A DEVICE FOR HOT ISOSTATIC PRESSING

Abstract: A device in hot isostatic pressing comprises first (24), second (26) and third (27) pump means. The first pump means is adapted to pump cooled pressure medium emanating from a cooling loop in the pressure vessel upwardly from a first space (18) to a second pump means (26), which is arranged in a second space (20) located above the first space but below a load space (11) with loads to be exerted to hot isostatic pressing. The second pump means is arranged to pump a mixture of the cooled pressure medium and warm pressure medium emanating from the second space (20) upwardly through the load space. The third pump means (27) is arranged in the second space and to pump warm pressure medium emanating from this space to the second pump means for pumping this pressure medium by the second pump means.

Description: A DEVICE FOR HOT ISOSTATIC PRESSING FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a device for hot isostatic pressing comprising: • a pressure vessel having a wall, • a heat insulating mantle surrounding a furnace chamber and arranged internally of said wall with a first gap therebetween, said mantle being through a top part closed at the top and in the lower part thereof provided with openings to said gap on two levels so as to allow pressure medium to enter a cooling loop in said gap through the upper openings and emerge from the loop into a first space located below the furnace chamber through the lower openings, • a first guiding means adapted to guide the pressure medium and which surrounds a load space in the furnace chamber adapted to receive loads to be pressed, said guiding means having an opening at the upper part thereof and an opening at the lower part thereof and being arranged to define a second gap therebetween and the heat insulating mantle so as to guide a flow of pressure medium upwardly inside the load space for, after reaching the top part of the heat insulating mantle, moving downwardly in the second gap to a second space located below the load space and above the first space, and • first and second pump means, said first pump means being adapted to pump cooled pressure medium emanating from the cooling loop upwardly from the first space to the second pump means, which is arranged in the second space and to pump a mixture of the cooled pressure medium from the first pump means and warm pressure medium emanating from the second gap upwardly through the load space. Hot isostatic pressing (HIP=Hot Isostatic Pressing) is a technique being more and more used thanks to the extraordinary results obtained thereby, and this technique is used e.g. to achieve a pressing out of so-called "shrinkages" in castings through heating in combination with very high gas pressures in said furnace chamber, such as for turbine blades for aircraft, so as to substantially increase the strength and lifetime thereof. Another field of use is manufacturing of products of a very com- pact material free from pores through pressing of powder and at the same time heating thereof. Typical pressures in hot isostatic pressing are 500-5 000 bars, in which the temperature usually varies between 500 and 2 200°C. A temperature being approximately 75% of the fusion temperature of the material in question is normally selected. An inert gas, such as argon, is usually used as pressure medium. A device of the type defined in the introduction is already known through the US patent 5 123 832 of the applicant, and said first and second pump means, which there are ejectors (jet pumps), are there driven for cooling of loads present in the load space after the heating phase has been terminated, but the invention is not restricted to a use of such a device for cooling purposes. Said pressure medium may also be a fluid as well as gaseous, but for simplifying the description and for illuminating the object of the invention the case of a gas as pressure medium will be described hereinafter. The device already known is as such well functioning, but it has drawbacks in some respects. It is extremely important for the result of the hot isostatic pressing of the loads that the cooling thereof takes place in a controlled manner and at a desired speed, i.e. the number of degrees Kelvin per minute. It is then also important that the cooling takes place substantially homogeneously in the entire load space, so that each load gets the same properties. The movement of the gases upwardly in the load space takes in the device already known place in the opposite direction to the natural convection, since the gases entering the load space have a lower temperature than the loads and are gradually heated during the movement upwardly in the load space while cooling the loads, which makes it necessary that the gases are given a certain impulse by the second pump means for making the movement of the gases upwardly in the load space and then downwardly in said second gap possible. This means that this flow would completely stop in the case that the first pump means, which drives the second pump means, would be switched off during a short period of time for regulating the cooling power in this way, which is completely unacceptable and would lead to defects of the loads. The flow of the first pump means and by that the impulse of the second pump means have to be regulated should the cooling power be regulated, which is possible to do in steps, but this regulation is not sufficiently precise and very inert, since it takes a considerable time before the gases already present in the load space have reached the upper part and come out of the load space after a change of the power of the first pump means. Furthermore, a certain size of the impulse generated by the second pump means upon the gases pumped thereby is required so as to overcome the natural convection, so that the cooling power of the device already known may only be regulated within a restricted interval. SUMMARY OF THE INVENTION The object of the present invention is to provide a device of the type defined in the introduction, which makes a more accurate regulation of the influence that the pressure medium pumped by the second pump means exerts on the loads in the load space possible within a considerably larger interval than in the device already known and discussed above. This object is according to the invention obtained by providing a device of the type defined in the introduction with a third pump means arranged in the second space and to pump warm pressure medium emanating from said second gap to the second pump means for pumping this pressure medium by the second pump means and a control unit adapted to optionally switch the first and third pump means on and off. By arranging said third pump means and said control unit for optionally switching the first and third pump means on and off, a possibility to a considerably more accurate regulation of the influence exerted by the pressure medium pumped through the second pump means through the load space upon the loads is obtained within a considerably broader interval than in the de- vice already known. Thus, when the first pump means is switched off and the third pump means is switched on substantially warm pressure medium emanating from said second gap will be pumped through the second pump means upwardly through the load space, so that in the case of cooling of the loads the cooling effect will be considerably smaller than if instead only the first pump means is driven, but a good stirring and transport of the pressure medium upwardly in the load space are nevertheless ensured by the ability of the second pump means to give said pressure medium a sufficient impulse through the third pump means. Thus, it is possible to achieve a very accurate regulation of the cooling effect by alternatingly switching the first and third pump means on and off through the control unit without disturbing the stirring of the pressure medium in the load space and causing ununiformities of the cooling and by that of the products pressed . The cooling effect may be controlled by the length of the periods of time during which the respective pump means is switched on. However, it is pointed out that the field of use of the device according to the invention is not in any way restricted to cooling, but it would also be pos- sible to keep the first pump means switched off and the third pump means switched on during the entire or parts of the heat- ing phase of the hot isostatic pressing so as to obtain a good stirring of the pressure medium and by that a good uniformity of the influence thereof upon the loads and by that uniform properties of the loads independent of the localization thereof in the load space. According to a preferred embodiment of the invention the device is adapted to cool said loads after a terminated heating phase and the second pump means is adapted to pump a pressure medium from the second space upwardly in the load space having a lower temperature than the temperature of the loads for heating thereof through heat transfer from the loads when moving upwardly in the load space, and the control unit is adapted to alternatingly switch said first and third pump means on and off, so that one of them at the time is pumping pressure medium to the second pump means. The cooling effect may be regulated accurately without disturbing the stirring through the second pump means of the gas in the load space by alternatingly switching the third pump means driving the second pump means without giving any substantial cooling effect and the first pump means driving the second pump means while generating a considerably larger cooling effect on in this way. According to another preferred embodiment of the invention the control unit is adapted to keep the third pump means switched on and the first pump means switched off during the heating phase of the hot isostatic pressing for stirring the warm pressure medium. It will by this be possible to utilize the second pump means to ensure a good stirring of the pressure medium in the load space also during the very heating phase, so that the second pump means by this will have a broadened field of use and may contribute to improving the uniformity of the influence upon the loads during the heating phase of the hot isostatic pressing. According to another preferred embodiment of invention the pressure medium is an inert gas and the second pump means is a jet pump adapted to be driven to pump warm gases emanating from said second gap through jets from the first pump means and the third pump means. It is by this possible to draw in considerably larger flows of warm gas emanating from the second gap into the second pump means through comparatively small flows from the first and third pump means and bring these flows into circulation passing the loads and downwardly in the second gap, so that a good stirring is obtained and the temperature difference between the gases passing the loads and the loads will not be too large. According to another preferred embodiment of the invention the first pump means and the second pump means are jet pumps arranged to be driven through jets of gas having a lower tem- perature than the warm gas from the second gap and which emanates from a compressor arranged outside the pressure vessel. The first and third pump means may advantageously be driven by such cold gases, which have a temperature being too low for allowing them to directly enter into contact with the loads, but in the flow achieved by these pump means in the second pump means this gas will constitute only a fraction of the mass flow, so that the temperature thereof will be acceptable. A thorough mixing of the flows emanating from the first and third pump means with the warm gas emanating from said second gap takes also place in the second pump means. In the case of only having the third pump means switched on during said heating phase the main part of the flow delivered thereby will be formed by said warm gases, whereupon this flow in its turn will generate a still larger flow of warm gases from said second gap out of the second pump means and into the load space, so that the cold gas introduced into the third pump means will not influence the temperature of the gases entering the load space from the second pump means to an extent worth mentioning. According to another preferred embodiment of the invention the first and third pump means are connected to the same compres- sor, and the control unit is arranged to control valve means of the outlet of the compressor for controlling the flow of cold gas from the compressor to the first or third pump means. This constitutes a very simple and reliable arrangement of the regulating possibilities of a device according to the invention, since it will reliably be ensured that only one of the first and third pump means is switched on at the time, which in practise is what is desired, although it would for sure be conceivable to have both switched on at the same time. Furthermore, the device and the control thereof will be simple by the use of one and the same compressor so as to drive both the first and third pump means. According to another preferred embodiment of the invention the device comprises a bottom plate arranged to separate the first and the second space and by that the flow of warm pressure medium from the second gap and cooled pressure medium from the first gap from each other. A well-controlled regulation of the flow of pressure medium through the second pump means with respect to the proportion of warm and cold pressure medium emanating from the third and the first pump means, respectively, is by this obtained. According to another preferred embodiment of the invention the third pump means is arranged in said bottom plate and has the outlet thereof directed upwardly, which constitutes an advantageous localization of the third pump means, and in a further development of this embodiment the device comprises a second channel means extending from the second space into the bottom plate for supply of warm pressure medium emanating from said second gap to the third pump means. The bottom plate may in this way in an advantageous way be used to conduct said warm pressure medium into the third pump means for pumping it through the third pump means to the second pump means. Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims. BRIEF DESCRIPTION OF THE DRAWING With reference to the appended drawing, below follows a description of a preferred embodiment of the invention cited as an example. In the drawing: The single fig 1 is a sectioned view illustrating a device according to a preferred embodiment of the invention for hot isostatic pressing. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A hot isostatic press utilizing an inert gas, such as argon, as pressure medium and designed to be able to achieve a rapid cooling of the loads received therein at the end of a cycle of hot isostatic pressing is illustrated in fig 1 . Such a rapid cooling of loads pressed is for example required in the manufacture of Ni- base alloys. It is for obtaining suitable material properties of these alloys without any demand of considerable heat treatment operations, such as heating and quenching after treatment in a hot isostatic press, required that the loads can be cooled rapidly also when they are present in the hot isostatic press. Ordinary treatment temperatures in such a hot isostatic press are 1 000- 1 400°C, and the loads should be cooled down from these tem- peratures to 600°C with a speed of 40-155°C/minute. The device has a pressure vessel 1 with a wall 2, which is provided with means 3 for water cooling thereof. The upper part and the bottom of the pressure chamber are provided with clos- ing means 4 and 5, respectively. The bottom closing means 5 is provided with through tubes 6, 7 for supply of gas from a joint compressor located outside the pressure vessel. Furthermore, a tube 9 is arranged for discharging gas from the pressure chamber. It is not desired to change the amount of gas inside the chamber during rapid cooling of loads, so that the gas leaving the chamber through the tube 9 is then led back to the compressor 8 for pumping it around. The loads 10 to be exerted to the hot isostatic pressing are placed in a load space 1 1 located in a furnace chamber 12, which is surrounded by a heat insulating mantle 13, which is closed at the top by a top part 14 and at the lower part thereof provided with openings 15, 16 to a first gap 17 between the wall 2 and the heat insulating mantle 13 on two levels so as to allow pressure medium to enter into a cooling loop in this gap through the upper openings 15 and emerging from the cooling loop into a first space 18 located below the furnace chamber through the lower openings 16. Furthermore, the furnace chamber is at the bottom delimited by a heat insulating bottom plate 19, which is arranged to separate the first space 18 from a second space 20 located above the bottom plate but below the load space. The bottom plate 19 is mounted separately at the bottom of the pressure chamber and is not tightly connected to the insulating mantle 13. A first guid- ing means in the form of a basket 21 surrounds the load space in the furnace chamber and is arranged to guide warm gas upwardly through the load space while exchanging heat with the loads and then downwardly in a second gap 22 between the latter and the heat insulating mantle. The warm gases leave the second gap at the bottom to said second space 20. The device has also second guiding means 23 formed by a sleeve for guiding the pressure medium circulation in said cooling loop in the first gap 1 7, so that the gas circulates in the di- rection upwardly without contact with the vessel wall and downwardly in contact with the vessel wall 2, and the second guiding means has an open upper part for guiding pressure medium arriving thereto to enter into a space between the second guiding means and the vessel wall for flowing downwardly therein. The device has also a first pump means 24 in the form of a jet pump or ejector, which is arranged to be provided with a jet of cold gas from the compressor 8 through the conduit 6. This first pump means is then arranged in the first space 18 and to give cooled gas emanating from the cooling loop in said first gap 17 an impulse and by that pump it into a first channel means 25 leading through the bottom plate 19 to a second pump means 26 located in the second space 20. The main flow through the channel means 25 will by that be constituted by gas emanating from said cooling loop, while only a proportion of at the most a fifth will consist of cold gas from the compressor 8. The flow formed in this way through the channel means 25 will drive the second pump means 26, which accordingly also is constituted by a jet pump or ejector, in which warm gases emanating from the second gap 22 will receive an impulse from the flow from the first pump means, the magnitude of said impulse being proportional to the mass flow and speed of said flow, and be mixed therewith, so that this mixture well stirred having a somewhat lower temperature than the loads will be pumped into the load space at the bottom. The device has also a third pump means 27, which , is arranged to receive cold driving gas from the compressor 8 through the conduit 7 and function as a jet pump or ejector and give warm gases emanating from the second gap 22 an impulse in the di- rection towards the second pump means 26 so as to drive it. The third pump means is arranged in the bottom plate 19, which has a second channel means 31 for conducting warm gases from the second space 20 to the third pump means. The device has also a control unit 28 adapted to influence two- way valve means 30 connected in parallel in the outlet conduit 29 from the compressor 8 for conducting the cold gas driving from the compressor 8 either to the first pump means 24 or to the third pump means 27. Thus, one of these valve means is always kept open and the other closed. A single three-way valve would instead in principle be possible, but there are at the present no three-way valves that can withstand the pressures in question. The device according to the invention functions in the following way. When the heating phase of the hot isostatic pressing has been terminated and it is desired to obtain a comparatively rapid, but nevertheless uniform cooling of the loads 10, the control unit 28 controls the valve means 30 to alternatingly drive the first pump means and the third pump means and by that let the mass flows thereof alternatingly drive the second pump means. When the first pump means is driven the gas jet driving the second pump means will primarily contain cooled gas emanating from the cooling loop through the opening 16, which will in the second pump means 26 draw warm gas from the second gap 22, so that these are well mixed and a gas flow upwardly in the load space 1 1 is formed. This gas flow will when entering the load space have a temperature being somewhat lower than the temperature of the loads and by that be heated during the movement thereof upwardly in the load space, so that this flow has to be pumped through the pump means 26 against the direction of the natural convection. A part of the warm gases entering the second space 20 from the gap 22 will be drawn into the second pump means 26, while a part will exit through the heat insulating mantle through the opening 15 and then circulate in the cooling loop formed therein through natural convection for emerging into said first space 18 through the opening 16. A part of this cooled gas from the opening 16 will then go upwardly and enter the cooling loop again through the opening 15 together with the warm gas, while a part moves to the first pump means 24. If the valve means 30 is then controlled by the control unit 28 to connect the third pump means through the conduit 7 to the compressor 8 instead for feeding cold gases thereto, these cold gases will instead give warm gases in the first space through the second channel means an impulse upwardly towards the second pump means 26 and form the jet driving it, which in its turn gives warm gases from the gap 22 in the second pump means 26 an impulse upwardly, so that a stirring is obtained and a substantially homogenous gas mixture with a temperature being only slightly lower than the temperature of the loads will be fed upwardly through the load space. The third pump means may during the very heating phase be operated to alone drive the second pump means 26 for good stirring of the warm gases passing the loads, in which heating elements not shown in the drawing and arranged along the heat insulating mantle will compensate for the somewhat lower temperature received by these gases as a consequence of the smaller proportion therein of cold gas mixed thereinto in the third pump means. The control unit 28 may control the valve means 30 to alternatingly switch in the first pump means or the third pump means during short time intervals when the loads 10 are cooled rapidly so as to obtain a very accurate regulation of the cooling effect without disturbing the stirring of the gas in the load space. The invention is of course not in any way restricted to the preferred embodiment described above, but many possibilities to modifications thereof would be apparent to a man skilled in the art, without departing from the basic idea of the invention such as it appears from the claims. It would for example be well possible to use another pressure medium than gas, for example oil. Such a press may be used for manufacturing explosives. It would also be possible to bring the two outlets of the two channel means from the first and third pump means together to a channel means in common emerging into the second pump means. Furthermore, the device may have more than one first and third pump means. The claim definition "third pump means" is to be given the meaning that it also comprises the case in which no pump means in the real sense thereof is present, but the pressure medium jet coming from the compressor is led directly out into the second pump means through the conduit 7. This jet is then considered to form said third pump means, which accordingly then forms a part of the second pump means. However, it is pointed out that it is advantageous to arrange the nozzle of the third pump means further below, such as shown in fig 1 , for protection thereof.

Claims: Claims 1 . A device in hot isostatic pressing comprising: • a pressure vessel (1 ) having a wall (2), • a heat insulating mantle (13) surrounding a furnace chamber (12) and arranged internally of said wall with a first gap (17) therebetween, said mantle being through a top part (14) closed at the top and in the lower part thereof provided with openings (15, 16) to said gap on two levels so as to allow pressure medium to enter a cooling loop in said gap through the upper openings and emerge from the loop into a first space (18) located below the furnace chamber through the lower openings, • a first guiding means (21 ) adapted to guide the pressure me- dium and which surrounds a load space (1 1 ) in the furnace chamber adapted to receive loads (10) to be pressed, said guiding means having an opening at the upper part thereof and an opening at the lower part thereof and being arranged to define a second gap (22) therebetween and the heat insu- lating mantle so as to guide a flow of pressure medium upwardly inside the load space for, after reaching the top part of the heat insulating mantle, moving downwardly in the second gap to a second space (20) located below the load space and above the first space, and • first and second pump means, said first pump means (24) being adapted to pump cooled pressure medium emanating from the cooling loop upwardly from the first space (18) to the second pump means (26), which is arranged in the second space (20) and to pump a mixture of the cooled pressure medium from the first pump means and warm pressure medium emanating from the second gap upwardly through the load space, characterized in that it comprises a third pump means (27) arranged in the second space (20) and to pump warm pressure medium emanating from said second gap (22) to the second pump means (26) for pumping this pressure medium by the second pump means, and that it also comprises a control unit (28) adapted to optionally switch the first and third pump means on and off. 2. A device according to claim 1 , characterized in that it is adapted to cool said loads (10) after a terminated heating phase and the second pump means (26) is adapted to pump a pressure medium from the second space (20) upwardly in the load space having a lower temperature than the temperature of the loads for heating thereof through heat transfer from the loads when moving upwardly in the load space, and that the control unit is adapted to alternatingly switch said first and third pump means on and off, so that one of them at the time is pumping pressure medium to the second pump means. 3. A device according to claim 1 , characterized in that the control unit (28) is adapted to keep the third pump means (27) switched on and the first pump means switched off during the heating phase of the hot isostatic pressing for stirring the warm pressure medium. A device according to any of claims 1 -3, characterized in that the pressure medium is an inert gas. 5. A device according to claim 4, characterized in that the sec- ond pump means (26) is a jet pump adapted to be driven to pump warm gases emanating from said second gap (20) through jets from the first pump means (24) and the pump means (27). 6. A device according to claim 4 or 5, characterized in that the first pump means (24) and the third pump means (27) are jet pumps arranged to be driven through jets of gas having a lower temperature than the warm gas from the second gap and which emanates from a compressor (8) arranged outside the pressure vessel. 7. A device according to claims 2 and 6, characterized in that the first (24) and the third (27) pump means are connected to the same compressor, and that the control unit is arranged to control valve means (30) of the outlet (29) of the compressor for controlling the flow of cold gas from the compressor to the first or third pump means. 8. A device according to any of claims 1 -7, characterized in that it has a bottom plate (19) arranged to separate the first (18) and the second (20) space and by that the flow of warm pressure medium from the second gap (22) and cooled pressure medium from the first gap (17) from each other. 9. A device according to claim 8, characterized in that said bottom plate (19) is made of heat insulating material. 10. A device according to claim 8 or 9, characterized in that an opening enabling communication between said first (18) and second (20) spaces is arranged between the heat insulating mantle and the bottom plate. 1 1 . A device according to any of claims 8-10, characterized in that it comprises a first channel means (25) arranged to conduct a pressure medium from the first pump means (24) through the bottom plate to the second pump means (26). 12. A device according to any of claims 8-1 1 , characterized in that the third pump means (27) is arranged in said bottom plate and has the outlet thereof directed upwardly. 13. A device according to claim 12, characterized in that it comprises a second channel means (31 ) extending from the second space (20) into the bottom plate for supply of warm pressure medium emanating from said second gap to the third pump means. 14. A device according to any of claims 1 -13, characterized in that it comprises second guiding means (23) for guiding the circulation of pressure medium in the cooling loop in said first gap (17), so that the pressure medium circulates in the direc- tion upwardly without any contact with the vessel wall (2) and in the direction downwardly in contact with the vessel wall, and that the second guiding means has an open upper part for guiding pressure medium arriving thereto to enter into a space between the second guiding means and the vessel wall for flowing downwardly therein. 15. A device according to any of claims 1 -14, characterized in that the openings (15, 16) in the heat insulating mantle (13) and the first pump means (24) have such a mutually location that a part of the cooled pressure medium entering into the first space from said first gap enters into the cooling loop again through the upper openings (15) in the heat insulating mantle.

Inventors: BERGMAN CARL, BERGMAN, CARL
Applicants: ASEA BROWN BOVERI, BERGMAN CARL, ASEA BROWN BOVERI AB, BERGMAN, CARL
Application year: 1998
Main classification: B22F3
IPC codes: B01J3, B22F3, B30B11, B30B15