Journal of the Textile Institute Proceedings
ISSN: 1944-7019 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/jtip20
QUALITY CONTROL IN WOOLLEN YARN
MANUFACTURE
R. T. D. Richards
To cite this article: R. T. D. Richards (1961) QUALITY CONTROL IN WOOLLEN YARN
MANUFACTURE, Journal of the Textile Institute Proceedings, 52:11, P620-P625, DOI:
10.1080/19447016108688594
To link to this article: http://dx.doi.org/10.1080/19447016108688594
Published online: 05 Jan 2009.
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Date: 12 June 2016, At: 19:58
QUALITY CONTROL IN WOOLLEN
YARN MANUFACTURE*
R. T. D. Richards
Wool Industries Research Association
An outline is given of the control of count and twist possible in woollen yarn manufacture.
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COUNT AND TWIST VARIATIONS
When a spinning machine has been stopped and twenty yards of each end
of yarn have been sampled, it has been known for the count readings to have
extremes which differ by an amount (the range) of half the average count :
such a ratio value of a half has been attained even when sampling only some
of the threads. The ratio of the range to the average count can often be
reduced to a third, and then to a quarter, after acting on the results of only a
few tests at the condenser and the hopper of a card.
Usually, the first step is to reduce the variation from thread to thread across
a condenser. The aim should be to reduce the range of the counts of all
slubbing ends across a card to an eighth or less of the average count of the
ends. For all carding machines with an intermediate-feed layering from side
to side, whatever the manner of condensing, particular attention should be
given to the uniform layering of the intermediate feed across the carder feed
sheet and to seeing that the layering is satisfactory at the sides. The old idea
of using a metal rod in place of the thong or tape at the Scotch feed to control
sliver tension has much to recommend it.
Next, it is advisable to check the variation along the web as a whole, either
automatically and continuously, using an instrument such as the recording
part only ofthe WIRA/BEP Autocount, or by weighing successive condenser
doffs when equal yardages of slubbing have been produced for each doff. The
first method also provides an excellent means of checking the over-all performance of the card. A few firms are showing a greater interest in estimating
the counts of both yarn and slubbing from the total weight and total length on
respective doffs from the machines. Using the total weights and total lengths
ensures good estimates of the over-all count and provides a basis for the
calculation of the spinning draft, particularly for low-twisted carpet or
blanket yarns.
As a result of any sensible form of checking, modifications are often
necessary at the hopper or to the instructions for filling the hoppers, particularly if the hoppers are ofthe older types where the weighings are sensitive to
the amount of fibre in the bin of the hopper. To maintain ratios ofthe range
to the average count of less than a quarter when the samphng is done as above
needs a determined and sustained effort by both testing and carding staff. An
ultimate practical target for many mills for this ratio would be a fifth or a
sixth, though, in a few mills spinning expensive blends with great care, it may
be possible to achieve a seventh or an eighth of the average count.
•Based on a lecture given to the Kidderminster and District Section of the Textile
Institute on October 20th, 1960.
P620
The variations in twist when short lengths of yarn are considered can be as
great as those for count, particularly for some of the twist periodicities apparent in mule-spun yarns. The first aim should be to ensure that the average twists
for each partofablendspunondifferentmachinesshould beequal. Presumably,
if the lowest average twist is really satisfactory, this is the twist value to aim
at for all machines. Jt should also be possible to reproduce a twist for a
similar blend processed at a later date. Jt is better to concentrate first on the
yarn count, since the mere fact of greater uniformity of count invariably
means that, if desirable, slight reductions can be made in the twist. It is
always advisable to check for twist directly rather than indirectly by noting
the yarn breaking load.
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INTERPRETATION OF RESULTS
Successful quality control schemes focus attention on the machines and
blends processed by them. This is most desirable, and the position and manner
of control should be decided after studying the basic details of the machines
and process variations. The details often provide ideas on how to maintain
and even improve good processing.
Increasing emphasis should be given to the reduction and, if possible,
elimination of variations in the earlier processes, so that a later process does
not have to contend with unnecessary variations, which often cannot be
adequately dealt with at this stage. For example, whereas it is not too serious
that the oil contents of ten-pound lots within a blend vary after blending, it is
serious if undue variation of slubbing count at the condenser is allowed to
persist. Neither mule nor frame spinning, whether the latter is separate or
combined with the card, ehminates much of the count variation present at
the carding condenser. As much information as possible is desirable about
the slubbing at the condenser, and this information is required both for the
end-to-end variation across the condenser and for that along the web as a
whole.
If, for some yarns, suthcient conlrol cannot be achieved as a result of the
information obtained by reeling, then cops of yarn must be graded to reduce
the effect of the residual variation across the condenser. This could be done,
for example, by the WJRA Cop Grader, where grading cops with a constant
length of yarn on them gives batches of cops whose average count is between
two known limits. Decisions can then be made about how the batches can be
selected for doubling or twisting. For a reduction in variation along the web
as a whole, the WJRA/BEP Autocount, operating automatically as a process
controller, can be used.
The practical reasons for measurement and possible control of variations
should be appreciated and understood thoroughly ; it is not enough just to
express satisfaction with a control scheme planned only on paper. There is no
doubt that one of the main advantages ofa co-ordinated scheme of control is
that proper use can be made of the undoubtedly great store of craftsmansliip
that exists among many of the technical staff in mills. A good craftsman is
most valuable to a firm and he should be encouraged and assisted to give of
his best.
Since variations exist, it is vital to isolate their source or sources whenever
possible. This often reduces the chances of studying the wrong variables when
P621
assessing, in the future, the machines or the blends. For example, minute-tominute (weigh-to-weigh) variations at the hopper do not cause the count
variations which are recorded at the condenser. This is because the irregularities are smoothed out by tbe reservoir of fibres on the card. However, it
is vitally important that the hopper delivers equal amounts about each five
minutes for a carpet card. Furthermore, the nearer the source of the variation
is to the condenser, the more it has a chance to affect the slubbings as the
reservoir becomes less.
The results obtained by testing must be interpreted usefully to make the
most of the test procedures. This interpretation is most important to the
success of any quality control scheme and it is here that teamwork and
co-operation between all members of staff can prove so beneficial to a firm.
Once some definite success has been obtained at this stage of interpretation,
the future of a quality control scheme is hardly in doubt. However, it must he
realized that progress is rarely achieved quickly.
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PERIOD OF INTRODUCTION
As a workable control scheme develops, the early sets of figures prove to be
only a start, and a reasonable amount of systematic knowledge about the
working ofthe machines and the behaviour ofthe blends is built up only after
about three years. Sometimes the period is shortened to two years, but more
frequently four years are required. This longer period gives time to attend to
the major machine-maintenance needs often discovered by the testing methods
introduced. The conversions of frames to those having a double nip at the
front rollers is a good example. Another fairly frequent discovery is the
inadequacy of older hoppers to deal with the higher production rates
demanded of them.
This period of three years is also necessary, so that the testing and processing
staff become fully acquainted with each other's problems. Much of the
textile industry is a craft industry and many ofthe traditional methods used
have a sound basis, so it is not enough to condemn a testing method after a
superficial examination. The production staff should also realize what
tremendous help can be provided by the results of measurements, carried out
as scientifically as possible, of the products or the machines.
TESTING ROOM
The testing room should be as near as possible to the production departments, but noise and vibration should be kept to a minimum. Preferably, the
room should not be subjected to extremes of temperature, and direct
sunlight should be avoided. Control of temperature and humidity is advantageous but practical results in mills suggest that this not essential. Much of
the checking of yarn count and breaking load is of a comparative nature, and
comparatively large changes of temperature and humidity are necessary to
alter the count by more than a twentieth ofthe average. Care should be taken
to avoid extreme conditions in testing for yarn breaking load when the blend
contains a considerable proportion of fibres with a low wet-strength.
However, a continuous record should be kept with a self-recording temperature-and-humidity instrument. In the previous section, it has been suggested
that three years is a typical period for the introduction of a control scheme
P622
and, after this time, a decision should be made concerning automatic control
of temperature and humidity.
All testing equipment should be as simple as possible and maintained so
that results are dependable. Maintenance is essential to ensure that both
testing and production staff have confidence in the results. Advice about
suitable equipment has been given to member firms in W.I.R.A. publications.
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CALCULATIONS AND CONTROL CHARTS
Many a successful control scheme in woollen yarn manufacture operates
with comparatively few calculations ; for example, no coefficients of variation
are used. Simple averages and clear graphs provide sufficient and excellent
summaries of results which are understood by all members of staff. Any
calculations should provide the utmost technological information with the
least amount of complication. The statistics required are numerical facts
systematically collected about the blends, machines, and processes.
It is desirable to have as effective a control of the machines and processes
as possible before attempting statistical control with limit lines, for example.
The function of control charts is merely to look for evidence of non-random
effects and, once this evidence is forthcoming, the production or technical
staff must be called in. It is their function to discover, if possible, the source
of the variation and to decide how it can be eliminated. Jf it cannot be
eliminated, then the testing staff must discuss with the production staff how
large is the variation from a technological viewpoint and in what manner it
can be minimized.
An illustration of this is the failure of firms to obtain control limit lines
which are close enough, when testing for woollen yarn count at the spinning
machine, until a systematic and thorough scheme of testing and control is
carried out at the card condenser. This failure proved costly to one firm
spinning carpet yarns, and improved yarn count regularity was eventually
achieved, after some years, by concentrating attention on the card condenser
rather than on control limit lines. There were very few clues to draw attention
to the real cause of the variation, namely, that from end to end across the
condenser. A further illustration is when initially the limit lines are arbitrarily
set too close and it proves difiicult to have some results between them because
only coarse differences in change wheels are available. Incidentally, firms
purchasing spinning frames should find out how small are the draft and twist
changes provided and how convenient it is to achieve such changes.
One feature of a good practical control scheme is that ultimately far fewer
changes than previously have to be made by the production staff. This
results, not only from the reduction in variation and better machine maintenance, but also from the greater confidence of the production staff arising
from their increased knowledge about count and twist variations and when
these are liable to cause faults. The emphasis in spinning is on the draft and
insertion of twist rather than on an attempt to correct for variations in
carding.
THE TECHNICAL
MANAGER
Real success has often been achieved with control schemes when a technical
manager or director is in charge of the scheme. Some of the reasons advanced
P623
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by firms for having such a manager are now given.
(1) He would have time to investigate innovations suggested in textile
literature with a view to their adoption.
(2) He would deal with problems arising from the increased tendency
to introduce instruments in the textile industry. The WIRA/BEP
Autocount, whether used as a recorder or controller at the carder web,
is an important example.
(3) He would make detailed technical reports, assessing the increasing
amount of new machinery becoming available. A typical report may
survey the implications with respect to the number of spindles, power
requirements, etc., of introducing frames with larger packages of woollen
slubbing and yarn.
(4) He would ensure thai the produciion and sales managers are able
to give full attention to their duties. His work would enable the sales
department to quote specific delivery dates more confidently.
(5) He would enable the trained production staff to have time to attend
to the mainlenance and keep the machinery in good running order for
maximum production. There are many instances where lack of attention
to machine details has ultimately caused lower quality and efficiency.
In many firms, an increasing amount of the lime of such staff is taken up
by unco-ordinated and wasteful testing ; proper maintenance and
supervision are neglected and irreparable damage is done to the machines.
This neglect has often increased variations and so this unorganized
testing, aiming at control, has defeated its purpose.
In addition, having a man on the staff with time to apply his wide knowledge
of the basic principles of the machines or processes would give the firm more
detailed information about the capabilities of the machines, from both a
technological and an economic viewpoint.
Recent experience has shown that, when a reasonable and established
control scheme is allowed to lapse, processing troubles are encountered later.
These troubles do not arise immediately and periods of up to five years have
been known before there was a definite change in the frequency of queries on
yarn faults. The chief cause of lhe lapse of a control scheme has been the
appointment of some or all of the testing staff to other positions in the firm.
COST AND BENEFIT
The size of the testing staff, in addition to the technical manager, depends
on the amount of testing required. For example, a woollen spinning plant
vvith twelve carding machines would require two junior staff to carry out the
physical testing. For carpet-yarn spinners with twelve cards and a production
of five million pounds weight of yarn per annum, the outlay on equipment
and salaries for the testing staff, including the manager, would mean oneeighth of a penny per pound of yarn. Many firms regard most of the outlay
on testing as returnable in various benefits and as a form of insurance premium
covering quality.
Finally, returning to the task of attempting at present to control the count
and twist of woollen yarn, it can be staled emphatically that experience in
mills has shown that, when the control is on the lines noted, the immediate
aim of increased production of a belter quality product for a given outlay
is achieved.
P624
ACKNOVVLEDGRMENTS
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The author acknowledges the advice and encouragement of Dr. A. B. D.
Cassie, Director of Research, Mr. G. H. Thorndike, Head of the Woollen
Carding and Spinning Department, and other colleagues of the Wool
Industries Research Association, and the directors and staffs of many firms
producing woollen yarns.
THE SELF-OSCILLATING INDUCTION MOTOR
AS A TRAVERSE MECHANISM FOR
CONE-WINDING MACHINES
E. R, Laithwaite, G. F. Nix, D. Brurmschweiler*,
and J. Biiia't
Elcclikal Engineering Dept., Manchester University
An account is given of the historical development of sclf-oscillaling lincar
induction motors applied to traverse the yarn guide of cone- and cheese-winding
machines. The limitations of the first e.xperimental machines are discussed,
and a description is given of recent developments designed to give improved
performance.
INTRODUCTION
Of the various factors which determine the maximum speed of winding
attainable in cone- and cheese-winding machines, limitations imposed by
the method of traversing are usually of considerable importance. This is
especially true when considering the winding of yarns for which it is found
necessary to have a positively reciprocated guide. The guide is moved by a
cam at approximately uniform speed in the body of the traverse, the reversal
at the traverse extremities being almost instantaneous. The substantial
forces encountered at reversal tend to fracture the connection between the
cam follower and the yarn guide and cause wear on the rubbing surface.
Under the most favourable conditions, using very light reciprocating parts,
the maximum rate of operation which can be sustained in mill practice is of
the order of 600 traverses per minute over a 6-in. length, although speeds
50% greater than this can be achieved experimentally. The majority of
machines at present in use probably operate at speeds little higher than 450
traverses per minute.
Much higher rates of traverse can be obtained by using a grooved drum
which simultaneously drives the package by surface contact and traverses
the yarn without the interposition of a yarn guide. With this type of motion,
there is virtually no mechanical limitation to the speed of traversing, but the
yarn tension required to maintain the yarn in the groove is now the limiting
factor and the motion is suitable only for yarns which can be wound under
*Now with William Hollins and Co. Ltd.
fNow with Sao Paulo Alpargatas S.A.
P625