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Automation Of Rotor Spinning Machines

 

The Need For Automation

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  • One of the objectives of open end spinning research & development has been to develop fully automated systems for rotor spinning machines in order to increase production.
  • Automation of the rotor spinning machine must include automatic piecing-up after an end-break during the spinning, automatic cleaning of rotors when cleaning of the rotors when cleaning is required,& automatic doffing of the full yarn packages.
  • The necessity for automation stems from technical, economical & social factors.
  • The technical factors can be summarized as follows :
    • A productivity increase ;
    • Quality improvement & quality assurance ;
    • The future oriented machine concept,
  • The economic arguments are :
    • Comparable with the ring spinning frame & manually operated rotor spinning frame, the automatic machine , under present day conditions, produces yarn more economically up to a count of 20 tex{ 30 ne} ; {refer fig.}.
    • If account is taken of the future increases in labour costs & further developments in the productivity of the automatic rotor spinning frame , then the economic viability of automation should increase year by year;
    • Automation offers the possibility to activate capacity reserves currently under-utilized {e.g. , Operation over the week end}.
  • These are the unique arguments in favour of the automatic rotor spinning machine, even if, in certain countries , the spinning costs are at present at the same level as those of competing systems.
  • As a machine, the rotor spinning frame is best suited, owing to the application of the latest construction experience, to fulfill the demands for the reduction of noise & dust levels .
  • If successful operation of an automatic rotor-spinning frame can be achieved with a greatly reduced work force during night shift, a further contribution to amenable working conditions can be realized.
  • The advantages for the social & human aspect therefore become self-evident.

Developments In Automatic Piecing-Up

  • In order to increase the productivity of the rotor spinning machine substantially, the rotor must run more quickly , i.E. In excess of 60000rpm .
  • This , of course, does not just mean that only the rotor speed has to be increased.
  • Associated with higher rotor speeds are:
    • A higher take-up rate, which can be up to 200 m/min.;
    • A higher fibre throughput via the opening roller;&.
    • A shorter dwell time for the yarn in the rotor.
  • An important condition for running at high rotor speeds is that it is still possible to make Piecings while meeting the requirements relating to the quality of Piecings , which are :
    •  An adequate extension ;
    • An adequate strength (an at least 80% of the yarn strength);
    • A low variation in mass ( i.e., In thick places a mass no higher than + 100% compared with the over-all yarn mass).
  • In one study, it was concluded that the optimum strength of of pieced -up section is very strongly influenced by the accuracy with which the requisite number of fibres in the yarn cross section is initially fed into the rotor , both too many & too few resulting in a weak resulting in a weak piecing .
  • Too many fibres will produce a thick piecing with a twist level lower than the set twist level, & too few will give a thin piecing with a high twist level.
  • By measuring the fraction of a second for which the feed roller supplies fibres to the rotor before piecing commences for a number of currently used commercial rotor speeds , it was found that the optimum piecing strengths were obtained after the following times :-.
    • For 45000/min. : After 0.55sec;
    • For 55000 /min. : After 0.45sec.;
    • For 67000/min. : After 0.33 sec.
  • This means that the feed time has to be reduced at higher speeds ,& thus a situation is reached at which piecing-up can no longer be managed manually.
  • Practical experience has also shown that the limit at which manual piecing is possible depends on the yarn count and material, as well as on the rotor speed.
oe spinning
  • Piecing-up with this system can be done on each unit separately, or on all units  in one assembly.
  • Because of the rapid reactions of the servo-mechanism, it is possible to piece up at almost full rotor speed.
  • Each unit is activated by central electronic-control circuitry.
  • For a fault in the system, it is possible to replace the faulty part immediately; Even the central control l unit can be exchanged.
  • This reduces  production losses during a breakdown. Fig.2 shows diagrammatically the traveling type of device.
  • The mechanism used for piecing up is positioned outside the delivery rollers & the normal package winding units & travels around one or more machines.
  • This means that, when an end breaks , an individual spinning unit has to wait until its position in the patrol route is reached before being pieced-up, which, of course , loses production time .
  • Any fault in the mechanism itself has to be removed from the machine.
  • A reserve device has therefore to be used, since it is impossible to replace any of the mechanisms in the traveling system quickly because of lack of accessibility & the handling of its considerable weight.
  • The use of a reserve device, however, increases the cost.
  • A comparative study of both systems showed that individual piecing-up was more advantageous than the traveling system.
  • With the individual system, the production losses did not exceed 0.25% , whereas, with the traveling system, losses can be from 0.15 to 20.7%.
  • However, the capital costs for fitting individual units to each spinning position are likely to far exceed those of traveling system.

Further Development Work

  • When a yarn breaks, the sliver feed has to be stopped & the rotating package braked.
  • With increasingly higher production rates, the stoppage of the fibre supply to the spinning rotor needs to be carried out as quickly as possible.
  • If the interruption in feed is too slow, then an overflow of fibres into the rotor will occur & will clog the rotor.
  • With rotor speeds in excess of 45000rpm , clogging of the rotor presents a fire hazard, owing to the frictional heat generated by the fibres being rubbed against the rotor casing.
  • To alleviate this problem , several new sensing devices have been developed to replace spring loaded trip wire switches commonly used on present commercial machines to detect yarn breaks & switch off the the feed roller drive.
  • Improved braking arrangements have also been designed for stopping the drives to the feed rollers, the delivery rollers & the wind up drum.
  • The fibre feed required for producing the ring of fibres for the piecing operation depends not only on the manner of restarting the feed but also , to considerable extent , on the condition of the sliver fringe offered to the opening roller.
  • In open end spinning, the fibre length has less significance with respect to the strength of the yarn than it has in ring spinning .
  • Thus , shortened fibres present relatively little problem.
  • On the other hand, short fibres permit the ring to be broken with less trouble, which improves the appearance & quality of the yarn piecing.
  • During piecing , irregularities can can result from bridging fibres , i.e. Wrapper fibres .
  • These are more pronounced when longer fibres are present.
  • The sliver feed therefore needs to be performed in two stages.
  • I.E. With shortened fibres fed first & followed by longer fibres.
  • To accomplish this, the opening roller, in combination with compressed air supply, serves as means for parting the two lengths, the compressed air acting on the sliver fringe before opening roller & removing the short fibres before the opening roller removes the larger lengths.
  • In the rejoining of a broken yarn , several operations are required, namely, cleaning the rotor, locating the end of the broken yarn on spool, returning the yarn to the doffing-tube outle, reinseting the yarn into the rotor, starting the feed & reinserting the yarn between the delivery rollers.
  • These operations are carried out as the rotor is accelerated up to its spinning speed.
  • Among the operations, two are particularly delicate, namely conveying the yarn to the doffing tube outlet & reinserting it into the rotor so that the end of the yarn attaches itself to the fibres in the rotor groove.
  • The success & quality of joint depend on this latter operation. Basically there exist three methods of conveying the yarn to the doffing tube outlet.
  • For one method, the piecing up device has a yarn locating head ( e.g.. A hook) which locates the broken end of the yarn on the package while a friction roller drives the package.
  • The device also has guides for determining its trajectory between the position of the package on the wind up drum & the position at which the retrieved yarn end is inserted into the doffing tube outlet.
  • In a second method, the piecing up device includes a two arm suction tube with a suction nozzle.
  • The suction tube is mounted on a pivot which enables it to scan the package for the yarn end.
  • The yarn end appears to be transferred from one arm to the other when being inserted into the doffing tube outlet.
  • A third method consists  in the yarn end is being returned from the package via the wind up drum & delivery rollers, which are switched to a reversed motion.
  • The yarn end enters the spinning rotor  through a withdrawl chamber .
  • When piecing up occurs, the delivery rollers are switched to their forward motion, & spinning recommences.
  • As mentioned earlier, timing has  a crucial effect on the quality of piecing up.
  • This means that automatic piecing up does not always produce good pieced up sections with the requisite quality criteria.
  • It has to be programmed to obtain maximum success rate.
  • In order to control the process & particularly the operation of feeding in the fibre & drawing off the yarn , the rotor spinning machine should be provided with a pulse generator, to generate pulses proportional to the rotor speed, the generator being connected to a control circuit box.
  • The preliminary feed to rotor of the number of fibres required for the piecing operation, the return to the rotor of the yarn end to be pieced ,& the removal of the yarn from the rotor during its acceleration up to speed can all then be automatically timed .
  • The advantages of the generated pulse system reside in the facts that the nature & quality of piecing position are adapted as accurately as possible to the nature & quality of the spun yarn & neither piecing apparatus nor the control unit will generally have to be readapted or reset if the operating speed of the rotor is altered or if the fibre being processed or count being spun is changed.
  • The pulse can be produced by means of a photo electric cell operated by suitable reflective marking applied to the surface of at least one spinning rotor, a high pulse frequency being obtained from a large number of markings.
  • The pulses are processed into control signals with counters or multipliers or both.
  • To further ensure an acceptable yarn-piecing, control of the rotor acceleration up to spinning speed should be provided so as to lengthen the time in which the piecing steps can be performed.
  • A non-contact electromagnet or electric-eddy- current braking can be provided for countering the driving torque to the rotors.
  • The result is a flattening of the acceleration curve & a lengthening of the time period for piecing.
  • In order to prevent or reduce the formation of the loops & kinking in the yarn during the acceleration phase after the initial piecing , due to the difference in the inertia of the spool & the thread & feed rollers, the piecing device should control the course of the yarn between the feed rollers & the the spool.
  • The driving mechanism for the wind-up drum should also be adjusted to ensure a correspondingly rapid acceleration because of the greater inertia of the drum compared with the delivery rollers.
  • A yarn-tensioning means for maintaining constant yarn tension can also be included.
  • When the yarn package is driven at a greater speed in the normal winding direction, the pieced end is returned under tension to the yarn guide.
  • The winding speed of the package is then restored to its normal value.
  • For conical packages , the tension is  maintained only when a special length store is provided.
  • The traversing of the yarn by the traverse guide should therefore not begin before the pieced joint is wound on the cheese, since otherwise a yarn break could occur & would be considered a failure of the automatic piecing operation.
  • In order to maintain a standard quality of piecing, a device for monitoring the yarn can be used. A data logger is provided for storing the information concerning the number of successful piecing operations at respective spinning units or machines.

Automatic Cleaning Of Rotors

  • It is now well known that , as the running time of the spinning unit of an open end spinning machine increases , the rotor becomes fouled , & the quality of the spun yarn deteriorates.
  • Cleaning of the rotor is therefore of importance not only in relation to the properties of the yarns but also for obtaining a good piecing after an end break, since otherwise the piecing-up operation will fail.
  • If the cleaning of the rotor is carried out manually, the degree of cleaning & the ultimate success in piecing will depend largely on the thoroughness & skill of the  operating personnel.
  • However, for consistently well-cleaned rotors, automatic cleaning is needed, which can be effected independently of the skill of the operating personnel.
  • If an interruption in the spinning process occurs, such as a yarn break or the doffing of full yarn packages , it is necessary to remove from the spinning rotor the fibrous ribbon & the yarn end that have been sucked into the rotor after the yarn has been severed.
  • Besides this, in order to confine the rotor-soiling within certain limits, it is recommended that the spinning rotor should from time to time be stopped & cleaned .
  • Cleaning of the rotor  can be  carried out by two methods : mechanically & pneumatically.
  • In the mechanical method, the cleaning elements are usually rotary brushes.
  • A mobile service device includes the brushes , having a diameter smaller than the open side of the rotor to be cleaned, a drive motor for rotably driving the cleaning brush around its support shaft, & a selectively movable lever mechanism for moving the brush into & out of the rotor.
  • The cleaning brush & its support shaft are carried by a crank mechanism for moving the the shaft & brush in a circular motion so as to ensure engagement of the brush with the yarn-collecting groove in the spinning rotor being cleaned.
  • Another arrangement is for the cleaning brushes to be connected to the drive by spring loaded lever, which gives the brushes a radial movement during the cleaning operation in response to centrifugal forces.
    With this arrangement, there is advantage that the cleaning elements can be pressed with sufficient force against the inner walls of the rotor, & especially against the yarn collecting groove, without danger of damage to the rotor.
    The adjustability of the cleaning elements radially with reference to the rotor axis further allows cleaning independently of the rotor diameter & shape.
    With the pneumatic method , compressed air is used for cleaning the spinning rotor. In one arrangement , the spinning rotor is moved from its normal operating position to one in which a nozzle can direct a pressurized air-stream towards the sliding surface & collecting groove of the rotor.
    In an alternative arrangement, the rotor is rotated at a speed less than the spinning speed.
    A first flow of cleaning air is directed to collecting groove of the rotor, & second flow of cleaning air is simultaneously directed to the periphery of the rotor at an angle different from first.
    At least one of the flows of air is directed in pulsating manner. The air flows  can be supplied through ducts machined into the cover plate of the rotor housing.
    It is claimed that in this way not only satisfactory loosening of the trash from the rotor wall is achieved , but, even with the rotor not stationary , positive removal of the trash also occurs.
    In order to produce a deliberate interruption in the spinning to enable the rotor to be cleaned, a yarn monitor should be positioned so that , on measuring a fall-off in the yarn properties, it switches off the sliver feed roller.
    Alternatively, to ensure that the length of yarn leaving the rotor after the break does not contain the fault , the yarn itself can be broken .
    In this case, a mechanical device slackens off the yarn tension in the vicinity of the monitoring sensor sufficiently for a cut to be made in the yarn & ultimately interrupt the supply of fibres to the rotor.

Automatic Yarn Of Full Yarn Packages

  • One of the most difficult tasks of the operative is undoubtedly the doffing of full open end spun yarn packages, which are situated above the rotor in nearly all makes of machine.
  • It requires a degree of skill & physical strength , especially if the mass of the full yarn package exceeds 1 kg. , & this applies to all bobbins whose width exceeds 85 mm. Moreover, it is important to replace full bobbins by empty tubes safely while the machine is running, without interrupting the spinning process.
  • In order to reduce the physical & mental exertion of the operative , automatic doffing of full open end spun yarn packages has been developed.
  • There are two systems:
    • Semi-automatic &.
    • Fully automatic.
  • For the semi-automatic system, a supply station is fixed at each spinning unit for storing a supply of empty spool tubes already wound with starter yarns.
  • A traveling  servicing carriage is guided on tracks adjacent to the spinning units & has lever mechanisms for effecting the removal of a full bobbin & its replacement with an empty spool tube at each supply station.
  • Package -changing with this system means repiecing the yarn.
  • Each supply station is filled manually while the traveling servicing carriage is automatically driven to effect the tube transfer operation.
  • In the fully automatic system, doffing is performed without interrupting the spinning process.
  • While the full package is being removed & replaced with an empty one, the running end of yarn passes through a suction tube into the machine's waste collection system.
  • After empty spool tube is in place, the running yarn is returned to the tube, where a transfer-tail is wound before releasing the yarn to regular winding traverse.
  • Doffing without interruption of spinning has the advantage that there is no loss in production; The spinning position does not stand idle while it waits for the subsequent piece up operation.
  • On removal by the automatic doffer, the package are placed on a conveyor  extending the length of spinning machine.
  • A second conveyor is positioned between the first conveyor & a container, which ultimately receives the packages.
  • This second conveyor is driven at a higher speed than the first to allow the packages to be automatically stacked in columns in the container.
  • On the whole fully automatic system greatly reduces the effort of the operative's job & in saving labour increases the number of machines per operative.
  • The net result is an improvement in the working conditions & a possible reduction in production costs

 



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