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.
The first flat bar machine was demonstrated in 1862 and patented in 1865 by the Rev. Isaac Wixom Lamb, an American clergyman. He later changed the arrangement to the inverted V-bed shape patented by Eisenstuck.
Table of Contents
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 for knitting garment-length sequences, which have a timing or counting device to initiate an additional garment-length programming (‘machine control’) mechanism.
This co-ordinates the knitting action to produce a garment-length structural repeat sequence in a wale-wise direction. The garment width may or may not vary within the garment length.
Warp knitting machines are:
Tricot warp knitting machine
Raschel warp knitting machine
Some Factors of Flatbed Knitting Machine
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 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).
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, set at between 90 and 104 degrees to each other, giving an inverted V-shape appearance.
Flatbed purl (links-links) machines have horizontal needle beds. They have been employed mainly in knitting simulated hand-knitted constructions of a specialty type, such as cable stitch, basket purl, and lace patterning.
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
The following figure shows that the trick walls are replaced at the needle bed verges by fixed, thinner, polished and specially shaped knock-over bit edges. In rib gating, a knock over bit in one bed will be aligned opposite to a needle trick in the other bed.
During knitting, the edges of the knock-over bits restrain the sinker loops as they pass between the needles and thus assist in the knocking-over of the old loops and in the formation of the new loops. The takedown tension and the needles in the other bed help to hold the old loops down on the needle stems as the needles rise to clear.
Many modern electronic flat machines have movable knock-over and holding-down elements, which assists in the knitting of shaped and single-bed structures.
On hand flat machines, after the first or set-up course of rib is taken by the needles, a fabric comb is hand-inserted into it, upwards from under the needle beds, so that the eyelet holes of the comb protrude above the course.
The comb wire is then inserted through the eyelets, over the set-up course, so that the comb is suspended from the course, and a takedown weight is attached to it. The cover plate is a thin metal blade, located in a slot across the top of the needle bed tricks.
It prevents the stems of the needles from pivoting upwards out of the tricks as a result of the fabric take-down tension drawing the needle hooks downwards, whilst allowing the needles to slide freely in their tricks.
The plate can be withdrawn sideways out of the needle bed to allow damaged needles to be replaced. Supporting the tail of each needle is a security spring that fits over the lower edge of the needle bed. When the spring is pushed fully into position, it locates into a groove on the under-surface of the needle bed.
The butt of the needle that it supports is then aligned with the knitting cam track on the under-surface of the traversing cam-carriage. When a needle is not required to be in action, its security spring is not located in the groove, so that the needle is nearer to the lower edge of the needle bed and its butt misses the traversing cam-carriage.
On machines employing jacquard selection, the function of the security spring is replaced either by the thrust of a jacquard steel onto the tails of the elements or by the raising or depressing of the knitting butts into the tricks, in order to position the needle butts for each carriage traverse.
Latch opening brushes are attached to the cam-plates of both needle beds to ensure that the needle latches are fully opened. The supports of the brushes are adjustable to ensure precise setting of the bristles relative to the needles.
The cam-carriage either slides, or runs on ball-bearings or wheels, along guide rails, one of which is fixed over the lower end of each needle bed. It is propelled either by hand or from a motor-driven continuous roller chain or rubber belt.
Each yarn carrier is attached to a block which slides along a bar, which, like the carriage guide rails, passes across the full width of the machine. The carrier bar may be of the double prism type so that yarn carriers may be attached to slide along both the front and the back surfaces.
The yarn carriers are picked up or left behind by the carriage, as required, by means of driving bolts or pistons that are attached to, and controlled either manually or automatically from, the carriage bow.
There is a bolt for each carrier bar track that, when lowered, entrains with a groove in the shoulder of a yarn carrier block. Stop plates having inclined edges are positioned on the carrier bars at the knitting selvedges.
On contact with a stop plate, the base of the bolt rises and is lifted out and disconnected from the groove of the carrier block so that the carriage continues its traverse without that carrier. Two levers are usually provided, one at each end of the needle bed.
One is for racking the back needle bed, to change the gating of the needle beds for changes of rib set-out or rib loop transfer. The other is to open the gap between the needle beds for easier access to the knitted fabric hanging from the needles.
Cam System of V-bed Flat Knitting Machine
The above figure shows the underside of the cam-carriage and the cams forming the tracks that guide the needle butts through the knitting system. The single knitting system cam-box is symmetrically designed for knitting a course of loops on both the front bed and back bed needles during a right-to-left traverse and a second course during the return left-to-right cam box traverse.
The needle butts will enter the traversing cam system from the right during a left-to-right carriage traverse and from the left during a right-to-left traverse. For each needle bed there are two raising cams (R), two cardigan cams (C) and two stitch cams (S).
In the direction of traverse, the leading raising cam is responsible for knitting and the trailing raising cam acts as a guard cam. The leading stitch cam is raised out of action and the trailing stitch cam is in operation.
In the reverse direction of traverse, the roles of the two raising cams and of the two stitch cams are reversed. A raising cam lifts the needle to tuck height, but if the cardigan cam above it is in action the needle is lifted to full clearing height. Thus, the cardigan cam is taken out of action if a tuck stitch is required.
To produce a miss stitch, both the raising cam and the cardigan cam are out of action. To produce a course of tubular plain knitting, a pair of raising cams that are diagonally opposite each other in each bed (RL and RR) are out of action.
A single system machine will knit one course of rib in one traverse whereas a double system machine will knit two courses of rib per traverse. 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:
Salma Hasin Shila, the author of this site completed her BSc. in Textile Engineering (Wet Processing Engineering) from Bangladesh University of Textiles www.butex.edu.bd (BUTEX). She has a passion for textile technology and love to write about it. She wants to share her knowledge to help the students in their studies and businessman & entrepreneurs in their business in making wise decisions fast.