Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the manufacture of asbestos
yarns from dis~ersions of asbestos fibre by a process such as
that described in the Complete Spècification of U.K. Patent
824,446. Common to processes of the kind described in this
latter specification are the steps of forming a dispersion of
asbestos in water using at least one surfactant and/or soap as
the dispersing agent, forming a strand or strands from the
dispersion which is thereafter coagylated, for example, by
contact with a coagulant solution, collecting the coagulated
strand or strands and twisting it or them into a yarn,
optionally foll~wed by extracting the residual processing
chemicals to leave a yarn comprised wholly of asbestos. For
practical purposes, this latter step is usually considered to
be a highly desirable, if not essential part of the process.
Yarns made by such a process will be referxed to as dispersion-
based yarns in this specification.
~, In general, dispersion-based yarns are smoother,
lighter and stronger than equivalent yarns made by conventional
` carding and spinning processes. However, they tend to be
stiffer than conventional yarns (lacking the flexibility of
the latter). It is well-known that a yarn made up from a
number of filaments is much more flexible than a monofilament
yarn of equivalent size. Accordingly, one way of increasing
the flexibility of a dispersion-based yarn is to make a number
; of fine yarns and after extracting the processing chemicals,to twist these together into a single yarn. This requires not
only an extra twisting or spinning operation, but also the
ability to produce suitably fine yarns.
A solution which would eliminate the extra processing
step is to form the dispersion into a number of fine strands
which after coagulating the dispersion are collected together
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and then twisted into a single yarn before extracting the
processing chemicals. This does not, however, impart the
desired flexibility to the final yarn, because the fine,
coagulated strands tend to stick together, becoming tightly
bound in the twisting process and removal of the processing
chemicals does not then give a yarn of significantly greater
flexibility.
According to the present invention, in one aspect
there is provided a process for making a dispersion-based asbestos
strand for later twisting to form a yarn, said process comprising
the steps of:-
(a) forming an elongate continuous stream from an
aqueous coagulable dispersion comprised of
asbestos fibres, water and dispersion-forming
chemicals;
(b) coagulating said dispersion in said stream to
form a self-sustaining asbestos fibre strand
containing coagulated dispersion-forming
chemicals together with uncoagulated residues
thereof and water;
(c) whilst said strand is in an untwisted state
removing substantially the whole of the
coagulated dispersion-forming chemicals and
said uncoagulated residues thereof, and
(d) adjusting the water content of the strand to
provide an untwisted strand formed substantially
wholly of said asbestos fibres and containing
not more than 20~ by weight of water.
According to the invention in a further aspect there is
provided the method of making asbestos yarn which comprises the
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step of
(a) providing an aqueous dispersion of asbestos
fibres in dispersion-forming chemicals;
(b) forming at least one elongate continuous stream
of said dispersion and c~ntacting said stream
with a coagulant for said dispersion to form at
least one self-sustaining wet strand of asbestos
fibres and coagulated dispersion-forming chemicals
together with uncoagulated residues thereof and
water;
(c) extracting substantially all of said coagulated
dispersion forming ehcmicals and uncoagulated
residues thereof from the wet strand;
~ 15 (d) adjusting the water content of the wet strand to
;- provide an essentially dry strand having a
moisture content of not more than 20% by weight
allowiny the twisting of said dry strand on a
spinning frame, and
(e) twisting said essentially dry strand to provide
said asbestos yarn.
Where it is desired to make a yarn of greater linear
density, advantageously at least two and preferably ten or
more strands are subjected to the extraction and moisture content
adjustment steps just referred to prior to twisting the strands
together into a yarn. It has been found that removal of the
processing chemicals and drying priox to the insertion of any
twist results in a yarn in which the component strands retain
their identity and are not tightly bound together, so that the
yarn is both softer and more bulky than a yarn made from a
single coarse strand.
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Even where the process of the invention is applied
only to a single strand there is an improvement in the
flexibility of the finished yarn when compared to a yarn
produced from the same strand by a conventional process in
which the processing chemicals are extracted after the
insertion of twist.
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The extraction of the residual processing chemicals
is also extremely beneficial in reducing corrosion of the
conventional textile winding and twisting machinery used;
hitherto this has been very serious practical problem in the
manufacture of dispersion-based asbestos yarns.
Although strands may be made individually, collected,
extracted and stored prior to twisting them together into a
single yarn, it is difficult to ensure that they are for
practical purposes identical as regards their properties. It
is therefore preferred that all the strands which are eventually
to be twisted into a single yarn are formed together and
processed together under exactly the same conditions right up
to the twisting operation. This may with advantage be
accomplished by using a single, multiple nozzle extrusion head,
each nozzle being supplied with dispersion from a common supply
reservoir fed by a metering pump so as to produce a number of
identical or very nearly identical filaments.
he number of nozzles employed to make a given yarn
will depend on the yarn nature of the product desired. For
a medium weight yarn in the range 500-1000 tex, the number of
nozzles will be of the order of from 20 to 50. A further
factor is that individual strands of less than about 10 tex
are difficult to process under normal production conditions.
Coagulation of the extruded strands may be carried
out in a number of ways, but it is preferred that each strand
is extruded downwardly through a nozzle, and allowed to fall
under gravity through an air gap into a bath of coagulant
solution, where it is eventually received on a slowly moving
mesh belt. The use of an air gap prevents the problems caused
by entry of coagulant into the nozzle, causing premature
coagulation.
Collecting the strands on a mesh belt enables them
to be handled whilst in the coagulant bath and then withdrawn
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from it without any other handling operation which might
damage them. It also facilitates transfer of the strands to
the next process step in which the residual processing
chemicals are removed. This latter may ~e effected by using
at least one solvent liquid, or by using heat to volatilise
the organic material. One example of a solvent extraction
process is described in detail in U.S. patent specification
3738~05 and a heat extraction process is described in U.S.
patent specification 3452532.
In either system, it is advantageous to thoroughly
wash and de-water the strands, thereby removing excess coagulant
as far as is practicable before the extraction step.
Conveniently, hot air could also be used for this purpose.
After solvent extraction, the strands should be
dried, preferably allowing them to retain a fairly small
moisture content to help reduce dust formation in the twisting
operation. Where heat extraction is employed, the desired
small moisture content may be provided by "conditioning" the
strands; that is, by subjecting them to a moistening process.
This is very important where the extraction is carried out by
heating, because the strand will have a very low moisture
content after extraction.
Hitherto, the twisting of medium weight dispersion-
based yarns has generally required the use of flyer frames or
pot spinning in order to deal with the relatively large water
content of the unextracted strand, because the mass of the
wet strand usually causes excessive ballooning on ring frames.
However, the dry strands which can be produced according to
the present invention are light in weight and can readily be
twisted on a ring frame, using a rather lower twist factor
than for a wet strand. The lower twist appears to help in
producing a bulky yarn which gives good "cover" when processed
into fabric.
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The invention also includes both yarns and never-
twisted strands produced by a process according to the invention
and textile products made from such yarns or strands.
In order that the invention be better understood, a
preferr~d embodiment of it will now be described by way of
example with reference to the accompanying drawing in which
the sole figure is a schematic diagram of part of a dispersion-
based asbestos yarn production unit.
In the diagram, asbestos dispersion 1 flows down a
nozzle 2 into a funnel 3 through which coagulant liquid 4 flows,
the funnel being part of a constant head box unit 5. Coagulant
is pumped into the unit 5 through a pipe 6 and escapes either
through the funnel 3 or over a weir 7, the latter returning
.
the coagulant through pipe 8 for re-circulation.
; Dispersion emerging from the nozzle 2 into the
coagulant stream forms a strand 9 which is drawn down by the
coagulant from the funnel into a short, flexible tube 10, the
free end 11 o~ which is travexsed with a generally circular
motion to deposit the strand and coagulant stream onto a moving
endless wire mesh belt 12. Surplus coagulant falls through the
belt into a tank 13, from which it can be re-circulated or
recovered. The belt carrying the strand then passes under a
water spray generated by a first "rainbox" 14, the excess
liquid being removed by a first roller nip 15 and the surplus
wash liquor plus coagulant is collected in a tank 16.
The washed and de-watered strand is then carried by
the belt under spray nozzles 17 which spray a solvent system
onto the strand, surplus/spent solvent plus residual processing
chemicals from the strand being collected in tank 18. A second
roller nip 15a assists in removing liquid from the strand prior
to its passage under a second rainbox 14a which sprays wash water
onto the strand. Excess wash liquid is then removed by a third
roller nip 15b and collected in a tank 19.
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The strand is then carried through a hot air drying
chamber 20 and finally collected off the end of the belt at
21. The "dry" strand contains less than 20~ by weight of
water, the precise water content being adjustable by changing
the drying air temperature and/or the speed of the belt. The
dry strand may be reeled or even twisted into a yarn directly
from the belt.
A plurality of strands can be extruded on to a single
belt and processed together prior to twisting into a single
yarn.
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