Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Reexamination Certificate
2001-10-10
2003-03-11
Wilson, Gregory (Department: 3749)
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
C432S126000, C432S128000
Reexamination Certificate
active
06530780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a continuous sintering furnace and the method of use thereof. The continuous sintering furnace concerned is a sintering furnace for continuously sintering work or material to be sintered into ceramics. The works or materials to be sintered may be carbonic, nitric and oxide ceramics such as alumina (Al
2
O
3
), silicon carbide (SiO) and boron nitride (BN) and their treatment temperature maybe more than 1600° C. Structure, furnace material and the mechanisms needed are essential factors for such sintering furnace being operated continuously at high temperature. Usually graphite is used as furnace material because of its excellence in heat resistance, which may bring about considerable restrictions in the structure and mechanisms needed because of its physicality.
2. Discussion of the Background
FIGS. 1 and 2
show a conventional continuous sintering furnace comprising an entrance-side deaerating chamber
3
through which trays
2
each with a work or material
1
to be sintered being mounted thereon may pass, a furnace body
5
which is arranged in a chamber
4
contiguous with said deaerating chamber
3
and into which the trays
2
are sequentially fed in a line or column and an exit-side deaerating chamber
6
which is contiguous with said chamber
4
and through which the trays
2
having passed through the furnace body
5
may pass.
A space between an inner face of the chamber
4
and an outer face of the furnace body
5
is filled with heat insulating material (not shown). A double-walled cooling structure is applied to the chamber
4
.
The deaerating chamber
3
is provided with vertically movable doors
7
and
8
at its upstream and downstream ends in a direction of transportation of the trays
2
, respectively. Likewise, the deaerating chamber
6
is provided with vertically movable doors
9
and
10
at its upstream and downstream ends in the direction of transportation of the trays
2
, respectively.
With the doors
7
,
8
,
9
and
10
being closed into their lowered positions, air-tightness is maintained in the chambers
3
,
4
and
6
. With the doors
7
,
8
,
9
and
10
being opened into their raised positions, the trays
2
are allowed to pass through the chambers
3
,
4
and
6
.
In the chambers
3
,
4
and
6
and along substantially the entire length thereof, pairs of laterally spaced skid beams
11
,
12
and
13
are provided to slidably support the trays
2
from below, respectively.
A plurality of vertically extending heaters
14
are disposed in a longitudinally intermediate portion of the furnace body
5
such that the heaters
14
are positioned laterally of the material
1
to be sintered on the tray
2
. The material
1
to be sintered is heated by the heaters
14
.
The continuous sintering furnace is also equipped with a pusher
15
which pushes the trays
2
one by one into the furnace body
5
from the deaerating chamber
3
as well as a puller
16
which pulls the trays
2
one by one from the furnace body
5
to the deaerating chamber
6
.
Upon starting of an operation of the continuous sintering furnace, the furnace body
5
is filled with non-oxidizing gas with the doors
8
and
9
being closed. Then, the heaters
14
are activated to heat the inside of the furnace body
5
to a predetermined temperature.
Next, the tray
2
on which the material
1
to be sintered is mounted is fed to the deaerating chamber
3
; and the door
7
is closed and air inside the chamber
3
is discharged. Then, the door
8
is opened and the tray
2
is pushed into the furnace body
5
by the pusher
15
; and the door
8
is closed again.
After the lapse of a predetermined time period, another tray
2
is pushed from the deaerating chamber
3
into the furnace body
5
according to the procedure described above to thereby push the tray or trays
2
already in the latter toward the deaerating chamber
6
.
Repetition of the procedure described above causes the tray
2
to reach the most downstream position in the furnace body
5
. Then, the door
9
is opened with the door
10
being closed; and the tray
2
is pulled by a puller
16
from the furnace body
5
into the deaerating chamber
6
. After closing the door
9
, the door
10
is opened to take the tray
2
to outside.
Thus, the material
1
is gradually raised in temperature for a predetermined time period in a preheating zone
17
in the furnace body
5
adjacent to the deaerating chamber
3
, is heated to a constant temperature for a predetermined time period in a heating zone
18
at the intermediate portion in the furnace body
5
and is gradually cooled for a predetermined time period in a gradual cooling zone
19
in the furnace body
5
adjacent to the deaerating chamber
6
.
In the continuous sintering furnace constructed as described above and when the amount of production is to be increased without changing a cross sectional area of the furnace, the heating zone
18
is prolonged in length and movement of the tray
2
is increased in speed.
When a variety of products are required to be produced for small quantities, the heating zone
18
is shortened in length and movement of the tray
2
is decreased in speed so as to reduce the number of production lots.
The continuous sintering furnace shown in
FIGS. 1 and 2
may be suitable for a single product with a certain degree of large-scale production. However, in multiple products with small-scale production in which the heating zone
18
is shortened in length and movement of the tray
2
is decreased in speed, tact time of the material
1
becomes longer so that thermal loss in the heating zone
18
increases, resulting in heat input to the gradual cooling zone
19
. Consequently, the gradually cooling zone
19
must be prolonged in length so as to secure sufficient cooling time for the work or material
1
.
Use of different process gases in the heating zone
18
and gradually cooling zone
19
would result in mixture of the two gases since the zones
18
and
19
are always in communication with each other.
An intermediate door cannot be provided between the zones
18
and
19
for avoidance of such mixture of the two gases since the construction is such that the tray
2
pushed into the zone
17
pushes the tray or trays
2
already in the zones
17
,
18
and
19
downstream in the direction of transportation.
A furnace floor structure is provided by skid beams
12
; there is high sliding friction coefficient between the tray
2
and the skid beams
12
, resulting in an increase of thrust of the pusher
15
and pushing force between the trays
2
. Therefore, when number of trays
2
used is increased, then upper faces of the skid beams
12
constituting a transportation path of the trays
2
may be deformed in a wave shape or formed with steps, with the disadvantageous result that the column of trays
2
on the skid beams
12
are not smoothly slid and may lift up like a bridge as shown in
FIG. 3
leading to failure of transportation of the trays.
If push-in load for the column of trays
2
applied by the pusher
15
is increased in this state, then the trays
2
may jump upwardly and buckle.
Furthermore, the amount of input heat conducted to the material
1
via the trays
2
from below is inevitably less than that conducted from above or from each side since, with the trays
2
being supported by the skid beams
12
longitudinally running through the furnace body
5
, the material
1
is heated by the heaters
14
at opposite sides of the path of transportation of the trays
2
so that heating of the material
1
may be insufficient at its lower portion, thereby decreasing production yields.
Heat treatment time period for ceramics are generally predetermined. Therefore, in order to increase the amount of production, the length of the furnace must be prolonged and transportation speed (tact) of the trays must be increased, which will thus cause an increase in the number of trays
2
in the furnace. The skid-type transportation mechanism is low in transp
Ishimoto Tetsuya
Iura Toru
Katsumata Kazuhiko
Machida Hiroshi
Mori Kazumi
Ishikawajima-Harima Jukogyo Kabushiki Kaisha
Wilson Gregory
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