Operations in the Blowroom
1. Opening
2. Cleaning
3. Dust Removal
4. Blending
5. Even feed of material to the card
Opening
The first operation required in the blowroom line is opening, carried out to the stage of tufts – in contrast to the cards, where it is performed to the stage of individual fibers. Tuft weight can be reduced to about 0,1 mg in the blowroom. The small improvements by each of the subsequent machines are obtained only by considerable additional effort, stressing of the material, unnecessary fiber loss and a striking increase in neppiness. If necessary the card is able to assume rather more of the overall task.
Cleaning
It has to be kept in mind that impurities can only be eliminated from surfaces of tufts. Within a progressive line of machines it is therefore necessary to create new surfaces continuously by opening the material. And even then the best blowroom line is not able to eliminate all, or even almost all, of the foreign matter in the raw material. A blowroom installation removes approximately 40 - 70% of the impurities. The result is dependent on the raw material, the machines and the environmental conditions.
It is clear from this diagram that the cleaning effect cannot and should not be the same for all impurity levels, since it is easier to remove a high percentage of dirt from a highly contaminated material than from a less contaminated one. Looking at the machine, the cleaning effect is a matter of adjustment. Increasing the degree of cleaning also increases the negative effect on cotton when trying to improve cleaning by intensifying the operation, and this occurs mostly exponentially. Therefore each machine in the line has an optimum range of treatment. It is essential to know this range and to operate within it.
In an investigation saw that the quantity of waste eliminated on a cleaning machine by modifying settings and speeds was raised from 0.6% to 1.2%: while the quantity of foreign matter eliminated increased by only 41%, the quantity of fibers eliminated increased by 240%. Normally, fibers represent about 40 - 60% of blowroom waste. Thus, in order to clean, it is necessary to eliminate about as much fibers as foreign material. Since the proportion of fibers in waste differs from one machine to another, and can be strongly influenced, the fiber loss at each machine should be known. It can be expressed as a percentage of good fiber loss in relation to total material eliminated, i.e. in cleaning efficiency (CE):
AT = total waste (%); AF = good fibers eliminated (%).
For example, if AT = 2.1% and AF = 0.65%:
Dust Removal
Almost all manufacturers of blowroom machinery now offer dust-removing machines or equipment in addition to opening and cleaning machines. However, dust removal is not an easy operation, since the dust particles are completely enclosed within the flocks and hence are held back during suction (because the surrounding fibers act as a filter). Since, as shown it is mainly the suction units that remove dust (in this example 64%), dust removal will be more intensive the smaller the tufts.
It follows that dust elimination takes place at all stages of the spinning process.
Blending
Blending of fiber material is an essential preliminary in the production of a yarn. Fibers can be blended at various stages of the process. These possibilities should always be fully exploited, for example by Transverse doubling transverse doubling. However, the start of the process is one of the most important stages for blending, since the individual components are still separately available and therefore can be metered exactly and without dependence upon random effects. A well-assembled bale layout and even (and as far as possible simultaneous) extraction of fibers from all bales is therefore of the utmost importance. Simultaneous extraction from all bales, which used to be normal in conventional blending batteries, is now no longer possible (automatic bale openers). Accordingly, intensive blending in a suitable blending machine must be carried out after separate tuft extraction from individual bales of the layout. This blending operation must collect the bunches of fibers arriving sequentially from individual bales and mix them thorough.
Even Feed of Material to the Card
Finally, the blowroom must ensure that raw material is evenly delivered to the cards. Previously, this was carried out by means of precisely weighed laps from the scutcher, but automatic tuft feeding installations are used nowadays. While in the introductory phase such installations were subject to problems regarding evenness of tuft delivery, today they generally operate well.
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