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Патент USA US2130715

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'- Sept. 20, v1938.
Filed July 9, 1955
men 72) r.- -
Patented Sept. 20, 1938
Marcel Marie Joseph Eugene Coupier, Paris,
Application July 9, 1935, Serial No. 30,578,
In France July 19, 1934
3 Claims. (Cl. 201-457)
It is well known that electric heating elements scribed hereinafter by way of example, without
may comprise a resistant helically wound wire
this description being in any manner limitative.
embedded in mineral insulating material such as
magnesia, the whole being enclosed in an outer
5 metal sheath. '
In the case of rectilinear elements, I may use
a sufliciently hard metallic core constituting a
mandrel which is removed after compression of 5
The mineral insulation may be introduced as a the insulating material, which removal may be
powder inside a metallic tube containing a hel- furthered by a conical shape given to the mandrel
ically wound resistance, after which said tube is <" or by a helical groove thereon which allows the
closed at its ends and is submitted to an outer removal of the mandrel through rotation, said
10 compression through tensioning or restriction of
helical groove being associated. if required with iii
area, so as to provide a good thermic contact and
su?icient compactness.
On the other hand the insulating material,
constituted say by magnesia, may be formed in
15 situ starting from magnesium in which case the
coiled resistance is held in place by reason of the
swelling of the magnesia when forming.
a conical shape of the mandrel.
In the same-case of rectilinear elements, 1 may
also use a central core, threaded or not, of in
sulating material, moulded or machined and
capable of retaining its electric properties at the
temperature of use. It is suf?cient for the ma~
terial of the core to show at the start a resistance
The ?rst method mentioned does not allow a
perfect contact to be obtained as the possible
20 compression may be limited by the fact that when
it is attempted to increase it, there is a risk of
breaking the coiled resistance. The second
method which provides a better contact shows
the drawback that it forms a limitation to the
25 choice of the insulating material, and further-
to deformation suchlthat it may resist the ?nal
compression to which the insulation embedding
the resistant coil is to be submitted. I may use Be
for instance small rods of compressed steatite or
special porcelain or even metallic cores enclosed
in sheaths of mica or the like hard insulating
‘ material.
In the case of a core formed of a cen
tral metal part enclosed in an insulating sheath 25
more that it requires a passage through the metallic stage, whereas it may be of interest to use
of insulating material such as compressed pow
der, the central metal part or core 1n\a\y be re
directly pulverized mineral material which may
moved or not after compression.
be set in place either directly or as compressed
When the resistances are to be folded after they
30 tablets of insulating material to be crushed have been embedded in compressed insulating so
through compression, once in place.
material, I may use for the inner core insulating
My invention has for its object a method for ‘material capable of being folded when hot or cold
making electric heating elements providing the
'without any damage to the resistant wire. Thus
advantages of the ?rst abovedescribed method
for instance the core may be constituted, in the
35 without showing its drawbacks.
It consists in ' part to be bent alone or throughout, by a mandrel 35
using when compressing the pulverized insulating
capable of deformation when hot or cold adapted
material, a solid core holding inwardly the resistto be removed or left in place according as to
ance coil so as to avoid the crushing of the latter whether it is electrically conductive or becomes
and to provide a more considerable compression
so for instance when hot or is not conductive.
40 of the insulation than with the methods used j
I may for instance use a mandrel of insulat- 40
ing material such as agglomerated mica and glass
The insulation may be simply'in the pulverized
state, or form tablets of compressed powder.
As to the solid core; it may be of insulating or
45 conducting material. Thus it may be of a pul-
60 h
verable compressed material similar to or diifer-
I may also in certain cases use a metal or
ent' from the pulverized insulating material, of
material-softening when hot, or fusible or friable
or of any desired metal.
alloy which melts su?lciently underneath the
melting point of the resistance and of its sheath
for preventing any alloying therewith and al
According to its nature or according to the de-
‘formations to be imparted to‘ the heating resistant element after compression of the insulating
material, the core may be left in place after said
compression or be removed. -.
which softens when very hot and thus allows
the bending of the hot core, while holding the
resistant winding which remains properly cen
tered inside its sheath of compact powder.
Di?erentpossible forms for execution are de-
lowing it to flow out so as to leave the central 50
part of the ?nished resistance free afterfcom
pression, I may in particular use to this end,
aluminium alloys which allow-an oxidation of any
traces of metal remaining after,‘ melting so as
to transform them into insulating particles. It 55
is, of course, also permissible to use any' other
metal or other suitable material which is fusible
enough to allow its being removed through melt
ing before or after the shaping of the resistant
One embodiment of my invention is shown,
solely by way of example, in the attendant draw
ing, wherein the single view is a longitudinal,
broken section through an assembly according
10 to my invention.
By way of example the single ?gure shows a
device according to the invention before it is
submitted to outer compression.
The device
comprises a cylindrical mandrel i of aluminium
it of the resistant wire and will resist the com
pression without breaking but it will crumble
into ?ne granular particles, which cannot damage
the wire, when the ?nal shape is being given
to the resistant element.
‘ I may of course introduce insulating powder
in any suitable manner round the winding and
in fact in the case of magnesia insulation ‘pre
pared in situ I may compress it after formation
over a removable or stationary core so as to im
prove its compactness.
In the case where the core, set in place dur
ing compression, is subsequently removed, it is
possible to submit the element constituted by‘
15 or an alloy thereof or of other convenient mate
the external tube or sheath, the compressed
mineral insulation and the winding inside which
wire /2 constituting the heating resistance; the a vacant space remains, to any of the usual treat
mandrel and wire are disposed inside a metallic
ments rendering the insulating material less
sheathing 3 and the hollow. space remaining be
hygroscopic or more compact such as for in»
20 tween the mandrel and sheathing is ?lled with stance an impregnation with boric acid.
On said mandrel is wound a conducting
mineral powdered material, say with magnesia.
The-sheathing is closed at both ends by conven
ient plugs to prevent the magnesia from falling
out; the assembly thus prepared is then sub
25 mitted to a pressure (rolling or drawing). After
said operation the assembly may eventually be
bent hot or cold, and then submitted to a tem
perature such that the mandrel melts and ?ows
out without damaging the wire.
The core may also be constituted by insulat
ing material of the same nature as or of a na
ture di?erent from the insulating materialisur
rounding the conducting coil. This core, being
thus made of compressed powder will, when'the
resistant element is deformed, be reduced into
powder without any modi?cation in volume. It
continues therefore ?lling without any lack of
continuity the inside of the element. The core
may in particular be constituted by small cylin
40 drical rods of very grea ly compressed magnesia.
This core may as stat d hereinabove, be com
pound and comprise an ‘inner part of metal en
closed inside a system of cylindrical rods of com
pressed insulating material which maintains the
insulation between the winding and ‘the core
during bending when the metal has not been
previously removed.
The heating element may be made by winding
the winding over the core or else by engaging
the core inside the winding and causing the coils
to bear against the core through a. traction ex
erted on the ends of the winding while it is en
gaged inside the ‘outer sheath and the insula
' tion is compressed round it.
When the outer insulating material is formed
I have only mentioned hereinabove the appli
cation of my invention to heating elements; but
obviously it applies also and still better to con
ducting windings/ and solenoids for which the
setting in place and winding over a core are ren
dered more easy by the larger size of the coils.
What I claim is:
l. A method for making an electric resistance
which comprises winding a conductor as a helix
over a ,core of aluminium, embedding said core 30
and conductors in a mineral insulation material,
enclosing said embedded core and conductor
within a metal sheath, subjecting said sheath
and its content to the action of pressure, bend
ing the whole to a desired shape and then sub 35
mitting it to the action of a temperature above
the melting point of the core, whereby the melted
core runs out of the sheath.
2. A method i'or'making a substantially cylin
drical electric resistance which comprises wind
ing a conductor as a helix over a core of alu
minium, embedding said core and conductor in
a mineral insulation material, enclosing said
embedded core and conductor within a metal
sheath, subjecting said sheath and its contents 45
to the action of pressure, and then submitting
it to the action of a temperature above the melt
ing point of the core, whereby the melted core
runs out of the sheath.
3. A method for making a curved electric re
sistance which comprises winding a conductor
as a helix over a core of aluminium, embedding
said core and conductor in a mineral insulation
material, enclosing said embedded core and con
ductor within a metal sheath, subjecting said
sheath and its contents to the action of pres
, of compressed tablets or blocks, I prefer giving
the core a rate of compression which is higher _ sure, bending the sheath and its contents to the
than that of the compression exerted on the
outer insulating material.
The core may also be constituted by a high
ly tempered glass rod. Such a core is sum
ciently resistant to allow a tight winding round
desired shape, heating said sheath and contents
su?iciently to melt the aluminium core, and al
lowing said melted core to run 011’.
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