Evenness of a fibre flow – Sliver, roving and yarn

During spinning, the process of transforming fibers into yarn, each machine produces fiber flows whose mass and/or volume regularity is essential to the final quality of the yarn. The parameters influencing this regularity must therefore be identified and then controlled in order to optimize the regularity of the yarn produced.

Fibers are discontinuous elements, as they have a finite length, from which the objective is to obtain a continuous and regular flow in terms of the number of fibers in the section. In this article, we will see that the fiber flow is not actually transported continuously but in bundles of fibers, called "clusters." The regularity of the flow depends on the size of these clusters, which must be as small as possible, and on the position of these clusters in relation to each other. The cluster theory will therefore be explained, along with the parameters that influence it. These parameters depend either on the fibers being processed, namely the distribution of fiber fineness and length, or on the machines used, such as their resolution (depending on the type of coating on the drafting cylinders). The models established by Martindale, Monfort, and Huberty, which formalize the role played by the above parameters on yarn evenness, will be presented, as well as the limit of evenness related to spinnability. In addition, the impact of the number of fiber flow reversals, directly related to the number of machines used in the spinning process, on the evenness of the fiber flows obtained will also be explained.

It should be noted that the regularity of a yarn also depends on other parameters that will not be taken into account in this article. Indeed, the law of doubling (itself dependent on the machine operating plan, i.e., the number of passes, the doubling of each of them, and the stretching) will not be discussed due to its practical and economic limitations. Also not considered will be the choice of machines (characteristics and operating condition of the machines), temperature and humidity conditions, natural (cotton wax and wool grease) or synthetic lubricants, the surface properties of the fibers (fiber friction), the choice of fiber blends, and the number of defects in the material or its state of cleanliness (presence of neps, flames, shells, straw, thistles, etc.).