S.P. Hersh

Simulation of Needle-Fabric Interactions in Sewing Operations

The nature of the forces involved when a sewing needle penetrates a fabric have been studied on an Instron in an attempt to identify some of the factors which influence the needle-fabric interaction leading to heat generation. The measurements were made at velocities three to four orders of magnitude lower than actual sewing velocities. Four major variables considered were needle velocity, needle diameter, needle surface finish, and number of fabric layers. The influence of these factors on the maximum penetration force and on the energy required to drive the needle into and out of fabric has been studied. All these factors and their interactions (except needle velocity in some cases) affect the maxi mum penetration force of the needle and the energy of penetration. The effect of needle velocity over the range covered, even when significant, was minor (of the order of about 10%). The needle diameter affects the maximum penetration force and energy of penetration to a much greater extent. They are found to increase at a greater than linear rate with in creasing needle diameter. In one fabric, these parameters increased with the third or fourth power of the diameter. Whereas certain special high-emissivity needle-surface finishes have been found to reduce temperatures of needles during sewing, more energy is expended when these needles pass through fabrics than is expended with regular-finished needles. In a series of exploratory experiments, no differences in behavior were observed for a variety of needle-point shapes (twist point, diamond point, and standard ball point) or for tests using sewing threads compared with tests made without sewing threads. The bulged eye needle was effective in reducing energy buildup, compared with ball-point needles. The maximum penetration force and energy of penetration were found to increase linearly with increasing numbers of fabric layers. Wherever feasible, attempts are made to relate observed penetration energy measurements with expected needle heating characteristics and with results reported in the literature.

Needle Heating during High-Speed Sewing12

A review of the literature and extensive field interviews have been conducted on the subject of needle heating in high-speed sewing. As a result of this investigation, a survey of the current state of the art and knowledge available in the field has been completed and is presented in the following categories: (1) the nature of the problem and the difficulties which arise in commercial operations; (2) quantitative methods of measuring needle temperatures; (3) the influence of machine factors such as sewing speed, length of sewing time, and needle design on the heat generated during sewing; (4) the influence of material factors such as fabric structure and finish, layers of fabric, and sewing thread on needle heating; (5) techniques for alleviating needle heating problems; and (6) the mechanism of generation and dissipation of heat in the sewing process. Some heretofore unpublished data are presented.

Chemical Composition of Cotton Dusts Part II : Analyses of Samples Collected in a Model Card Room

The ash and protein contents of Pneumafil (PN) trash samples collected in a model card room and of the aqueous extracts of these samples arc reported here. The average ash content of these samples is 12.5% (σ = 4.2%). The average ash content of the dried aqueous extracts of these samples is much higher than that of the raw samples (mean 36.9%, σ = 10.8%). The average protein content of these samples and their dried aqueous extracts are about the same (13.2 and 14.9%, respectively). Trash samples from cotton grown under dry, arid conditions tend to have relatively high inorganic contents. Steaming tends to reduce the inorganic fraction of both the raw samples and their dried aqueous extracts but has little effect on the protein content. Increasing the number of gin lint cleaning stages reduces the dust level in the card room but has little effect on the proximate chemical composition of the PN samples. The fraction of ash in the PN dust tends to increase as the grade of cotton improves. Respirable dust collected from an electrostatic precipitator and respirable dust separated from lint trash are shown to have very high inorganic contents (41.3 and 37.1%, respectively). The average ash content of five samples rollected on the vertical elutriator was 20.1%, a value close to the average ash content of leaf and bract samples.

Moisture Characteristics of Some Knit Fabrics Made From Blend Yarns 1

The moisture responses of plain jersey and 1 X 1 rib fabrics constructed from synthetic fiber-cotton blend yarns have been studied. The fabric responses include water vapor transmission, moisture imbibition, moisture regain, and air permeability. Measurements of the fabric strength and shrinkage are also reported. The fabrics were constructed from 24/1 yarn of cotton-nylon, cotton-polyester, and cotton-acrylic blends in 100/0, 80/20, 60/40, 50/50, 40/60, 20/80, and 0/100 percent. A simplified technique for measuring water vapor transmission through fabric was used to provide a means for com paring the blends. It was found that water vapor is transmitted through single thicknesses of plain jersey fabric faster than through equivalent rib fabrics, and significant increases in water vapor transmission occur as the synthetic com ponent of the cotton-synthetic blend is increased. Even greater relative increases in air permeability were observed with increasing synthetic-fiber content. It was, therefore, concluded that moisture vapor flow through knit fabric occurs almost entirely through the fabric interstices, and the hygroscopic nature of the fibers in the blend plays a minor roll in the moisture vapor transfer through fabric. Thus, it can be expected that garment comfort, at least as correlated with water and air permeability, should not be adversely affected by the addition of synthetic fibers to the blend. Moisture regain, moisture imbibition, and shrinkage decreased as the synthetic fiber content of the fabrics increased.

Evaluation of Cleaning and Washing Processes for Cotton Fiber Part III: Carding and Dust Levels 1

Washing decreases the dust concentrations emitted from cotton processed in a model card room. The higher the washing and rinsing temperatures, the greater the reduction. In 5 of 10 trials, the amount of dust added to the background concentration in the card room while processing washed cotton was 0.05 mg/m3 or less. The rate at which cotton can be carded is reduced by wash ing. Processability is improved by insuring that the cotton is not wet while carding, using a static eliminator at the doffer crush rolls, increasing the relative humidity of the ambient atmosphere, and using a wire-wound feed roll rather than a fluted feed roll at the lickerin. Processability is also im proved by applying a finish to the washed cotton. The effects of mechanically precleaning and washing the cotton on Shirley Analyser trash analyses were examined, but attempts to predict dust concentrations from these measurements were not successful.

Maximum Fiber-Packing Density in Electrostatic Flocking

The maximum fiber-packing density expected in electrostatic flocking or any process involving random impingement of fibers onto a substrate has been calculated using a Monte Carlo technique. This value was determined by generating random numbers to select the coordinates of points representing the location of fiber centers on a circular target, subject to the restriction that no two fibers overlap. The process was terminated after a specified number of trials failed to locate an unoccupied space large enough to accommodate an additional fiber. The fiber-packing density was then computed in terms of the number of fibers per unit area n and the fraction of total available space on the target occupied by fibers F. It is found that F is independent of fiber diameter and has a value of 0.531 with a standard deviation of 0.0038. This value (∼53% of available space occupied) is considerably less than the value of 90.7% expected for close-packed circles but much greater than those reported experimen tally.

Energy-Dispersive X-Ray Fluorescence Analysis of Dust Collected Using a Vertical Elutriator Cotton Dust Sampler

X-ray fluorescence (XRF) spectroscopy has been used to analyze trace-element concentrations in cotton dusts collected on vertical elutriator filter media. Twenty-three samples collected from ten bales of cotton processed in a model cardroom have been analyzed. The major elements in the dust detected by the XRF technique are Al, Si, P, S, Cl, K, Ca, Mn, Fe, Cu, Zn, and Ba. The XRF method has been shown to give reproducible results and may be used to show differences between airborne dusts in a cardroom. Similar analyses are reported of cotton dusts collected on an areal sampler.

The Effect of Cotton Grade, Variety, and Growing Location on the Dust Generated in a Model Card Room

The influence of cotton grade, growing location, and genetic variety on the amount of cotton dust generated while processing cotton in a model card room has been examined. Even though data collected from 140 bales were considered, an analysis of variance based on a standard linear additive model could not be made because the samples available were unbalanced with respect to the inde pendent variables. The data were therefore evaluated by determining whether any deviations in the amount of dust emitted by individual bales from that of the average measured on all bales of the same grade of cotton could be attributed to growing location and/or variety. In general, the results suggest that cottons grown in the eastern U. S. A. produce somewhat less dust in the card room for a given grade of cotton than the U. S. A. average; and cottons grown in the arid areas of the west, somewhat more than average. Quantitatively, deviations from the U. S. A. average ranged from -146 to +145 μg/m3, a spread that is almost inconsequential when compared with the 3.5 times greater range observed among bales of a single grade of cotton grown in a single state. Variety effects were even smaller than state effects. Many factors other than growing location and variety were observed to have large effects on the measured dust concentrations.

The Influence of Processing Variables on the Properties of Flocked Fabrics

The effect of 16 variables of the dc electrostatic flocking process has been investigated in a two-level factorial screening experiment. Properties examined include mass and number of fibers sifted, mass and number of fibers flocked, percent of available fibers flocked, percent of theoretical maximum packing density, and abrasion resistance of flocked fabric. The 16 independent variables included six machine variables (voltage, electrode separation, sifter speed and screen mesh, flocking time, and substrate vibration), three flock variables (fiber type, length, and denier), five adhesive variables (adhesive type, concentration, viscosity, thickness, and drying conditions), ambient humidity, and substrate (polyethylene film and aluminum foil). Only the three flock variables and the voltage were found to influence the properties of the flocked fabric. The quantity of fiber sifted was affected by the fiber denier and length and by the sifter speed, but the sifter speed did not influence the flocked fabric. The packing density of the flock on the fabrics ranged from 0.4 percent of the theoretical maximum (for low denier, long length nylon fiber flocked in a low electric field) to 13 percent (for high denier, short length nylon flocked in a high electric field). Of all the variables studied, fiber length had the greatest effect on the flocking properties; increasing the fiber length decreased the number of fibers sifted, number of fibers flocked, and percent of maximum flock density.

Cotton Dust Control Studies: Effects of Engineering Controls, Washing Cotton, and Additives

This paper reviews some of the cotton dust control technology studies carried out a North Carolina State University since 1973. The purpose of the investigations has been to examine means for reducing respirable dust emission during carding, as well as to evaluate the relative merits of various dust-sampling devices. Typically the results indicate that introducing lint cleaners at the gin reduces dust emission, while the use of two types of feeder/cleaners examined does not. Steaming of ginned cotton reduces the dust emission, while storage of ginned cotton (steamed or unsteamed) beyond three months increases it. Air-cleaning devices such as properly-designed electrostatic precipitators can be quite effective in diminishing the dust concentration in the card room. Similarly, washing of cotton, the use of cleaning devices such as COTTONMASTER®, or the addition of dust suppressants to cotton reduces the emission during subsequent carding. While some of the studies are complete, others are in progress.