Examining wear behaviour of latch needles by SEM stereoscopy

Dilli örme iğnelerindeki aşınmaların SEM stereoskopi yöntemiyle incelenmesi

Abstract

In this study, the wear occurred inside the latch needle hook was examined empirically to be able to explain how they were affected by the type of yarns. The wear of the needle hooks was represented numerically. Scanning electron microscope stereoscopy (SEM), which is a method of characterizing the surface topography by the application of computer image analysis to SEM images (stereoscopic pairs), was used for the evaluation of the needle surfaces. The average surface roughness parameter (Ra) was utilized for investigating the wear inside the needle hooks. To aid the investigation of the wear inside the latch needle hooks which caused by the yarn contact during the knitting production, a set of controlled test production was carried out. Mayer & Cie. with 14 systems, 14 Fayn-20 Gauge interlock knitting machine (2*876 needles) was employed for the fabric production. The production was realized under the commercial production conditions in terms of relative humidity and temperature. In order to examine the wear states of the needle hooks four different yarn types (100% cotton ring, 100% cotton OErotor, 100% viscose ring and 100% polyester ring) were chosen for the test productions. The knitting period for each production was determined to be five days (120 hours). The machine parameters, such as machine speed, yarn input tension and fabric takedown tension, were stabilized during all productions. At the end of the each knitting period, the needles taken from the same part of the needle bed were replaced with the new ones before starting to knit with the next yarn type. A challenging problem was the characterization of the surface topography of the worn needle surfaces. Currently available methods, such as laser confocal microscopy, phase shift interferometry and atomic force microscopy exhibit severe limitation regarding their applications to the acquisition of 3-D surface topography data. Therefore SEM stereoscopy was preferred to accurately recreate a 3-D image of the surfaces. Two stereoscopic images were taken by tilting the specimen holder from +6° to -6°. All images which have a resolution of 1024*760 pixels, 256 grey levels were taken with a Zeiss Supra 50VP SEM. For a comparative study regarding the differences in topography of the hook surfaces numerically, stereoscopic SEM images, acquired from the inner parts of the needle hooks were used for the reconstruction surfaces in 3D by means of image analyzing software. SEM images were also displayed in anaglyph mode. By viewing with anaglyph glasses, observer can get 3D impression of the surfaces. In addition to this, the topographic information and the average roughness parameter of the needle surfaces were measured by means of the image analysing software. In order to evaluate the change in topographical texture and surface roughness, the unused needles and the needles knitted with different yarns were compared with their SEM images and also their measured Ra values. For this purpose, two sample t-test was performed between the Ra values of the needles, knitted with four different yarn types, and the unused needle samples. Two sample t-test showed that there were differences between the Ra values, which means that the knitting period (five days) was found to be enough to wear off the surface of the needle hooks. After examining the SEM images and Ra values, the wear of the surface of the needle hooks were affected differently by the yarn types. Finally, the amount of wear formed during the knitting process at the inner surfaces of the latch needle hooks is affected by the type of yarns. After examining the Ra values and SEM images of those surfaces, it can be said that 100% cotton ring yarn and 100 % viscose ring yarn caused similar impact on the needle hook surfaces while 100 % cotton OE-rotor and 100 % polyester yarns showed different effect on the surfaces that means moving yarns on the needle hooks cause some chances on the texture of the surfaces. Furthermore, SEM stereoscopy method used for the reconstruction of the needle surface in 3D and getting the topographical information from those images, was suggested to compare the wear differences between the surfaces of the needles by means of roughness parameters. As a result, SEM stereoscopy could be used to understand the wear mechanism of the surfaces of needles.

Özet

Bu çalışmada, SEM stereoskopi görüntüleri ve yüzey pürüzlülük parametreleri kullanılarak, örme bölgesindeki iplik temasından dolayı iğnelerinin kanca kısmında meydana gelen aşınmalar incelenmiştir. İğnelerdeki aşınmaları sayısal olarak gösterebilmek ve belirlenen makine parametresinde, iplik kalitelerine bağlı olarak açıklayabilmek için bir seri kontrollü test üretimi gerçekleştirilmiştir. Hem her iplik kalitesine ait üretimi temsil eden iğneler, hem de kullanılmamış iğne yüzeyleri SEM’de incelenmiştir. İğnelerin kanca iç yüzeyinden alınan stereoskopik SEM görüntüleri, görüntü işleme yazılımı vasıtasıyla üç boyutlu hale getirilmiştir. Oluşturulan üç boyutlu yüzeylerden topografik bilgiler alınarak, yüzey pürüzlülük ölçümleri gerçekleştirilmiştir. İğne yüzeylerinin karşılaştırılmasında, “Ra” ortalama yüzey pürüzlülük parametresi kullanılmıştır. Sonuçlar istatistiksel olarak değerlendirilmiştir. Yapılan t-testi sonucunda kullanılan iğneler ile kullanılmamış iğnelerin yüzeyleri arasında fark olduğu belirlenmiştir. Kullanılan iğnelere ait SEM görüntüleri ve Ra ortalama pürüzlülük değerlerinin bir arada incelenmesi ile aralarındaki ilişki irdelenmiştir. Çalışmanın sonunda, hem üç boyutlu iğne yüzeyinin oluşturulmasında, hem de bu görüntülerden topografik bilginin elde edilmesinde kullanılan ve şimdiye kadar tekstil makinelerine ait malzeme yüzeyi değerlendirmesinde uygulaması görülmemiş olan SEM stereoskopi yöntemi, iğne aşınma davranışını açıklamada kullanılabilir bir yöntem olarak önerilmektedir. Böylece, SEM stereoskopi yöntemiyle elde edilen Ra ölçümlerinin mikron boyutlardaki aşınmaların değerlendirmesinde kullanılabilecek alternatif bir yöntem olduğu gösterilmiştir. Ayrıca iplik kalitelerinin kullanılan iğnelerin aşınmalarında farklı etkiler gösterdiği de belirlenmiştir.