The main work of the card, separation into individual fibers, is performed between the main cylinder and the flats. Only by means of this fiber separation is it possible to eliminate the last dirt, especially the finer particles and dust. These pass into the flats, the extraction system, or the droppings.
When a flat moves into the working zone, it first fills up. This occurs relatively quickly, i.e. after only a few flats have moved into the working zone. Thereafter, hardly any further take-up of fibers occurs, and only carding takes place. Accordingly, if a fiber bundle does not find a place in the first few flats, then it can be opened only with difficulty.
It will be rolled between the working surfaces and usually leads to nep formation .
Equally important at this working position is the reduction of neps. Kaufmann  indicates that 75% of all neps can be disentangled, and of these about 60% are in fact disentangled.
Of the remaining 40% disentanglable neps:
- 30-33% pass on with the sliver;
- 5-6% are removed with the flat strips;
- 2-4% are eliminated with the waste.
The intensity of separation depends on:
- the sharpness of the clothing;
- the spacing of the main cylinder from the flats;
- the tooth density of the clothing;
- the speed of the licker-in (high, but not too high);
- the speed of the doffer (high, but not too high).