Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21 76088
Tubular Heating Element for Heating Hot Channel Nozzles and
the Like
The invention concerns a tubular heating element for heating
hot channel nozzles or similar cylindrical bodies made of
steel having an axial through channel for fluids, in
particular molten substances, consisting of at least one
heating coil which is embedded so as to be insulated in a good
heat-conducting metal which forms the tubular shape and which
is preferably surrounded on the outside by a metal casing made
of a bad heat-conducting metal.
Heating elements of this type are known in the prior art. In
this case, tubular heating elements are used e.g. to heat hot
channel nozzles, said heating elements being furnished with an
outer metal casing having heating elements in the form of
coils situated on the inside along the inner surface of the
metal casing. This heating coil is usually a helical tube
cartridge. In addition, this coil is embedded in a good heat-
conducting metal, e.g. cast with this metal, as a result of
which a smooth casing surface is produced on the inside.
Due to the fact that the hot channel nozzles or similar
cylindrical bodies consist of steel, while the tubular heating
element as a good heat-conducting metal comprises another
metal with a different heat expansion, the inside diameter of
the cast heating element expands more than the nozzle part
made of steel, in particular during the heating phase. This
results in the danger that the heating element on the nozzle
can shift in axial direction or can even fall off completely
from the nozzle. Normally, such tubular heating elements are
merely pushed onto the respective nozzle or the like so as to
have a good seat.
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Proceeding from this prior art, the object of the invention is
to create a tubular heating element of the known type which is
also held securely and axially immovable on the nozzle element
or the like, especially in the heating phase.
To solve this object, the invention essentially proposes that
the tubular heating element have fastening means, by means of
which it can be fastened to the nozzle body or similar
cylindrical body.
It is possible to permanently fix the heating element to the
nozzle body or cylindrical body by means of these fastening
means, so that a secure seat on the nozzle body or the like is
ensured, even during the heating phase and the different
expansion of the heating element relative to the nozzle body
associated therewith.
In addition, it is provided in a known manner that brass
stands out as a good heat-conducting metal and high-grade
steel as a bad heat-conducting material.
In an especially preferred embodiment, it is provided that
setscrews are provided as fastening means and screwed into
radial threaded bores which pass through the metal casing and
the embedding material.
Furthermore, it is especially preferred that the fastening
means, in particular the setscrews, seal flush with the outer
surface of the metal casing or are arranged sunk vis-à-vis
these in the ideal mounted position.
It is hereby attained that the fastening means, in particular
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the setscrew, does not protrude beyond the casing of the
heating element in a troublesome manner, insofar as it is in
the ideal position. A covered and inconspicuous arrangement
is also possible by means of the arrangement of the setscrew
and the corresponding threading in the heating element itself,
whereby the arrangement of the fastening means is possible
even without additional structural features. Thus, it is, for
example, not necessary to arrange projections or the like in
axial direction on the heating element which must be passed
through by the fastening means and fastened to the nozzle body
or the like with the fastening means. The overall
installation length of the heating element is, therefore, not
increased or changed by the additional arrangement of the
fastening means.
Furthermore, it is preferably provided that fastening means,
in particular setscrews, are arranged on each axial end of the
heating element respectively, namely in the wedge-shaped areas
which are not covered by the heating coil.
In the helical arrangement of the heating coil, wedge-shaped
areas which are not covered by the heating coil result at the
start of the winding of the heating element and at the end of
the winding, proceeding from the connecting area, which is
usually located on the one end of the heating element and
radially leads into the heating element from the outside. The
threaded bore or the like can bé easily placed in this area
for the fastening means, without this arrangement in any way
interfering with the run of the coil.
An especially preferred further embodiment is seen therein
that two fastening means, in particular setscrews, are
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arranged on each of the two ends of the heating element,
diametrically opposite one another.
In order to avoid damage to the casing of the nozzle or the
like, it can additionally be provided that the ends of the
fastening means, in particular setscrews, to be attached to
the casing of the nozzle or the cylindrical body are
flattened.
It can also be provided that the casing of the nozzle or the
cylindrical body has counterbores for receiving the end of the
fastening means or the setscrew.
By means of this construction, it is, for example, possible to
attach the setscrew, even with the flattened end, to the
casing of the nozzle or the like, whereby it fits into the
counterbore of the casing or the like. If a relative radial
expansion of the heating element, which follows the screwed-in
setscrew by force and occurs due to the different heat
expansion, then the closing shape between the end of the
setscrew or the like and the casing of the nozzle or the
cylindrical body is ensured since the counterbore and the
screw-in depth of the fastenings means, in particular the
setscrew, is so large that the end of the fastening means or
the setscrew still engages in the counterbore of the casing of
the nozzle or the like, even when there is a maximum
difference in expansion. A radial or axial shifting of the
heating element is thus eliminated.
Alternatively, it is also possible that the fastening means,
in particular the setscrew, can be screwed into a threading in
the casing of the nozzle or of the cylindrical body and led
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through a boring coaxial thereto in the metal casing and
embedding material, whereby the fastening means project at
least partially into the boring in the ideal mounted position.
In this embodiment, the threading is not in the heating
element itself, but in the casing of the nozzle or the
cylindrical body, so that the respective setscrew or other
fastening means can be screwed into this threading. In this
case, there is a clearance of motion between the fastening
means (setscrew) and the casing of the heating element, so
that the latter can expand radially (during heating) without
the fastening means partaking in this movement or hindering
this movement. Nevertheless, it is ensured that an axial
shifting or radial turning of the heating element relative to
the nozzle body or cylindrical body is prevented.
An example of an embodiment of the invention is shown in the
drawing and shall be described in greater detail in the
following.
Fig. 1 shows a heating element of the invention in the
central longitudinal section;
Fig. 2 shows the same, seen from the front.
The tubular heating element, generally designated with 1, is
used to heat hot channel nozzles or the like. A hot channel
nozzle of this type, which is not shown in the drawing, is
usually made of steel. It has an axial through channel for
molten substances.
In the example of the embodiment, the heating element 1
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consists of two heating coils 2, 3 which are led off on the
one end of the heating element 1 via radially extended
connecting lines. In the embodiment, the heating coils 2, 3
are merely arranged in the two end areas of the heating
element 1 and wound in a tight helical position. In this way,
a wedge-like zone is produced in the area 5 or 6 which is free
of the heating coil 2 or 3.
The heating coil consists of a helical tube cartridge, that
is, of a self-supporting insulated heating element. The
heating element 1 has a metal casing 7 made of high-grade
steel on the outside which receives the coils 2, 3 wound on
the inside along this casing 7. The heating coils are thereby
cast with a sealing compound 8 of brass, the result of which
is a smooth cylindrical surface on the inside.
Due to the differing expansions of the nozzle body (not shown)
relative to the embedding material, consisting e.g. of cast
brass, the inside diameter of the heating element 1 expands
more in the heating phase than the nozzle body made of steel,
so that a secure seat of the heating element 1 on the nozzle
body made of steel is not ensured.
In order to obtain a secure seat of this type, the tubular
heating element 1 has fastening means 9 in the form of
setscrews, by means of which it can be fastened to the nozzle
body or the like. The setscrews 9 are screwed into radial
threaded bores 10 which pass through the metal casing 7 and
the embedding material 8. The setscrew 9 is thereby
dimensioned in such a way that it seals flush with the outer
surface of the metal casing-7 in the ideal screw-in position
or is arranged sunk vis-à-vis the latter.
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In the embodiment shown, a fastening means 9 each is allocated
to each axial end of the heating element 1, namely in the
respective wedge-shaped zones 5 or 6 which are not covered by
the heating coil 2, 3. The two fastening means 9 are thereby
arranged diametrically opposite one another on the two ends of
the heating element 1, as can be seen from the illustration in
Figures 1 and 2.
The ends of the fastening means 9, attached to the casing of
the nozzle or the like, are flattened, so that the nozzle
casing or the like is not damaged. It can also be provided
that the casing of the nozzle or the cylindrical body has
counterbores for receiving the ends of the fastening means 9,
so that these are still secured in the counterbores even when
there is a greater expansion of the heating element 1 relative
to the nozzle body and a radial or axial shift of the heating
element 1 vis-à-vis the nozzle body is thus prevented.
The invention is not restricted to the example of an
embodiment, but can be varied in many ways within the scope of
the disclosure.
All new individual and combined features disclosed in the
descripton and/or drawing are considered to be essential to
the invention.
