TECHNICAL FIELD
The present invention relates to a vertical muffle-type
heat treating furnace. More particularly, the invention
relates to a vertical muffle-type heat treating furnace
comprising: a vertically disposed muffle allowing metal strips
to be led therein from an upper side to a lower side thereof;
a heating zone for heating, from the outside of the muffle,
the metal strips passed through the muffle; and a cooling zone
disposed at place downstream from the muffle with respect to
a moving direction of the metal strips and serving to cool the
heated metal strips, the furnace characterized by being designed
to readily accommodate the elongation of the heated muffle.
BACKGROUND ART
The vertical muffle-type heat treating furnaces have
conventionally been used for annealing the metal strips such
as of stainless steel.
In such a vertical muffle-type heat treating furnace,
the muffle is vertically disposed with its upper end fixed to
place, whereas the heating zone is provided for heating the
muffle from the outside thereof. The metal strips are led into
the muffle from a lower side to an upper side thereof such that
the metal strips passed through the muffle may be heated in
the aforesaid heating zone. The metal strips thus heated are
cooled in the cooling zone disposed on an upper side with respect
to the muffle, whereby the metal strips are annealed. In some
cases, the aforesaid cooling zone may include a slow cooling
zone for slowly cooling the metal strips.
In such a vertical muffle-type heat treating furnace,
the muffle has its upper end fixed to place, as described above.
When the muffle is heated to about 900 to 1200° C in the aforesaid
heating zone, the muffle is thermally expanded and is also
elongated downwardly by gravity. The muffle is particularly
raised in temperature at an upper part thereof because the metal
strips are heated as led through the muffle from the lower side
to the upper side thereof. Hence, the muffle is elongated so
much as to encounter plastic deformation. This leads to a
progressive increase of the length of the muffle.
More recently, Published Japanese Translation of PCT
International Publication for Patent Application
No.2000-508712 has proposed a vertical muffle-type heat
treating furnace which includes the vertically disposed muffle
having its lower end fixed to place, and the heating zone for
heating the muffle from the outside of the muffle. The metal
strips are led through the muffle from the upper side to the
lower side thereof. The metal strips are heated in the heating
zone as passed through the muffle. The metal strips thus heated
are cooled in the cooling zone disposed on a lower side with
respect to the muffle, whereby the metal strips are annealed.
Unfortunately, in the case where the muffle has its lower
end fixed place, as described above, the muffle fails to be
elongated properly upwardly when heated to 900 to 1200°C in
the heating zone. This results in the buckling of the muffle.
In this connection, the furnace disclosed in the
aforementioned publication is provided with support means for
pulling upward the upper end of the muffle. The support means
pulls the muffle upwardly thereby preventing the muffle from
buckling.
However, the provision of the support means for pulling
upward the upper end of the muffle results in a complicated
construction of the furnace and thence, in increased costs.
In addition, it is difficult to provide a proper control of
the force of the above support means pulling upward the upper
end of the muffle. If the tensile force of the support means
is too great, the muffle is excessively elongated upwardly so
that the plastic deformation results. If, on the other hand,
the tensile force of the support means is too small, the muffle
buckles.
DISCLOSURE OF THE INVENTION
It is an object of the invention to solve the aforementioned
problems encountered by the vertical muffle-type heat treating
furnace used for annealing the metal strips such as of stainless
steel.
The invention is directed to a vertical muffle-type heat
treating furnace adapted to readily accommodate the elongation
of a heated muffle, the furnace comprising the vertically
disposed muffle allowing metal strips to be led therein from
an upper side to a lower side thereof; a heating zone for heating,
from the outside of the muffle, the metal strips passed through
the muffle; and a cooling zone disposed at place downstream
from the muffle with respect to a moving direction of the metal
strips and serving to cool the heated metal strips.
According to the invention, the vertical muffle-type heat
treating furnace comprises: a vertically disposed muffle
allowing metal strips to be led therein from an upper side to
a lower side thereof; a heating zone forheating , from the outside
of the muffle, the metal strips passed through the muffle; and
a cooling zone disposed at place downstream from the muffle
with respect to a moving direction of the metal strips and serving
to cool the heated metal strips, and is characterized in that
the muffle has its upper end fixed to place and that an extendable
muffle elongation adjusting zone is provided which maintains
a space between a lower end of the muffle and the cooling zone
in a sealed state. In some cases, the aforesaid cooling zone
may include a slow cooling zone for slowly cooling the metal
strips.
In the case where the muffle has its upper end fixed to place
as suggested by the vertical muffle-type heat treating furnace
according to the invention, the muffle is elongated downward
when the metal strips are heated in the heating zone as led
through the muffle from the upper side to the lower side thereof.
Thus, the muffle is prevented from buckling, which occurs in
the case where the muffle has its lower end fixed to place.
The vertical muffle-type heat treating furnace according
to the invention is provided with the extendable muffle
elongation adjusting zone which, as described above, maintains
the space between the lower end of the muffle and the cooling
zone in the sealed state. Therefore, the elongation of the
muffle, which is elongated downward as described above, is
accommodated by the muffle elongation adjusting zone.
Furthermore, the muffle elongation adjusting zone also prevents
a flammable gas containing a hydrogen gas from leaking out of
the muffle. In addition, the muffle elongation adjusting zone
also prevents the heated metal strips from being oxidized as
exposed to the outside air or the like.
The vertical muffle heat treating furnace according to
the invention negates the need for providing the support means
for pulling upward the upper end of the muffle and for performing
the difficult task to control the tensile force of the support
means for properly elongating the muffle upwardly, the need
stated in the aforementioned publication. Thus, the furnace
of the invention is adapted to readily accommodate the elongation
of the heated muffle.
In the vertical muffle-type heat treating furnace
according to the invention, the extendable muffle elongation
adjusting zone which maintains the space between the lower end
of the muffle and the cooling zone in the sealed state may be
arranged as follows, for example. A ring-like container having
a predetermined depth for containing therein a water-free fluid
may be provided on the cooling zone. On the other hand, the
muffle is provided with a cylindrical closing member extended
downwardly from the lower end thereof. The closing member is
inserted in the fluid held in the container thereby maintaining
the space between the lower end of the muffle and the cooling
zone in the sealed state. Alternatively, a heat-resistant
connecting member formed of an extendable bellows may be disposed
between the lower end of the muffle and the cooling zone, such
that the connecting member may maintain the space between the
lower end of the muffle and the cooling zone in the sealed state.
According to the vertical muffle-type heat treating
furnace of the invention, the muffle elongation adjusting zone
may preferably be provided with a cooling device for cooling
the muffle elongation adjusting zone or with a heat insulating
member for preventing the muffle elongation adjusting zone from
being heated, such as to prevent the water-free fluid in the
muffle elongation adjusting zone from being evaporated due to
heat or to prevent the heat-resistant connecting member from
being deteriorated by heat.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 is a schematic sectional view illustrating a
vertical muffle-type heat treating furnace according to an
embodiment of the invention;
Fig.2 is a sectional view illustrating a construction
of a muffle elongation adjusting zone in a vertical muffle-type
heat treating furnace according to Embodiment 1 of the invention;
and
Fig.3 is a sectional view illustrating a construction
of a muffle elongation adjusting zone in a vertical muffle-type
heat treating furnace according to Embodiment 2 of the invention.
BEST MODES FOR CARRYING OUT THE INVENTION
A vertical muffle-type heat treating furnace according
to an embodiment of the invention will hereinbelow be described
in details with reference to the accompanying drawings. It
is noted that the vertical muffle-type heat treating furnace
according to the invention is not limited to the following
embodiments and may be practiced in modifications or variations
as required, so long as such modifications or variations do
not deviate from the scope of the invention.
(Embodiment 1)
In a vertical muffle-type heat treating furnace according
to Embodiment 1 of the invention, as shown in Fig.1, metal strips
2 guided through a guide path 1 are led into a muffle 11 via
an upper end thereof, the muffle filled with a reducing gas
such as a hydrogen gas. In the muffle 11, the above metal strips
2 are moved from an upper side to a lower side of the muffle.
The muffle 11 is provided with a heating zone 12 around
an outer periphery thereof, the heating zone equipped with
heating means (not shown) such as a burner. The heating zone
12 heats, from the outside of the muffle 11, the aforesaid metal
strips moved through the muffle 11 from the upper side to the
lower side thereof. The aforesaid metal strips 2 are heated
to about 850 to 1150°C.
The metal strips 2 thus heated are led into a cooling
zone 20 via an extendable muffle elongation adjusting zone 30
provided in a manner to maintain a space between the aforesaid
muffle 11 and the cooling zone 20 in a sealed state. In the
cooling zone 20, the metal strips 2 are cooled so as to be annealed.
Incidentally, the cooling zone 20 may include a slow cooling
zone (not shown) for slow cooling of the metal strips 2.
According to the vertical muffle-type heat treating
furnace of Embodiment 1, as shown in Fig.1, a flange 13 is
assembled to the upper end of the muffle 11. Via the flange
13, the upper end of the muffle 11 is fixed to place by way
of fixing means 14, so that the muffle 11 is suspended. That
is, an arrangement is made such that the muffle 11 may be elongated
downwardly when the metal strips 2 passing through the muffle
11 are heated in the heating zone 12, as described above.
In the vertical muffle-type heat treating furnace of
Embodiment 1, as shown in Fig.2, there are provided, as the
aforesaid extendable muffle elongation adjusting zone 30 for
sealing the space between the muffle 11 and the cooling zone
20, a ring-like container 32 having a predetermined depth for
containing therein a water-free fluid 31 and disposed on the
cooling zone 20; and a cylindrical closing member 34 attached
to a lower end of the muffle 11 via a flange 33 and extended
downwardly from the flange. The closing member 34 is inserted
in the aforesaid fluid 31 contained in the container 32 thereby
sealing the space between the lower end of the muffle 11 and
the cooling zone 20. The aforesaid water-free fluid 31 may
be any fluid that does not affect a dew point of an interior
of the muffle 11. The fluid 31 may employ, for example, commonly
used turbine oil or the like, which is circulated with cooling.
In the vertical muffle-type heat treating furnace of
Embodiment 1, a ring-like cooling wall 35 of water cooling system
is provided on an inside circumferential side with respect to
the cylindrical closing member 34, the wall extending downwardly
from the flange 33 attached to the lower end of the muffle 11.
The cooling wall serves the purpose of preventing the water-free
fluid 31 from evaporating due to a raised temperature of the
aforesaid muffle elongation adjusting zone 30. Furthermore,
an inside circumferential portion constituting the aforesaid
container 32 is also formed of a similar cooling wall 32a of
water cooling system.
According to the vertical muffle-type heat treating
furnace of Embodiment 1, when the metal strips 2 are heated
via the muffle 11 by the heating zone 12 while being moved through
the muffle 11 from the upper side to the lower side thereof
as described above, the muffle 11 is elongated downwardly thus
moving the closing member 34 attached to the lower end of the
muffle 11 downwardly in the fluid 31 contained in the container
32. Thus, the elongation of the muffle 11 is accommodated by
the muffle elongation adjusting zone 30, so that the muffle
11 is prevented from buckling. When the muffle 11 is elongated
downwardly, as described above, the closing member 34 attached
to the lower end of the muffle 11 is merely moved downward in
the fluid 31 contained in the container 32. Hence, the space
between the lower end of the muffle 11 and the cooling zone
20 is maintained in the sealed state, so that the heated metal
strips 2 are prevented from being oxidized as exposed to the
outside air or the like.
In addition, the vertical muffle-type heat treating
furnace of Embodiment 1 is adapted to suppress the temperature
rise of the muffle elongation adjusting zone 30 in the
aforementioned manner and hence, the evaporation of the
water-free fluid 31 is prevented. It is thus ensured that the
furnace is operated in a stable manner over an extended period
of time.
(Embodiment 2)
A vertical muffle-type heat treating furnace of
Embodiment 2 is arranged the same way as the vertical muffle-type
heat treating furnace of Embodiment 1, except that the extendable
muffle elongation adjusting zone 30 for sealing the space between
the muffle 11 and the cooling zone 20 differs from that of the
vertical muffle-type heat treating furnace of Embodiment 1.
In the vertical muffle-type heat treating furnace of
Embodiment 2, a heat-resistant connecting member 36 formed of
an extendable bellows, as the aforesaid muffle elongation
adjusting zone 30, is provided between the lower end of the
muffle 11 and the cooling zone 20, as shown in Fig. 3. The space
between the lower end of the muffle 11 and the cooling zone
20 is maintained in the sealed state by means of the connecting
member 36.
In the vertical muffle-type heat treating furnace of
Embodiment 2, as well, a ring-like cooling wall 37 of water
cooling system is provided on an inside circumferential side
with respect to the connecting member 36 as extended upwardly
from the cooling zone 20, whereas the ring-like cooling wall
35 of water cooling system is disposed on an inside
circumferential side with respect to the cooling wall 37 as
extended downwardly from the flange 33 attached to the lower
end of the muffle 11. The cooling walls serve the purpose of
preventing the deterioration of the heat-resistant connecting
member 36 due to the raised temperature of the muffle elongation
adjusting zone 30.
According to the vertical muffle-type heat treating
furnace of Embodiment 2, when the metal strips 2 are heated
via the muffle 11 by the heating zone 12 while being moved through
the muffle 11 from the upper side to the lower side thereof
as described above, themuffle 11 is elongated downwardly thereby
contracting the heat-resistant connecting member 36. Thus,
the elongation of the muffle 11 is accommodated by the muffle
elongation adjusting zone 30, so that the muffle 11 is prevented
from buckling. Furthermore, the space between the lower end
of the muffle 11 and the cooling zone 20 is maintained in the
sealed state by the heat-resistant connecting member 35, so
that the heated metal strips 2 are prevented from being oxidized
as exposed to the outside air or the like.
INDUSRICAL APPLICABILITY
According to the invention as described above, the
vertical muffle-type heat treating furnace including: the
vertically disposed muffle allowing the metal strips to be led
therein from the upper side to the lower side thereof; the heating
zone for heating, from the outside of the muffle, the metal
strips passed through the muffle; and the cooling zone disposed
at place downstream from the muffle with respect to the moving
direction of the metal strips and serving to cool the heated
metal strips, has the arrangement wherein the upper end of the
muffle is fixed to place. Therefore, the muffle is elongated
downwardly when the metal strips within the muffle are heated
by the heating zone while being passed through the muffle from
the upper side to the lower side thereof. In contrast to the
case where the lower end of the muffle is fixed to place, the
furnace of the invention does not encounter the buckling of
the muffle.
In addition, the vertical muffle-type heat treating
furnace according to the invention is provided with the muffle
elongation adjusting zone which is free to extend or contract
and maintains the space between the lower end of the muffle
and the cooling zone in the sealed state. When the muffle is
elongated downwardly, therefore, the elongation of the muffle
is readily accommodated by the above muffle elongation adjusting
zone, which also prevents the flammable gas containing ahydrogen
gas in the muffle from leaking outside. In addition, it is
ensured that the heated metal strips are prevented from being
oxidized as exposed to the outside air or the like.