Sunday, May 5, 2013

AQL | Acceptable Quality Limits or Level

Major concept of Acceptable Quality Limit or Level:
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It is the allowable percent defective in a lot. This is introduced according to American military Standard of product inspection rules. There are generally 6 AQL used in textile which are as follows:- 1%,1.5%,2.5%,4%,6.5%,and 10%. Among them 2.5%,4%,6.5% and 10% are widely used and accepted according to price and type of garments.

Uses of AQL: In this system, sample is selected statistical method by using random sampling technique from a lot. After proper inspection along with the test results, the decision is taken, whether the lot will be accepted or rejected. Now a days this system is widely used in garments sector before the delivery. Although it is used from raw material to finished product also.

Acceptable sampling system consists of five parts:
1. Lot size
2. Sample size
3. AQL
4. Acceptable number
5. Reject number

Quality Inspection of factories:
According to JIS, Inspection is defined as “ to measure goods by some methods and by comparison with the results obtained against the criteria to judge whether the individual goods are defective or not

In textile factories the fabrics are inspected at the grey state, after pretreatment, coloration and finishing. After inspection the fabrics are classified according to their quality. Therefore fabrics are inspected to meet the requirements of the customers.

The fabrics are categorized in the following way depending upon the faults:

I. Fresh or First quality: Fabrics, hemming major, minor faults according to buyer specification and requirements.
II. Short length or two parts: It is a piece of cloth having a shorter length( More then 50 cm ). Jar parts become equal to fresh quality. Generally buyers gives (3-5)% discount value for the short length.
III. Seconds: Fabrics containing much objectionable minor defects and (8-15)% discount is allowed.
IV. Fents: Cut pieces of fabric measuring 90 cm or more but less than 150 cm lengths. For fents trade discount is (15-30) %.
V. Rags: Cut pieces of fabric measuring 25 c or more but less than 90 cm. This categories are sold by weight and realization is only about 50% of fresh fabric.
VI. Chilly: These are pieces of 25 cm length fabric less than this. These fabrics are bought & sold and trade discount generally given is ( 50-80).

Quality Parameters of Woven Fabrics to be inspected are as follows:

(1) Dimensional characteristics:
a) Length b) Width c) Thickness

(2) Weight of fabric:
a) Weight/unit area b) Weight/unit length

(3) Fabric strength & Elongation
a) Tensile strength b) Tearing c) Bursting

(4) Threads/inch:
a) Ends/inch
b) Picks/inch

(5) Yarn count
a) Warp count
b) Weft count

(6) Crimp
a) Warp count
b) Weft count

(7) Handle

a) Stiffness
b) Drape

(8) Crease resistance & crease recovery

(9) Air permeability

(10) Abrasion resistance and pilling.

(11) Shrinkages/Dimensional stability

(12) Different fastness properties:-
a) Washing fastness
b) Light fastness
c) Perspiration fastness
d) Rubbing

(13) Flameability

(14) Water resistance or absorption power

(15) Design of fabric

(16) Appearance of fabric

Quality parameters for knitted fabric to be inspected:


1. Strength & elongation
2. Course density
3. Wales density
4. Loop length
5. Deformation
6. GSM
7. Yarn count
8. Design

Wish You Good Luck..................................
You Should Interested to read RELATED POST on the topics


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Thursday, April 25, 2013

Bonded Fabric

Bonded fabric is a combined structure of fabric that is being created by joining two set of fabric. This attachment of two fabrics can be made with adhesive or thin bonding fabric with low melting point without any major changes of finished fabric thickness. Here a face or shell fabric is joined with backing fabric. Artificial leather products can be a good example of this type of fabric. Bonded fabric also used in design purposes and fabric stabilization.

An aqueous acrylic adhesive is used for joining bonded fabric. A latex adhesive such as, acrylate, a vinyl chloride or vinyl acetate or thermosetting resin also being used for this purpose. This bonding strength between these two layer fabrics is the main thing where the end uses of the finished product depends on.

Fabric Bonding Procedure:
There are two common methods for attaching fabric to fabric.
1. Wet adhesive method
2. Flame foam method

Wet adhesive method:
· An adhesive liquid is applied to the back of the face fabric.
· Face fabric is set on backing fabric and passed together between the heated rollers.
· Thus, the heat fixes the adhesive between two fabrics and makes the bonded fabric.

Flame foam method:
· Here, a thin layer of polyurethane foam is used to attach two set of fabrics
· First, polyurethane foam is melted a little by passing it over a fire/heat.
· Then this melted foam is set between two layers of fabric just like a sandwich.
· After that, when the foam got dries, it attach the two layers of fabric.

Actually the foam in the bonded fabric is so thin (around 0.010 inch). That why, It doesn’t make any significant changes on the thickness of the finished fabric. By this method fabric may got stiffer than the wet-adhesive method. Sometime foam may appear of the surface of the fabric. That’s why it is not better not to use this method with open-weave fabrics.

Advantages
· This bonded fabric is much cheaper in price
· This fabric is machine washable
· Fabric doesn’t crease easily

Thursday, March 14, 2013

Crimp based on warp and weft yarn on fabric

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CRIMP
When warp and weft yarns are interlaced in a fabric they follow a WAVE or CORRUGATED configuration, the plane of the weave being substantially perpendicular to that of the fabric. This WAVINESS OF YARN is called CRIMP of yarn and is expressed quantitatively either as a fraction, c or as a percentage, c per cent:

c = (Ly - Lf)/Lf; and, c per cent = (Ly – Lf) x 100/Lf

Where Ly = the un crimped length of the yarn, and, Lf = its extent in the fabric.

The expression c = (Ly – Lf) / Lf may be written as:

c = Ly / (Lf - 1), from which

(1 + c) = Ly / Lf;

where (1 + c) is called the crimp ratio. It is useful in fabric calculations.

MATH: Calculate the length of warp required to weave 160 yds. of cloth if the warp crimp is 12 percent.

We know,
Lf = 160 yd. and c1 percent = 12; so c1 = 0.12, where c1 is fractional warp crimp, and

Ly = Lf (1 + c) = 160 x 1.12 = 179.2 yd.

So, to prepare 160 yds of fabric 179.2 yds of warp is required.

MATH: What length of cloth can be woven from 800 yds of warp if the crimp is 8 percent?

We know
Ly = 800 Yd., and c1 percent = 8, so c1 = 0.08; where c1 is fractional warp crimp, and

Lf =Ly/(1+c) = 800/1.08 = 740.8 yds.

So, 800 yds. of warp will weave 740.8 yd of cloth.

When the shuttle inserts the weft in the open shed, the weft is un crimped, and each pick has a length Ly, which is equal to the width occupied by the warp in the reed. This is called the reed width. When it is beaten up by the reed and incorporated into the cloth at the cloth fell, the weft attempts to crimp under the scissors-like pressure exerted by the warp threads. At this stage, it is prevented from crimping freely by the temples, whose function is to hold out the cloth near the fell to reed width, so as to prevent excessive abrasion of the warp threads near each selvedge by the reed. As the cloth moves forward towards the breast beam, it leaves the temples and is free to contract to a length Lf, called loom-state width. The weft is now crimped. We have three variables, i) reed width, ii) the width of the loom-state cloth, and iii) the weft crimp in the loom-state cloth. If we know two of these variables, the third can be calculated as illustrated by the following examples.

MATH: Calculate the reed width required to give a cloth with a loom-state width of 38”, if the weft crimp in the loom-state cloth is known to be 6 percent.

We know
Lf = 38”, and c2 percent = 6; so c2 = 0.06, where c2 weft crimp, and

Ly = Lf (1 + c) = 38 x 1.06 = 40.28”

which is the required reed width.

MATH: Calculate the loom-state cloth width if the reed width is 60”, and the weft crimp is known to be 9 percent.

We know

Ly = 60” and c2 percent = 9; so c2 = 0.09, where c2 is weft crimp, and

Lf = Ly/ (1+c) = 60/1.09 = 55.05”

which is loom-state cloth width.

MATH: Calculate the weft crimp in the loom-state cloth if the reed width is 44” and the loom-state cloth width is 40”.

We know

Ly = 44”, and Lf = 40”.

Therefore (1+c) = Ly/Lf = 44/40 = 1.10, so c2 = 0.10 and c2 percent = 10

which is the weft crimp.

In any of the above examples we could substitute the width of the finished cloth for that of the loom-state cloth, provided that we also substitute the weft crimp in the finished cloth for that of the in the loom-state cloth. The calculation would be valid, if no unrecoverable shrinkage had occurred during finishing, but not, for example for a milled woolen cloth.

EFFECT OF CRIMP OF YARN ON FABRIC PROPERTIES
a) RESISTANCE TO ABRASION: With the increase of crimp %, the abrasion resistance will also increase
b) SHRINKAGE: With the increase of crimp %, shrinkage of fabric will decrease.
c) FABRIC BEHAVIOUR DURING TENSILETESTING: With the increase of crimp%, breaking load of fabric will also increase.
d) FABRIC COSTING: With the increase of crimp%, fabric costing will also increase. Because crimp decrease the length of yarn as a result more yarn will be needed for fabric manufacture in case of more crimp on yarn.
e) FAULTS IN FABRIC: If there is variation of crimp in the threads then the following faults may be found in fabric; A) Reduction in strength may occur, and B) Stripes will be seen in yarn dyed cotton fabric.
f) FABRIC DESIGN: To achieve satisfactory appearance and required shape in finished fabric control of crimp in warp and weft yarn is necessary..
g) FABRIC STIFFNESS: If crimp is increased then stiffness of fabric will decrease.
h) ABSORBENCY: With the increase of crimp % absorbency of the fabric will increase.
i) DIMENSIONAL STABILITY: Dimensional stability will decrease with the increase of crimp%.
j) FABRIC HANDLE: If crimp is increased then the fabric will be soft in handle.
k) DYE TAKE-UP: With the increase of crimp the take-up percentage of dye-uptake will also increase.
Wish You Good Luck..................................
You Should Interested to read RELATED POST on the topics
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