P. R. Lord

The Mechanics of Friction-spinning

Friction-spinning of staple-fibre yarns involves the supply of separated fibres to a torque zone within a shear field and the removal of yarn from it. The shear field is created by the movement of one or more solids of revolution. Usually, two parallel cylinders rotating in the same direction and in close proximity are used to create the desired shear field in the vicinity of the nip line. At least one of the cylinders is perforated, and air-flow into the cylinder causes force reactions to be generated between the yarn and the cylinders. The solid surfaces move in opposite directions in the vicinity of the yarn, and the drag forces acting on the yarn create a torque. The magnitude and pattern of the air-flow strongly affect the way in which fibres become assembled on the forming yarn, as well as the torque produced. The structure and performance of the yarn are very dependent on these factors. The yarn from first-generation machines is weak because of poor fibre structure, and this paper sets out some of ...

Assessment of the Tactile Properties of Woven Fabrics Made from Various Types of Staple-fibre Yarn

An investigation is described in which ring-spun, rotor-spun, and friction-spun yarns were used as weft in a series of woven fabrics and measurements were made of the tactile properties of the fabrics by manual and instrumental assessment in an attempt to establish a correlation between measured parameters and perceived properties. Reasonable correlation was found between human evaluation and surface-roughness properties over a wide range of thread-spacings. Correlations were also observed between surface roughness and many of the perceptions of the panel of assessors. It seemed likely that there were interactions and many of the perceptions were based on several attributes of the fabrics rather than single ones.

Fluid-flow Phenomena in Friction Spinning

An investigation is reported in which dynamic similarity was used to calculate a large–scale water analogue of a friction–spinning torque system that operated with water as the fluid. Reynolds numbers similar to those in an actual machine were used, and the model was geometrically similar. The results showed that leakage flows in the annuli between the rotating perforated cylinders and the stationary inner suction cylinders were very important, as were the relative positions of the suction slots in these inner cylinders. Yarn diameter and rotational speed were also important. With a particular port positioning, it was possible to create cross–flows that could pass behind the yarn from one cylinder to the other. Such cross–flows may be important in carrying portions of fibre from the ingoing roller to the outgoing one and thus help wrap the fibre around the forming yarn end.

Fiber Assembly in Friction Spinning

Both classic and novel research methods were used to study a number of questions concerning the mechanisms involved with fiber assembly in friction open-end spinning of cotton yarns. The equipment used was a much-modified DREF-3 friction-spinning unit with replaced suction rolls and equipped with a comber-roll assembly from a Platt 881 rotor-spinning unit Reynolds-number simulation in a water medium provided a means of determining the source of flow instabilities in the vicinity of the nip. Considerable energy losses were found as a result of flow inefficiencies in the inner cylinders, and methods of improving the cylinder design were suggested. The use of short-duration flash techniques provided a means of determining fiber orientation prior to accumulation and assembly on the yarn tail. These techniques made it possible to photograph the yarn tail forming as well as the gradual tightening of the structure upstream of the original yarn-forming position. Determination of mechanisms of capture of the fiber...

The Measurement of Sliver Properties on the Drawframe

Monitoring applications on the drawframe usually involve the measurement of the linear density of the sliver. However, this measurement is imprecise and inadequate. In this work, variations in fiber grouping and fiber-group length extent were measured on the drawframe. The mass profile in the draft zone was obtained by using a high-speed television camera and analyzed by using image-processing. The mass-profile curve in the draft zone was shown to contain similar information to a Fibrogram beard. In order to obtain the fiber-group length extent, averaging the mass-profile curve over a short length of the strand was necessary to reduce the noise due to variations in the number of floating fibers and in the fiber grouping. The presence of fibers as groups in the sliver leads to a higher thickness irregularity for the strand. A study on the dimensions and the relative number of groups was carried out. The length of the fiber groups was found to be about 1.5 times the nominal fiber length and varied from brea...

12—SHORT FIBRES AND QUALITY CONTROL

In roller-drafting, short floating fibres can accelerate to the front-roller speed before the longer ones, and they tend to move in bunches. The bunches of short fibres are displaced longitudinally with respect to the longer fibres, and, if there is an uneven input blend, an uneven output strand is produced. The thick spots have a higher concentration of short fibres than elsewhere, and the thick spots tend to be distributed regularly over limited distances along the output strand. Furthermore, in the next drafting process, the extent of the new output irregularity is dependent on the input fibre-length distribution. Thus the new output strand contains pulses of irregularity in which bursts of quite intense drafting waves may be interspersed with relatively long lengths of good evenness. In yarn, end-breaks are more likely to occur during spinning as the sub-concentrations of short fibres press through and produce the localized unevennesses.

Dynamic Measurements of Mechanical Errors in Sliver-drawing

An investigation is reported in which the lifts of the roller necks of the upper of each of the sets of drafting rollers in a drawframe were measured. Data expressed in the frequency domain showed that roller errors could be clearly seen at the fundamental frequencies of the various rollers when the error and the measurements related to the same set of rollers. Some harmonics were also visible. When errors were in one set of rollers and the measurements were made down the fibre-flow line, the sharpness of the peaks was greatly reduced by drafting waves in the fibres flowing through the system. It was deduced that drafting waves dispersed the singular frequencies produced. An absolute encoder was used on a bottom roller to average out asynchronous signal components and random errors. The averaged data demonstrated the roller shape under dynamic conditions even when the error was small. It was possible to use a ratio technique to produce a virtual encoder for the top roller. At start-up, the viscoelastic pr...

Balloon Irregularities in Ring Spinning

If a ringframe could be run nearer the ideal conditions assumed in theory, a better operational efficiency and quality of product would be obtained. This paper examines some of the many types of deviation that occur in ring spinning. Some end-breaks are caused by predictable cyclic variations in force applied to the yarn, some are caused by weak points in the spinline, and some are caused by transient forces. The paper concentrates on these transients. They cause short-lived changes in yarn speed and geometry, which are associated with peaks in tension. The locus of elements of yarn near the vertex of the balloon can deviate greatly from the circular, and it is thought that periodic torque surges may be generated.

23—DEBLENDING IN ROLLER-DRAFTING

Roller-drafting causes fibre shear, and the consequential longitudinal migration of short fibres with respect to long ones leads to fibre-deblending. Furthermore, the drafting of a strand with a varying blend ratio along its length leads to variations in drafting-wave activity along its length. Thus, even with a perfectly autolevelled sliver, variations in blend become translated into irregularity in linear density in later processes. The textile material carries potential errors with it as it passes from one process to the next. Data presented in this paper show quasi-harmonic variations in blend and in fibre properties along the length of slivers, rovings, and yarns. The error wavelengths of the variations were similar to those found in the normal testing of linear density. There is thought to be a connexion.

5—THE TESTING OF STAPLE-FIBRE BUNDLES TO DETERMINE VARIABILITY IN FIBRE-BREAKING ELONGATION

Blend irregularities can be determined by several methods if there are two or more discrete blend components that are chemically different. The present paper deals with a method of measuring blend inhomogeneities where only a single type of fibre is involved. A fibre bundle with a very short gauge length under a constant rate of tensile extension does not break suddenly. As each individual fibre reaches its breaking elongation, the total load is reduced by one decrement as it breaks. In a perfect bundle of parallel fibres, the others are unaffected by the event. Thus it is possible to find the statistical distribution of breaking elongation within the bundle in a single pull with a testing machine. Practical bundles exhibit similar characteristics. Tests have shown that coefficients of variation, determined by such bundle tests, vary along the length of the textile strands in a periodic manner, and this applies to several sorts, of fibre.