Test ing Fabric Weight (It is more complicated than it looks)

Overview

Testing a fabric's weight, how complicated can it be? More than you would think. In this article, I will show you some areas that are somewhat tricky. At the core of weight testing is:

"If  you  weigh  a  known  area  of  fabric,  you  can  calculate  the  fabric  weight  into  the  units  of  your  choice".  

Therefore, weight testing consists of two parts. Cutting a sample of a known size, and weighing that sample.

Part One, Cutting the Sample

Scissor Cutting

Very simple, a template is laid on the fabric, lines are marked and the sample is cut. This method is very inexpensive. However, it is slow and less accurate than die cutting.

Die Cutting

A metal die is used to stamp out the fabric sample. This method is more expensive than scissor cutting. However, it is very fast and accurate. There are a few sub-categories:

Multiple circles - This is the J. A. King method, which is by far the most widely used system. A six inch full width sample of the fabric to be tested is folded in half three times (making 8 layers). The cutter (supplied by J. A. King, either manual or pneumatic, see Appendix A for some pictures), cuts 8 circles with one punch. Each circle is 2.698” in diameter. The area of these eight circles when weighed on a gram scale read directly into oz./yd2. The test is very quick (< 30 seconds), and accurate. That there are 8 circles across the width of the fabric is an advantage, as opposed to a single sample.

Square(s) - Another way to determine fabric weight is to use a die to cut a known area(s) with a fabric pneumatic press. Most cut/sew facilitates have them out on the production floor. In Appendix A you will find some factors and formulas on how to calculate various size squares to oz./yd2 and gm./m2.

Testing tip - If you do a lot of testing consider using a pneumatic press (often called a “clicker” with a custom die for a variety of tests (see Appendix B pictures).

Used Versus New

Whenever testing equipment is discussed the question of new versus used is often asked. The manual J. A. King cutter is fairly common on the used market. The danger is more than likely it has been used a lot. It may have been (probably) used out on the production floor 24/7 and conditions are not lab-like by any means. Just be aware that the blade may be dull and have to be replaced.

Part Two, Weighing The Sample

Scales

There are three issues to consider:

Precision (Readability) - For fabric weight testing the scale needs to have a precision of 0.01 grams.

“Name Brand” versus others – I recommend either Mettler or Ohaus.

New or used – Beware of load cells that have been overloaded. Also, the scale’s calibration is likely to be out of date.

ASTM

The "official" ASTM test is D3776. They recommend a conditioned lab, which is very expensive. In my travels, conditioned weight testing is somewhat rare. In regards to cutting the samples, ASTM is somewhat vague with a leaning towards die cutting but leaving the scissor option open.

Final Remarks

How much money you want to spend on weight testing is a question only you can answer.

Here are some questions that may be helpful;

• How reliable are you vendors? • Do they supply test results, and you just want to spot check on occasion? • Do your customers check weight? • Have you ever had any returns due to low weight? • In elastic warp knits, low weight is almost always accompanied by low stretch and may cause a

fit problem. • How much testing are you going to do? If not a lot then go with the scissor method. If it going

to be a regular procedure and manpower is limited, consider die cutting. • How accurate do you need to be?

At present (February 2015), a “top of the line” system is less than $1,800.

Appendix A Ounce per Square Yard Conversion Formulas

Ounce  per  Square  Yard  Conversions  

 Sample  Size  (inches)   Factor  1  X  1   45.75  3  X  3   5.08  6  X  6   1.27  9  X  9   0.50  

12  X  12   0.32  

How to use the factor

1) Choose the factor that corresponds with the sample size you are using

2) Weigh the sample(s) in grams

3) Use the following formula:

𝑂𝑢𝑛𝑐𝑒𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑌𝑎𝑟𝑑 = 𝐺𝑟𝑎𝑚𝑠  𝑋 !"#$%&#  !"  !"#$%&'

Examples

1 12” x 12” square weighing 14.5 grams

𝑂𝑢𝑛𝑐𝑒𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑌𝑎𝑟𝑑 = 14.5  𝐺𝑟𝑎𝑚𝑠  𝑋 .!"!

= 4.6  𝑂𝑧.𝑝𝑒𝑟  𝑆𝑞.𝑌𝑑.

Examples

3 3” x 3” squares weighing 2.6 grams

𝑂𝑢𝑛𝑐𝑒𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑌𝑎𝑟𝑑 = 2.6  𝐺𝑟𝑎𝑚𝑠  𝑋 !.!"!

= 4.4  𝑂𝑧.𝑝𝑒𝑟  𝑆𝑞.𝑌𝑑.

Grams per Square Meter Conversion Formulas

Grams  per  Meter  Square  Conversions  

 Sample  Size  (inches)   Factor  1  X  1   1550.0  3  X  3   172.2  6  X  6   43.1  9  X  9   19.1  

12  X  12   10.8  

How to use the factor

4) Choose the factor that corresponds with the sample size you are using

5) Weigh the sample(s) in grams

6) Use the following formula:

𝐺𝑟𝑎𝑚𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑀𝑒𝑡𝑒𝑟 = 𝐺𝑟𝑎𝑚𝑠  𝑋 !"#$%&#  !"  !"#$%&'

Example

1 12” x 12” square weighing 14.5 grams

𝐺𝑟𝑎𝑚𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑀𝑒𝑡𝑒𝑟 = 14.5  𝐺𝑟𝑎𝑚𝑠  𝑋 !".!!

= 156  𝑔𝑟𝑎𝑚𝑠  𝑝𝑒𝑟  𝑆𝑞.𝑀.

Example

3 3” x 3” squares weighing 4 grams

𝐺𝑟𝑎𝑚𝑠  𝑝𝑒𝑟  𝑆𝑞𝑢𝑎𝑟𝑒  𝑀𝑒𝑡𝑒𝑟 = 4  𝐺𝑟𝑎𝑚𝑠  𝑋 !"#.!!

= 229  𝑔𝑟𝑎𝑚𝑠  𝑝𝑒𝑟  𝑆𝑞.𝑀.

Appendix B

J. A. Manual Sample

Cutter J. A. King Pneumatic Sample

Cutter

J. A. King Desktop Die Press (Clicker) J. A. King Desktop Die

Press (Clicker) on Stand

J. A. King Ful l Size Die

Press (Clicker)

Assorted Dies

Photos courtesy of J. A. King

J. A. King Complete System (scale

converts to oz.yd2 and Grams/M2)