DRAW FRAME AUTOLEVELLER

Auto leveler is an additional device which is meant for correcting the linear density variations in the delivered sliver by changing either the main draft or break draft of the drafting system, according to the feed variation.

There are two types of Auto leveling systems. They are

-  Open loop system

-  closed loop system

Most of the draw frame auto levelers are open loop auto levelers.

In open loop auto levelers, sensing is done at the feeding end and the correction is done by changing either a break draft or main draft of the drafting system.

In closed loop system, sensing is at the delivery side and correction is done by changing either a break draft or main draft of the drafting system.

Most of the earlier card auto levelers are closed loop auto levelers. But the latest cards have sensing at the feed rollers and as well as at the delivery calendar rollers. We can say, both closed loop and open loop systems are being used in such auto levelers.

Open loop system is very effective, because the correction length in open loop system is many folds lower than closed loop system. But in case of closed loop system, it is confirmed that the delivered sliver is of required linear density. In case of open loop system, since the delivered material is not checked to know whether the correction has been done or not, Sliver monitor is fixed to confirm that the delivered sliver has the required linear density

Let us discuss about an auto leveler system which is being used in most successful draw frames like RSB-951, RSB-D-30 etc.

This system is an electronic leveling system. The major components in the system are

·         Scanning roller

·         signal converter

·         leveling CPU

·         servo drive(servo motor and servo leveler)

·         Differential gear box(Planetary gear box)

Function of the scanning roller is to measure the variation in the feed material. All slivers fed to the machine pass thro a pair of scanning rollers. One of the scanning rollers is moveable. These scanning rollers are loaded either by a spring loading system or a pneumatic loading system. Pneumatic loading is always better, because the pressure in kgs will be always same (consistent), irrespective of the sliver feed variation. But in the case of spring loaded, the pressure on scanning rollers may vary depending upon the feed variation.

The variations in sliver mass of the incoming slivers displace the scanning roller. The distance moved by the scanning is proportional to the sliver mass fed. This displacement of scanning rollers are transformed into voltage by a signal converter and is fed to an Electronic Leveling processor. With analogue system, electronic leveling processor is a servo amplifier, but in the case of digital system, it a CPU.

It is the Electronic Leveling processor which furnishes the correct target value to the servo drive. (Servo motor and servo leveler).

Delivery speed of the machine and electric signal values arrived at by the slivers fed are the two important signals for the correction.

Servo drive takes the information and is converted in such a way that servomotor RPM and direction is decided for appropriate correction.

Planetary gearing (Differential gearing) with its controlled output speed drives the middle and back roller. I.e. Sliver entry of the drafting system

Because the servo motor RPM and direction varies according to the feed variation and the servo motor and servo leveler generates a control speed of the planetary gearing, the required change in main draft is accomplished, compensating for the weight variation of the sliver fed.

·         If the slivers fed are too heavy, the entry speed is reduced i.e. draft increased

·         If the slivers fed are too light, the entry speed is increased i.e. draft reduced

Delivery speed (the front roller speed) remains constant and hence the production remains constant.

POINTS TO BE CONSIDERED:

Mechanical draft or nominal draft should be selected properly. Before switching on the auto leveler, gears should be selected such that, the wrapping average (linear density of sliver) should be less than plus or minus 3%.

If the feed variation indicated in the A% display of sliver fed is continuously showing more than -5% or +5%, then the mechanical draft selected is not correct.

If the mechanical draft selected is correct, then the indication in a% display of sliver fed should be between -5% red lamps and 0% green lamp or +5% red lamps and 0% green lamp. In other words, green lamp (0% variation indication) should be on at least for 80% of the running time.

Auto leveler is meant for correcting

·         continuous long term variation in the fed sliver

·         medium term variation

·         seldom occurring abnormal variations in the sliver fed due to deviations in carding and comber

·         short term variations in the sliver fed

·         variations like comber piecing

Scanning rollers should be selected properly. In some draw frames like DX7-LT OR DXA7-LT, the scanning roller is same for all sliver weights and all types of material. But in case of RSB draw frame, there are different sizes of scanning rollers. It depends on sliver weight fed and the type of material processed.

Scanning roller pressure is not a constant. It depends on the material being used.  It is selected so that minimum a% is achieved in the sliver. For the same material if the scanning roller pressure is changed, the linear density of the delivered material will also change. Hence enough care should be taken so that whenever the pressure is changed, the wrapping should be checked and adjusted.

Following are the two important parameters for Quality Leveling

·         Leveling action point ( time of correction)

·         Leveling intensity

Both feed variation sensing and correction are being done when the machine is running (continuous process) at two different places (i.e. sensing is at one place and correction is at an other place). Hence the calculated correction should be done on the corresponding defective material. This is decided by Leveling action Point.  The time required for the defective material to reach the correction point should be known and correction should be done at the right time.

Leveling action point depends upon

·         break draft

·         main draft roller setting

·         delivery speed

Leveling Intensity is to decide the amount of draft change required to correct feed variation. The correlation between mass and volume for different fibers is not same. Therefore the leveling intensity may be different for different fibers.  Leveling intensity is selected based on the following trial.

Wrapping of the delivered sliver should be checked with”n", "n+1", "n-1" sliver at the feeding side.  The sliver weight of the delivered sliver should be same for all the three combinations or should be the minimum.

This can be checked if the sliver is checked at UT 3(uster) or premier tester 7000 for mass variations (U %).

If Leveling correction point and leveling intensity is selected properly, then the  cul length C.V% of 1 meter will be less than 0.5, if the sliver is tested in UT-3 instrument.

ADVANTAGES OF AUTOLEVELLER:

All variations are corrected

Count C.V. % will be consistent and good, hence the yarn will be suitable for knitting

Off counts will be very less in the yarn, hence off count cuts will come down drastically in auto coners

Thin places in the sliver, hence in the yarn will be low

Ring frame breaks will come down, hence

·         pneumafil waste will be less

·         fluff in the department will be less, therefore uster cuts will be less

·         fabric quality will be good because of lower number of fluff in the yarn

·         labor productivity will be more

·         machine productivity will be more

·         idle spindles will be less

RKM C.V. % will be low, because of low number of thin places.

Workability in warping and weaving will be good, because of less number of thin places and lower end breaks in spinning and winding.

Sliver U%, hence yarn U% will be good

Production calculated will be more accurate in auto leveler draw frame compared to non auto leveler draw frame

Variation in Blend percentage will be very less, if both the components are auto leveled before blending, hence fabric appearance after dyeing will be excellent.

IMPORTANT:  

As long as the auto leveling system is set properly and all the components are working properly, the above said benefits can be achieved. Otherwise, the negative impact will be very big compared to working without auto leveler. If the auto leveler malfunctions, it is better to run the machine without auto

Leveler.