GSM

Name of the Experiment: Determination of GSM of woven and knitted fabrics.

Introduction:
The GSM of fabric is one kind of specification of fabric which is very important for a textile engineer for understanding and production of fabric. ‘GSM’ means ‘Gram per square meter’ that is the weight of fabric in gram per one square meter. By this we can compare the fabrics in unit area which is heavier and which is lighter. 

GSM Cutter

Objectives:

1. To determine the GSM of the given samples of fabric.
2. To compare the GSM of them.

Theory:
The weight of a fabric can be expressed in two ways, either as the ‘weight per unit area’ or the ‘weight per unit length’; the former is self explanatory but the latter requires a little explanation because the weight of a unit length of fabric will obviously be affected by its width. In woven fabric, the weight per unit length is usually referred to as the ‘weight per running yard’. It is necessary therefore to know the agreed standard width upon which the weight per running yard is based. Usually this width depends upon the width of loom. Before coming the term ‘GSM’ there was another term called ‘lb/100 yards’. This expression is used by British Standard. For measuring this there are a template and a quadrant balance. The template area is 1/100 square yards of which each arm is 1/10 yards in length. For measuring GSM, a GSM cutter is used to cut the fabric and weight is taken in balance. Both of these measurement and method is equally used for both woven and knitted fabrics.

Apparatus:

1. Template
2. Quadrant balance
3. Scissor
4. GSM cutter
5. Electric balance.

Sample:

1. Finished cotton woven fabric
2. Finished cotton knitted fabric.

Atmosphere:
Temperature – 25oC and relative humidity – 67%
Standard atmosphere: temperature – 20oC and relative humidity - 65%.

M/c specification:
Name: Quadrant balance
Brand: Good brand & Co. Ltd.
Scale: 100 yards for fabric.

Working Procedure:

1. For measuring with Quadrant balance, at first we should cut the fabric sample according to the template area. By this way we cut 10 woven samples and 10 knitted samples.
2. Now weigh these samples in pounds by quadrant balance according to 100 yards scale.
3. By this way we get the weight in pound per 100 square yards fabric.
4. For Measuring GSM, we should cut the fabric sample by GSM cutter. By this way cut 10 woven samples and 10 knitted samples.
5. Now weigh these samples by electric balance in grams.
6. By this way we get the weight in gram per one square meter fabric.
7. Now find out the average of these found weights.
8. For woven fabrics find out the weight per running yards assuming the loom width 48 inches.

Data: 

Type	Woven Fabric			Knitted fabric
Sl No.	lb/100 yd2	gm/meter2		lb/100 yd2	gm/meter2
1	20	107.64		38	144
2	19	107.64		37	144
3	19	104.75		35	149.67
4	19	102.86		38	143.81
5	18	102.86		36	148
Average	19.2	106.83		36.8	145.37

Calculation:
For measuring the weight of woven fabric in weight per running yards, form data table we get the weight of 100 yd2 fabric is 19.2 lbs. Now assume the width of loom is 48 inches. Therefore the area of the fabric will be 1.33 yd2. So,

Weight of 100 yd2 woven fabric = 19.2 lbs. 

Weight of 1.33 yd2 woven fabric =  0.255 lbs.

That is weight of fabric per running yard is 0.255lbs or 116 gms.

Result:

1. The weight of woven fabric is 19.2 lbs/100 yd2 or 106.83 GSM.
2. The weight of knitted fabric is 36.8 lbs/100 yd2 or 145.37 GSM.
3. The weight of woven fabric per running yard is 0.255lbs or 116 gms.

Remark:
This is a direct measuring tester. So the result should be accurate. But as the samples are of both cotton fabrics, so there are effects of moisture content on the weight of fabrics. Besides the knitted fabrics are very much extensible and proper relaxed state is quite different during cutting of sample with GSM cutter. Therefore there are variations among their weights. The effects of moisture content can be accounted for either by conditioning the specimen in the standard atmosphere or by taking the specimen to oven dry weight and adding the official regain. 

 

Grey GSM VS Finished GSM of knit fabric

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After received the yarn we knit the yarn in knitting machine for producing knit fabric. In this stage the fabric remain uncolor formed. We called this as Grey Fabric. Then we dye the grey fabric in dyeing winch (machine) as per our required color.

In this regards the please not that, GSM of the followings Grey fabric are not remain same as our require finished fabric GSM. Normally the GSM of grey fabric remain lower then the finished fabric. After knitting when we dye and washed the fabric then the GSM increase and come to near as our requirement. This increasement of GSM depends on fabric constructions & some knitting variables. Lets see an example

Say,

Fabric Construction: Single Jersey

Yarn Count : 30/s

Require GSM(finished): 145 GSM

Grey GSM : will be what?

As per practical experience we know for Single Jersey fabric, if we knit the fabric with 30/s yarn then the grey GSM  will increase 15% to 20% after dyeing and finishing.

So, if we need 145 GSM S/J fabric with 30/s

Then we should keep the

Grey GSM = 145 – (15 to 20%), supposed it the percentage will be 18 then

Grey GSM = 145 – 18%

Grey GSM = 119 GSM

So, now we know that, if we need 145 gsm single jersey fabric with 30/s yarn, then we should keep the GSM of grey fabric as 119.

Please find below the GSM differents between Grey VS Finished for some more types of fabric.

  

For single jersey fabric:

If the yarn count is 30/s then the grey gsm will be 20% to 15% less from the finished Gsm

If the yarn count is 26/s then the grey gsm will be 22% to 20% less from the finished Gsm

If the yarn count is 24/s then the grey gsm will be 24% to 23% less from the finished Gsm

If the yarn count is 20/s then the grey gsm will be 24% to 21% less from the finished Gsm


G.S.M Calculation
GSM means grams per square meter. In knitting fabric it is the main parameter. It is controlled by loop length. If loop length increases GSM will decrease and vice versa. It is measured by GSM cutter & electric balance. It may also be calculated as below. 

             s x l x tex
GSM = ……………
                100

             s x l x 590
GSM = ……………
                  Ne

Calculate GSM of fabric from the given data:

• Total Weight of fabric = 15.5 Kgs
• Length of fabric = 35 meters
• Width of fabric in open form = 65 inches

Solution:

First we will calculate area of the fabric

Fabric length = 35 meters
Fabric width = 65 inches or 1.65 meters

Fabric area = Length x width
= 35 x 1.65
= 57.75 meters square

Weight of 57.75 Meter square is 15.5 kgs or 15500 grams

So weight of one square meter = 15500 / 57.075

= 268.39 grams per square meter 

Fabric GSM is 268.39 (ANS)

Yarn Count

S/J

L/S/J5%

L/S/J 8%

Pique

D/Lacoste

Rib 1*1

Rib 2*1

Rib 4*2

L/Rib 1*1

L/Rib 2*2

I/L

L/PK5%

F/T

L/F/T5%

Waffle

GSM