Blow Room:
Blow room is the first steps in spinning. The main object of blow room is to open and loosen the matted mass of bale cotton and to remove the foreign matter. Thus, the blow room tries to clean the cotton as far as possible. Blow room is not a single machine operation, but there is a sequence of machines arranged one after the other to progressively carry out the job of ‘opening’ and ‘cleaning’. Thus, the number of machines and their type in this sequence are generally governed by the condition and class of cotton to be processed. Now I will discuss about problems, faults / defects, causes and way to remedies in blow room section.
Problems / Faults/ Defects Associated with the Blow Room Process:
- Low cleaning efficiency
- High Lap C.V% or Tuft Size Variation
- Nep Formation in Blow Room
- High variability in the delivered hank
- Rich droppings
- Formation of cat’s tail
- Conical lap
- Lap licking
- Patchy lap
- Holes in lap
- Soft laps
- Ragged lap selvedge
- Ineffective suction in ducts
- Double lap observed in carding
Problems, causes and remedies in blow room section are discussed below:
1. Low cleaning efficiency:
Lower extraction of wastes than required for that mixing considering the trash content is one of the main reasons for low cleaning efficiency. Increase the wastes if the lint in the wastes is normal or nil. If the beater speeds are lesser than required, we get lower cleaning. Check the beater settings and correct them if needed. Increase the space between the grid bars. Close slightly the air-inlets under the grid bars towards the cotton entry side, and open those on the delivery side. Reduce the fan speed following the beaters by 100 to 200 RPM. If the grip of the feed roller is less, we shall get low cleaning efficiency. Therefore check for the grip. Also check the sharpness of the beaters. Check the synchronization of the machine working. The blending bale openers should work for 80 to 85% of the time of working of the final machine. If there is a back draught because of not cleaning the wastes under the machines, the cleaning efficiency shall come down.
2. High Lap C.V% or Tuft Size Variation:
Modern blow room lines can produce lap or tuft with high uniformity compared with conventional blow room line. High lap C.V% or tuft size variation will in turn affect the card sliver C.V% and yarn C.V%. Modern blow room line assures output tuft size in the range of 5 mg. The reasons for high C.V% in the lap are as follows:
- Improper action of feed regulators, viz., cone drums, pedals, photocells, direct driving gear motors, etc.
- Improper mixing especially with the manual process
- Insufficient preopening
- Improper levels in the hopper
The heavier lap causes excessive beating at the card causing lapups in the card cylinder and formation of too many neps.
3. Nep Formation in Blow Room:
Nep is a fiber entanglement. Nep can be classified as fiber neps and seed coat neps. Most opening and cleaning machines in the blow room process double the number of neps that were in the bale material. All cleaning machines generate neps, but the actual increase depends greatly on the aggressiveness of the machine’s components. The major reasons for nep generation in blow room process are:
- Blunt beaters, higher beater speed
- Lower fan speed, inappropriate ratio of fan to beater speed
- Cotton with high or low moisture content
- Too much reprocessing of laps and sliver in blow room
- Higher soft waste addition in mixing
- Closer setting between feed roller and beater
- Presence of immature fibers
- Long and too much bends in pneumatic transport duct
4. High variability in the delivered hank:
Improper levels in the hoppers, improper action of feed regulators viz, cone drums, pedals, photocells, direct driving gear motors, etc. are the normal reasons for variability in delivered hanks. The normal reasons for high variability in delivered hank are improper levels in the hoppers and improper action of feed regulators, viz. cone drums, pedals, photocells, direct driving gear motors.
Following actions are recommended:
- Watch the reserve box and find out whether the level of cotton in the box goes below the minimum level. If it is going below the minimum level, increase the feed.
- Check and ensure that the level indicating system, may be photo cell or electronic devices are performing properly.
- Check and ensure that the feed controls in blow room machineries like swing doors, solenoids, micro switches, relays, etc., are functioning properly.
- Check and ensure proper working of cone drum belts and PIV drives used for regulating the feed to the beaters.
- In case of chute feeding take the following actions:
- Adjust the chute width.
- Maintain the proportion of the running time and idle time of the feeding machine at about 90% and 10%, respectively.
- The feed roller in any chute feed should be run for the maximum possible time.
- Adjust the differential pressure switch in such a way that as soon as the material is filled in the chute, the feeding machine is switched off.
- Clean the material and dust accumulation on perforated sheet.
5. Rich droppings:
Normally the lint% should be less than 40% in the waste under any beater.
The normal reasons for rich droppings are as follows:
- Too close grid bar setting to beater with high beater speed gives more waste.
- Too wide feed roll to beater setting.
- Inadequate weighing of feed roller leading to plucking of materials in lumps.
- Angle between grids is too open.
- Waste plate setting is high.
- Using of short waste plates.
6. Formation of cat’s tail:
If material movement is less and cottons are over beaten, we get this defect.
To avoid cat’s tail take following action:
- Sharpen beater edges.
- Increase fan speeds.
- Increase the air-inlet below the grid bar area of cotton entry.
- Close the striping knife and beater setting.
- Straighten bent knife if any.
- Avoid chocking of materials in beaters by increasing fan speeds.
- Do not use excess cotton-spray oil, water, etc., in mixing.
7. Conical lap:
Conical laps are due to, either higher quantity of cottons coming on one side of the lap, or due to unequal calendar and rack pressures in scutchers.
Following actions are recommended:
- Make the opening between consecutive grid bars uniform.
- Ensure equal opening of air-inlets under grid bars.
- Replace torn leather lining at the cage.
- Clean the cage thoroughly with emery paper.
- Make pressure on lap spindle uniform on both the sides.
- Make calendar roller and rack pressure uniform on both the sides.
- Ensure uniform suction at the sides of cage.
- Remove the pedals and clean thoroughly, and check the pedals where it rests on fulcrum and also pedal fulcrum bar.
8. Lap licking:
Lap licking can be due to excessive addition of soft wastes in mixing, higher rack pressures, lower compacting of laps and excessive dampness in cotton. In case of polyesters, this problem shall be mainly due to static charges and higher bulk of fibers. The problem of lap licking can be reduced by increasing the pressure on calendar rollers, reducing the pressure on racks, increasing the quantity of antistatic, use of roving ends or lap fingers behind the calendar roller nip, blocking of top cage and by reducing the lap length.
9. Patchy lap:
Patchy lap is a result of unopened tufts. The normal reasons are the tension between the calendar roller and the shell roller being too high, too low fan speed at cages, damaged grid bars, less opening of cotton flocks and dust accumulation between the pedals affecting adversely the sensitivity of pedal levers.
Following actions are suggested:
- Ensure that the mixing is opened thoroughly, and increase opening points if feasible.
- Check tuft size at the delivery of each beater, and adjust the setting between feed roller and beaters, reduce the gauge between evener roller and inclined lattice, clean the cages, and increase effective suction at cages.
10. Holes in lap:
Holes in the lap can be due to different reasons. Check the cages for damage, and reduce tension draft.
11. Soft lap:
Lower calendar pressure, lower tension draft, high proportion of soft wastes added and low relative humidity makes the laps soft. Increase the calendar roller pressure and adjust the rack pressure.
12. Ragged lap selvedge:
Ragged lap selvedges are mainly due to uneven spots at the edges. Check for the rough spots on the sides of the feed plates, leather linings for the cages, and keep the edges of the scutcher clean.
13. Ineffective suction in ducts:
The reasons for ineffective suction in ducts are as follows:
- Air leakages.
- Low fan speed. Belt slippage or a loose belt is the main reason for low fan speed.
- High resistance to air flow due to choke ups.
- Too long pipe lines and sharp bends.
- Wrong direction of rotation of the fan.
14. Double lap observed in carding:
Improper folding at the start of the lap due to improper functioning of folding mechanism is the main reason. Adjust the functioning of lap folding device.
References:
- Process Management in Spinning by R. Senthil Kumar
- Principles of Spinning: Fibres and Blow Room Cotton Processing in Spinning By Ashok R. Khare
- Training and development of technical staff in textile industry by B. Purushothama
- Handbook on Cotton Spinning Industry by Purushothama
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