Note: Descriptions are shown in the official language in which they were submitted.
2042367
M-7764 :
WEL~ING M~FF AND A METHOD FOR THE MANUFACTURE THEREOF
The present invention relates to a welding muff in
accordance with t~ pr~ambl~ ~f ~laim ~ and a method for
manu~acturing a welding muff.
Welding muffs of the above-mentioned type are used
partlcularly for connecting pipes.
A welding muff for pipes of a thermoplastic and/or weldable ~ ;
material is known from European application EP-0222 287. The
welding muff has a heating wire arranged on an inner surface of
the welding muff. The heating wire is coiled into a heating
wlnding and current can be supplied to the heating wire for
welding. On the outer surface of the welding muff is arranged a
relnforcement in the form of a winding placed in a groove or in
the ~orm of a tubular component, wherein the thermal coefficient
of expansion of the reinforcement is smaller than that of the
muff body. ~ -~
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The reinforcement has the purpose to apply with reduced ~;
material used for the muff body the necessary welding pressure
during welding. -
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The above-described welding muff has the disadvantage that ,~
additional work steps are required after the manufacture of the
muff body and that the wire winding consisting of metal or the
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tubular component are not resistant to corrosion, so that a
permanent reinforcement of the welding muff is not provided.
Starting from this prior art, it is the object of the
present invention to propose a welding muff of the above-
described type in which with low material use a permanent
~tlf~ness of the muff is providéd, so that the muff is suitable
~or producing the necessary welding pressure during the heating
process and the welding process and for absorbing the medium
pressure after the pipe connection has been effected. The
welding muff should not be su~ceptible to corrosion and it
should be possible to manufacture the welding muff by a simple,
~utomated procees.
. .
The ob~ect mentioned above is solved in accordance with the
present invention by the characterizing ~eatures o~ claim 1.
Additional advantageous developments of the invention are
oharacterized in the dependent claims.
The invention is illustrated in the attached drawings with
the aid of an example and is described in the following. In the
drawing:
Fig. 1 shows a longitudinal sectional view of an embodiment
of the welding muff.
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Flg. 2 shows another embodiment of the welding muff shown
in Fig. 1.
Fig. 1 shows a welding muff with a muff body 1 composed of
a therTnopla~tic material, such as, polyethylene. A heating wire
wlndlng 3 i~ arranged in the known manner on the inner surface
o~ the muff body 1. The heating wire winding 3 has, for
example, connecting wires 4 or plug connections for the
connectlon to a current source. A reinforcement layer 6 is
arranged on the outer surface 5 of the muff body 1. The
rQinforcement layer 6 has a greater strength than the muff body
1. The reinforcement layer 6 ls preferably connected through an
integral material connection with the muff body.
The ~ollowing are the possible types of reinforcement
layers integrated with the outer surface of the muff body.
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The muff body is manufactured as a molded article by an
in~ection molding procedure or as a pipe section by an extrusion
method from a cross-linkable material wherein the muff body has
an outer dimension which includes the reinforcement layer. ~ "~
Subsequently, the reinforcement layer is produced by a
cross-linking reaction, wherein a chemical and/or physical
cross-linking process can be used for the reinforcement effect
at a predeterminable layer at the outer circumference of the ;;
muff body.
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This cross-linking reaction can be generatsd, for example,
by means of silane cross-linking, by means of peroxidic cross-
linking, by means of electron ray cross-linking or by means of
ultraviolet radiation.
In principle, a cross-linking reaction is a hardening
procedure which is irreversible. This means that thi~ harder or
etronger layer produced by cross-linking is not again
plasticlzed by the heat generated by the heating wire. Thus,
the rein~orcement layer 6 counteracts the radial expansion of
the muf~ material during the welding procedure.
I~ the thermoplastic material used for the muff body i5 not
eultable for good stiffening by meane of cross-linking, then a
compound mu~f body can be produced of two dif~erent
th~rmoplastic materials, wherein the well cross-linking material
le arranged on the outer circumference in an integrally
¢onnected manner with a necessary layer thickness by the
manufacturer of the muff body. This manufacture can be carried
out by coin~ection in an in~ection molded article, by
coextruelon in a pipe eection or by placing an appropriate
component in the in~ection mold.
In a second type of reinforcement layer arranged on the
outer circumference, the reinforcement layer may be composed of
a thermoplastic material which is reinforced with glass-fiber or
carbon-fiber. This reinforcement layer 6 which has a greater
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~tiffness than the muff body is produced by coinjection or
placement of a component in the injection mold when the muff
body i~ manufactured and is then integrally connected with the
mu~ body. In a muff body which i8 a pipe section, the
manufacture is obtained by the coextrusion method.
In Pig. 2, the reinforcement layer 6 is differently
arranged in the muff body 1 as compared to Fig. 1. The
r~in~orcement layer 6 is arranged integrated in the outer region
o~ the muff body 1 and is preferably surrounded on all sides by
the thermopla~tic material of the muff body 1 as shown in the
upper portion of Fig. 2.
The muf~ body 1 pre~erably is an injection molded article,
whereln the reinforcement layer 6 is placed as a tubular
component 7 into the in~ection mold when the muff body is
manufactur-d.
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This tubular component may be composed of a plastic
material reinforced with glass-fiber or carbon-fiber or of
another strong material, such as, metal. Since the component is
completely surrounded by the thermoplastic material, corrosion
is prevented. : ;
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As shown in the bottom portion of Fig. 2, the layer 6
reinforced with glass-fiber or carbon-fiber is arranged within
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the muf$ body 1 which i5 composed of a pipe section, wherein the
manufacture i~ effected by means of coextrusion.
The welding muffs described above are preferably used for
oonne¢tlng pipes with greater diameters and ensure, due to the
lntegrated rein$orcement layer having a higher ~tiffness while
requlrlng less material, the buildup of a welding pressure
roquired for a good weldlng connection and sufficient strength ..
during the duration o$ operation for absorbing the occurring
load~ due to the medium pressure and outer influences.
Bocau~e o$ the integral connection and/or frictional
connectlon o$ the reln$orcement layer with the muff body, the
connectlon can absorb axially acting forces in addition to
radially acting forces.
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