Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Patent
1996-03-25
1998-05-12
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
266252, 266254, 266257, 261 641, C23C 820, C23C 840, B01F 302
Patent
active
057499780
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a method and a device for the controlled formation and feeding of a gaseous atmosphere having at least two components, one of which under the form of vapour coming from a liquid. The invention also concerns the application of the aforementioned method and device particularly in plants of thermal treatment or in plants for carburizing processes.
BACKGROUND ART
A particularly interesting application, that will be described more in detail and claimed--without being considered for that as a limitation to the protective scope of the invention--is that of the thermal treatment in ovens and in particular of the gas carburizing treatment of steel products, namely a treatment that allows the absorption of carbon atoms in the superficial layers of the product in order to increase its superficial hardness and to improve its fatigue strength.
The formation and feeding of a gaseous atmosphere having two components, one of which under the form of vapour, have always represented and still now represent a serious problem in all cases in which it is necessary or advisable to maintain and/or to control the ratio between components. Not limiting examples of atmospheres of this kind are given by some types of comburent atmospheres and more specifically those in which the fuel is under liquid form, such as atmospheres suitable to feed burners with methanol or other liquid fuels, as well as comburent atmospheres for feeding motors. Other cases of application are those related with the creation and feeding of atmospheres for thermal treatments of steels in gaseous atmosphere, such as brazing, nitriding, annealing and carburizing treatments,. when one of the components of the atmosphere is obtained from a substance under liquid form.
As far as carburizing treatments are concerned, that at present represent those for which the application of the present invention has mainly been studied, they are generally carried out in heating ovens, where a gas mixture including a carburizing agent is present. Taking into consideration that the process takes place at temperatures exceeding 800 degrees C., the carburizing agent present in the oven dissociates, thus freeing carbon atoms that are absorbed by the superficial layers of the steel up to depths of a few millimeters.
At the present time the carburizing process of mechanical components, such as for instance gears for the motor industry, is performed in periodic kilns of large size or in continuous sections that use a gas atmosphere created therein or produced out of the oven by endothermic generators.
The currently used enrichment fluids to supply carbon required by the process are gaseous hydrocarbons such as methane or propane, and the monitoring of the carburizing process is performed by means of oxygen probes associated with computerised systems. The actual trend of the technology is to obtain "in situ" a protective atmosphere, for example by means of nitrogen and methanol directly introduced into the oven. In the hot chamber of the oven, necessarily kept at suitable temperature, methanol dissociates in CO and H.sub.2 with endothermic reaction in a way to create the "carrying" protective atmosphere that constitutes the necessary support for the carburizing process.
There are cases in which the poor local availability, if not the absence, of reliable hydrocarbons, such as methane or propane, necessarily involves the use of different carburizing agents that, though being economical and easy to be found, do not allow the direct application of the known technologies for carburizing processes. For example, according to a method known at the present time, the gas carburizing treatment is performed by producing "in situ" a carrying atmosphere with the help of nitrogen and methanol and a carburizing atmosphere by dripping organic liquids such as methyl alcohol (CH.sub.3 OH) and ethylacetate (CH.sub.3 --COO--C.sub.2 H.sub.5).
The control of the process is carried out manually by regulating the number of drops of liquid on the basis of the ope
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patent: 4445945 (1984-05-01), Schwalm
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patent: 4519853 (1985-05-01), Kostelitz et al.
patent: 4904419 (1990-02-01), Reynolds
patent: 5078922 (1992-01-01), Collins et al.
Colombani Piero
Stucchi Alessandro
Lentek S.r.l.
Yee Deborah
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