The flat knitting machine is a two-bed machine. The most important mechanical features of a flat knitting machine are the supporting frame, the yarn feeding system, a transmission system, a fabric take-down motion, a central programming unit, a needle-bed racking system
Flat Knitting Machines
The flat knitting machine is a two-bed machine. The most important mechanical features of a flat knitting machine are:
- the supporting frame
- the yarn feeding system
- two needle-beds made up of flat grooved plates
- a carriage provided with cam-locks for needle control
- a transmission system
- a fabric take-down motion
- a central programming unit
- a needle-bed racking system
The two flat beds can be:
- Inclined by 90°-100° with respect to one another, with a staggered arrangement of the grooves accommodating latch needles or compound needles. The two flat beds are the “front needle-bed” (indicating the needle-bed closer to the operator) and the “rear needle-bed” (indicating the farther).
- Both are arranged on a horizontal plane (at 180°) with the grooves, which are positioned opposite to each other. Double hook needles slide inside the grooves; these needles are moved by special sliders, which can transfer the stitches to the front bed - or to the rear bed for links-links or purl knitting processes - according to the type of patterns.
The Manual Flat Knitting Machine
The manual flat knitting machine is made up by a frame carrying the base; this structure supports all the needle beds and motions necessary for the knitting process
The yarn unwound from the spool is picked up by the feeding system: a tensioner, which adjusts the feeding tension and a thread guide, driven by the machine carriage, which provides the needle with yarn at the proper time.
The tensioner is made up by a spring-load flexible arm, that lowers when the yarn tension increases, to feed a bigger quantity of yarn, and lifts up when the tension decreases.
The Needle-bed of manual flat knitting machine
The needles (4) accommodated inside the grooves (1) of the needle-bed can be either in a knitting or in a non-knitting position and are moved by special springs (2).
Placed between the grooves in the upper part of the needle-bed, the knock-over jacks (3) act as supports for the yarn fed during the stitch formation.
A spring securing bar (5) and a needle securing bar (6) are also attached to the needle-bed to keep needles and springs in a correct sliding position.
The Carriage of a Flat Knitting Machine
The carriage is made up of two metal plates linked by a stiff bridge (P); the plates work individually and simultaneously on the front and the rear needle-beds.
The carriage carries out a double function and can be used:
- to select the needles and make them raise or lower to form the stitch;
- to select and drive the thread guides which feed the needles.
The plates include cam locks (F) bearing the drive and control systems of the needles, i.e. the cams.
When the carriage moves right- or leftwards, the thread guides (B),(C),(D),(E) are locked individually by the corresponding pistons (A) on the upper part of the bridge, that are manually driven.
Brushes are also mounted on the carriage to ensure a smooth needle latch opening and grant a correct feeding of the yarn.
The Cam-locks of a Manual Flat Knitting Machine
The cam-locks are a cam system which gives the necessary working information to the individual needles; they include a fixed part, working as support, and movable cams, which can be divided into raising cams and lowering or knock-over cams (2).
The raising cam includes:
- A tucking cam (1).
- A looping cam (3).
The fixed or movable cams form a symmetrical channel where the needle butt slides; the needle moves downward and upward in the groove to form the stitch.
The different parts of the cams are chamfered; their profiles are curvilinear to make the needle move smoothly.
The angle of inclination of the cams ranges between 40° and 50°; these values grant an optimum running of the needle and avoid high pressures between metal parts during the motion and excessive tensions on the yarn during the downward stroke of the needle.
The carriage allows three different work ways according to the needle stroke and to the positions of the raising cam:
- KNIT STITCH: when the needle carries out a complete stroke, reaching the maximum height on the looping plane
- TUCK STITCH: when the needle reaches the tucking plane and receives a new yarn while still holding its former loop, thus forming two loops in the one needle hook
- MISS (or FLOAT) STITCH: when the needle is not knitting and remains out of the knockover plane.
High-butt Needles and Low-butt Needles
The latch needle can have two different butt heights which make it a high-butt needle or a lowbutt needle.
The assembly of high-butt needles and low-butt needles on the knitting machine allows different selection and different manufacturing work ways, according to the positions of the tucking and looping cams.