DE3921321A1 - METHOD FOR BURNING THIN STEEL SHEET - Google Patents

Description

The invention relates to a method for annealing thin, too Protect a coil of rolled steel sheet in an oven the atmosphere containing hydrogen.

The rolling of very thin sheet steel, which is particularly popular in the Ver packaging industry requires a very good one Lubrication through an oil film adhering to the sheet or fat. This lubricating film interferes when in the final phase of the Rolling the sheet is annealed recrystallizing. The glow is in a known manner in an oven with a protective gas atmosphere performed. These ovens are mostly slipped over the coil bare hoods.

It is known that behind the rolling mill turned up into a coil unwrapped sheet steel again and for cleaning to carry out an alkaline and an electrolytic bath, too dry and then rewind it into the coil and then the coil to glow recrystallizing.

This cleaning process is very complex, but inevitable, because without cleaning when heating the coil, parts of the oil or burn fat onto the plate as coked residue would.

These residues leave what remains after the glow last rolling, and the sheet cannot e.g. with tin, other metals or organic substances be layered.  

The alkaline and electrolytic cleaning process can only for thicker sheets that have a thickness of more than 0.5 mm, save on. With thick sheets, rolling is not so good Lubrication required. An emulsion is therefore sufficient Water and easily evaporating fat or oil. The one on the waiter Adhesive few fat or oil constituents are in the Heating evaporated, so that the surface of the sheet even without special cleaning process is sufficiently pure or clean.

It is known to add hydrogen to the protective gas in order to achieve a faster heat transfer and thus a shorter up and down to reach cooling time. In these known methods, the Furnace from the beginning to the recrystallization temperature same, mostly maximum heating power operated.

The invention has for its object a method for re to describe crystallizing glow from very thin sheet steel ben, where the unwinding of the coil and the special cleaning of the sheet in the unwound state, especially in the alkaline and electrolytic bath, is saved, taking the usual time duration of the glow should be approximately maintained.

This task is carried out by the in the characterizing part of the An Proceed 1 described method solved, further training is in claims 2 and 3 described.

The total time it takes to glow is all the shorter the higher the hydrogen content in the protective gas. At high The hydrogen content not only ensures faster warmth transition, but also for a higher reaction speed in the formation of methane.

Because above a temperature of 450 ° C only a few of the fat remain or oil-based residues are present on the steel sheet, can here the oven with known from conventional methods  heating and cooling speeds are operated. The time is then long enough so that with increased hydrogen content the Protective gas atmosphere, the hydrogen with few residues reacted sufficiently.

The surprisingly strong cleaning effect after the fiction The procedure can be explained in such a way that the slow Warm up many volatile components of the oil or fat evaporate. The more difficult to evaporate components react with the hydrogen and form methane. Larger menus to be derived methane were measured in experiments.

It has been found that in the known methods for Glow in a protective gas atmosphere containing hydrogen Time in which the oil or fat can partially evaporate and in which the hydrogen chemically on the more difficult to evaporate residues is too short to dissolve a lubricating film.

The cleaning effect of the process is better than when it is used the conventional alkaline cleaning processes. A special Another advantage of the new method is that only flammable gases or vapors are generated that easily burn in layers that can be burned, on the other hand, the alkaline Cleaning procedures represent a much larger disposal problem.

When cleaned in an alkaline bath and in a conventional one Steel strip annealed under HNX gas are usually on one square meter surface as residues 50 to 120 mg of iron overlay and around 170 mg of carbon overlay measured. HNX gas is a mixture of 6% hydrogen and over 90% nitrogen.

In an experiment according to the invention, in which under pure water was annealed, around 1 mg of iron overlay and measured about 1 mg carbon layer. Palm was used for lubrication bold and Tinoil related.  

This experiment proved that the method according to the Invention not only in terms of economy, but also in the cleaning quality far superior to the known methods is.

Claims (3)

1. A process for the annealing of thin steel sheet with a thickness of less than 0.5 mm, which is wound into a coil, is recrystallized in a furnace with a protective atmosphere containing hydrogen re, characterized in that the coil in the condition containing rolling fat or rolling oil is introduced into the furnace and heated to a temperature range between 300 ° C and 450 ° C and 450 ° C are only exceeded after a period of 5 hours or longer and that the protective gas at least in over 250 ° C lie the heating area which extends to the annealing area and contains at least 20% hydrogen, the temperature data relating to the outer surfaces of the coil. 2. The method according to claim 1, characterized in that the Shielding gas in the entire heating area or in some areas of which contains over 80% hydrogen. 3. The method according to claims 1 and 2, characterized in that the heating rate above 450 ° C until Er range of recrystallization temperature more than 2 ° C per Minute.