Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1996-04-26
1998-03-24
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
266156, 266155, 134 2211, 134 2212, C21D 176, B01D 4600
Patent
active
057308136
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for annealing an annealing charge, in particular sheet steel, in an annealing chamber of an annealing furnace under a protective gas atmosphere. Furthermore, the present invention relates to such an annealing furnace.
The surface quality of the treated annealing charge depends among other things on the purity of the protective gas. As the protective gas absorbs impurities during the annealing treatment, it has so far, according to the prior state of the art, been continuously removed and replaced by fresh protective gas. The used protective gas is then disposed of. This causes considerable losses. To keep said losses within limits, the exchange of gas is allowed to take place at a relatively slow rate and a poorer surface quality of the sheet steel is accepted as a consequence.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a remedy and to guarantee high surface quality of the annealing charge whilst reducing the cost of the protective gas.
This object is achieved by the process according to the present invention characterised in that a partial-stream of the protective gas is led out of the annealing chamber of the annealing furnace, subjected to a cleaning treatment and then returned to the annealing chamber.
In this manner, the protective gas can be kept very clean. The throughput of the partial-stream can advantageously be set to many times the free volume of the annealing chamber, preferably to 100 to 300 m.sup.3 /h, as no protective gas losses are connected therewith. It has been shown that the cleaned protective gas produces, under some circumstances, better surface results than fresh protective gas, in particular if the latter is only available in poor quality.
The protective gas is advantageously cooled, whereupon the condensate forming from water vapour and rolling oil residues, possibly together with contaminating particles, is separated. Evaporation and crack products from the rolling oil residues mean considerable contamination of the protective gas, above all in the heating phase. Thanks to rapid separation of the condensate, together with the removal of any solid particles, a rapid and intensive cleaning of the annealing charge takes place without the impurities remaining in the protective gas for a prolonged period. The protective gas is advantageously cooled to below 100.degree. C., preferably to below 20.degree. C. as the former protects the downstream compressor and the latter additionally facilitates and accelerates the cleaning process.
In a further embodiment of the present invention it is proposed that the protective gas is cooled and is cleaned by adsorption of undesirable gas components, in particular water vapour and methane. Fillers, such as zeolite, are used for adsorption. The protective gas accumulates methane particularly towards the end, above all during the last third, of the annealing process. Thus the methane-related adsorption process becomes effective particularly towards the end of the annealing process. For the cooling temperatures the figures given above apply.
The adsorbent generally requires regeneration which is preferably performed by heating and/or evacuation.
The adsorption process may be performed independently of condensate separation or may be coupled with condensate separation. In the latter case, it is particularly advantageous to have a common cooling step upstream of condensate separation and the adsorption process. This reduces the amount of apparatus required as otherwise two sets of cooling equipment would be necessary.
Furthermore, it is advantageous to use the cooled protective gas without prior heating for cooling the annealing charge. Partial-stream cleaning is therefore integrated at the end of the annealing process into the cooling of the annealing charge which is then taking place.
The adsorption process can accumulate the entire water vapour and rolling oil residues. Its efficiency is comparable with that of a condensate separator which works at -70.degree. C. Therefore a
REFERENCES:
patent: 4668253 (1987-05-01), Lonardi et al.
LOI Thermprocess GmbH
Yee Deborah
LandOfFree
Process for annealing an annealing charge and suitable annealing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for annealing an annealing charge and suitable annealing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for annealing an annealing charge and suitable annealing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2285815