PRESSURE VESSEL FOR HOT ISOSTATIC PRESSING WITH MEANS FOR RAPID COOLING

Abstract: Hot-isostatic press adapted for rapid cooling of the hot zone after completion of pressing and sintering the charged articles. The press comprises a pressure vessel (2) with end closures (3, 4), a hot zone (5) for the articles to be pressed surrounded by thermal barriers (6, 7). Between the thermal barriers and the pressure vessel with end closures there are colder spaces (13, 14, 15). At least one connection (12) is located in the lower part of the thermal barrier (7) and is provided with a valve (19) able to separate the space (13) next to the pressure vessel from the space (14) below the bottom thermal barrier (6). This valve is controllable from outside the press. In the upper part of the thermal barrier, above the hot zone (5), there is an opening with a relatively large cross section area, which opening is provided with a valve which comprises a heat-insulated portion.

Description: The invention relates to a hot-isostatic press according to the precharacterising part of claim 1. Hot-isostatic presses (HIPs) adapted for rapid cooling of the load after pressing are previously known. Such a hot-isostatic press comprises a pressure vessel in which is arranged a hot zone surrounded by heaters and a thermal barrier. The walls of the pressure vessel are cooled to prevent harmful heating of the pressure vessel. This is utilized when cooling the load in such a way that a circulation loop is established between the hot zone and the space between the outside of the thermal barrier and the inside of the cooled vessel wall by providing the thermal barrier with at least one opening at the bottom and top, respectively, of the hot zone. Additional cooling of the gas may be achieved by channelling the gas through a heat exchanger, heat-absorbing bodies or the like. To prevent gas circulation during the press cycle, it is known to provide the openings at the bottom or the top with an externally controllable valve (see,e.g. SE-A-76 05 887-4). A type of HIP, a so-called modular HIP, for example according to EP-A-145 417, in which a furnace chamber is placed in a movable chamber, may be provided with an externally controllable valve in both the upper and lower openings in the thermal barrier sealing the furnace chamber during heating and transport outside the pressure vessel. When the chamber is installed in the furnace vessel, the upper valve is opened to allow pressurization to take place. During the pressing it is important to achieve a uniform temperature in the hot zone to obtain the desired properties of the material. Openings in the thermal barrier and open valves mean that colder gas falls into the hot zone during the pressing phase and cools parts of the load. This has resulted in a limitation of the size of the openings provided in the thermal barrier. During the cooling phase, however, the aim is to achieve a considerable gas circulation which provides rapid cooling. Therefore, it has entailed difficulties to combine requirements for high temperature uniformity during the pressing and a high cooling rate after the pressing. The invention aims at developing a hot-isostatic press of the above-mentioned kind which ensures a great temperature uniformity in the hot zone during the pressing and sintering phase and rapid cooling of the load in the subsequent cooling phase by allowing a large quantity of cooled gas to pass through the hot zone. To achieve this aim the invention suggests a hot-isostatic press according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention, a hot-isostatic press comprises a pressure vessel with a load carrying hot zone surrounded by heaters and thermal barriers. Between the thermal barriers and the pressure vessel and its end closures there are spaces in the press which contain pressure gas which is colder than the gas in the hot zone. In the lower part of the press at least one connection is provided through the thermal barrier between the colder space next to the pressure vessel and the hot zone or the space below the bottom thermal barrier, which communicates with the hot zone. At each connection through the lower part of the thermal barrier, a valve is arranged which is controllable from the outside of the hot-isostatic press. Further, a relatively large opening is provided in that part of the thermal barrier which is located above the hot zone, which opening allows large gas quantities to rapidly circulate through the hot zone during cooling. For this opening a valve is arranged which is provided with a heat-insulating layer or the like to prevent the valve from acting as a cooling surface in the hot zone. The valve may be adapted such that it is opened by the convection current which arises when the valve in the lower part of the thermal barrier is opened. Another embodiment may be a heat-insulated valve at the top of the thermal barrier which is controlled from the outside of the press. For such an embodiment the lower part of the thermal barrier may be open, allowing free communication of gas in the lower part. An additional embodiment may comprise the upper part of the thermal barrier being movable and being raisable upon cooling so that gas may pass out from the hot zone. It is also possible to have one or more openings in the top of the thermal barrier such that the total cross-section area of the opening is large enough for a large cooling flow. Each opening should be provided with a heat-insulated valve. The invention makes possible, in a hot-isostatic press, that a great temperature uniformity in the hot zone during the pressing and sintering phase is achieved and that the subsequent cooling of the material may take place very rapidly by allowing a large quantity of cooled gas to pass through the hot zone. The relatively large cross section of the opening or openings in the upper part of the thermal barrier permits large gas quantities to pass out from the hot zone, and, consequently, the cooling can be performed considerably more rapidly than in conventional hot-isostatic presses. Further, because the opening is provided with a heat-insulated valve, the pressing and sintering phase may be carried out without being adversely affected by inflowing colder gas or cooling surfaces in the thermal barrier. By way of example, the invention will now be described in greater detail with reference to the accompanying drawing, which shows an embodiment of a hot-isostatic press according to the invention adapted for rapid cooling of the hot zone. The figure shows a vertical section of a hot-isostatic press 1 comprising a pressure vessel 2 provided with end closures 3, 4. The load carrying hot zone 5 is surrounded by a thermal barrier 7 and a bottom thermal barrier 6. Between the thermal barriers and the vessel wall and the end closures, respectively, there are colder spaces 13, 14, 15. At least one connection 12 is arranged in the lower part of the thermal barrier 7 between the space 13 next to the vessel wall and the space 14 below the bottom thermal barrier. The connection 12 is provided with a valve 19 which is controllable from the outside of the press. The space 14 is connected to the hot zone via a gap 8. The location of the connection 12 through the thermal barrier with the valve 19 may be made in a plurality of ways. In the upper part, above the loading space 11 in the hot zone, the thermal barrier 7 is provided with an opening 9 that has a relatively large total cross-section area. A ratio of the cross section areas of the opening and the hot zone should be at least 0.003. For example, for a hot zone with an inner diameter of 1250 mm, the diameter of the opening should be at least 70 mm. For the opening 9, a valve 10 is arranged. The valve 10 comprises a plate, cone or the like which is provided with a heat-insulating layer to prevent the valve body for the opening from acting as a cooling portion. This can be implemented in several different ways; for example, a valve body may comprise a porously sintered ceramic material surrounded by a metal sheet, a graphite plate or the like. It is important that the valve be resistant to erosion since large gas quantities flow past the valve during the cooling phase. The valve 10 may be arranged so as to open without mechanical arrangements by the influence of the convection current which arises when the valve 19 in the connection 12 is opened. The valve may, of course, be provided with a guide means, a stop means and the like. At the bottom of the press chamber, a fan of the like may be arranged for distribution of the colder inflowing gas at the bottom. The space 15 above the thermal barrier 7 may house a heat-absorbing body, a heat exchanger or the like 16 for cooling the gas before it makes contact with the pressure vessel wall 2 where the gas is additionally cooled during the passage through the gap 13 before re-entering the hot zone 5 via the connection 12. It is also possible to force the circulating gas to pass a pump, a fan or the like in order to increase the flow rate still further. The insulated valve 10 or the upper part of the thermal barrier 7 may be provided with an open channel or the like to bring about pressure balancing between the hot zone and the space outside the thermal barrier during the pressing and sintering phase when the valves 19 and 10 are closed. To prevent cold gas from rushing in through the pressure balancing channel and cooling the material to be pressed, a horizontal sheet 17 or the like may be arranged in the upper part of the hot zone. The sheet 17 may be provided with transverse sheet strips 18 or the like. Cold gas penetrating into the hot zone will thereby accumulate on the horizontal sheet between the transverse strips and be heated before being mixed with the warm gas in the hot zone. In another embodiment of the invention, the valve 10 in the upper part of the thermal barrier is made gas-tight and its opening function is controlled from outside of the press. For such an embodiment, the lower part of the thermal barrier can be open, providing free communication of gas between the space 13 next to the pressure vessel, and the space 14 below the bottom thermal barrier and the hot zone 5.

Claims: Hot-isostatic press (HIP), comprising a pressure vessel (2), end closures (3, 4), a hot zone (5) for articles to be pressed surrounded by a thermal barrier (7) and a bottom thermal barrier (6), spaces (13, 14, 15) between the thermal barriers and the pressure vessel and the end closures, respectively, and at least one connection (12) located in the lower part of the thermal barrier (7) and provided with a valve (19) connecting the space (13) next to the pressure vessel and the space (14) below the bottom thermal barrier (6) and the hot zone (5), characterized in that the thermal barrier (7), in that part which is located above the hot zone, is provided with one or more opening/openings (9) with a total cross-section area which is relatively large, such that the ratio between the cross-section area of the opening or openings (9) and the cross-section area of the hot zone is at least 0.003, and that each said opening is provided with a valve (10) comprising a heat-insulating part. Hot-isostatic press according to claim 1, characterized in that the valve or valves (10) is/are arranged such that it is/they are opened by the pressure difference that drives the convection current when the valve (19) is opened. Hot-isostatic press according to any of the preceding claims, characterized in that the upper part of the thermal barrier (7) or the insulated valve or valves (10) is/are provided with a channel with a small cross section, which connects the hot zone with the space (15) between the thermal barrier and the end closure (3). Hot-isostatic press according to claim 3, characterized in that above the loading space there is arranged a sheet (17) provided with transverse sheet strips (18) in such a way that gas entering the hot zone through said channel in the thermal barrier or the valve is first collected on the sheet before it is mixed with the other gas in the hot zone. Hot-isostatic press according to any of the preceding claims, characterized in that the thermal barrier (7), in that part which is located above the hot zone, is arranged such that part of the barrier may be raised, allowing gas to pass out from the hot zone. Hot-isostatic press according to any of claims 1, 3 or 5, characterized in that the valve or valves (10) is/are controllable from the outside of the hot-isostatic press. Hot-isostatic press, comprising a pressure vessel (2), end closures (3, 4), a hot zone (5) for articles to be pressed surrounded by a thermal barrier (7) and a bottom thermal barrier (6), spaces (13, 14, 15) between the thermal barriers and the pressure vessel and the end closures, respectively, characterized in that a lower part of the thermal barrier (7) is open, providing free communication of gas between the space (13) next to the pressure vessel and the space (14) below the bottom thermal barrier and the hot zone, that in the part of the thermal barrier (7) which is located above the hot zone one or more openings (9) is/are provided with a cross-section area ratio to the hot zone of at least 0.003, and that said opening or openings is/are provided with a gas-tight valve (10) comprising a heat-insulated part, said valve being controllable from the outside of the hot-isostatic press. Hot-isostatic press according to any of the preceding claims, characterized in that in the space (15) between the thermal barrier (7) and the end closure there is arranged a heat-absorbing body (16) or a heat exchanger, through which the gas passes when the valve or valves (10) is/are open. Hot-isostatic press according to any of the preceding claims, characterized in that the valve or valves (10) comprises/comprise a plate or cone, whereby the valve body comprises a ceramic surrounded by a metal sheet or a graphite plate, to render the valve resistant against erosion by a large gas flow.

Inventors: BERGMAN, CARL, OHLSSON, LARS
Applicants: ASEA BROWN BOVERI AB
Application year: 1991
Main classification: B01J3
IPC codes: B22F3, F27D1, F27D7