[0001] This invention relates to the roller drafting of fibres.
[0002] The purpose of any drawing operation, whether for natural or synthetic material,
is to reduce the weight of the material being fed into the machine whilst at the same
time parallelising the fibres. Basically this is done by means of two sets " rollers
with a bed of pinned fallers between them. The material, fed through the first set
of rollers, known as the feed rollers, is penetrated by the pins of the fallers which
move in the same direction as the material. The second set of rollers, i.e., delivery
rollers, through which the material passes on leaving the fallers run at a greater
speed than that of the first set thus drafting the material and reducing its weight.
However, with some natural materials and flax, in particular, the delivery rollers
perform a dual function. As well as the drafting of the material, the fibres themselves
are actually sub-divided or split so as to create finer fibres and to increase the
number of fibres in the cross-section, which in turn, means that when the spinning
stage is eventually reached a finer and stronger yarn can be produced. In order, therefore,
to accomplish this splitting operation it has been common practice to use a hard wooden
pressing roller against a steel driving roller.
[0003] It has always been recognised that there is an inherent drawback with wooden rollers
in that the surface becomes uneven with dents, scratches, etc., with the result that
they require to be turned on a lathe to restore the smooth surface and this had to
be done about every two or three days. However, if the machine speed is increased
to give the higher production rates now required, the wooden roller becomes disfigured
after only about ten or fifteen minutes which is unacceptable. If a rubber pressing
roller is used then if the rubber is soft enough to draft the material it does not
sub-divide it, and with hard rubber not enough traction is created between it and
the bottom roller and the flax slips without drafting or delivering the sliver.
[0004] In accordance with the invention a drawing frame for drafting has at least one roller
positioned downstream of the nip of the drafting rollers, the downstream roller acting
with a co-operating roller to split the fibres after they have been drafted by the
drafting rollers.
[0005] Apparatus in accordance with the invention thus allows the material to be merely
drafted without splitting or with only partial splitting at the nip of the drafting
rollers, whilst splitting or further -splitting of the fibres is carried out downstream
of the nip of the drafting rollers.
[0006] One advantage of such an arrangement is that the heavy pressure originally required
on the wooden roller in order to effect both drafting and splitting is either no longer
necessary or it may be more evenly distributed and the "life" of the roller may be
extended to an acceptable span. The drafting rollers may now be of rubber since it
is no longer required to split the fibre or of any other suitable material.
[0007] A production rate of 80 to 100 metres per minute may be possible using a drawing
frame in accordance with this invention.
[0008] The invention will now be further described by way of example with reference to the
accompanying sketch drawings in which:-
Figure 1 is a diagrammatic illustration of the rollers of one embodiment of drawing
frame in accordance with the invention, and
Figure 2 is a perspective view of a different embodiment in accordance with the invention.
Figure 3 is a view similar to Figure 1 but of a still different embodiment.
[0009] Referring to Figure 1 a sliver 2 of flax which may be about 10 inches wide is fed
between a set of three feed rollers 4 so as to enter the frame at for example, a weight
of about 150 grams per metre. The sliver then passes through a standard faller bed
6 and the sliver then passes between the nip of two drafting or delivery rollers 8,
8'. The lower roller 8' is a steel driven roller and the surface of the upper pressing
roller 8 is of rubber, having a shore hardness of 75 on the A scale.
[0010] The rollers 8, 8' are rotated at about ten times the speed of the feed rollers 4
to produce a draft of ten.
[0011] The lower roller 8' is a steel driven roller and the upper pressing roller 8 is of
rubber.
[0012] The sliver is then fed in a relaxed condition without further drafting to a further
pair of "splitting" rollers 10, 10' located downstream of the delivery rollers 8.
The lower splitting roller 10' is driven and the upper roller 10 may be wooden or
may be of a very hard rubber or plastic or Tufnol or indeed iron or steel. Alternatively
it has been found that it may even be of the same rubber as the drafting roller. The
fibres are split as they pass between the splitting rollers and the sliver of weight
of about 15 grams per metre is fed into a standard can 12.
[0013] Referring to Figure 2, the arrangement of rollera is similar to that of Figure 1
but only two of the standard fallers 6 being shown for the sake of clarity. The set
of splitting rollers however comprises three rollers 10, namely, two lower driven
rollers 10' and 10", and a single top or pressing roller 10, which is cradled between
the two bottom rollers to create two nips so that the splitting action is enhanced
and/or the life of the top roller 10 may be extended due to the reduction in pressure
applied to it and/or by the better distribution of the pressure between the top roller
and the bottom roller 2.
[0014] Referring to Figure 3 the feed rollers 4 are omitted for clarity. An additional roller
8" is positioned downstream of the bottom drafting roller 8' with a pressing roller
8 cradled between them. The material is drafted between the nip of the bottom drafting
roller 8' and the pressing roller 8 and then splitting is effected between the nip
of the additional bottom roller 8" and the pressing 'roller 8. Any suitable pressure
arrangement, as diagrammatically illustrated, in which load is applied through a pivotted
arm 14, may be employed. By altering the direction of pull on the pressing roller,
as illustrated by the alternative position of the arm 14, shown in dash lines, concentration
of load towards either of the bottom rollers, or equally between the two, may be effected.
[0015] The pressing roller may be of wood or any other suitable material including rubber.
[0016] Instead of a single broad sliver being fed through the machine a plurality (e.g.
four) of narrower slivers may be fed in, side by side, and delivered into the same
number of cans from standard coiler heads at the front.
1. A drafting frame for drafting of textile fibres, having feed means and a pair of
drafting rollers positioned downstream of the feed means, characterised in that at
least one additional "splitting" roller is positioned downstream of the nip of the
drafting rollers, the "splitting" roller acting with a co-operating roller to split
the fibres after they have been drafted by the drafting rollers.
2. A drafting frame as claimed in Claim 1 wherein the surface of the "splitting" roller
is of rubber.
3. A drafting frame as claimed in either of the preceding claims wherein a pair of
'splitting' rollers are provided separate from, and downstream of, the pair of drafting
rollers.
4. A drawing frame as claimed in Claim 3 wherein a third "splitting" roller is positioned
adjacent the lower splitting roller of the said pair also co-operating with the top
"splitting" roller of the said pair, the top roller providing a relatively upstream
nip with one lower splitting roller and a relatively downstream nip with the second
lower splitting roller.
5. A drawing frame as claimed in either of claims 1 or 2 in which the splitting roller
is positioned immediately downstream of the lower drafting roller of the said pair
of drafting rollers, to co-operate with the top drafting or pressing roller, the pressing
roller providing a relatively upstream nip with the lower drafting roller and a relatively
downstream nip with the splitting roller. A drawing frame as claimed in Claim 6 in
which the load applied by the upper pressing roller on the lower drafting roller and
the splitting roller may be adjusted both in size and in direction.