Abstract
The one-dimensional characteristic of yarn has resulted in very little attention being given to the uniformity of carded web in the cross machine direction. The development of nonwovens has prompted researchers to reconsider the importance of cross machine uniformity in determining the total uniformity of the carded web. It is therefore important to develop manual and online techniques to quantify cross machine uniformity at both the input and output of the card.
At the card input, uniformity is taken as representing both mass and openness characteristics of the feed matt. While at the card output, there are many available techniques that allow the on-line measurement of the mass uniformity of the carded web, determination of uniformity at the input level is more difficult. The approach that was taken was to use an off-line technique to find the mass and openness of the feed matt at different locations across the card.
While traditionally mass as a property has been given a lot of importance, much less attention has been given to the concept of openness. This is due in part to the difficulty in quantifying openness. Openness is believed to have great significance in determining the overall quality of the carded web, especially with regard to the formation of neps. In order to make the concept of openness more clear, it was found necessary to develop a way of quantifying it. This was done by performing a compression test on the feed matt, and then fitting the compression data with an exponential curve. The coefficient of the exponent was used to represent openness. This approach was used to find the effect of the feed roller (pin type) on cross machine uniformity. It was found that the squeezing of the feed roller did not have an effect in redistributing the mass of the feed matt, but did have an effect in changing the openness of the feed matt.
Because of the difficulty involved in the handling of the feed matt, a newly developed technique is suggested to characterize openness. While this method still relies on the compression characteristics of the feed matt, it is more appropriate because it is performed on-line. Preliminary results are reported. It was found that thickness measurement under carefully selected pressure value could be used to characterize openness precisely.