Flatbed knitting machine is used in our garment industries to produce a lot of knitted products like half cardigan, full cardigan. Even seamless garments can be produced from here. This content is about the important factors for flatbed knitting machine and its knitting action along with the cam arrangement system.
An American clergyman Rev. Issac Wixom Lamb, first in 1862, illustrated the flat bar knitting machine and he patented it in 1865. Later, he changed the arrangement of the flat bar machine with an inverted V-bed shape which was then patented by Eisenstuck.
Types of Knitting Machines
There are mainly two types of knitting machines. They are:
- Weft knitting machines
- Warp knitting machines
Weft knitting machines may be broadly grouped according to end product as either:
• Circular machines, knitting tubular fabric in a continuous uninterrupted length of constant width
• Flat and circular machines that are used for knitting garment-length sequences. They have counting device that is used to initiate additional garment-length programming.
It synchronizes the knitting action so that it can produce a garment-length repeat unit in the direction of the wales. Within the garment length, it may or may be not vary the garment width.
Warp knitting machines are:
- Tricot warp knitting machine
- Raschel warp knitting machine
Some Factors of Flatbed Knitting Machine
- Machine Gauge
Flat machines are normally gauged on the English system (E) of needles per inch (npi). The Metric system, which is based on the distance in tenths of a millimeter from the center of one needle to the next, is rarely used.
The latter is a direct system, with a higher gauge number indicating a coarser gauge – the opposite of the English system.
Generally, flat machine gauges range from E 5 to E 14, with the main gauges being 5, 7 and 10, but there are machines as coarse as E 21/2 and as fine as E 18 or even finer now being built.
All flat machines can be half-gauged by removing every alternate needle; thus, an E 10 gauge machine will become an E 5 gauge. Also, different needle hook sizes are available, and gauge conversion by changing needle beds is possible.
- Cotton Patents to V-bed Gauge
To convert from Cottons Patent gauge (G*, needles per 11/2 inch) to V-bed gauge (E, needles per inch)
1. Convert from 11/2 inches to 1 inch needle bed width.
2. In the gauge range G9 and below, reduce the resultant E gauge by 1.
Above G 9 reduce the resultant E gauge by 2. This is to fit commercial practice in flat knitting, where a slightly coarser gauge is preferred.
Example: Convert G9 and G21 fully-fashioned (needles per 11/2 inches) to V-bed flat E gauge (npi)
- Knitting width
Knitting width of v-bed machines are:
- Strapping machine needle bed widths tend to range from about 14 to 50 cm (5.5–20 inches);
- Hand-operated garment-width machines range from about 80 to 120 cm (31–47 inches);
- Power-driven automatic garment length machines range approximately in width from about 66 cm to 240 cm (26–95 inches).
- Wider ‘blanket width’ machines are approximately 244 cm (96 inches) wide, to knit unshaped garment pieces for cut-and-sew knitwear.
- Narrow bed ‘compact’ machines are approximately 127cm (50 inches) wide for fashion shaped knitwear. For integral garment knitting, the approximate width is 183 cm (72 inches).
- Yarn count
An indication of an approximately suitable count for a flat machine may be calculated using the formula:
The following are typical NeK count ranges for particular E gauges:
12 npi – 2/26’s to 2/42’s
8 npi – 2/14’s to 2/22’s
5 npi – 6/14’s to 6/18’s
2 npi – 8/7’s to 8/9’s
It can be seen that a characteristic of the flat machine is the large number of ends of yarn that may be knitted at the same time. However, if light-weight structures are required, the number of ends may be much fewer.
Types of Flatbed Knitting Machine
There are two types of flatbed knitting machines. They are:
- V-bed machines have two rib gated, diagonally-approaching needle beds. The needle beds set at between 90 and 104 degrees to each other. It is employed to give an inverted V-shape pattern.
- Flatbed purl (links-links) machines have horizontal needle beds. These machines are occupied mainly in knitting simulated hand-knitted structures of a specialty type, such as basket purl, lace patterning and cable stitch.
They use double-headed latch needles that are transferred to knit in either of two directly opposed needle beds. The non-knitting hook is controlled in the manner of a needle butt by a slider that hooks onto it. There is a set of sliders in each needle bed whose butts are controlled by the traversing cam-carriage to produce knitting or transfer of the needles.
These complex and slow machines are no longer built because the modern electronic V-bed machines can knit all the links-links designs using the facilities of rib loop transfer and needle bed racking.
Early intarsia machines employed a different approach, using only one needle bed to knit solid color designs. Now, however, many modern V-bed machines have intarsia-patterning facilities and are no longer restricted to geometrical designs because the mechanically-controlled carrier stops have been replaced by more versatile electronic controls.
Simple V-bed Flat Knitting Machine
In simple v-bed flat knitting machine, fixed thinner and specially shaped knock-over bit edges replace the trick walls at the needle bed verges. A needle trick in a bed remains aligned opposite to the knock-over bit in the other bed in the rib gating.
At the time of knitting, while passing between the needles the edges of knock-over bits restrain the sinker loops. It helps in the knocking-over of former loops as well as the formation of a newer one. The old loops are held down on the needle stem while it rises to clear by takedown tension and the needles of the other bed.
Modern electronic flat knitting machines now offer movable knock-over and holding-down knitting elements. It helps to knit shaped and single-bed structures.
On the hand flat bed knitting machine, once the needles take up the set-up course, a fabric comb is inserted by hand to the upward direction from needle beds. It is done so to keep the eyelet holes of fabric comb protrude above the course.
Then, the insertion of comb wire takes place through the eyelets over the set-up course to suspend it from the course. After that, a takedown weight is added along with it.
The cover plate which is a thin metal blade, prohibits the needle stems from pivoting upwards out of the tricks. It results in drawing the needle hooks downwards by the fabric takedown tension. During the drawing process, it allows the needles to move freely in tricks.
Damaged needles can be replaced by withdrawing the plate out of the needle bed. The spring takes its place below the needle bed while pushing it fully into the position.
Then the needle butt it assists is aligned with knitting cam track. It occurs on the under-surface of traversing cam carriage. The security spring of any needle isn’t placed in the groove if the needle is not supposed to be in action. It results in the needle to be nearer to the lower edge of the needle bed and the butt of this needle misses the traversing cam carriage.
The machines where jacquard selection is employed, the thrust of jacquard steel replaces the function of security spring. It can also be done by lifting and lowering the needle butts into the tricks to set the position of the needle butts for each carriage traverse.
The cam plate of both needle beds have latch opening brushes. It ensures the fact that the latch needles are completely opened. A precise setting of bristles relative to the needles is ensured by the adjustable brushes.
The cam carriage can run or slide on ball bearings or wheels along with guide rails. One of the guide rails is fixed over the lower end of each needle bed. Motor-driven roller chain or rubber belt even sometimes it is propelled by hand.
Each yarn carrier is fixed to a block that can slide along a bar. It can pass across the full length of machine as like as the carrier guide rails. The yarn carriers are attached at both side of the slide through a double prism type carrier bar.
It can be adjusted according to the requirement whether the yarn carriers are picked up or left behind the carriage. The driving bolts or pistons that are attached to it assist in this activity. These things are controlled either manually or automatically from, the carriage bow.
Each carrier bar track has a bolt. When the bolt is lowered, it entrains in the shoulder of a yarn carrier block with a groove. At the knitting selvedges, The stop plate that has inclined edges are set on the carrier bar.
The base of the bolt rises and lifted out to contact with a stop plate. It is then disconnected from the groove of the carrier block to continue the traverse of the carriage without that carrier. Two levers are usually provided, one at each end of the needle bed.
One lever helps in racking the back needle bed so that it can change the needle bed gating for rib set-out or rib loop transfer. The other assists in opening gap between the needle bed to permit the easy access of knitted fabric that is hanging from the needles.
Cam System of V-bed Flat Knitting Machine
The cam-carriage underside is shown by the figure. The needle butts are guided through the knitting system by the tracks that are formed by cams. The single knitting system cam-box is designed symmetrically. During a right to left traverse, it knits a course of loops on both the front bed and back bed needles. A second course is formed at the time of return left to right cam box traverse.
At the time of a left to right carriage traverse, the needle butts enters from right to the traversing cam system. During a right to left traverse, it enters from the left. There are two raising cams (R), two cardigan cams (C) and two stitch cams (S) foe each of the needle bed.
In the traverse direction, knitting is carried on for the leading raising cam whereas the trailing raising cam does the job as guard cam. In this case, the trailing stitch cam remains in the operation keeping the leading stitch cam out of action.
In case of reverse direction, the actions of the two stitch cams and two raising cams are reversed. The needle is raised to the tuck height by a raising cam. But it is raised to a full clearing position if the cardigan cam above it kept in action. Thus for a tuck stitch, cardigan cam is kept out of action.
For a miss stitch, we need to keep both the raising cam and the cardigan cam out of action. A pair of raising cams which remains diagonally opposite to each other in each bed (RL and RR) kept out of action to produce a tubular plain knitting course.
One course of rib is knitted in a single system machine in one traverse but two courses of rib per traverse is possible to knit with a double system machine. Sometimes a set of cams in one bed is referred to as a lock.
Knitting Action of Flatbed Knitting Machine
In the above figure 1 to 4 position is assuming a carriage traverse from left-to-right. Similar positions may be plotted for the return traverse, using the cams given an (L) designation to provide the positive movements.
- The rest position: The tops of the heads of the needles are level with the edge of the knock-over bits. The butts of the needles assume a straight line until contacting the raising cams R (R) because the leading stitch cams S and AS (L) are lifted to an inactive position.
The lifting action is an alternating action that always lowers the trailing stitch cams and raises the leading stitch cams in each system as the traverse commences.
This action prevents needles from being unnecessarily lowered and a strain being placed on the old loops prior to the start-up of the knitting action.
- Clearing: The needle butts are lifted as they contact the leading edge of cams R (R), which raises the needles to ‘tucking in the hook’ height with the undersurface of cams S (L) acting as guard cams. The needles are lifted to full clearing height as their butts pass over the top of cardigan cams C (R) and C (L).
- Yarn feeding: The yarn is fed as the needles descend under the control of guard cam (G). The required loop length is drawn by each needle as it descends the stitch cam S (R).
- Knocking-over: To produce synchronized knocking-over of both needle beds simultaneously, the stitch cam S (R) in the front system is set lower than the auxiliary stitch cam AS (R), so that the latter is rendered ineffective.
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. In this case, stitch cam S (R) is not set as low as AS (R) number 5 in the above figure so that the depth setting of the latter cam produces the knock-over action. Delayed timing is only normally used on gauges finer than 8 npi and cannot be used for broad ribs.
Here, S = Stich Cam
R = Raising Cam
C = cardigan Cam
For better understanding the flatbed knitting machine action please check:
End Products of Flatbed Knitting Machine
- Half cardigan or royal rib
- Full cardigan or polka rib
- Fisherman’s rib
- Sweater stitch
- Racked rib
- The cable sticth
To Sum Up
Flatbed knitting machine is widely used in our country. These machines can easily be operated and can yield versatile products.
You can also check: Circular Knitting Machine