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The term ‘circular’ covers all those weft

knitting machines whose needle beds

are arranged in circular cylinders and/or

dials, including latch, bearded, or (very

occasionally) compound needle

machinery, knitting a wide range of fabric

structures, garments, hosiery and other

articles in a variety of diametres. Circular

knitting machines are either of body size

or larger, having a single cylinder or double

cylinder, cylinder and dial arrangement, as

is also the case with small diametre

machines for hosiery. The modern circular

knitting machine is a highly engineered,

electronically controlled, precision

knitting system capable of producing high

quality fabric at very high speeds.

The main features of a circular knitting

machine are:

1. The frame or body is circular according

to needle bed shape supports the

majority of the mechanisms of

the machine

VASANT R KOTHARI has done Master’s in Textiles Technology

from DKTE’s Textile and Engineering Institute, Ichalkaranji

(Shivaji University, Kolhapur), Maharashtra. He has also done

Diploma in Export Management (Apparel Export) from the

Indian Institute of Export Management, and Garment Export

and Merchandising Management from NIFT, Bangalore.

Presently, he’s working as an Assistant Professor in

Department of Fashion Technology, NIFT, Bangalore. (This is

his twelfth input from the series of articles in Knitting Views)

2. The yarn supply system or the creel

for holding the yarn packages

3. Yarn tensioning devices

4. Yarn feed control

5. Yarn stop motion

6. Yarn feed carriers or guides

7. The knitting system, which includes

the housing and driving of knitting

elements and needle selection device

8. The fabric take down mechanism

9. Start, stop and inching buttons

10. The automatic lubrication system

In circular knitting machine, the yarn from

the package is unwounded and comes

downward through guides, tensioners,

stop motion, for being supplied to the

needles. The knitted fabric is taken down

inside the cylinder and ultimately rolled

on the cloth roller. Since the needles are

arranged in a circle on a circular knitting

Fig 12.1: Circular knitting machine Fig 12.2: Closet view of tubular fabric

KNITTING VIEWS/NOVEMBER-DECEMBER 2011/25

machine, the fabric is a tubular. It is usually

slit open when used.

Normally, circular knitting also adopts the

same knitting principles as the flat bed

machines. The circular machine starts to

knit when the CAM systems on the

needle beds (cylinder and dial) move

along the surface quite similar to that of

the carriage on a flat bed machine. The

only difference is that the operation is

continuous as CAM system of the circular

machine does not need to stop during

knitting because there is no beginning

or end of a course.

CAM technology

Circular knitting CAM systems only

allow for unidirectional knitting. CAM

systems generate both the needle and

the sinker moment for single jersey

machines and cylinder and dial moment

for double jersey machines. The given

diagram shows both the sinker CAM

track above and the needle CAM track.

The needle track shows the typical three

stage needle displacement of (1&4) the

raising or clearing CAM, (2&3) the

lowering or stitch CAM and (5&6) the

guard CAM that returns the needle to

its entry position for the next CAM

system. The sinker track shows the

engaged position (section 7) when the

needle is clearing. The sinker

disengages in sections 8 and 9 so that

knock-over can take place and re-

engages into section 7. The moment

diagrams of the needles and sinkers are

also shown in between CAMs.

Multi system circular machine

Similar to a flatbed machine, multi-system

circular knitting is also possible. Fig 12.4

is a schematic diagram of a circular

knitting machine having eight systems.

As shown in figure, it is clear that every

CAM system is knitting at the same time

and each of CAM system is having its

own supply of yarn for its own course.

So, when the machine runs, all eight

systems move together and hence eight

courses of fabric are in knitting at the same

time. In other words, at the end of one

revolution of the CAM system, eight

courses of fabric are completed. Similarly,

if there is more CAM systems around the

machine, there will be more fabric courses

being produced in a single revolution of

the machine, for example, say if there are

30 CAM systems, 30 courses of fabric

will be completed in one revolution of the

CAM system.

As compared to a flatbed machine with a

circular machine, the CAM systems of a

circular machine always operate at their

maximum speed. Also, circular machines

always have much more CAM systems

than flat bed machines. A double system

machine with 100-inch needle bed

produces about 45 courses per minute and

a 30-inch, 90-feed circular machine

produces about 2,700 courses per minute.

Further, in circular knitting machine, needle

action is a result of the relative motion

between the CAM plates and the needle

butt. The same needle action will be

achieved whether the CAM plate is

moving across the needle butt or the

needle butt is moving across the CAM

plate. So basically, there are two types of

circular machines distinguished by the

rotation of the machine.

I. CAM box revolving machine

II. Cylinder revolving machine

If the CAM plates are moving across the

needle butts, the needle bed or the cylinder

will be stationary keeping the needle butts

in place while the CAM box carries the

CAM plates, yarn feeders with their yarn

packages are all rotating around the

machine. This type of machine is called

CAM box revolving machine.

On the other hand, if the needle butts are

moving across the CAM plates, the CAMFig 12.3: CAM system

It may be noted that the number of

systems around the machine is limited

by the circumference of the needle

cylinder. Usually all the space on the

circumference is issued up for placing

CAM systems. The actual number of

CAM systems depends on the cylinder

diametre and the dimensions (width) of

the CAM boxes. For example, a 30-inch

diametre machine may have 72 to 90

CAM systems. Since each CAM system

must have its own yarn supply and hence

a yarn feeder, such machine can be

referred as 30-inch, 90-Feed machine.

From above figure, further, it can be seen

that whether there are eight systems or

80 systems, the space taken up by the

machine will not be changed.

Fig 12.4: Multi system circular machine

Packagefor camsystem 1

Cam Box 1

Cylinder

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boxes will be stationary keeping the

camplates in place. The needle bed will

then have to move across the CAM boxes

with the needle butts in the needle tricks.

For a circular machine, the needle bed is

cylinder and then it rotates and that will

be the only moving part with the CAM

boxes, yarn feeders and yarn packages all

stationary. This type of machine is called

cylinder revolving machine.

It would be clear that cylinder revolving

machine is simpler in construction and

consumes less power than CAM box

revolving machine since there are less

moving components. As a matter of fact,

most of the circular machines are cylinder

revolving type. Only those machines such

as the garment length machines are CAM

box revolving because of their complexity.

Those are machines with 6-18 feeds

producing complex knitting structures

which cannot be accomplished if the

machine is cylinder revolving.

Circular knitting machine is naturally the

choice for the volume production. Since it

is ideal for volume production, there are

purposely built circular machines. For

example, plain knit fabric is always in

Reference: Weft knitting – Introductionby Dr TY Lo, Institute of Textiles &

Clothing, Hong Kong

demand and large quantities. Circular with

justone set of needles in the cylinder is

available for plain knit only. All other knit

structures requiring the second set of

needles will be impossible but just

producing plain fabric will be able to keep

it occupied all the time

(In the next session, we would bediscussing about warp knitting.)