Waste Control in Spinning Mills

With the ever-increasing price of cotton, huge investments on sophisticated machines, and increasing labor wages, it is a highly challenging task for any spinning mill to enhance the productivity. In order to survive the huge competition, it is absolutely essential that waste incurred during the yarn manufacturing processes should be kept under control. 

The waste occurring in the spinning mill can be classified normally as soft waste and hard waste. Soft waste is reusable in the spinning process, whereas hard waste is not reusable. To have a good control on the process waste it is important to assess the waste in blow room, carding, comber and ring frame at regular intervals. Controlling process wastes such as blowroom and card droppings, flat strips, comber noil, sweep waste and yarn waste, equal emphasis should also be laid on the control of soft wastes such as lap bits, sliver bits, roving ends and pneumafil and roller waste. This is because, apart from loss in production, reprocessing of soft wastes involves extra handling and deteriorates yarn quality. It should be noted here that the control on waste has to be concomitant with achieving the desired level of cleaning. 

Fig: Waste in spinning mill

List of waste in cotton spinning mill with percentage:

1. Blow-room of waste = [3%]
2. Carding of waste = [3-5%]
3. Draw frame of waste = [0.5%]
4. Lap former of waste = [0.5%]
5. Comber of waste = [12-18%]
6. Simplex of waste = [0.5%]
7. Ring frame of waste = [2-3%]
8. Winding section of waste = [1%]

Major Factors for waste generation in spinning mill:

• Errors and mistakes during weighing
• Loose cotton falling from bales while transportation
• Rejection from faulty work
• Poor sliver can topping and replenishing procedure
• Poor housekeeping
• Quality standards not met
• Poor work practices
• Improper material handling
• Poor condition and performance of machines
• Higher end breakage rate and lapping tendency

Control of process waste in spinning mill are described with section wise:

Blow Room Waste: 
Amount of waste extracted in blow room is mostly determined by the trash level in cotton. The cleaning at blow room should always be considered along with the following things:

1. The cleaning efficiency of blow room machines for, seed coats is much less than for leafy matter and sand dust taken together.
2. The cleaning efficiency and waste increases as trash content increases.
3. No aspect of yarn quality other than neps and foreign matter is influenced by the quality of blow room processing.
4. An optimum level of opening is essential for cleaning of cotton.

Improving cleaning efficiency and reducing waste at blow room:

To improve cleaning efficiency of beater, first examine the mechanical condition of machine, spikes on krischner beater, blades and fingers on bladed and porcupine openers and repair or replace as required. The inter grid bars space should be check for any chock up. 

The waste is affected by changes such as:

1. Distance between the grid bars and the angle of inclination of bars.
2. Speed of beater.
3. Fan speed in relation to the beater speed.
4. Setting between feed rollers and beaters.
5. Setting between beater and brid bars.

Carding Waste: 
Waste extracted in cards is usually in the range of 4%–7%, depending upon the type of card and mixing. Between the same type of cards and mixing, the waste% should not vary more than }0.5% from the average. The card waste is also governed by the cleaning efficiency achieved in blow room. Thus, while assessing the waste, combined waste extracted in blow room and cards should be taken into account. 

The behavior of waste and cleaning at cards depends on the following considerations:

1. The total collected waste at card does not show any close relationship with the trash in the lap feed to the card.
2. The cleaning efficiency achieved in mills is about 80% for most mixing. However, for fine and superfine mixing for which very high flat speed and low production rates are employed, a cleaning efficiency of 85% or more is achieved. The overall effect is that the lint loss in card waste will increases with decreasing trash content in lap.
3. There is a tendency for the card to compensate for any lack of cleaning in blow room. The overall cleaning efficiency achieved in the blow room and the card taken together remains within a narrow range of 93–95%.

Controlling the waste at carding: 
The following facts should be kept in mind while controlling the waste and cleaning at cards:

1. Use of only one mote knife, placed slightly below the normal position of the top mote knife to give less waste and better cleaning in cotton mixing.
2. Higher lickerin speed or greater wire point density on lickerin gives higher cleaning efficiency accompanied by some increase in the lint lost under the lickerin.
3. Use of perforated undercasing helps in reducing waste.
4. With other speeds and setting held constant, the flat strip waste varies almost proportionately with the flat speed.
5. Wider front plate and back plate setting increases flat strip waste.
6. For controlling cleaning of the card, almost the only place is the lickerin region.
7. Card is excellent cleaning machine for seed coats especially the cylinderflat region which removes 80% of the seed coats.
8. The tandem card gives 5–7% higher cleaning efficiency and better removal of seed coats.

Waste can be controlled by maintaining the correct setting in the licker-in zone and carding zone. The waste% to be removed in the carding process depends on the process and quality requirements of the product. Cylinder to cylinder undercasing setting influences air currents and leads to fly generation, and too wide setting causes the loss of fibers. Closer setting of licker-in to licker-in undercasing increases the good fiber loss with waste. If the setting between the feed plate and licker-in is too close, more lint loss will occur, and it will increase the waste%. The speed of the flat is also directly related to the amount of waste removed in the form of flat strips; that is, the higher the flat speed, the heavier the flat strips. 

Comber Waste: 
One of the main functions of combing is to remove short fibres through taking out a certain amount of comber waste. The waste thus removed also contains a large number of neps and foreign matter. Obviously, combing is not required for manmade fibres as they are free from short fibres and foreign matter. A higher % of comber waste need not always means that better removal of short fibres and neps, and therefore may not always be advantageous either for yarn quality or performance beyond a certain level. 

Technological consideration: 
For an effective removal of short fibres, retention of long fibres and removal of neps, the following considerations are of up-most importance:

1. The card trailing hooks are longer and more numerous than the leading hooks. They are removed when fed as leading hooks by keeping an even number of reversals between the cards and the comber.
2. The waste at comber can be reduced by increasing pre-comber draft without affecting the resultant yarn quality. However, a high comber draft also results in extremely low inter fibre cohesion causing excessive lap linking, frequent sliver breaks at comber, draw frame and the can feed inter creel. Therefore, a pre-comber draft of 30–40 for counts upto 40s is adequate. Pre-comber draft of above 20 is suitable only for very long staple cottons.
3. The proper place for controlling neps is carding and no combing. It is often more economical to run cards at somewhat low production rate than to take out extra comber waste.

The waste at comber needs to check and controlling due to the following reasons:

• More waste other than the nominal means financial loss.
• Less waste other than the nominal could lead to unacceptable yarn quality and performance.
• Comber waste variation could contribute to lea count variation.

Ring Frame Waste: 
At many stages of spinning process waste is removed to clear the cotton or to separate the short fibres but at the stage of ring spinning there is no need to remove waste. This step is exclusively for drafting twisting and packing the yarn in the shape of bobbin. Whatsoever material is wasted here is because of our inability to control the machine, process or processing condition. Thus to control the waste we have to control all factors. 

Factors responsible for waste generation in ring frame:

1. Yarn breakage rate.
2. Time taken in attending to the yarn breakage.
3. Working practice and culture.
4. Housekeeping and material handling.
5. Mechanical breakdown and failures.
6. Methods of attending to the break downs.

Waste control in ring frame: 
This is done in the following steps:

1. Analysis and segregation of the waste of different types.
2. Weigh that waste and recording that section wise, person wise, shift wise.
3. Comparison with the standards.
4. Feed backs and action to improve waste generation.

Control of Hard Waste: 
Waste generated in the yarn manufacturing process can be classified into soft waste and hard waste. Reusable wastes such as sliver, lap bits, roving ends, and pneumafil waste are normally termed as soft waste. Yarn waste obtained from ring frame and winding department is not reusable, hence it is called as hard waste. The occurrence of hard waste must be controlled as it affects the productivity of the spinning mill. Hard waste generation in winding department must be less than 1%. 

The various causes of hard waste generation are:

• Over end piecing of yarns while attending end breakage during doffing
• Control of end breakage immediately after doffing
• Reducing the cop rejection % in winding
• Adopting proper material handling procedures
• Proper work practices in ring frame and winding

In many mills, there is good scope for improving yarn realisation and reducing wastes. Because in the spinning mill wastes are generated in more amount and it can be controllable and reducible at some extent. 

For controlling waste in spinning mill need waste investigation. The waste investigation should be done in order to take preventive measure as well as to take action where abnormality is noted in processes. Investigate the existing system of waste collection for different types of waste. Follow up waste collection procedure. More effective and reliable method of collecting and reporting of wastes could be considered where there is malfunctioning. Besides for reducing waste and control in spinning mill these steps may taken. Such as investigation of waste problems, suggestions needed, work out details, and set-up control. I think these will be effective to control waste in spinning mill.