Search

A model of loop formation in the knitting zone of a non-linear weft-knitting system is described. The yarn tensions developed in this zone are analysed for the condition of negative yarn-feeding only. Detailed geometries of the yarn configuration in the initial stages of loop formation are proposed, to allow for accurate predictions of maximum yarn-knitting tensions. [ABSTRACT FROM AUTHOR]

The dynamics of a latch needle travelling with constant horizontal velocity through a symmetrical non-linear knitting cam are analysed in detail. Equations to calculate R and S--the reaction forces between the needle butt and cam face and needle butt and cylinder wall, respectively--are set up for any possible needle-cam contact and the boundary constraints described that determine that contact. A hypothetical knitting situation is examined with the aid of a simple harmonic cam shape. [ABSTRACT FROM AUTHOR]

A model of loop formation within the knitting zone of a non-linear cam system when positive-feed control is used is proposed. This model is found to simplify the analyses previously developed for negative feeding systems. [ABSTRACT FROM AUTHOR]

The design of prototype non-linear-cam profiles having simple-harmonic-motion characteristics is described in detail. Experiments are described in which the mechanical and textile performance of a single-jersey weft-knitting machine equipped with these cams was assessed at horizontal needle speeds of up to 200 cm/sec (i.e., approximately twice the commercial operating speeds of conventional linear-cam systems) in knitting poor-quality spun yarns. These tests proved that non-linear cam shapes can be successfully incorporated into the design of new machinery. [ABSTRACT FROM AUTHOR]

The theoretical model of high-speed non-linear-cam weft-knitting dynamics is compared with experimental tests on a multi-feeder machine equipped with prototype non-linear cams, the variable input tension being used as a basis for comparison. Agreement between theory and experiment is good, which suggests that the model can be used as a means of predicting the mechanical and textile performance of high-speed knitting machinery. [ABSTRACT FROM AUTHOR]

Dimensional stability of cotton Punto-di-Roma double-jersey fabrics can be attained by either mechanical-relaxation techniques (consecutive laundering and tumble-drying cycles) or chemical treatments (fabric mercerization without tension). Both treatments cause large linear-dimensional changes (shrinkages) leading to the same final stable condition, that is, to a fixed structural-knitted-cell configuration, categorized by unique values of ucand uw. Although, for all practical purposes, the ultimate u-parameters are close to constants, uw is not entirely independent of fabric tightness (K)nor uc of fibre type. They are very similar to those parameters found for wool fabrics prevented from felting. Geometrical fabric thickness is significantly dependent on both the fabric tightness and fibre type. Fabric stabilization is also induced by dry-cleaning (consecutive cycles in perchtoroethylene), but the final uc(DC)-parameter is not the same as that found after mechanical or chemical relaxation. The mean uw(DC)-parameter is similar only at the mean of the practical K-range. Like the plain-jersey structure, it seems that the stable double-jersey fabric made from hydrophilic yarns occurs when yarn-bulking leads to a completely 'jammed' structure. [ABSTRACT FROM AUTHOR]

Dimensional stability in cotton plain-jersey fabrics can be attained by either mechanical-relaxation techniques (consecutive laundering and tumble-drying cycles) or chemical treatments (fabric mercerization without tension). Both treatments cause large linear-dimensional changes (shrinkage) leading to the same final stable condition, that is, to a fixed loop configuration, categorized by unique values of ke and kw. Although, for all practical purposes, the ultimate k-values are close enough to constants, they are not entirely independent of fabric tightness (K) and some yarn variables. They are substantially the same as the values found for completely relaxed wool fabrics that have been treated to prevent felting. Geometrical fabric thickness and bulk density are significantly dependent on fabric tightness. Photographic evidence reveals that cotton yarns, like those of wool, bulk in the fabric during relaxation (both mechanical and chemical) to cause changes in 'cover'. It seems that the fixed loop configuration occurs when bulking leads to a completely "jammed' structure. [ABSTRACT FROM AUTHOR]

An account is given of a study in which the dimensional properties of five popular double-jersey structures, made from shrink-resist-treated worsted yarns and knitted under very different machine conditions at the optimum tightness factor (K = approximately 15), were investigated in various relaxed states, including the fully laundered condition, or the 'completely relaxed' stable state. In the initial experiment, the machine variables chosen--take-down tension, stretcher-board width, and dial height--were altered selectively to give the maximum distortion to the structural knitted cell (SKC) at the knitting stage. This experimental procedure was repeated in the second experiment at a variety of run-in ratios (but at the same average A: value) for three structures: Punto-di- Roma and Swiss and French double piqué. Whereas the machine variables markedly influence the linear (i.e., length and width) dimensions of all structures of the machine, and noticeably after steam relaxation, linear dimensions after further relaxation and laundering, although affected by the processing history of the fabric, are close to being equal within a structure. Thus, machine variables only temporarily distort the SKC: after correct relaxation, this distortion is, for all practical purposes, lost. However, the variable run-in ratio does affect the stable linear dimensions, even at a constant fabric tightness, although the magnitude of the effect of the run-in ratio on linear dimensions depends entirely on the structure. Consequently, the stable linear dimensions of double-jersey structures appear to be determined by two parameters: the structural-cell stitch length (Iu) and the run-in ratio. Speculations as to why the run-in ratio affects the stable linear dimensions are presented. [ABSTRACT FROM AUTHOR]

The information contained in this paper extends that given in a previous paper' where the effect of knitting stiffness on the bulk and dimensional properties of plain knit structures was detailed. In this paper, the effects of yarn collapse properties and yarn tension on the dimensions and bulk of the knitted fabric after relaxation are described. A method of measurement of yarn collapse is described, and the collapse measured in this way is compared with that in the knitted fabric calculated from the degree of fabric collapse. [ABSTRACT FROM AUTHOR]

A letter to the editor about the geometry of relaxed wool double-jersey structures is presented.

The dimensional behaviour of five non-jacquard wool double-jersey structures is investigated, both in relaxation (involving tumble-drying from the wet state) and in extensive laundering (Cubex washing followed by tumble-drying). Tumble-drying for 1 hr from the wet-fabric condition only approximates to the completely relaxed state. Some felting of untreated fabrics occurs, but the effect of tumble-drying on felting is very small. Adequately shrink-resist-treated fabrics cannot be considered completely relaxed even after two consecutive tumble-drying cycles of 1-hr duration. However, in general, this technique allows sufficient fabric relaxation for subsequent dimensional changes over extensive laundering cycles of treated fabrics to be compatible with domestic machine-washable tolerances. The felting rates of knitted wool fabrics in laundering from the "fully relaxed' condition of untreated fabrics are dependent on the cover factor and independent of fabric structure. Under no circumstances, however, can untreated double-jersey fabric be practically manufactured to such tight constructions that felting can be eliminated entirely. The linear dimensions of shrink-resist-treated fabrics in the fully laundered state are primarily dependent on the length of yarn in the structural knitted cell. In a semi-relaxed state, linear dimensions depend to a large extent on cover factor and the degree of distortion of the fabric [ABSTRACT FROM AUTHOR]

A geometrical model of the smallest repeating unit or structural knitted cell (SKC) of the fully relaxed 1 x 1 rib structure is proposed. This model, based on an elastica configuration, suggests that the dimensions of the SKC are independent of the yam flexural rigidity and yarn-deformative forces but are dependent on the ratio of structural-cell stitch length (lu) to yam diameter. Over the practical knitting range, however, this dependence is small. A series of four non-dimensional parameters, or u-values, is introduced to specify the dimensional properties of this structure. The average numerical values of these parameters are calculated. A comprehensive experimental analysis of fully relaxed 1 x 1 rib fabrics shows that the experimental w-values are close to those established theoretically. Full relaxation is obtained by tumble-drying the structures from a wet state for 1 hr at 70°C, this being followed by conditioning in a standard atmosphere. No felting is observed during this relaxation procedure. Empirical u-values of the fully relaxed state are found to be independent of most yam and machine variables. A small dependence on the machine-tightness factor (K) is noted, however. [ABSTRACT FROM AUTHOR]