Process for high efficiency hot isostatic pressing

A process for high efficiency hot isostatic pressing in a hot isostatic pressing treatment for sintering or densifying a ceramic or metallic work in a high temperature and high pressure gas atmosphere, comprising preheating the work outside a high pressure vessel prior to the hot isostatic pressing treatment, transferring the preheated work as surrounded with the gas in a hot state into the high pressure vessel, then treating the work at high temperature and high pressure in a gas atmosphere, thereafter taking out the work from the high pressure vessel together with the gas atmosphere, then cooling the work if necessary, and subsequently taking it out from the gas atmosphere, as well as an apparatus for practicing the above process, wherein a treating chamber for effecting the hot isostatic pressing treatment is covered with a hermetic casing, and at least one valve mechanism capable of providing communication and cut-off between the interior and exterior of the treating chamber is provided in each of upper and lower portions of the treating chamber.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to an improvement of modular type hot 
isostatic pressing (hereinafter referred to as "HIP") method and apparatus 
provided with preheating or cooling auxiliary stations for sintering or 
densifying ceramic or metallic powder at high temperature and pressure in 
an inert gas atmosphere to obtain a molded product having a dense texture 
of a nearly true density. 
(2) Description of the Prior Art 
The HIP treatment has recently been specially noted in various fields as a 
superior method for compressing a work isotropically at a high temperature 
using an inert gas as a pressure medium to produce a dense sinter from 
ceramic powder, metallic powder, or a mixture thereof, or for removing 
residual cavities in cemented carbides by squeezing, or for 
diffusion-bonding of metallic materials. 
According to the HIP method, there can be obtained various advantages such 
as, for example, high densification at low temperatures, obtaining of a 
dense and uniform texture having a density close to a theoretical value, 
improvement of mechanical and physical properties of powder, molding of 
powder unsuitable for molding, producing of large-sized products not 
restricted by the capacity of a press as in ordinary molding presses, 
molding of various composite materials such as metals and ceramics, and 
improvement of the material yield. By the HIP treatment, moreover, 
internal defects of an object can be removed, and the toughness and 
deflective strength can be enhanced, so methods which utilize this effect 
have been proposed other than the above-mentioned powder molding and 
sintering, such as improvement of the performance of sintered tool 
material, etc. and diffusion-bonding of the turbine blade and body by HIP 
to obtain extremely strong bonding. 
Since such HIP treatment is performed in an atmosphere of high temperature 
and pressure, it is necessary to use an HIP furnace of a special 
structure, and a long period of time is required for executing the 
operation cycle comprising raising the temperature, raising the pressure, 
maintaining the elevated temperature and pressure, lowering the 
temperature and lowering the pressure. Therefore, shortening this cycle 
time and thereby improving the efficiency has been an important technical 
problem. 
In a effort to solve the above-mentioned problem, various attempts have 
been made for improving the utilization efficiency per unit time of the 
HIP furnace by performing heating in a preheating furnace to raise 
temperature which requires a long period of time and performing in the HIP 
furnace only the raising of the pressure and/or raising the temperature to 
a slight extent. A typical example is the apparatus proposed in the 
specification of British Patent No. 1,291,459. However, this proposed 
apparatus is disadvantageous in that the equipment cost is increased 
because a preheating furnace is needed in addition to the ordinary HIP 
furnace although the shortening of the cycle time is attained, in that the 
heat loss caused by heat radiation from the work is very large because the 
conveyance of the work after preheating is performed in the air, and in 
that when the high-temperature work after preheating is charged into the 
HIP furnace, the lower inner wall surface of the furnace is overheated and 
the lower seal ring is easily damaged thereby, which is a serious problem. 
In this type of apparatus for which safety is strictly required, the 
adoption of the above-mentioned apparatus is very problematic even if the 
shortening to the cycle time is attained. 
As the material of heating element used in the heater, usually an electric 
heater, in the HIP furnace, there has been proposed Fe-Al-Cr, molybdenum 
of graphite. Among these materials, Fe-Al-Cr, which is resistant to 
oxidation at high temperatures, has been evaluated as the only material 
capable of being released to the air at a high temperature, but the 
temperature at which this material can be used stably is up to about 
1,100.degree. C. 
On the other hand, molybdenum- or graphite-based materials which are stably 
employable at above 1,100.degree. C. are severely oxidized at high 
temperatures, so cannot safely be exposed to the air unless the 
temperature range is below about 200.degree.-300.degree. C. Therefore, a 
long period of time is required for lowering the temperature to below 
300.degree. C. although the lowering of pressure can be done in a 
relatively short time period after performing the HIP treatment at a 
temperature as high as one thousand and several hundred degrees centigrade 
in a high pressure inert gas atmosphere. Thus, the long period of time 
required from opening the HIP furnace until taking out of the work greatly 
impedes efficient utilization of the apparatus. As an example, according 
to a certain conventional typical pattern in the HIP treatment, the time 
required for each treating step is as follows: 
______________________________________ 
Time required 
Step hr. min. 
______________________________________ 
Loading of workpiece 0. 10 
Vacuum suction, Gas replacing 
1. 00 
Raising temp., Raising pressure 
3. 00 
Maintaining elevated temp. and pressure 
2. 00 
Lowering temp. 8. 00 
Recovery under reduced pressure 
1. 00 
Taking out of workpiece 
0. 10 
Total 15. 20 
______________________________________ 
By the foregoing preheating, the 3 hours' temperature and pressure raising 
time is shortened to about 1 hour and 40 minutes, corresponding to only an 
8.7% reduction of the cycle time, that is, the time required for lowering 
temperature, which occupies the greater part of the cycle time, still 
remains as a serious efficiency impeding factor. 
For shortening the time required for lowering temperature, it has been 
previously attempted to perform cooling by providing a coolant jacket 
around the outer periphery of the HIP furnace and utilizing, in lowering 
the temperature, convection of gas induced by the difference between the 
specific gravity (small) of the high temperature gas at the furnace 
central portion and the specific gravity (large) of the low temperature 
gas in contact with the furnace inner wall, as disclosed, for example, in 
the specification of U.S. Pat. No. 4,217,087 and Japanese Patent 
Publication No. 8689/1973. According to such method, however, the cooling 
capacity deteriorates to a large extent with a decrease of the temperature 
difference between the high temperature gas and the low temperature gas. 
Therefore, the temperature lowering rate becomes smaller as cooling 
advances, and as a result, it is impossible to expect a remarkable 
shortening of the time required until reaching the temperature at which 
the HIP furnace can be opened. 
In such technical level, the applicant of the present invention has 
previously proposed (see Japanese Patent Laid Open Publication No. 
71301/1983) and HIP system capable of shortening the cycle time without 
exerting a bad influence on its components and having a high safety, as 
well as a method capable of improving the working efficiency remarkably by 
using such system. This proposed HIP system, called a modular type HIP 
system, comprises an HIP furnace, a plurality of auxiliary stations, the 
HIP apparatus and the auxiliary stations being disposed side by side along 
and above a horizontally laid track, and a carriage for travelling on the 
track. The HIP apparatus consists mainly of a high pressure vessel and a 
treating chamber and is provided with means for supply and discharge of an 
atmospheric gas for applying HIP treatment to a workpiece loaded into the 
treating chamber and is also provided with means for adjusting pressure 
and temperature, the high pressure vessel comprising a pressure-resistant 
vertical cylinder having a closed top removably fitted in the bottom of 
the cylinder, the treating chamber being enclosed with an inverted 
cup-like heat insulating barrier which barrier is mounted on the upper 
surface of the barrier and is internally provided with a heater. Each of 
the auxiliary stations mainly comprises a dome-like vessel having a size 
which permits the treating chamber to be completely enclosed therein, also 
having a bottom opening which permits the above plug to be fitted therein, 
and further having a coolant jacket provided around the outer periphery 
thereof. Each auxiliary station is also provided with the heater enclosed 
therein together with the treating chamber, means for supply and discharge 
of an atmosphere gas for heating or cooling the workpiece and temperature 
adjusting means. 
Thereafter, the applicant of the present invention has made various 
improvements on the above-proposed apparatus and filed the thus-improved 
apparatus (see Japanese Utility Model Laid Open Publication Nos. 
157,300/1983 and 54098/1984). According to these devices, in the foregoing 
modular type HIP system, a single valve mechanism is provided in the upper 
or lower portion of a casing which houses the treating chamber. This valve 
mechanism is opened when the treating chamber is inserted into the HIP 
furnace or an auxiliary station, to thereby provide communication between 
the interior and exterior of the treating chamber, and it is closed when 
the treating chamber is taken out. According to this construction, it is 
possible to take out the workpiece which has been preheated in the 
auxiliary station, from the auxiliary station integrally with the treating 
chamber together with the inert atmospheric gas, convey and load the 
workpiece into the HIP furnace, then after HIP treatment and upon dropping 
of pressure, taken out the workpiece from the HIP furnace integrally with 
the treating camber immediately without waiting for such becoming cold, 
and cool it in an auxiliary station. Thus, a remarkable shortening of the 
cycle time in the HIP treatment and a great improvement of the working 
efficiency could be attained. In these devices, however, since the casing 
which hermetically encloses the treating chamber is taken out from the HIP 
furnace also under a state of high temperature, there arises the foregoing 
serious problem that the seal ring attached to the lower portion of the 
high pressure vessel is easily damaged when opening the HIP furnace in a 
still hot condition of its interior and taking out the treating chamber 
held at a high temperature. 
SUMMARY OF THE INVENTION 
The present inventors have carefully reviewed the foregoing prior art and 
studied about the method of ensuring an efficient and safe operation of 
the entire system while making the most of the advantages of the modular 
type and without impairing the utilization efficiency of the HIP furnace. 
As a result, the present inventors have been able to solve all of the 
conventional problems by cooling the work rapidly to an appropriate 
temperature in the HIP furnace after HIP treatment, and have thus reached 
the present invention. 
As an apparatus employable for practicing such method of the present 
invention, there is provided according to the invention an apparatus 
characterized in that, in an HIP furnace consisting mainly of a high 
pressure vessel comprising a pressure-resistant vertical cylinder having 
one closed end and a plug removably fitted closely in an opening portion 
at the other end of the cylinder, and a treating chamber surrounded with a 
heat insulating barrier and capable of being attached to and detached from 
the high pressure vessel together with a workpiece loaded therein, the 
heat insulating barrier being attached to and detached from the high 
pressure vessel together with a workpiece loaded therein, the heat 
insulating barrier being internally provided with a heater. The HIP 
furnace is further provided with a gas supply and discharge means for 
subjecting the workpiece to a predetermined high temperature and high 
pressure treatment in a gas atmosphere. The auxiliary stations are each 
constituted mainly of a vertically oriented cylinder capable of enclosing 
therein the treating chamber hermetically, and provided with a gas supply 
and discharge means. The carrier device is for carrying the treating 
chamber together with the workpiece between the HIP furnace and each 
auxiliary station and loading and loading it to and from each vertical 
cylinder. In such HIP system, said treating chamber is covered 
hermetically with a casing and at least one valve mechanism capable of 
providing communication or cut-off between the interior and exterior of 
the treating chamber is provided in each of upper and lower portions of 
the treating chamber. 
A more complete appreciation of the invention and many of the attendant 
advantages thereof will be readily obtained as the same becomes better 
understood by reference to the following detailed description when 
considered in connection with the accompanying drawings, wherein:

The method and apparatus of the present invention will be described in 
detail hereinunder with reference to the accompanying drawings. 
FIG. 1 is a schematic explanatory view showing a positional relation 
between an HIP furnace and auxiliary stations in a modular type HIP system 
according to an embodiment of the present invention, in which a carriage 2 
is mounted for travelling on a track 1, and on the carriage 2 is mounted a 
support table 3 capable of being vertically moved by a known or commonly 
used drive means (not shown) such as, for example, a chain wind-up type, 
worm gear and rack type, or piston type drive means. Above and along the 
track 1 are disposed side by side a plurality of auxiliary stations 4, 4', 
. . . and an HIP furnace 5. The HIP furnace 5 is constructed mainly of a 
high pressure vessel comprising a vertical, pressure-resistant cylinder 7 
having a top portion closed hermetically with an upper plug 6 and a lower 
plug 8 capable of being fitted in the bottom of the cylinder 7 
hermetically and removably, and a treating chamber 11 surrounded with an 
inverted cup-like heat insulating barrier 10 which is mounted on the upper 
surface of the lower plug 8 and enclosed in the high pressure chamber and 
which is internally provided with a heater. The treating chamber 11 can be 
removed to the exterior of the HIP furnace 5 by removing the heat 
insulating barrier 10 and the lower plug 8 together from the 
pressure-resistant cylinder 7. On the other hand, the auxiliary stations 
4, 4', . . . mainly comprise vertical cylinders 13, 13', . . . and they 
each have capacity and size sufficient to completely enclose therein the 
treating chamber 11. The bottom opening of each of the vertical cylinders 
13, 13', . . . has size shape which permit the lower plug 8 to be fitted 
therein. 
The treating chamber 11, which is mounted on the support table 3 of the 
carriage 2, can be positioned just under the vertical, pressure-resistant 
cylinder 7 or any of the vertical cylinders 13, 13', . . . by travelling 
of the carriage 2, and can be inserted into or removed from the vertical 
cylinder 7, 13, or 13' in that position by operation of a lift means. A 
press frame 14 for grippingly supporting the upper plug 6 and the lower 
plug 8 is mounted on a carriage 15 and can travel on the track 1 and 
reciprocate between operating and retracted positions. The illustrated 
construction of the press frame 14 a mere example, and various 
modifications thereto may be made. For example, such may be hinged to a 
vertical fixed shaft and reciprocated between operating and retracted 
positions by a pivotal motion thereof. 
FIG. 2 is a schematic vertical section of the treating chamber 11 as a 
constituent member of the system of FIG. 1, in which a heat insulating 
barrier 10 internally provided with a heater 9 comprising an electric 
heating plate in an electrically insulated state is mounted on the upper 
surface of the lower plug 8. The power supply to the heater 9 is effected 
through a power lead wire (not shown) which is attached to the lower plug 
8 in an electrically insulated and hermetically sealed condition. The heat 
insulating barrier 10 surrounding the treating chamber 11, including the 
heater 9, is formed of a heat-resistant fibrous heat insulator such as 
ceramic fiber filled between substantially concentric inverted cup-like 
hermetic casings 16 and 17 formed of a gas impermeable material. The heat 
insulating barrier 10 is gas permeable and it is mounted removably on the 
upper surface of the lower plug 8. 
The heat insulating barrier 10 and the treating chamber 11 are in 
communication with each other through a through hole 18 formed in part of 
the hermetic casing 16. The upper surface of the lower plug 8 is covered 
with a heat insulating seat 19 of a similar structure to the heat 
insulating barrier 10, and a hermetic casing 20 which forms an outer 
periphery of the heat insulating seat 19 is also formed with a through 
hole 21 to provide communication between the seat 19 and the treating 
chamber 11. 
Further, the greatest feature of the present invention resides in that at 
least one valve mechanism is provided in each of upper and lower portions 
of the treating chamber 11 thereby permitting communication and cut-off 
between the interior and exterior of the treating chamber 11. In the 
illustrated embodiment, one valve mechanism 22 and one similar mechanism 
23 are provided in the top of the hermetic casing 17 and in the lower plug 
8, respectively. But, it goes without saying that a plurality of such 
valve mechanisms may be provided in each of those portions. 
The valve mechanism 22 comprises a valve 25 for opening and closing a valve 
hole 24 formed in the top of the hermetic casing 17 from the treating 
chamber 11 side, a stem 26 contiguous to the valve 25 and inserted 
slidably in the valve hole 24, and a flange 27 and the hermetic casing 17 
is interposed a spring 28, and the step 26 is urged upward by the biasing 
force of the spring 28. In the lower valve mechanism 23, which is of about 
the same structure as above, a seal ring 29 is disposed in an intermediate 
portion of a valve bore 24' to prevent communication of the treating 
chamber 11 with the outside air when a valve 25' is opened. The diameter 
of the valve bore portion above the seal ring 29 is made a little larger 
than the outside diameter of a stem 26' to form an annular hole 30, and 
the treating chamber 11 communicates with an upper side space of the lower 
plug 8 through a conduction hole 31 extending sideways from the annular 
hole 30. The valves 25 and 25' are opened by urging the respective flanges 
27 and 27' against the biasing force of springs 28 and 28' and are closed 
upon release of the biasing force. 
In the modular type HIP system of the invention having the above 
construction, the heat insulating barrier 10 is separated from the lower 
plug 8 together with the hermetic casings 16 and 17 to open, the treating 
chamber 11, then a workpiece 33 is put on a sample stand 32, and 
thereafter the heat insulating barrier 10 is fixed onto the lower plug 8 
to close the treating chamber 11. In this way, preparations are completed. 
The treating chamber 11 thus loaded with the workpiece 33 is then inserted 
into the vertical cylinder 13 of the auxiliary station 4. 
FIG. 3 is a schematic vertical section of the treating chamber 11 as 
received in the auxiliary station 4, in which a push rod 34 is provided in 
the top of the vertical cylinder 13 in a position coaxial with the valve 
mechanism 22, and it is urged upward by the biasing force of a spring 36 
which acts on an upper end flange 35, the push rod 34 being mounted 
hermetically through a seal ring 37. Further, the vertical cylinder 13 is 
provided with a gas supply and discharge port 38 which communicates with a 
vacuum exhaust system and a gas supply/discharge system (neither shown). 
In such auxiliary station 4, the work 33 is first subjected to a required 
heat treatment. For example, in vacuum sintering of a formed body of 
powder, the flanges 27' and 35 are pushed by suitable means to open the 
upper and lower valves 25 and 25', as shown in FIG. 3, then the heater 9 
is charged with electricity while vacuum suction is performed through the 
gas supply and discharge port 38. Alternatively, after replacing the 
vacuum with an inert gas such as argon or nitrogen, the upper and lower 
valves 25 and 25' are closed to seal the inert gas in the hermetic casing 
17, thereby performing atmospheric sintering. In the case of oxide type 
ceramics, there may be used a gaseous mixture consisting of an inert gas 
such as Ar or N.sub.2 and a very small amount of O.sub.2. 
After completion of the above heat treatment, and where the interior of the 
treating chamber 11 is vacuum, after replacing it with a predetermined 
gas, the lower plug 8 is removed from the lower opening of the vertical 
cylinder 13 together with the workpiece 33, treating chamber 11 and 
hermetic casings 16 and 17, which are then transferred to the HIP furnace 
in a hot state of the treating chamber 11 and inserted into the furnace 
interior from the lower opening of the vertical pressure-resistant 
cylinder 7. During their transfer, both the upper and lower valves 25 and 
25' are closed as shown in FIG. 2 and the interior of the treating chamber 
11 can be maintained with a predetermined gas atmosphere. Therefore, 
materials which are susceptible to oxidation at elevated temperatures 
despite being stably employable at elevated temperatures in a 
non-oxidative atmosphere can be used for the heating element, etc. 
FIG. 4 is a schematic vertical section of the treating chamber 11 as 
received in the vertical pressure-resistant cylinder 7 of the HIP furnace 
5, in which the HIP furnace 5 comprises the cylinder 7 and the upper plug 
6 which seals the upper end of the cylinder 7, with the lower plug 8 being 
hermetically fitted in the lower end of the cylinder 7, thereby forming a 
high pressure chamber 39 in the interior of the cylinder. 
In the upper plug 6 is formed a gas flow path or conduit 40 for supply and 
discharge of a gaseous pressure medium. In the illustrated embodiments the 
vertical pressure-resistant cylinder 7 is supported and fixed by a support 
structure (not shown), and the upper and lower plugs 6 and 8 are 
grippingly supported by the press frame 14 to prevent their disengagement 
during operation. The plugs may be fixed to the pressure-resistant 
cylinder by conventional means such as a threaded engagement, but the 
press frame gripping method is most recommended from the standpoint of 
ensuring safety in operation at high pressures. 
In the apparatus of such structure, the treating chamber 11 whose interior 
is in a hot state is inserted into the vertical pressure-resistant 
cylinder 7 by fitting the lower plug 8 which carries thereon the treating 
chamber 11 hermetically into the lower end of the cylinder 7. In this 
state, the valve 25 is opened and the valve 25' closed, and the gaseous 
pressure medium is introduced through the conduit 40 into the pressure 
chamber 39, while the heater 9 is charged with electricity to continue 
heating and raise the internal temperature of the furnace thereby 
performing HIP treatment. 
The pressurization is effected at a high pressure of at least about 500 atm 
using a gaseous pressure medium comprising an inert gas such as argon or 
helium gas alone or in combination with a small amount of oxygen, and as a 
high temperature is adopted sufficient to cause a plastic flow of the 
constituent material of the work such as ceramics or metal, but in the 
method of the present invention, the temperature range of about 
1,200.degree.-2,000.degree. C. is applied very effectively to the high 
efficiency and high temperature HIP treatment. By the HIP treatment, the 
workpiece is more densified and there is obtained a formed body of a high 
density close to the theoretical density. 
FIG. 5 is a schematic vertical section showing a forced cooling step which 
is carried out in the HIP furnace after completion of the HIP treatment. 
As shown in the figure, upon completion of the HIP treatment, the lower 
valve 25' is opened without reducing the pressure, and now both the upper 
and lower valves are open, whereby a circulating gas stream is created by 
convection of gas along the arrowed path in the figure. More particularly, 
the gas in the high pressure chamber 39 which has been cooled in contact 
with the inner wall of the vertical pressure-resistant cylinder 7 goes 
downward, then passes through the conduction hole 31, annular hole 30 and 
through hole 21 and enters the treating chamber 11, where it absorbs the 
interior heat, then passes through the through hole 18 and heat insulating 
barrier 10 and again flows into the high pressure chamber 39 from the 
valve hole 24 and radiates heat. 
According to the conventional HIP method, not of a modular type, the 
interior of the HIP furnace must be cooled to the temperature which 
permits opening to the outside air, namely, about 200.degree. C. or lower, 
and as the temperature lowers, the lowering rate becomes smaller, as 
reflected in a long time of about 8 hours required for the temperature 
lowering operation. After the adoption of a modular type HIP method, it 
became possible to perform only pressure reduction after HIP treatment, 
transfer the treating chamber as heated still hot to an auxiliary station 
and cool it to a predetermined temperature in that station. However, since 
there scarcely occurs convection of gas in the vicinity of the atmospheric 
pressure, a long period of required for cooling, for example, about 10 
hours is required for lowering the temperature from 600.degree. C. to 
300.degree. C. Consequently, there arises the necessity of increasing the 
number of auxiliary stations sufficiently to improve the utilization 
efficiency of the HIP furnace, or various improvements are needed for the 
forced cooling in auxiliary stations, thus leading to increase of the 
equipment cost. Additionally, the seal ring of the HIP furnace is apt to 
be damaged because the treating chamber as heated hot is taken out, and 
this is a serious problem. 
On the other hand, according to the foregoing method of the present 
invention, since cooling is done under high pressure after HIP treatment, 
there occurs a vigorous convection of gas, whereby the heat is absorbed 
rapidly and the workpiece is cooled in a surprisingly short time. For 
example, in the case of argon held at a pressure as high as 1,000 
kg/cm.sup.2, its viscosity is only 1.1 to 3 times that of argon gas at 
atmospheric pressure although the former has a density several hundred 
times that of the latter, so a slight temperature gradient would cause a 
vigorous convection providing an extremely large value of convective heat 
conductivity, that is, the conduction efficiency from the workpiece to the 
intra-furnace atmosphere becomes very high. Actually, when the temperature 
was lowered from 600.degree. C. to 300.degree. C. in a high pressure argon 
gas atmosphere of 1,000 kg/cm.sup.2, there was required only about one 
hour. 
Preferably, the rapid cooling in the HIP furnace according to the method of 
the present invention is carried out until the temperature of the 
workpiece is not higher than about 300.degree. C. After completion of the 
cooling step, the gaseous pressure medium is discharged from the conduit 
40 to let the internal pressure of the furnace revert to normal pressure, 
then the press frame 14 is removed and the lower plug 8 is removed from 
the pressure-resistant cylinder 7 in a closed state of the upper and lower 
valves 25 and 25', then taken out from the HIP furnace 5 together with the 
treating chamber 11 and the workpiece 33 loaded therein and attached to 
the auxiliary station 4. In this case, since the temperature of the 
hermetic casing 17 which encloses the treating chamber 11 is also quite 
low, it is not possible at all that the seal rings and other portions of 
the vertical cylinders 7, 13 and 13' of the HIP furnace 5 and auxiliary 
stations 4, 4' will be badly influenced during mounting or removal. After 
further cooling as necessary in the auxiliary station 4, the workpiece 33 
is taken out. 
In the HIP system of the present invention, a coolant jacket may be mounted 
around the outer periphery of the vertical pressure-resistant cylinder 7 
of the HIP furnace 5 to increase the cooling rate, and similar coolant 
jackets may be mounted around the outer peripheries of the vertical 
cylinders 13 and 13' of the auxiliary stations 4 and 4' to cause a forced 
circulation of the inside gas. The provision of these means is desirable 
for improving the function and effect of the method of the present 
invention although the equipment cost will be increased. 
The lower plug 8 of an improved type used in the present invention will now 
be described with reference to FIGS. 1 to 5. As shown in these figures, 
the lower plug of this type comprises an outer annular plug 8a which holds 
thereon the hermetic casings 16 and 17, heat insulating barrier 10 and 
heater 9, and an inner plug 8b which is removably fitted in the outer 
annular plug 8a and which supports the workpiece 33 through the heat 
insulating seat 19 and sample stand 32. 
Under such construction, at every loading or unloading of the work it is no 
longer necessary to remove the treating chamber 11 from the auxiliary 
station 4 and then separate the heat insulating barrier 10 from the lower 
plug 8; in other words, all that is required is only removing the inner 
plug 8b from the outer plug 8a while the treating chamber is received in 
the auxiliary station 4, and thus operation is extremely easy, affording 
great convenience. Where the lower plug 8 is of such a double structure, 
it is preferable in point of design and manufacture that the inner plug 8b 
be provided with the lower valve mechanism 23, and this is a matter of 
course. 
FIG. 6 is a schematic vertical section of an HIP apparatus according to 
another embodiment of the present invention. In the above embodiment 
illustrated in FIGS. 1 to 5, the heat insulating barrier 10, heater 9 and 
workpiece 33 can be loaded and unloaded from the lower openings of the 
vertical cylinders 7, 13 and 13' together with the lower plug 8. On the 
other hand, in the embodiment of FIG. 6, the upper plug 6 is removed 
thereby permitting those portions to be loaded and unloaded from the upper 
openings of the vertical cylinders 7, 13 and 13'. As shown, a base plate 
42 which serves as a part of the hermetic casing 17 is put on the lower 
plug 8 through support 41, and the lower end of the hermetic casing 17 is 
put on the base plate 42 through a seal ring 43. Further, the valve member 
23 for communication and cut-off between the interior and exterior of the 
treating chamber 11 is mounted in the base plate 42. In this apparatus, 
the heat insulating barrier 10, heater 9, workpiece 33 and base plate 42 
are loaded and unloaded from above the vertical cylinder in an integrally 
suspended state. 
As the heater 9, there is used Ni-Cr wire, Fe-Cr-Al wire, molybdenum wire 
or graphite, selected according to the temperature used. But, molybdenum 
and graphite are most preferred from the standpoint of stability of 
operation at high temperatures. As the material of the hermetic casings 
16, 17 and 20, there is used a gas impermeable material such as stainless 
steel, heat-resistant superalloy or molybdenum, selected according to the 
temperature used. 
The following is a working example of the method of the present invention. 
Example 
HIP treatment of high speed powder compact was performed using the lower 
loading type modular HIP system illustrated in FIGS. 1 to 5. First, in an 
auxiliary station, the upper and lower valve mechanisms were opened and 
the internal pressure of the treating chamber was brought to 10.sup.-1 
-10.sup.-2 Torr by vacuum suction, then the interior atmosphere was 
replaced with argon gas, followed by a preliminary sintering at 
1,000.degree. C. for 1 hour in an argon atmosphere. 
Then, the upper and lower valves 25 and 25' were closed to seal the argon 
gas in the treating chamber 11, which was then loaded into the HIP furnace 
5 in a hot condition of the workpiece. Then, the upper valve 25 was opened 
and argon gas was introduced from the conduit 40. At the same time, the 
heater 9 was charged with electricity and the internal temperature and 
pressure of the treating chamber 11 were raised to 1,400.degree. C. and 
1,000 atm over a period of 3 hours. While maintaining the interior of the 
treating chamber in this state for about 2 hours, there was performed HIP 
treatment. Thereafter, the powder supply to the heater 9 was turned off 
and the lower valve 25' was opened to start cooling. In about one hour the 
internal temperature of the HIP furnace was lowered to about 400.degree. 
C., whereupon pressure reducing and argon gas recovering operation was 
started. The internal pressure was returned to normal pressure over a 
period of about one hour. At this time, the internal temperature of the 
HIP furnace was 290.degree. C. Then, the upper and lower valves 25 and 25' 
were closed and the lower plug 8 was taken out together with the hermetic 
casings 16 and 17, heat insulating barrier 10 and work 33, and together 
loaded again into the auxiliary station 4. When the internal temperature 
was lowered to 200.degree. C., the inner plug 8b was pulled out together 
with the workpiece 33. Molybdenum was used as the material of both the 
heater 9 and hermetig casings 16 and 17. Heating could be accomplished 
stadly without sublimation of molybdenum in both the preheating stage and 
HIP treatment stage, and no substantial oxidation was recognized even 
after opening to the outside air. 
In the method and apparatus of the present invention, as set forth 
hereinabove, the HIP treatment is performed in the combination of the 
movable treating chamber 11 with the HIP furnace 5, and after completion 
of the HIP treatment, rapid cooling is effected by utilization of a large 
convective heat conductivity induced by a vigorous convection of high 
pressure gas, then the treating chamber 11 is taken out from the HIP 
furnace 5. Consequently, damage and deterioration of the seal ring caused 
by opening of the furnace in a state of high temperature, which is a 
safety impeding factor, is eliminated completely. Besides, since it is 
possible to preheat the workpiece 33 in an auxiliary station and load the 
preheated workpiece as enclosed with a predetermined gas atmosphere in a 
hot state into the HIP furnace 5, not only the heat-up time in the HIP 
furnace 5 is shortened, but also the time of occupying the HIP furnace 5, 
especially the time required for lowering temperature, is shortened to a 
remarkable extent. As a result, the working efficiency of the entirety of 
the modular type HIP system is improved remarkably, and hence not only the 
cycle time is shortened but also the cooling step which has heretofore 
been conducted over a long time period in auxiliary stations can be 
arrived at in an extremely shorter time. Consequently, the number of 
auxiliary stations for one HIP furnace can be reduced, it is not necessary 
to use a preheating-dedicated furnace which is expensive, thus permitting 
a remarkable reduction of the equipment cost, and the loss of heat energy 
can be kept to a minimum. 
Thus, the method and apparatus of the present invention have various 
advantages. The cycle time in the standard HIP treatment has heretofore 
been 15 hours and 20 minutes, while according to the present invention it 
is shortened to 8 hours and 20 minutes only through shortening of the time 
period for lowering of the temperature and is remarkably shortened to 7 
hours if preheating is adopted at the same time. Particularly, in the HIP 
treatment at a high temperature region of 1,200.degree. C. to 
2,000.degree. C., a specially outstanding effect is exhibited, thus 
greatly contributing to the improvement of productivity in the HIP 
treatment. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.