US2758564A - Apparatus for coating with dry dust - Google Patents

Description

g- 14, 1956 R. B. RANDALL APPARATUS FOR COATING WITH DRY DUST Filed May 15, 1951 T lilVENTOR Ralph ,B. Randal U I. R EBP lllllllll If I 1.1 \E 1., III N 9M, m

W w /m .1 3 w W 1L1. v a 6 MK 3 w x a I, m w m EV b ATTORNEY 2,758,564 APPARATUS FOR COATING WITHDRY DUST Ralph 3. Randall, Harrison, N. Y. Application May 15, 1951, Serial No. 226,403

1 Claim. (Cl. '118309) This invention relates to dusting apparatus andmore particularly to a device for coating dust.

It is an object of this invention to provide apparatus for applying dust, and more particularly dry dusting material wherever industrial uses require the controlled application of dusting powders, including those to eliminate sticking, packing, blocking offset or to effect the desired slip and hand to sheeting.

More specificallyit is an object of the present invention to provide dusting and coating apparatus whereby sheeting or other bodies of indeterminate length may have applied thereto an application of dusting powders beneficially to effect the surface in the further handling of the sheets or articles of indeterminate length and to otherwise desirably incorporatethe dust as part of the manufacturing procedure in the handling of materials of indeterminate length or in the flow of the article to be coated or treated.

Still more specifically it is an object of this invention to provide apparatus and a procedure for dry spraying of powders onto materials, such as rubber, sheeted plastics, printing matter as in the graphic arts, paper, insulating materials, tubes, and textiles, whereby substantial economies are effected in the application of uniform coatings of dry solids in mesh size ranging from '70 to micro-pulverized condition in that the deposition of agglomerated masses of powder is minimized and uniformity of distribution of isolated particles is assured.

Known to me is the provision of dust spraying apparatus wherein powder-laden air under pressure is blown over surfaces from a plurality of emitting apertures or jets in which the dust entrained in the emitted air fans out over the surface to be coated in overlapping streams. The source of supply of such air stream bearing entrained dust particles is derived from nebulizing equipment having both mechanical and pneumatic velocities tending towards accretion, impingement or agglomeration of the particles to result'in uneconomical depositions of these powders where required.

In accordance with the objects of the present invention, there is provided in combination a means for aerating the powder to be dusted to suspend itin air as a carri'er so that the dust and the air acquire the characteristics of a fluid in which-the particles tend to maintain themselves isolated from each other in air moving at low pressures to elfect deposition by gravitational release from the entraining air whereby phenomena of channeling tending to form accretions or agglomerates of the particles are minimized, if not entirely eliminated, and, upon aspiration of the dust so provided, thereby provide a uniform flow and distribution of the articles to be coated.

Still more particularly, it is an object of this invention to provide dust-suspending and dust-coating equipment wherein low velocity air pressure entrains by aspiration an aerated dusting powder which is discharged at a lower velocity countengravity to suspend the same in relatively still air and etfect deposition by a gravitational separanited States Patent V 2,758,564 Patented Aug. 14, 1956 'ice tion of the particles from the air' whereby the previously air-occluded particles are deposited free from accretions, agglomerations, flocculations or coalescence to provide an extremely uniform coating which may be economically controlled. I

Still more particularly, it is anobject of this invention to provide a method for coating articles with such dusting material as zinc stearate, corn starch, potato starch, resins, soapstone, by aerating the powder to be dusted in an aerating zone which is substantially in a nonturbulent condition and aspirating the dust from said zone in a chamber through which the article to be coated passes under reducedcarrier pressures of a gaseous material or air, whereby the dust deposited upon the article to be dusted is distributed uniformly, steadily to coordinate the feed of an article of indeterminate length to be coated with the flow of the dust to be deposited thereon.

Still more particularly it is an object of this invention to provide a dusting apparatus to apply dust to articles to be coated to supply a continuous, steady flow of powder of uniform density without pulsation or interruption of flow, whereby an article of indeterminate length may be uniformly coated as it is fed through the deposition zone.

Still further objects of this inventionreside in the provision of apparatus whereby dust may be deposited on articles to be dusted, involving simplicity of control at safe pressures, whereby the powder to be dusted is aerated and particles individually separated substantially in a non-turbulent atmosphere and the dust so suspended is aspirated to entrain the gaseous carrier in which the particles are suspended, to direct the air carrying the dust in a deposition zone, attwhich point the diminished velocity of air liberates the dusting powder upon the article to be coated under conditions'obviating the necessity for auxiliary dust collectors and separation apparatus occasioned by the introduction of the dust entraining carrier in a zone of mild turbulence and low pressure, to precipitate the dust from the gaseous carrier upon the surface to be coated.

Still more particularly this invention resides in the provision of a method for coating dust upon articles requiring a surface application of dust which includes suspending the dust to provide a dust-laden atmosphere substantially free from any turbulence by cascading the dust gravitationally against an ascending stream of a gaseous carrier, such as air, acting as a barrier to deposition and thereby suspending the dust in the air so that the dust acquires the characteristics of a fluid in which the particles of dust tend to maintain themselves isolated from each other, and then aspirating the mixture from the barrier zone into a deposition chamber, to change the velocity of the carrier and to entrain particles to the point where a gentle separation occurs between the air and the powder, to deposit the dust with uniformity upon the article to be coated and under conditions permitting synchronization of feed of an article of indeterminate length with the fiow of the dust, to secure a uniform deposition without interruption, and eiiminating the necessity for dust collecting equipment from adjacent the point of deposition.

Still more particularly it is an object of this invention to provide apparatus for dusting in which batches of the dust may be added to the apparatus without shut down and to secure continuity of performance and uniformity of deposition, notwithstanding the intermittency of loading characterized by the provision of means to suspend the dust in a gaseous carrier such as air, by gravitationally cascading the dust through an open chamber within which a uniform, counter-currently directed air stream, free from turbulence, provides a deposition barrier Within which the dust is" suspended, and from which barrier zone the dustis aspirated and deposited in a deposition charn her through which the article of indeterminate length passes, through entrance and exit slits, the chamber affording a reduction in velocity of the carrier laden with dust, to permit a gentle and uniform separation of the dust and a separation of the dust liberated carrier und'er reduced flow andpres'sures, obviating the necessity" for auxiliary dust collecting apparatus.

To attain these objectsand such further objects as may appear herein or be hereinafter pointed out, I make reference to the accompanying drawing, forming a part hereof, in which---- Figure l is a perspective view illustratingmy apparatus for dusting and carrying out the method;

Figure 2 is a magnified section taken on the line 2--2 of Figure 1;

Figure 3 is a sectional view of a deposition chamber in accordance with another embodiment of my invention for double coating a web;

Figure 4 is a side elevation of a deposition chamber for coating extrusions or tubes in accordance with another embodiment of my invention.

Summarizing my invention in accordance with the method and apparatus for carrying out the same, I pass air or a similar gaseous carrier through apparatus which filters and dries the carrier and then forms a non-turbulent aerating zone or stream by passing the air through an air distributing screen which has random orifices by reason of the cellular structure of the screen, distributing the air and reducing the velocity thereof to avoid turbulence. Into this upwardly ascending stream there. is cascaded the dust or powder to be deposited, forming a fluid condition of the dust and air, and an air barrier to the deposition of the dust upon the air distributing plate, effecting, however, a separation of the dust particles, free from agglomerates or accretions adjacent this air barrier zone, the dust so suspended being aspirated from the aerating zone and is then conducted into a deposition chamber where the velocity of the air is greatly reduced, and through which chamber an article to be coated is positionend and guided in indeterminate length through ingress and egress apertures. The gaseous carrier or air, by reason of this change in velocity, precipitates the dust upon the surface to be coated and liberates the airito pass out gently from the ingress and egress slits free from the dust.

Making reference to the drawing, I provide a cabinet with an upper closure lid and side door for supporting the various elements of my apparatus. Provision is made for a hose line 11 to be connected to a source of gaseous material, such as air, under pressure. The line leads to an oil filter 12 for removing oil, scale, dirt and some.

moisture. The internal construction of the filter, which includes honeycomb filter mechanism, need not be described in detail. The ex'itline 13 from the oil or solids filter 12- is directed through a pressure regulator control valve 14, including a manual turn knob 15. A gauge 16- is connected with the valve to indicate the pressure established by the valve 14. The knob 15 and gauge 16 are accessible and readable through opening 15a and 16a in the door when swung closed. The outlet line 17 from the valve 14 is connected with the dehydrator 18 at the coupling 19. The dehydrator comprises a chamber into which dehydrating material, such as silica gel, preferably with a telltale indicatoriof saturation, is packed to provide a highly t'ort'tiduspathfor the air entering at the bottom. The dehydrating chamber is threaded at the mouth 20' and' is closed by a cap 21 having a sight glass 22. Hand lu s 23 serve to provide an air-tight removable cap which may enable'speedyrernoval of the gel when observation through the side glass indicates exhaustion.

The dehydrator may include a cartridge which may be bodily lifted upon retrieval of the cap 21. A drain cock- 24 is provided to remove accumulated liquid separated from the air. The discharge outlet 25 provides a T-shaped coupling 26 for the lines 27 and 28, controlled by the cut-off needle valves 29 ancl'30, respectively, and controlling the lines 31 and 32.

Lines 31 and 32 lead to the dust-suspending chamher or powder hopper 33 which, as shown, is cylindrical throughout its length. Line 31 is connected to a coupling 34 in the bottom 35, over which is supported the air distribiitin'g screen er aerating disk 36. The aerating disk, in accordance with my invention, comprises a porous, stainless steel sheet made by sintering stainless steel powder after forming a uniform layer of the powder or the shotted fine powder of stainless steel on a surface where the powder is heated just below the melting point of the stainless steel to bond the powder together to form a porous sheet.

It will be observed that by making the dust sustaining chamber or owder hop er 33 cylindrical throughout its length and by extending" the air distributing screen or aerating disk 36 across the hopper for the entire width of the hopper, low turbulence is achieved in the air barrier with substantially little orno' evidence of channeling.

The porous sheet which I have found desirable is characterized by a mean pore opening of .0004 or 10 microns, a minimum tensile strength in pounds per square inch of 15,000 and in thickness of /s, having an airflow capacity in cubic feet of air per minute per square foot as follows:

and in the water flow capacity in gallons of water per minute per square foot as follows:

Pressure drop, p. s. i.:

The powder hopper has an open mouth 37 through which the powder to be suspended is charged in bulk. The powder cascades toward the bottom and encounters the upward counter-current drift of air through the aerating disk or spreader screen 36,- at which surface an air barrier zone 38 is generated, preventing deposition or" the dust on the aerating disk and forming adjacent thereto a suspension of the dust of. graduated density with the generation of a phenomenon wherein the powder and air exhibit the characteristics of a fluid. The powder is not, at this point, entrained in the air but may be stirred as any liquid, and may be referred to as fluidized.

Within this barrier zone I position a Venturi mixer 39 which has a line 40 connected with the line 32 previously described. The Venturi inlet 41 is directed to face toward the aerating disk 36. The Venturi nozzle 42 projects the air and the entrained dust into the port 43 which is connected by the line 44 with the Y 45, whose branches 46 and 47 are connected with the lines 48 and 49 leading to the deposition chamber 50, to direct the charge through the ports 51 and 52 positioned within the chamber in staggered relation.

The chamber 50' is large enough to greatly reduce the velocity of the incoming air drift and the eccentric or staggeredrelationship of the ports 51 and 52 assures circulation. In the reduced velocity and pressure the air which entrains the dust particle becomes separated from it, permitting the particle to precipitate without agglomeration, coalescence, or flocculation.

The chamber has an entrance slit 53 and an exit slit 54 through which the web W of indeterminate length enters and emerges. Closure whiskers, brushes or a flap of plush may be employed, though not necessary, to partially cover the slits and form air permeable slots, where the airdrift is controlled by the pressure regulator 14 which is adjusted with relation to the size of the chamber 50 that the powder liberated air gently escapes from the slits 53 and 54 without evidence of dust so as to require auxiliary dust catching and separating systems.

The material which may be treated may range in mesh size from 70 to micro-pulverization. A screen analysis of a typical powder or dust which may be employed is as follows:

Dusting talc, 89% passing a 325 mesh (Tyler) screen; 11% passing a 200 mesh screen; coarser than 70 mesh, none.

The pressure through the regulator may be adjusted from /2 pound to 20 pounds, depending upon the extensiveness of the chamber 50, the width of the Web and the rate of movement of the web of indeterminate length through and out of the chamber, and adjustment of the pressure is made in accordance with these operating conditions by a single control of the pressure regulator valve 14.

The combination of treatment, especially the initial fluidizing of the powder with the en-training thereof a through the aspirator or venturi mixer 39 produces a dry fog which is projected in the coating chamber 50, at which point there is complete absence of accretions, agglomerates, globs or coalescence of the powder, and the release of this mixture in the deposition chamber results in a separation or precipitation of the dust in a substantially still atmosphere.

The use of low air pressures prevents dust from floating into the atmosphere and the surrounding working areas, to eliminate respiratory problems and coating of operating machinery in the plant. The employment of an open powder hopper prevents any'accumulation of pressures, and accordingly the installation is unlikely to burst or require thick-walled vessels.

The minimizing of internal friction in entraining the particles into the coating chamber eliminates the generation of electrostatic charges, further to assure uniformity of deposition in predetermined quantities. The low pressure employed permit internal dusting of extrusions such as sausage casings, food envelopes, without altering the dimensions of the extrusion.

While I have shown and described the coating chamber 50 as dusting on one face of the web W, I may double coat the web, as illustrated in Figure 3, in which the web W may enter the chamber 50a through the entrance slot 53a and be guided over guide rolls 55, 56, 57, 58 and 59, and direct the emerging web through the slot 54a. The guide rolls thereby form loops 60 and 61 in which the face b anda, respectively, are upwardly faced.

With this arrangement, the hose lines 48 and 49 are multiplied to provide staggered ports 51a and 52a, 51b and 52b, and thereby create faces which are coated by the dust by precipitation from the atmosphere in the chamber without contacting with the guiding rolls until the point of emergence at the slot 54a, each of the faces b and a, respectively, being subjected to the gravitational deposition in a substantially quiescent atmosphere, as in the first embodiment described.

While I have described chambers 50 and 50a for coating fiat webbing, I may also coat tubular extrusions. In Figure 4 I illustrate a chamber 500 having circular openings 53c for ingress and 540 for egress of a tubular member T to be dusted. Ports 51c and 520 are arranged in staggered relation and connected With hoses 48 and 49, as in the prior embodiments. Conical ends 62 and 63 are provided to seal ofif the chambers and an additional port 51d may be included in the end wall 63, to assure a drift of the air for uni-form distribution.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent, is:

A dry dust deposition coating apparatus for applying dry dust coatings of the character to eliminate sticking, packing, and blocking, comprising; a deposition chamber having a substantially still atmosphere, means for releasing the dust as a dry, dust-laden fog in said deposition chamber, a hopper of substantially cylindrical contour having an open mouth through which the dust may be cascaded toward the bottom thereof, air supply means to form an air barrier of low turbulence in counter-current direction to the gravitating dust through said month, said air supply means comprising an air distributing, porous sheet providing an aerating disk to form the said air barrier of low turbulence above the bottom, thereby to re strain the dust from falling on said sheet, and arranged to form adjacent to said disk a fluidized suspension of the dust of graduated density from said sheet toward said month, an air aspirator having a feed-line intake port and discharge line adjacent said air barrier to withdraw the fluidized dust suspension from the air barrier zone in dry condition, and said discharge line being connected to at least a pair of branch lines extended to form shaped branch lines from which the charge may be directed to the deposition chamber, said spaced lines terminating with ports open within said chamber in opposed staggered relation to each other, the chamber being of a magnitude greatly to reduce the velocity of the incoming air drift and the staggered relationship of the ports assuring circulation of the incoming air drift, permitting particles to precipitate onto the material to be coated without substantial agglomeration, coalescence or flocculation.

References Cited in the tile of this patent UNITED STATES PATENTS 1,073,149 Lawrence Sept. 16, 1913 1,659,179 Wilson Feb. 14, 1928 1,736,969 Geiser Nov. 26, 1929 1,759,983 Houston May 27, 1930 2,375,766 Britcher May 15, 1945 2,419,835 Hester Apr. 29, 1947 2,509,983 Morrow May 30, 1950 2,614,528 Britcher Oct. 21, 1952 FOREIGN PATENTS 110,060 Great Britain -g. Oct. 11, 191 331,322 Great Britain July 3, 1930

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