DE2006066B2 - Process for the hot isostatic pressing of bodies pre-pressed from pulverulent material and an oven for carrying out the process - Google Patents

Description

The invention relates to a method for isostatic hot pressing of powdered material pre-pressed bodies and a furnace for carrying out the process.

High density and freedom from pores in powder metallurgy manufactured carbide bodies for tool

• nd a temperature of 800 to 1400 ° C iso- 50 means high quality. With machining be itatically hot-pressed. Tools means high density, among other things

increased wear and tear and lower risk of cutting edge breakage. In the case of rolls and the like, freedom from pores means increased strength and better surface fineness, which in turn means that a rolled product can have a greater surface fineness. Also in the production of electrical heating resistors, e.g. from MoSi ₂ , a very high density and freedom from pores mean that

8. The method according to claim 3, characterized in that that pre-pressed bodies made of cermets are "orsintered" and then hot isostatically pressed Will.

9. The method according to claim 8, characterized in that OaB is a cermet of 90 to 99% Alumina and 1 to 10% silver presintered at 0 to 10 ~ * Torr and then at 800 to

1500 ° C and 100 to 2CW0 bar isostatically hot - 60 «borrowed advantages. The strength increases, and the is pressed. Risk of local overheating and subsequent

10. The method according to claim 1 or 2, thereby combustion is lower.

in that preliminarily compact from Urandi- The advantages of high density and freedom from pores are oxide in hydrogen or under vacuum at an equally large for cermets of various types. For ErTemperatur of at least 1550 ⁰ C vorgesin- 65 livering great density and pore freedom is already tert and then at a pressure of 100 to a method has been proposed (DT-AS 2000 bar and a temperature of 1300 to 1953 036) in which a powdery material is hot-pressed at 1600 ° C. pre-pressed body in a gas-tight, heat-treated »

permanent envelope made of a suitable metal is enclosed, after which the envelope evacuated, sealed and. is placed in an oven in which the material is exposed to a high Print is sintered. Temperatures and pressures of up to 1500 ° C and 2000 bar are used. Attaching a sleeve to a molded body, especially if that one is a complex one Form has the evacuation and sealing of the envelope as well as the removal of the envelope after Sintering pressure leads to high costs. Means especially in the production of small cutting elements encapsulation is, in relative terms, considerably more expensive.

The invention is based on the object of developing a method in which the sintering and Hot pressing is feasible without the need for costly encapsulation, quality in terms of quality However, density and freedom from pores are retained.

To solve this problem, a method of the type mentioned is proposed that the im having the characterizing part of claim 1 mentioned features. Sintering the prepressed from Puiver Body is preferably carried out at a pressure below atmospheric pressure, this being the case Pressure reduction can reach down to the technically achievable vacuum.

The sintering of the bodies and the subsequent pressing are thus carried out without the bodies be encapsulated in a gas-tight envelope. E: are made from a powder or a powder mixture pre-pressed bodies at atmospheric pressure or lower pressure and at such a temperature sintered, that powder particles of the same material are connected or that one binder is another Powder particles contained in the powder mixture connects, after which the body under direct action of the pressure medium are isostatically hot-pressed.

One possible explanation for the fact that the density of presintered products is caused by isostatic Hot pressing can be increased even though the body is not enclosed in special envelopes are, consists in the fact that the pressure medium is backed up, the resulting cavities between the to fill in bound powder particles. The binding agent forms a closed capsule around each one individual cavity and prevents the pressure medium from penetrating into this. In the following Hot pressing the voids disappear in the same way as hot pressing material, which is enclosed in a shell, if the pressure and temperature are chosen so that the binder is sufficiently easy to define so that the bound powder particles slide against each other and fill in the empty spaces.

A special furnace of the type, one in a pressure chamber, is used for the process has enclosed, insulated furnace space. The pressing takes place immediately after sintering and begins at sintering temperature. During pressing, the temperature must be set to at least this value be that the binder is so easily deformed that the closed spaces are compressed will. Temperature and pressure depend on each other and on the powder composition.

The method can be used for powder bodies of various types, before Mlem for hard metal products, the WC. TaC. TiC or VC or a mixture of two or more of these substances, as well as a binder consisting of Co and / or Ni and possibly Fe. Bodies pre-pressed from powder in the usual way are only sintered at atmospheric pressure or lower pressure, preferably under vacuum, so that the carbide particles of the substances contained are joined together. The amount of binder and temperature are chosen so that most of the remaining cavities or pores between the powder particles are completely closed, after which the sintered body is isostatically pressed in a furnace with a furnace space enclosed in a pressure chamber. This pressing is preferably carried out at the sintering temperature, ie a temperature at which the binder is relatively easily plastically deformable or possibly flowing or at least almost flowing, and with a pressure medium that acts directly on the body surface. This eliminates the costly encapsulation in the Puh'erk body, which was previously ^{considered necessary in 1} pressure sintering or isostaiii.chem hot pressing. The hard metal bodies usually contain 0 to 9 Vo WC and / or TiC, 0 to 30% TaC, NbC and / or VC as hard particles, and 1 to 30% Co up.d / o'i: r Ni and possibly iron as a binder. Most common are bodies with 0 to 99%> WC and / or TiC, 1 to 30%> Co and / or Ni and other substances in small amounts, mainly in the form of impurities. The sintering itself can usually take place at a slightly lower temperature than normal sintering at atmospheric pressure or under vacuum, since the inter-particle spaces must no longer be filled as effectively as before during sintering itself. It is only important that the cavities and pores are well closed so that isostatic pressing can be carried out with good results without a special cover. For the same reason, a slightly smaller amount of binder may be used. A lower temperature also means that the risk of binder running down the body during sintering is reduced. It may be possible to be satisfied with only sintering the powder body on the surface before isostatic pressing. The sintering temperature is generally 1200 to 1600 ° C. The subsequent isostatic pressing is in most cases preferably carried out at 800 to 1500 ° C. and 100 to 2000 bar. As a general rule, as the pressure increases, a lower temperature will be used to achieve the same density. The sintering and subsequent pressing lead to the best result if both can be carried out in one and the same oven. If the sintering takes place in a vacuum, a pressure chamber with a separate vacuum valve with a large flow cross-section is necessary in order to achieve the required pressure. The size of the powder used is preferably 1 to 8 μm.

The process is also suitable for the produc- tion of electrical hot resistors, eg au: MoSi ₂ and Gh.s. Pre-pressed bodies from powder are sintered at a temperature of 900 to 1400 ° (after which the body is isostatically hot-pressed under the direct action of a pressure medium at 100 to 2000 bar at 800 to 1400 ° C. The particle size of the powder used is in the Re gel 1 to 75 µm.

5 6

A third group of products for which the procedure of an evacuation device. The furnace points to the

can be used, cermets are various- Invention in the characterizing part of the claim

ner Art. A cermet made of 90 to 99% Al ₂ O ₃ and 1 to 11 and in addition those in claims 12 to

10 ° / o Ag is produced by making a powder with part-14 mentioned characteristics. One receives on this

Chen size from 1 to 50 µm pre-pressed to form bodies 5 ways when vacuum sintering an opening with relative

which are sintered under vacuum, have a usual large flow cross-section. The described

borrowed at 10 ~ ² Torr or lower and at 900 to valve assembly is preferably located on the un-

1400 ° C, so that closed pores or hollow ends of the furnace,

spaces arise, after which the body is under direct Usually the vacuum line to such

Exposure to a pressure medium at 100 to 2000 bar to be connected to the furnace in such a way that it is in the

and hot isostatically pressed at 800 to 1400 ° C. annular opening of the end closure protrudes

A fourth product that can be manufactured, the suction tube can be used to remove the are sticks made of uranium dioxide. Powder of uranium dioxide valve disc in relation to the annular part will raise in hydrogen gas atmosphere or below Va-. To move or shake the The pipe is sintered in to avoid vacuum at a temperature of at least 1550 ° C 15 and then passed at a pressure of 100 to until it comes into contact with the valve disc 2000 bar and a temperature of 1300 to comes, after which the annular part of the end-1600 ° C hot pressed. A number of other products loss is lowered so that one has an opening should be produced according to the process between the furnace chamber and the vacuum pump. ao holds. In order to reduce the stress on the valve disc

For example, it has been possible to reduce pure silver powder, especially if it has a large diameter.

ver treat according to the procedure. If you have a SiI knife or a small thickness, this can be done with

powder in a plastic container at room temperature - be provided with a protruding part that

rature isostatically with a valve opening closed to a body 3 kilobars, the organ that supports the

pressed. The body was then exposed to the forces acting on the end closure in a vacuum.

Sintered at 930 ° C for one hour. The density of the takes

The sintered body was 8.18 g / cm ³ , which is about 78%. The furnace according to the invention is as follows

theoretical density is. The was then described with reference to the drawing, showing in this

sintered body without cladding at 900 ° and F i g. 1 and 2 a section through the lower part

a pressure of 1 kilobar for one hour. The pressure chamber for hot pressing or vacuum

presses. As a result, a density of 9.41 g / cm ^{3 was} re-sintered;

reached, which is about 90Vo of the theoretical density Fig. 3 and 4 cuts through an end closure

is equivalent to. Furthermore, tests with mechanical along the lines AA and BB in FIG. 2.

carried out from bodies pre-pressed from silver powder. In the figures, 4 denotes one yoke in one

These were under the values just mentioned for 35 press frames and 10 the inner tube in one

Temperature, pressure and time without covering hot-high pressure cylinder. From the press only those for

pressed. There was a density of almost 100%> the parts essential to the invention are shown. The rest

theoretical achieved. Before hot pressing, part of the press was and will be of known construction

the density about 90% of the theoretical density. for example described in the German interpretation

The advantage of the method according to the invention 40 documents 1 953 036 and 1 953 306. is shown in the fact that sintered bodies, which after the In the furnace space is a charge 16. The furnace chamber is covered by an insulating jacket 17 Surrounded by 100 to 500 times as many cavities per volume, that of three concentric metal tubes unit, such as bodies, according to the method 18, 19 and 20 with an insulating layer in between of the invention are made. With a ver 45 th 21 and 22 and a lower end ring 24 the same as the previous process for printing. The coat is on the upper one, not shown of powder bodies, which are suspended in an evacuated, set end closure of the press and are gas-heat-resistant Sheath are enclosed, tightly connected to these. In the oven sir *. Heating wins one has the advantage that a time-consuming and mente 47 is available, which from a pipe 40 getrakostspieliger No operation. The procedure will be carried out.

enables sintering without a shell, without cooling the pressure chamber has a «lower end

Body between sintering and hot pressing and without an end consisting of an annular part 50 with a

Complicated transport arrangements with locks, seal 51 is made against the inner surface of the

which seals the contact of the hot body with air damaging the pipe 10. The annular part 50 has one. When pressing uranium dioxide UO _{2 there} appears a 55 flat valve seat 52, which is located between the smaller one

Density of 99.5 »/ 0 of the theoretical to be possible. Boning 53 on its outer Tefl and the largest

The invention also relates to an oven in which it forms a bore 54 in its inner part

Both the sintering and the hot pressing are carried out. In the annular part 50 there is a valve disk 55

can be performed and the somh for the implementation with a seal 56 arranged against the development of the process is particularly suitable. Oven 60 seals valve seat surface 52

consists of a cylindrical pressure chamber with a downwardly protruding pin 57 with a sol-

a high pressure cylinder, in this protruding length that its lower surface when closed

Terminations, arrangements for receiving a valve on the same level as the lower one

axial forces which are applied by a pressure medium to the surface of the ring 50 and thus the yoke 4 of the Terminations are exercised, supported by a press frame, the pressure warned the termination.

Drackkammer arranged furnace space with Heizvor- circuit presses against this. The valve plate 55 is mil

directions, a surrounding the furnace chamber insulating a number of axial guides 58 provided, which of

mantle with insulating cover and base and the bore 54 are controlled and thus the

Valve head 55 in relation to the annular Center part 50. On the valve plate 55 rests a protruding into the insulating jacket 17 insulating Bottom, consisting of a sheet metal ring 60 attached to the valve disk with a thick Layer of insulating material 61. A plate 62 on which the charge 16 is placed rests on this. These The plate is expediently made of a material with good thermal conductivity and can with radial Channels 63 and 64 may be provided between their perimeter and a central space 65. Through this, that the plate 62 has a good thermal conductivity, the central part of the charge 16 over heat can be applied to this plate. The channels help to keep gas between the space 65 and the gap can circulate around the plate, so that the heat can thereby pass from or to the central part the plate can be directed.

An evacuation device (not shown) is provided to generate a vacuum in the furnace. which are connected to the pressure chamber via the valve-shaped lower end cap can. The connection is made by means of a suction pipe 70 which is inserted into the bore 53 of the annular Part 50 is pushed in and sealed against the bore with a sealing ring 71. The suction tube 70 has at its outermost end slots 72, between which remaining material protruding supports 73 forms. In the embodiment shown in the figures, the suction tube is in the bore 53 is pushed in so that the supports 73 come into contact with the valve disk 55, after which the annular part on the in F i g. 1 and 3 shown. The position is lowered and the valve is opened. There are now free connections between the

Oven space in the pressure chamber and the suction

tube, over the gap between the ven

tilteller, the bore 54 of the annular part

S 50 and the valve seat 52 and the columns 62 between

see the supports 63 of the suction pipe, The Venti

can also be opened by removing the suction tube

the valve parts / lifts.

The annular part is through brackets to a

ίο Sleeve fastened along a guide rail runs, which in turn is attached to a column. Di <sleeve and thus the ring-shaped part with valve point and the floor on top and the Chargi can be raised and lowered with a cylinder the.

The equipment works in the following way.The furnace is charged with material 16. The Chargi is placed on the oven floor when the bottom end cap is in the lowered position, where

ao after the cylinder the whole end closure with dei Bring the batch to an upper layer. Then there is: suction tube 70 in the opening of the end closure pushed, after which the annular part 50 it the in the F i g. 3 lowers the position shown. The valve valve Ler 55 with the charge 16 is carried by the support 73 of the suction pipe 70 and a gap bil det is between the valve plate 55 and the ring-shaped part 50. The batch is under vacuum sintered, after which the annular part 50 is raised and the suction pipe 70 is removed and the pressing frame is pushed over the pressure chamber. Pressure medium is supplied to the pressure chamber and there; Hot presses sintered material to the desired density.

IiC ΙΓίΙ

For this purpose 3 sheets of drawings

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Claims (1)

Patent claims: 1. A method of hot isostatic pressing of pre-pressed from powdery material Bodies, characterized in that the pre-pressed bodies at atmospheric pressure or lower pressure are exposed to temperatures such that the powder particles sinter together at least on the surface of the pre-pressed body in such a way that the between their pores and cavities are encapsulated, after which the pre-sintered body in an oven with an oven space enclosed in a pressure chamber under direct Exposure to an inert, gaseous pressure medium such as argon, helium, nitrogen or hydrogen, isostatically hot-pressed to high density. 2. The method according to claim 1, characterized in that in one and the same furnace is pre-sintered and then isostatically hot-pressed. 3. The method according spoke 1 or 2, characterized in that a pre-pressed powder mitchung is pre-sintered with at least one binder and then hot isostatically pressed. 4. The method according to claim 3, characterized in that carbides of tungsten, tantalum, Titanium, or vanadium, or a mixture of rwet or more of these carbides and cobalt lind / or nickel as well as gegetx. at best iron as Pre-pressed bodies containing binding agent are pre-sintered and then hot isostatically pressed. 5. The method according to claim 4, characterized in that the pre-pressed bodies are ^{pre-sintered at a temperature of 1200 to 1600 0} C end then at a pressure of 100 to 2000 bar end a temperature of 800 to 1500 ° C • isotatically hot-pressed. 6. The method according to claim 3, characterized in that mainly molybdenum _{disili-sid (MoSi 2} ) and glass-containing pre-pressed bodies »are orsintered and then hot isostatically pressed. 7. The method according to claim 6, characterized in that the pre-pressed bodies are ^{pre-sintered at a temperature of 900 to 1400 0} C • nd then at a pressure of 100 to 2000 bar 11 furnace for performing the method according to any one of claims 2 to 10 exist from a cylindrical pressure chamber with a high pressure cylinder, into these projecting end closures, arrangements for the absorption of axial forces which are exerted by a pressure medium on di end closures, a furnace chamber arranged in the pressure chamber with heating devices, an insulating jacket surrounding the furnace chamber with an insulating cover and Bode and an evacuation device, characterized in that one of the end closures (50-55) of the pressure chamber is provided with an annular part (50) and with an element (51) sealing against the cylinder (10), a di <opening of the annular part (50) cover the valve head (55), a sealing member (56) between the annular part (50) and the valve eller (55), a suction tube (70) protruding into the annular part (50) of the end closure and sealingly adjacent to it, as well as an element for separating the valve part (55) from the annular part (50) of the end closure. 12. Oven according to spoke 11, characterized in that the suction pipe (70) of the evacuator device lifts the valve disc (55) from the annular part (50) of the end closure. 13. Oven according to claim 11, characterized in that the annular part (50) of the end closure retractable and thus separable from the valve plate (55). 14. Oven according to claim 11, characterized in that the valve disk (55) with a central protruding part (57) is provided, which during hot pressing on the yoke (4) of the frame rests.