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Friday, 27 September 2013

All about Sewing

1. Seam: A seam is the application of a series of stitches or stitch types to one or several thicknesses of material.

Stitching is applied to situations where there is only one piece of fabric, such as when fabric edges are neated or hems created, and where decorative sewing is involved.

Objective of Sewing: Are the construction of seams whcih combine the required standards of appearance and performance with in appropriate level of economy in application.

Good Apppearance of Seams: It means smooth fabric joins with no missed or uneven stitches and no damage to the material being sewn.

Performance of Seams: It means the achievement of strength, elasticity, durability, security and comfort, and the maintenance of any specialised fabric properties such as waterproofing or flameproofing. 

1. Seams must be strong as the fabric, in directions both parallel to and at right angles to the seam.

2. Seams must be durable to the kind of abrasion experienced in washing and wearing as well as secure against fraying apart or the unravelling of the stitches. 

3. A seam in a close fitting garment must not present an uncomfortable ridge or roughness to the skin.

4. It must not damage the fabric along the stitch line. 


Factors to be considered while sewing

1. Seam Type: Particular configuration of seams in fabrics.

2. Stitch Type: Particular configuration of threads of in the fabric. 

3. The Sewing machine feeding mechanism- It moves the fabric past the needle and enables a succession of stitches to be formed.

4. The needle which inserts the thread into the fabric.

5. The thread which forms the stitch which either holds the fabric together, neatens it or decorates it.

Seam Types

Stitched seams are divided into eight classes according to the type and minimum number of components within the seam.

These components which can be the main fabrics of the garment or some additional items such as a lace etc, are termed as being of 'limited' or 'unlimited' width.


where a component is referred to as being limited on one side, that side might be the cut edge of the garment piece that is being seamed.

Where a component is referred to as being unlimited on one side, that edge might be the far edge of the garment panel irrelevent to the seam under consideration.( Figure-1)



Class-I (Superimposed Seams)

It is produced with a minimum of two components both limited on the same side. A variation of the superimposed seam is the french seam.



Class-II ( Lapped Seam)


Seams in this class are produced with a minimum of two components but with these, one is limited on one side and the second is limited on the other side. The components are opposite and at different levels and overlap each other.

Class -III ( Bound Seams)

In this class, seams are produced with a minimum of two components , one is limited to one side with the second is limited on both sides.

Class-iV (Flat Stitching)

In this class, seams are produced with a minimum of two components of which one is limited on one side and the second on the other. The two components are opposite and on the same level. These seams are referred to as flat seams because the fabric edges do not overlap. They may be butted together without a gap and joined across by a stitch which has two needles sewing into each fabric.

Class-V (Decorative Stitching)

Seams in this class are produced with a minimum of two components unlimited on two sides. Any other component is either limited on one side or limited on two sides.



Class-VI (Edge Neating)

It is produced with only one component limited on one side (either on the right or the left). Seam types in this class include those where fabric edges are neated by means of stitches as well as folded hems and edges.




Sewing Machine Needle


The way in which the fabric is penetrated by the needle during sewing has a direct effect on seam strength and on garment appearance and wearable life.

The functions of the sewing machine needle in general are:

a. To produce a hold in the material for the thread to pass through and to do so without causing any damage to the material
b. To carry the needle thread through the material and there form a loop which can be picked up by the hook on the bobbin case

Anatomy of a Sewing Machine Needle 



Butt:
 It is shaped end of the needle which facilitates insertion into the needle bar or clamp.

Shank:

It is the upper part of the needle which is located within needle bar. It is the support of the needle as a whole and is usually larger in diameter than the rest of the needle for reasons of strength.

Shoulder: It is the section intermediate between the shank and the blade.

Blade: The blade is the longest part of the needle down to the eye. The blade is subjected to the greatest amount of material through which the machine passes.

Long Groove: The long groove in the blade provides a protective channel in which the thread is drawn through the material during stitch formation. Sewing thread can suffer considerably from abrasion during sewing as a result of friction against the fabric. A correctly shaped long groove, of a depth matched to the thread diameter, offers considerable protection to the thread.

Short Groove: The short groove is on the side of the needle which extends a little above and below the eye. It assists in the formation of the loop in the needle thread.

Eye of the Needle: The eye of the needle is the hole extending through the blade from the long groove on one side to the short groove on the other. 

Scarf or Clearance Cut: It is a recess across the whole face of the needle just above the eye. This ensures that the loop of the needle thread will be more readily entered by the point of the hook.

The Point of the needle is shaped to provide the best penetration of each type of material.

The Tip is the extreme end of the point which combines with the point in defining the penetration performance.

Size of Needle

Choice of size is determined by the fabric and the thread combination which is to be sewn.

If needle is too small for the thread, the thread will neither pass freely through the eye nor fit properly into the long groove. As a result it will suffer from excessive abrasion. It may result in

Costly thread breakage in production because the machinist must stop to rethread the needle and possibly also to unpick some of the stitching so that a joint does not show in an important part of the garment. 

When sewing heavy plies of material, a fine needle tend to get deflated. It can affect the stitch loop pick up and cause slip stitches, or it can even lead to needle breakage

A break in the situation of multi-needle sewing with fabric running through the folders would be impossible to repair.

If the needle is too large, there will be poor control of the loop formation which may cause slipped stitches. 

There will also be holes in the fabric which are too big for the stitches and give an unattractive seam appearance.

In closely woven fabric, there will be a pucker along the seam line due to fabric distortion. 

Nomenclature for Needle Size

Metric 

d x 100 = Metric Number, where d is in millimeter,

eg. For d = 0.65 mm, number of needle is 0.65x100 =65




Selection of needle and thread size for a particular seaming situation is a question of achieving a balance between the minimum damage due to pucker which is a matter of small needle size and seam strength which requires a substantial needle and thread.



Sewing-5

Needle Point

These are divided into two parts- Cutting points and cloth points.

Cutting Points: These are needed for fabrics like leather where there are no gaps in the structure.

Cloth Points: These are needed for those fabrics where there are gaps in the structure.

Cutting point Neeedles

a. Wedge Point: It produces most durable seam on leather. It resists great stress, the incision lie at right angle to the seam direction and high stitch density can be achieved.

b. Cross Point: Here strength is considerably weakened. The material is likely to tear if stress is at the right angle. The incisions lie parallel to the direction of the seam.

c. Twist Point: The strength is intermediate and the incisions like 45 deg. to the direction of the seam.


Cloth Point Needles

These are used for sewing textile materials rather than the sheet material already described. The points have a round cross section.

The needles are different for the various woven and knitted fabrics.

Knitted fabrics consist of yarns with spaces between them and if a yarn in a knitted fabric is broken the knitted structure may begin to unravel. The requirement in sewing knitted fabrics is :

a. A needle which will slightly deflate the yarns and enter the spaces.

b. A needle of as small a size as possible consistent with needle strength and sewing thread size.

c. A fabric which is sufficiently lubricated that it has flexibility in relation to the movement of the needle.

The shape of the tip of the neele point which best achieves this deflation is a ball shape and the needle is referred to as a ball point needle.

Woven fabric consist of yarns which can have greater or lesser amounts of twist, interlaced with each other at various degrees of density.

For that a needle is needed that goes between the fibres and does not strike and break them.

The shape of the tip of the needle point which best achieves this penetration between the fibres has the appearance of being slighly cone shaped. It is usually referred to as a set point needle.


Sewing Threads


Selection of sewing threads depends upon the following factors:

1. Performance properties during sewing
2. Performance in the completed garment under conditions of wear and cleaning

Appearance and perfomance of the threads depends upon:

1. Fiber Type
2. Construction
3. Finish

1. Fiber Type

a. Linen- Useful in making strong, rather stiff threads for heavy sweing and also for button sewing.

b. Slk - Advantage- Good appearance and performance, Disadvantage- High Cost

c. Cotton - Good Sewing Performance, Disadvantages- Strength and abrasion resistance are inferior to synthetic threads of equal thickness.
It is more stable at higher, dry temperature than synthetics- less affected by hot needles during sewing.

d. Viscose- 1. Do not have the strength or durability of synthetic fibres. 2. Low tenacity and low strength when wet. 3. High lustre- can be used for embroidery.

Nylon/ Polyester Threads
1. Not affected by rot, mildew or bectaria
2. High Tenacity
3. High resistance to abrasion
4. Good resistance to Chemicals

2. Construction


When the fibres occur in short lengths, they must be twisted together, initially into a single yarn, and then that twist must be balanced by applying a reverse twist, as two or three such yarns are combined to form the thread construction.

- Twist in singles yarn consolidates the strenth and flexibility provided by the fibres themselves.

- Without the reverse twist, known as finishing twist, a conventional thread cannot be controlled during sewing. The individual plies would separate during their repeated passages through the needles and over the sewing machine control surface.

- Remember that the frictional forces acting on a thread during its passage through a sewing machine also tend to insert some twist, predominantly in one direction. 

Sewing Threads


Threads can be

Spun
Threads made from spun yarn have good sewing performance, good dimensional stability and good stitch locking properties in the seam due to their fibrous surface.

Monofilament
One filament of large size. It is harsh on machine and rather inflexible because the cross sectional shape never varies as it would with multifilaments.

Its cut ends are harsh on the wearer. It has virtually no seam grip and stitches tend to unravel easily.

Its good advantage is a translucency which reduces the need for shade matching.

Multifilament Form
Their fineness enables larger thread packages to be used, thus saving operator time changing them.

Corespun
In this a continuous multifilament core is wrapped around a sheath of spun fiber, two or three of these yarns are then plied together.

The majority of these corespun threads consist of a polyester core and a cotton cover.

Thread Finish

The final aspect of thread construction to be studied is that of surface finish.

The most important finish is lubrication.

The requirement of a lubricating finish applied to a sewing thread is that it should produce a regular level of friction, and that for synthetic threads in particular, it should provide protection from needle heat.

Without a controlled amount of lubrication applied to threads, unacceptable damage would be inflicted on them during the sewing process which would result in thread breaks during sewing and seam breakdown in wear.

A lubricant
- Must not clog the needle eye
- should not stain
- Must allow thread to unwind evenly from the package
- Must reduce friction with m/c surfaces but without creating too much slippage
- Must not react adversly to high temperature
- Must be inexpensive
- Easy to apply to the thread during manufacturing.

Other finishes
- Mildew or rot resistant finish
- Water resistant finish
- Soil Release
- Flammability finish

Thread Sizing


1. Metric Ticket Number system

eg if Nm 60/1 means 60m of it would weigh 1 gm.

of 120/2 means 120 m of it would weigh2 gms. In this case it would have a resultant count of 60 ( i.e. 60 gms) would weigh 1 m.

The metric ticket number of this thread based on a three fold equivalent is then three times that i.e.

Nm 80/2= Ticket Number 120
Nm 30/3 = Ticket Number 30 and so on..

2. Cotton Sewing threads are sized on the cotton ticket number system

eg. 3/60 Ne --> equivalent cT= 20--> Three fold equivalent = 60 ( Ticket Number)

3. Denier system--> Weight in gms of 9000 m of length

Thread Packages

1. Spool

a. Used for domestic sewing
b. Not suitable for delivering thread to high speed industrial machines.

2. Cops

a. Small cylinderical flangeless tubes onto which thread is cross bound for stability.
b. Lack of flanges facilitates regular offwinding from the top on sewing machines.
c. Their small diameter makes them less suited for the faster thread offtake of machines.

3. Cones

a. They contain 5000 m cross wound for stability and good offwinding performance.
b. They give troublefree thread delivery.
c. Ideal in situations where thread consumption is high.

4. Vicone- Contain any spillage

5. Large Package

a. Can hold in excess of 20000 m of spun or corespun thread

6. Container

cocoons: They are self supporting ie. centerless, thread packages.

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