knitting cams - apoorv mohan (8) fp tech ii

8/6/2019 Knitting Cams - Apoorv Mohan (8) FP Tech II

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KnittingCamsKnitting Technology

Details

Apoorv Mohan

4/19/2011


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Data Compiled and Presented By Apoorv Mohan (Foundation Programme Technology II) 2

Acknowledgments

This is to express our heartfelt gratitude to Mr. Shakeel Iqbal, faculty in-charge (knitting technology) for his constant guidance and support

throughout the course of the study. We would also like to thank our friendsfor all their help and assistance.

Apoorv Mohan

Roll Number 8

Foundation Programme

Technology Group


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Semester II

Index of Contents1. INTRODUCTION........................................................4 2. KNITTING CAMS.................... ...............................8 3. USAGE OF CAMS IN VARIOUS KNITTINGMACHINES ...............................................................................15

4. ANNEXURES...........................................................19 5. BIBLIOGRAPHY.......................................................20


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1. INTRODUCTIONA cam may be defined as a machine element having a curved outline or a curved

groove, which, by its oscillation or rotation motion, gives a predetermined specifiedmotion to another element called the follower. The cam has a very important function inthe operation of many classes of machines, especially those of the automatic type, such asprinting presses, shoe machinery, textile machinery, gear-cutting machines, and screwmachines. In any class of machinery in which automatic control and accurate timing areparamount, the cam is an indispensable part of mechanism. The possible applications of cams are unlimited, and their shapes occur in great variety.

The transformation of one of the simple motions, such as rotation, into any othermotions is often conveniently accomplished by means of a cam mechanism. It is arotating or sliding piece in a mechanical linkage used especially in transforming rotarymotion into linear motion or vice versa. A cam mechanism usually consists of twomoving elements, the cam and the follower, mounted on a fixed frame. Cam devices areversatile, and almost any arbitrarily-specified motion can be obtained. In some instances,they offer the simplest and most compact way to transform motions. A common exampleis the camshaft of an automobile, which takes the rotary motion of the engine andtranslates it into the reciprocating motion necessary to operate the intake and exhaustvalves of the cylinders.

A CAM has two parts,

Fig 1.1CAM WITH NOMENCLATURE


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TYPES OF FOLLOWERS There are different types of follower but they all slide or roll on the edge of the cam.

Follower Configuration:1. Knife-edge follower (Figure 1-2a)2. Roller follower (Figure 1-2b,e,f)3. Flat-faced follower (Figure 1-2c)4. Oblique flat-faced follower5. Spherical-faced follower (Figure 1-2d)

Fig 1.2 TYPES OF FOLLOWERS


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CLASSIFICATION OF CAM MECHANISMS :

We can classify cam mechanisms by the modes of input/output motion, theconfiguration and arrangement of the follower, and the shape of the cam. We can alsoclassify cams by the different types of motion events of the follower and by means of agreat variety of the motion characteristics of the cam profile.Cam classification on the basis of cam shape1. Plate cam or disk cam: The follower moves in a plane perpendicular to the axis of rotation of the camshaft. A translating or a swing arm follower must be constrained tomaintain contact with the cam profile.2. Grooved cam or closed cam :

This is a plate cam with the follower riding in a groove in the face of the cam.

Fig. 1.3 Grooved cam

3. Cylindrical cam or barrel cam (Figure 1.4a): The roller follower operates in a groovecut on the periphery of a cylinder. The follower may translate or oscillate. If thecylindrical surface is replaced by a conical one, a conical cam results.4. End cam (Figure 1.4b): This cam has a rotating portion of a cylinder. The followertranslates or oscillates, whereas the cam usually rotates. The end cam is rarely usedbecause of the cost and the difficulty in cutting its contour.

Fig 1.4 Cylindrical cam and end cam


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Cam classification on the basis of follower arrangement1. In-line follower: The center line of the follower passes through the center line of thecamshaft.

2. Offset follower: The centre line of the follower does not pass through the center line of thecam shaft. The amount of offset is the distance between these two center lines. The offsetcauses a reduction of the side thrust present in the roller follower.


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2.KNITTING CAMS

All needles have a reciprocating action .In knitting technology cams are the deviceswhich convert the rotary motion drive into a suitable reciprocating action for the needlesand other elements.The needle displacements necessary for knitting together with the closing elementdisplacements in the case of compound needles and the sinker movements are all derivedfrom cam systems that traverse the machine and are located within the carriage.In essence the butts of the needle are caused to impact with the inclined plane of the camsystem and the reaction forces cause the needle to move in the required direction for therequired displacement.The angular knitting cams act directly onto the butts of needles or other elements toproduce individual or serial movements in the tricks of a latch needle weft knitting

machine. The knitting cams are hardenedsteels and they are the assembly of differentcam plates so that a track for butt can bearranged. Each needle movement isobtained by means of cams acting on theneedle butts.In the diagram the cam moves from theright and strikes the projecting butt of theneedle. The normal reaction force rbetween the butt and the cam generates avertical component of force upwards of (Frcos a ) together with a vertical componentdownwards of (Fr sin a). The cam angle ais designed in such a way that Fr cos a > Frsin a and the needle moves upwards.However the balance of forces within theknitting zone is complex and the choice of cam angle has a profound effect on thequality of the fabric.


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Two cam arrangements exist in Knitting Machine:

1. REVOLVING CYLINDER MACHINE:

The needle butts pass through the stationary cam system and the fabric hanging fromthe needles revolves with them.REVOLVING CYLINDER CAM SYSTEM CONSISTS OF:

2. RECIPROCATING CAM-CARRIAGE FLAT MACHINES ORROTATING CAM-BOX CIRCULAR MACHINE:

The cams with the yarn feeds pass across the stationary needle beds.In weft knitting, the yarn feed position is fixed in relation to the cam system.The yarnfeed moves with or remains stationary with the cam system ,as do the yarn packages andtackle.( except in the case of flat machines where the cam-carriage only reciprocates awayfrom and towards the stationary yarn packages and does not revolve).In the past, most garment length knitwear and underwear machines have had revolving cam boxes because changes to the cam settings during the garment sequence can beinitiated from a single control position as the cam boxes pass by; also the garment lengthsare stationary and may be inspected or removed whilst the machine is knitting.

Fig. 2.1 SIMPLEST CAM DESIGN

2. RECIPROCATING CAM-CARRIAGE FLAT MACHINES ORROTATING CAM-BOX CIRCULAR MACHINE:The cams with the yarn feeds pass across the stationary needle beds.

In weft knitting, the yarn feed position is fixed in relation to the cam system.The yarnfeed moves with or remains stationary with the cam system ,as do the yarn packages and


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tackle.( except in the case of flat machines where the cam-carriage only reciprocates awayfrom and towards the stationary yarn packages and does not revolve).In the past, most garment length knitwear and underwear machines have had revolving cam boxes because changes to the cam settings during the garment sequence can beinitiated from a single control position as the cam boxes pass by; also the garment lengthsare stationary and may be inspected or removed whilst the machine is knitting.Now, most new electronically- controlled garment-length machines are of the revolving cylinder type as electronics have removed the need for the complex arrangement of therods and level found, for example, on mechanically-controlled half-hose machines.Knitting cams are attached, either individually or in unit form, to a cam-plate and,depending upon machine design, are fixed, exchangeable or adjustable. In the last case,on garment-length machines this might occur whilst the machine is in operation.Elements such as holding-down sinkers and pelerine(loop transfer) points are controlledby their own arrangement of the cams attached to a separate cam-plate.At each yarn feed position there is a set of cams consisting of atleast a raising cam, a stitch

cam and an upthrow cam whose combined effect is to cause a needle to carry out aknitting cycle if required. On circular machines there is a removable cam section or doorso that knitting elements can be replaced.

ROTATING CAM-BOX CIRCULAR MACHINE OR DIAL CAMSYSTEM CONSISTS OF:

-over cams

-over cam


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THE NEEDLE CAM RACE CONSISTS OF1. CLEARING CAM

Clearing cam is a cam which displaces needles to clearing height. a modified clearing cam that raises needles part-way to clearing height

such that the old loop remains on the opened latch when a new loop is taken technically known as tucking in the hook;

-knit cam a modified clearing cam that causes no displacement of the needles atthe point where clearing would take place so that the needles neither clear their old loopnor take a new loop into the hook.2. STITCH CAM

Stitch cam is that cam which displaces cleared needles to the knock over position. Thestitch cam controls the downward movement of the needles by adjusting its verticalmovement. If the stitch cam is raised then a shorter loop is drawn below the sinker leveland a tighter fabric will result. With lowering of the stitch cam, a stitch length willincrease and a flimsy fabric will result. It controls the depth to which the needledescends, thus controlling the amount of yarn drawn into the needle loop; it alsofunctions simultaneously as a knock-over cam.


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3. UP-THROW CAM (which are vertically adjustable together foralteration of stitch length.)The upthrow or counter cam takes the needles back to the rest position and allows thenewly formed loops to relax. The stitch cam is normally adjustable for different looplengths and it may be attached to a slide together with the up throw cam, so that the twoare adjustable in unison.

4. GUARD CAM

The guard cams are often placed on the opposite side of the cam-race to limit the

movement of the butts and to prevent needles from falling out of track A guard camwhen used in conjunction with a stitch cam at a feed in latch needle-knitting machines,which, with the stitch cam, provides there between a confined path of travel for theneedless in their stitch-drawing movement and which, by itself, prevents undesirableneedle overthrow and provides proper paths of travel for needles moving at the tuck andwelt levels. The guard cam is adjustable in a direction at right angles to the direction of adjustment of the stitch cam whereby a fixed distance may be maintained there between.

5. RETURN CAM


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Sinkers are supposed to move backward and forward in relation to needles. A separate setof separate cams is contained in the sinker ring. Its time is synchronised to needle timing and is called a return cam.

6. Raise CAM

The raising cam causes the needles to be lifted to either tuck, clearing, looptransfer or needle transfer height, depending upon the machine design.Sometimes, swing cams or auxiliary cams are placed between the rising cams and the stitch cams to change the path of the needle butts to form araceway and the needle butts travel in this restricted path according to thedifferent stitch requirements.

7. SINKER WITHDRAWING CAM

8. SINKER-RETURN CAM (which is adjustable in accordance with thestitch length.)

The swing cam is fulcrummed so that the butts will be unaffected when it isout of the track and it may also be swung into the track to raise the butts.The bolt cam can be caused to descend into the cam track to control theelement butts or be withdrawn out of action so that the butts passundisturbed across its face; it is mostly used on garment-length machines to

produce changes of rib set-outs.Separate cam-boxes are required for each needle bed or associated elementbed and they must be linked together or co-ordinated. If the cam-box itself is moving from right-to-left, the needle butts will pass through in a left-to-right direction.On circular fabric machines, the cams are designed to act symmetricallyarranged to act in both directions of cam-box traverse, with only the leading edges of certain cams in action.All cams systems are a compromise between speed, variety, and needle

control and selection systems.


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CARRIAGE MOVEMENT AND ITS INFLUENCE ON KNITTING:

The needle tracks through the cam system as shown by the blue line in the following diagram.


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USAGE OF CAMS IN VARIOUS KNITTING MACHINES

PURL KNITTING MACHINE (LINKS-LINKS)

In purl knitting machines, there is a cam carriage which moves from right to left and leftto right alternatively, above the needle beds. The carriage has cams which activate theneedles in knitting action.

DOUBLE CYLINDER MACHINES

The double cylinder machine, has divided cams with internal holding down sinkers andstationary cam boxes. The dividing cam is an internally profiled cut through recess in a

flat plate attached horizontally and externally to the cylinders at the position, half waybetween them. There is a recess cam position for the top cylinder and another for thebottom cylinder in a different position in the same plate. The principle of the dividing cam operation is that it forms a wedge shape of increasing thickness between the uppersurface of the needle hook and the under surface of the extended nose of the delivering slider, pivoting it away from the cylinder so that it disengages from the needle hook .

1) The delivering slider advances with its nose so that the nose of the slider enters theprofiled recess of the dividing cam so that the outer hook of the needle contacts the hookunderneath the head of the receiving slider pivoting it, out of the cylinder but itimmediately returns.

2) It engages with the needle hookdue to the pressure of the coiledspring band, which surrounds eachcylinder, so that the slider heads aredepressed into contact with theneedle hook.

3) As slider revolves with the

cylinder, it passes along with the wallof the dividing cam which whenincreases in thickness causes theslider pivot outwards and disengagesfrom the needle hook as shown inthis sketch. Slider then returns to itscylinder while the slider retires intoits cylinder taking the needle with it,ready for the next knitting head.


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FORMATION OF FLOAT AND TUCK LOOPSTo intermesh a newly formed loop, the needle hook in which the new looped yarn istrapped should rise high enough to clear the old loop resting in the closed latch or needlehook

by raising or clearing cam acting on the butt of the needle. The clearing cam is themost important cam in the system because by simple modification or adjustment of thisclearing cam, a float (or miss) stitch and tuck stitch can be formed in addition to a knitstitch

.

FLOAT (OR MISS) LOOP:

If the needle is not raised by the clearing cam it does not receive the new yarn and theyarn goes behind the needle. The yarn remains behind the needle and appears in thefabric as a float .The knit loop not cleared is called the held loop

. When the needle israised on the subsequent course the new knit loop is pulled through the held loop only.

TUCK LOOP:

If the needle is not raised to its clearing position or not raised at all but is partially raisedby the clearing cam so that the old loop is not cleared from the latch of the needle but thefeeder has fed a new yarn into the hook then a tuck stitch is formed when the needlemoves down. In this case the new yarn and the held loop is in the hook of the needle.This forms a tuck stitch

when the needle moves down. The held loop and the newyarn-both are in the hook.

THE SWING CAM:

In order to produce tuck/or float loop, the clearing cam must be modified. One commonway to this is to replace the solid clearing or raising cam

with an adjustable swing cam.Tuck stitches may occur singly or on the same needle at successive knitting cycles oracross adjacent needles.

many needle selection and controlling devices are required to be provided on a weftknitting machine. These machines are complex in their mechanism, just as dobbies or

jacquards are, for woven structures.

swing cams for dial are used. The needles used are not only long and short needles butneedles to work in different cam tracks to form knit, tuck and float stitches in the samecourse. With float or welt loops generally narrower and elastic fabrics than fabricscomprised entirely of normal knit loops are produced. Tuck loop fabrics are generallywider, thicker and shorter, than plain-knit ones.

CAMS IN SINGLE KNIT MACHINES

Plain knit or single jersey fabrics are made on machines having a single cam track. Cam

track is the guided that the needle butt takes through the group of cams. The adjustablecams in the system are the stitch cam and the raising (clearing cam). This swing cam


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may be actuated tocause all the needles toknit, tuck or miss. Pre-set positions areindicated on theexterior of the cylinder.The swing cams actonly on long butts.And the stitch cam actson both long buttneedles operating inthe track A and also onthe short buttsbelonging to needlesrunning in the other

tracks. With thesemulti-track machinesmany non-jacquarddesigns are produced.Jack raising cam is alsoused in multi-steppattern drum.

THE CAM SYSTEM OF THE V-BED MACHINEThe single knitting cam-box is symmetrically designed for knitting a course of loops onboth the front bed and back bed needles during a right-to-left traverse and a secondcourse during the return left-to-right cam box traverse.The cam system on a v-bed machine reciprocates and therefore the cam system mustallow the needle to travel through in either direction. For this reason v-bed cam systemsare essentially symmetrical.The needle butts will enter the traversing cam system from the right during a left-to-right cam box traverse and from the left during the right-to-left traverse. For each needlebed there are two raising cams, two cardigans cams and stitch cams.In the direction of traverse, the leading raising cam is responsible for knitting and thetrailing raising cam acts as a guard cam. The leading stitch cam is raised out of action and


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the trailing stitch cam is in operation. In the reverse direction of traverse, the roles of thetwo raising cams and of the two stitch cams are reversed. A raising cam lifts the needle totuck the height, but if the cardigan cam above it is in action the needle is lifted to fullclearing 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 diagonallyopposite each other in each bed are out of action.

V-bed Cam geometry


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ANNEXURES KEY TERMS RELATED TO CAMS

ONE CYCLE one rotation/revolution of the camDWELL when the cam rotates but the follower does not rise or fall

THE RISE that part of the cam that causes the follower to rise.RETURN is the motion of the follower toward the cam centre

CAM NOMENCLATURE Trace point: A theoretical point on the follower, corresponding to the point of a

fictitious knife-edge follower. It is used to generate the pitch curve. In the case of a rollerfollower, the trace point is at the centre of the roller.

Pitch curve : The path generated by the trace point at the follower is rotated about astationary cam.

Working curve: The working surface of a cam in contact with the follower. For theknife-edge follower of the plate cam, the pitch curve and the working curves coincide. Ina close or grooved cam there is an inner profile and an outer working curve.

Pitch circle: A circle from the cam centre through the pitch point. The pitch circleradius is used to calculate a cam of minimum size for a given pressure angle.

Prime circle (reference circle): The smallest circle from the cam centre throughthe pitch curve.

Base circle: The smallest circle from the cam centre through the cam profile curve.Stroke or throw: The greatest distance or angle through which the follower moves or

rotates.Follower displacement: The position of the follower from a specific zero or rest

position (usually it

s the position when the follower contacts with the base circle of thecam) in relation to time or the rotary angle of the cam.

Pressure angle: The angle at any point between the normal to the pitch curve andthe instantaneous direction of the follower motion. This angle is important in cam design

because it represents the steepness of the cam profile.


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BIBLIOGRAPHY

Knitting Technology By David J.SpencerKnitting Views

Www.Wikipedia.ComWww.Knitepedia.Co.Uk/.../Cam_Technology.Htm

knitting cams - apoorv mohan (8) fp tech ii

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