US3775043A

US3775043A - Means in furnaces for vacuum-pressure-sintering

Info

Publication number: US3775043A
Application number: US00233925A
Authority: US
Inventors: P Johansson; T Landa; H Larker
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1971-03-15
Filing date: 1972-03-13
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: SU420156A3; DE2211631B2; SE350714B; CA977548A; GB1382322A; FR2129424A5; DE2211631A1

Abstract

A furnace for vacuum-pressure-sintering has a furnace chamber which is enclosed in and insulated from a surrounding pressure chamber. The pressure chamber includes a bottom projecting into it at the lower end and has at the upper end a charging opening and a lid projecting into the charging opening. A housing can be applied over the charging opening and connected to a vacuum pump during the part of the operating cycle when the pressure in the furnace is to be below atmospheric pressure. The lid is formed of an outer annular part and an inner part, separate from each other, the outer annular part remaining in position when the inner part is removed. A heat radiation protection ring is provided for insertion into the opening into the annular part when the annular part is raised. A lifting device for the lid is provided inside the housing.

Description

United States Patent [191 Johansson et al.

[4 1 Nov. 27, 1973 MEANS IN FURNACES FOR VACUUM-PRESSURE-SINTERING [75 Inventors: Paul Johansson; Torstein Landa, 7

both of Vasteras; Hans Larker, Robertsfors, all of Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Mar. 13, 1972 [21] Appl. No.: 233,925

[30] Foreign Application Priority Data Mar. 15, 1971 Sweden 3276/71 [52] US. Cl. 432/205, 13/31 [51] Int. Cl. F271) 3/18 [58] Field of Search 263/40; 13/31; 432/205 '[56] References Cited UNITED STATES PATENTS 3,427,011 2/1969 Boyer et al.... 263/40 R 3,243,174 3/1966 Sweet 13/31 X 3,522,357 7/1970 Pine et al 13/31 9/1967 Westeren 263/40 R Primary Examiner-John J. Camby Attorney.lennings Bailey, Jr.

57 ABSTRACT A furnace for vacuum-pressure-sintering has a furnace chamber which is enclosed in and insulated from a surrounding pressure Chamber. The pressure chamber includes a bottom projecting into it at the lower end and has at the upper end a charging opening and a lid projecting into the charging opening. A housing can be applied over the charging opening and connected to a vacuum pump during the part of the operating cycle when the pressure in the furnace is to be below atmospheric pressure.

The lid is formed of an outer annular part and an inner part, separate from each other, the outer annular part remaining in position when the inner part is removed. A heat radiation protection ring is provided for insertion into the opening into the annular part when the annular part is raised. A lifting device for the lid is provided inside the housing.

15 Claims, 5 Drawing Figures sum 2 BF 3 PATENIEDnuv 21 I975 Fig. 2

///H////////M/// /////Z MEANS IN FURNACES FOR VACUUM-PRESSURE-SINTERING BACKGROUND or THE INVENTION 1. Field of the Invention The present invention relates to an arrangement for .use with a furnace for vacuum-pressure-sintering having a furnace chamber which is enclosed in and insulated from a surrounding pressure chamber composed of a pressure cylinder, a bottom projecting into this cylinder and a lid projecting into the charging opening of the furnace. t

2. The Prior Art 1 High density and freedom from pores gives high quality cemented carbide bodies produced metallurfgically from powder. In chip cutting machines the high density results in increased water and less risk of broken cutting edges. For rollers and the like the freedom from pores results in increased strength and surface smoothness and this also results in a smoother surface for a product being rolled. Even in the production of electrical resistance bodies of Mosi for example, there are considerable advantages in having a very high density and freedom from pores. The strength increases and the risk of local over-heating with resultant burning decreases. The advantages ofhighdensity and freedom from pores are equally great forcermets of various types. i v I High density and freedom from pores have previously been obtained (See, for example, Materialsin Design Engineering May 1965, pages 92-99), by enclosing a compacted powder body in a gas-tight, heat-resistant casing of some suitable metal, then evacuating the casing, sealing it and placing it in a furnace in which the material is sintered under high pressure. Temperatures and pressures of up to 1,500C and 2000 bars have been used. It is extremely expensive to apply a casing around a pressed body, particularly if it has a complicated shape, to evacuate and seal the casing and finally to remove the casing after the sintering. Especially in the production of small cutting elements the encapsuling is disproportionatelyexpensive. The problem has been how to make it possible to perform sintering and hot-moulding under such" conditions that the desired quality is obtained without expensive encapsuling.

I A method is known (See French pat. no.'2,036,654) for manufacturing sintered powder bodies having high density which comprises sintering, preferably under vacuum, powder bodies which have been moulded in the conventional manner by compressing powder and then hot-moulding the bodies after the sintering under direct influence of a pressure medium. The sintering of the bodies and the subsequent compression are thus carried out without the bodies being enclosed in a gastight casing. According to this method, bodies manufactured from a powder'or powder mixture are sintered at atmospheric pressure or lower pressure and at such a temperature that powder particles of the same material are bound together-or that binder binds together other powder particles in the powder mixture, after which the bodies are isostatically hot-moulded in the same furnace under direct influence of a pressure medium such as argon, helium, nitrogen or hydrogen. One possible explanation for the density increasing due to isostatic hot-moulding of sintered products although the bodies are not enclosed in special casing which prevent the pressure medium from coming into direct contact with the body may be that spaces'formed between powder particles bound together are completely sealed.

The binder thus forms a closed capsule around each individual space and prevents the pressure medium from penetrating into the body. During the subsequent hot-' moulding, these cavities disappear in the same way as they do when the hot-moulding is carried out with the material enclosed in a casing when pressure and temperature are chosen so that the binder is sufficiently easily deformed so that powder'particles bound to gether will slide towards each other and fill out the empty cavities.

To illustrate the technical progress brought about by the method of the French patent, it may be mentioned that sintered bodies which are manufactured according to. conventional methods usually contain 100 500 times as many cavities per unit of volume as bodies manufactured in accordance with that method. In comparison with previous methods comprising pressuresintering powder bodies enclosed in an evacuated heatresistant casing, the advantage is gained that a timeconsuming and expensive stage in the production is eliminated. The process makes possible sintering without encasing, without cooling of the bodies between sintering and hot-moulding and without complicated transfer means with sluices to prevent hot bodies from coming into contact with air. When compacting uranium dioxide, U0 a density ofup to 99.5 percent of the theoretically achievable density can be obtained.

There is a fumace for this method (See French Pat. No. 2,021,436) in which both sintering, and hotmoulding can be performed and which is therefore especially suitable for carrying out the method.The furnace is of the type comprising a cylindrical pressure chamber with a high pressure cylinder, end closures projecting into this cylinder, and means to take up axial forces exerted on the end closures by a pressure 'medium enclosed in the pressure chamber. The furnace chamber and heating means of the furnace are surrounded by an insulating casing in the shape of a sleeve with insulating lid and bottom. I I

Moulding is performed immediately after the sintering and is started at the sintering temperature. During the moulding the temperature must be setat at least such a value that the binder can be deformed enough to allow the sealed spaces to be compressed. Temperature and pressure are dependent upon eachother and on the powder composition.

SUMMARY OF THE INVENTION:

- during the part of the operating cycle when the pres sure in the furnace is to be below atmospheric pressure.

The lid is formed of an outer annular part and an inner part, separate from each other, the outer annular part remaining in position when the inner part is removed. A heat radiation protection ring is provided for insertion into the opening into the annular part when the annular part israised'. A lifting device for the lid is provided inside the housing.

By the introduction of a device according to the invention into the furnace, the risks of oxygen or air penet'ration which otherwise exist in such furnaces are completely eliminated and the lower side of the charging opening lid' can thus also be protected the whole invention includes a lid 14 to close the charging open time and by means of said protective collar and radiation protection means the sealing surfaces of the charging opening are effectively protected and, which is extremely important, the degassing time decreases which 7 is of great importance for the length of the process. Previously said furnaces have been used with a central hole for degassing. It is then desirable for this hole to be as large as possible in order to decrease the degassing time, but because of the strength required during the pressure cycle the size of the hole must be limited and there are also considerable problems with insulation.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 designates a press stand which is movable between the position shown in the drawing and a position where it surrounds the high pressure chamber 2. The press stand is of the type comprising yokes 3 and 4, spacers 5between the yokes and a strip mantle 6. The stand is carried by wheels 7 running on tracks 8. The high pressure chamber 2 is carried by a pillar 9. This comprises a high pressure cylinder consisting of an inner tube 10 and a surrounding strip mantle 11 with end rings 12 holding the strip mantle together axially and providing attachments for brackets .13 by means of which the high pressure chamber 2 is attached to the pillar 9. The chamber 2 has an upper end closure 14 which projects into the tube 10 of the high pressure cylinder through a pipe flange 15 attached to the tube and provided with sealing surfaces.

The pressure chamber 2 has a lower end closure which consists of an annular outer part 19 attached and projecting beneath the tube 10 and a lid 20 projecting into the tube. A ring 21 rests on the part 20 of the end closure. This is fixed to the part 20 in a manner not shown and supports the insulating casing 24 which surrounds the furnace chamber 22 where a billet-23 is being treated, the billet being supported by an insulating bottom joined to the lid 20. Inside the insulating casing 24 which surrounds the furnace chamber 22 are electrical heating elements 31 which are passed through conduits 32 connected to lead-ins in the annular part 19 of the end closure.

ing. The lid is suitably constructed in sections with decreasing radii, the section having the greatest radius resting on said pipe flange 15 when the lid l4-is placed over the opening. The lowermost section of the lid 14 suitably consists of an'insulating material. Channels 17 for coolant are provided in the lid.

The lid 14 is connected by an arm 18 to a lifting device 36 which is arranged to raise and lower said lid to highest and lowest positions, respectively. Channels 37 for coolant run through this arm 18 and the device 36. Both positions of the lid are shown sectioned in FIG. 1. In its lowest position (see the lefthand section) the lid 14 completely closes the charging opening 25. In its uppermost position the lid 14 is not in contact with the pressure chamber, but a gap 25 is formed between the lid 14 and the charging opening.

According to the invention a housing 26 is positioned above the charging opening 25 and the lid 14. The housing 26 is provided with an annular bottom flange 33 which rests against a base flange 34 on the pressure chamber 2. A sealing ring 35 is placed along the entire contact surface between the flanges. A vacuum pump equipment, notshown, is connected by a valved connection 28 to the housing 26, which can be lifted by means of the external lifting members 27. Cooling channels 29 are provided in the walls of the housing 26.

According to the invention there is a radiation pro.- tection means 40 between the charging opening 25 and the furnace chamber 22 and above the latter, (See FIG. 2). The radiation protection means 40 is divided into a lower annular radiation plate section 401 which, through the insulating support 404, rests directly-on the furnace chamber 22 and into an upper circular radia tion plate section 402 which is anchored to the lower section 401 and is held in place at a specific distance from the lower section by spacer elements 405. Lifting yokes 403 may be connected to the spacer elements 405 on the upper side of the upper section 402, which are used when the radiation protection means must be removed while charging the furnace. The

radiation plate sections

401 and 402 preferably consist of composite molybdenum plates. A channel 406, indicated with an arrow in the drawing, shows the path travelled by the gases during the vacuum cycle. It is important that the gas always flows through the same throughflow area so that the gas flow is not throttled and because of this the degassing time is considerably reduced.

According to the invention there is also a protective collar 50, shown in FIG. 3, this figure also showing an alternative embodiment of the pipe flange 15. The protective flange 50 is preferably positioned in the charging opening during the vacuum cycle of the furnace when the lid 14 is not closed, to prevent the sealing surfaces of the pipe flange 15 from being subjected to heat radiation and impurities. The protective flange 50 is suitably provided with heat radiation protective material. By means of a member 60 or connected in the wall or roof of the housing 26 in accordance with FIG. 4 or 5 said protective collar 50 can easily be applied and removed. The member 60 according to FIG. 4 starts with the collar in position 501. The collar is projected into the housing 26 to position 502 with the help of a toothed rack 61, after which it is lowered into position 503, for example by means of a trolley running means of a perpendicularly applied toothed rack 71 enclosed in a container 72 fitted to the housing 26. The toothed rack 71 is driven by means of a shaft 73 connected to a driving means 74 fixed by means of a stay 75 to the housing 26. FIG. also'shows an alternative 14 is lowered to its lowermost position and when the embodiment of the housing 26.

As described above, the process in said furnace takes place in two phases, a vacuum cycle and a pressure cycle.

During the vacuum cycle the charge is degassed and the lid 14 is then in its highest position and the housing 26 is positioned over the charging opening and' the lid, as shown in the righthand part of FIG. 1. During this cycle it is possible, as seen previously, to placea protective flange 50 in the charging opening as shown in FIGS. 3, 4 and 5..The radiation protection means 40 is in position according to FIG. 2 immediately after charging has taken place and before the furnace processing starts.

comprising an inner circular part and an outer annular part, the outer part remaining in the charging opening when the central part of the lid is lifted.

' 3. In a combination according to claim 1, the lower part of the lid consisting of insulating material,

4. In a combination accordingto claim 1, said lifting means being arranged on said housing.

5. In a combination according to claim I, cooling channels in the walls of said housing.

- When the vacuum cycle is complete,-the protective ring 50 is removed by a

member

60 or 70 and the lid charging opening has been closed the housing 26 can be removed by an external lifting device with the help of lifting members 27. The stand 1 is moved in over the furnace chamber 2 and the pressure cycle can start.

The invention is of course not limited to the embodiment shown and described. Many variations are feasible within the scope of the following claims.

We claim:

1. In combination with a furance for vaccum-pressure-sintering having a furnace chamber which is enclosed in and insulated from a surrounding pressure chamber composed of a pressure cylinder, a bottom projecting into said pressure chamber, a lid projecting into the charging opening of said furnace, the improvement comprising means for raising and lowering saidlid between upper and lower positions, and a housing which can-be applied over said charging opening and Eonnected to a vacuum pump during that part of the operating cyclewhenv the pressure in said furnace is below atmospheric pressure, said lid being enclosed by said housing in said furnace and forming a gap between said lid and said charging opening during the vacuum cycle, and said lid closing said charging opening when said housing is removed fromit.

2. In a combination according to claim 1, said lid 6. In a combination according to claim 1, the furnace around the charging opening being provided with a base flange fixed to the furnace said housing having a connecting flange applicable against said base flange.

7. In a combination according to claim 6, one of said flanges having a seal running along the entire contact surface.

8. In a combination according to claim 1, a heat radiation protection means arranged above the furnace chamber. I

' 9. In a combination according to claim 8, said radiation protection means comprising radiation plate sections.

10. In a combination according to claim 9, the radiation protection means comprising a lower and an upper section of radiation plates, the lower section being annular, support members at the upper part of said furnace chamber, said lower section resting on the support members, the upper section being circular and having a radius greater than the inner radius of said lower section, and a spacer element fixing the upper section at a distance from the lower section.

1 1. In a combination according to claim 10, the area of theopening of the lower radiation plate section, the

area of the gap between the radiation plate sections and the area between the upper radiation plate section and the surrounding wall being substantially equal.

12. In a combination according to claim 10, a gripping means for the upper radiation plate section on its upper side to permit lifting of the entire radiation protection means. 7

13. In a combination according to claim 9, said radiation plate sections comprising molybdenum plates.

14. In a combination according to claim 1, an annular protective collar mounted to be lowered into said charging opening and arranged to protect the area of the opening when in lowered position.

15. In a combination according to claim 14, operating devices inside said housing for positioning said protection collar in said opening.

Claims

1. In combination with a furance for vaccum-pressure-sintering having a furnace chamber which is enclosed in and insulated from a surrounding pressure chamber composed of a pressure cylinder, a bottom projecting into said pressure chamber, a lid projecting into the charging opening of said furnace, the improvement comprising means for raising and lowering said lid between upper and lower positions, and a housing which can be applied over said charging opening and connected to a vacuum pump during that part of the operating cycle when the pressure in said furnace is below atmospheric pressure, said lid being enclosed by said housing in said furnace and forming a gap between said lid and said charging opening during the vacuum cycle, and said lid closing said charging opening when said housing is removed from it.

2. In a combination according to claim 1, said lid comprising an inner circular part and an outer annular part, the outer part remaining in the charging opening when the central part of the lid is lifted.

3. In a combination according to claim 1, the lower part of the lid consisting of insulating material.

4. In a combination according to claim 1, said lifting means being arranged on said housing.

5. In a combination according to claim 1, cooling channels in the walls of said housing.

6. In a combination according to claim 1, the furnace around the charging opening being provided with a base flange fixed to the furnace said housing having a connecting flange applicable against said base flange.

8. In a combination according to claim 1, a heat radiation protection means arranged above the furnace chamber.

9. In a combination according to claim 8, said radiation protection means comprising radiation plate sections.

11. In a combination according to claim 10, the area of the opening of the lower radiation plate section, the area of the gap between the radiation plate sections and the area between the upper radiation plate section and the surrounding wall being substantially equal.

12. In a combination according to claim 10, a gripping means for the upper radiation plate section on its upper side to permit lifting of the entire radiation protection means.