Thread Tension

4 Stitching Parameters and Their Influence on the Fiher-Reinforced Polymer Composites 

The applied thread tension depends on the thread force being adjusted at the start of the stitching, so that knots are formed at the bottom of the laminate 

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The strength of the seam should be equal to that of the material it joins in order to have a balanced construction that will withstand the forces encountered during use (Nayak et al., 2010). The transverse strength of a seam is determined by a number of factors, such as stitch type, stitch density, thread strength, thread tension, needle size, and needle type. It will be observed that the seam failure in a garment can occur because of ... 

An increase in the values of these factors increases the fabric resistance to seam slippage. Seam slippage depends on weave, fabric raw material, type of seam, stitch density, and sewing thread tension. 

When a tensile load is applied to a fabric seam, it has to overcome two types of frictional forces. One is the inter-yam frictional forces within a fabric, and the other is the frictional force of the stitch assembly. The former is dependent upon the crimp, yam diameter, fiber content, and number of cross-over points. The latter, however, is dependent upon the fabric properties like fiber content, type of yam (spun or filament), thickness, lateral compression, cover factor (threads per cm), bending, shear, tensile and surface roughness, and coefficient of friction. It is also dependent upon the properties of the sewing thread like fiber content, diameter, coefficiait of Mction, initial modulus, and extensibility. All of these properties, together with the machine variables like needle and bobbin thread tension and the stitch length, make up the frictional force of the stitch assembly. Thus different combinations of these would be expected to provide different frictional resistance and hence different loads at which seam slippage may take place. 

The X-feed claims to sew with 35% lower thread tension (Stitchworld, 2012), which results in a flatter and pucker-free seam appearance, and the occurrence of ply slippage is also significantly lower in X-feed than in drop feed (Jana and Khan, 2014). 

Dimensional change of the sewing thread/tension pucker... 

This problem can be reduced by using lubricants or air cooling of the needle and sewing threads. Some sewing machine manufacturers provide devices for this purpose. A more straightforward solution is to reduce sewing spjeed and/or thread tension. 

When the needle thread loop is too loose, the joined fabric phes are not adequately held together, which may be acceptable in some situations (serging seams) and unacceptable in others (joining seams). If any of the interlacing spots of the threads do not match the pre-defined positions, there is an imbalance between the thread tensions. This will normally influence the seam s performance negatively, and should thus be avoided. 

Stitch distortion is a problem especially in knitted garments, which affects the size stability of the garments. In this case, the thread tension adjustment is not the cause of the problem, because the stitch shows balance before and aftCT the defect The distortion may have several causes, such as thread irregularity, improper handling by the operator, sharp speed variations, etc. Being an isolated occurrence, this kind of defect is often very difficult to detect. An isolated stitch distortion is shown in Figure 12.8. 

Thread breakage is more likely to occur at high speeds and when using higher thread tensions. Reducing these two factors certainly minimises the problem, but due to productivity or functional requirements it cannot always be done. 

Proper adjustment of the stitch length, sewing threads and needles, according to the type of fabric (structural jamming appears mainly in dense, lightweight fabrics) Correct adjustment of thread tensions Proper selection of the feeding system (on knits and stretch wovens, use differential feed and minimum of pressure-foot pressure)... 

Use of adequate lubricants or air coohng on the needles and sewing threads Reduction of sewing speed and thread tension... 

Skipped stitches Sewing thread tension use of adequate thread tensions to the... 

High sewing thread tension the machine s stitch formation... 

Thread-tension dial. Allows you to control the tension on the upper thread... 

The thread tension set during the stitching assists to improve the compaction and fixation of the reinforcing fiber bundles. Figure 5 shows the compaction instrument which is developed at the Institute for Composite Materials Ltd., and... 

Figure 6. Influence of thread tension on the compaction behavior of a dry lay-up based on CF-woven 5H satin, [0/90]4, polyester long fiber spun 73 tex, stitch length 2.5 mm, seam distance 40x40 mm, stitching direction 45 , presser-foot height such that the foot rests on...

Figure 11. Thread tension on-line data monitoring.

Figure 12. Thread tension control incorporated in a quality management (QM) tool for preform manufacturing.

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