KNITTING CALCULATIONS
Production Calculation of Knitted Fabric
In every mill, there maintains a sequences in production
processing in knitting. Production of
a mill depends on a production manager. Among the various factors of
calculation of knitted fabric are to be considered in the manufacture of
knitted fabrics, it is very important for the knitter or production manager to
calculate the productivity of a machine in order to be able to schedule
production and specify the delivery dates to the customer. For calculation
production manager need to know some formulas. Formula varies on different
types of fabric. Different formulas for
calculation of knitted fabric are given below with example.
Fabric
Type: Single Jersey Plain
Number of Feeder : 90 R.P.M. of Machine : 32
Machine Dia : 30 Machine Gauge : 24
Count of Yarn : 24/1 Ne Stitch Length : 2.74
Efficiency : 85 % No. of Machine : 20
Machine Dia : 30 Machine Gauge : 24
Count of Yarn : 24/1 Ne Stitch Length : 2.74
Efficiency : 85 % No. of Machine : 20
= 10746.33 Kg
Fabric
Type: 1 x 1 RIB
No of Feeder : 60 R.P.M. of Machine : 25
Machine Dia : 30 Machine Gauge : 20
Yarn Count : 34/1 Stitch length : 2.54
Efficiency : 80 % No. of Machine : 17
Machine Dia : 30 Machine Gauge : 20
Yarn Count : 34/1 Stitch length : 2.54
Efficiency : 80 % No. of Machine : 17
= 2441.65 Kg
Fabric
Type: Plain Interlock
No of Feeder : 108 R.P.M. of Machine : 26
Machine Dia : 34 Machine Gauge : 24
Yarn Count : 34/1 Stitch Length : 1.54
Efficiency : 80 % No of Machine : 5
Machine Dia : 34 Machine Gauge : 24
Yarn Count : 34/1 Stitch Length : 1.54
Efficiency : 80 % No of Machine : 5
= 1108.50 Kg
Most suitable count for
knitting machines
As a thumb rule knitting experts prefer to
use such knitting machine whose gauges is near to count of yarn (English count)
i.e. for 20-gauge machines most suitable yarn count is 20s. This rule is has
certain limitations, like, for 28-gauge yarn of 26s to 30s is most suitable.
But for very fine counts this rule is not applicable and also machines have
maximum gauge 32. Normally fine counts are not used as such rather they are
make double, like count 60s double, which means that net count is near to 30s.
And this 60 double count is suitable for 30-gauge machine.
To solve this problem some authors have
suggested following formulas.
For single Knitting
Machine
Suitable count = G*G/18
For Double knitting
machine
Suitable count= G*G/8.4
Where G is gauge of knitting machine
Some knitting machine manufacturers suggest a
range of yarn count for their machine.
There is another way to solve this problem
and that is to take help from old record. Every firm is producing many types of
fabrics and on the basis of experience they develop a database for ready
reference.
One can get a ready reference from the table
to produce fabric of certain grammage. We are also giving expected width of
fabric after wet processing.
This table can provide just a reference.
Knitters have to decide by themselves after doing a trial production, since
there are many more factors, which can affect yarn and gauge selection process.
Knitting Machine
Parameters
Every knitting machine is made to fulfil
certain demands of the customer.
There are number of characteristics of
machine which are intimated by the machine manufacturers while delivering the
machine to customers/users.
It is helpful for the user to be well aware
about these parameters. Furthermore machine specifications are given in
different unit. We will explain these parameters and will also give the
conversion factors to convert parameters from one system to other.
Machine Gauge
As per Oxford Dictionary the word “gauge” is
a noun and as well as verb. It is used to measure level of any thing or for an
instrument to measure width, length or height of any thing.
In knitting it is used to express the number
of needle in a unit length of the needle bed. This needle bed may flat or
circular.
In double knit circular machine it is used
for cylinder and as well as dial. Generally gauge is defined as number of
needles per inch.
According to German standard DIN 60917 (Iyer et al1995) alphabet “E “ is used to denote knitting machine
gauge.
E = Number of needles
1 inch (25.4 mm)
Machine Pitch
As per German DIN 62125 (Iyer et al1995) the
notation “gauge” is to be avoided in the future. Rather they prefer to use
notation “pitch” for comparison purpose.
Machine Pitch means the distance between the
centres of two neighbouring needles. It is denoted with small “t”. It is given
in mm.
Knitting Machine
Production calculation
Before explaining the method to calculate the
nominal production capacity of the knitting machine it is imperative to be well
aware of count and denier system and one should also be familiar with the
conversion factors.
Yarn is sold and purchased in the form of
cones and bags. Cones and bags have certain weights.
Still in the international market yarn is
sold in pounds not in kilograms. Bags are of 100 pounds, which is equal to
45.3697 kgs.
Previously there were 40 cones in a bag but
now there are bags available of 25 cones. In other words cones are of 2.5
pounds and four pounds.
Nominal Production of
knitting machines
One very simple way to calculate knitting
machine production by weighing the total production of one hour or one shift or
one day.
The practical way calculating production of a
machine is as follows. In this method following information for production
calculation are required:
- Machine
Guage and Dia
- RPM
Knitting Machine
- Yarn
Count
- Stitch
Length
From
these figures we can calculate the length of yarn being used by the machine in
one hour and then by converting this length into weight with the help of count
given we can calculate the quantity of yarn being consumed by machine in one
hour. This would be the optimum production of the machine. This optimum
production can be converted into nominal production by multiplying it with
efficiency. In the following pages we
will explain this with few examples.
In the following pages we will explain the
method to calculate nominal production capacity of knitting machine. It is
commonly believed that we can run knitting machine up to 85% efficiency.
However, by creating most suitable environment
one can increase machine efficiency.
For this we need following figures:
Machine speed RPM
Machine guage
Machine Dia
Count/ denier of yarn being used
Stitch length
From the above-mentioned figures we can
calculate the length of yarn being used in one revolution and if we know the
length and count of yarn then it is quite easy to calculate weight of yarn (see
Example: 03 for more details)
Example 01
Calculate nominal production of a single
jersey-knitting machine per hour from the data given:
Machine Gauge 24
Machine Dia 30
inches
Number of Feeders 90
Machine RPM 26
Yarn Count 24
Stitch length 4
mm
Efficiency 85%
Solution:
Step one
First we will calculate number of needles and
number of stitches produced in one revolution. This would help us in
calculating the total length of yarn consumed in one revolution.
Number of needles = machine dia * gauge * p (3.14)
= 30* 24*3.14
=2260 (exact 2260.8 but needles are always in even number
so we
will take nearest even figure)
Number of
stitches produced in revolution
Every needle is making one stitch on every feeder
because machine is producing single jersey fabric (full knit fabric).
Number of stitches produced in one revolution
= Number of needles * number of feeders
= 2260*90
= 203400
This figure shows that machine is making
203400 stitches in one revolution.
Step Two
Length of stitch is 04 mm (stitch length is
always calculated in metric system)
From this figure we can calculate yarn
consumption in yards in one hour
Yarn Consumption (in yards) in one hour
= number of stitches * length of (mm) *
RPM *60 (minutes)
1000(to convert mm into meters)
=203400 * 4 * 26 * 60
1000
= 1269216 meters or
= 1388015 yards
Step Three
In previous step we calculated quantity of
yarn consumed in yards. We can easily calculate weight of this yarn while its
count is known (see example 03).
Weight of cotton yarn = length of yarn
Count * 840
= 1388015
840 * 24
= 68.85 pounds or
= 31.23 Kilo grams
Efficiency 85%
= 26.55 Kilo grams
Answer: this machine can
produce 26.55 Kgs fabric in one hour at 85 % efficiency
Example 02
For Filament yarn,
Calculate nominal production of a single
jersey-knitting machine per hour from the data given:
Machine Gauge 28
Machine Dia 26
inches
Number of Feeders 120
Machine RPM 30
Yarn Denier 75
Stitch length 4.5
mm
Efficiency 85%
Solution:
Step one
First we will calculate number of needles and
number of stitches produced in one revolution. This would help us in
calculating the total length of yarn consumed in one revolution.
Number of needles = machine dia * gauge * p (3.14)
= 26* 28*3.14
=2286 (exact 2285.92 but needles are always
in even number so we will take
nearest even figure)
Number of
stitches produced in revolution
Every needle is making one stitch on every
feeder because machine is producing single jersey fabric (full knit fabric).
Number of stitches produced in one revolution
= Number of needles * number of feeders
= 2286*120
= 274320
This figure shows that machine is making
274320 stitches in one evolution.
Step Two
Length of stitch is 04.5 mm (stitch length is
always calculated in metric system)
From this figure we can calculate yarn
consumption in yards in one hour
Yarn Consumption (in yards) in one hour
= number of stitches * length of (mm) *
RPM *60 (minutes)
1000(to convert mm into meters)
=274320 * 4.5 * 30 * 60
1000
= 2221992 meters
Step Three
In previous step we calculated quantity of
yarn consumed in yards. We can easily calculate weight of this yarn while its
count/denier is known (see example 05).
Weight of filament in
grams = Length in meters * denier 9000
= 2221992*75
9000
Answer =18516 grams or
=18.516 Kgs
Efficiency 85%
=
18.516*85
=15.74
Kgs
Answer: this machine can
produce 15.74 Kgs fabric in one hour at 85 % efficiency
Note: if we are producing any textured
fabric, like fleece, then we use two different yarns at different feeders and
ultimately stitch length is also different. In such case we should calculate
separately consumption of different yarn at different feeders. Following
example will help in calculating production in case of use of more than one
kind yarn.
Example 9
Calculate nominal production of a
fleece-knitting machine per hour from the data given:
Machine Gauge 18
Machine Dia 30
inches
Number of Feeders for 60
Front yarn
Number of feeders 30
For loop yarn
Machine RPM 28
Yarn Count 26s for front
Yarn count for loop 16s
Stitch length of 4.5 mm
front yarn
Stitch length of 2.5 mm
Loop yarn
Efficiency 85%
Solution:
Step one
First we will calculate number of needles and
number of stitches produced in one revolution. This would help us in
calculating the total length of yarn consumed in one revolution.
Number of needles = machine dia * gauge * p (3.14)
= 30* 18*3.14
=1696 (exact 1695 but needles are always in even number
so we
will take nearest even figure)
In this example we will calculate consumption
of yarn in Kgs of both yarns and then we will add them to get final production
per hour
Consumption of
yarn for front knitting, Every
needle is making one stitch on every feeder because machine is producing single
jersey fabric (front of fleece).
Number of stitches produced in one revolution
= Number of needles * number of feeders
= 1696*60
= 101760
This figure shows that machine is making
101760 stitches in one revolution.
Step Two
Length of stitch is 04.5 mm (stitch length is
always calculated in metric system)
From this figure we can calculate yarn
consumption in yards in one hour
Yarn Consumption (in yards) in one hour
= number
of stitches * length of (mm) * RPM *60 (minutes)
1000(to convert mm into meters)
=101760 * 4.5 * 28 * 60
1000
= 769305 meters or
= 841312 yards
Step Three
In previous step we calculated quantity of
yarn consumed in yards. We can easily calculate weight of this yarn while its
count is known (see example 03).
Weight of cotton yarn = length of yarn
Count * 840
= 841312
840 * 30
= 38.52 pounds or
= 17.43 Kilo grams
Efficiency 85%
= 14.85 Kilo grams
Answer: this machine will
consume 14.85 Kgs of yarn to knit front of the fleece fabric in one hour at 85
% efficiency
Step Four
Yarn consumed for loop
knitting (back of the fabric)
Every needle is making one stitch on every
feeder because machine is producing single jersey fabric (front of fleece).
Number of stitches produced in one revolution
= Number of needles * number of feeders
= 1696*30
= 50880
This figure shows that machine is making
50880 stitches in one revolution.
Note: that we have put 30 cones of course
count for loops after every two feeders.
Step Five
Length of stitch is 2.5 mm (stitch length is
always calculated in metric system)
From this figure we can calculate yarn
consumption in yards in one hour
Yarn Consumption (in yards) in one hour
= number of stitches * length of (mm) * RPM *60
(minutes)
1000(to convert mm into meters)
1000
= 213696 meters or
= 233696 yards
Step Six
In previous step we calculated quantity of
yarn consumed in yards. We can easily calculate weight of this yarn while its
count is known (see example 03).
Weight of cotton yarn = length of yarn
Count * 840
= 233696
840 * 16
= 17.39 pounds or
= 7.89 Kilo grams
Efficiency 85% =
6.70 Kilo grams
Step Seven
Now we can add both yarn consumed
Yarn for front 14.85
Yarn for back 6.70
Total 21.55
This machine can produce
21.55 Kgs fabric in one hour at 85% efficiency
All above discussion to elaborate the way to
calculate the optimum production of a knitting machine. The following formula
is useful in every situation to calculate the optimum production capacity of a
knitting machine at 85% efficiency.
For cotton count
Production in one hour =
Gauge * Dia * 3.14 * RPM *60 * Stitch length
(mm) *1.0936 * 1 * 85
1000 *840 * yarn count *
100
Grammage Expressions
Generally grammage is expressed in Grams per
Meter Square (GSM) but in certain cases it is also expressed Ounces per Yard
Square (OSY). People, particularly working in marketing and merchandising
departments face problems in converting GSM into OSY. We will explain this
conversion method with examples before that it is imperative to know the
standard conversion factors of different measuring units. A complete conversion
chart is given at the end of the book. One should be much familiar with these
conversion factors.
Conversion of GSM
(grams per square meter) into OSY (ounces per square yard)
250 GSM means that weight of one meter square
fabric is 250 grams and 10 OSY means weight on one yard squares is 10
ounces. In the following lines we will
explain the method of conversion from GSM to OSY and vice versa with the help
of examples.
Example 10
Convert 10 OSY (ounces per square yard) into
GSM (grams per square meter).
It means weight of one yard square is 10
ounces or
Weight of one square yard is 280 grams (one
ounce is equal to 28 grams) or
Weight of one 0.836 meter square (one yard
square is 0.836 meter square) is 280 grams or
Weight of one meter square = 280* 1
0.836
Answer = 344.9 grams per meter square
Example 11
Convert 250 GSM (grams per square meter) into
OSY (ounces per square yard)
It means weight of one meter square is
250grams or
Weight of one square meter is 8.93 ounces (28
grams are equal to one ounce) or
Weight of 1.196 yard square (one meter square
is equal to 1.196 yard square) is 8.93 or
Weight of one yard square = 8.93* 1
1.196
Answer = 7.47 ounces per yard square
Relation between length,
width and grammage
It was observed during interaction with the
people working in garment business that they face difficulties in calculation
related to grammage, width and length of the fabric. In the following lines we
will explain relationship among these factors with examples.
Example 10
Calculate weight
of fabric from the given data.
Grammage 300
GSM
Width of fabric 35 inches (in tubular form)
Length of fabric 20 meters
First we will calculate area of the fabric
Area of fabric = Fabric length * fabric width
= 20 * 35*2 (since fabric is in
tubular)
39.37 (one meter is equal to 39.37 inches)
= 35.6 meter square
Weight of one meter square is = 300 (GSM)
And weight of 35.6 meter square = 300*35.6
= 10680 grams or 10.680 Kgs
Example 13
Calculate GSM from the data given
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 * width
=35 * 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 = 15500/57075
= 268.39 grams per meter square of GSM of
the
fabric
Calculation of
different fibre percentage in knitted fabric
Normally fabrics are knitted with one kind of
yarn but in some cases more than one type of yarn of different counts and
combination (mixing of two different fibres) are used. One very common example
is knitting of fleece fabric, which is knitted by using fine and course yarns,
and one yarn is made of polyester and cotton. Another example is knitting of
fabric by using spandex filament and cotton or pure polyester. In such condition there is a requirement to
mention exact percentage of different fibres in the fabric. Supplier has to
mention this ratio on label. In the following lines we discuss the methods to
calculate such percentage with the help of examples.
Example
Find exact composition of different fibres in
fleece fabric from the following data:
Yarn count front 30s
100 cotton
Yarn count for loop 20s 50:50 P/C
Consumption ratio Front: loop 2:1 (by weight)
Suppose for front we need 2Kg yarn and for
loop we will be requiring 1 Kg yarn
Front yarn 2 KGS 100
% cotton Cotton 2000 grams
Loop yarn 1 Kg 50:50 P/C Cotton
500 grams and
Polyester
500
grams
Exact Ratio
Cotton total 2.5
Kgs
Polyester 0.5 Kgs
Ratio:
Cotton:
83.33%
Polyester : 16.66
Knitting Equation
WPI:
Wales per
inch is called WPI.
CPI:
Course per inch is called CPI.
Needle calculation:
Single jersey circular knitting machine needle = ∏DG
Rib/Inter lock /Double jersey circular knitting machine
needle
= ∏DG×2
(two needle bed is here)
Single bed flat knitting m/c’s needle = width× gauge
V bed flat knitting m/c’s needle = 2× width× gauge
Here,
D = cylinder diameter
G = Machine gauge
Needle pitch = 1/G.
GSM:
Grams per squire meter of the fabric are called GSM.
GSM = {WPI× CPI ×(39.37)2×stitch length (mm)×Tex
/1000× 1000}g/m2
Stitch density = (WPI × CPI )inch-2
= (WPC ×CPC) cm-2
No of sinker = No of needle
No Wales =No of needle
No of course = No of feeders
=No of yarn (per revolution of
cylinder)
Course per minutes = No of feeders ×cylinder rpm
Course length = yarn required for each course.
= No of needle × stitch length
Fabric width = wale spacing ×Total no of Wales
= (1/WPI ×No of Needles) inch
= (No of Needles/WPI× 39.37) meter
For single jersey fabric = (∏DG/WPI×39.37) meter (open
width)
=(∏DG/WPI×39.37)
meter/2(Folded/Tubular width)
For double jersey fabric = (2 × ∏DG/WPI×39.37) meter
(open width)
= (2×∏DG/WPI×39.37)
meter/2(Folded/Tubular width).
Fabric Length =Course spacing ×Total course pr hour
= {(Feeder× cylinder rpm× 60)/CPI}
inch/hour
= {(Feeder× cylinder rpm× 60)/CPI
×39.37} m/hour
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