Experimental stand for determing fabric compresability during sewing processes.

Ionescu, Irina ; Loghin, Maria Carmen ; Hanganu, Lucian Constantin 等

1. INTRODUCTION

During sewing process the characteristics of the fabrics have a great influence over the specificity of the machines used and the process parameters.

The presses foot (1, figure1) and feed dog (2) are inducing a normal compression on the fabric (3). This compression takes place when the feed dog teeth are passing the needle plate level (4), generating the decrease of the textile material (Buhler & Dorfler, 1996).

The fabric compression is made by changing the yarns bending degree, growth of the filling angle, yarn flattening in joining points and fabric structure compaction with direct influence on fabrics' apparent density.

Fabrics compression behavior is important for establishing the presser foot force as a sewing parameter.

In order to establish and record the dinamic pressure force of the presser foot and its change according to sewing machine technical and technological parameters an experimental stand was attached to the sewing machine (figure 2) (Hanganu et al., 2009).

2. EXPERIMENTAL STAND

The experimental stand will allow (Ionescu & Comandar, 2007):

* The study of the technical and technological parameters (machine speed, stitch lengh, pressure of the presser foot) upon the sewing shrinking of the fabrics during sewing with emphasize of the optimum domain.

* Study of the dinamic pressure force variation depending on the technic and technological parameters.

* Study of the fabric deformation at feeding process during sewing.

[FIGURE 1 OMITTED]

For studying the evolution of pressure force of the pressure foot on the fabric, during sewing, a transductor was concived and placed under the helicoidally compression spring of the sewing machine.

The transductor has an "U" shape, the two horisontal parts being the elastic elements (figure 2).

The elastic elements of the transductors are two blades of rectangular shape, embeded at one edge on a spacer considered rigid. At the other end, the blades have a hole crossed by the compressions spring of the sewing machine.

After the transducer is placed, it is stressed by two forces F with equal values and in opposite directions, representing the action of the helicoidally compression spring, respectively the reaction of the supporting element.

In order to press the fabric with the presser foot, the sewing machine Brother DB2-B737-915 MarkII has an helicoidally compression spring.

The necessary compression force is adjusted by rotating a screw placed on the sewing head. Once the pressure force is adjusted, the screw is blocked.

The adjusting parameter on the sewing machine is the distance I between the sewing head and the screw end (figure 2).

The compression force corresponding to an deflection f is calculated using the equation:

[P.sub.s] = G x [d.sup.4]/8 x [D.sup.3] x n x f (1) 8-D -n (1)

where: G--transversal elasticity module, G = 8 x [10.sup.4] N/[mm.sup.2];

d--diameter of the spring wire;

D--spring medium diameter;

n--number of active whirls.

[FIGURE 2 OMITTED]

3. EXPERIMENTAL RESEARCH

The experimental works were developed for a static force of the presser foot of 6.3daN. An example for the recorded compressibility diagrams is shown in figure 3 for two different textile materials (Ionescu, 2002).

Because it was not possible to determine the moment of the contact between the textile material and presser foot, the thickness gradient was graphical established.

The tangent at the compression curve was traced and its intersection with Oy axes was considered as starting point of the compression point. By tracing a parallel at the Ox axis the initial point of the effective material compression was established.

The values of the fabric thickness after compression (gf) and compressibility (c) were established by direct measurement on the recorded diagrams.

Analyzing the curves can be noticed the resembling with the curve from the specific literature in the specific case of the presser foot action upon the textile materials (Comandar & Amariei, 1998). The shape of the curves is different according with the fabrics' characteristics.

4. RESULTS

The correlations between compressibility and the fabric characteristics (table 1) were established using Jardel Scientific, Table Curves programmer with the possibility of obtaining all the mathematical models describing the dependence.

One of the 3261 possible equations is chosen the one considered as better describing the dependence ([r.sup.2]) and with practical utility.

The correlations presented in table 1 have been determined for all the selected fabric. The analyze was focused on the knitted fabrics group, due to their great sizable the compression capacity is greater. The only weave type similar to the knitted fabric group is variant V2 (velvet). Analyzing the dependences presented in table 1 can be noticed the best correlation for the filling coefficient as correlation factor [[delta].sub.v] ([r.sup.2] = 0.99).

The regression curve c = (g) speaks for itself: for little thicknesses (under 0.55mm) the air volume included in knit structure is relatively low and the compression decreases to this value, for the thicker knit fabrics the compression capacity increases, due to the thickness growth based on the textile structure "breaking up" with a greater air volume integrated in fabric structure in detriment of fibrous content.

For the second regression curve g = f(m) a dependence between knit compressibility and specific mass is noticed beginning with the value of 175g/[m.sup.2]

On the segment corresponding to the specific mass values between 175-300g/[m.sup.2] a direct proportionality is noticed between its growth and the compressibility growth. For values of specific mass greater than 300g/[m.sup.2], fabric compressibility is approximate constant.

[FIGURE 3 OMITTED]

[TABLE 1 OMITTED]

The third regression curve c = ([??] [[delta].sub.v]) indicates an increasing of compressibility with the volume indicator growth until a value of 0.3 and over 0.65. The descendent tendency is placed on the segment 0,3-0,65.

In the sewing process fabrics compressibility has influence on the presser foot rising above the needle plate level.

The experimental stand was designed withing one of the most popular sewing machines, having a high flexibility.

A calibration of the transductors was made using the rising of the feed dog teeth above the needle plate.

The stand can be used for establish the optimum technic and technological parameters of the sewing machine for processing different types of fabrics.

5. REFERENCES

Buhler, G. & Dorfler, H. (1996). Study of the Transport Behavior of Knitted fabrics on the Sewing Machine, Knitting Technology, No. 5, ISSN 0946-7718

Hanganu, L. C. et al. (2009). Considerations Concerning the Oil Viscosity

Influence on Textile Spindles Dynamic Response, Materiale Plastice, 46, No. 1, pp 67-72, ISSN 0025-5289

Ionescu, I. & Comandar C. (2007). Experimental Stand for Determining the Fabrics Behavior during Sewing Process, Bulletin of the Politehnic Institute of Iasi, Vol. LIII (LVII), No. 5, ISSN 0253-1119

Ionescu, I., (2002). Research Regarding Improving the Transport of Textile Fabrics in Sewing Processes, PhD Thesis, Iasi, Romania

Comandar, C. & Amariei, N. (1998). Material Resistance, Cermi Editor, Iasi, Romania