Abstrict
An electric heater has an elongated cylindrical quartz tube provided
at each end with a terminal and a heater coil having one end connected
at each terminal has a helical portion disposed within the tube
and extending the length thereof. A ceramic support disposed in
the tube extends the length of the helical portion of the coil and
is formed with a heat-reflecting longitudinal groove having mutually
inclined opposing sides which flank at least a portion of the circumference
of the turns of the helical portion. Each of the opposing sides
of the groove engage the turns of the helix tangentially in point
contact, the support holding the helical portion with the turns
thereof in tangential point contact with the inner surface of the
tube. Each turn of the helical portion is supported at three separate
points.
Claims
I claim:
1. An electrical heater comprising:
an elongated cylindrical quartz tube;
a pair of terminals, one terminal being provided at each end of
said elongated cylindrical quartz tube;
a heater coil having one end connected at each of said terminals
and a helical portion within said elongated cylindrical quartz tube
and extending the length thereof; and
a ceramic support provided in said elongated cylindrical quartz
tube and extending the length of said helical portion, said ceramic
support being formed with a heat-reflecting longitudinal groove
having mutually inclined opposing sides which flank at least a portion
of the circumference of the turns of said helical portion, each
of said opposing sides engaging the turns of the helix tangentially
in point contact, said ceramic support holding said helical portion
with the turns thereof in tangential point contact with the inner
surface of said elongated cylindrical quartz tube, whereby each
turn of said helical portion is supported at three separate points,
each of said terminals comprising:
a cylindrical ceramic cap fitted over an end of said elongated
cylindrical quartz tube and formed with an opening through which
an end of said heater coil can be extended,
a metal sleeve fitted over a portion of said cap and connected
to said end of said heater coil, and
a metal spring clip mounted on a ceramic block and having opposing
curved arms adapted to removably engage said metal sleeve and forming
a mounting for said elongated cylindrical quartz tube, said portion
of said cap extending axially and being cylindrical and of reduced
diameter and said opening being a channel formed in the surface
thereof and communicating with the interior of said elongated cylindrical
quartz tube, and said sleeve being of slightly smaller diameter
than said portion and being provided with a longitudinal split for
allowing said sleeve to be force-fitted over said portion and overlying
said channel, whereby said end of said heater coil is connected
thereto, said cap being further provided with a second opening in
axial alignment with the longitudinal axis of said heater coil for
mounting a thermocouple therein extending within the turns of said
helical portion.
2. The heater defined in claim 1 wherein said arms of said spring
clip are connected by a web having a tongue extending laterally
therefrom, said tongue being formed with a threaded opening receiving
a screw terminal for providing electrical connection to said heater
and a second opening formed in said web between said arms for bolting
said spring clip to said ceramic block, said spring clip being of
unitary construction.
3. The heater defined in claim 1 wherein said arms of said spring
clip are connected by a web, said spring clip being further provided
with a tongue fastened to said web and extending laterally therefrom,
said tongue being formed with a threaded opening receiving a screw
terminal for providing electrical connection to said heater and
a second opening formed in said web between said arms and in alignment
with a third opening formed in said tongue for bolting said spring
clip to said ceramic block.
4. The heater defined in claim 2 or claim 3 wherein said ceramic
block comprises a recess for receiving the end of said screw terminal
enabling said spring clip to lie flush on a first surface of said
block, a first throughgoing bore formed in said first surface in
alignment with said second opening in said web, said first bore
having an enlarged end portion formed at a second surface opposite
said first surface, said enlarged end portion having a hexagonal
profile for receiving and holding a nut recessed from said second
surface against rotational movement, a second throughgoing bore
formed in said second surface and having an enlarged end portion
formed at said first surface, said enlarged end portion of said
second bore having a hexagonal profile for receiving and holding
against rotation the hexagonal head of a bolt recessed from said
first surface, and an indexing projection formed on said second
surface remote from the enlarged end portion of said second bore.
Description FIELD OF THE INVENTION
The present invention relates, in general, to electric heaters,
and, more specifically, to a clip-mounted quartz tube heater having
a helical heating coil disposed within the quartz tube.
BACKGROUND OF THE INVENTION
Quartz tube electric heaters are well known in the art and usually
comprise a quartz tube in which a heater wire is suspended. In an
effort to obtain greater heat output, these heater wires are sometimes
formed as helical coils which are suspended in the tube. However,
at the high temperatures at which these heaters operate, the resistance
wires suffer a reduction in stiffness and the unsupported turns
of the helix tend to collapse, losing their symmetry, which causes
"hot spots" in the wire and further loss of symmetry,
until a burn-out of the coil occurs.
Another disadvantage of conventional quartz tube heaters is that
they radiate heat over 360.degree., when a more limited area of
radiation is usually desired. In an effort to overcome this drawback,
external reflectors are positioned around a portion of the circumference
of the quartz tube, but these reflectors usually become tarnished
and dirty, losing their efficiency.
A good example of efforts to overcome these disadvantages can be
seen in U.S. Pat. No. 3,699,309, in which a coil is disposed within
a quartz tube between a reflective body therein and the inner surface
of the tube, the reflective body having a planar surface.
The disadvantage of this example is that the coil is only supported
at two diametrically opposite points of the turns thereof, so that
the coil can still collapse between these points, becoming elliptical
instead of circular, while the planar reflective surface gives a
radiation spread of no less than 180.degree., which for most applications
is still too wide.
A still further disadvantage of the known quartz tube heaters is
the fact that the tubes are mechanically mounted within the heater
housing, so that if a burn-out of the quartz tube occurs, which
is more likely in these types of heaters, removal of the heater
is awkward and time consuming.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to provide
an improved quartz tube heater in which the coil thereof is prevented
from collapsing.
It is another object of the present invention to provide a quartz
tube heater in which the angle of reflected radiation is less than
180.degree..
It is still another object of the invention to provide a quartz
tube heater element which can easily be removed from the heater
housing.
SUMMARY OF THE INVENTION
The above and other objects of the invention are attained in a
quartz tube heater in which the tube thereof is elongated and cylindrical
and is provided at each end with a terminal to which is connected
an end of a heater coil having a helical portion disposed within
the tube and extending the length thereof.
A ceramic support disposed in the tube extends the length of the
helical portion of the coil and is formed with a heat-reflecting
longitudinal groove having mutually inclined opposing sides which
flank at least a portion of the circumference of the turns of the
helical portion, each of the opposing sides engaging the turns of
the helix tangentially in point contact, the support holding the
helical portion with the turns thereof in tangential point contact
with the inner surface of the tube, whereby each turn of the helical
portion is supported at three separate points.
The end terminals on the tube are each comprised by a cylindrical
ceramic cap fitted over the end of the tube and formed with an opening
through which an end of the heater coil can be extended and directly
connected to a metal sleeve fitted over a portion of the cap or
connected thereto through an intermediate terminal. A metal spring
clip mounted on a ceramic block has opposing curved arms adapted
to removably engage the metal sleeve and forms a mounting for the
quartz heating tube.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features and advantages of the invention
will become more readily apparent from the following description,
reference being made to the accompanying drawing, in which:
FIG. 1 is an axial sectional view through a quartz heater tube,
according to the invention;
FIG. 2 is an end view taken from the right side of FIG. 1, showing
one embodiment of the spring clip of an end terminal;
FIG. 3 is an end view taken from the left side of FIG. 1, showing
another embodiment of the spring clip of an end terminal;
FIG. 4 is a sectional view taken along line IV--IV of FIG. 1, showing
one embodiment of the support;
FIG. 5 is a sectional view similar to FIG. 4, showing another embodiment
of the support; and
FIG. 6 is a sectional view similar to FIG. 5, showing still another
embodiment of the support.
SPECIFIC DESCRIPTION
FIG. 1 of the drawing shows an axial section through a quartz heater
tube generally designated 1, and comprises an elongated cylindrical
quartz tube 2 provided at each end with a respective terminal generally
designated 3 and 4.
A heater coil 5 has a helical portion 5' disposed in the tube 2
and extending the length thereof, with ends 3' and 4' connected
respectively to terminals 3 and 4 directly or through an intermediate
terminal.
A support 6a of ceramic or other refractory material is disposed
in the tube 2 and extends the length of helical portion 5' of the
coil 5, and is formed with a heat-reflecting longitudinal groove
6a', which extends the length of the support and has mutually inclined
opposing sides 6a" forming a V, which can best be seen in FIG.
4, the sides 6a" flanking at least a portion of the circumference
of the turns of the helical portion 5', each of the opposing sides
6a" engaging the turns of the helix tangentially in point contact,
the support 6a holding the helical portion 5' with the turns thereof
in tangential point contact with the inner surface 2' of the tube
2, whereby each turn of the helical portion 5' is supported at three
separate points P1a, P2a and P3, point P3 always being in the same
12 o'clock high position in all the embodiments of the support.
The end terminals 3 and 4 each comprised by a ceramic cap 7, fitted
over an end of the tube 2 and cemented in place. The caps 7 have
an axially extending portion 7' of reduced diameter, in the surface
of which there is formed a longitudinal channel 8 which communicates
with the interior of tube 2 and through which respective ends 3'
and 4' of the coil 5 are drawn and spotwelded at 9' to split metal
sleeves 9, which are of a slightly smaller diameter than axially
extending portions 7' and are force-fitted thereon. The caps 7 are
also provided with passageways 10 lying in axial alignment with
the longitudinal axis of helical portion 5', and through which a
thermocouple T, shown in phantom lines in FIG. 1, can be fitted
to extend within the turns of the helix.
Identical ceramic mounting blocks 11 form part of respective terminals
3 and 4 and are mounted on a heater housing not shown in the drawing
but understood to be of a standard type for quartz tube heaters.
Mounted on the block 11 of terminal 4 is a metal spring clip 12
having curved opposing arms 13 connected by a web 14 and adapted
to removably engage the sleeve 9. A tongue 15 extends laterally
from web 14 and is provided with a threaded opening 16, which receives
the screw terminal 17 for the power connection. The screw terminal
17 extends into a recess 18 formed in the block 11 for this purpose,
while a bore 19 formed in the block lies in alignment with an opening
22 formed in the web 14, through which a threaded fastener extends
into an enlarged hexagonal portion 19' and engages a nut held against
rotation therein, this serving to fasten the spring clip in place
on the block with the nut recessed from the lower surface of the
block to avoid short circuiting. Another bore 20 in the block also
has an enlarged hexagonal portion 20', which receives in a recessed
fashion the hexagonal head of a bolt which fastens the block 11
to the heater housing, the block being oriented thereon by an indexing
projection 11'.
The cap 7 and block 11 of end terminal 3 are identical to those
of terminal 4 and need not be described in further detail, except
to say that the end 3' of coil 5 is received in the channel 8 and
spotwelded at 9' to sleeve 9. However, spring clip 12' of terminal
3 differs from that of the spring clip 12 of terminal 4 in that
the spring clip 12' is of two-piece construction, with the opposing
curved arms 13' and connecting web 14' being unitary and spotwelded
at 21 to the laterally extending tongue 15', which underlies the
web 14' and has an opening 22' therein in alignment with an opening
22" formed in the web 14', these openings serving the same
purpose as opening 22. The tongue 15' is also provided with a threaded
opening 16' for receiving a screw terminal 17. Except for the unitary
and two-piece construction of respective spring clips 12 and 12',
their function and operation are identical.
In FIG. 5 there is shown another embodiment of the invention in
which the ceramic support 6b is formed with a heat-reflecting longitudinal
groove 6b', which extends the length of the support and has mutually
inclined opposing sides 6b", which are joined by another side
6b"' to define therewith a trapezoid. In this particular feature
of the invention, the contact points P3, P1b and P2b are equally
spaced around the turns of the coil.
In FIG. 6 there is shown still another embodiment of the invention
in which the ceramic support 6c is formed with a longitudinal groove
6c', in which the mutually inclined opposing sides 6c" are
curved and join to form a portion of an ellipse in which the major
axis M thereof lies coplanar with the longitudinal axis L of the
helical portion 5' of coil 5. In this embodiment, point contact
is made with the turns of helical portion 5' at P3, P1c and P2c.
FIGS. 4, 5 and 6 show with particular clarity the three point contact
with the coil in all of the embodiments, which offer superior support
to the coil which will greatly reduce collapsing of the turns thereof,
while the different groove configurations offering that support
also reflect the heat in the much more desirable narrow band width
in which the heat can be concentrated where it is needed most.
In operation, the quartz tube heater is used like any standard
electric heater, except that the quartz tube is held in place in
a heater housing by the spring clips which allow the tube to be
snapped in and out of place in case of a burn-out of the resistance
element, which is analogous to changing a light bulb in a lamp,
rather than throwing the lamp away. |