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Newsflash |
Knit is a medium that crosses all generations and is often learnt from
the lap of mothers and grandmothers who teach their children and
grandchildren the basic technique and introduce them to knitting.
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Principles of knitting technology |
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Written by Erin
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Saturday, 23 February 2008 |
The knitted loop structure
The knitted loop structure may not always be noticeable because of the effect of structural fineness, fabric distortion, additional pattern threads or the masking effect of finishing processes. However, unless the intermeshing of the loops is securely achieved by the needles receiving new loops of yarn into their hooks before the old loops are ‘cast-off’, and the ground structure is not fractured during finishing or wear, a breakdown or separation of the structure will result.
The properties of a knitted structure are largely determined by the interdependence of each stitch to its neighbours on either side and above and below it.
Knitted loops are arranged in rows, roughly equivalent to the weft and warp of woven structures. These are termed ‘courses’ and ‘wales’ respectively.
A course
A course is a predominantly horizontal row of needle loops (in an
upright fabric as knitted) produced by adjacent needles during the same
knitting cycle. (The last five words help to prevent confusion when
describing complex weft knitted fabrics).
A course length
In weft knitted fabrics (with the exception of structures such as
jacquard, intarsia and warp insertion), a course of loops is composed
of a single length of yarn termed a course length. Weft knitted
structures will unrove from the course knitted last unless it is
secured, for example, by binding-off.
A pattern row
A pattern row is a horizontal row of needle loops produced by
adjacent needles in one needle bed. In plain weft knitted fabric this
is identical to a course but in more complex fabrics a pattern row may
be composed of two or more course lengths. In warp knitting, every loop
in a course is usually composed of a separate yarn.
A wale
A wale is a predominantly vertical column of intermeshed needle
loops generally produced by the same needle knitting at successive (not
necessarily all) knitting cycles. A wale commences as soon as an empty
needle starts to knit.
• When loop transfer occurs it is possible to transfer a wale of loops
from one needle A to another B and to recommence knitting with the
second needle, in which case more than one needle will have produced
intermeshed loops in the same wale. (If needle B knits continuously,
the wale knitted by needle A will merge into it).
• In warp knitting a wale can be produced from the same yarn if the
same warp guide laps the same needle at successive knitting cycles.
• Wales are connected together across the width of the fabric by sinker loops (weft knitting) or underlaps (warp knitting).
• Wales show most clearly on the technical face and courses on the technical back of single needle bed fabric.
Stitch density
Stitch density refers to the total number of loops in a measured
area of fabric and not to the length of yarn in a loop (stitch length).
It is the total number of needle loops in a given area (such as a
square inch, or three square centimetres).The figure is obtained by
counting the number of courses or pattern rows in one inch (or three
centimetres) and the number of wales in one inch (or three
centimetres), then multiplying the number of courses by the number of
wales. (Using a measurement of three centimetres rather than one, is
preferable for accuracy in counting).
Stitch density gives a more accurate measurement than does a linear
measurement of only courses or only wales. Tension acting in one
direction might produce a low reading for the courses and a high
reading for the wales; when they are multiplied together this effect is
cancelled out. Pattern rows rather than courses may be counted when
they are composed of a constant number of courses.
Technically upright
A knitted fabric is technically upright when its courses run
horizontally and its wales run vertically, with the heads of the needle
loops facing towards the top of the fabric and the course knitted first
situated at the bottom of the fabric.
Design appearance requirements
The terms technical face, technical back, and upright are purely technically descriptive
terms. They do not necessarily indicate the orientation of the fabric from the designer’s viewpoint.
For example:
• Socks and ladies hosiery are usually worn upside-down compared to their sequence of production.
• The technical back of structures is often used for plush and pile effects.
• Curtains may be hung sideways compared to the wales.
• Diagonal stripes may be achieved for dress-wear by cutting the fabric at an angle.
The main features of the knitting machine
Originally, the term ‘machine’ used to refer to a mechanism on a
bearded needle frame such as the fashioning mechanism on the straight
bar frame. Today, it refers to the complete assembly.
A knitting machine is thus an apparatus for applying mechanical
movement, either hand or power derived, to primary knitting elements,
in order to convert yarn into knitted loop structures.
The machine incorporates and co-ordinates the action of a number of
mechanisms and devices, each performing specific functions that
contribute towards the efficiency of the knitting action.
The main features of a knitting machine are as follows:
1 The frame or carcass, normally free standing and either circular or
rectilinear according to needle bed shape, provides the support for the
majority of the machine’s mechanisms.
2 The machine control and drive system co-ordinates the power for the drive of the devices and mechanisms.
3 The yarn supply consists of the yarn package or beam accommodation,
tensioning devices, yarn feed control and yarn feed carriers or guides.
4 The knitting system includes the knitting elements, their housing,
drive and control, a well as associated pattern selection and
garment-length control device (if equipped).
5 The fabric take-away mechanism includes fabric tensioning, wind-up and accommodation devices.
6 The quality control system includes stop motions, fault detectors, automatic oilers and lint removal systems.
Machines may range from high-production, limited-capability models to
versatile, multi-purpose models having extensive patterning
capabilities. The more complex the structure being knitted, the lower
the knitting speed and efficiency.The simplest of the knitting machines
would be hand-powered and manipulated whereas powerdriven machines may
be fully automatically-programmed and controlled from a computer system.
The needle
The hooked metal needle is the principal knitting element of the knitting machine.
Prior to yarn feeding, the needle is raised to clear the old loop from
the hook and to receive the new loop above it on the needle stem. The
new loop is then enclosed in the needle hook as the needle starts to
descend. The hook then draws the new loop down through the old loop as
the latter slides over the outside of the descending bridge of the
closed hook.All needles must therefore have some method of closing the
needle hook to retain the new loop and exclude the old loop.
Fabric draw-off
The fabric loops are always drawn from the needles on the side remote
from their hooks.When two sets of needles are employed, either arranged
vertically back-toback or at some other angle to each other, each set
of hooks will face away from the other set and the fabric will be
produced and drawn away in the gap between the two sets.
The front of rectilinear needle bar machines
All rectilinear needle bar machines have a front and a back. The
front of the machine is the side to which the fabric is drawn away,
removed and inspected during knitting.
If the machine has a single vertical needle bar, its hooks will face
towards the back. If the machine has two vertical needle bars, the
fabric will be drawn down between them and will then pass underneath
one needle bar (the front bar) and will be removed from that side of
the machine.
On warp knitting machines, the guide bars and their corresponding warp
beams are numbered and described according to their position in
relation to the front and back of the machine.
On circular machines, there is no front or back as the fabric is drawn
towards the centre, usually below the needle circle.The cylinder face
loops show on the outside of the fabric tube as it is drawn downwards
during knitting.
The basic knitting action of a needle illustrates the basic action of a
needle. Except for the manner in which the hook is closed (in this case
by pressing the beard), the knitting action is similar for all
needles.The arrows indicate the relative movement of the loops along
the needles. (Whether the needle moves through the loops or the loops
are moved over the needle by some other elements depends upon the
machine design.)
1 The needle is in the (so-called) rest position, with the previously formed loop (a) held on its stem and covered by the hook.
2 The loop is cleared from the needle hook to a lower position on the needle stem.
3 The new yarn (b) is fed to the needle hook at a higher position on
the needle stem than the position of the previous (‘old’) loop.
4 The yarn is formed into a ‘new’ loop.
5 The hook is closed, enclosing the new loop and excluding and landing the old loop onto the outside of the closed hook.
6 The new loop (b) is drawn through the head of the old loop (a).
Simultaneously the old loop slides off the closed hook of the needle
and is cast-off or knocked-over.
7 The old loop now hangs from the feet of the fully formed new loop and the knitting cycle starts again.
 Basic knitting action of a needle
The bearded needle
The bearded or spring needle was the first type of needle to be
produced. It is the cheapest and simplest type to manufacture as it is
made from a single piece of metal, in machine gauges as fine as 60
needles per inch, with the needles being pliered to ensure accurate
needle spacing.
The bearded needle is essentially a frame needle, the needles being
fixed to move collectively with the straight needle bar or being
attached to a circular frame and
revolving with it.
When bearded needles are reciprocated in their bed, the action is a
collective one because of the problems of individual pressing and
needle movement.The serial action of weft knitting is thus achieved by
other loop-forming and controlling knitting elements that form the yarn
into new loops and may (on sinker wheel and loop wheel frames) move the
loops along the needle stems. A knitting section occupies a
considerable amount of space on bearded needle circular machines, thus
limiting productivity.
Selective beard pressing facilities used to be provided on some weft and warp knitting machines.
In weft knitting, accurate control of the loops throughout the knitting
sequence made the bearded needle sinker wheel and loop wheel frames
particularly suitable for the production of plush and inlay, whilst the
ease of flexing and deflection of the bearded needle made the sinker
wheel and straight bar frames useful for loop transfer effects.
However, bearded needle technology was unable to meet the challenging
requirements of modern knitting machinery, such as individual needle
selection of stitches, use of two needle beds and high productivity.
Once finegauge latch needle machines could knit, to a consistently high
quality, structures that were previously only knitted on bearded needle
machines, the latter were no longer competitive.
The main parts of the bearded needle
There are five main parts of the bearded needle:
1 The stem, around which the needle loop is formed.
2 The head, where the stem is turned into a hook to draw the new loop through the old loop.
3 The beard, which is the curved downwards continuation of the hook
that is used to separate the trapped new loop inside from the old loop
as it slides off the needle beard.
4 The eye, or groove, cut in the stem to receive the pointed tip of the beard when it is pressed, thus enclosing the new loop.
5 The shank, which may be bent for individual location in the machine or cast with others in a metal ‘lead’.
 Main parts of the bearded needle
The knitting action of the bearded needle
The knitting action of the bearded needle has been illustrated in
Fig. 3.1. Depending upon the machine, the needles are set vertically or
horizontally. The needle has the disadvantage of requiring a pressing
edge to close the bearded hook and enclose the new loop. The presser
may be in the form of a bar, blade, verge or wheel, with either the
presser or the needle remaining stationary whilst the other element
moves towards it.
Another feature of bearded needle knitting is that individual loop
formation has to be achieved by a loop forming element. This leads to a
more complicated knitting action but also provides for a more gentle
and careful loop formation.
The latch needle
The history and development of the latch needle
Fact and fiction envelopes the invention of the latch needle in a
similar manner to that of the bearded needle. Pierre Jeandeau patented
the first latch needle (also known as the tumbler needle) in 1806 but
there is no evidence of its practical use.There is also no evidence
that the pivoting of a broken pocket knife blade led to the development
of the latch spoon.
However, it was Townsend and Moulden’s practical patents applying the
use of this self-acting needle that, in 1849, began the challenge to
the 260-year reign of the bearded needle.
Matthew Townsend was a Leicester fancy hosier who was searching for a
simpler method of knitting purl fabrics than using a frame with two
sets of bearded needles and pressers. Townsend not only realised that a
latch needle, which dispensed with the need for a presser, could be
employed in a double-headed form to knit purl, he also foresaw the use
of single-headed latch needles in plain and rib circular machines, flat
machines and single and double needle bar warp knitting machines, as
well as the use of holding-down sinkers for single needle bed knitting.
Although the first needles were crude, a Mr.D. Fitchett used them to
knit borders for cravats which he exhibited at the Great Exhibition of
1851. Townsend, who lacked engineering skill and financial backing,
sold the rights of his latch needle to Joseph Pool of Leicester and
Hine Mundella of Nottingham, and emigrated to Canton, Massachusetts in
1858. In 1865 he was successfully sued for infringing the American
latch needle patent of James Hibbert, which pre-dated his own by a mere
month and four days. In his defence, Townsend stated that latch needles
had been in use in France for many years, but he was unable to provide
evidence. He died in 1879.
The latch needle was a more expensive and intricate needle to
manufacture than the bearded needle. It was more prone to making needle
lines as it slides in its trick, particularly if the latch was damaged
or there was dirt in the trick. However, the latch needle was quickly
employed by the newly emerging American knitting machine industry,
whilst British companies preferred the bearded needle.The latter
believed the bearded needle, which could be more precisely
manufactured, had a knitting action which produced a better quality
knitted structure.
It is now accepted that precision-manufactured latch needles can knit structures of the highest quality.
The features of the latch needle
The latch needle has nine main features:
1 The hook, which draws and retains the new loop.
2 The slot or saw cut, which receives the latch-blade (not illustrated).
3 The cheeks or slot walls, which are either punched or riveted to fulcrum the latchblade (not illustrated).
4 The rivet, which may be plain or threaded.This has been dispensed
with on mos plate metal needles, by pinching in the slot walls to
retain the latch blade.
5 The latch-blade, which locates the latch in the needle.
6 The latch spoon, which is an extension of the blade, and bridges the
gap between the hook and the stem covering the hook when closed, as
shown in broken lines.
7 The stem, which carries the loop in the clearing or rest position.
8 The butt, which enables the needle to be reciprocated when contacted
by cam profiles on either side of it, forming a track. Double-ended
purl type needles have a hook at each end; whilst one hook knits, the
inactive hook is controlled as a butt by a cam-reciprocated element
called a slider.
9 The tail, which is an extension below the butt, giving additional support to the needle and keeping the needle in its trick.
 Main features of the latch needle
The knitting action of the latch needle
The position of a latch needle as it passes through the cam system,
completing one knitting cycle or course as it moves up and in its trick
or slot.
1 The rest position. The head of the needle hook is level with the top
of the verge of the trick. The loop formed at the previous feeder is in
the closed hook. It is prevented from rising as the needle rises, by
holding-down sinkers or web holders that move forward between the
needles to hold down the sinker loops.
2 Latch opening. As the needle butt passes up the incline of the
clearing cam, the old loop, which is held down by the sinker, slides
inside the hook and contacts the latch, turning and opening it.
3 Clearing height. When the needle reaches the top of the cam, the old
loop is cleared from the hook and latch spoon on to the stem. At this
point the feeder guide plate acts as a guard to prevent the latch from
closing the empty hook.
4 Yarn feeding and latch closing. The needle starts to descend the
stitch cam so that its latch is below the verge, with the old loop
moving under it. At this point the new yarn is fed through a hole in
the feeder guide to the descending needle hook, as there is no danger
of the yarn being fed below the latch. The old loop contacts the
underside of the latch, causing it to close on to the hook.
5 Knocking-over and loop length formation. As the head of the needle
descends below the top of the trick, the old loop slides off the needle
and the new loop is drawn through it. The continued descent of the
needle draws the loop length, which is approximately twice the distance
the head of the needle descends, below the surface of the sinker or
trick-plate supporting the sinker loop. The distance is determined by
the depth setting of the stitch cam, which can be adjusted.
The rest position actually occurs between positions 1 and 2, when the
open needle hook just protrudes above the needle trick verge. In this
position, a feeder would be passed without the needle receiving a new
loop and the old loop would not be cast off, so that a float stitch
would be produced. The tucking in the hook position occurs between
positions 2 and 3, when the needle can receive the new yarn but the old
loop has not been cleared from the open latch.
The latch needle used on the Stoll CMS V-bed flat machine has a
spring-loaded latch so that it fully opens and fully closes. Also, the
latch spoon does not project beyond the needle head. Loops thus slide
easily over the hook and latch, the yarn is less likely to be split,
and there is greater security for the knitted loops.
NB: Although the above knitting action is described assuming the needle
to be moving through the knitted loops, the movement is relative and
the same effect can be achieved by moving the loops over a stationary
needle. Similarly, the knock-over surface can be moved in opposition to
the needle movement.
The advantages of the latch needle
The latch needle has the major advantage of being self-acting or
loop-controlled, so that individual movement and control of the needle
enables stitch selection to be achieved. It is ideally suited for use
with computer-controlled electronic selection devices. For that reason,
it is the most widely used needle in weft knitting and is sometimes
termed the ‘automatic’ needle (provided there are loops on the needle).
The old loop is cleared from the hook automatically when the needle is
lifted because the loop slides down inside the hook and contacts the
latch or tumbler, causing it to pivot open allowing the loop to slide
off the latch down onto the stem.
The hook is closed automatically after yarn feeding by lowering the needle because
the old loop, which was on the stem, slides upwards contacting and
pivoting the latch tightly closed and drawing and enclosing the newly
fed loop inside the hook.
Latch needles thus knit automatically as they are reciprocated and draw
the length of the new loop as they descend to knock-over. Except in
raschel warp knitting machines, they are arranged to move independently
in their tricks or grooves.
They can operate at any angle but often require a latch-guard or
latch-opening facilities as there is a tendency for latches to spring
closed as tightly-knitted loops are cleared from the open latches.
Individually moving latch needles can draw and form their own needle
loops in succession across the needle bed, unlike bearded needles and
needles in warp knitting machines which move as a unit and thus require
sinkers or guides to form the loops around their stems. The Germans
classify the first method as ‘Strickerei’ or loop drawing and the
second method as ‘Wirkerei’ or loop forming.
Variation of the height of vertical reciprocation of a latch needle at
a feeder can produce either missing, tucking or knitting, and depth of
descent normally determines loop length. Specially designed latch
needles are capable of facilitating rib loop transference by selective
lifting to a height above clearing height. Doubleended purl needles can
slide through the old loops in order to knit from an opposing bed and
thus draw a loop from the opposite direction to the previously knitted
loop.
Friction and frictionless needles
There are two types of latch needle – friction and frictionless.
Friction needles have a slight flex, crimp or bend in the tails so that
they contact the side-walls of the tricks in which they are housed.
They are used in open-cam systems, where cams may be introduced or
taken out of action to divert the needle path. Frictionless needles are
employed in closed cam-tracks that have guard or safety cams on the
opposite side to the knitting cams to produce a completely enclosed
track, through which the needles run (otherwise the freely-moving
needles would be thrown out of their tricks at high knitting speeds).
The bi-partite compound needle
Compound needles (Fig. 3.5) consist of two separately-controlled
parts – the open hook and the sliding closing element (tongue, latch,
piston, plunger). The two parts rise and fall as a single unit but, at
the top of the rise, the hook moves faster to open the hook and at the
start of the fall the hook descends faster to close the hook. It is
easier to drive the hooks and tongues collectively from two separate
bars in warp knitting than to move each hook and tongue individually,
as in weft knitting.
A compound needle with a sliding latch was first patented by Jeacock of
Leicester in 1856. It now dominates the warp knitting industry after
suffering a set-back against high-speed bearded needle machines in the
1960s. However, in weft knitting, where versatility and needle
selection are as important as knitting speed, it has only made limited
inroads in certain specialist or prototype areas.
Two types of compound needle have been employed in warp knitting machines.
The tubular pipe needle has its tongue sliding inside the tube of the
open hook. It was successfully employed in Sir James Morton’s
high-speed FNF tricot warp knitting machine during the late 1940s and
50s. Development then ceased and bearded needle tricot machines
recaptured their market with higher speeds, only to be later outpaced
by a more efficient type of compound needle, the slide compound needle.
The open-stem ‘pusher type’ or slide needle has a closing wire or
tongue that slides externally along a groove on the edge of the flat
hook member. This needle is now preferred because it is simpler,
cheaper, more compact and each of the two parts can be separately
replaced. |
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Last Updated ( Saturday, 23 February 2008 )
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