The invention relates to a quick heating and cooling mold. More particularly, the invention
relates to an induction heating and quick cooling device for a mold, designed for injection
molding plastic or metal in the liquid or pasty state.
The document EP 1 894 442 in the name of the applicant describes a mold equipped
with an induction heating device and cooling device using the circulation of a heattransfer
fluid. That device of the prior art comprises a mold made up of a fixed part and a
mobile part. Each of the parts can receive an induction heating circuit and a cooling
circuit. Each of these parts consists of a carcass to which a part is added to make up the
molding surface, giving its final shape to the workpiece made in the mold For each part
of the mold, the molding surface is the surface to heat and cool, which surface is in
contact with the material making up the workpiece. The inductors are placed in cavities
that extend under said molding surface. These cavities are most often made by grooving
the underside of said molding zone at the interface between that zone and the carcass of
the mold. For its part, the cooling circuit is made with conduits drilled in the carcass,
which are further away from the molding surface. That cooling circuit carries out both the
cooling of the carcass, which, in a common embodiment, is made in material that is
relatively insensitive to induction heating, and the cooling of the molding surface. Finally,
the carcass of each part is mechanically joined to a support.
That configuration provides satisfactory results but is difficult to implement when the
mold is large or when the molding surface has a complex shape. In such conditions, the
temperature gradients that occur both during heating and cooling lead to the distortion of
the shape of the mold overall, and secondly, on a smaller scale, differential distortion
between the molding zone and the carcass, which differential distortion leads to poor
contact between these two elements and has an adverse effect on the quality of the
cooling, by creating thermal barriers between said two elements, due to the differential
distortion.
The invention is aimed at remedying the drawbacks of the prior art and thus relates to a
mold including a first part comprising a carcass to which a molding zone is added,
making up a mechanical interface between said molding zone and the carcass, and
comprising inductors extending along a direction known as the longitudinal direction, in
cavities between said interface and the molding zone and a cooling device extending at
the interface between said molding zone and the carcass. Thus, the heating and cooling
devices are located as close to the interface as possible, so the differential distortions do
not affect thermal conduction between the heating and cooling devices and the molding
zone. The inductors are easily integrated in shallow grooves, forming cavities after the
molding zone is assembled with the carcass, making it possible to reduce the machining
cost of such a mold.
The invention can be implemented advantageously in the embodiments described below,
which may be considered individually or in any technically operative combination.
Advantageously, the mold according to the invention comprises, in one exemplary
embodiment, at the interface between the carcass and the molding zone, a sheet made
of heat-conducting material that can make up for the differences in shape between the
molding zone and the carcass.
In one particular embodiment, the sheet is made of graphite.
In an alternative of that embodiment, said sheet is made of nickel (Ni).
In another alternative of that embodiment, said sheet is made of copper (Cu).
Advantageously, said sheet is brazed on the molding zone.
In a second embodiment, compatible with the previous one, the inductors are enclosed in
sealed sleeves that can resist temperature of at least 250°C and the cooling device
consists in a heat-transfer fluid flowing in the cavities around the inductors.
In a third embodiment, the cooling device consists in the flow of a dielectric fluid in the
cavities around the inductors. Advantageously, the dielectric fluid is an electrically
insulating oil.
In a fourth embodiment, the cooling device comprises a cavity full of fluid exhibiting a
phase transition under the effect of temperature, the latent heat of transformation of
which is sufficient to absorb the heat of the molding zone at a determined temperature.
In a fflh embodiment, the cooling device includes the injection of gas in the cavities
around the inductors.
Advantageously, the gas is injected in a direction transversal to the longitudinal direction.
Thus, a turbulence is created in the air flow, which turbulence favors thermal exchange.
That turbulence depends on the gas injection pressure and the angle between the
injection conduit and the longitudinal direction of the cavities.
Advantageously, the cooling device of the mold according to the invention comprises, in
this last embodiment, several gas injection points on the length of the cavity along the
longitudinal direction.
Advantageously, the gas is air, injected at a pressure above 80 bars. The use of air as
cooling fluid simplifies the implementation of the device, particularly regarding sealing
problems.
In one particular embodiment, the mold according to the invention comprises a second
induction ,circuit remote from the first one in relation to the interface and supplied with
current by a separate generator.
In one advantageous embodiment, the carcass and the molding zone are made of iron
(Fe) and nickel (Ni) alloy of the INVAR type, the Curie point of which is close to the
transformation temperature of the molded material. Thus, when the material making up
the carcass and the molding zone is ferromagnetic, th&efore sensitive to induction
heating, its expansion coefficient is low. When, as the material heats, its temperature
moves closer to the Curie point, it becomes relatively insensitive to induction heating.
Thus, this constitution makes it possible to control the differential expansion of the
carcass and the molding zone but also that of the carcass and in relation to the
mechanical support of said carcass on the press.
The invention is described below in its preferred embodiments, which are not limitative in
any way, and by reference to figures 1 to 6, wherein:
- figure I is a transverse sectional view of a general exemplary embodiment of the mold
according to the invention;
- figure 2 is a transverse sectional view of a part of the mold according to the invention in
one embodiment comprising a sheet between the molding zone and the carcass;
- figure 3 is a transverse sectional view of the first part of a mold according to an
embodiment of the invention wherein the cooling device comprises a cavity filled with
material capable of changing phases at a given temperature by absorbing latent heat of
transformation;
- figure 4 is a transverse sectional view of a part of the mold according to the invention in
an embodiment wherein cooling is achieved by the flow of heat-transfer fluid in the
cavities receiving the inductors;
- figure 5 is a transverse sectional view of an embodiment of a part of the mold according
to the invention comprising a device for cooling by transverse injection of gas under
pressure into the cavities receiving the inductors, with, in the section SS, the direction of
the injectors in a longitudinal section;
- figure 6 is a transverse sectional view of an exemplary embodiment of a part of the
mold according to the invention comprising two remote and separate induction circuits.
In figure 1, according to a first exemplary embodiment, the mold according to the
invention comprises a first (101) part and a second (102) part. The description below is
provided with the first part (101) as the reference. Those skilled in the art will adapt all
the arrangements and embodiments described relating to this first part (101) to the
second part of said mold. In this exemplary embodiment, the first part (101) is fixed to a
mechanical support (120). Said first part of the mold comprises a carcass (1 11) fixed to
that mechanical support (120) and receives at its distal end of said support (120) a
molding zone (1 12) added to said carcass (1 11) by mechanical fastening (not shown).
Thus, a mechanical interface (115) is created between the carcass and the molding
zone. The mold comprises a heating device comprising inductors (132) extending in
cavities (131) at the interface (115) between the molding zone (112) and the carcass
(1 1 I), wherein said cavities are in this exemplary embodiment obtained by grooving the
inside of the molding zone. A cooling device (140) represented here schematically also
extends at the interface (1 15).
In figure 2 of an exemplary embodiment, the mold according to the invention comprises a
sheet (21 5) between the interface (1 15) and the cooling device. That sheet in graphite,
nickel (Ni) or copper (Cu), which is heat-conducting, is capable of making up for the
differences in shape between the molding zone (1 12) and the carcass (1 11) at the
interface (1 15), so as to allow uniform contact between the carcass and the molding
zone, and thus allow proper heat conduction between the two. The nature of the sheet is
selected depending on the temperature to reach during molding. Advantageously, the
sheet is brazed at the interface between the molding zone and the carcass, with the mold
closed, using the mold heating device for the brazing. Thus the shape adaptation is
perfect.
In figure 3, according to another exemplary embodiment, the cooling device comprises a
cavity (341, 342), which is filled by a material capable of phase transition at a determined
temperature, wherein that phase transition is accompanied by the absorption of high
latent heat. The phase transition is fusion or vaporization. Said material is water, for
example.
In figure 4, according to another exemplary embodiment of the mold according to the
invention, each inductor (132) is placed in a sealed sleeve (431) that is resistant to high
temperature. Depending on the target temperature for inductors, such a sleeve (431) is
made of glass or silica, preferably comprising closed porosities to be both sealed and
capable of withstanding the thermal shock of cooling.* When the temperature of the
inductors reached in operation is limited, for example for molding certain plastics, said
sleeve is made of heat-shrinking polymer, for example polytetrafluoroethylene (PTFE or
Teflon@) for inductor operating temperatures ranging up to 260°C. Thus, the cooling
device is made up of the flow of heat-transfer fluid, for example water, in the cavities
(131) receiving the inductors, wherein said inductors are insulated from contact with the
heat-transfer fluid by their sealed sleeve.
Alternatively, the heat-transfer fluid is a dielectric liquid, for example a dielectric oil. This
type of product is available in the market, particularly for cooling transformers. In that
case, the electrical insulation of the inductors (132) is not necessary.
In figure 5, according to another exemplary embodiment, cooling is carried out by
injecting gas in the cavities (1 31) receiving the inductors (132). To improve the efficiency
of the cooling, the gas is injected under pressure of about 80 bars (80. 10' Pa), by a
plurality of conduits (541) distributed longitudinally along the inductors (132). The
injection is thus carried out at several points, along the inductors, through injection
conduits (542), transversally to said inductors (1 32).
In section SS of a longitudinal sectional view, the injection conduit (542) is directed so
that the direction of the fluid jet in the cavity of the inductor has a component parallel to
the longitudinal direction. Thus, by appropriately selecting the injection angle, effective
cooling is obtained by a turbulence flow of the gas along the inductor (1 32).
The temperature gradients present particularly in the carcass, which is fixed to the
mechanical support, are liable to lead to distortions of the device or differential
deformation stresses. Thus, in an advantageous embodiment, the carcass ( I I I ) and the
molding zone (112) are made in an iron and nickel alloy comprising 64% iron and 36%
nickel, called INVAR, with a low thermal expansion coefficient for temperatures below the
Curie temperature of that material, when the material is in the ferromagnetic state, and
thus sensitive to induction heating.
In figure 6, according to a last embodiment compatible with the previous embodiments,
the mold comprises a second series (632) of inductors remote from the first. The first
(132) and the second (632) series of inductors are connected to two different generators.
Thus, heating is distributed dynamically between the two series of inductors, so as to
limit the deformations of the parts of the mold, which deformations are generated by
thermal expansion combined with the thermal gradients that occur in the heating and
cooling phase.

WE CLAIMS:-
1. A mold including a first part comprising a carcass ( I I I ) to which a molding zone
is added (1 12) making up a mechanical interface (115) between said molding
' zone and the carcass, and comprising inductors (132), extending along a direction
known as the longitudinal direction, in cavities (131) between said interface (1 15)
and the molding zone (1 12), and a cooling device (140) extending at the interface
between said molding zone and the carcass.
2. The mold according to claim 1, comprising at the interface between the carcass
and the molding zone, a sheet (215) made of heat-conducting material that can
make up for the differences in shape between the molding zone (1 12) and the
carcass (1 1 1 ).
3. The mold according to claim 2, wherein the sheet (215) is made of graphite.
4. The mold according to claim 2, wherein the sheet (215) is made of nickel fNi) or a
nickel alloy.
5. The mold according to claim 2, wherein the sheet (21 5) is made of copper (Cu).
6. The mold according to claim 1, wherein the inductors (1 32) are enclosed in sealed
sleeves (431), that can resist temperature of at least 250 "C, and the cooling
device consists in heat-transfer fluid flowing in the cavities (131) around the
inductors (1 32).
7. The mold according to claim 1, wherein the cooling device (140) consists in the
flow of a dielectric fluid in the cavities (1 31 ) around the inductors (1 32).
8. The mold according to claim 7, wherein the dielectric fluid is an electrically
insulating oil.
9. The mold according to claim 1, wherein the cooling device comprises a cavity
(341, 342), full of fluid exhibiting a phase transition under the effect of
temperature, the latent heat of transformation of which is sufficient to absorb the
heat of the molding zone (1 12) at a determined temperature.
10. The mold according to claim 1, wherein the cooling device includes a device (541,
542) for injecting a gas in the cavities ( I 31) around the inductors (132).
11. The mold according to claim 10, wherein the injection of gas is carried out by
injectors (542) extending in a direction transversal to the longitudinal direction.
12. The mold according to claim 11, comprising several injectors (542) for injecting
gas on the length of the cavity (131) along the longitudinal direction.
13. The mold according to claim 10, wherein the gas is air, injected at a pressure
equal to or above 80 bars (80.1 o5 Pa).
14. The mold according to claim 1, comprising a second (632) induction circuit remote
from the first one (132) in relation to the interface (1 15) and supplied with current
by a separate generator.
15. The mold according to claim 1, wherein the carcass ( I I I ) and the molding zone
(1 12) are made of iron and nickel alloy of the INVAR type.