Friction spinning

In a friction spinning process, a method is provided for preventing build up of dust and fly etc. inside a friction spinning machine (1) which method comprises the steps of introducing into the machine a flow of filtered air at a pressure just sufficient to substantially prevent the ingress of unfiltered air during spinning. The invention also provides apparatus for performing the method described, which apparatus comprises filter means (19), pressurizing means (20), ducting (22, 23) adapted to permit the outflow of clean pressurized air into the inside of the machine (1) adjacent the or each spinning head (3) at a pressure sufficient to substantially prevent the ingress of unfiltered air during spinning.

This invention relates to improvements in or relating to friction spinning 
and more particularly to the problem of substantially eliminating the 
build-up of dust and fly etc. within the spinning machine during the 
spinning process. 
Open-end or break-spinning machines are known, such as is shown in UK Pat. 
No. 1311420, in which the rotor or turbine spinning head comprises a 
chamber adapted to be rotated at high speed, typically 90,000 rpm, onto 
the inner surface of which is continuously deposited fibrous material 
which is then drawn off as twisted yarn under relatively high tension. The 
Patent describes a method of controlling the atmospheric conditions around 
the spinning rotor which are usually characterised by high temperatures 
caused by the high rotational speeds of the spinning rotor. Such 
temperatures can cause a loss of moisture which impairs the quality of the 
spun yarn and because of the high tensions involved, end-breaks occur from 
time to time. The invention described in the Patent overcomes this problem 
by blowing a current of cooling air onto the exterior surface of the 
rotor, which current of air is prevented from interfering with the normal 
operation of the spinning chamber by being separated from it by means of a 
baffle plate which fits snugly around the portion of the rotor of the 
greatest circumference such that the plate forms an enclosed chamber with 
the part of the housing on the opposite side of the rotor from which yarn 
is spun. 
An alternative method of spinning has been proposed which is not 
characterised by high rotational speeds of the machine parts and hence is 
not affected by the relatively high temperatures normally associated with 
open-end rotor spinning. This alternative method of spinning, which 
utilises a pair of friction rolls, is called friction spinning and is 
described in detail in an article by Dipl-Ing. K. J. Brockmanns in pages 5 
to 23 of the International Textile Bulletin, Yarn forming 2/84 and pages 
15 to 32 of the International Textile Bulletin, Yarn forming 3/84. From 
this article, it is apparent that the major technical advance in respect 
of friction spinning as opposed to open-end rotor spinning is that the 
former employes relatively modest spinning speeds, typically less than 
10,000 rpm but has a much higher throughput of yarn, typically 200 to 300 
meters per minute. 
However, in friction spinning a substantial volume of air is necessary to 
provide the required high pressure suction through the perforated friction 
rollers and trash box and this large volume flow of air tends to draw into 
the spinning machine large amounts of unwanted dust and fly etc. from the 
surrounding environment which then builds up inside the spinning machine. 
Such dust and fly, if it builds up to a sufficient extent, will clog up 
the perforations in the friction rollers and thereby adversely affect the 
pressure characteristics which are necessary for spinning the yarn. The 
ingress of dust and fly etc. will also tend to clog up the exposed working 
parts and ducting within the machine which can also adversely affect the 
quality of the spun yarn. Furthermore, because of the requirement for 
independent access to each spinning head by an operator of the machine in 
order to attend to end breaks etc., it will be appreciated that each such 
head must be provided with a hinged cover having a slot-like aperture for 
receiving a respective doffing tube which projects outwardly from the 
machine. Each such aperture must be a loose fit over the respective 
doffing tube because of the pivotal movement of the cover and consequently 
an air leakage path around the outside of the doffing tube is inevitable. 
The consequences of the ingress into each spinning head of the spinning 
machine of dust and fly etc. is that yarn of poor quality is spun. Whilst 
in a break-spinning machine such poor quality yarn would tend to break as 
soon as it was formed in view of the relatively high tension of the drawn 
yarn, with friction spinning this is not the case since it is inherently a 
low tension process. This means that if poor quality yarn is being spun it 
will continue to be spun by the machine until a sample is taken for 
analysis, after which the situation can be rectified. 
It is known to utilise the principle of over-pressurisation within e.g. 
textile drive housings by providing a fresh air forced ventilation by 
which an excess pressure is maintained within the interior of the housing 
to thereby prevent the ingress of dust and fly etc. Whilst such a forced 
ventilation system can work satisfactorily to prevent e.g. overheating of 
drive motors due to large deposits of dust and fly resting upon them, it 
is not immediately apparent as to how such a system could effectively 
operate within a friction spinning machine which requires large quantities 
of air to be drawn into it in order to operate satisfactorily. If, for 
example, high pressure air hoses were located at intervals along the 
friction spinning machine in order to blow dust and fly out of the machine 
and thereby prevent ingress of it, the result would inevitably be an 
alteration in the flow characteristics of the air required for friction 
spinning, which would give rise to the production of poor quality yarn and 
hence defeat the object of the exercise. 
According to the first aspect of the invention, there is provided a method 
of preventing the build up of dust and fly etc. inside a friction spinning 
machine, which method comprises the steps of introducing into the machine 
a flow of pressurised clean or filtered air at a volume flow rate just 
sufficient to substantially prevent the ingress of unfiltered air during 
spinning. The invention thus resides in the appreciation that by providing 
a supply of clean or filtered air sufficient to provide a positive 
pressure within the machine whilst also supplying the requirements for 
satisfactory spinning, the ingress of dust and fly can be substantially 
eliminated without altering the required flow characteristics of the 
machine. 
According to a further aspect of the invention, there is provided apparatus 
for performing the method described, which apparatus comprises means to 
introduce into a friction spinning machine a flow of pressurised clean or 
filtered air at a volume flow rate just sufficient to supply the air 
required to be drawn through the perforated friction rollers for spinning 
and to provide a positive air pressure within the machine to prevent the 
ingress of dust and fly into the machine which could clog the perforated 
friction rollers and adversely affect the quality of the spun yarn.

Referring to the drawings, an elongate spinning frame 1 is supported at 
intervals by legs 2 above which are disposed a set of forty-eight spinning 
heads 3 arranged symmetrically along each side of the spinning frame 1 in 
two rows of twenty four heads each. At one end of the spinning frame 1 is 
a drive housing 4 containing drive machinery (not shown). 
Each spinning head 3 comprises a sliver inlet aperture 5 adapted to receive 
a sliver 6 from a sliver can 7 from where it is drawn by a feed roll 8. A 
combing out roller 9 beats and separates the sliver into fibres in a 
conventional manner. Large particles of impurities including seed, trash 
etc. liberated by the combing out roller 9 as it rotates is collected in a 
trash box 10 from where it is delivered under suction pressure along duct 
11 to a trash exhaust duct 12 connected to a main trash exhaust pipe 13 
which extends vertically from the housing 4 of the spinning frame 1 and is 
connected to a conventional filtration plant incorporating a suction fan 
(not shown). 
Above the trash box exhaust ducts 12 (shown in FIG. 2) is disposed a main 
air exhaust duct 25, connected at the drive housing end of the spinning 
frame 1 to a single main air exhaust pipe 26 which extends vertically 
therefrom and is connected to the same filtration plant as the trash air 
exhaust pipe 13. 
After each sliver 6 has been separated into fibres by a respective combing 
out roller 9 the fibres are drawn up a transfer tube 14 and fed into the 
nip between a perforated friction roller 15 and an imperforate friction 
roller 16, by which the fibres are spun into yarn 6a. To perform the 
spinning operation, a suction pressure of typically 12,000 Pascals is 
applied to the inside of the perforated roller 15, along the duct 29, from 
a main air exhaust duct 25. From the rollers 15, 16 the spun yarn 6a is 
fed through a respective doffing tube 17 and onto a take-up package 18 
(only one of which is shown) above each spinning head 3. 
The machine thusfar described is generally conventional. 
The apparatus according to this embodiment of the invention comprises a 
pair of rotatable generally cylindrical filter elements 19 within which 
are disposed fans 20 driven by electric motors 21, shown in outline in 
FIG. 2. Above the filters 19 is a main air supply duct 22 which runs along 
the length of the spinning frame 1 and from each side of which projects at 
equally-spaced intervals a set of flexible hoses 23. Each of the hoses 23 
is provided with a respective outlet nozzle 24 arranged such that each 
nozzle 24 is in the general vicinity of a respective spinning head 3. 
Adjacent each of the filter elements 19, is a respective triangular vacuum 
nozzle 27 connected by ducting 28 to a conventional filter plant fan (not 
shown) such that, in use, dust and fly etc. which accumulates upon the 
filter units 19 is continuously removed. They are effectively 
self-cleaning, since each filter element 19 is rotated by a geared motor 
30 and pulley belt 31. 
In operation, as shown by the arrows, air is drawn in through and cleaned 
by each filter element and is then blown by the fans 20, along the main 
supply duct 22 and up into each hose duct 23 such that a balanced flow of 
air is emitted from the nozzles 24 and evenly distributed into the area 
surrounding each respective spinning head 3 inside the spinning frame 1. 
This flow of air forms a barrier which ensures that unfiltered air is not 
drawn into the spinning frame 1 through, for example, the apertures around 
the doffing tubes 17 and the clearances between each spinning head cover 
and the frame. 
In practice, it has been found desirable to ensure that the flow of air 
from each filter unit 19 is supplied to the spinning heads 3 at a volume 
flow rate above that sufficient for the spinning process but only just 
sufficient to ensure that there is no ingress of unfiltered air into the 
machine, typically at a flow rate of 10% above that required for spinning 
such that an even pressure of up to 250 pascals is present within the 
spinning frame above ambient pressure. In particular, it has been found 
that if the flow rate is too great, i.e. there is a considerable outflow 
of filtered air from the machine, this not only tends to be wasteful but 
has the important disadvantage in that the pressure required to produce 
the outflow can adversely affect the pressure characteristics required by 
the friction spinning process. 
It will be appreciated that the invention is not limited to the embodiment 
described but is intended to cover all kinds of apparatus which have the 
desired effect, as stated in the appended claims. For example, instead of 
filter means being provided on the spinning machine, it may be entirely 
separate, such that filtered air is channelled to the machine through 
ducting. It is also envisaged that the ducting could form part of a closed 
cycle in which air is continuously fed under pressure into the machine, 
exhausted, filtered and fed back again and so-on. As a further refinement 
each spinning head may be provided with its own supply of filtered air 
such that in the embodiment described each head is provided with a 
respective hose 23 and nozzle 24, to ensure that the air is evenly 
distributed.