Abstract:

Objective Fabric stitch is an important factor affecting the air permeability of knitted fabrics. In order to correctly evaluate the air permeability of double-sided weft knitting fabric before the actual production, the double-sided fabric stitch model is constructed, and the digital expression of fabric porosity is made, so as to realize the prediction of fabric air permeability.

Method According to the Peirce weft knitting classical loop model, the unit stitch model is constructed for knitting structure including three basic loop forms: knitting stitch, tuck stitch, and miss. Then, based on the above three basic unit stitch models, the weave model of the fabric formed by weft knitting was constructed and digitized, the theoretical porosity was calculated, and the air permeability was measured by YG461E-III automatic air permeability meter in turn, and the relationship between the theoretical porosity and air permeability was obtained by linear fitting. Finally, two fabrics were selected to verify the rationality and applicability of the prediction system.

Results The unit stitch model was constructed for the 3 basic loop forms including knitting stitch, tuck stitch, and miss assuming that the loop form in the fabric in a completely ideal state. Setting the yarn diameter as d, the knitting stitch model, tuck stitch model, miss model of yarn vertical mapping area are achieved to be approximate to 16.34d², 11.63d², 4d². For weft knitted double-sided fabrics in a rib configuration, when the front and back loops that can tuck or not knockover at most once, the assembly of loop units forming the front and back of the fabric is shown. When the front and back loops that can tuck or not knockover two or more times, the loop cell assembly is shown. By dividing all the loop forms by the structural unit division method of the stitch of the fabric and the morphological approximation method, it can be concluded that the front surface of the fabric contains 9 kinds of (F₁-F₉) different lattice yarn morphological models, the reverse side of the fabric contains 21 different (B₁-B₂₁) lattice yarn configuration models. Through the digital transformation of the stitch model and the construction of porosity matrix, the calculation method of the theoretical porosity of the fabric is obtained. The design of three weft double-sided stitch with different structures, calculating the theoretical porosity using the same method, and the theoretical porosity of the fabrics formed by the three stitch was 25.34%, 33.63%, and 27.01%, respectively. Then, the air permeability of the three fabrics was measured. The theoretical porosity and air permeability were analyzed by linear regression. And a linear regression equation is obtained. Through theoretical calculation, the air permeability of the three fabrics are 790.5, 1 128.4, and 858.6 mm/s, which are less accurate than the actual measured air permeability (the error rate is within ± 6%). The comparison results of the theoretical calculation and actual measurement of the two fabrics selected finally are in line with the above deduced results.

Conclusion This paper predicts the air permeability of complex fabric based on the three basic unit stitch models of knitting stitch, tuck stitch, and miss. Through the stitch model construction and digital transformation of the stitch of the three designed fabrics, the theoretical porosity of the fabric is calculated, and according to the measured air permeability, the linear regression analysis of the theoretical porosity and air permeability was carried out, and the linear regression equation which can explain the relationship between the two factors was obtained. In addition, through the air permeability analysis of the two selected fabrics, the analysis results are consistent with the above-deduced results, indicating that the construction method of the stitch model and the theoretical deduction method of the relationship between porosity and air permeability are reasonable and applicable, which provides a new method for the air permeability prediction of knitted fabrics.

Key words: weft knitted fabric, stitch model, vertical mapping area, porosity, permeability digitization prediction