METALLIC CARD CLOTHING
As Carding machine design improved in 1950's and 60's, it became apparent that card clothing was a limiting factor
Much time and effort was spent in the development of metallic card clothing.
There are two rules of carding
The fibre must enter the carding machine, be efficiently carded and taken from it in as little time as possible
The fibre must be under control from entry to exit
Control of fibres in a carding machine is the responsibilitgy of the card clothing
Following are the five types of clothings used in a Carding machine
CYLINDER WIRE: The main parameters of CYLINDER Card clothing
Tooth point dimensions
Shallowness of tooth depth reduces fibre loading and holds the fibre on the cylinder in the ideal position
under the carding action of the tops. The space a fibre needs within the cylinder wire depends upon
its Micronaire/denier value and staple length. ould have to be reduced.
The recent cylinder wires have a profile called "NO SPACE FOR LOADING PROFILE"(NSL). With this
new profile, the tooth depth is shallower than the standard one and the overall wire height is reudced
to 2mm , which eliminates the free blade in the wire. This free blade is responsible for fibre loading.
Once the fibre lodges betweent the free blade of two adjacent teeth it is difficult to remove it.Inorder
to eliminate the free blade, the wire is made with a larger rib width
Front angle not only affects the carding action but controls the lift of the fibre under the action
of centrifugal force. The higher the cylinder speed , the lower the angle for a given fibre. Different fibresM
have different co-efficients of friction values which also determine the front angle of the wire.
If the front angle is more, then it is insufficient to overcome the centrifugal lift of the fibre
created by cylinder speed. Therefore the fibre control is lost, this will result in increasing flat waste
and more neps in the sliver.
If the front angle is less, then it will hold the fibres and create excessive recyling within the carding
machine with resulting overcarding and therefore increased fibre damage and nep generation.
Lack of parallelisation, fibre damage, nep generation, more flat waste etc. etc., are all consequences
of the wrong choice of front angle.
Each fibre has a linear density determined by its diameter to length ratio. Fine fibres and long fibres
necessitates more control during the carding process. This control is obtained by selecting the
tooth pitch which gives the correct contact ratio of the number of teeth to fibre length.
Exceptionally short fibres too require more control, in this case , it is not because of the stiffness but
because it is more difficult to parallelise the fibres with an open tooth pitch giving a low contact ratio.
The rib thickness of the cylinder wire controls the carding "front" and thus the carding power.
Generally the finer the fibre, the finer the rib width. The number of points across the carding machine is
determined by the carding machine's design, production rate and the fibre dimensions. General trend is towards finer rib thicknesses, especially for high and very low production machines.
Rib thickness should be selected properly, if there are too many wire points across the machine for a
given cylinder speed, production rate and fibre fineness, "BLOCKAGE" takes place with disastrous results from the point of view of carding quality. In such cases, either the cylinder speed has to be increased or most likely the production rate has to be reduced to improve the sliver quality
The population of a wire is the product of the rib thickness and tooth pitch per unit area. The general rule
higher populations for higher production rates, but it is not true always. It depends upon other factors
like production rate, fineness, frictional properties etc.
The tooth point is important from a fibre penetration point of view. It also affects the maintenance and consistency of performance. Most of the recent cylinder wires have the smallest land or cut-to-point.
Sharp points penetrate the fibre more easily and thus reduce friction, which in turn reduces wear on the
wire and extends wire life.
Blade thickness affects the fibre penetration. The blade thickness is limited by practical considerations,but the finer the blade the better the penetration of fibres. Wires with thin blade thickness penetrate the more easily and thus reduce friction, which in turn reduces wear on the wire and extends wire life.
A lower back angle reduces fibre loading, but a higher value of back angle assists fibre penetration. Between the two extremes is an angle which facilitates both the reduction in loading and assists fibre penetration and at the same time gives the tooth sufficient strength to do the job for which it was designed.
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