Fiber preparation
The blowroom
Introduction
Fig. 1 – Technological
performance of a blowroom line and influencing factors
The first volumes of the Rieter Manual of Spinning are
mainly focused on the treatment of cotton. The task of the blowroom line is to:
- open the material into very fine tufts;
- eliminate most of the impurities;
- eliminate dust;
- provide a good blend.
And this has to be done:
- with very careful treatment of the raw material;
- with maximum utilization of the raw material;
- while assuring the optimum level of quality.
The requirements mentioned here are standard for all blowroom
lines; for modern high-performance lines the following are added:
- high operational efficiency;
- high economy;
- high flexibility;
- machines of ergonomic design, i.e. safe and easy to handle, maintenance friendly, reproducible and stable settings.
Considering the overall costs of a ring spinning plant, the
share of the blowroom line with about 5 to 10% is not very relevant. It is,
however, very significant in respect of raw material treatment, e.g. the best
possible utilization, the avoidance of deterioration, and optimum preparation
for further processing.Looking additionally at the cost structure of
a yarn in which the raw material accounts for about 50 - 70%, it is clear
that there is no better way to reduce costs than via the raw material. And this
can be done, e.g., with a modern high-performance blowroom line, as it
enables a somewhat cheaper material to be used than with an older blowroom
line. The main saving potential, however, is achievable with the introduction
of professional and competent raw material management. It enables the raw
material to be selected to conform exactly to requirements, and also guarantees
the optimum preparation and utilization of the raw material. The latter is not
so easy to achieve with regard to one of the tasks of the blowroom, i.e.
cleaning the raw material. Foreign matter cannot be eliminated without
simultaneous extraction of good fibers. This is unavoidable, only the amount of
good fiber loss can and must be influenced.
Another big problem with conventional blowroom lines is the deterioration of the raw material:
- about 50% of all shortcomings in the yarn;
- about 50% of all quality reducing factors;
- andaround 50% of all yarn break causes can be traced back to the operation of the blowroom and cards.
Errors or negligence in selection, composition or treatment of
raw material in this section can never and by no means be corrected in the
subsequent process stages.
Basic operations in
the blowroom
Opening
Fig. 2 – Openness of the fiber
material after the various blowroom machine stages; axis A: Degree of opening
(specific volume); axis B: Blowroom stages
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. Artzt, Schenek and Al Ali
[2]
indicate that the degree of opening changes along a blowroom line as shown
in Fig. 2. This line is a theoretical layout for study purposes only. The
flattening of the curve toward the end shows that the line is far too long. It
should end somewhere at machine No. 3 or (at least) No. 4. 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. The diagram by Trützschler in Fig. 3 illustrates the dependence of
cleaning on raw material type, in this case on the level of impurities.
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. However, as Fig. 4 shows, 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 by Siersch
[3], 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%:
Fig. 3 – Degree of cleaning (A) as a function
of the trash content (B) of the raw material in %
Fig. 4 – Operational efficiency and side effects
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 by Mandl
[4],
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. Fig. 5 shows Mandl’s figures for the various machines.
Fig. 5 – Dust removal as
a percentage of the dust content of the raw cotton (A) at the various
processing stages (B): 1 - 5, blowroom machines; 6, card; 7, drawframes; (a)
filter deposit; (b) licker-in deposit; I, dust in the waste; II, dust in the exhaust
air.
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
doublingtransverse
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 thoroughly (see Fig. 6, and
description
The
Rieter UNImix B 70).
Fig. 6 – Sandwich blending of raw material
components
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.
Feed material
Raw material
Fiber materials used in short-staple spinning can be divided into three groups:
- cotton, of various origins;
- man-made fibers, mainly polyester and polyacrylonitrile;
- regenerated fibers (viscose fibers).
An additional classification can be based on the degree of previous processing:
- raw fiber, direct from the ginning mill or the man-made fiber manufacturer;
- clean waste such as broken ends of sliver, lap and web;
- filter strippings from the drawframe, roving frame, ring spinning machine and rotor spinner;
- comber waste for the rotor spinning mill;
- recycled fibers from dirty waste in the blowroom and carding room;
- fibers torn out of hard waste such as roving, yarn and twisted threads.
Re-usable waste
Rieter
indicates average quantities of waste (in %) arising in the spinning mills of
industrialized countries as shown in Table 1.
Binder
References[5] gives the following figures for
the quantity of good fibers obtainable from waste material.
Table 1 – Amount of waste (%) from the different
machines in industrialized countries
Adding waste to the raw material
It will be apparent that raw fibers are usually better than
waste fibers because waste contains processed and therefore stressed fibers.
Furthermore, since waste fibers have experienced differing numbers of machine
passages, they differ from each other in their characteristics. For example,
lap web is very compressed, but waste from thread break suction systems is
barely compressed at all. Random and uncontrolled feeding of such fiber material back into the normal spinning process is to be avoided at all costs, since considerable count variation will result along with quality variations. It is preferable that:
- a constant, fixed percentage of waste fibers should be added to the fiber blend; and
- within this fixed proportion of waste, there should be a constant, fixed percentage of waste fibers of different sorts.
Ring-spun yarns:
- carded up to 5%
- combed up to 2.5%
Rotor-spun yarns:
- coarse up to 20%
- medium up to 10%
- fine up to 5%
Material from bales
Production
of a reasonably homogeneous product from inhomogeneous fiber material
requires thorough blending of fibers from many bales. In practice, fiber is
taken from 20 - 48 bales of cotton simultaneously; with man-made fibers 6 - 12
bales are sufficient. Simultaneous extraction of tufts from more than 48 bales
is seldom useful, because usually there is no space for additional blend
components in the blending chambers of the bale opener or blender without
disturbing the evenness of distribution. On the other hand, the constancy of
the blend can often be improved if care is taken with regard to homogeneity at
the bale layout stage. The bales can be chosen in such a way that, for the
layout as a whole, constant average values are obtained, for example for
length, fineness and/or strength, within predetermined upper and lower limits,
which is a bale management task. In order to achieve this, the quality of
each bale must be known. Today computer software is available for optimizing
bale grouping.
Fig. 7 – Bale layout in front of an automatic bale
opener
Acclimatization of the raw material
Air temperature in the blowroom should be above 23°C and
relative humidity should be in the 45 - 50% range. Damp air makes for poor
cleaning and over-dry air leads to fiber damage. It should be borne in mind,
however, that it is not the condition of the air that matters, but that of the
fibers. It is assumed, however, that the fibers adapt to the air conditions. To enable this to happen, the fibers must be exposed to the air for an appropriate period. This is not achieved if cotton or, what is even worse, man-made fibers, are taken from the cold raw material store and processed as soon as they have been laid on the extraction floor. Cotton bales should be left to stand in the blowroom in an opened condition for at least 24 hours before extraction starts, better still for 48 hours. Synthetic fiber bales should be left to stand for 24 hours longer than cotton bales, but in an unopened condition. This allows the bales to warm up. Otherwise, condensation will form on the surfaces of the cold fibers. Further adjustment to the air conditioning occurs within the pneumatic transport devices. In such devices, the relatively small tufts are continually subjected to the air current in the transport ducts.
The blowroom installation as
a sequence of machines
In
processing the material, different types of machines are necessary, namely
those suitable for
opening, those for
cleaning and those for
blending. Different
intensities of processing are also required, because the tufts continually
become smaller as they pass from stage to stage. Accordingly, while
a coarsely clothed cleaning assembly is ideal after the bale opener, for
example, it is inappropriate at the end of the line. Therefore, there are no
universal machines, and a blowroom line is a sequence of different
machines arranged in series and connected by transport ducts. In its own
position in the line, each machine gives optimum performance – at any other
position it gives less than its optimum. Also there may be advantages in
different modes of transport, feeding, processing, cleaning and so on from one
machine to another along the line. Finally, the assembly of a blowroom
line depends among other things on:
- the type of raw material;
- the characteristics of the raw material;
- waste content;
- dirt content;
- material throughput;
- the number of different origins of the material in a given blend.
In
most cases a modern blowroom line consists of the following machines, as
shown in Fig. 8 (Rieter) and Fig. 9 (Trützschler), illustrating two typical
blowroom lines.
Fig. 8 – Rieter blowroom line; 1. Bale opener
UNIfloc A 11; 2. Pre-cleaner UNIclean B 12; 3. Homogenous mixer UNImix B 75; 4.
Storage and feeding machine UNIstore A 78; 5. Condenser A 21; 6. Card C 60; 7.
Sliver Coiler CBA 4
Fig. 9 – Trützschler blowroom line; (conventional,
for combed cotton. One line with a number of variations.)
The components of
blowroom machines
Feeding apparatus
Feeding
material to the opening rollers of an
opening and/or
cleaning machine occurs
in free flight (gentle, but less intensive treatment of the fibers), or in
a clamped condition (intensive but less gentle treatment). Free flight
requires only a drop chute, suction pipe or vortex transport from rollers;
a clamped feed condition calls for special machine components. In this
case feed devices can be distinguished according to whether they comprise:
- two interacting clamping cylinders;
- a feed roller and a feed table;
- a feed roller and pedals.
Operating
with two clamping cylinders (Fig. 10) gives the best forward motion, but
unfortunately also the greatest clamping distance (a) between the cylinders and
the beating elements.
In
a device with a feed roller and table (Fig. 11) the clamping distance
(a) can be very small. This results in intensive opening. However, clamping
over the whole width is poor, since the roller presses only on the highest
points of the web. Thin places in the web can be dragged out of the web as
clumps by the beaters.
Where
pedals are used (Fig. 12), the table is divided into many sections, each of
which individually presses the web against the roller, e.g. via spring
pressure. This provides secure clamping with a small clamping distance
(a). As far as the feed system is concerned, influence can be exerted on
opening and cleaning only via the type of clamping, mainly via the clamping
distance (a) to the opening element.
Fig. 10 – Feed to a beater with two clamping
rollers
Fig. 11 – Feed with an upper roller and a bottom
table
Fig. 12 – Feed with a roller and pedals
Opening devices
Classification
Some of the operating devices in blowroom machines function
only for opening. Most of them work, however, in cooperation with cleaning apparatus such as grids, etc., and thereby function also as cleaning units. Consequently, they are designed to operate both in opening and cleaning machines.
Opening units can be classified as:
Depending on their design, construction, adjustment, etc., these assemblies exert enormous influence on the whole process.
Gripping elements (plucking springs)
Some
manufacturers, for example former Schubert & Salzer and Trützschler, have
used plucking springs for opening. Two spring systems, facing each other like
the jaws of a pair of tongs, are parted and dropped into the feed material
and are then closed before being lifted clear. They grasp the material like
fingers. This type of gripping is the most gentle of all methods of opening,
but it produces mostly large to very large clumps of uneven size. This type of
opening device is therefore no longer used.
Fig. 15 – Plucking springs
The grid
The grid as an operating device
In the final analysis, it is the grid or a grid-like
structure under the opening assembly that determines the level of waste and its
composition in terms of impurities and good fibers. Grids are segment-shaped
devices under the opening assemblies and consist of several (or many)
individual polygonal bars or blades (i.e. elements with edges) and together
these form a trough. The grid encircles at least 1/4, at most 3/4 and
usually 1/3 to 1/2 of the opening assembly. The grid has a major influence on the cleaning effect via:
- the section of the bars;
- the grasping effect of the edges of the polygonal bars;
- the setting angle of the bars relative to the opening elements;
- the width of the gaps between the bars;
- the overall surface area of the grid.
Fig. 25 – Two-part grid
The elements of the
grid
Fig. 26 – The elements of a grid
The following elements can be used in the grid:
- slotted sheets (a): poor cleaning;
- perforated sheets (b): poor cleaning;
- triangular section bars (c): the most widely used grid bars;
- angle bars (d): somewhat weak;
- blades (e): strong and effective.
Blades have been used as grid elements for a long time (the mote knife), almost always in combination with triangular section bars.
Today, grids are made up of knife blades alone, without other element types. Angle bars are somewhat less robust and can tend to create blockages.
Waste collecting chambers under the grid
Impurities and fibers fall through the grid gaps and
accumulate in large quantities in the chamber under the grid. Waste used to be
periodically removed manually, but pneumatic removal systems are used today. As
far as the cleaning effect is concerned, modern waste chambers are passive
elements, without influence on the operation. In older designs they sometimes
participated actively, and afforded the possibility of exerting
a significant influence on events by permitting some of the transport air
for forwarding the tufts (the so-called secondary air) to enter through the
waste chamber and the grid. Such systems enabled the interaction of airflow and
beating power to be exploited. Heavy particles could drop out, against the
airflow through the grid gaps, because of their high ratio of mass to volume.
However, fibers were taken up again with the airflow because of their low ratio
of mass to volume. Today, this principle cannot be exploited because of the
small size of the foreign matter, which would now be carried back along with
the fibers. Accordingly, a so-called dead chamber is now used; none of the
transport air now passes through the grid gaps.
Grid adjustments
The grid can be in one, two or three parts.
Correspondingly, it can be adjusted only as a unit or in individual
sections. Three basic adjustments are possible:
- distance of the complete grid from the beater;
- width of the gaps between the bars (Fig. 28, a=closed, b=open);
- setting angle relative to the beater envelope (Fig. 27 and Fig. 28c).
Fig. 27 – Changing the grid bar
angle to the beater
Fig. 28 – Adjustment of the grid
bars
Interaction of feed assembly, opening
element and grid
Fig.
29 to Fig. 32 demonstrate the influence of adjustments to these elements:
- Fig. 29, distance between feeding device and beater;
- Fig. 30, grid gap width;
- Fig. 31, beater speed 740 rpm (and setting angle of the grid bars);
- Fig. 32, beater speed 550 rpm.
The
figures do not show fiber deterioration, or even damage, that can be caused.
Nevertheless, very fine settings and high rotation speeds can produce very
negative effects. On the other hand, the number of neps is scarcely affected.
The design of the machine and its components exerts the strongest influence on
neppiness.
Fig. 29 – Influence of feed pedal distance (Δs; B,
mm) on waste elimination (A, %)
Fig. 30 – Dependence of waste elimination: (A, %) on
the width of the grid gaps (B) (1 closed, 4 open). a = proportion of good
fibers; b = trash content.
Fig. 31 – Dependence of waste elimination: (A, %) on
the setting angle of the grid bars relative to the beater (B in degrees). I,
fiber content; II, trash content; III, filter drum loss. (Beater rotation
speed: 740 rpm.) Fig. 32 – The same function as Fig. 31 but with a beater
rotation rate of 550 rpm.
Alternative cleaning possibilities
Fig. 33 – Airflow cleaner
An alternative to the commonly used mechanical
cleaning
was the airflow cleaner from the former Platt Company. The ‘Air-stream-cleaner’ comprises two parts, a Kirschner roller as opening assembly (and pre-cleaner) and the airstream cleaner itself, as shown diagrammatically in Fig. 33.
The cotton passes from the Kirschner roller (in front of A) into duct A. The transporting air is subjected first to acceleration due to convergence of the duct bore, and to an additional airstream created by fan (V).
In region C, the whole airstream undergoes a sharp diversion (of more than 90°) towards E.
While the relatively light cotton tufts can follow the change of direction, the heavier foreign particles fly through an opening in the duct, beyond region C, into the waste chamber.
This is an extremely gentle cleaning technique, but it requires foreign matter significantly less able to float than the fibers, i.e. it must be substantially heavier than the fibers.
Unfortunately, this is no longer true for all cotton varieties, and therefore this good cleaning idea is not applicable today
General factors influencing opening and
cleaning
two stages of opening must be distinguished:
- opening to flocks: in the blowroom;
- opening to fibers: in the card and OE spinning machine.
In addition, the technological operation of opening can include:
- opening out – in which the volume of the flock is increased while the number of fibers remains constant, i.e. the specific density of the material is reduced; or
- breaking apart – in which two or more flocks are formed from one flock without changing the specific density.
Table 2 shows opening devices;
Table 3 shows opening variants.
Table 2 – Opening devices
Table 3 – Opening variants
Fig. 13 – Dependence of degree of
opening upon throughput; A, degree of opening (flock weight, mg); B, material
throughput (kg/h)
Fig. 14 – Increase in the degree
of opening from machine to machine in a certain blowroom; A, degree of opening,
flock weight in g/flock; B, machine passages; V, feed material; M1-M5, machines
1-5.
Fig. 15 – Ideal form of the
opening curve (green line) in an older blowroom; A, degree of opening, flock
weight in g/flock; B, machine passages; M1-M5, machines 1-5. It is clearly
apparent that machines 4, 5 and 6 are superfluous; in modern lines, they should
be omitted.
General considerations regarding opening
and cleaning
The
degree
of cleaning
cannot be better than the
degree
of opening.
Accordingly, the following should be noted:
- Dirt can be removed practically only from surfaces.
- New surfaces must therefore be created continuously.
- The form of the opening machine must therefore be adapted to the degree of opening already achieved.
- The Type and degree of openingopening devices should become continually finer, i.e. within the blowroom line, a specific machine is required at each position.
- The degree of cleaning is linearly dependent upon the degree of opening.
- Newly exposed surfaces should as far as possible be cleaned immediately.
- This means that each opening step should be followed immediately by a cleaning step without intervening transport, during which the surfaces would be covered up again and would require re-exposure.
- Ideally the opening and cleaning machines should form a unit.
- A high degree of opening in the blowroom facilitates cleaning in the carding room.
- A high degree of opening out in the blowroom reduces shortening of staple at the cards.
- Opening and cleaning of cotton on only one (universal) opening machine is very difficult owing to the requirement for continual improvement of the degree of opening.
- On the other hand, each machine in the line represents often considerable stress on the fibers.
- Aside from economy, therefore, quality considerations indicate the smallest possible number of machine passages in the blowroom.
- Feeding of flocks in a clamped condition gives an intensive but usually not very gentle opening action.
- Feeding in a loose condition gives gentle, but not very intensive opening.
- Opened flocks should approach as closely as possible a spherical shape. Long narrow flocks lead to entanglements during rolling movements and pneumatic transport. Finally, they form neps.
- Narrow setting of the feed device relative to the roller increases the degree of opening, but also the stress on the material.
- Demands
The
subjects dealt with in the previous chapters are the main technological demands
on a modern high-performance blowroom line, but another aspect is becoming more
and more important: easy handling of machines everywhere. In detail this means:
- simple, time-saving adjustment;
- flexible adjustments, i.e. adaptable to all requirements;
- reproducible adjustments;
- durable adjustments, i.e. no uncontrolled changing of settings by the machines.
Above
all, reliability and operational safety are vital in this respect. A system of
this kind will be explained by means of the Rieter
VarioSet, a component of
the
UNIclean
B 12
and
UNIflex
B 60.
Rieter VarioSet
All performance and treatment alterations on both machines
mentioned can be made very easily and electronically during the normal
operation of the machine from outside the machine without any stoppages. An easily understandable and clearly arranged display is available at one side of the machine for this purpose. This display includes a special setting arrangement called VarioSet (Fig. 65). It enables operating personnel to adjust the degree of cleaning and the cleaning efficiency (to a certain extent the unavoidable loss of fibers) exactly to the raw material and the requirements of the mill. All that is needed is to push a few buttons on the operating panel at the side of the machine. Various setting positions can be fixed on the screen, e.g. for the degree of cleaning from 1 to 10 (marked here in the example from A to Z), and for cleaning efficiency from 0.0 to 1.0 (marked here from A to X).
VarioSet:
Changes in the extraction of trash and good fibers when changing the settings from A to X, Z till H.Example:
Indian cotton: 1 1/8 inch, 2.2% trash|
From/to
|
Setting A
|
A→X
|
A→Z
|
A→H
|
|
Waste amount |
0.62
|
0.80
|
0.65
|
1.08
|
|
Trash [%] |
90
|
78.5
|
67
|
66
|
|
Good fibers [amount]
|
0.07
|
0.22
|
0.32
|
0.55
|
|
Good fibers [%]
|
10
|
21.5
|
33
|
34
|
|
Ratio of trash/fibers
|
9:1
|
3.6:1
|
2:1
|
2:1
|
Fig. 65 – VarioSet cleaning field
Fig. 66 – Practical examples and
their effect on waste composition
The need for transport
Blowroom installations consist of a combination of
a number of individual machines arranged in sequence. In processing, the
material must be forwarded from one machine to the next. Previously, this was
performed manually, but now it is done mechanically or pneumatically, i.e.
using air as a transport medium. Mechanical transport is limited
exclusively to forwarding within the machine; outside the machine, material is
now transported only pneumatically.
Mechanical transport equipment
This
comprises conveyor belts, lattices and spiked lattices. Conveyor belts permit
high speeds.
They
are used as collector belts in mixing batteries or as infeed or horizontal
conveyors in openers and hopper feeders. They have the disadvantage that
sometimes the material slips on them.
The
forwarding effect is often better on lattices (Fig. 67). They are used as
horizontal feed lattices and as short transport belts within a machine. They
are endless and consist of circulating belts to which closely spaced,
individual hardwood crossbars are screwed or riveted. Today’s conveyor belts
(Fig. 68) no longer use crossbars. The belts consist of different layers with a
fiber-free surface. The belts are driven by shafts that simultaneously serve
for belt tensioning. The forwarding speed is usually very low.
Inclined
lattices or
spiked
lattices
(Fig. 13) are the same in terms of structure and drive. However, steel spikes
are set at an angle in the crossbars, so that the raw material can be
transported upward. Inclined lattices are operated at speeds up to
100 m/min. They usually interact with evener rollers, and thus function
mainly as opening devices.
Fig. 67 – Georg Koinzer lattice
Fig. 68 – Habasit conveyor belt
Pneumatic transport
Basic principle
Air is not inherently a very efficient transport medium.
Very large quantities must be moved at high speeds in order to keep the tufts
that are being transported floating. The current of air itself is a further
disadvantage, since the air flows in a turbulent fashion through the ducting,
i.e. vortexes are created. Since the tufts are subjected to these vortexes,
entangling of tufts can arise in long ducts and finally neps can be formed. A
closed duct (generally a pipe) and a source of partial vacuum (a fan) at one
end of the duct are needed to move the air. The air speed should be at least
10 m/sec, and 12 - 15 m/sec is better; it should never
exceed 20 - 24 m/sec. At a given air speed, the required
quantity of air can be calculated as:where L is the quantity of air; A is the cross section of the duct in m2; v is the air speed in m/s. The duct must terminate in a device that separates the air from the material.
Separation of air and material
By
far the most widely used assembly for this purpose is the perforated drum (Fig.
69). It is used in various machines and parts, often in so-called suction boxes
(condensers).
A
partial vacuum is created in the drum, and thus in the duct, by a fan at one
end of the drum. Air and material flow toward the drum. However, while the air
can pass through the perforations in the drum, and is then passed to filters
for cleaning, the fiber tufts remain on the surface of the rotating drum and
are carried along with it. In the lower region, the drum surface is screened
off from the partial vacuum in its interior. The tufts are no longer retained
by suction and fall into a chute. Another assembly for separating air and
material is the slotted chute of the Rieter
UNIflex (Fig. 57),
where the transport air is extracted through the slot, while the material
slides down on the aluminum ribs of the rear wall of the chute.
Fig. 69 – Separation of air and material
Control of material flow
Classification
Since,
as already discussed, the blowroom line is a sequence of individual machines,
each machine must always receive an exact quantity of material per unit of time
from the preceding machine, and must pass on the same quantity per unit of time
to the next. To ensure an adequate flow of material, the machines are adapted
to each other so that each machine can produce a little more than the
succeeding machine requires. Since each machine has excess capacity, a control
system must be provided to ensure the correct delivery quantities. Two basic
principles are used: batch operation and continuous operation.
In
a hopper feeder, for example, the conveyor (1, Fig. 70) places material into
the hopper until sensing lever (a) is pushed so far to the right that a contact
is made to switch off the drive of conveyor belt (1). In exactly the same way,
during filling of the reserve hopper (R), the pressure exerted by the column of
material eventually becomes so great that sensing lever (b) is depressed; this
causes the preceding machine to be switched off . When the column of material
has again been largely removed by conveyor (1), the sensing lever rises, the
preceding machine is switched on and the reserve chute is refilled.
Unfortunately, in practice the individual machines actually produce during a
period that is often only 50% of operating time and are unproductive during the
remainder of the operating time. On the other hand, in continuous operation
created by changing the speeds of the machines, the machines’ production rates
are much more closely adapted to each other. They operate almost continuously
and without stops. A fine control device serves to maintain material throughput
by adjusting the production speeds of the individual machines. Batch operation
has the advantage that the machines always run at the same speed and with the
same production rate when they are in operation. The treatment of the material
remains uniform all the time. That means that the raw material is always
processed under the same conditions, since there are only two treatment levels
– full on or off . In continuous operation, however, there are continual
slowdowns and accelerations, with possibly varying intensities of treatment of
the raw material. Data provided by Trützschler indicate that there are no
negative effects, provided variations in production rates do not exceed ± 20%.
The disadvantage of batch operation lies in the incorrect handling of the
material throughput. As machines often do not operate during 50% of the time,
in their productive periods they are not working at, e.g., 300 kg/h as
calculated by the spinner; instead they are actually processing material at a
rate of 600 kg/h. The loading of the machine is high, and that might lead
to a correspondingly poor cleaning effect. In the mill, therefore – and this is
very important – an attempt should be made to regulate the installation so that
the productive time of the individual machines is very high, and only few
non-productive periods occur.
Fig. 70 – Regulated feed of material in the hopper
feeder
Optical regulating systems in batch
operation
Fig. 72 – Optical regulation
(Example: Marzoli horizontal cleaner) Four optical monitoring devices (Fig. 72) are mounted in the filling chute, conveyor belt and mixing chamber of the machine.
If the column of material falls below light barrier (2), the preceding machine is switched on and delivers material. When the chute has been filled to such an extent that the material interrupts the light beam in light barrier (1), the machine is switched off again. Light barrier (1) is also an over-fill safety monitor. Light barrier (3) monitors the amount of material in the mixing chamber and controls the drive to conveyor belt (6) and the feed roller of the chute. Light barrier (4) will trigger an alarm if there is no material left on feed conveyor (5).
Continuous operation
As
a concept, this is not new in the blowroom; it has been used for a long time in
the scutcher as pedal regulation of the feed to the beater. What is new is that
now the whole blowroom line operates continuously and regulation is performed
electronically. This installation, developed by Trützschler, will be presented
briefly (see Fig. 71).
The
central regulating unit, to which all the individual machines are connected, is
the “CONTIFEED”. This receives an analog signal from the tacho-generators of
the cards; the instantaneous demand for material is continuously calculated
from this signal. Using this demand, the microcomputer can establish the basic
speeds of all drives that determine the throughput and the drives can be
correspondingly controlled. A second signal is superimposed on this basic speed
signal, derived from the contents of the storage unit of the succeeding
machine. In this way, the successive machines are linked via individual control
loops. The programs for speeds, production quantities and allocation are first
established manually, which represents a fairly substantial initial outlay.
When balanced operation is achieved, they can be transferred to the “CONTIFEED”
and stored there.
Fig. 71 – Trützschler CONTIFEED
Rieter UNIcommand
Fig. 73 – UNIcommand control system
As
already mentioned, the blowroom line is a sequence of several machines. In
their operation these machines have to be very well coordinated, requiring a
good, reliable system for monitoring and controlling the individual machines,
groups of machines and the total blowroom line. UNIcommand works on an
electronic basis, and is a combination of PLCs (programmable logic) and PCs
with a central control unit somewhere near the blowroom line, plus an
additional PC in the supervisor’s office as an option. No computer or software
knowledge is required to handle the system. As everywhere, Rieter standardized
panels are used. A language-independent color graphic representation and
touch-sensitive monitors are chosen for the display. The main functional and
operational requirements are:
- switching on/off ;
- display of operational status of all system components;
- simple switch-over of the process sequence, e.g. from one- to two- or three-blend operation;
- automatic shift switch referring to the shift schedule;
- alarm indication of malfunction;
- machine remote control for adjusting and changing the operating mode.
The
user interface is exactly the same as on the machine itself.
Metal detecter
Magnetic metal extractors
Magnetic metal extractors
Fig. 74 – Magnetic extractor (Marzoli)
Magnets
have been used for decades in ducting or in special parts of machines in order
to eliminate pieces of ferrous material. The most effective form of device is
a knee-bend within the feed duct having permanent magnets at the two
impact surfaces. When tufts are driven against the magnets, ferrous particles
are retained and can be removed from time to time. Magnetic extractors provide
only a partial solution to the problem because they can eliminate only
magnetizable metal particles, and let all others pass. Electronic extractors
are needed to remove the other particles, too.
Electronic metal extractors
The
material is fed from an
opening
machine
such as Blendomat (Fig. 75, 1). The next device, normally a fan in front
of the mixing machine, extracts the material by suction (5). Spark sensor (2)
detects smoldering material and metal detector (3) any kind of metal. In either
case, active operating flap (4) is opened by a signal from the detector
and feeds the material into the receiving waste container, which is equipped
with a fire extinguisher device (7) and a temperature sensor (8) to
monitor the container (Fig. 75).
Fig. 75 – Electronic metal extractor (Trützschler)
ComboShield (Rieter)
This
comprises a spark detector, a metal extractor and an eliminating device,
and is built into the transport duct (Fig. 76). The spark detector pivots the
rapidly operating flap as soon as the latter detects sparks or burning
material. The material passes into a receiving container, which preferably
stands outside the room. Simultaneously, an alarm is given and the blowroom
line as well as the filter installation is switched off.
The
pivoting flap remains in the eliminating condition until the line is switched
on again. This device has a second function, the detection of metallic
material. If such a piece of material is detected, the same rapidly operating
flap is pivoted and the foreign material is ejected into a container.
After an adjustable time the flap moves back into its normal position. In
contrast to detected sparks, the blowroom line remains switched on.
Fig. 76 – ComboShield (Rieter)
Waste management
Economy of raw material utilization
Raw
material costs make up more than half the yarn costs. It is unlikely that much
can be done about this, since rising raw material prices are to be expected in
future. Increasingly, therefore, spinners will be forced to improve
exploitation of the raw material. Without doubt, one possibility lies in
recovery of fibers from waste: after all, on average about 50% of blowroom and
carding droppings consist of good fibers. Their recovery is not especially
difficult and the saving in raw material costs is significant, as illustrated
by the following very approximate, and not very exact calculation for
a small spinning mill:
|
Quantity
of raw material processed per year
|
10 000 t
|
|
Total
waste from blowroom and carding room
|
800 t
|
|
Recoverable
waste
|
360 t
|
|
Price
of the raw material (net) per kg (US$)
|
1.32
|
|
Saving
on raw material per year (US$)
|
475 000
|
An
additional advantage of such recycling installations is that a somewhat
higher
degree
of cleaning
can be used in the blowroom machines, since with recovery of waste fibers the
level of their elimination in blowroom and
cards becomes
relatively insignificant.
Fig. 77 – Material flow diagram for raw material and
waste
Quantity of waste material
In spite of the emphasis on the proportion of waste in the
diagram, it is clear that the quantities to be expected here are relatively
small. On average, about 6 - 8% primary waste, consisting of 50% good fibers
and 50% contaminants, can be expected. About 90% of the good fiber elimination
can be recovered as secondary raw material, and this still contains about 6%
trash. Such secondary raw material can be mixed into the same blend up to
a proportion of 2.5% without any effect on quality. Up to 5% can be
blended with hardly noticeable changes in quality. As far as possible, no more than 5% should be returned to the blend (for ring spinning).
Classification of spinning mill waste
A spinning mill produces the following waste, some in significant quantities:
- directly reusable waste;
- dirty waste; and
- dust and fly.
Recycling installation for reusable
waste
Fig. 78 – Integrated recycling
plant by Rieter
Fig. 79 – Rieter recycling
installation
As mentioned above, a considerable amount of waste can
be reused in the same mill by feeding it through a
bale
opener (
waste
opener) into the normal blowroom line. Beyond that, in rotor
spinning it is common to spin useful yarns from waste or by adding waste to the
normal raw material. Since in this case the amount of waste is larger, the
admixing cannot be performed by a single waste opener; a complete
feeding installation as shown in the illustration (Fig. 79) is required. Dirty
waste first has to pass through a special
waste recycling
plant before a portion of it (about 30 - 40% good fi bers) can be
reused.
Recycling of dirty waste
The
various processes in the blowroom create various waste materials which cannot
be reused for textile purposes, such as:
- coarse dirt remaining after recycling;
- fly from the preliminary filters;
- dust from the fine filters.
Dirty
waste consists of a large amount of impurities and a smaller amount
of fibers. The latter can be recycled in different recycling plants.
In
Rieter installations, for example (see Fig. 79), waste from all blowroom
machines and cards is sucked directly through the
UNIclean
B 12
cleaner of the recycling equipment (1) to a mixing bale opener (2). The
mixing bale opener continuously feeds the cleaned material back into the
blowroom line (3). If dirty waste is involved, an additional
UNIflex
B 60
cleaner should be inserted between the
mixing
bale opener
(2) and the point of feed into the blowroom line. This installation can also be
operated in off-line mode if the secondary raw material is not re-blended
immediately but pressed into bales in a bale press (4).
Recycling plant for all types of waste
Almost
all manufacturers of blowroom machines, and several others, now offer recycling
installations. That of Rieter in conjunction with LUWA (Fig. 80) will be
described here as representative of all the others. Primary waste is
pneumatically fed via condensers into the
B 34
mixing opener,
pre-cleaned in the
UNIclean
B 12,
dedusted in the A 21 condenser and cleaned further in the B 51R fine
cleaner. The transport air is always separated from material and fed to the
pre-filter.The yield of good fibers is fed into the bale press. Secondary waste
from the recycling machines and pre-filter is fed into the bale press for black
waste. Since the same types of machines are used in this recycling installation
as in the blowroom, handling is easy for the operators.
Fig. 80 – Recycling system
On-line recycling plant for the entire
spinning mill
Installed equipment can be designed for continuous
(on-line) or batch (off-line) operation. Continuous operation implies that
secondary raw material is blended with the primary raw material again in the
same quantity, and that this takes place permanently and immediately after
recovery. For this purpose, the reclaiming installation can deliver to a
bale
opener (e.g.
waste
opener), or the material can be blown directly into the ducting of
the blowroom line. Here, the reclaiming installation is an integral part of the
blowroom. On the other hand, batch operation implies that the secondary raw
material is first pressed into bales following recovery, and is then fed to the
blowroom in the same way as other bales. In this system, all waste chambers of
the blowroom machines,
cards
and combing machines are connected by suction ducts to central suction
equipment that leads to pneumatic bale presses (or silos). In order to keep the
various types of waste (comber waste, licker-in droppings, etc.) separate from
each other, a bale press is required for each specific type. Such presses
are available from Autefa, Bisinger, etc. If only one bale press is available,
an individual silo must be provided for each type of waste. About three bale
presses (or silos) should be sufficient for a normal cotton spinning mill.
Waste chambers (one or more at a time) are selected intermittently and
cyclically for suction, and the contents are blown into the presses, e.g. first
from all blowroom machines. After automatic changeover to the second press, suction
draw-off, for example of the flat strippings, is carried out. If the
installation does not operate intermittently, then an extra duct is needed for
each waste group. Both systems are used in practice. The Rieter plant is described here briefly by way of an example.
Fig. 81 – A feasible arrangement
for the disposal of dirty waste; Blowroom (a); cards (b); drawframes (c);
combing room (d); disposal installation with silos (1 - 3) and bale presses, or
disposal installation with horizontal bale presses.
The problem of dust and fly
Dust is released at each machine, often in great
quantities, owing to turning-over, plucking apart, etc., of the material. In
processing it is important to ensure that this dust cannot bind with the fibers
again and also that it cannot settle in the atmosphere. Today, almost all
machines up to the drawframe are enclosed as far as possible and connected to
dust extraction lines. Released dust passes immediately into this suction
system, in which it must be separated from the air and carried away.
Dust filtering
Usually
two filter stages are used because a great deal of fly is carried along in
the removal of dust by suction. The stages are preliminary filtering and fine
filtering. These operations can be performed with individual filters or
a central filter.
In
new installations in new buildings a central filter (part of the
air-conditioning plant) will probably be chosen; individual filters may have to
be used in older premises for reasons of space availability and room height.
The dust-laden air flows against a slowly rotating filter drum (Fig. 83,
1). A layer of dust and fly forms, is removed by rollers and falls into
a carriage located beneath the drum. Before the air returns into the room,
it is passed through the fine filter in the form of a filter drum (Fig.
83, 2).
Fig. 82 – Principle diagram of filtration
Fig. 83 – Flow diagram of waste removal plant
Fig. 84 – Panel pre-filter (LUWA)
Fig. 85 – Rotary fine filter (LUWA)
Central filter installations
Complete disposal of fly, dust and waste requires high air
circulation with corresponding energy consumption.Simultaneously, a second
system with high circulation is required, namely the air-conditioning
installation. Of course, it is possible to install a self-contained,
independently operating waste disposal system with its own air circulating
arrangements, and additionally a second system - the air-conditioning
installation – with similarly high air circulation. But it is more rational and
economical in energy terms to combine these two systems into an integrated unit
and to use the air circulation required for the waste disposal system as part
of the air circulation in the air-conditioning installation. The waste disposal
installation should then be incorporated into the air-conditioning system.
Final disposal of waste
Dirty waste materials are preferably collected, baled,
packed and removed so that manual handling is excluded as far as possible.
There are several possibilities for baling and packing:|
Baling density
(kg/m3)
|
|
|
After passage through a condenser, eject or press
into container
|
100
|
|
Fill into sacks via fiber separators (compactor)
|
60 - 80
|
|
Re-used
- heavy-duty bale presses - lighter bale presses |
80 - 120 200 - 250 |
|
Press into cakes or briquettes by briquetting presses
|
600 - 1 200
|
In this form, mainly as briquettes, waste can be composted or burned. The heating value is approximately 4 kWh/ kg (for comparison, the value for heating oil is just over 12 kWh/kg).
Functional description of the Bale Press System (BPS, Fig. 86):
- The textile waste (material) is usually pneumatically conveyed (1) (and separated according to quality) directly from the production plant to the fiber separators.The fiber or waste separators are used as standard separators. It is essential that the dusty conveying air in the fiber separator is discharged into a filtering installation.
- The waste is discharged from the fiber separator (2) into the material silo (3).
- The discharge unit (4) moves the waste from the material silo to the internal material conveying system (8).
- The material can then be fed to the bale press (11) by means of waste separator WS (9).
- Subsequent pressing of the material is performed in the bale press (12).
Fig. 86 – Example: Bale Press
System with pneumatic material conveying
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