U.S. patent number 3,904,444 [Application Number 05/463,238] was granted by the patent office on 1975-09-09 for method for heat treatment for protected electric elements having a mineral insulator in a rust-proof covering.
This patent grant is currently assigned to Les Cables de Lyon. Invention is credited to Yves Grange.
United States Patent |
3,904,444 |
Grange |
September 9, 1975 |
Method for heat treatment for protected electric elements having a
mineral insulator in a rust-proof covering
Abstract
This method for heat treatment for protected electric elements
comprising at least a conductive core, a coating of an insulating
mineral substance and a covering made of a rust-proof substance, is
applied between two successive drawing operations of a rough from
which the said elements are made. The essential part of the method
consists in re-heating separately the covering and the core, the
rough tempered on leaving the re-heating operations. This method
may be applied, by means of a device comprising a high frequency
furnace, a thermally controlled enclosure and tempering enclosure,
to any protected element having a rust-proof covering.
Inventors: |
Grange; Yves (Paris,
FR) |
Assignee: |
Les Cables de Lyon (Lyon Cedex,
FR)
|
Family
ID: |
9118475 |
Appl.
No.: |
05/463,238 |
Filed: |
April 23, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Apr 25, 1973 [FR] |
|
|
73.14975 |
|
Current U.S.
Class: |
148/526;
266/108 |
Current CPC
Class: |
C21D
8/065 (20130101); C21D 9/52 (20130101) |
Current International
Class: |
C21D
8/06 (20060101); C21D 9/52 (20060101); H01B
013/00 (); C21D 009/60 () |
Field of
Search: |
;148/127,11.5R,154,34,12B ;238/243,244 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stallard W.
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn &
Macpeak
Claims
I claim:
1. Heat treatment method for protected elements having at least one
conductive core, a coating of an insulating mineral substance and
an outside covering made of a rust-proof substance, the said
elements undergoing several drawing operations, a suitable heat
treatment being effected between two successive drawing operations,
the said method comprising the steps of
a. annealing the covering,
b. annealing of the cores, and
c. tempering of the said covering and said cores.
2. Heat treatment method according to claim 1, characterized in
that the step of annealing the covering is carried out by passing
the element through a high frequency furnace.
3. Heat treatment method according to claim 1, characterized in
that the step of the annealing the cores of the element is effected
by passing said element through a thermally controlled
enclosure.
4. Heat treatment method according to claim 1, characterized in
that the step of tempering the covering and cores is carried out by
spraying said element with a coolant.
Description
FIELD OF THE INVENTION
The present invention concerns a method for heat treatment intended
for a particular family of protected electric elements, protected
conductors and protected cables, in which the insulation consists
of a mineral substance and whose external protection is provided by
means of a metallic covering, more particularly a rust-proof
covering. The invention also relates to a device for applying the
method in question, as well as to the products obtained by the
applying of the said method.
DESCRIPTION OF THE PRIOR ART
It is known that, to manufacture elements in the family in
question, a succession of drawing operations which are shaped into
the finished product, starting from a blank having substantially
larger dimensions than the finished product. Throughout this
manufacturing method, it is nevertheless necessary to insert,
between two successive drawing phases, an annealing operation.
A virtually unsolvable difficulty arises, however, in the majority
of cases, because the annealing temperatures required for the
coverings are greater than those imposed for the cores. Thus, there
is a constant danger of obtaining blanks having, on the one hand,
casings which are insufficiently annealed and, consequently, having
insufficient ductility and having poor resistance to corrosion, and
on the other hand, cores which are too annealed and thus made
fragile on account of the presence, in the mass, of certain large
crystals. In the particular case where the cable to be manufactured
is required to be used for constituting thermo-electric cables,
cores which are too annealed lead to the producing, of interference
electromotive forces disturbing the main measuring electromotive
force.
That difficulty for the annealing of the various stainless metals,
is all the greater as the temperatures brought into force come,
within a range going from 850.degree. to 1300.degree.C, whereas
those corresponding to the annealing of the cores are comprised
between about 400.degree. and 1000.degree.C.
It should, however, be stated that, in all cases, temperatures for
the annealing of coverings always correspond, for the annealing of
cores, to a temperature lower than the previous one, each of the
two temperatures being, nevertheless, taken within the range which
was previously assigned to it.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the difficulty thus
revealed, during the effecting of any one of the annealing
operations.
According to the invention, the method constituted by each of these
annealing operations taken separately must be subdivided into three
distinct phases which are spaced out one after the other throughout
the run of the cable being treated.
The first of the three phases concerns exclusively the annealing of
the covering of the rough without taking into consideration that of
the cores. Use is made, for that purpose, of a high-frequency
electrical heating process which, acting by a film effect, succeeds
in bringing the covering very quickly to the required annealing
temperature, long before a substantial heating has occurred in the
mass of the cores.
In the second phase of the method according to the invention, the
cores of the rough are to be brought to their annealing
temperature, taking into account more particularly the slight heat
conductivity of the insulating material, while maintaining the
effective temperature of the covering, which is already annealed,
above a limit level, which is that of the annealing of the cores of
the rough.
Thus, it appears that, as it is a case of a heat treatment to be
effected continuously and, disregarding the values assigned to the
various temperatures to be reached, disregarding also the frequency
of the heating current which should be suited to the thickness of
the covering to be annealed, the most important production
parameters are, in this specific case, the respective lengths of
the elements subject to the three operational phases.
It is, moreover, necessary to take into consideration, when
determining the duration of the intermediate phase of the treatment
according to the invention, of the reaction, during that phase, of
the three components of the cable. Indeed, the covering will have
to undergo a certain cooling, due to the fact that the environment
temperature during that second phase, will be less than that of the
preceding phase; the insulant will become heated up progressively
and much more slowly and will transmit the heat flux to the copper
cores, which will become heated up in their turn.
During the third and last phase of the method according to the
invention, the reaction of the three components of the blank will
be as follows: the tempering of the covering, which will be
suddenly and directly put into contact with the cooling liquid and
will undergo a sudden drop in temperature, until it reaches that of
the structural stabilization sought; the cores will become cooled
down more slowly, because of the slight heat conductivity of the
insulating material.
The device for bringing the method according to the invention into
effect is characterized by the existence of three items which are
independent but situated one after another along the path of the
cable to be treated, the latter being driven along by a suitable
device.
The first of these items is constituted by a high-frequency furnace
comprising essentially a muffle made of a refractory substance,
quartz, for example, that muffle being surrounded by an inductor
conveying the high-frequency supply current of the furnace.
Inside the muffle, a reducing atmosphere or, even, a neutral
atmosphere, is provided by a flow of an appropriate gas.
As has already been specified, particular attention will be given
to the determining of the length of the muffle, as the conditions
required for the annealing of the covering include the keeping of
the latter for a certain time at the required temperature or at a
slightly higher temperature. As for the frequency of the current,
it will be chosen as a function of the thickness of penetration
sought, so that only the covering receives the heat energy
applied.
As for the temperature reached by the cores when they come out of
the furnace, there is no need to be particularly concerned on this
matter; the run speed defined by the condition previously set forth
is indeed such that, taking into account the heat conductivity of
the insulant, the temperature reached by the cores will always be
very substantially below the annealing temperature of the said
covering.
The annealing of the cores of the blank will be effected inside the
second item of the device according to the invention, an element
which is constituted by a thermally controlled enclosure and in
which is to be effected the transmission, to these cores, of the
heat energy stored, during the passing of the rough in the high
frequency furnace by the covering, as, nevertheless, the heat
energy which the cores must receive is strictly limited to the
required value with a view to the annealing of the said cores. The
duration of the stay of the blank inside the thermally controlled
enclosure should be defined as a function of that condition, here
again taking into account the coefficient of heat transmission of
the insulant.
In the majority of cases, the heat energy stored previously by the
covering is over-abundant, this involving the dissipation, during
the following phase, of the corresponding excess.
If, in certain particular cases, the contrary situation occured,
namely, if there were an insufficiency of heat energy at the input
of the controlled enclosure, it would always be possible to supply
to the blank a make-up quantity of heat energy, by any known means,
more particularly by electric heating with resistors or by gas
heating; the thermally controlled enclosure could then be a
furnace.
The said enclosure or, possibly, the furnace which would substitute
it, is crossed longitudinally, right through, by a muffle which may
be made of steel and which must follow that of the high-frequency
furnace, to which it will be assembled by a suitable connecting
means.
The atmosphere inside the said enclosure will also be a reducing or
neutral atmosphere. Preferably, a unique gaseous flow will be
provided, in the downstream to upstream direction, in the assembly
constituted by the said two muffles; in the case of a reducing gas
and if it is required to avoid the setting up of a closed circuit
flow, it would be sufficient to burn the said gas at its output, at
the upstream end of the quartz muffle of the high-frequency
furnace.
The reaction of the various components of the blank inside the
thermally controlled enclosure will be essentially as follows: the
temperature of the covering will undergo a certain drop, between
the input and the output of the enclosure; the cores which had
already undergone a beginning of heating up inside the
high-frequency furnace, will have their temperature raised
progressively as a function of their inherent heat conductivity as
well as of the coefficient of heat transmission of the
insulant.
Indeed only the temperature reached by the cores will fix the
length of the enclosure, it being compulsory for the said
temperature to be that of the annealing sought, taking into account
the period during which the said cores must be kept at that same
temperature or at a slightly higher temperature; this condition
alone will determine, finally, the length of the enclosure. In
general, the temperature in question will remain very clearly lower
than that which the covering of the blank would have reached at the
same instant, that is, at the output of the enclosure.
The third item of the device, namely, a tempering enclosure, in
which the blank will be put into direct contact with the cooling
fluid, which may be water, will be arranged following the
maintaining furnace; a forced flow of the said fluid in the
enclosure will be set up, so as to be absolutely certain that the
blank will effectively be tempered at the required temperature as
soon as it enters inside the said enclosure. The reaction, during
the tempering of the three components of the rough is substantially
the same, even if it is only because of its inherent thermal
inertia and the slight heat conductivity of the insulant; the core
of the rough will cool down less rapidly than the covering.
Needless to say, the fluid-tight connections must, more
particularly, be made at points where the blank will enter the
tempering enclosure and come out therefrom.
The device according to the invention will, of course, be completed
by the drive system of the blank, that drive being effected,
preferably, simultaneously, according to the invention, at the
input and at the output of the device. The drive system could, more
particularly, be constituted, at each of these points, by a double
caterpillar drive belt made of an elastic substance, india rubber,
for example, the said double caterpillar belt driving the blank
along two generating lines diametrically opposite to that belt.
The finished product, that is, the conductor or the cable obtained
subsequent to the successive drawing operations and intermediate
heat treatments, has the following essential characteristics: the
internal structure of the covering is essentially austenitic and
free from slippage lines which are liable to cause as many
beginnings of breakage; whereas the structure of the cores is that
of as many crystalline systems having fine meshes, that structure
being free, more particularly from any accumulation of any size,
constituted by crystals having rounded edges.
Among the characteristics of the cables according to the invention,
in the first instance, it is necessary to mention their faculty of
being folded without breaking at a curve radius of practically
zero. To appreciate the advantage thus constituted, it is
sufficient to state for reference that the curving radius usually
imposed for cables of this type never falls below a limit figure,
representing substantially one and a half times the inherent
diameter of the cable.
Another test to which this type of cable is also frequently
subjected consists in suspending a determined weight at a point of
the cable, at the end of a wire having a sufficient length, to be
able to form several turns round the cable; the latter is then made
to pivot on its axis, between two points, relatively close together
and situated symmetrically in relation to the point of suspension
of the wire; the pivoting movement will continue until the wire is
completely wound. The cable is then made to pivot in the opposite
direction, to unwind the wire completely. The operation is repeated
as many times as is necessary, to make a beginning of breakage
appear. Subjected to this test, a cable obtained according to the
method described by the invention easily withstands, in relation to
a currently manufactured cable, twice the number of wire winding
and unwinding operations before the beginning of breakage
appears.
Other particularities and advantages of the invention will become
apparent from the following description and on referring to the
accompanying drawings, that description and those drawings
concerning a particular embodiment of a device constituting the
applying of the invention and given only by way of an illustration
having no limiting character.
DESCRIPTION OF DRAWINGS
FIG. 1 shows a view, partially in section, of the device of the
present invention;
FIG. 2 is a diagram of the variations in the temperature
respectively in the covering and in the cores of the article being
treated; and
FIG. 3 is a longitudinal sectional view, magnified, of the detail A
in FIG. 1.
DESCRIPTION OF THE INVENTION
In FIG. 1, the rough 1 being treated crosses right through the
device, in the direction of the arrow F, the driving of that blank
being provided by means of the two systems 5 and 6, each of these
systems being constituted by a double caterpillar drive belt.
The first element of the device, shown at 2, comprises a
high-frequency furnace, in which the longitudinal muffle 7, made of
a refractory substance, preferably quartz, is surrounded by the
inductor 8, which is connected to the electric power source, not
shown.
The cable blank 1 then enters inside the muffle 11 of the thermally
controlled enclosure. A neutral atmosphere or, preferably, a
reducing atmosphere prevails inside that muffle 11. The feed tubing
for the corresponding gas, which, entering inside the muffle,
propagates also inside the quartz muffle 7 of the high-frequency
furnace, connecting to the aforesaid muffle 11 by a fluid-tight
clnnection, is seen at 12. The gases leave through the upstream end
9 of the muffle 7, where they may be burnt, as shown at 10.
A forced flow cooling fluid runs through the tempering enclosure 4,
whose function is to bring the cable blank 1 leaving the preceding
enclosure 3 as suddenly as possible to the required temperature,
the said fluid entering simultaneously into the tempering enclosure
4, preferably, through the two ends 13 and 14 of the latter to
leave it through the only output 15, situated essentially in the
middle of the said enclosure 4.
An injector fixed to each of the ends of the enclosure 4 has the
function of making the fluid enter into the said enclosure at a
certain speed, the two jets being directed towards the middle of
the latter in directions opposite to each other, thus causing a
depression at the level of the input connections and output
connections of the rough. This device aims at avoiding or, in any
case, reducing very substantially the leaks of fluid which might
occur at these points.
The detail of the injector is shown in FIG. 3, which will be
described further on.
The thermal diagram in FIG. 2 groups together the curves 16 and 17
diagrammatically showing the variations in the temperatures
reached, at different points of the circuit, respectively, by the
covering and by the cores of the cable blank. That illustration has
been given with reference to the corresponding points of the
treating circuit, such as they are shown in FIG. 1.
Thus, the curve 16, denoting the temperature of the covering,
starting from the ambient temperature, has, when the cable blank
enters into the high-frequency furnace, at the point 18, an
ascending portion which is very steep up to the point 19. The rise
of that temperature continues up to 20 at the output of the
high-frequency furnace, then the cable blank enters into the
enclosure 3. The temperature of the covering then lowers until it
leaves the enclosure at 21, in the diagram; for its part, the curve
17 corresponding to the temperature of the cores shows a much
slighter increase of the temperature inside the high-frequency
furnace, up to the point 24, that increase continuing at a lower
rate, in the enclosure 3, up to the point 25.
The entering of the rough into the enclosure 4 causes a sudden
drop, down to the point 22, in the temperature of the covering,
that of the cores following with a certain delay, down to 23, at
the output of the enclosure.
The variations in temperature of the insulant have not been shown.
It must, however, be stated that the successive drawing operations
cause, on account of the increase in compactness of the insulant,
an increase in its heat conductivity.
FIG. 3 shows one of the injectors 27, intended for inserting, in
the tempering enclosure 4, the cooling fluid.
That injector, in the form of a nozzle, comprises a substantially
truncated cone shaped converging space 28 through which the fluid,
water, for example, is made to penetrate, that penetration taking
place at a certain speed, from the input tubing 13.
In this way, the occuring of leaks of fluid in the tubular space
remaining free between the central bore of the injector, extended
by a tube such as 29 and the cable blank 1, is avoided, as
explained before. Nevertheless, if such leaks should occur, they
could be collected in a suitable receptacle such as 30, fitted with
a drain cock such as 31.
On the downstream side, the injector 27 is connected to the wall 26
of the tempering enclosure 4.
It should be noted that the leaks likely to occur at the point
where the cable blank leaves the enclosure are not specially
detrimental.
The following text sets forth a few approximate figures of the
temperatures read on a particular example of embodiment.
Thus, for a covering made of 18/8 stainless steel, whose melting
point is relatively low, a rated annealing temperature comprised in
a range going from 900.degree. to 1000.degree.C is taken, the said
temperature admitting, for its part, only a tolerance of about
50.degree.C.
If a maximum temperature of 600.degree.C is then fixed for the
annealing of the cores of the rough, with a tolerance in the same
order as previously, the temperature of the cable blanks may be
allowed to rise up to about 300.degree.C at the output of the
high-frequency furnace (reference 24) and the annealing temperature
of 600.degree.C will be found at the output of the enclosure 3
(reference 25).
Inasmuch as concerns the lengths, for a cable blank having an
outside diameter of 22 mm, the figures 0.30, 2.50 and 2.00 m may be
quoted respectively for the high-frequency furnace 2, the thermally
controlled enclosure 3 and the tempering enclosure 4.
The above lengths may respectively be brought to 0.20, 1.00 and
0.50 m for a cable blank having an outside diameter of 4 mm.
Run speeds of the rough, ranging between 0.15 and 2.00 m/min., for
diameters ranging between 22 and 4 mm, correspond to these
lengths.
Contingently, it is possible to indicate, for the current
frequencies, the figures 350 Kc/s and 2 Mc/s respectively for the
already quoted diameters of 22 and 4 mm. As for the voltages, they
may be in the order of 5000 V with, possibly, peaks of 7000 V.
It should also be stated, moreover, that blanks having an outside
diameter of less than 4 mm may, during treatment, more particularly
during finishing runs, have a tendancy to creep; it is then
preferable to set the device according to the invention as a whole
in a vertical position.
* * * * *