Apparatus for separating snakeskins and fines from polymeric pellets

Apparatus for separating snakeskins and fines from pellets in a collection of polymeric material wherein a first nozzle impinges the collection of polymeric material in a stream of air on a moving screen having a mesh size such that the screen will allow the air and fines to pass but will retain the pellets and snakeskins, the air stream carrying the fines through the screen into a closed compartment. A second nozzle is positioned to allow air from the closed compartment to move upwardly through the screen at a different location from the first nozzle to lift and remove snakeskins from the screen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to apparatus for removing fines and snakeskins from 
pellets in a collection of polymeric material. 
2. Description of the Prior Art 
It is known to use certain apparatus for removing fines or dust from a 
collection of polymeric material. Other apparatus is known which is 
suitable for removing angel hair or snakeskins from collections of 
polymeric material. The apparatus of this invention effectively separates 
both fines and snakeskins from pellets in a collection of polymeric 
material. 
SUMMARY OF THE INVENTION 
Apparatus for separating snakeskins and fines from pellets in a collection 
of polymeric material wherein a first nozzle impinges the polymeric 
material in an airstream on a moving screen at a first location, the 
screen having a mesh size such that fines and conveying air will pass 
through the screen while pellets and snakeskins will be retained on the 
screen. The airstream passing through the screen enters a closed 
compartment and exits from the compartment in an upwardly direction 
through a second nozzle positioned at a second location to lift snakeskins 
off the screen and remove them from the pellets.

DETAILED DESCRIPTION OF THE INVENTION 
In the manufacture of fibers and other products from polymeric materials, 
these polymeric materials frequently exist at some point in the 
manufacturing process in the form of beads or pellets. For example, in 
making polyester or nylon fibers a polyester or nylon polymer is melt spun 
to form large strands or rods which are cooled and cut into pellets. The 
pellets are conveyed by a pneumatic conveying system from the cutting 
station to another station for further processing. In order to prevent 
settling and maintain movement of the pellets in the conveying system, it 
is necessary to move the pellets through conduits or tubes in a stream of 
air traveling at a relatively high velocity. When a pellet traveling at 
this velocity contacts the wall of the tube, frictional heat will melt a 
portion off the pellet and leave a tissue-thin strip of polymeric material 
attached to the inner surface of the tube. This thin layer of polymeric 
material adhering to the surface of the tube will eventually break loose 
from the tube, travel with the pellets, and contaminate the process 
downstream. These thin strips of polymeric material which are deposited on 
the walls of the tube by the moving pellets are referred to as 
"snakeskins" or "angel hair". 
It is desirable to remove these snakeskins from the polymeric pellets in 
order to obtain a uniform final product. Also, the cutting and conveying 
of the pellets forms a certain amount of dust or fines which also should 
be removed from the pellets prior to melting the pellets to form the final 
product. 
Referring now in detail to the drawing, there is shown an enclosure 11 
having secured thereto a dished cover 12 to form a sealed or closed 
separation chamber, the enclosure 11 and the cover 12 having a circular 
cross-section. A plate 13 secured between the enclosure 11 and the cover 
12 serves to divide the chamber into a lower compartment 16 and an upper 
compartment 17. 
A circular mesh screen 20 is mounted for rotation above the plate 13, the 
screen being attached to a rim 21 which rests on bearings 22 secured to 
the cover 12. The screen is driven by a gear motor 23 mounted on a bracket 
24 attached to the cover 12 and acting through a drive shaft 27, the 
screen 20 being attached to the drive shaft 27 by means of a hub 28. The 
screen 20 has a mesh size such that air carrying dust and fines will pass 
through the screen while polymer pellets and snakeskins will be retained 
on the upper surface of the screen. A flange 30 secured to the cover 12 
extends outward from the cover 12 to overlap the edges of the screen 20 
and thereby prevent any pellets from passing between the cover 12 and the 
edge of the screen 20. 
A first nozzle 31 extends through the cover 12 and terminates above the 
screen 20 in the position illustrated in the drawings. The first nozzle is 
positioned at an angle to the screen to impinge the polymeric collection, 
made up of polymeric pellets, fines and snakeskins, onto the surface of 
the screen 20 in a stream of air. A frustoconical converging duct 36 
mounted in an opening in the plate or wall 13 in alignment with the nozzle 
31 directs the airstream carrying any fines into the enclosure 11. 
The relatively large cross-sectional area of the enclosure 11 causes the 
velocity of the airstream to drop considerably in the enclosure 11, 
thereby causing the fines to fall out of the airstream to be withdrawn 
from the enclosure through a tapered conduit 37 connected to a pipe 38 
which carries away collected fines. A gate valve 39 mounted in the pipe 38 
is opened intermittently for intermittent removal of the fines. The nozzle 
31 is reduced in diameter by about 1/3 through a gradually converging 
conical section at its exit end in order to accelerate the air passing 
through converging duct 36 and maximize the static pressure developed 
inside the enclosure 11. This, in turn, maximizes the velocity of the air 
passing through the moving screen from the nozzle 43. The relatively 
sudden air velocity increase in the converging exit end of the nozzle 31 
produces an insignificant acceleration of the polymer pellets due to the 
short time exposure to the faster moving air. It is desirable to prevent 
the velocity of the polymeric pellets impinging on the moving screen from 
exceeding normal pneumatic conveying velocities in order to prevent damage 
to the pellets and excessive wear or erosion of the screen mesh. 
The converging shape of duct 36 serves to collect the gradually diverging 
pattern of high velocity air exiting from the nozzle 31 and funnels all or 
most of this air into the enclosure 11 with little or no air backflowing 
through the duct 36. The converging duct 36 thus serves to prevent 
backflow as the velocity pressure of the conveying airstream changes into 
static pressure inside the enclosure 11. 
A tapered second nozzle 43 mounted in an opening in the plate 13 and having 
a rectangular cross-sectional configuration is positioned for directing 
air from the enclosure 11 upwardly through the screen 20 to lift off and 
remove snakeskins and any fines remaining with the polymer pellets. FIG. 2 
best shows the configuration and positioning of the nozzle 43, portions of 
the screen being broken away in this view to show the nozzle 43 and the 
converging duct 36. 
Referring to FIG. 2, the collection of polymeric material is impinged on 
the screen 20 above the converging duct 36. It is necessary to have that 
portion of the polymeric collection which does not pass through the screen 
at the converging duct 36 to be carried past the nozzle 43. This is 
achieved by rotating the screen 20 in a counterclockwise direction as 
indicated in FIG. 2 and by providing a baffle 44 which is secured to the 
cover 12 and extends to a position sufficiently close to the screen 20 
that pellets will not pass between the screen and the lowermost edge of 
the baffle 44. The positioning of the baffle 44 prevents movement of the 
pellets in a direction countercurrent to screen movement to cause the 
pellets to pass through the stream of air from the nozzle 43. 
To insure movement of the pellets toward a collection point, to be 
described hereinafter, the apparatus is inclined at an angle of about 
35.degree. to horizontal, as best illustrated in FIG. 1. The moving 
pellets impinge on the screen 20 and bounce, roll and are carried by the 
rotating screen downward to the collection point at the lower edge of the 
inclined screen. 
As best illustrated in FIG. 2, the second nozzle 43 extends from a position 
below the hub 28, i.e. between the hub and the lower edge of the screen, 
almost to the edge of the screen 20 to insure that all of the polymeric 
material remaining on the screen is exposed to the upwardly directed 
stream of air from the nozzle 43. The stream of air moving upwardly 
through the second nozzle 43 has a velocity sufficient to lift off and 
remove snakeskins and angel hair, these being withdrawn from the apparatus 
through a discharge duct 46. This moving stream of air also removes any 
fines or dust remaining with the polymeric pellets. Undersized pellets 
will also be removed from the screen 20 at this point and withdrawn 
through the duct 46. 
The upper end of the discharge duct 46 is enlarged in cross-sectional area 
to reduce air velocity at this point such that any full size pellets which 
are picked up by the stream of air exiting from the second nozzle 43 will 
drop downward through the discharge duct 46 back onto the screen 20. 
The clean pellets, with fines and snakeskins removed, reach the lowermost 
edge of the inclined screen 20 and fall off this edge into a conduit 50 
leading to a collection bin 51 having an outlet line 52. A gate valve 53 
in the outlet line 52 is intermittently opened for an intermittent removal 
of the pellets by gravity. 
The apparatus is tilted or inclined at such an angle that any fines which 
pass through the screen 20 and fail to pass through the duct 36 slide down 
the upper surface of the plate 13 and into a tapered conduit 56 connected 
to a tube 57 leading to the discharge line 46. The lowered pressure in the 
air moving through the discharge duct 46 will cause any fines entering the 
tapered conduit 56 to be withdrawn through the tube 57 to be carried away 
through the discharge duct 46. 
In operation, the collection of polymeric material, including pellets, 
fines and any snakeskins, is fed downwardly in a stream of air from the 
first nozzle 31 to impinge on the screen 20 above the converging duct 36. 
The airstream passes through the screen 20, carrying the fines with it. 
Because of the large cross-sectional area of the enclosure 11, the air 
velocity drops significantly in this enclosure and the fines fall out of 
the airstream to be withdrawn through the pipe 38. The air in the 
enclosure 11 flows upward through the second nozzle 43 and the screen 20 
to remove any snakeskins and any remaining fines from the polymeric 
collection and carry them out of the apparatus through the discharge duct 
46. 
The pellets impinged on the screen 20 bounce and roll and are carried by 
the movement of the screen downward toward the outlet pipe 50 where the 
clean pellets fall into the container 51. Air passing upwardly through the 
screen from the nozzle 43 lifts any snakeskins and remaining fines and 
carries them away through the discharge duct 46, leaving only clean 
pellets to be collected. The nozzle 43 is shown positioned below the 
center of the screen. It should be understood that this nozzle may be 
positioned at or above the center of the screen. 
During the separation cycle described above, both gate valves 39 and 53 are 
closed to insure that only air from the nozzle 31 flows through the 
apparatus and that no unwanted air flows into or out of the apparatus 
through pipes 38 and 52. When the bin 51 is filled to a desired level with 
clean pellets, the air supply to the nozzle 31 is briefly shut off and the 
gate valves 39 and 53 are briefly opened to allow the pellets and fines to 
discharge by gravity to empty the bin 51 and the enclosure 11, 
respectively. The valves 39 and 53 are then closed and the air supply to 
nozzle 31 is turned on to continue the separation operation.