Carded ring spinning is employed for coarser yarns (up to Ne 40) and makes use of less valuable cotton types in terms of fibre length, diameter and cleaning degree.
After one or two drawing frame passages, the sliver coming from the cards is laid into cans which feed the roving frame (Fig. 5). This machine has the purpose of reducing through draft the weight of the sliver, forming a roving which receives a certain twist by a flyer system. This roving is wound onto bobbins suited to feed the ring frame.
The roving frame can be equipped with a manual doffing, in which case the bobbins are positioned on trolleys and carried to the spinning room.
Alternatively the roving frames offer, now quite frequently, automatic linkage systems between the roving frame and the spinning frames. The bobbins are laid by this system on a storage line in front of the spinning frame.
The machine is equipped with automatic cleaning and suction systems of the broken rovings. The next machine is the ring spinning frame (Fig. 6). The roving coming from the bobbin of the roving frame is drawn up to 50 times. Fibres up to 60 mm length can be processed.
The drawn and parallel fibres coming out of the draft unit are imparted a twist through the ring-traveller system.
Special systems have been worked out, which at the delivery of the draft unit improve the control on the fibres and prevent the edge fibres from moving with their ends outwards, which would cause a certain hairiness to the yarn as well as a loss of tenacity. These developments offer following advantages:
· improve yarn quality and reduce hairiness, with ensuing advantages in the subsequent singeing and sizing operations
· increase yarn tenacity while leaving twist unvaried, or increase production, as it is possible to confer a lower twist while leaving tenacity unchanged.
The yarn thus obtained has the final dimensions and, through the fibre twist, attains the desired tenacity according also to the fibres used.
The yarn is wound on bobbins weighing about 50 to 100 grams. Bobbin removal from the ringframe is at present generally carried out by automatic doffing devices, as also the loading of the empty tubes, ready to be wound.
The bobbins can be discharged into containers which feed the following machines: the winders. The spinning frame can be also linked through automatic conveyor systems to the winders, a machine which we shall examine more in detail in the chapter concerning yarn finishing.
The spinning frame can produce a wide range of counts and handle both up to 60 mm long cotton and man-made fibres, with a wide range of ring diameters, depending on the count being processed. Spindle speed can attain up to 25.000 rpm. The spindle can be operated either by tangential drive through a single belt for each side of the machine, or by tangential drive divided into sections of 48 spindles each and a single shaft along the machine.
At the moment the single motor systems are too expensive, even if they have inferior energy consumption and are less noisy.
