Posted in Denim fabric

Evalution of Denim Fabric

The following standards for denim fabric quality in terms of inspection, packing, shade and physical requirements are of general nature considering varied requirements of end-uses / customers, however holds good for major universe.

This chapter details classifying fabrics according to color and defects so that the fabrics are made to garments at ease with defects eliminated, grouped according to shade and perform satisfactorily.

INSPECTION REQUIREMENTS

Fabric Group Classification According to Yarn Type

Group One

All Basic Denims (OE/OE)

Group Two

All Denims (RING/OE) & (RING/RING)

Group Three

Specialty Denims: Linen Denims, Vintage

Acceptable Defect Point Levels According to Yarn Type

TABLE-11.1:DEFECT POINTS PER 100 SQUARE YARDS
TABLE-11.2:DEFECT POINTS PER 100 SQUARE METRES
TABLE 11.3: QUALITY CATEGORISATION OF DENIM FABRICS

Defect Grading:

A. Point Grading System: Denim fabrics are normally graded using the “4-Point” system. This numeric grading system is endorsed by ASTM, AAMA (American Apparel Manufacturer’s Association) and ECMA (European Cloth Manufacturers Association). All defects which are clearly visible from one meter (three feet) are scored as defects and demerit points assigned according to severity.

B. Length of Defect Points: Demerit points are assigned to warp and filling defects as follows (Defects in any direction)

v 1 point – Defects 7.5 cm(3”) or less
v 2 points – Defects exceeding 7.5 cm(3”) up to 15 cm(6”)
v 3 points – Defects exceeding 15cm (6”) up to 22.5cm(9”)
v 4 points – Defects exceeding 22.5 cm(9”)

C.Counting of Lengthwise 4 Point Defects: No linear meter is penalized more than 4 points.

v Defect length 22.6cm (9”) to 100cm (40”) – 1 no of 4 point defect
v Defect length 100.1cm (40.1”) to 200cm (80”)–2 no of 4 point defects
v Defect length 200.1cm (80.1”) to 300cm (120”)–3 no of 4 point defects
v If length of defect is more than 3 meters (120”) the length containing the defect is removed.

D. Full Width Defects:

v A full width defect running over 6” in length shall be removed.
v More than four full width defects per one hundred linear meters shall not be accepted as first quality.
v A full width defect in first or last three meters of roll shall not be allowed.

E. Flagging of Defects:

v Only 4 point defects are flagged with a metallic sticker. One may find the metallic sticker at the start of the defect. Metallic flags should be a minimum of 2 cm wide and 7.5 cm length.
v Defect points 1, 2, 3 shall be counted but not flagged.
v All splices shall be flagged.
v All holes shall be removed. There must be two or more yarns broken at the same place to consider a defect as a hole.

F. Roll Length and Splicing:

v Roll length tolerance should be agreed upon the first delivery. Say maximum 135 meters and minimum 85 meters.
v No pieces shall be accepted as first quality with length less than 30 meters.
v No roll shall be accepted as first quality containing more than one splice.
v The shade continuity between parts must allow for the mixing of garment components within a garment.
v Two part rolls should be identified as such, No more than 25% two part roll should be allowed in any shipment.

G.Shading:

v No pieces shall be accepted as first quality that exhibits a noticeable degree of shading from side- to -side or side- to –centre.
v No pieces shall be accepted as first quality that exhibits a noticeable degree of shading from end– to –end.

Skew

A. All 3/1 and some 2/1 twill fabrics for bottoms require skewing. Since the optimum skew varies depending on the fabric (anywhere from 5% to 9%), this must first be determined by the supplier and agreed upon before bulk fabric orders are placed. Target for individual rolls = +/- 3%

B. No fabric shall be accepted as first quality exhibiting more than 3% skew movement.

Waviness

No roll shall be accepted as first quality exhibiting a noticeable degree of looseness (waviness) or tightness along either or both selvages.

Ripples or puckers in the body of the fabric, which prevents the fabric from lying flat when spread in a conventional manner, is unacceptable.

The woven selvage or fringe should be the same on both sides of the fabric.
Tolerance wavy selvage: 2% in length

Width

Cuttable width variations must meet the minimum fabric width specification. In addition width variation within a roll should not exceed 2 cm.

PACKING REQUIREMENTS:

Put- up- Specifications

A. Fabric shall be rolled onto a spiral-wound tube with necessary wall thickness [OD: 60 mm; ID: 45 mm] and strength [Radial Crushing Strength > 500 Kgf for 8” length] to insure it reaching to customers in good condition, provided it is handled by reasonable and acceptable methods.

B. Rolls are wrapped in such a manner that will protect the fabric from all types of damage during transportation and storage.

C. The outer edge of each roll shall be taped down to prevent unrolling during shipment and storage.

D. Roll Identification

Two stickers must be attached one to the end of the roll and another on side of the roll. The stickers shall contain the following information.
1. Roll /Bale Number.
2. Fabric Style number
3. Shade Group
4. Roll length in meters
5. Roll length in yards
6. Fabric width in inches
7. Total square meters
8. Demerit points per 100 square Yards
9. No of fabric pieces
10. Gross weight in Kg
11. Net weight in Kg
12. Quality Category
13. Total number of 4 point defects
14. Total number of Demerit points
15. Security code

COLOUR EVALUATION / SHADE GROUPING

Option 1: Instrumental Shade Evaluation Procedure of Wash Swatches

Instrumental Color Measurement: The color measurement shall be carried out using Spectrophotometer.

Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll – Instrumental Evaluation”

Blanket Preparation: The blanket preparation procedure is given under the head “Blanket Preparation”

Shade Evaluation: The color measurement shall be carried out using Spectrophotometer and shade grouping shall be carried out according to wash color reference of master roll. Before assessment, all fabric swatches must be conditioned for at lease 1 hour in a controlled atmosphere. Samples must be conditioned from a dry state. All measurements must be done as soon as possible after conditioning.

Classifying Rolls by Color Groups: LMD grouping shall be followed. (L= Light, M = Medium, Dark = D), the taper standards are defined as color difference (dEcmc) by Standard, Average, Range and Roll to Roll. L: C [Lightness: Chroma]

The tolerance to be followed is

Average : 1.2
Standard : 2.0
Range : 1.5
Roll : 0.5
L: C Ratio : 2.0

Visual Evaluation: All roll sequences shall be evaluated visually by laying the swatches in standard lighting conditions and remove abnormal rolls.

Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux.

Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D and the same shade group shall be mentioned in the packing list by tracking via roll number.

Swatch Service: The system shall be to send two set of unwashed and washed swatches to customers. The washed swatches are being sent so that customer can review the shade at their end and the unwashed swatches will be used for additional use if any.

Option 2: Visual Shade Evaluation Procedure of Wash Swatches

Visual Color Assessment: Each wash swatch representing one roll in the shipment needs to be compared to the master swatch under standard light conditions.

Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll – Visual Evaluation”

Blanket Preparation: The blanket preparation procedure is given under the head “Blanket Preparation”

Shade Evaluation: Each wash swatch shall be evaluated versus reference shade swatch on shade, color, wash-down, abrasion and overall appearance. Based on this comparison swatches representing rolls shall be accepted/ rejected.

Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux. Make sure a matt grey background is used with reference of Munshell grey N5 or N7 to assess colors.

Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D and the same shade group shall be mentioned in the packing list by tracking via roll number.

Swatch Service: The system shall be to send two set of unwashed and washed swatches to customers. The washed swatches are being sent so that customer can review the shade at their end and the unwashed swatches will be used for additional use if any.

Option 3: Visual Shade Evaluation Procedure of Unwashed Swatches

Visual Color Assessment: Each wash swatch representing one roll in the shipment needs to be compared to the master swatch under standard light conditions.

Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll”

Shade Evaluation: Each unwashed swatch shall be evaluated versus reference shade swatch on shade, color and overall appearance. Based on this comparison swatches representing rolls shall be accepted/ rejected.

Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux. Make sure a matt grey background is used with reference of Munshell grey N5 or N7 to assess colors.

Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D or D+, D, D- and the same shade group shall be mentioned in the packing list by tracking via roll number..

Swatch Service: The system shall be to send three set of unwashed swatches to customers.

Blanket Preparation

Swatch Size: Use uniform swatch size of 8” x 6”

Preparation of Blankets: All blankets for washing shall have standard shade swatch from Master Roll. Swatch shall be cut from every roll of a shipment each 8” x 6”. Identify each roll no at the back of the swatch. In case of light weights identify by serial nos at the backside corner with indelible ink.
Waste material of same style

Wherever less number of swatches is available use dummy swatches of same style nos.

Do not use washed swatches for dummies.

v Dummy swatch size shall be of same size as that of blanket swatches.

v To make wash load if required, use dummy swatches of same style only.

v Sew the two panels together to avoid entangled panels in washing.

v All panels from one shipment to be washed in same wash load.

Washing of the Blankets: Wash blankets according to the recipe for various classes of products.

Procedure for Selecting the Master Roll

Instrumental Evaluation

v From the average of the washed lot select about five roll which are near to the average values.
v Check their UNWASHEDED L*a*b* values, these must belong to 555 block. If not then select 5 more rolls near to average values from the washed lot.
v The roll which belongs to 555 shade block, check the preceding and succeeding rolls L*a*b* values, these must also belong to 555 shade block. This will ensure that there is no shade variation within the roll.
v Now check the consistency of the complete beam. There should not be much variation within the beam.
v The dyer will use the yarn latti of this particular beam as shade reference for dyeing.

Visual Evaluation

v Select about five rolls which represent middle of the washed lot.
v Check unwashed swatches as well, for their true representation of the middle of the lot.
v Check the preceding and succeeding swatches. These must also belong to the same shade. This will ensure that there is no shade variation within the roll.
v Now check the consistency of the complete beam. There should not be much variation within the beam.
v The dyer will use the yarn latti of this particular beam as shade reference for dyeing.

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