TYPES OF NEEDLES

The functions of the sewing machine needle are :

• To create a passage in the material for the thread to pass through.
• To form a loop which can be picked up by the hook or looper or a similar mechanisms.
• To pass the needle thread through the loop form by the looper mechanisms on the machines other than locked stitch.

PARTS OF A NEEDLE

The following are the major components or parts of the sewing machine needle.

• Butt : the top end of the needle
• Shank : The upper circular part of the needle which is inserted in the needle bar and be held by a set screw. It is usually larger in diameter than the rest of the needle for strength reasons.
• Shoulder :This section in between the shank and the blade.
• Blade : The long part of the needle between the shoulder and the eye.
• Long Groove(S) : The long groove runs down the length of the blade to provide a space so as to hold the thread along the blade while the needle pierces the material with minimum friction and to ensure that the thread does not get caught between the needle blade and the material when it passes through. The groove depth should be sufficient enough with respect to thread diameter used in needle.
• Short Groove(S) : This is on the side of the eye facing the hook and extends a little above and below the eye to facilitate initial thread passage into the material and to assist in loop information. On needles with clearance cut it doesn’t exist.
• Eye : The hole extending through the needle blade from the long groove to the short groove. The shape of the inside top of the eye is critical, both in reducing thread damage during penetration of the material and in producing a good loop information. Some needles may have a bulged eye, i.e, having a larger cross section at the eye than in order to reduce needle or fabric friction.
• Clearance : A recess across the whole face of the needle, above the eye, which can vary in shape and length. It permits a closer setting of the hook or looper to the needle to aid loop pick up and reduce skip stitching under difficult conditions.
• Point : It gives easy penetration of different materials and best appearance and less damage on the seams produced.

NEEDLE SIZES – RELATED TO FABRIC AND THREADS

• Each needle system is available in different sizes & the choice of needle size is determined primarily by the fabric and also by the thread combination which is to be sewn. The metric size (Nm) of a needle defines the diameter at a point at the middle of a blade above the short groove as one hundredths of a millimetre. For example, needle with Nm90 has a diameter of 0.90mm at the middle of blade above short groove.
• The correct choice of needle size is very important to good sewing performance. If the needle size is too small for the thread to pass freely through the eye the thread will suffer excessive abrasion and may snarl or break. On the other hand, if the needle size is too large for the thread, poor control of the loop formation may result in skip stitches.

CLASSIFICATION OF NEEDLES

Machine needles are classified on the basis of

• Needle system
• The needle thickness
• The needle point

Needle system

The needle system refers to the fitting measurements of the needle which enable it to be suited for a model/ type of machine. The dimensions / measurements generally stipulated are

• The needle length
• The shank diameter of thickness
• The shank length

The version with regard to the thread grooves and clearance cut.
The basic needle system is the 134 in which the shank diameter is 2 mm and the needle length 38.5mm

Needle thickness

The needle thickness or needle size refers to the diameter of the needle blade immediately above the needle eye. The needle sizes are indicated according to number matrix (Nm) system, the thickness being indicated is in hundredths of a Nm. For example, a sewing machine needle with a blade diameter of 0.80mm correspond to a size 80 needle and diameter 1.50mm to size 150. The required size depends upon the type and size of sewing thread used and the amount of penetration force needed. The other commonly used system of numbering needle is the simonco or the singer machine.

Needle Point

According to points , needles can be classified as under:-

• Normal round point needles (SPI) - They are used for woven material, textiles
• Light ball point needles (SES) - They are used for thin material, silk etc
• Medium ball point needles (SUK) - They are used for hosiery material etc.
• Heavy ball point needles (SKF) - Used for sewing heavy weight materials like rubber
• Special Ball point needles (SKL) - They are used for sewing elastics etc.

NEEDLE MEASUREMENT

English measurement – (#) used in Japan e.g. DB * 1#14
Numerical measurement – Nm used in Germany e.g.DB * 1Nm 90
Conversion from one system to another (-------------#*5)+20 = --------------Nm --------------Nm/100 = ---------------mm

CHARACTERISTICS OF A GOOD NEEDLE

• Needle should be sharp
• Needle should be brittle
• Needle elasticity should be very less
• Needle should withstand high temperature
• Needle should be made up of stainless steel with chromium coating.

Selection of right needle for right fabric.

NEEDLE SYSTEMS AND SIZES FOR DIFFERENT TYPES OF SEWING MACHIENS

THREAD SEWABILITY FACTORS

FOR EXCELLENT SEWABILITY Threads have been designed to be as tolerant as possible to the normal variations which must be expected in production sewing conditions. In the manufacture of good quality sewing threads the following factors are taken care of specially.

Lubrication / Finish

Maximum attention is given to lubrication and finish application methods to ensure short and long length regularity during its passage through various parts of the sewing machine. Optimum lubrication facilitates smooth passage of thread through the hot needle, prevents wear and tear of machine parts and increases seam strength. Through its own R & D efforts, Vardhman threads has developed best lubricants for different threads to meet stringent and high speed sewing applications. .

Loop formation

Thread elongation and recovery properties are very important in determining the thread loop forming properties. Balanced and controlled elongation in thread , helps to prevent skipped stitches.

Freedom from Faults

Obviously a thread in passing through a sewing machine is controlled by guides and contact surfaces of the machine and needle. The presence of faults and knots in a thread will mean that the thread cannot pass smoothly over the surfaces and will cause variations in thread tension leading to irregular stitching and ultimately thread breakage.
Vardhman employs sophisticated manufacturing and process control techniques to ensure that our threads have minimal levels of faults and are continually evaluating methods of identifying and eliminating causes of thread imperfections.

Twist balance

A thread needs to be twisted to consolidate the fibres into the thread structure and ensure good sewing performance. The number of turns in both thread and individual yarns is carefully chosen to give optimum thread strength and sewing performance.

THREAD PROPERTIES AND SEAM PERFORMANCE

Thread is by no means the only factor which determines the value of the properties of seam, namely strength, elasticity, durability, security, comfort , appearance and performance. The other factors are the type of stitch, seam, needle and feed mechanism and the nature of the material being sewn

Seam Strength

When two pieces of woven fabric are joined by a seam, and an increasing force is applied to the assembly at right angles to the seam line, seam rupture ultimately occurs at or near the seam line.
Increasing the seam allowance and edges may help especially if there is an additional problem of seam edges fraying. A lining edge on the inside of a garment , and an increase in stitch density, upto a certain point, does have a useful effect. A change of seam type from a simple superimposed seam to one such as a lap felled seam can help considerably

Seam Slippage

Fabrics have on occasions been rejected for garment use without having been worn after trial garments failed at the seams during wash testing for reasons of seam slippage. Garment failure due to fabric breakdown is more common than that due to thread breakdown and it is usually seam slippage that is the cause.

Stitch Type

Knitted fabrics are normally more extensible than woven fabrics and in some instances, much more extensible. Care is needed in the selection of stitch types so that when a seam in a knitted fabric is extended along its length, the extension limit of the sewing threads is not reached before that of the seam, with seam cracking possibly resulting. Thus the behaviour of seams under longitudinal rather than transverse stress, is of much greater importance in knitted fabrics than in woven ones.

Loop Strength of Thread

Seam failure in a woven fabric which is due to thread breakage could be said to be less of a problem than that due to fabric failure because it can at least be repaired. The majority of thread-breaks in a seam occur at a looped part of a stitch and the loop strength of a thread is more closely related to stitch strength than is linear tensile strength. Loop strength is the load required to break a length of thread which is looped through another thread of the same length and it is influenced by stiffness, fibre or filament type, ply and twist construction and regularity of these factors. The measure of thread strength which most closely relates to stitch strength is minimum loop strength- the strength of the weakest loop in a series, tested in a continuous length of thread. Synthetic threads have higher loop strengths than cotton threads and technical developments have increased even these so that finer speciality thread (core spun threads) can now be used which have the same strength as coarser threads.

Stitch Density

Variations in stitch density affect seam strength and if other factors remain unchanged, then seam strength normally increases with stitch density up to a point where the concentration of needle holes starts to weaken the material. Alternatively, a stronger thread should be used at a lower stitch density. This will require a larger needle size with all the attendant problems of possible needle damage, emphasising again the need to use thread with higher specific strength so that the size of thread and consequently of needle can be used, consistent with other sewing properties.

Seam Stretch

SEAM ELASTICITY

With comfort stretch fabrics stretching up to 30 per cent and action stretch fabrics stretching 100 per cent or more, it is necessary to create seams which will stretch and recover in excess of this so that they do not restrict the flexibility of the garment or break at their limiting extension.

Stitch & Seam Type

Choice of stitch and seam type is very important. Both lock stitch 301 and chain stitch 401, if carefully adjusted, will give adequate stretch for sewing comfort stretch fabrics when used with superimposed or lapped seams. With lock stitch, there is a limit to the extent to which the stitch tension can be loosened to increase stretch and possible to set the stitch looser but only at the expense of an increase in seam ‘grinning’, a temporary appearance of the stitch opening up in the seam when stressed transversely. This feature has given 401 the reputation of having higher stretch than 301. For action stretch fabrics and for cut-and-sew knitwear, it is not possible to achieve high enough stretch in a seam using stitch types 301 or 401. In many garments, a class 500 over edge stitch is acceptable, despite the bulky seam it inevitably produces. The 504 three thread over edge stitch provides the maximum attainable extensibility. The length of the looper threads in the class 500 stitches, together with the compressibility of the enclosed fabric edges, enables these seams to extend to over 100 per cent without cracking.

Stitch Density

Seam Durability

Seam durability is the third aspect of seam performance originally identified as necessary to satisfactory seaming. The length of life of a seam in a garment should be as long as that of the other materials and both should be appropriate to the required end use of the garment. The seam can be considered to have failed in durability terms if either the thread or the fabric in the seam fails at an early stage. Jeans and work wear garments, underwear, school wear, etc. all suffer considerable abrasion in wear and threads must be selected to resist this abrasion as effectively as possible. Duro soft i.e. Polyester/Cotton core spun threads are best known for their high abrasion resistance. The durability of a thread in a seam depends on a tightness, seam type, thread type and the nature of the material being sewn. The critical factor is the extent to which the thread beds into the material. Seam sewn in a densely woven or coated material cannot bed in and are therefore more quickly abraded than those sewn into softer materials. A different problem of seam durability and abrasion can arise with denim jeans when they are subjected to stonewashing. In this process they are severely abraded to produce a worn and faded look. Careful thread selection is required to prevent damage to seams requiring immediate repair or damage which shortens the life of the garment. A satisfactory result can be obtained with DURO polyester/cotton core spun thread. A stitched component of a garment which is both functional and decorative and is subject to much abrasion is the buttonhole, especially when the button is being undone. Synthetic threads give greatly superior performance to cotton threads or polyester-covered core spun give both good durability and good appearance. The use of continuous filament button thread may significantly shorten the life of a spun fibre buttonhole thread by its abrasion

Seam Security

Seam security is another important seam performance factor. The securest of stitches, lockstitch, is formed by the interlocking of the threads together. If a thread breaks in a lockstitch seam, the stitches may run back for a short distance, depending on the longitudinal and transverse stress applied to the seam, the stretch in the fabric and the surface nature of the thread used. Additionally, the stitches can be back tacked at the end of the seam which makes the seam even more secure. The least secure stitches of all are the single thread chain stitches in class 100.

THREAD CONSUMPTION RATIOS

Over a period of time Technical Service Cell have been involved in thread surveys for many customers which have included thread recommendations and measured thread consumption. Table shows examples of the average thread lengths consumed per article, derived from these measurements, for general information.

Careful thread selection will increase cohesion within each stitch and reduce the tendency to fun back. Intermediate in security between the two already described are the chain stitches in classes 40, 500 and 600. Here the threads are interlooped - that is, needle threads are looped through one or more loops of one or more other threads.
Although run-back is still possible, the greatly increased friction within each stitch, subject as always to smoothness of thread surface, ensures that in many cases tangling of the thread in the stitch occurs before it has run very far. In dealing with insecure ends of stitching careful thought must be given to the overall method of construction of a garment and particularly to the sequence of the various stages, to ensure that weak ends of seams are not left and those where sewing across is necessary do actually receive it.

In many cases, there is no alternative but to bar-tack the chain end of thread back into the seam. Where seams become insecure because of thread breaks, the problems are usually those of seam strength and stretch described earlier. Thus the stitch type used influences the initial likelihood of a thread breaking in a seam and also the extent to which the stitching will further unravel. The type of seam break familiar to many consumers is that of a hem which comes apart as a result of catching in it the heel of a shoe or the zip tag of a knee-high boot.

Most of these problem can be avoided by care on the part of the wearer, but, nevertheless, the garment tends to be given the blame. Slip-stitching arises as a result of a failure of the bobbin hook or the looper to pick up the loop in the needle thread. Thread elongation and recovery properties are very important in determine the thread loop forming properties.

Threads which form large, consistent loops are much more safely picked up by the looper, even if the timing is imperfect or the needle is badly deflected in passing through heavy material. Other causes of slip-stitching are bent needles, incorrect needle size or type for the thread size or type, incorrect thread tensions or poor material control arising from a large throat plate hole or poor presser foot control. Comfort is the last of the five seam performance factors.

Seams may be locally tight against the body, they may present a ridge or roughness to the skin because of an unsuitable choice of stitch, seam or thread, or there may be local discomfort because of such things as thread ends or label corners. All may be aggravated by poor garment fit. If a seam is tight against the body it suggests that the extension in the fabric is greater than that in the seam which in turn suggests that seam cracking is a strong possibility.

There is a high level of complaint as a result of the types of labels used in many garments and the methods of attaching them. Greater care in choosing label positions, in deciding how to sew the seam which attaches them, and in covering over the cut edges with a textured thread, will produce more satisfactory garments.

• Needle Thread Breakage
• Skipped Stitches
• Bobbin Thread Breakage
• Un-balanced Variable Stitching
• Staggered Stitching
• Seam Pucker

Seam Pucker

It may be defined as a ridge, wrinkle, or corrugation of the sewn fabric running across the seam. It is a sort of differential contraction occurring along a particular line usually along the seam line, in fabric,
Seam Puckering can be attributed to following causes:-

• Incorrect tension setting
• Structural jamming or inherent pucker
• Fabric and / or thread instability
• Un-balanced Variable Stitching
• Poorly controlled fabric feed
• Extension in sewing thread

Diagnosis

• Without distorting the thread loops in the fabric, cut entire top and bottom threads of all the stitches along a fixed length of the seam. If the pucker vanishes, then it is due to incorrect thread tension setting.
• If pucker does not vanish then remove the stitches. on removal if both faces of seam come to a normal surface, structural jamming has occurred.
• If pucker appears after during post sewing operations or washing, due to dimensional changes in the thread /fabric. It is due to fabric /thread instability.
• Cut the area of maximum pucker, if on removal of stitch, one ply of fabric is longer than the other, then it is due to poor control on feed.

Incorrect Tension Setting - tension setting
Sewing with too much tension in thread causes pucker sewing takes place in stretched state of the thread. After sewing the stretched thread relaxes and attempts to recover its original length, it gathers up seam, which causes pucker.

• Check tension level in the thread, Sew with minimum tension possible. Always adjust bobbin thread tension first then needle thread tension.
• Check dirt / fIy accumulation in the thread guides and eyelets. Check rough or worm out heard guides.
• Check if the coefficient of friction of the thread with metal is high. Contact Customer Technical Service Cell.
• Adjust feed timing and fabric control for maximum pulling of the fabric.
• Check for proper threading or fitting of bobbin case.