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
3. The electric heater for a heat treating furnace according to
claim 7, 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 7, 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 7, 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; the resistance
heat emitting portion 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.
6. The electric heater for a heat treating furnace according to
claim 7, wherein the inner insulating material and the outer insulating
material each comprise a pouch made of a heat-resistant cloth which
encloses a great number of hollow microspheres of microporous thermal
insulating material.
7. 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.
Description BACKGROUND ART
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] In this regard, the above-mentioned electric heater of the
applicant has solved these problems by utilizing a light gauge metal
wire.
[0006] 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.
[0007] 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.
[0008] 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
[0009] An electric heater for a heat treating furnace according
to the present invention is characterized by an electric heater
of which main thermal insulation body is installed at its inside
surface a heating element which is made using a metal wire, wherein
the heating element comprises a plurality of resistance heat emitting
portions, the resistance heat emitting portions being connected
in parallel through a pair of connecting members.
[0010] 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
{fraction (1/10)} of that with a heavy gauge wire. Thus, heat capacity
of the wire is reduced to about {fraction (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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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
[0016] FIG. 1 is an exploded perspective view of an electric heater
according to the present invention.
[0017] FIG. 2 is a transverse cross-sectional view of the electric
heater.
[0018] FIG. 3 is a fragmentary perspective view of the main thermal
insulation body and a heating element of the electric heater.
[0019] FIG. 4 is a development view of a heating element of the
electric heater.
[0020] FIG. 5 is an enlarged transverse cross-sectional view which
shows a connection condition at one end of the heating element.
[0021] 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.
[0022] FIG. 7 is an enlarged cross-sectional view of a part shown
in FIG. 5.
[0023] 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
[0024] An embodiment of the present invention is explained in the
following making reference to the drawings.
[0025] 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).
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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).
[0031] 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.
[0032] 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).
[0033] 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.
[0034] 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).
[0035] 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').
[0036] 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.
[0037] 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.
[0038] 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 (ll) is twenty as noted earlier, and each
5 grooves (21) correspond to each of #1 through #4 resistance heat
emitting portions (61)-(64).
[0039] 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).
[0040] 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).
[0041] 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).
[0042] 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.
[0043] 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.
[0044] 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).
[0045] 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.
[0046] 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.
[0047] 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).
[0048] 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).
[0049] 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.
[0050] All connecting members (91)(92)(94)(95)(104)(105)(1.11)(112)(114)(1-
15), 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.
[0051] 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.
[0052] 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
[0053] 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. |