Muffle convection brazing/annealing system

Abstract

A convection muffle furnace for brazing and/or annealing a workpiece includes a muffle having towers formed integrally therewith and being mounted movable relative to a top wall of a furnace. Circulation fans are mounted in the towers so as to move along with the muffle during its expansion and contraction for producing forced convection heat transfer.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to heat-treating furnaces used for brazing and/or annealing of workpieces. More particularly, it relates to an improved method and apparatus for brazing and annealing of a workpiece which includes a furnace having a muffle formed therein and circulation fans disposed in towers which are an integral part of the muffle so as to produce forced convection heat transfer.

As is generally well-known in the art of heat-treating, brazing and annealing require a close tolerance on the temperature control in order to achieve a desired temperature profile or to maintain temperature uniformity within a workpiece. Convection heat transfer has been found to provide faster heating or cooling of the workpiece on a more uniform basis. In such convection heat transfer, the hot gases are typically directed at the workpiece by means of jets or fans, with the fans being the more common means to impart velocity to the gases.

Further, the brazing and annealing processes may also have to be carried out in a special or protective-treatment atmosphere, such as nitrogen or an exothermic gas, which creates conditions that prevent oxidation of the workpiece or imparts other desirable characteristics such as the reduction of oxides. When a combination of rapid heat transfer and a controlled atmosphere has been required, the conventional practice has been to introduce the desired atmosphere into a sealed furnace. For furnaces of the so-called reaches reach the proper temperature. As At this time, the workpieces are allowed to "soak" so as to insure uniform temperatures throughout the workpieces for melting the braze material. From the last convective brazing zone (i.e., zone 45n), the workpieces are transported to a cooling zone 100 in which it is cooled so as to solidify the brazed material. Upon leaving the cooling zone 100, the workpieces are conveyed to the exit chamber 36 through the atmospheric curtains 38 and then out the rear door 40. A continuous flow of the process gas is supplied in the exit chamber 36 so as to prevent air infiltration, thereby avoiding contamination of the controlled atmosphere in the brazing zone.

While conventional muffle furnaces could be used to braze aluminum sheet exchangers by heating them by natural convection and radiation, the length of these furnaces would, however, be required to be extremely long so as to prevent localized temperatures from melting the aluminum heat exchangers. This is because certain braze materials for aluminum have a melting point which is very close (within 100° F.) to the melting point of aluminum. The forced convection muffle furnace 10 of the present invention produces temperature uniformity throughout the convective brazing zones so as to effect a substantially uniform heating rate. Further, since the present muffle furnace is direct-fired, there is less fuel cost than the prior art furnaces utilizing radiant tubes. By comparing the tests performed on the operation of the direct-fired forced convection muffle furnace 10, it was found to be approximately 30 to 40 percent more thermally efficient than the radiant tube heated atmospheric furnaces of the prior art.

From the foregoing detailed description, it can thus be seen that the present invention provides an improved convection muffle furnace for brazing and/or annealing a workpiece which includes a muffle having towers formed integrally therewith and being mounted movable relative to the top wall of the furnace. Circulation fans disposed in the towers so as to move along with the muffle during its expansion and contraction thereby producing forced convection heat transfer.

While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the central scope thereof. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A convection muffle furnace for brazing and/or annealing a workpiece comprising:

a heating chamber formed by a bottom wall, a pair of side walls, a front wall, a rear wall and a top wall;

a D-shaped muffle formed by side walls, a floor and a roof;

the side walls of said muffle being disposed in a parallel, spaced-apart relationship to said side walls of said heating chamber and extending from the front wall of said heating chamber to the rear wall thereof;

said muffle being divided into a plurality of successive individual convection brazing zones which are spaced apart from each other;

a plurality of towers each being formed integrally with the roof of said muffle in each brazing zone and being mounted movably relative to the top wall of said heating chamber;

a plurality of fans each being mounted and sealed in a corresponding one of said plurality of towers for creating an atmospheric convection current in each of said brazing zones; and

direct-fired burners for heating the exterior of said muffle so as to increase the temperature of the atmospheric convection current;

whereby said plurality of fans in said plurality of towers are movable along with said muffle during its expansion and contraction so as to provide increased heating rates and high thermal efficiencies.

2. A convection muffle furnace as claimed in claim 1, wherein said muffle has its one end adjacent said front wall of the heating chamber being fixed and has its other end adjacent said rear wall thereof being freely movable.

3. A convection muffle furnace as claimed in claim 1, further comprising expansion zone means disposed adjacent the front and rear walls of said heating chamber for permitting longitudinal expansion and contraction of said muffle.

4. A convection muffle furnace as claimed in claim 1, wherein said side walls, floor and roof of said muffle are corrugated so as to impart rigidity thereto.

5. A convection muffle furnace as claimed in claim 1, further comprising expansion cylinder means disposed adjacent the rear wall of the heating chamber so as to maintain a constant tension on said muffle and thereby preventing its deformation.

6. A convection muffle furnace as claimed in claim 1, wherein said towers are mounted in openings formed in said top wall of the heating chamber, said openings being somewhat larger than the diameter of said towers to define spaces which permits lateral movement of said towers relative to said top wall for absorbing expansion and contraction of said muffle.

7. A convection muffle furnace as claimed in claim 6, further comprising sliding seal means disposed over said openings in said top wall to provide a gas-tight seal between said top wall and said towers.

8. A convection muffle furnace as claimed in claim 1, further comprising an entrance chamber disposed upstream of said front wall of the heating chamber for preventing contamination of the atmosphere in said brazing zone as workpieces to be heat-treated are supplied.

9. A convection muffle furnace as claimed in claim 8, further comprising an exit chamber disposed downstream of said rear wall of the heating chamber for preventing contamination of the atmosphere in said brazing zone as the workpieces that have been heat-treated are removed.

10. A convection muffle furnace for brazing and/or annealing a workpiece comprising:

a heating chamber formed by a bottom wall, a pair of side walls, a front wall, a rear wall and a top wall;

muffle means disposed inside of said heating chamber and extending longitudinally from the front wall of said heating chamber to the rear wall thereof, said muffle means comprising a D-shaped muffle having planar side walls parallel to the side walls of the heating chamber, a planar floor connected to the planar side walls and a dome-shaped roof positioned above and connected to the planar side walls;

said muffle means including tower means formed integrally therewith and being mounted movably relative to the top wall of said heating chamber;

circulating means being mounted and sealed in said tower means for creating an atmospheric convection current; and

direct-fired burners for heating the exterior of said muffle means so as to increase the temperature of the atmospheric convection current,

whereby said circulating means in said tower means are movable along with said muffle means during its expansion and contraction so as to provide increased heating rates and high thermal efficiencies.

11. A convection muffle furnace as claimed in claim 10, wherein said muffle means has its one end adjacent said front wall of the heating chamber being fixed and has its other end adjacent said rear wall thereof being freely movable.

12. A convection muffle furnace as claimed in claim 10, further comprising expansion zone means disposed adjacent the front and rear walls of said heating chamber for permitting longitudinal expansion and contraction of said muffle means.

13. A convection muffle furnace as claimed in claim 10, wherein said muffle means includes side walls, a floor and a roof which are corrugated so as to impart rigidity thereto.

14. A convection muffle furnace as claimed in claim 10, further comprising expansion cylinder means disposed adjacent the rear wall of the heating chamber so as to maintain a constant tension on said muffle means and thereby preventing its deformation.

15. A convection muffle furnace as claimed in claim 10, wherein said tower means are mounted in openings formed in said top wall of the heating chamber, said openings being somewhat larger than the diameter of said tower means to define spaces which permits lateral movement of said tower means relative to said top wall for absorbing expansion and contraction of said muffle means.

16. A convection muffle furnace as claimed in claim 15, further comprising sliding seal means disposed over said openings in said top wall to provide a gas-tight seal between said top wall and said towers.

17. A convection muffle furnace as claimed in claim 10, further comprising an entrance chamber disposed upstream of said front wall of the heating chamber for preventing contamination of the atmosphere in said muffle means as workpieces to be heat-treated are supplied.

18. A convection muffle furnace as claimed in claim 17, further comprising an exit chamber disposed downstream of said rear wall of the heating chamber for preventing contamination of the atmosphere in said muffle means as the workpieces that have been heat-treated are removed.

19. A convection muffle furnace for brazing and/or annealing a workpiece comprising:

a heating chamber formed by a bottom wall, a pair of side walls, a front wall, a rear wall and a top wall;

a D-shaped muffle having planar side walls parallel to the side walls of the heating chamber, a planar floor connected to the planar side walls and a dome-shaped roof positioned above and connected to the planar side walls, said muffle having at least one tower formed integrally therewith which is mounted movably relative to the top wall of said heating chamber; and

a circulating fan being mounted in said at least one tower so as to move along with said muffle during its expansion and contraction.

20. A convection muffle furnace for brazing and/or annealing a workpiece, comprising:

a heating chamber formed by a bottom wall, a pair of side walls, a front wall, a rear wall and a top wall;

D-shaped muffle means disposed inside of said heating chamber and extending longitudinally from the front wall of said heating chamber to the rear wall thereof;

said muffle means including tower means formed integrally therewith and being mounted movably relative to the top wall of said heating chamber;

a first thermocouple positioned within the muffle means and a second thermocouple positioned outside the muffle means and within the heating chamber, said first and second thermocouples providing temperature signals;

circulating means being mounted and sealed in said tower means for creating an atmospheric convection current; and

direct-fired burners for heating the exterior of said muffle means so as to increase the temperature of the atmospheric convection current,

whereby said circulating means in said tower means are movable along with said muffle means during its expansion and contraction so as to provide increased heating rates and high thermal efficiencies.

21. A convection muffle furnace for brazing and/or annealing a workpiece comprising:

a heating chamber formed by a bottom wall, a pair of side walls, a front wall, a rear wall and a top wall;

a D-shaped muffle having at least one tower formed integrally therewith which is mounted movably relative to the top wall of said heating chamber;

a first thermocouple positioned within the muffle and a second thermocouple positioned outside the muffle means and within the heating chamber, said first and second thermocouples providing temperature signals; and

a circulating fan being mounted in said at least one tower so as to move along with said muffle during its expansion and contraction.