Carding segments TREX and TREX plus
As carding production rates have progressively been increased, it has become necessary to include additional stationary carding segments around the cylinder. They are located between the licker-in and the flats and between the flats and the doffer.
In the first versions, the carding segments between the licker-in and the flats were used to progressively open up the tufts carried by the cylinder wire before the fibers encountered the flats.
Additionally, carding segments between the flats and the doffer were found to be beneficial in preparing the fibers for the doffing action.
In the Rieter card these segments are referred to as the TREX- system.
Developments of the carding elements and of suction plenums located between the elements have led to TREXplus that removes dust, trash and very short fibers.
The TREXplus carding elements:
1 holder with a knife (1a) and 3 carding elements
2 holder the guide element (2a) and 2 carding elements
3 holder with 3 carding elements
4 holder with knife, guide element (4a) and 2 carding elements
TREXplus selective trash removal:
Pre-carding zone,
1 Fiber opening,
2 Dust, trash and short fiber separation.Post-carding zone,
3 Fiber opening,
4 Dust trash and short fiber separation.
The TREXplus system incorporates the toothed guiding elements that were developed to keep the good fiber on the cylinder wire while allowing the trash to ride on the surface and be removed at the trash slot.
The benefits of the TREXplus are:
Higher efficiencies in the ring and rotor spinning operations, significantly better IPI values in the yarn.
C 51 Hi•Per•Card TREXplus
Flats
The primary carding action takes place between the cylinder and the flats. The fibers carried by the cylinder wire tend to move toward the flats that resist fiber movement. Many of the fibers “float” between the flats and the cylinder wire.
This “carding action”:
• Separates individual fibers,
• Opens entangled fibers,
• Separates and retains the neps in the flats,
• Frees / removes trash particles and vegetable matter from the fibers,
• Removes dust collected in the flat strips,
• Orients the fibers in the direction of the cylinder movement.
The carding surface of the flats is ground at a slight incline to allow the fibers to enter the space between the flats and cylinder. In conventional cards this means that the flat setting and closest distances between flat and cylinder is only at the trailing edge of the flats.
Rieter uses a flat design with a “Heel” that increases the degree of carding at the trailing edge.
The setting of the flats is extremely important and has to be performed carefully according the instruction manual.
Direction of flats movement
The flats on Rieter’s cards are moved backwards, that means the working flats move from over the doffer to over the licker-in. This is in the opposite direction of the cylinder movement.
The advantages of backward movement are:
• The first four or five flats over the licker-in take up the vast majority of the trash removed by the flats. This occurs regardless of the direction of movement of the flats.
• When the flats move in the backward direction, the trash taken up by the flats at the entry to the carding zone is immediately removed from the carding zone.
• The fibers passing through the carding zone move passed progressively cleaner flats as they approach the doffer. There is less tendency for impurities to be returned to the fibers on the cylinder because the last few flats are relatively clean.
Doffer
The fibers are removed from the cylinder by the “doffer”. They rotate so that the cylinder and doffer surfaces move in the same direction at the transfer zone.
• The doffer rotates at a considerably slower surface speed than does the cylinder and consequently fibers accumulate on the doffer wire.
• The doffer speed is normally in range of 50 to 120 m/min and the cylinder surface speed is in the region of 1500 m/min.
• The doffer takes some of the fibers carried by the cylinder, but the majority stays on the cylinder. There is a transfer factor in the order of 0.2 to 0.3,
• Fibers, on average, pass around the cylinder 3 to 5 times.
• The fibers taken up by the doffer are caught (hooked) on the wire and partially combed out by the passing cylinder wire. Consequently the fibers on the doffer have a majority of “trailing” hooks relative to the movement of the doffer and subsequent sliver.
• The fibers taken up by the doffer have to held securely by the wire and not drop from the wire as the doffer rotates.
The fiber transfer factor largely depends upon:
• the setting of the doffer to the cylinder,
• the type of doffer and cylinder clothing,
• the wire tooth geometry, particularly of the doffer,
• the number of points on the cylinder and doffer,
• the sharpness of the doffer wire.
• the aerodynamics at the exit region of the cylinder doffer zone.
Cylinder plates and tongue
The tongue is located between the doffer and cylinder underneath the doffing zone. It is used to minimize air disturbance and facilitate a smooth and consistent transfer of fiber to the doffer. The tongue is pre set and normally does not need to be adjusted. On the other hand, for certain carding conditions, re-setting may be necessary or even a modified tongue may be needed.
Under the cylinder Rieter installs cylinder cover plates that do not allow waste to be discharged. In high speed carding the quality is better when solid plates are used and the air turbulence under the card is eliminated.
Hook formation
The doffer clothing has a limited filling capacity. It depends upon the fiber fineness and for a one-meter wide card is limited to about 3 to 5 g/m (42 to70 grains/yard).
When the filling approaches or exceeds maximum loading, the extra fiber tends to be entangled and produces a cloudy web.
This cloudy characteristic has poor fiber orientation and produces a weak web that can be difficult to control. With short staple fibers this cloudiness can be drafted out in the drawing processes and will have only a limited effect.
However, with long staple fine fibers the extra web material responds to the drawing process by forming an excessive number of knots or neps. This phenomenon occurs with both long staple cotton and fine man-made fibers.
In general, lighter web weights/ cm² are better than heavier web weights for quality spinning.
As mentioned earlier, in the doffing process, the fibers are hooked around the doffer wire and this creates “trailing” hooks. According to Morton and Yen the percentages of the various fiber shapes in the card sliver are as follows:the same.
|
Designation |
Approx. % |
|
|
|
|
|
|
|
|
|
|
Trailing hooks |
Over 50% |
|
|
|
|
|
|
|
|
|
|
Leading hooks |
15% |
|
|
|
|
|
|
|
|
|
|
Double hooks |
15% |
|
|
|
|
|
|
|
|
|
|
No hooks |
20% |
|
|
Direction of movement |
||
No rule can be stated regarding the distribution of hooks in a cloudy web. In this case, the sliver weight and the cylinder speed primarily govern the percentage distribution of hooks.
For Rotor spun yarns and coarse ring spun yarns, fiber hooks and their distribution is of minor significance.
Sliver formation
The web on the doffer is removed by a detaching roller that has to be set to peal the web in a smooth continuous action. The setting distance between the detaching roller and the doffer depends upon the web weight and the bulkiness of the fibers being carded.
A “protective plate” is provided under the detaching roller to prevent the pealed web from breaking or dropping from the detaching roller.
The web is then taken up by the top and bottom delivery rollers, there being a transfer roller nestled between the detaching roller and the delivery rollers to ensure a smooth web movement.
The web emerging from the delivery rollers is gathered by the traversing cross apron that carries the fiber assembly to the sliver-forming zone. The material first passes through a “condensing” trumpet and is then pulled through the compacting trumpet by the stepped rollers. From the stepped rollers the sliver is transported to the coiler.
The relative speeds of the elements of the delivery section have to be adjusted according to the delivery speed and the nature of the material being processed. The respective drafts should be set according to the instruction manual.
Sliver coiling
There are two types of coilers available:
The rotating can coiler in which the coiler plate deposits the sliver coils into a can that is revolving.
The planetary coiler in which the can is stationary and the coiler plate is moved to lay the coils and form the sliver column.
In either system the setting of the coiler has to be done to prevent sliver damage, stretching, or over filling the can. The sliver column should be 8 to 10 mm clear of the can sides to allow easy withdrawal of the sliver at the drawframe. Needless to say damaged cans should be avoided to ensure a good quality of sliver.
Autoleveling
In modern spinning plants it is essential that the card sliver weight be controlled. The uniformity of matt weight delivered to the card is dependent upon the chute feed system and the condition of the material being processed. Unfortunately irregularities of feed are inherent and have to be corrected at the card.
The C 51 and C 51 Hi•Per•Card can be equipped with sliver autoleveling systems. The basic system is schematically represented below.
Key:
1 Input signal obtained by measuring the thickness of the matt being fed to the card.
2 Input signal from the sliver delivery rollers.
3 Input signal from the light sensor in the A 70 chute.
SCU control unit.
A) Inverter controlled drive to vary the feed roller speed according to the measured matt thickness and the sliver output signal.
B) Control for the drive of the feed rollers in the A 70 chute.
The autoleveler can correct matt weight, but cannot eliminate faults that occur in the carding operation.
The Rieter autoleveler acts as a mid-term leveler by measuring the matt thickness and varying the card feed roll speed to compensate for thickness variations. Even though the system responds to short variations of matt thickness, because the card draft is usually more than 100:1 the card sliver improvement can be seen as the CV% correction of 2 to 3 m lengths.
Adjusting of the autoleveling system must be carried out according to the instruction manual depending upon the controls being used.
IGS-classic
The IGS-classic was developed to solve the problem of maintaining cylinder wire in good condition. The manual operation of grinding the clothing when the carding performance had deteriorated to below a predetermined level is problematic. The operation is not always performed correctly; skilled technicians may not be available.
The cards must be correctly ground or sharpened to ensure a good carding action. This is best carried out by the IGS-classic system in which the sharpening action is performed automatically while the card is in normal production.
without IGS
IGS-classic
with IGS Classic
An aluminum holder mounted underneath the cylinder supports the grindstone.
The IGS system is set to maintain wire sharpness throughout the lifetime of the wire. The controls are programmed to traverse the stone 400 times during the wire lifetime. The frequency of sharpening changes throughout the wire lifetime. When the wire is new the interval between passes is several days, whereas when the wire is worn out the cycles are very frequent.
The carding action requires that the point of the wire be sharp. When the point is worn and the tip is round, the fibers tend to slide over the wire and this sliding action accelerates the wearing action. Although the IGS sharpening stone removes small amounts of the wire as it passes, the wire lasts longer because of the reduced amount of sliding fiber- wearing action.
Wire condition throughout lifetime
With the IGS-classic the wire life is extended by 25 to 30% depending upon fibers, production rates and plant quality requirements.
The advantages of the IGS-classic are:
• Automatic sharpening of the cylinder wire,
• No wire damage or excessive grinding due to technician performance.
• Uniformly sharp wire with consistent carding performance through out the lifetime of the wire,
• Minimal fluctuation of nep and trash removal due to changes of cylinder wire condition,
• Increased lifetime of the cylinder wire,
• No machine down time required for grinding the cylinder wire.
When the wire is installed, the expected lifetime has to be entered in the program. Part way through the wire lifetime, it may become obvious that the wire is being sharpened too frequently. If this occurs, it is possible to enter a longer wire lifetime and the program will automatically adjust the times between the remaining cycles.
The sharpening stone should be changed when a new wire is put on the cylinder.
IGS top
The success of the IGS-classic led to the development of the IGS - top that automatically maintains the sharpness of the clothing on the flats.
IGS – top Automatic Flat Sharpening System
The IGS – top is installed over the returning flats after they have been cleaned.
Periodically the system is activated and the flats are raised one at a time and pressed against the rotating abrasive brush.Short bristles sharpen the points of the pins.Longer more flexible bristles work against the sides of the pins to keep the leading edges sharp.
As the pins wear down, the form of the pins is maintained by the combined actions of the long and short abrasive bristles.
Flat setting
The IGS-classic and IGS – top eliminate manual grinding however, as the clothing wears it is still necessary to periodically set the flats to maintain optimum carding performance.
Trash removal and classification
By using the MDTA trash and dust analyzer the following results have been established as a means of classification.
|
Trash in cotton bales: |
|||
|
Up to |
1.20% |
very clean |
(e.g. El Paso) |
|
1.2 to |
2.00% |
clean |
(California) |
|
2.0 to |
4.00% |
average |
(Texas, Africa) |
|
4.0 to |
7.00% |
trashy |
(Pakistan) |
|
> 7.0% |
Very trashy |
||
|
Trash in card sliver |
|
|
Up to0.05% |
very clean |
|
0.05 to 0.10% |
clean |
|
0.10 to 0.15% |
average |
|
0.15 to 0.20% |
fair |
|
> 0,20% |
high |
Effect of overall system cleaning
The cleaning efficiency of the card ranges from 80 to 95%.
From bale to sliver the overall trash removal is in the range of 92 to 99%. This means that from cotton with a 3% trash level the card sliver trash content would be in the range of 0.25% to 0.03%.
For the card to be able to reduce the trash level to 0.03% when working at the high performance of 95% trash removal, the blowroom has to reduce the trash level in the matt to 0.6%. This means that the overall blowroom cleaning efficiency has to be 80%, which is also very high.
NOTE: The overall cleaning efficiency is NOT found by adding individual machine cleaning efficiencies. For example, in the blow room, if the first cleaning machine removes 40% of the trash and the second cleaning machine removes 50% of the remaining trash, the overall cleaning efficiency is only 70%.
Calculation: Using original cotton with a trash content of 3%.
1st cleaner at 40% efficiency removes 3 x 40% = 1.2%, leaving 1.8% trash.
2nd cleaner at 50% efficiency removes 1.8 x 50% = 0.9% leaving 0.9% trash.
Total trash removed = original 3% - remaining trash of 0.9% = 2.1%.
Overall cleaning efficiency is 2.1% x 100 = 70%
No comments:
Post a Comment