GINNING AND MIXING MACHINES.
(24) When the cotton is ready for harvesting it is picked from the
shrubs by hand. There have been many attempts to pick it by machinery,
but these have not hitherto been very successful. After picking, it is
subjected to the action of a machine called a “gin,” which is sometimes
arranged to be worked by hand, but more often by power. In the latter
case the machines are placed in a shed, and the cotton is brought there
for treatment. The object of ginning is to remove from the cotton the
seeds, which adhere closely to the fibre, and which have of late years
acquired considerable value for oil-producing purposes. In order to
remove them it is necessary that the fibre should be held in some way
while it is submitted to a rubbing or scraping action, by which the
seed is separated. To effectually perform this function great care is
required, as otherwise a quantity of the seed is broken, and the fibres
are rubbed up into “neps.” If either of these effects is produced
additional labour is thrown on the spinner in his subsequent treatment,
and it is therefore desirable to avoid such a manipulation of the
machine as would lead to so undesirable a result.
(25) In Figs. 1 and 2 a single Macarthy gin is illustrated in part
sectional side elevation and front elevation. This is a type which, in
principle, is now largely adopted. It consists of a roller =A=, rotated
in the direction shown by the arrow, by means of a strap passing over
a pulley fixed on the end of the roller shaft. The latter is square,
and is passed through the centre of the roller, fitting a corresponding
hole in the latter, and being carried by suitable bearings fixed on the
machine frame. In constructing the roller =A= the following method is
adopted. Wood segments are fitted together so as to form the complete
cylinder, or the latter may be made in one piece. Having produced the
body, it is fixed on the shaft, and is then turned quite round and
parallel. Upon the surface so prepared a thick covering of walrus
leather =B= is fixed, in which spiral grooves are formed. The rough
surface of the leather, as the roller is revolving, seizes the cotton
fibres as they are fed along the table =F=, which has a grid =G= at
its inner end, a special feed being sometimes fitted. When the fibres
are drawn in by the roller they are taken under a knife blade =C=,
which is fixed above the roller by means of the sets of clamps =D= and
=E=. The clamps =D= bind the blade to its bearings, and those marked
=E= are used to regulate its pressure on the roller =A=. As the roller
occasionally becomes hollow the wisdom of this procedure will be seen.
A crank shaft is placed and driven from the shaft of the roller, and
gives a rapid reciprocating motion to a connecting rod =I=, which has
at its upper end a blade =H=. The height of the blade =H= is regulated
by means of the adjustment of the connecting rod strap, to which it is
jointed, and which can be packed to any desired amount. The blade is
coupled to radius arms =J=, adjustable by nuts at their outer ends, and
oscillating on a rod fixed below the feed-table.
(26) As the fibres are drawn under the upper blade =C=, the lower blade
=H= pushes up the seeds, which cannot pass between the roller and the
blade =C=. In this way the seeds are freed from the fibre, which is
carried forward and thrown off at the front of the machine, or it may
be stripped by a fixed blade. The setting of the blades =C= and =H=
should be arranged so that the necessary pressure is applied to the
seeds to free them, but care must be taken that the lower blade does
not rise so high as to crush them. It should also be set relatively
to the roller, so as not to roll up the fibre by having close contact
with either the roller or upper blade, while effectually removing the
seeds. Other forms of ginning machines are made, including one in which
rollers formed of a number of saws are employed, but their use is not
so large as that of the Macarthy machine, which may be taken as typical.
(27) After the cotton is ginned, it is pressed in large hydraulic
presses into bales of various sizes and weights, ranging from 400
to 600lbs. each. In this form it is imported into this country, and
delivered to the mill-owners. The purchases of the material are made
from samples of a few pounds taken from one or two bales of a lot of
the same brand, and it is essential in purchasing that not only the
“staple” but the condition in which the cotton is packed should be
taken into account. In some seasons the percentage of moisture is much
higher than in others, and in wet seasons a large weight of adherent
sand is certain to be found. This, indeed, is the case always, but it
is much greater after a bad season than when the weather is normal
during picking. The question of the delivered condition of the fibre
is a very sore one commercially, as it results in serious loss to the
millowner, and there is little doubt that in many cases a fraudulent
intermixture of sand is made.
[Illustration: FIGS. 1, 2. J.N.]
[Illustration: FIG. 3. J.N.]
[Illustration: FIG. 4. J.N.]
(28) Whatever may be the condition in which the cotton is received,
the first operation at the mill is to open out the bale and break it
up into pieces of a convenient size. For many years this was conducted
purely as a manual operation, but an arrangement which was made by
Messrs. Platt Bros. and Co., in 1855, and has been working ever since,
is shown in Fig. 3. This consists of a lattice feed table =F=, which
delivers the cotton and brings it into the range of action of an opener
cylinder =C=. The latter opened the material to a considerable extent,
and threw it on to a second lattice =H=, by which it was delivered
to a third one, and conveyed to the mixing stacks in a manner to be
afterwards described. The operation is now almost always carried out
by a machine known as a “bale breaker,” a perspective view of which,
as made by Messrs. Platt Bros. and Co. Limited, is shown in Fig. 4.
It consists of a feed table, placed between the projecting framework,
and is usually of the lattice type. The lattice feed apron consists of
a number of narrow strips of wood fixed to two endless bands passing
round rollers at each end of a longitudinal frame fixed to the machine.
By suitably driving one or both of the rollers a continuous motion
is obtained, and the wood strips being each free from the other no
difficulty is experienced in forming an endless apron or feed table.
The cotton is placed upon the table in large pieces or lumps, just as
these are taken from the bale, and they are carried forward until they
come into contact with the first pair of rollers. There are usually
four pairs of rollers driven by means of the spur pinions shown in the
illustrations. The first pair are provided with coarsely-pitched blunt
teeth or spikes, which seize the cotton and pass it onward to the next
pair, which are of similar construction. The last pair of rollers are
usually made with coarse, longitudinal corrugations, or flutes, as
shown in Fig. 4, which deliver the cotton either on to the floor of
the room, or on to lattice aprons arranged as hereafter noted. The top
rollers are weighted by helical springs in the manner shown, and can
easily yield if any obstruction or unusually large piece of material
passes between them. The speed of the rollers increases rapidly, but
there is a divergence of opinion as to the proportion of increase over
the whole series. It will be well, therefore, at this point to state
the conditions of the case fully.
(29) Before doing so, however, it is necessary to explain a term which
even at this early stage is used, and which is a common one throughout
the whole series of operations constituting spinning. The variation in
the speed of the rollers of the bale breaker is known as its “draught.”
In other words, an elongation or enlargement of the bulk of the cotton
occurs in exact proportion to the velocity of the rollers. Thus, if
the relative speed of the first and last of the series of rollers is
as 1: 30, the draught of the machine is the same. In the case of the
bale breaker the draught results merely in an increase in the bulk of
the cotton, but subsequently it leads to an elongation of the sheet or
sliver into which it is formed.
(30) It being highly desirable that the naturally open fleecy condition
of the cotton shall be restored at the earliest moment, the question
arises, What shall be the draught of the bale breaker rollers? Is it
necessary to do more than break up the lumps of cotton into smaller
pieces, which can be readily treated by the subsequent machines? To
these questions different answers are given. On the one hand, it is
contended that what is required is to reproduce the conditions of
hand breaking, by which the cotton was pulled from the bales in small
tufts ready for delivery to the opening machinery. Another practice
advocated is to so pull the lumps into which the bale is broken up that
the cotton when delivered is in an open fleecy condition. It would be
preferred by spinners if they could obtain the cotton in the loosely
packed condition in which it is received by the Indian spinners, for
instance. As this cannot be done, owing to commercial and transit
considerations, the question arises whether the first stage in the
processes conducted in this country is not the right one to restore
this condition.
(31) Between the two positions formulated there is a wide divergence,
but, to the author, the latter appears to possess the balance of
advantage. There can be no doubt that the preparation of the fibre
cannot be commenced at too early a stage, and, as efficient cleansing
is one of the first objects to be attained, it follows that the earlier
the open condition of the cotton is reached the more readily can
cleaning be effected. It must not be forgotten that care is necessary
to avoid possible damage to the fibres, but, with rollers properly
speeded, there appears to be no reason to expect such a result.
(32) In consequence of the divergent views held, the draught of a bale
breaker varies considerably. In some cases it is only 2: 1, while in
others it reaches 30: 1. The former is the rule adopted by Messrs.
Crighton and Sons, who advocate the first course named, and the latter
that adopted by Messrs. Lord Brothers, who prefer the second. Messrs.
Platt Brothers and Company recommend a wise variation in this respect,
proceeding upon the principle that different staples require different
treatment. Thus one machine made by them has four rollers with a large
draught, this being used for good staples, and producing as much as
90,000lbs. weight in 50 hours. In dealing with Surat cotton, which
is more hardly pressed, two sets of rollers are used, followed by a
beating cylinder by which the cotton is thoroughly broken up (Fig. 8).
In each case it is customary to attach lattices to the machine, by
which the cotton is carried forward and deposited in the mixing bins
(=E= Fig. 13). (See also Figs. 6, 7, and 8). Another method is to treat
Surat cotton by first passing it through breaker rollers, and thence
through a Crighton cylinder, described in Chapter IV. The bale breaker
may in this case be used either singly or as part of the combination.
(33) The rollers are made in two ways. They are cast in one piece and
are mounted upon the shaft; or are built up from a number of discs
threaded and fastened upon the shaft and bolted together. The latter
is the preferable course, the breakage of a few teeth being easily
remedied.
[Illustration: FIG. 5. J.N.]
(34) Before proceeding further, reference may be made to Fig. 5, which
is a transverse section of the machine as made by Messrs. Dobson
and Barlow. The top rollers of the machine, as ordinarily made, are
provided with spring weighting, in order to permit them to rise if an
unusually large piece of cotton is passed between them. If this enters
at one side of the machine it will be at once seen that the roller will
be raised at that side, and that its axis will be angularly disposed to
that of the bottom roller. The two rollers will only be near each other
at one side, and between them, across the whole of the width of the
machine, will be a gradually increasing space through which lumps of
cotton can pass unpulled. This is a defect of more or less magnitude,
but is one which is ingeniously remedied in the machine shown in Fig.
5. Only one line of rollers, marked =U V Y Z=, is used, by two of
which the pulling is effected. Below these the noses of iron bars or
levers, =Q R=, fulcrumed on knife edges, are placed. The bars are a
few inches wide, and extend below the rollers over their entire width.
The cotton passes over these “pedal” levers, which are weighted at
their other end, and yield, as shown by the dotted lines, when an extra
large piece of cotton passes. The weight is sufficient to enable the
cotton to be held until it is pulled by the roller. It will be at once
seen that only the pedals affected by the lump will be depressed, the
remainder occupying their normal relative position to the roller, which
is fixed by the stop shown. In this way the presence of a thick piece
at one point in the width of the rollers does not affect the pulling at
another point.
[Illustration: FIG. 6. J.N.]
[Illustration: FIG. 7. J.N.]
(35) The cotton being palled, it is necessary to mix it. This is
effected by delivering it upon a second lattice, =B= Fig. 13, which
can be made of any desired length, and by which the cotton can be
delivered on to a third lattice =C= running transversely or in any
other direction. Three such arrangements—the sketches supplied by
Messrs. Platt Bros. and Company—are shown in Figs. 6, 7, and 8, but
there is practically no limit to them. By means of these devices as
much as 90,000lbs. weight can be laid down per week by two workmen.
To avoid the risk of fire, the flutes are so arranged as not to come
into contact, but it is advisable to place the machine in a building
removed, if possible, from the main structure.
(36) Having broken up the bale as described, the cotton is in a
condition to be mixed. This operation is one of the most important
in the economy of a cotton mill, and on its judicious and thorough
accomplishment depends very often the production of a profit or loss.
In order to obtain the best possible yarn the longest-stapled cotton
should be used, and should be selected so that the fibres, when spun,
are as nearly as possible of one length. By careful selection a
practically perfect yarn can be produced, but it would naturally be a
dear one. It is, however, possible to apply the same principle in the
production of cheaper qualities of yarn. Briefly stated, the principle
is, that to spin a good yarn it is necessary to use cotton in which the
fibres are of approximately the same length. The longer the “staple” of
the cotton the better the yarn; but, even when short staples are used,
this selection is still essential to success. This does not necessarily
mean that the same grade of cotton should be used exclusively, but,
on the contrary, several can be mixed, provided that the staples are
equal, even if they are not of the same commercial value, and differ in
other characteristics. By a careful selection of cotton a mixture can
be obtained from which a good even yarn of fair strength can be spun,
the cost of which would be lower than it would be if a single good
grade only was used.
[Illustration: FIG. 8. J.N.]
(37) It is the practice in making a mixing to place round the breaker
bales of the various grades which are to compose it. The attendant
takes a layer from each bale in succession, and places it on the feed
lattice of the bale breaker, by which it is broken and partially mixed,
so that when stacked the elements of the mixing are well incorporated.
The size of the stack depends very largely on the requirements of
the spinner, but as most mills now are employed on a small range of
counts, some of them on one or two, it is most usual to make a large
one containing sufficient cotton to last for several weeks. By pursuing
this course there is a very much better chance of getting a regular
quality of yarn, which is essential to the commercial success of the
mill. In taking cotton from the heap it is the best plan to begin
at the top of the face and work downwards in a straight line, as by
this procedure a uniform quantity of the different elements in the
mixing is obtained. It is desirable to make a small stack of the same
classes of cotton as the larger one is to be composed of, and in the
same proportion. By passing this through the various machines a test
can be made of its yarn producing qualities, and the mixture of the
larger stack can be varied so as to remedy any defects discovered in
the smaller one. It is impossible to lay down any definite rule as to
mixings, the production of which is a matter of experience, and can
only be arrived successfully at in that way. Not only must the strength
and cost of the yarn be considered, but also its colour, and it is for
this reason essential that a thorough knowledge of the structure and
characteristics of various growths should be acquired in addition to
one of commercial values.
(38) It will be easily seen, when the operations of the various
machines employed in cotton spinning are considered, how essential it
is that the fibres in a mixing should be approximately equal in length.
Unless this condition is observed there is likely to be a good deal of
loss from fly in the carding engine, and the slivers in the drawing
frame would tend to have the long fibres in the centre and the short
ones on the surface, owing to the difficulty experienced in drawing
different lengths with the same setting of rollers. These remarks are,
of course, only relatively true, as it is possible to mix different
staples economically, but the process is a difficult one. For instance,
in the scutching room, laps, each consisting of cotton of different
staples, can be fed simultaneously on the same lattice, and so produce
a lap of the mixed staples. It is found to give the best results when
the laps are made on the opener and mixed on the intermediate scutcher
in the proportion required. By these means a better mixing is obtained
than if the laps are put on the finishing scutchor only. Individual
experience is the guide to a thorough comprehension of this department
of spinning, and beyond enunciating these general principles no aid
can be given to the student which is likely to be of value. The actual
condition of even the same class of cotton, in different seasons,
varies so largely that a mixture which is valuable one season is
unsuitable in the next.
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