US 3219520 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Nov. 23, 1965 R. J. BOX
PAPER MAKING APPARATUS AND AEHATING DEVICE WITH ELECTRICAL CLEANING MEANS 2 Sheets-Sheet 1 Filed Oct. 21, 1960 HOV. A.C. 3 1 2 4 FIGJ IN VEN TOR.
RICHARD J. BOX BY 42 6 ATTORNEYS Nov. 23, 1965 R. J. BOX 3,219,520
PAPER MAKING APPARATUS AND AERATING DEVICE WITH ELECTRICAL CLEANING MEANS Filed Oct. 21, 1960 2 Sheets-$heet 2 F I G 6 INVENTOR.
RICHARD J. BOX "@25 M ATTORNEYS United States Patent Office 3,219,520 Patented Nov. 23, 1965 PAPER MAKING APPARATUS AND AERATING DEVICE WITH ELECTRiCAL CLEANING MEANS Richard J. Box, St. Charles, liL, assignor to Hawley Products Company, St. Charles, Ill., a corporation of Delaware Filed Oct. 21, 1960, Ser. No. 64,575 3 Claims. (Cl. 162-274) In the various processes used for manufacturing pulp moldings, there is a need to clean the preforming or felting tools. Fine fibers, resinous materials, salts from water and other materials precipitate on the foraminous surfaces and gradually clog them to the point that improper formation, thin spots and even holes in the wet preform occur.
In usual practice, the preforming dies are removed intermittently from service for cleaning. T he cleaning is done by soaking in detergent solutions, dipping in hydrochloric acid, hosing with high pressure steam or water, and burning out with a torch. All of these methods consume appreciable time and labor and make it necessary to shut down the manufacturing operation temporarily.
One object of this invention is to provide a method for keeping felting dies clean.
Another object is to provide a method which can be used to keep dies continuously in a clean condition and can also be used intermittently for cleaning dirty dies.
A further object is to provide a method which cleans the dies while they are in use without interruption of manufacturing operations.
Another object is to provide a method which is generally applicable in the presence of water to the cleaning and maintenance in a clean condition of metallic foraminous devices of many kinds including water filters, filter presses, and air diffusion devices used for aeration of water and sewage.
Other objects and advantages of the invention will be apparent by reference to the following description and the accompanying drawings, in which,
FIG. 1 represents diagrammatically and partly in section an apparatus for cleaning a felting or forming die used for forming a preform or molding from an aqueous slurry of fibers, for example, cellulose fibers;
FIG. 2 is a plan view with parts broken away of the structure shown in FIG. 1 taken along the line 22 of FIG. 1;
FIG. 3 is a plan View of a part of the structure shown in FIG. 2 with the other parts removed;
FIG. 4 is an exploded elevational view, partly in section, of the structure shown in FIG. 2;
FIG. 5 is a perspective view, with parts broken away, of another embodiment of the invention, namely, an air diifuser tube; and
FIG. 6 is a cross sectional view of the air diffuser tube shown in FIG. 5, taken along the line 66 of FIG. 5.
Generally stated, the method of this invention comprises passing a relatively small direct current from the metallic preforming mold or other electrically conducting object to be cleaned as the anode through the surrounding aqueous material to a cathode such as metal walls of the tank containing the aqueous medium. The object to be cleaned is positive with respect to the receiving electrode or cathode by several volts, generally less than 5 and ordinarily in the range of l to 3 volts.
The invention embodies the principle of maintaining a positive electrical potential on a metallic (or other electrically conducting) foraminons device relative to a surrounding aqueous suspension or medium for the purpose of maintaining said foraminous device in a relatively clean or non-clog ed condition. the use of such an electrical potential for cleaning such devices after they have become clogged.
It also embodies It is very important that the correct polarity be maintained. If it is reversed, the rate of accumulation of dirt on the mold is increased rather than decreased. The positive polarity of the mold, or other part being kept clean or being cleaned, totally prevents the deposition of dirt, regardless of the charges carried by the dirt itself. For example, it has been found in the practice of the invention that negatively charged emulsions of polyvinyl acetate resin which normally deposit on the preforming molds rapidly are totally prevented from depositing on the molds by the method of this invention. Similarly, positively charged melamine colloids, such as that sold under the trade name of Parez 607 (a melamine-formaldehyde resin), and calcium salts from the water are prevented from precipitating. All of these materials precipitate on copper screens and cause substantial clogging in a few hours unless the method disclosed herein is used to prevent it.
FIG. 1 shows diagrammatically by way of illustration an electrical circuit suitable for use for keeping felting dies clean. It will be understood that the invention is not limited to the use of this circuit. In this circuit, a stepdown transformer 1 in series with a 2 microfarad capacitor 2 is connected to a volt 60 cycle alternating current power source, not shown, through Wires 3 and 4. The secondary of the transformer, which is wound to produce 6.3 volts when 110 volts is applied to the primary, is connected in series with a silicon rectifier 5, the preforming tank 6, the preforming slurry 7, the preforrning mold 8 and an ammeter 9. The polarity of the preforming mold is positive with respect to the slurry. This arrangement results in passage of a direct current in the range of about 0.4 to 1.0 ampere during the time that the preform mold is under water with molds of the size used for luggage shells, typewriter cases and other items of similar size. In instances where it is desired to adjust or limit the current to less than 0.4 ampere, a variable resistor is inserted in series with the secondary circuit. The 2 microfarad capacitor limits the current in case of accidental short circuiting of the mold to the tank to a current within the handling ability of the component parts. The ammeter serves as a guide to show that the circuit is functioning properly. The invention is not limited to the particular current values used above but these values are adequate for most purposes.
The electrical connection to the preforming mold may consist of rubber covered flexible cable such as will minimize leakage of current from the wire when the preform mold is under water.
It is important to insulate the preforming mold 3 from the associated moving platform 10 and tank 6 by means of a rubber gasket 11 or other non-conductive material so that the flow of current is directed from the surfaces of the preform mold into the slurry.
The amount of current used depends upon the conductivity of the slurry and the size of the preforming mold. For example, where the water of the slurry has a conductivity equivalent to 20 grains per gallon hardness reported as calcium carbonate, about 300 milliamperes keeps a perform mold for 21 inch luggage shells perfectly clean. Under the same conditions a 30 inch luggage preforming mold requires about 600 milliamperes to keep it clean.
If desired, the cleaning circuit may be operated intermittently whereby the preform mold is cleaned without removing it from use.
For example, in a given run a 25 inch luggage felter was used approximately 8 hours per day for ten days without cleaning except for occasional rinsing with water by the tank operator. At this time, the felter had become clogged to the point that some rejections of parts for cracks and thin spots were being made. At this time,
a current of 150 milliamperes was applied to the felter in accordance with the method diagrammed in FIG. 1. Operation of the felter was continued in this manner for 20 days more. During this time, the condition of the felter worsened slightly. Then the current was increased to 450 milliamperes and operation of the felter was continued. Three days later the felter had become perfectly clean and remained clean for days more at which time the run was discontinued.
FIGS. 2, 3 and 4 show in more detail the felting die, insulating washer and movable platen assembly. The washer or gasket 11 has a central opening 12 through which suction or partial vacuum may be applied from a suitable vacuum pump, not shown, or the like, connected to a passageway 13 in the platen 10.
The gasket 11 is preferably constructed of rubber about 4; inch thick but may be made from any other electrically non-conducting sheet material, e.g., polyethylene, neoprene, or the like, which seals the joint against vacuum leaks and electrically insulates the felting die from the moving platform.
The felter or forming die preferably consists of a cast bronze support 14 containing holes 15 over which is placed a 40-mesh copper screen 16 which is spot welded to the bronze support.
The felter assembly is mounted on a piston rod 17 which is advanced and retracted in a cylinder 18 and operated by air or hydraulic pressure from a suitable source, not shown. In operation, the felting or accretion of fibers on to the felting screen 16 is carried out by applying suction thereto (through flexible hose 30 and passageway 13, see FIG. 4) from within the felter beneath the liquid level where the resultant preform is removed a mixture of cellulose fibers and cut bundles of glass filaments, and the felting scheen 16 is then moved above the liquid level where the resultant perform is removed and, if desired, subjected to additional processing.
The connection from a positive source of potential at 19 causes the felting screen 16 to be anodic and the sides of the tank 6, which are usually made of steel, are cathodic by virtue of the connection at 20 to a negative source of potential. In this manner, clogging of the holes in the screen 16 and screen support 14 is prevented. As previously indicated, the current may be allowed to flow continuously without interfering with the felting operation or it may be applied intermittently.
In the examples given, the total screen surface areas exposed to the aqueous slurry during felting are calculated to be 3300 square inches for a 21-inch luggage case, 5100 square inches for a -inch luggage case, and 6100 square inches for a -inch luggage case. As previously observed, currents of approximately 300, 450 and 600 milliamperes, respectively, applied to said felters while immersed in the slurry keep them clean and free from deposits of various kinds.
Although the method of the invention is especially useful for keeping felting dies clean and for cleaning felters, it has applications in the field of water and sewage treatment where the cleaning of aeration devices is an important problem, as hereinafter described, and for other purposes where electrically conducting articles having holes therein are brought into contact with electrically conducting media which normally tend to clog said holes by depositing solids therein.
In present day sewage plants, it is common practice to fasten large numbers of air diffuser tubes to a pipe manifold installed inlarge aeration tanks. These dififuser tubes comprise a foraminous surface through which air is injected into the sewage to be treated. The perforations of the foraminous surfaces are tiny and gradually clog in use in much the same manner that pulp preforming molds clog. They are removed from operation periodically for cleaning.
The method of the present invention may be advantageously employed here to avoid the clogging and the concomitant labor and shutdown period necessary for cleaning.
A diffuser tube suitable for use in conjuncton with the method of the invention is shown in FIGS. 5 and 6. The tube consists of an insulating support 21 for a cylindrical wire screen 22 for diffusing the air into the sewage, two band-type clamps 23 and 24 for clamping the Screen 22 to the support 21, and a pipe fitting 25 affixed to the support for fastening the tube to a pipe manifold, not shown, and introducing air into the inside of the unit. In operation air enters the tube through the opening 26 and then enters the passageways 27 from which it passes through the openings in screen 22 into the liquid being treated.
The insulating support 21 may be molded of glass fibers and polyester resin, the pipe fitting 2.5 may be molded in, the clamps 23 and 24 and the wire screen 22 may be stainless steel or copper so as to resist corrosion by immersion in sewage. The electrical connection 28 may be made by brazing a wire for the positive connection to one of the band clamps or the bared end of the wire may be merely slipped between the clamp and the screen before tightening the clamp. The negative connection 29 may be made to the metal pipe manifold that brings air to the diffuser tubes.
The current required to keep such a screen clean may be in the range of about 1 to 50 milliamperes per diffuser tube depending upon whether the operation is continuous or intermittent and upon the conductivity of the sewage. The optimum conditions should be determined for each particular installation.
In some installations, especially where the electrical conductivity of the sewage is relatively high, it may be preferred to apply the electrical current intermittently in order to minimize electrolytic corrosion of the diffusion screens. This can be accomplished automatically by means of control circuits operated by an air flow rate controller, not shown, inasmuch as clogging of the diffusion screens reduces the air fiow through them. Such a control system can be readily applied by those skilled in the art.
It will be seen that the invention makes it possible to clean, and keep clean, in a very simple manner electrically conducting surfaces in processes where such surfaces are normally in contact with fluids that are electrically conducting and contain substances that normally tend to deposit on said surfaces.
The invention is hereby claimed as follows:
1. An apparatus comprising a vessel adapted to contain a conductive liquid, a support member mounted in said vessel and adapted to be submerged in liquid in said vessel, means on said member defining a fluid passage, an electrically-conductive, foraminous member mounted on said support member over said passage, means electrically insulating said foraminous member from said support member, means for applying a small, positive, electric potential of about 15 volts to said foraminous member, and means spaced from said foraminous member adapted to serve as the cathode for current passed through the liquid in said vessel.
2. A sewage treating apparatus adapted to be im mersed in sewage comprising an elongated support member including a tubular member adapted to be connected to an air supply line, said elongated member having formed on its outer surface elongated ribs with longitudinal grooves therebetween, said grooves serving as air passages, an electrically-conductive, hollow, cylindrical, metal screen mounted about said support member on said longitudinal ribs, said longitudinal grooves serving as means for conducting air supplied through said tubular member to and out of said screen, means electrically insulating said screen from said support member, and means for applying a small, positive, electrical potential of about l5 volts on said screen.
3. An apparatus for felting fibers from a liquid slurry of fibers which comprises a vessel adapted to hold a liquid slurry of fibers, a felter assembly having a foraminous, electrically-conductive felting member thereon mounted in said vessel, means for applying a suction in said felter assembly to draw said slurry toward said member and to felt fibers from said slurry on said fol-aminous member, means electrically insulating said foraminous member from said felter assembly, means for applying a small, positive electric potential of about 1-5 volts on said member, and means spaced from the foraminous member in said vessel adapted to serve as a cathode for current conducted through said liquid slurry when said potential is applied.
References Cited by the Examiner UNITED STATES PATENTS 190,654 5/1877 Wheeler 162-228 736,669 8/1903 Zoeller 204-130 855,389 5/1907 Dawkins 204-180 Allen 204-181 Cooper 162-387 Sheppard 204-183 Eberlin et al 204-181 Taylor et a1. 204-181 Taylor 204-181 Klein 204- Randall 162-382 Lyons 204- Subkow 204-300 Cottrell 204-188 Irons 204-180 Hayward 204-180 Hayward 204-180 Ricks 204-288 Whalen 162-192 JOHN H. MACK, Primary Examiner. JOHN R. SPECK, MURRAY TILLMAN, Examiners,
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,219,520 November 23, 1965 Richard J. Box
It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 3, line 33, for "where the resultant preform is removed" read of an aqueous slurry of fibers, for example, line 35, for "scheen" read screen Signed and sealed this 25th day of October 1966.
SEAL) RNEST .5mm EDWARD J. BRENNER Offioer I Commissioner of Patents