Vacuum technology / Coval - Vacuum managers

Twitter Facebook Linkedin

Gripping air-tight and porous objects

Gripping air-tight and porous objects

The job of the vacuum pump is to generate a relative vacuum within a capacity. For vacuum handling, this capacity generally consists of:

.the internal volume of the suction pads to be emptied,
. the volume of the network (piping).

Air-tight objects
This is the only capacity to be taken into consideration.
The choice of vacuum pump will be made according to the time to create the vacuum corresponding to the function.
The maximum rate of vacuum it is possible to attain. It is useful to take the 90% vacuums (version N).

Porous objects
In this case it will not be possible to empty the capacity. The leakage rate from the suction pad network will therefore be taken into account.
The vacuum pump adapted to this type of handling is therefore a vacuum pump for which the fl ow will be signifi cantly greater than the leakage in order to create sufficient pressure drop in the suction pads.
High fl ow rate will be chosen in preference to a high vacuum,75 % vacuum (version T), 60% vacuum, or 50 % vacuum (version X) for very porous objects such as light cardboard, or foam, etc. 

Calculating the leakage rate

Apply a suction pad with a diameter suited to the object to be gripped.
Fit out a vacuum pump (for which the characteristics are known) with a pressure gauge and a vacuum gauge. Feed the vacuum pump with the optimal pressure (e.g. 5 bar).
Apply the suction pad to the surface to be tested.

Three possible cases can arise:
The vacuum gauge indicates the maximum vacuum achieved for this type of gauge: the object is air-tight.
. The vacuum gauge does not measure any vacuum: choose a more effi cient vacuum pump as the leakage rate is higher than the maximum vacuum pump flow.
. The vacuum gauge displays a vacuum value, e.g. -300 mb (30% vacuum), refer to the vacuum pump curve. Read the fl ow corresponding to -300 mb (e.g. 75 NI/ minute)

The leakage rate is 75 Nl/minute for the surface of the suction pad used at -300mb.
Using this data, calculate the forces to be applied to handle the object:
At -300mb the theoretical force of the suction pad is: F = S x 0.3 with:
S = surface of the suction pad in cm2
F in DaN

To grip the object safely, (factor of 2 for horizontal gripping and 4 for vertical gripping), the different characteristics of the vacuum pumps must be exploited.

Things to remember

"An installation must breath properly".

The throughput for a machine includes:

. gripping time,
. transfer time,
. release time.

Study of efficient vacuum handling should ensure the release of the object is processed correctly, as this is often the most diffi cult point to resolve.

. place vacuum pump as close as possible to the suction pads,
. choose suction pads with the smallest possible internal volume,
. identify suitable sizes of piping and fi ttings to reduce pressure losses.