear in mind that in vertical transport, the friction between the suction disc and the transported goods, the glass pane, is all that ensures that the transported goods are held in place.
Everyone has experienced what it's like when there is no friction when there is black ice and you can no longer keep your feet on the ground. The same applies if the vacuum cups no longer have any friction on the glass, for example. If there is no friction, the load (e.g. the glass pane) slides off the suction disc during vertical transport. The lower the friction factor, the lower the vertical load capacity.
External contact with release agents and other materials, as well as the migration of grease and fillers in rubber compounds to the surface and similar things change the friction behaviour of the vacuum cups. We also speak of ageing of the suction cups. The more deposits accumulate on the suction surface and also penetrate this surface, the lower the friction factor of the vacuum cups becomes. This reduces the load capacity.
That can't be much use, can it?
We tested this on a suction cup that was about 5 years old. If the 388-4N-K suction cup is new, it can hold 90 kg with double safety. This means that the suction cup can hold 180 kg for at least 5 minutes at a vacuum of -0.6 bar.
So what could such a vacuum cup still be wearing after 5 years?
We got to the bottom of this question with tensile tests on our suction cup testing device. For this purpose, the vacuum cup was sucked onto a vertical glass pane. The vacuum was approx. -0.6 bar. We generated this vacuum with a battery-powered vacuum unit and then switched it off. Vacuum losses were therefore not compensated. A crane scale is installed between a threaded spindle and the suction cup, which reflects the holding force applied. The holding force was then increased to approx. 140 kg via the threaded spindle until the suction cup slipped. Even if the holding force is not stated in kg, the weight held by such a vacuum cup can be easily determined. Please bear with us if we now simply state the weight held as the size. The vacuum cup was left like this and maintained for 5 minutes.
What do you think will happen during this time?
The vacuum suction cup slowly slipped further and so the holding force became less and less. In the end, the crane scales displayed a full 47 kg. This is how we determine the load capacity of vacuum cups. In the dynamic range, vacuum cups always achieve a significantly higher load capacity than in the quasi-static range, which we assume to be the case after about 5 minutes.
What can you do about it?
Now clean with a cloth soaked in methylated spirits and rub the vacuum cup vigorously with this cloth.
We have found that regular cleaning of the suction cups with methylated spirits can go a long way towards maintaining the friction factor of our suction cups for as long as possible. To do this, use a clean cloth soaked in methylated spirits and then rub the suction cup vigorously. To protect your skin, you should wear appropriate protective gloves so that you only remove grease and the like from the suction cups and not from your skin.
What can cleaning do?
I'm sure you're going to ask yourself, what's the point?
Well, we ourselves were surprised by the result. We could now bring the crane scale to a value of approx. 270 kg at the beginning and after 5 minutes it was still approx. 218 kg. This won't always be the case, but it shows how much cleaning vacuum cups can achieve.
If you would like to watch a video recording of the whole thing, you can find it on our YouTube channel.
Example with a 7411-DS7Z combi vacuum lifter
We once received a 7411-DS7Z vacuum lifter combi for an annual inspection after one year. The basic device with 4 488-K vacuum suction cups should be able to carry 500 kg in-house and 375 kg on construction sites.
We sucked the vacuum lifter onto our steel plate, installed a crane scale between the device and the crane hook and tightened it. At 475 kg, the device slipped over the steel plate.
With all 4 vacuum cups, the appliance was supposed to hold 2 x 500 kg = 1000 kg. However, it could not even hold the nominal load.
The first step was to clean the vacuum cups with methylated spirits. The test was then carried out again and the value was increased to approx. 900 kg. This resulted in a significant improvement in load capacity.
If you would like to watch a video recording of the whole thing, you can find it on our YouTube channel.
It was used in this condition, despite the many instructions in the operating instructions for cleaning the vacuum cups. Unfortunately a single Cleaning alone does not fix everything.
Our advice
The vacuum cups should be cleaned regularly so that friction is maintained for as long as possible.
It's about your safety and that of your fellow human beings.