A woollen card produces a number of rovings in readiness for spinning, by passage through a condenser.
Preparing for spinning
Prior to carding, an accurate amount of synthetic processing lubricant and water is mixed together and applied to the now blended and conditioned scoured loose wool. The purpose of the lubricant is to reduce fibre to metal friction and water reduces the formation of static. If either occurs during the carding process it is more than likely this will lead to excessive fibre breakages and reduce processing efficiency.
Typically, the amount of residual grease remaining on scoured wool is about 0.3% to 0.5% by weight, which is positive because wool grease in itself is a good processing lubricant. In the woollen system a significantly larger amount of synthetic processing lubricant is applied in comparison to the worsted system. This can range between 4% and 10% depending upon the actual components of the wool blend, for example Lambswool blends (4% to 5%) and for Shetland (8% to 10%). The purpose of adding higher quantities of processing lubricant is to reduce wastage by minimising the number of short fibres which fall out during the carding process and accumulate under the machine.
A woollen carding machine differs from that of a worsted one. A woollen card produces a number of rovings (thin strands of condensed sliver) in readiness for spinning, by passage through a device known as a condenser. Whereas a worsted card produces a thick card sliver which has to undergo combing to remove short fibres (noils) and residual contaminants such as burrs and seeds.
Although during the scouring process one of the aims is to minimise the degree of fibre entanglement, a certain degree invariably occurs. The result is that the scoured loose wool tends to form in clumps or flocks of entangled fibre.
The purpose and objectives of carding is to:
- Disentangle these clumps, by separating them into individual fibres
- Align the fibres more parallel to each other
- Further blend the fibres by intermixing, a woollen card usually comprises of two sections, with a device known as a cross-lapper or a scotch feed, located between them. The purpose of this device is to take the carded web, and turn it and lay it at an angle of 90 degrees, before feeding it into the second section of the card. This allows for more adequate blending of the wool, and eliminates side-to-side variations (from one side of the carding machine to the other).
- Remove as much of any remaining contaminants, such as vegetable matter (seeds, grass, burrs), as well as dirt and dust
- Formation of a homogeneous web in terms of weight per unit area
- Produce strands of condensed roving ready for spinning.
The card, or carding machine, comprises a series of horizontally aligned rotating rollers or cylinders which are covered in pins. Some of the rollers or cylinders rotate in different directions - clockwise and counter-clockwise - whilst others in the same directions. Some rotate at the same speed (RPM), whilst others rotate at different speeds. Some are of the same size in terms of diameter, whilst others vary. Similarly, the pins are the same on some in terms of density, length and orientation, whilst on others they vary.
These different configurations enable differing types of mechanical actions to be exerted on the wool as it passes through the carding machine in order to achieve the objectives as described above. These differing mechanical actions, in order as the wool passes through the machine, include:
- a combing action as the wool enters the machine, to assist in parallelisation of the fibres, and removal of short fibres
- a carding action to disentangle the clumps of fibres, and thoroughly inter-mix the fibres to form a homogenous blend
- cross-lapping action to further blend the wool and minimize any side-to-side variation.
- a stripping action, which works in conjunction with the carding action, assisting in further blending, parallelization of the fibres and contaminant removal
- a doffing action to produce a homogenous web of fibres of uniform mass
- a splitting and condensing action which separates the web, and by a rubbing action produces a number (dependent upon the width of the carding machine) into continuous lengths of roving ready for spinning.