33—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART II: CYLINDRICAL SNARLING

An account is given of an experimental investigation of the cylindrical snarling of highly twisted monofilaments.

The theory underlying cylindrical snarling is set out, and an expression is derived for calculating the critical twist level at which normal snarling will be replaced by cylindrical snarling. Experiments on rubber filaments are described, and it is shown that there is good agreement between the theoretical and experimental results. Further experiments, in which the specimen was allowed to contract freely or forced into other forms, are also described.

It is shown from these experiments that it is difficult to establish the true equilibrium behaviour, since the situation appears to be dominated by frictional effects or by direct barriers to relative movement.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

41—THE RETRACTION AND STRETCH OF WRAPPED ELASTOMERIC-FIBRE CORE YARNS

Equations are given that relate the structure of spirally wrapped elastomeric-fibre core yams to their stretch properties. The model employed improves upon previous ones by considering the effect of covering-yarn diameter. Graphs are given that facilitate the use of the theory for manufacturing purposes.

A comparison with available experimental data indicates an improved agreement between actual and predicted values of retraction in the most important case, where the input and output yarn lengths are measured. It is expected that the improved theory given here will show to much greater advantage with the present commercial fine-core wrapped structures.

In the special case where the wrapping or covering yarns have very low twist, the basic theory is inadequate. Modifications to account for compression of the cover yarn are accordingly included to enable an approximate relationship between yarn structure and stretch to be obtained in this case.     

The Air-flow Diameter of Wool Tops: The Effect of Coefficient of Variation

The fleeces from a single flock are sorted into visually fine and coarse ‘lines’ by the wool classer on the basis of staple-crimp frequency. The differences between the measured mean fibre diameters of these lines can be predicted from the variation in fibre diameter and staple-crimp frequency. The theory offers a simple explanation for the small differences observed in the mean diameters of fine and coarse lines from the same flock.     

IP网络业务联合认证技术 第1讲IP网络业务安全认证系统发展现状及相关问题分析

IP网络天然的不安全性促使IP网络业务提供者采用各种安全认证技术来保证其所提供的业务的安全性。本文主要介绍IP网络业务安全认证系统发展情况及存在的相关问题。     

Influence of die geometry on undershooting phenomenon and bending phenomenon in cold extrusion of steel tube

Abstract

Numerical and experimental investigations were carried out on the excessive decrease in outside diameter occurring on a tube cold extruded through two conventional types of die, a taper die and an R die. Wide ranges of the parameters of die profile were adopted in order to precisely examine the influence of die geometry on the undershooting phenomenon, and appropriate die geometries for the suppression of the undershooting phenomenon were shown. The R die is more practical in the manufacturing operation compared with the taper die. Bending was also investigated, and it was shown that the bending intensity becomes lower as the undershooting intensity decreases. However, it is not necessary to suppress bending sufficiently, even if the undershooting is suppressed to zero in the case of adopting the ordinary types of die – there seemed to be another governing factor for the occurrence of bending and this is a remaining problem.     

6—STAPLE-LENGTH VARIATION IN GREASY WOOL

Estimates are reported for the variance of staple length within bales for each of 33 bales taken from separate sale lots of skirted classed merino wool. These variances range from 0.59 to 2.90 cm², with an average of 1.53 cm². Variances between bales, within sale lots of merino wool, were small and not significant. Within-bale variances for comeback and crossbred fleece ranged from 0.61 to 4.62 cm², with an average of 2.64 cm². The highest variances occurred within lots of broken and pieces, these ranging from 1.83 to 6.33, with an average of 3.44 cm².

Evidence is presented which suggests that the removal of short wool during skirting makes the largest contribution to staple-length uniformity, classing having a secondary effect. Of the variation occurring within a bale, about half is found within fleeces and half between fleeces.     

9—THE PROPERTIES OF AIR-TEXTURED CONTINUOUS FILAMENT YARNS

A processing programme is outlined in which yarn pre-twist, applied air-pressure, and supply-yarn overfeed are systematically varied in the air-jet bulking process to investigate their effects on air-textured nylon 6.6 continuous-filament yarns.

Optical magnification of the air-textured yarns enables the average loop sizes and frequencies to be measured. The experimental results are shown to be in general agreement with a suggested mechanism of the process, which argues that the initial filament twist in the parent yarn redistributes itself as snarled loops and that the overfed yarn contributes to the size of such loops; the deflexion of filaments by air-drag forces is also shown to make a contribution to a looping effect, which can be estimated theoretically. Increasing the yam overfeed increases both the loop size and the loop frequency. Increasing the yam pre-twist decreases the loop size and increases the loop frequency. Increasing the air-pressure also decreases the loop size and increases the loop frequency. Experimental and theoretical results are in general agreement.

As would be expected, the only processing condition that effects a change in linear density is the overfeed, but all the processing conditions that have an effect on loop dimensions also have an effect on the change in volume, i.e., on the physical bulk. Overfeed is the greatest single contributor to physical bulk, since both loop size and loop frequency increase with overfeed, occluded air spaces being thereby created in yarn and fabric form; conversely, with varying twists and air-pressures, the effects of decreasing loop size and increasing loop frequency are to some extent self-balancing in their contribution to physical bulk.

It is shown how the various processing parameters affect the stability of air-textured yarns. Textured yams produced from parent yarns possessing small amounts of pre-twist have a high instability because of the lack of binding twist for securing the entangled structure. Increasing the overfeed greatly increases the number and size of loops, and this causes greater instability. Increases in the applied air-pressure also increase the yarn instability. Two new mechanical techniques have been devised to measure the yarn instability, and these have been found to be greatly superior to the stability-testing apparatus normally used, which has serious defects from the viewpoint of accuracy.

The tenacity of the air-textured yarns tends to decrease for increasing values of all the main processing variables considered. Increasing the yarn pre-twist tends to reduce the percentage elongation at break, but independent increases in the supply-yarn overfeed and the applied air-pressure both tend to increase this characteristic. These results are interpreted in the light of the bulking mechanism previously postulated.     

30—YARN HAIRINESS: A SURVEY OF RECENT LITERATURE AND A DESCRIPTION OF A NEW INSTRUMENT FOR MEASURING YARN HAIRINESS

This paper is intended to supplement one published in 1966 containing a survey of the literature on yarn hairiness, and the review of the literature is brought up-to-date at the time of writing.

A new electronic instrument for measuring yarn hairiness is outlined. This apparatus enables three parameters to be obtained directly and simultaneously, these being hairiness, hair length, and yarn diameter.