Blending-2

How to select Blend Constituents


Selection of Blend Constituents depends upon the following factors:

1. Type of Fibre
- Depending upon the end use of the fabric, blend constituents are chosen.

- For example, it is well known hat a polyester-cotton yarn looks fuller as compared to the lean look of polyester-viscose yarn.

- Therefore for light constructions like shirtings, polyester-cotton blend is used.

- However polyester-viscose blend is preferred for medium and heavy construcitons such as suitings.

2. Compatibility of blend fibres

Compatibility must be there in terms of the following properties:

a. Length and Denier of Fibres:

- As a general rule, these two fibre properties should be nearly the same for all the constituents.
- For example in a viscose rayon cotton blend, the rayon staple of 1.5 denier and 29-32 mm length is generally used since the cotton component used has a denier of around 1.5 and a length of 28mm.

b. Extensibility

- A large difference in the breaking elongation of the fibres in a blend adversly affects the yarn tenacity.

c. Density
- The blend fibres should prefereably have the same density. Any large differences on this account will lead to selctive separation while conveying the blended stock through ducts under the influence of air suction in the blow rooms.

d. Dispersion Properties
- This property describes the ability of an individual fibre to separate from its group and disperse thoroughly within the fibre matrix of the blend to produce an intimate and homogeneous blend.

e. Drafting Properties
- Some fibres like viscose are outstanding it terms of draftability. These fibres, when blended with other fibres act as good carriers to obviate the trouble relating to drafting.

f. Dyeing Properties
- In case the blend yarn or fabric is to be dyed subsequently, due consideration should be given to the dyeing properties of individual fibre components.

CHARACTERISTICS DESIRED IN A BLEND YARN

A. The constituent fibres should be arranged at random in the yarn cross section.

B. The ratio between the blended fibres should be uniform at any cross section of the yarn.

C. There should not be any long-term or short-term irregularity in blend ratio of blended fibres.

Blending-1

Blending-1

Neither natural or manmade fibres are optimally suited to certain fields of use, but a blend of these two fibres types can give the required characteristics.

Objectives:

1. Improvement in Functional Properties

A 100% single fibre yarn cannot impart all the desired properties to a fabric.

For example 100% viscose rayon suffer from low tensile strength, poor crease resistance and low abrasion resistance.

Similarly 100% polyester fabrics are not desirable as they are prone to static accumulation, hole melting and pilling. They are moisture resistant, difficult and expensive to dye and have a poor hand.

These negative attributes of polyester and viscose can be reasonably neutralised by addition of a certain percentage of each fibre.

2. Improved Process performance

Some fibres like polyester at times are quite troublesome to work in 100% form especially at cards. Addition of fibres like cotton or viscose rayon in the previous process has been seen to facilitate the smooth carding of such fibres.

The blending of manmades which are longer and finer to cotton which is shorter influences the spinnablility as well as productivity.

3. Economy

The price of manmades is much more stable than that of natural fibres like cotton. Price stability can enable the mills to pursue optimisation of their fibre purchase programme.

Blending could also be used for reducing the mixing cost. For example, a fibre like viscose can be blended with cotton for producing specific yarns with reduced raw material costs.

4. Fancy Effect

Fibres with a variety of colour mixture or shades can be produced by blending different dyed fibres at the blowroom, drawframe or roving stage.

5. Aesthetics

The aesthetics of a fabric can be developed by selecting specific blend components and their properties.

Receipes for different shades of Denim

Receipes For Different Shades on Denim


A) Black-on-Black
Black-on-Blue

Recipe

Liquid Sulphast Black= 200 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI = 10 gpl
Soda Ash= 10 gpl

B) Blue-on- Blue

Receipe

Liquid Sulphar Navy Blue = 100 gpl
Liquid Sulphast Black= 50 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI= 10 gpl
Soda Ash= 10 gpl

C) Reactive Series

Receipe

01) Ramazol Turquoise Blue G = 110 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate= 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

D) Ramazol Coffee Brown G

Receipe
01) Coffee Brown G = 100gpl
Urea = 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda= 10 gpl

Ratio of 01) and 02) = 3:1

E) Ramazol Parrot Green

Receipe
01) Ramazol Turquoise Blue G = 90 gpl
Ramazol Yellow FG = 40 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

F) Ramazol Blue

Receipe
01) Ramazol Black B = 70 gpl
Urea = 100 gpl
Swanic 6L = 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

Sewing Problems

Sewing Problems

1. Problems of stitch formation

It gives rise to poor seam appearance and performance

These are

- Slipped stitches
- Staggered stitching
- Unbalanced stitches
- Variable stitch density
- Puckering
- Needle, bobbin or loops thread breakage

a. Slipped Stitches

Arise from the hook or loopes in the machines not picking up the loop in the needle thread.

b. Staggered Stitches

Can be caused by yarns in the fabric deflecting the needle away from a straight line of stitching, giving a poor appearance.

c. Unbalanced stitches

It can reduce the potential of stretch in a seam in a knitted fabric and may lead to seam cracking.

d. Variable stitch density

It arises from insufficient foot pressure in a drop feed system, causing uneven feeding of the fabric through the machine.

PROBLEMS OF PUCKER

Pucker is a wrinkled appearance along a seam in an otherwise smooth fabric. It generally appears as if there is too much fabric and not enough thread in the seam.

Causes of Pucker

a. Seam pucker due to differential fabric stretch

Remember that the upper fabric would tend to move forward by an amount always less than the movement of lower one. This is due to the fact that the lower layer is positively gripped by the feed dog and upper layer is driven by the friction by the lower layer.

b. Differential pucker caused by fabric dimensional instability

The essential feature causing differential pucker is the relative change in dimensions of upper and lower fabric after the seam has been made.

Differential pucker due to dimensional instability may be suspected when the two fabrics being joined are markedly different or when one shows noticeably more pucker than the other.

c. Seam pucker due to extension in the sewing threads.

All sewing threads have some extensiblity and they are extended by the action of the tension devices and pass into seam in an extended state. When removed from the machine they will tend to contract.

When thread extension is proved to be the cause of puckered seam, consideration must be given to the type of thread being used and to the tensiton settings on individual machines.

d. Seam pucker due to sewing thread shrinkage

Cotton sewing threads increase in diameter and shrink in length when wet and these distortions may cause pucker in sensitive fabrics. Synthetic sewing threads have negligible wet shrinkage and should always be used for such fabrics.

e. Seam pucker due to structural jamming

The presence of the seam itself may introduce a distortion. It is in no way dependent on the action of the sewing machine, but it invariably appears as soon as the seam is formed.

As soon as a woven fabric has been constructed so as to be close to the practical weaving limit, that is very less space left between the yarsn either warp or weft ways, it may be extremely difficult to force in any more threads in either direction.

The term 'structural jamming' is given to this type of pucker because it results directly from the act of jamming extra threads into a structure which is already too closely set to accommodate them.

Seam pucker due to mismatched patterns

This is due to the discrepency between the lengths of the stitching lines on the pattern pieces that go together in the seam. Thus there is a difference in the lengths of the cut parts which the machinist is sewing together.

Problems of damage to the fabric along the stitch line

a) Mechanical damage

1. Needles can strike and break fabric yarns and burst the loops in knitted fabrics. For this appropriate set and ball point needles are necessary.

2. Needles should always be as small as possible.

3. Sometimes the combination of the machine speed and nature of the fabric prevents the yarns from moving out of the way of the needle sufficiently fast to avoid damage .To solve the problems either reduce the speed - which means lesser production or ensure that the fabric is adequately lubricated. It calls for having resin finish on the fabric.

- All sample lengths of the fabric should be tested for sewability and the necessary finishes should be specified before the bulk fabric is ordered and bulk fabric should be tested before production to ensure that finishing treatment has been effective.

b) Needle Heating Damage


Needles heating occurs as a result of friction between the needle and the fabric being sewn.

In high speed sewing of dense material, temperatures as high as 300 deg or even 350 deg can be reached.

At this temperature it is possible that the needle may suffer damage and lose its hardness.

Natural fibres in a fabric or thread can withstand these temperatures for a short time.

With synthetic fibres, the position is more critical since the fibres melt at around 100 deg C, polyamide and polyester soften at about 230 deg C and polyacrylics will only withstand temperatures upto 280 deg C.

Overheated needes can
- Soften the synthetic fibres
- Weaken them
- Produce rough seam with
- harsh stitch holes

Melted fibres stick to the surface of the needes
- Increase its friction
- cog the eye and the groove
- No sew
- Skipped stitches

Reduction of Friction
- Reduce the sewing speed
- Changing the shape or surface of the neede
- long seams will ensure more heat build up in the needle
- Jet of compressed air.
- User spun or corespun yarns.