Electric heating – Inductive heating – Metal working
Reexamination Certificate
2002-11-29
2004-02-17
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Metal working
C219S628000, C219S651000, C432S025000, C432S057000, C228S234100
Reexamination Certificate
active
06693263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brazing apparatus for metal workpieces such as aluminum, copper, copper alloys, iron or stainless steel and so forth in which a convection type furnace (thermal convection furnace) is employed, more specifically to a brazing apparatus for brazing aluminum parts on large-sized aluminum workpieces such as a heat exchanger for an automobile, utilizing an index type (intermittent motion type) convection furnace.
2. Description of the Related Art
A convection furnace for brazing large-sized metal workpieces made of aluminum such as a heat exchanger for an automobile etc. is generally designed to heat the workpieces fixed or carried within a brazing chamber, by circulating using a fan etc. inside the brazing chamber a heating medium gas composed of an inactive gas for example nitrogen gas etc. heated in a combustion chamber.
Brazing temperature varies depending on metal materials, brazing materials and types of flux, and normally it is 550° C. to 640° C. for brazing aluminum of AA1000 series with a fluoride flux, and 700° C. to 850° C. for copper and stainless steel.
For example, brazing temperature for aluminum of AA1100 with aluminum of AA4045 or 4047 as brazing material and a fluoride as flux is approx. 600° C. In a convection type brazing furnace, workpieces are usually heated up to approx. 350° C. in a preheating furnace. The workpieces carried into a brazing chamber of the brazing furnace is rapidly heated by heating medium gas heated to approx. 610° C. to 620° C., so that the workpieces temperature is raised up to 600° C. in several minutes.
Normally such temperature is maintained during the heating to fuse the flux and to complete the brazing, however despite maintaining the furnace temperature at 600° C. by controlling the heating medium gas temperature, a temperature slope of 30° C. to 40° C. is generated among the surface of the workpieces which the heating medium gas directly hits, the opposite side thereof and interior sections of the workpieces, because of which a flow of the brazing material becomes uneven, and resultantly brazing quality is lowered.
The inventors of the present invention proposed method and an apparatus by which workpieces temperature can be made uniform and a high-quality brazing can be executed, wherein temperature of heating medium gas to be applied to the workpieces in a convection type brazing furnace is varied up and downward in small increments (hereinafter referred to as “pulse heating”) during a temperature raising process and after reaching a predetermined brazing temperature. (Ref. JP-A No.2001-340958: U.S. Pat. No. 2001-0051323)
However, according to the convection type brazing furnace disclosed in JP-A No.2001-340958 wherein heating medium gas temperature is varied up and downward to perform the pulse heating, lowering the heating medium gas temperature does not instantly lower the brazing chamber temperature because of a large thermal capacity of the brazing chamber itself, therefore it takes some time before reaching a desired temperature. Likewise, when the heating medium gas temperature is raised also, there is a certain time lag before the brazing chamber temperature reaches a desired level.
Because of the inadequate thermal response, by the conventional method of varying the heating medium gas temperature up and downward it is difficult to shorten a cycle time (cycle of high-temperature heating and low-temperature heating) of the pulse heating, therefore a brazing time inevitably becomes longer, resulting in a lower productivity.
In view of the foregoing, it is an object of the invention to provide a convection type brazing apparatus for metal workpieces that can shorten an operation time for brazing metal workpieces such as aluminum, copper, copper alloys, iron or stainless steel and so forth to achieve a higher productivity, and enables uniform heating of the workpieces to improve a yield of products.
SUMMARY OF THE INVENTION
As a result of persistent studies for achieving the mentioned object, the inventors of the present invention have discovered that in a brazing operation for metal workpieces such as aluminum, copper, copper alloys, iron or stainless steel, etc. utilizing a convection furnace, intermittently supplying heating medium gas can effectively shorten a cycle time of the pulse heating and minimize a temperature slope of the workpieces especially large-sized workpieces, and further shorten the brazing operation time to improve productivity.
Accordingly, the invention provides a convection type brazing apparatus for metal workpieces having a brazing furnace provided with at least a thermal medium gas heating chamber, a brazing chamber and a heating medium gas circulation path through which the heating medium gas heated in the thermal medium gas heating chamber returns to the thermal medium gas heating chamber via the brazing chamber, comprising a heating medium gas circulation path switching mechanism for periodically switching the heating medium gas circulation path so that a blowing phase during which the heating medium gas heated in the thermal medium gas heating chamber is blown into the brazing chamber and a suspension phase during which blow of the heating medium gas into the brazing chamber is suspended are alternately repeated; and a bypass circulation path through which the heating medium gas returns directly to the thermal medium gas heating chamber halfway of the heating medium gas circulation path without running through the brazing chamber during the suspension phase.
For the heating medium gas circulation path switching mechanism, an ordinary switching valve such as a damper valve, slide valve, butterfly valve, etc. may be employed. Also, though the heating medium gas circulation path switching mechanism can have separate valves in the heating medium gas circulation path and the bypass circulation path, it is more economical to provide a single valve to be used in common for switching the both circulation paths.
Also, the heating medium gas circulation path switching mechanism comprises means for controlling for closing the bypass circulation path while the heating medium gas circulation path is opened during the blowing phase and opening the bypass circulation path while the heating medium gas circulation path is closed during the suspension phase.
The heating medium gas circulation path switching mechanism controlling means is provided with a function to set a cycle time of the blowing phase and the suspension phase of the heating medium gas circulation path in a range of 5 seconds to 5 minutes.
In an ordinary convection furnace with a capacity of 1 cubic meter, a normal time range of the suspension phase is 5 seconds to 5 minutes, most preferably approx. 10-30 seconds. If the suspension phase is too short it is difficult to lower the heating medium gas temperature to a desired level. On the contrary if it is too long total operation time is undesirably prolonged, though workpieces may have a better finish.
Also, for adjusting the furnace temperature, it is effective to vary a time ratio of the blowing phase and suspension phase of the heating medium. For example, in case where the furnace temperature exceeds a preset value a time ratio of the blowing phase is reduced, while when the furnace temperature becomes less than the preset value the time ratio of the blowing phase is increased.
For such purpose, the heating medium gas circulation path switching mechanism controlling means comprises means for correction for executing feedback control of a ratio of the blowing phase and the suspension phase in accordance with a temperature inside the brazing chamber.
The control correction means is provided with a sensor for detecting the furnace temperature and a programmable controller for varying the time ratio of the blowing phase and suspension phase according to the furnace temperature detected by the sensor. A preferable range of the time ratio of the blowing phase and suspension phase is 30:70 to 70:30.
According to
Leung Philip H.
Oak Nippon Co., Ltd.
LandOfFree
Convection type brazing apparatus for metal workpieces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Convection type brazing apparatus for metal workpieces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Convection type brazing apparatus for metal workpieces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3314479