DE2748164A1 - METHOD AND DEVICE FOR MANUFACTURING AN EXTERNAL CALIBRATED TUBE FROM A THERMOPLASTIC PLASTIC BY Means of EXTRUSION - Google Patents

Description

October 25, 1977 2748 D 5622 - dlsp

Jan Floris INGEN HOUSZ, Enschede, Netherlands

Method and device for producing an externally calibrated pipe from a thermoplastic Plastic by means of extrusion

The invention relates to a method for producing pipes from a thermoplastic material, in particular of pipes with a calibrated outer diameter, as well as a device for applying the method.

The invention aims firstly to shorten the residence time of the plastic at the processing temperature in such a way that that the plastic is at a higher temperature than usual or with a smaller amount of stabilizer to be added to the plastic, with which the so-called thermal degradation or

809821/0624 _ ₂ _

Oxidation at higher temperatures is prevented, can be processed.

Second, the invention aims to obtain an increased production rate of the pipe extrusion or the whole To be able to shorten the cooling path length

Third, the invention aims at the manufacture of the tube avoid the creation of internal tensile stresses on the inner wall of the pipe; these internal tensile stresses force to Choosing a pipe with a greater wall thickness than it actually reflects the pure strength properties of the pipe material would be necessary, in addition to which the tensile stresses increase the sensitivity to stress corrosion.

Fourth, the invention aims to be able to extrude a tube which arise without tensile stresses on the inner wall, but not on the outer wall dee tube tensile stresses introduce which were notably increase during dee transports the risk of damage to the pipe.

They purposes mentioned above are achieved in that in the method of the invention which is cooled on the outside in the Auetritt from the mold still in a plastic state tube located both on the inside as well as, where for the fatiMHiMimg dee tubes a coolant through a central cavity in the mandrel belonging to the molding tool is passed into the space that passes through

809821/0624 ' ³ '

the end area of the dome pointing in the direction of extrusion, through the inner wall of the tube over the part of the circumference that is being cooled, at which this inner wall leaves the mandrel, to at least the circumference at which the inner wall is strong enough for the cooling due to the cooling The use of sealing means has become, and is limited by these sealing means themselves, a cooled external caliber being available for the external cooling of the plastic pipe section, while said internally introduced coolant is kept under excess pressure in order to keep the plastic pipe section with the outer wall against said external caliber to press; after the circulation in said interior space, the coolant is diverted. The said end region of the dome is preferably kept cooled to a temperature which is lower than the temperature at which the processed plastic is at least almost solid. The preferred coolant is water. Furthermore, the overpressure of the coolant during circulation in the interior must generally be at least JQ kN / m.

By using a method such as that described above, a significant reduction in the residence time of the plastic at high temperature can be achieved; this shortening can be set at about 75% with regard to the cooling and calibration apparatus and used either to work at higher temperatures than usual or to increase the extrusion speed or to select the overall length of the apparatus mentioned to be smaller for the pipe being manufactured. Any combination of the effects mentioned can of course also be selected .

809821/0624

It is also possible to work with little or no stabilizing additive against thermal degradation and / or oxidation.

As a result of the effective cooling of the plastic pipe section from the inner wall, such a favorable radial shrinkage course is achieved in the pipe wall during the cooling after the Hardening received so that no internal tensile stresses arise in the inner wall area, but rather internal compressive stresses, which act as favorable preloads when the pipe is loaded by internal pressure. As a result of this favorable inner Stress distribution in the pipe wall can be used for a pipe that must be able to withstand a certain internal pressure Select a smaller wall thickness than for pipes manufactured using other methods · The selected smaller wall thickness still has an effect a further shortening of the dwell time of the pipe in the extrusion machine, so that mutually beneficial Benefits can be talked about.

The method according to the invention is particularly useful when processing polyvinyl chloride (PVC) into pipes. A considerably higher working temperature can now be selected, e.g. B. 215 ° compared to 195 ° Celsius with known extrusion methods. In the case of PVC, it is increased according to the invention maximum working temperature of particular importance, since it is to be expected that at higher temperatures, e.g. B. 205 ° Celsius with thick-walled and 210 ° Celsius with thin-walled PVC pipes, a product with better mechanical properties is obtained can be.

809821/0624 -5-

The invention also relates to an apparatus for applying the invention according to the method. Especially if the coolant is water, the plastic, which is in a plastic state, becomes one immediately after leaving the mandrel be subjected to intensive cooling. However, the problem arises that the mandrel also has a considerable Length before its end region a cooling is experienced, whereby the extrusion process is disturbed, z. B. by clamping of the pipe on the mandrel. This problem has been solved in the device according to the invention by that the outermost end region of the mandrel is separated from the remainder of the mandrel by thermal insulation.

To illustrate the invention, some exemplary embodiments are described with reference to the drawings, wherein some other special features and advantages are shown.

Figure 1 is a schematic longitudinal section of the essential Part of an extrusion device according to the invention.

Figure 2, like Figure 1, is a schematic longitudinal section, but of a variant.

In Figure 1, 1 denotes the pump part, in which a disk-shaped pump body 2 by means of an axis 3 is rotatably suspended. The disk body can be driven in any known manner, e.g. B. with help a V-belt pulley 4 · and a V-belt 5 »the through

809821/0624

smock not shown is driven. Sem pump part 1 the molded part 6 of the extrusion device follows. It includes a cuff-shaped tree 7 "which is through a Outer wall 8 and a mandrel 9 is limited and adjoins the pump chamber 10 in which the blades 11 of the disk body 2 rotate. The outer wall 8 and the mandrel 9 hold the cuff-shaped tree 7 with the help of the heating elements or 13 at the desired temperature. A calibration jacket 14 for the calibration is attached to the outer wall 8 the outside diameter of the pipe being manufactured 15 on; Water jackets 16 are attached around this calibration jacket 14. The dumbbell 14- for calibration is with holes provided, which serve that when starting the extrusion process, the first lengths of the forming hole 15 by means The negative pressure generated in the bores 17 mentioned can be sucked onto the calibration wall 14 for good guidance can. Downstream in the direction of extrusion of the drill seen, the drill 15 itself can be used directly as a wall be present using water jacket 18, which can be used independently of the first-mentioned water jacket 16.

In the example shown in the drawing, the mandrel 9 forms a solid whole with the disk body 2 and thus rotates with this. The whole of the axis 3, the disc body 2 and the mandrel 9 is with a central one Bore 40 provided through which two concentric lines 20 and 21 enter. The lines 20 and 21 have the connecting pieces 22 or 23 · The line

- 7 809821 / 06Π

is also concentric to the mandrel 9 and in one Distance from him; in the resulting circulation space 24 insulating material 25 is attached.

Downstream, the line 20 continues to the end region of the dome 9, where it is attached to the head end 26 of the dome 9 is. This head end 26 is connected to the mandrel via an insulating element 27, which is also centering for the Head end 26 can act. The material of the insulating element must meet various requirements; there must be temperatures can withstand temperatures of around 220 ° C without losing its rigidity or its load-bearing capacity; besides, it must be im In connection with the rotating mandrel 9, they have good sliding properties, and the plastic pipe passing through has little resistance offer and ultimately be machinable with exact dimensions. There are several materials known that can be used for this purpose suitable.

The line 21 protrudes in the direction of extrusion to approximately the end of the cooling part 16, 18 in the molding 6 of the extrusion device, while 21 bores 28 are made in the end region of the line.

The line 21 is connected at its end to a piston 29 which is provided with seals and to the conclusion of the Interior of the tube 15 is used.

With the device according to the invention described above the method according to the invention is as follows

809821/0624 " ⁸

43 274816A

applied. The disk body 2 pumps a plastic material that enters the pump chamber 10 in powder or granular form and there has been brought into a liquid state by heating means (not shown), into the heated cuff-shaped Tree 7i where the liquid hates, at the right temperature brought, assumes the drill shape and reaches the end of the mandrel at the end piece 26, where the mandrel is exited.

Cooling water is fed into the line 21 via the connecting piece 23 let in, which flows through the openings 28 into the tree 30, which passes through the wall of the drill 15, the end piece 26 of the dome 9 and the final piston 29 is limited. The piston is arranged at such a distance from the end piece 26 that that the drill 15 is already sufficiently hardened to the final piston 29 without being able to endure deformation.

The water in the tree 30 flows against the end piece 26 and cools this expediently, preferably so that a temperature is maintained which is lower than the temperature at that the processed plastic is at least almost solid. The drill 15 then normally receives before exiting of the end piece a firm, even thin skin on the inside. This drill comes out at 31 immediately after exiting the cuff-shaped tree 7 in contact with the cooling water, flowing through tree 30. So it's going to be extremely Intensive cooling of the inner wall area of the drill 15 under construction was obtained. Add to that, preferably a little downstream, the cooling brought about by the cooling jacket 14 with the water jacket 16. This Ab-

809821 / Oen -9-

cooling acts inwards from the outer wall of the pipe. The solidifying layers of the inner wall area and the outer wall area of the pipe meet each other about half the thickness of the pipe wall. Overall it can be said that the cooling time here about a fourth ·! from the time which is necessary to cool the same wall thickness from only one side until it has completely hardened.

The cooling water that flows out of the openings 28 into the space 30 has flowed, is discharged via the annular space 19 and the connecting piece 22; it is thus in countercurrent Exchanged heat. When regulating the cooling water circulation, it is ensured that the pressure of the cooling water in the room 30 has a sufficiently high value to prevent the solidifying tube 15 to press against the mold wall 14 that the desired Outside diameter of the finished pipe is obtained exactly. The saving in setting time, which, as I said, is set at 75% can be used, on the one hand, to determine the processing temperature of the molten plastic to choose at the optimal temperature, on the other hand to increase the production speed, or to increase the length to choose a shorter wall shape or to combine these possibilities with one another.

The cooling of the pipe wall from the inside leads to an internal stress curve after the maintenance, which at the inner wall area of the pipe has compressive stresses. These compressive stresses influence the stress curve in the pipe wall as a result of the internal pressure of the medium that the pipe is at

809821/0624 - ¹⁰ "

Use transported in a cheap way. This has the consequence that you can choose a thinner wall thickness for a drill, which must be suitable for a certain internal pressure and is produced by the method according to the invention than when made by any known method. In addition, compressive stresses in the area of the transported medium comes into contact with the inner wall, the material of the pipe is less sensitive to stress corrosion.

In the embodiment described above, the End area 26 of the cathedral 9 held still by means of the Hohr 20. This can be useful in some cases, but the Invention not limited to this embodiment · In others In cases it can be more expedient for the end region 26 to constitute a rotationally fixed part of the dome 9. In this case a rotatable coupling type must of course be selected for the connection 22.

Figure 2 shows an embodiment example with a stationary mandrel, in which the molten plastic is passed through an extruder known construction is delivered. The melt is fed in via channel 51 in connection piece 50 and via a Pre-distributor 52 passed into the helical channels 54 of the screw distributor 53. In such a distributor, the design of which is well known, the melt is fed via the in Extrusion direction flatter screw flights 55 of the channels gradually distributed over the entire circumference, namely

809821/0624

- 11 -

such that in the annular gap 57 between the housing 56 and the smooth end 73 of the distributor 53 a homogeneous extrudate, namely without web marks, is present, the mean flow rate of which in the extrusion direction is the same at every point on the circumference of the gap 57.

Downstream of the screw distributor 53 is the forming tool in the narrower sense, which comes from the housing 58 and the mandrel 59. The material from the annular gap 57 is conducted via a transition channel 60 to the outlet channel 61. The exit channel 61 mainly consists from the cylindrical inner wall 62 of the housing 58 and the with its concentric outer wall 63 of the dome 59 · The end area of the dome is formed by the head part 64, which is attached to the Coolant discharge pipe 65 is fastened, which in turn is attached to the end piece 68 by the nut 66 via some disc springs 67 of the distributor 52, 53 is screwed tight. In this way, the relative Change in length of the tube 65 compared to the core unit 52, 531 59 are caught by the disc springs 67. Of the Head part 64 connects by means of a profile edge 69 to the remaining part of the dome 59, which for this purpose with a corresponding profile edge 70 is provided.

In order to reduce the heat transfer between the head part 64 and the remaining part of the dome 59, in this case the head part with a taper 71 in the cylindrical part providing the surface available for heat conduction

809821/0624 -12-

- Y-

is kept small, while the head part 64 is also made of a material that the heat is relatively poor directs, e.g. B. 37% nickel steel. The mandrel 59 is with heating wire 72 provided, the capacity of which is chosen so that it releases the heat through the taper 71 of the remaining part of the dome can compensate exactly.

The installation shown in Fig. 2 is particularly suitable for making thick-walled polypropylene bores and made of high density polyethylene. A particular advantage of the embodiment of the device shown in Figure 2 is the possibility to make the head part 64 rotatable with respect to the rest of the dome, with a the end of the drill 65 acting drive. It has been shown that in the manufacture of a drill made of polyethylene high density a particularly flawless exterior surface by using a cooling water pressure in the order of 200 kU / m is obtained. Generally the inner surface the drill must be smooth, but somewhat wavy. The extent to which this wave formation occurs depends on the uniformity of the throughput of the extruder. This evenness is never ideal. The wave formation can, however can be largely suppressed when the head part 64 is slightly elongated. About the axial component of the friction vector between the head portion 64 and the ready hardened inner layer of the drill, it is useful that the Head part 64 rotates. The axial component of the friction

_ 13 _ 809821/0624

vector W is then equal to W times tangent alpha, where tangent alpha is equal to V / r ^w . V is the extrusion speed of the pipe in cm / sec, r is the inner radius of the pipe in centimeters and w is the speed of rotation of the head part 64 in radials per second.

809821/0624

■ 4 *

Blank page

Claims (16)

October 25, 1977 D 5622 - dlsp Jan Floris INGM HOUSZ, Easchede, The Netherlands Method and device for producing an externally calibrated drill from a thermoplastic Plastic by means of extrusion Expectations (1.! A method for producing a drill hole from a thermoplastic material by means of extrusion, with the Exit from the mold still in the plastic state drilling both on the inside and on the The outside is cooled, with the internal cooling of the Drill a coolant through a cavity in the mandrel that comes with the mold in the tree that passes through it the ead area pointing in the direction of the extrusion ÖO9821 / O6J4 of the dome, through the inner wall of the tube over the in cooling located plastic part of the perimeter on which this Inner wall leaves the mandrel, up to at least the circumference, on which the inner wall has become strong enough for the use of sealing means due to the cooling, and by this Closing means itself is limited, a cooled outer caliber being available for the external cooling of the plastic Hohrstück is while said internally introduced coolant is kept under positive pressure to the plastic earpiece to press with the outer wall against said caliber; after the circulation in said interior space, the coolant derived. 2. The method according to claim 1, characterized in that the coolant after circulation in said interior is drained through the cavity in the mandrel. 3. The method according to claim 1 or 2, characterized in that said end region of the dome is cooled to a temperature which is lower than the temperature at which the processed plastic is at least almost solid. 4. The method according to any one of claims 1 to 3 »characterized in that that the coolant is water. 5. The method according to any one of claims 1 to 4, characterized in that that the overpressure under which the coolant circulates in said interior of the pipe 809821/06? '«" ³ " is held, is at least 50 kN / m. 6. The method according to any one of the preceding claims, wherein the thermoplastic is polyvinyl chloride, characterized in that said material when leaving the actual extruder part of the extrusion machine ^{has an average temperature of at least 2CX) 0} Celsius, preferably at least 210 ° Celsius. 7. Device for applying the method according to one of the preceding Claims, characterized by extrusion means of any suitable type, forming tool, which among other things consists of a mandrel provided with a cavity, a piston that acts as a closure in the drill at the point, where the inner wall has acquired enough hardness, brackets to hold the piston in place, via the cavity in the Mandrel-directed supply and removal means for supplying and removing coolant into and out of the through the mandrel, the inner wall of the tube and the piston limited interior space, cooling medium for the outside of the tube, the part of the dome facing said interior space having an end region which is isolated from the rest of the cathedral. 8. Apparatus according to claim 7 »characterized in that in the case of a rotating mandrel, the cooled part of the dome stands still. 809821 / Oen 27A8164 9. Apparatus according to claim 7 »characterized in that when a standstill / mandrel rotates the cooled part of the dome, stands. 10. Device according to one of claims 7 to 9 »characterized in that that the holders for the piston are made out through the supply pipe of the coolant. 11. Vorric-htung according to claim 10, characterized in that the supply pipe for the coolant close to the piston in the named interior opens. 12. Device according to one of claims 7 to 11, characterized characterized in that the length of the cooled front part of the dome is greater than a quarter of the wall thickness and less than four times the wall thickness of the pipe produced. 13 »Device according to one of claims 7» 8 »10 to 12, characterized in that the pump element is a disk extruder, with the extruder disk of which the mandrel is firmly connected is. 14. Device according to one of claims 7 to 13 »thereby characterized in that the beginning of the cooled end region of the dome rises higher upstream than the beginning of the coolant on the outside of the pipe. 15. The device according to claim 14, characterized in that the distance between the beginning of the cooled end region of the dome and the beginning of the coolant on the outside of the tube is at least as great as the wall thickness of the tube, 809821/0624 while said end region is at least downstream a wall thickness of the tube extends beyond the beginning of the coolant on the outside of the tube. 16. Pipe made of thermoplastic material produced using the method according to any one of claims 1 to 6. 17 pipe made of thermoplastic material, produced with the aid of the device according to one of claims 7 to 15 809821/0624