Abstrict
A heating element (12) made of metal wire is installed at an internal
circumferential surface of a cylindrical main thermal insulation
body (11) of an electric heater according to the present invention.
The heating element (12) comprises a plurality of resistance heat
emitting portions (61) (64) (71) (74) (81) (84) as segments along
its length direction. The resistance heat emitting portions (61)
(64) (71) (74) (81) (84) are connected in parallel.
Claims
What is claimed is:
1. An electric heater for a heat treating furnace comprising: a
heating element which is made using a metal wire and installed at
an inside surface of a main thermal insulation body; an inner thermal
insulating material layer and an outer thermal insulating material
layer jacketing outside the main thermal insulation body; and the
heating element comprising a plurality of resistance heat emitting
portions which are disposed in parallel in the circumferential direction
of the main thermal insulation body, wherein: a pair of connecting
members which are flat in thickness direction of the main thermal
insulation body and extend along the circumferential direction of
the main thermal insulation body are positioned between a inner
thermal insulating material layer and the outer thermal insulating
material layer respectively at a distance corresponding to a span
between the heat emitting portions; and ends of each of the resistance
heat emitting portions pierce through the main thermal insulation
body and the inner thermal insulating material layer, and are connected
to a connecting member of corresponding side, respectively.
2. The electric heater for a heat treating furnace according to
claim 1, wherein the inner insulating material and the outer insulating
material layers each comprise a pouch made of a heat-resistant cloth
which encloses a great number of hollow microspheres of microporous
thermal insulating material.
3. The electric heater for a heat treating furnace according to
claim 1, wherein: a sleeve is fitted on respective ends of respective
resistance heat emitting portions, and fixed by at least either
of calking and welding; a number of open holes corresponding to
the number of resistance heat emitting portions are opened in respective
said connecting members; and the sleeve is put through an open hole
at corresponding end, and the sleeve and fringe of the open hole
are welded.
4. The electric heater for a heat treating furnace according to
claim 1, wherein: a cap is fitted on respective ends of respective
resistance heat emitting portions, and fixed by at least either
of calking and welding; a number of open holes corresponding to
the number of resistance heat emitting portions are opened in respective
said connecting members; the cap is put through an open hole at
corresponding end, and the cap and fringe of the open hole are welded;
and the resistance heat emitting portions, the connecting members,
and the caps are formed out of a same kind of material.
5. The electric heater for a heat treating furnace according to
claim 1, wherein: a plurality of parallel grooves not less than
the number of the resistance heat emitting portions are formed on
the inside surface of the main thermal insulation body; each of
the resistance heat emitting portions is formed to sinuous shape
with an amplitude bigger than width of the groove, supported unitedly
by the main thermal insulation body with both end portions of the
amplitude plunging beyond the sidewalls of the corresponding groove
into the main thermal insulation body, and extending over to at
least one neighboring groove.
Description BACKGROUND ART
The present invention relates to an electric heater for heat treating
furnaces, and, particularly, it is suitably used for heat treating
equipments to perform, for example, heat treatments such as oxidation,
diffusion, and/or CVD of semiconductor wafers.
Conventionally, an electric heater is known which uses a heating
element installed at an internal circumferential surface of its
cylindrically shaped main thermal insulation body, the heating element
being formed to coil shape out of a metal wire referred to as "heavy
gauge" whose diameter is 7 to 10 mm.
Then, as a replacement to the above-mentioned electric heater,
the present applicant proposed previously an electric heater which
is disclosed by a Japanese Patent Application Publication Number
2001-267261. This utilizes a metal wire referred to as "light
gauge" of which diameter is 1 to 3 mm, and a plurality of parallel
grooves are formed at an internal circumferential surface of its
main thermal insulation body extending along its length direction
at an interval in its circumferential direction. And a heating element
which is made out of a continuous matal wire and formed to sinuous
shape with an amplitude bigger than width of the groove is supported
unitedly by the main thermal insulation body with both end portions
of its amplitude plunging beyond the sidewalls of each corresponding
groove into the main thermal insulation body, and meanders in the
circumferential direction of the main thermal insulation body so
as to extend over all grooves from one to next.
Because a heavy gauge metal wire is used in the aforementioned
conventional electric heater, weight of the heating element is heavy,
then, it has a large heat capacity. A problem with such a heater
is that a fast heat-up or cool-down cannot be achieved. Besides,
energy loss per heat cycle is large.
In this regard, the above-mentioned electric heater of the applicant
has solved these problems by utilizing a light gauge metal wire.
However, since there is a difference in current specification between
the former and the latter types of heater, the latter type heater
cannot be employed directly to an existing heat treating equipment
where the former type heaters have been installed. This is because
wire diameter is different between both types, then, in order that
both types of electric heater have an equal output, the latter has
to be driven under a high voltage and small current condition, while
the former under a low voltage and large current condition. For
example, a step-down transformer is required for a low voltage and
large current drive, while transformer-less usage is presupposed
for a high voltage and small current drive.
Difference in power supply specifications between two types of
conventional heater was mentioned above. Then, to enable an utilization
of a light gauge electric heater with improved thermal characteristics
to replace an existing heat treating equipment where a heavy gauge
heater has been used, compatibility in physical or constitutional
aspect is also required in addition to its adaptation to power supply
specifications. In other words, compatibility related to such as
outside diameter, inside diameter, and length of the heater is required,
and further, compatibility related to such as division of temperature
zones and its power allotment is required to achieve a temperature
profile.
Purpose of the present invention is to provide an electric heater
which can heat-up and cool-down at a high rate, and moreover, can
be driven at a low voltage and large current.
DISCLOSURE OF THE INVENTION
An electric heater for a heat treating furnace according to the
present invention is characterized by an electric heater for a heat
treating furnace comprising: a heating element which is made using
a metal wire and installed at an inside surface of a main thermal
insulation body; an inner thermal insulating material layer and
an outer thermal insulating material layer jacketing outside the
main thermal insulation body; and the heating element comprising
a plurality of resistance heat emitting portions which are disposed
in parallel in the circumferential direction of the main thermal
insulation body, wherein: a pair of connecting members which are
flat in thickness direction of the main thermal insulating body
and extend along the circumferential direction of the main thermal
insulating body are positioned between the inner thermal insulating
material layer and the outer thermal insulating material layer respectively
at a distance corresponding to the span of the heat emitting portion;
and ends of the resistance heat emitting portion pierce through
the main thermal insulation body and the inner thermal insulating
material, and are connected to a connecting member of corresponding
side, respectively.
With the electric heater for a heat treating furnace according
to the present invention of which main thermal insulation body is
installed at its inside surface a heating element which is made
using a metal wire, since the heating element comprises a plurality
of resistance heat emitting portions connected in parallel, the
resistance value of the heating element is lower than that of a
heating element made of a continuous metal wire. Although the heating
element uses a light gauge metal wire, it can be driven under low
voltage and large current condition which is equivalent to that
of the heating element using a continuous heavy gauge metal wire.
In addition, weight of the wire can be reduced to as small as about
1/10 of that with a heavy gauge wire. Thus, heat capacity of the
wire is reduced to about 1/10. This allows one to provide a heater
which can heat-up and cool-down at a high rate, and moreover, can
be driven at a low voltage and large current.
Besides, because a pair of connecting members are made to interpose
between the plural resistance heat emitting portions, the resistance
heat emitting portions need not be connected directly among each
other.
Further, in case where an inner thermal insulating material layer
and an outer thermal insulating material layer jacket outside the
main thermal insulation body, and where both connecting members
are positioned between the inner thermal insulating material layer
and the outer thermal insulating material layer, then, the connecting
members can be isolated from high-temperature section of the heater,
therefore, unfavorable influence of the parts of the parallel connections
on temperature profile can be avoided, and their thermal distortion
hardly occurs as well, which secures a construction with high thermal
stability.
Furthermore, in the event where a sleeve or a cap is fitted on
each end of respective resistance heat emitting portion and fixed
by calking and/or welding, a number of open holes corresponding
to the number of resistance heat emitting portions are opened in
each connecting member, and where a sleeve or a cap is put through
an open hole at a corresponding end, the sleeve or the cap and fringe
of the open hole are welded, and where the resistance heat emitting
portions, connecting members, and sleeves or caps are formed out
of a same kind of material, then, the discontinuity of physical
property, particularly discontinuities of metallurgy and thermal
expansion coefficient can be avoided between the resistance heat
emitting portion, the connecting member, and the sleeve or the cap,
thus, even higher thermal stability can be achieved.
Additionally, in case where a number of parallel grooves not less
than the number of the resistance heat emitting portions are formed
at the inside surface of the main thermal insulation body, each
resistance heat emitting portion is formed to a sinuous shape with
an amplitude bigger than width of the groove, supported unitedly
by the main thermal insulation body with both end portions of the
amplitude plunging beyond the sidewalls of each corresponding groove
into the main thermal insulation body, and extending from one groove
over to next one at least, then, a construction is achievable which
enables easy use of a light gauge metal wire for a heating element.
Moreover, when the inner insulating material and the outer insulating
material each comprise a pouch made of heat-resistant cloth which
encloses a great many hollow microspheres of microporous thermal
insulating material, both the inner and the outer thermal insulating
materials exhibit extremely high thermal insulating characteristic
due to the function of the hollow microspheres.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an exploded perspective view of an electric heater according
to the present invention.
FIG. 2 is a transverse cross-sectional view of the electric heater.
FIG. 3 is a fragmentary perspective view of the main thermal insulation
body and a heating element of the electric heater.
FIG. 4 is a development view of a heating element of the electric
heater.
FIG. 5 is an enlarged transverse cross-sectional view which shows
a connection condition at one end of the heating element.
FIG. 6 is an enlarged transverse cross-sectional view which shows
a connection condition of a part other than the one shown in FIG.
6.
FIG. 7 is an enlarged cross-sectional view of a part shown in FIG.
5.
FIG. 8 is an enlarged cross-sectional view which shows a modified
example of a part shown in FIG. 8.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention is explained in the following
making reference to the drawings.
Referring to FIGS. 1 and 2, an electric heater comprises a cylindrical
main thermal insulation body (11), a heating element (12) installed
at an internal circumferential surface of the main thermal insulation
body (11), layers of inner thermal insulating material (13) and
outer thermal insulating material (14) jacketing thereof intervened
by a flexible mat as a buffer (22) consisting of ceramic fiber covering
the external circumferential surface of the main thermal insulation
body (11), and a metal shell (15) mantling the contour of the outer
thermal insulating material layer (14).
With reference to FIG. 4, the electric heater is, from left to
right successively, allotted for left zone (L), center zone (C)
and right zone (R). In FIG. 1, only the left zone (L) and part of
the center zone (C) are shown.
The main thermal insulation body (11) is vacuum formed ceramic
fiber, which is heat insulating material. At the internal circumferential
surface of the main thermal insulation body (11) a plurality of
parallel grooves are formed extending along the length direction
of the main thermal insulation body (11) at an interval in its circumferential
direction. Concretely, the number of grooves (21) in this embodiment
is twenty.
The heating element (12) consists of iron-chromium-aluminum alloy,
and uses a light gauge metal wire of which diameter is 1 3 mm, as
explained in the beginning.
Part of how a heating element (12) is installed is shown in FIG.
3. The heating element (12) is formed to sinuous shape. Amplitude
of the sinuous shape heating element (12) is made bigger than width
of the groove (21). The heating element (12) formed to sinuous shape
is supported unitedly by the main thermal insulation body (11) with
both end portions of its amplitude plunging beyond the sidewalls
of the grooves into the main thermal insulation body.
In FIG. 3, at the left end of first groove (21) from this side,
one end of the heating element (12) pierces through bottom of the
groove (21) and is made to protrude out of the main thermal insulation
body (11). From this end, the heating element (12) meanders, extends
to the right in the groove (21), and reaches the right end of the
groove (21). At the right end of the groove (21), the heating element
(12) pierces through the ridge (wall) in between and gets into the
adjoining groove (21) which is second from this side. From there,
then, toward the opposite direction, it extends to the left in the
second groove (21). From the left end of the second groove (21),
it gets into the third groove (21), and extends therein to the right,
the same direction as in the first groove (21) of this side. In
this way, the heating element (12), meandering in the circumferential
direction of the main thermal insulation body (11), moves between
grooves (21) next to each other sequentially from the first groove
(21) of this side to the fifth groove (21) from this side. The heating
element (12), after extending in the fifth groove (21) and reaching
its right end, pierces through all the walls (ridges) between adjacent
grooves (21) there from, and returns back to the right end of the
first groove (21) of this side. From the right end of the first
groove (21) of this side, the other end of the heating element pierces
through bottom of the groove (21), and is made to protrude out of
the main thermal insulation body (11).
The above is an example, and configuration of the heating element
(12) may be modified appropriately for optimum design. For example,
instead of piercing through walls (ridges) between adjacent grooves
(21), a heating element (12) may be configured so as to lay over
them.
The inner thermal insulating material (13) includes two types,
long pouch (31) and short pouch (32), each formed in half cylinder
shape. Each pair of the long or short half cylinder pouches (31)
(32) of the same type abut at their hems (31a) (32a) surrounding
the main thermal insulation body (11) to make a complete long or
short cylindrical pouch (31) (32), respectively. The long and short
pouches (31) (32) are arranged alternately in this order along the
length of the main thermal insulation body (11) from its left edge,
and thus, the whole external surface of the main thermal insulation
body (11) is surrounded by the long and short pouches (31) (32).
Additionally, respective abutting position at hems (31a) (32a) of
adjacent long and short half cylinder pouches (31) (32) is shifted
between each other along the circumferential direction of the main
thermal insulation body (11).
The long and short pouches (31) (32) respectively encloses hollow
microspheres of microporous thermal insulating material in a heat-resistant
cladding-material made of silica or glass fabrics, and is compressed,
for example, to form half cylinder shape. It is hardly flexible,
and not easy to deform. Each hollow microsphere is of micron-order
size containing silica as main constituent, and accumulates to include
a large number of micropores. Silica fabrics as cladding-material
are resistant to temperatures higher than 600 degrees Celsius. Inside
diameter of a hollow microsphere is made to be less than mean free
path of the atmospheric gas molecules. Therefore, it is understood
that the atmospheric gas molecules are isolated by walls of hollow
microspheres, and that the probability of a gas molecule being bounced
by the wall becomes so high that collision between gas molecules
is suppressed. Consequently, both the long and short pouches (31)
(32) show a superior thermal insulating characteristic.
Although the outer thermal insulating material (14) differs from
the inner thermal insulating material (13) in diameter etc., it
consists of both long and short pouches (31') (32') in the same
manner as the latter. These long and short pouches (31') (32') are
arranged in the same way as the long and short pouches (31) (32)
of the inner thermal insulating material (13), yet surrounding the
entire outside surface of the inner thermal insulating material
(13). However, arranging order of long and short pouches (31) (32)
(31') (32') along the length of the main thermal insulation body
(11) is opposite between the inner thermal insulating material (13)
and the outer thermal insulating material (14), and thus, the positions
where the facing edges (31b) (32b) (31b') (32b') of the neighboring
cylindrical long and short pouches (31) (32) (31') (32') meet are
shifted along the length of the main thermal insulation body (11).
Additionally, two slits (32c) (32d) are opened in the short pouch
(32') of the left end of the outer thermal insulating material (14).
The shell (15) is made of a plurality of stainless steel sheets
(41) formed in half cylinder shape. The two shell sheets (41) abut
their hems (41a) each other in similar way as two pouches (31) (32)
(31') (32'), and cover the outer thermal insulating material (14).
In one of the shell sheet (41) of the left end are opened slits
(41c) (41d) corresponding to slits (32c) (32d) of the short pouch
(32').
Again, referring to FIG. 4, overall configuration of a heating
element (12) is explained in detail. In FIG. 4, the main thermal
insulation body (11) is developed in its circumferential direction,
and the heating element (12) as viewed from outside direction of
the main thermal insulation body (11) is represented.
The heating element (12) comprises a group of resistance heat emitting
portions for left zone (51L), a group of resistance heat emitting
portions for center zone (51C), and a group of resistance heat emitting
portions for right zone (51R). These groups of elements (51L) (51C)
(51R) are configured such that they are controllable independently
each other as described below.
The group of resistance heat emitting portions for left zone (51L)
comprises four resistance heat emitting portions #1 through #4 (61)
(64), which are like splitting a heating element (12) along its
length. The #1 through #4 resistance heat emitting portions (61)
(64) usually employ portions having a same electric resistance value,
are disposed in this order from top to bottom in FIG. 4, and connected
electrically in parallel. The fourth resistance heat emitting portion
(64) corresponds to the heating element (12) that was explained
referring to FIG. 3. The first through third resistance heat emitting
portions (61) (63) are supported by the main thermal insulation
body (11) in the same manner as the fourth resistance heat emitting
portion (64). The number of grooves (21) of the main thermal insulation
body (11) is twenty as noted earlier, and each 5 grooves (21) correspond
to each of #1 through #4 resistance heat emitting portions (61)
(64).
In the same way as the group of resistance heat emitting portions
for left zone (51L), the group of resistance heat emitting portions
for center zone (51C) comprises #1 through #4 resistance heat emitting
portions (71) (74), and the group of resistance heat emitting portions
for right zone (51R) includes #1 through #4 resistance heat emitting
portions (81) (84). These resistance heat emitting portions (71)
(74) (81) (84) are also supported by the main thermal insulation
body (11) in the same manner as the fourth resistance heat emitting
portion (64) of the group of resistance heat emitting portions for
left zone (51L).
At the left side of the group of the resistance heat emitting portions
for left zone (51L) are disposed two, i.e. upper and lower, first
connecting members (91) (92) in strip form so as to extend along
top to bottom direction. The first upper and lower connecting members
(91) (92) are connected by first joint bar (93). Similarly, at the
right side of the group of the resistance heat emitting portions
for left zone (51L) are disposed two, i.e. upper and lower, second
connecting members (94) (95) in strip form. The second upper and
lower connecting members (94) (95) are connected by second joint
bar (96).
In the same way as the group of resistance heat emitting portions
for left zone (51L), the group of resistance heat emitting portions
for center zone (51C) comprises connecting members (101) (102) (104)
(105) and joint bars (103) (106), and the group of resistance heat
emitting portions for right zone (51R) includes connecting members
(111) (112) (114) (115) and joint bars (113) (116).
The left ends of the first and second resistance heat emitting
portions (61) (62) of the group of resistance heat emitting portions
for left zone (51L) are connected to the first upper connecting
member (91), and their right ends are connected to the second upper
connecting member (94). The left ends of the third and fourth resistance
heat emitting portions (63) (64) of the same group of resistance
heat emitting portions (51L) are connected to the first lower connecting
member (92), and their right ends are connected to the second lower
connecting member (95). Parallel connections of the group of resistance
heat emitting portions for left zone (51L) are realized by the above
method. The embodiment of the connection is similarly applicable
to the groups of resistance heat emitting portions for center zone
(51C) and right zone (51R) as well.
To the first lower connecting member (92) to the group of resistance
heat emitting portions for left zone (51L) is connected first terminal
(121) of L-shaped strip. To the second upper connecting member (94)
to the group of resistance heat emitting portions for left zone
(51L), and to the first upper connecting member (101) to the group
of resistance heat emitting portions for center zone (51C) is connected
left middle terminal (122) made of L-shaped strip, extending over
both connecting members (94) (101). Further, to the second upper
connecting member (104) to the group of resistance heat emitting
portions for center zone (51C), and to the second upper connecting
member (111) to the group of resistance heat emitting portions for
right zone (51R) is connected right middle terminal (123) made of
L-shaped strip, extending over both connecting members (104) (111).
To the first lower connecting member (115) to the group of resistance
heat emitting portions for right zone (51R) is connected second
terminal (124) made of L-shaped strip. Thus, the heating element
(12) is connected such that the group of resistance heat emitting
portions for left zone (51L), the group of resistance heat emitting
portions for center zone (51C), and the group of resistance heat
emitting portions for right zone (51R) are electrically controllable
independently.
FIG. 5 shows where connections are made between left ends of the
first and second resistance heat emitting portions (61) (62) of
the group of resistance heat emitting portions for left zone (51L)
and the first upper connecting member (91). Over a respective end
of the first and second resistance heat emitting portions (61) (62)
is fitted first and second cylindrical sleeves (131) (132), respectively.
Each sleeve (131) (132), caulked and then welded, is fixed to the
corresponding end of the resistance heat emitting portions (61)
(62). The connecting member (91) has a round hall (141) and an oval
hole (142). In agreement with the round hall (141) and the oval
hole (142), two round holes (143) (144) are opened in the inner
thermal insulating material (13). The first sleeve (131) pierces
through the two round holes (141) (143). The external surface of
the sleeve (131) is welded to the fringes of the round holes (141)
(143). The second sleeve (132) pierces through the oval hole (142)
and the round hole (144). The external surface of the sleeve (132)
is welded to the fringes of the oval hole (142) and the round hole
(144).
An embodiment of the above-mentioned welding of the first sleeve
(131) is shown in detail in FIG. 7. A welding aperture (145) is
opened through the circumferential wall of the first sleeve (131).
A weldment (146) is formed so that the welding aperture (145) is
full. Further, another weldment (147) is formed which jackets the
end of the first resistance heat emitting portion (61), the first
sleeve (131) and its perimeter.
FIG. 6 shows where a connection is made with the first lower connecting
member (92) at left end of the third resistance heat emitting portion
(63) of the group of resistance heat emitting portions for left
zone (51L). Over an end of the third resistance heat emitting portion
(63) is fitted a cylindrical sleeve (151) also. An oval hole (162)
is formed in the connecting member (92). A round hole (163) is opened
in the inner thermal insulating material (13) in agreement with
this oval hole (162). The sleeve (92) pierces through an oval hole
(162) and a round hole (163), and is connected to the connecting
member (92) by welding. Additionally, FIG. 6 shows the way how the
first terminal (121) is welded to the connecting member (92). Although
not explained, an embodiment of the connection of other resistance
heat emitting portions (64) (71) (74) (81) (84) with connecting
members (91) (94) (95) (104) (105) (111) (112) (114) (115), and
an embodiment of the connection of the connecting members (94) (101)
(104) (111) (115) with terminals (122) (123) (124) are similar to
the above.
FIG. 8 shows an example using a cap (181) instead of a cylindrical
sleeve (131) shown in FIG. 7. A welding aperture (182) is opened
to the circumferential wall of the cap (181). The welding aperture
(182) is filled with a weldment (183), and top face of the cap (181)
and its periphery are covered with another weldment (184).
Moreover, the first and second sleeves (131) (132) pierce through
the inner thermal insulating material (13) and are made to protrude
to its outside, where they are welded to the first upper connecting
member (91). The first upper connecting member (91) is put between
the inner thermal insulating material (13) and the outer thermal
insulating material (14). Referring to FIG. 6, the sleeve (151),
to which is inlayed the third resistance heat emitting portion (63),
also pierces through the inner thermal insulating material (13)
and is made to protrude to its outside, where it is welded to the
first lower connecting member (92). Additionally, the first lower
connecting member (92) is put between the inner thermal insulating
material (13) and the outer thermal insulating material (14). Although
not illustrated, other connecting members (94) (101) (104) (111)
(115) are, likewise, put between the inner thermal insulating material
(13) and the outer thermal insulating material (14).
Again, referring to FIG. 1, one can understand that the first terminal
(121) is put through the slits (32d) (41d) on one side of the outer
thermal insulating material (14) and the shell (15), while the left
middle terminal (122) is put through slits (32c) (41c) on the other
side.
All connecting members (91) (92) (94) (95) (104) (105) (111) (112)
(114) (115), joint bars (93) (96) (103) (106) (113) (116), terminals
(121) (122) (123) (124), sleeves (131) (132) (151), and a cap (181)
consist of a same material as the heating element (12), namely metal
of iron-chromium-aluminum system. By this configuration, one can
overcome the troublesome sigma brittleness which is peculiar to
this material, namely a property of getting brittle once it is heated
to a high temperature.
As is apparent from the above-mentioned description, the present
invention is neither limited to a heater of cylindrical shape, nor
to semi-conductor heat treating furnace. For example, it can also
be applied to flat plate type heater, and therefore find many applications
in engineering fields.
Moreover, the present invention is not limited to what is disclosed
in the above description, and various kinds of modifications are
possible without departing from the scope of the present invention.
INDUSTRIAL APPLICABILITY
The electric heater of the present invention is particularly suitable
for use as an electric heater for heat treating furnaces to perform,
for example, heat treating equipments for oxidation, diffusion,
and/or CVD of a semiconductor wafer. |