textile ebooks: RIETER SPEEDFRAME TECHNOLOGY

Roving Frame

The drawframe produces a sliver that already exhibits all the characteristics required for the creation of a yarn, namely an ordered, clean strand of fibers laying parallel to one another. It is a fair question to ask why this sliver is not used as infeed material for the ring spinning machine, instead of being processed in an expensive manner to create a roving as feed material for spinning. The roving machine itself is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. Use of the machine is forced upon the spinner as a necessary evil for two principal reasons.
The first reason is related to the required draft. Sliver is a thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this to a yarn is in the region of 300 - 500. The drafting arrangements of ring spinning machines, in their current forms, are not capable of processing this strand in a single drafting operation to create a yarn of short-staple fibers that meets all the normal demands on such yarns. The fine, twisted roving is significantly better suited to this purpose.
The second reason is that drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame. In spite of this, considerable effort has been expended over decades to eliminate the roving frame. The effort is justified, but unfortunately in relation to ring spinning it remains without success. On the other hand, in all new spinning processes in the short staple spinning mill, the roving frame has been made superfluous.

Demands placed upon the modern roving frame

If the spinner is forced to use such an inadequate machine, which is in principle superfluous, then it should at least provide the optimum in operating capacity. Even in this respect, however, the roving frame still leaves room for improvement. The efforts of machine manufacturers should be directed toward the following aspects:

design of simpler machines, less liable to faults;
increase in spindle rotation speeds;
larger packages;
automation of the machine and of package transport.

These improvements must be achieved without any increase in production costs for the spinner.

Tasks of the roving frame

The chief task of the roving frame is the attenuation of the sliver. Since the resulting fine strand has scarcely any coherence, protective twist must be inserted in order to hold it together. The third task cannot be directly attributed to spinning: it lies in winding the roving into a package that can be transported, stored and donned on the ring spinning machine. It is the winding operation above all that makes the roving frame a relatively complex and problem-plagued machine. This winding operation requires, in addition to spindle and flyer, a cone drive (or variable transmission), a differential gear and a package build motion

Operating sequence

Fig. 2 – Cross-section through a roving frame

Drawframe sliver is presented to the roving frame in large cans (Fig. 2, 1). The can diameter does not correspond to the spindle gauge, so the cans are not arranged in one row but in several, which have to be set out behind the machine. Driven transport rollers (2) are provided above the cans. These draw the slivers from the cans and forward them to drafting arrangement (3). The drafting arrangement attenuates the slivers with a draft of between 5 and 20. The strand delivered is too thin to hold itself together and a strengthimparting step is necessary immediately at the exit of the drafting arrangement. This is performed by inserting protective twist, usually in the range of 25 - 70 turns per meter. The turns are created by rotating flyer (6) and are transmitted into the unsupported length of roving (5) between the flyer and the delivery from the drafting arrangement. The flyer itself forms part of driven spindle (7) and is rotated with the spindle.

To ensure that the roving is passed safely and without damage to the wind-up point, it runs through the flyer top and the hollow flyer leg, and is wound 2 - 3 times around the presser arm before reaching bobbin (8). To enable winding to be performed, the bobbin is driven at a higher peripheral speed than the flyer so that the roving is drawn off the flyer leg. The coils must be arranged very closely and parallel to one another so that as much material as possible is taken up in the package. For this purpose, bobbin rail (9) with the packages on it must move up and down continuously. This can be effected, for example, by continual raising and lowering of lever (10), on which the bobbin rail is mounted. Since the diameter of the packages increases with each layer wound, with a corresponding increase in the length of roving wound per coil, the speed of movement of the bobbin rail must be reduced by a small amount after each completed layer. Similarly, owing to the increase in package diameter, the bobbin‘s rotation speed must be reduced after each layer, because delivery is constant and hence the difference between the peripheral speeds of the package and the flyer must also be kept constant throughout the winding operation. Only in this way can a controlled winding operation be achieved.

Effects of the arrangement of the bobbins in two rows

The arrangement of the take-up packages is rather unusual for a spinning machine. The bobbins are not arranged individually or in a single row. Instead, they are arranged in the delivery section in two rows one behind the other, with the bobbins of one row offset relative to those of the other.
This arrangement is extremely economical in terms of space, but has several disadvantages: the design is made more complicated; operation of the machine is made less convenient; and automation is hindered. The technological disadvantages are still more significant.

The angle of approach of the roving to the flyer top is different for the two rows (Fig. 3, α). This results in different rolling conditions at the entry point of the roving to the flyer top. There is also a difference in the angles of withdrawal (β) of the two rovings at the front cylinder and thus in the lengths of the spinning triangles. Another effect is produced by the difference in the unsupported lengths (L), i.e. the lengths between the drafting arrangement and the flyer top (L1 + L2).

Together, these differences result in uneven take-up of twist, different degrees of integration of the fibers and finally to variations in roving fineness between the front and rear rows. Modern roving frames no longer suffer this technological disadvantage. In fact, the flyers in the rear row are equipped with an extension, which eliminates the above-mentioned differences in angles (Fig. 4).

Fig. 3 – Thread path geometry at the delivery and flyer top

Fig. 4 – Thread path in modern roving frames

The creel

Fig. 5 – Creel framework

Above the cans there are several rows of driven rollers to help the slivers on their way to the drafting arrangement, which is often a considerable distance from the cans. On account of the high degree of parallelization of the fibers in the slivers (especially in the case of combed sliver), strand coherence is often not very great. Accordingly, transport at this place can easily create false drafts. Mills should take account of this source of possible faults. Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance; that they are drawn, for example, more or less vertically out of the cans; and that the guide rollers run smoothly. Perfect drive to the rollers is correspondingly important. It is usually effected by chains, gear transmissions or cardan shafts.

The drafting arrangement

Description

Of the various high-draft systems that have been proposed, some of which were only in use for a short period, only the 3-over-4 cylinder system and the double-apron arrangement are still to be found in modern machines offered by manufacturers. The 3-over-4 arrangement is found relatively rarely, while the double-apron system is standard. Only the double-apron arrangement permits drafts of 20 while holding the fibers more or less under control during their movements. In general, three-cylinder arrangements are used, but four cylinders may be needed for high drafts. They usually comprise fluted lower rollers and rubbercoated pressure rollers. The hardness of the upper rollers is between 80° and 85° Shore, but the rollers over which the apron runs often have a hardness only slightly above 60° Shore. This permits better enclosure and guidance of the fiber strand during drafting. The draft often has limits not only at the upper end (20 - 22) but also at the lower end, namely to about 5 for cotton and 6 for synthetic fibers. If drafts below these lower limits are attempted, the fiber masses to be moved are too large, drafting resistance becomes too high and the drafting operation is difficult to control.

Break drafts are usually selected around 1.1 (1.05 to 1.15) for cotton, and slightly higher for synthetics and strongly compressed cotton sliver delivered from high-performance drawframes. Values of 1.3 and slightly higher can be achieved. The main effect of the break draft is seen in roving evenness.

Modern double-apron systems exist in 3- or 4-cylinder versions. The 4-cylinder version is usually operated with a low draft in the final drafting zone. This may slightly reduce roving hairiness.

Fig. 6 – Three-cylinder, double-apron drafting arrangement

The aprons

The upper aprons (Fig. 7, 2) are short and made either of leather or, more commonly, of synthetic rubber. They are about 1 mm thick and are held taut by tensioning devices (4). In contrast, the lower aprons (1) are longer and usually made of leather, although synthetic rubber is also used. They run over guide bars (nose bars) (3) to positions close to the nip line of the delivery rollers. Leather aprons are usually about 1 mm thick. The aprons cooperate with each other to guide and transport the fibers during drafting and they exert a very significant influence on the drafting operation. It is important that the aprons should extend as closely as possible to the nip line of the front rollers. The guiding length, referred to as the cradle length (a), must be adapted approximately to the staple length. In accordance with data provided by Rieter, the following cradle lengths should be used:

Cradle length (mm)	Material
short	Cotton up to 1 1/8˝; 40 mm synthetic fibers
medium	Cotton above 1 1/8˝; 50 mm synthetic fibers
long	Synthetic fibers, 60 mm

Fig. 7 – Apron guidance in the drafting arrangement

Applying pressure to the top rollers

The top rollers must be pressed with relatively high force against the lower rollers to ensure guidance of the fibers. Pressures are in the range of 100 to 250 N (300 N) per roller (shaft) and they depend upon raw material and volume. Adjustment may be continuous or in several steps. Today, the required pressure is achieved by springs or by pneumatic means (i.e. Texparts PK 5000). In the past, Platt Saco Lowell also offered a magnetic weighting system.

The condenser

Sliver trumpets (infeed condensers) are mounted on a reciprocating bar (sliver traverse mechanism) behind the rear cylinder of the drafting arrangement. They are designed to guide the sliver into the drafting arrangement. The traverse motion spreads wear evenly over the whole width of the roller coatings.

A second sliver condenser is provided in the break draft zone, also on a reciprocating bar, and a third is located in the main drafting zone. However, the latter rests on the moving fiber strand, without being fixed. The purpose of these condensers is to control the width of the fiber strand, since during drafting it continually tends to spread out. Spreading fiber masses are more difficult to maintain under control in drafting, and they cause unevenness. In addition, a widely spreading strand leaving the drafting arrangement results in high fly levels and hairiness in the roving, since the fibers either are not integrated (and are lost), or are held only at one end so that the second end projects as a so-called „hair“. The condensers should be adapted precisely to the volume of the fiber sliver. The appropriate dimensions can be found in tables.

Spacing the top and bottom aprons

The top aprons are forced by spring pressure against the lower aprons. The intensity of fiber clamping, and thus fiber guidance, depends upon this pressure and also upon the distance between the two aprons. The pressing effect should be considerable, but not too high, otherwise it is impossible to achieve controlled drawing of fibers out of the clamped strand. The arrangement must also permit precise adaptation of the minimum distance to the fiber volume. In order to be able to maintain this closely defined minimum distance between the aprons, „distance pieces“ (Fig. 8, a) of variable height are interchangeably inserted between the nose bar of the lower apron and the cradle edge of the top apron, i.e. at exit opening M.

These distance pieces are given various names, such as spacers (Rieter), distance clips (Texparts), cradle spacers (Suessen). The correct distance piece to use can be determined within a broad range from tables provided by the manufacturers, but fine settings have to be established by experiment.

Fig. 8 – Exit opening M.

Imparting twist

The flyer inserts twist. Each flyer rotation creates one turn in the roving. In the final analysis therefore, since the flyer rotation speed is kept constant, twist per unit length of roving depends upon the delivery speed, and can be influenced accordingly. High levels of roving twist represent production losses and might lead to draft problems in the ring spinning machine. On the other hand, low twist levels can cause false drafts or even roving breaks during bobbin winding. Normal twist levels are shown in the following diagram (as provided by Rieter).

Various designs of flyers

Limits on the performance of the roving frame are determined by both the delivery speed and the rotation speed of the flyer. The influence of the flyer depends upon its form and drive. Using these criteria as a basis, the following distinctions can be drawn between three flyer types:

spindle-mounted flyers (Fig. 9, a);
closed flyers (Fig. 9, b);
top-mounted flyers (Fig. 9, c).

The standard form has in the past been the spindle-mounted flyer (Fig. 9, a). This is simple as far as design and drive are concerned, but not from the service point of view or for automation purposes.

In this design, the spindle is simply a support and drive element for the flyer, without any ancillary function. It is a long steel shaft, mounted at its lower end in a bearing and supported in the middle by the vertically reciprocating shaft of the package tube acting as a neck bearing. Rotation is caused very directly and over a short transmission distance from the main shaft by way of a gear train and a longitudinal shaft that extends past all spindles and is fitted with bevel gears driving bevels on the spindles themselves. The spindle tip is conical and provided with a slot. When the flyer is set on the spindle cone, a pin on the flyer projects into the slot so that the flyer and spindle are converted into a unit for drive purposes (Fig. 10). The closed flyer (Fig. 9, b), supported both above and below, has been used only by Platt Saco Lowell in the „Rovematic“ machine. It has the advantage of reduced spreading of the legs at high operating speeds. Today, the standard design is the top-mounted flyer (Fig. 9, c). Among other things, this form facilitates automation of the doffing operation. The flyer is supported by ball bearings at the neck and is driven by gear wheels or toothed belts from above.

Fig. 9 – Various flyer designs

Fig. 10 – Spindle, flyer and spindle drive

The flyer

Fig. 11 – Component parts and structure of the flyer

Earlier flyers were invariably made of steel, but they are now mostly made of light alloy (Fig. 11). At the high speeds currently considered normal steel flyers would spread at the legs considerably; this is detrimental to the operation of the machine, and even more so to the winding operation. The amount of spreading depends upon the rotation speed. When this varies, e.g. during starting and stopping, the presser arm (5) adopts a continually varying inclination, which causes continual shifting of the winding point of the bobbin. It becomes impossible to ensure a controlled build over the complete package. In addition, light alloy flyers have lower weight. Flyers can have varying sizes, which are specified in inches. The stated sizes are actually winding dimensions, i.e. the maximum height (first number) and the maximum diameter (second number) of a wound package of material. Roving frames are supplied in the following sizes:
12˝ x 5 1/2˝ ; 12˝ x 6˝ ; 14˝ x 6˝
14˝ x 6 1/2˝ ; 16˝ x 6˝, 16˝ x 7˝

As well as imparting the roving twist, the flyer has to guide the very sensitive strand from the flyer top to the package without introducing false drafts – not exactly an easy task. For one thing, the strand has only protective twist and is very liable to break. For another, the flyer is rotating, along with the roving, at a speed of up to 1 500 rpm. The fiber strand must therefore be protected against strong air currents. For this purpose, in most roving frames to date, one of the two flyer legs (4) has usually been „hollow“, i.e. with a deep guide groove that is open in a direction opposite to the direction of rotation. The strand is drawn through this groove. The second, solid flyer leg serves to balance the grooved leg. Newer designs no longer feature this easily accessible, „service-friendly“ groove. Instead, they have a very smooth guide tube set into one flyer leg. In this case, the strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in the previous designs. Frictional resistance is significantly reduced, so that the strand can be pulled through with much less force. This reduces false drafts and strand breaks while allowing high production speeds. However, piecing of strand breaks is somewhat more difficult.

The flyer top

The manner in which the roving is carried along and guided at the entrance to the flyer determines the degree of twist and the winding tension. Where the roving has only low twist or is coarse, so that there is a risk of false drafts, the strand passes through the flyer top to the guide groove with half a wrapping (Fig. 12, A). A one-turn of wrap, as shown in (B), is selected for high-speed frames winding large packages with high twist levels. The wrap permits better control of roving tension and the package build becomes more even owing to the harder coils. Older flyers have flyer tops of smooth metal. However, most modern flyers have an insert of rubber formed with grooves, notches or indentations (Fig. 13). These flyer inserts exert a strong influence on the level of twist in the roving between the drafting arrangement and the flyer, and also on winding conditions at the bobbin. Their formation enables them to carry the roving along substantially better while imparting twist, and they additionally insert the very favorable false twist. One result of this false twist is that the roving is already strongly twisted in the unsupported length leading to the flyer. Roving breakage rates in the spinning triangle are thus reduced, and fly and lap formation are decreased. A second result of the false twist is a more compact roving, which increases the capacity of the bobbin and permits higher flyer speeds. The capacity of the bobbin is still further increased because the compactness of the roving permits winding with higher tension.

Fig. 12 – Entry of the strands into the flyer top

Fig. 13 – The flyer top

The presser arm

A steel yoke, the so-called presser arm, is attached to the lower end of the hollow flyer leg. The arm has to guide the roving from the exit of the flyer leg to the package. The roving is wrapped two (A) or three (B) times around the yoke. The number of turns determines the roving tension. If this is high, then a hard, compact package is obtained. If it is too high, false drafts or roving breaks can be caused. The number of wraps depends upon the material and twist level.

Winding of the bobbin

Fig. 15 – The bobbin form

A roving bobbin is a cylindrical body with tapered ends (Fig. 15). It is created by building layer upon layer of parallel coils of roving on wooden or plastic bobbin tubes acting as package cores. To form the tapered ends, the height of the lift must be reduced after each layer has been completed. The roving bobbin is the ideal package form for supplying material to the ring spinning frame; when full, the bobbin carries a relatively large quantity of material, owing to its compactness; when empty, it occupies a relatively small volume, convenient for transport and storage.
The angle of taper of the ends is normally between 80° and 95°, and depends upon the adherence of the material. The angle is made as large as possible, so that as much roving as possible is wound onto the package. However, the angle must be small enough to ensure that the layers do not slide apart.

Main drive system

Mainly in order to achieve the desired bobbin form, a very sophisticated drive system is necessary. Until very recently, this problem had to be solved purely by mechanical means, resulting in a really complex drive mechanism.
It has only recently been possible to simplify the drive system of the roving frame considerably by the use of modern electronic drive technology.
The two drive systems are explained in the next chapters.

Bobbin drive

During winding of a roving bobbin, the flyer rotation speed is usually kept constant. The difference between the peripheral speeds of the flyer and the bobbin must also be kept constant. However, the bobbin diameter increases stepwise, after each layer of roving. The bobbin rotation speed must be reduced accordingly to maintain the required difference between the peripheral speeds. This necessitates a relatively complicated drive for the bobbin.
Variation in bobbin speed originates from the cone drums. When the builder motion shifts the cone belt, the rotation speed of the lower cone is changed. This declining rotation speed is transmitted via gearing (Fig. 16, 80/67) to the differential and is there superimposed on the constant speed of the main shaft. Further gearing then transmits the resulting rotation speed to the bobbin drive (Fig. 17, 4/3). On the bobbin rail, bevel gears (4) fixed to the longitudinal shaft drive the bevel gears (3) of the bobbin supports. But a variable drive, e.g. a PIV unit, can be used instead of the cone drums. A further difficulty in relation to the bobbin drive is the fact that the bobbins are carried on a rail that is continually moving up and down. A flexible (relatively movable) connection is needed between the main drive shaft in the gear box and the longitudinal bobbin shaft. Previously, a kneejoint (swinging joint) was used for this purpose (between wheels 80 and 67 in Fig. 16, and see Fig. 18).
However, gear wheels arranged in a knee-joint have the disadvantage that they roll on each other during the up-anddown movements. This causes additional revolutions that are either added to or subtracted from the basic package rotation, depending upon the direction of the lift stroke. Tension variation then arises. Today, transmission of rotation is mostly effected by means of cardan shafts, telescopic shafts or chain drives.

Fig. 16 – Bobbin drive (gearing plan)

Fig. 17 – Bobbin drive (side view); drive transmission to the bobbin

Fig. 18 – Swinging joint at the bobbin drive shaft

Cone drive transmission

Variation of the bobbin rotation speed originates in the cone transmission and occurs in small steps through shifting of the cone belt after each lift stroke. Bobbin rotation must be changed in accordance with a linear function. Unfortunately, shifting the belt by constant amounts on straight-sided cones does not vary the transmission ratio in a linear manner and thus does not produce the required linear variation in bobbin rotation speed. To obtain the desired linear variation function, the cone faces have been made hyperbolic (see Fig. 19), namely convex on the upper driving cone and concave on the lower driven cone. Hyperbolic cones are difficult to design. Additionally, during the winding operation, the belt is then always moved on surfaces of varying inclination. As a result cones are now mostly made straight-sided. However, in transmissions of this kind the belt must be shifted through steps of varying magnitude, the initial steps being relatively large (Fig. 20, W1) and the later ones smaller (W4). Instead of a hyperbolic profile on the cones (left), an eccentric is used in the belt-shifting mechanism (right).

Fig. 19 – Convex and concave cones

Fig. 20 – Shifting the belt with hyperbolic (a) and straight-sided cones (b)

Shifting the belt

Belt-shifting device

Shifting of the belt is controlled by the ratchet wheel (on axle Fig. 21, 10). In the course of each change-over operation (after each stroke), the ratchet wheel is permitted to rotate by a half tooth. By way of a gear train including change wheels and an eccentric, this ratchet steps out the wire rope (1) and hence permits movement of the belt guide (5) to the right. The tensile force required to induce movement of the belt is exerted by a weight (7). Bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. The degree of shift, which depends upon the thickness of the roving, is modified by replacing the ratchet wheel or (generally nowadays) by substituting change wheels. If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it progresses more rapidly, and vice versa. When the bobbin is fully wound, the belt must be moved back to its starting point. Today, this is usually done automatically by an auxiliary motor.

Correction rail (Compensation rail, correction rod)

Functional diagram of the correction rail

If the movement of the belt does not correspond to the increase in bobbin diameter, the change wheel or ratchet must be adjusted accordingly. Sometimes, however, the adjustment resulting from changing by one tooth would have an over-large effect; a change by only half a tooth might in fact be suitable. In order to deal with such borderline cases, i.e. to provide a degree of fine setting, several roving frames are now fitted with a correction rail (Fig. 22). This is a rail (1) which is mounted in the region of the belt guide (not shown) and in its normal position is parallel to that guide. At position 4, however, the rail can be shifted to bring it into another position relative to the belt guide. A roller runs on the correction rail. The belt shifting rope is guided around this roller and is secured to the belt guide at 5.
If the rail and belt guide are not parallel, i.e. if the correcting rail has a greater inclination than the belt guide as shown in the illustration (2), the roller (dotted lines) moves further upward (3), away from belt guide (5). The distance between roller (2) and the anchoring point of the rope increases from A1 to A2. This means that the extension of the rope as determined by the builder motion is not transferred completely to the belt guide; instead, part of that extension is taken up in increasing distance A from A1 to A2. Shifting of the belt takes place through smaller steps than those corresponding directly to the paying out of the rope in the builder motion. The reverse effect is obtained if the correction rail is offset in the other direction relative to the belt guide. The increase in diameter of the bobbin is in principle a linear function of the number of layers. This relationship may not hold true in practice, because the winding conditions do not remain absolutely constant. At the start of a winding operation, roving is wound onto a hard core (bobbin tube); toward the end of the winding operation the receiving body may be softer – depending on the compactness of the roving – since the material itself now provides that body. This change, and also other changes in associated conditions, can give rise to tension variations during winding. In order to be able to adapt to these, the correction rail is often made in several parts, which are adjustable relative to each other. In this way, any desired tension level can be set from beginning to end of the winding operation by relative raising or lowering of the individual rail sections.

Lifter motion

In the package, each turn must be laid next to its neighbors. For this purpose, the lay-on point must continually be moved. This can be brought about only by raising and lowering the bobbins. This requirement cannot be met by raising and lowering the flyers, because then the unsupported roving length (from drafting arrangement to flyer top, see Fig. 3) would vary correspondingly and the angle of departure from the drafting arrangement and of approach to the flyer top would change continuously. The winding point must be shifted by moving the bobbins, which are supported on a movable rail for this purpose. The necessary raising and lowering can be carried out by means of several racks attached to the rail (Fig. 23). Some manufacturers have mounted the bobbin rail on a lever and move the rail by moving that lever up and down (Fig. 24).

The individual coils of the bobbin must be laid closely adjacent to each other, not only in the first layer but also in all subsequent layers. However, since the package diameter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer. As can be seen from Fig. 24, the lift drive is also transmitted via the cone transmission (as for the bobbin drive), but not via the differential.

In addition, a reversing drive must be provided so that the bobbin rail is alternately raised and lowered.

Fig. 23 – Lifter motion with racks (a)

Fig. 24 – Lifter motion with levers (b)

Builder motion

This device has to perform three important tasks during a winding operation:

shift the cone belt corresponding to the increase in bobbin diameter;
reverse the direction of movement of the bobbin rail at the upper and lower ends of the lift stroke;
shorten the lift after each layer to form tapered ends on the bobbins.

The required moment for each change-over and the magnitude of the adjustment both depend upon the roving hank and the material, and must therefore be adapted to the prevailing conditions by means of change gear positions. In the following sections, a short description of a builder motion for a roving frame will be given. In this arrangement, most of the movement changes are effected electro-pneumatically.

Shifting the cone belt

Fig. 25 – The reversing assembly of the lifter motion

The machine unit that induces all changes is the changeover mechanism, which comprises metal brackets (3/7) and rods (5/6). This mechanism is attached to the bobbin rail (at 2) and is raised and lowered as a unit with the rail. A stationary pin is struck by one of the rods (5/6) on the upward stroke and by the other on the downward stroke, and each time a microswitch (4) emits a pulse. Each pulse from microswitch (4) actuates a release mechanism to permit rotation of the ratchet wheel through one half-tooth.

Reversal of the bobbin rail movement

Fig. 26 – Mechanism for reversing the bobbin rail movement

Reversal of the rail movement originates from the reversing gear (Fig. 26, 1/2/3). An electrically operated valve pressurizes the left- and right-hand chambers of double-acting cylinder (9) alternately. Thus left-hand clutch (1) and righthand clutch (2) are operated successively so that pinion (3) engages with either gear wheel 1 or gear wheel 2. The rotation itself comes from the shaft 10, on which gear wheels 1 and 2 are mounted, always rotating in the same direction. Operation of clutch (1) or (2) causes left- or right-hand rotation of pinion 3 and shaft 4, accordingly. The bobbin rail is correspondingly raised or lowered via bevel gear 5, pinion 6, sprocket 7 and lifting chain 8.

Shortening the lift

Fig. 27 – The assembly for building conical ends on the bobbins

Rods 5 and 6 (Fig. 25) are inclined. The inclination is adjustable and corresponds exactly to the taper of the bobbin ends (angle alpha). During winding of a package, the ratchet is rotated at every change-over, and the microswitch (Fig. 27) is also gradually shifted further to the right on a slide.
Therefore, the rods engage the microswitch steadily earlier in the lift stroke, and reversal occurs correspondingly earlier. This results in a continuous reduction in the lift of the rail. The bobbins are thus built with a taper.

Special design (Saco Lowell „Rovematic“ frame)

While almost all manufacturers of roving frames were building their machines on the same basic principle, Saco Lowell went down a new path several decades ago. One new feature was the closed flyer ( Fig. 9, b), supported above and below and driven at the top. Still more noteworthy is the elimination of the bobbin rail. The bobbins are raised and lowered by a system of nuts and screw-threaded elements in a manner depending only upon the relative speeds of these two parts. However, this machine has not been available for some time now.

Gear change positions of the roving frame (on old roving frames)

Fig. 28 – Gearing diagram of roving frame (Rieter)

Main shaft drive discs (P)

These drive discs provide the only opportunity to adjust spindle rotation speed.

Infeed change wheel (A)

This influences the tension in the slivers between the creel and the infeed to the drafting arrangement.

Break draft wheel (V)

This enables the rotation speed of the middle cylinder (d2) to be changed, thereby changing the break draft with simultaneous alteration of the main draft. The break draft must be adapted to the material.

Main draft wheel (N)

A change here results in simultaneous variation of the rotation speeds of the middle (d2) and infeed (d3) cylinders. Since the rotation of delivery cylinder (d1) remains unchanged, the main draft is altered, as is the total draft.

Twist wheel (D)

Replacement of this wheel results in a variation of all speeds, except that of the flyers. Since the roving twist arises from the relationship between flyer rotation and delivery speed, a change in twist level arises from adjustment here.

Auxiliary change wheels (H,G)

This is an auxiliary twist change in order to adjust the twist level within broad ranges.

Lift change wheel (W)

The lift speed of the bobbin rail is influenced by this element, and hence the laying density of roving coils on the bobbin. A wheel should be chosen such that the coils of the first layer lie close to each other and practically hide the tube. The coils should also be arranged closely adjacent, but not on top of each other. In this way, the bobbin is made to take up a lot of material.

Auxiliary change wheels (F,E)

These are ancillary to the lift change wheel and again enable adjustments over broad ranges.

Cone drum change wheel (K)

If the diameter of the tube is altered, the starting speed of the bobbin must be adjusted accordingly. Since the ratchet wheel has not been operated at this stage, the adjustment cannot be made by means of the builder motion. The starting position of the cone belt can be changed or, when this is no longer possible, another cone change wheel can be substituted.

Ratchet change wheel (S)

This determines the amount by which the belt is shifted at each operation of the ratchet and therefore must be adjusted precisely to the increase in bobbin diameter.

Electronic drive system

Fig. 29 – Electronic drive system

Electronic devices such as frequency converters and individual servomotors have enabled the drive system of the roving frame to be considerably simplified. Fig. 29 clearly illustrates this fact using the modern Rieter F 35 roving frame as an example.

Monitoring devices

The need for such devices

Roving bobbins are built up from a core outwards, i.e. the diameter increases steadily. For each bobbin dimension there is an associated defined bobbin speed and lift speed. If one roving breaks, while the frame continues production, the diameter of that one bobbin stays constant while the others continue to increase. If an attempt is made to piece the broken roving end after a certain time, this end will always break again because the peripheral speed of the smaller bobbin is no longer appropriate in the new winding conditions. In order to enable winding to continue on all bobbins after a break, it is necessary to stop the machine immediately after the break occurs: automatically operating stop motions are required.

Sliver stop motions

Monitoring at the infeed is usually carried out by light barriers, with a light emitter at one side of the frame and a light receiver (photocell) at the other. The device is located between the last transport roller of the creel and the drafting arrangement. If a sliver breaks or runs out, the end falls from the transport roller, passes through the light barrier and stops the machine.

Roving stop motion

Fig. 30 – Roving stop motion by Luwa

Monitoring at the delivery of the drafting arrangement can also be performed by light barriers. In this case, the light beam is usually directed straight past the flyer tops. In the event of a roving break, the broken roving end whirls around the flyer top or so-called „hoods“ form at the flyer top. This interrupts the light beam and causes the machine to be stopped.

An alternative is the use of the capacitive detection principle in a monitoring unit. The Luwa company offers such a device under the designation „Pneumastop“. The device is associated with the pneumatic suction system in the delivery of the drafting arrangement. This suction system (Fig. 30, a) is an absolute necessity in order to avoid a series of roving breaks along a bobbin row following the first break in the row. If one end breaks, the suction system draws the sliver into a large collector duct extending over the full length of the machine. Fibers entering this duct pass through it into a filter chamber at the end of the machine after passing the capacitive detector (Fig. 30, b). In the detector there is an electric field between two comb electrodes. If fiber material passes through this field, the change in capacitance generates a signal to stop the machine. Modern machines are mostly equipped with individual electronic roving detectors placed at the outlet of the drafting unit. These electro-optical detectors ensure that in the case of a roving break the machine is stopped immediately.

Blower apparatus

Roving frames not only produce a significant quantity of fly – they also continually stir it up. This necessitates a corresponding effort to keep the installation clean. To relieve attendants at least partly of this burden, traveling blowers are now increasingly being used. These consist essentially of a powerful fan that moves back and forth on rails above the machines. Tubes hang down from the fan, some as far as the ground, and have air exit jets at the appropriate heights.
The airflow created by the fan is directed by the jets onto exposed parts of the machine. Fly is blown off onto the floor and can be sucked away by a second hose system, or can be brushed up periodically by hand (see Ring Spinning).

Potential for automation

Much of the work required on the roving frame is costly, time-consuming, physically demanding and ergonomically unfavorable. Automation is therefore most desirable in order to improve working conditions, to reduce errors, to prevent damage to the roving packages and to increase productivity.
The layout of a roving frame (with its double row of bobbins arranged one behind the other, flyers directly in the forefront, and the expansive creel), is far from ideal for automation. Nevertheless, considerable advances have recently been made. The following picture emerges.

Can changing. Full automation would be too complex and would bring only minor benefits because the change occurs too infrequently. However, can transport might be at least partly automated.
Piecing sliver breaks. This occurs even less frequently and is therefore hardly worth consideration.
Piecing roving breaks. This also occurs infrequently and could only be automated with considerable effort that would make it highly uneconomic.
Bobbin doffing. This is the most useful opportunity for automation and is long overdue since the doff is a costly, frequent and ergonomically unsatisfactory operation that has a significant influence on efficiency. Fortunately, bobbin doffing is state-of-the-art nowadays.
Bobbin transport. This is also an obvious candidate for automation, since about 60% of wage costs in a spinning mill using ring spinning machines can be attributed to the cost of transport. Such systems are now available with varying degrees of automation.
Cleaning. Cleaning has already been automated to a great extent by means of cleaning aprons, clearer rollers and suction systems at the drafting arrangement, and also by the traveling blowers that keep the machine clean.
Machine monitoring. Stop devices are now standard equipment on roving frames. In this area, automation has already been satisfactorily achieved and the burden on personnel has effectively been removed.
Production monitoring. Short-staple spinning mills operate with small profit margins that are generated at a number of individual positions. Many parameters exert an influence. Raw material is the main one, but utilization of personnel and of the installation are also important. An optimum is attained if the machines produce day and night with a minimum of interruptions. One possibility for optimizing efficiency and keeping it under control is a production monitoring system, such as the Zellweger Uster MILLDATA-SLIVERDATA system, in which interruptions in operation of all machines in the preparatory installation are recorded, evaluated and stored. Other companies offer similar systems (for instance, SPIDERweb by Rieter).
Quality monitoring. In contradistinction to the drawframe, where an almost complete quality check can be carried out on the machine itself, total quality control on the roving frame would be too expensive, since too many production positions would have to be checked. Checking roving quality remains the province of the laboratory.
Maintenance and servicing. Much, but not all, has already been achieved in this area by way of central lubrication, low-maintenance design and so on.

Several of the points listed have already been dealt with elsewhere in the text, so that here only package doffing and transport will be briefly discussed in more detail.

Preparation for doffing

For successful doffing, the roving end must be placed in a specific position on the roving package. Three positions are possible (Fig. 31):

Roving end as top bunch
Top bunch is ideal for automated roving frames with automatic roving bobbin transport systems.
Roving end in the middle of the roving bobbin
This position is mainly used for machines with manual doffing.
Roving end as bottom bunch

Bottom bunch is also used for automated roving frames with an automatic transport system, but in addition it simplifies the piecing procedure of the roving in the ring spinning machine.

Fig. 31 – Positions of the roving end

Manual doffing

The F 15 roving frame is equipped with a doffing aid for manual doffing. In order to facilitate the doffing procedure, the bobbin rail with the full bobbins is lowered and tilted. This enables the bobbins be removed easily (Fig. 32).

Fig. 32 – Manual doffing with tilted bobbin rail

Automatic doffing

Automatic doffing enables labor requirements and doffing times to be drastically reduced. The fully automated Rieter F 35 roving frame performs doffing in less than 2 minutes. This has been made possible by separate actuation of bobbin rail and doffer rail by two independent frequency converters.

The doffing sequence of the F 35 roving frame is illustrated in Fig. 33.

Fig. 33 – Doffing sequence; 1. – The bobbin rail (1) moves out and at the same time the footboard is set up. – The doffer beam with the empty tubes is lowered between the full bobbins (2).; 2. – The empty bobbin pegs of the doffer beam grasp the full bobbins. (All the bobbin pegs are now occupied). – The doffer beam moves up to reversing position.; 3. – The conveyor belt in the doffer beam moves into intermediate position.; 4. – The doffer beam puts the empty tubes onto the spindles.; 5. – The doffer beam moves into top position with the full bobbins. – The slide moves in and the footboard is lowered at the same time. – The safety zone is free again.; 6. – The bobbin rail (1) is raised to spinning start-up position. – The full bobbins (2) are transported to the transfer station. – The roving frame starts up automatically

Transport of bobbins to the ring spinning machine

Transporting individual roving bobbins manually from the roving frame to the ring spinning machine is labor-intensive and often results in damage to the roving. The answer to this problem is a roving bobbin transport system. Today, therefore, various solutions are available for bobbin transport from roving frame to ring spinning machine with different degrees of automation to suit customer needs, for example from Rieter, Schönenberger, Electro-Jet and other companies.
Such transport systems have a number of advantages with regard to quality and costs:

Quality

elimination of manual bobbin handling
elimination of intermediate storage, which can result in damage, soiling and aging of the roving
elimination of the likelihood of confusion between different roving bobbins
ensuring the application of the “first-in, first-out” principle

Costs

space saving
quality assurance and enhancement
labor savings of up to 25% compared to manual bobbin transport by reducing physical effort, reducing the distance covered by operating personnel, improved access to the machines and improved ergonomics

Fig. 34 shows an example of automatic bobbin transport between roving frame and ring spinning machines. Two separate circuits in the area of roving frame and ring spinning machines guarantee a continuous supply of roving bobbins to the ring spinning machines.

Fig. 34 – Automatic bobbin transport system (Rieter SERVOtrail system)

Technical data (normal values)

Spindles per machine	48 - 160
Flyer rotation speed, rpm	up to 1 500
Production rate, g/sp.h	250 - 2 000
Sliver hank, ktex	3.8 - 5.5
Roving hank, tex	170 - 1 500
Draft	5 - 22
Bobbin weight, kg	up to 3

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Saturday, August 31, 2019

RIETER SPEEDFRAME TECHNOLOGY