US3361864A

US3361864A - Furnace for treatment of wax-bonded sinterable preforms

Info

Publication number: US3361864A
Application number: US423509A
Authority: US
Inventors: Vollmer Helmut; Huchler Kurt
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1964-01-09
Filing date: 1965-01-05
Publication date: 1968-01-02
Anticipated expiration: 1985-01-02
Also published as: FR1419364A; BE656841A; CH406792A; DE1265346B; GB1018049A; NL6413038A

Description

1968 H. VOLLMER ETAL 3,361,864

FURNACE FOR TREATMENT OF WAX-BONDED SINTERABLE PREFORMS Filed Jan. 5, 1965 gm 4. array/v52.

United States Patent 3,361,864 FURNACE FOR TREATMENT OF WAX-BONDED SINTERABLE PREFORMS Helmut Vollmer, Heiligwies, and Kurt Huchler, Balzers, Liechtenstein, assignors, by mesne assignments, to The Bendix Corporation, Detroit, Mich, a corporation of Delaware Filed Jan. 5, 1965, Ser. No. 423,509 Claims priority, application Switzerland, Jan. 9, 1964, 237/64 2 Claims. (CI. 13-27) ABSTRACT OF THE DISCLOSURE A furnace for the treatment of wax-bonded sinterable preforms. The furnace consists of an evacuated housing containing a sealed container into which the sinterable preforms are inserted. The first passage leads from within the container to the space between container and housing. A second passage leads from the space between container and housing externally to associated condensing and pumping mechanism. Externally-controllable valve means are operative to selectively interconnect the first and second passages. The arrangement permits, without handling of the wax-bonded sinterable preforms, first the wax removal and condensing in the associated mechanism, and secondly, vacuum sintering of the preforms.

In the sintering technique it is useful to press the powdered raw material with the use of a binding material into preforms, which then are treated in a furnace at correspondingly higher temperatures to become the end prod uct. Various materials are used as the binding means among which are waxlike substances. Before or during the real sintering process the binding material must be removed. One of the known processes in the case of use of wax as the binding material involves the following: after the pressing of the preforms to attain a sufficiently permanent shape, they are heated to a temperature sufficient to vaporize the wax so that the wax vapor can be pumped off or trapped with cooled condensers. The use of special vacuum dewaxing furnaces with their auxiliary equipment is costly, time consuming and unsatisfactory. It also possesses the disadvantage, that by dewaxing before the sintering-the binding is more or less generally removed from the preforrns and they lose their durability and on account of this they must be handled with the greatest of care in removal from the dewaxing furnace and loading into the true sintering furnace.

Up to the present time the dewaxing and sintering processes could not be carried out in the same furnace, because with the present furnace construction the wax vapor removed from the sintering material has led to a contamination and dirtying of the whole inside of the furnace and the connected pump, which becomes intolerable for succeeding sintering operations.

It is the object of the present invention to overcome the above mentioned difficulties and to be able to carry out the dewaxing and sintering processes in one and the same vacuum furnace.

The furnace according to the invention for the treatment of wax-bonded preforms to be sintered consists of a closed furnace housing with an evacuation connection, a container situated within it and heating means for the exposure and heating of the preforms to be dewaxed and sintered and is characterized in that the aforementioned container on the inside of the evacuable furnace housing is built with an evacuation opening which is connected to a wax vapor condenser by a second separate evacuation pipe. One example of the carrying out of the invention is represented in the accompanied schematic drawing in which:

FIGURE 1 is a schematic view of a furnace embodying the present invention, and

FIGURE 2 is a fragmentary view similar to FIGURE 1 but showing another embodiment of the present invention.

Referring now to the drawings, numeral 1 designates a closed furnace housing which can be evacuated by means of a high-vacuum pump (not shown) through the evacuation connection 2. Inside the furnace housing are arranged two containers 3 and 4 and a heating arrangement for the container 4 such as an induction heating coil 5 surrounding the container 3. Container 4 is located within container 3 and may be either metal or graphite depending on temperature requirements. Container 3 is made of quartz or quartz-like material. The container 4, as shown in the drawing, consists of a graphite cup 6 with a removable cover 7 embedded in carbon grit 8 which surrounds the sinter material on all sides. The carbon grit 8 above the cover 7 may be loosely packed to facilitate removal of the carbon grit 8 and allow insertion and removal of the sinter material. The container 4 has an opening 11 in the bottom which is connected to a second evacuation connection 12. Conduit 13 extends from connection 12 through the wall of the furnace housing in a vacuum tight manner to the wax condenser 18 which is adapted to be heated by well known means (not shown). A shaft 15 is disposed within conduit 13 and is connected to a small plate valve 16 to open and close said valve and thereby respectively connect conduit 12 and the interior of container 4 to the space 9 of the evacuable furnace housing 1 or to conduit -13 as desired. The shaft 15 is likewise carried out from the furnace housing in a vacuum tight manner and is provided with a hand-wheel 1'7. The valve plate 16 and the hand wheel 17 are shown in the closed position of the valve in FIGURE 1. The open position is shown by dotted lines. The possibility of the connection of the container 4 with the space 9 permits the bringing of the sinter material container to high vacuurn before the beginning of sintering, with the pumps connected at 2. The vacuum pump 19, connected to the pipe 13 and to the condenser identified as a whole as 18, then only serves for the separate pumping off of the wax vapor during dewaxing. Under other conditions pump 19 can be used with suitable capacity to evacuate container 4.

The condenser '18 is of a well known construction and consists, in the example given, of a vessel 20, in which are arranged coolable baffie plates 21 for the condensation of the wax vapor. The centrally arranged carrier 22 for the baffle plates is hollow and suitable cooling fluid can be circulated through it.

The removal of the wax vapor from the sinter material container 4 and the permanent gases evolved during the dewaxing process takes place through the

pipes

12, 13 and 23. The outlet from the condenser leads through the pipe 24 to the pump 19. The entrance to and exit from the condenser 18 may be shut-off by valves 25 and 26 respectively.

The described furnace is suitable for dewaxing as well as sintering. The sinter material is introduced into the container 4 which is then closed. The container and the furnace housing 1 are evacuated through the open valve 16 and the pump connected at 2. The valve 16 is then closed and the sinter material brought to the dewaxing temperature by energizing the heater. The evolving wax vapor is removed through the pipe 13 and condensed in condenser 18. The non-condensable gases, which emerge at the same time from the container 4, as was previously mentioned, are removed by the pump 19. The induction coil 5 may be connected to an electrical A-C current 3 source, not shown, through vacuum tight connectors, out of the plane of the drawing and therefore not shown, which are known to those skilled in the art.

It is often advantageous during the dewaxing to maintain an overpressure of an auxiliary gas in the furnace which does not disturb the carrying out of the dewaxing process. The auxiliary gas can, for example, be argon, nitrogen or hydrogen and may be admitted through the evacuated connection 2. Overpressure during the dewaxing process hinders the possible escape of the wax vapor into space 9 through the lack of thightness of the sinter material container 4. An auxiliary gas atmosphere in the furnace may also be used in the sintering process itself to reduce the vaporization of components of the sinter material at the higher temperature used.

After the carrying out of the dewaxing it is not necessary to remove the material from the container. In most cases the condenser can be simply shut off from the furnace by means of valve 25. The valve 16 is opened and the space 9 is well as the sinter material container .are brought to high vacuum and after increasing the heat the sintering is carried out in the usual manner.

The necessary reduced pressure adjusts itself after a short time to the sintering process and lies somewhere between 10 to torr.

The operating technique is especially advantageous if two or more of the sintering furnaces according to the present invention can be combined into a single operating unit. The charge of one furnace may be dewaxed white the other is being sintered. For this purpose the pipe 23 in FIGURE 1 may be removable from the furnace.

A further possibility for such manifold arrangement is shown in FIGURE 2. The same parts are designated by the same reference numbers as in FIGURE 1. The connection between pipe 12 from the bottom of the sinter material container 4 and the condenser 18 is different from that in FIGURE 1.

In this embodiment the connection comprises a flexible rubber tube 32 and with its connection piece 30 is detachably connected to pipe 12 through a shut-off valve 31 secured to the furnace housing 1. Tube 32 is retractable from the evacuated furnace to the position (30732) as shown by the dotted lines in FIGURE 2. Tube 32 may be heated in practice by suitable well known means (not shown).

The shut-off valve 31 is of known construction and will therefore not be further described. An 0 ring gasket seal 33 prevents the entrance of atmospheric air into the furnace while the valve 31 is opened for the insertion or removal of the evacuation tube. After drawing back the pipe or tube 32 from the furnace the valve 31 can be again closed and the tube detached from the furnace. The condenser with its attached pumps is then ready for use in dewaxing of sinter material in other furnaces of the same type.

Wax in the sense of the present invention will be understood to mean every principle binding material of the higher hydrocarbons, which can find use in the sintering technique, especially in the production of hard metal preforms.

We claim:

1. A furnace for the treatment of wax-bonded sinterable preforms comprising: a housing; an enclosed container adapted to hold sinterable preformsin the interior thereof and in said housing, defining a space adapted to be evacuated intermediate said housing and said container; induction means for heating said container; a first evacuation connection opening on one end into the interior of said container and on another end into said space intermediate housing and container; a second evacuation connection opening into said space on one end and extending exterior of said housing; valve means controllable externally of said housing for selectively interconnecting said first and second evacuation connections, condenser means exterior of said housing means and conduit means interconnecting said second evacuation connection and said condenser means.

2. The furnace of claim 3 wherein said conduit means is detachably connected to said second evacuation connection and a shut-off valve is connected to said second evacuation connection to close said connection when said conduit means is detached.

References Cited UNITED STATES PATENTS 2,789,153 4/1957 Mark 133l RICHARD M. WOOD, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

Claims

1. A FURNACE FOR THE TREATMENT OF WAX-BONDED SINTERABLE PREFORMS COMPRISING: A HOUSING; AN ENCLOSED CONTAINER ADAPTED TO HOLD SINTERABLE PREFORMS IN THE INTERIOR THEREOF AND IN SAID HOUSING, DEFINING A SPACE ADAPTED TO BE EVACUATED INTERMEDIATE SAID HOUSING AND SAID CONTAINER; INDUCTION MEANS FOR HEATING SAID CONTAINER; A FIRST EVACUATION CONNECTION OPENING ON ONE END INTO THE INTERIOR OF SAID CONTAINER AND ON ANOTHER END INTO SAID SPACE INTERMEDIATE HOUSING AND CONTAINER; A SECOND EVACUATION CONNECTION OPENING INTO SAID SPACE ON ONE END AND EXTENDING EXTERIOR OF SAID HOUSING; VALVE MEANS CONTROLLABLE EXTERNALLY OF SAID HOUSING FOR SELECTIVELY INTERCONNECTING SAID FIRST AND SECOND EVACUATION CONNECTIONS, CONDENSER MEANS EXTERIOR OF SAID