FR2514980A1 - METHOD FOR MANUFACTURING AN ELECTRIC RESISTANCE HEATING BODY, AND HEATING BODY MANUFACTURED ACCORDING TO THIS METHOD - Google Patents

Abstract

The method according to the invention permits the simple and cost-effective production of a high efficiency electrical resistance heating element, by means of which workpieces which are pushed into the heating element can be heated. A heating element produced according to the method consists of a support (8) which is of stable shape, has an annular cross-section over its entire length and consists of a material which conducts heat well and of at least one heat conducting coil (2) whose heat conductor is surrounded in a shape-enclosing manner by a ceramic jacket (3) and whose turns are inserted in a shape-enclosing manner into the support wall, following the circumference of the support (8).

Description

The present invention relates on the one hand to a method
for manufacturing an electric resistance heating body
stick for the heating of susceptible mechanical clamps
also surrounded by this body, in particular soft tools
the mainly intended for worker materials
synthetic, on the other hand a heating body manufactured by this process.

It is so far known to wrap around a
such a molding tool, to heat it, a target of heating
flexible faq electrically insulated. This way of proceeding
results in a space-saving layout, but the cable
heater has only practically linear contact with
the mechanical clamp to be heated, from a transmission
relatively poor calorific from target to said
pibce and an excessively bad coefficient of return.

Furthermore, in this known arrangement the target of
heating runs the risk of being damaged from the outside,
for example by massive synthetic materials
which could lead to the conspiratorial destruction of this target.

The problem to which the invention has provided a solution
therefore consisted in creating a process of the kind described in prb-
bugger with the help of which it is possible to manufacture,
good account and simple manufacturing methods,
heating bodies which, while having a low thickness-
wall sor and a cross section of small dimen
sions, can withstand high loads and
are protected from damage.

The solution that the invention provides to the problem con
sistrum
a) to wind a cone on a shaping mandrel
uncoated heating duct,
b) to be coated with a ceramic slip layer
the heating conductor wound on this mandrel,
c) drying and therefore stabilizing the layer of
slip,
d) removing the mandrel (1) from the winding
whose helical shape has been stabilized by drying the slip layer (3),
e) applying a second layer of slip onto the heating conductor winding,
f) drying this second layer of slip,
g) to drown by molding in a carrier made of a very good conductive material of heat the winding of electrically insulated heating conductor on all sides, this carrier having an annular cross section over its entire length, and
h) b remove the finished heating element from the molding tool.

 The operations e) and f) above are necessary so that the heating conductor winding is electrically insulated also at the places where this winding was in contact with the shaping mandrel retird after drying of the first layer of slip.

 Thanks to the process detailed above, a heating body is obtained by which the heat energy generated by the heating conductor winding is now transmitted without losses first to the wearer in a very good conductive material of heat, more 1 hour, through a large contact surface, to the mechanical part to be heated; the desired effects are thus fully assured. The production of heating bodies according to this process can be carried out with simple means and arrangements.

 In addition, the electric heating conductor winding is protected by the wearer against damage of any kind.

 It is possible, and in some advantageous cases, to provide a second heating conductor between operations c) and d) defined above. Preferably, this second conductor has a reverse winding without that of the promise.

 In a preferred form of implementation, the slip layers which stabilize the shape are deposited by temporary immersion in a slip.

 To drown the heating conductor winding in the carrier, pulverulent materials can be compressed around it; this operation can be completed by molding carried out by additional heating of the compressed powder material. The latter is advantageously composed of copper and glucinium.

The method and the article according to the invention and the technical advantages of these are described in detail below using examples of execution illustrated in the appended drawing; on the latter
FIG. 1 shows in elevation a heating conductor wound helically on a mandrel,
FIGS. 2 and 3 are cross-sectional views through two different manufacturing stages, of the heating conductor wound in short pitch and shown on a larger-than-life scale,
FIG. 4 is a view in longitudinal section of a molding tool in which the heating coil is pressed,
FIG. 5 is a view in longitudinal section of a heating body produced by the method according to the invention,
- Figure 6 is a cross-sectional view of the heating body shown in fig-. 5, and
- Figure 7 is a cross-sectional view of a heating body according to another example of execution.

 The scale of Figures 5 to 7 of the drawing is larger than that of Figure 4 thereof.

In accordance with the method according to the invention, a bare heating conductor 2 is wound helically on a reusable cylindrical mandrel 1, so that the turns do not touch, then the ends of this conductor are bent to become parallel to the axis of the mandrel. 1
(fig.l). Then, the assembly constituted by the mandrel 1 and the heating coil 2 is immersed in a ceramic slip so that a layer of ceramic 3 is deposited on this assembly. The thickness of this layer 3 depends on the consistency of the slip and also on the duration of the immersion.

 After drying of the slip layer 3, this forms on the winding of the heating conductor 2 a sort of substantially tubular support corset which extends between the turns of this winding.

 The mandrel 1 is then removed from the coated winding 2, then the latter is again dipped temporarily in the slip so that it also deposits on the parts of the winding side which, during the first immersion, were in contact with the mandrel 1 and, therefore, are still devoid of ceramic. Afterwards, winding 2 is thus electrically isolated from all sides (fig. 3).

 During a following operation (fig. 4), the winding 2 of the heating conductor thus coated and electrically insulated and whose helical shape has been stabilized and installed on a molding core 4 with which it can title fixed in position correct.

This core 4 carrying the winding 2 is then introduced coaxially into a mold 5 in the form of a sleeve comprising end pieces 6 and 7. The mold 5 is then filled with copper and glucinium powder which is then pressed to stabilize the shape of the filling. This last operation can be carried out simply by exerting an axial pressure on the end pieces 6 and 7 mobil.es in the axial direction in the tool 5.

 But it would be preferable for the copper and glucinium powder to be subjected to pressures also in the radial direction, so that the carrier 8 which surrounds the heating coil 2 and is embedded between the turns of the latter has a density even higher and more uniform. The entire molding tool can then be removed.

 The mandrel 1 can, as well as elsewhere than the assembly of the molding tool, between conical. It is also possible to give a polygonal section to the core 4 of the molding tool and / or to this tool.

 It is also possible to adjust the wrapped winding 2 in position indirectly or directly by the molding tool 5. In addition, it is also possible to fix the coated winding 2 by means of the ends of the heating conductor. in the molding tool.

 The heating body shown in Figs. 5 and 6 consists of a carrier 8 made of a heat conducting material, the shape of which has been stabilized and has an invariable annular section over the entire length of this body. Dens this carrier 8 is arranged a heat conductive winding 2 spaced from both the inner wall and the outer wall of the carrier 8. The turns of this winding 2 are thus embedded in the carrier thickness. The heating conductor 2 is embedded in a ceramic sheath 3 and the ends of this conductor are bent to become parallel to the axis of the assembly and exit from the carrier 8 to be connected to electrical conductors (not shown in the drawing).

Said ends are shown directed in sounds opposite to each other, but nothing prevents them from leaving axially from carrier 8 both in the same direction.

 In the carrier 8 can between provided a second heating winding. In this case, this second winding must have a larger diameter of turns than that of the winding 2 and it is preferable that the two windings are coaxial in the carrier 8.

The invention also makes it possible to use a two-wire winding for the heating conductor 2,
So that the shape stability provided by the ceramic sheath to the winding of the heating conductor is particularly great, it is advantageous that the winding pitch is chosen small enough so that the sheaths of the successive spiros touch and , preferably, interpenetrate as shown in figs. 3 and 5.

 The carrier 8 consists of a copper and glucinium powder formed into a stable form by compression.

 The radial distance between the winding of the heating conductor and the interior wall of the heating body can be varied by using a mandrel, the diameter of which is either substantially the same or greater than the diameter of the core, for winding this conductor. used when pressing the powder. The conductive winding is very close to the interior wall of the finished heating body when the said diameter is substantially the same, while when it is larger, the wall thickness between the interior enclosure empties of the body heating and the conductive winding is also larger.

 The heating bodies according to the invention are used for example to heat the punches of injection molding machines with a heated channel. In this application, the heating elements are threaded on the punches and heat them.

 All the new features described above and / or shown in the drawing are considered, alone or in combination, essential to the implementation of the invention.

Claims (11)

 1. A method of manufacturing an electric resistance heating body for heating mechanical parts capable of being surrounded by this body, in particular molding tools essentially intended for working with synthetic materials, this method being remarkable in that 'it consists  a) winding an uncoated heating conductor (2) on a shaping mandrel (1),  b) coating the heating conductor (2) wound on this chuck (1) with a layer of ceramic slip (3),  c) drying and therefore 3 stabilizing the slip layer (3),  d) removing the mandrel (1) from the winding, the helical shape of which has been stabilized by drying the slip layer (3),  e) applying a second layer of slip to the heating conductor winding,  f) drying this second layer of slip  q) to drown p * nr molding in a carrier (8) in a very good conductive material of heat the heating conductor coil electrically insulated from all sides, this carrier having an annular cross section over its entire length, and  h) removing the finished heating body (2,3,8) from the molding tool (4,5,6,7)  2. Method according to claim 1, remarkable in that a second heating conductor is wound after having carried out operation c) and before carrying out operation d).  3. Method according to claim 2. remarkable in that the second conductor is wound in the opposite direction to the first.  4. Method according to any one of the preceding claims, remarkable in that the layers of slip are deposited which stabilize the shape of the winding by immersing it temporarily in slip.  3. Method according to any one of the preceding claims, remarkable in that the winding is coated in the carrier by compressing around it powdery materials.  6. Method according to any one of the preceding claims, remarkable in that the molding of the carrier is carried out by complementary heating of the pulverulent material which constitutes it.  7. Method according to any one of the preceding claims, remarkable in that the winding is coated in the carrier by compressing around it a powder of copper and glucinium.  8. Electric heating body manufactured according to the method defined in any one of the preceding claims, intended for heating mechanical parts capable of being surrounded by said body, in particular molding tools essentially intended for working with synthetic materials. , this heating body being remarkable in that it comprises on the one hand a carrier (8) made of a material with high thermal conductivity, of annular cross-section over the entire length of this  carrier, on the other hand at least one helical heating coil (2) whose heating conductors are coated with a ceramic sheath (3) and whose turns follow the circumference of the carrier (8) and are embedded in the wall of the last.  9. Heating body as claimed in claim 8, remarkable in that the carrier (8) has circular annular cross sections.  10. Heating body according to claim 8, remarkable in that the carrier (8) has polygonal annular cross sections.  11. Heating body according to claim 8 or 9 or 10, rc-marqurble in that in the carrier (B) are arranged several coaxial helical windings (2), electrically insulated and having different winding diameters.  12. Heating body according to claim 11, remarkable in that the helical windings (2) are in opposite directions.