DE2502181A1 - Welded joint - for fixing thermoplastic tubes to a transverse panel for automated production of (polyethylene) heat exchangers - Google Patents

Abstract

Ends of thermoplastic tubes are fixed into a transverse supporting plaque by providing the holes through the plaque with a conical mouth, using a heated block to soften the end of the tube from both the external and internal surfaces, and then using a shaped or inflatable mandrel to reshape the tube end to fit and weld with the mouth of the hole through the plaque. The heating block has a core mandrel of slightly smaller o.d. than the i.d. of the tube, extending within the tube to >= twice the depth of the conical mouth. The skirt of the heating block is ahped to heat the conical mouth and the corresp. outer surface of the tube simultaneously. Method is suitable for mfr. of heat exchangers etc., esp. using crystalline matls., viz polyethylene. Method provides a positively anchored bond without creating any flash or weld lip on the face of the plaque. The procedure is readily automated. Application of heat to both faces of the tube end and the adjacent region of the tube reduces thermal shock and gradient effects in the material. Weld pressure is applied evenly over a substantial proportion of the weld area.

Description

"Method for connecting pipes made of thermoplastic material with plate floors made of thermoplastic Eunststoff't The invention relates to a method For connecting pipes made of thermoplastic material with plate floors made of thermoplastic material Plastic in which a tube is inserted into a through hole in the plate base and the outer surface of the pipe end with the jacket surface of one formed on the bore conical recess is carbonized.

In the manufacture of heat exchangers, dry cooling elements or exchangers for air conditioning requires a variety of pipes to combine into bundles. The pipes are held in slab floors with the pipe ends are connected. For this purpose, the slab floors have through holes, in which the pipe ends are held and fastened.

In the case of heat exchangers, pipes can e.g. B. by heating element butt welding or welded to the bottom of the panel by heating wire welding with filler metal will.

Pickling gas welding is carried out in such a way that a conical recess is created at the end of each hole, along with the hole and the inserted The end of the pipe forms an annular gap in which the weld seams are laid.

Heizelementstumtfschweißung: The welding of full pipes and plate bottoms has also applied nan in the manufacture of heat exchangers from tubes and r Slab floors made of thermoplastic material.

To do this, you have to go into the ring-shaped notch that goes around the outside of the pipe extends, weld metal made of appropriate thermoplastic material inserted and the weld metal with the help heated by hot gas so far, that it is on the one hand with the lateral surface of the conical recess on the Bchrung and the outer surface of the pipe end on the other hand. This under the name Process known from hot gas welding processes can practically only be carried out by hand and requires great experience and skill. When heating the weld metal it must be ensured that the amount of heat supplied to the welding point sufficient to weld the weld metal and the corresponding parts of the panel bottom as well to melt the pipe, it must be ensured at the same time that the supplied The amount of heat is not so great that parts of the plate bottom or the parts to be welded Thermally dismantle the pipe.

Because in this process, the heat supplied to the weld can not be locally limited, also arise on the surface of the slab floor Irregularities which are aggravated by the fact that the amount of the in the Notch between the pipe end and the outer surface of the recess of the weld metal introduced does not exactly match the content of this column. In the then on the surface The irregularities of the slab floor often form fine cracks and notches, which are the reason for the formation of stress cracks and thereby for Destruction of the connection are. Due to the uncontrolled supply of heat there is also the danger that the extremely thin-walled pipes implode and the free pipe intersection is reduced.

It is also disadvantageous that in the method described as good as there are no possibilities for mechanization or automation.

The invention is based on the object of a method and a device specify that allow thermoplastic pipes with slab bottoms to combine from thermoplastic material quickly and economically so that a solid and permanent connection between the pipe and the plate floor is created.

In addition, a high degree of mechanization and the possibility of Aim for automation.

The solution to this problem consists in a method of the above described type in that the outer surface of the pipe end over a length that corresponds to the length of the conical surface, and the surface of the conical Recess are melted, and that then widened the melted pipe end and is pressed against the outer surface. In this process, the first result is the advantage that no additional scrap material is brought up to the connection point must be because the outer surface of the recess in the bore and the outer surface of the pipe end are welded together directly. The one to melt the The amount of heat required to be welded together depends on the type of the thermoplastic used. You can with help mechanical devices, one of which is described below, to the thermoplastic plastic can be transferred in a defined manner, while at the same time the material the pipe ends is softened so far that the subsequent expansion of the Pipe ends a destruction of the material is prevented and the expanded pipe end can be pressed against the outer surface. The pressing is done with a defined Contact pressure and a contact time, which in turn depends on the properties of the thermoplastic used.

Are pipes and plate floors together according to the method described welded, then a homogeneous connection is created.

The strength properties of this connection are then improved when, according to a further proposal of the invention, simultaneously with the Melting the outer surface of the pipe end the pipe end inside over a length, which corresponds to at least two to three times the height of the recess, to one The temperature is above the reach temperature of the plastic will. This achieves that too those to the actual welding zone subsequent parts of the pipe end are put into a state by heating, in which they allow further deformation chuze. Especially when it comes to run-up times of the pipe end is avoided that between the expanded and welded Area of the pipe end and the adjoining area of the pipe end Spann # r # -gen that arise in the event of a permanent change in stress, in particular permanent alternating bending stress, can lead to the destruction of the pipe ends.

The procedure described above is a combination of the Heating element butt and heating element socket welding processes, each type of process is technically improved.

The process described can be largely mechanized and automate with a device which, according to the invention, is characterized by a heating element with a heatable sleeve-shaped extension, the inner annular surface of which encloses a cylindrical interior space for receiving the pipe end and a heatable one Contains inner pin and its outer surface towards the free end of the approach conically tapered. The fused pipe end is widened by a press mandrel and pressed against the outer surface of the recess in the plate base. Heating element and Press mandrels can be attached individually or jointly to moving parts of the device be so that they one after the other over a hole in the plate floor in which a pipe to be attached, can be brought. For melting the outer surfaces of the pipe end and the conical surface of the recess in the bore becomes the heating element so driven over the hole that the pipe inserted through the hole with the to be melted Part of the pipe end inserted into the cylindrical interior of the sleeve-shaped extension can be. Accordingly, according to a preferred embodiment of the invention the diameter of the interior be dimensioned so that a melting of the Outer pipe surface is guaranteed. The height of the interior should be equal to or greater than that Length of the Itzantel.

The heating element is then introduced into the interior along with that Tube lowered onto the bore until the conical outer surface of the heating element is on the lateral surface rests in the recess of the hole. The required thermal energy to melt the outer surface of the pipe and the jacket surface, heating devices, either in the heating element or on its outer surface and its annular surface are housed, are transferred to the surfaces to be melted.

The importance of this process is characterized by the fact that im Inside the approach a mandrel is arranged concentrically to the inner ring surface, whose diameter is smaller than the channel diameter. This thorn serves the Heating of the tube up to one above the softening temperature of the one used Plastic lying temperature. It should therefore have a length that is at least corresponds to twice the length of the lateral surface. This ensures that During the subsequent expansion of the pipe end, there is no tension between the melted one Area of the pipe end and the adjoining area can occur. Simultaneously This mandrel serves to reduce the cross-section of the thermoplastic pipes, which often due to deformation after extrusion when pulling off or storing the pipes Has ovality, so that the introduction of the pipe end into the cylindrical Inner space, which is an annular space in the last-described embodiment, to facilitate.

When the surfaces to be welded are melted using the heating element are, the heating element is removed and the pressing mandrel over the bore or over brought the end of the pipe. According to a preferred embodiment, the press mandrel has Invention of a conical part and an adjoining connecting pin, whose diameter is smaller than the inside diameter of the pipe. Of the Press mandrel is lowered onto the connection point, with the guide pin in the Pipe end slides in. With increasing lowering of the press mandrel, it penetrates conically trained part of the press mandrel into the pipe end and expands this. Included the outer surface of the pipe end lies on the outer surface of the recess on the plate base and is pressed against this so that the two surfaces are welded together. Of course, the conical part of the press mandrel will be made as long as that depending on the type of plastic used, different contact pressures are applied can be.

The melting of the surfaces to be welded together, the expansion of the pipe end and pressing the surfaces to be welded together against one another under defined conditions is best achieved when the taper of the The outer surface at the recess of the plate base is equal to the characteristic of the outer surface is on the heating element and on the press mandrel.

Another possibility, that of expanding the pipe and pressing it on to apply the required forces on the surfaces to be welded together in that the pressing mandrel is cylindrical and has a removable jacket made of stretchable, temperature-resistant material, and that pressure medium channels in the press mandrel are provided which extend to the surface of the press mandrel. With this one Press mandrel are the forces required for deformation and pressing from one Pressure medium applied between the actual press mandrel and its expandable Jacket is pressed Since the pressure of the pressure medium is the same in all areas, are also the forces that the mandrel expands or presses on the pipe end applies, distributed very evenly over the press mandrel, so that the deformation of the The end of the pipe takes place under constant conditions and the contact pressure is applied to the parts to be welded Surfaces is very uniform.

In the following the invention is based on an exemplary embodiment Illustrative drawing explained in more detail; They show: FIG. 1 a section by means of a device allowing the connection of pipes made of thermoplastic material with plate bases made of thermoplastic material with the heating element in the working position is shown before lowering on the plate floor, Fig. 2 is a section through the device for connecting, in which the pressing mandrel is in the working position, Fig. 3 is a part of the object of Fig. 2 in a different embodiment.

The device shown in the figures is used to connect Tubes 1 made of thermoplastic and plate floors 2 made of thermoplastic Plastic. Of the device, only the essentials are essential for an understanding of the Invention required parts have been shown.

In the plate base 2 there are holes 3 in which the pipes 1 are held and attached. The holes 3 have on the free side of the plate bottom a recess 4, which is formed by a conical outer surface. 5 is limited.

The device has a heating element 6, which is attached to a not shown, movable part of the device is attached and with this via a bore 3 of the plate floor can be brought.

With the movable part, not shown, the heating element 6 are lowered onto the bore 3 or the pipe 1.

The heating element has a heatable, socket-shaped extension 7th

The inner annular surface 8 of the sleeve-shaped extension 7 encloses a cylindrical interior, which, as will be shown later, in the illustrated embodiment is designed as an annular space 9. The outer diameter of the annular space 9 corresponds the diameter of the tube 1, so that, as shown in the figure, that in the annulus introduced pipe end 10 rests with its outer surface 11 on the annular surface 8.

The annular space 9 is bounded on the inside by a concentric to the annular surface 8 arranged mandrel 12, which is firmly connected to the approach 7. This mandrel 12 has a diameter that is slightly smaller than the inner diameter of the pipe 1 so that it can be inserted into the pipe with tolerance. The length of the thorn 12 is twice the length of the illustrated embodiment Outer surface 5.

The outer surface 13 of the extension 7 is also conical, it tapers towards the free end of the approach 7. The conicity of the outer surface 13 of the projection 7 corresponds to the conicity of the lateral surface 5 of the recess 4.

The heating element shown in FIG. 1 is heated with the aid electrical resistance wires 14, which are on the outer surface 13 and the annular surface 8 of the approach 7 and on the outer periphery of the mandrel 12 are laid. These resistance wires 14 lead to the electrical connections, not shown in detail.

With the heating element 6 shown in Fig. 1, the outer surface 11 of the pipe end 10 and the jacket surface 5 of the recess 4 are melted. The amount the heat energy supplied depends on the properties of the thermoplastic Plastic from which the pipes 1 and the plate base 2 are made. To melt down the surfaces 5 and 11, the heating element 6 with the help of the 'not shown in detail movable part so far lowered on the plate base 2 until the outer surface 13 of the projection 7 rests on the lateral surface 5 of the recess 4. Simultaneously with melting the surfaces 5 and 11 is on the Resistance wires 14 routed around the circumference of the mandrel 12 heat energy to the inside Tube 1 delivered, causing the tube 1 over a length equal to the length of the mandrel corresponds, heated to a temperature above the softening temperature will.

After the heating process has ended, the heating element 6 is removed from the plate bottom 2 and the tube 1 lifted and replaced by a pressing mandrel 15, which is attached to a movable Part 16 of the device is attached. The press mandrel consists of a cone 17 and an adjoining Funrungadorn 18. The conicity of the cone 17 is the same the conicity of the lateral surface 5 of the recess 4.

When lowering the pressing mandrel 15, the slightly conical slide slides Guide mandrel 18 into the interior of the pipe end 10, so that the pipe 1 with respect to the cone 17 penetrating into pipe end 10 upon further lowering of press mandrel 1 is centered. In the course of the further lowering of the press mandrel i5, the cone penetrates 17 into the pipe end 10 and gradually expands this until the outer surface 11 of the pipe end rests on the jacket surface 5 of the recess 4. By further Assenken the press mandrel 15 can now apply compressive forces through which the Surfaces to be welded together are pressed together. Because the required Compressive forces from the properties of the plastic, from the pipes 1 and plate bottom 2 exist, depend> the cone 17 is longer than the surface 5, so that through Different lowering of the mandrel also generates different compressive forces can be.

In Fig. 3, another embodiment of the press mandrel 15 is shown. This press mandrel is cylindrical and has a removable jacket 19 made of stretchable, temperature-resistant material. In the press mandrel 15 are pressure medium channels 20th provided, which extends up to the surface of the press mandrel 15 extend.

The diameter of this press mandrel 15 is smaller than the inside diameter of the pipe, so that it can slide into the pipe end 10 when it is lowered. When the press mandrel 15 located in the pipe end 10, pressure medium is supplied through the pressure medium channels 20, which lifts the jacket 19 from the press mandrel 15. Under the effects of the pressure medium becomes the pipe end 10 is expanded and, as described above, lies with its outer surface 11 against the lateral surface 5 of the recess. Can by metering the pressure medium the contact pressure between the surfaces to be welded can be adjusted very sensitively.

The device described and the method to be carried out on it are particularly suitable for connecting pipes and slab floors made of polyolefins. The process of joining can be largely mechanized and automated, because the transport of the heating element and the pressing mandrel from a hole in the plate bottom on the other hand, as well as the change of heating element and press mandrel, no complex construction require. Also the insertion of the tubes into the associated holes in the panel floor can be mechanized, whereby it is only necessary to ensure that the pipes on the side of the recess slightly protrude the hole, so after completion of the welding process, the end faces of the pipes with the surface of the plate base finish smoothly. This removes the unevenness on the surface of the slab floor and the risk of cracking is reduced.

Patent claims:

Claims (10)

P a t e n t a n s p r ü c h e Process for connecting pipes made of thermoplastic material with plate floors made of thermoplastic material, in which a tube is inserted into a through hole in the plate base and the Outer surface of the pipe end with the lateral surface of one formed on the bore conical recess is welded, d u r c h e k e n n z e i c h n e t that the outer surface of the pipe end over a length that is the length of the cladding surface corresponds and the outer surface of the conical recess-be melted, and that the fused pipe end is expanded and pressed against the outer surface. 2. The method according to claim 1I d a d u r c h g e k e n n -z e i c h n e t that simultaneously with the melting of the outer surface of the pipe end the Pipe end over a length that is at least twice the height of the recess, to a temperature above the softening temperature of the plastic Ses is heated. 3. The method according to claim 2, d a d u r c h g e k e n n -z e i c h n e t that the heating of the pipe end takes place from the inside of the pipe. 4. Device for performing the method according to the claims 1 to 3, a heating element (6) with a heatable, socket-shaped extension (7), the inner annular surface (8) of which has a cylindrical interior (9) for receiving the pipe end (10) encloses and its outer surface (13) tapered conically towards the free end of the projection (7), and by a press mandrel (15) for hoof-widening and pressing the fused-on pipe end (10) onto the outer surface (5) the recess (4) in the plate base (2). 5. Apparatus according to claim 4, d a d u r c h g e k e n n -z e i c h n e t that the diameter of the inner space (9) corresponds to the pipe outer diameter and its height is equal to or greater than the length of the lateral surface (5). 6. Device according to claims 4 and 5, d a d u r c h g e k e n n z e i c h n e t that in the interior (9) of the approach (7) concentric to the inner Annular surface (8) a mandrel (12) is arranged, the diameter of which is smaller than the Inside pipe diameter is 7. Device according to claims 4 to 6, d a d u r c it is noted that the length of the mandrel (12) is at least twice as long Length of the lateral surface (5) corresponds. 8. The device according to claim 4 and one or more of the claims 5 to 7, d a d u r c h g e k e n n z e i c h -n e t that the press mandrel (15) a conical part (17) and an adjoining guide pin (18) whose diameter is smaller than the inner tube diameter. 9. Device according to claims 4 to 8, d a d u r c h g e k e n n z e i c h n e t that the conicity of the lateral surface (5) at a recess (4) of the plate base (2) is equal to # the conicity of the outer surface (13) on the heating element (6) and the press mandrel (15). 10. The device according to claim 4 and one or more of the claims 5 to 7, d a d u r c h g e n n n z e i c h -n e t that the press mandrel (15} is cylindrical is formed and a removable jacket (19) made of stretchable, temperature-resistant Has material, and that pressure medium channels (20) are provided in the press mandrel (15), which extend to the surface of the press mandrel (# 5).