Opening the tufts into individual fibres;
Eliminating all the impurities contained in the fibre that were not eliminated in the previous cleaning operations;
Selecting the fibres on the basis of length, removing the shortest ones;
Removal of neps;
Parallelising and stretching of the fibre;
Transformation of the lap into a sliver, therefore into a regular mass of untwisted fibre.
Fig.A Section view of the card with hopper
The carding operation is carried out by the card, a machine that in practice is a system of rotating organs, mobile and fixed flats, covered with steel spikes that go by the name of wiring. It is a good idea to know what the wiring and its functions are before going onto a description of the card.
Wiring and Clothing
There are different types of cylinder wiring, in particular:
rigid wiring, for rotating parts;
elastic clothing, for mobile flats;
clothing for fixed flats.
The most common on the machine are the wiring type. They are made up of a steel wire with sharp cutting teeth, the sawtooth like edge of the wiring is hardened in order to better resist wear caused by the abrasive action of the fibres. The base of the wiring is thicker than the toothed parts, both to guarantee support to keep the teeth in a vertical position, as well as to prevent lateral contact between the teeth and to permit the necessary momentary penetration of fibre into the wiring.
The sizes of the teeth vary notably and depend on how compact the material is, on the quantity and on the fineness of the fibre. The parameters which permit one type of wiring to be distinguished from another are:
Concentration, meaning the number of teeth in a square inch of the wiring (for the various devices of the card the concentration is different and is strictly linked to the type of fibre used; for fine fibre, for example, wiring with a high concentration is used);
The height of the teeth, which can vary according to the wired element;
The angle between the teeth and the base in a longitudinal sense.
It is a known fact that a wired element moves in:
a positive way when it moves in the same direction as the inclination of the teeth;
a negative way when it moves in the opposite direction to the inclination of the teeth
The fibrous material is found between the two wired elements which, by moving, act on the fibre in an alternate manner: first they trap it then they remove it. Depending on the layout of the teeth, the direction travelled and the speed of the devices, two conditions are possible, called:
Carding position which is obtained when the teeth of the wired elements are inclined in an opposite direction and their movement occurs with a certain speed and in a direction that permits a reciprocal grasp of the fibre and then the disentangling of the neps and elimination of trash and dust.
Position of cleaning or brushing , which is obtained, on the other hand, when the devices have converging teeth and their movement occurs with such a speed and in such a direction to permit the passing of fibre from one organ to another.
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