US2508500A - Apparatus for applying metal coatings on insulators - Google Patents

Description

May 23, 1950 c. DE LANGE ETAL APPARATUS FOR APPLYING METAL commas on INSULATORS Filed May 9, 194a INVENTORS.

AT TOKWX Patented May 1950 APPARATUS FOR APPLYING METAL COATINGS ON INSULATORS Cornelia de Lange and Paulus Antonius Wilhelmus Maria Sleegers,

Eindhoven, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application May 9, 1946, Serial No. 668,336 In the Netherlands May 23, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires May 23, 1962 3 Claims. (Cl. 91-122) In the manufacture of condensers it has previously been proposed to produce an electrode by vaporizing a layer of metal on the material of the dielectric, for example paper. In order to work with the lowest possible vapour pressure of the material to be applied by vaporisation and therefore at the lowest possible temperature and to avoid oxidation of the electrode material, it is desirable to effect the application by vaporisation in a vacuum. Thus, there arise, however, various drawbacks, for the required quantity of material to be applied by vaporisation has to be introduced beforehand into the vaporisation chamber, which implies that when this quantity is being used the level of the material to be vaporised contained in the vessel sinks. Experiments have shown that one of the factors which prejudicially influence the properties of a layer applied by vaporisation and which cause undesired irregularities in these properties, is due to the varying level of the material to be vaporised during the application by vaporisation. The invention has for its principal object to provide means by which these drawbacks are eliminated.

The invention is characterized in that means are utilized for keeping constant the level of the material to be vaporised which is contained in a vessel present within the vaporisation chamber.

By the use of these means the path to be traversed by the vapour particles on their way from the vaporisation vessel to the substratum to be coated is maintained constant. Since during the application by vaporisation the pressure prevailing in the vaporization chamber and therefore the length of the free path of the vapour particles are kept constant, the requirement of keeping equal the conditions under which the application by vaporization takes place, is satisfied to a large extent so that there also is uniformity in the layer applied and in its properties.

In practice this rule may be carried into effect in a very simple manner it, according to one advantageous mode of realisation of the invention, the regulation of the level is eifected by acting upon the contents of part of the vessel containing the material to be vaporised, which part protrudes from the vaporisation chamber.

One method, which is preferably carried out for keeping constant the level in the vaporisation vessel, consists in that the level is adjusted by modifying the volume of the vessel which contains the material to be vaporised. Such a. method can be carried out in a particularly easy manner if part of the vaporisation vessel protrudes from the vaporisation chamber.

One advantageous method of modifying the volume of the vaporisation vessel consists in that during the application by vaporisation a movable immersion body present in the vessel is drawn, a

in dependence on the quantity of material vaporised, into this vessel over a distance such that the level of the liquid remains constant. The change of volume may however also be advantageously obtained by bringing about the change of the volume of the vessel by moving inwardly a movable portion of the wall of the vessel, in dependence on the quantity of material which is vaporised. It is also possible to obtain the movement of the bottom relatively to the vessel by providing both elements with a screw thread.

In carrying out the method of application by vaporisation wherein the material to be vaporised has to be introduced from the outside into the vaporisation chamber, the following should be borne in mind. When the material in the vapomust take place once more.

risation vessel has been used up, the entire installation necessary for the application by vaporisation must be put out of service in order to fill the vaporisation vessel, whereupon exhaustion Under the action of the air there are produced metal compounds which, after the material to be vaporised has melted, form slags on the surface of the vaporisation vessel, which slags generally have a lower vapour pressure than the metal in question and consequently counteract the vaporisation. This drawback is eliminated, according to one advantageous mode of realisation of the invention, wherein the level of the material to be vaporised is kept constant by means of the difierence in the pressures exerted on the level of the liquid contained in the vaporisation vessel and on the level of the liquid contained in a vessel (filling vessel) outside the vaporisation chamber which communicates with the vaporisation vessel.

Because the filling device and the vaporisation vessel are separated from one another, no oxide is formed on the surface of the metal where the vaporisation is executed so that in consequence thereof no material is lost. This mode of realisation has the particular advantage that the filling vessel can be filled independently of the vaporisation method, which is of particular advantage if the material to be coated is continuously supplied and discharged from the exterior, a perfect continuity of the method being thus ensured. For applying metal by vaporisation to a substratum we know already a method wherein within an' xhausted chamber an arc is maintained between two electrodes of which the one has a central drawback that the metal particles in the vapour current, which particles have extremely small dimensions, envelop themselves with a film of gas, which is a harmful circumstance in the manufacture of a condenser electrode. As a result of the latter, one of the deleterious consequences is an increase in direct-current resistance of the electrode. Furthermore, an arc and the continuous supply of gas to the exhausted chamber gives rise to unpleasant complications.

In the embodiments of the invention thus far described atmospheric influences on the metal in the vaporisation chamber have been avoided. Although it would be possible to utilize atmospheric pressure to drive the metal from the filling vessel to the vaporisation chamber, it is desirable to avoid the reaction of air with the metal because of the slight oxidation of the metal that would take place in the vessel. Moreover, the level to which the metal rises in the vaporisation vessel depends in the first place on the atmospheric pressure. To eliminate these drawbacks it is advantageous that within the filling vessel a pressure should be exerted by a neutral gas. Such a gas consequently does not attack the metal; therefore it does not form slags and consequently causes no loss of material. Furthermore, the adjustment of the pressure and therefore of the level in the vaporisation vessel may be effected in a far simpler and exacter manner.

It is evident that with the use of material to be applied in molten condition the filling vessel must be heated in order to keep the material contained therein in the molten condition. Especially however the material contained in the vaporisation vessel should be heated since this material must be vaporised. It has been found that the heating element destined for this purpose need not be arranged within the vaporisation chamber but advantageously may surround the tube which establishes the communication between the two vessels. This arrangement has the further advantage that the material which would cool down most rapidly within the tube because of the slight cross-sectional area thereof with respect to those of the vessels is now heated-in the most favourable manner. This construction is especially advantageous when paper or similar materials which are easily decomposed at an increased temperature are utilized as the substratum, since the material of the substratum is not exposed in this case directly to the heat radiated by the heating element and therefore need not be cooled separately. v

These considerations apply more particularly to those cases where, according to one advantageous form of construction, the tube which connects the two vessels to one another has. at least in the neighbourhood of the vaporisation vessel, a very slight cross-sectional area. This is particularly advantageous if in a device wherein the method of application has to be intrrupted, for example in order to insert a fresh roll of paper, the cover has to be lifted from the vaporisation chamber so that the free air enters into the said chamber. If now the level of the liqud to be vaporised is maintained in the vaporisation vessel, a large surface of this material is liable to oxidize, which implies loss of material and heat. If, however, the liquid is repelled as far as into the nar-.'

4 rowed portion of the connecting tube. the loss of material due to oxidation and the loss of heat are considerably decreased.

The invention will be explained more fully with reference to the accompanying drawing in which several embodiments of the invention are illustrated and in which:-

Fig. 1 represents a device wherein the level of the material to be vaporised is kept constant by means of a movable immersion body.

Fig. la shows an alternative ement of the device illustrated in Fig. 1 wherein the immersed body is positioned by a driving'mechanism controlled by a float switch;

Fig. 2 shows a device which comprises a vessel provided with a screw bottom.

Fig. 3 represents a device wherein the level obtained by means of the difl'erence in the pressures exerted on two vessels.

Fig. 1 represents the vaporisation vessel while Figs. 2 and 3 show, in addition. the take-up and supply rolls which are located in Fig. 2 outside the vaporisation chamber and in Fig. 3 within the said chamber.

The vaporisation chamber, which is denoted by I, may be connected, through the intermediary of a connecting piece I. to a-vacuum pump by which during operation a pressure of about 0.002 mm, of mercury is maintained in the? chamber. Within the chamber I is provided a vessel 3 which contains the material to be vaporised, for example zinc, in the- -liquid condition. -The vessel exhibits a projecting part '5' whichiis surrounded by a heating'element I. The, vessel contains an immersion body s which is movable in the verti isationchamber is closed by means of a removable lid Ill.

An alternative embodiment for controlling the movement of the immersed. body 0 is illustrated in Fig. la wherein the rollers I are driven by the motor ll which is controlled by a float switch 43 whichswitches the motor into the power supply circuit when the level of the molten metal falls within vessel 3.

In Fig. 2 the adjustment of the level is brought about by a screw bottom H which can be displaced by means of a driving mechanism. The automatic adjustment of the level may be obtained again by means of a contact device as shown in Fig. 1. In Fig. 2 the vaporisation vessel 3 is covered at the top but comprises two nozzles l2 and I3 arranged in such manner that the paper strip to be coated I4 is coated on both sides. This strip of paper is unwound from a roll I! and passes through a preliminarily exhausted chamber it which exhibits at the beginning and at the endnarrow slits I] and It which serve to reduce the leakage in the chamber as far as possible. After the paper has passed over a roller 30 it is again led through apertures II and 2| which form the beginning and the end of a preliminarily exhausted chamber 2|, Then the strip of paper is wound on a roll 22. Although the figure shows two separate chambers for the bine them so as to form a single chamber.

Furthermore, the figure shows diagrammatically the manner in which an interruption of the vaporised material on the substratum may beobtained without putting the source of vaporisation itself out of service. For this purpose a template is arranged between the path of the material to be coated and the corresponding nozzle. In the present case this template is located between the lower strip 01' paper and the correspondingnozzle. It consists of a strip of metal 23 which is arranged in a direction perpendicular to the direction of travel of the paper strip and is supported by two parallel bands 28 which pass on guide rollers 24 and 25 (only the foremost band and the corresponding rollers are shown). The spacing between the parallel bands must be such that the surface to be coated remains free over its full width. The movement of the template 23 may be'infiuenced from the outside by electromechanical or electromagnetic means. This occurs, for example, it on the lower side or the paper strip there must be an interruption for cutting through the strip at this point. If at the point of cutting through a metal layer were present on both sides, a short-circuit might readily be produced between the said layers, which is completely avoided owing to the present 'step, for to that end it is only necessary to impart to the template '23 a motion'such that it travels at the same speed as the strip of paper and this only until it has passed the nozzle l3. Then the template may be drawn into the initial position, which, when efi'ected rapidly, has no infiuence on the thickness 01 the layer applied to that portion 0! the strip which just passes along the nozzle at the moment when also the template passes along this point.

In Fig. 3, which shows a device wherein the filling with the material to be vaporised takes place from the outside, the vessel 3 communicates through the intermediary of a tube 21, with a vessel 28 which likewise contains molten material,

in the present case zinc. In the vessel 28 this material is maintained at a temperature above the melting point, about 430 C. The vessel is closed at the top and exhibits a connecting piece 28 through which a neutral gas under pressure, for example nitrogen, can be admitted. The level at which the zinc rises in the vessel 3 is determined by the pressure of this gas, which does not attack the zinc. A heating element 5 is provided to keep the zinc present in the tube 21 as well as that contained in the vessel 3 in-the molten condition. Owing to the presence of the heating element at this point, solidification of. the zinc present in the long tube 01' slight cross-sectional area is avoided.

Two spools are arranged in the interior oi the vaporisation chamber, the spool 3| being the supply spool and the spool 32 the take-up spool.

The paper strip present on these spools is caused to travel along the upper portion of the vessel 3 in such manner that first the one side oi the paper comes into contact with thezinc vapours flowing out of the aperture 33 and then the other side by vapours flowing out 01 the aperture 30.

As may be seen from theffigure, the tube 21 has a narrowed portion immediately below the vessel 3. For exchanging the spools 3| and 32 the lid III, which hermetically fits to the receptacle which encloses the chamber I, is removed so that the free air fiows into this chamber and repels the liquid from the vessel 3 into the tube.

preliminary exhaustion it is also possible to com- I During this action the pressure prevailing above the liquid level in the vessel 23 is kept at a value such that the liquid level of the vessel 3 is driven back as far as into the narrowed portion 35 of tube 21. Owing to the very slight cross-sectional area at 35 only a very small metal surface is exposed to the action of the air.

It is true that the manipulation necessary for the exchange of the rolls oi. paper as above described disturbs the continuity of application, but it should be considered that the supply of paper present on the supply spool may amount to a few kilometers. Since the rapidity oi vaporisetion and therefore the speed of the travelling strip of paper is about 0.5 m. per sec., this implies that the operation for treating a single paper "charge" may last several hours.

We claim:

1. A device for applying an electrode on a layer of dielectric material, comprising'an evacuated chamber, a vessel for containing a heated metal disposed within said evacuated chamber, a heating element for raising the temperature oi said metal to the temperature of vaporization and to maintain said metal in a molten condition within said vessel, means to expose said dielectric material to said molten metal, a body inert to said molten metal partially immersed therein, and means to continuously alter the position 0! said body in said molten metal to thereby alter the effective volume of said vessel and to maintain a constant level of said molten metal in said vessel.

'2. A device for applying an electrode on a layer 01' dielectric material, comprising an evacuated chamber, a vessel for containing a metal in a molten condition within said chamber, a heating element for raising the temperature 0! said metal to the temperature of vaporization, means to expose said dielectric material to said molten metal, a body inert to said molten metal partially immersed therein, a driving member for vertically moving said body in said molten metal, and means to energize said driving member to continuously alter the position of said body in said molten metal to thereby maintain a constant level oi said molten metal in said vessel.

3. A device for applying an electrode to a capacitor and the like, comprising an evacuated chamber, a vessel tor'containing a metal in molten condition within said chamber, a heating element for raising the temperature 01' said metal to the temperature of vaporization, means to expose the dielectric to the molten metal, a piston member inert to the molten metal movable within said vessel, and means to actuate said piston to move upwardly in said vessel toward the dielectric to alter the effective volume of the vessel and to maintain a constant level of the molten metal therein.

CORNELIS n! LANGE. PAULUS ANTONIUS WIlL-HEIMUB MARIA BLEEGERB.

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

UNITED STATES PATENTS Number Name Date 1.710.747 Smith Apr. 30. 1920 2,153,786 Alexander et al. Apr. 11, 1933 .273.94 Dorn Feb. 24, 1942 2,384,500 stoll Sept. 11, 1043 2337,97) Alswnnrlmme an nus

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