Monday, November 30, 2009

[ Technical Textiles - Developments in Testing Seams ,Written by Administrator.]

Developments in Testing Seams
Written by Administrator   

Tinius Olsen and SDL Atlas both attend and work within the Working Groups at BSI, CEN and ISO meetings and the Tasks groups at ASTM on the revision and development of standards. If you are a Retailer specifying end-use performance, these are the methods of test and standards you should be looking at to ensure your products are fit for purpose.

When it comes to making sure the final garments are fit for the end-use; Tensile Strength and Seaming Properties are key performance tests. One of the major reasons for the consumer being dissatisfied with a garment after poor colour fastness and stability is when the seams in a garment fail due to seam breakdown caused by tearing at the seam, sewing thread breaking or what is commonly referred to as fabric slippage or thread pull out. Fabric slippage occurs when warp or weft yarns of a woven fabric are able to slide through the seam structure this can be as a result of several factors. The loose weave or construction of a specific fabric, the type of yarns used or the final finishing processes can all play a part in achieving a fabric fit for the design; the selection of an appropriate seams structure of the final end use of the product. The methods referred to below allow the garment designer to make a judgement as to whether the basic fabric of the garment has a potential to fail using a standard laboratory seam (Type 301 lockstitch seam) with a 12 mm seam bite. If the fabric fails this test there are several ways correct action can be taken before the fabric is made up. This can be by slightly altering the weave and finishing specifications. Where results are marginal maybe the final selection of seam construction and sewing thread types can be modified, especially in the areas that will take on maximum stress during wearing or use of the product.

So what is happening at the moment? For the European market the following current key standards are:

EN ISO 13934 -1;1999 Ravel Strip Strength
EN ISO 13934 – 2;1999 Grab method for Tensile Strength

EN ISO 13935 – 1;1999 method for Seam Strength Strip.
EN ISO 13935 – 2;1999 method for Seam Strength Grab method.

The above four EN ISO are currently going through an amendment process to accommodate the vast range of fabrics with built in stretch characteristics now being sold in the market place. The above methods also link closely with EN ISO 13936 series of methods for evaluating the threads in fabrics potential to move and slip through a standard seam construction causing seam failure.

ISO have already revised EN ISO 13936 series of methods to take into account Stretch fabrics. It is important that you use the appropriate method depending on the fabric type. Many people seem to have a problem deciding this, when the stretch is imparted by a non elastane fibre. A guide for Retailers should be, if you are marketing ‘Comfort Stretch’ you should be specifying testing in accordance with EN ISO 13936-2 which is a Fixed Load method of test.

At Tinius Olsen we frequently get requests for customer support when the initial choice of method has not taken into account the scope of each method.

Note: The software relating to standards EN ISO 13934 Parts 1 -2, EN ISO 13935 Parts 1-2 and EN ISO13936 Parts 1-3 or specific Retailer methods can all be found in the Data Base of the current version of Qmat Professional.

Seam testing:

Standard fabric test specimens are prepared 400 x 100mm with a seam at one of the specimen. The standard seam methods relies on evaluating paired data taken from 2 tensile strength curves, the 1st curve is the tensile strength of the fabric and a 2nd curve has a standard laboratory seam sewn across the centre, so you are pulling on the same warp or weft threads with and with out a seam. When it comes to Stretch fabrics the specimens are 200 x 100 mm with a standard seam sewn across the middle of the specimen and we have to change the way this is done by dropping the paired data technique and reverting to physically measuring the seam opening of the standard laboratory seam after stretching to a load depending on the end use and returning to a nominal force of 5N. Both methods look for the force required to open the seam 6 mm or the force at a 6 mm opening. However some Retailers request at alternative seam bite and seam opening that will reflect the final seam type that will be used when the garment is produced (these can range from a 5 – 12 mm seam bite and an opening of 2 – 6 mm opening).

* EN ISO 13936-1;2004 Slippage Resistance – Fixed Opening Method (used for standard fabrics)
* EN ISO 13934-1:1999 + 13935-2:1999 + 13936-1:2004 Seam Properties
* EN ISO 13936-2;2004 Slippage Resistance – Fixed Load Method (used for fabrics that have Stretch characteristics).

ASTM D13 also have a Task Group looking into all aspects of testing stretch fabrics, so watch this space and we will inform you when things have progressed to full documents for use by the industry.

If you are visiting ITMA-Asia this year come and see us where we will have all this equipment available for demonstration and discussion.

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