Troubleshooting in the Sewing Room
rough seams with harsh stitch holes. Melted fibres stick to the surface of the needle, increasing its friction and clogging the eye and grooves so that eventually no thread will sew because of breakage or skipped stitches. Before this state is reached, damage to the sewing thread by melting or abrasion may have produced weak seams. Different approaches to the problem of needle overheating are possible, namely preventing the heating occurring, cooling down the needle as it heats, and preventing the heated needle from damaging the fabric or thread. Since the heating is the result of friction, reducing the heating requires reducing the friction. The primary means of achieving this is by the incorporation of a suitable lubricant during fabric finishing. All other approaches provide only partial solutions. The sewing speed can be reduced but, as with mechanical damage, this is unpopular because of its effect on production. Reduction of friction can also be achieved by either changing the shape or surface of the needle or by changing the material it rubs against. Needles were described earlier which have a reinforced shoulder area and a bulged eye, both of which open up the needle hole in the fabric to allow freer passage of the main part of the needle blade. The extent to which the blade is reinforced is limited by the size of needle hole that is acceptable, since it can give a poor appearance in fine fabrics. The amount of reinforcement normally used enables an increase in stitches per minute sewing rate of 15 to 20 per cent above that which could be used with an ordinary needle without causing damage. The application of a roughened surface to the needle has also been found to reduce friction and heat development, and to resist the accumulation of any melted debris that does form. In fabric terms, there is the same need that there is with mechanical damage to enable the yarns to move away from the needle easily and the application of a lubricant to the fabric is again the answer. The length of seam sewn in a garment also has an effect on the temperatures built up in the needle. If long seams are sewn, high temperatures will be generated, and if there are only short time intervals between seams there will not be much opportunity for the needle to cool down. By contrast, short seams such as shoulder seams can be sewn at high speed without so much build-up of heat. Air coolers have been used to reduce needle temperature, usually making use of existing compressed air lines within the factory. However, the effectiveness of air cooling is limited to marginal cases, and the air blast can lead to missed stitching and to operator discomfort. If needle overheating is accompanied by mechanical damage, as it often is, air cooling will not address the yarn breakage problem. The sewing thread has a part to play in needle cooling with spun or corespun threads being the most effective. All threads cool the
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