US2449972A - Elimination of static electricity - Google Patents

Description

R. BEACH ELIMINATION OF STATIC ELECTRICITY Sept. 28, 1948.

Filed June 27, 1945 INVENTOR fat/A J1me BY .2 ATT RNEY' Patented Sept. 28, 19 48 UNlTED STATES I PATENT OFFICE Claims.

The invention here disclosed relates to the elimination, neutralization or dissipation of static electricity.

Particular objects of the invention are to neutralize and remove static electricity impressed on moving surfaces, such as travelling belts or webs.

More particularly it is a purpose of the invention to accomplish this without resort to separately generated, neutralizing voltages and without connection of any sort to local power sources. 7

Further objects, in line with the above, are to provide electrostatic eliminating means which will be safe in every way and of a character not to injure the web or other material in case of accidental contact therewith.

Further important objects are to provide practical and efficient electrostatic eliminating means of simple, inexpensive form, easily installed, occupying but small space, wholly automatic in its action, requiring no servicing and of a nature to last indefinitely without attention of any sort.

Other desirable objects and the novel features by which the purposes of the invention are attained are set forth or will appear in the course of the following specification.

The drawing accompanying and forming part of the specification illustrates a typical practical embodiment of the invention but it is to be appreciated that structure may be modified and changed as regards the immediate illustration, all within the true intent and broad scope of the invention as hereinafter defined and claimed.

Fig. 1 in the drawing is a diagrammatic view illustrating the invention as applied to the elimination or neutralization of the static electricity generated bya travelling web;

Fig. 2 is a broken cross sectional view as on substantially the plane of line 22 of Fig. 1, illustrating details of the actual physical structure:

Fig. 3 is a cross sectional .view of the brush and supporting structure taken on substantially the plane of line 3-8 of Fig. 2;

Figs. 4 and 5 are diagrammatic views illustrating the high potential gradient of the convergent field effect attained by the use of separate tufts of wire bristles spaced from the surface of the travelling material;

Figs. 6 and 'l are similar views illustrating the absence of high potential gradient under conditions of a uniformly distributed electric field.

Fig. 1 illustrates more or less diagrammatically a typical installation of the invention for overcoming static effects on a travelling Web ID. This web which may be any processed stock, such as rubber plystock, paper web, or various types of fabric, acquires electric charge as it leaves the supporting, guiding or processing rolls I2 over which it passes.

These charges are neutralized in the present invention by tufts ll of fine wire bristles, preferably supported in separated, relatively insulated relation spaced from the charged surface and electrically connected together and to round. While this separated relation is preferred, the tufts may be disposed to form a continuous line of bristles.

For practical reasons the sepanate tufts are preferably all mounted in spaced insulated relation on' a single common support, such as a bar l3 of hard, kiln-dried, paraffin treated, wood or generally similar dielectric material. Su'ch material has a constant insulating strength comparable with wax and is thus suited to the need for providing a support of substantially constant insulating or dielectric strength of a high order. This provides a unitary brush structure which may be handled as such and mounted in proper spaced relation at one side of, that is, either over or under, the material being discharged.

In the illustration the brush is mounted above the web and usually this may be preferred as themost convenient position.

Any suitable means may be employed for so mounting the brush, such as in the illustration, brackets i4 attached to the frame or base portions I5 of the machine and carrying an angle bar I6 extending across the web and to which the insulating brush bar is attached, as by screw fastenings l'l.

Preferably and as indicated in Fig. 3, the angle bar i6 is of insulating material, such as hard fibre or the like. In place of this angle bar, a sufficiently strong bar of wood or other insulating material .may be used.

The tufts of bristles are shown as mounted by having the base portions of the same engaged in sockets l8 in the wooden or other insulating supporting bar l3. I

The tufts of bristles, while relatively insulated, are electrically connected together by a suitable conductor, which is connected to ground.

A combination connecting and securing effect is accomplished in the illustration by using a flexible bare conductor wire l9 formed into loops engaged in the tufts. -These loops, as indicated at 20, Figs. 2 and 3, may be formed by doubling the wire down through openings 2| in the top of the bar in line with the sockets l8 and, after catching such loops in the bristle wires, pulling them back up through such holes, with intervening sections of wire left connecting the bristle securing loops to serve as a continuous connecting conductor.

One or both ends or any intermediate portion of the connecting wire is brought out and extended to some grounded connection, for example as shown in Fig. 2, clamped to one of the bolts or screws 22 securing the angle bar on the supporting brackets l4.

The wire bristles may be of fine brass wire about 0.002" to 0.004". The spacing of the tufts ordinarily may be about 1 to 3 inches apart and the tufts should project from the insulating support on which they are mounted usually about 1 inches orbetween 1 inch and 2 inches. The connecting wire should be strong enough to pull and hold the tufts firmly in place and heavy enough to easily carry the grounding current. The length of the brush made up of the spaced tufts should be approximately equal to the width of the web, sheets or stock under treatment.

The principle involved in the neutralization of the charges generated on the moving surface is that of ionizing the molecules of air at the tips of the fine wire bristles by virtue of an exceedingly high potential gradient. The air ions of opposite polarity to the charges on the stock are strongly attracted to the stock, combining with them and neutralizing the charges.

To appreciate how the essential potential gradient is produced at the tips of the bristles even with relatively low voltage between the charged stock and the grounded brush, reference is directed first to Figs. 6 and '7. These views indicate the effect of a D. C. voltage V impressed across two parallel plates A and B spaced the distance (1. These plates being oppositely charged, there is produced a uniform electric field, as indicated by the uniformly spaced lines, Fig. 6. This field being uniformly distributed in the space between the plates, the distribution of the impressed voltage at any part of the. intervening space can be designated by the potential gradient of V/d or as so many volts per centimeter. 'I'his voltage across the plates is distributed lineally with respect to the spacing between the plates. and hence the voltage gradient is uniform or constant, as indicated in the corresponding graph, Fig. '7.

Fig. 4 shows how by substituting a tuft of fine wire bristles for plate A, all the lines of electric force from plate B will converge upon the extremely small areas of the tips of the bristles. The electric field then, instead of being uniformly disposed, is highly concentrated in the space near the tips of the bristles with the gradient approximately as indicated by the graph in Fig. 5. Most of the voltage between th electrodes is thus concentrated in the short space directly in front of the bristles. The voltage gradient at this location is high enough to ionize the neutral molecules of air to the extent of forcing electrons out of the intervening air molecules.

Considering the process of ionization, it is known that in a neutral atom the orbital electrons, the small negative charges, are counterbalanced by an equal number of Positive electric charges in the nucleus. In the presence of a sufficiently high electric field an electron farthest from the nucleus may be forced out of the neutral atom, to form two ions,,one a freely moving negative ion, the electron, and the other a positive ion, which is the remainder of the atom. The atom, having lost a negative charge, then possesses a preponderance of positive electricity by the amount of one unit of charge. This process of ionization of the atoms of the molecules of air by the brush of the present invention is attained by the high potential gradient created at the tips of the bristles.

To maintain the convergent field essential to the high potential gradient, it will be seen that it i important that the tips of the bristles be an appreciable distance from the charged surface, so as to coliect'the convergent energy from an appreciable area, that the tips of the bristles be an appreciable distance from the support which carries them and that the supporting means be of.

dielectric material, so that the lines of force will concentrate on the tips of the bristles and not stray off to the support at the back of or at the sides of the bristles.

For a further understanding of the invention reference is made to the fact that with any two dissimilar substances in contact an unbalance of atomic forces occurs at their interfacial boundary and that as a result of this the electrons pass from the substance of higher dielectric constant to the other. The substance receiving the electrons becomes negatively charged and the other, by losing electrons, acquires an equal value of positive electrification. The voltage created between the two bythis migration of electrons is the contact difference of potential."

When the substances are separated, if one or both are insulators, the electrons which migrated from one to the other are entrapped there and the substances have thus acquired a certain amount of electricity. Two other kinds of substances'would acquire a greater or a lesser charge, depending upon their physical properties,

As the charged substances are moved apart the capacitor effect between them decreases and the voltage increases and to great magnitudes.

The relationship for this action may be expressed- Q-the charge C-the capacitance from which it follows that voltage increases as separation of the plates increases, for a fixed charge Q of the condenser.

In illustration of the above, it can be considered that stock is charged in moving over processing or idler rolls,- as in Fig. 1. When such stock is in contact with the metallic surface of a roll, the two materials, the stock and the steel of the rolls, are no closer together than the diameter of an average atom, which is 10- cm. The contact voltage between the two substances may be considered to be one millivolt (0.001 volt), As the moving stock passes the break-away line of tengency with the roll and separation increases 1,000 fold, the separation becomes 10" em, but the voltage. on the above relationship, will have increased 1,000 fold or to one volt. As separation increases another 1,000 fold, the physical separation becomes em, but voltage has increased to 1.000 volts. As the separation increases still more, say 100 fold, and becomes the appreciable distance of one centimeter, the voltage. having increased one hundred fold, will be 100,000 volts.

This linear increase or voltage with distance of separation does not, however, continue indefinitely, because with further separation the electric field becomes diverted to other parts of the condenser system and because at these high voltages the air molecules become ionized, causing some of the condenser charges to be neutralized.

For such reasons it has been found best to locate the tips of the bristles, in most cases, about 4 to 5 inches away from the break-away line and about 3 to 4 inches from the surface oi the stock.

Direct electrification is produced only on the side of the stock in contact with the roll. Assuming this electrification to be negative, the charges will repel electrons from the atoms within the stock, causing them to migrate to the opposite side of the stock. For this reason the electrons may be neutralized on either side of the stock. since those on the other side return to the ionized atoms within the material, so that the stock is no longer electrified.

The ultra sharp corner edges at the ends of the fine wire bristles, in the arrangement of the tufts described, create a high. potential gradient, with only a relatively small impressed voltage between the tuft and charged stock sufficient to effect ionization of the air molecules to neutralize charges on the stock. a

The ends of the bristles or the several tufts should be approximately the same distance away from the stock and the ends should be far enough away from the dielectric support so that the convergent electric fields terminate on thepoint's instead of partly on the dielectric support. The use of insulating material for the support rather than conductive material maintains the convergent state and prevents distribution partly into the supporting structure.

Each tuft composed of many fine wires provides sufllcient mechanical strength but is resilient enough to avoid injury either to an operator or to any stock that might contact it.

The metallic structure of the bristles and the 55 interconnecting wire constitutes, in conjunction with the charged stock, an extremely small elec trical capacitance or'condenser effect, and this is of particular importance. Only a small amount of electrical energy can be'stored in this small capacitance and hence if an electric spark should pass between the charged plystock and the bristies, the energy of such spark would be insufficient to ignite any flammable vapor-air mixture that, might be present within the sparking zone.

where C=capacitance of the brush, and V==voltage between the brush and the charged stock.

From this equation the voltage which would produce the minimum energy of 0.001 or 10- Joule for ignition would be calculated- V=4.4 8 x 10-=44,800 volts, approximately and hence Hence about 45,000 volts would be the minimum voltage that would produce sufl'icient energy in a spark, if one should occur, to ignite an explosive mixture of solvent vapors from a capacitor 10 of one micromicrofarad. With the brush of this invention, however, such a high voltage could not occur as the ionizing influence or the ultra high voltage gradient at the ends of the bristles would create such copious amounts of neutralizing ions as to lower the voltage to almost nil.

In actual practice the capacitance of the antistatic brush of thisinvention would ordinarily be considerably less than one micromicrofarad, and hence an even higher voltage than 45,000 would be required to cause a hazardous spark, if one could occur. The ionization of the ambient air produced by the high potential gradient is so intense that sparking is practically impossible.

Being self-energized through the voltage estab- 30 lished between the charged stock and the groundgated, yielding tufts of fine, flexible, sharp ended spring wire bristles on said insulating bar and projecting a substantial distance away therefrom, said bristles-terminating with their ends all in substantially the same common plane.

means mounting said insulating bar with said substantially coplanar ends of the bristles spaced away from the charged surface a distance normally of substantially three to four inches and sufflcient to create and maintain intense convergent electric fields of high potential gradient from said charged surface to the ends of said tufts to produce copious ionization at the tips of the bristles and a conductor of small mass connecting said fin wire bristles and connected to ground, said apparatus being thereby or low electrical capacitance and being unconnected with any local power source.

2. The herein disclosed self-energizing apparatus for eliminating static electricity on an electrostatically charged surface, comprising a bar of insulating material having substantially constant dielectric strength of high value. elongated, yielding tufts of fine, flexible, sharp ended spring wire bristles on said insulating bar and rojecting a substantial distance away therefrom, said bristles terminating with their ends all in substantially the same common plane, means mounting said insulating bar with said substantially coplanar'ends ofthe bristles spaced away from the charged surface a distance normally of substantially three to four inches and suiilcient to create and maintain intense convergent electric fields of high potential gradient from said charged surface to the ends of said tufts to pro- 7 duce copious ionization at the tips of the bristles and a conductor of small mass connecting said fine wire bristles and connected to ground, said apparatus being thereby of low electrical capacitance and being unconnected with any local power source, said projecting tufts of the bristles being mounted in separated, relatively insulated relation on said insulating bar spaced about from one to three inches apart to thereby create at the respective tufts separate convergent fields of high potential gradient.

3. The herein disclosed self-energizing apparatus for eliminating static electricity on an electrostatically charged surface, comprising a bar of insulating material having substantially constant dielectric strength of high value, elongated, yielding tufts i fine, flexible, sharp ended spring wire bristles on said insulating bar and projecting a substantial distance away therefrom, said bristles terminating with their ends all in substantially the same common place. means mounting said insulating bar with said substantially coplanar ends of the bristles spaced away from the charged surface a distance normally of substantially three to four inches and sufficient to create and maintain intense convex-gent electric fields of high potential gradient from said charged surface to the ends of said tufts to produce copious ionization at the tips of the bristles and a conductor of small mass connecting said fine wire bristles and connected to ground, said apparatus being thereby of low electrical capacitance and being unconnected with any local power source, said insulating bar having sockets in one side and communicating openings in the other'side of the same, said tufts having base portions seated insaid sockets and said connecting conductor being a flexibl bare wire extending along said other side of the bar and having loops extending through said openings into holding engagement about said base portions of the tufts seated in said sockets to thereby mechanically secure as well as to electrically connect said tufts.

4. The herein disclosed self-energizing apparatus for eliminating static electricity on an electrostatically charged surface, comprising a bar of hard, kiln-dried, wax-treated wood having substantially constant dielectric strength of high value, elongated, yielding tufts of fine, flexible, sharp ended spring wire bristles on said insulating bar and projecting a substantial distance tense convergent electric fields of high potential gradient from said charged surface to the ends of said tufts to produce copious ionization at the tips of the bristles and a conductor of small mass connecting said fine wire bristles and connected to ground, said apparatus being thereby of low electrical capacitance and being unconnected with any local power source.

5. The herein disclosed self-energizing apparatus for eliminating static electricity on an electrostatically charged surface, comprising a bar of insulating material having substantially constant dielectric strength of high value, elongated, yielding tufts of fine, flexible sharp endedspring wire bristles on said insulatin bar and projecting a substantial distance away therefrom, said bristles terminating with their ends all in substantially the same common plane, means mounting said insulating bar with said substantially coplanar ends of the bristles spaced away from the charged surface a. distance normally of substantially three to four inches and sufilcient to create and maintain intense convergent electric fields of high potential gradient from said charged surface to the ends of said tufts to produce copious ionization at the tips of the bristles and a conductor of small mass connecting said fin wire bristles and connected to ground, said apparatus being thereby of low electrical capacitance and being unconnected with any local power source, said spring wire bristles being approximately 0.002" to 0.004 in diameter and the tufts of said bristles projecting away from the insulating bar a distance of approximately one to two and one-half inches.

ROBIN BEACH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 777,598 Chapman Dec. 13, 1904 836,576 Hardwicke Nov. 20, 1906 878,273 Chapman Feb. 4, 1908 997,085 O'Toole July 4, 1911 1,093,491 Smith Apr. 14, 1914 1,394,211 Morgan Oct. 18, 1921 1,680,310 Wehrle Aug. 14, 1928 1,712,294 Cox May 7, 1929 2,023,321 Gutman Dec. 3, 1935 FOREIGN PATENTS Number Country Date 107,005 Switzerland Jan. 9, 1924 581,695 France Dec. 3, 1924

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