STATIC ELIMINATORS
United States Patent 3619719
A static eliminator for blowing a stream of ionized air on to an exposed surface having a static charge to neutralize its charge and blow off attracted particles, the eliminator comprising an electrode within an insulating sleeve through which air under pressure is passed and ionizing voltage being applied between the electrode and a metal surface hidden from the electrode by the sleeve.
US Patent References:
Gaseous-ion generator for rooms in which there is a danger of explosion
Muller et al. - November 1963 - 3111605
Gaseous-ion generator for rooms in which there is a danger of explosion
Muller et al. - November 1963 - 3111605
Inventors:
Waller, John Reginald (London, EN)
Radington-meech, John Richard (London, EN)
Radington-meech, John Richard (London, EN)
Application Number:
04/832605
Publication Date:
11/09/1971
Filing Date:
06/12/1969
View Patent Images:
Export Citation:
Assignee:
Industrial Electrical Company Limited (London, EN)
Primary Class:
International Classes:
H05F3/04; H05F3/00; H05F3/00
Field of Search:
317/2,2.6,4
Primary Examiner:
Hix, Lee T.
Claims:
We claim
1. A static eliminator comprising a metal wall defining a chamber having a connection for communicating it with a source of air under pressure, said wall having at least one side opening, a high tension electric cable extending within said chamber and at least one needle electrode coupled to said cable within the chamber, a body of electrical insulating material within said chamber having a tubular portion surrounding said electrode in spaced relation therefrom and extending through said wall opening at least as far as the external surface of said wall so that there is no direct discharge path between said electrode and said wall, aperture means in said tubular portion providing communication between the interior of said chamber and said space around said electrode so that air under pressure may pass from said chamber around said electrode, a power unit for supplying electrical current to said cable, said power unit including a pressure switch which electrically disconnects the unit from the cable when the pressure of the air from the air source is below a preselected value.
2. A static eliminator as defined in claim 1, wherein said tubular portion projects through said metal wall and has a closed bottom wherein said electrode is fixed and an open outer end for discharge of air externally of said chamber.
3. A static eliminator as recited in claim 1, wherein said electrode is in contact with the cable.
4. A static eliminator as recited in claim 1, wherein said electrode is capacitatively coupled to the cable.
5. A static eliminator as recited in claim 4, wherein the electrode is in contact with a metal ring surrounding the cable.
6. A static eliminator as recited in claim 1, wherein the tubular portion of insulating material extends beyond the external wall of the metal chamber.
7. A static eliminator as recited in claim 1, wherein the metal wall comprises an elongated air box and includes a row of the said electrodes coupled to the cable.
1. A static eliminator comprising a metal wall defining a chamber having a connection for communicating it with a source of air under pressure, said wall having at least one side opening, a high tension electric cable extending within said chamber and at least one needle electrode coupled to said cable within the chamber, a body of electrical insulating material within said chamber having a tubular portion surrounding said electrode in spaced relation therefrom and extending through said wall opening at least as far as the external surface of said wall so that there is no direct discharge path between said electrode and said wall, aperture means in said tubular portion providing communication between the interior of said chamber and said space around said electrode so that air under pressure may pass from said chamber around said electrode, a power unit for supplying electrical current to said cable, said power unit including a pressure switch which electrically disconnects the unit from the cable when the pressure of the air from the air source is below a preselected value.
2. A static eliminator as defined in claim 1, wherein said tubular portion projects through said metal wall and has a closed bottom wherein said electrode is fixed and an open outer end for discharge of air externally of said chamber.
3. A static eliminator as recited in claim 1, wherein said electrode is in contact with the cable.
4. A static eliminator as recited in claim 1, wherein said electrode is capacitatively coupled to the cable.
5. A static eliminator as recited in claim 4, wherein the electrode is in contact with a metal ring surrounding the cable.
6. A static eliminator as recited in claim 1, wherein the tubular portion of insulating material extends beyond the external wall of the metal chamber.
7. A static eliminator as recited in claim 1, wherein the metal wall comprises an elongated air box and includes a row of the said electrodes coupled to the cable.
Description:
The invention relates to a static eliminator of the kind comprising means for blowing a stream of ionized air on to an exposed surface having a static charge to neutralize its charge and blow off attracted particles.
Static eliminators of this kind are known which have a tube of insulating material with a central needle or electrode and through which air is blown. The exit end of the tube is surrounded by a metal ring and a high voltage is applied between this ring and the electrode. Such static eliminators produce corona discharge during use and there is also a substantial risk of arcing. They are therefore unsafe for operation in the presence of inflammable or explosive materials or vapors.
An object of the present invention is to provide an improved static eliminator of the kind described which is safe for use in the presence of inflammable or explosive materials or vapors.
To this end a static eliminator according to the present invention, comprises a metal chamber for receiving air under pressure and containing a needle electrode or electrodes coupled to a cable for supplying a high tension to the electrode or electrodes, the or each electrode being surrounded by a tube of insulating material which extends at least as far as the external wall of the chamber so that there is no direct discharge path between the electrode and the chamber wall, the tube having a cavity surrounding the electrode and an airhole or holes connecting the cavity to the chamber so that air is blown around the electrode under pressure.
The or each electrode may be directly connected to the cable. Alternatively the or each electrode may be capacitatively coupled to the cable to provide a shockless static eliminator.
Embodiments of the invention will be described with reference to the accompanying drawings in which:
FIG. 1 is a side view of a static eliminator according to the present invention,
FIG. 2 is a section of an electrode and tube which may be used in the eliminator of FIG. 1, and
FIG. 3 is a section of another form of electrode and tube which may be used in the eliminator of FIG. 1.
FIG. 1 of the drawings shows a static eliminator suitable for removing static charge from printed paper or other material after processing which is contained in an elongated air box 1 adapted to fit transversely across the web. The box is of metal and is earthed during use, being provided with a metal lid 2 which has an airtight seal around its edges with the box. A high tension cable 3 in an insulating sleeve 4 extends longitudinally within the box, being led out of the box through a sealed solid-drawn conduit 5 for connection to a power unit or supply indicated at P. An inlet 6 is provided for the supply of air to the box from a single or multistage blower B. A pressure switch S may be incorporated in the power unit connected to be subject to the pressure supplied by the blower as shown in FIG. 1 to ensure that the high tension can only be applied when the air pressure in the box is above a preselected minimum value.
At spaced intervals along the length of the box are disposed tubes 7 of insulating material, such as P.T.F.E. the high tension cable passing through transverse openings 8 formed in the lower end portions of these tubes while at their upper ends the tubes are located in holes 9 in the lid, the insulated tubes being shouldered near their upper ends and urged by a spring 10 into engagement with the lid around the holes. This arrangement gives a reasonable seal but it is not necessarily airtight.
In the embodiment shown in FIG. 2 there is, along the axis of each tube, a needle electrode 11 which is screwed into the material of the tube 7 and extends through the cable sleeve 4 to the conductor 3 of the cable.
In the embodiment of FIG. 3 a needle electrode 11 is screwed into the material of the tube 7 and extends to a brass or metal tube 12 surrounding the insulating sleeve 4 of the cable and providing a shockless capacitive coupling. The tube shown is a ring fitting inside the opening 8 of each tube. However, the same effect could be achieved by applying a layer of metal to the outer surface of the insulating sleeve 4.
In both embodiments the upper tip 3 of the needle is a sufficient distance below the rim for electrical discharges to be avoided. The tubes are bored with one or more narrow airholes 14 to permit air under pressure to enter from the box into the space around the electrode and to be forced out through the tube end.
Because the insulating tubes extend through the lid the electrical field must curve round the rim and there is no direct discharge path. Electrical discharges are thus inhibited and the eliminator is safe for use in the presence of inflammable or explosive materials or vapors. The shape of the tubes also reduces the risk of arcing due to any metallic objects entering the tube. The pressure switch ensures that there must be an air pressure in the air box to drive out any vapor which may have leaked back before the high tension is applied.
The enclosure of the cable lead ensures that there can be no voltage leaks outside the air box. The air blower and power unit can either be isolated from the hazardous area or can be constructed from intrinsically safe components.
Static eliminators of this kind are known which have a tube of insulating material with a central needle or electrode and through which air is blown. The exit end of the tube is surrounded by a metal ring and a high voltage is applied between this ring and the electrode. Such static eliminators produce corona discharge during use and there is also a substantial risk of arcing. They are therefore unsafe for operation in the presence of inflammable or explosive materials or vapors.
An object of the present invention is to provide an improved static eliminator of the kind described which is safe for use in the presence of inflammable or explosive materials or vapors.
To this end a static eliminator according to the present invention, comprises a metal chamber for receiving air under pressure and containing a needle electrode or electrodes coupled to a cable for supplying a high tension to the electrode or electrodes, the or each electrode being surrounded by a tube of insulating material which extends at least as far as the external wall of the chamber so that there is no direct discharge path between the electrode and the chamber wall, the tube having a cavity surrounding the electrode and an airhole or holes connecting the cavity to the chamber so that air is blown around the electrode under pressure.
The or each electrode may be directly connected to the cable. Alternatively the or each electrode may be capacitatively coupled to the cable to provide a shockless static eliminator.
Embodiments of the invention will be described with reference to the accompanying drawings in which:
FIG. 1 is a side view of a static eliminator according to the present invention,
FIG. 2 is a section of an electrode and tube which may be used in the eliminator of FIG. 1, and
FIG. 3 is a section of another form of electrode and tube which may be used in the eliminator of FIG. 1.
FIG. 1 of the drawings shows a static eliminator suitable for removing static charge from printed paper or other material after processing which is contained in an elongated air box 1 adapted to fit transversely across the web. The box is of metal and is earthed during use, being provided with a metal lid 2 which has an airtight seal around its edges with the box. A high tension cable 3 in an insulating sleeve 4 extends longitudinally within the box, being led out of the box through a sealed solid-drawn conduit 5 for connection to a power unit or supply indicated at P. An inlet 6 is provided for the supply of air to the box from a single or multistage blower B. A pressure switch S may be incorporated in the power unit connected to be subject to the pressure supplied by the blower as shown in FIG. 1 to ensure that the high tension can only be applied when the air pressure in the box is above a preselected minimum value.
At spaced intervals along the length of the box are disposed tubes 7 of insulating material, such as P.T.F.E. the high tension cable passing through transverse openings 8 formed in the lower end portions of these tubes while at their upper ends the tubes are located in holes 9 in the lid, the insulated tubes being shouldered near their upper ends and urged by a spring 10 into engagement with the lid around the holes. This arrangement gives a reasonable seal but it is not necessarily airtight.
In the embodiment shown in FIG. 2 there is, along the axis of each tube, a needle electrode 11 which is screwed into the material of the tube 7 and extends through the cable sleeve 4 to the conductor 3 of the cable.
In the embodiment of FIG. 3 a needle electrode 11 is screwed into the material of the tube 7 and extends to a brass or metal tube 12 surrounding the insulating sleeve 4 of the cable and providing a shockless capacitive coupling. The tube shown is a ring fitting inside the opening 8 of each tube. However, the same effect could be achieved by applying a layer of metal to the outer surface of the insulating sleeve 4.
In both embodiments the upper tip 3 of the needle is a sufficient distance below the rim for electrical discharges to be avoided. The tubes are bored with one or more narrow airholes 14 to permit air under pressure to enter from the box into the space around the electrode and to be forced out through the tube end.
Because the insulating tubes extend through the lid the electrical field must curve round the rim and there is no direct discharge path. Electrical discharges are thus inhibited and the eliminator is safe for use in the presence of inflammable or explosive materials or vapors. The shape of the tubes also reduces the risk of arcing due to any metallic objects entering the tube. The pressure switch ensures that there must be an air pressure in the air box to drive out any vapor which may have leaked back before the high tension is applied.
The enclosure of the cable lead ensures that there can be no voltage leaks outside the air box. The air blower and power unit can either be isolated from the hazardous area or can be constructed from intrinsically safe components.