Studie zahřívání jehly průmyslového šicího stroje
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Abstract
Sewing process is one of the most important operations in the clothing industry. It is also an important part of assembling some technical textile products. Every day, millions of products ranging from shirts to automotive airbags are sewn. Hence, even a minor improvement may result in significant commercial and performance benefits. The biggest issue with high speed sewing is the damage caused by heating of the needle on the sewing thread and the fabric. Sewing thread undergoes repeated abrasion and passes through the needle eye resulting in a friction with the needle; on the other hand the friction between the needle and the fabric during its penetration through the fabric layer(s) causes an increase in the needle temperature. This hot needle causes damage to the thread, the fabric and finally a loss in productivity. This work described in this dissertation aims at understanding the various processes causing a heating of the needle, with the needle's temperature measurement and prediction. It also explores certain methods which may possibly improve the productivity of the sewing operation by reducing the needle temperature without compromising the sewing speed.Chapter 3 of this work covers the experimental techniques to measure the sewing needle temperature. Three methods (thermal camera, inserted thermocouple and thermocouple touch method) are compared under different sewing conditions. It was found that the thermal camera got influenced by the low emissivity of the needle and it is very difficult to measure at speeds higher than 3000r/min. Inserted thermocouple method showed repeatable results with the lowest deviation. On the other hand, the thermocouple touch method could be used to provide an estimation of the needle temperature since the delay in contact between the needle and the thermocouple provides lower values of needle temperature as compared to the inserted thermocouple method.Chapter 4 presents the effect of different factors on the sewing needle temperature; it was observed that the sewing speed, the thread count, the sewing time, the fabric structure and thickness had major impact on sewing needle temperature. On the other hand, ambient humidity, ambient temperature, stitch density and needle parameters played a minor role in heating of the sewing needle.Chapter 5 is based on the cooling of hot needle by a vortex stream of cold air, which is the common method in industry to decrease the needle temperature.Chapter 6 presents the effect of the lubricant amount on sewing needle temperature. Lubrication is the second most common technique in industry for decreasing the needle temperature after the cooling air.In Chapter 7 the effect of the needle temperature on the tensile properties of the sewing threads is discussed. It was observed that the tensile properties of the used sewing threads decreased dramatically for machine speeds higher than 3000r/min; where about 40% loss of tensile strength was recorded for sewing threads at machine speed of 4000 r/min.Chapter 8 presents the methodology for evenly coating the sewing needle with a diamond like carbon (DLC) layer. DLC coatings are well known for decreasing the friction properties of heavy machine parts like engines and pistons.Finally, in Chapter 9 a simple analytical model was developed to calculate the needle temperature at its steady state from a set of parameters that includes: friction coefficients, friction forces and thread tension. A linear equation was obtained for the temperature of the needle related to the machine speed as an independent variable. It was found that the model could predict the maximum needle temperature that can be attained during a continuous sewing process of more than 10 seconds with a reasonable accuracy. The important role of the sewing thread in contributing towards the needle temperature was also established by this simple theory which corroborates with the experimental observations.