US3497918A - Apparatus for making a nonwoven fibrous sheet - Google Patents

Description

March 3, 1970 F. s. PbLLocK. JR, ETAL 3,497,918

APPARATUS FOR MAKING A NONWOVEN FIBROUS" SHEET Filed April 6, 1967 4 Sheets-Sheet 1 March 3, 1970 Filed April 6, 1967 F. s. POLLOCK, JR., ET AL 3,497,918

APPARATUS FOR MAKING A NONWOVEN FIBROUS SHEET 4 Sheets-Sheet 2 g 0.40 =I g 0.60 500 3 g 40. E so" "2 3 A "20' t 0.00 l0 RADIAL HORIZONTAL DISTANCE FRBII SIDE OF BAFFLE BOSS March 3, 1970 F. s. POLLOCK. JR., ETA!- 3,497,918

APPARATUS FOR MAKING A NONWOVEN FIBROUS SHEET Filed April 6, 1967 4 Sheets-Sheet 5 FIG-9 FIG. IO

March 3, 1970 F. s. POLLOCK, JR., ETAL 3,497,913

APPARATUS FOR MAKING A NONWOVEN FIBROUS SHEET Filed April 6. 19s? 4 Sheets-Sheet 4 Iinited States Patent 3,497,918 APPARATUS FOR MAKING A NONWOVEN FIBROUS SHEET Frank Scott Pollock, Jr., Richmond, Va., and James Gerald Smith, Newark, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Apr. 6, 1967, Ser. No. 628,871 Int. Cl. B22d 23/08 US. Cl. 182.6 Claims ABSTRACT OF THE DISCLOSURE An apparatus for making a nonwoven fibrous sheet, including a spinneret for spinning a fibrous strand, a rotatable baflle for receiving the strand and deflecting it downward while simultaneously spreading the strand into a web and causing the web to oscillate, means for rotating the baffle, and a collection surface located below the baffle and spinneret. The baflle is an integral body composed of a disc portion, a boss portion, and a lobed fillet portion.

Background of the invention This invention concerns an apparatus for making a nonwoven fibrous sheet, including a spinneret for spinning a fibrous strand, a bafiie for receiving and deflecting the strand while simultaneously spreading the strand into a web and causing the web to oscillate, and a collection surface for collecting the web as a sheet.

In the preparation of fibrous nonwoven sheets various methods and apparatus have been developed for dispersing the filaments from a bundle into a wide band and for directing a strand by oscillating means in a programmed manner to various locations across the width of a moving collecting surface. For example in Frickert US. 2,736,676 several methods are described for directing glass fibers by the use of wobble plates or by deflection from the perimeter of a cylinder rotating about an axis at an angle a few degrees from the longitudinal axis of symmetry.

In Steuber US. 3,169,899 an apparatus is described for spreading and directing a strand of flashspun polymer in a flowing stream of solvent gas by utilizing the combined action of the hot expanding solvent gas and a curved, oscillating baffle. The curved batfle serves to spread the strand into a wide web. The oscillating motion serves to direct the web to various areas across the width of a moving collecting belt. A randomly oriented fibrous nonwoven sheet is thereby obtained. The flash-spun strands which are used in the Steuber sheet are prepared by spinning from a solution of polymer in solvent under pressure and at a temperature far above the atmospheric boiling point. When this solution passes from a spinneret to the surrounding atmosphere, the solvent evaporates almost instantaneously and forms a strand comprising a three-dimensional network of film-fibril elements. The strand has been termed a plexifilament and has been described in detail in Blades and White US. 3,081,519.

In developing web lay-down systems which will produce uniform fibrous sheets from these networks at high speed, certain difliculties have arisen. In order to obtain uniform dispersion of the fibril networks, relatively small distances between the baflles and the collecting surface are required to minimize the loss of momentum due to viscous drag by the surrounding atmosphere. Furthermore, these ice problems in space conservation are made more critical by the neceessity for charging the fibrils electrostatically while the web is in an open configuration. In recent studies it has further been shown that electrostatic charging and pinning is handled more uniformly if the diverted fibers from the baflie are presented to the charging zone in a smooth flow and at a uniform distance from the charging electrode. Many of the earlier oscillating baflles presented a problem when used for this purpose since they caused the diverted web to traverse in a non-planar configuration. The combination of electrostatic requirements and aerodynamic requirements therefore raises imposing restrictions on the design. In addition, electrohydraulic servo control mechanisms for such an oscillating baflie operating at high speed are expensive and have limited upper frequency. In addition, the oscillated baffle tends to collect residues in a concentrated area, thereby promoting instability of the network and promoting uneven deposit on the collecting surface.

Summary of the invention This invention is an apparatus for making a nonwoven fibrous sheet. The apparatus comprises a spinneret for spinning a fibrous strand in a generally horizontal direction, a rotatable baflle for receiving the fibrous strand and deflecting it into a generally vertical plane downward while simultaneously spreading the strand into a web and causing the web to oscillate in the generally vertical plane, means for rotating the baflle, and a collection surface located below the spinneret and baffle for collecting the Web as a sheet. Since in use the baflie is rotated rather than oscillated, it provides the capability of operating at high speeds and for directing the web uniformly through an electrostatic device to apply a uniform electrostatic charge on the web and to promote uniform deposit of the web on a moving collecting surface.

The baflie used in the apparatus of the invention, as viewed with its axis of rotation in a vertical position, is an integral body composed of a circular boss portion on a flat disc portion with a fillet portion extending around the boss portion and providing a concave surface from the side of the boss portion to the top flat surface of the disc portion. The axis of rotation of the baflile is perpendicular to the top, circular edges of both the boss portion and the disc portion. The centers of the top, circular edges of both the boss portion and the disc portion coincide with the axis of rotation of the baflie. The fillet portion includes at least one lobe which rises above the general contour of the fillet portion.

Brief description of the drawings FIGURES 1, 2, and 3, respectively, are front, vertical section, and plain views of the preferred trilobal baflile used in this invention.

FIGURE 4 is a plot of fillet portion dimensions for a bafflle of the type shown in FIGURES 13 taken at rotational angles of 0, 10, 20, 30, 40, 50, and 60 degrees from the center of the lobes.

FIGURE 5 is a cross-section drawing of a rotating baflle used in the invention in operating position receiving a flash-spun plexifilamentary strand from a spinneret and deflecting the strand downward between a flat, annular target electrode and an ion gun where it is exposed to corona discharge.

FIGURES 6A-6D show a baflle of the type shown in FIGURES 1-3, the baflie being shown in operating position as viewed from the spinneret. The four views illus- 3 trate the effect of the baflie on the direction of web travel as it rotates through 90.

FIGURES 7, 8, 9, and illustrate possible variations in the design of the rotary bafiie used in this invention. FIGURE 11 is a diagrammatic elevation view of an apparatus of this invention, including spinneret, rotatable baffie, means for rotating the baffle, and collection surface located below the spinneret and bafile.

Description of the preferred embodiment The preferred embodiment of the rotary bafile used in this invention is shown in FIGURES 1-3. The baffie is in integral body composed of a boss portion 10, a disc portion 12, and a fillet portion 14. In this embodiment, the boss portion 10 is a right circular cylinder standing on a planar disc portion 12. When the baffle is viewed with its axis of rotation 16 in a vertical position, as in FIGURES 1 and 2, the axis is perpendicular to, and coincident with the centers of, the top, circular edge 18 of the boss portion 10 and the top, circular edge 20 of the disc portion 12.

Fillet portion 14 extends around boss portion 10, as shown in FIGURE 3, and provides a concave surface from the side 22 of boss portion 10 to the top, fiat surface 24 of disc portion 12. Fillet portion 14 includes three radially disposed, equi-spaced lobes 26 which rise above the general contours of fillet portion 14.

The upper surfaces 28 of the lobes 26 are slightly wedge-shaped, i.e., the surfaces are wider near the boss portion 10 than they are near the disc portion 12. This can best be seen in FIGURE 3. The edges of the wedges are indicated by lines 30; however, it should be understood that in actual construction all inflections in the surface of the fillet portion 14 are gradual. The reason for this will be apparent from the description hereinafter of the manner of using the baffle.

The intersection of fillet portion 14 with the side 22 of boss portion 10 forms a continuous line, hereinafter referred to as the boss intersection line (B.I.L.), below the top 18 of boss portion 10. The B.I.L. is identified in FIG URE 1 by the numeral 32; as shown, the B.I.L. 32 for the preferred embodiment is an S-shaped curve.

The intersection of fillet portion 14 with the top surface 24 of disc portion 12 forms a continuous line, hereinafter referred to as the disc intersection line (D.I.L.), inside the top, circular edge of the disc portion 12. The D.I.L. is identified in FIGURE 3 by the numeral 34; as shown, the D.I.L. 34 for the preferred embodiment is an equilateral triangle with rounded corners.

Although the B.I.L. 32 and D.I.L. 34 are shown in the figures as distinct lines, it should be understood that in actual construction the fillet portion merges smoothly into the side 22 of boss portion 10 and the top surface 24 of disc portion 12. That is, there is no sharp inflection at either the B.I.L. or the D.I.L. In the preferred embodiment the lobes 26 of the fillet portion 14 are so contoured that a line drawn radially from the axis of rotation 16 on the upper surface 28 will have a straight por' tion in the middle with curved portions at either end. The straight portion which can be as much as say 90% of the length of the line forms acute angles with both the side 22 of boss portion 10 and the top surface 24 of disc portion 12, preferably both angles are approximately 45. The curved portions are arcs of a circle; the upper curved portion is tangent to the side 22 of boss portion 10 and the lower curved portion is tangent to the top surface 24 of disc portion 12.

The contours of fillet portion 14 for a baflie of the type shown in FIGURES 1-3 are shown by the set of curves in FIGURE 4. Each curve is a plot of measurements taken at the surface of fillet portion 14 at a specified angle of rotation away from the center of a lobe. The curves represent measurements taken after rotation of 10 from the previous measuring position. The reference axes for measurement are the top circular edge 18 tion. Further, it Will be seen that at every angle of rotation the fillet portion forms a generally triangular section at the junction of the boss portion and disc portion surfaces, and that the size of the section increases gradually from the minimum at 60 rotation (i.e. midway between lobes) to the maximum at 0 rotation (i.e., the center of the lobes). It will also be noted that the amount of straight surface on the fillet at zero degrees rotation is greater than at intervening fillet areas.

Any arbitrary units may be used for measuring if one is interested in contour shape. The actualmeasurements in FIGURE 4 were in inches. As indicated in figure, the height of the boss portion ltlabove the surface 24 of disc portion 12 was 1 inch. The diameter of boss portion 10 Was about 2 inches and the diameter of disc portion 12 was about 4 inches for this particular bafile.

Contours of fillet portion 14 for the next 60 rotation, i.e. from 60 to would be described by the same set of curves in reverse order. These would relates to the opposite side of a lobe. Three such 120 portions are needed to complete the mathematical construction of the battle contour.

The baffle of FIGURES 13 is mounted for rotation by inserting the shaft of an electric motor in bore 36 and tightening a set screw in bore 38 in base portion 40.

The manner of using the preferred embodiment of the baffle in making nonwoven sheet from flash-spung plexifilamentary material will now be described with reference to FIGURES 5 and 11. In FIGURE 5, the baflie is shown with its axis of rotation 16 in horizontal, operating position, parallel to the longitudinal axis 42 of spinneret 44. Spinneret 44 comprises a chamber 46 terminating in an office 48. A solution of an organic polymer in a volatile organic solvent is fed continuously to chamber 46 at a temperature near the critical temperature of the solvent and under very high pressure, and is extruded through orifice 48. Upon passage through the orifice the solvent evaporates instantaneously and the polymer precipitates, forming a flash-spun plexifilamentary strand 50.

The bafiie is positioned with its axis 16 above axis 42 of spinneret 44 so that the flash-spun strand 50 passes along the straight side 22 and is intercepted by fillet portion 14 of the baffle. The point at which the strand is intercepted depends upon the particular degree of rotation of the bafiie. In FIGURE 5 the strand is shown being intercepted by a lobe 26 of fillet portion 14. It will be noted that the opposite side of the fillet portion, as oriented in FIGURE 5, has no lobe 26; thus, upon turning the baffle will present a fillet surface with no lobe to the plexifiamentary strand.

As the strand 50 passes along the side 22 and over the surface of fillet portion 14, the combined action of the baffle and the expanded solvent gases spread the strand into a planar web 52. When the web 52 reaches the flat surface 24 of disc portion 12 it i diverted vertically downward toward a collection surface 64 (FIG. 11) moving horizontally in a direction opposite to the direction of solution flow in spinneret 44. As the web 52 leaves the edge of disc portion 12 it passes over the flat face of annular, grounded target electrode 54. The face of electrode 54 is aligned with or, as shown, offset slightly behind the edge 20 of disc portion 12 in order to avoid hangup of web 52 in the space between the bafiie and the electrode.

An ion gun 56 is positioned opposite target plate 54 and applies an electropositive or electronegative charge to the web 52 as it passes over the surface of target electrode 54. This charge maintains the web in open configuration until it is deposited on the moving collectiorr surface. The collection surface is preferably an oppositely charged metal belt which attracts and pins the fibers.

FIGURE 11 diagrammatically illustrates the apparatus of the invention, including the spinneret 44, the rotatable baflle 62, an electric motor 60 for rotating the baflie 62 through shaft 58, and collection surface 64. As shown, collection surface 64, is preferably an endless belt trained to run about driven rolls 66. Strand 50 issuing from spinneret 44 is spread into web 52 by bafile 62 and collected on belt 64 as a nonwoven sheet 70. Before the sheet leaves belt 64 it is compacted by pressure exerted by roll 68, and the compacted sheet 72 is removed to storage or further processing.

Ion gun 56 is preferably a multineedle ion gun which is U-shaped, with the needles arranged along the arc of a circle having a diameter intermediate the inside and outside diameters of the target electrode 54. A suitable ion gun is described in detail and claimed in -U.S. application of Rapp Wallace Crook III, Ser. No. 628,983, filed simultaneously herewith. Target electrode 54 is mounted for rotation in the plane of its face so that it can be continuously cleaned outside the corona discharge zone. The rotating annular target electrode is further described in US. application of Claude M. Kilby and James G. Smith, Ser. No. 628,868, filed simultaneously herewith. A charged frame and belt laydown machine suitable for collecting and pinning the charged web is described and claimed in US. application of IE. Owens and S. P. Scheinberg, Ser. No. 628,870, filed simultaneously herewith. The spinneret 44 is preferably part of a spinneret pack comprising an L- shaped solution supply tube adapted for mounting in the ceiling of a spinning cell The spinneret pack is described in detail and claimed in US. application of James G. Smith, Ser. No. 628,888, filed simultaneously herewith.

The entire disclosures of said Crook, Kilby and Smith, Owens and Scheinberg, and Smith applications are thereby incorporated in and made a part of this disclosure.

As shown in FIGURE 5, the baflle is mounted for rotation on a shaft 58 of an electric motor inside housing 60. The effect of the lobes 26 in fillet portion 14 as the baflle rotates in a clockwise direction is illustrated in the four views (A-D) of FIGURE 6. Since the baflle of FIG- URE 6 is identical to the baffle of FIGURES 13, drawn to a smaller scale, numerals identifying parts of the baflle have been omitted for clarity; notice that the orientation of the baflle in FIGURE 6B is identical to the orientation in FIGURE 3. The plexifilamentary strand and planar web are designated in FIGURES 6A*6D by numerals 50 and 52, respectively.

Referring to FIGURE 6A, it will be observed that at this particular orientation strand 50 impinges on the fillet portion at a point half-way between two lobes. The strand is spread into a web 52 and is deflected vertically downward; that is, the center line of the web as it leaves the edge of the disc portion is vertical.

As the baffle rotates the web 52 begins to be deflected to the left. For this particular embodiment, the center line of the web 52 as it leaves the disc is approximately perpendicular to the disc intersection line. Thus, one degree of rotation as the baffie turns from the position shown in FIG. 6A to that shown in FIG. 6B results in the center line being deflected about 1 from vertical.

At 30 rotation strand 50 impinges on the point of maximum slope on the left slope of a lobe, as shown in FIGURE 6B. At this degree of rotation, the center line of the web 52 is deflected approximately 30 from the vertical, and this is the point of maximum deflection to the left for this particular embodiment.

As the baffle continues to turn, the strand 50 begins to impinge on the upper surface of a lobe and the center line of the web 52 begins to shift back to vertical. When the baffle has rotated through another 30 (60 from FIG. 6A), the strand 50 impinges upon the center of a 6 lobe and is again deflected vertically downward, as shown in FIGURE 60.

Upon further rotation of the baffle, the web begins to impinge upon the right slope of the lobe, and the center line of the web is diverted to the right. When the baflle has rotated another 30 from FIG. 6A) the web center line is deflected approximately 30 from the vertical, as shown in FIG. 6D, and this is the point of maximum deflection to the right for this particular embodiment.

As the baffle continues to turn through another 30 from the position shown in FIGURE 6D (120 from FIGURE 6A), the center line of the web moves gradually back to the vertical unitl it again assumes the position illustrated in FIGURE 6A.

From the above discussion, it will be apparent that 360 rotation of the preferred trilobal baflie of this invention produces three complete oscillation cycles of web 52.

The oscillating motion of the web 52 as it leaves the baflle causes it to be deposited in a wide swath on the collection surface. In making a wide nonwoven sheet numerous spinning units of the type shown in FIGURE 5 are positioned above the collection surface so that the webs are collected in intersecting, multidirectional, overlapping layers. Further information on the positioning of multiple spinning units above a collection surface is given in US. application of James G. Smith, Ser. No. 628,872. filed simultaneously herewith. The last mentioned Smith application also describes a mechanism for making fine adjustments in the transverse distance between the baflie axis 16 and the axis 42 of spinneret 44 for varying the laydown pattern of the web 52 on the collection surface. The entire disclosure of the last mentioned Smith application is hereby incorporated in and made part of this disclosure.

In a typical flash-spinning apparatus using the deflector of FIGURES 1-3 a solution containing 11.5-15 linear polyethylene in trichlorofluoromethane is continuously supplied to a spinneret orifice. The polymer density is typically 0.956 and the melt index 0.8. A spinneret orifice 0.030 inch in diameter is used. The orifice empties into a right cylindrical shroud 7 inch in diameter and inch long, the axis of which is concentric with the orifice axis. The solution' is continuously pumped through the orifice at a temperature of 178 to 188 Crand a pressure of 800 to 1200 p.s.i.g., but in any case above the twoliquid-phase pressure boundary. The rotary baffle is located just opposite the flat end of the shroud. The fiat end of the shroud is located 0.015 inch from the face of the baffle boss. The distance from the baflie axis to spinneret axis is approximately 1.03 inches. The bafile has a boss portion 2 inches in diameter while the total baffle diameter in the disc portion is 4 inches. The end of the boss portion is 1 inch from the plane of the disc portion and the disc portion is about A inch in thickness.

As the polymer solution is extruded from the orifice it forms a plexifilamentary strand which expands to a diameter of approximately inch. This occurs as the strand passes along the side of the boss portion. The strand impinges upon the fillet portion of the baffle. When a threelobed baflie is used the baffie is turned preferably at a speed to provide 25 to cycles per second of strand oscillation. In the three-lobed baflle the speed of rotation of the baflie must then be 8 /3 to 33 /3 revolutions per second. The rotary deflector or baffle is turned by a A; horsepower synchronous motor. The annular target plate typically has a width of 1% inches. The oscillating strand passes over the annular target plate and then is directed to amoving belt which collects the deposited wide web. The directed strand collects a charge as it passes over the target plate, this charge being provided by a U-shaped ion gun with multiple needles. Each needle is spaced inch from the target plate. The potential between the needles and the target plate is about 60,000 volts.

Variations in bafiie design and use As will be apparent to those skilled in the art numerous variations in the design and manner of using the baffle may be made. Some of the possible variations in design are shown in FIGURES 7-10. The numerals in these figures have the same significance as the numerals in FIGURES 13.

FIGURE 7 is a perspective view of a two-lobed baflle used in this invention. The two-lobed baffle shown has an S-shaped B.I.L. 32 and an oval shaped D.I.L. 34. This baffle produces two complete Web oscillation cycles per revolution. A single-lobed baffie (not shown) can also be used in this invention; such a bafile, of course, produces one web oscillation cycle per revolution.

The type of web laydown pattern obtained by a given baflle may be determined by plotting the weight per square centimeter of deposited sheet for each 2.54 centimeter of width using a single bafiie. For this test the web is deposited on a slowly moving belt. Strips 2.54 cm. wide and 1 meter long are then out along the length of the deposited web for each 2.54 cm. of width. The area and weight are then measured and the weight per unit area calculated. The weight per square centimeter is constant across the width of the sheet except for portions deposited at each extreme of oscillation.

The preferred trilobal baffle of FIGURES 1-3 produces an approximate trapezoidal laydown pattern. That is, the profile of the deposited web is approximately trapezoidal in shape. A bafile having lobes of a diiterent shape (and consequently a B.I.L. and/or D.I.L. of different shape) can be used to produce a different web laydown pattern. For example, a baffle of the type shown in FIG- URE 9 having a D.I.L. 34 made up of concave sections produces an approximate cosine laydown. This bafile also produces higher oscillation amplitudes than does the bafiie of FIGURES 1 through 3. Bafiies have been designed which are capable of producing web oscillation amplitudes as high as about :52", i.e. 52 or higher in each direction away from a vertical line through the baffle axis.

FIGURE 10 shows a means for producing varying oscillation amplitudes. Lobe 26 alone produces an oscillation amplitude of about :30 with a trapezoidal laydown pattern. Lobe 26a produces an oscillation amplitude of about i20 with an approximate cosine laydown pattern. Lobe 26b produces oscillation amplitudes of about 150 With approximate trapezoidal laydown pattern.

In all of these embodiments it is important that the fillet portion 14 provide a concave surface from the side of boss portion 10 to the top, flat surface of disc portion 12, and that the fillet portion merge smoothly at either extreme with these surfaces of the boss and disc portions. It is also important that the B.I.L. 32 be at all points below the top, circular edge of boss portion 10. In other words, the lobes should not extend to the top of boss portion 10. It has been found that a baflle in which the B.I.L. 32 extends to the top of the boss portion results in poor sheet dispersion. Further, it is important that the D.I.L. 34 be at all points inside the top, circular edge 20 of disc portion 12; that is, the lobes should not extend to the edge of the disc portion 12. This insures that the web 52 will leave the fiat surface 24 of disc portion 12 in a plane essentially parallel to the flat face of target electrode, thereby avoiding entanglement of the web 52 in the space between the edge 20 of disc portion 12 and the inner edge of annular target electrode 54. In this regard, it is also important that the edge 20 of disc portion 12 be relatively sharp. Any significant radius of curvature (i.e. greater than about 1 mm.) will cause the web to foil around the edge and tend to hang-up between the baffie and target electrode 54.

Numerous other variations in fillet contours will be apparent to those skilled in the art. For example, the superposition of small secondary lobes on the fillet portion 14 of the battle of FIGURES 13 provides a baflle which produces a trapezoidal laydown pattern but in addition, produces a web 52 with areas of local spreading and condensing.

In the preferred embodiment the boss portion 10 is a right circular cylinder and the disc portion 12 is planar. However, either one or both of these can be slightly conical. FIGURE 8 shows a battle in which both boss portion 10 and disc portion 12 are slightly conical. In bafiles having conical boss and/or hub portions the angle b between the side 22 of boss portion 10 and the flat surface 24 of disc portion 12 should be no greater than and the angle a between the side 22 of boss portion 10 and the bafiie axis of rotation 16 should be no greater than 15.

In the preferred manner of using the bafiie, as described previously, the baffle is positioned so that its axis 16 is parallel to the axis 42 of spinneret 44. This is not always necessary, however. Using a baflle having a cylindrical boss portion 10, the baflle can be tilted upward so that its axis 16 forms a small acute angle, preferably no greater than about 15, with the spinneret axis 42. Using a bafiie having a slightly conical boss portion 10, it can be tilted downward so that its axis 16 forms an angle of 15 or less with the spinneret axis 42. If the baffle is tilted, of course, target electrode 54 must also be tilted so that the plane of its face remains flush with or slightly behind the edge 20 of the baffle at all degrees of rotation.

What is claimed is:

1. An apparatus for making a nonwoven fibrous sheet which comprises a spinneret for spinning a fibrous strand in a generally horizontal path, a rotatable battle for receiving the strand and deflecting it into a generally vertical plane downward while simultaneously spreading the strand into a web and causing the web to oscillate in the generally vertical plane, means for rotating the batfie, and a collection surface located below the spinneret and baffie for collecting the web as a sheet, the baflle, as viewed with its axis of rotation in a vertical position, being an integral body composed of a circular boss portion on a disc portion with a fillet portion extending around the boss portion and providing a concave surface from the side of the boss portion to the top surface of the disc portion, the axis of rotation of the baffie being perpendicular to, and coincident with the centers of, the top, circular edges of both the boss portion and the disc portion, the fillet portion including at least one lobe which rises above the general contour of the fillet.

2. Apparatus of claim 1 wherein, in the baffle, the inter section of the fillet portion with the side of the boss portion forms a continuous line below the top of the boss portion and the intersection of the fillet portion with the top surface of the disc portion forms a continuous line inside the top, circular edge of the disc portion.

3. Apparatus of claim 2 wherein, in the bafile, the disc portion is a planar disc and the boss portion is a right circular cylinder.

4. Apparatus of claim 2 wherein, in the baffie, the fillet portion has 2 to 4 equi-spaced lobes.

5. Apparatus of claim 4 wherein, in the baffle, the boss intersection line is S-shaped.

6. Apparatus of claim 5 wherein, in the bafiie, the disc intersection line is an equilateral triangle with rounded corners.

7. Apparatus of claim 6 wherein, in the bafilc, the upper surface of each of the lobes is wedge-shaped.

8. Apparatus of claim 7 wherein, in the baffle, any line drawn radially from the axis of rotation of the baffle on the upper surface of a lobe, has a (1) straight central portion which forms an acute \angle with both the side of the boss portion and the top flat surface of the disc portion and (2) curved portions at either end which are arcs of a circle, one curved portion being tangent to the side of the boss portion at the boss intersection line and the other curved portion being tangent to the top, flat surface of the disc portion at the disc intersection line.

9 10 9. Apparatus of claim 8 wherein, in the bafiie, the fillet 1,613,318 1/ 1927 Fedler 68-134 portion has 3 equi-spaced lobes. 1,617,030 2/1927 Rocke 68-134 10. Apparatus of claim 9 wherein, in the baffle, the 1,753,521 4/1930 Labisky 68134 straight central portion of the radial line forms an angle 2,192,944- 3/1940 Thomas 182.6 XR of about 45 with both the side of the boss portion and 5 2,304,130 12/ 1942 Truthe 182.6 XR the top, flat surface of the disc portion. 2,748,045 5/1956 Kelley 68-134 XR References Cited WILLIAM J. STEPHENSON, Primary Examiner UNITED STATES PATENTS 65,339 6/1867 Butcher et a1. 10

757,035 4/1904 Gr-amm. 659, 15

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