Drafting mechanism for spinning machines

The drafting mechanism comprises an entry roller pair, an intermediate roller pair and a delivery roller pair. An apron hair is mounted such that one of the two aprons projects deeper than the other into the converging space of the pair of delivery rollers, so that the fiber sliver is still diverted, and is thus guided, after the exit or delivery opening of the aprons, on the apron projecting more deeply into the converging space. Further, both aprons are guided sufficiently close to their related delivery roller such that the aprons do not contact these rollers but leave open a minimal air gap, so that only a minimal quantity of the circulating air produced by the rotating delivery rollers can penetrate into the converging space.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved drafting mechanism for 
spinning machines, in particular for air jet spinning machines. 
In its more particular aspects, the drafting mechanism of the invention is 
of the type comprising at least one delivery roller pair together with a 
further roller pair located upstream from the delivery roller pair 
considered in the direction of movement of the fiber sliver or the like, 
the rollers of the further roller pair being provided with respective 
aprons for guiding the fiber sliver, the exit opening of the apron pair 
being so arranged in relation to the nip line of the delivery roller pair 
that the fiber sliver undergoes at least one diversion or deflection in 
the region between the exit opening and the nip line. 
In the course of drafting short staple fiber sliver to yarn or the like , 
with increasing fineness of the yarns there is increasingly present the 
necessity to guide the fibers as far as possible between the nip points of 
a drafting passage. 
This requirement is especially important in so-called jet spinning 
processes, in which drawing frame sliver is drawn by a drafting mechanism 
having only three or two drafting zones into feed material ready for 
formation of yarn by the jet spinning process. 
In addition, in the jet spinning method, the air flows prevailing at the 
circumference of the delivery rollers of the drafting mechanism, caused by 
the high peripheral speeds of approximately 150 m/min., can cause edge 
fibers to be separated or spread out from the body of fibers shortly 
before being grasped by the nip of the delivery roller pair. This 
phenomenon results either in loss of fibers or irregularity in the yarn. 
The separation or spreading of the fibers occurs in the converging space 
or region of the delivery roller pair, that is in the region of the entry 
zone to the nip of the two delivery rollers. In this zone, the 
peripherally directed air flows or air streams of the rotating rollers are 
diverted to air flows or air streams directed substantially parallel to 
the axes of the rollers, which causes the aforementioned undesirable 
separation and/or spreading of the edge fibers. Since the separation and 
spreading of the fibers as a result of these airstreams is highly 
variable, this results in the already mentioned irregularity in the yarn. 
In order to avoid this, it is proposed in German Published Patent 
Specification No. 3,039,149, to displace the exit opening of the apron 
drafting mechanism relative to the nip location of the delivery rollers in 
a direction normal to the "path of the fiber flow" (see claim 2 and FIG. 2 
of the just mentioned German Patent Specification). Through this 
displacement, the fiber path is supposed to evade the transverse air 
flows, that is to say, this fiber path to a certain extent is to bypass 
such transverse air flows, in order to reach the nip in the region close 
to the surface of the adjacent roller. 
The disadvantage of this system is that the peripherally directed air flow 
of the adjacent roller flows through the fiber sliver from one side 
thereof and thus causes transverse bending and from which bent fiber 
sliver fiber ends are spread-out in the transverse flow zone, so that the 
disadvantage which was to be eliminated is reproduced in another manner. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind it is a primary object of the present 
invention to provide a new and improved construction of drafting mechanism 
for spinning machines which is not afflicted with the aforementioned 
drawbacks and limitations of the prior art proposals. 
Another more specific object of the present invention is to substantially 
avoid loss and/or spreading-out of fibers by the action of air streams. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds, the 
drafting mechanism of the present development is manifested by the 
features that, one of the two aprons projects into the converging space or 
region of the delivery roller pair, the fiber sliver is deflected or 
diverted about that apron which projects into the converging space of the 
delivery roller pair, and both aprons are guided close to the delivery 
rollers such that, on the one hand, the aprons do not contact the delivery 
rollers and, on the other hand, the air gap between the aprons and the 
delivery rollers is as small as possible. 
Either the lower or the upper apron can project into the converging space. 
The advantages of the invention are to be seen in that, on the one hand, 
the unguided length of fiber sliver is shorter than in drafting mechanisms 
in which neither of the two aprons projects into the converging space or 
region and, on the other hand, the circumferential air streams of the 
rotating rollers are practically excluded from the converging space, so 
that the irregular fiber spreading and separation of edge fibers is 
substantially prevented, and thus, the regularity of the yarn is improved. 
In a further advantageous embodiment, the upper delivery roller can be 
arranged displaced in a direction towards the upper apron. 
The advantage of this embodiment is that the reduction of the diameter of 
the upper delivery roller, which is normal after a certain operating time, 
can be carried out practically without increasing the size of the air gap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawings, it is to be understood that only enough of the 
construction of the drafting mechanism for spinning machines has been 
shown as needed for those skilled in the art to readily understand the 
underlying principles and concepts of the present development, while 
simplifying the illustration of the drawings. Turning attention now to the 
first exemplary embodiment depicted in FIGS. 1 and 2 there is depicted 
therein a two-zone drafting mechanism 1 of a spinning machine, for example 
a jet spinning machine, which comprises an entry or infeed roller pair 2 
with an upper entry or infeed roller 2.1 and a lower entry or infeed 
roller 2.2, an intermediate roller pair 3 with an upper intermediate 
roller 3.1 and a lower intermediate roller 3.2, and a delivery roller pair 
4, with an upper delivery roller 4.1 and a lower delivery roller 4.2. The 
drafting zone between the entry or infeed roller pair 2 and the 
intermediate roller pair 3 is designated a preliminary drafting zone and 
that between the intermediate roller pair 3 and the delivery roller pair 4 
is designated a main drafting zone. 
In the main drafting zone, a fiber sliver 5, which is to be drafted and 
which is moving in the direction of the indicated arrow at the right-hand 
side of FIGS. 1 and 2, is guided by an apron pair 6 comprising an upper 
apron 7 and a lower apron 8. 
The upper apron 8 is driven by the upper intermediate roller 3.1, and is 
diverted or turned at the exit end by a bar or web 9, while the lower 
apron 8 is driven by the lower intermediate roller 3.2 and is diverted or 
turned at the exit end by a plate 10. The two diversion or turning 
locations of the aprons 7 and 8, defined respectively by the bar 9 and 
plate 10, form the exit or delivery opening of the apron pair 6. 
The lower rollers 2.2, 3.2 and 4.2 and the plate 10 are stationarily 
mounted on a support 11 (indicated with dotted lines), and the upper 
rollers 2.1, 3.1 and 4.1, and the bar 9 are pivotably mounted by means of 
a bracket or yoke 12 (indicated with dotted lines) which is pivotable 
about a pivot point (not shown), so as to be liftable away from the lower 
situated elements 2.2, 3.2, 4.2 and 11. 
The upper rollers 2.1, 3.2 and 4.1, and the bar 9 are resiliently mounted 
in a known manner in the bracket or yoke 12, so that the upper rollers 
2.1, 3.1 and 4.1 and also the upper apron 7 are pressed with a bias 
against the lower rollers 2.2, 3.2 and 4.2 and the lower apron 8, 
respectively. 
The lower apron 8 projects at its diversion or turning location defined by 
the plate 10 beyond the upper apron 7 into the converging space or region 
13 (FIG. 2) of the delivery roller pair 4 such that, on the one hand, the 
fiber sliver 5 undergoes a diversion or deflection at the diverting or 
turning location of the lower apron 8, and, on the other hand, the spacing 
M between the lower apron 8 and the lower delivery roller 4.2 is as small 
as possible but such that no contact can occur between this lower apron 8 
and the delivery roller 4.2. In this manner, on the one hand, the unguided 
length of the fiber sliver 5 is maintained as short as possible and, on 
the other hand, penetration of circumferential air from the delivery 
roller 4.2, rotating in the direction of the indicated arrow, into the 
converging space or region 13 is reduced to a minimum, that means 
practically prevented. 
The upper apron 8, in turn, also arranged close to the upper delivery 
roller 4.1 such that the spacing N substantially corresponds to the 
spacing M in order to perform the same function as previously described 
for the spacing M. 
As a modification as shown in FIG. 3 instead of the heretofore described 
greater extent of the lower apron 8, the upper apron 7 can be made to 
extend further than the lower apron 8 into the converging space or region 
13 in order to fulfill the same purpose. The spacings or distances M and N 
are likewise maintained in the manner previously described. 
It is further mentioned that in such drafting mechanisms the upper rollers 
2.1, 3.1 and 4.1 are generally made of hard rubber and during operation 
wear in such manner that at least once during their operating life they 
are reduced to a smaller diameter, in order to thereby once again obtain 
an as-new surface. Through this reduction to a roller diameter in 
accordance with the roller 4.1.1 (indicated in FIGS. 3 and 4 with dotted 
lines) there occurs in the embodiment according to FIG. 3 an increase in 
the size of the air gap or space N, so that as a result an undesired 
increased amount of circumferential air can flow into the converging space 
13. This increase in the size of the air gap N in the modification 
according to FIG. 3 is somewhat less than in the arrangement according to 
FIGS. 1 and 2, since in the arrangement according to FIG. 3 the upper 
apron 7 projects further into the converging space 13, and thus, the 
diameter difference has a lesser effect. 
In order to practically avoid this widening of the air gap or space N, the 
upper delivery roller 4.1 is advantageously shifted or displaced towards 
the upper apron 7 as shown in FIG. 4. By virtue of this measure, the line 
of contact of the upper and lower delivery rollers 4.1, 4.2 is lower, 
after carrying out the diameter reduction, by an amount corresponding to 
an arc length B circumscribed on the circumference of the lower delivery 
roller 4.2, that is, is displaced further towards the upper apron 7 
relative to the position such upper delivery roller 4.1 assumes without 
diameter reduction. Through this displacement, a substantial part of the 
air gap widening is compensated, that is the air gap N' corresponds 
substantially to the air gap N. The optimal arc length, through which the 
upper delivery roller 4.1 is to be displaced towards the upper apron 7, 
depends upon the type of apron and its arrangement. 
In an arrangement as illustrated in FIG. 4, the arc length C (FIG. 4) 
through which the upper delivery roll 4.1.1 is shifted corresponds 
substantially to one-third of the diameter of the upper delivery roller 
4.1 prior to any diameter reduction thereof. The arc length C extends from 
an imaginary plane E which passes through the rotational axis of the lower 
delivery roller 4.2 and extends perpendicular to an imaginary plane F in 
which lies the rotational axes of the lower delivery roller 4.2 and the 
lower intermediate roller 3.2. 
While there are shown and described present preferred embodiments of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto, but may be otherwise variously embodied and practiced 
within the scope of the following claims. Accordingly,