BASICS OF AUXILARIES USED IN FOOTWEAR AND LEATHER GOODS

BASICS OF AUXILIARIES USED IN FOOTWEAR AND LEATHER GOODS

REINFORCEMENT:

Reinforcement is used to give extra strength to the weaker areas of the shoes, which are prone to failure. In shoe making, reinforcement are small pieces of leather or other material or tapes which are stitched to the upper in between upper shell and lining shell, to strengthen the points where strain and wear are greatest for example, the top lines, back seam, Punches and Derby stay etc.

Different types of reinforcements are available in the form of particular shapes or tapes and sheets to suit the different category of footwear. Now-a-days various materials like nylon, Polyester, cotton, Paper etc are being used as reinforcement for footwear.

Reinforcements are available in different width and colures and thickness of reinforcement may vary from 0.2mm to 0.5mm.These may be either pressure sensitive or heat sensitive or self adhesive and may be woven, non-woven, knitted or braided.

TYPES OF REINFORCEMENT

Based on the basis Construction  

Woven cotton:

 Woven cotton like Flamelettes or swansdown (interlining/ reinforcement) are given to add body on light leather or PU coated fabrics, but it is not strong enough.

Woven Nylon:

It is stronger but lacks softness, when used, results in pipeness & wrinkles in leathers. So not popular for general reinforcement.

Non-woven:

This is a kind of material that is clotted instead of woven. It is used in the areas having perforation, eyelet stay and straps with raw edge.

Knitted cotton

These are used where high degree of shape is required as these have greater stretch. They are used for uppers where blocking or pre-shaping is required. This is also find suitable for back seam and closed seam to obtain high degree of stretch during lasting pulls.

Acme:

Backers are plain flat weave fabric, coated on one side with a heat sensitive adhesive. It is available in different weights and degree of stretch.They adds strength to the concerned area and pressed under specific temperature.

Based on basis of Application

A. General Reinforcement:

Refers to Backers/ Doublers, interlinings etc. Backing or doubling is the addition of a tightly woven material to the back of a thin or very stretchy outside component. This helps in:

Adding body especially on thin, soft leathers or making the thickness of the component more even when increased overall thickness in the upper is required, controlling stretch and adding strength.

Shape Retention.

To improve appearance and wearing qualities.

To bear the lasting pulls. 

Top line Reinforcement

These are important and a must, since

1.Top line area is always being under stress & strain during lasting pulls, so it may weaken and d-shape the top line of shoe after D- lasting.

2.It may stretch & cause a loose & irregular top line making it baggy. This is called BOATING of shoes and causes the shoe to slip off while walking.

3.To avoid distortion to the shoe.

4.It is important for the top line reinforcement to be stitched at the back seam, otherwise the strain will not be evenly distributed and top line may split.

5.Use an extra reinforcement for extra protection like on a “V’’throat court shoe.

6. Examples include Folded Top lines, French bound edge, U- binding, etc.

7.During wear, the cumulative effect of thousand steps can result in breakdown of the top line.

8.Provides comfortable FITTING all around the ankle area. 

Selection of Reinforcement

Selection of reinforcement for top line depends upon Material of upper, style of upper and top line.

According to Style of Upper:

Style of upper assumes importance in case of open shoes, especially, ladies court shoes because, the higher the vamp and quarters, greater will be the strain on the top line. Also, the wider the radius of the curve, the less the strain. So for vamps with narrow curves, additional reinforcement will be needed. 

According to Top line:

For Folded Top lines: It is important to use a narrow (2-3 mm) woven or braided tape. It should be fixed and set in the center of the folding margin and becomes top edge after folding. For very thin materials, especially ladies high quality shoes, a thin nylon folding tape is fixed in between the folded edge, to make the top line tight snuggly fit. This would increase the tensile strength; give a nice thin edge and good elasticity to the top line. The tape must be stitched in during top line stitch (lining stitch) to avoid slippage.

For French Bound: Reinforcement (3mm) is stitched in, on the reverse side of the upper, while stitching the binding. Best results are by a pre- coated edge tape. But higher stretch ability can be obtained from nylon- braided tape.

For U- bound: A light nylon tape, slightly narrower than the U- binding should be used before stitching. A secondary top line tape (3mm strong woven) may be stitched onto the top line before putting the binding. The reinforcement tape should come under stitch.

Bagged Top line: Top line should be pre-taped before stitching with lining. Braided 3-4 mm nylon tape is used for proper top line shaping and gripping.

B. Local (Restricted/Centralized/Confined) Reinforcements

These are required for vulnerable areas where there is localized weakness or stress concentration is high. These are applied only to the areas affected. Local reinforcement is used, to strengthen the areas of upper, against a particular risk of failure in shoe making or in wear. These are pieces of material with pressure sensitive adhesive coating, for ease of attachment and are available in many shapes and sizes. The only consideration is that the reinforcement piece must be big enough to cover the concerned area. Examples include tight throat curves, stay, perforated uppers, eyelets, saddles and Derby intacting.

For Tight Throat Curves

1.            For this area, reinforcement should be of right shape and right size, so it can bear the strain and spread the stress.

2.            It can be pre-cut to shape and stitched with the top line. For this high strength polyester are good.

3.            If it is not pre-cut to shape, then 4 cm x 2.5 cm piece of reinforcement could be placed accordingly, to the concerned area and stitched with the top line. Non woven stays are found most suitable for this purpose. 

For Perforated Uppers

1.            On uppers that have been perforated (punched),it is usual to put reinforcement tape behind the holes, which do not lie on top of another section, e.g. the wing cap punching on the vamp. The reinforcement must extend at least 1cm beyond the edge of the perforated area. For this, a lightweight, flexible, non –woven material with good tear resistance, low stretch, uniform tightness and bonding is required.

2.            In perforated upper, resist the temptation to put 3-4 smaller pieces of reinforcements. One large piece will spread the load and provide a stronger support.

3.            The tape serves a number of functions like it make the upper more presentable as you cannot see inside the shoe. It restores some of the water resistance to the upper and reinforces the upper and prevents distortion of the perforations.

4.            Particularly with semi-brogue shoe, it is usual to put at least one row of stitching on each side of punching. If the tape is stuck on before stitching-then the stitching passes through the tape to make a stronger job and holds the tape in position during wear.

5.            In case of Brogue shoe, large backers are used to cover the back of centre designs punched on toes of vamps.

For Stay:

1.            Stay is a piece of non stretchy, thin, strong material which is put in parts of an upper which are subject to strains. Since if upper is not reinforced in some way, these strains would cause tearing, causing upper failure.

2.            To avoid breakage of seams at the top line, use a 15 mm wide stay extending 1 cm on each side and stitch while stitching the top line.

3.            These stays usually have a thermo-plastic adhesive backing and are applied by hand, using a domestic iron or in a heated press. 

For Tabs and saddles:

A nylon sheet or tape offers good stitch holding properties. It should be positioned before stitching and should of a greater width than the saddle. 3 mm extra at each end would be enough. 

For Buckles Straps, Sandals, etc.

These are required because very often straps break at featheredge, pullouts from lasted margin, failure at attachment point of buckle/ straps, etc. So the reinforcement to be used should be having good breaking strength and tightness. Straps less than 10 mm in width must be reinforced. Woven nylon top line tapes are good as they restrict stretch and distortion. The tape should extend to the full width of the strap and should be low stretch. For raw edges, non-woven tape should be used to avoid fraying. A function straps are subjected to substantial stresses during wear therefore reinforcement may be necessary to prevent:

1.            Permanent stretching resulting in loss of fit.

2.            Tearing or distortion of adjustment in holes.

3.            Complete breakdown of the straps.

4.            Detachment from the upper.

For Eyelets (Lacing Holes, Tie Holes)

1.            Eyelets are the holes in the quarter. Latchets or tongues through which a string, ribbon, or thong is passed to hold the shoe on the foot. It is a small metal disc with hole in the center used to reinforce lace holes.

2.            When the laces are pulled tight, considerable strain is put in the area of eyelets. Also, when blind or invisible eyelets are used, these do not clench through the upper & lining, but only clench on the lining, all you see on the outside is a hole punched in the leather. To give, the eyelets extra thickness to clench on and support for the facing, an additional piece of material is often attached to the linings before eyeleting. For eyelets, it is very important to put reinforcement stays with high tear strength, good bonding, some plumpness and softness to be perforated. Compressed paper and non - woven polyester are the best. The stay must extend 1cm on all sides of the eyelets. 

For Fastenings and Decorative Trims:

1.            Do not have to face high stress but must be held securely. A high strength yet thin stay must reinforce attachment points. Woven nylons are good and should be applied before trim attachment, giving 5mm allowance around the trim area. Trim must not be attached across a seam and also not positioned in flexing area.

2.             For closed seam, the tape must have strong adhesion properties and must conform easily to curves, esp. on long seams. Light upper materials need light tapes. Light materials need a low stretch tape. Long seams need elongation quality in tape. Knitted nylon tape is required for close seam.

3.            For lapped seams and blind seams, tape is required only if the edge/ material is very thin and may tear while stitching. The tape must be very thin-a lightweight nylon tape.

4.            For French/Silked seam, a strong tape with low side stretch.

5.            For Welted/Piped seam, bias cotton tapes or polyknit tapes are required.

6.            Some men’s shoes have the quarters joined together with a seam and dog tail. To prevent the top lines splitting or bursting when the lasts are removed, a piece of woven fabric adhesive tape is stuck just below the top line before the quarters are folded (beaded).

TEST METHOD: REINFORCING TAPES

Pressure sensitive tapes are used to reinforce the seams on parts of shoe uppers which are subjected to strain during and after shoe fabrication. They consist of a backing material- paper, or fabric. Coated on one or both sides by a pressure sensitive adhesive. The tapes are tested for Tensile strength, elongation at break, Resistance to tearing and colour fastness for dyed tapes.

S.No.	Property/ Test Method	Standard	Unit	Test value	Remarks
1	Elongation at break	DIN 53857 SNV 198461	%	12, 20
2	Ultimate Tensile Strength	SNV 198461	km	40	Calculation on tear resistance and metre weight
3	Resistance to tearing	DIN 53857 SNV 198461	N/ width	280-320, 280-330, 300-350	3 mm thick, 4 mm thick, 5 mm thick
4	Colour fastness for dyed uppers		Visual		Rub by hand a moist cloth

Direct & Indirect Reinforcement:

1.            Direct reinforcement is the materials which are directly given to the materials, to give strength.

2.            Indirect reinforcement is used to assist in shoe making in any area, which is weak and has to face the pulling strains during lasting. These reinforcement are provided to withstand the stress, due to lasting pulls at the time of lasting, such as

1.            In the direction of the pincer pull (Lasting pull areas).

2.            In elastics to prevent excess pull. This reinforcement is removed after lasting. 

TOE PUFFS AND STIFFENER AS A REINFORCEMENT MATERIALS

TOE PUFFS

The function of the toe puff is basically to provide shape to the fore part of the shoe, and in certain case, in the industrial boot, to give protection to the foot of the wearer. It is the mean by which the shape of the last forepart is reproduced in the finished shoe, and thus plays an important part in the appearance and the general performance of the majority of the footwear types. The choice of the toe puff for any given footwear type is influenced by many factors of the last shape, upper material type, production methods to be used, fashion and individual customer; all must be considered before a decision can be reached.

The basic types of toe puffs are used by the footwear industry:-

1.            Paint on liquids

2.            Impregnated fabrics

3.            Thermoplastic (heat activated)

4.            Solvent  activated

5.            Print on hot-melt resin

6.            Extruded film ( heat activated)

7.            Pre-molded steel & Plastic puffs

STIFFENER-

A stiff material similar to that of the toe puff which may be moulded to the shape of the last back part or, alternatively, inserted flat and moulded during the subsequent process. It is normally inserted between the lining and the upper to support the back of the shoe and grip the foot.

Apart from the material used which is similar to that used for toe puff expect for the thickness, leather board can also be used.

The three types of stiffener are flat stiffener, Semi-moulded stiffener, and the fully-moulded stiffener.

TEST METHOD:  TOE PUFFS AND STIFFENERS

Toe puff is attached to the flesh side of the leather or fabric of synthetic coated fabrics. The material should have, required strength and stretch, resist foot’s moisture and distortion from repeated flexes, abrasion from toe nails, confirm to the contours of the last, should not stick to the last or the fusing press.

1.            Tensile strength and elongation at break

The toe puff is pulled during toe lasting and stiffener is moulded to the contours of the last. The test sample is mounted in between the jaws of the tensile tester and pulled apart until the material breaks. The test samples are cut from, the warp, weft and bias. The extension at break and the breaking load are noted.

2.            Bond Strength

The toe puff or stiffener is attached to the upper material in a press. The temperature of the upper plate is maintained at 180 degree Celsius. The material is cut into test samples. The peel strength is determined using universal testing machine. As the temperature of the top plate increases the bond strength also increases, but at a particular temperature the adhesive becomes fluid.

3.            Shape retention / Dome strength / Hardness

A toe puff or stiffener when attached to the upper and lasted, should retain shape, resist collapse, after the last is removed and also during wear.

           The test piece is activated. Thermoplastic material is heated to 80 degree Celsius for 8 minutes in an oven. Cellulose acetate toe puffs are solvent activated for one or two seconds. Fiber board stiffeners are exposed to a jet of steam at 50 degree Celsius for six minutes. The material is then placed on a dome forming jig. A dome of test sample is formed by pushing the material, by and screwing up,  to give the material shape of a dome. The initial height of the dome is measured by using a micrometer. The jig is screwed down and the test piece relaxed for 24 hours. The height of the dome each time is directly proportional to the area. Thus the area of shape retention is calculated.

d)       Collapsing Load

The material is moulded to the shape of the dome. The jig is unscrewed. The top of the dome is compressed at a constant rate in a tensile testing machine. A cylindrical plunger is used to compress the dome recording maximum compression load. The material is again shaped to the dome, compressed load determined again. The experiment is repeated ten times in total, recording each time the compression load. The experiments are repeated on wet samples.

Hardness: This is a measure of the collapsing load.

Resilience: [10th collapsing load / 1^st collapsing load] x 100

Moisture resistance:      [1st collapsing load (wet)]

                                      -------------------------------------    X 100

                                       [1st collapsing load (dry)]

GUIDELINES/PROPERTIES

S.No.	Property	Test Method	Unit	Test value	Remarks
1.	Hardness	SATRA	N	>130 130-81	Very hard Hard
2.	Resilience all types except filmic	SATRA	%	20-24 25-34	Very hard Hard
3.	Area shape retention	SATRA	After ten collapses	60-80 55-85 ( depending upon category	Toe puffs Stiffeners
4.	Moisture resistance	SATRA	%	50-80
5.	Peel strength	SATRA	N/mm	0.5 1.0 and 0.6 0.6 and 0.3	Stiffener Toe puffs Unlined/Lined

THREADS

CLASSIFICATION OF THREAD

Threads are made from fibers.

                                                          Fibers

 

             Natural (cotton, jute)                                                    man made

                                                                             (Polyamides, nylon, polyester etc.)

CONSTRUCTION OF THREADS

Fibers are twisted together to make yarns/filaments. This twist is called first twist/singling twist. Two or more yarns are joined together by a reverse twist to form a thread. This is important as otherwise the individual plies would separate while sewing. This twist could be either clockwise or anti-clockwise.

Clockwise twist produces a Z-twist and an anti clockwise twist produces S-twist. The twist of the thread is known by the finishing twist.

                          

1.            Twist is defined in terms of the no. of twists inserted/cm., increase of too much twist, thread gets lively, while in case of too less twist, yarns open up and fray.

2.            In the stitching room, all machines are with clockwise movements of hooks, so necessary to use Z-twist thread in closing room. In case, S-twist thread is used, it will untwist and break.

3.            In case of heavier threads, these twisted threads are further twisted to form cords. It is very important to remember that with every twist, direction of twist reverses.

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TYPES OF THREADS

Multifilament/monochord: These are very fine threads formed by twisting polyester filaments. A light bonding finish is given to these filaments.

Monofilament: is only one filament which is thick.

Braided threads: are plaited threads of polyester/nylon and are useful for automatic machines.

THREAD SIZE/TICKET

There are two methods to size a thread.

Fixed length system:

Weight in grams, of a fixed length of thread. So the heavier the thread, the higher the no.

Fixed weight system:

Length in meters, of a fixed weight of thread. So the finer the thread, the higher the no.

THREAD CONSUMPTION

For lockstitch,

Thread consumption = 2*(material thickness + stitch length) * stitches/cm + 10-15% wastage allowance.

PHYSICAL PROPERTIES:

Cotton threads

1.            Good sewing performance

2.            Poor abrasion resistance

3.            High wet shrinkage which may cause seam puckering

4.            Less affected by needle heat

5.            More stable at higher and dry temperature.

Synthetic threads

1.            High abrasion resistance

2.            Less shrinkage

3.            Soften at a temperature of 230 degree Celsius

4.            Not much affected by moisture, not on mildew

HOW TO CALCULATE THREAD REQUIREMENT FOR STITCHING

A. No of stitches/cm ………………………………………………… mm

B.   Therefore 1 stitch…………………………………………………mm

C.  Total thickness of material to be stitched……………………… mm

Thread required for 1 cm of

Stitching if no of stitches is A then …………………………… = A*(2B + 2C) mm

                                                                                                = A (2B + 2C)/10cm

Example:

No of stitches per cm……………………. = 6

Therefore 1 stitch………………………... =10/6mm = 1.67mm

Total thickness of material to be stitched... =1.4mm

Thread required for 1 stitch………………. = 2*10/6 + 2*1.4 = 20/6 + 2.8mm

                                                                    =3.33 + 2.8mm = 6.13mm

Thread required for 1cm of

Stitching is……………………………….. = 6*6.13mm

Thread required…………………………  = 36.78mm

                                                                 = 3.8cm

                                                                  

Note: the quantity of thread depends on the no. of stitches/cm and the thickness of material.

Thread required for 1 cm of stitching =

[(2*stitch length in mm) + (2*material thickness in mm)]*no of stitches per cm*1/10 + 10-15% wastage allowance.

THREAD – NEEDLE RELATIONSHIP

THREAD	TICKET NO.	SINGER	METRIC
continuous filament, nylon, bonded & or twisted	80 60 40 20	12 -14 14 -16 16 – 18 18 – 20	80 – 90 90 – 100 100 – 110 110 – 120
core spun polyester/cotton	75 50 36 20/18	12 -14 14 -16 16 – 18 18 – 20	80 – 90 90 – 100 100 – 110 110 – 120
continuous filament polyester	70/65 50 36 14 18	11 – 13 13 – 15 15 – 17 18 – 20 20 – 22	75 -85 85 -95 95 – 105 110 – 120 120 – 130

MAIN QUALITIES OF THREAD REQUIRED FOR FOOTWEAR ARE:

 Strength:-

Thread should be strong enough so as to be able to penetrate two or more layers of leather without breaking.

Stretchiness:-

Thread should be stretchable enough to withstand all shoe making operations without breaking but should not stretch too easily.

Elasticity:-

Thread should be elastic enough so that the seam can recover well after stretching and not become loose in wear.

No shrinkage/expansion, when exposed to heat or water.

Flexibility and resistance to flex cracking.

Uniform thickness, to avoid snagging during stitching.

Good loop formation property i.e. properly twisted to avoid missed stitches.

Good abrasion resistance: to withstand rubbing in wear and high speed stitching.

Resistance to needle heat.

Resistance to bacteria.

Resistance to damage from sunlight

Colour fastness.

Retain a good appearance in finished seams.

Tests on Sewing Threads:

There are large number of tests available for assessing the quality of sewing threads and the most common tests conducted by the manufacturers and users are physical and fastness properties. However, the most critical test for sewing thread is the ‘sewability’ in the dynamic conditions. The principles and methods for evaluating some of the important sewing thread properties are discussed in this paper.

INTRODUCTION:

Sewing thread is considered to have been the first textile material. History tells us that some 25000 years ago sewing threads were made by the persons living in caves and jungles by rubbing and twisting together the long fur fibers pulled from animal skins. The crude threads, by means of needle were used to join animal skins to form the primitive clothing of the early civilization.

The most affected was the textile industry especially the textile fabrication and sewing thread industry. In India till 1990 we are used cotton threads only, but technical developments have given us a wide range of synthetic threads which are for most purpose now superior to cotton threads.

THREAD DIAMETER:

The diameter of sewing thread is an important parameter for effective sewability. It must be appropriate to the size of the needle eye. If the thread diameter does not match with the size of the needle eye, the thread may break during sewing deteriorating the appearance of the seam. When the diameter of the thread is large enough, it displaces the yarn in a fabric, resulting seam puckering. Generally the width of the needle eye is about 40% of the size of the needle. Sewing thread must not occupy more than 60% of the width of the eye to avoid the fraying of thread during sewing.

SHRINKAGE:

Measurement of shrinkage of sewing thread is very important because it may cause puckering along seams and thus adversely affect the seam appearance.

The following combinations may change the influence of sewing thread shrinkage on the seam: the construction and mass of the seamed fabric, the nature of the seam assembly, or the tension on the sewing thread during sewing. Shrinkage testing of thread due to its Exposure to;

»Dry heat

» Boiling water

DRY HEAT SHRINKAGE:

After preheating the drying oven to 176+3oc, the specimen is suspended freely from a stationary rack side the oven away from the side walls. After the oven returns to the original temperature, the specimen is then exposed for 30+2min. Then the specimen is removed, conditioned and the loop length is measured.

LOOP AND KNOT STRENGTH

The thread, after proper conditioning is withdrawn from the thread holder very carefully to avoid any change in twist or any stretching of the specimen. For measuring loop strength and elongation, two pieces of a thread are taken from one thread holder or end. Then both ends of one piece are fixed in one clamp of a tensile testing instrument without a change in twist. The length of the loop is approximately one half the gauge length. One end of the second piece is then passed through the loop formed by first piece and both the ends of a second piece are fixed in the other clamp of the machine. The loop breaking strength and elongation is then measured in the same way as that of tensile strength and elongation.

ABRASION RESISTANCE:

A sewing thread is subjected to vigorous abrasion during sewing operation while it moves through needle eye and different parts of a sewing machine. In a garment or any other finished goods the sewing threads need to withstand a great deal of abrasion while in use. Abrasion resistance of sewing thread is thus very important quality parameter of a sewing thread. There are different methods available for assessment of abrasion resistance.

UV RESISTANCE:

Ultra-violet rays are a part of spectrums of electro-magnetic radiation emitted by sun. They severely damage the thread if exposed continuously for long periods.

What happens when seams are exposed to sunlight:
Base polymer of sewing thread is irradiated by ultraviolet/visible light. And this results in change in the physical and chemical properties of polymer of sewing thread due to absorption of energy. This energy absorption promotes the degradation of the polymeric chain and ultimately the strength loss to the sewing thread. Not only this, UV radiations also attack the dyes present thread leading to spotting and fading of color of sewing thread.

CHEMICAL PROPERTIES:

Testing of some important chemical properties are briefed here;
1. Color fastness to washing
2. Color fastness to dry cleaning
3. Color fastness to water migration
4. Color matching

NEEDLE

NEEDLE PARTS AND FUNCTION

Butt: facilitate easy entry of needle in to the needle bar.

Shank: provides a firm seating for the needle in the needle bar for stability during stitching. The shank diameter varies according to the needle system.

Blade/shaft: is in between the shank and eye of needle. The shape and diameter of the blade determines the penetration strength and size of the perforation.

Shoulder: in reinforced needles, blade tapers gradually from shank diameter to the blade diameter and this tapered area is called shoulder. This tapering gives more strength to the needle and reduces vibrations at high speed. It also reduces friction between the needle blade and material, thus reduces needle heat vibration.

Long groove: is on the threading side along the blade of the needle. The function of long groove is to hold the thread along the blade when the needle pierces in to the material, so that friction is reduced and thread is not caught between the needle blade and the material when it passes through.

Clearance cut: is a flat cut in blade of the needle above the eye on the thread exit side.

Whenever needle insertion is done, the clearance cut should always face towards the hook.

The clearance cut helps in a better stitch formation as hook could come closer to the needle to pick up the thread loop. Also, it reduces the chances of damage to needle or hook point.

Needle eye: is always elongated in shape to help the diagonal movement of the thread. Since the thread has to pass through the needle eye 25-30 times before it forms a stitch, so it is very necessary that the needle eye should be highly polished to make it smooth.

Head groove: is the thread groove between the eye and point of the needle. This groove protects the thread from undue friction, when the needle eye and the point rise out of the material. This groove is sometimes twisted either to the left or to right in order to ease the stress on thread during sewing.

Needle point: is tapered at the end so as to perforate the material.

Is done on the basis of:-

1.                  Needle system  

2.                 Needle size and

3.                 Needle point

1.            Needle system: refers to the fitting measurement of the needle which enables it to be suited for a particular model/type of machine. The measurements which are taken into account while constituting a needle system are: shank length, shank diameter, blade length, needle length, thread grooves and clearance cut.

1.            134 system: needle length = 38.5mm;shank diameter = 2mm

2.            134-35 system: needle length = 42.0mm;shank diameter = 2mm

           E.g. Cylinder bed/slipper binding m/c

3.            34 system: needle length = 38.5mm; shank diameter = 1.6mm                             (E.g. Bar tacker machine )

4.            134 kk system: needle length and shank diameter remain same as 134 systems but the shank length gets reduced and blade length is increased. It was found that in case of materials heavier than 1.2-1.5mm. The higher part of the needle entered the material leaving holes which looked ugly as well as reduced the rest strength of the material. Thus, kk was introduced as a subclass of 134 systems. But kk should not be used on high speed machines as due to longer blade and shorter shank, strength of the blade is reduced.

5.            438 systems: needle length and shank diameter same to the 134 system but clearance cut is long.

                  E.g. Zigzag machine

II. Needle size/thickness: refers to the diameter of the needle blade just above the needle eye. The choice of needle size depends up on type and size of thread, penetration force required. Needle size could be indicated by the number metric (N.M) system or singer system, in case of N.M system, thickness is indicated in 100^th of a mm. for e.g. If blade diameter = 0.8mm then needle size = 0.8*100 = 80.

Comparison table for different types of needle sizing system:

Metric(Schmitz)	60	65	70	75	80	85	90	100
Simon co.(singer)	8	9	10	11	12	13	14	16

2.            Needle points: the purpose of needle point is to perforate the material either by pushing aside the fibers or by cutting through the material in order to make way for the top thread to be passed down and being taken up by the book in the process of stitch formation. Thus, the needle is tapered, so as to open the hole to the size of the blade diameter.

In case of synthetics/fabrics: needle should perforate the material by pushing aside the fibers so that the fibers are not cut and damaged. So we use round(R) point needle for synthetics/fibers.

But in case of leather and similar material, due to the hardness and thickness of material needle couldn’t perforate the material, unless and until material is cut through. So, we use cutting point needles for leather/similar material. Since, when cutting point will cut the material, a hole will be formed of a particular shape, so cutting points classified according to the shape and position of the cutting edge.

POINT FORM	OPERATION
P,PS,PSS,PCL,PCLs,PCR,PCRs	Whenever the stitch density is high .e.g. French binding, Italian binding, lapped seams, closed seam etc.
S.SS	Whenever stitch density is less. E.g. for decorative seams
LR,LL,LRs,LLs	For lapped seams, decorative seams, zig zag machine.
R	Fabrics, knitted, very fine and soft materials, elastics, bindings.
Sd1	Synthetics, French bindings, elastics, fine leathers.

TYPES OF NEEDLES USED IN MACHINE SEWING

TYPE OF SEAM	NEEDLE TO BE USED
Back seam Decorative seam Top line stitch French binding U – binding Butt seam Counter seam Intacting stitch Zip stitch	PCL, P, PS LR, S PCL, PS PCL, PS SDI, R LL, LR LR, P, PCL SDI SDI,R

POINTS TO REMEMBER:

1.            Twisting the needle even by 5 degree could change the seam appearance.

1.            Use of a heavy needle on a soft thin material leads to puckering which looks ugly.

2.            Don’t use S point needle where stitch density is high.

3.            Don’t use CL and CR where stitch density is more than 7 st. /cm. as it reduces the rest strength of the material.

4.            Don’t use SD1 on leathers thicker than 1.8mm.

5.            Never use P point on a zigzag machine as the direction of the cut changes.

6.            Always check the system while changing the needle and the machine.

7.            Needle heat could be overcome by using as thin a needle as possible, lubrication of sewing thread; with silicon oil/emulsion just before it passes the needle eye; using a cooling stream; using chromium plated needle or needles treated in a phosphate bath.

8.            For automatic stitching machines which are multi-directional, most cutting point needles are unsuitable. The best is SD1 as it does not have any effect on the appearance of the seam.

9.            Imitation leathers are synthetic materials which are given leather like structure and are supported by woven, non woven or knitted material. For these, we use SD1 or PS point needles.

EYELETS

                                        

  

    Brass eyelets                                                           Different types of eyelets

                         

                            

 Curtain grommets, used among others in shower curtains       a boot with eyelets and hooks

DEFINITION:

The eyelet is the smooth circular piece that laces is thread through. Eyelet can be made of metal or plastic, and are used to cover the edges of holes made in shoes or clothing.

An eyelet provides a smooth, rigid surface for laces to be fed through, and the fabric from fraying where the hole was made.

Eyelets are put into an upper by hand/ machine, which first punches a hole, then inserts the eyelet, clenching over the reverse side. The eyelets may be invisible or blind type or it may have a visible outer rim which can be plain or decorative as visible eyelets.

Purpose of eyeleting

1.            To provide a reinforcement to lace holes in materials.

2.            To secure two or more pieces of material together.

3.            To provide decoration or Ornament for a material.

Clenching

 Clenching is done by a pair of dies, one of which causes the “Tail “of the eyelet to spread.

Types of eyelets

1.            Plain round eyelets (Metals; like brass & aluminum).

2.            Pentagon eyelets (Metal).

3.            Hexagon eyelets (Metal).

4.            D-rings (Metal & Plastic).

1.            Hooks (Metal & Plastic).

Eyelet sizes

As such, there is no standard form of eyeleting or nomenclature linked with dimensions, but even after this, most prevalent sizes are 200 No.,  400 No., 600 No.In this figure, a partly cut-away, round headed celluloid eyelet with brass shank has been shown with its dimension. Arrows are depicting the essential measurements.

Eyelet Setting & its type

The method by which an eyelet is made to clench in the material is known as its setting.

Setting types:

Starred type: When a eyelet is clenched between a pair of dies, the tail of the barrel splits along the vertical grooves forming six or eight tongues, which spread and grip the material.

Round setting: In a round setting, barrel of the eyelet is plain but the die itself is nicked to produce the splitting which is usually slight since only smaller eyelets are clenched in this way.

Ordinary setting: Normally uses an eyelet nicked round the tail, but does not have the regular appearance of starred setting.

Non-split setting: Which is especially suitable for short-barrel eyelets on canvas shoes?

General rule for eyeleting is that if the eyelet is plain, the dye should be grooved or nicked and if eyelet is grooved or nicked, the die should be plain.

Eyeleting on the basis of effects in uppers

In addition to these above variations in the manner of clenching, there are also four possibilities in the method of eyeleting, according to the effect required in the finished shoe

Surface eyeleting: This is the commonest method, in which the eyelet penetrates both the outside and lining material with the head outside and the clenched barrel tail showing inside.

Disadvantage of this method is that the clenched tail may cause damage to stockings. 

Invisible eyeleting:

Here eyelets are inserted through and clenched on the lining only (or sometimes taking in reinforcement tape, next to the lining). In finished shoe, all that is visible is a small punched hole outside and the head of the eyelet resting on the lining inside. The range of these eyelets is very small, only one length of barrel is needed.Colours and finishes are reduced to a minimum (plain nickel is generally accepted) and two sizes are enough for most manufacturer. 

Blind eyeleting:

Often confused with previous method and not today very commonly used. Here, the eyelet head shows on the outside but the barrel does not penetrate the lining, the clench taking place on the reverse of the outside material (or on a reinforcing tape).The lining covers the clenched barrel (and so protects the stockings) and only a row of holes is visible. For this, as before, a short barrel is necessary but since the head shows, various sizes, finishes and colors are required.

Double eyeleting: is carried out on footwear, intended for heavy duty, such as army boots.

 The operation takes place in two stages:-

1.            First, a large eyelet is inserted from inside the upper through the lining and outside material, and clenched on the surface (ordinary setting).

2.            Then, a second eyelet with smaller diameter barrel is inserted from outside and clenched within the head of the first one. The second head completely covers the clench of the first eyelet.

This method is also used for some rubber-soled Canvas shoes. 

Eyelet Finishing

Most eyelets, today, have brass as their basis, but the finish supplied varies with the requirements of the shoe manufacture. Majority of the fancy styles are plain brass, so that they are more obvious in the finished shoe, acting as ornament as well as a hole reinforcement. Ordinary round shoe eyelets, however, are available in following finishes: 

Japanned finish:

It is available in black or brown color and is the cheapest one. It has not durability of finish as constant lacing soon wear off the Japan, leaving the metal exposed.

Celluloid dipping: It is better than earlier one and available in wide range of colors. The eyelets heads are covered with a heavy coating of a viscous celluloid solution which after a lengthy drying period becomes hard and will stand up to reasonable wear. 

Solid Celluloid:

The best quality eyelet has the brass head, specially formed to take a moulding of solid celluloid to give either a round or a flat effect on the head. The finishes are extremely durable, does not reveal the metal or change colour.Several sizes, and in a wide range of color are available.

Antique finish: A finish that replicates rusticated or distressed textures, produced through mechanical or chemical means to simulate naturally.

Oxidized Finish:

Oxidized sterling silver is a darkened metal of sterling silver which is decorated mostly to improve its appearance. The oxidizing happens when the sterling silver is exposed to oxygen. One can control the colour and deepen the dark appearance. You can also use a finishing gloss to make the colour a permanent darkened metal hue.

EYELET TESTING

 Footwear test labs often test eyelets for attachment strength. A typical strength test would consist of:

A tensile testing machine with a traverse rate of 50 mm/min. Specimens are removed from the footwear. An eyelet puller is inserted into the upper portion of the tensile tester and the test eyelet stay is clamped into place. The test is started and the force will reach a peak, decline slightly, and then increase to complete failure. The value at which the force declines is recorded and reported as the initial failure point, since this is the separation point of the material around the eyelet.

Metal eyelets are also tested for corrosion. The most common test for this is ASTM B 117, Standard Method of Salt Spray (Fog) Testing. Eyelets are exposed to a 5 percent, ± 1 percent, saline solution for a period of 20 hours. Specimens are then rinsed under warm running tap water, dried with compressed air and inspected. Some Standards’ pass/fail requirements state that metals that are inherently resistant to corrosion can show no more than light surface-type corrosion or oxidation and ferrous metals can not show any corrosion of the base metal.

So the next time you lace up, pause and take a moment to think and appreciate the importance of this little piece known as the eyelet.

RIVETS

                     

Different types of rivets        High-strength structural steel rivets        Solid rivets

      

Sophisticated riveted joint          a riveted buffer beam       A riveted truss bridge over the

   On a railway bridge                on a steam locomotive               The Orange River                                 

                                                                            

DEFINITION

A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or drilled hole, and the tail is upset, or bucked (i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. To distinguish between the two ends of the rivet, the original head is called the factory head and the deformed end is called the shop head or buck-tail.

Because there is effectively a head on each end of an installed rivet, it can support tension loads (loads parallel to the axis of the shaft); however, it is much more capable of supporting shear loads (loads perpendicular to the axis of the shaft). Bolts and screws are better suited for tension applications.

Fastenings used in traditional wooden boat building, such as copper nails and clinch bolts, work on the same principle as the rivet but were in use long before the term rivet was introduced and, where they are remembered, are usually classified among nails and bolts respectively.

1 Types

1.            1.1 Solid/round head rivets

1.            1.1.1 High-strength structural steel rivets

2.            1.2 Semi-tubular rivets

3.            1.3 Blind rivets

4.            1.4 Oscar rivets

5.            1.5 Drive rivet

6.            1.6 Flush rivet

7.            1.7 Friction-lock rivet

8.            1.8 Rivet alloys, shear strengths, and driving condition

9.            1.9 Self-pierce rivets

We’ll discuss here only one type that is Semi-tubular rivet.

                             A typical technical drawing of an oval head semi-tubular rivet

Semi-tubular rivets (also known as tubular rivets) are similar to solid rivets, except they have a partial hole (opposite the head) at the tip. The purpose of this hole is to reduce the amount of force needed for application by rolling the tubular portion outward. The force needed to apply a semi tubular rivet is about 1/4 of the amount needed to apply a solid rivet. Tubular rivets can also be used as pivot points (a joint where movement is preferred) since the swelling of the rivet is only at the tail. Solid rivets expand radially and generally fill the hole, limiting movement.

The type of equipment used to apply semi-tubular rivets range from prototyping tools (less than $50) to fully automated systems. Typical installation tools (from lowest to highest price) are hand set, manual squeezer, pneumatic squeezer, kick press, impact riveter, and finally PLC-controlled robotics. The most common machine is the impact riveter and the most common use of semi tubular rivets is in lighting, brakes, ladders, binders, HVAC duct work, mechanical products, and electronics. They are offered from 1/16-inch (1.6 mm) to 3/8-inch (9.5 mm) in diameter (other sizes are considered highly special) and can be up to 8 inches (203 mm) long.

A wide variety of materials and plantings are available, most common base metals are steel, brass, copper, stainless, aluminum and most common plantings are zinc, nickel, brass, tin. Tubular rivets are normally waxed to facilitate proper assembly. An installed tubular rivet has a head on one side, with a rolled over and exposed shallow blind hole on the other. Semi-tubular rivets are the fastest way to rivet in mass production, but require capital investment.

Testing

Solid rivets for construction

A hammer is also used to "ring" an installed rivet, as a non-destructive test for tightness and imperfections. The inspector taps the head (usually the factory head) of the rivet with the hammer while touching the rivet and base plate lightly with the other hand and judges the quality of the audibly returned sound and the feel of the sound traveling through the metal to the operator's fingers. A rivet tightly set in its hole returns a clean and clear ring, while a loose rivet produces a recognizably different sound.

Testing of blind rivets 

A blind rivet has strength properties that can be measured in terms of shear and tensile strength. Occasionally rivets also undergo performance testing for other critical features, such as push out force, break load and salt spray resistance. A standardized destructive test according to the Inch Fastener Standards is widely accepted^.

The shear test involves installing a rivet into two plates at specified hardness and thickness and measuring the force necessary to shear the plates. The tensile test is basically the same, except that it measures the pullout strength. Per the IFI-135 standard, all blind rivets produced must meet this standard. These tests determine the strength of the rivet, and not the strength of the assembly. To determine the strength of the assembly a user must consult an engineering guide or the Machinery's Handbook.