Knitting Calculations

(1)

KNITTING CALCULATIONS

Knitted fabric is made with the help of yarn loops. Yarn of different counts is used to produce fabric of different grammage. There is also a need to calculate optimum

production of knitting machines. It is the job of knitting manager to do certain calculation for proper use of machines and production of fabric according to the demands of the customer. This chapter is aimed at explanation of different calculations.

Most suitable count for knitting machines

As it has been discussed in Chapter Two that needle hook has to take yarn to convert it into a loop and finally latch has to close the needle hook so that loop is properly held by the needle hook and ultimately this helps in passing new loop through the previously held loop. It is clear from this explanation that there should be a proper balance between needle hook size and the thickness of the yarn or filament. If the yarn is thicker than needle hook then there will a chance that needle hook will not able to hold this loop and consequently there will be a small hole in the fabric. If the situation is reverse, means yarn is thinner than the size of the needle hook then the fabric produced will look like a net. Both situations are not wanted. This situation demands a balance between needle hook size and count of yarn. It is worth to note that needle hook size depends upon the machine guage. Furthermore for different garments, fabric of different grammage is required. Every time knitter has to decide about the yarn count. There are many ways for the selection of proper count. In the following lines we will discuss most common methods to select count for different machines of different guage. It is also important to note that selection of yarn counts also depends upon the machine manufactures and type of machines, like, single and double knit machine. However a general guideline will be given hereunder.

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-gaugemachines 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

(2)

firm is producing many types of fabrics and on the basis of experience they develop a database for ready reference. In the following line we give a table for guidance (table is under construction). 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

(3)

other words cones are of 2.5 pounds and four pounds. Big size cones are most suitable for knitting. When these cones are used in warping then there is a need to know the length of certain weight of yarn. And some time length is available and some one wants to know the weight of the yarn and in some cases count of the yarn is required. In the following lines we will give methods to calculate above-mentioned figures.

It is imperative to be well aware of count system. In the end of the book we have given different tables and explanation of different terms. Before going ahead students are asked to consult tables and explanation for better understanding of this chapter.

Relationship between count, length and weight of yarn Length (in yards) = Count *840 *weight of yarn in pound Count = Length / weight of yarn in pounds*840

Weight of yarn = length/count *840

Note: as per definition count is a relationship between length and weight of yarn. English count is defined as number of hanks in one pound. Hank means a certain length. It is different for different fibers. For details see tables given in the end of book. For

explanation purpose we will use English count of cotton. For cotton length of hank is 840 yards. For other fibers use relevant length of hank

Examples: Example:01

Calculate count of cotton yarn from the given data: Weight of yarn = 2.68 pounds

Length of yarn = 33600 yard

Formula: Count = Length / weight of yarn in pounds*840 =33600/2.68*840

Answer =14.93s Example :02

Calculate length of cotton yarn from the given data: Weight of yarn = 3.5 pounds

Count = 40s

Formula: Length (in yards) = Count *840 *weight of yarn in pound = 40*840*3.5

Answer =117600 Yards Example :03

Calculate weight of cotton yarn from the given data: Length of yarn = 40600 yards

Count = 30s Formula:

(4)

= 40600/30*840 Answer = 1.61 pounds

Next examples are related to filament. Note that for filament we use direct system. In which most popular is denier. There are other units too. For detail consult the tables at the end of the book. Denier is number of grams per 9000 meters of filament.

For calculation related to denier we use following equations: Length of filament in meters = Weight of filament in grams* 9000 Denier

Weight of filament in grams = Length in meters * denier 9000

Denier = 9000* Weight of filament in grams Length of filament in meters

Example 4

Calculate length of polyester filament from the given data: Weight 690 grams

Denier 75

Equation: Length of filament in meters = Weight of filament in grams* 9000 Denier

= 690 * 9000 75

Answer =82800 meters Example 5

Calculate weigh of polyester filament from the given data: Length in meters = 50900

Denier = 50

Equation: Weight of filament in grams = Length in meters * denier 9000 = 50900*50

9000

Answer =282.8 grams Example 6

(5)

Length in meters = 550,000 Weight = 4.5 kgs (4500 grams)

Equation: Denier = 9000* Weight of filament in grams Length of filament in meters

= 9000*4500 550,000

Answer= 73.66 Denier

Note: this calculation is up to two digits. For more accurate answers use calculation up to 9 digits.

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. This will be most realistic production value but we cannot get knitting machine capacity in this way. There is a scientific way to calculate optimum production figure of any machine. This needs certain information and some calculation. In the following lines we will explain this method in detail and will give some example so that one can be familiar to this process. In the end we will give an equation to calculate the knitting capacity of the machine. 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

(6)

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 07

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 * (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 feeders 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

(7)

= 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 08

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

=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

(8)

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

=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

(9)

Stitch length of 2.5 mm Loop yarn

Efficiency 85% Solution: Step one

=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

=101760 * 4.5 * 28 * 60 1000

= 769305 meters or = 841312 yards Step Three

(10)

= 841312 840 * 30

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

=50880 * 2.5 * 28 * 60 1000

= 213696 meters or = 233696 yards Step Six

= 233696 840 * 16

(11)

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. We have develop a equation which is useful in evey 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

(12)

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)

(13)

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.

(14)

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

Shortcut to Loop length calculation for knitting

(24 GG) SINGLE JERCY = 1257.765 /(COUNT x GSM )

(18 GG) 1 X 1 RIB = 1257.765 X 1.4 /(COUNT x GSM) (24 GG) INTERLOCK= 1257.765 X 1.9 /(COUNT x GSM) LL / GSM =(1.91 X 5906 )

___________ / COUNT LL/GSM

YARN CONSUMPTION = LENGTH X WIDTH X 0.GSM X 2 /10000 (IF TUBLER)

Posted by my fabric notes Labels: Knitting, Yarn