DE1227150B - Process for manufacturing electrical capacitors - Google Patents

Description

Method of making electrical capacitors The invention relates to a method for manufacturing electrical capacitors with alternating superimposed metal foils and layers of insulating material, in which the capacitors are immersed in an impregnation bath containing the capacitors Bath is heated and then the capacitors for a long enough time in the Bath must be left so that the impregnation liquid completely enters the joints between can penetrate the layers.

A process for the production of impregnated paper is known, which can be used in particular for the production of capacitors. Through the process, which a weighting of the paper among other things with metal oxides and provides impregnation with a mineral oil or with clophen, the dielectric losses can be reduced.

There is also known a method for producing capacitors, in which the capacitor coil is placed in a bath of organic material such as paraffin or wax, with the impregnation bath during the immersion time is heated.

Finally, there is also a method for making electrical capacitors known, in which the capacitor winding loosely wound and then under Vacuum impregnated, whereupon the capacitors are removed from the impregnation bath and pressurized in a device.

The invention is based on the object of creating a method with which capacitors are manufactured with relatively little effort can that even with extreme temperature fluctuations and with high mechanical Work properly under stresses without showing significant changes in capacity. According to the invention, this is achieved in a method of the type mentioned at the outset achieves that the impregnation bath is a solution of boric acid or of boric acid and an electrically insulating oxide or boric acid and an electrically insulating, oxide-forming salt or from an electrically insulating, oxide-forming salt in distilled water is used and that the capacitors after removal from the impregnation bath heated in this way in several stages with increasing temperature that the water is evaporated and expelled and that from the impregnation bath The excreted solid components have been decomposed until they enter the metaRfoli and the insulating material layers form tightly connecting inorganic dielectric. Capacitors manufactured by such a method have excellent in addition to mechanical strength excellent electrical properties. They are, by the way extremely reliable.

The individual components can be added to the solution until it is saturated. The solution preferably consists predominantly of boric acid with water and contains about 2 1 / o of the powdery, electrically insulating oxide in uniform distribution. As an electrically insulating oxide, magnesium oxide can be used. Aluminum nitrate or magnesium nitrate can be used as the electrically insulating, oxide-forming salt.

Preferably, the broad sides of the capacitors are during the Impregnation and subsequent heating essentially completely enclosed, and the capacitors can be pressurized to interconnect the layers keep in close contact.

The invention is explained in more detail below with reference to the drawing of some exemplary embodiments. In the drawing, FIG. 1 shows a side view of a capacitor wound up in teff, FIG. 2 shows a plan view of a capacitor during the winding process, FIG. 3 is a side view of a compressed capacitor having a plurality of layers of cover film prior to its impregnation, Fig. 4 is a view of several jacketed capacitors in a printing apparatus, Fig. 5 is a perspective view of a capacitor of the first-mentioned embodiment, after its impregnation and its drying, a portion the protective cover layers has been removed, FIG . 6 shows a perspective view of a further exemplary embodiment of a round capacitor manufactured according to the invention, FIG . 7 is a perspective view of a round capacitor after it has been impregnated and dried, a part of the capacitor being shown without protective layers.

A capacitor manufactured according to the method according to the invention is particularly suitable for those applications in which it is exposed to a wide temperature range, for example between -55 and +4300 C. Temperatures in such a range can occur in a facility used in the Arctic where the condenser is connected to a . Missile, a jet engine or a jet engine is connected. It is essential that such capacitors do not show any adverse effects or significant changes in capacitance when their temperature is changed, even though they experience considerable mechanical shocks due to acceleration, e.g. B. od the landing of an aircraft. Like. Are exposed.

The so-called capacitor discharge ignition system for internal combustion engines has become common in recent years, especially with missiles, jet or gas turbine drives for airplanes and rockets, in which a spark with -high Energy is required. In these systems, a capacitor is charged repeatedly and discharged to produce the necessary ignition sparks with the required high energy to create. As a result, the capacitor is an essential part of such ignition systems, and its failure causes a failure of the drive and means the loss of the Life or serious damage to personnel as well as loss of valuable Aircraft or other values. It is therefore an essential aim of the invention to improve this essential element of today's ignition system by this - is made more effective and durable, especially with regard to its resistance to aging under conditions which cause significant changes in the working temperature.

The two exemplary embodiments shown in the drawing show capacitors which have been produced in accordance with the invention. These capacitors have a capacity of 0.14 NEkrofarads and are suitable for use as charging capacitors in an engine ignition system. The conductive coverings of each of the capacitors are formed by two strips 10 and 11 of thin metal foil. In one embodiment produced, aluminum foil approximately 6 li thick has been found to be sufficient. These strips are preferably of the same width and are spirally wound up directly on top of one another, but separated and insulated from one another by two # layers 14 and 15 made of suitable insulation material. In the preferred embodiments of the present invention: Layers 14 and 115 are made from a mica paper. In the exemplary embodiments described, each insulating film 14 and 15 is approximately 33 g thick and sufficiently wide to project beyond each edge of the metal foils 10 and 11 by approximately 1.57 mm. The Metattfolien are preferably arranged offset by about 12.5 mm in the longitudinal direction, so that their adjacent ends are offset by the same amount. They are of course insulated from one another throughout the capacitor by insulating layers 14 and 15 , and a few of the outer turns of the capacitor are preferably free of metal foil.

Terminals 16 and 17 preferably protrude laterally from opposite ends of the capacitor. These connections can consist of thin metal strips, preferably of nickel, with one connection having good electrical contact with the metal foil 10 and the other connection having good electrical contact with the metal foil 11 . The connection strips can be placed loosely in the position shown when the capacitor is about half-wound. Then, when the capacitor is impregnated and compressed in the novel manner described below, the leads have excellent contact with the metal foils and are well secured in place without the use of solder or the like. The rolled-up layers of metal foils and the insulation strips are held in their essentially flat and non-round or round shape by a special insulation mixture which is applied in the manner described below. In Fig. 3 , the metal foils and the insulation strips are pressed tightly together to form a flat shape, the seam filling the pores and joints in the interposed layers of mica paper and thereby improving the insulation properties of this layer. The mica paper layers are not stressed by the action of the impregnating agent, and the strength and density by compression are considerably greater than they were before when the capacitor was manufactured.

In the second embodiment of the capacitor this is in left its round shape. It goes without saying that the capacitor is the can have various forms, e.g. B. the successive layers also stacked instead of wrapped.

The condenser is preferably prepared by the following process: The metal foils 10 and 11 and the mica paper layers 14 and 15 are tightly wound on a flat highly polished dome 19, as shown in Fig. 1. To make it easier to remove the dome after the capacitor has been wound, the edges of the dome can be slightly tapered, namely by about 0.001 mm per millimeter of length. When winding, care must be taken to avoid wrinkles. When about half the length of the mica paper and the metal foils have been wound up, the connection strips 16 and 17 are inserted into the positions shown. These leads should be smooth and free of any particles which could damage the insulation layers 14 and 15 or the pressurized metal foils. The winding should be carried out in a room that is free from dust and similar foreign matter in the air. When the required number of turns has been wound, the individual foils are cut off with the adjacent ends staggered by about 12.7 mm or more and with at least the outer layer of mica paper being completely wound to cover the outer metal foil.

After completion of this winding, the capacitor is wrapped with a number of turns of foil 21 in order to form a protective layer which makes the capacitor impermeable. Aluminum foil 2.54 mm thick, wound on the capacitor with six full turns, has been found to be a sufficient envelope. Such a winding of the envelope is preferably also carried out on the winding machine so that the envelope can be arranged tightly on the capacitor, whereby the foil 21 and the insulation layers of the capacitor are kept in firm contact with one another after the capacitor has been in the process shown in FIG g. 3 has been flattened.

The capacitor wound and sheathed in this way is then pulled off the mandrel, and a plurality of such capacitors is pressed together in a suitable stack form 23 , as shown in FIG. 4, each capacitor being separated from the others by a plate 22 of suitable non-corrodible metal. The stack mold 23 contains means in the form of a press by which the stacked capacitors can be subjected to a considerable pressure which can be maintained during the impregnation and drying of the capacitors. In accordance with the invention, satisfactory capacitors are made when subjected to a pressure of about 21 kg / cm 2. The capacitors are now ready for impregnation.

The impregnation substance according to the invention consists of a solution from boric acid or from boric acid and an electrically insulating oxide or from boric acid and an electrically insulating, oxide-forming salt or from an electrically insulating, oxide-forming salt in distilled water. Such an impregnation material should any small voids between the stacked layers of metal foils and fill strips of insulating material in the capacitor and the sticking together of such Layers cause a solid, block-like structure, which is against mechanical Is resistant to vibrations and thermal shocks.

In the preferred embodiment of the invention, the impregnating agent consists of distilled water, boric acid and magnesium oxide in the following ratio: Distilled water ......... 500 ml Boric acid (H,, iB03) .......... 200 g Magnesium oxide (Mg0) ..... 15 g The impregnation agent is first prepared by boiling the distilled water, and the mixture of boric acid and magnesium oxide is then slowly added in the above ratio. After the resulting solution has come to a boil and the mold with several capacitors contained in it has been compressed, it is completely immersed in the boiling solution 24 in a heated container or tank 25 . The mold is left in the solution for a long enough time to ensure complete impregnation of the capacitors. The time is usually 20 to 60 minutes after reboiling the solution and immersing the mold. The impregnation solution should be freshly prepared before each series of impregnation processes. The solution should not be cooled after its preparation and before its use.

The mold is then removed from the impregnation solution and left to stand at room temperature for 6 to 8 hours. The parts are then dried by heating the mold and the capacitors it contains while they are still in the mold, initially to a temperature of 88 ° C., which is maintained for 10 to 12 hours. The temperature is then increased to 320 ° C. and maintained for 12 to 15 hours. After this treatment at 320 'C, the capacitors are removed from the mold challenges, there are the protective layers of the film 21 is removed (g F i. 5), and the capacitors are finally at a temperature of 430' C for 12 to Dried for 15 hours.

In the manufacture of round capacitors, as shown in FIGS. 6 and 7 , essentially the same processing steps are carried out, only no printing form is used. The round capacitor windings 26 are mounted on a round collapsible dome in much the same way as in FIG. 1 shown wound. A plurality of layers of protective film 27, similar to that used in the first embodiment, are wound on the capacitor coil thus formed. A fastening part or a plurality of fastening parts, such as. B. a wire 29 wound around the capacitor winding are provided to prevent the film 27 from unwinding.

The capacitors prepared in this way remain on their winding mandrels and are immersed in a boiling impregnation solution, which can be the same as that described in connection with the first exemplary embodiment. The capacitors are then cooked in the same way as in the first embodiment described. The capacitors are then removed from the solution and left to stand at room temperature for 6 to 8 hours. They are then dried in the following manner: at 88 ° C. for 10 to 12 hours, at 3201 ° C. for 12 to 15 hours.

After such a treatment, the capacitors are cooled, removed from their mandrels, and the outer protective layers are removed from the foil 27 from the coils. The capacitors are then dried further for 12 to 15 hours at a temperature of 4301 C. The exposed ends of the leads 16 and 17 are then cleaned, and the capacitors are individually tested for their capacitance, their power factor, their breakdown voltage and their insulation resistance. For best results, the capacitors should be placed in a moisture-proof case or a moisture-proof cover, or both, during storage and use.

Those made by using the method disclosed above Capacitors are due to their strength, fatigue strength and shock resistance as well as due to their ability to withstand a wide range of temperature changes without To withstand damage, better quality than the previously known capacitors. Since the capacitors according to the invention do not contain any organic material the temperature at which they can be used without damage the softening temperature and / or the deformation of the metal foil limits which the two layers of the capacitor form.

Since the capacitor body produced by the method according to the invention completely free of internal voids or air bubbles and the layers free of If there are harmful internal voltages, these capacitors can have higher voltages and withstand higher temperatures than previously known capacitors more comparable Size and comparable weight, and they have a higher insulation resistance than any previously known capacitors of comparable capacity. You own also lower electrical losses, a smaller loss factor and lower Corona phenomena.

In the preferred impregnant mentioned above, boric acid is present in such an amount that the result is a fairly concentrated solution, and the magnesium oxide is present in such an amount that the saturation point is achieved. The boric acid is said to be impregnated in the course of the subsequent heat treatment Capacitor form a binder, which effectively forms the various layers of the capacitor connects to each other. The magnesia is an excellent one electrical insulator and improves the electrical properties of the impregnating agent. The impregnation agent can only consist of a solution of boric acid and water exist. Considerably improved dielectric and insulation properties will be however, when combined with boric acid, an electrically insulating one is achieved Oxide, such as B. magnesium oxide or an oxide-forming salt is used.

According to the invention, the boric acid can be used in a wide range of concentrations which depends on the desired results. To -a sufficient To maintain connection between the layers of the capacitor, there must be enough boric acid be brought into the condenser to have a strong during its heating To effect bonding. The upper concentration limit of boric acid is of course that Saturation of the impregnation solution. Preferably, however, the solution is not complete fully saturated so they make the capacitors complete and uniform can impregnate and penetrate into all spaces before solidifying in the solution Particles occur.

The concentration of magnesium oxide can be in the same way to a large extent Scopes can be changed. It can optionally be used in amounts which from small but effective amounts to about saturation of the solution. As stated above, the electrical insulation properties and the dielectric Properties of the insulation material improved by the presence of magnesium oxide.

One or more of various electrically insulating soluble oxides or oxide-forming salts can be used in place of the magnesia in the above preferred impregnation solution. All salts which are soluble in water and which produce an electrically insulating oxide when heated, for example in the above-mentioned work cycle, can be used. Aluminum nitrate and magnesium nitrate are typical of such salts. When aluminum nitrate is dissolved with boric acid in water to form an impregnation solution and a capacitor is impregnated therewith, it is believed that subsequent heat treatment of the impregnated capacitor converts the impregnation to aluminum oxide with traces of aluminum hydroxide and boron nitride.

It has been found that the quality is better and higher Temperature-resistant capacitors can also be manufactured in such a way that a solution of aluminum nitrate alone in water is used as impregnation the aluminum nitrate in a range from an effective value to substantial saturation may be present. When heating the impregnated Condenser breaks down the aluminum nitrate into altiminium oxide and a small proportion of aluminum hydroxide. These products effectively bind the layers of the capacitor together and also form a suitable dielectric. Essentially the same results are achieved when a solution of magnesium nitrate is used as an impregnation for the Condenser parts is used. In this case a solution of magnesium nitrate can be used can be used alone in water, with the magnesium nitrate in a range of an effective amount is present to saturation. When heating the impregnated Condenser breaks down the magnesium nitrate into magnesium oxide and a small proportion of magnesium hydroxide. These products effectively bind the layers of the capacitor together and also form a suitable dielectric.

The use of enveloping layers around the capacitor and the maintenance of substantial pressure on the layers of the capacitor during the impregnation of the capacitor and its subsequent skin treatment ensure that the insulation layers remain intact. This is particularly necessary when the insulation layers are made of a material such as e.g. B. mica paper are made in which the various small plate-like elements which büden sheets 14 and 15 are apparently held together by essentially electrostatic forces. If such a material is immersed in boiling water for some time, while it is not held together and compressed, it will almost completely dissolve and fall apart. On the other hand, if it is held together and compressed as described above during impregnation, the insulation material retains its uniformity and integrity, and when the impregnant is subjected to the heat treatment, it is solidified by the dried impregnation.

The capacitors produced by the process according to the invention are particularly resistant to radiation in areas of high -y radiation intensity. this results from the high resistance of the inorganic impregnation agent to Decay when exposed to radiation, including γ-radiation.

In addition to the illustrated embodiments of the method according to In accordance with the invention, further embodiments are possible. For example, the Mica paper existing insulation layers by layers of other high temperature resistant Sheet materials with suitable properties are replaced, such as. B. Glass paper.

Claims (2)

Claims: 1. A process for the production of electrical capacitors with alternately superimposed metal foils and layers of insulating material, in which the capacitors are immersed in an impregnation bath, this bath containing the capacitors is heated and then the capacitors are left in the bath for a sufficiently long time so that the impregnation liquid is completely can penetrate into the joints between the layers, d a - characterized in that the impregnation bath is a solution of boric acid or of boric acid and an electrically insulating oxide or of boric acid and an electrically insulating, oxide-forming salt or of an electrically insulating, oxide-forming salt in distilled Water is used and that the capacitors are heated in several stages with increasing temperature after being removed from the impregnation bath in such a way that the water is evaporated and expelled and the out of the impregnation bath The different solid constituents are decomposed until they form an inorganic dielectric that tightly connects the metal foils and the layers of insulating material. 2. The method according to claim 1, characterized in that the individual components of the solution are added to saturation. 3. The method according to claims 1 and 2, characterized in that the solution consists predominantly of boric acid with water and contains about 219 / o of the powdery, electrically insulating oxide in uniform distribution. 4. Process according to claims 1 to 3, characterized in that magnesium oxide is used as the electrically insulating oxide. 5. The method according to claim 1, characterized in that aluminum nitrate or magnesium nitrate is used as the electrically insulating oxide-forming salt. 6. The method according to claim 1 or the following, characterized in that the broad sides of the capacitors are fin substantially completely enclosed during the impregnation and the subsequent heating. 7. The method according to any one of the preceding claims, characterized in that the capacitors are pressurized to keep the layers in firm contact with one another. Documents considered: French Patent No. 1 221 007; British Patent No. 718 330; U.S. Patent Nos. 719,973, 1307,341.