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Garments, Fashion & Retail
  Fabric drape & its measurement

The drape of fabric is a very important property to be analysed before selecting a fabric for garment Production, says S V Bhalerao, who discusses the development of drape measuring instruments and issues related to it.

The inherent properties such as strength, permeability, thickness, etc all are considered to be objective performance characteristics. They can be measured and evaluated in quantitative terms on the basis of scientific knowledge, independent of personal preferences and psychological experiences.

There are certain equally important subjective performance characteristics, which are evaluated at least in part by personal reaction. These can be expressed only in relative qualitative terms although quantitative physical parameters in part govern the subjective rankings. These three important subjective tests are hand or handle, drape and lustre. Handle describes the feel of the material and qualitatively includes such terms as stiff, limp, hard, soft, rough and smooth. Flexibility is the ease with which a specimen may be bent. In certain cases the weight of the material acts to bend it about an axis. Rigidity is the measure of resistance offered by the specimen to bending. It is a measure of stiffness. Drape differs from rigidity in that the weight of material in-fluences a deformation at some angle to the line of action. The article discusses the issues covering drape of fabric with emphasis on two aspects: One is the stages of developments in drape meters & their limitations. The other is the recent developments in drape measuring instruments, their advantages and modern features.

Literature Review
Drape of fabric

In 1950, C C Chy and others defined(5) the drape as - drape and drapability are terms for that property of textile materials, which allows a fabric to orient itself into graceful holds or pleats when acted upon by force of gravity. Hence a fabric is said to have a good draping qualities when the configuration is pleasing to an eye.

In 1965 G E Cusick defined(6) the drape as-it is a description of the deformation of the fabric produced by gravity when only part of it is directly supported.

Drape Co-efficient

According to IS-8357/1977 the drape is defined as the extent to which a fabric will deform when it is allowed to hang under its own weight. According to BS-5058/1973 the drape of fabric is defined in similar way.

According to BS-5058/1973, it is defined as the percentage of the total area to an annular ring of fabric obtained by vertically projecting the shadow of the draped specimen.

According IS-8357/1977, it is defined as the area covered by the shadow of the draped specimen expressed as percentage of the area of the annular ring of fabric.

T
he extract(7) of BS 5058/1973:
A circular fabric specimen is held concentrically between smaller horizontal disc and an annular ring of fabric is allowed to drape into folds around the lower supporting disc. The shadow of the draped specimen is cast onto an annular ring of paper of same size as the unsupported part of the fabric specimen. The outline of shadow is traced onto the ring of paper, the mass of which is then determined. The paper is then cut along the trace of shadow and the mass of inner part representing the shadow is determined. The drape co-efficient is calculated from two masses.


The extract(8) of IS 8357/1977:


A circular fabric specimen is sandwiched between two horizontal discs of smaller diameter and the unsupported annular ring of fabric is allowed to hang down under the action of gravity. A plan projection of the contour of the draped specimen is recorded on light sensitive paper. The drape pattern obtained is cut along the outline and its area determined gravimetrically. The drape co-efficient is calculated as the ratio of projected area of the drape specimen to its theoretical maximum.

Significance of drape measurement(1,2,3,4)

The drape co-efficient is a measure of drape. It is a single number with a theoretical maximum of hundred and minimum of zero. The specimen deforms with multi-directional curvature and result is therefore dependent upon the shear stiffness of the fabric in addition to bending stiffness.

Stages of developments of drape measuring instruments:

S No Year Drape Meter Developed
1   - M I T Drape-o-meter
2 1950 Original F R L Drape Meter
Improved F R L Drape Meter
3 1964 Cusick’s Drape Meter
4 1977 BTRA Drape Meter
5 1993 Developments by Marathwada University(10)

Drape measurement can be employed for study of the effects of fabric geometry, chemical processing treatment and finishes for woven and knitted fabrics, certain qualities of nonwovens. Drape co-efficient can also be used as an index for control of batches in production. The drape measurement is significant in garment industry where the fabric is selected according to the end use. The drape is one of the most important properties in selection criteria of fabric of garment industry. For eg, the fabrics for suiting should possess fewer drapes and the fabric for shirting and ladies wear should possess high drape.

The details of M I T Drape-O-Meter, Original F R L Drape Meter(5), Improved F R L Drape Meter(5), Cusick's Drape Meter(6) and BTRA Drape Meter(9) are available in the given references. It is beyond the scope of this publication to describe the same. The comparison of the same is given in Table 1.

Table1: Comparison of Drape Meters (Till 1977)

S No Point of comparison F R L (1950) Cusick (1964) BTRA (1977)
1 Sample Size  (dia in CM) 25 30 (15) 25
2 Supporting Disc
(dia in CM)
10 cm, 12.5 cm 18 (9) 12.5
3 Area of draping the fabric 412.33cm2 368.16 cm2 452.38 cm2 113.09 cm2 386.15 cm2
4 Shadow Tracing Technique Photo sensitive method Shadow due to reflection Shadow due to light divergence
5 Drawing of draped pattern Pen-recorder By hand By Ammonia Treatment
6 Light source Used Ordinary Ordinary High pressure mercury vapor Lamp (125 w)
7 Complexity of instrument More Less More
9 Actual Testing Time** 1 min N A 25-30 min
10 Maintenance Maximum Less Less
** Excluding sample preparation Time    

In 1993, constructive attempts(10) were also made by the present author to develop the slightly improved drape meter, but the development was limited and of academic interest only and not up to the mark for commercial aspects.

Recent developments

In last decade of 2000 century, lots of improvements were witnessed by textile and garment industry, thanks to microprocessors, electronics chips and IT industry. Drape measurement is not the exception for the same as it was then very easy & accurate to analyse the draped pattern/image with the help of different sensors. The following are the instruments developed recently.

D H L Drape Meter (According to BS - 5058/1977)

In 2005, the author(11) developed the D H L Drape Meter. The development was based on BS 5058/1977.

The characteristics of drape of fabric are complex in nature. The instrument is developed to test the fabric drape in a simple way. The drape is due to the deformation by gravity of an initially horizontal annular ring of fabric. A measure of drape is obtained as a single number with theoretical maximum of 100% and minimum of zero %. The specimen deforms multidirectional curvature and the result therefore depends upon the shear stiffness of fabric and bending stiffness.

Principle

A circular fabric specimen is held concentrically between smaller horizontal disc and an annular ring of fabric is allowed to drape into graceful folds around the lower supporting disc. The outline of shadow is traced on paper and then its mass is determined. Initially, the weight of paper of 15 cm dia is determined and the drape co-efficient is calculated.

Constructional details

The instrument consists of three parts, viz, 1. Mirror Unit; 2. Sample Holder; 3. Shadow Tracing Surface.

The parabolic mirror is used to obtain the perfect parallel light beam. The light source is located at focal point of the said mirror. In absence of fabric sample, the illuminated light circle is perfectly obtained as of 15 cm dia. The fabric sample of 15 cm dia is prepared and located in between two supporting disc of either 6 cm or 9 cm depending upon the quality of fabric. The drape pattern of fabric is traced on a white paper placed on top glass of an instrument. The paper is cut perfectly on the drape pattern. The weight of the paper is noted. The standard weight of 15 cm circular paper is already known. The drape co-efficient is calculated from these two readings. It is advisable to test the fabric sample from both sides and minimum two samples per test. The nodes, ie, curving of folds appeared due to draping also can be noted.

Drape co-efficient (DC%) =

        (W/w-a)
 ------------------------ x 100
           A-a
Where, mass of drape pattern (gms) = W

mass/unit area of white paper (gm/cm2) = w

Area of supporting disc of 6 cm dia = a

Area of fabric sample of 15 cm dia = A

Specifications

  1. Measuring principle - Measurement of shadow area obtained due to parallel light.

  2. Recording Technique - Manually drawing/tracing of shadow edge.

  3. Test Specimen - 15 cm dia.

  4. Template to prepare sample - 15 cm dia.

  5. Light source - 15 w clear ordinary bulb.

  6. Fuse - Socket type.

Features of the D H L Drape Meter

  1. The instrument is lightweight, handy & compact; an ordinary salesman can lift it. Moreover, the instrument is supplied with 5 templates, each one indicating a range of drape co-efficient and its probable application, say dress material, shirting, curtains, etc. So during counter sale also, the instrument can provide the primary judgment of drape. All the time the exact numerical value of drape co-efficient is not necessary/required. In garment industry, quick judgment of drape can be obtained from this instrument by using pre-defined templates.

  2. Comparatively, the initial investment cost is low.

  3. As the light, which is reflected from the mirror, is in parallel form, the true shadow will obtain. The problem of amplification of shadow due to diverging light rays is eliminated in this instrument.

  4. The ordinary light source is used (15 W clear), which is easily available at low cost and it is not necessary to put on the light in advance to warm-up the same.

  5. The re-production of results is excellent.

  6. The other advantages are: Minimum testing time (15 min), less fabric consumption, less power consumption, dual power supply, no necessity of dark room, low maintenance cost, few electric connection and many more.

Limitations

  1. There may be a human error while tracing the shadow of drape pattern.

  2. The area available for draping the fabric in annular ring shape is of 6 cm width in earlier instruments but in this instrument it is limited to 4.5-cm width.

  3. The range of drape co-efficient is 30% to 90%.

Computerised Drape Meter(12)

D & M Technology Co Ltd, based in Korea, offers a computerised drape meter under the model name Drape Analyser DM 02.

Basically the instrument is a computerised version of Cusick's Drape Meter. The detailed information is not made available due to language barrier. Even tough few clips are collected as below:

Features

  1. An instrument is running under operating system MS Windows.

  2. It is implemented with currently used Drape Testers and attachments for camera setting.

  3. It uses an image captured by digital camera or scanner without paper marking & cutting.

  4. It supports 3-dimensional texture mapping to drape image.

  5. It reports statistical & shape parameter analysis as well as drape co-efficients.

  6. It outputs an on-line documentation with drape image.

  7. It is easy to implement with any existing drape meter.

  8. Expert & academic versions are also available.

  9. Compatible with Pentium PC at 800 x 600 resolution.

Output report

  • Drape co-efficient

  • Number of drape waves or nodes

  • Drape wave amplitude and wave length

  • Statistical data: Max & Minimum, Average wave amplitude & its variance.

The comparison of the above two instruments is tabulated in table 2.

Table 2: Comparison of Drape Meters (After the year 2000)

S No Point of comparison D H L Drape meter (2005) Computerised Drape Meter
1 Sample Size
 (dia in CM)
30 (15) 30
2 Supporting Disc
(dia in CM)
18 (9,6) 18
3 Area of draping the fabric 113.06 cm2, 148.44 cm2 Can be varied
4 Shadow Tracing Technique Shadow due to reflection Image captured by Digital Camera
5 Image Capture By hand Digital Camera or Scanner
6 Drape
Co-efficient
By Weight By Image processing
7 Shape Analysis Not available Yes
9 Statistical Analysis Manual Calculation Computerised
10 Operator Human Computer
  Initial Investment Cost Very Less Very High
11 Origin India Korea

Conclusion

With the summarised details of these instruments, one can conclude that, the issue of drape testing should be addressed in detail with the help of available modern technology. The reference study of existing drape meters till 1977 (Ref Table I) uncovers the limitation of the instruments in terms of type of output of results, ease of operations, cost, use of special type of light source, etc. The garment industry will welcome the handy & user-friendly instrument that can be managed by the counter sales. But the above-referred instruments are required to be developed for the same.

Hence in recent developments (after the year 2000, Ref Table II) mainly two distinct alternatives are addressed. Keeping the economical views in mind, D H L Drape Meter is suitable for garment industry, academic institutes, shops, malls, factory outlets & many more. The computerised instrument is also suitable but the constraints in availability of finance may not allow us to opt for this alternative. In short, facility of drape testing from user's point of view should be made available at low investment cost.

References

  1. Grover E B: Handbook of Textile Testing & Quality Control.

  2. Booth J E: Principles of Textile Testing.

  3. Kaswell E R: Textile Fibre, Yarn and Fabric.

  4. Hearl J W S: Structural Mechanics of Fibre, Yarn & Fabric, Vol I.

  5. Textile Research Jr, 1950, (20), 539.

  6. Journal of Textile Institute, 1665, (56), T 596.

  7. BS 5058/1973.

  8. IS 8357/1977.

  9. BTRA, Instruction Manual, 1977.

  10. Bhalerao S V: Project Report, Marathwada University, 1993.

  11. Bhalerao S V: Instruction Manual, D H L Drape Meter, 2005.

  12. www.dnmco.com.

The author is a Textile Engineer & Consultant residing at 1, Devgiri, Ekata Nagar, Gangapur Road, Nashik 422 013. E-mail ID: bhaleraosatish@yahoo.com.

published July , 2007
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