Saturday 7 February 2015

Knitting Calculation




A) Circular Knitting

Find out the production rate (kg/hour) for the following knitted structure on a fine gauge circular knitting machine.

Knitted structure                     Plain
Fabric Weight                         120 g/m
Courses per centimeter            18
Number of feeders                  100
Machine speed                        30 rpm
Working efficiency                 90%

B) Flat-bed Knitting

Calculate the production rate (pieces/hour) for the following knitted structures of a V-bed knitting machine using different number of feeders.

Knitted structure                     Plain
Courses per piece                    250 courses
Number of cam systems          3
No of strokes per minute        25
Working efficiency                 90%

Find out the production rate (pieces/hour) if  a) only use ONE feeder per stroke; and
                                                                        b) Two feeders per stroke.




Answer

A) Circular Knitting

Production (courses/hour) = 100 x 30 x 60 x 0.9 =162,000 courses/hour
Production (meters/hour) = 162,000 / (18 x 100) = 90 meters/hour
Production (kg /hour) = 90 x 120 g/m /1000 = 10.8 kg/hour


B) Flat Bed Knitting

One feeder production:

One stroke = TWO courses

Production (courses/hour) = 25 x 2 x 60 x 0.9 = 2700 courses/hour
Production (pieces /hour) = 2700/250 = 10.8 pieces/hour

TWO feeder production

Production (courses/hour) = 25 x 2 x2 x 60 x 0.9 = 5400 courses/hour
Production (pieces/ hour) =5400/250 =21.6 pieces/hour



Knitting Instruction for Flat-bed Machine

Apart from production calculation (pieces/hour) on V-bed machine, one of the key elements for the knitting factory (sweater factory) is to prepare knitting instruction.

What is knitting instruction?

Knitting instruction is the statement used to knit the garment parts and expressed in terms of courses (fabric length), needles width (fabric width) and fashioning frequencies.

In other words, if a fabric piece is given with how many inches in length and width, you need to find out the correct number of courses to produce the required length and correct number of needles width to produce the required fabric width.

A swatch (a small piece of fabric) in correct knitting instruction and knitting tension is normally prepared before bulk production. One of the common methods used by industry to determine the stitch tension is to stretch the fabric course wise to its utmost limits manually and measure the dimension of 10 wales board.


Example

Find out the widening (Part A in diagram) and narrowing (Part B in the diagram) of the sleeve panel as shown.





Given

Wales per inch : 8
Courses per inch : 6
No. of needles at bottom : 64 needles
Height of A = 13 inches
Height of B = 3 inches
Fabric narrowing by 2 needles each time on each side
Each small square is 1 square inch.







A) Widening (for each side) of  A:

Number of needles to be added (on each side)
((16 x 8) – 64) /2 = 32 needles (width)

Number of turns for widening: 13 inches x 6 = 72 turns (height)

72 turns / 32 needles = 2 turns ……14 needles

ie every 2 turns add 1 needles for 32 times, we will have 14 needles left.
   ( 2 + 1 + 32 ….14)

To make such adjustment, we modify as follows: every 3 turns we add 1 needle for 14 times.

The widening will have two parts:

2 + 1 + 18 (part 1) and 3 + 1 + 14 (part 2)

Check : Part 1 we add 18 needles on 36 courses (2 x 18)
             Part 2 we add 14 needles on 42 courses (3 x 14)
            Total we add 32 needles (18 + 14) on 72 courses (36 + 42)


B) Narrowing (on each side) for B

No. of needles on each side to be narrowed: (16-12) /2 x 8 = 16 needles
Number of turns for narrowing: 3” x 6 =18 turns

If narrowing by 2 needles each time, number of times will be 16 needles/2 =8
Dividing 18 turns by 8 times = 2 turns…..2
which means 2 turns will be less if every 2 turns less 2 needles by 8 times ( 2-2-8).
To make the adjustment, the last 2 turns will have 3 turns instead. The answer should be


2-2-6 (Part 1) and 3-2-2 (part 2)

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