CONTROL OF HARD WASTE IN SPINNING MILLS

CONTROL OF HARD WASTE IN SPINNING MILLS

Waste management is always a serious issue for many spinning mills. Though generation of wastes during fibre to yarn conversion process is inevitable, nevertheless, when it exceeds the stipulated level, it would result in a monetary loss to mills. Therefore, every effort must be made to optimise the generation of various types of wastes. At the same time, mills should try to fetch a maximum possible sale value for wastes in order to minimise loss due to generation of wastes.

The extent of generation of various types of wastes depends upon a number of factors such as quality of raw material, yarn quality requirement, type of machinery and their condition and work methods of operatives. Nevertheless, their incidence could be controlled to a maximum extent without affecting the machine productivity and yarn quality, by exercising a good control over the process, maintenance of machines, workers' efficiency, etc.

The following wastes are being generated by the cotton spinning mills:

• Saleable wastes: Blow room droppings, licker-in droppings, flat strips, comber waste (noil), hard (yarn) waste, sweep waste, fan/suction wastes and gutter/filter waste.
• Useable wastes: Lap bits, sliver bits, roving ends, pneumafil waste and roller wastes.

Except hard waste, incidence of other wastes happens at different stages of yarn manufacturing. The hard waste occurs mostly at the final stage, ie, in post spinning process which means that it carries almost entire conversion cost besides raw material cost. Considering the fact that the price fetched for the hard waste is only about 25 per cent of yarn selling price, any quantity of hard waste more than that normally permitted would result in a significant financial loss to a mill.

This article covers hard waste particulars pertaining to automatic cone winding as well as the price realised for hard waste that were furnished by the mills in the 29^th CPQ (Costs, Operational Performance and Yarn Quality) study covering April - June 2013 data. Measures to reduce hard waste are also included in the article.

Hard waste

The hard waste (%) data pertaining to automatic cone winding have been compiled for some popular counts and given in Table 1. Data relating to three important process parameters in automatic cone winding, viz, clearer cuts, cop rejection, and repeaters, which have a detrimental effect on the incidence of hard waste, are also given in Table 1.

The following observations have been made on the data given in Table 1.

• Average hard waste in automatic cone winding with round magazine cop feed was high at 0.68 per cent which is more than 2 times the SITRA standard of 0.30 per cent. Between counts, the average waste level ranged from 0.60 to 0.80 per cent.
• Between mills, the incidence of hard waste showed a mindboggling variation of 2 to 5 times in various counts.

Major reasons for the high hard waste are discussed below:

Inadequate maintenance of machinery

Poor maintenance and upkeep of ring frames would result in vibrating spindles, spindles out of centre, soft cops, improperly built cop bottom, etc, all of which have a detrimental effect on clearer cuts, slough off and cop rejection in automatic cone winders which in turn would increase the hard waste. Inadequate maintenance of automatic cone winders would also affect the proper functioning of splicers which would invariably increase the hard waste.

Clearer cuts in automatic cone winders

Since defects in yarn are cleared electronically, yarn breaks are termed as clearer cuts. After each clearer cut, while splicing, considerable length of yarn, depending upon machine setting, will be cut and removed from the delivery package which in turn will go as a waste.

As seen from Table 1, the average number of clearer cuts, reported by the mills, was about 80 per one lakh metres of yarn, ranging from 65 to 95 cuts between counts. Between mills, however, the number of clearer cuts varied very considerably by 3.5 times in various counts. To control the incidence of clearer cuts, the quality of feed yarn (ring yarn) and its package must be improved. Higher clearer cuts would not only increase the hard waste but also reduce the machine efficiency in automatic cone winding.

Cop rejection

Cop rejection is another parameter which has a significant impact on the incidence of hard waste. For each cop rejection, considerable length of yarn will be wasted either by removing the defective portion manually or cutting and removing the remnants from the cop. Though the overall cop rejection, reported by the mills, was under control at 5 per cent (SITRA standard: 5%), nevertheless, in some mills a high level of rejection (say, over 10%) was noticed.

Major reasons for the high cop rejection are:

• Package defects like double gaiting, yarn entanglement, soft/hard cops, etc.
• Poor yarn quality including count mix-up.
• Machine related faults like improper tension setting, malfunctioning of gripper arm, etc.

Repeaters

Though the overall 'repeaters (%)' was at par with the SITRA norm of 10 per cent, nevertheless, a very wide difference was noticed between counts and mills. Probable reasons for the high 'repeaters' are: defects in the feed and delivery package, splicer failure and improper upper arm to cone setting.

Wrong work practices

Ring frames

• Removing more length of yarn from cop during piecing an end break.
• Inadequate patrolling by tenters leading to production of more number of lean cops.
• Running the frames without overhead travelling cleaners, resulting in inappropriate yarn quality.
• Rough handling of cops, thereby damaging them.
• Poor doffing practices by the doffers, ie, not performing doffing and donning simultaneously, performing double-gaiting, etc.
• Over filling of cops leading to formation of ring cuts which in turn would get rejected in automatic cone winders.
• Maintaining more number of under winding coils in cops.

Automatic cone winders

• Manually removing more length of yarn while feeding cops in round magazine.
• Following the wrong practice of taking more than 3 cops at a time and removing more length of yarn from all the cops before feeding in the magazine.
• Using all the fingers of the right hand to take the end from a cop which may cause slough off, particularly in the case of hosiery yarns.
• Manually removing more length of yarn from "alarm cops' and feeding the cops in the magazine, instead of treating them separately.
• Feeding the frequently rejected bad quality cops without removing the defective portion. Improper selection of clearer settings and tension levels in automatic cone winders.

Materials handling & housekeeping

Poor materials handling and housekeeping would increase the hard waste level significantly. Some of the wrong materials handling practices and poor housekeeping observed in the mills during consultancy assignments are given below:

• Dropping full cops on the floor, thereby staining and damaging them. Using Hessian bags/bamboo baskets for full cop transportation will lead to more yarn entanglement and hence the yarn waste.
• Taking 5 to 10 cones on hands at a time for weighing which would create a chance for the cones to fall on the floor, thereby damaging them.
• Keeping ring cops openly in cone winding department, thereby allowing fluff to settle over them.
• Cleaning winding machines with compressed air without keeping partition boards between machines, thereby allowing fluff to accumulate on the adjacent winding machines.
• Using damaged containers/empty cops.

Hard waste selling price

As mentioned earlier, mills must endeavour to get a better price for the hard waste, since higher the price lower will be the loss due to generation of waste. An analysis of the data on price fetched by the mills for hard waste reveals the following observations:

• Average price realised by the mills for the hard waste was about Rs 60 per kg. Between mills, the price ranged very considerably from as low as Rs 25 to over Rs 70 per kg (Table 2 and Figure 1).

One-tenth of the mills had realised a higher price of over Rs 70 kg per for the hard waste which is almost one -fourth more than the all mills' average.

On the other hand, nearly one-fifth of the mills had fetched a lower price, say less than Rs 50 per kg with the average being one-third lower than all mills' average at Rs 37.

A further analysis of the data reveals that there was no significant difference in the price realised for the hard waste between count groups.

Count group-wise selling price:

Such a wide difference in the hard waste price between mills would have a significant impact on the income realisation from the sale of waste.

Impact of higher hard waste

Since the sale of hard waste accounts for only about 25 per cent of the yarn selling price, ranging from 30 per cent in coarse counts to 15 per cent in super fine counts, the impact of higher hard waste on the financial performance of a mill is significant. With an illustration, this has been explained in Table 3.

It can be seen from Table 3 that for every 0.1% hard waste, a 30,000 spindle mill would incur a loss of Rs 3 lakh per year in super fine counts (100s C) and about Rs 9 lakh per year in coarse counts like 20s. Hence, for a mill maintaining 0.68% hard waste and Rs 60 per kg selling price, the loss would be about Rs 60 lakh per year in 20s count and Rs 22 lakh per year in 100s count. With a low waste selling price, say Rs 30 per kg, the loss would be higher by Rs 13 lakh per year in 20s and about Rs 2 lakh per year in 100s counts.

Measures to reduce hard waste

Various measures to reduce hard waste are given below:

• Improve the quality of cops by reducing defects like ring cuts, over filled cops, double gaiting, etc.
• Maintain the number of under wound coils on the cop at below 5.
• Ensure a high cop content for the given package size.
• Avoid using damaged cops in ring frames.
• Maintain the number of clearer cuts at below 80 per one lakh metres for single yarn and 30 per one lakh metres in doubled yarn in automatic cone winding.
• Maintain the machinery in good condition.
• Train the workers for correct work methods.
• Ensure that cop rejection does not exceed 5 per cent.
• Control the 'repeaters' at below 10 per cent.
• Allow only minimum amount of yarn in the suction while feeding full cops in the magazine.
• Avoid removing remnants on the cops using knife.
• Maintain proper records for hard waste.