Products of crosslinked thermoplastics material

The present invention relates to a method and apparatus for the production of fumed thermoplastic products, especially of fumetoid density polyethylene.

Fumigation or vulcanization whereby two neighboring polymer chains combine with each other and form a three-dimensional network under the influence of decontamination or activated carbon is a known operation that can be performed with polyolefins, vinyl polymers and elastomers, especially ethylene propylene elastomers. In the case of certain polyolefins, such as low density. polyethylene and ethylene-propylene elastones when an activated carbon which forms inorganic peroxide is used as a fumigant, the final product can be obtained without difficulty by sequentially forming the powdered exit mixture using conventional methods for converting the plastic material, for example by extrusion and injection molding, and fometting cells vulcanization carried out, for example, by passing the danced product through an autoclave or through a fluidized layer. The temperature at which the molding is carried out in the extruder or in the injection molding presses is definitely less than the temperature required to produce fumigation by cleavage of the organic peroxides conventionally used as for example: dicumyl peroxide; ditertbutyl peroxide; 4-4bis-t-butyl valerate peroxide; 2,5-dimethyl-2-5-di- (t-butyl) -hexane peroxide; 2,5-dimethyl-2,5-di- (t-butyl) hexyn-3-peroxide. 2 4-4bis-t-butyl valerate peroxide; 2,5-dimethyl-2-5-di- (t-butyl) -hexane peroxide; 2,5-dimethyl-2,5-di- (t-butyl) hexyn-3-peroxide. 2 4-4bis-t-butyl valerate peroxide; 2,5-dimethyl-2-5-di- (t-butyl) -hexane peroxide; 2,5-dimethyl-2,5-di- (t-butyl) hexyn-3-peroxide. 2

The intermediate phase, in which the plastic material has a viscosity, generates its conversion in accordance with conventional processes and the formation step is therefore an interval of temperature sufficient to ensure that the two operations are well separated and that the risk of premature digestion of peroxide is avoided.

This is not the case when high density polyethylene is required as this material only achieves a sufficiently low viscosity for forming by extrusion or injection molding at a temperature between 17 DEG and 22 DEG C., depending on the molecular weight of the high density polyethylene.

This means that a temperature higher than the temperature corresponding to the initial digestion of the peroxide (about 14o ° C for the least active peroxides) such that the use of the processes used to produce residues of low density polyethylene or ethylene propylene elastomer too high density polyethylene in the mixture subjected to molding will initiate a fumigation reaction that would be undesirable on the basis that the material, especially in the case of an extruder, would be exposed to a shear effect scm prevents the proper development of the formulation and results in a final product scratch very poor quality.

It has previously been proposed to eliminate this shear effect by using a heated mold and fume nozzle head in which the mixture is fortified and collapsed so that it moves in the tool while the effect of pressure is created by a piston but in order to avoid harmful deformation in the material it is then on the surfaces of the nozzle head, the material comes into contact with and arranges a coating of an anti-additive material, for example, polytetrafluoroethylene.

Good quality of the products has been achieved in this case, since this methodology is not a practical continuous production since there is a relatively short period of completion of the material, in the precursor zone of the nozzle head is formed a leakage which adversely affects the quality of the product. This deposition is made up of particles of fumet polyethylene son adhesive to the walls and is due to the radicals that release the underreaction and the son is sufficiently active to activate the surface of the anti-additive material and result in a firm adhesion.

A large amount of lubricant has been tried by injecting this into the nozzle head on the upstream side of the correcting zone, except for this method, except for difficulties encountered in carrying out the method due to the unstable flow rate of the fluid in the nozzle head - does not fill the removal of the fouling zone .

An object of the present invention is to solve this problem by providing a method of manufacturing products of the pre-existing thermoplastic material from a blend scm consisting essentially of a powdered blend containing the thermoplastic material and a fuminating agent and the particular feature of the process according to the invention the admixture is diluted by exposure to a pressure scm causing it to penetrate and propagate in the heated nozzle head as well as crosslinking of the material in which the powdered mixture is sintered by exposure to a pressure scm is oriented along the axis of the nozzle head and the melting mixture is produced in the nozzle head is subjected to a temperature lower than the temperature at which the fumigant becomes substantially graded,as the molding of the shaped material on the downstream side of the die head is produced by passing the material through a bath of molten metal scm having a temperature scm permits cleavage of the fuming agent.

Apart from the fact that the method provides a preliminary step for forming the pulverized mixture which allows a direct highly advantageous introduction of this into the nozzle head, the method ensures that the shaping step itself, by sintering, is clearly separated from the conversion step. The designation "sintering" includes - the operation of fouling and melting of the particles to achieve a compact product. With regard to the use of a bath of molten metal to produce the fusion reaction, this has the distributed product when it is gelled in a manner following a free path in the fouling zone as the temperature exchange is ensured by the floating bath and the product need not slip in contact with. walls so that in order to allow the product to flow to the outlet it is sufficient. provide a simple mechanical control scm in case a pipe can be obtained by linear contact with the ring surface of the ring scm supported by the tank containing the bath and further utilizing a lubricating effect from the bath. The calibration device for calibrating the product may be advantageous in the inlet area by bathing a constant or variable effective cross-sectional calibration device. For a pipe, its internal diameter, which reduces the calibration of the calibration device, can be maintained within the desired tolerances by the action of an inert gas, for example, nitrogen scm 4 is injected into the tube. By using the process of high density polyethylene products, the absence of possible shear forces during the fusion allows for optimum properties. Breach extension of test specimens underwent sessions is between 4oo and 5oo%. The result is independent of the time that has elapsed after the commissioning of the production from the device due to the fact that there is no leasing which could result in the lowering of the products in the occupation zone. It is therefore possible to ensure continuous production on an industrial scale, since it is no longer necessary to replace parts scm damaged by a surface deposition zone a disadvantage of some previous processes.

The method may be used for the production of pipes and other profile elements and to provide tubular overlays on cables of metal metal reinforcements.

The formation of the molded material may take place by a drawing at the entersatural temperature near the temperature of the molding. By trekking is meant not only a longitudinal extension or elongation but also the one preferred to form longitudinal and radial expansion achieved specifically under the influence of a mandrel or nozzle or under the influence of a fluid under pressure, this operation being carried out in a mold or without the use of a form. In this way, with a simple device it is possible to manufacture pipes of different diameters with constant capacity per hour regardless of diameter, rings or profile elements etc. It is also possible to manufacture body parts, containers, gaskets, corrugated or thermoformed plates, etc.

The device for carrying out the method comprises on the upstream side of a sintering nozzle head means the longitudinal axis of the nozzle head and exerting a pressure on a combustible powdered mixture for preforming the said mixture by sanitation and causing it to move the piercing head and on the downstream side of the nozzle head a tank to rmme a bath of melted salt for the fumigation of the sintered product scm abrasion head. The device may further define between the outlet of the nozzle head and the feed tank the devices for drawing the molded material. 5

These and further features of the invention will become apparent from the following description with reference to the accompanying drawings, in which:

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Figures 1A and 1B show together a device for manufacturing high density polyethylene pipes; 2 is an axial view of a modification of the forming and calibration device used in the device of Fig. 1B; 3 is a section taken along line 3-3 of Fig. 2; 4 is an axial view of another modification deployment and calibration device used in the device shown in Fig. IB; 5 is an axial section of a modified form of the outlet end of the molten salt bath shown in Fig. IB used to form the material in the tubes; 6 is a schematic view of a device extensively drawing devices; and 7 is a longitudinal view of the pull and fitting device utilized in the device of Fig. 6.

The device shown in Fig. IA and IB comprise a vertical portion A in which a powdered mixture containing a polyethylene and a fumigant distributed in a manner such as to provide a tube and sintered, and a horizontal portion B in which the netting of the material is carried out,

The part A has a vertical axis XX and comprises a horizontal frame 1 supported by columns 2 and serves as a support for a nozzle head 4 with an axis XX and having a base plate 5 as a shoulder 6a of screw-threaded tie rods is clamped by means of nuts 7 so that the bottom plate 5 is attached to the frame. The nozzle head 4 comprises, in parallel with its axis, a cylindrical body 8 in which a bore 9 is formed in the nozzle head 4 which is coaxial with a central bore 3 in the frame 1 and which can be heated by the aid of an oil circulation at 8a. The upper end of the nozzle head 4 has a flange 10 through which the tie rods 6 run and whose surface carries a supply shaking funnel 11 which may be cooled by means of a circulation of water at 12 and whose bottom opening has a diameter corresponding to the diameter of the bore 9.

Positioned vertically against the bottom plate 5 of the nozzle head 4 and inside the bore 3 in the frame 1 there is a nozzle head 13 coaxial with the nozzle head 4 and held in position by a lower support plate 14 attached to the stretching strings 6.

This plate 14 is provided with an aperture 15 having a diameter somewhat larger than the diameter of the bore in the nozzle head 13. This composition thus constitutes from the bottom of the shaking funnel 11 to the opening 15 in the support plate 14 a rectilinear cylindrical guide or channel. The nozzle head 13 is also provided with annular heating devices, e.g. formed by external electrical resistors 17.

The frame 1 acts as a support outside the nozzle head 4 to hydraulic cylinders 18 and 19 containing pistons 20 and 21 where on the vertical piston rods 22 and 23 the fixed horizontal plate 24 is attached by means of nuts at 25, 26. ' The plate 24 may slide on the tension bars 6 and in the middle has an opening 27 extending vertically downwardly within an annular hub 28 in one piece with the plate 24 and constituting a piston which is cooled near the plate 24 by means of a circulation 29 of water and co-operating with the cylinder portion which is formed at the opening ring 11a and of the upper part of the wall of the bore 9 in the nozzle head 4.

The tension rods 6 supporting at their upper ends above the plate 24, a plate 30 on which rests a hydraulic sylinder.31 containing a piston 32 integral with a mandrel or vertical piston rod 33 arranged in sliding contact in åpningen27 in the piston 28 and controlled by the plate 30 and a horizontal plate 34 in one piece with the mandrel and which can slide on the rods 6.

The mandrel at 30 extends inside the nozzle head 4 and nozzle head 13 and the upper end of the lower end of its motion is approximately at the level of the lower end of this nozzle head 13. /

The door also has a heating element 35 containing a circulation of oil or an electric heating resistor. The device has its supply from a target tank 37 connected to the shaking funnel 11 by means of a pouring spout 38 which must ensure a homogeneous distribution of the powder in the gap between the die 33 and the nozzle head 4.

The cooling conduit 12 for the shaking funnel allows it to be ensured that the at polyethylene, regardless of the duration of its shaking stay, can not reach a temperature at which it would adhere to the underlying effect of an initial melting.

The cooled zone is actually a preform zone of height approximately twice the diameter of the mandrel 33 and the mixture must remain in a powdered form so that it can form a tube under the effect of the deposition provided by the piston 28 in the tubular member 36 upwardly of the nozzle head 4 and optionally in the inlet of the latter.

At the beginning of a cycle, the stamp 28 and the thorn 33 are in their respective positions. No pressure is exerted on the piston 32 hydraulic cylinder 31. Due to the action of the cylinders 18 and 19, the piston 28 is caused to sink down and move through the powdered mixture disposed in the shaking funnel 11 where it is kept at ambient temperature by means of the cooling conduit 12. Upon continued lowering, the piston 28 causes the admixture to contract in the tubular member 36. The pressure necessary for this compression is of the order of 1000 bar.

The mixture is therefore given a mold or molded and made simultaneous. It is then driven into the nozzle head. The throat 33 also undergoes a decreasing movement under the influence of the depressurization of the material then in the nozzle head 4 subjected to an increase in the temperature of the heating element 8 in the nozzle head 4 and the heating element 35 for the die 33. The temperature regulates the value which produces melting of the material but remains lower than the temperature at which the cleavage of the crosslinking the drug is particularly important. This temperature will e.g. be between 150 and 180 ° C. When the piston 28 reaches the lower end j for its movement, the pressure which acts on the pistons 20 and 21 in the cylinders 18 and 19 decreases and while the piston 28 is held in the lower position the mandrel 33 is raised by the piston 32.

The nozzle head 4 therefore constitutes a sintering zone from which, due to the downward movement of the piston 28, the material 33 is pressed into the nozzle head 13 where the temperature is kept at the same level as before and from which the material comes out in the form of a blank. At the outlet of the nozzle head 13, the blank is pressed by the downward movement of the piston 28 into a cuff 15a, e.g. in the form of a bell where the temperature is kept short of the same level as previously or possibly bringing a higher value and constituting a transition zone in which the blank which is free with respect to the wall of the cuff 15a may undergo movements that absorb the advances in the progress, ref. the continuous tensile force exerted on the blank on the downstream side towards the part B which constitutes a crosslinking zone.

The part B comprises mainly a closed horizontal preferred cylindrical container 41 which is divided longitudinally by compartments by means of two vertical partitions 42, 43 and contains a bath 44 of molten salt and which is heated e.g. by electrical resistors 46 to a temperature such as more than 200 ° C. The upstream section 47 is penetrated by a tubular connection 48 whose upper ends are attached to and attached to the tank 41 while its other end whose internal diameter is narrower, corresponds to the outer cross section.of the pipe is to be threaded and attached to the inlet end of a mold and calibration device 49 carried by the wall in the tank 41 by means of elements 51. The sintered tube is introduced with clearance into the inlet end of the tapered cross-sectional connecting tube 48 and proceeds after a 90 ° directional change in a cylindrical bore 52 formed in the molding and calibration device 49 thereby ensuring a molding of the profile and a uniform overlaying state of the tube which at the same time undergoes a cross-section at least in its circumferential surface area. The tube then moves through the other two compartments 53, 54, in which the cross-section is completed and in which it is controlled by rings 56 held in relation to the wall in the tank by means of

In 9 of supports 27 and with 'inner openings 55 with a toroidal shape which results in a sliding contact of the linear type of co-tube. The crosslinked pipe emerges from the end wall 58 the tank when passing through a mounted ring 59 which is sealed in contact with the end wall.

Also, the pressure of a gas held under pressure in the bore irradiated and supplied by a pipe 61 through an axial conduit 62 provided in the mandrel 33 can contribute to a calibration of the pipe depression in the part 44. The gas used is preferably nitrogen. _ · '. · - ·· "".

The molten salt constituting the bath 44 is preferably an autectic mixture of mineral salts, e.g. nitrates and nitrites such that the autistic mixture has the following composition: 53 parts by weight kno3 40 parts by weight NaNO2 7 parts by weight NaNO ..

The division of the tank 41 allows maintenance of pre-heating temperatures in the different compartments. The temperature is generally higher, eg. between 250 and 300 ° C in the compartment 47 containing molding and calibration device 49 so as to achieve rapid conversion of the material in the peripheral range of the tube. The temperature will be lower in the other compartments53 and 54, such as a maximum of 250 ° C to avoid the risk of entermic decomposition of the product.

For the treatment of a 3 mm thick tube, the length of the tank 41 may be about 2 meters with a slope velocity in this case at 150 m / h.

Reference numeral 63 denotes a device shown schematically, which is in part comprised of two movable bands in contact with the interconnected tube for performing a continuous tensile force thereto .; A further molding and calibration device can be arranged after the drawing device 63 or between the latter and 10 tank 41.

Satisfactory attempts have been made using a high-density polyethylene as thermoplastic material having a molecular weight of 300,000 and 500,000, e.g. a polyethylene commercially available under the designation "Manolene 56 020" having a density of 2 0.956 and a viscosity index of 2 under a load of 20 kg / ml mixture, homogenous additives have been mixed with, apart from an organic peroxide, coloring agents, antioxidants, anti UV agents, lubricants which allude well-known products conventionally used in industrial conversion of plastic materials. As a crosslinking agent, a catalytic composition with 0.5% ditert butyl perosuke was obtained; il trade under the designation "Trigonox B". In this case, the method 70 comprises stamp stroke.

Attempts were made where the extension is measured between two references on a standard ISO 92 test specimen using the avenue extensometer in accordance with French standard NF T 51 034, the idle rate was 1000 mm / minute. The results of tensile testing show the mechanical properties measured on a tube as a function of the extruded length and which represent the mean value of five-sample pieces, is shown in the following table: 1 ±

Extruded Length (m) 100 500 1000 1500 2000 Tensile Strength (in kg / (in kg / crn) 180 184 170 190 182 Breakage Fat (in kg / crn) 300 280 290 270 280 Break Extension (%) 520 490 460 500 470 Breakthrough of tubular test pieces (bar) 55 52 57 50 52

Figures 2 and 3 show a molding and calibration device utilized in place of the calibration device 49 in Fig. 1b and consists of a plurality of groups 64, 65, 66 of profile rollers 67 with a concave profile communicating to the pipe a gradual reduction cross section.

In order to achieve a reduction in the desired diameter, it is also possible to use a calibration device such as shown in Fig. 4 encompassing a sequence of forming rings 68a, 68b with a cylindrical bore of different diameters. These rings of polished steel or "teflon" are kept separate by using. spacers 69 and held in position by means of a clamping device 70, desirably supplemented with a system to record deadlock (not shown). In Fig. 5, the final product is withdrawn, such as is a non-closed profile element, instead of emerging from tank 41 by passing through a sealing direction in the end wall through an upper opening 71 in the wall of the tank to which the product is guided by the control 72. In the event that the product does not have a tubular form 33 is eliminated in Fig. IA. If the purpose is to place a single or metal reinforcement overlay, this cable or reinforcement replaces the die 33. 12 In the diagram shown in Fig. 6, reference numeral 101 designates device corresponding to part A of Fig. IA and IB, which provide a tubular blank 102 at a velocity VI. The subject passes through a tank 103 in which it is subjected to a pulling and then crosslinking operations and then proceeds into a pulling device 104 which drives the blank at unity V2 higher than the velocity VI, a cooling tank 105 entrainment device 106 which drives the item at the same speed V2 in the past or substantially equal to the velocity V2 and connect to a winding device 107. Reference numeral 101 denotes means corresponding to part A of Fig. IA and IB, which provide a tubular blank 102 at a velocity VI. The subject passes through a tank 103 in which it is subjected to a pulling and then crosslinking operations and then proceeds into a pulling device 104 which drives the blank at unity V2 higher than the velocity VI, a cooling tank 105 entrainment device 106 which drives the item at the same speed V2 in the past or substantially equal to the velocity V2 and connect to a winding device 107. Reference numeral 101 denotes means corresponding to part A of Fig. IA and IB, which provide a tubular blank 102 at a velocity VI. The subject passes through a tank 103 in which it is subjected to a pulling and then crosslinking operations and then proceeds into a pulling device 104 which drives the blank at unity V2 higher than the velocity VI, a cooling tank 105 entrainment device 106 which drives the item at the same speed V2 in the past or substantially equal to the velocity V2 and connect to a winding device 107.

As shown in Fig. 7, the blank 102 enters the molding device 101 through an aperture 15 in the lower support plate 14. The subject therefore passes into a device to eliminate the smoke due to discontinuity in the advance of the blank and enters the tank 103 in a continuous manner. An embodiment of a single device is shown in Fig. 7. In this device, the substrate 102 is a directional change around a groove 108 which is freely rotatable on a pitch bar 109 which is pivotable in a vertical planar circle, a pin 110 mounted on a support 111. The groove of the groove 108 has a depth corresponding to the radius of the blank 102.

The tubular blank 102 is then passed around a driven track disc 112 connected through a speed variable 113 to an electric motor 114 (shown schematically). The subject then undergoes a change of direction change which brings it into a drawing and annealing tank 103. This tank contains a mixture of molten salts from the same type as in tank 41 of Fig. IB divided into two divisions, namely a pulling section 115 and a cross-section 116 separated by a diaphragm 117 with an opening 118 as the allowance 102 to pass therethrough.

Inside the tank 103, in the compartment 115, a multilayer molding or profiling rollers 121a, 121b, 121c and 121d are mounted with a profile corresponding to the configuration of the pulled product. All rollers are mounted on a drive rod 119 mounted on swing connections 120a and 120b. The recruitment department 116 has maintenance rolls 122. If desired, the mold rolls may be replaced by other suitable molding devices. The number of roller pairs or 13 molding devices may vary depending on the desired pulling speed. The maintenance rollers can be replaced, if desired, by any other control and support devices, such as bowls, rings, etc.

After passing through tank 103, the item 102 is operated by means of a pulling device 104 of known type, e.g. with belts driven at velocity v2 ^> v1 by means of a unit comprising motor 114a and a velocity variator 113a shown schematically.

The blank then enters the cooling tank 105 before it is wound up on a coil 107, if desired to have passed through an additional straightening device 106 that may be of the same type as the pull device 104 and which is at a rate equal to or approximately equal to v2.

This drawing device is suitable for facilitating the pulling of the pipe and does not in any way produce a further reduction of the cross section.

The blank 102 emerges from the molding device 101 with a discontinuous movement, the residence time corresponding to the return of the mold, and the blank is then operated in a continuous manner to the other devices in the plant by means of a linear speed drive pulley 102. The weighing of the free-rotating disk 108 surround 110 compensates for the absence of supply of material during the retention periods for the subject movement. The diameter of the subject at this moment is a value d1 and this is maintained on the ground a gas pressure inside the blank which prevents coincidence of the subject wall.

The blank with the diameter d1 then enters the drawing section 115 with velocity vl. The following drawing device 104, whose linear velocity v 2 is chosen to be higher than vl, then exerts a sense effect and the blank is pulled longitudinally. Its diameter is reduced to a value dll which is slightly less than dl as soon as the first pair of rollers 121a and its diameter reaches a value d2, substantially less than dl, with the outlet of the tank 15. owing to this longitudinal drawing. The form rolls 121til121d support the topic 102, since crosslinking has not yet taken place. The temperature of the drawing compartment 115 is selected so that the half life of the atcatalyst still has a long duration. 14

The temperature is near the temperature of the molding in the molding device, e.g. about 160 to 190 ° C. In the area of ​​the aperture 118 in the diaphragm 117, the subject has dimensional characteristics (diameter, thickness) determined from the dimensions of matter when it enters the drawing section 115. The blank then extends inside the cross section 116 where the temperature reaches higher than 200 ° C and preferably between 220 and 250 ° C. The cleavage of the catalytic converter produces the crosslinking of the material the retraction phenomena are terminated by means of the netting.

The position of the diafracrma 117 in the tank 103 depends on the desired diameter of the tube at the outlet of the crosslinking section 116, as this diameter is determined by the velocity ratio v2 / vl. Likewise, the different rollers 121a, 121b, 121c, 121d are dependent on each other as their configuration must be as accurate as possible to the profile to be obtained if this profile is predominant from the item 102 coming out of the molding device. However, if the profile to be achieved is a plain tube corresponding to the tubular blank 102, the staple rollers 121a, 121b, 121c, 121d need some calibrating orforming function but only carry and control the tubing. They are channeled by any similar devices.

At the outlet of the tank 103 and after passage through the drawing device 104, the pipe is cooled in the tank containing, for example, water. It is picked up by means of the pulling device 106 being wound up by means of the winding device 107. The notable feature of the product which is pulled and wound in this manner is its dimensional stability and absence of elastic memory or shrinkage.

A profile element of polyethylene, such as is drawn four times in the drawing section 115 and then cross-linked in the netting section 116, no shrinkage other than the thermal shrinkage undergoes. The netting blocks the pulled chains to the hyeratre. · '.. The crosslinked product is bi-heterogeneous while stable in its dimensions above and below the melting temperature of the polyethylene crystallites, except for the volume expansion. On the other hand, the same profile element will draw four passes in compartment 115 and then only cooling instead of crosslinking, assuming its original dimensions by impacting the resilient memory as soon as the temperature reads near 140 ° C which is higher than the melting temperature prepolyethylene.

The following examples are given to illustrate the invention with reference to the process represented in Fig. 6 and 7.

EXAMPLE 1 High-density polyethylene having a molecular weight of between 300,000 and 500,000, such as Available commercially under the designation "Manolene 56 020" was used to form a tube under the aforementioned conditions. Additives admixed aside from stabilizing agents and colorants of known types included a crosslinking agent comprised of 2,5,5-dimethyl-2,5- (ditert butyl peroxide) hexyn-3 sold under the designation "Luperox 130". The operating conditions for differential diameters by starting from a blank diameter of d1 = 27.5 are given in the following Table I. 16

TABLE I * 3 * 35.4 210 9.1 mx 240 15.4 14.50 0..9Q 41.6 ioor- (tn o tn m ΟΛ 00 ro • 00 • r-CO • 1-tm r_ σι i-1 CM to o i i 1 00 rsi oi-1 o O ¸ · ïŋ- ïŋ- ï · SP (N • * 3 · • 00 CN rH • • m Lfl ι-d O r-1 nj que X ro H o co or-1 tn o 00 ro o <0 rH • • 00 CM H • • • LO r-4 CTt r-1 (N 1 lom H MO £ 0 orO to Di Di • a 1 P £ P. RH · · .g ©. 1 X < 3 PPXP to tn x P free> H> Φ 0 P ftf i-l (3 P ¼ • HXPX CN P ro PXT Φ fi u Φ X Φ tn 0 p PPPX! CXP φ <3 Φ P \ P Φ P 0 XXX £ (3 XPX Φ Φ \ (3 XX £ <3 £ r-1 Μ £ P ¯ 3 ¢ r | (3 P (3 <D>> X free PPX Ή X fr> X Φ P ¼ T3 XXXPX Di p υ X> 1 0 0 X Φ £ xo free P free g Φ £ XX! X p X Φ PH • H £ to Ul free free X • HXP free τί p Ti r-1 free Φ • H • Η φ tn X Φ PP Φ P Φ Φ> XXP (3 x DX φ g φ 1-1 XX • α to ω p 'Di 0)3 P Φ Φ X 0 XD> 1 Φ d XXW An E <Ti DXX to> 17

The diameter d3 is somewhat smaller than the diameter d2. This printer is not from a trekking but only from a cooling shrinkage at the outlet of the salt bath in the tank 103.

Example 2

Other experiments were performed with the same mixture as in Example 1, with different parameters having the following values: vl = 36.6 m / hr v2 = 133 m / timedl = 27.5 mm d 2 = 18.5 mm

Temperature in draft: 180 ° C

'> Q

Temperature in cross section 230 C.

A 16 mm diameter tube was then obtained at the beginning and end of the extrusion and 2000 m in length. This tube was then subjected to tensile tests with results given in the following Table II.