DE924086C - Annealing of transformer sheets - Google Patents

Description

Annealing transform: ator sheets The annealing of transformer sheets After your rolling process, the aim is to reduce iron losses in boxes that are protected against the ingress of atmospheric air, but are not vacuum-tight. The annealing temperature of approximately goo ° C is calculated in such a way that that once the rolling stresses are released, the other time the transformation of the magnetically harmful cementite is effected in the harmless graphite. For This soft annealing, which is also known elsewhere in steel technology, is the temperature range around goo ° C substantially; Temperatures over 100 ° C are caused by overheating declined.

On the other hand, however, a method has become known according to which at a temperature of at least i i oo ° C, the initial permeability of the transformer sheets should be increased by annealing in a vacuum. Albeit according to scientific Investigations reached this type of improvement only at 1350'C and thus the The value of the known method is reduced, one recognizes the importance high annealing temperatures for special processes.

But one can theoretically and practically prove that the increase the initial permeability is effected by chemical cleaning of the material, while the reduction of the coercive force and thus the hysteresis losses also through the Merely transferring highly dispersed particles of the foreign substances in the steel especially of cementite, are brought about in larger particles as a result of diffusion can. For the reduction of the total iron losses, to which eddy current and aftereffect losses It is also important that the silicon content is evaporated during the annealing process is not reduced, so very high temperatures must be excluded. There dissolved in vacuum annealing at and above i oo ° C and through chemical reactions Developed gases emerge from the sheet metal and thus cause the material to be cleaned the increase in the initial permeability no longer occurs as soon as after the Results of the known method, the container pressure selected to be higher than 10-2 mm Hg will.

The combustion of carbon in the sheet metal to form CO or CH at the high temperatures of the known processes for the purpose of increasing the initial permeability is synonymous with cleaning the sheet metal material during annealing.

Technically usable and effective processes, especially high-temperature annealing, which follow the methods of box annealing and only the reduction which have iron losses for the purpose are available for hot-rolled transformer sheets not yet today, which alone is due to the great demand for cold-rolled textured sheets proves.

It therefore represents an advance in the course of the present invention to have proven that by annealing in a vacuum at 1200 ° C and during 24 Hours for transformer sheets with 4% Si with a thickness of 0.35 mm a loss value V10 = 0.6o W / kg achieved compared to the value of i, 15 W / kg.

This fact gets a technical meaning after being proven it became clear that similar loss values can also be achieved at atmospheric pressures, provided that the annealing temperature 120o ° C is kept within narrow limits with the exclusion of oxygen adheres to and glows for a long time. The glow effect can be explained by the fact that as a result the diffusion taking place at high temperature carbide particles, which in highly dispersed Distribution in the crystallite are embedded, are pushed to the grain boundaries and so come together to form larger particles; after the local enrichment these on cooling due to the exceeding of the solubility limit as pearlite islands eliminated. Fig. I shows the micrograph of an unannealed sheet in which no carbon can be seen, Fig. 2 that of the one annealed at 1200 ° C for 512 hours Sheet metal with distinct pearlite islands; crystal growth can be observed at the same time. This collective excretion is to be distinguished from the transformation of cementite into Graphite during soft annealing at 90o ° C. Regarding the magnetic effect Such collective excretions, however, mean the transfer of the smallest particles into larger particles reduce the coercive force and thus the hysteresis losses, without a decrease in total carbon having taken place. This is also true for all other types of pollution too.

This clears the way for a technical annealing process to effectively reduce iron losses from transformer sheets without having to use the costly method of vacuum annealing or hydrogen treatment at the highest temperatures. According to the invention, transformer sheets are annealed at about 1200 ° C for a long time in a welded container and in the presence of calcium carbide (Ca C.2), which binds the oxygen in the air.

Calcium carbide without an activating agent only binds oxygen slowly and the 'nitrogen above 100 ° C only completely after 30 hours. It differs therefore essentially different from all so-called metallic getters with vapor formation and Hydrides that break down into metal and hydrogen between 400 and 10,000 ° C. the Metal vapor gettering is well known in the vacuum tube art, however afflicted with the disadvantage of steam formation.

The application of calcium carbide according to the new process has only the purpose of binding not only the oxygen present in the container but also the oxygen the by at every tech! niche weld penetrates pores, you don't always want to do a leak test. So the annealing takes place at around i2oo ° C in an inert mixed atmosphere made of residual argon, Nitrogen and carbon monoxide.

It is the airtight sealing of a transformer steel inside a container in the presence of a substance that is at elevated temperature active against non-metallic elements inside the container is known and also heating the steel in such a way that diffusion of the non-metallic Elements made in the steel have been protected. Yet indicates this kind of heating only a wide temperature range, insofar as dissolved nitrogen already exists at 80o ° C, but carbon does not diffuse quickly out of the steel until 135o ° C; so the instruction does not give a preferred annealing temperature.

The new process just sees the temperature as low as i2oo ° C Deviations, because below 1150 ° C the effect caused by collective excretion the hysteresis loss reduction is practically not achieved and above 125O ° C so much silicon has already evaporated that the hysteresis loss improvement due to the . The increase in eddy current and after-effects loss is compensated for again.

The use of metallic getters is also used for the known method essential, the vapors of which remove the impurities of the silicon steel C, S, P by action on their 'oxygen, nitrogen and hydrogen compounds by deposition to render the elementary C, S, P harmless; the same applies to those mentioned Metal hydrides.

This reaction cannot be caused by the calcium carbide that i'm familiar with Process is also not mentioned, to be expected, as the requirement of steel cleaning does not apply because at 1200 ° C Ca C2 neither has a vapor pressure nor dissociates. In addition, the reduction of the C O requires a dissociation, which occurs at 1200 ° C Boudouard's judgment is not the case. Are the other way around precisely the getter of the known process that is most effective for CO reduction, Mg and Ca, not applicable in the new process, since they individually or together are vapor pressures greater than i at at 1200 ° C and therefore the airtight container would blow up. The vapor development of all metallic getters is due to diffusion at 1200 ° C a strong embrittlement of the sheets result, especially if they lie as a separating layer between the sheets. Ca C2 can in the known process not be included, as it would carburize the sheets as a separating layer.

The known method makes of the surface scale of the sheets Use as an oxidizer of foreign elements. At 1200 ° C, however, the iron oxide would are consumed by all metal vapors, which is not to be expected from Ca C2.

Also the mechanical improvement of the sheets through the getter annealing the known method cannot be generalized, since an annealing occurs at 1200 ° C is the bending number of the sheet metal in any case due to the formation of iron silicide degrades.

From all comparisons it follows that the new process is not included in the known getter annealing process. The latter also does not achieve the purpose of complete steel cleaning and thus an effective reduction in loss. According to his application example, the annealing at 1950 ° F equal to 1065 ° C. improves the V, () value by only a few percent. The percentage improvement in the annealing of 0.35 mm thick transformer sheets with 4% Si, which results in an optimal hysteresis loss value of 0.6o W / kg, is noticeably higher. The process is repeatable.

After all, it is not identical to the cold rolled annealing process Sheets, which at high temperatures produce the desired texture in a few minutes.

Claims (1)

PATENT CLAIM: Process for annealing transformer sheets for Reduction of iron losses in airtight welded iron containers with a getter material, characterized in that the sheets at i2oo ° C in the presence of calcium carbide (Ca C2) are annealed. Printed publications: French U.S. Patent No. 892,858; Eisenhüttenwesen archive, 1943, issue 9, p. 363; U.S. Patent No. 2,389,497.