DE2409178C2 - Process for the manufacture of pipes from polytetrafluoroethylene - Google Patents

Description

The present invention relates to a process for the production of pipes made of polytetrafluoroethylene, a multi-layer polytetrafluoroethylene tape being wound onto a core, after which the wound tape is heated to a temperature above the gel formation temperature, but below temperatures in the range from 380 to 400 ° C, is heated for a period of time which is sufficient for the geiification and then the tube thus formed is cooled on the core and this is then pulled out.

In this method known from US Pat. No. 2,941,911, a sintered cold-drawn strip is used assumed 0.05-0.25 mm, which is wound up in several layers. This should include the gelling process of the wound tape with no more than four layers. Furthermore, the thickness of the wound Pipe limited by the strong tensile stresses, which causes the risk of cracking. For this Basically, it is also necessary to make the heating of the wound tape slowly, which is has an unfavorable effect in terms of time.

If you want to go to greater wall thicknesses of the pipes, you have to have several winding and gelling processes perform one after the other, reducing the clumsiness of the procedure given its limitation to practical every four winding layers is increased. It has also been found that the permeability of the tape as with other methods that work with many layers of winding, not with the number of Layers increases, but decreases again after reaching a certain number of layers.

Another known method (GB-PS 9 67 808), in which First a metallic wire is wound onto a core, onto which several layers of one Tape made of raw unsintered PTFE is wrapped, which in turn is wrapped with a wire winding on the outside are covered, after which the whole is then heated to sintering temperature. The one by squeezing the PTFE layers obtained between the two pressures is practically completely useless for the transport of liquids in chemical engineering, because the inner and outer surfaces are smooth as a result of the wire layer miss.

The invention has the task of creating a method which allows a pipe from to produce several layers wound on top of one another, which has a low permeability for all thicknesses has and wound in one process despite numerous layers and relatively quickly on the Gelation temperature can be brought.

According to the invention, this object is achieved by the technical teaching of the characterizing part of claim 1.

Preferred embodiments of the method according to the invention are described in claims 2 and 3. the Pipes produced according to the invention have, compared to pipes of the same thickness, those according to known processes are produced, have a lower permeability and can be produced more quickly, especially since that from multi-layer pipe can be treated in a single winding and gelling process.

Although it is already known (DE-OS 22 19 811), tubes wound using a single layer Manufacture polytetrafluoroethylene tape and then the single-ply wound on a core. to the To subject tape overlapping edges to a gelling process.

These known methods, which are not based on the object of the invention, also work together Raw PTFE strips formed only by molding or calendering or extruding PTFE powder and are not suitable for achieving the object of the invention.

The invention allows a PTFE tube to be achieved. which is provided with a flange, whereby the Pipe and the flange have extremely low permeability and good mechanical strength values bo has. The connecting flange shows no signs of aging, cracks or weak spots. self after a relatively long period of use.

It goes without saying that the exemplary embodiments described below do not encompass the invention and that all changes that appear desirable can be made without the To leave the scope of the invention.

pi In particular, it is clear that the formation of the flange can be done without the PTTE tube c going inside a steel pipe can be used, which only serves as a support. It is indeed possible that To form the flange of the PTFE tube, if this is cingc-S in any suitable Halicrungsvorrichtung is.

It should also be noted that the invention is not limited to the production of straight tubes. but is then also applicable to curved pipes or connecting pieces. when one as a thorn Can use structure that can either be destroyed or dismantled if you use the Has completed the sintering process of the PTFE.

For a better understanding of the invention, it is explained in the following figures.

F i g. 1 schematically illustrates the various phases of a process for producing the PTFE tape according to claim 1;

F i g. Figure 2 shows schematically the winding of the tape on a tubular mandrel, with adjacent one another Overlap turns;

F i g. 3 shows a winding process on a tubular mandrel, in which the successive windings ίο genes butt with their edges;

F i g. 4 illustrates schematically the winding of a tape on a cylindrical mandrel, in which the adjacent Turns are spaced apart;

F i g. 5, 6 and 7 schematically illustrate, on an enlarged scale, partial axial sections of winding layers, as in the F i g. 2, 3 and 4 explained methods can be achieved; F i g. Figures 8 and 9 show schematically the formation of end flanges on the pipes;

10 and 11 show two exemplary embodiments of pipe reinforcements for increasing the resistance Negative pressure.

In FIG. 1 shows the various production phases of the raw PTFE tape. The preform 1. obtained by pressing a mixture of fine PTFE powder and a lubricant inserted into the chamber of an extruder 2, where a piston 3 pushes the PTFE through a slotted nozzle, which leads to the formation of a flat band 4.

The strip 4 is then rolled out between the two cylinders 5 and 6 to form a strip 7 of to get thinner thickness. The rolling takes place while practically without changing the width of the strip the elongation of the belt five to twenty times the initial length before the calendering process amounts to.

The tape 7 is then introduced into a container 8 which is e.g. B. is filled with trichlorethylene to the Eliminate lubricant used to facilitate extrusion and calendering. You get in this way the tape 9, which is then further processed.

The Fig.2 illustrates how to take the winding of the tape 9 on a cylindrical mandrel Can carry out overlapping of the adjacent turns. In the present case one notices that the Turns overlap each other by about half their width, so that when you have finished a row of turns, a total of two layers of tape are applied to the mandrel 10.

In FIG. 3 shows how, according to another variant, the belt 11 is placed on a cylindrical mandrel

10 winds by making coils 10a, 10Z>. 10c 10t / applies, whereby one winding step corresponds to the width of the tape.

The F i g. Fig. 4 shows how it is possible to wind a tape 12 on a cylindrical mandrel 10 by between each turn 12a. 126, 12c, 12d, 12c leaves a gap 13 which is the width of the belt 12 is equivalent to.

In the F i g. 2 to 4 only the first winding layer is illustrated. It goes without saying that the The number of PTFE layers that are necessary is between 10 and 100.

It is also possible to combine the aforementioned types of winding, i. H. some layers with overlap, others with spaces between the turns and still other layers with at the edges to wind colliding turns.

In FIG. 5, a partial section of the cylindrical hollow mandrel 10 is schematically illustrated, on which the layers 9a, 9b, 9c. 9d. 9c etc. are wound, which, as you can see, partially overlap.

Further successive layers are wound over the first winding layer, which in the present case Fall from layer to layer with alternating turns to the mandrel axis until the boundary line 14 is reached, which corresponds to the desired thickness of the tube, which then the gel formation process is subjected.

The F i g. 6 illustrates schematically in section and on an enlarged scale a according to the one in FIG. 3 described winding process tube obtained. It can be seen from FIG. 6 the adjacent turns 11a. 11 b, and Wd lic as well as the above-bearing layer consisting of the windings Wa, Wb, 11 'and 11 c' d. If you want to make the inner wall of the pipe antistatic, you only use it for the turns 11a, Wb,

11 c, 11 d a PTFE tape with graphite intercalation. It will be noted that the butt lines between the turns of the first and second layers are offset from one another. A sufficient number of layers are wound in this way until the desired thickness of the PTFE tape coating is reached, which is indicated by the boundary line 14 in FIG. 6 is indicated.

The F i g. 7 corresponds to FIGS. 5 and 6, but the winding of the tape takes place as shown in FIG. 4th is illustrated, i. H. with turns whose distance from one another is the width of the tape.

From FIG. 7 shows the turns 12a, 12b or 12c, which form the first layer, while the turns 12'a , 12'b, 12'c form the second layer and the turns 12 "a, 12" b, 12 "c form the third layer The tape with which the turns 12a, 126, 12c, etc. are wound, can possibly be provided with embedded graphite.

The successive layers consist of edgewise touching turns, the Turns of land interlock due to the fact that the spaces between two turns one row of turns are equal to the width of the tape of the other row of turns.

If you want to heat the pipes, you can advantageously choose between two layers,

E.g. between the 10th and 11th layers, a conductive wire with a sufficiently high electrical resistance introduce, which is wound, for example, helically on the 10th layer before it is removed from the 11th layer is covered. In another variant, the wire can extend longitudinally from the 10th layer be applied before it is covered by the winding of the 11th layer.

In the F ^r ig. 10 illustrates a tube before the baking or sintering process, the mandrel not being illustrated in the drawing for the sake of simplicity. It can be seen that the tube consists of a large number of layers, each of which is formed from juxtaposed turns 23 of the raw PTFE tape. On the turns 23 of the last layer, a rib 24 is wound which has the shape of a circular ring on the circumferential surface of the tube. Each rib 24 is produced by

ίο you use a tape made of raw PTFE that is identical to your edge, which is used for wrapping the Windings 23 was used and wound spirally one above the other on the tubular body will. With the reference number 25, the spirally superposed turns are illustrated in section, which together form the annular rib 24.

For example, with an outer diameter of the pipe of 200 mm, very good stiffening is achieved

and excellent resistance to tube compression by having the ribs 24 with a tape 15 mm wide and winds the turns 25 over each other over a height of 15 cm, vault: two adjacent ribs 24 separated by a distance of the order of magnitude of 300 mm run from each other. In the embodiment variant illustrated in FIG. 11, instead of separate Ribs 24 a continuous helical rib is provided, which, for example, the slope

the turn 23 has. It can be seen that the continuous rib 26 obtained in this way passes through helical winding of a tape is obtained with the turns on the same helical line be stacked on top of each other. The width of the ribbons that make up the rib 26 and the height of the rib depend on the degree of strength sought.

If desired, one can use the spaces 27, which extend between two successive ribs 24 or

result between the turns of the continuous rib 26, fill with a filler material. For this is for example a material suitable that is granular, powdery or fibrous and which is between the ribs is filled until a cylindrical body results, the diameter of which is the diameter of the ribs 24 or 26 corresponds. Further layers of PTFE tape can then be placed on the tubular body obtained in this way to obtain a continuous superficial skin of PTFE material after the subsequent

The baking or sintering process is complete.

In the F i g. 8 and 9 is illustrated how a connecting flange at the end of a pipe according to the invention will be produced. 8 shows a PTFE tube as it is after the baking or sintering process looks like, which has been described in the foregoing and after the mandrel 10 has been taken out became. This tube is inserted into the interior of a steel tube 16, which serves as a protective tube. That

Steel pipe has a flange 17 which serves to connect the pipe end with another flanged pipe end

connect, the connection being made by bolts which pass through openings 18 of the flange 17.

At the end 15a of the PTFE tube 15, the flange is to be attached, which serves to ensure the continuity of the

PTFE tube to ensure. To form this flange, the expansion tool 19 is used, which on

a temperature of 250 ⁰ C to 350 "C was heated and then stretched into the end of the tube, like

this in FIG. 8 is illustrated.

The expansion tool 19 has a cylindrical piece 20, the diameter of which corresponds to the inner diameter of the pipe 15, and a subsequent conical section 21 which is used to cause a first expansion of the pipe end 15a of the PTFE pipe. The conicity of the section 21 is approximately 60 ^° C. with respect to its axis.

It is clear that. if you use the expanding tool 19 in the sense of the in F i g. 8 illustrated arrows moves, a conical deformation of the end 15a of the tube 15 takes place. In FIG. 9 is then illustrated how after completion of the conical deformation of the end 15a, the flange is finally formed by cutting in same temperature range by means of a tool 19.7. which instead of the conical section has a having cylindrical portion 22, the diameter of which is greater than the diameter of the coaxial cylindrical

see section 20, the final pressing of the already conically deformed end 15; i of the pipe against causes the flange 17, as indicated by dash-dotted lines, which the position of the tool 19a illustrate in its end position.

Thanks to the properties of the pipe, it is possible to carry out this operation without difficulty and to obtain connecting flanges which have a high mechanical strength and a low permeability which are of the order of magnitude of the corresponding properties of the pipe 15.
Several exemplary embodiments are given below.

example 1

so you use a fresh PTFE powder, which is obtained by coagulating a dispersion, which has an average grain size of 500 ± 75 microns. You mix this powder with an oil that is made from Is composed of hydrocarbons and that serves as a lubricant. Here, 18 percent by weight of lubricant is used and 82 weight percent powder used.

You then make a blank. by exerting a pressure of 15 kg / cm ² on the mixture of the powder p5 with the lubricant Thickness forms. This tape has a density of 1.72.

The strip prepared in this way is left between two driven calender rolls at room temperature

of a Kalandricrwal / werkcs run, resulting in a band of about 7.5 I hundredths of a mm. Sj

This bundle is then placed several times in Koniaki with hot triehloroethylene. That fit after this

Treatment present tape has a thickness of I, b5 and is then made in the desired widths ||

cut. £

The winding of the 28 mm wide tape onto a mandrel with a diameter of 49.5 mm is done with -. fj

a winding pitch of 7 mm, which corresponds to an overlap of adjacent spirals of around 75%. Man I

In this way, four layers of tape are superimposed on each pass. Then you bring nine si

further layers, which corresponds to a factor of the tape thickness, i.e. 2.7 mm. i |

After completion of the winding process, the mandrel and the wound PTFK tape are placed in a |

Oven which is kept at a temperature of 365 "C. This temperature is left for 90 minutes with §,

act, after which a controlled cooling of to 30 "C per hour in the temperature range from 365 to f,

down to 285 ⁰ C performs. .;.

Below a temperature of 285 ° C, the cooling can then be faster, e.g. B. in the open air. ;

After this treatment, the mandrel can be pulled out, possibly with a slight warming of the ^; , v

PTFE tube takes place in order to achieve a certain expansion of the same for easier removal of the dome η; i

obtain. ψ

After the PTFE tube has been filled into the interior of a steel tube serving as a protective device, the [i- ^:

Pull the end of the PTFE tube on which the flange is to be provided a little out of the steel tube;>

and one proceeds to the formation of the flange as shown in FIGS. 8 and 9 is illustrated by first adding a ίί

conical tool 21 with a conicity of approximately 60 ° and then a flat tool 22 $

is used. In this way a flange is made with a diameter of 85 mm. . _; ,

The density of the PTFE tube obtained in this way is 2.1b.

In a variant of this exemplary embodiment, the winding of the PTFE tape can be done in different

Execute way, e.g. B. according to the F i g. 3 or 4 or a combination of these types of winding. Substantially ||

is. that there are a sufficient number of layers and that the turns of the tape are as uniform as 25 8

are distributed as possible. p

In the following, other exemplary embodiments are described, basically as in the example

Execution example 1 proceeds, but works with other characteristics as indicated in the following list

are clear. |

■ ■ · 30 i;

Example! Example 2 Example i Example 4

Thickness of the strip after calendering 0.075 0.050 0.09 0.13 |

in mm §

Density of the calendered tape 1.65 1.7 1.65 1.60 3i IJ

Width of the belt in mm 28 40 20 28 |

Winding step in mm per full turn 7 20 20 56 Sj

Number of 36 70 40 30 | wound on the mandrel

Tape layers |

Thickness of the PTFE tube in mm 2.7 3.5 3.6 3.9 au I

before sintering 1

Diameter of the dome in mm 49.5 201 152 433

Baking or sintering temperature in "C 365 365 365 365

Cooling speed in the range of 30 70 10 50

365-285 ⁰ C ( ⁰ C per hour) 45

Thickness of the pipe '2 2.7 2.6 3

after the baking or sintering process in mm

Density of the PTFE material 2.161 2.153 2.170 2.160

after the baking process

Diameter of the flange in mm 85 255 205 500 50

Forming temperature both 350 350 350 350

Formation of the flange in "C

Permeability in 1.20x10 "1.35XiO- ¹¹ 1.05x10-" 1.30x10- "

cniVcm χ cm ² χ sec χ atm

For this purpose 4 sheets of drawings

Claims (1)

Patent claims: 1. A process for the manufacture of pipes from polytrafluoroethylene, with a tape made from a core Polytetrafluoroethylene is wound in multiple layers, after which the wound tape is heated to a temperature above the gel formation temperature, but below temperatures in the range from 380 to 400 ° C, upper is heated for a period of time that is sufficient for the geiification and then the tube so formed is heated the core cooled and this is then pulled out, characterized in that a Raw tape is produced in the paste extrusion process, that then the raw tape with an elongation is rolled out by 5 to 20 times that the winding of the raw strip in at least 10 to 100 layers ίο takes place and that then the raw strip is sintered in the wound state. Z Method according to Claim 1, characterized in that the tape is wound onto the mandrel in such a way that the edges of adjacent turns collide. 3. The method according to claim 1, characterized in that after the sintering process, the cooling of the Tube in the temperature range around 380 ° C to 400 ° C to about 285 ° C with a cooling rate takes place, which is about 10 to 100 ° C per hour, preferably about 20 ° C per hour.