Knitting Elements in a Latch Needle Raschel Machine | Cross-section ofa Latch Needle Raschel Machine

Raschel machines (Figures A and B) originally had a gauge expressed in needles per 2 inches (5 cm), so that, for example, a 36-gauge raschel would have eighteen needles per inch. Now, the standard E gauge (needles per inch) is generally used. There is a wide gauge range, from E 1 to E 32.

Their chain links are usually numbered in even numbers, 0, 2, 4, 6 etc., generally with two links per course. Raschel sinkers perform only the function of holding down the loops whilst the needles rise.They are not joined together by a lead across their ends nearest to the needle bar so they can move away clear of the needles, towards the back of the machine, for the rest of the knitting cycle.The needle trick plate verge acts as a fabric support ledge and knock-over surface.
The fabric is drawn downwards from the needles, almost parallel to the needle bar, at an angle of 120–160 degrees, by a series of take-down rollers. This creates a high take-up tension, particularly suitable for open fabric structures such as laces and nets. 

Fig. A. Knitting elements in a latch needle raschel machine

Fig. B. Cross-section of a latch needle raschel machine

The warp beams are arranged above the needle bar, centred over the rocker shaft, so that warp sheets pass down to the guide bars on either side of it.The beams are placed above the machine so that it is accessible at the front for fabric inspection and at the back for mechanical attention to the knitting elements. The guide bars are threaded, commencing with the middle bars and working outwards from either side of the rocker-shaft. They are numbered from the front of the machine.

With the raschel arrangement, there is accommodation for at least four 32-inch diameter beams or large numbers of small diameter pattern bars. The accessibility of the raschel machine, its simple knitting action, and its strong and efficient take-down tension make it particularly suitable for the production of coarse gauge open-work structures employing pillar stitch, inlay lapping variations and partlythreaded guide bars. These are difficult to knit and hold down with the tricot arrangement of sinkers. Additional warp threads may be supplied at the selvedges to ensure that these needles knit fabric overlaps, otherwise a progressive press-off of loops may occur.

Introduction of a Needle | Specifications of Needle

The typical “European” specifications for a needle includes a word, a number (usually a four digit number) and a final combination of letters and numbers. For example: Vota 78.60 G.02 The capital letter at the beginning of the word ( “V”), identifies the origin of the needle (obtained from a wire, pressed or die-cut), the type, the number of butts and the type of tail. The other capital letters have a very precise meaning, except for the vowels “e” and “a” which are added to make the word pronounceable, and indicate the shape and the height of the butt, the eventual existence of a groove and its size, the length of the tail and some other features of the

needle.

Neddle

The next group of numbers identifies the needle according to the length and the gauge. The first part indicates the whole length rounded off to the mm (in our case that makes 78 mm); the second part indicates the gauge of the needle in hundredths of millimetres (in our case the gauge of the needle is equal to 0.60 mm).

The final group of letters and numbers has to be read as follows. The first capital letter indicates the needle manufacturer (For example Z for Torrington, E for Exeltor, G for Groz-Beckert). The next number is used to distinguish a specific needle among all the needles produced by the same manufacturer.

The next letter refers to some particular features of the needle: for some needles an “A” indicates that the latch has been fixed with an angular pressed pin while an “R” means that the latch has been fixed with a straight pressed pin. For other needles, the latch fixing method is indicated by a “0” before the last number. A “0” indicates that the latch has been fixed with a standard pressed pin; no “0” means that the latch has been fixed with a screw pin.

Knitting Action of Bearded Needle Simplex Machine

Fig: Knitting action of bearded needle simplex machine

Figure: Shows the knitting action on the front needle bar; an identical sequence occurs afterwards on the back needle bar to complete the machine cycle.

(a) First rise of the needle bar. The knitting action has been completed on the back needle bar for the previous machine cycle. The front sinker/presser bar has withdrawn, leaving the back sinker bar to support the fabric. The guide bars have completed their third swinging movement so that they are now swinging towards the back of the machine, allowing the front needle bar to rise with the back needle bar still near to knock-over and thus helping to hold down the fabric. The front needle bar rises sufficiently to enable the old overlaps under the beards to slide down onto the needle stems.

(b) Return swing, second rise then lowering and pressing. As the guides swing to the back of the machine, the warp ends are wrapped over the needle beards. The front needle bar is now lifted to a higher position so that the new overlaps slip from the beards to a high position on the needle stems. As the front needle bar is lowered to cover the new overlaps, the front sinker presser bar moves to contact and press the beards so that the old overlaps slide onto the closed beards which descend through them.

(c) Completion of landing and knock-over, underlap and third guide bar swing. Whilst the needles descend further to knock-over the old overlaps, the guide bars make their underlap shog behind the front needle bar and then commence their swing towards the front of the machine to allow the back needle bar to rise for the second part of the machine sequence.

Knitting Cycle of the Bearded Needle Tricot Machine

Fig.A:Knitting Cycle of the Bearded Needle Tricot Machine

Figure.A: illustrates the knitting cycle of the bearded needle tricot machine

1. The rest position (a). The needles have risen to 2/3 of their full height from knock-over and have their beards towards the back of the machine.The presser is withdrawn and the guides are at the front of the machine with the sinkers forward, holding the old overlaps in their throats so that they are maintained at the correct height on the needle stems.

2. Backward swing and overlap shog (b, c). After swinging through the needles to the beard side, the guides are overlapped across the beards, usually by one needle space in opposite directions.

3. The return swing and second rise (c, d). As the guides swing to the front, the needles rise to their full height so that the newly-formed overlaps slip off the beards onto the stems above the old overlaps. This arrangement reduces the amount of guide-bar swing necessary and therefore the time required.

4. Pressing (e). The needle bar descends so that the open beards cover the new overlaps. There is a slight pause whilst the presser advances and closes the beards.

5. Landing (f). As the sinkers withdraw, the upward curve of their bellies lands the old overlaps onto the closed beards.

6. Knock-over and underlap shog (g). The presser is withdrawn and the continued descent of the needle bar causes the old overlaps to be knocked-over as the heads of the needles descend below the upper surface of the sinker bellies. The underlap shog which can occur at any time between pressing and knock-over usually occurs in opposite directions on the two guide bars.

7. The sinkers now move forward to hold down the fabric loops and push them away from the ascending needles, which are rising to the rest position.

Knitting Action of the Compound Needle Warp Knitting Machine | KnittingAction of the Compound Needle Tricot Machine

Needle rise and guide bar swing: 

With the sinkers forward holding down the fabric, the hooks and tongues rise, with the hook rising faster, until the head of the latter is level with the guide holes and is open.The guides then swing through to the back of the machine.

2. The overlap and return swing:
The guides shog for the overlap and swing to the front of the machine; immediately, the hooks and the tongues start to descend with the tongues descending more slowly, thus closing the hooks.

Fig.  Knitting action of a compound needle tricot machine

3. Landing and knock-over:
The sinkers start to withdraw as the needles descend so that the old loop is landed onto the closed hook and then knocked-over as it descends below the sinker belly. At this point the underlap occurs before the needles begin their upward rise and the sinkers move forward to hold down the fabric.

The Karl Mayer tricot model HKS 2–3 E is designed to knit elastic fabrics and has a maximum speed of 3300 cpm with reduced noise levels and energy consumption.The vertical staggered arrangement of the guide bars enables the stroke to be reduced.The bars are hollow section which reduces their weight and expansion due to heat.

Features of the Latch Needle

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.

The latch needle has nine main features (Fig. A):

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 latch blade (not illustrated).

4 The rivet, which may be plain or threaded.This has been dispensed with on most 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.

Fig.A. Main features of the latch needle.

Main Parts of the Bearded Needle

The Main Parts of the Bearded Needle

There are five main parts of the bearded needle (Fig:A):

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’.

  Fig. A:  Main parts of the bearded needle.

Basic Knitting Action of a Needle

The basic action of a needle are shown in below. 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.

Fig. Basic knitting action of a needle.

Introduction of Latch Needle | Advantages of Latch Needle

Latch Needle:

The needle which have a right hook and a latch easily around the axis is called latch 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.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. Latch needle action is comparatively easy.

Advantages of 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.