U.S. patent number 3,829,261 [Application Number 05/356,486] was granted by the patent office on 1974-08-13 for apparatus for isostatic hot pressing of powder.
This patent grant is currently assigned to Allmanna Svenska Elektriska Aktiebolaget. Invention is credited to Carl Bergman, Hans-Gunnar Larsson.
United States Patent |
3,829,261 |
Larsson , et al. |
August 13, 1974 |
APPARATUS FOR ISOSTATIC HOT PRESSING OF POWDER
Abstract
In isostatic hot pressing of powder in a collapsible container,
the powder is enclosed in a container which is provided with one or
more evacuation openings, and a conical support is held in position
adjacent the evacuation openings. A funnel-shaped body of sheet
metal is secured above the support and the evacuation openings by
welding its edge to the wall of the container. The body is
evacuated through a suction tube connected to the funnel and the
tube is sealed. Thereafter the container is subjected to heat and
pressure, and the funnel-shaped member collapses into engagement
with the conical support.
Inventors: |
Larsson; Hans-Gunnar (Vasteras,
SW), Bergman; Carl (Vasteras, SW) |
Assignee: |
Allmanna Svenska Elektriska
Aktiebolaget (Vasteras, SW)
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Family
ID: |
27354844 |
Appl.
No.: |
05/356,486 |
Filed: |
May 2, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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297648 |
Oct 16, 1972 |
3777877 |
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Foreign Application Priority Data
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Oct 14, 1971 [SW] |
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13011/71 |
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Current U.S.
Class: |
425/78;
425/405.2 |
Current CPC
Class: |
B22F
3/1258 (20130101); B22F 3/15 (20130101) |
Current International
Class: |
B22F
3/14 (20060101); B22F 3/12 (20060101); B22F
3/15 (20060101); B30b 005/02 () |
Field of
Search: |
;425/405,45H,78 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Flint, Jr.; J. Howard
Parent Case Text
This is a division of U.S. Pat. application Ser. No. 297,648, filed
Oct. 16, 1972, now U.S. Pat. No. 3,777,877.
Claims
We claim:
1. Apparatus for isostatic hot pressing of powder including a
collapsible container having at least one evacuation opening
therein, an outwardly extending support carried by the container
adjacent said evacuation opening, a funnel-shaped member arranged
over and covering said evacuation opening and said support and
having its edge secured to the wall of the container, and an
evacuation tube connected to said funnel-shaped member.
2. Apparatus as claimed in claim 1, in which said support is
conical.
3. Apparatus as claimed in claim 1 having a single evacuation
opening, and having means mounting said support above said
evacuation opening.
4. Apparatus as claimed in claim 1, in which said container
includes a wall having a plurality of evacuation openings and
having a wall portion within said evacuation openings, said support
being carried by such wall portion.
5. Apparatus as claimed in claim 1, in which said support is
conical and has parts of different angles of conicity.
6. Apparatus as claimed in claim 5, in which said support has an
intermediate section of greater conicity than the end sections.
7. An apparatus as claimed in claim 6, in which the said
intermediate section of the support has approximately the same
angle of conicity as the top section of the funnel-shaped body.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for manufacturing
products by bonding together the powder in a shaped object to form
a dense body by means of isostatic hot pressing of the powder under
high pressure, (pressure sintering). During the sintering the
powder billet is enclosed in a metal container which is placed in a
pressure furnace and is subjected in this furnace simultaneously to
a high, all-sided gas pressure and high temperature. As a rule, the
object formed by the powder is degassed during the first part of
the heating prior to the sintering by means of vacuum suction in
the container, in order to remove gases which have combined with
the powder or been bound to the surface of the powder grains. As a
rule, this degassing takes place at very low pressure by connecting
the container enclosing the powder body to a vacuum pump. The
invention is of particular interest in the manufacture of billets,
for example billets of material of high-speed steel type or
so-called superalloys, said billets being further processed to the
desired shape by rolling, forging or machining.
2. The Prior Art
Powder Metallurgy 1964 Vol. 7 No. 14, pages 168-201, contains a
detailed article on pressure sintering by E. S. Hodge, Interceram
No. 4 1967 and Nos. 1,2, and 3 1978 contain a detailed description
of Isostatic pressing by E. L. J. Papen. The invention can be
applied in the method described in, for example, Lundstrom U.S.
Pat. application Ser. No. 866,885, filed Oct. 16, 1969, now
abandoned, of which a continuation-in-part U.S. Pat. application,
Ser. No. 68,665 was filed on Sept. 1, 1970, now U.S. Pat. No.
3,695,597. The equipment described therein may be used.
The apparatus according to the invention relates to a way of
connecting a suction line to a metal container which encloses a
powder body, and the design of the connection of an evacuation tube
to the container.
Metal powder which is brought into contact with air absorb gases
present in the air on its surface and forms compounds with these,
especially oxides. These absorbed gases and oxides are removed to
the greatest possible extent since the powder is degassed during
the heating prior to the sintering. In the degassing of powder
bodies which are enclosed in a metal container, the container,
mostly a lid, has been provided with a welded-on tube which is
connected to a vacuum pump during the degassing process. However,
it has proved very difficult to arrange a large evacuation opening
in the container which gives little resistance to evacuation of
gases, and at the same time achieve a connection between the
container and a welded-on tube which withstands the following
isostatic pressure sintering. The weakest spot is the welded joint
between the container and the tubular element, by means of which
the container is connected to the vacuum pump. This welded joint
has burst when affected by the gas pressure acting on the container
during the sintering. The difficulties in achieving a solid welded
joint have increased with the increased size of the evacuation
opening and the resultant increased diameter of the connection tube
welded round the opening.
SUMMARY OF THE INVENTION
By means of the invention, it has become possible to use a large
evacuation opening which permits a quick evacuation and in spite of
this achieves a connection to a vacuum line which withstands the
pressure sintering, and this is an important condition for
obtaining the intended bonding and density in the treated body.
According to the invention, a body of powder is enclosed within a
collapsible chamber having an evacuation opening or openings. A
conical outwardly extending support is held by the container in the
area of the evacuation opening or openings. A funnel-shaped element
of sheet metal having a tube attached thereto is applied over the
opening or openings and its edge is welded to the wall of the
container. The evacuation opening or openings are thus left
substantially unobstructed. A tube is welded to the funnel-shaped
element and connected to vacuum so that the powder is degassed.
Thereafter the tube is sealed, thereby also sealing the
funnel-shaped member, and the container is subjected to isostatic
pressure while being heated. The pressure is sufficient to collapse
the funnel-shaped member against the support.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described with reference to the
accompanying drawings which show a cylindrical body of powder, for
example a billet for further machining to the desired shape by
means of rolling or forging, said body being enclosed in a metal
container. FIGS. 1-5 show perspective sketches of the metal
container with a connection tube for the vacuum pump and enclosed
powder body of powder billet at different times of a work cycle,
and FIGS. 6-8 show sections and views of the invention more in
detail.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a powder billet which is enclosed in a collapsible
container having an exposed evacuation opening 1 in the lid 3 of
the container 2, or an evacuation opening made in said lid. In the
opening 1, the end surface of the powder billet 4 is visible. The
powder billet may be packed to high density in connection with the
filling or, besides this, be further compressed by means of
isostatic cold pressing in a pressure chamber while being exposed
to a liquid or gas with high pressure. In the evacuation opening 1
a conical support element 5 is placed on the powder billet 4. The
support element can be fixed in the middle of the opening 1 by
means of holders 6, as shown in FIG. 2. Over the opening 1 a
funnel-shaped element is placed, this being constituted by a sheet
metal cone 7. A tube 8 is welded to said sheet metal cone, said
tube being intended for connection to a vacuum line during the
degassing period. The cone 7 and the tube 8 are joined by means of
a weld 10. The cone at its larger end is provided with a flange 11.
This is connected to the lid 3 by means of a weld 12. The
appearance after the attachment of the funnel-shaped connection
element is clear from FIGS. 3 and 6. FIGS. 4 and 8 show the
appearance of the funnel-shaped element after the pressure
sintering. FIG. 7 shows the funnel-shaped element when the cone 7
has collapsed under an external gas pressure, but before this
pressure has been able to compress the tube 8.
In the alternative embodiment shown in FIG. 5, there are a number
of openings 9 in the container within an annular area on the lid 3.
The cone 5 is placed in the middle of the group of holes. If the
powder is only mechanically packed in connection with the filling,
the powder body has low firmness. In order to prevent loose powder
from running out through the opening or openings in the handling of
the container filled with powder or during the vacuum suction, a
mat of steel wool having suitable, generally low, carbon content
can be positioned between the lid 3 and the end surface of the
powder billet 4.
As is shown in FIG. 6, the conical support element 5 has three
different angles of conicity. The acute angle 2.beta.of the central
part 5 b is larger than the acute angles 2.alpha. and 2.gamma. of
the lower and upper parts. The angles .alpha. and .gamma. may be
equally large. The acute angle of the sheet metal cone 7 is
preferably as large as the acute angle of the part 5 b that is
2.beta.. The diameter of the evacuation opening is d.sub.1 and the
bottom diameter of the support element 5 is d.sub.2. Between the
lid 3 and the support element 5 an annular surface is thus formed
having a width l.sub.1, where gases may escape unimpededly. In
addition to this, it is possible to place the support element 5
somewhat above the upper surface of the powder body so that gases
may freely escape also below the support element. A mat of steel
wool may be used. Because of the large, free surface of the powder
body, the escape of gases during the degassing is made easier,
making it possible to obtain efficient degassing in a short
time.
The relative strength of the tube 8 and the cone 7 is preferably
chosen so that the cone 7 when the pressure increases in the
pressure furnace is first pressed downwards against the central
part 5 b of the support element 5 and then downwards against the
powder billet 4 in the annular space between the lid 3 and the
lower part 5 a of the support element 5. After this is done, the
tube 8 is compressed as shown in FIG. 7. In the embodiment
according to FIG. 6, the sum of the distance l.sub.1 and l.sub.2 is
somewhat larger than l.sub.3. If the difference between l.sub.1 +
l.sub.2 and l.sub.3 is chosen to be approximately equal to the
decrease in diameter of the powder billet and the container, this
results in insignificant extension of the cone material during the
pressing. In this way, the strain in the welds 10 and 12 is
moderate when the cone is pressed down. After the cone 7 has been
pressed down, the tube 8 is compressed, as shown in FIG. 7. Because
of the support from the conical part 5 c, the weld 10 is exposed
only to insignificant strain.
* * * * *