Spinning unit for open-end spinning machine

A spinning unit for an open end spinning machine is disclosed. The unit includes a rotor having a short cylindrical portion defining a central aperture, a frustoconical portion connected at one end to and converging toward the cylindrical portion, and a portion connected to the other end of the frustoconical portion with air discharge openings. The unit further includes a casing having a first portion, and a second portion connected to the first portion of the casing and surrounding the portion of the rotor connected to the other end of the frustoconical portion to define an annular chamber into which air is discharged through the air discharge openings during rotation of the rotor. The first portion has an inner surface substantially surrounding both the cylindrical and frustoconical portions of the rotor in spaced relationship therewith thereby to provide a relatively long and narrow bent passage defined between the first portion of the casing and the cylindrical and frustoconical portions of the rotor and extending between the central aperture of the rotor and the chamber of the casing.

BACKGROUND OF THE INVENTION 
This invention relates to spinning units for an open-end spinning machine 
and, more particularly, to prevention of entrance of once discharged dirt 
and flies into the rotors of the spinning units. 
In general, each spinning unit of an open-end spinning machine includes a 
rotor with discharge openings through which air is ejected during rotation 
of the rotor. The rotor is surrounded by a casing or cover which is open 
at the bottom for the discharge of ejected air. The rotor has a 
frustoconical portion converging from the largest diameter portion of the 
rotor toward the axis thereof, and a short cylindrical portion defining a 
large center aperture. The casing has a sealing wall disposed about the 
cylindrical portion of the rotor in a manner allowing the rotor's 
rotation. 
The spinning unit further includes a stationary means having a closure 
portion closing the center aperture defined by the rotor's cylindrical 
portion. 
In such a spinning unit, upon rotation of the rotor, air present in the 
rotor is ejected through the discharge openings by the centrifugal force 
applied thereto, thus creating a negative pressure condition in the rotor, 
which condition causes a flow of air toward the inside of the rotor to be 
developed in a fiber inlet channel formed in the stationary means. 
Therefore, individual opened fibers as well as the flow of air are fed 
into the rotor through the inlet channel, and formed into a yarn at the 
largest diameter portion of the rotor. The resulting yarn is discharged 
from the rotor through an outlet channel formed in the stationary means. 
In order to allow the negative pressure created in the rotor to operate on 
the fiber inlet channel of the stationary means as effectively as 
possible, a conventional spinning unit has been generally provided with a 
labyrinth between the short cylindrical portion of the rotor and the 
sealing wall of the casing. Such a labyrinth is shown in U.S. Pat. No. 
3,874,751, for example. However, the labyrinth can result in various 
disadvantages including entrance of once discharged flies, dirt and so on 
into the labyrinth from the side of the casing, and much difficulty in 
forming the labyrinth in the associated portions. 
SUMMARY OF THE INVENTION 
It is therefore a principal object of this invention to provide a spinning 
unit for an open-end spinning machine, which can eliminate the above 
disadvantages of the prior art arrangement by a simple provision for 
preventing once discharged dirt and flies from re-entering the rotor of 
the spinning unit through a center aperture of the rotor. 
In brief, a spinning unit according to the present invention comprises a 
rotor having a short cylindrical portion to define a center aperture and a 
frustoconical portion connected to and converging toward the cylindrical 
portion, and a casing or cover surrounding the rotor. The rotor further 
includes a portion having discharge openings formed therein, through which 
air is discharged during rotation of the rotor. The casing defines a 
chamber to receive the air discharged from the rotor through the discharge 
openings. To keep the central aperture of the rotor as far as possible 
away from the chamber, the casing cooperates with the rotor to provide a 
relatively long and narrow bent passage therebetween, which has a portion, 
on the side of the chamber, inclined radially outwardly toward the chamber 
with respect to the axis of the rotor. The inclined portion of the passage 
may have a varying width, which increases progressively in going from the 
aperture side to the discharge chamber side.

DESCRIPTION OF THE EMBODIMENTS 
Referring to FIGS. 6A and 6B, there is shown a typical prior art 
arrangement, which will be explained hereafter to facilitate the 
understanding of this invention. In FIG. 6A, each spinning unit for an 
open end spinning machine generally includes a rotor 2 defining a rotor 
chamber into which individual opened fibers are fed through a fiber inlet 
channel 1 and directed, while sliding along the inner frustoconical 
surface of the rotor 2, toward the maximum inner diameter portion 3 of the 
same, at which they are formed into a yarn. The formed yarn is then 
discharged out of the rotor through a fiber discharge channel 4. Both 
channels 1 and 4 are formed in a body of stationary means generally 
indicated by reference numeral 20. The body 20 includes a closure portion 
15 slightly extending into the rotor 2 to close a central aperture 6 of 
the same. Provided in the bottom of the rotor 2 are air discharge openings 
5 which extend radially outward and permit air within the rotor 2 to pass 
outward therethrough due to centrifugal force applied to the air during 
rotation of the rotor 2. Upon such discharge of air within the rotor 2, 
the inside of the latter comes to be in a condition of negative pressure, 
which causes a flow of air accompanied by the opened fiber and directed 
toward the inside of the rotor to be developed in the fiber inlet channel 
1. 
In order that the negative pressure in the rotor 2 can effectively affect 
the development of the air flow in the fiber inlet channel 1, it has been 
proposed to form a labyrinth A around the rotor's aperture 6, which 
labyrinth comprises, as best shown in FIG. 6B, an annular coaxial 
depression 7a and projection 7b formed in the end surface of the short 
cylindrical portion defining the aperture 6, and an annular coaxial 
depression 10a and projection 10b formed in a seal ring 9, which is 
attached to a cover or casing 8 to seal a discharge chamber 8a surrounded 
by the casing 8. The annular depressions 7a and 10a receive the annular 
projections 7b and 10b, respectively, in axially and radially spaced 
relationship therewith so as to provide a zigzag passage or clearance 
having a limited width. 
However, various disadvantages have resulted from the prior art 
arrangement. Since the aforementioned labyrinth is in fluid communication 
through a relatively extensive vacancy 9a with the chamber 8a and is 
positioned relatively close to the chamber 8a, undesirable matter or 
debris, such as flies and dirt once discharged from the rotor 2 through 
the discharge openings 5, can enter the labyrinth through the vacancy 9a. 
In other words, since the inside of the rotor 2 is in a negative pressure 
condition while the chamber 8a is in a positive pressure condition because 
of the air discharge from the inside of the rotor through the openings 5 
into the chamber 8a, undesirable matter once discharged through the 
openings together with the air are apt to be forced into the labyrinth 
under the positive pressure in the chamber 8a. After a relatively short 
duration of the spinning machine's operation, a considerable amount of 
flies and dirt will be collected in the labyrinth so that the rotation of 
the rotor may be adversely affected by the trapped flies and dirt. In such 
a case, it is necessary to disassemble the spinning unit concerned to 
clear away the trapped flies and dirt. This is time consuming and 
troublesome. Furthermore, the labyrinth consisting of the zigzag passage 
not only involves difficulty in forming it, but also requires a high 
machining technique particularly where a bearing 12 to support a rotor 
shaft 11 for rotation is supported by elastic members 13, because the 
depressions and projections of the labyrinth must not come into contact 
with each another during possibly eccentric rotation of the rotor shaft 
11. 
The aforementioned disadvantages of the prior art arrangement can be 
eliminated by the present invention, of which various embodiments are 
shown in FIGS. 1 to 5. 
Referring to FIGS. 1 and 2, as in the prior art arrangement, there is a 
rotor 2 having a short cylindrical portion defining an aperture 6, into 
which the closure portion 15 of a body 20 centrally extends with a narrow 
spacing between the inner surface of the rotor's cylindrical portion and 
the outer cylindrical surface of the closure portion 15 to restrict any 
flow of air passing through the spacing. To isolate the aperture 6 from 
the outside of the body 20, a seal member 16 is disposed between the body 
20 and an annular wall portion 9 of a casing 8 surrounding the rotor 2. 
According to this invention, a relatively long and narrow passage 14 is 
defined by a cylindrical outer surface 17 and a frustoconical outer 
surface 18 of the rotor and an inner surface 19 of the annular wall 
portion 9 surrounding the rotor's cylindrical and frustoconical portions 
to cause the aperture 6 to be fluidly isolated from the chamber 8a. As 
best shown in FIG. 2, the narrow passage 14 can be obtained by forming the 
inner surface 19 of the wall portion 9 so as to extend along both the 
cylindrical outer surface 17 adjacent to the rotor's aperture 6 and the 
frustoconical outer surface 18 connected thereto. Since one end of the 
passage 14 away from the aperture 6 is adapted to extend as far as 
possible toward the chamber 8a, the distance between the aperture 6 and 
the chamber's boundary can be increased. 
With such an arrangement constructed in accordance with the present 
invention, because of the increased distance between the aperture 6 and 
the boundary of the chamber 8a, the narrow passage 14 gives much 
resistance to the positively pressurized air in the chamber 8a when it 
back flows therethrough, thus causing the back flow from the chamber 8a 
through the passage 14 to the aperture 6 to be substantially prevented. 
Even if any back flows occurs, it will be prevented from reaching 
substantially into the passage 14, because the passage 14 is bent at the 
junction of the rotor's cylindrical outer surface 17 and frustoconical 
outer surface 18. Furthermore, it is an important feature of this 
invention that the passage 14 is so inclined as to be gradually spaced 
apart from the axis of the rotor 2 as a position in the passage 14 
approaches to the chamber 8a. This feature causes the flow of air 
generated in the passage 14 as an accompaniment of the rotor's rotation to 
be directed toward the chamber 8a by means of differential centrifugal 
force, thereby forcing back the positively pressurized air, which 
hypothetically has flowed from the chamber 8a into the passage 14, toward 
the chamber 8a. 
Thus, it is apparent that the aforementioned bent and inclined passage 14 
having sufficient length serves favorably to increase the distance between 
the rotor's aperture 6 and the boundary of the chamber 8a thereby to 
fluidly isolate the aperture 6 from the chamber 8a. 
With respect to the width or thickness l of the annular passage 14, it has 
been experimentally decided that its minimum value is to be 0.3 mm or more 
in view of the facts that the rotor 2 in rotation must not be in contact 
with the wall portion 9 and its rotation must not be disturbed by a 
frictional resistance to air present in the passage 14. To find an 
allowable maximum value of the passage's width, changes in static pressure 
within the rotor and in the amount of dirt and flies collected in the 
rotor have been measured for various widths of the passage 14. According 
to the experiments on a spinning rotor rotating at a speed of 45,000 
r.p.m. and having an outer frustoconical surface 18 with a 30.degree. 
inclination angle relative to the axis of the rotor, it has been found 
that where the static pressure within the rotor decreases below -300 mmAq, 
the amount of air for transporting individual opened fibers in the fiber 
inlet channel 1 becomes insufficient to maintain the desired straightness 
of each opened fiber, resulting in a decreased yarn strength. The decrease 
in static pressure of the spinning rotor appears to be due to the back 
flow of air from the chamber 8a into the aperture 6. Therefore, it can be 
understood from FIG. 7 that the passage 14 is to be designed to have a 
maximum width of 1.0 mm or less so as not to cause the static pressure to 
be decreased below -300 mmAq. With respect to the amount of dirt and flies 
collected in the rotor, it has been found that although the collected 
amount abruptly increases, as shown in FIG. 8, when the width l exceeds 
1.0 mm, the amount for a width of just 1.0 mm does not unfavorably affect 
either yarn quality or spinning operation. 
Thus, it has been proved that the width of the passage 14 is to be within 
the limits 0.3 to 1.0 mm, and that if it falls within such limits, the 
rotor's static pressure and the amount of collected dirt would both be 
extremely close to those (indicated by the mark "X" in FIGS. 7 and 8) in 
the case of the prior spinning rotor with the labyrinth A of 0.3 mm width 
clearance. 
FIGS. 3 to 5 show modifications of the embodiment shown in FIGS. 1 and 2, 
which modifications disclose a passage 14 having a portion of varying 
width on the side of the chamber 8a. The width is so selected as to 
progressively increase as the clearance 14 approaches the chamber 8a. 
Therefore, the flow of air generated in the clearance 14 due to the 
differential centrifugal force as above-described with reference to the 
embodiment shown in FIGS. 1 and 2 can be subject to less resistance when 
such air flow is directed toward the chamber 8a, and the flowing of the 
air through the clearance 14 toward the chamber 8a can be greater 
facilitated, resulting in effective prevention of the back flow of the air 
from the chamber 8a into the aperture 6. 
In FIG. 3, a portion 19a of the wall's surface 19 provides the continuously 
varying width l.sub.2 with the largest value at the boundary of the 
chamber 8a and the smallest value at the junction with the remaining 
portion of the surface 19, which has a constant width of l.sub.1. The 
lower limit of the width l.sub.1 is 0.3 mm and if the value of the width 
l.sub.1 is equal or close to 0.3 mm, the upper limit of the width l.sub.2 
may exceed 1.0 mm to the extent that there occurs no unfavorable influence 
on yarn quality or spinning operation. In FIG. 4, the portion 19a is 
connected to the remaining portion through a transient surface portion 
19b, which also has a varying width of l.sub.3 with the largest value at 
the junction with the innermost end of the surface portion 19a. 
The number of transient surface portions is not to be limited to one and 
may be selected at will. The surface 19 may include a curved surface 
portion or portions. 
FIG. 5 shows the modified arrangement in which the surface portion 19a 
extends to the end of the short cylindrical portion of the surface 19. 
In view of the above, it will be apparent that many modifications and 
variations are possible in light of the above teachings. It therefore has 
to be understood that within the scope of the appended claims, the 
invention may be practiced other than as specifically described.