DE7327559U - Polytetrafluoroethylene tube with electrically conductive areas - Google Patents

Description

FRANKFURT (MAIM), January 24, 1974

Pierre Viennot, 32, rue des Garrements, Glaaart (Hauts-de-Seine), Pr an "α-calibr.

Made of jrolyte tetrafluoroethylene With electrically conductive areas J * ¹

The innovation concerns tubular bodies made of i-olyteti-aXluor- ■ ethylene, which are made electrically conductive.

-. ■ lexi ^ je Pipelines made of lolytctraxluorL / bhyloxii üie for the transport of liquid or gasxör:. ". I (those substances under pressure" are intended, in particular for Ξν / corners of the Lui'tfuhrtindustrie, must with regard to the Laterialei / jenüchui'xei ) comply with very strict regulations. Regardless of your required mechanical behavior, such products are required to have an internal electrical conductivity which "favors the dissipation of the static charges arising as a result of the rare flow." The serious inconveniences caused by such charges are known. In particular are to be mentioned

a) the risk of fire in the event of flammable substances being transported,

b) the Bntlaäiuig across the pipe wall, with this can be broken,

To remedy these disadvantages are also: uen l ^; 3-l'atentr; writings 2 1o8 759, 3 o7o 759, 3 o7o 132 and : ■: 7 ^l j> 2 637 different proposals known. The classic ... ',. Uoi'ührunn consisted in incorporating into the Honrmasce a: luhtriuch leading jtof.i', u ::. orCj .Lear in cjir.jr .: Oo ^ amtvolunen το1α \ · τγ ι ni t.nnri: ru! iaoii, · ΐ ;. ¹ JiOoGS Yov`` .uen .u'krt jsuooli su oiiiei. in his ^ eijuuten h; i :::.: c hetero, c.ier. hatorial, wodurcii the physical una i'ol.-jlich you: .cc! .anirehe: - ' ¹ . ^ i: oj: _t ; chuit'jn entwined verder .. Dice botrii '.' t in: jb; n vii ^ orc;: ie i-oror; i " _u : '. t.

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It has now been found that excellent results are obtained when using pipes that are predominantly made of the pure polymer "and have continuous strips made of an aqueous dispersion of the polymer with a content of at least one powdery, electrically conductive material in an amount uia <δ \ χ 50 70 of the polymer, / icr are divided _e

The subject of the increase in prices is a pipe made of polytetrafluoroethylene with electrically conductive areas, characterized in that? these areas consist of continuous parallel to the pipe axis Bands "consist of a small cross-section in relation to the pipe cross-section and a mixture of polytetrafluoroethylene and at least one powdered electrically conductive material in an amount up to 50 percent by weight, based on the mixture.

Jas powdery conductive material is advantageous from graphite, carbon black or mixtures of these, it can but metal powder can also be used, e.g. B. of copper and its alloys, aluminum, gold, silver, gerrites and other conductive powders.

In the preferably used graphite or graphite-carbon black mixture, the best results are obtained with mixtures with Einein content of about 2o percent by weight of graphite and carbon black 1o $ as well as with mixtures having a content of about 35 i »C pure graphite.

The percentage of conductive powder incorporated can be varied from 1 to 50 weight percent. The lower one The limit depends on the conductivity that is to be achieved. The upper limit results from the fact that nan a sufficiently low viscosity of the mixture is required to achieve this in the case of a product of increased porosity and with interstices or cavities of small dimensions can be cast without pressure.

The innovation has the advantage that in contrast to the known Executions the granulometry of the admixed conductive

Powder is not critical. With spielav / eiße the powder can have a grain size of 4 to 5o μm. The invention Conductive Eäncor produced have a high conductivity in the order of magnitude of 500 mi kr 0 ampere -niter 1 volt per cm.

The conductive tapes germinate on the inside, on the Outer surface or be provided in the mass of the pipe. In the latter case, we are dealing with Rohrfcr.aii; e canals which part.llel to the pipe axis'> n.

Pipes according to hexification: "Can be produced by deforming a preform in a fitting press and using powdery electrically conductive material, using a single preform made of pure polytetrafluoroethylene with continuous channels running parallel to the pipe axis and with a small cross-section during üxtrusion in these channels an aqueous dispersion of polytetrafluoroethylene with a G-ehalt from 1 to 5o weight percent άοε pulverförmi ^ egg conductive Ilaterials pours and the Vox molding in a ^ h known V / else extruded.

Pipes geiaäss the firing can be manufactured with conventional "expansion presses, starting from a single preform of the polymer, on which continuous longitudinal grooves or channels are provided, into which the conductive mixture is poured without pressure during extrusion of the preform.

The preform is z. Bo a cylindrical pipe socket made of pure polytetrafluoroethylene, the wall thickness of which corresponds to the dimensions of the annular space between the die and the extrusion die. One or more continuous channels are provided on the cylindrical inner surface and extend linearly in the longitudinal direction of the tube. The number and distribution of these channels can vary. Their dimensions are small in relation to the transverse dimensions of the pipe and

lie ζ. B. in the order of a few millimeters.

Such channels can also be on the outer wall or in an annular shape Distribution within the Y / andung of the preform can be seen

The preform is produced in the middle of a use borrowed press using a pressure that is just sufficient is to agglomerate the lolytetrafluoroethylene powder. This gives an increased porosity, which the subsequent impregnation with the conductive mixture or the penetration of the same favors.

The preform is then introduced between the die and the extrusion die a mixture consisting of polytetrafluoroethylene and conductive powder is poured into the channels.

As a precursor or starting material for the conductive Gemiscli one uses an aqueous dispersion of · polytetrafluorethylene, as it is commercially available «

The Geiuisoh is easy to make by adding a elastic vessel arranges a magnet, which by a usual magnetic stirrer is set in rotation and the mixture is homogenized, v / uring the entire operating time of the extrusion, the mixture can be used without difficulty be kept in constant motion and is available at all times in a completely homogeneous jj'orm.

To produce the mixture, for example, 200 g of graphite are used in an aqueous dispersion of 500 g of dee polymers incorporated. Commercially available polytetrafluoroethylene disperse ions can be used for this purpose Use with a dry content of about 60 ^.

An exemplary embodiment is provided to further explain the invention described with reference to the drawings.

1 is an axial section of a preform

Fig. 2 is a radial section along the line II - II of the Mg. i'ig * 3 is a section analogous to FIG. 2 of a modified one Embodiment on a reduced scale

Fig. 4 is the section of an extrusion die with a preform according to the invention

Fig. 5 shows the device of Fig. 4 during the extrusion. Fig. 6 is the cross section of a pipe according to the invention

According to FIGS. 1 and 2, the preform 1 is a cylindrical pipe socket made of pure poly te met Iv. Ethylene, its interior and outer diameter of the e-g and die 3 (Fig. 5) corresponds to the extrusion press on the inner wall of the preform 1 there are three continuous open channels 4 'in the illustrated case, each offset by 120 ° are. The dimensions of the channels are a few millimeters »

The channels 4 can. dip, as shown in Fig. 3, within be arranged on the wall or on the outer surface of the preform. 3s, a different number of channels can also be selected be.

, / ie seen in FIGS. 4 and 5, the preform is 1 in known .eise between the inner wall of the Itiatrize 3 and the mandrel 1o introduced into the press.

The preform can be produced in a separate device outside the extrusion line. But you can also connect a corresponding device with the extrusion system to a fabrication unit and make the casting of the conductive mixture in the extrusion cylinder. Here, π «τι receives a significantly better centering in the finished tube with the corresponding mechanical advantages.

In the channels 4 is an aqueous dispersion of polytetrafluoroethylene Poured in with a high content of graphite or a mixture of graphite and Ruse · Das! Singlessen

can by means of the outflow pipe 5 of the Misohgefiisses or on be done in another way

While the stamp 2 of the Ertrusionspreeae against the forming Part 6 of the die protrudes, "forms around the spinous process 7 of the tubular body 8 and arise along its inner wall three strips 9 made of a conductive mixture that was previously poured into the channels 4 as a dispersion without printing

As soon as the channels 4 are filled, the extrusion » druok exercised. This is where the previous impregnation takes place perfect and sins Oberfläohenbisä ^ ng gwisolien the leading Mixture and the preform brought about. Pig. 6 shows the finished pipe. It consists of the actual tubular body 11 made of polytetrafluoroethylene and the three conductive ones Bands 12 on the inner surface. The bands 12 measure only a few hundredths of a millimeter in cross section.

Since the proportion of graphite and / or the cover in the polytetrafluoroethylene dispersion fluctuates within very wide limits you can get any drill with good dielectric properties, high resistance to cracking, low porosity and excellent properties regarding the dissipation of electrostatic charges.

By having a liquid as a dispersion medium for powdery material is used »you get a better distribution of the conductive filling and you can increase its percentage, which improves the resulting« conductivity will.

The impregnation of a porous preform by means of a liquid allows the realization of conductor channels extremely as high as dioke (a few hundredths of a millimeter), dl · trotadem are sufficient to ensure the required conductivity su and without the physical and meohanieehtn Properties are impaired

An electrically conductive mixture is always and also in In the best case, heterogeneous and consequently porousWhen incorporating such a component in a polyethylene tube, that is intended for the passage of liquids under high pressure are therefore normally the mechanical properties required for such purposes, especially resilience, weakened. In a tube according to the invention, however, the volume is the conductive Channels reduced to a minimum, but sufficient for drainage · The integrated heterogeneous foreign body therefore does not reduce the thickness of the pipe and practically the same mechanical properties are obtained like a pure polytetrafluoroethylene pipe

Because the static electricity through narrow belts and not is diverted through a cover covering the entire inner wall, the condition of the inner wall can be checked visually and any cracks or structural defects resulting from any Reasons have arisen, determine "

Pipes according to the invention are suitable for all cases in which static electricity is to be diverted _9, especially when transporting liquids or gases under pressure (avoidance of destructive discharges across the pipe wall) and when transporting flammable substances (avoidance of ignition).

Products according to the invention are of particular interest to the aerospace industry

Claims (1)

* Ί Protection claims 1. Polytetrafluorätiaylen tube with electrically conductive Areas in the form of at least one continuous, axially parallel route, characterized in that these areas are made up There are continuous bands running parallel to the pipe axis, which are small in relation to the pipe cross-section Have cross-section and from a mixture ^ or. Polytetrafluoroethylene and at least one powdery electrically conductive one Material in an amount of 1 "to 5o percent by weight," based on the mixture, "consists of» 2. Pipe according to claim 1, characterized in that the conductive strips have a thickness of a few hundredths of a 1.IxIIimeter and a conductivity on the order of · of Have 5oo Liikroamps below 1 volt per cm * 5. Tube according to claim 1 or 2, characterized in that the conductive strips are arranged on the inner surface of the pipe. 4. Tube according to claim 1 or 2, characterized in that the leading countries in porin of channels within the Rohrv / andung are arranged. 5. Tube according to claim 1 to 4, characterized in that the pulverformiije conductive Uateiial graphite, carbon black or there is a mixture of these. 6. A stirrer according to claim 1 to 5, characterized in that the mixture consists of rulytetrafluoroethylene and l3itf; ihi _c ; eu l, material approximately 2o percent by weight graphite and 2o jev / ich-uspros .:: t iiue.ü, based on Polytetrafluoräthylsn, err ^ hd.lt. 7. Pipe according to claim 1 to 5, characterized in that the mixture av.t; Polytetrafluoroethylene and leitfc.hiceir! ] .uitüv: Val contains approximately 35 percent by weight of graphite, based on polytetrafluoroethylene.