The Sewability Of Elastic Fabric

I N F O R M AT I O N F O R T H E S E W I N G I N D U S T R Y

THE SEWABILITY OF ELASTIC FABRIC

THE SEWABILITY OF ELASTIC FABRIC The processing of elastic fabric for women‘s and men’s outer garments, shirts and blouses is increasingly popular and is well liked by customers. These garments are pleasant and comfortable to wear, allow movement, and look casual but elegant. For these reasons, elastic fabric garments are unlikely to be merely a passing fad.

There are two basic problems:

This was reason enough for Amann to take up this topic, and in particular to deal with the technical demands when processing elastic fabric.

In order to avoid such complaints and to ensure problem-free production, the following sewing parameters must be taken into consideration:

Elastic fabrics are those fabrics with stretchable threads (such as Dorlastan®, Lycra®) worked invisibly in warp and/or weft direction. These special characteristics are provided for by an approximate 2-5% part of the elastane threads. These new fabric qualities are either monoelastic (extensible in warp or weft direction) or bielastic (extensible in warp and weft directions). The elasticity of the available elastic fabrics available on the market at present ranges from approximately 20% for fashion wear to around 30-50% for functional clothing. These fabrics find a variety of uses ranging from traditional areas such as sportswear and beachwear, to sporty skipants and regular outer garments for ladies, gents and boys such as blouses, shirts or blazers. The decisive factor when processing elastic fabric is the correct setting of the sewing parameters. Production conditions are often set for non-elastic material, and not changed when processing elastic fabric. Experience shows that this often leads to complaints about the quality of the seams.

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왘 INSUFFICIENT ELASTICITY OF THE SEAMS The seams break under longitudinal strain 왘 ELASTANE DAMAGE Surface migration of the light-colored elastane yarn

1. SEWING PARAMETERS FOR SUFFICIENT SEAM ELASTICITY When seams are created on elastic fabric, it is very important that they have sufficient longitudinal elasticity for the strain caused by being worn. Under strain, the seams must not „restrain“ the elasticity of the fabric. Rather, they must „follow“ the movements. Sufficient seam elasticity is primarily determined by the thread storage, which is the amount of thread contained in the seam. 왘 The more thread contained in the seam, the higher the seam elasticity! The potential thread storage is mostly influenced by the selected stitch type, the stitch density in use and the thread tension. Details on these essential sewing parameters and the use of appropriate sewing thread are presented below. Other sewing parameters, such as the seam design or the thickness of the fabric, also influence the thread storage. For example, the seam elasticity is higher for thick fabric and for fabric with many layers. However, in practice it is often not possible to change these parameters.

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1.1 SELECTING THE APPROPRIATE STITCH TYPE Above all, the stitch type determines the potential amount of thread in the seam, independent of the stitch density and the thread tension. Under standard sewing conditions, for example,

1.2 SELECTING THE APPROPRIATE STITCH DENSITY The thread storage is also highly influenced by the stitch density. More stitches per centimeter of seam result in having more thread in the seam. A simple rule of thumb applies: 왘 The higher the stitch density, the higher the seam elasticity.

왘 the lockstitch provides thread storage of 2.80 m 왘 the double chainstitch provides thread storage of 4.80 m

Imperative when selecting the appropriate stitch density is the material to be processed, in conjunction with the desired seam elasticity value. A standard value is a stitch density of 5 stitches/cm, depending on the selected stitch type.

왘 the four-thread overlock stitch provides thread storage of 17.10 m for a 1-m seam. This shows clearly that if an inappropriate stitch is selected there will not be enough thread and that even a slight strain would cause the seams to break. The tuck seam is an excellent example. It is not often made with a two-needle seaming stitch (stitch type 402), but rather with a lockstitch (stitch type 301) when the required special machine is not available. However, the lockstitch cannot supply enough thread to make tuck seams sufficiently elastic at parts of the body with much motion, such as the knee area. This remains true even for loose thread tension and high stitch density.

The adjacent diagram shows the in-fluence of the number of stitches per centimeter on the elasticity of seams. Seam elasticity in % 90 80 70 60 54 % 50 46% 40

Essential stitch types in the manufacture of knitwear and thread requirements based on sewing technological standard parameters (see page 4).

30 20 10

4 Material: elastane fabric Sewing thread: SABAC Nr. 120 Stitch type: double chainstitch 401

5 Stitch density (stitches per cm)

Very high stitch densities can cause damage to the elastane, displace-ment pucker and wavy seams. The appropriate stitch density is best determined by a sewing test to guarantee both flawless appearance of the seam and sufficient seam elasticity.

Foto: Brax

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It might be necessary to select a different stitch type if the highest possible stitch density is chosen but the seam is not elastic enough.

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THE MOST IMPORTANT STITCH TYPES WITH SEWING THREAD REQUIREMENTS FOR STANDARD SEWING PARAMETERS*

*Basis: Standard sewing material 1mm with 4 stitches/cm

More information can be obtained from our brochure „Determining your sewing thread requirements” STITCH TYPE

ISO 4915 DIN 61400

Lockstitch

SEAMCONSTRUCTION NF

301

THREAD REQUIREMENT PER 1m SEAMLENGTH % NT: UT:

GF

Lockstitch zigzag

NF

304

NT: UT:

GF

Double chainstitch

NF

401

NT: UT:

GF

Tucking stitch

NF NF

402

NT: UT:

GF

Two-needle double chainstitch

NF NF

406

NT: UT:

GF

Three-thread overedge stitch interlaced at needle hole

Four-thread overedge stitch interlaced at needle hole

Two-needle double chainstitch with cover thread

Three-needle covering chainstitch with cover thread

NF

504

GF GF

NF NF GF GF

514

LF NF NF

602

NT: UT:

NT: UT: CT:

GF LF NF

605

NT: UT: CT:

GF LF

Four-needle covering chainstitch with cover thread

NT: UT:

NF

607

NT: UT: CT:

GF

1,40 m 1,40 m

50% 50%

2,80 m

100%

2,70 m 2,70 m

50% 50%

5,40 m

100%

1,70 m 3,10 m

35% 65%

4,80 m

100%

3,40 m 6,80 m

33% 67%

10,20 m

100%

3,40 m 8,40 m

29% 71%

11,80 m

100%

1,70 m 12,10 m

12% 88%

13,80 m

100%

3,40 m 13,70 m

20% 80%

17,10 m

100%

3,40 m 8,40 m 5,10 m

20% 50% 30%

16,90 m

100%

5,10 m 11,60 m 5,80 m

23% 52% 25%

22,50 m

100%

6,80 m 14,80 m 5,80 m

25% 54% 21%

27,40 m

100%

CT= cover thread · UT=underthread (looper or bobbin thread) · NT=needle thread 54

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1.3 MAINTAINING OPTIMUM THREAD TENSION For proper thread distribution and a sufficient amount of thread in the seam, the thread tensions must be adjusted properly. If the thread tension is too tight, only a slight amount of strain can cause seam breakages.

Correct and incorrect thread balance, shown using an example of a double chainstitch seam (stitch type 401)

Well balanced tension

The following distribution patterns show the interlocking of needle and underthread. 왘 on lockstitch seams (301) On lockstich sewing machines the needle and bobbin thread tensions are adjusted so that both threads interlock in the centre of the material, if possible. This adjustment ensures that an equal amount of each thread is used in the seam. Both thread tensions should be set as low as possible, however without risking gaping seams. Optimum and incorret thread balance for a lockstitch seam:

Well-balanced stitch pattern, indicating that the seam possesses maximum elasticity and tensile strength.

Needle thread tension too strong or bobbin thread tension too low, indicating insufficient elasticity and tensile strength of the seam.

Incorrect tension

In some cases it is advantageous to loosen the looper thread tension, in order to develop the thread loops on the underside of the seam. Attention should be paid to the fact that gaps may appear in the seam, should the looper thread tension be set too loosely. 1.3 USING APPROPRIATE SEWING THREAD A particularly elastic sewing thread is often required when processing elastic materials. In contrast to these considerations, however, the previously applied sewing thread approach can still be used. 왘 The more thread contained in the seam, the higher the seam elasticity. Use of core-spun thread is recommended. The diameter of the sewing thread should be chosen according to the fabric and the strain upon the garment when in use. Core-spun threads with diameter no. 120 cover a wide range of applications. The following quality demands should always be met:

Bobbin thread tension too strong, or needle thread tension too low, indicating insufficient elasticity and tensile strength of the seam.

왘 on chainstitch seams (401) On all chainstitch, covering stitch and overedge stitch sewing machines the thread tensions are set correctly when the needle thread loops appear as dots on the bottom side of the fabric and the optimally relaxed looper thread can be pulled through these dot-shaped thread-loop ends without any effort.

왘 Compactness and uniformity ot thread 왘 High tensile strength despite small diameter 왘 Brilliant colours of high stability 왘 Precise winding slidability 왘 Shrink proof, harmonious care 왘 Heat resistance – during sewing – during ironing 왘 Elasticity suppleness, no skin irritation 왘 Abrasion resistance

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Recommanding sewing thread SabaC Polyester core-spun thread No. 80, 100, 120 Rasant Cotton-polyester core-spun thread No. 75, 100, 120

The following information on processing technique should be considered to avoid elastane damage:

Applications

Closing and assembling seams, ornamental seams, buttonholes and serging

2.1 USING THE PROPER NEEDLE SIZE The suitable needle size mainly depends on the density and sensitivity of the fabric. The following rule applies: 왘 The more thread contained in the seam, the higher the seam elasticity! Needle sizes between 70 and 90 Nm should be used to avoid elastane damage.

Saba 150 Polyester Advanced Technology No. 150

Closing and assembling seams, overedging lightweight fabrics

Serafil Polyester multifilement thread No. 120/2 oder 200

Serging and blind stitch seams

Texturan Polyester-bulky thread No. 120

Overlock and cover seams (looper and cover thread), serging seams

2. ELASTANE DAMAGE

2.2 SELECTING THE PROPER NEEDLE POINT When processing elastic fabric, it is recommended to use needles with a slightly rounded point „SES“ or „SAN 10“ (for fine fabrics), or a medium ball-point „SUK“ (for coarser fabric). As a rule, these point shapes do not puncture the elastane yarn but rather slide past them. 2.3 REGULAR NEEDLE CHANGES Even slight damage to the needle point harms the fabric when it is penetrated by the needle. As a preventative measure, the needle should be replaced frequently. The sewing conditions (nature of the material, sewing machine speed, etc.) determine how often the needle should be replaced.

There are two basic reasons for elastane damage: 왘 Needle penetration damages the elastane yarn, or pulls it out of the fabric. 왘 The elastane yarn is not sufficiently bound in the fabric. Latitudinal strain pulls it out of the fabric along the seam. Certain stitch types and seam constructions are likely to alleviate this, i.e.: • a seam allowance less than 1cm • flatlock seams etc. The figure to the right shows the elastane yarn which were pulled out.

2.4 ADJUSTING THE SIZE OF THE STITCH HOLE In any case, the size of the stitch hole of the stitch plate must match with the size of the needle. Fine fabric is damaged by stitch holes which are too large as the material is in the form of a funnel is forced through the recess. 2.5 REDUCING THE SEWING SPEED If damage to the elastane continues, even following implementation of the above recommendations, it may help to try a slower sewing speed. 2.6 MODIFYING THE SEAM ALLOWANCE AND SEAM DESIGN Current problems with the migration of elastane yarn can be prevented by increasing the seam allowance. A further possibility would be changing the construction of the seam. For a french seam or lap seam, for example, the elastane yarn is sewn tighter into the seam by deflecting the fabric. Depending on the model

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design, however, it may not always be possible to implement these modifications. 2.7 CREATING SEAM SAMPLES Before processing elastic fabric, seam samples of various quality should always be made. This helps to prevent production difficulties.

Our experience shows that there are definite limits to optimization of the sewing usability of materials with a tendency to elastane damage. The fabric supplier should be contacted if the information provided above does not lead to satisfactory sewing results. The supplier might be able to make technical construction or finishing modifications to the properties of the material.

A simple test shows the extent to which material of a given quality tends to damage the elastane: For the manual stress test, the pieces of material sewn together are firmly moved back and forth along the seam, using both hands.

The following notes will make it easier to process elastic fabric, and to help improve the quality: CHECKLIST: PARAMETER

AMANN general guideslines

RECOMMENDATION

Stitch type

Use stitch types with larger thread storage

g. stitch type 401, 514

Stitch density

Match with the material to be processed. The elasticity will be greater for the higher stitch densities.

approx. 5 stitches/cm (individuelle Tests erforderlich)

Thread tension

as low as possible (=> increases the thread storage),

Lockstitch

Your own production specification

Needle thread: approx 70 – 90 g (for fine to normal fabrics)

as high as necessary (=> avoid seam gaps)

Looper thread: approx 20 –40 g (for fine to normal fabrics)

Sewing needle

Thin needles, matched to the material; rounded point preferable (SES, SUK or SAN 10)

Nm 70 – at most Nm 90 (depending on the material)

Sewing thread

Quality sewing thread; keep the proven sewing thread concept

SABAC/ Rasant: closing and assembling seams, ornamental seams, buttonholes and serging seams Serafil: serging and blind stitch seams Texturan: overlock and cover seams (looper and cover thread), trimming seams

Avoiding elastane damage

• Use the proper needle size and needle point shape • Regularly replace the needle on a regular basis • Consider reducing the sewing speed • For fine materials, tailor the stitch hole size • Check the seam allowance and construction

Sewing usability tests before beginning production serve to harmonize sewing parameters, and help avoid processing problems during production.

SEWING APPLICATION SUPPORT We will be glad to provide you with support in relation to any application and process issues. Please do not hesitate to contact us at:

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[email protected] phone +49 (71 43) 277-250

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Amann & Söhne GmbH & Co. · Hauptstraße1 · D-74357 Bönnigheim · phone +49 ( 7143) 2 77- 0 · fax +49 ( 7143) 2 77 - 200 · http://www.amann-online.de 100542 GB05000120