Welding method in the manufacture of a spirally wound tube and a

Details Welding method in the manufacture of a spirally wound tube and a Welding method in the manufacture of a spirally wound tube and a

1994-10-04

1997-01-07

Ball, Michael W.

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

15624422, 15624427, 156425, 156429, 156433, 156447, 156500, B29C 5378, B29C 6540

Patent

active

055912923

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a welding method in the manufacture of a spirally wound tube, as well as to a welding head for performing the method.
2. Description of the Relevant Art
Previously, welding of spirally wound tubes having a polyethylene hollow profile was performed in two steps. During a first rotation of a welding drum, whereby the hollow profile was provided around the welding drum, an inner seam was welded onto the closest previous winding of the hollow profile with a single welding keel; and during the following rotation, an outer seam was welded with a single extruder shoe.
A drawback of this previously used method is that it requires two extruders, and the controlling of the total welding operation is relatively difficult partially because the heating is carried out by means of hot-air insufflators, not integrated with the welding keel, so they have to be separately adjusted resulting in a very varying heating results, and partially because of great fluctuations in the welding 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 condition for a good weld seam in polyethylene is, besides cleanliness, the basic material being heated to correct temperature and the surfaces to be seamed together being pressed together under pressure.


SUMMARY OF THE INVENTION

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 includes the steps of winding a continuous thermoplastics hollow profile, having a substantially rectangular cross-section, helically around a welding drum; and inserting a welding keel of a welding head coupled to an extruder between a profile surface of the hollow profile entering the welding drum and an adjacent profile surface of a closest previous winding of the hollow profile around the welding drum, which profile surfaces are to be welded together. Such method further includes the steps of blowing hot air out through two pairs of air openings provided at a front portion of the welding keel facing a rotational direction of the hollow profile against edge portions of the adjacent profile surfaces; arranging a keel nose located between the two pairs of air openings to guide four hot-air streams from the two pairs of air openings and to prevent heating of a middle portion of the adjacent profile surfaces; and pressing out an extruded welding mass strand on each heated edge portion of the profile surfaces through two pairs of welding mass opening in a rear section of the welding keel, mainly onto the same level as the two pairs of air openings. The method of this invention further includes the steps of pressing the edge portions of the two adjacent profile surfaces coated with welding mass together by means of at least one press roller having an axis radially directed relative to the welding drum, so that a double weld seam is formed between each winding of the hollow profile; and maintaining a welding pressure on a desired level by regulating friction between the hollow profile and the welding drum.
The above-noted welding method of this invention, which provides a double weld seam in a simple and reliable way, resembles a pure butt welding. 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 reproduce.
These and other features of the invention will be understood upon reading of the following description along with the drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an outline diagram 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
FIGS. 3, 3A and 3B show an outline diagram of a welding head according to the invention during a welding operation, seen partially in section as well as a cross-section of the

REFERENCES:
patent: 2671939 (1954-03-01), Everhart et al.
patent: 3839126 (1974-10-01), Haller
patent: 4642158 (1987-02-01), Steinel et al.
patent: 5271794 (1993-12-01), Jarrell et al.

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