A WELDING METHOD IN THE MANUFACTURE OF A SPIRALLY WOUND TUBE AND A WELDING HEAD FOR PERFORMING THE METHOD

Abstract: The present invention relates to a welding method in the manufacture of a spirally wound tube having a thermoplastic profile (1) of a mainly rectangular cross-section. A hole profile (1) is wound in a screw line form manner on a welding drum (2) simultaneously as profile surfaces (1a, 1b), which are to be welded together are heated with hot air to a desired temperature, whereafter a welding mass (S) is extruded onto the heated profile surfaces (1a, 1b) in two streams along each edge of the profile surface (1a, 1b) and the welding mass coated hole profile portions are pressed together by means of a press roller (10). The invention is characterized in that the welding is performed with a welding head (3) coupled to an extruder and provided with a welding keel (4), which from the outside is inserted between two profile surfaces (1a, 1b) to be welded together. Hot air (L1, L2) is blown out through two pairs of air openings (5, 7) in the welding keel (4) against the edge portions of the profile walls (1a, 1b). A keel nose (9) located between the two pairs of air openings is arranged to guide the four hot-air streams (L1, L2) and to prevent heating of the middle portion of the profile surfaces (1a, 1b). The extruded welding mass (S) is pressed out on the heated portions of the profile surfaces (1a, 1b) through two pairs of welding mass openings (6, 8) in the rear section of the welding keel (4). The welding pressure is maintained on a desired level by regulating the friction between the hole profile (1) and the welding drum (2).

Description: A welding method in the manufacture of a spirally wound tube and a welding head for performing the method The present invention relates to a welding method in the manufacture of a spirally wound tube having a thermoplas¬ tic profile of a mainly rectangular cross-section, where¬ by a hole profile is wound in a screw line form manner on a welding drum simultaneously as profile surfaces, which are to be welded are heated with hot air to a desired temperature, whereafter a welding mass is extruded onto the heated profile surfaces in two streams along each edge of the profile surface and the welding mass coated hole profile portions are pressed together by means of at least one press roller, whose axis is directed radially relative to the welding drum such that a double seam is formed between the hole profile rotations located besides one another. The present invention also relates to a welding head for performing the method. Previously, welding of spirally wound tubes having a po¬ lyethylene hole profile was performed in two steps. Du¬ ring a first rotation, which the hole profile run around the welding drum, an inner seam was welded onto the clo¬ sest previous rotation with a single welding keel and during the following rotation an outer seam was welded with a single extruder shoe. A drawback in connection with this metdod used previously is that it requires two extruders as well as that the total welding operation is relatively difficult to super¬ vise, partially depending on that the heating occurred by means of a fanned air heater, which was not integrated with the welding keel, but they had to be adjusted sepa¬ rately resulting in a very varying heating result, and partially resulting from great fluctuations in the wel- ding pressure. This previously used welding method does not satisfy all the requirements for a good weld for a polyethylene, which especially concerns the outer seam. A codition for a good weld seam in polyethylene is besi¬ des cleanliness that the basic material is heated to correct temperature and that the surfaces to be seamed together are pressed together under pressure. The purpose of this invention is to provide a double weld seam, which satisfies all requirements and is also simple and reliable to perform. This is achieved with a method which is characterized in that the welding is performed with a welding head coupled to an extruder and provided with a welding keel, which from the outside is inserted between two profile surfaces to be welded together, whe¬ reby hot air is blown out through two pairs of air ope¬ nings on that side of the welding keel which is turned against the rotational direction of hole profiles against the portions of the profile walls, wherein the weld seams are to be formed, whereby a keel nose located between the two pairs of air openings is arranged to guide the four hot-air streams and to prevent heating of the middle por¬ tion of the profile surfaces, that extruded welding mass is pressed out on the heated portions of the profile sur¬ faces through two pairs of welding mass openings in the rear section of the welding keel mainly onto the same level as the two pairs of air openings, and that the wel¬ ding pressure is maintained on a desired level by regula- ting the friction between the hole profile and the wel¬ ding drum. This welding method, which in a simple and reliable way provides a double weld seam, resembles a pure butt wel- ding. The fact that makes the method so attractive is that the welding occurs in one operation from the outside with only one extruder and that it is easy to repeat. The remaining characteristics of the invention are described in the enclosed claims 2 to 10. The invention is next described in more detail with refe- rence to the accompanying drawing, wherein: Fig. 1 shows a scheme in principle of the manufacture of a spirally wound tube; Fig. 2 shows an enlarged section of a tube wall of Fig. 1 along the line A-A; and Fig. 3 shows a scheme in principle of an inventive wel¬ ding head during a welding operation, seen partially in section as well as a cross-section of the welding head and of a keel nose. When manufacturing a spirally wound tube of a thermoplas¬ tic hole profile 1 with a mainly rectangular cross-secti- on, the hole profile 1 is led to a rotatable welding drum 2, with a diameter corresponding to the inner diameter on the tube to be manufactured, whereby the hole profile 1 is wound in a screw-line form around the welding drum 2. A welding head 3 with a welding keel 4 is inserted from the outside into the gap, which is formed between the hole profile 1 entering the welding drum 2 and the hole profile 1 wounded around the welding drum of the first full rotation. The welding head 3 is connected to an ext¬ ruder (not shown), which is arranged to lead to the wel- ding head 3 a welding mass S as well as to two hot-air sources (not shown). The welding keel 4 has a length, which mainly corresponds to the wall thickness of the completed tube, and has three main zones. Closest to the welding head 3 is located an upper welding zone 4a with a pair of slantingly forwards against the rotating directi¬ on of the welding drum 2 directed air openings 5, through which hot air L is intended to the blown out against the upper portions of both profile surfaces la, lb, which are to be welded together, and a pair of welding mass ope¬ nings 6 on the rear edge of the welding keel 4 mainly on the same level as that of the pair of the air openings 5, and the welding mass S x extruded through these openings 6 is intended to be pressed out onto the portions preheated by the hot-air streams L x of the profile walls la and lb. This welding mass S r is intended to form an outer weld seam F x . The lowermost section of the welding keel 4 has a lower welding zone 4b, which is constructed in mainly the same way as the upper welding zone 4a with a pair of air openings 7 and a pair of welding mass openings 8, with which lower welding zone 4b an inner welding seam F 2 is intended to be formed. Between these two welding zones 4a and 4b, the welding keel 4 has a central shadowing zone 4c with a forwardly directed keel nose 9, which is inten¬ ded to guide the air streams L x and L 2 from the two pairs of air openings 5, 7 and to prevent overheating of the central portions of the two profile walls la, lb, which are to be welded together, by preventing the hot air streams L x and 2 f om coming into diuect contact with these portions. In connection with a strong overheating of the middle portion of the hole profiles, a too soft and unstable profile is in fact obtained. In connection with thin-walled profiles 1, the keel nose 9 acts simul¬ taneously as a support for the profile walls. The op¬ posite portions of the hole profiles 1, which are coated with the welding mass S r and S 2 , are pressed together by means of a press roller 10, whose axis is radially direc- ted relative to the welding drum 2. The welding pressure achieved by the press roller 10 is maintained on a desi¬ red level by regulating Jrhe friction between the hole profile 1 and the welding drum 2. According to the inven¬ tion is thus obtained a spirally wound tube with a double weld seam in one operation. For achieving an absolutely correct tempereture in the outer and inner edge areas, respectively, of the profile walls la and lb, the two pairs of air openings 5 and 7 are coupled to separate, individually adjustable air supply systems provided with their own hot air elements. The hot air stream L x to the upper pair of air openings 5 is led via a first air channel 11 and the hot air stream L 2 is led to the lower pair of air openings 7 via a second air channel 12. This arrangement possibilitates an indi- vidual temperature regulation on the preheated portions of the hole profile walls la and lb by regulating the air temperature and the air stream for hot-air streams through respective air channels 11, 12. The air tempera¬ ture may preferably be controlled by means of temperature controllers arranged in the inlet channels for hot air connected to the welding head 3, and an air stream may preferably be read from flow meters, which may be instal¬ led into a feeding line in the corresponding air supply system. The quantity of the welding mass S to\ be fed to the wel¬ ding head 3 is regulated with the extruder, while the welding mass stream between the upper pair of the welding mass openings 6 and the lower pair of the welding pair openings 8 occurs by means of an adjusting screw 13 ar¬ ranged on the welding head 3. The adjusting screw 13 may be e.g. arranged to throttle the welding mass flow S 1 up to the upper welding zone 4a about to a point, where the main channel 14 for the welding mass is divided into two partial channels 15 and 16, of which one partial channel 15 leads to a pair of welding mass openings 6 in the up¬ per welding zone 4a and the second partial channel 16 to the pair of welding mass openings 8 in the lower welding zone 4b. The two partial channels 15 and 16 are branched immediately for a respective pair of welding mass ope¬ nings 6, 8 such that as identical welding mass strings as possible are applied onto both hole profile surfaces la and lb. As an alternative to the case that only the shor¬ ter mass channel S 1 is provided with a throttle valve, both mass channels S x and S 2 may be provided with a throttle valve. The width on the welding mass strings 17, 18 to be ap¬ plied to the preheated portions of the profile walls la and lb are in the first place defined by the width of chamberings 19, 20, which are received around the respec- tive welding mass openings 6, 8, but also the amount of the applied welding mass affects the width of the welding mass strings 17, 18. For maintaining as optimal direction as possible on the outflowing hot-air streams L j and L 2 , both pairs of air openings 5, 7 are preferably arranged in a plough-formed bevelled front portion 21, 22 of a corresponding welding zone 4a resp. 4b. Corresponding pairs of air openings 5, 7 may e.g. be achieved so that the mouth for the respec- tive air channel S 1 and S 2 is divided into a pair of air openings by means of a vertical tranverse beam, having an inside prerably formed such that it contributes to the fact that it guides the corresponding hot-air streams L x and L 2 , in a plough-formed manner. In connection with the keel nose 9 is arranged a welding keel 4 of a mainly uniform thickness, which closest to the front tip of the keel nose somewhat decreases, as is shown in the schematic cross-section of Fig. 3. The wel- ding head 3 itself has, as is shown in the same way rela¬ tive to Fig. 3, a mainly circular cross-section. Fig. 2 shows on the left gap between the hole profiles 1, how the welding mass strings 17, 18 have been applied along the preheated upper and lower edge portions of the two hole profile surfaces la and lb, which are to be sea¬ med together, and in the right gap may be seen, how the final double weld seam may be formed, when the welding pressure is adjusted onto such a level that the welding mass S x and S 2 from the upper 17 and lower 18 welding mass strings fall together. The outer weld seam F x is prefera- bly ground off by means of a teflon shoe (not shown), which is located against the outer surface of the welded profiles 1 immediately after compression with the press roller 10. When the welding pressure is applied, the friction bet¬ ween the hole profile 1 and the welding drum 2 may be regulated e.g. so that the welding drum 2 is cooled down, whereby the portions of the hole profiles 1 located against the welding drum 2 shrink and result in a higher friction. Along with the fact that the welding pressure is regulated by varying the friction between the hole profile 1 and the welding drum 2, according to the inven¬ tion is used a longer welding drum 2 than in connection with previous welding methods. The friction between the welding drum 2 and the hole profile 1 may also be adjus¬ ted totally mechanically by using a welding drum 2 having a variable diameter. The amount of the friction may also be affected by varying the application tension for the profile 1, when it is wound onto the welding drum 2. The invention is applicable to hole profiles of different thermoplast materials, of which polyethylene and polypro- pene are the ones used most commonly. An advantage in connection with the inventive welding method is the fact that the welding is performed in one operation with a minimum of equipment and under fully controlled conditions relative to the application of the welding mass, adjustment of the welding pressure and the preheating of the profile surfaces to be seamed together. Claims 1. A welding method in the manufacture of a spirally wound tube having a thermoplastic profile (1) of a mainly rectangular cross-section, whereby a hole profile (1) is wound in a screw line form manner on a welding drum (2) simultaneously as profile surfaces (la, lb), which are to be welded together are heated with hot air to a desired temperature, whereafter a welding mass (S) is extruded onto the heated profile surfaces (la, lb) in two streams along each edge of the profile surface (la, lb) and the welding mass coated hole profile portions are pressed together by means of at least one press roller (10), the axis of which is radially directed relative to the wel- ding drum (2), such that a double weld seam is formed between the hole profile rotations located besides one another, characterized in that the welding is performed with a welding head (3) coupled to an extruder and pro¬ vided with a welding keel (4), which from the outside is inserted between two profile surfaces (la, lb) to be wel¬ ded together, whereby hot air ( L lf L 2 ) is blown out through two pairs of air openings (5, 7) on that side of the welding keel (4) which is turned against the rota¬ tional direction of hole profiles (1) against the por- tions of the profile walls (la, lb), wherein the weld seams (F lr F 2 ) are to be formed, whereby a keel nose (9) located between the two pairs of air openings is arranged to guide the four hot-air streams (L lr L 2 ) and to prevent heating of the middle portion of the profile surfaces (la, lb), that extruded welding mass (S) is pressed out on the heated portions of the profile surfaces (la, lb) through two pairs of welding mass openings (6, 8) in the rear section of the welding keel (4) mainly onto the same level as the two pairs of air openings (5, 7), and that the welding pressure is maintained on a desired level by regulating the friction between the hole profile (1) and the welding drum (2).

Claims: 2. A welding method according to Claim 1, characterized in that the two pairs of air openings (5 and 7) are coup¬ led to separate, individually adjustable air supply sys¬ tems provided with their own hot air elements for regula- ting the temperature and the air flow. 3. A welding method according to Claim 2, characterized in that the amount of the welding mass (S) is regulated by means of the extruder and the balancing of the welding mass stream between the two pairs of welding mass openings (6, 8) occurs by means of at least one adjusting screw (13) arranged in the welding head (3).' 4. A welding method according to Claim 3, characterized in that the width of the applied welding mass strings (17, 18) is defined by a chambering (19, 20) received around a each welding mass opening (6, 8) in the welding keel (4). 5. A welding method according to Claim 4, characterized in that the friction between the welding drum (2) and the hole profile (1) is regulated by cooling down the welding drum (2). 6. A welding method according to Claim 4, characterized in that the friction between the welding drum (2) and the hole profile (1) is regulated by varying the diameter of the welding drum (2). 7. A welding head for welding a thermoplast hole profile (1) in the manufacture of a spirally wound tube, which welding head (3) is coupled to an extruder and has a wel¬ ding keel (4), which may be inserted into a gap between two rotations located besides one another of a screw line formed wound hole profile (1), which welding keel (4) has welding mass openings for supplying welding mass (S) to a presupposed weld seam, characterized in that the welding keel (4) has mainly three main zones (4a, 4b, 4c) comp¬ rising an upper welding zone (4a) with a pair of slan¬ tingly forwards directed air openings (5) on the front edge of the welding keel (4) for blowing out hot air (L t ) against each of the profile walls (la, lb), which are to be welded together, and a pair of towards both-sides di¬ rected welding mass openings (6) on the rear edge of the welding keel (4) for applying the welding mass (S) on the profile surfaces (la, lb) preheated by the hot-air streams (L x ) for achieving an outer weld seam (F x ), a central shadowing zone (4c) with a forwards directed keel nose (9), as well as a lower weld zone (4b) having a pair of air openings (7) and a pair of welding mass openings (8) for achieving an inner weld seam (F 2 ). 8. A welding head according to Claim 7, characterized in that the two pairs of air openings (5, 7) are arranged in a plough-formed bevelled front portion (21, 22) of the corresponding welding zone (4a resp. 4b) as well as a chambering (19, 20) is received around each welding mass opening (6, 8), which chamberings (19, 20) are intended for stating the width of the applied welding mass strings (17, 18). 9. A welding head according to Claim 8, characterized in that the two pairs of air openings (5, 7) are connected to separate, individually adjustable air supply systems with their own hot-air elements for regulating the tempe¬ rature and the air flow. 10. A welding head according to Claim 9, characterized in that it has at least one adjusting screw (13) for balan¬ cing the welding mass stream ( S lr S 2 ) to both pairs of welding zones (4a, 4b) of the welding mass openings (6, 8).

Inventors: BLOMQVIST GUNNAR, BLOMQVIST, GUNNAR
Applicants: BLOMQVIST GUNNAR, KWH PIPE AB OY, OY KWH PIPE AB
Application year: 1993
Main classification: B29C53
IPC codes: B29C53, B29C65, B29L23