Spray spinning collection unit

A spray spinning collection unit includes a cylindrical collection mandrel and a cooperating press roll. The cooperating press roll has a peripheral surface disposed adjacent to a cylindrical surface of the mandrel so as to define a gap therebetween. To provide a predetermined radial density gradient in a cylindrical nonwoven product formed by the gap between the press roll and the mandrel, the gap has a varying height defined by the contour of the peripheral surface. The contour is selected to give the predetermined radial density gradient. Portions of the peripheral surface of the press roll may be either convex, concave, or both.

BACKGROUND OF THE INVENTION 
The present invention relates generally to collection devices for 
fashioning a tubular member of indefinite length from substantially 
continuous filaments of synthetic resinous material. More particularly, 
the present invention relates to configurations of a press roll which 
permit controlled radial density variation in the tubular product. 
In the spray spinning art, synthetic resinous material is plasticated and 
pumped through filament shaping orifices to produce one or more filaments. 
Gaseous jets then act on the filaments to attenuate the filaments to a 
comparatively fine diameter and convey the filaments to a downstream 
collection device. Non-woven products of various configurations can be 
manufactured in this manner. For example, when a downstream collection 
device is a flat or curved surface or a set of parallel rolls, the 
resulting product is a generally a planar web of indefinite length. 
Another type of collection device which may be used with spray spinning 
apparatus is a rotating mandrel on which the filaments accumulate while 
the previously deposited filaments are withdrawn axially thereby producing 
a generally cylindrical member of indefinite length. 
In the past, the production of cylindrical or tubular members of spray spun 
material has also been accomplished using a cylindrical mandrel and one or 
more generally cylindrical rolls which urge the tubular member axially off 
the mandrel. In some instances, these cooperating rolls may also compress 
the spray spun material during its accumulation on the mandrel. In either 
event, this cooperation between the press roll and the mandrel produces a 
tubular element having a radial density variation which decreases in a 
radially outwardly direction. In many applications for nonwoven tubular 
members it is desirable to have a uniform radial density variation, or a 
radial density variation which changes in a predetermined manner. 
Accordingly, the prior art devices have not been entirely satisfactory. 
One specific example of a use for nonwoven tubular spray spun elements is a 
filter medium. If the filter medium has a high density on the fluid 
entering side, the particles will accumulate on the surface and 
prematurely clog the filter. Naturally, there are instances in which a 
predetermined radial density gradient in a filter medium is desirable: for 
example, where the particles to be filtered passes radially inwardly 
through the body, it may be desirable to have a density variation which 
increases in the radially inward direction. In this manner, larger 
particles accumulate in the lower density portions of the filter so as not 
to prematurely block the finer or higher density portions of the filter. 
Conversely, where a fluid passes radially outwardly through the filter 
medium, it will occasionally be desirable to have a density variation 
which increases in the radially outward direction. Similar considerations 
to those just discussed apply as to particle size and blockage for an 
outwardly increasing density variation. 
It has been proposed to fabricate a cylindrical filter element with a 
radial density gradient by using a fiberizing assembly having a plurality 
of filament-producing orifices arranged in a row and inclined at an acute 
angle, with respect to the axis of the collection mandrel, see for example 
U.S. Pat. Nos. 3,933,557 and 4,021,281, issued to Pall. In this type of an 
assembly, the spacing between the filament-producing orifices may be 
varied and/or the angle at which the row of orifices inclined with repsect 
to the mandrel itself may be varied. 
Such devices as those disclosed by the Pall patents do not, however, permit 
density variations to be created which exceed that naturally laid down by 
the spray spinning head. Moreover, the tubular product requires a separate 
device to physically withdraw the tubular product from the mandrel. 
Another difficulty with varying the orifice spacing and inclination angle 
is that the spray spinning mechanism must be changed or reoriented for 
each different density gradient. Such adjustments and orientation changes 
require substantial expense and consume much time since the plasticated 
material must pass through any adjustable or adjusted connection which is 
made. 
U.S. Pat. Nos. 3,787,265 and 3,801,400, both assigned to the same assignee 
as the instant invention, show processes wherein weight changes in tubular 
idler rolls are used to compress the tacky fibers thereby inducing density 
variations in different layers of cylindrical self-bonded non-woven 
structures. 
Accordingly, the need continues to exist for an economical and efficient 
means whereby the radial density gradient of a nonwoven tubular spray spun 
product may be varied at will with comparative ease. 
SUMMARY OF THE INVENTION 
Problems of the type noted above may be avoided by using a collection 
device having two parts: a collection mandrel which is rotatably mounted 
and includes a generally cylindrical external surface; and a press roll 
having a peripheral surface positioned adjacent to the cylindrical mandrel 
so as to define a gap therebetween that extends generally axially along 
the mandrel with a varying height relative to the mandrel. 
By appropriately configuring the peripheral surface of the press roll, a 
predetermined radial density variation in the collected spray spun 
material may be developed as the material is projected against and 
accumulates on the mandrel. Moreover, known variations in the distribution 
of filamentary material axially along the mandrel can be accommodated in 
the design of the press roll. 
In order to avoid the need for an independent device to physically withdraw 
the tubular product from the rotating mandrel, the press roll and the gap 
defined between the press roll and the mandrel are configured so as to 
squeeze the tubular product as it is formed and urge it axially off the 
mandrel. 
Moreover, depending upon the angle of inclination between the press roll 
shaft and the mandrel, portions of the surface of the press roll may be 
either concave, convex, or both. 
The pressure exerted between the press roll and the mandrel is also 
effective to enhance the filament-to-filament bonding that occurs as 
filaments are deposited on the mandrel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to FIG. 1, spray spinning apparatus is disclosed which 
incorporates a collection device in accordance with the present invention. 
The spray spinning apparatus includes a spray spinning means 10 and a 
collection means 12. While the present invention is primarily concerned 
with the improved collection means 12, it will be instructive to describe 
briefly some of the features of the spray spinning means 10. 
The spray spinning means 10 is preferably located at the end of an 
extrusion device 13 which supplies a substantially continuous flow of 
plasticated synthetic resinous material from which one or more filaments 
are eventually formed. One extrusion device which has been found to 
perform satisfactorily is a Modern Plastic Machinery Corp. 1" extruder. 
Flow from the extruder 13 is supplied to each of a plurality of melt pumps 
14, 16, 18, which are arranged in a generally planar row in a manifolding 
device 15. A suitable melt pump is a Zenith Corp. high temperature 
metering pump having a capacity of 1.168 cc/revolution. While three melt 
pumps are disclosed in FIG. 1, it is within the scope of the invention to 
supply a plurality of melt pumps greater than or less than three. 
Eavch of the melt pumps 14, 16, 18, pressurizes the synthetic resinous 
material supplied thereto from the extruder 13 and delivers the 
pressurized melt flow to a corresponding filament-forming nozzle assembly 
20, 22, 24. 
Preferably, each of the nozzle assemblies 20, 22, 24, is identical. It 
will, therefore, suffice to only describe the details of one such nozzle, 
it being understood that the other nozzle assemblies exhibit similar 
features. The nozzle assembly 20 includes a filament-forming orifice body 
26 having an orifice opening through which the pressurized molten 
synthetic resinous material is forced and shaped into a substantially 
continuous filament. Surrounding the orifice body 26 is a plurality of 
gaseous jet conduits 28a, 28b, 28c, from which a corresponding plurality 
of gaseous jets are discharged. These jets convey the continuous molten 
filament emanating from the opening of the orifice body 26 downstream 
toward the collection device 12 by attenuating the molten filament to 
reduce its diameter and impart molecular orientation to it thereby 
rendering it a substantially continuous solidified filament. Preferably, 
pressurized air at essentially ambient temperatures may be used as the 
gaseous fluid of the jets. 
Each conduit 28a, 28b, 28c, extends forwardly from an air manifold 30 which 
receives pressurized air from a suitable conventional source (not shown). 
Action of the air jets emanating from the conduits 28a, 28b, 28c, on the 
continuous molten filament causes the filament to be randomly distributed 
within the confines of an imaginary spray cone, the boundaries of which 
are identified at 32, 34, 36, for each corresponding nozzle assembly 20, 
22, 24. As will be apparent from FIG. 1, the imaginary cones 32, 34, 36, 
have parallel axes, and laterally intersect one another before actually 
reaching the collection means 12. To assure that the imaginary spray cones 
32, 34, 36, do intersect one another prior to reaching the collection 
means 12, lateral spacing between the orifice openings of the nozzle 
assemblies 20, 22, 24 (or the axes of the imaginary cones) must be 
selected in accordance with the typical shape of the imaginary spray cone 
32 for the specific nozzle assembly being used. In this connection, the 
angular divergence of each imaginary spray cone 32 will be a function of 
several variables including, for example, the number of attenuating 
gaseous jets, the angular inclination of the gaseous jets relative to the 
axis of the nozzle body 26, and the velocity of the gaseous jets relative 
to the filament itself. 
Turning now to FIG. 2, it will be seen that the overlapped portions 38, 40 
of the imaginary spray cones 32, 34, 36 are designed so as to ensure the 
best uniformity of "mass-laydown" concommitant with the density gradient 
sought to be established by the curvature configuration of the press roll. 
For purposes of the present discussion, the distribution of the 
substantially continuous filament throughout each of the imaginary cones 
32, 34, 36 is assumed to be predetermined and, preferably, uniform. The 
axes of the imaginary spray cones 32, 34, 36 are (see FIG. 1) generally 
perpendicular to the axis of a collection mandrel 43 in the collection 
assembly 12. In this fashion, the filaments at any lateral location in the 
imaginary cone is likely to have the same level of thickness. When the 
imaginary spray cone axes are aligned to perpendicularly intersect the 
axis of the mandrel 43 (see FIG. 2), filaments are equally distributed on 
each side of the mandrel. However, equal distribution of filaments on each 
side of the mandrel is not necessary. As long as a fraction of the 
imaginary cone intersects with the mandrel axes, filaments can be wound up 
onto the mandrel due to the rotation of the mandrel. 
Returning now to FIG. 1, the collection device 12 includes the mandrel 
means 43 which is rotatably mounted by means of a suitable conventional 
driving assembly 44. The driving assembly 44 is adapted to rotate the 
generally cylindrical mandrel 43 at a predetermined rate of speed. The 
preferred range of speed is from about 300 rpm to about 3000 rpm. The 
mandrel 42 has a very smooth external cylindrical surface which defines 
the inner diameter of the tubular product 42 produced by the spray 
spinning apparatus. The mandrel is slightly tapered towards the free end 
to facilitate the axial movement of the non-woven tube. 
In order to define the outer cylindrical surface of the tubular product 42, 
a press roll 48 is rotatably mounted on a shaft 50 and is operatively 
positioned adjacent to the cylindrical mandrel 43. As can be seen from 
FIG. 3, the axis of the press roll 48 and the axis of the mandrel 43 are 
slightly skewed to assist in the continuous movement of the tubular 
product toward the free end of the mandrel. 
With the mandrel 43 rotating in a counterclockwise direction as viewed in 
FIG. 3, the press roll 48 is rotated in a clockwise direction. 
Accordingly, as the substantially continuous filaments within the 
imaginary cone 36 are projected against and deposited on the mandrel 43 
(see FIG. 4), they are collected by the mandrel 43 as well as a contoured 
peripheral surface of the press roll 48 and compressed in the space 
between the press roll 48 and the mandrel 43. For purposes of this 
invention, "contoured" as used in connection with the press roll surface 
is intended to include portions of the peripheral surface which are 
concave, convex, or both. 
The press roll 48 cooperates with the mandrel 43 to define a gap 52 which 
varies from a minimum value at one end 54 to a maximum value at a second 
end 56 in accordance with a predetermined variation. The gap 52 may be 
considered to have a radially extending height measured in a direction 
relative to the axis of the mandrel 43. It will be observed from FIG. 4 
that at the second end 56, the gap 52 has a maximum radial height. The 
final radial thickness of the tubular product depends on the extreme end 
of the last fiber spray pattern. 
The press roll 48 may include a frustoconical surface portion 60 which will 
diverge from the cylindrical surface of the mandrel 43 so as not to 
mechanically interfere therewith. In addition, the press roll 48 includes 
a generally conical peripheral surface portion 62 which, in cooperation 
with the cylindrical surface of the mandrel 43, defines the varying height 
gap 52. 
The contour of the surface 62 is selected to provide a predetermined radial 
density distribution, or gradient, in the nonwoven tubular product 42 
produced by the spray spinning apparatus. An example of the manner in 
which the contour of the surface 62 may be utilized will now be discussed. 
If it is assumed that the filaments projected against the collection means 
12 (see FIG. 2) are distributed uniformly throughout the imaginary spray 
cones 32, 34, 36, the substantially continuous filaments will accumulate 
on the mandrel 43 at a rate which is uniform between the first end 54 (see 
FIG. 4) and the second end 56. If it is desired to create a tubular 
nonwoven member having a uniform radial density, i.e., one which is 
constant in the radial direction, it is preferred that the filament volume 
laid down on the volume of filaments previously laid down in each 
successive annular incremental volume around the mandrel, be the same for 
each incremental distance on the mandrel between the ends 54, 56. More 
particularly, if it is assumed that there are three axial increments in 
which the fibers are deposited on the mandrel, corresponding generally to 
the lateral extent of the three imaginary cones 32, 34, 36 (see FIG. 2), a 
uniform radial density will be attained if the volume per unit length 
(i.e., area) deposited by each of the three spray cones in the tubular 
cross section is equal. 
Thus, as shown in FIG. 5 in the cross section of a tubular product, the 
area 64 defined between radii R.sub.1 and R.sub.2 must be equal to the 
area 66 defined between radii R.sub.2 and R.sub.3 which in turn must be 
equal to the area 68 defined between the radii R.sub.3 and R.sub.4. That 
is to say, the volume of fibers deposited per unit area is the same for 
each of the annular areas 64, 66, 68. The radii R.sub.2, R.sub.3 can be 
determined from elementary mathematical principles and are translated into 
a gap height 52 at specific points (see FIG. 4), for example, at points 70 
and 72 along the axis of the mandrel 43. The peripheral surface 62 of the 
press roll is then provided with a contour which satisfies the conditions 
of the minimum gap height at the first end 54 and the maximum gap height 
at the second end 56 and a gap height which varies so as to provide the 
determined radial gap heights at points 70, 72. Naturally, this analysis 
can be broken down into as many axial and corresponding radial increments 
as may be desired. 
Where the distribution of filaments deposited by the spray spinning head is 
non-uniform, such non-uniformity variations can also be accommodated in 
the design of the surface contour 62 by appropriate weighting factors 
which are distributed axially along the mandrel 43. Moreover, 
predetermined radial density gradients are attained by applying a 
corresponding weighting factor to volume per unit length of the 
incremental annular volumes. Another condition which is applied to the 
surface contour is that the press roll and the mandrel must cooperate to 
urge the nonwoven tubular product off the mandrel by virtue of a skew 
angle between them. 
Where the radial density variation is desired to decrease radially 
outwardly, the contour of the peripheral surface of the press roll 48 may 
also be convex as illustrated at 64 in FIG. 6. In this manner, the 
filamentary material deposited in the region close to the first end 54 of 
the gap is not only deposited but is also greatly compressed, whereas the 
material deposited near the second end 56 is not compressed to as 
appreciable an extent. 
It will thus be apparent that in designing the contour of the press roll 
peripheral surface it is possible to provide a tubular product 42 having a 
radial density distribution which can be uniform; which can decrease 
radially outwardly; which can increase radially outwardly; or have any 
other desired distribution. 
Moreover, in order to change the density characteristics of the tubular 
product 42, it is only necessary to change the press roll 48, providing a 
substantial savings in time and capital expense while having the attribute 
of simplicity. 
An annular area of defined for example, as the difference between the area 
determined by R.sub.3 and the area determined by R.sub.2 i.e., 
(R.sub.3.sup.2 -R.sub.2.sub.2). The annular area must vary axially along 
the mandrel means in accordance with a predetermined relationship. That 
predetermined relationship will cause a surface having a specific contour 
on the press roll. Where a constant radial density is desired, the annular 
area will increase linearly with length along the mandrel 43 in a 
direction away from the first end 54. For radially increasing or radially 
decreasing density distribution, the variation of annular area axially 
along the mandrel 43 will be determined according to the desired density 
variation. 
For example, by knowing the radii of the various annular areas, one can 
determine the center of gravity of each annular area. By assuming this 
center of gravity radius is located above the spray cone axes and also 
knowning the position of each axis along the mandrel length, one can 
determine the curve, i.e., curvature of the surface of the press roll. 
In operation, a particulate synthetic resinous feed material, such as 
nylon, polyethylene terephthalate, or polypropylene, is plasticated in the 
extruder 13 and supplied to the melt pumps 14, 16, 18 where the 
plasticated material is pressurized and advanced to orifice openings of 
the corresponding plurality of nozzle assemblies 20, 22, 24. Air jets 
surrounding each nozzle body 26 attenuate the corresponding filament to 
reduce its diameter and convey the substantially continuous filament that 
results downstream toward the collection device 12. 
The substantially continuous filaments are thus sprayed by the air jets at 
the rotating mandrel 43 (FIG. 3) which, in cooperation with the press roll 
48, collects and compresses the filaments with a pinching motion between 
the rotating members. More specifically, since the mandrel rotates in a 
counterclockwise direction and the press roll rotates in a clockwise 
direction, the substantially continuous filaments are guided and 
compressed by the press roll 48 onto the mandrel 43. 
The mandrel 43 and the press roll 48 cooperate to define a gap of variable 
radial height in which the substantially continuous filaments are 
collected as a nonwoven tubular structure 46. As the filaments are 
compressed between the press roll 48 and the mandrel 43, they are still in 
a sufficiently softened state that fiber-to-fiber bonding occurs. This 
bonding is enhanced by the pressure exerted between the press roll 48 and 
the mandrel 43. In addition, the surface of the press roll 48 is 
configured so that the radial height of the gap 52 increases toward the 
distal end of the mandrel and that, combined with a skewing of the 
respective axes results in a rector force which urges the tubular product 
42 being formed axially off the mandrel 43. 
It should now be apparent that a press roll constructed in accordance with 
the present invention may be easily changed with a relative minimum of 
time and expense in order to change the characteristics of the density 
gradient in the resulting tubular product. In addition, the press roll 
itself is easily fabricated and does not require an enormous capital 
investment. On the other hand, where variations in radial density are 
effected by changing the inclination and lateral spacing of spinning 
orifices, it will be apparent that there would be a substantial time and 
financial investment required to easily change the density distribution of 
the resulting tubular product. 
It is now apparent that a collection device constructed as described above 
has many advantages when compared to the prior art. Moreover, it will be 
apparent to those skilled in the art that numerous modifications, 
variations, substitution and equivalents for the features of the invention 
exist which do not materially depart from the spirit and scope of the 
invention. Accordingly, it is expressly intended that all such 
modifications, variations, substitutions and equivalents which fall within 
the spirit and scope of the invention as defined in the appended claims be 
embraced thereby.