Heating – Having condition responsive control – Of or by pressure of fluid work or work chamber atmosphere
Patent
1998-08-20
2000-06-13
Ferensic, Denise L.
Heating
Having condition responsive control
Of or by pressure of fluid work or work chamber atmosphere
432 37, 432 38, F27B 940
Patent
active
060742038
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of tunnels or chambers supplied with gas in order to carry out operations under an atmosphere, such as, for example, heat-treatment operations, soldering operations, operations of packaging food products or cooling operations using cold gases.
The present invention relates to: in a chamber; method; and heat-treatment ovens or soldering ovens, or else of ovens or machines for soldering/tinning electronic components, or alternatively of chambers for the packaging or cooling of food products.
By way of illustration, such "tunnels" or "chambers" might thus, for example, consist of heat-treatment ovens, soldering ovens, ovens for the reflow soldering of electronic components on circuits, or else machines for the wave soldering/tinning of electronic components, whether these machines are designed as tunnels which are completely sealed over their entire length or they are provided with shrouding systems extending above the solder bath or to a greater or lesser extent largely around this solder bath in order to enclose, for example, the preheat zone.
2. Description of Related Art
Two problem areas encountered by users of such plants are:
Mention may be made here of the widespread example of applications in which the user tries to stabilize the residual oxygen content of the nitrogen-based atmospheres employed in these chambers.
This problem area of stabilizing the atmosphere employed is, of course, closely linked with the user's desire for excellent reproducibility of the quality of the components or products treated in the chamber in question.
Still by way of illustration, variations in the quality of the components treated in the chamber may, for example, be related, in the case of inert-type atmospheres, to the oxidizability of the atmosphere (therefore to the level of residual oxygen or other oxidizing gas in this atmosphere), or else to instabilities in the heat transfer employed in the chamber due to the observed instabilities in the atmosphere employed, whether this be instability in terms of composition or in terms of gas flow rates.
The observed instabilities in the atmosphere are more generally related to the production rate of the chamber or to the external conditions surrounding the oven, for example possible droughts.
In this first problem area, mention may be made of the case of ovens for the reflow soldering of electronic components on circuits, so-called "convective" ovens, which therefore carry out the heat transfer necessary for soldering the component in an essentially convective mode, circulating very large volumes of gas in each zone of the oven.
It is known in fact that at least some of the zones of such convective ovens (in particular the hot zones) operate with a gas recirculating (recycling) system. In these recirculating zones, only a "relatively low" volume is regularly added, in order to compensate for the gas losses involved, in particular via the extraction chimneys or the inlets/outlets of the oven.
These convection reflow ovens are therefore characterized, on the one hand, by very large consumptions of gas but also, on the other hand, by great difficulties encountered by users in regulating these ovens, any modification of the gas flow in certain zones of the oven having considerable repercussions on the distribution equilibrium of the gas movements in the oven (turbulence) and on the existing heat profile (and therefore necessarily on the quality of the components produced).
Studies carried out by the Applicant on this subject show, in fact, that these ovens must be adjusted in the production phase in order to perform correctly and be representative of the subsequent operating conditions. It is then necessary to modify the flow rate selectively supplying such or such a zone of the oven manually, thereby giving rise to considerable variations in the flow rate in the other zones of the oven which require manual readjustments to be made zone by zone.
In order to illustrate these considera
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Patent Abstracts of Japan, vol. 095, No. 003, Apr. 28, 1995 and JP 06 344176.
Leturmy Marc
Pioger Frederic
Ferensic Denise L.
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Wilson Gregory A.
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