Pinhole detection in aluminium foil separator

 

APPLICATION

Aluminium foil is a very thin sheet of aluminium which range from 0,006 mm to a limit of 0,2mm as defined by the International Standards Organization.
The aluminium foil manufacturing process begins by rolling sheets of aluminium down to coils between 2mm and 4mm thick. After this process the aluminium coil is then successively cold rolled until the coil reaches the desired thickness.

As aluminium foil acts as a complete barrier to light and oxygen, odours and flavours, moisture, and bacteria, it is used extensively in food and pharmaceutical packaging.

To obtain the very thinnest foils
(gauge ranging from 6 to 30 µm),
two foils are laminated simultaneously and separated after this double rolling mill process.
Those thinnest foils could become slightly permeable due to pinholes caused by the production process.
These pinholes can not be detected visually on 100% of the foils.

In order to detect those defects, Arck Sensor offers an automatic detector named 
Cephee-AS especially designed for foil separator, testing 100% of the two foils at the exit of the separator.

      
 

WORKING PRINCIPLES

The principle is based on the use of a laser girder as a light source and of photo sensors suited for the reception of the light through possible holes in the foil.
The detector receives the light passing through the hole.
This very small among of light generates a signal telling the system there is a hole.
In addition the position of this hole along the detector is measured.

                     

For technical reasons, an optical module does not cover more than 65 millimeters.
The average useful width of optics becomes 64 mm.
This implies the use of several optical modules with a covering of 0,5 mm on each side.

The following drawing represents the arrangement of the lasers and detectors seen from the top and the overlap between every device. The number of modules needed is related to the foil’s width.

Advantages of using laser light :
A laser is focused in only one direction and not in all direction like LEDs light source.
This avoids the risk of reflection on the metal foil and the risk of false alarms.


Réalisation SYSTONIC 2008