NL1007746C2 - Mirror welding process for joining together thermoplastic material pipe sections end to end - Google Patents

Abstract

A closure part is pressed tightly against the opposite end of the pipe section to the heating plate and a vacuum is generated inside the resulting sealed cavity in order to clamp the pipe section against the plate. A method for joining together by a mirror welding process two pipe sections (1, 2) comprising a thermoplastic polymer material, each pipe section having a connector end with a ring-shaped wall and end wall, comprises the following steps : (a) each connector end is heated to a temperature at least equal to the processing temperature of the thermoplastic material, using a mirror welding machine containing two heating plates (3, 4), the first pipe section (1) having its end wall pressed against the first plate (3) and the second pipe section (2) having its end wall pressed against the second plate (4) in order to soften the connector ends ; (b) the mirror welding machine is removed ; (c) the softened connector ends of the two pipe sections are pressed together to form a bond ; and (d) the bond region is cooled. Prior to step (a) an airtight seal is formed by pressing a closure part (5, 6) against the opposite end of the pipe section to the heating plate, forming a sealed cavity (7, 8) bordered by the pipe section, heating plate and closure part. An underpressure is then created inside the cavity to assist clamping of the pipe section against the heating plate. An Independent claim is also included for the mirror welding machine.

Description

Short indication: Method and device for mirror welding of plastic pipe parts.

The invention relates to mirror welding of pipe parts of thermoplastic plastic material.

Mirror welding is a well-known technique for joining pipe sections together. The 5 pipe parts are each pressed with their end face against an associated heatable plate of a mirror welding machine, so that the temperature of the end of the pipe part pressed against the plate rises above the softening temperature of the plastic material. The mirror welding device is then quickly removed and the still soft connection ends of the pipe parts are pressed together, whereby the desired connection is created.

Mirror welding machines are known for small pipe diameters, wherein the pipe parts must be pressed by hand against the heatable plates of the mirror welding machine. Mirror welding installations are known for mirror welding of larger pipe diameters, in which a pipe support for clamping a pipe is included on either side of the mirror welding device. In order to press the tubes against the plates 20 of the mirror welding device, each tube support is displaceable perpendicular to the surface of the heatable plate over an associated straight guide. The tube can be displaced here by hand or with the aid of controllable mechanical pressing means, for instance with hydraulic cylinders.

It is known that as a result of the softening of the connecting ends of the pipe parts lying against the heatable plates, the length of those pipe parts decreases, as a result of which a pipe part has to be moved towards the plate of the mirror welding device during heating in order to obtain the desired contact between the pipe. and guarantee the heatable plate.

It has been found that when pressing the pipe parts against the heatable plates by hand, the quality of the compounds obtained is insufficiently controllable and varies undesirably. The known mirror welding installations with controllable mechanical clamping and pressing means for the pipe parts do provide a reliable connection between the pipe parts, but are undesirably complicated and expensive.

The present invention aims to improve the known mirror welding method in such a way that a good and reproducible quality of the connection between the pipe parts can be guaranteed with simple means. In particular, the invention contemplates an application of the method in the production of elbows, which are composed of elbow segments joined together by means of mirror welding.

The present invention provides a method according to the preamble of claim 1, characterized in that for pressing the pipe parts against their heatable plates of the mirror welding machine with their end faces, each pipe part is at a distance from the associated heatable plate of the mirror welding machine with a the associated first and second closing members are hermetically sealed, so that in the first and second tube sections, respectively, a first and second closed space is obtained, which is bounded by the respective tube section, the associated heatable plate and the associated closing member, and because in each closed space a underpressure is effected, which underpressure provides at least a part of the contact force of the pipe section concerned against the associated heatable plate of the mirror welding apparatus.

Due to the negative pressure in the closed spaces relative to the environment, the pressure of the tube parts against the plates of the mirror welding machine is automatically maintained at a constant value despite the aforementioned decrease in the length of the tube parts due to the softening of the heating connection ends. . The value of the underpressure in the 10 0 7 746¾ - 3 - pipe sections can be easily regulated, so that an expensive control such as in the known mirror welding installation with hydraulic pressure means can be dispensed with.

The invention provides a preferred embodiment, in which after forming the softened areas on the pipe parts to be joined using the mirror welding device, underpressure in the interior of the pipe parts is used to press the pipe parts together to form the intended connection. .

A further advantageous embodiment of the method according to the invention provides for the production of bend pieces, which are composed of several bend segments which are attached to each other by means of mirror welding.

The present invention further provides a mirror welding installation with which the method according to the invention can be carried out. This mirror welding installation and advantageous embodiments thereof are described in the subclaims and the following description.

The present invention will be explained in more detail below with reference to the drawing. In the drawing: Fig. 1 shows a side view, partly in section, a schematic representation of a first embodiment of the method and installation according to the invention, Fig. 2 shows in side view, partly in section, a schematic representation of a second embodiment of the method and installation according to the invention, fig. 3 in side view, partly in section, a schematic representation of a third embodiment of the method and installation according to the invention, fig. 4 in side view, partly in section, a schematic representation of a fourth embodiment of the method and installation according to the invention, fig. 5 schematically in cross-section connecting the pipe parts heated with the aid of a mirror welding device, fig. 6 in vertical section schematically a device 10077 4 S. i - 4 - for simultaneously mirror welding of several pipe parts, fig. 7 partly in cross-section and schematic of the production of a bend of three bend segments prior to heating the bend segments in the manner according to the invention by means of mirror welding, fig. 8 a later stage of the production of the bend piece of figure 7, fig. 9 schematically an arrangement for simultaneous production of several elbows in the manner according to the invention, and Fig. 10 schematically a mirror welding installation for welding together pipe sections of considerable length in the manner according to the invention.

Figure 1 shows a first pipe part 1 and a second pipe part 2 of thermoplastic plastic material, for example polyethylene, which must be connected to each other by means of mirror welding. In this example, the first and second pipe parts 1, 2 are cylindrical and have an identical cross section. The invention is of course not limited to such a cross-section and shape of the pipe parts, the pipe parts can for instance also be rectangular profiles, for instance for a plastic window frame, or a pipe part can be a bend, T-piece or the like.

Each tube part 1, 2 has a connecting end with an annular wall and associated end face and it is intended that the connection ends with their end faces are joined butt-to-butt.

In figure 1, a first heatable plate 30 and a second heatable plate 4 of a mirror welding apparatus can also be recognized. The plates 3, 4 are substantially flat and parallel to each other and can be heated by heating means of the mirror welding machine, for example a hot air heating or an infrared heat radiator, which are not known and known per se. As is well known in mirror welding, the first pipe part 1 with its end face against the first heatable plate 3 and the

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: <: '- ·; The second tube part 2 with its end face pressed against the second heatable plate 4, the heating of the plates 3,4 and the heating period being such that at each connection end a softened area is formed with a temperature above the softening temperature of the plastic material is lying.

Then, the mirror welding machine is removed and the tube parts 1,2 are pressed together with their softened ends so that the desired connection is formed. Finally, the heated area is cooled and the joint is firm.

For pressing the pipe parts 1, 2 against the heatable plates 3, 4 of the mirror welding apparatus with their end faces, a first and a second sealing member 5, 6 are provided, respectively, with which the first and second pipe parts 1, 2, respectively, at a distance of the associated heatable plate 3, 4 of the mirror welding machine must be hermetically sealed. The closing members 5,6 are provided with locking means, which prevent the closing members 5, 6 from sliding into the relevant pipe section under the influence of an underpressure to be effected later. In the first and second tube part 1, 2, a first and second closed space 7, 8 are respectively obtained by the closing members 5,6, which is bounded by the respective tube part, the associated heatable plate and the respective closing member.

The pressing force with which the tube parts 1,2 are pressed against the associated plate 3,4 of the mirror welding apparatus is here provided in that an underpressure relative to the environment is effected in each closed space 7,8. This negative pressure provides, if possible, the total required pressing force of the pipe section concerned against the associated heatable plate of the mirror welding machine, if necessary additional pressing means can be provided. Tests have shown that for many pipe cross-sections an underpressure of 0.4 to 0.2 bar is sufficient to provide the total contact pressure, so that the process can be carried out in the absence of others. Ü i; * v ö "Ή - 6 - means providing a contact force.

The effect of the underpressure is realized in figure 1 in that a vacuum line 9 extends through each of the shut-off members 5,6 which communicates with the closed spaces 7, 8 in the tube parts 1,2 and which leads to a vacuum pump 10. By using internal negative pressure in the pipe sections 1,2 to press it against the mirror welding apparatus, the decrease in the length of the pipe sections 1,2, which is due to the softening of the heating pipe ends, is automatically compensated and the pressure against the plates 3,4 remains guaranteed. The arrangement ensures that the underpressure in both closed spaces 7, 8 is equal, so that the force with which both tube parts 1,2 are pressed against the plates 3,4 is also the same. This leads to uniform heating and a symmetrical connection when the pipe sections 1,2 are pressed against each other later. Furthermore, no resulting lateral force is exerted on the mirror welder, and any base 20 of the mirror welder, if present, may be light.

Naturally, a control device can be provided which varies the value of the underpressure in the tube parts according to a predetermined program during the softening of the ends of the tube parts. Furthermore, if necessary, an internal support can be provided for the ends of the pipe sections to be heated, in order to prevent these softened pipe sections from moving inwards. However, tests have shown that an internal support is often not necessary. Instead of an internal support of the areas of the pipe parts to be heated, provision can also be made for applying a negative pressure to the outer surface of the areas to be heated, so that there is no inwardly directed pressure on these areas.

When the pipe parts have a great length, it is advantageous not to mount the closing members on the end thereof which faces away from the mirror welding device,

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Lu:. 0 - 7 - as shown in figure 1, but closer to the heatable plates 3, 4, so that the closed spaces 7,8 have a smaller volume and thus less air has to be extracted to achieve the desired underpressure. In another variant 5, a filler body, for example a tube closed at both ends, can be introduced into the space between the heated plates and the closing members in order to reduce the volume of the closed spaces 7, 8. This filling body can also form part of the mirror welding machine and protrude from the plates 3,4 as a kind of pin 10.

In order to be able to relieve the realized underpressure in the pipe parts 1,2 in order to remove the mirror welding device, an aeration valve 11 is provided, which can also be designed as a pressure control valve or in combination with such a pressure control valve 15.

Figure 2 shows a variant of the arrangement of Figure 1, in which a passage 15 is provided between the plates 3,4 of the mirror welding device, so that the closed spaces 7 and 8 communicate with each other via this passage 15. In Figure 2, therefore, only a vacuum line from the interconnecting spaces 7, 8 leads to the vacuum pump 10 via the first shut-off element 5. The method is substantially identical to the description in Figure 1 and need not be further explained here.

Figure 3 shows an arrangement in which the vacuum pump 10 is connected to the mirror welding device and not to the shut-off members 5,6 in the pipe parts 1,2 as in Figures 1 and 2. Vacuum channels 17 are formed in the mirror welding device, which lead to the pipe sections 1,2 oriented surface of the two plates 3,4. Via those channels 17, the mouths of which in the plates 3,4 are located within the contour of the adjacent pipe parts 1,2, a vacuum can be effected in the closed spaces 7,8 by means of vacuum pump 10 or the like.

Figure 4 shows an extension of the arrangement of Figure 2, which extension comprises a pressure vessel 18, which connects via a corresponding pipe with a valve 19 1007746-1 - 8 - to the vacuum pump 10 and via a branch pipe with controllable valve 20 on the closed spaces 7, 8 in the pipe parts 1, 2. When manufacturing a mirror weld, an underpressure is effected in advance in the pressure vessel 18 by operating the pump 10 with open valve 19 and closed valve 20. When the intended negative pressure has been reached in the pressure vessel 18, the pump 10 is stopped and the valve 19 is closed. When the pipe parts 1, 2 are placed against the mirror welding device, both shut-off valves 19, 20 are opened, so that the closed spaces 7, 8 come into contact with the pressure vessel 18. This will allow the pressure in the closed spaces 7, 8 to drop rapidly. to the desired negative pressure value. This arrangement makes it possible to use a vacuum pump with limited capacity and yet quickly achieve the desired negative pressure. A negative pressure in the pressure vessel 18 can also be obtained by first filling the pressure vessel with water vapor, then closing the vessel and then condensing the water vapor, for example by spraying cold water into the pressure vessel 18.

Figure 5 shows the pressing of the tube parts 1,2 against each other after the connecting ends of the tube parts to be joined together have been heated above the softening temperature of the plastic material with a mirror welding device. For pressing the pipe sections 1,2 against each other, each pipe section is hermetically sealed at a distance from the connecting surface by an associated closing member 5,6. As a result, a closed space 20 is formed by the two tube parts 1,2 and the closing members 30 5,6. A pipe passing through the shut-off member 5 is connected to a vacuum pump 10, so that underpressure can be realized in the closed space 20 and the softened end faces of the pipe parts 1,2 are pressed firmly together and the intended connection between the pipe parts 1,2 35 is obtained. Optionally, a temporary internal support for the pipe parts to be connected can be provided at the location of the welded connection, which internal support 10077 4 6. - 9 - prevents the soft ends of the pipe sections from bulging inwards.

Figure 6 shows an arrangement with which several mirror welded connections can be realized simultaneously in several products. The arrangement comprises a frame 30 with a plurality of first shut-off members 5, a common conduit passing through each of them, connected to a vacuum pump 10 or the like. A first pipe part 1 is placed on each first closing member 5, so that that pipe part 1 is closed airtight on that side. A mirror welding machine of the type shown in Figure 2 can be placed on each of the first pipe parts 1, optionally a single mirror welding machine can be arranged for manufacturing several mirror welds. The second tube parts 2 are then placed on the mirror welding devices 15, which in turn are each closed at the top by an associated second sealing member 6. With the arrangements described here, mirror welding connections can be manufactured in the manner described above.

Figures 7 and 8 show different stages of manufacturing a bend of thermoplastic plastic material. The elbow shown by way of example is composed of a first, second and third elbow segment, respectively. 70.71.72. These bend segments 70, 71, 72 are each a straight cylindrical pipe section with non-parallel end faces and have the same cross section. The bend segments 70, 71, 72 are connected to each other by placing a first mirror spindle 75 between the first and second bend segment and between the second and third bend segment 30 a second mirror splicer 76, the first and second mirror splicers 75, 76 being provided with a passage resp. 77, 78 between heatable plates thereof as has been explained with reference to figure 2.

Furthermore, the first and third bend segments 70, 72 are hermetically sealed at a distance from the first and second mirror welding apparatus 75, 76 with a first and second closing member 80, 81 respectively. On the closing member 81 closes' UU i-> 'ru' i - 10 - a vacuum line leading to a vacuum pump 10 or other vacuuming device. When, contrary to the one shown in figure 7, all bend segments lie with their end faces against the heatable plates of the mirror welding machines and the 5 closing members 80, 81 are fitted in place, in the closed space now formed in the bend segments 70, 71, 72 effected an underpressure. As a result, the bend segments 70, 71, 72 are pressed against the plates of the mirror welding machines 75, 76 with a suitable pressure. This does not require complex clamping and pressing mechanisms for the bend segments, and the pressing of all end faces against the heatable plates is also the same. When the end faces are sufficiently heated and softened, the underpressure in the closed space is released, for example via a vent valve (not shown) in the line to the vacuum pump. Subsequently, the mirror welding devices 75, 76 are removed, after which the bend segments are soon placed with their end faces against each other, so that the arrangement 20 shown in figure 8 is achieved. By subsequently again creating an underpressure in the closed space in the bend segments 70, 71, 72, the softened areas of the bend segments are firmly pressed together and the intended connections are obtained. In many cases a recognizable thickened edge is formed at the end of each bend segment, as can be seen from figure 8.

Figure 9 shows an arrangement with which three elbows of the type described with reference to Figures 7 and 8 can be manufactured simultaneously. For this purpose, six mirror welding machines of the type shown in Figure 2 are used, each one in the places circled in Figure 9, and two closing members at the outer ends of the axially opposite bend segments. At the locations indicated by arrows A and B no mirror welding apparatus is set up and the end faces lie directly against each other. If desired, a seal can be fitted at or around the seam between the two end surfaces to achieve a single closed space in all bend segments. By connecting via one or both shut-off members to a vacuum pump or the like, the required pressing of the 5 bend segments against the mirror welding devices can be obtained. Mirror welding machines of the type shown in Figure 3 can of course also be used. After softening the ends of the bend segments to be joined together, the underpressure in the bend segments 10 is released and the mirror welding devices are removed. Then, as shown in Figure 8, the bend segments can be pressed firmly together using internal negative pressure.

Figure 10 shows an arrangement suitable for welding long pipe sections together, for example the pipe section 1 is twelve meters long and the pipe section 2 is an already long pipe which has already been laid. The arrangement comprises a mirror welding machine of the type shown in figure 2 with two heatable plates 3,4 and a connection between two plates 3,4. The pipe part 1 is airtightly closed at a relatively short distance from the end face thereof to be joined by an expandable sealing member 90. This sealing member 90 is introduced into the pipe part 1 in a reduced diameter state and expanded when it is in place so that it is firmly seals on the inner wall of the pipe section. A hollow rod 91 protrudes from the free end of the pipe part 1 and is connected to a vacuum pump 10. The pipe part 2, which has already been laid, is closed at a distance from the connection to be fitted by a closing member 95 which, like a robot, is independently driven is movable in the tube 2. The closure member 95 has an electric battery for the energy supply and an electric drive with caterpillar tracks 96 running against the inner wall of the tube.

Furthermore, the shut-off member 95 has a command expandable sealing ring 97. A radio-controlled control 99 1 is provided for controlling the shut-off member 95, the signals of which are received by an antenna 100 of the shut-off member. 95. The expandable sealing ring 97 is designed such that, in the event of failure of the electric battery or the control, it automatically compresses, whereby the closing member can be removed from the tube 2.

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Claims (15)

Method for mirror welding of pipe parts of thermoplastic plastic material, wherein a first pipe part and a second pipe part each have a connecting end with an annular wall and associated end face and 5 wherein the connection ends are joined together with their end faces, which method comprises the steps of: heating each connection end to at least the softening temperature of the plastic material with a mirror welding apparatus comprising a first and a second heatable plate, the first pipe part having its end face against the first heatable plate and the second pipe part with its end face against the second heatable plate is pressed, whereby a softened area is formed at each connection end, - the removal of the mirror welding device, - the pressing surfaces of the first and second tube sections pressed together by a pressing force, whereby the softened areas form a connection , 20. finish it off cooling of the interconnected softened areas, characterized in that for pressing the tube parts with their end faces against the heatable plates of the mirror welding machine, each pipe part-at a distance from the associated heatable plate of the mirror welding machine with an associated first or respectively the second closing member is closed airtight, whereby a first and second closed space is respectively defined in the first and second tube part, which is bounded by the respective tube part, the associated heatable plate and the associated closing member, and that an underpressure is effected in each closed space which underpressure provides at least a part of the contact pressure of the pipe section concerned against the associated heatable plate of the mirror welding machine 1007746. 14. 2. Method according to claim 1, wherein an equal negative pressure is provided in the first and second closed space. 3. Method as claimed in claim 1 or 2, wherein the tube parts with their softened end faces are placed against each other and each tube part is airtightly closed by an associated closing member, so that a closed space is provided, and a negative pressure is created in the closed space. press the pipe sections together. 4. Method according to one or more of the preceding claims, wherein a pressure vessel is used to provide the underpressure in a closed space, which pressure vessel is selectively connectable to the closed space via pipe means provided with a valve, in which pressure vessel is previously provided with a pressure vessel. underpressure is effected, and the pressure vessel is then connected to the closed space. 5. Method according to one or more of the preceding claims, in which the method is used for manufacturing a bend piece composed of a plurality of bend segments joined together by mirror welding, which bend segments are straight pipe sections which are equal in diameter and each two are not have parallel end faces. 30 A method according to claim 5, wherein the method is used for manufacturing a bend with three or more bend segments, wherein a first, second and third bend segment are connected to each other by placing a first mirror welding device between the first and second bend segment and to place a second mirror welding machine between the second and third bend segment, 1 "Λ774β, - 15 - the first and second mirror welding apparatus being provided with a connection between heatable plates thereof, and through the first and third bend segment at a distance from the first and second mirror welding machine 5 can be closed airtightly with the first and second closing members, after which an underpressure is effected in the closed space formed by the two closing members and the bend segments. 7. Mirror welding installation for mirror welding of pipe parts of thermoplastic plastic material, wherein a first pipe part and a second pipe part each have a connecting end with an annular wall and associated end face and in which the connection ends are connected to each other with their IS end faces, which mirror end installation is a first and a second heatable plate and associated heating means for heating each connection end to at least the softening temperature of the plastic material, wherein the first pipe part is pressed with its end face against the first heatable plate and the second pipe part with its end face against the second heatable plate , whereby a softened area is formed at each connecting end, characterized in that the mirror welding installation further comprises a first and second sealing member for airtight sealing of the first and second tube part, respectively, at a distance from the associated heatable plate of the mirror welding apparatus, as a result of which a first and a second closed space are formed in the first and second pipe part, respectively, and that the mirror welding installation further comprises vacuum means for effecting an underpressure in the first and second closed space. 8. Mirror welding installation as claimed in claim 7, wherein one of the closing members is provided with a vacuum line leading to the vacuum means and wherein a passage is provided between the first and second heatable plate of the 1007745: mirror welding device for providing a connection between the first and second second closed space. - 16 - 9. Mirror welding installation according to claim 7, wherein the mirror welding device is provided with vacuum channels which debouch at the heatable plates thereof and which are connectable to the vacuum means. Mirror welding installation according to one or more of claims 7-9, wherein the vacuum means comprise a vacuum pump, which can be connected via associated pipe means to a closed space in the tube parts. 11. Mirror welding installation according to one or more of claims 7-10, wherein the vacuum means comprise a pressure vessel and a means for effecting an underpressure in the closed pressure vessel, which pressure vessel can be connected to a pipe means via associated and operable shut-off valve. closed space in the pipe sections. 12. Mirror welding installation according to one or more of claims 7-11, wherein for the simultaneous production of several mirror welding connections a plurality of first closing members are arranged in a frame and are connected to common vacancy means. 13. Mirror welding installation according to one or more of the claims 7-12, wherein at least one of the closing members is a mobile closing member, which is provided with a driving device for moving the closing member in the relevant pipe section. . , f) - ^ · - £ L 'I KJ * Mirror welding installation as claimed in claim 13, wherein the mobile closing member is provided with a sealing member which can be expanded on command. - 17 - Mirror welding installation according to claim 13 or 14, wherein the mobile closing member is provided with an electric battery and electric driving means connected thereto. ';,! '<I Γ 1 / R i' r) r.