Combing brings about the following changes in fibre properties:

The first three beneficial contributions of combing will result in a reduction of the irregularity of the combed yarn, and therefore, in an increase in the CSP of the combed yarn.

Combing also endows the sliver with two other advantages: an improvement in the alignment of fibres within the sliver; reduction in the number of hooked fibres in the sliver, and in the extent of fibre hooks. These additional beneficial contributions of combing also result in a reduction of yarn irregularity, and therefore, in a further increase in yarn CSP.

We now recall another beneficial contribution of combing to yarn tenacity, which has been pointed out by Lord (8) “……. it is hardly surprising to find that, for carded yarns, the bundle strength measured at zero test length provides information less useful than measurements at 1/8-in. The increased regularity and parallelization of fibre arrangements in combed yarns suggests a decrease in effective length of yarn element –that breaks in yarn tenacity testing -- a feature which may also occur in doubling when fibres are brought into more intimate contact with each other. For such material the best test length for fibre-bundle strength determination may be one closer to zero than that found suitable for the looser, carded yarns.” 

One method of using The General Equation to estimate combed yarn CSP comes to mind. This is to test the combed sliver for fibre characteristics, and then substitute these values in The General Equation for carded yarns. This method, however, will take into account only one aspect of the contribution of combing towards the increase in yarn CSP. We will still have to modify the equation to take account of the effects of improved fibre parallelization, reduction in fibre-hooks, and any reduction in the length of the yarn-element that breaks in tenacity test of yarn, as postulated by Lord. Preliminary attempts showed that this approach could possibly be successful.

In other words the compounded fibre parameters that we constructed for estimating the fibre-slippage fraction and the irregularity fraction stand extrapolation for combed sliver.

In practice, at the time taking the decision as to whether to buy the lot of cotton on offer or not, we will, obviously, not have fibre-tests on combed sliver. We should, therefore, be able to predict combed-yarn CSP from bale-cotton fibre-tests. In other words, what we need for combed-yarns is a prediction equation that has been so constructed that it will give estimates of combed yarn CSP on substitution of bale-cotton fibre-tests. Surprisingly, we have been able to derive such an equation.

The Modified Equation for combed yarns at near about optimum T. M. has been derived by taking advantage of some practical observations:

Furthermore, one would expect the factor, which gives the ratio of combed to carded yarn CSP, to be dependent upon the fibre-length distribution of the cotton.

In order to formulate the equation we should have data on carded and combed yarns spun from cottons of known fibre characteristics. The cottons should cover a wide range of fibre properties. We followed a short-cut to collect such data: we combed the card slivers from the experiment in which one long and fine cotton, and another short and coarse cotton were spun to yarns in isolation as well as in three mixings of differing proportions; we prepared combed slivers at 10% and 18% noil extractions; we spun each combed sliver to NE 30 at T.M. of 4.6, and NE 40 at T.M. of 4.2.

Table I –10 -i shows that this equation gives very accurate estimates of the CSP of combed yarns, at the two noil-extraction levels and for the two counts. This is so for both the long and fine cotton and for the short and coarse cotton, and for the three mixings.

We must clarify a point here. The ratio of combed yarn CSP to carded yarn CSP, which can be calculated for any cotton from the equations, should tend to unity with increasing yarn count. This is found to be so in the case of VL cotton, but the ratio becomes less than unity for G11 cotton beyond NE = 90 or so. Obviously, this is because we have derived the equation for combed yarns from data on just two yarn-counts. More work is required to fine-tune this equation.

We can conclude that The General Equation can be modified to get estimates of CSP of combed yarns at near optimum T.M.  from fibre-test data on bale-cotton.

Table I –10 -i  Accuracy Of Estimates Of CSP Of Combed Yarns

NOTE: we spun only NE 30 yarn from carded slivers, but both NE 30 and NE 40 yarns from the combed slivers. % ERR: % error in CS estimate