JPH066329B2 - Method and apparatus for extrusion of plastic tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a hose of plasticized plastic material that includes a mandrel, a core having a substantially constant diameter and forming an extension of the mandrel, and surrounding the mandrel and the core. Passing between chill molds that move continuously in the machine longitudinal direction; pressing a hose against the mold surface of the chill mold by pressure molding; and of the sleeve portion formed on the mold surface of the chill mold. A sleeve portion is formed in the hose by pushing the hose portion into a recess having a shape corresponding to the shape, and the hose portion is depressed by exposing the inner surface of the hose to a medium of higher pressure than the outer surface of the hose. It relates to a method for the extrusion of plastic tubes, which comprises pushing in.

The ends of plastic tubes often have an expanded portion, or sleeve, which allows the tubes to be joined into a pipeline. Extension pieces are often used. Such an extension piece is a short tube having sleeves at both ends.

Presently, sleeves are generally formed by first heating the end of the tube and then pressing it against a mandrel having a diameter greater than the inner diameter of the tube, thereby expanding the end of the tube into a sleeve. Instead of a mandrel, for example as in DE-A-1,801,179, the extension can also be formed by pressing the end of the tube against an external mold by means of a pressure medium. Gas or liquid is used as the pressure medium.

The above manufacturing method is not only slow but also expensive. These processes require that the tube be manufactured in two steps, ie the tube must be fed to and removed from the sleeve machine in addition to the steps for forming the sleeve including heating, molding and cooling. Because, it takes time. These methods are expensive because the sleeves are formed by special machines, which are usually automatic.

U.S. Pat. No. 4,003,685 discloses a device for the production of corrugated plastic tubes by the blowing method. The device consists of a nozzle, a mandrel, an ejector tube and a plug at the end of the tube for contacting the inner surface of the tube. The tube is provided with openings so that pressurized air can be blown into the space between the nozzle and the tube of the plug, thereby cooling the plastic hose and pressing it against the mold surface of the mold. A portion of the mold surface of the chill mold contains a relatively large recess for the formation of a sleeve in the tube.

The disadvantage of this device is its complicated structure and the unreliable sealing effect of the plug, and in addition, this method may provide a two-layer tube with a sleeve for the inner wall to drop in at undesired places. Can not.

It is an object of the present invention to provide a method and a device that can be used to form a sleeve in a plastic tube in a way that is considerably simpler than was previously possible. The method according to the invention comprises a space for the high-pressure medium in the hose, which is formed by the sealing material formed by the plastic material located between the core and the cooling mold in contact with the front and rear walls of the recess, by means of a seal. It is characterized by being limited to.

In the process according to the invention, the plastics material itself acts as a sealing for the high-pressure medium space, so that no sealing element of any kind is required in the device.
Therefore, this method can be implemented at low cost.
Furthermore, the sealing method according to the invention is extremely reliable since no leaks occur.

In the production of pipes with a ribbed outer surface and a smooth inner surface, the cold die ribs located first after the mold cavity are at the entry point of the plastic material, or the ribs pass past the entry point. It can be carried out by creating a pressure difference when The ribs are preferably located in the area of the nucleus.

The wall of the finished sleeve portion is usually thinner than the wall of the tube portion because the recess forming the sleeve portion has a greater distance from the mandrel than the rest of the mold surface. In ribbed tubes, the sleeve portion has no ribs, which to some extent compensates for the thinning of the wall.
If necessary, the thickness of the wall of the sleeve part is made equal to that of the tube part by advancing the cooling mold at a slower than normal speed to the tube of formation of the tube part located in the area of the depression. Can be kept equal. It should be noted that the wall thickness of the sleeve section produced by the known method is always less than the wall thickness of the tube section.

The present invention further provides a substantially cylindrical mandrel, a core having a substantially constant diameter and forming an extension of the mandrel, a mold surrounding the mandrel and continuously formed along a circulation path. A moving cold mold, the mold surface of the cold mold including at least one recess corresponding in shape to the sleeve portion, for supplying a mandrel and a hose of plasticized plastic material between the core and the cold mold. Nozzle,
And a device for the extrusion of plastic tubes, which comprises means for pushing a part of the hose into the recess.

The device of the invention is characterized in that in the axial direction of the nucleus, the nucleus has a length of at least a mold cavity.

According to the invention, the sealing of the pressure medium space is such that the space defined between the mold surface of the chill mold and the core is completely filled with plastic material at the front and rear walls of the recess,
It is formed automatically when the core has at least the length of the mold cavity. The device is simple as it does not require a separate sealing.

The means for pushing into the recess of a portion of the hose can be produced by a pressure medium supply element located in the nucleus. Therefore, in terms of reliable operation, it is advantageous that the distance of the feed element from the nozzle for the plastic material is at least equal to the length of the depression in that direction.

Most simply, the pressure medium supply element is a peripheral groove formed on the surface of the nucleus, which is in communication with the source of pressure by means of a passage provided with a valve.

Alternatively, the hose portion can, of course, be pressed at the bottom of the well by a vacuum or vacuum created between the hose and the bottom of the well.

One preferred embodiment of the present invention will be described below in more detail with reference to the drawings.

The device shown in FIG. 1 comprises chilling dies 1 and 2 which move along two circulation paths and abut one another in the area of the guide rails to form a cylindrical dies. An extrusion sleeve 4 connected to the extrusion head 6 of the extruder 5 extends into this mold. FIG. 1 also shows how the finished tube 7 projects from the other end of the mold formed by the cooling mold.

FIG. 2 shows in more detail the parts of the device involved in the extrusion of the tube. A mandrel 8 having a straight part and a conical enlarged part is located on the central axis of the device,
A core 9 having a constant diameter forms an extension of the mandrel. A cavity (not shown in the figure) for the coolant is provided at the end of the nucleus. The extrusion sleeve 4 and the core 9 define a ring nozzle 10 between them, through which the plasticized plastics material is fed in the form of a hose 11 into the space formed between the cooling mold and the mandrel. To provide a tube with a ribbed outer surface, an annular rib 12 is provided on the inner surface of the chill mold, with a groove 13 formed therebetween, and a rib 14 is formed by pushing plastic material therein. The chilled groove 13 is
As shown in FIG. 2, a passage 15 extending from the bottom of the groove to the outer surface of the cooling mold communicates with the atmosphere.

Instead of ribs 12 and grooves 13, at least one pair of chills has a relatively large recess 16 whose side and bottom walls conform in shape to the outer surface of the sleeve portion of the tube, thus In the direction perpendicular to the axial direction of the device 1
Deeper than 3 and long in the axial direction of the device. On the other hand, the nucleus 9 has a peripheral groove 17 formed on its surface, and a passage 18 communicating with a source (not shown) of a pressure medium such as air is formed in the groove 17. It has an opening in the side wall. The passage 18 is equipped with a valve 19. Groove 17 acts as a thermal barrier between the hottest part of the core closest to the mandrel and the cold part at the free end of the core.
From FIG. 2 it can be seen that the plastic material filling the space between the cold mold and the core forms the sealings 20 and 21 near the walls before and after the depression and the distance of the groove 17 from the sealing point 21 is the axis of the device. It is clear that in the direction it is greater than the length of the recess 16. The length of the nucleus in the axial direction is at least equal to the length of the depression 16 in the same direction.

The device shown in FIG. 2 operates as follows. For the production of ribbed plastic tubes, plasticized plastic material is fed through the nozzle 10 in the form of a hose into the space defined between the cooling molds 1, 2 and the mandrel 8. As shown in FIG. 2, ribs and grooves 1 are formed on the mold surface.
When the chill with 2, 13 is located at the nozzle 10, the plastic material completely fills the space between the chill and the mandrel, as also shown in FIG. As the chill moves to the right in FIG. 2, a solid walled plastic tube is created with a ribbed outer surface and a smooth inner surface.

However, when the dimple 16 reaches the nozzle 10, the hose 11 cannot fill the entire dimple due to the large volume of the dimple, but the hose is slightly thicker than the normal wall thickness around the nucleus 9. Form the layers. This increase in thickness is due to the absence of ribs 14. This continues until the entire depression has passed by the nozzle 10, and then again the production of the ribbed tube begins.

FIG. 2 shows the depression 16 just past the nozzle 10 and the depression already filled with plastic material. The hose 11 then completely fills the space between the cooling mold and the core before and after the depressions at points 20 and 21, resulting in an isolated area at the depression 16. After the wall in front of the recess has passed the groove 17 in the core, pressurized air is blown from the groove between the hose 11 and the core, as indicated by the arrow, as a result of which the hose resting on the core is , Pressed against the wall of the depression, as shown in the figure. Pressurized air may be supplied continuously from the groove 17, however, valve 19 is used to regulate the air supply such that air is supplied only when the recess 16 is located in the groove. It is also possible to do so. The passage 15 in communication with the atmosphere allows the air filled in the well to be expelled from the well together with the shaping of the sleeve portion. The sleeve portion is designated by the reference numeral 22. The tube formed in the device is cooled at the free end of the core 9 and in the cooling molds 1, 2 by a cooling liquid flowing in a passage not shown in the figure.

FIG. 3 shows a section of a tube produced using the device according to the invention. Cutting the cooled tubes in the middle of the sleeve section results in two tubes, each tube having a sleeve at one end. As can be seen, there is a shallow groove 23 on the inside of the tube at the cut point. This groove can be easily formed by providing a shape corresponding to the bottom of the depression. This groove facilitates pushing the straight tube end into the sleeve. If desired, cutting the tube at the groove 23 in the device by increasing the internal pressure of the tube above the breaking limit of the hose, thereby removing the hose portion located at the groove through the passage 15. You can also

Instead of the pressurized air or to increase the effect on the pressurized air, the suction action for pressing the hose against the wall of the depression 16 by connecting the passage 15 opening into the depression 16 with a vacuum source. Can be used.

The device and method according to the invention have been described above in connection with the manufacture of tubes with solid walls and external ribs. However, the method according to the invention can also be applied to the production of tubes with smooth inner and outer walls or tubes with a hollow two-layer wall, the outer layer being corrugated. An embodiment of this kind is shown in FIG. The operation of the device is similar to that of the device of FIG. 2 except that pressurized air is supplied from the groove only when the indentation 16 is located in the groove, for the following reasons. Otherwise, the walls could sink. Thus, when the ribs 12 of the cooling die, which are located first after the depression of the die, reach the core 9, a pressure difference is created, and this rib 12 produces a groove in the core 1.
Remove the pressure differential before reaching 7.

In addition to air, the medium supplied from the groove 17 may be other gas or liquid. Although it is advantageous from a manufacturing process standpoint that the hose is not pressed against the wall of the depression 16 until a sealing 21 is formed between the depression and the nozzle 10, the distance from the nozzle 10 to the groove 17 is the axial direction of the device. Smaller than the length of the dimple at
It is also possible thereby to configure the device in such a way that the molding of the sleeve portion 22 already starts before the entire depression has passed the nozzle. Passage 15
Can be omitted in some cases.

The wall of the sleeve portion 22 advances the cooling mold forward at a lower than normal speed when the indentation 16 is located in the area of the nozzle 10 and, as a result, the plastic material into the nozzle at a normal speed. As long as it is supplied, the plastic layer on the surface of the mandrel can be made as thick as the wall of the tube section by making it particularly thick in the area of the depression. It should also be noted that the invention makes it possible to produce double sleeves, ie short pieces of tubing having sleeves that open in different directions at both ends. Such a double sleeve is used as an extension piece.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for manufacturing corrugated or ribbed tubes. FIG. 2 is an enlarged vertical sectional view of a detail of an apparatus used for manufacturing a ribbed tube. FIG. 3 shows the finished ribbed tube. FIG. 4 is a vertical cross-sectional view of details of an apparatus used for manufacturing a two-layer tube.

Claims (10)

[Claims] 1. A hose (11) made of plasticized plastic material, a mandrel (8), a core (9) having a substantially constant diameter and forming an extension of the mandrel, and a mandrel and core. It passes between the cooling molds (1, 2) that surround and move continuously in the axial direction of the device; the hose is pressed against the mold surface of the cooling molds (1, 2) by pressure molding; Recess (16) having a shape corresponding to the shape of the sleeve portion formed in the surface of the die (1, 2)
Hose (11) by pushing the hose part inside
A sleeve portion (22) is formed therein, the hose portion being adapted to the medium of higher pressure than the outer surface of the hose (1).
1) A method for manufacturing a plastic pipe, which comprises pressing the inner surface of the hose (1) into the hollow (16) to make the space for the high-pressure medium in the hose (11) a core (9) and a cooling mold (1). , 2) with a sealing material (20, 21) formed in contact with the front and rear walls of the space by means of a plastic material located between the mold recesses (1
Method characterized by being limited to the area of 6). 2. The ribs (12) of the cooling mold which are initially located after the depression of the mold create a pressure difference when they reach or pass the entry point (10) of the plastic material. Method according to claim 1, for the manufacture of a tube (7) having a ribbed outer surface and a smooth inner surface. 3. A method according to claim 2, characterized in that a pressure differential is created when said ribs (12) reach the core (9). 4. When forming the hose part to be placed in the cooling mold (1, 2) in the area of the recess (16),
A method as claimed in claim 1, characterized by advancing at a speed lower than the normal speed. 5. A pressure difference is produced when the rib (12) of the cooling die which is located first after the depression of the die reaches the core (9), and the pressure provided by the rib (12) in the nucleus. Media source (1
Characterized by eliminating the pressure difference before reaching 7),
The method according to claim 1. 6. A substantially cylindrical mandrel (8), a core (9) having a substantially constant diameter and forming an extension of the mandrel, a mold surrounding the mandrel and continuous. A cooling die (1, 2) moving along an endless path, the cooling die surface including at least one depression (16) corresponding in shape to a sleeve portion (22), a mandrel (8) and A nozzle (10) for supplying a hose (11) made of a plasticized plastic material between the core (9) and the cooling molds (1, 2) and a part of the hose (11) are placed in a recess (16). In a device for the extrusion of plastic pipes comprising means (17) for pushing in, the core (9) is at least in the axial direction of the core the mold cavity (1).
A device having the length 6). 7. Means for pushing the hose part into the recess is a pressure medium supply element (17) located in the core (9).
A device according to claim 6, characterized in that it is formed by means of: 8. Device according to claim 7, characterized in that the distance of the feed element (17) from the nozzle (10) is at least equal to the length of the recess (16) in the same direction. 9. The pressure medium supply element is formed by a peripheral groove (17) provided on the surface of the nucleus (9), the groove being a source of pressure through a passage (18) provided with a valve (19). Device according to claim 7, characterized in that it is in communication. 10. Device according to claim 6, characterized in that it comprises a passage (15) opening in the recess (16) and in communication with the vacuum source.