Powder metering system

A system for distributing powder which is stored in a hopper and delivered from the hopper to distributing nozzles. A metering construction is interposed between the hopper and the distributing nozzles, this construction comprising a roller which receives powder from the hopper. The roller carries powder at a controlled rate to a passage where the powder is exposed to a pressurized fluid such as air. The powder is moved with the fluid to the distributing nozzles. Separate inlets, preferably for the introduction of air at atmospheric pressure, communicate with the passage. The distributing nozzles are designed for the distribution of the powder evenly over wide sheets of paper, foil or plastic, and over the printed surfaces of a web of paper or plastic.

This invention is directed to constructions for the handling of powder and, 
in particular, to constructions which serve to deliver powder in a 
carefully controlled fashion. The invention is particularly usable in 
operations which involve the application of powder to the printed surfaces 
of sheets of paper or plastic and the like. 
Electrostatic powder sprayers are widely employed as a means for applying 
anti-offset powders to the printed surfaces of sheets, webs and the like. 
Such application of powders takes place after printed material emerges 
from a printing press. 
Powder utilized in such operations typically comprises a random mixture 
ranging in size from 5 to 100 microns. Because of the size of the 
particles involved, numerous problems have developed when attempting to 
uniformly distribute th powder over a sufficiently long period of time to 
provide an efficient operation. The small particle size coupled with the 
size range involved, results in a material which cannot be handled on a 
predictable basis with systems currently available for use. 
One attempt to solve the handling problems involved the use of a carburetor 
which fluidized powder in a jar-like container with the powder being 
contained in a rapidly moving air stream for movement to distributing 
means. Such systems utilize a needle valve or the like for increasing or 
decreasing the introduction of fluidizing air, and the air flow is 
continuously interrupted to provide for agitation of the powder. This 
arrangement leads to the removal of the smaller particles in the size 
range during the early stages of operation leading eventually to the 
presence of only the coarser fraction of the material for distribution. 
This necessitates continuing changes in operating conditions in order to 
maintain uniformity. 
An alternative system utilizes a vibrator for sifting powder into a 
receiver where the powder is picked up by an air stream. It has been 
found, however, that the vibration of the powder results in packing and 
clogging. Futhermore, the necessity for agitation limits the size of such 
systems. Difficulties in providing uniformity are also experienced so that 
constant attention to flow control is required. 
Another system utilizes a long fountain-type powder hopper placed across 
the path which the sheets must pass on the way to the delivery pile, and 
this system is an improvement. Typically, the system employs a textured or 
engraved roller upon which powder is metered by using a steel or plastic 
blade in contact tangentially with the roller. This provides an even 
coating of powder which is carried out of the hopper into an alternating 
high voltage field generated by a neon static tube. The powder particles 
are blasted off the roller surface and then fall, sometimes assisted by a 
gently flowing curtain of air, to the sheets. The degree of powder 
application is controlled by varying the speed of the roller. 
In this system, the hopper, blade, roller and tube must extend across the 
entire width of the press, as close to the sheets as possible, and in the 
correct position. The result is that filling of the hopper requires 
shutting down the machinery, and a man then ladles powder into the hopper. 
This is not easily done on some machines. 
Automatic filler equipment has been proposed for feeding powder into such 
hoppers. This equipment is limited in application to systems where nearly 
straight line access is available at the end of the hopper, from outside 
the press frames. This sometimes results in awkward or impossible 
placement of the filler hopper. In any event, the system has not proven 
reliable enough to receive general acceptance. 
The system of this invention is designed to overcome the problems 
experienced with prior art systems. This invention provides for large 
capacity as well as great uniformity of operation so that the attention 
necessary for insuring uniform powder distribution is greatly reduced. 
It is, accordingly, the principle object of this invention to provide a 
powder distributing system which is characterized by a control arrangement 
which permits the distribution of powder onto printed sheets and the like 
in a highly efficient manner. 
It is a more specific object of this invention to provide a system of the 
type described which is characterized by a metering arrangement for the 
powder including unique means for delivering the powder to nozzle 
constructions, whereby the mechanism of the invention substantially 
eliminates problems characterizing prior art systems.

The construction of this invention involves a system for distributing 
powder wherein the powder is stored in a hopper and delivered to 
distributing means for the application of the powder to printed surfaces 
or for similar purposes. One aspect of the invention relates to metering 
means which are interposed between the hopper and the distributor. The 
metering means comprise a roller, and means are employed for maintaining a 
substantially constant amount of powder on the roller surface. A doctor 
blade structure is preferably utilized for this purpose. 
In accordance with the preferred form of the invention, a source of 
compressed air is introduced into a passage which communicates with the 
roller surface. As the roller introduces powder into the vicinity of the 
passage, the compressed air picks up the powder for movement to the 
distributing means. 
The preferred form of the invention further includes one or more secondary 
air inlet openings into the passage. These secondary openings supply air 
or other fluid which is maintained at a pressure, such as ambient 
pressure, which is lower than the pressure of the compressed air. The 
low-pressure fluid is introduced in response to negative pressure 
conditions which are developed within the passage. 
The invention also utilizes a manifold system whereby the powder-fluid 
mixture in the passage is divided. Specifically, a manifold is employed 
for directing the mixture into separate flexible hoses, and these hoses 
are connected to nozzle units. Each nozzle units includes a plurality of 
openings, and nozzle heads defining distribution orifices are attached at 
these openings. The nozzle heads direct the powder-fluid mixture onto the 
printed web or the like which is running through the system. 
The accompanying drawings illustrate in detail the concepts of the 
invention. Referring to FIG. 1, a web or sheet 10 which is to be exposed 
to powder is positioned below an assembly employed for delivering powder 
to the web surface. This assembly includes a mounting bar 12 supported at 
its ends by any suitable means. The mounting bar carries a plurality of 
nozzle units 16. Each nozzle unit carries four nozzle heads 18. 
Flexible hoses 20 extend from intermediate manifolds 22 to fittings 24 
associated with each nozzle unit 16. As noted, three intermediate 
manifolds 22 are utilized in conjunction with seven nozzle units 16. In 
the embodiment illustrated, the right-hand manifold 22 directs a 
fluidpowder mixture to two nozzle units 16, one at each end of the bar 12, 
while the other two manifolds direct the mixture to the remaining five 
nozzle units. Many variations in the arrangement of these structures are 
available. 
As shown in the illustrated example, three flexible hoses 26 are utilized 
for feeding the mixture to the intermediate manifolds 22. The hoses 26 are 
connected to a main manifold 28 shown in FIG. 3. A pipe 30 is connected to 
the manifold 28 for feeding the mixture to this manifold. 
One of the hoses 26 is utilized for directing the mixture to the right-hand 
manifold 22, and a valve (not shown) associated with the manifold 28 is 
utilized for controlling the delivery of the mixture to this manifold 22. 
Accordingly, by shutting off this valve, the two end nozzle units 16 are 
deactivated so that powder will not be dispensed when a sheet or web of 
lesser width is moving through the equipment. A second on-off valve for 
the manifold 28 will be provided for controlling delivery through a second 
hose 26 to thereby control movement of mixture to a separate manifold 22 
thereby permitting the deactivation of additional nozzle units 16. 
Preferably, the two nozzle units spaced inwardly from the end units will 
be so-controlled. In a typical system, a nozzle unit 16 will spray six 
inches of surface area so that closing of the first mentioned valve will 
cut off six inches of spraying at each end, while closing of the second 
mentioned valve will cut off an additional six inches from each end. With 
this system, selectively for minimizing waste is provided in a highly 
efficient fashion. 
As best shown in FIGS. 2, 3 and 4, the powder employed for forming the 
mixture is stored in a hopper 32. This hopper tapers downwardly to a 
discharge end, defining a discharge opening 34, and means for metering 
powder discharged from the hopper are located in this position. 
The opening 34 is defined in a bottom wall 36 of the hopper, and a 
plurality of openings 38 are provided for attaching a plate 40 to the 
hopper. The plate 40 in turn defines openings for receiving bolts 42 which 
serve to attach a second plate 44. A gasket 46 is preferably interposed 
between the plates 40 and 44 to avoid seepage of powder from between the 
plates. 
The plate 44 serves as a means for supporting metering units 48. This 
metering unit is attached to the plate by fasteners (not shown), and a 
gasket 50 is again utilized to provide a seal at this joint. 
The metering unit 48 consists of a cylindrical housing 52, the housing 
defining a horizontal bore 54 for receiving shaft 56. Bearings 58 defining 
flanges 60 are provided in the bore 54. 
A motor (not shown) is provided, the motor having a driving shaft 61 and an 
associated sprocket 63. The chain 65 extends to sprocket 67 which is tied 
to the shaft 56. The motor utilized is preferably a gear motor adapted to 
run efficiently at variable speeds. A metering roller 62 on the shaft 56 
defines an engraved surface area 64. This may be a two-piece unit with the 
roller tied to the shaft or the combination may be machined from one 
piece. 
A typical roller comprises a No. 17 Quadqravure roller produced by Pamarco. 
It will be understood, however, that a variety of engraved, knurled or 
etched roller surfaces are contemplated since this is only one variable to 
be considered when determining the feed rate. Roller width, diameter and 
speed are also factors which can be varied for purposes of controlling the 
feed rate. Furthermore, different feed rates are contemplated, depending 
upon the particular application involved with a typical setup involving a 
twoinch diameter, 5/8 inch wide roller rotating at 80 RPM delivering 5 
pounds of powder per hour. The same roller running at speeds as low as one 
RPM will deliver in the order of 1/4 pound per hour. 
The roller is positioned within a cavity 66 defined by the housing 52. A 
pair of sealing sleeves 68 are positioned within this cavity so that the 
inner edges of these sleeves are positioned immediately adjacent the side 
walls of the engraved roller portion 64, this arrangement being provided 
for avoiding passage of powder into the cavity 66. The various seals 
referred to herein may be formed of tetrafluoro ethylene, for example, as 
marketed under the name Teflon by du Pont, or similar materials which have 
good wear resistance and sealing qualities. 
The upper portion of the housing 52 defines a chamber 70 communicating with 
the opening 34 in the bottom wall of the hopper 32 and with aligned 
openings in plates 40 and 44. As best illustrated in FIG. 3a, a pair of 
doctor blades 76 are positioned in the chamber 70, and immediately 
adjacent the periphery of the engraved portion 64 of the roller 62. The 
doctor blades define slots, and screws 78 are utilized for adjustably 
positioning these blades whereby the pressure between the blade surfaces 
and the roller periphery can be varied. 
The cylindrical housing 52 defines a passage 80 which is exposed to the 
roller portion 64. A pressurized fluid inlet pipe 82 is connected to 
fitting 84 which includes internal passages for directing the fluid to 
inlet port 86 which communicates with the passage 80. A second line 88 
associated with the fitting 84 is connected to a pressure gauge whereby 
the pressure of the fluid directed into the passage 80 may be monitored. 
Air is a satisfactory fluid for utilization in this system; however, other 
fluids are contemplated. 
A secondary air port 90 has its inner end communicating with the passage 80 
and, in the embodiment illustrated, its outer end communicates with the 
atmosphere. The provision of this port results in the introduction of air 
into the passage 80 over and above the compressed air entering through the 
port 86. Additional secondary air ports 91 (FIG. 3a) may be utilized for 
introducing air into the cavity 66. 
FIG. 3b illustrates an alternative arrangement for controlling the movement 
of powder onto the roller 62. This structure includes a plate 140 held in 
position to span the passage 142 by means of screws 144. A gasket 146 is 
positioned on the underside of the plate 140 to prevent all powder leakage 
from around the periphery of the plate. 
The central opening defined by the plate receives a metering shoe 148, and 
the gasket 146 extends between the underside of the plate and flange 150 
formed on the shoe. Accordingly, leakage between the adjoining surfaces of 
the plate and shoe is eliminated. The bore defined by the shoe thus 
provides the sole avenue for movement of powder onto the roller surface, 
and the size of this bore can be varied as one means for controlling the 
rate of powder delivery. 
As with the doctor blades of FIG. 3a, the metering shoe is adapted to be 
fit snugly against the surface of roller 62. Since this surface is 
engraved, the provision is made for the carrying of powder by the roll 
beneath the edges of the shoe. In order to minimize maintenance, the shoe 
is preferably formed of a wear-resistant material such as nylon or Delryn. 
FIGS. 5 through 8 illustrate details of a nozzle unit 16 which may be 
utilized in the practice of the invention. As shown in FIG. 1, these 
nozzle units are attached to support bar 12, and any suitable fasteners 
may be utilized for this purpose. 
The fittings 24 for each nozzle unit are connected at the threaded openings 
92 shown in FIG. 7. The fluid-powder mixture which enters the nozzle units 
is received within circular chamber 94, it being understood that the inner 
face 93 of the nozzle unit is held tightly against the surface of 
supporting bar 12 whereby the mixture in the chamber 94 is confined. 
The chamber 94 has an outlet passage 96 and branch passages 98 
communicating therewith. The branch passages extend to end portions 100 
beyond chambers 102. The chambers 102 are utilized for equalizing the 
powder flow to both of the branch passages. The threaded openings 104 
shown in FIGS. 6 and 8 provide a means for attaching the fasteners that 
hold the nozzle 16 to the bar 12. 
As best shown in FIG. 7, a plug 95 defining a flange 97 is press fit into 
the chamber 94 whereby the air and powder mixture entering through opening 
92 is split and flows around the sides of the plug. At the exit end of the 
chamber 94, the separate streams are rejoined, and turbulence results 
whereby an increased mixing tendency is developed. 
The fastener elements threaded into the openings 104 define shoulders which 
develop a similar mixing in this area. The extent of these shoulders 
relative to the chambers 102 is shown in dotted lines at 105 in FIG. 5. It 
is to be understood that the mixing concepts achieved by the plug and 
fastener arrangement is not a part of this invention. 
The portions 100 of the branch passages 98 communicate with small diameter 
openings 106 with these openings extending to bores 108. Nozzle heads 18 
are adapted to be pressed into these openings 108 whereby the fluid-powder 
mixture is directed to a sheet or web of material moving adjacent to the 
nozzle heads. 
FIGS. 9-11 illustrate a form of the invention which includes means for 
collecting excess powder from areas adjacent the fluid-powder distributing 
means. This arrangement includes inner walls 108 and outer walls 110 which 
serve as collecting areas for excess powder. Baffle elements 112 are 
located within these chambers to minimize the collection of powder 
directly from the distributing nozzles and before the powder has more 
permanently associated itself with the web or sheet being sprayed. Exhaust 
openings 114 are positioned beyond the baffles 112, and these openings may 
be connected to any suitable evacuating source. As best shown in FIG. 10, 
the excess powder collecting structures 116 are preferably in modular form 
so that such structures can be readily added or replaced in the system. In 
addition, the number of structures in use can be readily varied as the 
width of a web or sheet is varied. 
FIGS. 9-11 also illustrate a modified form of nozzle means. In this 
embodiment, the nozzle supporting bar 118 is attached by means of bolts 
120 to the transverse wall 122. The nozzle units 124 are attached to the 
supporting bar at spaced intervals along its length. A fitting 126 is 
associated with each nozzle unit for purposes of introducing the 
fluid-powder mixture into the nozzle unit. 
The nozzle heads 128 are attached by press fitting of the heads into 
position. It is also contemplated that the nozzle heads be threaded into 
position. 
It will be noted that each nozzle head is provided with a cone-shaped 
extension 130. It has been found that this head design more effectively 
delivers the powder-fluid mixture, and at the same time, the extended 
design avoids build-up of powder on the surfaces of the supporting bar and 
the nozzle units. 
The construction of this invention provides for the efficient distribution 
of powder onto the surfaces of moving webs. The hopper 32 utilized in the 
construction may comprise a large hopper, typically a 25-pound capacity 
hopper. Accordingly, the system has advantages over prior systems which 
required the use of substantially smaller sources of powder supply. 
In handling the powder, it is not necessary to provide an interrupted flow 
of air or any extensive equipment for purposes of agitating the powder as 
a part of or prior to the powder feeding operation. FIG. 2 illustrates a 
solenoid operated device 132 utilized for bumping the hopper at regular 
intervals to maintain the powder in the hopper at a reasonably constant 
level. This action generally takes place every one to five seconds, and is 
fully sufficient for purposes of insuring continuous flow of powder to the 
metering construction located at the bottom of the hopper. 
As noted, the system utilizes a gear motor drive for the metering roller 62 
whereby readily controlled roller speed is maintained. The utilization of 
the doctor blades coupled with the regulated speed of the roller 62 
provides a highly uniform powder distribution over the surfaces of sheets 
being treated. In this connection, particle separation which occurs during 
use of fluidizing or vibrating is not a factor in the system described. 
The powder fed into contact with the metering roll is always from the 
bottom of hopper 32 and will be essentially uniform in size composition 
during operation of the system. 
It will be appreciated that the flow of fluid into the passage 80 through 
port 86 is maintained constant, for example, at a rate in the order of 
four to four and one-half cubic feet per minute. The uniformity of 
operation is enhanced by the use of the inlet port 90 since this serves as 
a means for equalizing air pressure in the passage 80. More specifically, 
the introduction of compressed air through port 86 develops a venturi 
effect in the passage 80. Air is, therefore, fed into the passage through 
the secondary air hole 90, and a balance of pressure is maintained. This, 
in particular, prevents the problem of siphoning while also serving to 
increase the total volume of air carried with the powder. 
As noted, additional air ports 91 communicate atmospheric air with the 
chamber cavity 66 which receives roller 64. These additional air ports 
also serve to equalize air pressure thereby stabilizing the rate of 
delivery of powder by the roller 64. 
In a typical system, four nozzle units may be attached to a supporting bar; 
however, on a large 60-inch press, 10 such units have been utilized. This 
results in 40 nozzle outlets spaced approximately one and one-half inches 
apart. As discussed, the manifold structures employed preferably have 
means for cutting off one or more of the nozzle heads mounted on a nozzle 
supporting bar. Thus, in a 60-inch system involving 10 nozzle heads, it 
may be desirable to run webs or sheets of smaller than normal width. As 
noted, the manifold 28 includes valves, and by turning off one or more of 
the nozzle openings through operation of the valves, the powder dispensing 
can be selectively controlled. Similarly, it is contemplated that the 
manifold structures 22 include means for selectively distributing the 
powder. 
With reference to the metering roller, the face width of the roller, the 
degree of engraving, and the speed of operation, will all effect the rate 
of delivery of powder to the passage 80. Accordingly, means are readily 
available for controlling the flow rate without affecting the basic 
principles of operation. 
The ability to maintain continuous and uniform feed provides for extremely 
uniform powder distribution on the web or sheets being handled. This 
uniformity is particularly true from edge-to-edge of the sheet or web 
since the various manifold controls utilized in the system provide for 
flow of material from the nozzle head uniformly irrespective of the nozzle 
head position along the length of the supporting bar. 
The uniform flow also minimizes build-up of material in pipes, tubes and 
the like. Furthermore, there is no necessity for locating the powder 
supply hopper in the immediate vicinity of the distributing nozzles. The 
hopper can be located in any convenient place without in any way affecting 
the uniformity of the powder distribution. 
It will be understood that the powder spraying system described above can 
be modified in various ways without departing from the spirit of the 
invention particularly as defined in the following claims.