DE3640966A1 - Method of producing a corona electrode - Google Patents

Abstract

A corona electrode provided as a whole with the reference symbol (4) comprises a core (5) and a dielectric (6). The core (5) may be made, for example, of mouldable graphite. The dielectric (6) is applied to the core (5) in the form of a thin coating of non-oxidic ceramic, for example of silicon nitride, boron nitride, aluminium nitride or the like. This makes possible, on the one hand, very far-reaching freedom in the shaping of the corona electrode (4) and ensures, on the other hand, a high wear resistance and a high efficiency. <IMAGE>

Description

The present invention relates to a method for manufacturing position of a corona electrode, with at least one partially electrically conductive core a dielectric Coating is applied.

It is known that adhesion to material surfaces improved by applying a corona discharge can be or this at all with non-polar materials can only be created.

For such a surface treatment using a coronaent On the one hand, being able to carry out the charge requires one electrical energy source in the form of a with change voltage-working, high-frequency high-voltage genes rators and one of the corona electrodes, which is provided with a dielectric and on which the desired Corona discharge occurs when the generator is operating.

When performing such surface treatments the Dielek according to the previously known state of the art trikum, which for an even corona formation important is a vulnerability.

The coronaent used in surface treatment Charge loads the dielectric in continuous operation, conditionally  through the production process. It has been shown that depending on the type of dielectric, a different time Wear occurs, which in any case is not wishes hires quickly.

The reasons for this are the following:

Due to possible porosity of the dielectric on the one hand and due to the demand for short-circuit proof training On the other hand, the dielectric has hitherto been called Di Electrical performed with a relatively large thickness, whereby the efficiency of the corona electrodes ver worsened. The consequence is an unfavorable, electrical corona active power conversion per area unit, combined with low, achievable adhesion values of the treated material.

This shortcoming is now only with large generator outputs and balance large device dimensions, which in turn leads to greater heat development at the corona electrodes and corresponding wear.

Overall, wear and tear cause bad Efficiency in surface treatment with corona charge considerable cost and drop in quality at the treated material.

The present invention is based on the object a method of manufacturing a corona electrode develop after which it is possible to use corona electrodes low susceptibility to wear and high efficiency manufacture.  

This object is achieved in that a coating of predominantly nonoxy on the core the material is applied.

By applying such a coating it is possible to keep the dielectric thin overall, at the same time, however, there is a non-porous and dense Coating the core so that even with very thin ones Layers and permanent point load with a highly fre high voltage over several hours Impact-proof insulation is possible, like relevant Have shown attempts. The dielectric properties the coating changes when Tempe changes rature and frequency not essential.

In the case of corona electrodes produced using the method it was also observed that the so-called corona ignition voltage is significantly lower, which also means achieved, better efficiency can be explained.

A useful development of the invention The process is that it is malleable and good thermally conductive core material is used, which almost the same thermal expansion coefficient like the material used for the coating sits.

A further development of the method is that the Coating with a minimum density of 95% of theo retic density is applied.

Further features of the invention are the subject of further Subclaims.  

Based on the accompanying drawings, the invention is thanks again explained in detail.

In detail show:

Fig. 1 a high voltage generator for the operation of a corona electrode,

Fig. 2 shows a section through a corona electrode,

Fig. 3 shows another embodiment of a Koronaelek trode in a perspective view;

Fig. 4 shows a section through a corona electrode according to a further embodiment,

Fig. 5 shows an embodiment of another Koronaelek trode.

In Fig. 1, the reference numeral 1 designates a high-voltage generator which, during operation, can deliver a high-frequency high voltage to a corona electrode shown in FIGS . 2 to 5 via its connections 2 and 3 .

The corona electrode shown in FIG. 2 is provided overall with the reference number 4 .

This corona electrode 4 consists of a core 5 and a dielectric 6 in the form of a coating of the core 5 .

The core 5 is preferably made of a moldable core material which has good thermal conductivity and has almost the same coefficient of thermal expansion as the material of the coating. The core 5 preferably consists of graphite.

The dielectric 6 consists predominantly of non-oxide material, preferably of a ceramic material such as boron nitride, silicon nitride or aluminum nitride, and a mixture of the aforementioned materials is also conceivable. However, a mixture of ceramic materials made of non-oxidic and oxidic components is also conceivable.

The core 5 is preferably coated with a minimum density of 95% of the theoretical density.

The core 5 can be coated both in the PVD process (physical vapor disposition) and in the CVD process (chemical vapor disposition).

It is also conceivable to carry out the coating of the core 5 in the sintering process or by chemical reaction sintering.

Coating of the core 5 by the plasma spraying method is also possible.

If only boron nitride ver it is advantageous to use boron nitride in hexagonal, to use anisotropic form.

The use of a core material, which on the one hand is good thermal conductivity and on the other hand almost to that same coefficient of thermal expansion as that for the Coating used material offers the advantage part that no dilulations in the material boundary layer ten. This makes it electrically breakdown-proof Corona electrode created.  

The use of mixed ceramics for coating enables the production of inexpensive corona electrodes in high Quality.

The dielectric 6 of the corona electrode 4 consists overall of a relatively thin layer made of the materials mentioned above.

When high voltage is present at the connections 7 of the corona electrode 4 and 8 of a counter electrode 9 designed as a roller, an electrical corona charge 10 is formed between the corona electrode 4 and the counter electrode 9 .

Fig. 2 clearly shows that the corona electrode 4 is not provided with a dielectric 6 at the point for the electrical contact cable, so that there is the possibility of being able to assemble several, so designed, short-circuit proof corona electrodes 4 .

Fig. 3 makes it clear that by a thin coating of the electrode core 5 with the already mentioned dielectric 6 there is the possibility of being able to form the discharge webs 11 extremely sharp-edged and thus increasing efficiency. The corona discharge 10 takes place here against a metal plate 12 which is connected to ground.

In the exemplary embodiment according to FIG. 3, the core 5 of the corona electrode 4 is provided with a cooling bore 13 running in the direction of its longitudinal axis, the reveal of which is again coated with a dielectric 6 .

The corona electrode 4 shown in Fig. 4 has a hollow core 5 which is partially coated in its interior completely and externally with a dielectric 6.

This corona electrode 4 can be vented in the same direction in which the corona discharge 10 occurs. The venting direction is indicated by arrow A in FIG. 4.

Only a partial application of the dielectric 6 in the outer area of the corona electrode makes it possible, for example, to attach a thread 14 to the corona electrode 4 in the non-coated area.

In Fig. 5, a corona electrode 4 is shown in which angled an internal electrode gap 90 ° turn with a thin dielectric is coated. 6 In this electrode gap z. B. a metal wire 15 may be exposed to a corona discharge 10 .

Claims (11)

1. A method for producing a corona electrode, a dielectric coating being applied to an at least partially electrically conductive core, characterized in that a coating of predominantly non-oxidic material is applied to the core ( 5 ). 2. The method according to claim 1, characterized by the Use a malleable and good heat conductive Core material, which has almost the same tempera expansion coefficients like that for coating tion used material. 3. The method according to claim 1 or 2, characterized in that the coating is applied to the core ( 5 ) with a minimum density of 95% of the theoretical density. 4. The method according to one or more of the preceding claims, characterized by the coating of the core ( 5 ) in the CVD process (chemical vapor disposition). 5. The method according to one or more of claims 1 to 3, characterized by the coating of the core ( 5 ) in the PVD process (physical vapor disposition). 6. The method according to one or more of claims 1 to 3, characterized by the coating of the core ( 5 ) by sintering or chemical reaction sintering. 7. The method according to one or more of claims 1 to 3, characterized by the coating of the core ( 5 ) by the plasma spraying process. 8. The method according to one or more of claims 1 to 7, characterized by the use of ceramic materials such as boron nitride, silicon nitride or aluminum nitride for coating the core ( 5 ). 9. The method according to one or more of claims 1 to 7, characterized by the use of ceramic mixtures of boron nitride, silicon nitride or aluminum nitride for coating the core ( 5 ). 10. The method according to one or more of claims 1 to 7, characterized by the use of ceramic material mixtures of non-oxidic and oxidic components for coating the core ( 5 ). 11. The method according to one or more of claims 8 to 10, characterized by the use of boron nitride in hexagonal, anisotropic form for coating the core ( 5 ).