GB2121935A - Vacuum furnace for heat treatment - Google Patents

Abstract

A vacuum furnace for the heat treatment of metals comprises a heating furnace proper 101, and pre- exhaust chambers 3, 4, one 3 adapted to feed a workpiece A into the furnace proper therefrom and the other 4 adapted to discharge the workpiece out of the furnace proper. Vacuum valves 2, 2% are provided for partitioning the furnace proper from the pre-exhaust chambers 3 and 4 respectively, and a line assembly 5 conveys the workpiece from the feed chamber through the furnace proper and into the discharge chamber. A heating chamber 102 forming part of the furnace proper is positioned on the upper part of the furnace proper 101 above the line assembly 5, and an externally operable elevating means 105 is disposed in the furnace proper for lifting the workpieces carried by the line assembly to the heating chamber where they are heated, and then returned to the line assembly for discharge. <IMAGE>

Description

SPECIFICATION Vacuum furnace for heat treatment The present invention relates to a vacuum furnace for the heat treatment of workpieces and materials.

In general, vacuum furnaces are used for melting or brazing of metal workpieces such as aluminium workpieces. This is primarily due to the fact that the metal may be oxidized by atmospheric oxygen resulting in deterioration of the workpiece itself or its junction with another workpiece. Fig. 1 of the accompanying drawings shows a typical known example of vacuum furnace available for this purpose and constructed from horizontally extending, cylindrical bodies, viz., a furnace proper 1, a pre-exhaust chamber 3 adapted to feed workpieces therethrough and being comminicatable with the furnace proper 1 through a partitioning vacuum valve 2, and a preexhaust chamber 4 adapted to discharge the workpieces therefrom and being communicatable with the furnace proper 1 through a partitioning vacuum valve 2'.Within and extending along the furnace proper 1, and the chambers 3 and 4 there is a line assembly 5 for conveying the workpieces through the furnace. Air-tight doors 6 and 7 close the outer ends of the chambers 3 and 4 respectively.

During the treatment of a workpiece A, both valves 2 and 2' are closed to seal the furnace proper 1 from the chambers 3, 4 and, together with doors 6 and 7, maintain them in an air-tight condition, whilst the furnace proper 1 is maintained in a given vacuum condition and preheated to a suitable temperature in a normal state. After door 6 is opened to deliver the workpiece A into the preexhaust chamber 3 and then closed, the chamber 3 is evacuated to the degree of vacuum substantially equal to that prevailing in the furnace proper 1. The vacuum valve 2 is then opened to communicåte the preexhaust chamber 3 with the furnace proper 1.

Thereupon, the workpiece A is fed from the chamber 3 into the furnace proper 1, and the vacuum valve 2 is closed to cut off communication between the furnace proper 1 and the pre-exhaust chamber 3. Subsequently, the furnace proper 1 is brought to a desired high temperature under the given vacuum to work or treat the workpiece A.

After the given heat treatment is completed, the vacuum valve 2' is opened to communicate the furnace proper 1 with the pre-exhaust chamber 4 which has been exhausted in advance to the degree of vacuum prevailing in the furnace proper 1. The workpiece A is then fed from the furnace proper 1 into the pre-exhaust chamber 4 by means of the conveying line assembly 5. The valve 2' is then closed to cut-off communication between the furnace proper 1 and the pre-exhaust chamber 4, after which the chamber 4 is brought to atmospheric pressure, the door 7 is opened and the workpiece A is carried out of the chamber 4 into the atmosphere through the open end of chamber 4.

In the known furnace described above, the heating furnace proper 1 is arranged on a level with the pre-exhaust chamber 3 and 4. As a result, the partitioning vacuum valves 2 and 2', which are also arranged on a level with the furnace proper 1 are exposed directly to radiant heat, and heated while the furnace is operated. (Convection heat poses no problem under vacuum). As a result, the valves may be subject to deformation, or their sliding parts may lose their lubricating properties, so that difficulties are encountered both in closing and opening thereof and in the maintaining airtight conditions. There may also be certain deformation of the delivery line assembly such as a conveyor or chain block assembly for delivery of a workpiece A from the chamber 3 into the chamber 4 through the furnace proper 1.

Practically, this interferes with the running of the furnace and this becomes increasingly marked the larger the size of the furnace.

A main object of the present invention is therefore to provide a vacuum furnace in which the above-mentioned problems are minimized or eliminated.

To this end, the present invention consists in a vacuum furnace for heat treatment, comprising a heating furnace proper, preexhaust chambers adapted to feed a workpiece into the furnace proper therefrom and to discharge the workpiece out of the furnace proper thereinto respectively, vacuum valves for intercommunicating and cutting off communication between the furnace proper and the respective pre-exhaust chambers, and a line assembly for conveying the workpiece from the feed chamber through the furnace proper and into the discharge chamber, characterized in that a heating chamber forming part of said furnace proper is located on an upper part of the furnace proper above said conveying line assembly, and in that an elevating means is disposed in said furnace proper and is externally operable to lift the workpiece from said conveying line assembly to said heating chamber where the workpiece is heated.

With the vacuum furnace according to the present invention, there is no high temperature heat radiation striking directly upon the vacuum valves provided along the conveying line, with the result that neither thermal distortion of the conveying line or thermal deformation of the valves takes place. This ensures that the conveying line is always driven satisfactorily, the opening and closing of the valves is performed without difficulty and the valves are satisfactorily air-tight when ciosed.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Fig. 1 is a side elevation of the known vacuum furnace for continuous heat treatment of metals which has been previously described herein; Fig. 2 is a side elevation of a vacuum furnace for continuous heat treatment of metals and constructed according to the present invention; and Fig. 3 is an enlarged, partially cut-away, perspective view of a part of the furnace proper of the heating furnace of the vacuum furnace of Fig.

2.

The vacuum furnace illustrated in Figs. 2 and 3 is constructed similarly to that of Fig. 1 in that it comprises horizontally extending, cylindrical bodies, viz. a furnace proper 101, pre-exhaust chambers 3 and 4, vacuum valves 2 and 2' and a delivery line assembly 5. The chamber 3 is adapted to feed a workpiece therethrough and is communicatable with the furnace proper 101 through the partitioning vacuum valve 2, and the chamber 4 is adapted to discharge the workpiece therefrom and is communicatable with the furnace proper 101 through the paritioning vacuum valve 2'. The delivery line assembly 5 comprises a conveying means which may be in the form of a belt(s), rail(s), roll or ball bearing(s) or the like and is mounted inside the vacuum furnace on the bottom of the furnace proper 101,the chamber 3 and the chamber 4.The chambers 3 and 4 are provided with air-tight doors 6 and 7, respectively.

As will be appreciated, the furnace illustrated in Figs. 2 and 3, described with reference to Fig. 1 by the following features. The furnace proper 101 has mounted thereon in air-tight manner, a heating chamber 102 defined by a hollow, cylindrical member. Within the heating chamber 102, there is a known heating means such as an electric heater (not shown). The heating means is connected to an external temperature controller 103. The top portion of the heating chamber 102 is fitted with an air-tight cover 104.

An elevating device 105 is hermatically mounted through the bottom of the furnace proper 101, and is ascendable ordescendable substantially along the axial line of the heating chamber 102.

The elevating device 105 comprises an elevating shaft 106 and a table 107 mounted on top of the shaft. The elevating shaft 106 has its lower end coupled to a driving device which may be of any suitable known kind, such as a hydraulic device (not illustrated). It should be understood that the table 107 is of such a size that it can pass between a pair of rails 5a forming the delivery line 5. As shown in Fig. 2, a carriage 108 supports a workpiece A thereon, and is movable on the rails within the chamber 3, the furnace proper 101 and the chamber 4. The carriage 108 may be constructed for example from a frame 110 of rectangular configuration and defining an opening 109, through which the elevating shaft 106 is vertically movable together with the table 107 on which the workpiece A is supported whilst being moved by the elevating device.

Referring more particularly to Fig. 3, a driving mechanism for the carriage 108 may for example comprise a number of toothed rails 111 on the under surface of frame 110 extending in parallel along one rail 5a and a plurality of gears 114 to mesh therewith. Each gear 114 is fixed to one end of a respective shaft 11 3 extending hermitically through the side wall of the chamber 3, the furnace proper 101 and the chamber 4 as the case may be. Each shaft 11 3 is connected at its outer end to a respective drive motor 112.The number of gears 114 is dependent upon the length of the carriage 108 and may be chosen in such a manner that the carriage 108 can be run continuously on the rails 5a with no difficulty.

The heating furnace of the vacuum type described in Figures 2 and 3 operates as follows.

In operation, both valves 2 and 2' are closed in air-tight manner to cut off communication between the furnace proper 101 and the respective chambers 3 and 4. The furnace proper 101 is then maintained in the desired vacuum condition by a vacuum exhaust device (not shown), and the temperature in the heating chamber 102 is controlled at a given temperature by the temperature controller 103. Subsequently, the door 6 is opened to enable the workpiece A to be introduced into the chamber 3 and placed on the carriage 108 disposed in advance therein. The door 6 is the closed. The chamber 3 is then evacuated by a vacuum exhaust device (not shown), and after the degree of vacuum substantially equal to that prevailing in the furnace proper 101 is reached, the valve 2 is opened.

Then the driving motors 112 shown in Fig. 3, are sequentially driven to turn the gears 114, and thereby move the carriage 108 along the rails 5a.

As a result, the workpiece A is carried to just above the elevating device 105 positioned in the furnace proper 101. Thereupon, the valve 2 is closed, and the elevating device 105 is driven to lift the workpiece A to a given position in the heating chamber 102.

The heating chamber 102 is heated to a given internal temperature by manipulation of the temperature controller 103, at which the workpiece A is treated. Although the heating chamber 102 may reach a temperature of as high as 5000C the heat conduction occurring in this process is due virtually only to radiation since the furnace proper 101 including the heating chamber 102 is under vacuum. The arrangement in which the heating chamber 102 is disposed at the upper part of the furnace proper 101 above the delivery line 5 does not substantially permit the heat radiated from the heating chamber 102 to conduct to the delivery line 5. Accordingly, the workpiece A disposed in the heating chamber 102 is effectively heated. As mentioned above, the amount of heat radiated from the heating chamber 102 to the delivery line is reduced, and the radiated heat from the heating chamber 102 does not strike directly upon the partitioning vacuum valves 2 and 2'. This makes it possible to prevent heat deformation of the valves 2 and 2', so that they can be manipulated in a constantly stabilized state and in a good air-tight condition.

After the workpiece A has been heated in the heating chamber 102 for the required time, the workpiece A is caused to return to the carriage 108 by the elevating device 105. Subsequently, the valve 2' is opened to communicate the furnace proper 101 with the chamber 4 which has been exhausted in advance to the degree of vacuum substantially equal to that prevailing in the furnace proper 101. The driving motors 112 are again sequentially driven to move the carriage 108 along the rails 5a, to carry the workpiece A from the furnace proper 101 into the pre-exhaust chamber 4. The valve 2' is then closed to cut off communication between the chamber 4 and the furnace proper 101 , and the chamber 4 is brought to atmospheric pressure. The door 7 is then opened to enable the workpiece A to be removed from the chamber 4.

If the above-mentioned procedures are repeated, a number of workpieces are then continuously heat-treated under vacuum.

Whilst the delivery line has been described as comprising a pair of rails, it should be understood that the delivery line, may comprise any other suitable known means such as belt conveyor(s), chain block(s), roll or ball bearing(s), if required.

Claims (8)

1. A vacuum furnace for heat treatment comprising a heating furnace proper, pre-exhaust chambers adapted to feed a workpiece into the furnace Drover therefrom and to discharge the workpiece out of the furnace proper thereinto respectively, vacuum valves for intercommunicating and cutting off communication between the furnace proper and the respective pre-exhaust chambers, and a line assembly for conveying the workpiece from the feed chamber through the furnace proper and into the discharge chamber, characterised in that a heating chamber forming part of said furnace proper is located on an upper part of-the furnace proper above said conveying line assembly, and in that an elevating means is disposed in said furnace proper and is externally operable to lift the workpiece from said conveying line assembly to said heating chamber where the workpiece is heated.

2. A furnace as claimed in claim 1, characterised in that said conveying line assembly includes a pair of rails.

3. A furnace as claimed in claim 1, characterised in that said conveying line assembly comprises a conveyor, a chain block, or roll or ball bearing means.

4. A furnace as claimed in claim 2, characterised in that the conveying line assembly includes a carriage for supporting the workpiece and is movable on said rails.

5. A furnace as claimed in claim 4, characterised in that the carriage is moved by means of a number of teeth on the carriage and extending in parallel along one of said rails, and gears to mesh with said teeth, said gears being fixed to one of the ends of respective shafts extending hermetically through the side wall of the furnace proper and said pre-exhaust chambers, and said shafts being connected at their other ends to respective driving motors.

6. A furnace as claimed in any one of claims 1 to 5, characterised in that said elevating means comprises an elevating shaft having one end coupled to a driving means, and a table fixed to the top of the other end of said shaft.

7. A furnace as claimed in claim 6, as appendant to claim 4 or 5, characterised in that the carriage has an opening therein through which the table and the shaft can pass to lift the workpiece from the carriage to the heating chamber.

8. A vacuum furnace for heat treatment substantially as hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.