The point about needles and threads
When sewing certain fabrics, operators may be instructed to change the needle on a regular basis since damaged needles can cause many problems. But is the best needle for the job being used in the first place, and what about the thread?
Taking a basic every-day operation such as an eight stitches per inch straight seam, sewn with a general-purpose lockstitch machine, sewing speeds can be 5500 stitches a minute. The needle moves downward roughly one inch through the fabric, and then back up again the same distance for every stitch it forms whilst the feed mechanism moves the fabric along. Thus the needle on that machine has the potential to move up and down sixteen times, or inches, per inch sewn.
So it is hardly surprising that needles get broken, bent, points and throat plates damaged, stitches slipped and fabric damaged, puckered and distorted.
At 5500 stitches per minute, with both an up and down movement every stitch, the needle actually moves 11000 inches per minute - a speed equivalent to approximately 10.5 miles per hour.
The top thread, however, not only goes the distance of the needle but is looped round the bobbin and then pulled taught. If the distance of the thread from the top needle point, down through the fabric and throat plate, round the bobbin and back up again and pulled tight is approximately double that of the needle movement, the thread is travelling at over twenty miles per hour, through a fabric whose individual yarns are normally smaller than the thread and tightly woven or knitted together. When the needle penetrates the fabric being sewn, the yarns have to give way to the needle within a timeframe that can be as low as 0.0003 seconds.
Passing through a thick, tightly woven fabric causes considerable resistance, friction, and heat build-up - all of which affect the needle and the thread. Research work shows, for example, that needle temperature can rise within seconds to 350°C (100°C above the melting point of polyester). So it is little wonder that the research and development departments of the large international companies manufacturing these products are so large and complex.
Needle profiles from Groz-Beckert
High quality seams
Whether manufacturing outerwear, underwear, footwear or technical textiles, it is the seam that ultimately joins everything together. Which means that the seam is critical to the overall quality of the end product. High quality sewing threads sewn with the most appropriate needles are key.
Apart from the detriment to garment quality and performance, there is a major cost disadvantage resulting from the use of 'cheap' thread.
An independent survey carried out for sewing thread producer Donisthorpe found that the total hourly sewing cost of a machinist in the UK, inclusive of overheads, depreciation etc, was £12 per hour. It was also found that the average downtime caused by using imported 'cheap' spun polyester was 40 minutes per operator, while its cost per metres used per day worked out at £0.40 per operator.
High quality corespun, on the other hand, cost £1.60 per day for meterage used, though downtime was reduced by half - to 20 minutes. With these facts, simple arithmetic shows the total daily cost per operator of using the cheaper spun polyester may actually amount to £8.40 against £5.60 with quality corespun. As the saying goes: 'Penny wise, pound foolish'.
Many other evaluations, comparing costs in high and low cost labour countries, all prove the same general equation.
Automation, flexible short run production, rationalisation, higher machine speeds, new working methods and rising costs, together with new fibres, yarns, fabrics and trims all create new challenges and opportunities and with them problems which need to be addressed.
Little wonder, then, that the leading needle and thread producers have invested a lot of time and money in educating manufacturers and retailers about recurring problems. Slipstitching, thread breakage and puckered seams can often be attributed to incorrect thread sizes, thread types, needles, and feed and tension adjustments. Some excellent technical information bulletins have resulted, such as the series from American and Efird, Groz-Beckert, Gütermann and Amann, many of which can be downloaded or ordered from their websites.
Coats has produced an extremely comprehensive, pocket-sized booklet on 'The Technology of Threads and Seams'. On the understanding that 'prevention is better than cure' - a necessity in a fast moving, global industry - nearly all the leading suppliers have also developed extensive pre-production customer services to ensure the correct selection of needles and threads before manufacturing commences (as opposed to resolving problems after they occur).
The most recent of these services is the Amann Material ID Card. Here, submitted materials are checked for the major potential problems of seam pucker, snags and mechanical damage on knitted and woven fabrics. These tests result in detailed processing recommendations which, considering all the relevant sewing parameters, Amann claims will "guarantee an optimised seam". The service will also provide fabric suppliers with early access to important processing information - enabling them to offer advice to apparel manufacturers working with the new materials.
Another new initiative is aimed specifically at the career and workwear industry. The Sew-Right construction guide, produced by Donisthorpe and Company Limited in conjunction with the International Careerwear Consulting group (ICC), is an interactive CD-ROM providing designers, buyers and specifiers with advice on the best fabrics to use for individual applications. It also gives manufacturers all the key technical information required to sew a high performance garment before it goes into full production. This includes detailed technical data and advice on needle selection and use, as well as seam construction information such as stitches per inch and the best needle and thread type and size to use for a specific fabric.
Apart from providing a lot of excellent printed technical information, many companies are using their websites to help guide manufacturers to the products most suited to their requirements. Dial up the www.schmetz.com website, for example, to see the complete Schmetz catalogue broken down into needles for specific purposes such as blind stitching, button sewing, button-holes, embroidery, quilting and top stitching, and special applications. There is information on needle sizes, and even individual technical illustrations, along with advice on how to avoid specific sewing problems.
Look, for example, at needles for avoiding skipped stitches. This brings up written and graphical information on what is meant by skipped stitches, the effect they have on the seam, and the causes broken down into different reasons with descriptions as to why they are happening - highly elastic fabrics, layers of different materials, cross seams, needle deflection and thread.
Diagrams illustrate the problem; the required needle type is given, along with technical reasons why it is the most appropriate; and further non-needle related tips further help solve the problem. In this case, Schmetz needles of Serv 7 design are recommended as they provide optimum loop formation, needle stability, and the special design-enabling hump between the eye and scarf pushes the loop much further out so that the hook can reliably grasp the loop, regardless of the material and thread properties. The reinforced blade gives the needle the necessary stability to prevent deflection.
Just launched is a very useful new pocket-sized publication, 'Make or Break'. This independent, technical guide to needles, threads, and stitches has been produced by the Association of Suppliers to the British Clothing Industry (ASBCI) in association with American & Afird (GB), Bellow Machine Company, Coats, Donisthorpe and Co, Durkopp Adler (UK), Everbond/William Clark Group. and Oxley Threads.
It purports to represent "a unique and definitive guide on how thread, stitches and seams are produced, perform and applied in today's apparel industry." Available to the industry internationally, it is offered to ASBCI members at a cost of £21, and to non-members at £35 (plus postage). It is a concise "no waffle" guide, with many useful diagrams. For copies contact Stephanie Ingham, NASBCI national executive, at firstname.lastname@example.org
Niki Tait, C.Text FTI, FCFI heads Apparel Solutions, a consultancy that provides independent assistance to the apparel industry in the areas of manufacturing methods, industrial engineering, information technology, and quick response.
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