24/KNITTING VIEWS/SEPTEMBER-OCTOBER 2011

Flat knitting machines, also referred to

as “Flatbeds” or “V-beds,” have two

rib gated, diagonally-approaching

needle beds, set at between 90 and 104

degrees to each other and are positioned

so that the upper ends form an inverted

“V”. The interactions between the yarn

and the knitting elements that create the

fabric occur at the apex of the V and the

fabric moves away downward between

the two beds, drawn down by the take-

down system.

This knitting machine stitch potential

includes needle selection on one or both

beds, racked stitches, needle-out designs,

striping, tubular knitting, changes of

knitting width, and loop transfer. Further,

a wide range of yarn counts may be knitted

for each machine gauge, including a

number of ends of yarn at each knitting

system; the stitch length range is also

wide; and there is the possibility of

changing the machine gauge.

The modern V-bed knitting machine is a

highly engineered, fully automated,

electronically controlled, precision

knitting system. The operation and

supervision of the machines of the simpler

type are also less arduous than for other

weft knitting machines. The number of

garments or panels knitted across the

machine depends upon the knitting width,

yarn carrier arrangement, yarn path and

yarn package accommodation.

(The machine shown in fig. 11.2 is a

member of the Stoll CMS family of

machines. The knitting needles, beds and

other active elements are enclosed within

sliding covers to reduce noise and fibre

contamination and to enhance safety.)

V-bed knitting machine

A solidly built machine frame supports the

two rigid needle beds. Needles slide up

and down the beds in slots known as

“tricks,” cut into rigid needle beds, which

maintain the orientation and spacing of

the needles and support them when they

impact with the CAM system. The tricks

in the opposing beds are arranged so that

the needles can pass between each other

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 eleventh input from the series of

articles in Knitting Views)

Fig 11.1: Needles in V-bed

Fig 11.2: V-bed machineThe flat knit machines are the most

versatile of the weft knitting machines.

KNITTING VIEWS/SEPTEMBER-OCTOBER 2011/25

Fig 11.7: CAM plate and knitting carriage

The yarn supply is situated above the

machine and the yarn is fed to the needles

via yarn feeders that culminates in a tube

or bore to precisely position the yarn. The

feeder is fixed to a feeder block that slides

along a feeder rail located above the needle

bed. Modern machines typically have four

feeder rails with 4/6 knitting feeders/rail.

The feeder precedes the needle

movement across the bed in such a way

that the yarn is placed across the open

latch of the needle during the clearing

displacement so that when the needle

retracts and the latch closes the yarn is

trapped in the hook.

On the most basic V-bed machines a roller

traction system pulls the fabric down

between the needle beds to provide the

take-down tension necessary to maintain

the position of the old loop against the

verge of the needle bed during the clearing

displacement.

The modern flat knit machine also has its

own on-board control and programming

computer and the LCD monitor display

built into the sliding machine covers.

Normally, in a production environment

these machines can be networked and

knitting programmes can be downloaded

from the CAD/programming stations

directly to the machine's computer.

Equally, production statistics can be

collected centrally.

Knitting action of flat knitting

machine

Fig 11.3: Line diagram of V-bed knitting machine

Fig 11.6: Carriage movement and itsinfluence on knitting needle

Fig 11.4: Rib gaiting

Fig 11.5: Needles in tricks

The front edge of the needle bed also acts

as a knock-over support by helping to

maintain the position of the fabric during

knock-over.

The needle then tracks through the CAM

system as shown by the blue line in the

following diagram

1 The rest position: The tops of the heads

of the needles are level with the edge of

the knock-over bits.

2 Clearing: The needle butts are lifted as

to raise the needles to ‘tucking in the

hook’ height.

3 Yarn feeding: The yarn is fed as the

needles descend under the control of

guard cam. The required loop length is

drawn by each needle as it descends

the stitch CAM.

4 Knocking-over: To produce synchronised

knocking-over of both needle beds

simultaneously, the stitch CAM in the

front system is set lower than the

auxiliary stitch CAM, so that the latter

is rendered ineffective.

5 Delayed timing: If, however, delayed

timing of the knock-over is employed,

knock-over in the front bed will occur

after knock-over in the back bed.

Delayed timing is only normally used

ongauges finer than 8 NPI and cannot

be used for broad ribs

during loop formation. This arrangement

of the beds is called rib gaiting.

The two CAM systems are contained

within the carriage. The carriage or “CAM

box” traverses across the needle beds and

selects needles to be knitted as it

reciprocates side to side. The carriage

effectively raises and lowers the needles

on both beds simultaneously as it passes

over them, depending on the desired

pattern. Needle bed lengths can vary from

1.0 m to 2.2 m width and each is designed

for a specific task or purpose.

Fig 11.8: Knitting action of flat knitting machines

(In the next session, we would be discussingabout circular knitting machines.)

Bow

Yarn feeder

Yarn take-backspring Yarn guides

Yarn

Carriage

Needle bed

Fabrictake-down roller

Controlunit

Lowering cam(Stitch cam)

Guidingcam

High buttneedle

Low buttneedle The raising CAM

is in half position

Brushes

Yarncarrier